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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Monday
• 
• High: 29 °
• Low: 13 °
• Snow

• Tuesday
• 
• High: 36 °
• Low: 14 °
• Chance of Snow

• Wednesday
• 
• High: 34 °
• Low: 11 °
• Chance of Snow

• Thursday
• 
• High: 41 °
• Low: 18 °
• Partly Cloudy

• Friday
• 
• High: 43 °
• Low: 20 °
• Partly Cloudy

Area forecast discussion...updated 
National Weather Service Reno Nevada 
527 PM PST sun Feb 12 2012 


Update... 
update this evening to increase chance of snow from Tahoe north 
to Lassen and into northern Washoe County. Precipitation is rapidly 
advancing in the California Central Valley with radar returns 
showing up over the Sierra. While the Sierra returns are likely 
virga due to the low-level dry air, it will rapidly moisten in the 
next couple hours. We are already seeing this at Ridgetop level as 
the Slide Mountain dewpoint depression has decreased from near 20 
degrees to 3 in the last three hours. 18z model suite picked up on 
this and even show up to a 1/4 inch of liquid near the Sierra 
crest by 06z. Therefore, have moved up start times of Lassen/Tahoe 
advisories to 7 PM with the faster timing. Expect snow will begin 
to accumulate on the passes around then or shortly thereafter. 


Otherwise, everything seems on track for now. May need to increase 
timing later for points further east including the Reno area and 
the I-80 corridor. Other concerns still lie with the amount of 
precipitation in the Reno area Monday morning. Models show main band just 
to the north, but I have seen this before in similar situations 
(tonopah low type setup). In past situations the band was shown 
about 50 miles too far north and if this occurs tonight, Reno- 
Carson-Minden will likely see 2-4 inches of snow in the morning. 
Will be watching the surface pressure/changes carefully to determine 
where the surface low develops. The location will provide clarity 
as a position more toward Minden proves model positioning to be right. 
However, if the low is more toward Bishop-Hawthorne then the band 
will be further south. Wallmann 


&& 


Previous discussion... /issued 258 PM PST sun Feb 12 2012/ 


Short term... 
current water vapor imagery shows a jet streak digging into the 
base of the trough offshore near 41n 130w. Forecast models remain 
fairly consistent with this feature moving on shore along the 
Oregon coast this evening then dropping southeast along the Sierra 
through Monday afternoon. Precipitable water plume ascd with this trough is up to 
about 1 inch off shore according to latest AMSU satellite data. 
Forecast precipitable water is around 0.8 inches as the low tracks southeast tonight and 
Monday. 


The track of the low is critical to the location of the best snowfall. 
It will generally be snow as forecast soundings show a quick drop 
in snow levels as precipitation starts. The only areas that may see a mix 
will be south of Highway 50 and along and east of Highway 95 early 
Monday. So have lowered snow levels most locations. As the 
European model (ecmwf)/NAM/GFS/Gem and most ensemble members track the low along or 
just west of the Sierra am fairly confident that Sierra will get a 
good amount of snow...at least enough for advisories to pan out. 
There will be an upslope component early for the Sierra crest but 
this will not be long lived and flow is not very strong. So 
heaviest precipitation in the Sierra will likely be late tonight and early 
Monday in the proximity of the upper low. This precipitation will taper off 
by late Monday afternoon. 


Questions on location of accumulating snowfall remain for east of 
the Sierra. Current track of the low puts much of the basin and 
range north of I-80 and east of Highway 95 in a favorable area for 
diffluence/deformation aloft late tonight and Monday. So have 
increased probability of precipitation and quantitative precipitation forecast over this area and will issue an advisory 
for zone 4 with a concentration along I-80 north of Lovelock and 
Highway 50 east of Fallon. If the track of the low shifts to the 
west this diffluent area will shift west as well. That would put 
the Reno/Carson City in a more favorable location for heavier 
snow. For now will leave the Reno/Carson out of any advisory...but 
all concerned parties should be cognizant of the potential for 
snow accumulations of 2 inches or more...especially in the 
foothills...for the Monday morning commute. 


The upper low continues to sag south Monday night with snow 
tapering to showers. Higher probability of precipitation will hang on longer in the west 
central portion of Nevada and also into Mono County where there will 
be a brief period of enhanced upslope...although this will be 
fairly weak. Short wave ridge develops for Tuesday with some 
drying and warming. European model (ecmwf) and GFS are now dropping another low 
into the region late Tuesday night. NAM does not have a closed low 
like the European model (ecmwf) and GFS but does drop a trough south into far eastern Nevada. 
With this big departure from the GFS and European model (ecmwf) have opted to 
largely ignore the NAM after Tuesday. Added some probability of precipitation for late 
Tuesday night to the far northern and western areas of the 
County Warning Area...but most of the impact of this low will be in the extended 
forecast. Mlf 


Long term...Wednesday through Sunday... 
cooled Wednesday several degrees for most areas, otherwise little 
change to the extended grids. 


Another slider will be dropping down into the region for Wednesday. 
There is large uncertainty as to where the low will pass by the 
region, with models flopping between near the Sierra crest and 
central Nevada and the 15z sref sporting a large Standard deviation 
bullseye over the northern Sierra (on the backside of its mean low). 
With all the uncertainty it has made pop easier as a broad brush 
slight chance to low end chance (mono County with possible upslope 
flow) the best way to go for now. The only thing that seems fairly 
clear is that if any precipitation falls it will likely be in the form of 
snow with a significant cold pool with the upper low in all models. 
In addition, I have lowered highs Wednesday given the strength of 
the cold pool. 


Wednesday night through Thursday night, there is good agreement with 
an upper ridge building overhead until the next system arrives by 
next weekend. As this system looks like another bowling Ball low 
breaking off from the main northern branch flow it has an inherent 
uncertainty as to where it will wind up moving through the southwest 
Continental U.S.. therefore, I have not gone to drastic on changing grids so we 
still have some chance of precipitation Friday and Friday night down to 
about Highway 50. However, the latest models would have US push the 
precipitation chances back 12-24 hours to the Saturday timeframe. 


With the eventual location of next weekend's system very hard to 
ascertain at this time, I have lingered pop through the weekend as 
precipitation cannot be ruled out. Snyder 


Aviation... 
for the Sierra, conditions will deteriorate by around midnight for 
ktvl/ktrk and the northern Sierra with IFR/MVFR conditions 
persisting through Monday and several inches of snow accumulation on 
runways. For the Mono County Sierra and kmmh, most of the snow 
tonight and Monday morning will be restrained to west of Highway 395 
with breezy conditions and perhaps a few brief -shsn elsewhere. 
Conditions will deteriorate east of 395 and for kmmh later in the 
afternoon and into Monday evening as a wrap-around snow band 
develops. 


For krno and the western Great Basin, snowfall is a bit more 
uncertain and depends on where the incoming system's snow band sets 
up Monday morning, although at this time snow looks heaviest well 
north and east of krno in the basin and range. The critical time for 
runway accums will be before 10 am when the heaviest snow combines 
with the coolest ground temperatures. For krno, the best shot for a light 
runway accumulate will be between 2 and 7 am Monday when around a 
half-inch will be possible on untreated surfaces. However, if the 
system moves just 40 miles or so west heavier accums will be 
possible. 


By late morning and into Monday afternoon, the snow band is expected 
to decrease in organization and intensity as the best forcing moves 
into central Nevada. Also, paved surfaces should warm up for the 
melting of snow. Snyder 


&& 


Rev watches/warnings/advisories... 
Nevada...Winter Weather Advisory from midnight tonight to 4 PM PST Monday 
nvz005. 


Winter Weather Advisory until 4 PM PST Monday nvz002. 


Winter Weather Advisory from 4 am to 4 PM PST Monday nvz004. 


California...Winter Weather Advisory until 4 PM PST Monday caz071. 


Winter Weather Advisory from midnight tonight to 4 PM PST Monday 
caz070. 


Winter Weather Advisory until 4 PM PST Monday caz072. 


&& 


$$ 


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