719
FXUS66 KSGX 310530
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PST Thu Jan 30 2025

.SYNOPSIS...
A warming trend will occur through Monday as high pressure aloft
builds. Low clouds will be sparse tonight and then generally
restricted to immediate coastal areas Friday night through Monday. A
trough of low pressure will deepen along the West Coast the middle
of next week and bring a chance of precipitation along with cooler
weather and gusty mountain and desert winds.

&&

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

Skies cleared out entirely this evening as the deep marine inversion
is weakening, aided by the passage of the final shortwave associated
with the upper low now over the Central Plains. Ultimately the
marine layer will reset to a shallower form but probably not until
Friday, so we should mostly be clear overnight tonight. With
generally light winds, some of the inland and even coastal valleys
will have lows in the 30s with patchy frost. Ramona Airport is
already 38 and could drop in the upper 20s, though that is not rare
for them in winter.

We will have quite a notable warming trend Friday through Monday
with 850 MB temperatures as high as the 17-19 deg C range, so
temperatures should reach the 80s in the deserts Sunday/Monday and
possibly up to 80 deg F in warmer valleys west of the mountains.
Sunday/Monday should have temperatures inland which are 8 to 18 deg
F above normal, with greatest departures from normal in the
mountains and high deserts. The subsidence will result in a shallow
marine layer, so there could be fog associated with the mainly
night/morning coastal low clouds, though it is too early to
determine at what elevation any near-coastal dense fog could form.

Long-wave troughing over SW Canada and the Pac NW will gradually dig
south over the West Coast early next week, and by Tuesday night or
especially Wednesday, we should have at least some precip here. The
LREF grand ensemble has around 50% of members having measurable
precip in southern San Diego County and 75% in northern Orange
County, and there will likely be a good gradient of precip amounts
as well, with ENS members generally more favorable for precip than
GEFS members. The deterministic ECMWF even shows an atmospheric
river moving through our area around Wednesday, though it is not
nearly as strong or persistent as it will be in northern/central
California. That trough should bring cooling as well, plus gusty
winds in the mountains and deserts, especially with the rather tight
height/temperature gradients from north to south.

&&

.AVIATION...
310420Z...Mostly clear except FEW-SCT low clouds through 15Z. Any
clouds that form would have bases around 1500 ft MSL but chances are
low for CIG impacts at TAF sites through Friday afternoon.

&&

.MARINE...
No hazardous marine conditions are expected through Tuesday.

&&

.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...Maxwell
AVIATION/MARINE...PG