Debris Flows and Flooding in California, March 28 to 29, 2022

Area Forecast Discussion
National Weather Service San Diego CA
527 AM PDT Mon Mar 28 2022

.SYNOPSIS...
A Pacific storm from the west will move across the area through
tonight and move east on Tuesday and Tuesday night. It is expected
to bring locally heavy precipitation at times for late this
morning into late tonight with heavier snowfall in the mountains
above 6500 to 7000 feet. Wind will strengthen this morning, then
diminish from the northwest tonight. Dry and warmer on Wednesday,
then a slight chance for light showers on Thursday. Then dry and
warmer for Friday through next weekend.

&&

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

.SHORT TERM (Today through Wednesday)...
Little has changed with a major Pacific storm that will move
across the area with the biggest impacts today and tonight.
Lighter precipitation will develop this morning toward the coast
with the more widespread and heavier precipitation with the front
moving eastward across the area during the late morning into the
afternoon. After a break during the late afternoon except near the
mountains, more widespread showers will develop during the
evening and continue into tonight as cold air aloft with the upper
center destabilizes the atmosphere. There is also a slight chance
of thunderstorms for this afternoon into tonight with the
greatest chances toward the coast. NBM CAPE peaks at SNA at more
than 500 J/kg at 7 PM and SAN at 10 PM at more than 400 J/kg.

Gusty south winds will strengthen this morning, then become
southwesterly during the afternoon and diminish from the northwest
tonight. In the mountains and deserts, the more widespread
stronger winds are expected along and near the desert slopes of
the mountains. Cross-sections of higher-resolution models show
support for mountain wave development with bands of stronger
winds downstream in the deserts. One of these bands across the
Victorville airport brought gusts to nearly 50 mph with
reductions in visibility to as low as one-quarter mile in blowing
dust.

The ECMWF Extreme Forecast Index continues to highlight the
rainfall potential for this afternoon into tonight, and the
prefrontal south winds along the coast and in the San Bernardino
County mountains and deserts.

Lighter showers may linger in the mountains into Tuesday
afternoon. Dry and warmer for Wednesday with Wednesday high
temperatures a few to around 5 degrees below average for the coast
and valleys and a few degrees above average in the deserts.

&&

.LONG TERM (Thursday through Sunday)...
A weak low pressure system in northwest flow aloft could bring
some light precipitation around Thursday. Then dry and a little
warmer for Friday through the weekend with high temperatures a few
degrees above average. Another low pressure system from the
northwest could bring some light precipitation around next Sunday
night. There is greater model spread with that system. The model
that is slower with greater amplitude as greater precipitation
potential which would be light versus none.

&&

.AVIATION...
281000Z...Low clouds with varying bases between 2000-3500 feet MSL
will continue over the coastal basin this morning. RA to move
through the region from west to east after 16Z. During heavier RA,
cigs will lower to about 1000 feet MSL and vis 2-4SM. Isold TSRA
after 18Z. Higher terrain obscured for much of the late morning
through afternoon. -SHRA diminishing and improving cig/vis
conditions from north to south Tuesday morning.

Strong southerly to westerly winds 30-40 kt with gusts 45-55 kt in
the mountains/deserts today and tonight and 20-30 kt along coast
through early evening. MOD-STG up/downdrafts and LLWS can also be
expected north and east of the mountains.

&&

.MARINE...
Strong southerly winds and choppy seas will make conditions
hazardous for small craft today and tonight. Winds will turn more
westerly late today and tonight. Winds in the inner waters diminish
early Tuesday, but hazardous winds and seas persist in the outer
waters into Tuesday night. Check the Small Craft Advisory for
details. After winds and seas subside, no additional hazardous
conditions are expected Wednesday through Friday.

&&

.BEACHES...
Elevated surf of 3 to 6 feet with occasional sets 7 to 8 feet today
through Tuesday. Strong rip currents will make hazardous swimming
conditions. Check the Beach Hazards Statement for details. The surf
will subside Tuesday night and Wednesday.

&&

.HYDROLOGY...
A Pacific storm from the west will bring precipitation into
Tuesday with the most widespread heavier precipitation for this
afternoon and evening. Through Tuesday, rainfall is expected to
range from three-quarters to 1.5 inches near the coast to 2 to 3
inches in the mountains with isolated amounts to 4 inches on south
facing slopes. In the deserts, one-quarter to one-half inch is
expected with less than one-quarter inch in the lower deserts.
There is also a slight chance of thunderstorms for this afternoon
and evening with greatest chances toward the coast. The snow
level will rise above 7000 feet during this afternoon, then fall
to around 5500 feet late tonight with the heaviest snowfall above
6500 to 7000 feet.

Lighter precipitation will develop this morning toward the coast
with the more widespread and heavier precipitation with the front
moving eastward across the area during the late morning into the
afternoon. After a break during the late afternoon except near the
mountains, more widespread showers will develop during the
evening and continue into tonight as the cold air aloft with the
upper center destabilizes the atmosphere. There is also a slight
chance of thunderstorms for this afternoon into tonight with the
greatest chances toward the coast.

Peak rainfall rates could reach one-half inch per hour with the
front. However, the front will be moving quickly which will
minimize flood potential. After this band moves eastward across
the area during the late morning into the afternoon, there should
a break except near the mountains before more widespread showers
move into the area during the evening and continue into tonight.
Locally heavy rainfall rates of 0.50 to 0.75 inch per hour are
possible, but should be isolated.

While there could be some local flooding in poorly drained areas,
river flooding is unlikely. Smaller creeks and streams may swell
and locally overflow their banks where heavier rainfall rates are
concentrated. The San Diego River could reach Monitor Stage,
overtopping some of the low water crossings in Mission Valley by
tonight or Tuesday morning. See RVSSGX (River Statement) for
details on water levels.

&&

.SKYWARN...
Skywarn activation is requested for this afternoon and evening. Weather
spotters are encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from noon today to 6 AM PDT Tuesday for San Diego
     County Deserts-San Diego County Mountains.

     Wind Advisory until 8 PM PDT this evening for Apple and Lucerne
     Valleys.

     Winter Storm Warning from 1 PM this afternoon to 8 AM PDT
     Tuesday for Riverside County Mountains.

     Wind Advisory from 9 AM this morning to 5 PM PDT this afternoon
     for Orange County Coastal Areas-Orange County Inland Areas-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Coastal Areas-San Diego County
     Valleys-Santa Ana Mountains and Foothills.

     Wind Advisory from noon today to 10 PM PDT this evening for San
     Gorgonio Pass Near Banning.

     Wind Advisory until 11 AM PDT this morning for San Bernardino
     County Mountains.

     Winter Storm Warning from 11 AM this morning to 8 AM PDT Tuesday
     for San Bernardino County Mountains.

     Beach Hazards Statement through late Tuesday night for Orange
     County Coastal Areas-San Diego County Coastal Areas.

PZ...Small Craft Advisory until 8 PM PDT Tuesday for Waters from San
     Mateo point to the Mexican Border Extending 30 to 60 nm out
     including San Clemente Island.

     Small Craft Advisory until 5 AM PDT Tuesday for Coastal Waters
     from San Mateo Point to the Mexican Border and out to 30 nm.

&&

PUBLIC/HYDROLOGY...17
AVIATION/MARINE/BEACHES...MM