FXUS66 KSTO 090833
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
133 AM PDT Mon Sep 9 2024
Synopsis...
Not quite as hot today, then a cool down into the mid to upper 80s
through Thursday. Weather system moves through NorCal Wednesday
bringing potential showers to the southern Cascades and northern
Sierra. Breezy to gusty winds at times, especially on Wednesday
and Thursday.
.Discussion...
Clear skies and mild temperatures prevail around interior NorCal
this morning. We can expect another day of slightly above normal
high temperatures around the region, by 2-7 degrees in most
locations. Upper level ridging is expected to begin breaking down
over the area as me move through Monday, which will lead to cooler
high temperatures to begin on Tuesday. With offshore troughing set
to develop, onshore flow will be enhanced today and lead to
locally breezy conditions at times. Coupled with lower humidity
values, elevated fire weather conditions will continue throughout
the day.
On Tuesday and Wednesday, troughing will continue to build in over
the PacNW and move closer to coastal California. The increased
onshore flow will help increase relative humidity values across
the area as well. High temperatures will begin to fall in response
to the troughing and onshore flow, with the National Blend of
Models (NBM) showing roughly 60-90% chances of high temperatures
not reaching 90F Tuesday, however temperatures will likely hit 90
or higher in the northern Sac Valley (only a 20-40% probability of
less than 90F for Redding/Red Bluff). Wednesday, a closed low is
projected to develop and move inland in the PacNW and dig
southeast which will introduce a chance for showers for the far
northern Sac Valley, southern Cascades, and northern Sierra (best
chances north of I-80, around 15-30% probabilities). Moisture
with the closed low looks to be minimal for our area, as the EC
shows very limited precipitable water content and the Valley
likely getting shadowed from any significant precipitation. The
NBM having around a 10% chance of of total rainfall exceeding 0.10
inches in the aforementioned areas.
Breezy to gusty westerly winds are also expected Wednesday with
wind gusts up to 25 mph or greater across the area. Thursday, the
low will continue to move into the Rockies and transition our
winds into a northerly pattern throughout the day. The NBM is
projecting northerly wind gusts up to 30 mph, mainly along the
I-5 corridor and adjacent foothills (north of I-80 into Redding).
High temperatures will continue to be cooler than normal for the
second week of September. Highs will look to remain in the mid to
upper 80s for the Valley, cooler 70s for the foothills, and upper
60s to low 70s for the higher elevations in the Sierra.
.EXTENDED DISCUSSION
(Friday THROUGH Monday)...
Drier weather Thursday as 560 DM upper low pushes into the
Intermountain West. Below normal high temperatures continue across
the CWA Thursday with mid to upper 80s forecast in the Central
Valley with 50s to 70s for the mountains and foothills. Some
locally gusty wind continues Thursday.
Weak upper ridging moves through Friday with minor warming of the
AMS to near normal. Upper troughing then deepens over NorCal over
the weekend with synoptic cooling into Monday and some areas of
gusty wind. Models differ with progression of next short wave
trough through CA. NBM showing some light precip possible mainly
over the mountains Sunday into Monday.
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