Weather Service Report


756 
FXUS66 KSGX 281651
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
950 AM PDT Thu Mar 28 2024

.SYNOPSIS...
A Pacific storm moving down the coast will strengthen the onshore 
flow today and Friday bringing gusty west winds to the mountains and 
deserts. The storm will then bring widespread rain and mountain snow 
to Southern California Saturday and Sunday. Steady precipitation 
Saturday will transition to showers and isolated thunderstorms 
Saturday night and Sunday. Lingering showers Monday will be followed 
by dry and warmer weather Tuesday and Wednesday. 

&&

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

The infrared satellite loop this morning showed the circulation 
center of the deep 530 dm closed low west of the state of 
Washington. A strong shortwave diving south out of the Gulf of 
Alaska tonight will deepen a longwave trough down the West Coast and 
spin up a 535 dm west of SFO Friday evening. Surface pressure 
falling over the Great Basin this afternoon will result is strong 
onshore gradients that will bring blustery westerly winds to the 
mountains and deserts this afternoon through Friday. Blowing dust 
and sand will impact some deserts areas. 

The upper low digs south toward Pt Conception Saturday, tapping into 
a moisture plume over the Pacific that will make landfall over the 
Southwest Friday night and Saturday. Moderate to heavy rain over 
Santa Barbara Friday evening will move south across the LA basin 
Friday night, and then spread south into Orange, San Bernardino, 
Riverside and San Diego Counties Saturday morning. This is when 
steady moderate to heavy rain is likely. The combined effects of the 
PVA aloft, the lifting along and ahead of the surface cold front and 
the orographics over the mountains will produce rainfall rates of 
0.50" or more. 

After the AR passes Saturday afternoon, the cold core low behind the 
trough will settle over the Southwest, and a second trailing vort 
max which will help fuel showers and a thunderstorms in the unstable 
airmass Sunday. 

Showers will linger into Monday in the broad cyclonic flow trailing 
the upper low which will dig all the way to central Baja Monday 
evening. Ridging slowly builds over the Southwest Tuesday through 
Thursday for warmer days. 

&&

.HYDROLOGY...
Rain and mountain snow will begin as early as Friday night in Orange 
County and the San Bernardino Mountains, then move south across the 
Riverside and San Diego Counties Saturday morning. On Saturday night 
and Sunday, showers will be fairly widespread with locally heavy 
rain rates in any thunderstorms that form in the cold unstable 
airmass behind the trough. 

Forecast Rain Totals Through Monday:

Coastal and Valley........1.00"-2.00" 
Mountains.................2.00"-3.50" locally 5.00" in the SBD mtns  
Highs Deserts.............0.50"-1.00"
Lower Deserts.............0.25"-0.50" 

The snow level between 5500-6000 feet Saturday morning will fall to 
4500 feet Saturday night, then fluctuate around 5000 feet on Sunday. 

Projected Snow Totals Through Monday: 

4500-5500 ft...0-3" 
5500-6500 ft...3-6" 
6500-7500 ft...6-12" 
Above 7500 ft..12+" 

The current forecast for the San Diego River at Fashion Valley has 
the river rising on Saturday, but remaining below the low-water 
crossings. With additional rainfall on Sunday, the river could rise 
sufficiently to flood the low-water crossings late Sunday. 

&&

.AVIATION... 
280930Z...Coast/Valleys... Low clouds will continue through the 
morning hours at some of coastal sites. Bases will be 1000-1400 feet 
MSL with tops to 2000 feet. Vis reduced 0-5SM in BR along inland 
extent of clouds and higher coastal terrain. Scatter out 16-19Z. Low 
clouds will push ashore and inland after 01Z in San Diego County and 
after 06Z in Orange County. Bases will be around 1500 feet MSL but 
will rise to over 2000 feet MSL and fill most of the coastal basin 
overnight into Friday. Partial and intermittent cigs near the coast. 

Mountains/Deserts...Increasing westerly winds after 23Z with gusts 
of 25-35 kt, locally up to 55 kt. MOD up/downdrafts and turbulence 
expected over and east of the mountains. Surface winds should 
decrease after 09Z.  

Otherwise...occasional high clouds above 20000 feet MSL today and 
tonight.

&&

.MARINE...
No hazardous marine conditions are expected through Friday. Strong 
southerly winds and choppy conditions are expected Friday night and 
Saturday morning. A distinct wind shift from south to west will 
occur with a front moving through the coastal waters Saturday 
morning, with weaker winds and less chop thereafter. There is a 
slight chance of thunderstorms Saturday night through Sunday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC/HYDROLOGY...Moede
AVIATION/MARINE...Suk

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Western Regional Climate Center, wrcc@dri.edu