Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 221043

Area Forecast Discussion
National Weather Service Reno NV
343 AM PDT Sun Sep 22 2019


Warmer temperatures and increased winds are expected today as a
cold front begins to move into the region. Breezy conditions,
shower chances, and a cool down is likely for this evening through
Monday. A warmup will occur Tuesday and Wednesday before another,
stronger weather system brings gusty winds late week along with
much colder temperatures and shower chances Friday through the



Minor changes to the short term forecast this cycle:

*Reduced POPs and QPF across the region for tonight into early
Monday AM.

*Issued a Lake Wind Advisory for Lake Tahoe from 2 pm today until
11 pm tonight.

Tranquil weather will continue this morning with mild temperatures
through this afternoon. Cloud cover and southwest winds are set
to increase this afternoon ahead of an approaching shortwave trough
and cold front from the northwest. The pick up in the winds should
mix the boundary layer, contributing to the warmer temps with highs
in the 70s for the Sierra valleys and upper 70s, low 80s for western
Nevada. Expect winds 10-20 mph with gusts up to 30 mph for this
afternoon transitioning to the northwest and decreasing in magnitude
by late in the evening. A Lake Wind Advisory has been issued for
Lake Tahoe due to the gusty afternoon/evening winds. Stronger winds
are likely for wind prone areas such as the Sierra ridges, the US-395
corridor, and US-95 near Walker Lake.

The overall timing of the frontal passage remains the same, mainly
from this evening through early Monday morning. As stated previously,
POPs and QPF across the region have been slightly reduced as short
range model guidance continues to suggest less instability, moisture
and overall coverage. Having said that, rain showers and high elevation
snow showers (>8500 ft) are still possible starting in the northern
portions of Lassen and Washoe counties by late afternoon before
migrating towards the southeast into Pershing, Churchill, and
Mineral counties later in the evening following along the frontal
boundary. Isolated showers could linger along the Sierra in Mono
County Monday morning, potentially lasting into the afternoon as
upslope flow will be present on the backside of the shortwave.

Weather conditions are likely to begin to improve for the rest of
Monday as the trough makes a quick exit towards southern Nevada and
Arizona. Breezy northeasterly flow and cooler temperatures will
result with highs roughly 10 degrees cooler compared to today`s and
lows around normal. Heights increase on Tuesday as high pressure
noses into the region warming up temperatures once again. -LaGuardia

.LONG TERM...Wednesday through Saturday...

The overall pattern evolution and reasoning for the extended part of
the forecast has changed little this model cycle. Thus...there were
limited changes made to the inherited forecast. The changes were
primarily in the Friday/Saturday time frame and largely involved
adjusting POPs and a lesser extent...upward. We also made
some minor changes to lower temperatures a bit further from Saturday
morning through late Saturday night.

Dry west-northwest flow aloft and some warming in the low levels for
Wednesday should give way to a change starting late Thursday. Model
simulations are pushing a jet streak across the northern half of the
forecast area by late Thursday and the jet streak brings along a
lobe of cyclonic vorticity advection. While moisture is a bit
limited...the presence of vorticity advection and a jet streak
should allow some showers to form near the Oregon border late
Thursday afternoon into Thursday evening.

A more substantial change will occur Friday as a rather broad and
anomalously cold trough of low pressure begins to dive south out of
the northeast Pacific before settling over the region for the
weekend. Most operational models and ensemble members are converging
on this solution. That raises the confidence in a cold...showery

Gusty winds are likely to develop ahead of the main trough Friday
and again Saturday as low level thermal and pressure gradients
increase...and another jet streak develops over the region Friday.
The strongest winds are likely to be east of the forecast area...but
some valley locations in western Nevada may see gusts approaching 35
to 40 mph both days.

Much colder air aloft drives increasing instability late Friday into
Saturday even as surface temperatures fall. The trajectory of the
upper level trough is not conducive to transporting huge amounts of
moisture into the region...but the shear increase in instability and
lift interacting with the upper level jet is likely to aid in
efficiently wringing available moisture out as showers. It is not
out of the question that we could see some thunderstorms...but we
have left those out for now.

High temperatures are likely to drop some 15-20 degrees from
Thursday to Saturday. Highs Saturday may struggle to get out of the
50s in the far western Nevada valleys and stay locked in the 40s in
the Sierra valleys. Snow levels fall as well; snow levels could drop
to as low as 5000 feet over northeast California by Saturday
morning. It will not be unusual to see a couple of inches of
snow...or more...above 7000 feet by late Saturday night in the
Sierra...northeast California...and far northwest Nevada.
Significant accumulations on roadways should be limited by the warm
ground...but passes above 8000 feet may see a period of
accumulation Saturday and Saturday night.



VFR conditions expected this morning for all area terminals, besides
for KTRK where FZFG, leading to LIFR/IFR visibilities, is
forecast to develop from ~11Z-15Z this morning.

Cloud cover and southwest winds increase this afternoon ahead of an
approaching cold front set to move through the region tonight into
Monday morning. Anticipate winds 10-15 kts with gusts up to 25 kts
for all area terminals before decreasing and shifting to the
northwest overnight.

Isolated rain showers are possible for KRNO, KCXP, KMEV, NFL, and
KLOL mainly for late tonight along the frontal boundary. KMMH could
also see some showers Monday morning due to upslope flow.
Mountain obscuration can be an issue as well with the presence of
low level clouds and rain showers during this time.

Weather conditions improve late Monday afternoon through Wednesday
before the active pattern returns for the end of the week.


.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory from 2 PM this afternoon to 11 PM PDT this
     evening for Lake Tahoe in NVZ002.

CA...Lake Wind Advisory from 2 PM this afternoon to 11 PM PDT this
     evening for Lake Tahoe in CAZ072.



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