Small Craft Advisory 10, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
953 AM PDT Mon Mar 11 2019

.SYNOPSIS...
A low pressure system moving inland across northern Baja tonight
and into southern Arizona Tuesday will bring periods of showers to
portions of southwest California for late this morning into
Tuesday morning with the most widespread showers and the greatest
precipitation amounts across the mountains tonight through
Tuesday morning. Snow levels will be near 5000 to 5500 feet with
the most significant snowfall above 6500 feet. Another low
pressure system moving southward through the western states will
bring a slight chance of showers for late Tuesday night and early
Wednesday. Otherwise, dry weather with a warming trend will
prevail Thursday through next weekend with periods of stronger
and gusty northeast winds along and near the coastal slopes of the
mountains and below passes and canyons.

&&

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

...Update...

Storm system centered southwest of SoCal will move inland into
Baja tonight through Tuesday. Moisture will wrap around this
feature and spread from south to north into SoCal today. GOES-17
satellite imagery shows high level cloudiness streaming northward
into SoCal east of this system. Top down moistening of the
atmosphere will take place today, and with the dry low levels,
it will take awhile for showers to reach the ground, but that is
expected to begin this afternoon. Max precipitation coverage and
intensity is expected after 5 PM this evening and continuing
throughout the night with the focus/highest amounts over the
mountains. Precip will then taper off Tuesday morning with just a
few left over showers during the afternoon.

Flash flooding is not expected with maximum rates to 0.25"/hr and
most cells 0.05-0.10"/hr.

Hi-res models continue to be bullish on amounts with 1"+ over the
mountains with some runs even to 2+" (latest HRRR eastern San
Bernardinos). WRF less aggressive than the HRRR, but still higher
than WPC and RFC QPF. Given uncertainties, decided to use a blend
of these models while incorporating 50% of the inherited QPF. This
allowed a trend upward in amounts, but not a full throttle change.

Snow will really add up in the mountains tonight. How much is
uncertain, even this close to the event. We are forecasting
amounts of 6-8"+ at Big Bear and mountain peaks to 12"+. If some
of our hi-res models pan out, snowfall tonight could become more
significant.

...Previous Discussion (Issued at 335 AM PDT Mon Mar 11 2019)...

.SHORT TERM (Today through Wednesday)...
Early this morning, a closed upper level low pressure system is
over the eastern Pacific centered to the southwest of Point
Conception with satellite imagery show mid and high level moisture
streaming northward into southern California.

This low pressure system will move slowly southward today, then
eastward and inland across northern Baja tonight, and into
southern Arizona Tuesday. It will bring periods of showers to
portions of southwest California for late this morning through
Tuesday morning. The most widespread showers with the greatest
precipitation amounts are expected for the mountains for tonight
through early Tuesday.

Rainfall in the mountains will generally range from one half to
one inch with one quarter to one half inch in the lower deserts,
and mostly less than one quarter inch for coastal and valley areas
and in the high desert.

Snow levels near 4500 to 5000 feet early this morning, will rise
to 5000 to 5500 feet for this afternoon through Tuesday morning.
Snowfall will mostly be a few inches above 5500 feet, 4 to 8
inches from 6500 to 7500 feet, and a foot or more on the highest
peaks.

For late Tuesday night and early Wednesday, a weak low pressure
system moving southward through the western states will bring a
slight chance of light showers, most likely across portions of San
Diego County from the coast to the mountains. This will also bring
stronger and gusty west winds along the desert slopes of the
mountains for Tuesday night with the stronger gusts to around 45
mph.

Below average high temperatures today will warm on Tuesday but
remain below average, then cool slightly on Wednesday.

&&

.LONG TERM (Thursday through Sunday)...
High pressure aloft will be centered near the West Coast early
Thursday with a weak low pressure system moving inland through
southern California late Thursday night and early Friday. High
pressure aloft will then return near the West Coast through next
weekend. Dry weather with a warming trend will prevail, but with a
brief break in the warming trend on Friday as the weak low
pressure system moves inland across southern California. High
temperatures will warm to near average late in the week, and to
around 5 degrees above average next Sunday. There will also be
periods of stronger and gusty northeast winds along and near the
coastal slopes of the mountains and below passes and canyons.

&&

.AVIATION...
111630Z...Coast/Valleys/Mountains...Widespread BKN-OVC clouds will
continue to lower today with bases 4000-6000 feet MSL by 19Z.
Scattered -SHRA this afternoon will become more widespread by early
evening, with -SHSN above 5000 feet MSL. Mountain terrain will be
obscured at times, and local vis will be 3-5 miles in -SHRA
coast/valleys mainly tonight. Precipitation will diminish Tue after
16Z.

Deserts...Increasing clouds above 10000 feet MSL and unrestricted
vis will occur this morning, thickening and lowering to around 6000
feet MSL this afternoon. Scattered -SHRA will develop late this
afternoon and continue through around 16Z Tue with cigs possibly
lowering to 3000 feet MSL and local vis 3-5 miles.

&&

.MARINE...
No hazardous marine conditions are expected through Tuesday morning.
Winds and seas will increase and become hazardous Tuesday afternoon
and continue Tuesday night. Latest guidance suggests winds will not
reach gale force, but gusts could still reach 25-30 knots Tuesday
afternoon and night. A short-period WNW swell could exceed 10 feet
in the outer waters due to a wind fetch just beyond the coastal
islands Tuesday night and early Wednesday morning. The combination
of strong winds and steep waves will create conditions hazardous to
small craft. No additional hazardous marine weather is expected
Wednesday afternoon through Friday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 3 PM this afternoon to noon PDT
     Tuesday for Riverside County Mountains-San Bernardino
     County Mountains.

PZ...NONE.
&&

PUBLIC...Gregoria (Update)/17 (Prev Discussion)
AVIATION/MARINE...Maxwell