National Weather Service Forecast Discussion

Dicussion provided by the National Weather Service Forecast Office located in San Diego, California

000
FXUS66 KSGX 212042
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
140 PM PDT Mon Oct 21 2019

.SYNOPSIS...
Warmer and drier conditions will prevail through at least Tuesday,
with periods of gusty northeast winds near the coastal slopes of the
mountains. A little cooler for coastal and valley areas on Wednesday
as the offshore weakens. Offshore flow returns and may be stronger
Thursday into Friday with very low humidity. Temperatures will be
well above average all week long with sunny days and clear nights.
Cooler next weekend with higher humidity as onshore flow spreads
some marine air inland.

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

Skies were clear across SoCal at midday. The sfc pressure gradient
was holding near 7 MBS offshore SW NV to KSAN and nearly flat to the
east. The temperatures were running anywhere from 8 to 16F above
values observed yesterday at noon. Winds peaked earlier this morning
and were weaker now with peak gusts from the NE at 30-35 MPH. It
will be a clear and mild night with east winds continuing near the
coastal slopes and passes. Some bump up in winds is likely again in
the morning and it will be even warmer and drier.

The strong ridge over the EastPac will sharpen northward helping to
redirect a shortwave in the westerlies SE over the Rockies early
Thursday. This helps to strengthen sfc pressure over the Great Basin
Thu/Fri, and set up another round of gusty offshore winds,
maintaining the very dry conditions. In the meantime, the current
offshore will slowly weaken Tue/Wed and even turn onshore briefly
Wednesday. This should make for modest cooling, followed by warmer
weather again Thu/Fri. by Friday, the core of the ridge actually
drifts over CA, this nullifies any upper support for winds, which
will still have a healthy sfc gradient to support them, particularly
west of the peninsular ranges of San Diego and Riverside Counties.

Temperatures will be well above average for the remainder of the
week with sunny days and clear, mild nights. Relative humidity will
be very low, even over coastal areas later in the week, before a
stronger onshore push develops over the weekend. This is the result
of a slight retrogression of the longwave pattern which weakens and
shifts the ridge back to the west. The operational model solutions
have been interesting, but hardly consistent regarding the strength
and ultimate positioning of the digging trough this weekend. The
ECMWF is the most aggressive, which applies to the current pattern,
but successive runs tend to show less amplitude and resultant
weather here.

&&

.AVIATION...
212000Z...Clear skies and unrestricted vis will continue through
Tue. Local northeast winds 15-25 knots with gusts to 35 knots will
occur through Tue morning, mainly near and just southwest of
mountain crests, along with LLWS and moderate up/downdrafts.

&&

.MARINE...
No hazardous marine weather is expected through Saturday.

&&

.FIRE WEATHER...
Isolated spots in the San Diego Mts were reporting critical fire
weather conditions late this morning, but most areas were below this
threshold. Strongest winds were 15-25 MPH with peak gusts 30-40 MPH.

Weak to moderate offshore flow will continue into Tuesday in the
favored coastal slope and pass areas with lowest inland humidity of
10 to 15 percent later today, and around 10 percent Tuesday. The
winds will be strongest and most widespread this morning and again
late tonight into Tuesday morning at 15 to 25 MPH with gusts 30 to
locally 40 MPH. This will continue elevated fire weather conditions
inland into Tuesday, with some spots reaching critical levels
briefly.

Conditions moderate slightly for Wednesday/Wednesday night as the
offshore weakens and turns temporarily onshore, but minimum RH
levels will still be 10-15% inland.

Stronger offshore flow is possible on Thursday and Friday with
lowest inland humidity of 5 to 10 percent. Elevated, to possibly
critical fire weather conditions may develop over the mountains,
inland valleys, and inland Orange County. However, there is still
some uncertainty with regard to the strength and duration of the
offshore winds this period. San Diego County is still favored for
the wind and duration.

Onshore flow is expected to return next weekend with cooling and
higher coastal humidity spreading inland.

&&

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

&&

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

$$

PUBLIC/FIRE WEATHER...10
AVIATION/MARINE...Maxwell

NWS SGX Office Area Forecast Discussion