Weather Service Report


583 
FXUS66 KSTO 202229
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
329 PM PDT Fri Jul 20 2018

.SYNOPSIS...
Temperatures will gradually decrease this weekend with the 
potential for thunderstorms in the mountains. Hot weather returns 
next week.

&&

.DISCUSSION...
Temperatures are a little less hot today as the upper ridge
weakens, about 2 to 5 degrees less than this time yesterday. 
Temperatures at 3 pm were generally in the 90s across the Valley, 
with Redding reaching 100. A Delta breeze is apparent through the
Delta and extending through Sacramento inland as far as
Marysville.

A combination of a onshore flow along with a slightly cooler
airmass with bring a little less hot temperatures across the 
region over the weekend. 

Monsoon moisture is bringing scattered thunderstorms around the 
Sierra crest from around Lake Tahoe southward. Most of these are
east of the crest. Thunderstorm activity will become more 
widespread across the mountains through the weekend as the
monsoonal moisture spreads northward. Most of the action is 
expected to be in the afternoons and early evening and mainly over
the mountains.

The ridge is forecast to strengthen again early next week 
resulting in a return to hot weather. An Excessive Heat Watch has
been issued for the Valley and adjacent foothills Tuesday through
Thursday. The pattern and 850 temperatures are similar to what we
saw this past week. Temperatures could again approach 110 over the
northern and central Sacramento Valley during that period, and in
the 100-108 range elsewhere in the Valley and lower foothills. 
The exact position of the ridge is uncertain though, and if far 
enough east could bring some relief with onshore flow and a Delta 
Breeze. This should become more clear over the weekend, so stay
tuned!

Some mountain thunderstorms are possible in the northern Sierra 
early in the week. Drier weather is expected later in the week. EK

&&
.EXTENDED DISCUSSION (Tuesday THROUGH Friday)


An expansive upper level ridge will bring hot weather across the 
region next week. By even July standards, this upper ridge will 
likely be rather anomalous, with NAEFS (North American Ensemble 
Forecast System) guidance projecting 500mb heights to be 3-4 
standard deviations higher than normal over AZ/NM. We will be on 
the northern fringe of this upper ridge, but with high confidence 
in the pattern we nudged temperatures up a few degrees across much
of the extended period. Current consensus of solutions has 
widespread triple digit heat across much of the Central Valley 
through the extended period, with temperatures potentially 
approaching 110 degrees again across the northern Valley. An
Excessive Heat Watch is in effect Tuesday through Thursday.
Slightly less hot weather is expected late in the week. EK/TD

&&

.AVIATION...

VFR conditions the next 24 hours across TAF sites. South to west
winds 5 to 15 knots, except gusts to 30 kt near the Delta.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Tuesday afternoon through Thursday 
evening for Central Sacramento Valley-Clear Lake/Southern Lake 
County-Motherlode-Mountains Southwestern Shasta County to 
Northern Lake County-Northeast Foothills/Sacramento Valley-
Northern Sacramento Valley-Northern San Joaquin Valley-Shasta 
Lake Area / Northern Shasta County-Southern Sacramento Valley-
Western Plumas County/Lassen Park.

&&

$$

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Western Regional Climate Center, wrcc@dri.edu