118
FXUS66 KSTO 280911
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
111 AM PST Fri Feb 28 2025

.SYNOPSIS...
Seasonably warm and dry weather prevails today, with a more
pronounced pattern shift beginning by the weekend. Cooler
temperatures expected, with periodic chances for moderate
rain/mountain snow into next week. Some isolated thunderstorms
possible Sunday afternoon as well.

&&

.DISCUSSION...
The streak of clear sky nights comes to an end for interior
NorCal as high clouds have filtered into the region while a cutoff
low approaches central California. While a partly cloudy start to
the morning is anticipated, as the system promptly drifts
southwestward, skies look to clear with another seasonably warm
afternoon in store. High temperatures in the 60s to 70s are once
again expected region wide, with lower to potentially mid 80s
possible into the northern Sacramento Valley as well. Saturday
likely will not see a precipitous drop in high temperatures with
the next wave trending a bit slower, with 60s to 70s expected for
most locations.

Given the general consensus toward a slower trajectory,
precipitation onset for interior NorCal is trending toward the
overnight period rather than late Saturday. Forecast precipitation
totals from Sunday through Monday remain largely unchanged, with
0.25 to 0.5 inches throughout the Valley and foothills and 0.5 to
1.0 inches along the Sierra/southern Cascades and into portions of
Shasta County. While thunderstorm potential will remain
conditional upon the timing of attendant clearing as the system
moves through, still 10 to 20 percent probabilities of
thunderstorm development persist, primarily from Interstate 80
southward at this time. Any thunderstorms that do develop will be
capable of brief heavy rainfall, gusty winds, small hail, and
possibly a brief funnel cloud.

Snow levels at the time of heaviest expected snowfall are
expected around 4000 to 5000 feet, before falling to 3500 to 4500
feet late Sunday into Monday. As a result, most accumulating
snowfall is anticipated above 5000 feet, where probabilities of
snowfall greater than 8 inches sit around 40 to 60 percent from
Interstate 80 southward and 20 to 40 percent north of the
Interstate 80 corridor along the Sierra/southern Cascades.
Resultant mountain travel impacts are expected through the late
weekend period into early next week with slick travel conditions
and potential for travel delays.

Precipitation chances are expected to remain largely confined to
the Sierra/southern Cascades on Monday, although some low (20 to
30 percent) probabilities of isolated to scattered showers at
lower elevations will be possible as a weak reinforcing shortwave
traverses the flow pattern. As a result, overall lighter
precipitation is expected for Monday, as below normal temperatures
prevail. With the system looking to linger from Sunday into early
next week, breezy south-southwest winds are anticipated, gusting
15 to 25 mph on Sunday, becoming lighter by Monday.

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...
Ensembles still consistent regarding a brief break in widespread
precipitation activity early Tuesday and into the afternoon. EC
500mb heights show a brief period of upper level ridging
developing the wake of the trough that is forecast to move through
earlier in the week, however ridging will quickly move east
during Tuesday afternoon and be replaced with another PacNW
trough. Compared to yesterday`s model runs, precipitation totals
for this mid-week system have remained relatively unchanged.
Current National Blend of Models probabilities for 0,50" inches of
rain from Tuesday night through Thursday afternoon are around 20
to 50% in the Valley, with highest probabilities in the northern
Sacramento Valley, and a 50-70% chance for the foothills and
mountains. Snow amounts trended similar to last night`s model runs
as well, with probabilities of 6 inches of snow or more around
40-60%. Current snow level forecasts show fluctuations, with
levels starting around 6000 feet Tuesday night, lowering to
4500-5500 Wednesday and Thursday. Lingering showers and mountain
snow showers will be possible late Thursday night and into Friday,
but the bulk of the precipitation is expected Wednesday and
Thursday afternoon.

Looking beyond the extended forecast period, cluster analysis
reveals around a 60/40 split in our upper level pattern. 60% of
clusters show a broad zonal flow regime, while 40% show weak
ridging aloft. Also analyzing the GFS/EC IVT probabilities for
March 8th-11th, the GFS shows slight chances of a moisture plume
moving inland, while the EC shows higher chances but the main
moisture axis residing further north of NorCal. The NBM seems to
be more aggressive, showing continued precipitation during the
aforementioned timeframe. We will continue to monitor trends as we
move into the weekend and next week when details will become more
clear.

&&

.AVIATION...
VFR conditions expected across interior NorCal for the next 24
hours. Northerly surface winds below 12 knots in the Valley and
Delta. Easterly wind gusts up to 20 knots in the foothills and
mountains through around 18z today. Slight chance (~10%) of
visibilities dropping to less than 1/2SM due to BR/FG in the
central and southern Sacramento and San Joaquin Valley`s until
around 18z.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$