National Weather Service Forecast Discussion

Dicussion provided by the National Weather Service Forecast Office located in San Diego, California

000
FXUS66 KSGX 220406
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
905 PM PDT Sat Oct 21 2017

.SYNOPSIS...
A Santa Ana weather pattern will bring hot, dry weather and very low
humidities Sunday through Wednesday. The strongest Santa Ana winds
will impact the area Monday and Tuesday. Lighter winds are forecast
for Wednesday but it will continue to be hot and dry. Cooler
Thursday and Friday.

&&

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

The Santa Ana winds have relaxed this evening but another surge of
Santa Ana winds is very likely to develop late tonight with gusts up
to 30 mph late tonight into Sunday morning. Sunday will be the first
day of the hot weather, with stronger Santa Ana winds slated for
Monday and Tuesday and temperatures to the century mark for most
areas away from the immediate coast and the high elevation
mountains. No changes were needed to the ongoing forecast database
this evening and the previous forecaster`s discussion remains
accurate (below).

At 1 PM, blustery Santa Ana winds were surfacing in the mountains,
passes and valleys. Campo had NE winds of 25g33 mph, Riverside 13g20
mph, Crestline Ridge 24g33 mph, and Fremont Canyon 16g29 mph. This
is just the beginning of a prolonged hot, dry offshore Santa Ana
event that will continue through Wednesday. Dewpoints had fallen
from 10-30 degrees in the mountains and deserts over the past 24
hours, and were mostly in the 20s and 30s, with a few teens in the
SBD mountains.

UPDATE: The Santa Ana winds may be a little stronger with this event
on Monday and Tuesday than previously thought. Currently a 1024 mb
surface high over Nevada is producing a -6.0 mb offshore pressure
gradient from SAN-TPH. The surface high strengthens to 1028 mb
Sunday for stronger winds tomorrow...and then on Monday and Tuesday
the pressure increase to 1038 mb over southern Idaho. The 12Z WRF is
now stronger with the winds Monday night into Tuesday with more
widespread gusts of 40-50 mph in the mountain passes and valleys,
with peak gusts to 60 mph. This is Wind Advisory criteria and
perhaps even a low end High Wind Warning for the SBD/ORA county and
I.E., and will wait to see if the 00Z model continue this stronger
wind trend before issuing any Wind products. Red Flag Warnings are
in effect from Sunday morning through 6 PM Tuesday.

The other big story is the heat with a strong upper ridge that will
peak at 597 dm over Nevada Monday night. This is slightly stronger
than previous runs, and both Monday and Tuesday will be very hot
days. Max temperatures west of the mountains were raised another 1-2
degrees west of the mountains with coastal and valley highs now
forecast to be 97-107. A few hot spots will flirt with 110. The
strong northeast winds will push the hot, dry air all the way to the
coast in Orange County where Newport Beach and other beach
communities have a good chance to reach 90+. The coolest air will be
found in the mountains above 6000 feet where highs will be from 65-
75.

The Santa Ana winds decrease Tuesday night into Wednesday but the
weaker offshore will continue. That will keep the cooling influence
of the marine air at bay, and Wednesday will be another very
warm/hot day.

It will be cooler Thursday and Friday, but in a relative term. It
will be cooler compared to Monday and Tuesday, but still 5-8 degrees
above average compared to where we should be for the end of October.

The long range progs have also shifted from a somewhat cooler weak
onshore flow pattern Thursday through Saturday to a more neutral or
weakly offshore pattern. On Thursday a strong shortwave digs south
across Utah and into New Mexico Friday. This deep trough props up a
high amplitude ridge along the West Coast, a pattern conducive to
bringing back weak to moderate offshore flow next Friday through
Sunday.

&&

.AVIATION...
220400Z...Coast/Valleys...Skies will be mostly clear with
unrestricted vis through Sunday. Areas of northeast winds will occur
through/below passes and canyons at times after 18Z through Sunday
and beyond, mainly vcnty KONT, KSBD, KRAL, KSNA, with speeds 15-30
kt with local gusts 35-45 kt. LLWS will occasionally affect the
above airports, though northeast winds may not surface at KONT and
KSNA until Sunday morning.

Mountain/Deserts...Areas of northeast winds will continue through
Sunday and beyond. Winds will be 15-30 kt with gusts to 35-45 kt
with strongest winds near ridges and through passes/canyons.

&&

.MARINE...
San Clemente Basin Buoy still had 9-10 foot seas from long and short
period WNW swells at midday, but the seas will lower this afternoon.
Otherwise, no hazardous marine weather is expected through next
Thursday.

&&

.BEACHES...
A short-period northwest swell from 290 degrees and a long-period
northwest swell from 295 degrees will continue this afternoon. This
will bring more elevated surf of 3-6 ft and an increased rip current
threat. Highest surf will be at west-facing beaches of San Diego
County. Although surf lowers somewhat Sunday, rip currents will
still be a concern. A Beach Hazards Statement is in effect through
Sunday afternoon.

&&

.FIRE WEATHER...
Red Flag Warnings are in effect from Sunday through Tuesday. A small
fire ignited near Campo today, and with stronger winds and even
drier air moving in Sunday-Tuesday, the fire risk will be extreme.

Concerns today involve the model projections of stronger winds on
Monday and Tuesday. Sunday will be hot and dry, with the most
extreme heat, wind and fire potential Monday and Tuesday when highs
will top 100 and RH will fall to 5-8 percent.

Winds weaken Wednesday but it will still be hot and dry will very
little humidity recovery. Thursday shows greater humidity recovery
with brief, weak onshore trends. But the long range outlook favors a
return to a weak offshore flow pattern Friday-Sunday with above
average temperatures and lowering humidities.

&&

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

&&

CA...Red Flag Warning from 6 AM Sunday to 6 PM PDT Tuesday for Orange
     County Coastal Areas-Orange County Inland Areas-Riverside
     County Mountains-Including The San Jacinto Ranger District
     Of The San Bernardino National Forest-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.

     Excessive Heat Warning from 10 AM Monday to 8 PM PDT Tuesday for
     Orange County Coastal Areas-Orange County Inland Areas-San
     Bernardino and Riverside County Valleys-The Inland Empire-
     San Diego County Coastal Areas-San Diego County Valleys.

     Red Flag Warning until 6 PM PDT Tuesday for 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-Santa Ana Mountains-Including The Trabuco
     Ranger District of the Cleveland National Forest.

     Beach Hazards Statement through Sunday evening for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...None.

&&

$$

PUBLIC/FIRE WEATHER...Moede/Gregoria
AVIATION/MARINE/BEACHES...Maxwell/JMB

NWS SGX Office Area Forecast Discussion