830
FXUS66 KSTO 122102
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
202 PM PDT Fri Jul 12 2024

.SYNOPSIS...
Hot and dry weather will continue through Saturday with Moderate
to Extreme HeatRisk persisting across much of the region. Elevated
fire weather conditions will also continue. Isolated thunderstorm
chances today-Sunday, mainly along the Sierra crest, best chances
from US-50 southward. Cooler temperatures on Sunday and into next
week.

&&

Key Points
- Long-duration, dangerous heat event persists through Saturday,
  followed by some cooling over the weekend into next week.
- Chances of showers/isolated T-storms along the Sierra Crest
  today through the weekend.
- Red Flag Warning has been issued for Fire Zones 221 and 269 for
  elevations greater than 6000 feet.

.Discussion...
Another hot day in store for interior NorCal today. At the time
of this writing, it is 106 F at our Downtown Sacramento weather
observation site, and the temperature is forecast to climb to
around 110 as we move into the peak heating hours. Tomorrow we
expect a slight cooldown across the central Sacramento Valley,
Delta, and northern San Joaquin Valley with highs in the 90s to
105, with the coolest temperatures in the Delta thanks to onshore
flow. The Heat Advisory for the Delta and Sierra, as well as the
Excessive Heat Warnings for the Valley and Foothills remain in
effect until 9PM PDT tomorrow night.

We are still under the influence of a broad area of high pressure
in the Four Corners region and will remain affected by the high
pressure until at least Sunday night. Monsoonal moisture is
embedded within the high pressure, and is beginning to move into
our area this afternoon. Some flashes of lightning have been
observed this afternoon, mainly in far southeastern Tuolumne
County just east of Hetch Hetchy. This activity is moving off to
the northeast and out of our coverage area, however an isolated
shower or thunderstorm cannot be ruled out the remainder of the
day in the far southeastern sections of the forecast area.
Tomorrow, temperatures will cool as monsoonal moisture will
advect into interior NorCal, bringing some high clouds and
possible sprinkles across the Valley. Some Hi-Res Convective
Allowing Models (CAMS) such as the NAM and HRRR reveal the
potential for thunderstorms across the Sierra crest, with the best
chances south of HWY-50 tomorrow and Sunday. Forecast soundings
suggest a north-northeast steering current, so any storms that
develop could drift along the Sierra crest. Current National Blend
of Models probabilities for thunderstorms are around a 15-30%
chance for tomorrow and Sunday. With the elevated ERC values in
the Sierra and the potential for dry thunderstorms, a Red Flag
Warning has been issued for Fire Zones 221 and 269 for elevations
above 6000 feet beginning tomorrow at 5AM PDT and lasting through
Sunday at 8PM PDT.

Weak off-shore troughing develops Sunday as well and will promote
more onshore flow into the Delta and central Sacramento Valley,
which will help lower temperatures across the region. Confidence
has increased in relatively cooler temperatures as we move into
the next work week, with the return to near-normal highs. Moderate
HeatRisk will persist across the region beginning Sunday. Upper
level heights will remain in a westerly flow pattern, so the
relative cool down is expected to persist as we move into the
extended period.

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

Heat Safety Tips: weather.gov/safety/heat

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...

Tuesday and Wednesday, we will still have westerly flow aloft
which will promote more onshore flow and help us remain near
normal temperature wise. Widespread Minor and isolated Moderate
HeatRisk return, which will be a welcome relief after our record-
setting heat wave. Forecast high temperatures are currently
90-100, with the warmest temperatures in the northern Sacramento
Valley. Thursday and Friday, a ridge of high pressure will once
again try to build in over the Four Corners region, which will
increase high temperatures around the area again, but at this
time, will not compare to our latest heat event. Minor to Moderate
HeatRisk will remain in the forecast, and high temperatures are
forecast to be in the low 90s to around 105, with the Delta being
the coolest and the northern Sacramento Valley once again being
the warmest.

&&

.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.

Red Flag Warning from 5 AM Saturday to 8 PM PDT Sunday for
Northern Sierra Including the Tahoe and ElDorado NF/S West of
the Sierra Crest-Stanislaus NF West of the Sierra Crest.

&&

$$