Scientific Forecaster Discussion

000 
FXUS65 KREV 122150
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
150 PM PST Thu Dec 12 2019

.SYNOPSIS...
Breezy winds will continue into Friday along with some light
Sierra showers. A stronger system will arrive by Friday afternoon
with continued gusty winds, but with more rain and snow into
Saturday morning. Snow levels will gradually decrease with 
significant travel impacts likely in the Sierra. A colder, but 
weaker, storm for Saturday may bring light snow to all elevations.
A break in the wet pattern is anticipated for early next week.

&&

.SHORT TERM...
We have continued to make a few adjustments to the forecast. The
first is to increase winds for the next 24 hours for the Sierra
and adjacent lee side valleys. The other is to indicate a better
chance of snowfall in western Nevada Saturday night.

For the next 18 hours, occasional upslope showers will continue
in the Sierra from highway 50 north with light amounts. Ridge 
winds will continue to gust to 75+ mph with some gusts in the lee 
side to 40 mph at times, especially this evening.

The next wave still looks on track to arrive mid to late morning
Friday in the Sierra from the Tahoe Basin northward. The heaviest
precip still looks to occur in the afternoon to evening time fame.
Spillover will be somewhat limited with the best chance in the
evening. Central Nevada will have a better chance of precip as 
the front reforms in this area. Amounts still look on track from
the morning update. The front weakens as it slides south into 
Mono County Friday night with most precip near the crest and very 
limited east of 395.

A break for Saturday with another, colder system for Saturday
night. This one is smaller and weaker so who gets the heaviest
snow is yet to be determined. This system will have decent forcing
as it moves through for a quick burst even into the valleys. While
we have yet to determine who will get the heaviest amounts, there
is high confidence it will occur north of Highway 50. X 

...LONG TERM...Sunday through next weekend...

Snow showers may continue during the day on Sunday, especially in
west central Nevada, as the backside of the trough moves through 
the region. Much cooler temperatures are expected Sunday through 
Tuesday with daytime highs about 5-7 degrees below normal. 

By Wednesday another low pressure, mostly cut-off from the upper 
level flow, will likely begin to bring precipitation back to the 
region into Thursday morning. Overall precipitation from this 
system is expected to be modest by Sierra standards, but could 
still cause some travel disruptions over the passes. 

Regarding the 19-22nd moisture influx- while confidence in an 
another round of incoming moisture along the California coast 
during this time period continues to increase, so does the 
uncertainty with impacts in the Sierra and western Nevada. The 
main reason is that the moisture transport could be from a more 
southerly direction which would significantly limit the orographic
lifting mechanisms. We've seen this before, where large amounts 
of AR moisture move into California with limited impacts east of 
the Sierra crest and especially western Nevada. Important point ->
High confidence in precipitation DOES NOT necessarily mean large 
amounts of precipitation. 

Ensemble EC & GFS precipitation accumulation, are showing some of
the widest spread we've seen. Where some ensemble members show 
significant precipitation and others show little to none. This 
time frame is still worth watching, especially if you are 
traveling during this period, but there is still a lot of 
uncertainty in potential impacts. -Zach

&&

.AVIATION...
Gusty winds to continue with some LLWS particularly around Lake
Tahoe. Ridge winds will gust to 70 kts the next 24 hours. At least
until 15Z Friday, most areas will remain VFR with local MVFR CIGS
in the Sierra with mtn obscuration. 

High confidence in MFR/IFR CIGS in -RA after 18Z Friday for the 
Sierra from KTVL northward transitioning to -SN after 03Z. Areas
of MVFR CIGS in western Nevada, mostly north of I-80. LLWS will 
continue around the Tahoe Basin, with more localized LLWS for the 
395 corridor (KMMH north to KRNO).

After a break Saturday, -SN possible for all elevations including
the western Nevada terminals. Chances of at least a dusting for
the terminals is 60%, except for KMMH which will be too far south.
X

&&

.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 10 AM Friday to 10 AM PST Saturday 
     above 6500 feet in NVZ002.

CA...Winter Weather Advisory from 10 AM Friday to 10 AM PST Saturday 
     above 6500 feet in CAZ072.

&&
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