Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 211555
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
855 AM PDT Sun Sep 21 2014

.Synopsis...
Lingering Sierra showers/t-storms are possible through this
evening. Otherwise, dry and warmer temperatures into early next
week. Cooler and possibly wetter weather for the middle to end of
next week.

&&

.Update Discussion...
Upper low centered over central California a little slower to
exit than some model runs suggested, and continues to bring wrap around
moisture from the east into the forecast area. This system will
move into Nevada later today, but showers and thunderstorms will
continue to be a possibility into this evening. Current radar
shows some showers extending into Shasta, eastern Tehama, western
Plumas, Butte, and Sierra. This will continue and spread a little
farther westward, with a better chance of thunderstorms by early
afternoon. Have updated forecast to extend area of convection
farther west, into the east side of the northern and central
Sacramento Valley for today and as far west as the foothills this
evening. Have also increased cloud cover and lowered temperatures
a little for today. EK

.Previous Discussion...Upper level closed low center now appears from
satellite imagery to be somewhere over the northern San Joaquin
valley. IR image shows abundant cloudiness in the deformation zone
in the northeast section of the low. A short wave trough rotating
out of this zone and westward across north central California
brought light showers and isolated thunderstorms over the northern
Sierra and westward into the southern Sacramento valley overnight.
This disturbance has moved westward and weakened and the showers
have ended most areas. The upper low is forecast to move rapidly
to the northeast today with the center moving into Nevada by 18z
today. Instability progs show some minor instability still over
the eastern portion of northern California today near the back
side of the low so left a slight threat of showers and
thunderstorms over the east side mountains through this evening.
The remainder of the forecast area should see clearing skies as
the low continues eastward. Slightly cooler airmass today should
bring slightly cooler daytime high temperatures. Upper level high
pressure ridge sliding over the north state will bring fair skies
and warmer temperatures on Monday. The high will shift quickly
eastward on Tuesday as a low pressure system in the Pacific moves
towards the coast. Daytime temperatures Tuesday will be similar to
Monday before a bigger cooling trend expected to begin Wednesday.
Mid range models in fair agreement in bringing a Pacific frontal
system onto the north coast sometime early Wednesday. If current
models hold...parts of the CWA will be seeing light precipitation
as early as mid day Wednesday.

.Extended Discussion (Thursday through Sunday)

Extended models in fairly good agreement in moving a Pacific
Frontal system across the Pacific Northwest and NORCAL Thursday.
Nearly all of the CWA will see at least a chance of precipitation.
With cloud cover and cooler airmass...daytime highs will drop to
well below normal. Extended models begin to diverge a bit by next
Friday. GFS model progresses the upper trough axis east of the
forecast area by 00z Friday while the ECMWF lingers it offshore. GEM
model takes a middle of the road approach to the other two.
Regardless of the solution...next Friday looks to be a mainly
cloudy day with at least a threat of precipitation most areas.
Significance of model variance grows by next Saturday as GFS
would bring clearing and warming under a ridge pattern while a
less progressive ECMWF would keep showers in the region. Have kept
with the more middle of the road GEM and kept precip threat mainly
over the eastern portions of the CWA. Rap around moisture could
still be an issue for the Sierra next Sunday if ECMWF solution is
correct. GFS and GEM models show drying under a ridge of high
pressure.


&&

.Aviation...

VFR conditions next 24 hrs except locally with SHRA/TSRA over Sierra and
northern/central Sacramento Valley this afternoon. Isolated TSRA
may linger through 06z for the foothills/Sierra. Lcl MVFR vsbys
vcnty King Fire from smoke near KPVF. EK

&&

.STO Watches/Warnings/Advisories...
None.
&&

$$







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