Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 152040

Area Forecast Discussion
National Weather Service San Diego CA
140 PM PDT Tue Oct 15 2019

Wednesday will be another warm day with gusty offshore winds in
the mountains and foothills. The weather will turn a little cooler
Thursday through Saturday with onshore flow and night and morning
low clouds spreading a little farther inland each night. A stronger
Santa Ana pattern will bring warmer days and stronger offshore winds
next Sunday through Tuesday.



Temperatures made a double-digit jump upward today in the Inland
Valleys due to ridging aloft and downsloping easterly flow. At 1 PM
today, Ramona was 89 degrees (+18), Ontario was 84 (+13), and
Chino was 87 (+12). Tomorrow will be another warm day with
little change in the overall synoptic pattern.

Easterly offshore flow will continue through Wednesday with
sustained winds of 10-20 mph with gusts of 30-40 mph in the wind
prone mountain passes and foothills. There were a few gusts above 40
mph this morning including 47 mph at Big Black Mountain and 43 mph
at Sill Hill, but most gusts were below 40 mph.

This weak offshore pattern will shift onshore Thursday-Saturday as a
Pacific trough moves ashore along the West Coast for cooling and
slow marine layer deepening. Low clouds are forecast to spread into
the western valleys Friday and Saturday mornings. The marine layer
will become a little shallower Saturday night as the trough starts
moving inland.

then revert back offshore Sunday through Tuesday, albeit a little
more strongly and more widespread in coverage.

The transition back to offshore flow begins on Sunday when a
stronger surface high builds over the Great Basin. This will bring a
period of stronger Santa Ana winds Sunday through Tuesday than
we are having with the current event with wind gusts of 45 to
55 mph in the mountains and foothills. Coverage will be a little
more widespread with some of these stronger winds lowering into the
valley zones.

Sunday will be a mild day in the coastal and valleys zones, but then
it will turn much warmer Monday and Tuesday with warm downslope flow
pushing highs well into the 80s and low 90s. Mountains and desert
will be a little cooler Sunday with the onset of the cooler
northeast flow from the high plateau, then trend slowly upward
Monday and Tuesday.

The long range ensembles from next Wednesday through Friday (Oct
23-25) are advertising a high amplitude upper ridge over the eastern
Pacific just west of California. This pattern remains more or less
locked in place through the end of October and will bring above
average temperatures and no chance for any precipiation through


151945Z...Coast...VFR conditions expected through this evening.
Isolated areas of patchy low clouds may develop overnight with bases
around 1000 feet MSL. Any cigs that do develop will clear by 16Z

Valleys/Mountains/Deserts...Wildfire smoke VCTY KTRM possible,
otherwise clear with unrestricted vis through tonight.


No hazardous marine conditions are expected through Sunday.


Elevated (but not critical) fire weather concerns through Wednesday
with gusty offshore winds in the mountains and foothills and
afternoon humidities between 15 and 25 percent. The east winds
will be strongest in the east-west passes of San Diego and Riverside
Counties with gusts of 20 to 30 mph.

A period of weak onshore flow and higher humidity returns Thursday
through Saturday.

From Sunday through Tuesday a stronger and more widespread Santa Ana
event will bring critical fire weather conditions with lower
humidities (8 to 15 percent) and stronger wind gusts from 40-50 mph.


Skywarn activation will not be needed this week.





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