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185
FXUS66 KSTO 232126
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
226 PM PDT Mon Sep 23 2024

.Synopsis...
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Elevated fire weather conditions persist into tonight due to
breezy northerly winds and low humidity. Hot weather with Moderate
HeatRisk through Tuesday with temperatures cooling off midweek.
Dry and warmer weather on Friday and through the weekend.
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.Discussion...
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Breezy northerly surface winds gusting 10 to 15 mph are being
observed along the I-5 corridor in the Sacramento Valley as of
2:22 pm this afternoon. Winds in the Valley will weaken through
this evening with periodically breezy northeasterly winds across
the adjacent Sierra foothills tonight gusting 15 to 20 mph.
Alongside the locally gusty northerly winds, limited overnight
humidity recovery and daytime minimum humidity values into the
teens to single digits are anticipated as well. This will result
in period of elevated fire weather conditions through this tonight
where strongest winds and lowest humidity coincide (generally
Interstate 5 westward in the central/northern Sacramento Valley).

Broad ridging aloft will allow above normal temperatures to
continue today and Tuesday, resulting in fairly widespread
Moderate HeatRisk across the Delta, Valley, and foothills. Despite
the favorable pattern, current probabilities of high temperatures
exceeding 100F run around 20% to 35%, with highest probabilities
in the northern Sacramento Valley today shifting to the southern
Sacramento and northern San Joaquin Valleys on Tuesday.

Heading into Wednesday, a deepening upper level trough offshore
will promote cooler, near normal inland temperatures and breezy
onshore flow. Winds are forecast to gust between 15-25 mph through
the Valley during the afternoon and evening hours, with gusts up
to 30 mph in the Delta. Humidity values are expected to increase
slightly with shift in the flow pattern as well with daily RHs in
the low 20s to low 30s and improved overnight recoveries.
Temperatures begin to rise by Thursday continuing into late week,
as broad ridging sets in over NorCal.
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.EXTENDED DISCUSSION (Friday THROUGH Monday)...
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Latest ensembles and clusters continue to show warmer
temperatures for Friday, with above normal temperatures continuing
through the weekend. This is due to atmospheric heights
rebounding in the wake of a departing upper level trough, with the
main ridge centered over the 4 Corners area(desert Southwest). So
while temperatures will be unseasonably warm, significant heat
impacts are not expected. Friday highs are projected to be around
7-10 degrees above normal (90s for the Valley), with scattered
Moderate HeatRisk across the area. The weekend has forecast highs
5-7 degrees above normal, with Pacific Northwest troughing
projected to bring some lowering heights and slight cooling over
the area. There is still quite a bit of uncertainty in the exact
pattern Sunday into early next week, so NBM temperatures reflect
this with a fairly large range of possibilities. Overall,
temperatures suggest a gradual cooling trend.

The primary concern with this pattern will be the shift from
onshore surface flow to predominantly northerly/offshore surface
flow. Potentially breezy north to east winds and daytime humidity
into the teens to 20s with limited overnight recovery could bring
some elevated fire weather concerns for early next week. There
remains a lot of uncertainty in the exact pattern, so stay tuned
for details.
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.AVIATION...
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VFR conditions over interior NorCal next 24 hrs. Surface wind
mainly below 12 kts except vicinity of the Delta, where there will
be southwesterly surface wind up to 20 kts at times, and in
mountains.
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.STO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$