FXUS66 KSTO 150533
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
1033 PM PDT Mon Jun 14 2021
SYNOPSIS...
Warming trend this week with widespread triple digit heat expected
by mid-week across the Valley continuing into the weekend.
Temperatures are forecast to be upwards of 15 to 20 degrees above
average for this time of year across much of interior Northern
California. Record high temperatures possible Thursday and Friday
with high to very high heat risk expected.
.DISCUSSION
...
The Evening Update: Dry subsiding air spreading into Norcal this
evening in the wake of short wave energy moving into ORE/NV. Next
short wave near 40N/130W will be passing farther N into/across ORE
with rising 5H heights over Norcal on Tue. This will allow for a
slight/modest uptick in temps (except for +10 at KSUU) due to weaker
onshore gradients as the short wave passes to our N. Tue will be the
last "near normal" temp day for the rest of the week in Norcal as
the 4-Corners High brings a "heat wave" to Norcal with record-
breaking-beastly temps Thu/Fri. Some moderation over the weekend is
expected although triple digit heat will continue into Sat in the
Valley, then just the Nrn Sac Vly on Sun. JHM
.Previous Discussion...
A weak AR that brought precipitation to far northwestern California
the last few days is currently bringing some scattered showers to
the higher terrain of western Shasta County as of this afternoon.
More scattered showers are possible this evening as the low starts
to shift out of our region. Otherwise, generally clear skies and
seasonable temperatures are being observed across Northern
California.
While this low is moving out of the region, high pressure is
building out of the desert southwest. This has lead to tightening
pressure gradients over Northern California. Subsequently, breezy
onshore flow through interior Northern California is being observed
today. Gusts 20 to 30 mph are expected to continue into this evening.
By Wednesday breezy northerly flow though the Valley is expected in
response to the building high pressure. This will also be
accompanied with very dry conditions and could lead to some elevated
fire weather concerns in the Valley. This flow pattern will also
inhibit the influence of cooling from the Delta to the region with
warm overnight lows expected by thursday morning.
Temperatures associated with this large scale high pressure building
into the region are anomalously high as indicated by shift of tails.
Cluster analysis is also indicating large confidence in this
dangerous heatwave impacting our region. Widespread triple digit
high temperatures are forecast across the Valley by Wednesday and is
expected to continue for several days. Forecast highs for the Valley
soar to 105 to 112 with some areas possibly reaching 113 Thursday
and Friday. Warm overnight lows in the upper 60s to 70s are also
forecast in the Valley with some areas in the thermal belts of the
foothills only cooling into the low 80s. Record high temperatures
are possible for several locations both Thursday and Friday. This
type of heat risk is dangerous to the entire population. An
Excessive Heat Warning has been issued from 11 am Thursday through 9
pm Saturday. Now is the time to prepare.
SLL
.EXTENDED DISCUSSION
(Friday THROUGH Monday)...
Very hot weather continues Friday and Saturday with some mild
relief by Sunday into Monday. The delta breeze looks to start to
pick up a little bit each day starting Thursday. This could mean
delta influenced areas could be slightly cooler by a few degrees
on Friday compared to Thursday. However, relief will be minimal as
the Delta Breeze is forecast to remain relatively weak.
Elsewhere, Friday looks to be the slightly warmer day for the
Northern Sacramento Valley and areas further from the Delta.
Saturday will be a few degrees lower, however will continue to be
warm with widespread triple digit expected.
This weekend models start to diverge somewhat but, in general a
very gradual cooling trend is expected into next week. Although
warm, above average temperatures are expected to continue
throughout the extended forecast period as the Eastern Pacific
Ridge starts to become the dominant synoptic feature.
SLL
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