San Diego Forecast Discussion

000
FXUS66 KSGX 292146
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
146 PM PST Sun Jan 29 2023

.SYNOPSIS...
A winter storm will bring, rain, low elevation mountain snow, and
gusty winds to the area through early Tuesday. Snow levels will be
low through the duration of the storm, resulting in significant snow
accumulations, which are expected to impact our mountain passes. Dry
and warmer weather, with periods of offshore flow Tuesday through
the end of the week.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Forecast Highlights:
*Winter storm will bring rain, wind, and mountain snow Sunday
through Tuesday.
*Impacts expected on major mountain passes, including I-15 through
the Cajon Pass and I-8 in the San Diego County mountains.
*Locally heavy rainfall accumulations are possible for southern San
Diego County on Monday and Monday night.

Scattered light showers have been moving west to east through the
day. So far, rainfall totals have been light with highest
accumulation at 0.12 inches in Beaumont and Banning over the past
6 hours. A rainfall summary has been headlined on our
weather.gov/sandiego website. Precipitation will become more
widespread tonight through Monday night before coming to an end
from northwest to southeast Tuesday morning. Cool conditions are
expected through early this week. High temperatures through
Tuesday are forecast to be 10 to 15 degrees below average.

Widespread rain and low-elevation mountain snow expected with this
storm system. More details surrounding the rainfall forecast can be
found in the Hydrology section below. In regards to snow, the snow
levels have been 5000-5500 feet so far today. Snow levels are
expected to lower to 4000-45000 feet on Monday, and to 3000-3500 by
early Tuesday as the precipitation tapers off. Snow will likely
impact I-15/Cajon Pass and I-8 through the San Diego mountains by
Monday night. Significant snow will impact the mountains. We
continue to forecast 8"+ for places such as Big Bear, Wrightwood,
Idyllwild, Palomar Mountain and Mt Laguna. Up to an inch of snow
is possible in the higher elevations of the High Desert.

Winds are expected to peaking early this evening before tapering off
into early Monday. Gusty west winds up to 60 mph expected over the
mountains. Winds near 60 mph possible on the desert slopes of the
San Bernardino mountains into the High Desert. Peak gusts will be
closer to 50 mph on the desert slopes of the Riverside and San Diego
mountains into the lower deserts.

The storm will exit the region on Tuesday with dry conditions
expected through the end of the week. Gusty offshore winds from the
north/northeast are expected north of San Diego county Tuesday.
Strongest winds expected through the Cajon Pass into the Inland
Empire and on the foothills of the San Bernardino and Santa Ana
mountains. Winds will diminish by Tuesday evening. Cold conditions
will prevail through Wednesday morning, with the potential for
widespread frost over the inland valleys. By Wednesday afternoon, a
warming trend will have started and is expected to continue into the
weekend as a ridge builds in from the west. Another trough could dig
south for the first full week of February. Global ensemble clusters
are showing an incoming trough push the upper level ridge east. Of
course this far out there are still uncertainties in the details of
the forecast including how quickly the trough will move across the
US West Coast and how far south it will dig. Cloudier, cooler and
breezier conditions are possible with another shot of precipitation.

&&

.AVIATION...
292115Z...Coastal/Valley Areas and inland to the Coastal Slopes
SCT-BKN clouds based 3000-5000 feet MSL merging with higher BKN-OVC
layers to near 8000 feet MSL. Coastal slopes of the mountains
obscured. Isold -SHRA. Local vis 3-5SM in -SHRA. After about 30/08z
conditions becoming locally BKN-OVC 1500-3000 feet MSL with -RA
developing overnight. Visibilities locally 2sm in RA/+RA.
Cloud tops near 20000 feet MSL. Moderate confidence in
cloud timing and coverage at KSAN.

Desert Slopes and Desert Areas...SCT-BKN 12000 feet MSL with
unrestricted visibilities early. After about 30/08z desert slopes
and desert areas SCT-BKN clouds based near 5000 feet MSL merging
with higher BKN-OVC layers to near 8000 feet MSL with -RA
developing. Cloud tops to near 20000 feet MSL and mountains
frequently obscured in clouds and -RA. Moderate to high confidence
in surface gusts 30-45 kt 18Z-05Z Mon, mainly along the ridges,
desert slopes, and below the passes. MOD-STG up/downdrafts, pockets
of LLWS, and rotors possible over the mountains and adjacent deserts.

&&

.MARINE...
No hazardous marine weather conditions are expected through
Thursday. High confidence in west winds occasionally gusting near
20 kt over the coastal waters this afternoon through the night.

&&

.HYDROLOGY...
Showers will continue through the afternoon becoming more widespread
into this evening and overnight into Monday. Global deterministic
models are holding steady with a more westerly track of the low.
This will result in slightly higher snow levels, allowing for more
rain 4500-5000 feet and below in the mountains, especially during
the first part of the storm tonight into Monday morning. The
majority of the rainfall is still expected to fall over San Diego
County. Rainfall will average 0.25-0.45 inches over Orange County
and the Inland Empire to 0.45-1.00 inches over the San Diego coast
and valleys, 1-1.75 inches over the San Diego mountains below the
snow level, and 0.40-0.75 inches over the San Diego desert region.

Showers will linger the longest over San Diego County, with
precipitation expected into Tuesday morning. Current high resolution
guidance has hourly rainfall rates between 0.25-0.35 inches per hour
on Monday. A few locally heavier cells with rates closer to 0.50
inches per hour are possible mainly late Monday morning into the
early afternoon. High resolution ensemble guidance has 10-15% chance
of thunderstorms, mainly over the coastal waters/coast near the
upper level low.

A prolonged period of light to occasionally moderate rain rates over
ground that will quickly become saturated, could result in
considerable runoff, and ponding of water in poorly drained and
urban areas. Rivers and streams will rise once again, and could
inundate, normally dry areas by late Monday. Current focus is on
rivers and streams along the International Border, as there is a
potential that rainfall could exceed guidance there. All interests
should continue to monitor later forecasts.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning until 7 AM PST Tuesday for San Bernardino
     County Mountains.

     Winter Storm Warning until 10 AM PST Tuesday for Riverside
     County Mountains-San Diego County Mountains.

     Wind Advisory until midnight PST tonight for Apple and Lucerne
     Valleys.

     Wind Advisory until 7 AM PST Monday for Coachella Valley-San
     Diego County Deserts-San Gorgonio Pass Near Banning.

PZ...None.

&&

$$

PUBLIC...CO
AVIATION/MARINE...Small

NWS SGX Office Area Forecast Discussion