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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 160341

Area Forecast Discussion
National Weather Service San Diego CA
840 PM PDT Mon Oct 15 2018

Low pressure aloft over Arizona and surface high pressure over the 
Great Basin will bring Santa Ana winds through Tuesday, although the 
winds will be a little weaker tonight and Tuesday. This dry, 
offshore flow pattern will be in place through Friday and bring 
sunny, warm days and clear, cool nights. Over the weekend a trough 
of low pressure off the Southern California coast may pull in enough 
moisture to generate a few showers at times. 



The strongest winds with this Santa Ana event surfaced this morning 
with gusts of 82 mph at Fremont Canyon in Orange County and 60 mph 
at the Ontario Airport. Although the winds won't be as strong 
tonight and Tuesday morning, it will still be quite windy in the 
Santa Ana favored locales. 

There was the precipitous drop in the Precipitable Water today from 
0.92' on the 12Z NKX sounding to 0.17" on the 00Z sounding this 
evening. The dry offshore winds sent dewpoints and RH's plummeting 
into the single digits in Orange County and the Inland Empire this 
afternoon. At the L.A. Airport the dewpoint was -6F at 6 pm with an 
RH of 3%. 

It was a warm day in the coastal zones with highs in the 80s, a mild 
day in the Inland Empire and Lower Deserts with highs in the 70s 
(held down by strong mixing), and a downright cold day in the San 
Bernardino Mountains with highs in the 40s. Palm Springs set a 
record for the lowest high temperature today with a high of 78, 
besting the previous lowest high of 79 set in 1980. 

*From Previous Discussion*

The upper low moving into Arizona will meander over that area 
through late week with a piece of the low moving west towards 
coastal southern California by the weekend.  Some moisture will wrap 
around the low, with a likely increase in clouds, probably cumulus, 
Wednesday, then perhaps enough moisture and instability this weekend 
for showers and thunderstorms. With the low-level east flow, chances 
will be best from the mountains east to the deserts, but enough 
moisture could spread west of the mountains, even with the 
downsloping winds, to produce a few showers or thunderstorms there. 
Temperatures will increase in most areas Tuesday with warm weather 
continuing through the weekend, possibly in the lower 90s in some 
locations by Saturday west of the mountains. The only exception 
would be any places along the coast that get westerly low-level 
return flow, which should happen each afternoon Tuesday through at 
least Friday. The offshore flow, based on current model projections, 
could actually increase Saturday, but nowhere near the strength of 


160330Z...Coast/Valleys/Mountains...Wind will continue to be the 
primary concern over the next few hours. KSNA, KONT and KSBD 
currently experiencing 10-15 kts sustained with gusts of 25-30 kts. 
MDT-STG up/downdrafts can be expected over and S/SW of the 
mountains. Winds will decrease to 5-15 kts overnight at the above 
TAF sites. Periods of LLWS up to 2500 ft AGL are likely at these 
locations, mostly before 15Z Tue. Winds will increase again after 
15Z but will be more localized and not as strong as Mon. Much weaker 
offshore flow expected after Tue afternoon, with no marine layer 
stratus. Clear with unrestricted visibility throughout.

Deserts...NW winds 10-15 kts, gusting to 20-25 kts expected at KPSP 
and KTRM into Tue evening. Clear with unrestricted visibility.


No hazardous marine weather is expected.


Red Flag Warning through 8 PM Tuesday. Critical fire weather 
conditions will continue with periods of gusty northeast to east 
winds and very low humidity around 10 percent Tuesday afternoon. 
Winds will not be quite as strong as they were this morning. 

Wednesday through Friday: Weaker and less widespread northeast winds 
are expected with a slow recovery of humidity. Northeast winds could 
increase again Saturday.


Skywarn activation is not requested. 


CA...Red Flag Warning until 8 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 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-Santa Ana Mountains-Including The 
     Trabuco Ranger District of the Cleveland National Forest.