543
FXUS65 KREV 180903
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
203 AM PDT Wed Sep 18 2024

.SYNOPSIS...

* Well-below average temperatures continue through most of the week.

* The next storm system brings additional precipitation and
  thunder chances today and tomorrow.

* Afterwards, a warming and drying trend starts on Friday and
  into the weekend as the storm leaves the area.

&&

.DISCUSSION...

Nighttime Microphysics satellite imagery continues to show multiple
layers of clouds across the whole region very early this morning.
Radar shows a few very light showers in portions of the CWA. Conditions
will slowly deteriorate during the morning hours as the upper low
seen offshore of the CA coast slowly moves inland this afternoon
and evening. Therefore, expect more clouds and better chances for
rain, snow above 8500 ft and thunder.

This afternoon, the HREF members continue to indicate showers and
isolated thunderstorms across the Sierra, the Sierra Front and
vicinity as the upper low swings to the southeast towards southern
NV. The best dynamics with this system remain to the north of it,
where the jet streak is located in the vicinity of the Eastern
Sierra. The HRRR has been showing this consistently since yesterday.
So, there is moderate confidence on this. However, the uncertainty
comes with the intensity of the shower activity. Ensemble members
have drastic differences. Therefore, expect light to moderate
rain with isolated areas of heavy rain. That would be the best
bet. The best timing for the precipitation will be from 2 - 7 PM.
Showers should slowly dissipate and moves south from the northern
Sierra and the Sierra Front overnight. Then the focus
continues/shifts more to the south towards the Eastern Sierra.

Down in Mono County and the Eastern Sierra is where we have the
best chances of seeing snow in the higher elevations above 8500
ft. Snow amounts have gone down a bit, but we are still expecting
2-4 inches of snow above 9 kft. NBM probabilities for amounts
greater than 4 inches went down, but it is still showing a 20-50%
chance. Amounts greater than 6 inches went down below 20% above 10
kft. Sierra passes including Ebbetts, Sonora and Tioga have only
a 10-20% chance of seeing 4 inches of snow. This came down
significantly from yesterday when it was up to 40%. The main
reason is snow levels have come up to 9000 to 10000 ft, which
means that this system is pulling on some warmer subtropical
moisture. We still have a Winter Weather Advisory, but have
lowered the snow amounts to reflect this change in the forecast.
Anyways, isolated higher amounts are still possible, especially
near the highest peaks along the Sierra crest.

Once the system leaves on Friday morning, drier conditions return
to the area along with a slow warming trend. A north to northwesterly
flow is set aloft as an upper ridge develops in the Eastern Pacific.
There is good agreement among the ensemble members of the GEFS,
ECMWF and CMC for this scenario over the weekend. Afternoon
temperatures will reach near seasonal values by the weekend, and
slowly climb to above normal next week.

-Crespo

&&

.AVIATION...

VFR conditions are expected through the morning hours, then VFR to
MVFR conditions due to lower CIGS after 18Z. Periods of SHRA and -TSRA
are expected between 19Z Wed to 04Z Thurs across the Sierra and Sierra
Front with a 25-35% chance of lightning for all TAF sites, except KRNO
with a 10-20%. The stronger cells could drop VIS down to 4 SM. Snow
is expected generally above 8.5 kft, but KMMH may see a light RA/SN
mix tonight. Also expect mountain obscurations through Thursday late
morning or early afternoon. Winds will be generally less than 10 kts
from the northeast, except KMMH/KTRK been from the south this afternoon.
Light and VRB winds expected during the overnight hours.

-Crespo

&&

.REV Watches/Warnings/Advisories...
NV...None.
CA...Winter Weather Advisory from 2 PM Wednesday to 8 PM PDT Thursday
     CAZ073.

&&

$$