Tuesday, September 25, 2018

El Nino: Recent Science and Forecast For Winter 2018-2019


1. EL NINO DOES NOT ALWAYS MEAN A WET WINTER FOR CALIFORNIA! Warming of the tropical Pacific Ocean with El Nino (or cooling with La Nina) is one of the only predictable features for seasonal (beyond 1-2 months) precipitation forecasting. Climate scientists know there are other features that affect winter precipitation; however, they are not predictable beyond a couple weeks or so. Depending on El Nino/La Nina alone can lead to large seasonal forecasting errors for California winter precipitation.

2. EL NINO NOT USUALLY MUCH HELP PREDICTING WINTER PRECIPITATION IN NORTHEAST CALIFORNIA AND WESTERN NEVADA. A weak-moderate El Nino is expected for the winter of 2018-2019. That strength El Nino does not provide much help for forecasting winter precipitation for the northern and central Sierra, northeast California, and western Nevada...with only the strongest El Nino events nudging chances for higher precipitation up slightly. Therefore, there are equal chances for above, near normal, or below normal precipitation this winter.

* Read on if you want more in-depth details!


The above average water temperatures of the central and eastern tropical Pacific Ocean associated with El Nino increases the area of tropical thunderstorm formation in that region. In turn, the thunderstorms affect the position (extending it closer to North America) and strength of the mid-latitude jet stream and storm track across the Pacific Ocean and into North America. Here are the usual winter effects of the jet stream extension:

The stronger the warming/El Nino has historically meant that the effects were more predictable. For strong El Nino events between 1957 and 1998, here is a map showing the typical precipitation changes from normal between November and March. As you can see, for strong El Nino events up until 1998, California has seen much wetter than normal conditions...with slightly above normal conditions spreading farther east into the Desert Southwest, the Sierra, and far northeast California.

As you will see below, this concept was thrown for a loop for the 2015-16 winter which featured a very strong El Nino. Remember, as was stated at the beginning of this article, depending on El Nino/La Nina alone can lead to large seasonal forecasting errors for winter precipitation. 



During the winter of 2015-2016, there was a very strong El Nino event...in fact, one of the strongest since the 1950s. Based on previous experiences with very strong El Nino winters, precipitation chances in much of California was favored to be above average (image below). For much of the Sierra and western Nevada, there was only a slight increase at best in the chances for above normal precipitation.

December 2015 - February 2016 Climate Prediction Center Forecast
December 2015 - February 2016 Climate Prediction Center Forecast

So what actually happened? Southern California actually received MUCH below normal precipitation (below)...the most unlikely scenario according the forecast from the Climate Prediction Center! For western Nevada and northeast California, precipitation between November and March wound up near or slightly above average...not too out of line from previous strong El Nino events.

November 2015 - March 2016 Precipitation Compared to Normal

Recent research has tried to figure out what caused the shift in the expected pattern in central and southern California. One paper has suggested that abnormally warm waters over the North Pacific Ocean and unpredictable atmospheric patterns unrelated to El Nino may have caused the shift in wetter weather from southern California to the Pacific Northwest. In any case, it is good to remember that there are still missing pieces to the seasonal forecasting puzzle. In addition, the Climate Prediction Center's forecasts highlight probabilities/chances for certain climate conditions to occur. There are no guarantees, especially with the current lack of predictability for some atmospheric conditions beyond a couple weeks.


It may come as no surprise, but based on what we have discussed the forecast of a weak to moderate El Nino doesn't tell us much about the potential for winter precipitation across the Sierra, northeast California, and western Nevada. With the main seasonal forecasting tool that is El Nino/La Nina not helping much historically, there is little to hang one's hat on regarding winter precipitation in the area.
The El Nino is predicted to be weak enough that even southern California isn't showing a tendency towards above average precipitation at this time.

SIDE NOTE: While there aren't a lot of signals to help with forecasting rain and snow on the seasonal (several months out) scale in our area, there is research showing the potential for predicting when chances are increased for atmospheric rivers / moisture plumes out to perhaps 2-3 weeks. As strong atmospheric rivers can cause travel issues, bring heavy rain and snow, and increase flooding concerns, being prepared well ahead of time could be of major importance to many government and private entities.



The California Weather Blog: (September 18, 2018)

National Weather Service's Climate Prediction Center

NOAA's Earth System Research Laboratory

Western Regional Climate Center


Friday, June 9, 2017

Hiking in the High Sierra? Attn: PCT through hikers!

Let's Talk Total Snow Amounts

  • Our reliable snowfall measurement sites in the Sierra, certainly near the PCT, are very limited. So it would be better to show a map of snow depth using automated sensors and satellite data. This was taken on April 1, typical peak snowpack date. Values of 16-25 feet were fairly common along the PCT from near Tahoe to southwest of Bishop!

    April 1.jpg

    Here’s June 8th's plot for comparison
    June 8.jpgYellow line = PCT
  • Mammoth Mountain in January alone received 20.5 feet of snow, earning the month the Twitter hashtag #januburied.
  • Of course snowfall was variable, but on a big picture this was a particularly impressive season for the Sierra from Tahoe to Bishop. The section between Tioga/Tuolumne and Sonora Passes got particularly crushed. That’s where some of the deepest snowpack still exists. A snow measurement by Jeff Anderson, NRCS, and Tim Bardsley, NWS, made just Tuesday at Leavitt Lake near Sonora Pass - 15 feet deep, containing 102.5 inches of water content!!
  • This is the area where numerous strong atmospheric rivers brought large amounts of snow to areas above 8,000 feet. Much of the snow fell in a short period of time - late January through February. Earlier in the winter the storms were much warmer, with more rain and less snow.
  • From a meteorologist perspective, this was probably a “once in a career” winter - with relentless blizzards, floods, wind storms, ice, and even critical fire weather conditions. At least we certainly are crossing our fingers it’s a once in a career winter...
  • Right now - Big gradient in snowpack. Still have 30-40% of peak snowpack left in many areas above 8000’, with some spots of 60-80% left at snow-favored or higher elevation NRCS SNOTEL sites (e.g. Leavitt Lake, Mt Rose, Independence). Right now Leavitt Lake is at 175% of the normal year-round peak! Conversely, below 8000’ snowpack has eroded considerably.
  • We’re likely looking at a 4-6 week delay in snow meltoff at the highest elevations. Based on the previous big snow years of 1982-83, 1994-95, 2010-11.

Let's Talk PCT...
  • We can’t directly make a comparison to the entire timeframe the trail has been official but this winter is clearly one of the bigger ones we’ve seen in 2-3 decades. Snowpack was 200-250% of normal! More than double normal, which makes for a striking contrast to the peak-drought winter of 2014-15 with snowpack 1/4 of normal in many areas!
  • We use 1982-83, 1994-95, and 2010-11 as comparative years on snowpack due to overall similarities, but each of those years has some contrasts to this big snow year 2016-17. Note that 1968-69 was also an enormous snowpack year, similar to 1983 and 2017, but we have very limited data to make comparison with. 1969 is the one long-time locals talk about around Mammoth and Bishop.
  • The graph below shows snowpack trends for those years compared to 2016-17 for the region around Sonora Pass. In general for the Sierra the snow situation was close to 1982-83, but in many cases not as quite as big due to warmer temperatures limiting snow accumulations early on in winter. Spring this year was also not as big for snow as 1983 and 1995.

  • 2016-17 winter started off quite warm, at least until mid-January. So until then we were actually still in a “snow drought” with more rain and less snow. Then the pattern shifted colder and brought more snow to lower elevations.
  • This overall theme created a big vertical gradient in snowpack - areas above 8000-8500’ were plastered with big snow pretty much all winter while areas below 8000’ were more variable. As a result, snowpack below 8000’ has decreased rapidly with spring/summer sun, while above 8000-8500’ it remains quite thick. This spring’s temperatures has also slowed the snowmelt some above 8000’ with “roller coaster” temperatures peeling off the snowpack in a slow, methodical fashion. Good news for flooding concerns, but bad news for quickly getting rid of the snow along the PCT trail.
  • The analog winters had similar snowpacks at some point but those winters were also colder with more snowpack at lower/mid elevations and also tended to have more snow in spring compared to this year. 2016-17 snowpack set records for peak values this year but confined to above 8000’. Below 8000’ while snow depth was considerable it largely did not set records set in those previous big winters, due to warmer temperatures and more rain.

    Source: Jeff Anderson, NRCS
  • So overall our assessment is that this will certainly be one of the rougher seasons to be on the trail in the Sierra at least through July. The worst? Maybe. Maybe not. There are other factors (noted following) that could add to the complications of hiking the PCT this summer.

Other Stuff Worth Noting

  • The prolonged deep snowpack by itself will present enormous challenges to hikers in the Sierra at least through July, and probably into August at the highest elevations. There is evidence of huge drifts and cornices remaining along the Sierra crest on the leeward sides of ridges. These are quite dangerous. Caltrans continues to plow the mountain passes and has encountered drifts on the order of 50 feet along Tioga Pass earlier in April-May. Could end up being one of the latest openings on record.
  • But there are other concerns too --
    • The amount of intense wind events this winter (Squaw hit 199 mph at one point & Mammoth Mountain had several cases of gusts over 150 mph) will create a ton of tree damage on the trails. Fallen trees will be numerous. Those that didn’t fall could be weakened where even just a moderate wind this summer would tip them over. Wet ground also contributes to more falling trees with shallow root systems.
    • Large amounts of water will be flowing from snowmelt. Not a surprise! Creek crossings will be numerous and flowing much later than normal - perhaps all summer. Crossings will also be larger/deeper with more swift water that can easily catch inexperienced folks off-guard. On a positive note, running short on water during the hot summer shouldn’t be a problem.
    • The snow covered trails and frequent high water crossings are likely to result in increased instances of search and rescue for local public safety agencies this summer.
    • Bugs, mosquitos are likely to be an extra nuisance this summer due to the copious amounts of water around. We’re already seeing that around Reno.
Be safe out on the trails this summer and make sure you are prepared or at least have some intel from fellow hikers on the conditions of the high Sierra trails. For up-to-date weather information along the PCT be sure to follow one of the many National Weather Service Offices that forecast along the trail. You can find an NWS social media site using this interface.

Happy Hiking!

Wednesday, June 22, 2016

Top 5 Things People Say to Meteorologists

Credit: Perceptionvsfact.com
Since the NWS has ventured out into the social media realm, we tend to get WAY more questions and comments than back in the day. Many of these questions or comments are repeated so often that we figured we should try to demystify some of them. So here are the top 5 things people say to meteorologists and here are some facts to clear up the confusion. Enjoy!

1.  "Wish I could get paid to be wrong all the time,"

  • We know it may be hard to believe, but weather forecasting has come a LONG way over the past 20 years. Even over the past 5 years, substantial advances have been made to forecast dangerous weather. Now, can we predict exactly what is going to occur a week from now? Probably not, but we can give you a pretty good idea of what you can expect, especially over the next 48 hours. Predicting the exact location and timing of thunderstorms can be super tricky, but there are high resolution models being developed that will help us to do our job better.
  • NWS Meteorologists are evaluated at their job just like anyone else. We are also are hardest critics. We despise when we don't get it right, probably even more than you do, especially if we were forecasting an epic powder day and it just didn't work out. During widespread severe weather events that devastate a large area, a team will be brought in to conduct a case study. This usually involves reviewing the actions of the individual forecasters as well as the teams of forecasters at each office. A lot is on the line for us from day-to-day so we really do try to get it right.
  • A humorous side note on this:

2.  "Don't like the weather? It's <city, state> just wait a few minutes and it will change."

  • I am sure we have all heard this one once or twice, but the fact is that the weather constantly changes. Just how fast it changes is obviously variable from day-to-day and from location-to-location.
  • The important part of this is to remember to look at the forecast from day-to-day, even frequently during the day if you have plans outdoors! Persistence (what happened the days before) doesn't always rule, even during the summer.

3.  "It came out of nowhere" and "Unpredictable Weather Continues"

  • This one really bothers meteorologists and weather forecasters alike. In this day and age where information is readily available from multiple sources: TV, radio, cell phones, internet, you name it! Accessibility to weather information is everywhere!
  • Weather impacts us every single day. From what you choose to wear in the morning, how you feel, your commute to work, and maybe even what you decide to eat! I am definitely more in the mood for an iced latte on those hot summer days. Being proactive and following our weather updates, posts, and forecasts will help you be weather aware and also keep you, your family, and friends prepared and safe.

4.  "What about the global warming now?"
  • This comment always seems to pop up when we get the occasional snow in the Spring and Summer in the higher elevations. We get it. Someone is trying to be funny, but just because it’s snowing that doesn’t disprove the idea of global warming.  Often these same people are curiously quiet when we have a heat wave ;-)
  • Global warming is a part of a much larger topic of discussion, climate change, which is a separate topic from the day-to-day weather that affects you and me. Our expertise is in day to day weather forecasts, so we tend to shy away from questions about climate change projections. For more information on climate change check out this link.
  • This just bears the reminder that weather and climate are two different things. Here is a great short post about it from our friends at the National Ocean Service

5.  "What channel are you on?"
  • Actually that is funny you ask! In a way, we are on all of them! No really :) Here at the National Weather Service we have strong relationships with our media partners so we can all work together to get the message out about critical weather events. Whether it is the local radio host, your friendly tv meteorologist or column writers at the local newspaper, we work hard with them ahead of big events to share preparedness information.
  • The media are especially important to us at the NWS because, although we can utilize social media, NOAA Weather Radio, and our website, we don’t have the access to the public via TV and the radio that our local media partners do. The relationships with our local media are crucial to what we do, and we appreciate them very much!
  • Here is a great blog post by one of our local media partners about our working relationship.

We hope that you enjoyed this little walk through some of the things we hear on a day-to-day basis and that it gives you a little glimpse into what people say to us. Thanks for checking out the post and as always if you have questions go to our webpage, Facebook, or Twitter. Thanks!

Monday, June 13, 2016

Windy Week Ahead

Water vapor satellite imagery from June 13th.
It has been a bit of an unusual summer thus far. Although June started out hot and unusually dry, the temperatures have moderated quite a bit. As of late we had quite a bit of rain as well as snow across Mono and Mineral counties this past weekend as a cold area of low pressure trekked across the West. Southern parts of Mono County received a good dousing of rain through the overnight hours of the 11th into the morning of the 12th with some portions of the southwest part of the county recording more than 1 inch of rain. Snow was reported down to 9000 feet in the heavier showers and thunderstorms with up to 3 inches reported near the summit of Mammoth Mountain above 10,500 feet.

Webcam photos are from June Mountain (~9,200 ft), Mammoth Mountain Main Lodge (8900 feet), and Mammoth Sesame Snow Study (9014 feet).
Now we are looking at a trough pushing into the Pacific Northwest that will bring windy conditions across the Sierra and western Nevada. While gusty winds aren't that unusual for the area, it is breezy almost everyday from the afternoon Zephyr winds. These wind gusts will be a bit stronger than our typical westerly winds and will make for some unpleasant impacts across the area. Let's take a look at what will bring these stronger than usual winds, and what you should be concerned about this upcoming week.

Here is the latest GFS simulation of the jet stream (images courtesy of TropicalTidbits.com) through Thursday afternoon. Notice the trough pushing into the Pacific Northwest with the jet dropping south into the Sierra and western Nevada. This jet stream along with tightening surface temperature and pressure gradients will allow the winds to increase across the region for Tuesday and Wednesday afternoon.

Computer simulations are showing wind gusts increasing to around 30 to 40 mph for Tuesday afternoon and then increasing further to up to 50 mph Wednesday afternoon as the cold front is forecast to push though the area. Ridge winds will be between 50 to 70 mph for mid week as well. While wind gusts like this are not unheard of during the summer, they do cause for some concern when it comes to outdoor enthusiasts in general; including, but not limited to hikers, fishers, cyclists, fire folks, and boaters.

The primary impacts from these winds will be choppy lake conditions and increased fire danger. Let's first address the lake conditions, and when we say "the lake" that can be any lake from Lassen county down to Lake Tahoe, to Mono Lake or even out east to Pyramid Lake. Our forecast area covers all those areas. There are currently Lake Wind Advisories out for area lakes, and if you plan on being at any lakes this week then you should be carefully looking over that product. Another page that you can look at for information is the NWS Reno Lake Forecasts website where you can see current observations at Lake Tahoe and Pyramid Lake, as well as the forecast wind speeds, wind gusts, and the wave heights.

All very important information if you plan on recreating at the lakes. Conditions can change rapidly, so being prepared is crucial. ALWAYS wear your personal flotation device when out on the lakes, especially if you are kayaking or paddle boarding. There have already been incidents on Lake Tahoe this year and you don't want to become part of that statistic.

For official weather forecast information please go to www.weather.gov/reno

Monday, June 6, 2016

Welcome to Summer! (and soon-to-be fire season)

Wow. We have been MIA for a little while!  Hope you all haven't missed us too much ;-)

We have only just started meteorological summer and the wildfires have already started popping up here and there. Just in the past week we have dealt with at least 3 in the local area, with a couple of them a little too close for comfort to the NWS Reno office (two fires on highway 395 near the Parr exits in Reno).

Photo Courtesy of Reno Fire Department Facebook Page

So we aren't fire fighters or fuels specialists, but here at the NWS we do have to stay in tune with the fuels status so we can be ready for the fire season. Namely, if the fuels aren't ready, then we aren't issuing Red Flag Warnings. Whoa whoa whoa... what is a red flag warning? Check out this short video and it will cover the basics. So as the video stated (you should really take the time to watch it), we at the NWS have to coordinate with our local fire partners to issue Red Flag Warnings for when the fuels and weather combine to create dangerous fire weather conditions.

Although we aren't fully into fire season yet, because all the fuels aren't "ready", we are still seeing some decent fires - especially in the grasses. Thankfully, the sagebrush is still green and not quite ready to burn yet.  This will not be the case when we go into July and August because the sagebrush and grass will all be dry enough to burn at that point.

There are a few important things to remember about our behavior during these hot and dry summers to reduce the threat of wildfire. One of those things is to practice target shooting responsibly, especially during hot and dry afternoons or if there is any wind like the Washoe Zephyr.  Here are a few tips from the Bureau of Land Management in Carson City...

Here at 10 tips for safe target shooting:
  • Bring water. This may seem obvious, but shooters often forget to bring enough water to put out a fire. A five gallon bucket of water could help prevent a fire disaster.
  • Bring a shovel. Use the shovel to dig a trench around your targets before shooting. This will help ensure any fires can easily be contained.
  • Shoot at quality steel targets designed to minimize risk. Don’t shoot steel during hot, dry, and windy days.
  • Place your targets on dirt or gravel away from any vegetation.
  • Don’t shoot trash and remove your spent cartridges. Illegal trash such as couches and televisions can be a fire hazard when shot.
  • Know that all types of ammunition can start fires under the right conditions, especially steel core ammunition. Don’t use steel core ammunition, and avoid shooting in rocky areas.
  • Don’t use exploding targets.
  • Don’t smoke. You can easily start a wildfire. If you’re shooting in a dry area, make sure the cigarette butts are fully extinguished or avoid smoking.
  • Park your vehicle away from dry grass. While it may not seem like a hazard, the hot undercarriage of the vehicle can heat up the grass and cause a fire.
  • Shoot responsibly. Clean up after shooting.
Source: Bureau of Land Management
Let's all have a safe and smart summer!
For the latest weather information go to www.weather.gov/reno or search NWSReno on Facebook and Twitter. 

Sunday, April 17, 2016

How Are National Weather Service Storm Reports Used?

For many years, the National Weather Service (NWS) has relied on spotter/public storm reports to help in the issuing of critical weather statements, verifying warnings and advisories, and to document the impacts of weather on life and property.  In recent years, posts on Facebook and Twitter which contain photos or videos have helped to streamline the event verification process across northeast California and western Nevada. Remember, "a picture (or video) is worth a thousand words!"

So...what are some of the ways NWS storm reports are used and distributed?  Most immediately, storm reports help NWS forecasters decide whether to update the forecast or issue a statement...
as can be seen from the Area Forecast Discussion below.

A second use for storm/spotter reports is verification of National Weather Service watches and warnings. Below is a map with NWS warnings (red boxes) overlaid with storm reports. Besides helping forecasters glean whether or not warnings were warranted, verification can aid forecaster training for future events by combining recognition of a weather pattern with what actually occurred based on the storm reports. In other words, spotter reports are very critical to the mission of the National Weather Service of protecting life and property.

Storm Reports and Warnings July 1 - 7, 2015

A third use for storm reports is dissemination to government officials, scientists and the general public for various purposes. This includes (but certainly not limited to) research, financial concerns and for general public interest.

**In case you are interested, here are a couple of links to storm report sites (there are many more!).

- The National Climatic Data Center's Storm Events Database (used to make the Storm Data publication...delayed several months).
- The Storm Prediction Center's Storm Reports (preliminary data...more recent info available)

Monday, January 25, 2016

Wet Weather Returns for the Weekend

Wet Weather this weekend? Where is it coming from?

We start off this week relatively quiet as high pressure builds across the region. However, the main forecast item of interest turns to our next potential winter storm this weekend. If you have been reading our recent forecast discussions,  you've read about the potential for a deep layer of moisture in the atmosphere to make its way across to the West Coast this weekend.

These plumes of moisture are known by several different names such as "Atmospheric Rivers" or a "Pineapple Express" due to their ability to transport large amounts of moisture from tropics near Hawaii to the West Coast.  We often use the term Atmospheric River or (AR) for short in some of our forecast discussions.

Figure 1:  Loop of Total Precipitable Water from Jan 22-Jan 25, 2016.
Courtesy of CIMSS/University of Wisconsin-Madison

The animated gif above shows a loop of "Total Precipitable Water" (TPW) over the last few days. This data is a combination of satellite and model data to help show where moisture is concentrated around the globe. Notice how much of the moisture is concentrated at the tropics with a few streams extending northward into higher latitudes. 

As an example, notice the plume that extends just off the East Coast of the U.S that pushes its way off into the central Atlantic by the end of the loop. What is that? That's the plume of moisture that helped feed the blizzard that buried portions of the mid-Atlantic states last weekend.  See the plume northwest of Hawaii near 170W longitude? That's our moisture for next weekend. 

The Important Matter of Confidence

Confidence in the outcome of a forecast is typically not an all or nothing proposition. Some portions of a forecast can have a high degree of confidence while another aspect of the same forecast can have low confidence. As an example let's take a look at our upcoming storm this weekend.  

Confidence is med-high that we will experience a winter system this weekend but low confidence exists on the timing and especially on the amount of expected precipitation by the end of the event.  How is it that this is the case?  Well as far as the higher confidence in having this winter storm materialize comes for a few reasons. First, this moisture plume already exists, as was evident from the loop of TPW above. Second, models and ensemble runs have been consistently picking up on this feature for days. 

An ensemble model is a lower resolution of the common models we use in forecasting (e.g. GFS, ECMWF, Canadian, etc). which are run many times using slightly different starting points or model physics to come up with a spread of possible scenarios. Say we run the GFS model with slightly different initial conditions 21 separate times, we will come up with 21 different possible solutions. If the majority of those solutions look fairly similar, then we know the model is pretty stable and probably has a firm grasp on the situation, If the outcome shows 21 different solutions, then there is absolutely no confidence in the model and likely the forecast as a result. 

Figure 2:  GFS Ensemble Members for this weekend. 
Courtesy of Plymouth State University

The figure above shows an example of  a case for this weekend where roughly 18 of the 20 members show some form of moisture plume or AR making it across the West Coast this week. This is good agreement but they do differ significantly on timing and intensity. This is where lower confidence comes into play. 

Figure 3:  GFS Total Accumulated Precipitation

The figure above is a model representation of total accumulated precipitation through Monday morning. The white bulls-eye across the northern Sierra represent the highest totals in the region that model came up with. How much is it?  Well, it depends when you decide to look at the model on a particular day. This model has shown wild variability in terms of precipitation amounts in just the past 24 hours. As little as 2 inches of liquid equivalent accumulation in the northern Sierra to as much as a whopping 16 inches.  Not to mention that does not agree with other models which have their own amounts. As another example take a look at what some of these ensembles yield for rainfall for Reno.  You don't need to fully understand the plot but the takeaway is that as little as a few tenths of an inch to above 3" is  possible. Not very helpful, and a low confidence proposition due to large spread in solutions. 

Figure 4:  Ensemble Spread for precipitation this weekend in Reno.

In the internet age with quick access to data and model output, its becoming increasingly common to find one big model run being posted on the internet without regard to its stability with recent runs. So what to believe? This is where the forecaster's experience and pattern recognition comes into play. So far this winter and over the past several years, very few storms have lived up to the models long range expectations and without a favorable pattern with a slowly evolving system, don't think this one will either. 

At this point in time, the most likely solutions begins with what we've seen so far this year, that is, amounts more in the 2-3" liquid equivalent along the northern Sierra versus a monster run of 16"+. Once individual model runs begin showing more agreement in both their individual and ensembles runs, confidence will improve and the precipitation forecast will be adjusted accordingly. 

Takeaways for this Weekend

Confidence is increasing that we'll see a winter storm impact the Sierra this weekend with a potential for periods of heavy precipitation. Confidence is lower in regards to the impacts and intensity. These will become much more refined in the upcoming days in which we can then start speaking specifics. 

Snow levels are likely to begin high which may lead to heavy rains for Tahoe and increased river flows, but then fall as the event wears on. Sierra pass travel above 6500 ft is likely to be a Sierra cement mess, with periods of strong shadowing and high winds likely Friday/Saturday in western Nevada and areas along Hwy 395. 

Bottom line -- for anyone with weather sensitive events, travel, or projects Friday-Sunday please keep an eye on the forecast and updates!