Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 241025
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
325 AM PDT Tue Apr 24 2018

.SYNOPSIS...
Mainly dry and warm this week except for a chance of a few showers
or thunderstorms over the mountains each day.

&&

.DISCUSSION...
Mostly clear skies across interior NorCal early this morning.
Current temperatures range from the 30s in the mountain valleys to
the 50s to lower 60s in the Central Valley.

Ridge of high pressure will shift slightly eastward the next few
days as a large scale upper level trough edges closer to the
coast. This trough will bring enough instability for a few
afternoon and early evening showers and thunderstorms along the
Sierra crest. Warm weather will continue with above average
temperatures, then readings will start a gradual cool down across
the forecast area Thursday.

Still some uncertainty on where the low will move ashore late in
the week. However, the cool down will accelerate Friday with a
chance of showers and thunderstorms mainly across the mountains.

&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)
Extended models consistent in idea of large upper low over the
western U.S but differ on details. Either GFS or ECMWF would
indicate a threat of showers over most of the forecast area
especially during the afternoon hours. Stability progs indicate
some instability over the northern mountains and Sierra Cascade
crest on Saturday so limited thunderstorm threat to these areas.
Instability spreads westward on Sunday so may see some isolated
thunderstorms dropping down into the northern and central
Sacramento valley. Cloud cover and cooler airmass associated with
the low will bring cooler temperatures over the weekend down to a
little below normal for this time of year. Models diverge early
next week so confidence in forecast lowers but keeping a threat of
showers over the Sierra Cascade range. Upper low should begin to
shift inland by next Tuesday whichever model verifies making
Tuesday the last day of any shower or T-storm threat before upper
ridging builds over the west coast the middle of next week.
Daytime highs start a warming trend with a slight warm up to near
normal on Monday then climb to several degrees above normal on
Tuesday as upper ridging starts to build in. At this point the
second half of next week looks dry.

&&

.AVIATION...
VFR conditions at the TAF sites the next 24 hours. Isolated
thunderstorms possible northern Sierra this afternoon. Winds
generally 10 kts or less.

&&

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

&&

$$


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