209
FXUS66 KSTO 312233
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
333 PM PDT Fri May 31 2024

.SYNOPSIS...
Slight cooldown Saturday through Monday before the return of
triple digit heat in the Valley Tuesday through Friday. Hottest
temperatures expected Wednesday. Slight chance of showers for
Shasta and Tehama counties Monday afternoon.

&&

.DISCUSSION...

Discussion at a Glance
- Less hot Saturday-Monday with increased onshore flow and Delta
  Breeze.
- 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; Some triple digits in the
  northern Sacramento Valley (areas north and including Chico)
  with cooler low to mid 90s in the Delta and Sacramento metro
  area as the Delta Breeze lowers temperatures.


Short Term Discussion

Today was a warm day, with high pressure moving over the area. Latest
temperatures are 2 to 6 degrees higher than the same time yesterday.
Skies are mostly clear, except for over the higher mountains,
where some fair weather afternoon cumulus have developed. Breezy
northerly winds died down this morning. Some light onshore flow
has begun in the Delta, with a Delta Breeze spreading inland
bringing cooling into influenced areas.

Saturday, weak upper level troughing moving through the Pacific
Northwest will help reduce high temperatures, as the axis of the
trough will slide through NorCal. High temperatures for the
weekend will be in the upper 80s to lower 90s for the Valley, and
cooler mid 80s for the Delta. Breezy winds will be possible in
the Delta, with wind gust speeds 15 to 20 mph. Further cooling is
expected Monday, when another Pacific Northwest shortwave trough
will eject from a closed low in the Gulf of Alaska and will brush
through the area, with a westerly, onshore flow pattern. There is
a slight chance (20-40%) of showers Monday for Shasta and Tehama
counties, with highest probabilities in the mountains north of
Redding, though there is a small chance of showers extending into
the far northern Sacramento Valley. There is decent (100-200%)
Precipitable Water (PW) with this trough, however most of the
Valley will remain dry as the trough will stay well north of our
area. The trough will quickly vacate the area, and upper level
ridging will begin to build in the eastern Pacific and spread
eastward. Locally breezy conditions may exist for the Delta and
Valley as the trough leaves the area, with wind gusts of 20-25 mph
possible.

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...Tuesday will see
upper level ridging moving inland, increasing heights and
temperatures around the region. Daytime high temperatures in the
upper 90s for the Valley, with widespread areas of Major HeatRisk
in the Valley and extending into the foothills and portions of the
Delta. National Blend of Models (NBM) probabilities of reaching
100 for the area are around 50-75% on Tuesday. Peak temperatures
are expected Wednesday with the ridge firmly over the area, with
hot temperatures continuing Thursday. An Excessive Heat Watch has
been issued from 11 am Tuesday to 8 pm Thursday. The Delta Breeze
could bring some slightly less hot weather to influenced areas,
and how strong this effect will be should become more clear over
the next few days.

Major HeatRisk affects everyone without effective cooling and/or
adequate hydration. Consider canceling outdoor activities during
the heat of the day. Clusters show there is some uncertainty
between ensembles over the strength and location of the ridge late
in the week. As a result the NBM has a large spread between the
25th and the 75th percentiles, which means a large range of
possible high temperatures for late in the week and into the
following weekend. Currently widespread Moderate HeatRisk is
expected for Friday, with isolated Major HeatRisk for the
Valley/foothills.

&&

.AVIATION...VFR conditions expected over the next 24 hours.
Sustained surface winds under 12 kts except winds 15 to 25kts in
the Delta after 00Z this evening.

&&

.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.

&&

$$