Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 281230
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
530 AM PDT Thu Mar 28 2024

.SYNOPSIS...
An approaching Pacific storm will strengthen the onshore flow
today and Friday with cooling spreading inland and with periods
of gusty southwest to west winds for the mountains and deserts
for this afternoon into Friday evening. That storm will bring
widespread moderate to heavy precipitation and mountain snow this
weekend from late Friday night into Monday. Moderate to locally
heavy precipitation with the cold front will move across the area
on Saturday followed by periods of showers and a slight chance of
thunderstorms for Saturday night and Sunday with showers lingering
into Monday. Then drier and warmer for the middle of next week
with high temperatures on Wednesday around 5 degrees above
average.

&&

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

.SHORT TERM (Today through Saturday)...
A low pressure system centered off the coast of Washington early
this morning is expected to be centered west of Point Conception
late Saturday afternoon. Strengthening onshore flow will spread
cooling inland today and Friday with periods of gusty southwest to
west winds for the mountains and deserts for this afternoon into
Friday evening with the stronger gusts along the desert slopes of
the mountains to 45 to 55 mph.

Precipitation is expected to begin increasing late Friday night
with the more widespread moderate to locally heavy precipitation
with the cold front moving southward and eastward across the area
during the day on Saturday. South winds will strengthen ahead of
the cold front with the stronger winds over the coastal waters
into coastal areas with gusts near the coast around 35 to locally
40 mph.

While model soundings near the front near the southwestern
California coast on Saturday morning have low level vertical shear
sufficient for storm rotation, but with marginal instability. The
greater instability is for late Saturday night and Sunday,
greatest across the San Diego County coastal waters into San Diego
County.

High temperatures on Saturday will be several degrees cooler than
Friday and as much as 20 to 25 degrees below average for mountain
areas above 6000 feet.

&&

.LONG TERM (Saturday night through Wednesday)...
Periods of showers with a slight chance of thunderstorms will
continue for Saturday night and Sunday with another round of more
widespread precipitation possible during the day on Sunday.
Showers will linger into Monday and be increasingly focused toward
the mountains on Monday.

Warmer and drier for Tuesday and Wednesday with Wednesday high
temperatures around 5 degrees above average, mostly in the 70s for
the valleys and the 80s for the lower deserts.

&&

.HYDROLOGY...
Widespread moderate to locally heavy precipitation will occur
this weekend. Rain and mountain snow will begin as early as Friday
night, with the heaviest and most widespread activity occurring
through the day on Saturday, and again early Sunday morning
through the afternoon.

Through Monday, rainfall is expected to range from around 1.5
inches near the coast to 2 to 3 inches in the mountains, locally
to around 5 inches on the south slopes of the San Bernardino
County mountains. For the deserts, one-half to one inch is
expected for the Apple and Lucerne Valleys, and one-quarter to
one-half inch for the lower deserts.

The snow level will rise to 5500 to 6000 feet for early Saturday
morning, fall to around 4500 feet for Saturday night, then
fluctuate around 5000 feet on Sunday. For the mountains of San
Bernardino and Riverside Counties, there could be snowfall of 1
to 3 inches from 4500 to 5500 feet, 3 to 6 inches from 5500 to
6000 feet, 6 to 12 inches from 6000 to 6500 feet, 12 to 18 inches
from 6500 to 7000 feet, with local amounts to 36 inches on the
higher peaks above 9000 feet with the greater potential for
heavier snowfall on Saturday.

For San Diego County, snowfall of 2 to 4 inches is expected above
5000 to 5500 feet, locally 4 to 8 inches on the highest peaks. The
greater potential for heavier snowfall in the San Diego County
mountains is on Saturday night and Sunday.

The current forecast for the San Diego River at Fashion Valley has
the river rising, but remaining below the low-water crossings
following the rainfall on Saturday. With additional rainfall on
Sunday, the river could rise sufficiently to flood the low-water
crossings for late Sunday into Sunday night. The 25th percentile
forecast keeps the river below the low-water crossings through the
weekend. The 75th percentile forecast would flood the low-water
crossings for a longer duration during the weekend, but remain
below minor flood stage.

&&

.AVIATION...
280930Z...Coast/Valleys...Low clouds will continue to cover most
coastal areas and western valleys through 14Z. Bases will be 1000-
1400 feet MSL with tops to 2000 feet. Vis reduced 0-5SM in BR along
inland extent of clouds and higher coastal terrain. Scatter out 16-
19Z. Low clouds will push ashore and inland after 01Z in San Diego
County and after 06Z in Orange County. Bases will be around 1500
feet MSL but will rise to over 2000 feet MSL and fill most of the
coastal basin overnight into Friday. Partial and intermittent cigs
near the coast.

Mountains/Deserts...Increasing westerly winds after 23Z with gusts
of 25-35 kt, locally up to 55 kt. MOD up/downdrafts and turbulence
expected over and east of the mountains.

Otherwise...occasional high clouds above 20000 feet MSL today and
tonight.

&&

.MARINE...
No hazardous marine conditions are expected through Friday. Strong
southerly winds and choppy conditions are expected Friday night and
Saturday morning. A distinct wind shift from south to west will
occur with a front moving through the coastal waters Saturday
morning, with weaker winds and less chop thereafter. There is a
slight chance of thunderstorms Saturday night through Sunday.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


&&

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

&&

$$

PUBLIC/HYDROLOGY...17
AVIATION/MARINE...MM


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