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000 
FXUS65 KREV 240953
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
253 AM PDT Fri Mar 24 2017

.SYNOPSIS...
Active weather pattern will continue through early next week as a
couple of springtime storms bring mountain snow and valley rain.
Travel impacts are likely in the Sierra Friday through early 
Saturday and then again on Sunday and Monday. Breezy winds may
produce choppy lake conditions through the weekend along with turbulent
air travel.

&&

.SHORT TERM...
Forecast is on track for the storm moving into the region early
this morning. This spring system will bring mountain snow, gusty
winds, and some valley rain to the Sierra and western Nevada, but
is expected to push through pretty fast. Travel impacts are likely
along the Sierra passes from early this morning through Saturday,
so if you have travel plans be sure to check the road conditions
before you leave. There is another storm for Sunday-Monday as
well, so travel over the Sierra passes through the weekend could
be troublesome. Plan accordingly! 

Storm through Saturday...

Winds...Winds along the Sierra ridges are already gusting in the 
50 to 70 mph range and will continue to increase through the day.
Surface winds should peak with cold frontal passage this 
afternoon with brief wind gusts up to 50 mph possible. There could
be a brief period of choppy lake conditions at Pyramid Lake later
this afternoon as the cold front quickly moves through the area.

Rain & Snow...Precipitation will begin to push into the Sierra 
around sunrise today with snow levels right around 5000-5500 feet.
Snow levels will rise up through the day to around 6500-7000 feet
which should limit snow accumulations on most roadways through 
the day. The cold front will move through this afternoon and bring
down the snow levels with it, and that is when the highest 
potential for snow accumulation will occur, along with the most 
intense snow and rain rates. By this afternoon and evening snow 
accumulation will be possible down to lake level as well as 
Fredonyer Summit and Yuba Pass. For Highway 395 down through Mono 
County, it looks like it will stay pretty shadowed out during the 
day but we could see a few inches late tonight before snow 
diminishes behind the cold frontal passage. Total snowfall for the
higher Sierra will be in the 10 to 20 inch range overall with QPF
ranging from 1.5" along the crest, 0.75-1.00" from Lake Tahoe 
north along Highway 89, and generally 0.10-0.25" elsewhere as 
spillover will be limited to a quick burst with the front.

Sunday-Monday Storm...
Warm air advection precipitation begins to push into the Sierra
and western Nevada on Sunday afternoon along with an uptick in the
winds. Fortunately, the winds don't appear to be much of a 
concern with this second storm. Generally, the WAA precipitation 
will be light showers with the snow levels starting around 6500 
feet. With WAA precipitation, terrain will not limit spillover 
potential so there will be a decent shot at rain/snow across the 
Sierra and western Nevada. Even though these showers will be 
relatively light, we could see impacts to travel over the Sierra 
passes, especially since it is at the end of the weekend. 

The main swath of precipitation will push into the Sierra 
starting late Sunday night into early Monday morning with cold 
frontal passage progged between 12-18z Monday morning. Snow levels
will drop to near 5000 feet by Monday night with rain/snow 
showers continuing through the evening. Snow amounts by Monday
afternoon above 7000 feet could be around 1 foot with between 6-10
inches possible below that 7000 foot mark in the Sierra, 
including the Tahoe basin, Mono and Alpine counties. Snow will be 
possible down to as low as 5000 feet by Monday night into early 
Tuesday, but any accumulations should be relatively light if any 
at all. Above 5500 feet in the foothills of western Nevada, 
including Virginia City, we could see up to 5 inches of snow with 
this system. 

Residual light convective showers will be possible through the day
Tuesday, but generally much of the precipitation will have ended.
-Edan


.LONG TERM...Tuesday through Thursday... 

Minor changes were made to the inherited long term forecast this 
cycle. The main changes were made in the Tuesday time frame where 
pops were removed as the operational models now favor a weak short 
wave ridge for that day.

Model agreement tends to start breaking down after Tuesday. Both the 
ECMWF and GFS go into a brief period of zonal flow before another 
trough begins to impact the western U.S. The differences between the 
models start to amplify as the GFS is a little more progressive with 
this trough Wednesday and Wednesday night...bringing the trough 
farther inland than the ECMWF. The ECMWF has the trough axis along 
the coast by Thursday morning. Both models bring a period of 
precipitation back to the forecast area. This starts later Wednesday 
over the northern CWA then spreads east-southeast with a band of 
precipitation along a cold front by Thursday morning. This could 
bring snow levels close to many valley floors.

The ECMWF closes this low over western NV by late Thursday while the 
GFS shows the first hints of trying to close the low along the UT/NV 
border...but this does not fully develop into a closed low until 
Friday morning in AZ. That location of a closed low has direct 
implications for the forecast. The ECMWF would be far wetter and 
cooler for Thursday than the GFS. Each have support from GEFS 
ensemble members. With a fairly wide spread in forecast 
solutions...we opted to maintain the slight chance to low chance 
pops inherited from the previous forecast for Thursday/Thursday 
night.



&&

.AVIATION...
We are starting to see ridge top winds increase ahead of approaching 
upper level trough. By late morning ridge top winds could be gusting 
over 70 knots with turbulence along and down wind of the mountains 
and LLWS at terminal locations. Precipitation associated with this 
trough will move into northeast CA and the northern Sierra later 
this morning. Cigs/vsbys deteriorate through the day with IFR 
conditions at times. By late afternoon a few inches of slushy snow 
are possible at KTRK/KTVL/KMMH. 

East of the Sierra precipitation should hold off until late 
afternoon or early evening when the surface front moves through. 
This will result in a brief period of moderate or heavier 
precipitation at the lower elevation terminals and gusty surface 
winds reaching as high as 35-40 knots. Cigs/vsbys should mostly drop 
into the MVFR category...but a brief period of IFR conditions for 
KCXP/KMEV is not out of the question.

After a brief break early Sunday...another storm system will move 
through the region late Sunday into Monday. This one will be similar 
to today's system. 

&&

.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 7 AM Friday to 4 AM PDT Saturday 
     NVZ002.

CA...Winter Weather Advisory from 4 PM Friday to 4 AM PDT Saturday 
     above 5500 feet in CAZ071.

     Winter Weather Advisory from 7 AM Friday to 4 AM PDT Saturday 
     CAZ072.

&&

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