910
FXUS66 KSTO 021905
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1205 PM PDT Thu May 2 2024

.Synopsis...
Dry and warm weather through Friday with breezy northerly winds.
Active weather returns this weekend as a weather system drops down
bringing showers, mountain snow, isolated thunderstorms, gusty
winds and colder temperatures.

&&
Things remain on track with high confidence of a pretty strong late
spring...winter like storm system for the area this weekend.
Upper level low system will drop south Friday night then exit the
area by Sunday afternoon. EC standard anomaly data showing 500 mb
heights impressive at a -2 with return interval of 10 to 20 years
for this time of the year. Ensemble means in good agreement that
the upper low will basically slide south across central California
with a good period of upper dynamics. Could be stronger if the
low was further west but still some good dynamics with this
system. Pretty much a classic winter system orginiating from the
Gulf of Alaska with a nice Atmospheric River and PW plume with
climo PW values of 150 to 230% above normal. System is a pretty
quick hitter so biggest challenge is level of impacts with snow
and blowing snow above 5000 feet. NBM probabilities showing
bullseye of higher snow right in the I80 corridor with 70% to 80%
chance of 8" and about 50% chance of a foot at highest elevations.
Snowfall rates have a chance to exceed an inch an hour in
intensity Saturdday afternoon and evening. So with all this the
biggest question will be the impacts of this snow and wind. With
collaboration with area offices given time of year, sun angle,
road and ground temperature and quickness of storm will stick with
a winter weather advisory for the event.

In the valley, would expect a band of rain to push across from
north to south. NBM QPF probabilities have been pretty consistent
for low probs of half an inch and solid chances of quarter of an
inch.

High EFI values for cool high temperatures Saturday and Sunday as
well with high temperatures dropping a solid 10 to 20 degrees from
Friday to Saturday.

&&
.EXTENDED DISCUSSION (Monday THROUGH Thursday)...

Higher confidence above 50% that extended period looks to be
farily dry and on the cool side. Cluster analsys showing majority
of solutions point to lower 500 mb heights with dry northerly
flow. Biggest risk would be mid to late week of some northerly
flow looks to set up with general troughing across the Great
Basin. How amplified that low gets will determine strength of wind
which right now proabilties of 40 mph guest are down around 30% to
40%. WMR


&&

.AVIATION...


VFR conditions persist across interior NorCal through the forecast
period. Gusty north-northwesterly winds increase through the
afternoon, with some Valley gusts 20 to 25 kts. Winds then decrease,
but remain breezy this evening into the overnight hours.


&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 11 AM Saturday to 8 AM PDT Sunday
for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

&&

$$