Thursday, June 25, 2015

IMET Blog Post: Washington Fire Weather Decision Support

Hey everyone! I’m out here working on the Washington Fire near Markleeville, CA as an Incident Meteorologist, or “IMET” for short. I was dispatched to support an Incident Management Team from the Great Basin that has been assigned to manage the fire suppression efforts for the Washington Fire. As the IMET, I give direct decision support to the Incident Commander and the rest of the wildland firefighters that are working hard to contain this fire.  

Courtesy of Sierra Front Wildfire Cooperators

One of my primary functions is to keep the firefighters informed on weather conditions that are favorable for suppression efforts such as letting them know about light winds that were going to be favorable for their firefighting efforts earlier this week. With that information, the team was able to put together a plan that was very aggressive for fighting the fire directly with many hand crews and fire engines, taking advantage of the favorable weather.

On the other extreme, I also let them know when the weather is going to be unfavorable. In this case, we are expecting thunderstorm activity over the fire area Friday, Saturday, and Sunday. Even though there is only a chance that a thunderstorm will affect the fire directly, I still let them know of the potential of thunderstorms and probability that it will impact their operations. These impacts can include increased fire activity, grounding of helicopters and air operations, and most importantly impacts to the personal safety of the firefighters in the field.

In the next few days, the threat will be lightning, strong outflow winds, the potential for flash flooding and debris flows on the burn scar. So, by telling the fire leadership ahead of time and briefing the crews on the impacts from weather, they are able to plan for and mitigate those impacts.

An IMET is only one part of the 900 people assigned to fight this fire. Most of the time, our role is a very small piece of the whole operation, but when firefighter and public safety is on the line, we are here to help everyone come home safely!

Reno IMET briefing Nevada Governor Brian Sandoval, U.S. Secretary of the Interior Sally Jewell, and California Secretary for Natural Resources John Laird. The briefing included the weather impacting the fire and how the upcoming weather over the next couple weeks will impact the fire season going forward.

For updates on the Washington Fire, follow Sierra Front Wildfire Cooperators on Facebook and/or @mindendispatch on Twitter. 

Wednesday, June 24, 2015

Guest Post by Washoe County Air Quality: Wildfire Smoke in Northern Nevada


Special thanks to Washoe County Air Quality for being our first Guest Post! Enjoy! - NWS Reno 
Wildfires happen in the Sierra Nevada every year. The intensity and frequency of wildfires has been exacerbated with the increasingly dry conditions during the exceptional drought period across California and Nevada. If you are not close enough to the fire to be concerned with life and property, the next concern is your health in relation to smoke from wildfire. Let's take a look back at how much fine particulates (PM2.5) found in smoke has impacted the Northern Nevada region. 

Here are the top three 24-hour average PM2.5 air quality indexes (AQIs) for downtown Reno (2000-2015): 
1. CA Wildfires 6/25/08 - AQI 182 Unhealthy
2. King Fire 9/18/14 - AQI 174 Unhealthy
3. Rim Fire 8/23/13 - AQI 169 Unhealthy
For all three wildfire events, Northern Nevada experienced several days to over a week of smoke impacts above the 24 hour average National Ambient Air Quality Standard of PM2.5 set by the Environmental Protection Agency (AQI≥101).


Although these three wildfire days were considered Unhealthy with AQIs above 151, there were several hours during each of these days in which the air quality was not so bad. Here is a graph of the hourly PM2.5 AQIs from AirNow during one and a half days of the King Fire and how quickly the air quality can change:






When the air quality is in the Unhealthy for Sensitive Groups range or higher due to wildfire smoke, Be Smoke Smart and take precautions such as:
  • checking local air quality forecast and current conditions on AirNow.gov or your local air district website 
  • staying indoors with the windows closed; if too warm go to evacuation center or away from the area 
  • running an air conditioner if you have one, but keeping the fresh-air intake closed and the filter clean 
  • reducing activity and staying hydrated 
  • keeping 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.) 
  • following the advice of your doctor 
  • not relying on dust masks 
  • evacuating or temporarily relocating if needed 
Thanks to the National Weather Service 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.


Friday, June 12, 2015

Forecasting "Dry Microburst" Potential From Soundings and Observations

Summer afternoons in the valleys of eastern California and western Nevada usually feature dry low level relative humidity. In certain cases where low levels are very dry (single digit relative humidities) and enough instability for showers and/or thunderstorms exists, there is the heightened possibility for severe (over 60 mph) outflow winds. Now, severe winds are possible from strong thunderstorms in many cases, even without very dry surface relative humidity. However, what makes very dry surface or low level conditions special is that severe outflow winds are possible even with weak convection such as light showers...or even just cumulus clouds! When severe winds are produced by convection with little or no rainfall reaching the ground, it is referred to as a "dry microburst". Microbursts can be of significant danger to aviation and, if they are strong enough, life and property.

Before we move onto what conditions we look for to determine the threat for dry microbursts, let's examine some of the features of general convective outflow winds. First, here is a diagram of the process and motions in a typical thunderstorm with precipitation:


The yellow arrows in the diagram show the airflow involved in the the development and dissipation of a typical thunderstorm. Note the highlighted area in the dissipating stage image, which represents the outflow from a convective cell formed as precipitation and/or hail drags the surrounding air down with it as it falls towards the ground. This is known as "precipitation loading". Here is a more detailed diagram of outflow:

Finally, here is an excellent, very short conceptual video to show outflow movement, both simulated and with a wet downburst thunderstorm:


When the main forcing for outflow is from precipitation loading, it can be labeled as a "wet microburst" if the outflow is very strong or severe. However, if  precipitation falling from a cloud does not reach the ground ("virga") due to sufficiently dry air below the cloud base, precipitation loading cannot explain severe outflow winds. In these cases, the mechanism for severe outflow winds is related to the evaporation (or in the case of ice crystals, sublimating) of the precipitation into the surrounding air, which cools it. This is called evaporational cooling. This concept is easy to experience if you have ever gone outside wet during a summer afternoon...the chill you feel is due to evaporation taking heat from the air around your body. Since cooler air is denser/heavier than warmer air, the pocket of evaporatively-cooled air below the cloud begins to accelerate towards the ground and will continue to do so until all the moisture is evaporated from the air.  In extremely dry air with well-mixed atmospheric conditions, this acceleration can be quite profound...reaching in extreme cases over 100 mph! This is known as a "dry microburst".

Now that we have explained the dry microburst concept we can venture into what forecasters look for to determine the threat for dry microbursts. Here is an observed Reno sounding from a dry microburst event in July, 2014:


At the time of this sounding, it was 95 degrees with 8% relative humidity at the National Weather Service office. Notice the very dry air (shaded pink) in place between the very high cloud bases (red line) and the surface...this is often referred to as an inverted-V sounding due to its appearance. Another crucial factor is the weak instability (yellow shaded area) in the atmosphere for the formation of convective clouds.  Many times in summer eastern California and western Nevada will see inverted-V soundings due to very dry lower level air and strong heating/atmospheric mixing. However, there is often little or no instability aloft for the formation of convective clouds (cumulus or thunderstorms).

So, what happened on July 1, 2014?  Here is an excerpt of events within a few miles of the NWS Reno office:



So, as you can see, wind gusts up to 71 mph and damage to trees and fences were reported in the Reno-Sparks area around 6 PM.

To conclude, microbursts can be of significant danger to aviation and, if they are strong enough, life and property. Meteorologists use a combination of soundings and surface observations along with model forecasts for convective development to determine the threat for dry microbursts. If you typically check out NWS Area Forecast Discussions, keep an eye out for mention of severe outflow winds on those very hot and dry summer days! Now, we will leave you with a short video of a dry microburst from our neighboring office in Elko, NV:



Monday, June 1, 2015

We Got a Lot of Rain in May...Where Does This Leave Us?

After a brutally dry winter, May finally brought some welcome precipitation to the region. Now, where exactly does this leave us? Is the drought over? In a word, No. Does the recent rain and high elevation snow help? Most definitely! The rain did bring a bit of a recharge to area lakes, rivers, and reservoirs, but the relief is unfortunately short-lived. What we really need is a deep snowpack to slowly replenish water storage...of course with it being nearly June, we are out of time this season.

So, how did May 2015 stack up across California and Nevada...see for yourself below:



The greatest departures from average were through Mono County due to a snowfall event on May 8 which brought over a foot of snow (and liquid equivalents of 1-2 inches) to many locations. Here are some incredible photos and snow totals from the event:


June Lake - Photo Courtesy of Michael Cohen

McGee RV Park Across from Crowley Lake - Photo Courtesy of Anna Maier
After starting the month with a few of these winter-like systems, we transitioned to more showers and thunderstorms. This made the rainfall totals very hit or miss, with some places getting significant rainfall totals and others not nearly as much. Overall, totals for the month across the region ranged from a quarter inch upwards over 5 inches.

Now the big question...where does this leave us in terms of the drought? Well, we have had such a large deficit the past several winters that, to be honest, this is only a blip on the radar. Picture dropping a cup of water in a 5 gallon bucket - that leaves a lot of empty bucket still! Here is how many years worth of annual rainfall would be needed to even reach what is considered normal:


Of course, there remains one other big question...what about fire season? Well, this just delayed it, and in theory could actually make it worse. With the recent rains and now warmth, it will allow grasses and fine fuels to grow. These will then dry out in the summer heat, creating a new bed of fuels that can burn. The larger fuels - such as timber in the Sierra - are all quite dry already due to the past 4 years of drought. The rains have delayed their ability to burn, but these too will dry out again. A large number of wildfires are human caused, so make sure to do your part to help lower the risk of fire starts.

We'll have to see what winter of 2015-2016 brings us, but lets hope that it's a large Sierra snow pack!

The incredible winter of 2010-2011 (Look at the speed limit sign!)