River Flood Warning 3, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
941 AM PST Thu Feb 1 2024

.SYNOPSIS...
A fast-moving Pacific storm will bring strong gusty south winds
this morning with widespread moderate to heavy precipitation into
this afternoon with a slight chance of thunderstorms, then showery
through tonight with decreasing showers for Friday and Friday
night. Dry for Saturday into Sunday with minor warming. More
precipitation from a slow moving low pressure system off the
California coast may develop later on Sunday into Monday with more
widespread moderate to heavy precipitation centered some time
around Tuesday.

&&

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

This morning, the frontal band of clouds and rainfall is moving
across SoCal from northwest to southeast at about 5-10 mph while
the rain-producing elements are moving along the boundary from
southwest to northeast at about 30-35 mph. Heavier rainfall is
spreading across the region and the frontal band should move to
the east by 7 PM. South winds and will strengthen this morning
with the strongest south winds ahead of the cold front. Winds for
coastal areas could gust to 45 to 55 mph with the stronger gusts
near higher coastal terrain. Winds will turn westerly behind the
front and then the strongest winds will be over the mountains and
deserts for tonight and Friday. Today and Friday will have cooler
days followed by minor warming for Saturday through Monday.
Lightning strikes overnight have mostly been in the colder air to
the northwest well behind the cold front. Please refer to the
hydrology section below for more details on the expected
precipitation.

A low pressure system off he California coast will move slowly
eastward and inland during the early and middle part of next week.
There remain significant differences among model solutions with
respect to the timing, trajectory and intensity of the low
pressure system. This will affect which areas get the most
precipitation as well as the onset and duration of periods of
moderate to heavy precipitation. The deterministic NBM continues
to show impressive totals through the end of next week with 12.92
inches at Lytle Creek, 7.77 inches at Fullerton, 10.59 inches at
Palomar Mountain, and 5.13 inches at San Diego. There remains a
significant flood threat during the early and middle part of next
week, but with lower confidence in the details. At this time, the
most we can say with confidence is that from Sunday through the
middle of next week we will have cool and unsettled weather.

&&

.HYDROLOGY...
Precipitation will spread across the region from northwest to
southeast with a cold front that will move through SoCal during
the late morning and early afternoon. Bands of showers with
isolated thunderstorms will continue for the afternoon and early
evening. High-resolution short-range models show more isolated
and intense cells for late tonight with small hail possible.

Through Friday night, rainfall is expected to range from 1.5 to 2
inches near the coast, 2 to 3 inches in the mountains with one-
quarter to one-half inch in the deserts. Much of this rainfall is
expected to occur through this afternoon. Peak hourly rainfall
rates will mostly be one-half to three-quarters of an inch.
However, high-resolution models show the potential for isolated
hourly rainfall rates of 1 to 1.5 inch. This would be most likely
with thunderstorms or with narrow cold frontal rain bands near
the cold front during the late morning. These narrow  with the
cold front could produce brief heavy downpours and strong wind
gusts of 50 to 60 mph.

The snow level has fallen to around 5000 ft and will continue to
fall through tonight and could get down to near 4000 feet by
Friday morning. Heavy snow is expected to develop in the
mountains today above 5000 feet with snow showers continuing into
tonight. Snowfall of 2 to 6 inches is expected for elevations
from 5000 to 7000 feet with 6 to 12 inches from 7000 to 8000 feet
and 12 to 24 inches above 8000 feet, with a few inches of snowfall
possible down to around 5000 feet.

Dry weather is expected for Saturday into early Sunday. A slow
moving low pressure system off the California coast will bring
more widespread moderate to heavy precipitation during the early
and middle part of next week with lower confidence in the timing
of periods of heavier precipitation. Additional rainfall for late
Saturday night through Wednesday night for Orange and
southwestern San Bernardino Counties from 3 to 4 inches for
coastal areas to 5 to 8 inches in the mountains with locally
greater amounts with 1.5 to 2.5 inches in the Apple and Lucerne
Valleys. For San Diego and western Riverside Counties, additional
rainfall could range from 2 to 3 inches near the coast to 3 to 5
inches in the mountains with one-half to one inch in the lower
deserts.

The forecast for the San Diego River at Fashion Valley has the
river rising high enough to reach the low-water crossings by late
afternoon, cresting near flood stage late tonight, then falling
below the low-water crossings by Friday night.

&&

.AVIATION...
011630Z...Coast/Valleys/Mountains...A band of rain will
move through the region between 01/16Z and 02/00Z. BKN-OVC clouds
will lower to 700-900 feet MSL with 1-5SM vis in +RA and mountains
obscured. Isold TSRA. Gusty and erratic winds possible vcnty TSRA.
Gusty S-SE winds 25-35 kt, local gusts to 40 kt until about 21Z,
strongest along coast and in mountains. Winds turn to the WNW
after a FROPA between 01/22Z and 02/00Z. Cigs 2000-3000 feet MSL
after 22Z, with SHRA and briefly lower cigs/vis, areas of terrain
obscured through 02Z. SHRA gradually decreasing in coverage and
frequency after 02Z into Friday.

Deserts...Clouds lowering with RA moving in. Cloud bases 1000-3000
feet AGL and RA reducing vis 2-5SM between 20-02Z. SHRA to decrease
and bases lift to 2500-4500 feet MSL and improving vis. SCT-BKN 4000-
5000 feet after 08Z into Friday.

&&

.MARINE...
Gale force winds and hazardous seas are expected through early
afternoon. Winds will turn westerly and weaken this afternoon behind
a cold front, but conditions will continue hazardous for small craft
this afternoon into Saturday morning. Check the Gale Warning for
details. There is also a slight chance of thunderstorms this
afternoon through tonight. Westerly winds will decrease Saturday.
South to southeast winds will increase and seas will build late
Sunday and Monday, possibly generating hazardous boating conditions.

&&

.BEACHES...
A large west swell with a period of 13-15 seconds will bring high
surf today into Saturday, with surf reaching 6-10 feet. There is
also a slight chance for lightning this afternoon and night. High
surf is possible again on Monday.

&&

.SKYWARN...
Skywarn activation is requested.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory until 6 AM PST Saturday for Orange County
     Coastal Areas-San Diego County Coastal Areas.

     Wind Advisory until 2 PM PST this afternoon for San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Coastal Areas-San Diego County Valleys.

     Flood Watch through Friday morning for Apple and Lucerne Valleys-
     Coachella Valley-Orange County Coastal Areas-Orange County
     Inland Areas-Riverside County Mountains-San Bernardino
     County Mountains-San Bernardino and Riverside County
     Valleys-The Inland Empire-San Diego County Coastal Areas-
     San Diego County Deserts-San Diego County Mountains-San
     Diego County Valleys-San Gorgonio Pass Near Banning-Santa
     Ana Mountains and Foothills.

     Winter Storm Warning until 6 AM PST Friday for Riverside County
     Mountains-San Bernardino County Mountains.

     Wind Advisory until noon PST today for Orange County Coastal
     Areas-Orange County Inland Areas.

PZ...Gale Warning until 1 PM PST this afternoon for Coastal Waters
     from San Mateo Point to the Mexican Border and out to 30 nm-
     Waters from San Mateo Point to the Mexican Border Extending
     30 to 60 nm out including San Clemente Island.

     Small Craft Advisory from 1 PM this afternoon to 8 AM PST
     Saturday for Coastal Waters from San Mateo Point to the
     Mexican Border and out to 30 nm-Waters from San Mateo Point
     to the Mexican Border Extending 30 to 60 nm out including
     San Clemente Island.

&&

PUBLIC...PG
AVIATION/MARINE/BEACHES...Small

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Preliminary Local Storm Report
National Weather Service San Diego CA
1015 AM PST Thu Feb 1 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0943 AM     Snow             Lake Arrowhead          34.25N 117.19W
02/01/2024  M1.5 inch        San Bernardino     CA   Trained Spotter

            At 5600 feet, 33 degrees Fahrenheit turning
            to a rain/snow mix. Storm spotter measures
            1.5 inches of snow.

&&

APR

Preliminary Local Storm Report
National Weather Service San Diego CA
1031 AM PST Thu Feb 1 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1010 AM     Rain             3 WSW San Juan Capistra 33.49N 117.70W
02/01/2024  M0.77 inch       Orange             CA   Mesonet

            Mesonet station GW2590 Laguna Niguel past 1
            hour.

&&

AOT