Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 230444 AAA

Area Forecast Discussion
National Weather Service San Diego CA
944 PM PDT Sun Oct 22 2017

A Santa Ana weather pattern will bring hot, dry weather through
Wednesday with record setting high temperatures west of the
mountains. The gusty Santa Ana winds and very low humidities will
elevate the fire threat. Cooler Thursday and Friday with a return of
weak onshore flow and a shallow marine layer near the coast.



No changes were needed to the forecast this evening. Offshore
pressure gradients are still quite healthy but Santa Ana winds have
decreased greatly from earlier today, which is of course normal
during Santa Ana events, and will pick up again late tonight into
Monday morning. Offshore gradients remain moderate this evening with
the Los Angeles to Tonopah gradient around 11 mb attm. Winds late
tonight into Monday morning will be strong with gusts of 40 to 50
mph in the favored canyons and foothills. Monday will see much
warmer conditions west of the mountains as the high strengthens with
temperatures over 100 in some of the valley communities.

...Remainder of previous forecast discussion...

Even stronger winds are forecast Monday night into Tuesday when the
surface high strengthens to 1040 mb. In contrast, a 1015 mb low will
be over the SoCal coastal waters, setting up an 18 mb offshore
gradient from San Diego to Nevada. Sustained winds of 20-30 mph with
gusts of 50-60 mph are likely in the wind prone areas during Monday
morning with a few gusts to 65 mph possible at Pleasants Peak,
Fremont Canyon, or Sill Hill. The models slow the movement of the
surface high out of the Great Basin, and are trending windier
Tuesday Night into Wednesday, so the Red Flag Warnings were extended
through 6 pm Wednesday.

The 850 mb support is also a little stronger with winds from 25-30
kts on Monday increasing to 35-40 kt Monday night into Tuesday.
There is also weak cold air advection at 850 mb on Monday night. All
signs point to the strongest winds Monday night through midday
Tuesday. There will be a drop off in winds on Wednesday, but it will
still be noticeably windy in the mountain passes and foothills, and
linger longest in San Diego County.

Wind Advisories were issued for the mountains, valleys and all of
Orange County, and will be in effect from Midnight tonight to 2 PM
Wednesday. The WRF and CANSAC guidance advertise gusty northeast
winds reaching all the way to coastal Orange County, strongest on
Tuesday and extending out over the coastal waters. These strong
winds will force the heat all the way to the coast, and high
temperatures in the beach communities will be unusually high. Record
highs are possible at Newport Beach Monday (89), and likely on
Tuesday (85), but perhaps a bit out of reach on Wednesday (95).

Thursday and Friday: Shortwave energy from the Gulf of Alaska
moves southeast across the Pacific Northwest and across the Great
Basin, breaking down the monster 596 dm ridge in the process. Heights
lower to 585 dm Thursday/Friday, and the pressure pattern turns
briefly onshore. But over the weekend a high amplitude ridge
reforms along the West Coast for warmer than average weather and
weak offshore flow.


230355Z...Clear with unrestricted vis through Monday evening

Coast/Valleys...Areas of northeast winds 15-25 kt and gusts 30-40 kt
developing after 10Z. Strongest winds will be through and below the
passes and canyons, on coastal mountain slopes and foothills, and
locally extended into the coastal basin. This will produce MDT-STG
UDDFS and LLWS over and W/SW of the mountains, strongest after 15Z.
This could impact vcnty KONT, KSBD, KRAL and KSNA at times.


No hazardous marine weather is expected through next Thursday.


The Red Flag Warning that was in effect until 6 PM Tuesday was
extended to 6 PM Wednesday.

Extreme fire potential Monday and Tuesday with the strongest Santa
Ana winds, lowest RH and very dry fuels. The winds on Monday with be
about 10-15 mph stronger than today with 20-30 mph winds gusting to
45-55 mph in the windiest areas. Even stronger winds are forecast
Monday night into Tuesday morning with peak gusts of 50-60 mph,
perhaps 65 mph in a few spots. Wednesday the winds won`t be quite as
strong but it will still be breezy/windy.

Humidities will fall to 5-10 percent Monday through Wednesday with
poor overnight recovery. Lighter winds Thursday through Saturday
with cooling and some recovery in humidity spreading inland.


Skywarn activation will not be needed today.


CA...Red Flag Warning until 6 PM PDT Wednesday 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 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.

     Wind Advisory from midnight tonight to 2 PM PDT Wednesday for
     Orange County Coastal Areas-Orange County Inland Areas-
     Riverside County Mountains-San Bernardino County Mountains-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Mountains-San Diego County Valleys-
     Santa Ana Mountains and Foothills.

     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.



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