FXUS66 KSTO 142122
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
222 PM PDT Fri May 14 2021
SYNOPSIS...
Cooling trend continues today and into the weekend, with warmer
temperatures Sunday and Monday. Scattered showers and thunderstorms
are possible today and into the weekend, mainly over the mountains
and northern Sacramento Valley as a low pressure system moves
over the region. Some showers may spread into the southern
Sacramento Valley Saturday night.
.DISCUSSION
...
GOES-West visible imagery reveals some passing high clouds over
the northern third of California this afternoon, as well as some
convective cumulus starting to bubble up in the higher elevations.
Temperatures are generally running several degrees cooler compared
to 24 hours ago, and expect this to similarly translate over to
this afternoon`s highs in the 80s to near 90 deg F. Delta breeze
is pumping in Bay-cooled air to Solano county where some
communities may struggle to get out of the 70s today. Could see
some marine stratus try to push into the Delta overnight and on
early Friday.
Over the next several days, the main weather concern will be the
potential for showers and thunderstorms. An upper level trough
will drop south from the Pacific Northwest over the next 24 hours,
becoming a closed low over the Golden State by tomorrow. For the
short-term from now through around midnight, the best opportunity
for showers and isolated thunderstorms will be confined to far
northern California, including the areas around Trinity, Western
Shasta, and Western Tehama counties. The best chance will be
farther north around the Oregon border. Some non-zero thunder
probabilities spill into the northern Sacramento Valley; the
National Blend of Models gives Redding around a 20 percent chance
of thunder through about midnight.
On Saturday, shower and thunderstorm chances will expand south
and east over the Sierra as the upper low moves inland.
Additionally, precipitable water values will increase upward to
around an inch, and combined with plenty of CAPE for California
standards (approx 500-1000 J/kg), do expect showers and
thunderstorms to be more numerous compared to today. Decaying
convection will likely linger into the evening hours and beyond
sunset, perhaps bringing showers to portions of the southern
Sacramento Valley with the east/southeast flow.
Main threats associated with these storms will be locally brief
heavy rainfall (more on Saturday than Friday), some gusty winds,
small hail, and lightning. Fuels remain at record dryness for this
time of year with at least one location (Stonyford/Western Sac
Valley) approaching the 90th percentile on the Energy Release
Component (ERCs) charts. Best chance for dry lightning will be
today, but that threat will mostly be to our north in Siskiyou
county. As more moisture makes its way into California on
Saturday, the showers and thunderstorms in the Sierra will become
"wetter", and will mitigate (to an extent) dry lightning. That all
said, even with "wetter" showers/thunderstorms, small fire
ignitions will be very possible, especially if lightning strays
away from the cloud base.
Shower and thunderstorm chances will be more limited to the Sierra
Nevada and foothills on Sunday as the upper low exits toward the
Great Basin/Desert Southwest. Some ridging across northern
California will allow temperatures to rebound to the upper 80s/low
90s around Redding by Sunday or Monday afternoon. // Rowe
.EXTENDED DISCUSSION
(Tuesday THROUGH Friday)...
Ensemble guidance advertises the arrival of another trough to the
California coast around Tuesday/Wednesday. Given the uncertainty
with the timing/strength of this trough, official forecast follows
with the National Blend of Models. This includes the chance of
showers over portions of Shasta, Tehama, and Butte counties on
Wednesday. Looking at the latest Climate Prediction Center`s 6-10
day outlook -- valid May 20 to 24 -- below normal temperatures are
slightly favored for much of the West Coast.
|
|
