Wildfire in California, July 12 to 15, 2020

Area Forecast Discussion
National Weather Service San Diego CA
930 AM PDT Sun Jul 12 2020

.SYNOPSIS...
Today will be another hot day with record high temperatures likely
in a few areas. Moisture aloft will bring occasional high clouds
this afternoon along with a slight chance for showers, mainly over
the mountains. Cooling will spread inland on Monday and Tuesday as
the high aloft weakens, onshore flow increases and the marine layer
deepens. Seasonal summer weather will prevail next week as a weak
trough sets up along the West Coast.

&&

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

Temperatures so far this morning are on pace to reach the same
levels as yesterday, perhaps even higher in the deserts where
Thermal was already 101 at 9 AM (6 degrees higher than 24 hours
previous). The main reason for the rapid desert warmup is that the
airmass is much drier than yesterday, with dry northwest winds
lowering dewpoints into the 30s and 40s. Dewpoints will increase
once the winds shift southeast in usual diurnal fashion, but this
warm start will bring an extremely hot day to the lower deserts,
perhaps as high as 120 in some spots.

Here are some record highs that are within reach today:

Newport Beach (82)
San Diego (85)
Big Bear (91)
Anaheim (98)
Ramona (99)
Alpine (101)
Riverside (107)
Borrego (116)
Palm Springs (120)
Thermal (120)

Debris clouds from overnight convection over Sonora are not as
widespread as yesterday and the threat for shallow high-based
convection is low.

*From Previous Discussion*

Another weak impulse drifting NW around the high will bring another
shot of moisture aloft and a small chance of showers. The 00Z HREF
Ensembles show low return echoes developing over the mts once again,
and time/height cross sections of the atmosphere shows the moisture
will be above 600 MBS with a dry layer continuing below to the sfc.
Once again, it appears the main impact of these would be gusty sfc
winds from potential microburst activity as the elevated convection
initiates evaporative downdrafts.

Forecast trends however are clear. The high will weaken and shift
south through Monday. This accelerates onshore flow, winding up a
coastal eddy, which in turn, will deepen the marine layer along the
coast and spread cooling inland. Noticeable cooling will be felt on
Monday over and west of the mts, and somewhat into the high deserts,
reaching into the lower deserts by Tuesday.

For next week, Strong upper-level ridges are in place over the
EastPac and the Southern Plains states, leaving a weak trough
position prevailing along the West Coast. This maintains onshore
flow and a shallow marine layer over SoCal. The pattern retrogrades
late in the week into next weekend, resulting in warming but still
mostly dry with SW flow aloft.

&&

.AVIATION...
121535Z...Coast...Mostly clear for the morning with SCT-BKN clouds
15-25K ft MSL approaching from the south will stick around this
afternoon into this evening. A coastal eddy will slowly spin up
brining in low clouds more widespread in coverage tonight.
Confidence on coverage is high, but timing a little less so. Looking
like low clouds could make it to VCTY KSAN 07-09Z, and closer to 10-
12Z near KSNA. Bases a few hundred feet higher than this morning
with clearing by 15-17Z Monday morning.

Valleys/Mountains/Deserts...FEW-SCT clouds AOA 15000 ft MSL and
unrestricted vis through tonight. A few CU/ISO TCU with bases near
8000 ft MSL may develop over the mountain ridges this afternoon,
dissipating in the evening.

&&

.MARINE...
Slight chance of patchy fog over the coastal waters tonight morning,
with visibility near 1 mile. NW winds will strengthen this afternoon
and evening over the outer waters, but gusts are expected to remain
below 20 kts. Otherwise, no hazardous marine conditions are expected
through Friday.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning until 8 PM PDT Monday for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Gorgonio Pass Near Banning.

     Heat Advisory until 8 PM PDT this evening for 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.

PZ...NONE.

&&

PUBLIC...Moede
PREVIOUS DISCUSSION...10
AVIATION/MARINE...APR