FXUS66 KSTO 222102
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
202 PM PDT Mon Apr 22 2024
Synopsis...
Warm and dry weather continues today. Onshore flow bringing
cooler temperatures for Tuesday, along with a chance for a few
late day showers and thunderstorms over the mountains.
Precipitation chances increase Thursday afternoon through Friday
afternoon as a weather system moves through, best chances in the
foothills and mountains.
.Discussion...
Besides some high clouds, mostly clear skies have remained across
the region along with warm temperatures. As of 1:30pm, Downtown
Sacramento has gotten to 84 degrees.
As the upper ridge responsible for our warm and dry weather the
last several days begins to shift east, those offshore winds will
transition to onshore, allowing the cooler Delta breeze to spread
further east later this evening. Southwesterly flow will bring
breezes of 15-20 mph Tuesday and Wednesday to mainly the Delta and
mountains.
Some hires models are indicating a weak vorticity lobe may trigger
some brief light showers/sprinkles tomorrow morning as a surge of
moisture moves northward tonight-tomorrow morning (as shown by
PWATs). Even so, there isn`t much in the way of forcing, and
forecast soundings still indicate fairly dry low levels, so not
anticipating much reaching the surface, at least for the Valley
and communities in the lower foothills. Cooler and more moist
upper foothill locations may briefly see a few sprinkles as this
weak feature moves through the area.
The southwesterly flow is prompted by a more pronounced incoming
closed upper low which will primarily impact SoCal, but enough
moisture/instability is forecast to be drawn northward for a
chance of late day showers and thunderstorms over the northern
mountains and northern Sierra during the middle of the week. Best
chances being Tuesday afternoon across the Coastal Range, Shasta
County and southern Cascades/Lassen Park area. Less of a signal
Wednesday, but non-zero chances for isolated showers and
thunderstorms as well with lingering moisture around. Better
chances for precipitation and stronger winds will be Thursday
afternoon-Friday as a shortwave digging into the PacNW will
influence NorCal. As pressure gradients tighten, southwesterly
winds will increase, with more widespread gusts of 15-25 mph
Thursday ahead of a weak cold front. Snow levels with this system
will be pretty high, generally remaining above 7 Kft, so the bulk
of the (minimal) precip will fall as rain. Storm total forecast
increased a tad for Thursday-Friday now showing 0.25-0.50" in the
mountains and foothills. Those amounts will likely only produce
little, if any, impacts though.
//Peters
.EXTENDED DISCUSSION
(Friday THROUGH Monday)...
Ensembles and cluster analysis depict a system dropping down from
the PacNW and into the Great Basin late Thursday into Friday.
This will bring cooler temperatures and the potential for
widespread light showers, mainly over the foothills and mountains.
There is a 20 to 55% probability of at least a quarter of an inch
of precipitation over the foothills and mountains. Latest
precipitation amounts from WPC generally range from 0.10 to 0.50
inches, locally higher. A few inches of snow might be possible near
Lassen Park and south of I-80, but very little to no impacts are
expected due to high snow levels. NBM still indicates a 5 to 35%
probability of at least an inch of snow south of HWY 50 late
Thursday into Friday. There is also a 15 to 25% probability of
isolated thunderstorms Friday afternoon and evening, mainly over
the Sierra and associated foothills. Potential impacts include
brief downpours, gusty winds, lightning, and small hail.
A brief, weak flat ridge will move over the area on Saturday and
Sunday, nudging temperatures back up to seasonable levels through
early next week. Early next week, a low pressure system centered
over the Pacific Northwest will keep high temperatures near
seasonal averages, with Valley temperatures in the mid 70s.
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