Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 231630
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
930 AM PDT Fri Jun 23 2017

.SYNOPSIS...
Hot again today into Saturday then increased cooling Sunday into
early next week. Isolated afternoon/evening thunderstorms possible
over the mountains through Sunday.

&&

.DISCUSSION...
Strong high pressure ridging continues over the West Coast keeping
the heat wave going over Interior NorCal. Beginning to see some
cooling influence though from the Delta. Marine layer has
deepened to around 1500 feet and we are seeing some decent flow
through the Carquinez Strait this morning. As a result, morning
temperatures are running anywhere from 4 to 13 degrees cooler in
Delta, Central and Southern Sacramento Valley and Northern San
Joaquin Valley. Guidance maintains a good Delta breeze today which
should result in some cooling for Delta influenced areas. Heat
warning has been downgraded to advisory for the Delta and Northern
San Joaquin Valley. May also need to downgrade for the Southern
Sacramento Valley. Hottest temperatures expected in the Northern
Sacramento Valley today with highs around 109. Isolated afternoon
thunderstorms developed near the Sierra Nevada crest yesterday and
some model data is pointing to a slight chance of that occurring
again today.

Delta breeze expected to continue moderate to strong overnight
into Saturday bringing additional cooling to areas influenced by
it. Remainder of Interior NorCal expected to see similar
temperatures Saturday with excessive heat warning likely to
continue for the Northern and Central Sacramento Valley. High
pressure from the Desert SW builds NE towards the EPAC high,
turning mid level flow more SEly on Saturday. This could extend
the threat of afternoon thunderstorms from the Sierra Nevada to
also include the Coastal Range.

Upper ridging weakens over NorCal Sunday and shifts east as closed
upper low off the CA coast deepens and approaches. This should
help deepen the marine layer and strengthen onshore flow. Some
synoptic cooling will also result and expect around a 3 to 8
degree drop in max temperatures. Threat of isolated afternoon
thunderstorms continues over the Sierra Nevada Sunday and possibly
along the coastal range as some models hint at vort max lifting
across that area in southerly flow aloft.

Cooling continues on Monday as weakening upper troughing shifts
inland over NorCal. Main dynamics look to remain northwest and
north of our CWA for any potential deep moist convection threat.
High temps on Monday forecast to be back in the 90s throughout
the Central Valley.

PCH

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)
Further cooling expected on Tuesday as weak trough moves across
the area. Models depicting a few showers across the northern
mountains but confidence is low and given limited moisture return,
have continued dry forecast. Upper flow becomes more zonal on
Wednesday into Thursday with high temperatures within a few
degrees of normal. Cooler overnight temperatures will continue the
relief from this week`s heatwave. Delta Breeze should be going
with further cooling across influenced areas. CEO

&&

.AVIATION...
VFR conditions expected at the TAF sites the next 24 hours.
Isolated thunderstorms possible over the northern Sierra crest in
the afternoon. Southwest winds 15 to 30 kt through the
delta...otherwise winds generally below 15 kt.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 11 PM PDT Saturday for Carquinez Strait and
Delta-Clear Lake/Southern Lake County-Motherlode-Mountains
Southwestern Shasta County to Northern Lake County-Northeast
Foothills/Sacramento Valley-Northern San Joaquin Valley-Shasta
Lake Area / Northern Shasta County-West Slope Northern Sierra
Nevada-Western Plumas County/Lassen Park.

Red Flag Warning until noon PDT today for Central Sacramento
Valley in Glenn, Colusa, Yuba, Northern Sutter, and Butte County
Below 1000 Ft-Eastern Mendocino NF-Eastern Portion of
Shasta/Trinity NF-Lake County Portion of Lake-Napa-Sonoma Unit-
Northern Sacramento Valley to Southern Tehama County Line Below
1000 Ft-Northern Sierra Foothills from 1000 to 3000 Ft. Includes
portions of Shasta-Trinity and Butte Units-Southeast Edge Shasta-
Trinity NF and Western Portions of Tehama-Glenn Unit.

Excessive Heat Warning until 11 PM PDT Saturday for Central
Sacramento Valley-Northern Sacramento Valley-Southern Sacramento
Valley.

&&

$$



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