Saturday, December 5, 2015

What is the Rain Shadow and What's Wind Gotta do With It?

The dreaded rain shadow - something that those of us who live east of the Sierra crest are more than familiar with and hate to hear. So what is this rain shadow and why does it even exist? Lets start with the topography just to our west...


The Sierra Nevada mountain range runs 400 miles from north-to-south and is approximately 70 miles wide. It includes the highest peak in the lower 48, Mt Whitney at 14,505 feet, and rises above 10,000 feet in many locations.
Left: The Sierra Nevada Mountains highlighted in blue. Right: A relief map showing elevation (in meters) of the Sierra.


The Sierra are a significant barrier for Pacific storms which typically move from west to east. The movement of air masses and associated weather cannot go through the mountains and is forced up and over the mountain range. As Pacific moisture is driven eastward by the wind, the air mass is lifted up and over the Sierra. Rising air will cool and once it reaches the point of saturation, condense into clouds. These clouds can then produce the rain and snow in the mountains that millions of us depend on for water. The majority of the moisture will precipitate out on the west side of the Sierra, not leaving much for the eastern slopes. To add insult to injury, once the air crosses the Sierra, it begins to sink into the Great Basin and this sinking motion acts to warm and further dry the air. This is the basis of our rain shadow and rain shadows seen across the world. The rain shadow can clearly be seen in the average annual precipitation and snowfall maps below as well.


A graphic showing the rain shadow effect of the Sierra Nevada Mountains on top, with the average annual precipitation on the bottom.

Average annual snowfall. Some great examples of the rain shadow: Average for Donner Pass: 412", Truckee: 200", Reno: 24". Span from Donner Pass to Reno: About 40 miles as a bird flies!


Now that we know in general terms what the rain shadow is, lets talk about what enhances it and what type of Pacific storms will actually bring better rain and snow to the eastern Sierra and western Nevada.

Obviously we are going to need a lot of moisture in a storm if we are going to get a decent amount of precipitation east of the crest. One thing we like to see is a moisture tap known as an Atmospheric River (AR). An AR is a relatively narrow region (250-375 miles wide) of the atmosphere that is responsible for transporting a large amount of water vapor. In a strong AR event, the amount of water vapor transported is roughly the same as 7.5 to 15 times the average flow of water at the mouth of the Mississippi River. In fact, on average we will get up to 50% of our total annual precipitation in the western coastal states from just a few AR events! Several of our flood events have been caused by warm ARs dropping a ton of rain on a large snow pack, but not all ARs are this devastating. If we are able to combine a significant moisture tap with a cold low pressure system this is a recipe for significant amounts of snow. In fact, some of these events have brought us up to 10 feet of snow in just a couple days in the high Sierra! For more information about ARs, please check out the NOAA Earth System Research Laboratory page.


An example of an Atmospheric River pushing into the west coast in the yellow and green shading.

The other significant factor in how much shadowing or spillover we will see is the wind. Many think it has to do with wind speed, and yes that can play a role, but direction is much more important. Think about crossing the Sierra--which is faster...going directly west to east or slowly moving eastward on a north to south route? As we talked about earlier, it's a much shorter distance going west to east and you guessed it...a west wind is much more favorable for getting spillover! Southerly winds will create a significant rain shadow almost every time. Just look at the event we had on Dec 3-4 -- 12 to 15 inches of snow fell along the Sierra crest and not much more than sprinkles in western Nevada. What did we have ahead of and with this storm? Strong southerly winds! If we have a strong westerly wind along with moisture it helps to bring the moisture eastward quicker and can actually lead to less shadowing on the eastern side of the Sierra. Now, what if the winds are southwesterly? Well, then it depends on a variety of factors including the degree of which the winds are turned more south or west, how much moisture is available, and what the terrain is like southwest of the area of interest. Will it completely block the flow of moisture or are there gaps in the terrain which could aid in spillover? 

While there are still other factors that can contribute to whether we'll be shadowed, or on the other side of the spectrum, see spillover, just keep in mind that the amount of moisture and wind direction are two of the biggest factors. No matter what, for storms that cross the Sierra, western Nevada will almost always see some degree of shadowing, but certain factors can at least help us to get additional precipitation. The good news is that the forecast over the next 7-10 days looks to remain active, so we have additional chances for rain and snow throughout the area! 


Wednesday, November 25, 2015

Unusually Frigid Thanksgiving Weekend

Hope that everyone travels safely for the holiday! Let's check out what is in store for Thanksgiving and going into the weekend.

We have an early season cold outbreak on tap for Thanksgiving weekend once the wind and snow move through the region. Post-frontal conditions will keep the maximum temperatures near and below freezing for the Thanksgiving Holiday weekend! Note that it would have been even colder in western Nevada if we had deeper snow cover and were expected clearer skies.


From Wednesday through Saturday we are forecasting maximum temperatures near 30 or into the middle 30s with lows in the teens to low 20s for western Nevada valleys, while highs in the Sierra will be in the 20s with lows ranging from the single digits to low teens. These frigid temperatures may result in broken water lines if they are not well insulated, as well as very chilly temperatures for late night/early morning Black Friday shoppers. A few things to keep in mind...if you're heading up to the ski slopes or to shop on Black Friday, dress warmly, especially if you plan to wait outside before stores open. We also urge you to provide adequate shelter and warmth to your outdoor pets. Considering that the past couple of winters have been relatively dry and warm, this will be quite a change for much of the region, so take these cold temperatures seriously! 


The last significant cold outbreak was waaay back in January 2013. Here is a Facebook post highlighting the weather from January 2013. It was most notable for strong inversions, producing areas of fog and haze in valleys on many days of the month. Temperatures were well below normal for most of January 2013, with the coldest air mass between the 11th and 14th producing low temperatures below -10 degrees in the Lake Tahoe basin, and single digits for Reno.




OK, so we know it can get pretty cold in January, and that is expected but just how unusual are these cold temperatures for late November? Let's take a look at typical November normal temperatures for the Reno airport (link to more graphs). Normals are highlighted in green with record temperatures on either end of the spectrum highlighted in red and light blue. The bars on the chart indicate the observed temperatures so far this month. For November 27th, the record temperatures are as follows:

     Highest Max Temperature  73/2014
     Lowest Max Temperature  26/1919 
     Highest Min Temperature  41/2014 
     Lowest Min Temperature    7/1948

For now the forecast temperatures for the 27th in Reno are a minimum of 18 degrees and a maximum of 34 degrees, which would not be records for that date, but impacts from these temperature will still be of concern to the communities in the Sierra and western Nevada. 




Since we haven't had cold temperatures like this for awhile here are some reminders and tips to be prepared for the wintry conditions! Now is the time to prepare before the cold weather impacts the region. For up-to-date information on the storm and details please go to www.weather.gov/reno


Saturday, October 31, 2015

Winter Weather Returns to the Sierra


Winter Weather Returns

Our first winter storm of the season with significant amounts of rainfall and Sierra snowfall is poised to affect Northeast California and Western Nevada Sunday into Monday.   A Winter Weather Advisory has been issued for Sunday Evening into Monday for portions of the Sierra from the Tahoe Basin down to Mono County. (areas in the purple shading)


Link to view this map here


Incoming Moisture
This storm system will usher in a solid band of moisture off the Pacific Ocean and will provide healthy rainfall and high elevation snowfall totals to the region. The animation below shows a model depiction of this moisture band (orange and yellow shading).  


This will also coincide with the expected precipitation timing. Rainfall enters northern Lassen County Sunday morning then drops across the Tahoe Basin Sunday Evening and finally Mono County Monday morning. 

Rainfall & Snow Level:
An important note to take away from this storm: Snow levels will be high to start and the bulk of the precipitation will fall as rain. Only areas above 9,000 feet will see all snowfall from the start. 

Snow levels will crash to near 6,000 feet by Monday morning but the bulk of the moisture will have already passed. Monday morning will be the best time frame to see some snowfall at lower elevations but we are mainly looking at just a few inches at most at lake level. You can see the approximate snow level drop on the graphics below. (Can be found here, then click "Snow Level Forecasts")




Rainfall Amounts:
Heaviest rains near and south of the I-80 corridor.
  • Sierra Crest:  2 to 2.5 inches.  (liquid equivalent)
  • Tahoe Basin & areas west of U.S. 395:   1.0 to 1.5 inches
  • Western Nevada: 0.25 to 0.75+ inches. 



Snowfall Amounts:

Tahoe Basin
  • Above 8,500':    1+ feet
  • around 7,000':   3 to 5 inches (including Echo and Donner Summits)
  • Lake Level:        Generally less than 2 inches


Mono County
  • Sierra Crest above 9,000':    1 to 2 feet
  • around 7,000':   3 to 5 inches 


Impacts
  • Travel: As this is the first solid storm of the season, many may not be prepared for winter driving conditions. The highest Sierra passes (Tioga, Sonora, Carson, Mt. Rose) will see the heavier amounts of snow (1+ feet) with Echo/Donner summits seeing a few inches. 
  • Winds: Moderate, possibly blowing around Halloween decorations left unsecured. 
  • Cold: Tue-Thurs with widespread freezes each night. The coldest mornings are expected to be Wednesday and Thursday.

For additional forecast details see our Area Forecast Discussion








Thursday, October 8, 2015

Welcome Tim Bardsley to the NWS Reno Team

NWS Reno is happy to announce that Tim Bardsley recently arrived as the new Senior Service Hydrologist (SSH). As SSH, Tim is the primary NWS contact for hydrologic decision support, forecast and warning services in Nevada and the eastern Sierra.  

SSH Tim Bardsley enjoying the great outdoors.
Tim first became interested in hydrology as a college student while exploring the rivers, mountains and canyons of the West. His undergraduate degree in civil/environmental engineering (University of Colorado at Boulder) and Master’s in hydrology (University of Nevada at Reno) give him a solid framework for hydrologic research. As a researcher at Niwot Ridge, CO, and as a hydrologist at the NRCS Utah Snow Survey Office, he conducted numerous hydrologic investigations as well as repairs and maintenance at well over one hundred hydrometeorological sites in four states, including extensive field work throughout Nevada and the Sierra Nevada.  

Tim's latest position was the Utah Liaison and Research Integration Specialist for the Western Water Assessment applied research program. While in this position, he was stationed at the NWS Colorado Basin River Forecast Center (CBRFC) in SLC, UT.  Among numerous other projects to support resource managers faced with climate variability and change, he used the NOAA Community Hydrologic Prediction System (CHPS) to model the potential impacts of climate change on local and regional water supplies.  He also convened workshops and networked with stakeholders to assess water supply system vulnerabilities and adaptive strategies to improve resilience in the face of climate change and variability.

What is the role of a Service Hydrologist?

There are 124 NWS Weather Forecast Offices and most employ a Service Hydrologist (SH). The SH is responsible for supporting all hydrology operations within a NWS Forecast Office Hydrologic Service Area (HSA). Hydrology operations includes collecting daily observations, monitoring river stages, and issuing river flood warnings or statements when needed.  The Senior Service Hydrologist (SSH) is responsible for more than one HSA.  

Other duties of a SH include:
  • Support development and application of the Community Hydrologic Prediction System (CHPS).
  • Utilize technical skills in information technology and data processing to improve hydrometeorological operations.
  • Conduct and facilitate research and develop training resources for the evolution of the NWS Hydrology Program.
  • Perform simulation testing and provide decision support.
Interested in a NWS Hydrology Position?

A useful reference for learning about NWS hydrology positions and qualification requirements is the NWS JetStream Online School for Weather and all NWS job opening are posted to The Federal Government Jobs Site



Friday, October 2, 2015

Guest Post: Nevada Bureau of Mines and Geology; Nevada's Great 1915 Earthquake

Enjoy this post put together with information from Nevada Bureau of Mines and Geology about the 1915 Pleasant Valley, Nevada Earthquake on its 100th anniversary. All information was taken from The 1915 Pleasant Valley, Nevada Earthquake website.
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When folks talk about earthquakes most people consider California to be earthquake country, but Nevada gets its fair share of seismic activity too! Northern Nevada was very active geologically during 1914 and 1915, as you can see on this short video which shows activity from 1850-2012. Magnitude 6 and 6.4 earthquakes occurred in Reno during February and April of 1914 and Mt. Lassen had several eruptions between May 1914 and October 1915, occasionally dusting Winnemucca with fine ash.   


The Pleasant Valley earthquake of October 2, 1915 was the largest earthquake in Nevada's recorded history. The 1915 Pleasant Valley earthquake was preceded by a rare, highly energetic foreshock sequence that forecasted the ensuing large earthquake. For a detailed description of the sequence check out the October 5, 1915 Silver State Newspaper to read L. Roylance's account of the seismic activity. The mainshock occurred at 10:54pm. Shaking lasted for 40 to 55 seconds over a large area of northern Nevada. Nearly continuous aftershocks created continuous ground motion in Kennedy for at least 15 minutes after the mainshock! It ruptured the ground about 50 miles south of Winnemucca, and left a scar along the range front that was more than 35 miles long. In places, the ground surface was offset vertically by as much as 19 feet. 


The earthquake had a magnitude of 7.3 and was felt throughout Nevada as shown on the Modified Mercalli Intensity Map. The most devastating effects of the earthquake were to buildings on ranches in Pleasant Valley where total and partial collapses devastated some homes and barns. Although the 1915 earthquake took place in a rural setting with only a half a dozen ranches in Pleasant Valley, 100% of the people in the Valley were severely impacted by the earthquake. 

Modified Mercalli Intensity Map of 1915 earthquake. Areas with Intensity VIII to X had partially and totally collapsed buildings, surface rupture from fault movement, and ground cracking. Areas with Intensity VII had shaking strong enough to damage chimneys, within Intensity VI areas walls were cracked, and shaking in Intensity V areas was strong enough to awaken people. 
Winnemucca was the Nevada community with the most earthquake damage. Several brick and adobe buildings in this area had portions of walls thrown down and some plate-glass windows were broken. Damaged chimneys and building contents occurred throughout Winnemucca. For more detailed information check out The 1915 Pleasant Valley, Nevada Earthquake Centennial website.



On the centennial of the October 2, 1915 Pleasant Valley, Nevada earthquake, it is wise to reflect back on this event so that we can be prepared for future earthquakes. Here are some of the important lessons from this large earthquake:

Earthquake Country: The 1915 earthquake underscores beyond a doubt that Nevada is earthquake country and that Nevadans should be earthquake ready. Drop, Cover, and Hold On. Twenty-three earthquakes of magnitude 6 or greater have occurred in Nevada since 1857.

Widespread Damage: The Pleasant Valley earthquake caused damage to multiple communities that were as much as 50 miles away. This illustrates that large earthquakes cause widespread damage and can affect many communities at the same time. It is important for emergency managers to be mindful of these possible effects when planning for earthquakes and considering potential available resources.

Foreshock Activity: The 1915 earthquake had an extraordinary foreshock sequence, including earthquakes of magnitude 5.0 and 6.1. Foreshocks are earthquakes that precede a mainshock. Although usually less energetic, foreshock activity has preceded most magnitude 6 and greater historical earthquakes in the state, making Nevada an excellent area to conduct foreshock studies and experimental earthquake forecasts.

Foreshocks as Early Warnings: Foreshocks associated with the 1915 earthquake could have triggered a useful earthquake warning. Post-earthquake warnings, such as a statement that over the next 72 hours there is an elevated chance of having an earthquake of equivalent magnitude or larger, can be used to initiate temporary mitigation measures and alert emergency responders. As a natural reaction to the 1915 foreshocks, the Pearce family in Pleasant Valley removed the horses from a barn that collapsed during the mainshock.

Building Damage: Building damage from the 1915 earthquake is similar to what might be expected from strong earthquakes occurring today in Nevada. Seismically vulnerable buildings, like unreinforced masonry buildings, commonly have the most damage and have high earthquake risk.


Great Nevada ShakeOut

Join millions of people worldwide practice Drop, Cover and Hold On during Nevada's largest earthquake drill! Register at http://shakeout.org/Nevada/


Friday, September 25, 2015

The Affect of Western Pacific Typhoons on Weather in the West

Western Pacific typhoons are not always just a curious side note. In fact, they can affect the storm pattern over our region significantly, especially in the fall and winter. If a tropical system over the western Pacific gets absorbed into the storm flow at the right location, it can amplify/energize the pattern, potentially leading to stronger storms over North America.
Check out the video** below, which shows a typhoon (red symbol) just before absorption followed by the movement of the energy (shaded area) downstream after the typhoon is ingested into the flow. Notice how the flow (indicated by white lines) amplifies as the former typhoon energy moves across the Pacific and into Canada and the United States. Amplified flow can bring about a significant clash of air masses (cold Canadian and subtropical) and initiate the development of powerful winter storms.
Computer models often have trouble predicting how exactly tropical systems will be absorbed into the flow, which until the system is fully absorbed can make for a very uncertain forecast for the 4-7 day period. Watch for discussions about typhoons in our fall/winter forecast discussions, as that may indicate a highly uncertain forecast for the 4-7 day period!

**Video courtesy of a blogger at americanwx.com



Sunday September 27: Rare Supermoon Lunar Eclipse and the Sky Cover Forecast

On the evening of Sunday September 27th (mainly between 7 and 8:30 pm), we will be able to view an astronomical treat that hasn't happened in over 30 years! There will be a combination of a supermoon (perigree full moon) along with a total lunar eclipse! So what exactly is a supermoon? It's a new or full moon closely occurring with perigree - the moon's closest point to Earth in its orbit. This particular supermoon will be the closest supermoon of the year (other full moon supermoons this year: August 29th and October 27th) being only 221,754 miles away from Earth.
About three or four times a year (in the spring and the fall), the new or full moon coincides closely in time with the perigree of the moon - the point when the moon is closest to the Earth. Image Courtesy NOAA
Like I mentioned earlier, this September supermoon will be a treat because it will coincide with a total lunar eclipse! Check out this great animated video by NASA's Goddard Space Flight Center explaining the Supermoon Lunar Eclipse and its rarity. On the night of September 27th, 2015 this supermoon lunar eclipse will be viewable in the night sky for those living in North and South America. Those living in Europe and Asia can view it in the early morning hours of September 28th. The total eclipse will last one hour and 12 minutes. Earth's shadow will begin to dim the supermoon slightly beginning at 5:11 pm PDT. A noticeable shadow will begin to fall on the moon at 6:07 pm, and the total eclipse will start around 7:11 pm. Good thing that sunset will be around 6:48 pm here in Reno, so as the moon rises in the eastern sky the eclipse will already be in progress! NASA's Scientific Visualization Studio has a great website that will continue to update as September 27th-28th approaches. The next lunar eclipse that coincides with a supermoon won't occur until 2033 (and the next lunar eclipse viewable from the western U.S. won't occur until January 2018), so be sure to check this one out!


The Moon moves right to left, passing through the penumbra and umbra. Courtesy of NASA Scientific Visualization Studio 
Now that we have all the astronomical formalities out of the way, we will move on to an important aspect of this event...the meteorology! No, not meteors obviously. We are switching gears and need to see if clouds are going to limit the viewing of this rare event. 

The main concern for viewing will be the presence and thickness of cirrus clouds Sunday evening. Unfortunately, the latest forecast models are indicating a large area of cirrus clouds spreading across eastern California and western Nevada, due to southwest flow aloft ahead of a low pressure in the eastern Pacific. While this cloud cover could affect the viewing, all is not lost as the cirrus may be thin enough at times to allow for the eclipse to be visible. The presence of some thinner cirrus may even produce a more dramatic view (or photo) of this eclipse. At this time, there does not appear to be any specific nearby location where less cloud cover is expected, so planning a long drive to chase more favorable conditions is not recommended. 

The good news is that unlike a solar eclipse where the totality stage typically only lasts a few minutes, Sunday's event will last over an hour so there will be more opportunities to view at least a portion of this eclipse, even if some cloud cover is present. The evening timing is also more convenient for most people to make plans, without interrupting typical sleep time.   

Thursday, September 17, 2015

Meteorological vs Astronomical Fall and a quick Summer 2015 Overview

Let's take a look back at Summer 2015. Although astronomical fall hasn't begun, meteorological summer has ended. What? There is a bit of a difference between the two. Astronomical summer ends (or fall begins) when the Autumnal Equinox occurs, around September 22-23 (specifically September 23, 2015 at 8:20 UTC in the northern hemisphere) So why would meteorological summer end (or fall begin) at a different time? It's basically because the astronomical seasons are based on the Earth's position related to the Sun while the meteorological seasons are based on the temperature cycles through the year. For a more in depth discussion on what the difference is between the two, check out this great write-up by NOAA's NCEI (National Centers for Environmental Information).

 Anyways, back to the Summer summary for Reno. Looking back at the summer, we had a VERY active monsoon pattern which resulted in multiple days of thunderstorms and flooding for the Sierra and western Nevada. The most active period was during late June and early July where we received multiple reports of flash flooding, hail, and quite a bit of rain and lightning! We even had a waterspout at Lake Tahoe! Here are just a few of the pictures from some of the summer thunderstorms. 

This active period of weather kept temperatures relatively "cool" compared to normal for that late June and early July time frame. We typically will see some of our hottest temperatures during July but due to the cloud cover from thunderstorms we didn't see as many triple digit days. The chart below shows the amount of days that Reno airport hit 100 degrees or more during June, July, & August since 1996. One thing to keep in mind is that this chart only shows the temperature for the Reno airport since that is the official climate site that we use for the Reno area. You can really see that 2014/2015 didn't have nearly as many 100 degree or hotter days as 2013 did!

Let's take a look at July though. July historically is the hottest time of the year for the Sierra and western Nevada so let's compare previous July 100 degrees and hotter days. Here you can really see a difference. On average we will hit 100 degrees or hotter at the Reno airport around 4 times during July and we only did twice in 2015. Also notice how many more times 100 degrees or hotter was hit during 2014 and 2013! So 2015 did have less 100 degrees or hotter days than the previous few years.

Taking a look at the data just one more way.. here is table of the monthly mean maximum temperature for the Reno airport. Looking at July you can see that the monthly mean temperature for July was just below 90 degrees for 2015! Looking at this table this hadn't happened since 1997, so it really is reflective of just how much cloud cover and thunderstorms that we had in the local Reno area this past July. If you are interested in digging into more climate data be sure to check out the Climate page available on our website. There is a ton of neat data available there.


In other news, it really is starting to feel like fall out there! Did anyone see the snow on top of the mountains this morning? Although it does look like we will be warming up again going into the weekend. For all the forecast details please check out the discussion. Thanks!



Friday, August 21, 2015

Guest Post by Washoe County Air Quality - Monitoring Wildfire Smoke

Well the smoke has returned... it seems like an appropriate time to have Washoe County Air Quality guest blog about the smoke again.

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     Wildfire smoke contains many different pollutants with fine particulates (PM2.5) being the most concerning (see blog post "Wildfire Smoke in Northern Nevada). The Washoe County Air Quality Managament Division's PM2.5 monitoring network has been monitoring since 1999. In addition to the two permanent PM2.5 monitors at our Reno3 and Sparks monitoring sites, we recently deployed portable beta attenuation monitor (E-BAM) for PM2.5 monitoring at Pleasant Valley Elementary to expand our network during wildfire season (see map). An E-BAM's purpose is to get accurate PM2.5 data so that the public can make health based decisions as soon as possible. Decisions like keeping windows closed at night, having recess or practice indoors, and cancelling events like a triathlon are just some of the decisions that can and have been made because of this type of air monitor. 



How do BAMs work?

Beta attenuation monitors sample each hour by emitting high-energy beta rays through a spot on a filter tape that has outside air flowing through it. These beta rays are counted by a scintillation detector to determine an hourly PM2.5 concentration. This concentration is then translated into an air quality index to make it easy to understand what an hourly sample value like 38 µ/m3 means for your health (Unhealthy for Sensitive Groups).

What can I do to protect myself?

#BeSmokeSmart ! We are asking the public to Keep it Clean. Be Smoke Smart. Pay attention to your local air quality by going to AirNow.gov. The new portable PM2.5 monitor will also be sending data to AirNow in addition to our other monitoring sites. Due to the limitations of monitoring every hour, transferring the data, and having AirNow update at 30 minutes past the hour, data on AirNow can be delayed up to 90 minutes. Here are some other things you can do to Be Smoke Smart:

  • Stay indoors with the windows closed; if too warm go to evacuation center or away from the area
  • run an air conditioner if you have one, but keep the fresh-air intake closed and the filter clean
  • reduce activity and stay hydrated
  • keep indoor air as clean as possible
    • eliminate tobacco smoke 
    • don't use candles
    • don't vacuum (yes, I am giving you an excuse not to clean.)
  • follow the advice of your doctor
  • do not rely on dust masks
  • evacuate or temporarily relocate if needed 
Thanks to the NWS in Reno for being a partner in getting wildfire smoke information out to the public. For more information on local air quality for Washoe County, go to OurCleanAir.com 



What Exactly is El Niño and La Niña? Bonus: What does this mean for us?

El Niño and La Niña are weather catch phrases that are thrown around pretty frequently, but how many of us truly know what these features are? They are complex atmospheric-oceanic circulations, and to be honest, it's more than we could even explain in a short blog post, but we will cover some of the basics here.

Let's start with El Niño since we currently have these conditions in place. El Niño is the warm phase of the El Niño Southern Oscillation (ENSO) and refers to warming in the equatorial Pacific sea surface temperatures (SSTs) compared to normal. Here is a quick video explaining this phenomenon:



La Niña is the cool phase of ENSO and refers to cooling in the equatorial Pacific SSTs compared to normal. One more quick video to explain:





The strength of El Niño and La Niña episodes is determined by the difference in SSTs compared to normal and are measured in a region of the east-central Pacific Ocean known as the Niño 3.4 Region:


The Oceanic Niño Index (ONI) is a measure of the departure from the normal sea surface temperature in this region. This is the standard by which the strength of El Niño and La Niña episodes are measured. The average sea surface temperature in the Niño 3.4 Region is calculated each month and then averaged with values from the previous month and following month. This running three-month average is then compared with the average sea surface temperature for the same three months during the 1981-2010 30-year climate normal period giving a value for the ONI. Positive values of 0.5°C or greater reference the warm phase, or El Niño, while negative values of 0.5°C or less reference the cold phase, or La Niña. Curious how these have measured up through the years? All the values can be found here, or you can also check out this graph which shows January 1950 through late spring 2015:


The data for this graph was provided by the Climate Prediction Center (CPC), with the graph produced by Golden Gate Weather Services





Now that we know what these phenomena are, let's talk about what is really important - how does each impact us locally. Quick...is El Niño or La Niña more likely to bring the Sierra and northwest Nevada a wet winter? Do you have your answer? Chances are it isn't what you think. There seems to be the notion that El Niño equates to a wetter than average winter and La Niña the opposite. How many of you remember the incredible winter of 2010-2011? Here's a couple pictures to refresh your memory:



Believe it or not, this was a moderate to strong La Niña year! 

Being in the Sierra and northwest Nevada puts us right in between the greatest El Niño impacts, which brings better chances for rain to southern California and better chances for drier conditions to the Pacific Northwest. We have had both wet and dry El Niño years and La Niña years as well as ENSO neutral years. Unfortunately there is just not much correlation with ENSO for our part of the world. Since the 1930s we have had 6 strong El Niños and even these have ranged from dry to very wet in the Sierra and western Nevada. There have been two winters with particularly strong El Niños (1982-83 and 1997-98) and both of these winters were very wet in the Sierra with instances of significant flooding in both California and Nevada. However, this is only 2 data points in the admittedly short 65-year data set and does not guarantee that we will have a wet winter this year! Anyone who has lived in the region since the mid-1990s will likely remember the destructive January 1997 floods, but this occurred in the previous winter (1996-97) during an ENSO neutral year.



Now, I know what you're thinking...wasn't last year forecast to be an El Niño? Well, that is true, but the difference is last year we were in an ENSO neutral phase and only a weak El Niño was forecast, which took longer to develop than expected. This year we are already observing moderate El Niño conditions in the tropical Pacific Ocean (image below) with the forecast for it to only intensify. There is now high confidence in strong El Niño conditions persisting through the winter of 2015-2016 (strong being ONI values of +2 degrees C or warmer). I'm sure many of you have been hearing the hype about this being a "Godzilla-like" El Niño, and while a strong one is forecast, whether this becomes a record-breaker remains uncertain.

This graphic from the Climate Prediction Center is showing sea surface temperature (SST) anomalies in the Niño 3.4 region


There is one other big question mark...the Blob! The warming in the eastern Pacific Ocean along the west coast is unprecedented and climate experts have no idea how this feature will interact with a strong El Niño. This "blob" has been linked to the ridge of high pressure which has been plaguing the west the past 4 years and could affect how El Niño drives weather patterns into California.

Seasonal Sea Surface Temperature (SST) anomalies showing the "blob" and El Niño. 
A composite showing the overall pattern during the past 4 winters which has driven the west into a major drought.
So, with all these details in mind, what does this mean for us here in the Sierra and northwest Nevada? The latest Climate Prediction Center outlook for January through March 2016 favors better than average chances for above normal precipitation from about Lake Tahoe south, with below normal chances favored in the Pacific Northwest. With this being said, however, it is only an outlook, not a guarantee, and confidence remains low to medium for our region. The other factor is medium to high confidence in above normal temperatures this winter, which could indicate an increased frequency of warm storms with high snow levels.

The official CPC outlook for January through March 2016 precipitation as of August 20, 2015.

We know the drought is on everyone's mind and it would be incredible if we had a wet winter! Just remember, it took 4 years to create the precipitation deficits we now have, so it will take more than one wet winter to end the drought! If we combine the last 4 years, much of northeast California, the Sierra, and northwest Nevada are more than one year behind on precipitation. Even if we had the incredible winter of 2010-2011 again, we still wouldn't be caught up to normal.

For a great reference on the latest state of the ENSO and predictions for the upcoming season check with the Climate Prediction Center. You can also view our short YouTube video on El Niño which is our office's take on keeping it real with what you can expect for the upcoming winter.

Tuesday, August 18, 2015

Smoke and Radar: American Fire Smoke engulfs Reno 2 years ago today.


Everyone is familiar with weather radar and how it can detect areas of precipitation, but radar is also an indispensable tool when it comes to helping identify storms which have the potential to become severe. Normally when we refer to severe storms in the West, we are referring to storms that are capable of producing damaging winds/hail and also flash flooding. Here in the Sierra and western Nevada, tornadoes are fairly uncommon but still can happen as was the case this past June in Hawthorne, NV where an EF-1 tornado formed. 


Smoke on Satellite

  The satellite image below (fig 1) shows a true color view from the afternoon of the 8/18/13. What is notable is the smoke plume from the American Fire hovering over the Sierra west of Lake Tahoe. The next image later that afternoon (fig 2) show thunderstorms had formed across the Sierra south of Tahoe while smoke had begun to travel up slope of the Sierra. 



Figure 1: MODIS-Terra satellite image from the afternoon of 8/18/13.
Wildfire smoke can be seen along the west slopes of the Sierra.

Figure 2: MODIS-Aqua satellite image later that afternoon.
Thunderstorms can be seen developing along the Sierra south of Lake Tahoe.
Smoke from the fire can be seen travelling up the Sierra
near the developing clouds and storms. 

Smoke on Radar


Thunderstorms continued to develop across the Tahoe Basin and clouds began to hide the view of the smoke from satellite imagery. How do you then track the movement of smoke when clouds are hiding them from view on satellite???  That's where radar came into play that day.  Although it is not always possible, the smoke plume was able to be detected by radar that day as it was located at an elevation and distance within sight of the radar. 


The image below shows (fig 3) shows an outflow wind boundary from a thunderstorm that was traveling east over the Carson Range and towards Reno. The big question was: Is this outflow going to bring smoke with it?  Without webcams or spotter reports to provide the answer, we turned to our radar.  


outflow.JPG
Figure 3: Thunderstorm outflow boundary pushing eastward towards Reno.


The radar loop below shows this north-south oriented outflow boundary pushing cross the Carson Range.  The WSR-88D radar sitting on top of Virginia Peak received an upgrade to include Dual-Polarization technology (or Dual Pol for short) back in 2012.  One of dual-pol’s benefits is that it’s able to distinguish not just where precipitation is but what type it likely is (hail, snow rain) and even if it's not precipitation at all (insects, birds, dust, smoke).





The loop below shows one of those complex dual-pol products called Differential Reflectivity. Basically with dual-pol, the radar can now send out a vertical and horizontal radar pulse, in the process it can get a rough idea on the orientation and what the shape of the detected object might be. In this case, the radar was detecting something that wasn’t rainfall but most likely was detecting the smoke being caught up in the outflow boundary. 




A few minutes later suspicions were confirmed as the wall of smoke became visible over the top of the Carson Range. (fig 4)

smokeCarson.JPG
Figure 4: Once this boundary pushed over the Carson Range, the wall of smoke 
became visible from the NWS office.


This wall of smoke rapidly descended down into Reno in about 30 minutes and resulted in a rapid deterioration of air quality and visibility. Dual-pol radar proved extremely useful in getting an early alert of the possible smoke threat and we were able to get the word out with short-term products and social media about the oncoming smoke! We managed to capture a timelapse of the smoke descending the mountains and completely engulfing Reno. The 9 second time lapse that afternoon runs from 5:20pm-6:00pm.




Below are a few links to our social media outlets and also some air quality sites that we find quite useful year-round. Thanks for reading!

Bureau of Air Quality Planning: http://nvair.ndep.nv.gov/ UNR PM2.5 Sensor: http://www.patarnott.com/pas532/ Map of Particulate Sensors: http://smoke.airfire.org/monitoring/#/ NWS Reno Social Media: NWS Facebook: https://www.facebook.com/NWSReno NWS Twitter: https://twitter.com/nwsreno NWS YouTube: https://www.youtube.com/user/NWSReno







Sunday, August 16, 2015

Guest Post by Washoe County Air Quality - Summer is the Season of Ozone

Enjoy this guest post from our friends at Washoe County Air Quality

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Forecast calls for sunny skies and hot temperatures for Northern Nevada. The air quality should be good as long as there isn't any wildfire smoke, right? Well, not necessarily. Let me explain. 

Summer is the season of ozone (O3). There is both stratospheric and ground level O3. The stratospheric ozone protects us from the Sun's harmful ultraviolet radiation. Ground level ozone is an air pollutant that harms humans and the environment especially during hot and sunny summer afternoons. 

Ground level Ois created by the chemical reactions between volatile organic compounds (VOCs) and oxides of Nitrogen (NOx) in the presence of sunlight. NOx and VOCs, also ozone precursors, come from motor vehicles, industrial processes, power generation, and consumer products among many other things including wildfire smoke. Urban and suburban areas will have higher levels of ozone than rural areas, but it can travel hundreds of miles. 

Breathing levels of ozone can cause a variety of health problems including throat irritation, coughing, chest pain, and congestion. Ozone can also worsen bronchitis, emphysema, and asthma. It can reduce lung function and inflame the lungs. Repeated exposure may permanently scar lung tissue. Even healthy people can experience difficulty breathing. Because Ozone typically forms during hot, sunny days, anyone who spends time enjoying the outdoors especially children, the elderly and active adults are at risk. 

You can protect yourself and those around you from Ozone by paying attention to your local air quality forecasts and real-time AQI. Go to OurCleanAir.com for Washoe County air quality information or AirNow.gov for your local area (some areas may not have monitoring data on AirNow.) Exercise, play, or work outside when ozone levels are not high, typically during the morning and evening hours. 

You can also reduce your emissions by: 
  • driving less, 
  • not idling your engine, 
  • commuting by bike or public transportation, 
  • filling your gas tank up at dusk, 
  • using environmentally friendly paints and cleaners, 
  • and bring energy efficient at home and work. 

 The Washoe County Health District Air Quality Management Division (AQMD) is also doing its part to reduce Ozone precursors and educating the public. The annual smog check program is one of the measure in Washoe County to reduce emissions from motor vehicles. AQMD also permits sources of VOCs and NOx from business and industrial facilities. Under our award winning public education "Keep it Clean" campaign, we implement clean air strategies like having idle-free areas around schools and encouraging and advocating for biking, walking, public transit, alternative fuel vehicles, and other sustainable practices. 

Everyone can do something to take care of our air so we can all enjoy summertime in the Sierra and western Nevada. For more information go to OurCleanAir.com and follow us on Facebook, Twitter, and YouTube

-Washoe County Air Quality 

Saturday, August 15, 2015

Hot Temperatures This Week

Hot temperatures are returning to the Sierra and western Nevada this week (forecast details). Although some new record maximum temperatures may be hit this week, we are largely past the climatologically "hottest" part of the year. We typically see our hottest temperatures during July where the city of Reno can easily surpass 100 degrees for multiple days in a row. Although this past July was an exception to that rule since we had a significant monsoon push with thunderstorms for much of the month.



Here are a few snapshots at the forecast maximum temperatures we are expecting for early this next week. 


So what? It is going to be in the 90s and near 100 degrees out in central Nevada, no big deal right? Well it can be a big deal for those who spend their days working outside, especially for fire suppression personnel out on many of the large ongoing fires in the region. Since we are looking at multiple days of these hot temperatures, it would be a good idea to have some plans for mitigating the heat and to have some cooling options, especially if you plan on being outdoors! 

Here are some additional steps you can take to stay safe during a heat wave:
  • Drink plenty of water or other non-caffeinated and non-alcoholic beverages. 
  • Wear loose, lightweight clothing.
  • Find a place to cool off. If you don’t have air conditioning at home then spend some time in a public location that does, like a shopping mall or a library.
Avoid spending time outside during the peak heat of the day (typically 10am – 3pm). If you exercise outdoors, avoid the worst of the heat by going early in the morning. If you work outdoors, check out the heat safety tips for workers from the Occupational Safety and Health Administration.

One of the most important things to remember is to NEVER leave pets or children in cars, even for just a few minutes. There have already been 14 heatstroke deaths of children THIS YEAR

Courtesy of http://www.noheatstroke.org/ through San Jose State University

There is also a very telling video going around the internet asking "How Long Can This NFL Player Tough It Out in a Hot Car?" Basically never EVER leave children or pets in a car unattended, even when it isn't that hot. There have been hyperthermia deaths during the fall, winter, and spring!
 
  • Honolulu, HI, March: A 3-year-old girl died when the father left her in a child seat for 1.5 hours while he visited friends in a Waikiki apartment building. The outside temperature was only 81 degrees. 
  • North Augusta, SC, April: A mother left her a 15-month-old son in a car. He was in a car for 9 hours while his mom went to work. She is now serving a 20-year prison sentence. 
  • Greenville, TX, December: A 6-month-old boy died after being left in a car for more than 2 hours by his mother. She was charged with murder. The temperature rose to an unseasonably warm 81 degrees on that day.
For more information on Heat Safety please check out this website and be sure to follow #BeatTheHeat on Twitter.