Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 191545 CCA
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
844 AM PDT Thu Apr 19 2018

.SYNOPSIS...
Light showers over the northern Sierra today and this evening with
light snow over the passes. Dry Friday through early next week. A
few showers possible over the mountains during the middle of next
week.

&&

.DISCUSSION...
Update: Temps at sunrise this morning started out some 2 to 11
degrees cooler than yesterday, but began to recover by mid morning
over much of the Wrn 2/3 of the CWA with April sunshine. It will
still be a cloudy and cool day over the Sierra with at least a
chance of some light showers as cyclonic flow from the Srn NV low
spreads some "backwash cloudiness" and isolated snow showers from E
to W over the Sierra Crest. Nly flow behind the low will also result
in a modest Nly wind most locations. High temps today will be below
normal over most of our CWA, except for the Nrn Sac Vly and along
the W side of the Sac Vly and into Solano Co where a few degrees of
adiabatic Nly winds will boost temps some 1 to 3 deg or so above
normal. This will be just the start of several days of spring-like
temps, (60s mtns to 80s Valley) into next week, with Sat thru Mon
the warmest days most locales.   JHM

.Previous Discussion...

Dry upper level trough currently working its way across northern
California. Trough axis is currently shifting into the Sierra
with main cloud cover now south and east of the CWA. Therefore,
most of the forecast area is under mainly clear skies this
morning. Clear skies allowing for temperatures this morning to run
a few to several degrees below 24 hours ago. Shortwaves dropping
down the back side of the low as it shifts into the Great Basin
could bring a few showers over the Sierra Cascade range today
through this evening. Fair skies and warming airmass will bring up
daytime highs to a few degrees above normal. Upper ridge axis
forecast to slide over the north state on Friday bringing fair
skies and more warming with highs Friday expected to reach 10 or
more degrees above season normals. Still more warming in store for
Saturday under upper level high pressure bringing highs in the
valley up into the 80s with upper 80s expected in the northern
Sacramento valley. ECMWF and GFS both weaken the west coast ridge
temporarily Sunday as a weak Pacific trough quickly moves through
the Pacific Northwest and Norcal. Both models indicate light
showers over the northern most CWA so included some spotty showers
there Sunday afternoon and evening. Northern forecast area will
see a slight cooling as well. Otherwise the shortwave will have
little impact with daytime highs Sunday most areas remaining well
above normal.

&&
.EXTENDED DISCUSSION (Monday THROUGH Thursday)

Upper level shortwave ridging rebounds on Monday as a weak
disturbance exits to the east. Temperatures will be well above
normal, with Valley highs in the low to mid 80s. Models diverge
significantly on timing of an upper low moving inland next week,
though, so confidence in the forecast is low. For now, have
temperatures slightly cooler with a slight chance of some light
mountain showers. Overall, this looks like a typical mid-spring
pattern, unsettled but without any particularly strong storm
systems/wet weather expected. EK
&&

.AVIATION...

VFR TAF sites next 24 hours. Northerly winds increasing in the
afternoon, gusting to 20-25kt. EK

&&

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

$$



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