113
FXUS66 KSTO 201802
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1102 AM PDT Wed May 20 2026


.KEY MESSAGES...

 - Well-above normal temperatures, with areas of Moderate HeatRisk
   today-Friday.

 - Chances (10-20%) for isolated mountain showers and
   thunderstorms Friday afternoon.

 - Cooler, breezier weather by the weekend;
   strongest west-southwest winds in the Delta and vicinity
   locations.

&&

.DISCUSSION...

...Today-Friday...
Heights continue to rise as ridging builds off the Pacific
Northwest coast, resulting in well-above normal temperatures today
through Friday. High temperatures will be 10 to 20 degrees above
normal today-Thursday, with widespread Moderate HeatRisk. Warmest
temperatures, into the mid to upper 90s in the Valley, are
anticipated on Thursday before gradually cooling into the weekend.
Delta breeze influence will aid in relief from the heat in the
vicinity Delta, keeping highs in the mid 80s to low 90s. Meanwhile
Valley highs will be in the mid to upper 90s, with highs in the
80s in the foothills and mid 60s to mid 70s in the mountains.

Additionally, weak troughing and attendant moisture over the
mountains will lead to a 10-20% chance of isolated
showers/thunderstorms Friday afternoon. Latest guidance depicts
shower/thunderstorm activity setting up along the crest of both
the Sierra and Coastal Range.

...The Weekend-Tuesday...
Cooler temperatures are on track for this weekend and into early
next week as broad troughing builds over the region, strengthening
onshore flow. High temperatures cool to near-seasonal for mid to
late May by Saturday. Onshore flow will steadily increase through
the weekend, peaking on Monday with west to south gusts 20 to 30
mph in the Sacramento Valley/Delta.

More uncertainty appears in the ensembles and clusters regarding
the synoptic pattern Tuesday onward. The majority are in agreement
showing a trough descending from the Pacific Northwest into the
region, but diverge on it`s track and strength. This would mean
the difference between increased onshore flow or north winds
developing in the Valley mid next week.

&&


.AVIATION...

VFR conditions are expected over the next 24 hours. Light and
variable winds less than 10 kts expected through the period. West-
southwesterly winds increase through the Delta after 22Z
Wednesday with gusts 15 to 20 kts at times through 06Z Thursday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$