Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 192215

Area Forecast Discussion
National Weather Service Sacramento CA
315 PM PDT Thu Apr 19 2018

Light showers over the northern Sierra will end later this evening.
Dry and warm Friday through early next week with just a chance of
showers over the Shasta County mountains on Sunday.


Afternoon temps running some 5-10 degrees warmer over most locations
as the upper level low drifted away from our CWA. It was still a
cloudy and cool day over the High Sierra as cyclonic from around the
Srn NV upper low spread "backwash cloudiness" and isolated/scattered
showers from the E to the W over the Sierra Crest. Nly flow behind
the low also resulted in a modest Nly wind most locations, with
some afternoon gusts to 20 kts in the Valley. 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 warming Nly winds will boost temps some
1 to 3 deg or so above normal.

The NV low will move into CO on Fri and the Ern Pac ridge will push
inland over Norcal. A Nly zephyr (gentle breeze) is expected over
most of the area with strong warming as the ridge moves inland. 850
mbs temps and low to mid level thicknesses warm some 5-6 deg C/15
dam or so over the CWA allowing max temps to warm some 5-14 degrees
over the CWA on Fri from today. This will be just the start of
several days of quite warm, well-above normal max temps most
locations (by double digits), and very spring-like temps, (60s
mtns to 80s Valley) into next week. Sat thru Mon look to be the
warmest days over most locales. A strong temperature inversion
will form causing some good thermal belts to develop over the
Foothills through the weekend.

Short wave moving across WA on Sat will increase Nly pressure
gradients over the Nrn mtns/Vly which could result in locally
stronger winds/breezy conditions Fri nite into Sat. Then on Sun,
the models forecast a progressive short wave trof to move through
Norcal during the day with at least the ECMWF indicating a chance
of showers over our Nrn mtn zones during the afternoon/evening.



An upper level low somewhat cut off from the main flow will be
dropping south into the region during the extended period.
Unfortunately the placement of this feature has low predictability
especially this far out and models have been flip flopping on
where it sets up. Because of this went with slight chances for
showers in the higher elevations Tuesday onward during the
afternoon and evening hours. With the cold air aloft there will be
some instability and cant rule out some thunder and lightning
with the showers. Seasonal to mild temperatures will continue
throughout the period running 5-10 above average.




VFR conditions at the TAF sites the next 24 hours. Northerly winds
10-15 knots gusting to 20 knots diminish by 3z this evening and
become 5-10 knots overnight.



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