789
FXUS66 KSTO 042021
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
121 PM PDT Sat May 4 2024


.SYNOPSIS...
A weather system moves through the area today bringing showers,
mountain snow, isolated thunderstorms, gusty winds and cooler
temperatures. Drier, warmer conditions return next week with
gusty north to east winds mid-week.

&&

.DISCUSSION...
The late-season system is upon us bringing with a variety of
impacts including Valley rain, mountain snow, and breezy winds.
Radar earlier this morning presented with a classic narrow cold-
frontal rain band (NCFR) aligned north-south that passed through
the Sacramento Valley. Surface observations reported periods of
gusty winds with the NCFR -- upwards of 40 to 46 mph in the
northern Sacramento Valley around Redding, Red Bluff, and Chico.
In the wake of the frontal passage, winds have subsided
considerably. Can`t rule out some isolated thunderstorms
developing in the afternoon in the Valley; the National Blend of
Models (NBM) advertises roughly a 15-30% north of Sacramento.

Up in the mountains, snow levels started this morning in the 6000
to 7000 foot range. As the cold air ushers in, expect snow levels
to plummet to less than 5000 feet by mid-afternoon, and further
drops to below 4000 feet by the evening. Snow levels will drop
even more overnight as precipitation begins to taper off. This
will result in a rain-to-snow transition for a handful of mountain
communities through the rest of the day. A period of heavy snow
will impact travel corridors such as Interstate 80 and Highway 50
this afternoon and evening with the HREF advertising peak
afternoon/evening snowfall rates between 1-2.5 inch per hour. The
Winter Storm Warning remains in effect for elevations 4000 ft and
above through 8 AM Sunday. For a probabilistic sense, the National
Blend of Models gives locations above 5000 feet a 50-90% chance
of >= 12 inches of snow. Minor accumulations of up to an inch are
expected between 3000 to 4000 ft.

Precipitation ends in the late afternoon for the Valley and
overnight in the mountains. Aside a few lingering snow showers at
along/south of Interstate 80 day break Sunday, dry conditions are
forecast to return to interior northern California. Despite the
drier conditions, temperatures won`t be quick to rebound as Valley
highs will remain in the 60s. For comparison, normal highs for the
Sacramento Valley are in the upper 70s. That said -- this will be
the start of day-to-day warming through the week as high pressure
rebuilds over the eastern Pacific. // Rowe

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Warming temperatures are expected for the second half of next
week as an upper-level ridge builds west of California and short-
wave drops from the Pacific Northwest to the Great Basin. This
synoptic pattern does favor dry, northerly winds for northern
California: both the Extreme Forecast Index (EFI) and NBM are
picking up on these increasing winds in the Wednesday-Thursday
timeframe. During this same time, the day-to-day warming will see
afternoon highs return to near-normal by Wednesday, and above
normal for Thursday and into next weekend. While today may not
seem very May-like, next weekend certainly will: the NBM gives
roughly a 50-80% chance of exceeding 90 deg F for Saturday for
many Valley communities. (That`s not a typo -- yes, I mean
ninety!) // Rowe

&&

.AVIATION...
Quick moving late season storm system moves across interior
NorCal today into Sunday. Gusty south-southwesterly winds and
Valley rain showers through the afternoon. Isolated thunderstorms
with MVFR/IFR conditions also possible between 20z and 03z from
Sacramento northward. VFR conditions then expected in the Valley
late this evening into Sunday. In the Sierra, widespread IFR/LIFR
with moderate snow expected and periods of heavy snow possible
through this evening and into the overnight hours. Snow levels
4000-5000 feet this afternoon, fall to 3000-4000 feet this
evening. Southwesterly Sierra winds gusting 40-45 kts at times
this afternoon, decreasing after 00z Sunday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 8 AM PDT Sunday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

&&

$$