495
FXUS66 KSTO 020851
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
151 AM PDT Sun Jun 2 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 mountains on Monday. Slight chance for late-day
shower/thunderstorm over the Sierra Nevada Thursday-Sunday.

&&

.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

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

Similar weather today as Saturday with warm afternoon temperatures
and onshore flow moves across the Southern Sacramento and
Northern San Joaquin Valleys. West-southwesterly winds continue
across the Delta into the Northern San Joaquin with periods of
15-30 MPH gusts until Tuesday morning. Today`s highs will be in
the upper 80s and low 90s for the Valley with 70s an 60s across
the foothills and mountains. Monday looks to be several degrees
cooler with Valley highs in the mid to upper 80s.

A weather system is impacting the Pacific NW, resulting in
slightly cooler temperatures with chances for showers across the
mountains on Monday for Northern CA. There is a 20-40% chance of
precipitation over the Coastal Range and Southern Cascades,
highest chances late Monday morning. Forecast still indicate this
will be a marginal rain event if anything does develop. Latest WPC
totals show 0.01-0.25" on Monday with highest totals forecasted
for the Southern Cascades near Lassen National Park. NBM
probabilities indicate a 20-40% chance of seeing 0.10" or greater
so no impacts are anticipated from this brief weather passage.
There will be increased cloudiness as a result which can help with
relief from hot temperatures.

The focus of our forecast will be the Tuesday into the late week
period as upper level ridging develops over Northern CA with the
aforementioned weather system exiting the Pacific NW. Major
HeatRisk develops in the Valley, primarily from the Central
Sacramento Valley to the Northern San Joaquin on Tuesday. Also,
north winds pick up late Tuesday morning with gusts of 15 to 25
MPH before tapering off overnight. Conditions peak on Wednesday
with widespread Major HeatRisk across much of the Central Valley
and adjacent foothills. Afternoon highs of 95-108 degrees are
possible Tuesday and Wednesday with little overnight relief with
low temperatures in the 60s to mid 70s. Area waterways will
continue to run cold and fast, creating dangerous conditions for
those seeking relief in rivers and lakes.

As a result an Excessive Heat Watch continues today from Tuesday
morning into Thursday evening. NBM probabilities of exceeding 100
degrees on Tuesday is 45-95% and on Wednesday, 75-100%. This level
of hear affects anyone without effective cooling and/or adequate
hydration, particularly those working outdoors or apart of
heat-sensitive groups. 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

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...

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 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. The National Blend of Models (NBM) shows a
50 to 95 percent probability of 100 degree highs or greater in the
Valley on Thursday, with a 20 to 65 percent probability in the
lower foothills over the same timeframe. The Delta
Breeze should help cool temperatures across the Delta and Southern
Sacramento Valley Thursday night to begin seeing relief from the
stretch of warm temperatures.

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 Sunday, 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.

&&

.AVIATION...

VFR conditions expected over the next 24 hours. Sustained surface
winds generally under 12 kts except southwest to west wind gusts
15 to 25 kts in the Delta. Local northwesterly wind gusts up 20
kts in the northern San Joaquin Valley after 20Z 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.

&&

$$