Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 260436
AREA FORECAST DISCUSSION
National Weather Service San Diego CA
930 PM PDT SUN SEP 25 2016
Strong high pressure aloft off the California coast, and surface
high pressure over the Great Basin, will keep dry and warm Santa Ana
conditions over the southwest California through Monday with periods
of gusty northeast winds near the coastal foothills. Upper level low
pressure over the Baja Peninsula will bring increasing moisture and
slow cooling beginning Tuesday as it drifts northward bringing with
clouds, and a small chance for sprinkles or scattered, light showers
at times. Onshore flow and seasonal temperatures return for the
latter half of the week as a developing trough of low pressure moves
inland across the West.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Today was as expected quite hot west of the mountains. Record high
temps were set today at Chula Vista and El Cajon. Monday will be
even a bit hotter yet than what we saw today, for most locations
west of the mountains. A heat advisory remains in place there due to
the excessively hot conditions. Meanwhile, locations in the
mountains and deserts are actually quite nice, with the high deserts
enjoying relatively cool weather with highs in the lower to mid 80s!
Gradients this evening continue to hover around 10 mb offshore from
the Socal coast to the Great Basin. Don`t think we`ll get much
stronger than this. By late Monday the high over the great Basin
begins to break down so relief is in site.
Gusty offshore winds will continue into Monday, but don`t think
we`ll get much stronger than what we`ve already seen today. A strong
wind gust report was just sent for updated max wind speeds.
No other changes were made this evening. A slight chance of
thunderstorms remains in the forecast for Wednesday and Thursday
afternoons as we see some return moisture working in from the SE.
...Remainder of Monday afternoon forecast discussion...
A strong 596 DM Ridge off the California coast and low pressure
digging southwest across northwest Mexico will keep E-NE winds and
Santa Ana conditions across southern California through Monday.
Strongest winds/gusts will be along the coastal mountain foothills
and especially San Diego County. Temperatures will be well above
average again on Monday with highs well into the 90s to 105 west of
the mountains. A Heat Advisory and Wind Advisory has been posted.
Please see LAXNPWSGX or check our web page for details. The windy,
warm and dry weather has increased the wildfire danger. See the Fire
Weather discussion below for details.
The digging trough will cut-off a low tonight over the central Baja
Peninsula, then drift slowly northward and become centered over the
Lower Colorado River Valley Wed morning. This will bring increasing
clouds and moisture from the SE, and gradually decrease the offshore
flow. Cooling aloft and increased mid-level moisture will bring a
small chance of shwrs/tstms, especially over the mts mid week.
The low will be absorbed by the westerly winds to the north by Thu as
a longwave trough amplifies southward along the West Coast. This
will bring increasing onshore flow, a return of the marine layer,
and cooler weather into next weekend.
The Models/Confidence...The 12Z ECMWF/GFS runs are in fair agreement
through 240 hours, so there is moderate to high confidence out into
the extended period. A few sprinkles are possible on Tue with a
slight chance of shwrs/tstms over the mts midweek. Any precip that
manages to develop looks light and scattered at this point.
260330Z...Most wind gusts will be 15-30 kt through 09Z tonight, but
winds will increase 09Z through 22Z Mon from the E with gusts 25-35
kt, strongest over San Diego County. STG LLWS will prevail in many
areas west of the mountains when NE/E winds do not reach the surface
through Monday. Mdt to strong up/down drafts will also affect much
of the region over and west of the mtns through Mon. Expect LLWS
returning tonight to KONT, while KSNA will only have a few hours of
NE surface winds, with LLWS at other times.
Otherwise mostly clear with unrestricted vis through Monday.
No hazardous marine weather is expected through Friday.
Swell and surf will subside tonight into Monday.
Critical fire weather conditions will continue today along the
coastal mountain slopes and adjacent foothill areas, with RH at or
below 15 percent, and northeast winds of at least 25 MPH. The most
critical combination of heat...lowest humidity...and strongest winds
is expected today. Still quite hot on Monday, but winds look weaker
and may not sustain critical thresholds in many areas north of San
Diego County, but minimum RH in these areas will remain near ten
percent. For San Diego County...some increase in RH is likely from
the mountains eastward, possibly holding the coastal slopes just
below critical Red Flag criteria, however winds will sustain 25 MPH
or better in many areas.
The offshore flow may remain strong over San Diego County on Tuesday,
but the trend will be for weakening most areas. Tuesday into
Wednesday there will be a moderation in the heat, and significant
RH recovery. There will even be a chance of sprinkles on Tuesday, and
a few showers over the mountains, mainly Wed/Thu.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
CA...Red Flag Warning until 3 PM PDT Monday for 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-San
Gorgonio Pass Near Banning-Santa Ana Mountains-Including
The Trabuco Ranger District of the Cleveland National
Wind Advisory until 5 PM PDT Monday for San Diego County
Mountains-San Diego County Valleys.
Wind Advisory until 4 PM PDT this afternoon for Orange County
Inland Areas-Riverside County Mountains-San Bernardino
County Mountains-San Bernardino and Riverside County
Valleys-The Inland Empire-Santa Ana Mountains and Foothills.
Heat Advisory from 11 AM this morning to 8 PM PDT Monday for
Orange County Coastal Areas-Orange County Inland Areas-San
Bernardino and Riverside County Valleys-The Inland Empire-
San Diego County Coastal Areas-San Diego County Valleys-
Santa Ana Mountains and Foothills.
Beach Hazards Statement through this evening for Orange County
Coastal Areas-San Diego County Coastal Areas.