751
FXUS66 KSTO 032059
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
159 PM PDT Mon Jun 3 2024

.SYNOPSIS...
Near normal temperatures and breezy south to west winds continue
through the remainder of today. A rapid warm up to well above normal
temperatures and periods of moderate to major HeatRisk is then
anticipated from Tuesday through the end of the week. Cooler, but
still seasonably warm weather then follows into the weekend.

&&

.DISCUSSION...

Discussion at a Glance
- Cooler today with breezy to gusty 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 afternoon, an upper level trough ejecting
eastward out of the Pacific Northwest, is resulting in scattered
mid to high level clouds gradually beginning to filter out of
interior NorCal as breezy south to west onshore surface flow
persists. Additionally, high temperatures this afternoon look to
settle around seasonal averages, with 80s in the Valley and 60s to
70s at higher elevations. As the trough transitions toward the
Intermountain West late today into Tuesday, heights aloft are
expected to rise over the western CONUS as an upper level ridge
begins to build. This will result in a rapid warm up to well above
normal temperatures for the remainder of the week ahead, along
with a period of northerly surface winds developing on Tuesday and
Wednesday.

Current forecast high temperatures have the Valley and foothills
firmly in the 90s to triple digits from Tuesday through Thursday and
limited nighttime recovery with overnight low temperatures in the
mid 60s to low 70s. This will result in generally widespread Major
HeatRisk in the Valley and foothills from Tuesday through Thursday.
While comparatively not as hot, mountain high temperatures still
look to reach the 80s to 90s with attendant widespread Moderate
HeatRisk from Tuesday through Thursday. Current probabilities of
exceeding 100F in the Valley are around 50% to 80% on Tuesday, 85%
to 95% on Wednesday, and 70% to 95% on Thursday. As a result, an
Excessive Heat Warning goes into effect at 11 am PDT on Tuesday,
June 4 for much of the Valley and foothills.

Additionally, a period of gusty north-northwesterly winds is
expected on Tuesday throughout the Valley. Strongest winds are
anticipated through the central and southern Sacramento Valley and
northern San Joaquin Valley, where gusts of 20 to 30 mph will be
possible at times. This dry northerly component to the wind will
also lead to afternoon minimum relative humidity values into the
upper teens to low 20s. As a result, elevated fire weather
conditions will be possible in the Valley on Tuesday. Winds are
generally expected to lighten moving into Wednesday, with
periodically breezy onshore flow returning by 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

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)...

Ensemble guidance remains in relatively good agreement on
southwesterly flow aloft persisting into the weekend and early next
week as interior NorCal remains wedged between ridging across the
Intermountain West and broad troughing over the eastern Pacific.
High temperatures are still expected to reach the 90s to low
triple digits in the Valley on Friday, with 80s to 90s at higher
elevations. This should then transition into comparatively
cooler, but still seasonably warm, temperatures for the weekend,
with primarily Moderate HeatRisk persisting in the Valley.
Periodically breezy to gusty, late day onshore winds are also
expected to continue.

Cluster analysis is indicating some uncertainty in the upper
level pattern by early next week. The majority of guidance
introduces a reinforcing ridge and warming temperatures into next
week, but still 25% of cluster analysis membership depicts a
closed low moving in off the coast of SoCal. The latter scenario
would likely result in a continuation of seasonably warm
temperatures with some higher potential for showers over the
Sierra as well.

&&

.AVIATION...

VFR conditions prevail across interior NorCal through the
forecast period. Breezy south to west winds continue through the
early evening with gusts 20 to 25 kts at times, then become light
and shift to a north to west direction overnight into Tuesday
morning. Winds are then expected to become breezy to gusty again
after 15z Tuesday, with gusts of 20 to 25 kts possible throughout
the Valley.

&&

.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.

&&

$$