253
FXUS66 KSTO 030854
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
154 AM PDT Mon Jun 3 2024

.SYNOPSIS...
One last day of onshore flow bringing near normal temperatures
and isolated showers across the Northern Sierra and Northern
Sacramento Valley. Hot weather develops Tuesday through late week
with periods of breezy north winds in the Valley. An Excessive
Heat Warning is in effect for the Valley and foothills Tuesday
through Thursday.

&&

.DISCUSSION...

Discussion at a Glance
- Cooler today with periods of increased onshore flow and Delta
  Breeze.
- An Excessive Heat Warning goes into effect from Tuesday morning
  through Thursday evening across the Valley and adjacent
  foothills.
- Areas of Major HeatRisk Tuesday for the Valley, become
  widespread Wednesday 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).
- Areas of Major HeatRisk continue on Thursday, with primarily
  Moderate HeatRisk by Friday; Triple digits in the Northern and
  Central Sacramento Valley and adjacent Valley foothills with mid
  to upper 90s in the Delta and Sacramento metro area.

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

As of early this morning, satellite imagery shows clouds and
virga moving into the area from the northwest as a weather system
moves through the Pacific NW. Radar shows virga moving through the
Southern Cascades and portions of the Northern Sacramento Valley.
Impacts will be minimal from this weather passage but isolated
showers mainly over the Northern Sierra/Southern Cascades and
Northern Sacramento Valley are expected this morning into the
early afternoon. Latest WPC amounts show 0.01-0.30" of total rain
accumulations with highest amount in the Lassen National Park
area.

By this afternoon, the weather system exits eastward from the
Pacific NW replaced by ridging over Northern CA by Tuesday. This
will result in a rapid warm up to well above normal temperatures
from Tuesday through the end of the week. Resultant Valley high
temperatures look to rise firmly into the upper 90s to low triple
digits on Tuesday, with widespread triple digits in the Valley
anticipated on Wednesday. Even at higher elevations, high
temperatures into the 80s to 90s are expected. Overnight low
temperature recovery will remain limited as well, with 60s to low
70s in the Valley and foothills and 50s to 60s across the
mountains. This will lead to areas of major HeatRisk throughout
much of the Valley and foothills, with moderate HeatRisk
elsewhere. As a result, an Excessive Heat Warning goes into effect
for much of the Valley and foothills at 11 am PDT Tuesday, June 4
and continues through 8 pm PDT Thursday June 6.

Additionally, as the ridge builds in on Tuesday and Wednesday,
surface winds are expected to shift to a north-northwesterly
direction. Strongest winds are expected to occur Tuesday late
morning through the afternoon across the Sacramento and northern
San Joaquin Valleys, with gusts of 20 to 25 mph possible at times.
This dry northerly wind combined with hot temperatures and
forecast relative humidities into the upper teens to low 20s will
likely result in some elevated fire weather conditions midweek.
Lowest RHs will be over the Northern Sacramento Valley and
northeastern foothills with minimum RH values of 15 to 25
Wednesday and Thursday.

Remember, 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

Lastly, the aforementioned ridge axis shifts as it sinks into the
Southwest US to allow a shortwave trough to move through Northern
CA. This will see weak onshore flow move through the Delta and
portions of the Sacramento Valley, seeing temperatures cool
several degrees. With this there is a chance for afternoon and
evening showers and thunderstorms over the Sierra, mainly south
of I-80. With the forecasted flow pattern, storms will form over
the crest then exit our forecast area to the east.

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)...

Upper ridge axis extends from the Desert SW northwestward over
NorCal early Friday. Ridge axis shifts east Friday as upstream
upper troughing in EPAC progresses. Triple digit heat continues
Friday over northern and central portions of the Sacramento
Valley. Delta breeze will help to taper the heat some in the S
Sac/Northern San Joaquin Valleys where 90s are forecast. Upper
troughing in EPAC progged to weaken Sat/Sun as it approaches the
West Coast and encounters strong downstream upper ridge. EPAC
ridge then builds Sun into Mon as upper trough forms closed low.
Models differ with placement of synoptic features late in the
extended period. NBM advertising 90s in the Central Valley Sat
into Mon with dry weather.

&&

.AVIATION...

VFR conditions over interior NorCal next 24 hrs except isolated
MVFR possible over mtns in shwrs til 00z Tue. Sfc wind mainly at
or below 12 kts thru 12z Tue except vcnty of Delta SWly sfc wind
15-25 kts.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning from 11 AM Tuesday to 8 PM PDT Thursday
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.

&&

$$