000
FXUS66 KSTO 212045
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
145 PM PDT Sun Apr 21 2024


.Synopsis...
Warm and dry weather continues into early next week. Locally
breezy winds at times through the Delta. Cooler, near-normal
temperatures return Tuesday through the end of the week with
onshore flow. Precipitation chances return late Tuesday through
Saturday, best chances in the foothills and mountains.

&&

.Discussion...
GOES-18 Satellite reveals mostly clear skies around interior
NorCal this afternoon. Temperatures are climbing into the upper
70s and low 80s in the Valley, and are expected to continue to
climb into the mid and upper 80s. Upper level ridging continues to
be the primary synoptic feature over the region through Monday.
Late Monday, a trough will approach the coast and transition our
flow into a southwesterly component, which will allow for a Delta
breeze to setup Monday evening. Southwest wind gusts up to 30 mph
will be possible in the Delta. There will also be a chance (15%)
for some isolated mountain showers Monday evening, along the
Sierra Crest from HWY-50 southward. Trough will continue to move
through the area on Tuesday and Wednesday, which will promote
onshore flow and allow high temperatures in the Valley to cool
into the low to mid 70s for Valley locations. Some CAMs
(Convective Allowing Models) are hinting at isolated showers and
thunderstorms to develop somwehere from Placer to Plumas counties
Tuesday morning, however confidence is very low in any morning
convection.

The main energy associated with the trough will be in SoCal, but
enough instability and forcing will be present for an isolated
shower or thunderstorm in the mountains on both Tuesday evening
and Wednesday evening. Tuesday evening, the best chances for
showers and t-storms will be mainly in northern Shasta county and
on Wednesday, the best chances will in Alpine and Tuolumne
counties. Best moisture will likely remain to the south of our
area, but there still remains around a 10-20% chance of shower and
t-storm development advertised by the National Blend of Models.
QPF totals will be very light, generally below 0.10" inches for
areas that experience an isolated shower. Locally higher amounts
possible if any thunderstorms develop will be possible.

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...

As we move into Thursday, the upper level low located in SoCal
will move eastward towards the Four Corners region, while another
trough moves into NorCal. Unsettled and cooler weather will
prevail across the area during this time, with periods of
showers/t-storms and the potential for some high elevation snow
showers. Thursday evening is when the active weather may start for
the region, beginning in the northern Sac Valley and the foothills
of the Sierra before spreading across the area Friday afternoon.
Depending on the exact track of the low, a few rumbles of thunder
could be possible Friday morning across the Valley floor as well.
Precipitation chances exist through the weekend, with the best
chances remaining in the foothills and higher elevations in the
Sierra and Southern Cascades.

Afternoon models runs have increased precipitation totals in the
foothills and Sierra slightly, with a storm total from Thursday
afternoon through Sunday morning to be around 0.50" to 1.25"
inches. Lower amounts of around 0.10" to 0.50" inches for the
Valley are currently forecast. Snowfall amounts have also trended
slightly upwards over the same time period. Around 2" inches or
less are now forecast for I-80 and HWY-50 passes, with the
highest peaks possibly receiving a fresh 10" inches from this
storm. Snow levels look to be relatively similar to yesterday`s
forecast, around 6000-7500` feet when the heaviest QPF is expected
(Thursday- Saturday AM). High temperatures will be mid to upper
60s for the Valley on Thursday and Friday, before warming slightly
on Saturday and Sunday into the low to mid 70s, which should keep
temperatures slightly below to near climatological normal.

Still a great bit of uncertainty regarding exact track and timing
of this system and precipitation totals, so stay tuned for
forecast updates as we move into the work week.

Wood

&&

.AVIATION...

VFR conditions over interior NorCal next 24 hrs with sfc wind
mainly at or below 12 kts.

&&

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

$$