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154
FXUS66 KSTO 090957
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
257 AM PDT Sun Jun 9 2024

.SYNOPSIS...
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A warmup is expected early this week with Major HeatRisk for the
northern and central Sacramento Valley on Monday, widespread for
much of the Valley and foothills Tuesday and Wednesday. Isolated
mountain shower/thunderstorms late today, but should be limited
to far northeastern Shasta County, Lassen National Park, and far
eastern Tuolumne County. Weather trends cooler late in the week.
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&&

.DISCUSSION...

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Key Points

- Minor HeatRisk this weekend with very localized areas of
  Moderate HeatRisk in the northern Sacramento Valley
- An Excessive Heat Watch remains in effect for Monday morning
  through Wednesday evening with areas of major HeatRisk
  throughout portions of the Sacramento Valley with widespread
  triple digit highs by Tuesday
- Cooler temperatures return Thursday into next weekend
- Local waterways are still running cold and fast from snowmelt

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

The trough along the coast that brought a cooling trend on
Saturday will continue with the onshore flow pattern today. This
will again bring near normal temperatures to Delta Breeze
influenced areas today. Highs there will be in the mid to upper
80s, as well as for the foothills. The northern and central
Sacramento Valley are forecast to again be 3-5 degrees above
normal, with highs in the low to mid 90s. The mountains should see
temperatures ranging from the mid 60s to around 80. Minor
HeatRisk is expected across the area. With increased onshore flow,
periods of breezy conditions are expected this weekend, with
onshore gusts of 15 to 25 mph in the mid afternoon through
evening hours, primarily across the Delta and into the southern
Sacramento Valley and northern San Joaquin Valley.

The trough will bring the potential for isolated high elevation
mountain showers or thunderstorms in the afternoon and evening,
but these are expected to be limited to far northeastern Shasta
County, Lassen National Park, and far eastern Tuolumne County.
Convection Allowing Models (CAMS) are pretty consistent in
showing this. There is a 10-20% chance for thunderstorms in those
areas, with the best potential focused over areas east of the
crest. Dry weather is expected over the vast majority of the
forecast area. By Monday the trough will have exited to the east,
with dry conditions across the area returning. A pattern of high
pressure ridging will dominate over Northern California, with low
pressure developing off the Southern California coast.

Confidence is increasing in a significant warmup by Monday, with
widespread Moderate HeatRisk returning 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, with Valley highs
forecast 100-107, 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 influenced areas. An Excessive Heat Watch
remains in effect for Monday morning through Wednesday evening
for the Sacramento Valley and adjacent foothills with forecast
highs of 95 to 107. Strongly reconsider outdoor activities during
the hottest part of the day (3:00-7:00 PM) and take frequent
breaks in the shade if you must spend time outdoors.

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
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&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...

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Ensemble guidance and cluster analysis indicate a closed low over
southern California with some ridging over the West Coast in the
middle of next week. Hot temperatures are forecast to continue on
Wednesday, with the National Blend of Models (NBM) showing a 60
to 90 percent probability of high temperatures reaching or
exceeding 100 degrees in the Valley on Wednesday. For the rest of
the week, ensembles are suggesting a trough approaching and moving
across the west, bringing a relative cool down late-week and into
next weekend. HeatRisk looks to mainly be Minor for the foothills
and mountains, with areas of Moderate in the Valley from Thursday
through Saturday. Valley forecast highs are generally in the 90s
over this timeframe.
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&&

.AVIATION...

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VFR conditions over interior NorCal next 24 hrs. Sfc wind mainly
below 12 kts except vcnty of Delta SWly sfc wind 15-25 kts.
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&&

.STO WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Monday morning through Wednesday
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.

&&

$$