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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

                            
000
FXUS66 KSGX 180925
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
225 AM PDT Wed Sep 18 2019

.SYNOPSIS...
Low pressure over the West will bring cooler weather this week, 
with more extensive coastal clouds during nights and mornings. 
Gusty winds are expected in parts of the mountains and deserts 
each afternoon and evening today and Thursday. The low pressure 
weakens Friday, bringing warmer weather and less coastal 
cloudiness this weekend. A deeper low pressure system could arrive
next week, creating a small chance of showers by Tuesday.

&&

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

Coastal low clouds are patchy again this morning, much as they
were yesterday at this time. Early this morning they are fond of 
Camp Pendleton, southern OC and Tijuana. The random coverage won't
mean much since skies will be mostly sunny today. Our longwave 
trough pattern will continue until basically further notice. Today
will be almost a carbon copy of yesterday with temps a few degrees
below average again. The next shortwave rotating through the 
longwave comes Thursday. This will make max temps about 5-15 
degrees below average. It will also boost onshore winds through 
mountain passes and into adjacent deserts. Top gusts in favored 
pockets will be around 40 mph during the afternoon and evening. 
The shortwave will generate a coastal eddy, which will try to 
develop more marine layer clouds and extend them farther inland 
early Thursday and early Friday mornings. Coverage won't be full 
or uniform, but some inlanders could wake up to gray those 
mornings. Following the shortwave, a touch of offshore flow 
develops Friday morning. Not much wind to talk about, isolated 
northeast breezes in the foothills. The very weak offshore flow
continues over the weekend. Combined with a weakening version of 
the longwave trough, the marine layer and coastal clouds will
diminish some and turn more patchy again. Temps will bump up to 
around average for the weekend. Next week things get interesting. 
Deterministic models and ensembles have impressive consensus for 
the moment. They bring a deep, digging trough down the West Coast 
Sunday and Monday, and cut off an unseasonably deep low right over
SoCal that sits on top of the region for a couple days. This 
guidance also reaches down and grabs some subtropical moisture 
out of Mexico to wrap around the cutoff low. It's just enough to 
forecast a small chance of showers on Tuesday. Now the current 
consensus between models might be a mirage and a random 
coincidence, hence the slight chance wording. There are still 
several days and many model runs to go before we arrive at Monday 
and Tuesday, but the prospects for actual water falling from the
sky next week look intriguing.

&&

.AVIATION...
180845Z...Coast/Valleys...Patchy CIGS with bases 1000-1400 FT MSL 
and tops to 2000 FT MSL will likely expand in coverage after 10Z, 
affecting terminals up to 20 miles inland. However, there is some 
uncertainty regarding onset time at the TAF sites, and CIGS could be 
delayed 1-2 hours, especially at KSNA. VIS restrictions are not 
anticipated at the terminals, but valleys and elevated coastal 
terrain will see VIS 3-5 SM. High confidence in clearing occurring 
near 16Z, with VFR conditions prevailing after. Low clouds with 
bases 1400-1700 FT MSL will redevelop after 09Z Thu, extending 
farther inland (about 25 miles) with moderate confidence in eventual 
CIGS at KONT early Fri AM. 

Mountains/Deserts...VFR conditions will prevail through Thursday, 
with unrestricted VIS and CLR skies. W SFC winds 20-30 kt with local 
gusts 40 kt will occur during late afternoon and evening Wednesday 
from mtn crests eastward into the desert slopes. Periods of LLWS and 
MOD UDDFTS will be possible in those areas. 

&&

.MARINE...
Somewhat stronger winds Thursday evening over the outer waters 
nearest San Clemente Island may bring gusts that approach, but do 
not exceed, 20 kts. Otherwise, no hazardous boating conditions are
anticipated through Sunday. 

&&

.FIRE WEATHER...
Gusty and locally strong westerly winds are expected each afternoon
and evening today and Thursday. Top gusts should reach 35 to 45 
mph. These local winds will combine with low inland humidity to 
elevate fire weather conditions for favored pockets along mountain
ridges, through mountain passes and into adjacent deserts.

&&

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

&&

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

&&

$$

PUBLIC/FIRE WEATHER...MM
AVIATION/MARINE...Rodriguez