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373
FXUS66 KSTO 180846
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
146 AM PDT Tue Jun 18 2024

.SYNOPSIS...
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Critical fire weather conditions from gusty northerly winds and low
relative humidity continue through midday today across the Delta,
Valley, and adjacent foothills locations below 2000 feet. Dry and
generally seasonable weather then persists through midweek, with
a warming trend late week into the weekend.
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&&

Key Points
- A Red Flag Warning is in effect until 12 PM PDT Today across
  the majority of the Delta region, Valley, and adjacent foothills
  below 2000 ft, due to low daytime relative humidity, gusty
  northerly winds, and poor overnight recoveries.
- Generally seasonable temperatures continue through most of
  the week, with a gradual warming trend late week into the
  weekend.
- Widespread Moderate HeatRisk is expected from Friday through
  Sunday, with some Major HeatRisk in the foothills on Saturday.

Short-Term Discussion (Today THROUGH Friday)...
Another morning of mostly clear skies is evident across interior
NorCal via latest GOES-West satellite imagery. Winds have trended
down from yesterday, although still breezy northerly winds persist
this morning, primarily across the northern and central
Sacramento Valley. Otherwise, early morning low temperatures
should continue to fall a few more degrees into the upper 50s to
low 60s throughout the Valley and foothills, with upper 30s to low
50s at higher elevations.

The primary troughing feature that produced the gusty northerly
winds yesterday has since shifted eastward toward the Intermountain
West. A subtle mid level shortwave moving through a similar flow
pattern aloft today though will result in a brief period of gusty
northerly winds increasing early this morning and continuing through
midday today. Strongest winds, with gusts of 15 to 30 mph, are
anticipated across the northern and central Sacramento Valley. Some
modest overnight RH recovery is anticipated, but this additional
period of heightened northerly winds will work against any overnight
recovery. As a result, critical fire weather conditions are expected
to persist through midday today and the attendant Red Flag Warning
has been extended through 12 PM PDT Today.

This mid level shortwave is expected to transition eastward by the
afternoon, with winds expected to rapidly drop off as this occurs.
Broad troughing then looks to remain in place over interior NorCal
through the remainder of the week, although heights aloft will
gradually be lowering as well. This will result in the return of
onshore flow and breezy to gusty, late day, south to west winds from
Wednesday onward, with strongest winds across the Delta and its
vicinity. Otherwise, high temperatures are expected to remain more
or less seasonable, with 80s to 90s across the Valley and foothills
and 70s to 80s at higher elevations through Thursday.

Moving into Friday, ensemble guidance is in good agreement that the
broad troughing aloft will become more nebulous as heights aloft
rise and a ridge begins to build in across the Great Basin. This
combination of factors will result in a warming trend from Friday
into the weekend, with high temperatures in the upper 90s to triple
digits throughout the Valley and foothills, and 80s to 90s at higher
elevations by Friday afternoon. This will result in fairly
widespread moderate HeatRisk for much of interior NorCal.

&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)...
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Cluster analysis continues to favor the somewhat muddled upper
level pattern over interior NorCal across the early weekend period
as heights aloft continue rising and ridging continues to become
more pronounced across the Great Basin. While the ridge axis looks
to remain well to the east, temperatures on Saturday are still
expected to be the warmest of this upcoming event. Fairly
widespread triple digit readings are anticipated throughout the
Valley and adjacent foothills locations by Saturday afternoon,
with current probabilities of exceeding 100F in the 70% to 95%
range in these areas. This will still muster primarily widespread
moderate HeatRisk for the region, although a few pockets of major
HeatRisk will be possible throughout the foothills on Saturday.

As quickly as this heat arrives however, current ensemble trends
indicate broad troughing being reinforced across interior NorCal
from late weekend into early next week. Resultant forecast high
temperatures are then expected to fall back toward the 90s to low
triple digits for most Valley and foothills locations, with 80s to
90s at higher elevations into early next week. Widespread moderate
HeatRisk looks to hang on through Sunday, before reverting to
predominantly minor HeatRisk by early next week.
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&&

.AVIATION...
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VFR conditions across interior NorCal for the next 24 hours. In
the Valley, widespread northerly surface winds up to 15 kts with
gusts 15-25 kts until around 19Z. In the Delta, winds shifting
southwest around 21Z with speeds of 5-15 kts. In the mountains,
expect surface winds from the northwest to northeast with local
gusts up to 25 kts until 17z.
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&&

.STO WATCHES/WARNINGS/ADVISORIES...
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Red Flag Warning until noon PDT today for Carquinez Strait and
Delta-Central Sacramento Valley in Glenn, Colusa, Yuba, Northern
Sutter, and Butte County Below 1000 Ft-Eastern Mendocino NF-
Northern Sacramento Valley to Southern Tehama County Line Below
1000 Ft-Northern San Joaquin Valley in San Joaquin and
Stanislaus Counties Below 1000 ft-Northern Sierra Foothills from
1000 to 3000 Ft. Includes portions of Shasta-Trinity and Butte
Units-Northern Sierra Including Lassen NP and Plumas and Lassen
NF/S West of the Sierra Crest (West of Evans Peak-Grizzly Peak-
Beckworth Peak)-Southeast Edge Shasta-Trinity NF and Western
Portions of Tehama-Glenn Unit-Southern Sacramento Valley in Yolo-
Sacramento Far Western Placer, southern Sutter and Solano County
Below 1000 Ft.
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&&

$$