High Wind Watch 4, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
931 AM PDT Sat Oct 26 2019

.SYNOPSIS...
Mostly sunny and warm today, followed by much cooler weather Sunday
as a trough approaches from the north. The trough passes quickly
Sunday afternoon with gusty Santa Ana winds returning Sunday night
and Monday. It will be much cooler over the deserts, while
temperatures west of the mountains hover within a few degrees of
average. More gusty Santa Ana winds are expected midweek, followed
by quieter weather next weekend.

&&

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

Most areas are trending a bit cooler this morning as the onshore
trends develop. As of 8 AM PDT...skies were clear and there were
still some light NE winds to 15 MPH. Dewpoints remain low inland,
but should trend upward later today. Expect another warm day, but
not as hot as yesterday as the onshore flow develops.

Sunday will be cooler. A strong shortwave over the Pacific Northwest
will dig a deep trough south across the Great Basin and bring a 24-
hour period of fairly strong onshore flow. A coastal eddy spins up
over outer waters Sunday morning and that will also contribute to
rapid marine layer deepening early Sunday morning. Low clouds will
move into the coastal zones shortly before sunrise and perhaps push
into the inland valleys through midday. The strong onshore flow
continues through the afternoon and there may even be a few pockets
of drizzle in San Diego County Sunday evening. Highs will be mostly
in the 70s west of the mountains, the 60s in the mountains and high
deserts, and the 80s in the lower deserts. The onshore gradients
will support gust west winds in the mountains and deserts Saturday
afternoon and evening.

Offshore flow returns Sunday night as the trough axis races
southeast into Arizona. This stronger offshore solution was
advertised by the ECMWF a couple days ago, whereas the GFS was
farther east with the trough and weaker with the offshore flow. A
1028 mb surface builds over northern Nevada bringing a burst of
colder north-northeast flow into SoCal Sunday night through Monday.
This offshore event will be as strong nor as widespread as the
Friday event, but still notable with northeast winds of 20 to 30
mph, with gusts to 50 mph, especially in Orange and San Bernardino
Counties.

After a respite Tuesday, another strong offshore wind event will
impact the area Wednesday and Thursday. As with the Sunday-Monday
system, the ECMWF ensemble mean has been consistently farther west
and more accurate with the trough digging over the Intermountain
west than the GFS. However, the most recent GEFS ensembles and the
00Z operational run are now more in line with the EC solutions.
Confidence is growing that we will be impacted by a strong Santa Ana
event Wednesday and Thursday.

&&

.AVIATION...
261600Z...Coastal Areas...Low clouds will form along the coast after
07Z Sunday, impacting coastal TAF sites after 09Z. Bases will be
around 400-700 ft MSL then will lift to around 1000 ft MSL after
12Z. Areas of visibility 1-3 miles possible in fog between 09Z and
15Z. Low clouds may persist throughout the day on Sunday, but
confidence is low for impacts at TAF sites after 15Z.

Otherwise, clear with unrestricted vis through Sunday.

&&

.MARINE...
Patchy dense fog may impact the coastal waters for a few hours
tonight into Sunday morning with visibility less than one mile
possible. Otherwise, no hazardous marine weather is expected through
Thursday.

&&

.FIRE WEATHER...

...FIRE WEATHER WATCH LATE SUNDAY THROUGH MONDAY...

Continued dry inland today with min RH values near 10% but winds
will be light. fire weather conditions remain elevated due to the
low RH and changing wind conditions and the sea breeze develops.

Winds will start to turn onshore this afternoon and accelerate
overnight as a strong coastal eddy develops. High RH values will
prevail west of the mts on Sunday as the marine layer deepens
rapidly with increasing onshore flow. Strong westerly winds of 30 to
40 MPH and gusts to 60 MPH will develop over the mtn crests and on
the desert slopes through early Sunday evening.

The winds will turn back offshore Sunday night and Monday, with
strong north to northeast winds of 30-50 MPH and peak gusts 65 to 75
MPH possible in the wind-prone areas of the Santa Ana Mts and
through and below the Cajon Pass. Winds will not be as strong as
they develop across San Diego County early Monday Morning with peak
gusts closer to 50 MPH probable on the wind-prone coastal slope
areas later in the morning. Offshore gusts of 25-30 MPH are possible
over far northern coastal San Diego and Orange Counties. Inland
Orange County could see northeast gusts of 40 MPH or more briefly
Monday morning. Minimum Rh values fall back to 5-10% in these areas.
A Fire Weather Watch is in effect for the valleys/mtns/inland O.C.

Wednesday and Thursday: Model consensus is improving and confidence
is growing that there will be another strong offshore wind event
during this time.

&&

.SKYWARN...
Skywarn activation is not requested.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Fire Weather Watch from Monday morning through Monday afternoon
     for San Diego County Inland Valleys-San Diego County
     Mountains-Including The Palomar And Descanso Ranger
     Districts of the Cleveland National Forest.

     Fire Weather Watch from Sunday evening through Monday afternoon
     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 Gorgonio Pass Near Banning-Santa Ana Mountains-
     Including The Trabuco Ranger District of the Cleveland
     National Forest.

PZ...NONE.

&&

PUBLIC...10/Moede/
FIRE WEATHER...10
AVIATION/MARINE..PG