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NWS Area Weather Forecast Discussion
County Warning Area [CWA]: STO
Regional NWS Weather Office: Sacramento, CA

000
FXUS66 KSTO 260930
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
230 AM PDT Tue May 26 2020

.Synopsis...
High pressure will continue to build over the region resulting in
hot weather. The hottest days will be through Thursday with
moderate to high heat risk expected. A pattern change is expected
on Friday, which will lead to cooler temperatures and chances of
mountain showers and thunderstorms over the weekend.

&&

.DISCUSSION...
Skies are clear across the region early this morning except for a
few high clouds near the OR/CA border moving around the periphery
of the strong high pressure. Winds remain generally light except
for a weak Delta Breeze (13 kts at Travis AFB). Current temps are
warmer compared to 24 hours ago across most of the area and
generally range from the mid 40s in the colder mountain valleys,
to the upper 60s to upper 70s across the Central Valley.

Little change expected through Thursday as strong high pressure
covers the region. Max temperatures in the Central Valley will
mainly be in the 100-105 degree range with a few daily record
highs possible. Overnight lows will also be very mild, generally
in the mid 60s to lower 70s through the Central Valley. Thus,
widespread moderate to high heat risk will continue with an
Excessive Heat Warning remaining in effect through 7PM Thursday
for elevations below 3500 feet.

With the prolonged heat in the forecast, the general population
should take precautions to prevent heat related illnesses given
the potential for moderate to very high heat risk. Stay hydrated,
limit outdoor activities, and check on sensitive groups.

If you plan on enjoying the outdoors, be sure to practice heat
safety and a cold water safety if visiting area waterways. Area
waterways continue to run very cold and fast, and precautions
should be taken if heading to the water.

General consensus in medium range models is that the developing
pattern change over the eastern Pacific late in the week will lift
the cutoff low, presently parked west of 130W well off the coast
of Baja and SoCal, northeastward toward NorCal late in the week
leading to a cooldown and a return of unsettled weather.

&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)...
558 DM closed upper low approaches the Central CA coast early
Saturday, increasing thunderstorm potential over interior NorCal.
Models differ on how quickly to progress low northward with GFS-20
more progressive. Ensemble solutions do suggest the feature
weakening as it lifts to the north. Elevated instability progs
showing highest modified TT`s north of a KUKI-KOVE-KBLU line by
midday Saturday. Increased cloud cover and precipitation
potential, along with synoptic cooling associated with the low
will result in high temperatures Saturday 10 to 25 degrees lower
than Friday. Upper 70s to mid 80s expected in the Central Valley
with mainly 50s to 70s for the mountains and foothills.

Closed upper low weakens to trough as it lifts into the PacNW
early Sunday. Long wave trough position then moves to the West
Coast and lingers into early next week. Embedded disturbances
moving through will keep a threat of showers through the remainder
of the extended forecast period. Best chances for measurable
precipitation will be over the foothills and mountains. Below
normal high temperatures continue Sunday and Monday, returning to
near normal Tuesday. PCH

&&

.AVIATION...
VFR conditions over Interior NorCal the next 24 hours with
surface winds generally below 12 knots.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 7 PM PDT Thursday for Carquinez
Strait and Delta-Central Sacramento Valley-Motherlode-Mountains
Southwestern Shasta County to Western Colusa County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Southern
Sacramento Valley.

Excessive Heat Warning until 7 PM PDT Thursday for Northern San
Joaquin Valley.

Excessive Heat Warning from 7 AM to 7 PM PDT Thursday for Shasta
Lake Area / Northern Shasta County.

&&

$$

Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather