Wildfire in California, June 5 to 9, 2021

Area Forecast Discussion
National Weather Service San Diego CA
103 PM PDT Sat Jun 5 2021

.SYNOPSIS...
Weakening high pressure over the Southwest will bring cooling
through Sunday, while onshore flow maintains a marine layer and
associated clouds west of the mountains with gusty westerly winds
through and below the passes. On Monday, an upper-level disturbance
will bring scattered high clouds, a deeper marine layer, and further
cooling. Patchy drizzle is possible west of the mountains nights and
mornings Monday into Tuesday. Cooler weather will dominate the
coming week under an upper-level trough along the West Coast. Some
warming slated for late in the week.

&&

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

Satellite imagery through midday showed the low clouds had
completely cleared the coast, but were still well offshore. Some
return development is possible this afternoon along the immediate
coast, if not, the clouds will come back inland later this evening
and overnight with increasing onshore sfc pressure gradients. The
better clearing has helped push midday temperatures above values
observed yesterday along the Coast. Strongest west winds continue
near and below the San Gorgonio Pass where peak gusts were around 40
MPH. Most other areas reported peak gusts around 25 MPH or less.

A developing trough along the West Coast will draw a weak upper low
inland across SoCal on Monday evening. At this time, very little
moisture is forecast to accompany the low, so despite favorable
looking jet dynamics, PVA, and diurnal timing on the GFS control,
the latest SREF runs have failed to generate any chance of elevated
convection or dry lightning over the mountains. The system may be
dry in the mid-levels, but not lower in the atmosphere, where the
marine layer will be nearly saturated nights and mornings. This has
prompted some patchy drizzle in the forecast for Mon into Tue
morning. The upper low will help to enhance the onshore flow through
the passes and into the deserts as well, where gusts of 40-50 MPH
are expected in the more wind-prone areas late each day and
overnight. The onshore flow and deepening marine layer will drop
daytime highs over the next few days, pushing temperatures well
below average inland.

by Monday, daytime highs will be running from 10-15F below average
deep into the valleys and across the mountains, while the deserts
and coastal areas are just a few degrees below average. It will be
gradually warmer through the work week and into the weekend as
the trough aloft eases, allowing heights/thickness values to rebound.
The seasonal thermal gradient from the coast to the deserts will
remain however, and that will keep moderate onshore flow intact and
coastal areas seasonally cool with some marine clouds at times.

There is a clear ensemble consensus for cooler than average weather
over SoCal much of the coming week. After that, we see more spread
as the warm ridge to the SE tries to muscle it's way back to the NW,
bucking the West Coast trough. Given this backdrop, the various
model ensemble solutions have created a much wider temperature
forecast spread for us after next weekend. Place your bets!

&&

.AVIATION...
051930Z...Coast/Valleys...Some patchy low clouds could stick around
the Orange County beaches this afternoon. Otherwise, FEW-SCT high
clouds at/above 20,000 feet and unrestricted vis through this
afternoon. Low clouds will reform after 02Z and spread up to 30
miles inland overnight, with bases 1500-2000 feet MSL. Clouds should
reach KONT after 11Z, and KSBD after 12Z. Local vis 1-3 miles where
clouds and terrain intersect. Scatter out expected 16-18Z Sunday for
most areas, though clouds could stick around the beaches through the
afternoon.

Mountains/Deserts...Mostly clear with unrestricted vis through
tonight. Gusty west/northwest winds will continue in through the San
Gorgonio Pass and in the lower deserts through this evening.
Strongest winds will be through the passes, where gusts to 50 knots
are possible. For the lower deserts, gusts of 25-35 knots expected
through this evening.

&&

.MARINE...
No hazardous marine conditions are expected through Tuesday. Breezy
northwest winds will occur each afternoon and evening over the outer
waters Wednesday through Saturday, with gusts 20-25 knots expected.

&&

.BEACHES...
A long-period south swell from 190 degrees will continue to generate
surf of 3-5 feet, with some local sets to 6 feet, through Sunday
across Orange County. Highest surf will occur on south-facing
beaches. High rip current risk and dangerous swimming conditions are
expected. Surf will gradually decrease Monday.

&&

.FIRE WEATHER...
Gusty westerly winds peaking 40-50 MPH through and below the San
Gorgonio Pass will be accompanied by minimum RH values of 10-15%
later today, elevating the wildfire threat for a time. Over the
deserts, RH values of 15-20% and westerly wind gusts of 30 to
locally 40 MPH by late afternoon/evening, and temperatures of 95-105
will elevate fire weather conditions for a time as well. A little
cooler there on Sunday, otherwise little change across the deserts.

&&

.SKYWARN...
Skywarn activation will not be needed this weekend.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

PUBLIC/FIRE WEATHER...10
AVIATION/MARINE/BEACHES...Connolly