513
FXUS66 KSTO 120908
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
208 AM PDT Fri Jul 12 2024

.SYNOPSIS...
Hot and dry weather will continue this week with Moderate to
Extreme HeatRisk persisting across much of the region. Elevated
fire weather concerns will also continue. Cooler temperatures on
Sunday and into next week.

&&

Key Points
- Long-duration, dangerous heat event persists this week.
- Very hot through Saturday, followed by some cooling over the
  weekend into next week.
-Chances of showers/isolated T-storms along the Sierra Crest this
  weekend.

.Discussion...
Hot and dry conditions persist across interior NorCal this
afternoon, with areas of Major and Extreme HeatRisk across the
Sacramento Valley and adjacent Foothills. Upper level ridging
persists near the Four Corners region and is expected to meander
in that area for the next few days, which will keep our area very
hot with widespread triple-digit high temperatures are expected
to persist through Saturday. Right now National Blend of Models
(NBM) probabilities remain ~100% for reaching 100 degrees F today
through Saturday across the Valley and Foothills, with around
70-85% chances of exceeding 110 degrees F in the Northern
Sacramento Valley today through Saturday. With the hot
temperatures and areas of Major to Extreme HeatRisk, the Heat
Advisories for the Delta, Sierra, southern Cascades, and Burney
Basin and the Excessive Heat Warnings for the Valley and Foothills
have been extended to last until Saturday evening.

As the high pressure sits over the Four Corners region on
Saturday, it will attempt to tap into some monsoonal/sub-tropical
moisture, which will follow the upper level steering winds in a
south-to-north orientation and move over the Sierra. Coupled with
an area of low pressure off the California Coast that ensembles
continue to project to develop, which will increase onshore flow,
there is around a 15-35% chance of thunderstorms over the Sierra
on Saturday afternoon/evening and around a 10-30% chance on
Sunday afternoon/evening. Forecast soundings at the mid-levels
show some elevated CAPE and some moisture, but a lack of synoptic
forcing may inhibit growth. Models attempt to push some elevated
convection through the Valley and over the Coastal Range but there
is even less confidence in that versus the Sierra Crest. Chances
for thunderstorm development on Sunday for northwestern Shasta
County is 10-20%, peaking in the late afternoon and evening
hours. No matter what, any storms that develop could be capable of
gusty winds and possible fire starts from lightning strikes. If
you are out and about in the mountains this weekend, remember when
thunder roars, head indoors!

Thanks to the aforementioned onshore flow and low pressure that is
projected to develop this weekend, a slight relief in high
temperatures is anticipated around the Central/Southern Sacramento
Valleys, Delta, and mountains. Saturday high temperatures are
forecast to be in mid 90s to around 105 in the previously
mentioned areas, while the northern Sacramento Valley will remain
the in the 105-113 range. Sunday, our upper level heights
transition into a westerly component, which will spread some more
relief to high temperatures around the entire area. The northern
Sacramento Valley will see temperatures drop to around 100-104,
with low 90s to 101 for the rest of the area. We will continue to
see temperatures and HeatRisk decline as we move into next week.

Latest HeatRisk: wpc.ncep.noaa.gov/heatrisk/

Heat Safety Tips: weather.gov/safety/heat

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...
As we move into the next work week, upper level flow pattern with
onshore flow will allow better relief from the heat we have been
experiencing. HeatRisk will fall into the Minor to Moderate
categories Tuesday through Wednesday. Temperatures will be close
to climatological normal until Thursday, where we could climb to
around 3-5 degrees above normal. Forecast high temperatures are
around 90 to the low 100s for the Valley and Foothills, with low
to mid 80s for the mountains Thursday and Friday with Friday being
the hotter of the two days. Clusters show a ridge developing once
again over the Four Corners region, which will increase our
heights aloft and slightly increase our afternoon high
temperatures, where triple digits are forecast for the area except
in the Delta. By Friday, Valley locations can expect to be under
Moderate HeatRisk throughout the Valley with Minor to Moderate
over the foothills/mountains.

&&

.AVIATION...

VFR conditions next 24 hrs, except local MVFR possible vicinity
isolated thunderstorms northern Sierra 22Z until about 02Z
Saturday. Surface wind gusts generally below 12 knots except
southwest wind gusts 15-20 knots vicinity west Delta after 00Z
Saturday.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 9 PM PDT Saturday for Central
Sacramento Valley-Motherlode-Mountains Southwestern Shasta
County to Western Colusa County-Northeast Foothills/Sacramento
Valley-Northern Sacramento Valley-Northern San Joaquin Valley-
Shasta Lake Area / Northern Shasta County-Southern Sacramento
Valley.

Heat Advisory until 9 PM PDT Saturday for Burney Basin / Eastern
Shasta County-Carquinez Strait and Delta-West Slope Northern
Sierra Nevada-Western Plumas County/Lassen Park.

&&

$$