NATIONAL WEATHER SERVICE FORECAST DISCUSSION
Area Forecast Discussion
Issued by The National Weather Service
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000
FXUS66 KSTO 012110
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
210 PM PDT Mon Jun 1 2020

.Synopsis...
Threat of showers and afternoon thunderstorms will continue
over the mountains this week. Warming trend with high temps
climbing to 10 to 15 degrees above average by mid-week, then
cooling with an increased chance of showers by the weekend.

&&

.DISCUSSION...
Some light showers moved through the Valley into the mountains
this morning, which have since dissipated. There is a chance of
mountain showers and isolated thunderstorms this afternoon and
evening as a weak upper level trough continues to move over the
area. Radar shows showers are now beginning to move into Tuolumne
County. Temperatures early this afternoon are a few degrees
warmer than yesterday and will peak in the mid to upper 80s in the
Valley and 50s to 70s in the mountains and foothills.

Heat then becomes the main concern Tuesday through Thursday. The
longwave trough moving over the West Coast today will split late
today, creating a cut off low that will linger off the SoCal and
Baja coast through the week. The high pressure ridge over the
Desert SW will build into the area just enough to result in
another significant warming trend. Tomorrow`s temperatures will
be 10 to 15 degrees warmer than today, peaking in the upper 90s in
the Valley. Wednesday will be hotter with Valley temps 99 to 103,
then upper 90s to 102 on Thursday. Morning lows will only cool to
the upper 60s to low 70s in the Valley and foothills, which will
not provide much overnight relief from the heat. This will result
in Moderate to High Heat Risk across the Valley and foothills. A
Heat Advisory has been issued for Valley and portions of the
foothills for 11am tomorrow through 8pm Thursday.

There is also a chance of isolated afternoon mountain showers and
thunderstorms Wednesday, mainly limited to locations south of
Highway 50, as an impulse along the flow could produce enough
instability. The shower chances for Tuesday and Thursday have
diminished with recent guidance as the position of the cutoff low
has moved farther south. HEC

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)...
A quasi-stationary upper low which had been cut off in the
vicinity of the southern California coast will finally make its
way inland on Friday. This eastward progression is forecast to
nudge the Four Corners ridge out to the Great Plains.
Consequently, the influence of this ridge on northern California
will diminish as heights lower across the region. From Friday into
the weekend, a rather broad longwave trough over the Pacific
should encompass much of the West Coast. While temperatures drop
considerably from the mid-week numbers, higher elevation
precipitation chances will also be on the increase. Some showers
could spill into the Valley although it likely will not amount to
much aside from the northern Sacramento Valley. Residual cyclonic
flow across the region should keep lingering mountain showers into
Sunday, possibly continuing into Monday over the northern
mountains. The mentioned drop in temperatures will bring Valley
and Delta highs into the upper 70s over the weekend while
initially starting in the mid to upper 80s on Friday. Occasionally
breezy onshore flow is possible this weekend, particularly in
Delta influenced locations. ~BRO

&&

.AVIATION...
VFR conditions over Interior NorCal the next 24 hrs except local
MVFR/IFR conditions possible in showers over the mountains.
Isolated afternoon thunderstorms possible over the mountains
through 03Z. Surface winds generally below 10 knots except in the
vicinity of the Delta where local sustained winds up to 15 knots
can be expected.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM Tuesday to 8 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-
Northern San Joaquin Valley-Southern Sacramento Valley.

&&

$$
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