Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 211039
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
339 AM PDT Sun May 21 2017

.SYNOPSIS...
Dry and very warm the next several days. NorCal`s first triple
digit heat possible Monday and Tuesday across portions of the
Sacramento Valley. A chance of Sierra thunderstorms Tuesday
southward of Highway 50. Delta Breeze begins Tuesday and
especially Wednesday with cooler afternoon temperatures.

&&

.Discussion (Today through Wednesday)...
Upper level ridging and heat dominates interior NorCal through
Tuesday. The weak wave centered over the Great Basin today
will not impact NorCal much. In fact, 500 mb heights increase
around 3 dm and the 1000-500 mb thickness also increases around 3
dm, which will cause temperatures to warm a few degrees over
yesterday.

High pressure will continue to build Monday and Tuesday when the
warmest airmass will be over the area. Dry conditions are
expected for Monday, but Tuesday a weak low located near 30N and
130W may help draw some moisture northward along the crest to
bring a chance of thunderstorms southward of Highway 50. This low
has trended slightly weaker and farther offshore, which has caused
the Tuesday thunderstorm coverage and chances to decrease. On the
other hand, the upper level low to the southwest in combination
with an approaching Pacific NW trough will likely increase the
Delta Breeze Tuesday for some relief in southern Sacramento and
northern San Joaquin Valleys and adjacent foothills.

Expect continued cooling Wednesday from a Delta Breeze, and
onshore flow in general, with maximum afternoon temperatures down
5-10 degrees from Tuesday.       JClapp
&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)
Models consistent in forecasting a pattern change with a weak
upper trough over NorCal later this week. With west-northwest flow
over the region, the pattern will not be favorable for showers
and thunderstorms. Temperatures will cool significantly from
earlier in the week and will be near or below average for late-
May.

&&

.AVIATION...
VFR conditions the next 24 hours. Southwest winds 10-15 kts near
the Delta, otherwise variable winds less than 10 kts at valley TAF
sites.

&&

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

$$



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