Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 260907

Area Forecast Discussion
National Weather Service Sacramento CA
207 AM PDT Sun May 26 2024

Warmer weather returns to the region today, with generally above
normal temperatures and primarily minor HeatRisk expected through
the week ahead. Weak onshore flow also persists through Tuesday,
before dry, northerly flow arrives from Wednesday through the end
of the week.


Much calmer weather is being observed across interior NorCal as of
early this morning, with generally light winds across the region and
only a handful of lingering clouds across far northern Shasta
County. These mostly clear skies and calm winds will allow for early
morning low temperatures to dip a few degrees cooler than previous
nights. As a result, most areas should settle in the upper 40s to
mid 50s by sunrise, with a few higher elevation locations into the
upper 30s to low 40s.

Broad troughing aloft is already progressing eastward and rising
heights look to fill in behind it, with upper level ridging
amplifying across the Great Basin and Intermountain West. Despite
this, broad troughing aloft will continue to influence interior
NorCal as another trough builds in from the Gulf of Alaska toward
the Pacific Northwest by the early week period. As this occurs, a
few isolated, late day showers will be possible along the Sierra
crest on Monday, generally south of the Highway 50 corridor.
Otherwise, this pattern will lead to warming temperatures today into
the early week ahead, with afternoon high temperatures in the mid
80s to low 90s. Onshore, south to west winds are also expected to
continue, but overall remain breezy at most, with late day gusts 20
to 25 mph through the Delta and its vicinity.

Ensemble guidance is trending toward a consensus of the trough
ejecting eastward from the Pacific Northwest across the mid to late
week time frame. While initial impacts for interior NorCal will be
limited on Wednesday, the surface flow pattern is expected to at
least begin transitioning to a northerly direction. This looks to
result in somewhat split flow on Wednesday, with northerly winds
from roughly the I-80 corridor northward, while onshore flow
persists further southward. Temperatures overall still look to
remain slightly above normal, Valley high temperatures in the mid
80s to low 90s, and 70s to 80s at higher elevations, today through
Wednesday. Minor HeatRisk is expected to accompany these temperatures
as well.


Ensemble guidance is in generally good agreement on the trough
finally ejecting eastward on Thursday while transient ridging
builds in behind it. With this upper level transitional period on
Thursday, dry, northerly surface flow should overtake most areas,
with some gusty winds possible throughout the day on Thursday as
well. While ensemble means are still working to incorporate the
increasing trend in winds for Thursday, current NBM 50th
percentile forecasts indicate some gusts nearing 40 mph along wind
prone portions of the Sacramento Valley (namely the central and
western Valley along the I- 5 corridor). Resultant probabilities
of wind gusts reaching 40 mph are in the 40% to 60% range as well.
These breezy to gusty winds, combined with dry antecedent
conditions could see afternoon humidities dropping into the low to
mid teens for much of the region on Thursday and Friday, with a
few localized instances of single digit humidities certainly
possible also (primarily within the northern Sacramento Valley).

While the ridging aloft should remain fairly transient, the ridge
axis does look to position itself over interior NorCal on Friday. As
a result, firmly above normal temperatures are anticipated from
Thursday into the early weekend, with Valley high temperatures in
the 90s and 70s to 80s at higher elevations. Even with the warming
trend, probabilities of reaching triple digits remain fairly low
at this time, around 15% to 30%, with highest probabilities on
Friday across the central and northern Sacramento Valley. Current
forecasts do depict some scattered moderate HeatRisk in these
areas as well. Ensemble guidance is then indicating the return of
broad troughing aloft amidst high heights, signaling a trend
toward above normal temperatures persisting, but onshore flow
returning and limiting the upper bounds of the high temperature
forecast next weekend.


VFR conditions next 24 hours, except for local southwest wind
gusts to 20 kts near the Delta.