Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 011829
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1029 AM PST Mon Mar 1 2021

.SYNOPSIS...
Periods of gusty easterly Santa Ana winds will continue into
Tuesday through the mountain passes. Dry weather and warming will
occur through Tuesday. Gusty south winds will develop on
Wednesday in advance of a low pressure system that will deliver a
round of showers Wednesday afternoon and night. There is even a
slight chance of thunderstorms near the coast Wednesday afternoon
and evening. Dry and warmer conditions will return Thursday
through Friday. Another storm will pass to the north this
weekend. This will lead to increasing west winds in the mountains
and deserts, but dry weather will likely prevail.

&&

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

...Update...

Gusty east Santa Ana winds continue through the mountain passes
this morning with peak gusts to about 40 mph, but are
diminishing. However, they will pick back up again tonight-Tue
morning with gusts peak gusts to about 40 mph in the wind-prone
locales through the San Gorgonio Pass and along and south of I-8
through the San Diego County mountains.

It is a nice first day of meteorological Spring with bright
sunshine over the region and seasonably warm. Dry weather will
continue through Tuesday with further warming under a ridge of
high pressure.

The weather will take an abrupt change on Wednesday with a round
of showers expected Wednesday afternoon and evening as a Pacific
storm moves from west to east across SoCal. There is even just
enough instability to support a slight chance of thunderstorms
near the coast Wednesday afternoon/early evening. GFS and EC
ensembles have converged on most likely rainfall amounts being in
the 0.20-0.50 inch range, except slightly higher along the
coastal mountain slopes, particularly in San Diego County.
Rainfall rates are forecast to remain below thresholds for debris
flow near recent burn scars, but heavier cells could pose an issue
for minor urban flooding, mainly near the coast closest to the
instability.

Gusty south winds will develop ahead of the low on Wednesday.
South to southwest wind gusts of 30-40 mph appear possible along
the coast. EC ensemble mean has wind gusts near 35 mph at San
Diego Wednesday afternoon.

No changes to the forecast were made this morning. However, a
look at the latest model guidance shows that precipitation
amounts and winds will need a slight upward adjustment for the
Wednesday storm system.

...Previous Discussion (Issued at 421 AM PST Mon Mar 1 2021)...

.SHORT TERM (Today through Wednesday night)...
Gusty easterly Santa Ana winds will continue at times into
Tuesday, mainly along the coastal slopes of the mountains in San
Diego and Riverside Counties and the adjacent inland valleys. The
winds are expected to be relatively stronger and more widespread
this morning and again late tonight into Tuesday morning with the
stronger gusts to around 45 mph this morning, and 40 mph for late
tonight into Tuesday morning.

Gusty south winds will develop on Wednesday in advance of a low
pressure system that could bring showers, mainly for Wednesday
afternoon through Wednesday night. Winds at the coast could gust
to 35 to 40 mph from late morning into the afternoon. Rainfall
could range from around one quarter to one third inch near the
coast to around two thirds of an inch in the mountains with a few
hundredths in the deserts. The snow level will be between 5000 and
5500 feet with a few inches of snowfall possible above 6000 feet.
Rainfall could be locally greater in some locations depending on
the eventual track of this low pressure system.

&&

.LONG TERM (Thursday through Sunday)...
Drying with slightly below seasonal high temperatures on Thursday,
then high temperatures 5 to 10 degrees warmer on Friday as high
pressure moves inland across California.

There remain timing and amplitude differences among the ensemble
members of the global models with a low pressure system moving
inland through California on Saturday. It is primarily a portion
of the ensemble members of the ECMWF and Canadian models that have
enough amplitude of the trough to bring some light precipitation
to southwest California with stronger support for keeping most
precipitation north of Point Conception. High temperatures for the
weekend will be a little cooler, generally around to slightly
below average.

&&

.AVIATION...
011610Z...Mostly clear with VFR conditions through Tue AM.

Starting around 05Z Tue until around 18Z Tue, areas of east to
northeast sfc winds with gusts 25-35 kt expected in foothills and
portions of adjacent valleys. Strongest winds will be through and
below mountain passes. Areas of locally moderate up/downdrafts and
LLWS possible over and west of the mountains.

&&

.MARINE...
Gusty south winds expected ahead of an approaching storm system on
Wednesday. Wind gusts will be near 20 kt. Otherwise, no hazardous
marine weather conditions are expected through Friday.

&&

.FIRE WEATHER...
Gusty easterly Santa Ana winds will continue at times into
Tuesday, mainly along the coastal slopes of the mountains in San
Diego and Riverside Counties and the adjacent inland valleys. The
winds are expected to be relatively stronger and more widespread
this morning and again late tonight into Tuesday morning with the
stronger gusts to around 45 mph this morning, and 40 mph for late
tonight into Tuesday morning. The lowest inland humidity will
fall to around 10 percent today and recovery slightly to 10 to 15
percent on Tuesday. This will maintain elevated fire weather
conditions into Tuesday.

An approaching low pressure system is expected to bring stronger
and gusty south winds and a greater recovery in humidity on
Wednesday with a chance for wetting rainfall for Wednesday
afternoon and night.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

$$

PUBLIC...Gregoria (Update)/17 (Previous Discussion)
AVIATION/MARINE...CO



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