Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 271640
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
940 AM PDT Wed Mar 27 2024

.SYNOPSIS...
Sunny and warm today with weak high pressure aloft. Thursday will be
another mild day, then a trough deepening down the West Coast
Thursday night and Friday will bring cooler weather. This trough
will bring rain and mountain snow Saturday and Sunday as it moves
across Southern California. Scattered showers on Monday will end
Monday night as the storm exits. Dry and warmer next Tuesday and
Wednesday as high pressure builds over the Southwest.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

Today will be the warmest day of the week in the coastal, valley and
mountain zones with high pressure aloft bringing sunny skies.
Coastal highs will be from 63-68, valley highs 68-74, and mountain
highs 52-62. High desert highs will be near 70 and lower desert
highs near 80.

Thursday will be a couple degrees cooler over and west of the
mountains as the onshore flow picks up ahead of a deepening trough
down the West Coast. The lower deserts will be a couple degrees
warmer with highs reaching the low to mid 80s.

The stronger onshore flow Thursday will result in gusty mountain and
deserts winds Thursday afternoon through Friday. West of the
mountains there will be a steadily deepening marine layer with low
clouds spreading a little farther inland each day.

Over the weekend a strong winter storm will bring rain, mountain
snow and gusty winds. A deep West Coast trough will impact the
entire West Coast from British Columbia down to northern Baja. On
Friday night this trough will be centered just west of SFO as a deep
534 dm closed low that will direct an atmospheric river into
Southern California and bring rain and high elevation snow Saturday
and Sunday.

The models are in good agreement on the track and timing of the
arrival of the atmospheric river in SoCal Saturday morning with a
PWAT of 1.00". This is a potentially impactful rain event, so much so
that the Weather Prediction Center has the coastal, valley and
mountain zones in their Excessive Rainfall Outlook this weekend. The
heaviest rain will fall on the west and southwest facing mountain
slopes where 2-4" of rain is forecast in the enhanced southwest
upslope flow ahead of the trough. Amounts as high a 5" are possible
in the San Bernardino Mountains. Rain totals west of the mountains
are for 1-2" of rain. In the high deserts 0.50-1.00" is forecast,
and 0.25-0.50" is forecast in the lower deserts.

The bulk of the rain will fall on Saturday with the AR, with more
intermittent convective showers and isolated thunderstorms on Sunday
as lapse rates steepen in the cold core low that will move over
SoCal. Showers Sunday night and Monday will taper off and end Monday
night as the storm moves east.

The snow level will be around 5500 feet Saturday morning, then
fluctuate between 5000 and 5500 feet Sunday. More than 12 inches of
snowfall is possible above 6000 feet in the San Bernardino County
mountains.

&&

.AVIATION...
271630Z...Coast/Valleys...Occasional high clouds above 20000 feet
MSL will prevail through Thu morning. Areas of low clouds will occur
05Z-18Z Thu, most frequent near the coast, including at/near KSAN,
KCRQ and KSNA, but extending locally in the valleys. Bases will be
1500-2000 ft MSL with tops to 2500 ft MSL. Local VIS 2-4 miles in BR
will occur in the valleys 07Z-18Z Thu.

Mountains/Deserts...Occasional high clouds above 20000 feet MSL will
prevail through Thu morning with unrestricted VIS.

&&

.MARINE...
Breezy northwest wind gusts around 20 knots will be possible
Thursday afternoon and evening in the outer waters. Southerly wind
gusts over 20 knots will occur late Friday night through Saturday
before turning to the west and diminishing. There is a slight chance
of thunderstorms Sunday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...Moede
AVIATION/MARINE...Maxwell


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