National Weather Service Forecast Discussion

Dicussion provided by the National Weather Service Forecast Office located in San Diego, California

FXUS66 KSGX 042100

Area Forecast Discussion
National Weather Service San Diego CA
100 PM PST Thu Mar 4 2021

High pressure will bring warming and drying through Friday. A low
pressure system moving inland through California on Saturday will
strengthen onshore flow with cooling and gusty southwest to west
winds in the mountains and deserts. Slight warming on Sunday. For
Monday through Thursday, a low pressure system over the eastern
Pacific will move slowly toward the West Coast. This will bring
chances for precipitation as early as Monday night and continuing
through Thursday. Stronger onshore flow will also bring periods
of stronger and gusty southwest to west winds in the mountains and



Scattered shallow cumulus have developed along and ahead of the
sea breeze front this afternoon, otherwise skies are nice and
clear. Temperatures are running a solid 10 to 20 degrees higher
than this time yesterday. Expect fair weather prevailing through
the afternoon and any cumulus clouds to dissipate shortly after
sunset. Patchy stratus may redevelop near the coast overnight,
otherwise it will be clear and cool.

Warmer and drier weather will take hold on Friday as the upper
level low that brought the wind and precipitation yesterday
continues to move off to the east and a weak upper level ridge
moves overhead. High temperatures will be 5-10 degrees above
seasonal averages tomorrow, warmest in the inland valleys and low
deserts. Weak offshore flow will develop in the mountains and
foothills Friday morning, but will remain well below advisory
strength with isolated gusts around 30-35 mph on the western
slopes of the Cuyamaca Mountains and below the San Gorgonio Pass.

An upper level trough moves across central and northern CA on
Saturday. While we won`t see any precipitation from this system,
it will bring a return of some marine layer low clouds, cooling,
and gusty southwest to west winds in the mountains and deserts.

A low develops over the Gulf of Alaska and slowly drops south off
the BC coast on Sunday. We will be sandwiched between the trough
off the coat and a weak upper level ridge over interior So Cal and
AZ on Sunday, which will maintain slightly below normal
temperatures, especially west of the mountains, weak onshore flow,
and a deeper marine layer.

The upper level low drops ever so slowly southward without much
eastward progression early in the week. The marine layer could
deepen enough for some drizzle or light rain as early as Monday,
with a better chance on Tuesday morning as a weak short wave moves
through the mean flow and into So Cal. Beyond about Tuesday
morning, ensemble spread increases drastically with regards to the
evolution of the upper low and timing of individual short wave
passages. While it is too early to nail down specific details, the
main point is that this large trough will very slowly progress
east, meaning a multiple-day precipitation event is likely Tuesday
through at least Thursday, with a good possibility of lasting into
Friday. Right now ensemble consensus points to the heaviest
precipitation sometime late Tuesday into Wednesday, followed by
lighter showers on Thursday. There is some potential for rain
continuing into Friday, but the 12Z suite of guidance has trended
towards a faster eastern progression of the trough late in the
week followed by another wave digging through the Great Basin
Fri/Sat, leaving us dry.

This system will also be quite cold, with 700 mb temps ranging
from -8 to -12C, coldest Wednesday and again on Friday. If this
holds, we could see snow down to the 3000 ft level, possibly
down to 2500 ft or lower during the mornings and in heavier
showers. There is a good potential for accumulating snow on the
I-15 through the Cajon Pass and upper portions of the Mojave
Desert near the San Bernardino Foothills and I-8 through the San
Diego Mountains.


042030Z...VFR conditions will be predominant through the period.
Scattered low clouds around 1500 ft MSL will impact the immediate
coast at times 02-15Z Friday but only a small chance of BKN
ceilings occurring at KSAN/KCRQ/KSNA. Confidence too low to place
in TAFs. Elsewhere, expect mostly clear skies/light winds.


Northwest winds could occasionally gust above 20 knots in the outer
waters during afternoons beginning Friday night and lasting through
mid next week, with a lull on Sunday. Otherwise, no hazardous
marine conditions are expected.


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





NWS SGX Office Area Forecast Discussion