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000 
FXUS66 KSGX 162302
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
300 PM PST Sat Nov 16 2019

.SYNOPSIS...
Santa Ana Winds will prevail through Monday with locally strong
winds occurring along the coastal mountain slopes and through 
valley corridors below passes and canyons. The strongest winds
will occur after midnight tonight through Sunday afternoon. Winds
will subside on Monday, but low humidity will remain inland from 
the coast. On Tuesday, winds will turn onshore ahead of a storm
system approaching from the north. The first winter storm of the
season will arrive from the north Tuesday night, moving over 
Southern California Wednesday through Thursday. This will deliver 
the first widespread, and potentially significant, precipitation 
of the season to SoCal. The precipitation will gradually taper off
Thursday night into Friday as the storm departs to the east. 
Upper level high pressure will build in from the west next 
weekend.

&&

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

.Highlights...

* Red Flag Warning for inland parts of SoCal 1AM-6PM Sunday
* First Winter Storm of the season to impact SoCal mid week

Santa Ana winds have have returned to Southern California and 
will peak late tonight-Sunday with max gusts to 50 mph in the 
favored areas, such as below the Cajon Pass, Santa Ana foothills 
(Freemont Canyon), below the San Gorgonio Pass and along the 
coastal mountain slopes of the San Diego County mountains. 
Relative humidity has lowered into the teens into portions of the
inland valleys. Critical fire weather conditions will occur in the 
wind-prone areas late tonight through Sunday afternoon. High 
temperatures will soar with some inland valley locales reaching into 
the lower 90s with a few record highs possible. See Fire Weather 
section below for more details on the fire weather concerns late 
tonight-Sunday.

Santa Ana winds will subside on Monday and winds by Tuesday 
transition back to onshore ahead of the first winter storm of the
season poised to impact Southern California during the middle 
part of next week. 

There is high confidence that widespread precipitation will occur
across SoCal Wednesday-Thursday, but there is low confidence on
the details.

A cut off low off the Baja Peninsula will meander there through 
Monday. Southerly mid/high level wind flow on the east side of 
the low will slowly draw moisture northward from Tropical Storm 
Raymond, but that moisture stays south of the border through
Monday. On Tuesday, a northern stream shortwave will dive
southward and into SoCal Wednesday-Thursday. However, GFS and
ECMWF and their ensembles diverge with regards to the track of 
the low. The 12Z run of the GFS is over SoCal and more open, 
while the ECMWF has a track over the ocean, closing off, slower 
and grabbing more moisture, and hence is a wetter scenario.

There is an extremely large spread with regards to rainfall 
amounts when looking at ensemble model data, ranging from light 
amounts (around 0.10 inches) to hefty amounts (3-4"+). Our current
forecast is placed towards the mean, depicting a widespread 
0.50-1.00 inches. NBM is slightly higher overall with a more 
coastal focus. Trended towards NBM, but did weigh some of the 
inherited forecast to trend/not jump. QPF adjustments will be the
norm in the coming days. Users should keep in mind that a wide 
range of solutions is possible, ranging from little rainfall to 
significant rainfall, capable of producing flash flooding. 
Mountain snowfall will depend on the low track as well. Currently,
the snow level is forecast to fall to around 6000 feet with 
several inches of snow possible above. Thunderstorms may occur 
with this storm system as some runs do show enough instability, 
particularly the ECMWF. Stay tuned as we fine tune the details in
the days ahead.

Lingering showers are possible on Friday as the storm system
departs the area to the east. Upper level high pressure will build
in from the west, promising a tranquil next weekend after
(hopefully) the region receives a much needed, appreciable 
rainfall.

&&

.AVIATION... 
162135Z...Coast/Valleys...A few patches of low clouds remain at the 
immediate coast vcnty KSAN. Patches of low clouds may return to the 
immediate coast after 03Z Sunday, but impacts at coastal TAF sites 
is unlikely. 

Areas of northeast winds 15-25 knots with local gusts to 35 knots 
will continue through tonight. LLWS and weak to moderate 
up/downdrafts are likely vcnty KSNA, KONT AND KSBD.

Mountains/Deserts...SCT-BKN high clouds at/above 20,000 ft MSL and 
unrestricted vis will continue through tonight.

&&

.MARINE... 
No hazardous marine weather is expected through Tuesday. Stronger 
west winds gusting to 20 knots could occur Tuesday night through 
Wednesday, along with showers.

&&

.FIRE WEATHER...
Santa Ana winds have begun with the top wind gust measured today
standing at 48 mph this morning at CSU San Bernardino. East to 
northeast winds have subsided this afternoon, but will pick back up
again tonight with slightly higher speeds than occurred this 
morning. Also, relative humidity will continue a dive this 
afternoon with poor overnight recovery. Low relative humidity 
will prevail inland with a minimum of near 10 percent on Sunday. 
Fuel moisture is at record lows. Given these factors and in 
coordination with fire partners and WFO Oxnard, a Red Flag 
Warning was issued for areas along the coastal mountain slopes 
and through valley corridors below the passes and canyons 
effective from 1 AM Sunday through 6 AM Sunday. Note that this 
will not be a widespread wind event, rather the strong winds will 
be contained through these wind-prone corridors where east to 
northeast winds will blow at 20 to 30 mph with peak gusts to 50 
mph.

Winds will subside on Monday with wind-prone locations out of the
east to northeast at 15-20 mph with peak gusts to 35 mph before
relaxing during the afternoon. Relative humidity will remain low
at near 10 percent Monday afternoon.

The humidity will increase beginning on Tuesday as winds turn back
onshore ahead of a storm system moving down the coast from the
north.

The storm system from the north will arrive late Tuesday, poised 
to bring our first widespread wetting rain of the season! The 
brunt of the precipitation will occur Wednesday-Thursday. 
There is a large spread of outcomes in relation to the track of
the storm system and precipitation amounts. A solid 0.50-1.00
inches is currently forecast, but note that this could change up
or down drastically, depending on the track of the storm. 

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning from 1 AM to 6 PM PST Sunday for Orange County 
     Inland Areas-Riverside County Mountains-Including The San 
     Jacinto Ranger District Of The San Bernardino National 
     Forest-San Bernardino County Mountains-Including The 
     Mountain Top And Front Country Ranger Districts Of The San 
     Bernardino National Forest-San Bernardino and Riverside 
     County Valleys  -The Inland Empire-San Diego County Inland 
     Valleys-San Diego County Mountains-Including The Palomar 
     And Descanso Ranger Districts of the Cleveland National 
     Forest-San Gorgonio Pass Near Banning-Santa Ana Mountains-
     Including The Trabuco Ranger District of the Cleveland 
     National Forest.

PZ...NONE.
&&

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