057
FXUS66 KSTO 012023
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
123 PM PDT Sat Jun 1 2024

.SYNOPSIS...
Slight cooldown through Monday before a significant warmup to
widespread Major HeatRisk and triple digits in the Valley by mid-
week. An Excessive Heat Watch remains in effect for the lower
elevations from Tuesday morning until Thursday evening. Peak heat
expected Wednesday. Slight chance of showers for the Coastal Range
and northern monutains on Monday. Slight chance for late-day
shower/thunderstorm over the Sierra Nevada Thursday-Saturday.

&&

.DISCUSSION...

Discussion at a Glance:

- Cooler through Monday with periods of increased onshore flow
  and Delta Breeze.
- An Excessive Heat Watch remains in effect from Tuesday morning
  through Thursday evening across the Valley and adjacent
  foothills.
- Areas of Major HeatRisk Tuesday for the Valley, becoming
  widespread Wednesday & Thursday for the Valley & Foothills with
  widespread triple digit high temperatures. Prepare now for
  elevated daytime highs and overnight lows and reconsider
  outdoor activities during the hottest part of the day (3:00-7:00
  PM).
- Moderate HeatRisk next Friday, with a few isolated spots of
  Major HeatRisk in the Valley; Triple digits in the Northern
  Sacramento Valley and adjacent Valley foothills with low to mid
  90s in the Delta and Sacramento metro area
- Slight chance of showers for the Coastal Range and northern mountains
  on Monday. Slight chance for late-day shower or thunderstorm
  over the Sierra Nevada Thursday-Saturday.

Short-Term Discussion (Today THROUGH Tuesday)...

Current GOES-West visible satellite imagery illustrates mostly
sunny skies with just a few passing high level clouds and a few
mountain cumulus over the southern Cascades and northern Sierra
Nevada. Temperatures are currently trending approximately 2 to 12
degrees cooler than this time yesterday afternoon, valid at 1 PM
PDT. This slight cooling is a result of upper level troughing over
the region. These cooler temperatures will continue through
Monday, with generally Minor HeatRisk, and areas of Moderate
HeatRisk in portions of the northern and central Sacramento
Valley. Periods of onshore flow will also aid in the cooler
temperatures over this timeframe, with afternoon and evening gusts
of 15 to 25 mph in the Delta area and adjacent Valley locations.

On Monday, a weather system will move through the Pacific
Northwest. For interior northern California, we can expect
slightly cooler temperatures, increased onshore flow, and
increasing cloud cover. This system will also allow for slight
chances for showers over portions of the Coast Range and northern
mountains. There is a 15 to 35 percent probability of
precipitation amounts of 0.10" or greater on Monday over those
aforementioned locations, so overall little to no impacts are
expected from any precipitation that falls. Dry conditions will
continue elsewhere in the Valley, foothills, and Sierra Nevada.

Upper level ridging begins to build in on Tuesday, bringing along
the start of a significant warming trend to interior NorCal. An
Excessive Heat Watch remains in effect starting Tuesday morning.
On Tuesday, Major HeatRisk is in the forecast for much of the
Valley and even into portions of the foothills. The probability
for reaching or exceeding 100 degrees for the daytime high on
Tuesday is 50 to 80 percent in the Valley. This significant warm-
up will continue into the extended forecast period.

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...

Ensemble guidance indicates that upper level ridging continues to
build mid-week over the Western US, bringing along the potential
for dangerously hot temperatures through at least Thursday.
Widespread Major HeatRisk is currently expected to impact the
Valley and foothills on Wednesday and Thursday, with triple digit
temperatures in the Valley and warm overnight low temperatures.
The Excessive Heat Watch remains in effect through Thursday
evening to address the significant heat. Peak heat is currently
projected to be on Wednesday. The National Blend of Models (NBM)
shows a 65 to 95 percent probability of 100 degree highs or
greater in the Valley on Wednesday and Thursday, with a 30 to 70
percent probability in the lower foothills over the same
timeframe.

By Friday, slightly cooler but still hot temperatures are in the
forecast with Moderate HeatRisk, as ensemble guidance indicates
the ridge shifting east. However, there is still some uncertainty
with the details in the cluster analysis that is resulting in a
larger spread of potential high temperatures for Friday and into
next weekend. Late-day mountain shower and thunderstorm chances
return to the Sierra Nevada as well, with generally a 10 to 20
percent probability over the High Sierra mainly south of
Interstate 80 from Thursday through Saturday, in the afternoon and
evening hours. Additionally, area waterways continue to run fast
and cold from snowmelt, creating dangerous conditions for those
seeking relief in rivers and lakes next week. Stay tuned for
updates as we get closer and plan ahead now to practice heat and
cold water safety!

To view the latest HeatRisk, please visit
www.wpc.ncep.noaa.gov/heatrisk/

To view current water temperatures, please visit
www.cnrfc.noaa.gov

&&

.AVIATION...

VFR conditions expected over the next 24 hours. Sustained surface
winds generally under 12 kts except wind gusts 15 to 25 kts in
the Delta and into the southern Sacramento Valley and northern San
Joaquin Valley until 06Z-12Z Sunday. Local northwesterly wind
gusts up 20 kts in the northern Sacramento Valley after 00Z
Sunday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...

Excessive Heat Watch from Tuesday morning through Thursday
evening 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-Shasta Lake Area /
Northern Shasta County-Southern Sacramento Valley.

&&

$$