NWS Area Weather Forecast Discussion
County Warning Area [CWA]: STO Regional NWS Weather Office: Sacramento, CA
FXUS66 KSTO 260650 AAA
Area Forecast Discussion
National Weather Service Sacramento CA
1050 PM PST Sat Jan 25 2020
Rain and high elevation snow will move through the Norcal tonight
and Sunday. The system moves east of the area by early Sunday
evening. A couple of weak systems will clip the far northern part of
the state through the middle of next week but for most areas
conditions will remain dry.
The Evening Update: Rainfall rates have been at a steady 0.05"-
0.10"/hr at many locations N of the I-80 corridor this evening. This
system will arrive in two parts, with the initial wave of precip
moving through Sun morning (~15-16z), and the 2nd by early afternoon
(~21-22z). The back edge of the precip will likely precede these
upper air features by an hour or two or so. This is noted in the NAM
REF forecasts which virtually end precip in our CWA by around 2 pm
(22z). Highest NAM REFs in Ern Shasta Co behind the initial wave of
precip could be considered potential for thunder, otherwise the
various BUFKIT forecast soundings for our area have very limited
CAPE. This trof is not nearly as cold as previous systems which
trigger thunder earlier this winter. Satellite indicates a few CG
strikes with the 2nd wave near 41N/138W, and this feature is
forecast to track across Shasta Co supporting the NAM REFs in
the same area early Sun afternoon.
Snow levels remain high with the snow profilers indicating the snow
levels around 8500 ft, so very little impacts over the passes until
the snow levels lower to pass levels a couple of hrs before sunrise.
Some light showers are currently moving across the northern coastal
mountains. Heavier precipitation is expected to move along the
coastal range and northern valley and mountains early this evening
and then spread south and east through the evening to bring most
areas some rain. Snow levels are high through most of the night and
above major trans- Sierra pass levels before lowering late tonight
and Sunday morning.
There is a slight chance of a couple of weak post-frontal
thunderstorms Sunday morning through early afternoon. The
instability does not look all that great and conditions will
quickly stabilize during the afternoon hours so confidence is
The system moves through Sunday morning with some residual
showers remaining in the afternoon and mainly in the mountains
before ending Sunday evening.
Storms through mid week will stay focused on moving into the
Pacific Northwest with only the extreme northern part of
California having any chance of showers on Monday night and
Wednesday from the tails of those systems. Further south in the
central valley we will be watching out for possible fog to form
.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
By mid week, upper ridging across California will keep the
majority of the area dry with above average temperatures expected.
A few systems passing to the north will bring some clouds to the
area next week, along with some small precipitation chances
primarily in Shasta County. The upper ridge looks to amplify and
continue through the weekend. Highs by Friday and Saturday may be
roughly 10 degrees above normal for the end of January and early
Reduced conditions through the period as a system moves inland
across NorCal tonight. Widespread MVFR to IFR ceilings/visbys
expected with -RA after 04-06Z. Local areas of southerly wind
gusts 15-25 kts develop after 08Z Sunday. Conditions look to
improve at sites after 18Z.