656
FXUS66 KSTO 310902
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
202 AM PDT Fri May 31 2024

.SYNOPSIS...
Warm temperatures again today, with a chance to break triple
digits in the Valley. Slight cooldown Saturday-Monday before the
return of triple digits Tuesday through Friday. Slight chance of
showers in Shasta County Monday afternoon.

&&

.DISCUSSION...

Discussion at a Glance
- 20-40% chance of Sacramento Valley climbing into the triple
  digits today, followed by a slight cool down Saturday-Monday
  and increased onshore flow.
- Major HeatRisk Wednesday & Thursday for the Valley & Foothills
  when there is the potential for widespread triple digit high
  temperatures. Prepare for elevated daytime highs and overnight
  lows, reconsider outdoor activities during the hottest part of
  the day (3:00-7:00 PM).
- Moderate HeatRisk next Friday (June 7), with isolated Major
  HeatRisk across the Valley; triple digits in the northern
  Sacramento Valley (areas north of and including Chico) and
  cooler low to mid 90s in the Sacramento area as onshore flow
  cools temperatures.

Short Term Discussion

Mostly clear skies prevail across interior NorCal this morning
with breezy northerly winds still observed in the northern
Sacramento Valley. Winds should calm as we move into the
morning/afternoon hours. High pressure is forecast to move inland
today and build over the area, increasing daytime temperatures for
the region. Warmest temperatures are forecast for the northern
Sacramento Valley, where the better probabilities (20-40%) reside
for breaking 100 exist. The Delta will remain in the low 90s,
thanks to onshore flow reducing the highs slightly. Northern San
Joaquin Valley and the Sacramento area will be in the mid to
upper 90s as well.

Tomorrow, weak upper level troughing moving through the PacNW will
help reduce high temperatures, as the axis of the trough will
slide through NorCal. High temps will be in low to mid 90s for the
Valley, and cooler mid 80s for the Delta. Breezy winds will also
be possible in the Delta, with speeds up to 20 mph possible. This
"cool down" will last until Monday, when another PacNW trough will
eject from a closed low in the Gulf of Alaska and will slide
through the area, flattening our heights into a more westerly
component. Sunday high temps will be similar to Saturday`s across
the region. Monday, the trough axis slides through the area and
will help lower temps into the 80s for the Valley and cooler 60s
to low 80s for the foothills and mountains. A slight chance
(20-40%) of showers Monday morning are possible in Shasta County,
with the higher probabilities north of Redding. There is decent
(100-200%) precipitable water with this trough, however 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 develop in the eastern Pacific. 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, we will see upper level ridging moving inland, increasing
our heights and also increasing our high temperatures around the
region. Daytime high temperatures in the upper 90s for the Valley,
with areas of Major HeatRisk in the central Sacramento Valley.
National Blend of Models (NBM) probabilities of reaching 100 for
the aforementioned area are around 50-75% on Tuesday. Wednesday
the ridge will be firmly over the area, once again increasing
daytime temperatures on both Wednesday and Thursday.

Widespread triple digit temperatures are anticipated in the Valley
on Wednesday and Thursday. High probabilities from the NBM of
70-100% exist for temperatures greater than 100 degrees, and there
is a 20-40% chance that areas in the central and northern
Sacramento Valley break 110. With the expected hot temperatures,
widespread Major HeatRisk is expected across the Valley. Major
HeatRisk affects everyone without effective cooling and/or
adequate hydration. Consider canceling outdoor activities during
the heat of the day. There is some discrepancies between
ensembles regarding the strength and location of the ridge, as the
ECMWF has the deep ridge stronger and located over NorCal while
the GEFS has the ridge slightly weaker and further to our east. If
the ECMWF where to verify, warmer temperatures could be
experienced as to what is currently forecast. Regardless of which
ensemble verifies, triple digits are very likely Wednesday and
Thursday.

Next Friday (June 7), there is a large spread on potential
temperatures, as well as location/strength of the upper level
ridge. Cluster Analysis reveals high confidence of the overall
synoptic pattern still dominated by ridging, but a number of the
clusters (11%) have our area in a more zonal pattern, which would
help ease temperatures. The NBM reflects this disagreement on
which pattern will occur, as the high temperature spread is
currently 15 degrees (86-101 for Sacramento/KSAC). Regardless,
upper 80s to low 100s will still be possible on Friday for the
area, with widespread Moderate HeatRisk and 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 Saturday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$