432
FXUS66 KSTO 062046
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
146 PM PDT Sat Jul 6 2024

.SYNOPSIS...
Widespread Major to Extreme HeatRisk continues through early next
week, with a gradual cooling trend and HeatRisk decreasing toward
primarily Moderate to Major from Tuesday onward. Elevated fire
weather conditions from persistent hot and dry weather prevail into
the week ahead across the Valley and adjacent foothills locations as
well.

&&

Key Points
- Long-duration, dangerous heat event through early next week,
  impacting outdoor events.
- Excessive Heat Warning remains in effect for the Valley, Delta
  and foothills through 11 PM Tuesday.
- Heat Advisory remains in effect for the Sierra, southern
  Cascades, and Burney Basin until 11 PM Tuesday.

.Discussion...
As of early this afternoon, sunny skies prevail across interior
NorCal via latest GOES-West satellite imagery. Generally light south
to west winds are continuing as well, although will become breezier
though the early evening hours, especially within the Delta
vicinity. Otherwise, upper level ridging has become centered over
interior NorCal today and looks to gradually transition eastward
toward the Great Basin and Intermountain West from Sunday into the
week ahead. At the same time, a weak shortwave looks to move through
the upper level pattern Monday into Tuesday as well.

The resultant impacts of the upper level pattern will be a
continuation of very hot, likely (at least daily) record breaking,
high temperatures for much of the region today. As of 1 pm PDT,
Redding AP has officially reached 117F, with the all time record
high at Redding currently sitting at 118F (July 20, 1988 and July
5, 2024). Additional records throughout the Valley and foothills
will be tested as well. Additionally, some Delta breeze influence
is expected to intrude into the Delta vicinity this evening, which
will provide at least some overnight relief for the immediate
Delta area. A trend toward comparatively cooler temperatures is
then anticipated to begin on Sunday as the upper level ridge
starts to shift eastward. Valley and foothills high temperatures
still look to breach the triple digits, with high temperatures of
105F to 115F still possible by Sunday afternoon.

As the aforementioned shortwave begins to move within the flow
pattern, a bit more stout of a Delta Breeze is expected to set up.
This should help to provide a bit more widespread overnight relief
into portions of the central/southern Sacramento Valley and northern
San Joaquin Valley through the early week period. This is leading to
a reduction in HeatRisk values to primarily Moderate to Major (with
some lingering Extreme values in the foothills) across the region
moving into the week ahead. Resultant daytime high temperatures look
to fall into the lower triple digits in the Delta breeze influenced
areas, as 105F to 115F temperatures persist in the northern
Sacramento Valley and adjacent foothills. High temperatures across
the Sierra are also expected to remain abnormally hot as well, with
high temperatures in the 90s to low triple digits into the early
week ahead. Given the continuation of hot and dry conditions,
elevated fire weather concerns will persist through the weekend and
into early next week across the Valley and adjacent foothills.

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...

Current trends within ensemble guidance indicate a slight warm up
through Thursday as heights rise following the earlier shortwave
passage. This will reintroduce more widespread Major and areas of
Extreme HeatRisk into the central and northern Sacramento Valley
on Wednesday and Thursday as the Delta breeze influence weakens on
these days. There is then increasing confidence within cluster
analysis in broad troughing beginning to influence the region from
Friday into next weekend. This will allow the return of broader
onshore flow and will help bring temperatures down a few
additional degrees as well. Current probabilities of high
temperatures less than 100F are in the 50% to 80% range for areas
within the central/southern Sacramento Valley and northern San
Joaquin Valley and adjacent foothills by Saturday. &&

.AVIATION...

VFR conditions throughout interior NorCal next 24 hrs. Sustained
onshore surface winds mainly below 12 kts, except in the Vicinity
Delta where southwesterly winds 15-20 kts with periodical gusts
15 to 25 kts beginning 23z Saturday and continuing through
Sunday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 11 PM PDT Tuesday 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.

Heat Advisory until 11 PM PDT Tuesday for Burney Basin / Eastern
Shasta County-West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

&&

$$