Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 200941

Area Forecast Discussion
National Weather Service San Diego CA
241 AM PDT Fri Oct 20 2017

A trough of low pressure will move through the West Coast today,
resulting in further cooling trend and patchy drizzle or light
showers through this afternoon from the coastal mountain slopes
west to the coast. Local gusty west winds will continue in the
mountains and deserts through this evening. A Santa Ana event will
develop this weekend and continue early next week, bringing hot
and dry weather along with occasional gusty winds, especially
through and below passes and canyons. A gradual cooling trend will
likely occur Wednesday and Thursday of next week.



The marine layer has deepened quite a bit with low clouds pushing
through the Cajon and San Gorgonio Passes, though cloud coverage
remains somewhat patchy. No reports of drizzle let alone any
measurable precipitation yet, but with the trough axis approaching
perhaps something will develop later this morning. Have left
slight chance of showers in the forecast for this morning and
afternoon. Aside from the clouds and potential showers, the trough
will bring further cooling today and slightly stronger west winds
in the mountains and deserts. Strongest winds will be along the
ridges and upper desert mountain slopes as well as below the
passes where gusts of 50-60 mph are likely. A Wind Advisory will
be in effect for the mountains and deserts excluding the Coachella
Valley from 5 AM through 9 PM.

Not much change in the extended as the main story continues to be
the strong building ridge of high pressure and developing offshore
flow. Some warming will occur Saturday behind the departing
trough. North-northeast winds will develop by mid-morning, mainly
below the Cajon Pass and Santa Ana Mountains. 00Z model runs have
changed the timing/strength of the winds, now showing them
strengthening slightly and becoming more widespread on Sunday and
weakening Monday, then peaking Tuesday morning. Winds below the
passes/canyons and along the coastal slopes and foothills will
generally be in the 30-45 MPH range for the duration of the event,
with gusts to around 50 MPH in the favored spots Sunday and
Tuesday mornings. The upper level ridge 500 mb heights peak at
around 596-598 dm Monday and Tuesday, with widespread temps in the
upper 90s to around 105 possible west of the mountains and in the
low desert. The Fire Weather Watch and Excessive Heat Watch remain

Gradual cooling will take place Wednesday with more significant
cooling later in the week as the ridge breaks down and onshore
flow returns.


Critical fire weather conditions are likely due to a Santa Ana wind
event Saturday through Tuesday, with biggest concerns Sunday through
Tuesday as temperatures peak and widespread daytime humidity of 10
percent or less develops. The concern is more of the long duration
of the hot, dry, and windy conditions, though Red Flag conditions
won`t necessarily be widespread each day. Current guidance has
strongest winds Sunday and again Tuesday when local gusts to 50
MPH are possible in the favored passes/canyons and coastal
mountain slopes. A Fire Weather Watch remains in effect from
Saturday for the San Bernardino mountains, Inland Empire and
Santa Ana mountains, then starting Sunday for the rest of Orange
County, the valleys and mountains of San Diego County and the
mountains of Riverside County, with all areas continuing through


200900Z...Coast/Valleys...Low clouds, increasing in coverage this
morning, will likely impact all TAF sites west of the mtns with BKN-
OVC cigs 2000-3000 ft MSL through 20Z. Coastal mountain slopes below
5000 ft will be obscured at times. Partial clearing after 20Z with
bases around 3000 ft MSL.

Elsewhere, SCT AOA 20000 ft with unrestricted vis.

Windy in the mountains and deserts through this evening with west
winds 15-30 kt gusting to 40 kt over the mountains. This will bring
mod-stg uddfs/llws over and east of the mtns. Areas of BLDU in and
around PSP and TRM will be possible today.


Small Craft Advisory in Effect Through 1 AM Saturday. A low pressure
system with a weakening cold front moving in from the northwest will
bring strong northwest winds to the coastal waters today. Wind gusts
of 25 kt with steep waves will result in hazardous boating for small
craft. Highest seas and strongest winds will be near and south of
San Clemente Island. Conditions will slowly improve on Saturday.
Lighter winds and calmer seas are expected next week.


A 2-3 ft/14-15 second south swell from 200 degrees will continue to
subside today. A short-period northwest swell from 290 degrees and a
long-period northwest swell from 295 degrees will build late today
through Saturday. This will bring another round of elevated surf
from 3-6 ft and an increased rip current threat. Although surf
lowers somewhat on Sunday, rip currents will still be a concern. A
Beach Hazards Statement is in effect through Sunday afternoon.


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


CA...Fire Weather Watch from Sunday morning through Tuesday afternoon
     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.

     Wind Advisory from 5 AM early this morning to 9 PM PDT this
     evening for Apple and Lucerne Valleys-Riverside County
     Mountains-San Bernardino County Mountains-San Diego County
     Deserts-San Diego County Mountains-San Gorgonio Pass Near

     Excessive Heat Watch from Monday morning through Tuesday evening
     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

     Fire Weather Watch from Saturday morning through Tuesday
     afternoon 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...Small Craft Advisory for winds until 1 AM PDT Saturday for
     Coastal Waters from San Mateo Point to the Mexican Border
     and out to 30 nm-Waters from San Mateo point to the Mexican
     Border Extending 30 to 60 nm out including San Clemente



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