Portola, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

541
FXUS65 KREV 241037
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
237 AM PST Tue Dec 24 2024

.SYNOPSIS...

* A winter storm will bring periods of gusty winds, lower elevation
  rain, and heavy mountain snow through this afternoon.

* Dry, cooler weather prevails on Christmas with additional storms
  likely late this week into the weekend.

* A colder storm is possible early next week with dry conditions
  favored to begin the new year.

&&

.DISCUSSION...

Today`s winter storm is almost here as a pre-frontal band of showers
is beginning to approach the Sierra per 10Z radar obs. This morning
and early afternoon (roughly 4 AM thru 2 PM PST) will feature this
storm`s greatest wind and snow impacts before weather conditions
improve during the afternoon and evening as the storm departs. We`ll
dive into the details shortly, but the main takeaway is this: Be
prepared for moderate to heavy snowfall to make holiday travel much
more difficult in and across the Sierra today with strong winds
impacting air travel and driving conditions (especially for high-
profile vehicles) in the Sierra and Sierra Front.

Winds are already increasing along exposed Sierra ridges in response
to intensifying winds aloft with gusts eventually reaching 100+ mph
along the Sierra crest later this morning. It`ll be quite windy for
Sierra Front communities through the afternoon, but strongest S/SW
gusts of 35-45 mph are favored in the 4 AM thru 10 AM PST window
when pressure gradients tighten ahead of an advancing cold front.
Wind prone locales such as stretches of the US-395/I-580 corridors
and in the vicinity US-95 from Schurz to Hawthorne may see gusts
approach 60-70 mph at times. Winds will subside in the late
afternoon and evening in the wake of the cold frontal passage.

The aforementioned band of rain and snow will arrive in earnest to
the Tahoe Basin after 6 AM and will expand southward towards Mammoth
by 10 AM PST. Snow levels begin above 7000 feet at the onset and
fall to near 5500 feet in a north-to-south fashion in the late
morning and afternoon. Thus, p-type will begin as rain for Tahoe
communities near lake level before switching to snow after 8-9 AM
PST. However, it may begin to snow earlier if a narrow band of
heavier showers can effectively drag snow levels down towards lake
level. There is also the potential for isolated lightning as this
heavier band of showers moves through the Sierra.

Heaviest snowfall of 1-2"/hr is likely from the late morning until
the early afternoon with highest Sierra peaks having a 30-40% chance
of achieving 3+"/hr rates, contributing to 8-16" of total snowfall
along the Sierra crest by Wednesday AM. Lake level communities
(e.g., Truckee, South Lake Tahoe, Bridgeport) will likely see 1-3"
of snow while "snowier" locales west of Lake Tahoe and Mammoth Lakes
likely see 3-6" by Christmas AM. While not a White Christmas in a
technical sense, foothills/VC have a 10-30% chance of a dusting of
snow by Christmas AM. Lower western Nevada valleys will only see
rain with this storm, heaviest during the late morning hours. Once
the cold front passes, rain and snow becomes more showery in nature
during the afternoon before tapering off around/after sunset.

The weather outside on Christmas Day will be much less frightful as
dry, albeit a tad chilly conditions prevail. A series of quick-
moving troughs will maintain periods of increased winds and showers
Thursday into the weekend. The weather pattern keeps us mostly on
the warmer side of these storms, so mild temps and higher snow
levels are favored. A colder, stronger storm is possible around the
29th, but after that a drier pattern will likely help us ring in the
new year.

-Salas

&&

.AVIATION...

A winter storm will bring periods of LLWS and mountain wave
turbulence, lowered CIG/VIS, and mountain obscuration into the early
afternoon before flight conditions improve in the late afternoon and
evening.

SW FL100 winds increase to 45-55 kts through 15Z, which will be when
greatest LLWS and turbulence concerns are expected for regional
terminals. S/SW surface gusts approach 25-35 kts through 18Z before
winds shift to W/NW between 18-21Z with additional gusts to 20-25
kts through the afternoon. The passage of a cold front may yield
additional LLWS concerns during the 18-21Z window. Winds become
light and VRB in the evening and overnight.

Periods of MVFR/IFR conditions are expected into the afternoon for
Sierra terminals with occasional MVFR conditions for KRNO/KCXP/KMEV
between 15Z and 21Z. Mountain obscuration expected through much of
the afternoon. There is a 5-10% chance of lightning within 10 miles
of KTRK/KTVL/KMMH this morning. Runway snow accumulation of 1-2"
is likely for Sierra terminals with a 20% chance of exceeding 2"
by Wednesday AM.

-Salas

&&

.AVALANCHE...

A winter storm is expected to bring strong ridgetop gusts and heavy
mountain snow into the afternoon today. Key impacts include:

* Snow levels begin above 7000 feet early this morning before
  falling to near 5000-5500 feet in the evening.

* Snowfall rates of 1-2"/hr are likely this morning with a 30-40%
  chance of 3"/hr rates along highest Sierra peaks.

* Total snowfall along the Sierra crest will be between 8-16". There
  is a 50-70% chance of SWE of an inch or greater by Wednesday AM.

* Strong southwest gusts exceeding 100 mph are expected along
  exposed Sierra ridges this morning.

-Salas

&&

.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory until 7 PM PST this evening NVZ002.

     High Wind Warning until 3 PM PST this afternoon NVZ001.

     Wind Advisory until 3 PM PST this afternoon NVZ003-004.

CA...Winter Weather Advisory from 7 AM this morning to 7 PM PST this
     evening CAZ071-073.

     Winter Weather Advisory until 7 PM PST this evening CAZ072.

&&

$$