834
FXUS66 KSTO 092101
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
201 PM PDT Sun Jun 9 2024

.SYNOPSIS...
Today will be the last relatively cooler day before conditions
warm early next week, with Major HeatRisk and widespread 100s
developing across much of the foothills and Valley by Tuesday.
Slight chance of afternoon/eventing t-storms today, primarily
near Lassen Park area and eastern Tuolumne County.

&&

.DISCUSSION...

Key Points

- An Excessive Heat Warning for areas north of I-80 is in effect
  from Tuesday morning through Wednesday evening with areas of
  Major HeatRisk and widespread triple digit highs by Tuesday.
- A Heat Advisory for areas south of I-80 is in effect from
  Tuesday morning though Wednesday evening with widespread
  Moderate HeatRisk and areas of Major HeatRisk.
- Local waterways are still running cold and fast from snowmelt

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

Early this afternoon, we are seeing the influence of a trough
slide across Northern CA, eventually moving eastward to the
Rockies and a upper level low developing over SoCal. This will
help moderate temperates one last day with today`s afternoon highs
in the upper 80s to mid 90s in the Valley with 70s and 80s across
the mountains and foothills respectively. Additionally, the
trough has enough lift and moisture with it to see thunderstorm
chances this afternoon and evening (10-25% chance). Current
projections keep them fairly north and east of our forecast area
but still a glancing chance that a storm could develop on our side
of the crest before quickly exiting the area. NBM probabilities
show the best for anything to develop will be in the far eastern
Tuolumne County or the Lassen National Park area.

After today, this pattern will transition into more zonal and weak
northerly flow with periods of ridging over the Pacific NW and
Northern CA as a upper level high pressure sets up in the Eastern
Pacific. This will help warm the area 5-10 degrees on Monday with
areas of the Northern Sacramento Valley reaching triple digits.
With this, widespread Moderate HeatRisk returns on Monday, and
areas of Major HeatRisk in the northern and central Sacramento
Valley and northern San Joaquin Valley. The NBM continues to show
Valley highs in the mid to upper 90s south of Interstate 80, with
100-104 to the north.

The heat peaks on Tuesday into Wednesday, with Valley highs
forecasted 95-107, warmest over the northern Sacramento Valley.
There will be widespread Major HeatRisk in the foothills and much
of the Valley, though a very weak Delta flow could mitigate this
to some extent for the Delta Area into the Southern
Sacramento Valley.

As an result, an Excessive Heat Warning for areas north of I-80 is
in effect from Tuesday morning through Wednesday evening with
areas of Major HeatRisk and widespread triple digit highs by
Tuesday. Drink plenty of fluids, stay in an air-conditioned room,
stay out of the sun, and check up on relatives and neighbors.
Please continue to monitor the latest forecast and watch out for
sensitive groups such as the elderly, children, and your pets.

Additionally, a Heat Advisory for areas south of I-80 is in
effect from Tuesday morning though Wednesday evening with
widespread Moderate HeatRisk and areas of Major HeatRisk.
Afternoon highs of 95 to 103 is expected, hottest on Tuesday.

By Wednesday night, we will start to feel relief in the Southern
Sacramento Valley and Delta regions with overnight lows in the
mid 50s to mid 60s. Warmer overnight lows will continue across the
northeastern foothills and Northern Sacramento Valley, albeit
still a few degrees cooler Wednesday night vs. Tuesday night.

Again, be sure to check on your loves ones during our heat event
and reconsider outdoor activities during the hottest parts of the
day!

To view the latest HeatRisk, please visit
www.wpc.ncep.noaa.gov/heatrisk/

Area waterways continue to run fast and cold from snowmelt,
creating dangerous conditions for those seeking relief in rivers
and lakes.

To view current water temperatures, please visit
www.cnrfc.noaa.gov

&&
.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...


For late-week, ensemble guidance and cluster analysis are
suggesting a trough approaching and moving across the northwest,
with the upper level low moving inland across the southwest. This
pattern is resulting in a relative cool down late-week and into
next weekend, with periods of breezy winds. HeatRisk looks to
mainly be Minor for the foothills and mountains, with areas of
Moderate in the Valley over the extended forecast period. Valley
forecast highs are generally in the 90s over this timeframe, with
80s to 90s in the foothills, and 70s to 80s in the mountains.
Relief from the slightly above normal high temperatures can be
expected in the overnight hours as well, especially in the
vicinity of the Delta and adjacent Valley locations from onshore
flow later this week.
&&

.AVIATION...


VFR conditions prevail across interior NorCal over the next 24
hrs. Surface winds generally at or below 12 kts with the exception
of the Delta with southwest surface winds of around 15-25 kts
through about 09Z Monday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning from 11 AM Tuesday to 8 PM PDT Wednesday
for Central Sacramento Valley-Mountains Southwestern Shasta
County to Western Colusa County-Northeast Foothills/Sacramento
Valley-Northern Sacramento Valley-Shasta Lake Area / Northern
Shasta County.

Heat Advisory from 11 AM Tuesday to 8 PM PDT Wednesday for
Carquinez Strait and Delta-Motherlode-Northern San Joaquin
Valley-Southern Sacramento Valley.

&&

$$