Area Forecast Discussion
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FXUS66 KSGX 271552
AREA FORECAST DISCUSSION
National Weather Service San Diego CA
852 AM PDT MON JUN 27 2016
High pressure aloft will continue hot weather for inland areas
through Wednesday followed by slow cooling into next weekend as
high pressure aloft weakens and a weak trough of low pressure
develops over the Pacific Northwest. Mid and high level moisture
associated with a disturbance moving through the region will
bring a slight chance of afternoon and early evening thunderstorms
with gusty winds through Wednesday, mainly near the mountains.
The marine layer and onshore flow will keep coastal high
temperatures cooler with areas of night and morning low clouds and
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Visible and radar imagery is showing an easterly upper level wave
moving through the region, bringing mid and high level clouds and
some light radar returns which are likely producing only virga or
sprinkles. The 12Z Miramar sounding shows precipitable water
having increased to 1.48 inches, although the majority of the
moisture appears to be above 700 mb, with a dry layer noted below
700 mb until you reach the 10 deg C marine layer inversion near
1000 ft MSL. It is due to the dry layer below 700 mb that most of
the precipitation may evaporate before reaching the ground, which
is why most of it will appear as virga or maybe some sprinkles.
These clouds will continue to move through Southern California
through the day, although the moisture field from the NAM12 shows
clearing skies intruding in from the south in the afternoon. The
amount of cloud cover we have today, and which locations receive
more sunlight than others, will play a factor in not only how hot
we get today, but also the amount of day-time heating induced
instability. Due to the mid and high clouds, temperatures may be
reduced slightly compared to yesterday. However, with some higher
surface dewpoints in the area (low 60s shown currently over most
coast, valley and desert areas), it may feel more muggy and
Despite the increase in moisture and the wave moving overhead, the
elevated instability parameters shown by the forecast models for
this afternoon are not impressive. Also, the strong easterly flow
is not conducive for thunderstorms that develop over the mountains
to maintain their structure. Thus, the latest HRRR run doesn`t
show much shower or thunderstorm activity this afternoon.
Nevertheless, a slight chance for thunderstorms remains in the
forecast today for the mountains, with some activity possibly
being blown west into the valleys.
Meanwhile, marine layer stratus was able to develop over coastal
areas today. Stratus should be able to clear out of inland areas by
late morning, although the decently strong inversion could keep
some low clouds hanging around at the coast.
Models show drier air intruding into Southern California Tuesday
as flow turns southerly in the wake of the easterly wave,
resulting in less of a chance for afternoon mountain
thunderstorms. However, the clearer skies and strong ridge over
the four corners region should result in hotter conditions, with
highs 5-10 degrees above normal. Continued hot for inland areas on
Wednesday, with 850 mb temperatures in the deserts reaching 27-29
deg C, and near 26-27 deg C in the valleys. A Heat Advisory
continues for the deserts, mountains and valleys through
Wednesday. Despite the ridge weakening on Thursday, looks like
the 850 mb temperatures do not decrease much, if at all, so hot
conditions may continue.
Cooler Friday into the weekend as a trough moves into the Pacific
Northwest, with a deepening of the marine layer as well, resulting
in night and morning stratus into the coast and portions of the
271530Z...Coast/Valleys...Areas of sct-bkn clouds based 800-1200
feet MSL with tops around 1800 ft MSL will burn back to out over the
coastal waters. Local vis 2-4 miles along higher coastal
terrain/mesas. After 28/06z this evening low clouds bkn-ovc based
800-1200 feet MSL with tops around 1800 ft MSL will push inland
about 15 miles with local visibilities 2-4 miles along higher
coastal terrain/mesas. There is a moderate risk that the coastal low
clouds will again be patchy so the confidence is low on the timing
and duration of the bkn low clouds at KSAN tonight.
Mountains and Deserts...Sct-bkn clouds based around 10000 feet MSL
with unrestricted visibilities. This afternoon between 27/19Z and
28/00Z isolated SHRA/TSRA with cloud bases 9000 ft MSL and tops to
35000 ft MSL will be possible over the mountains.
830 am...No hazardous marine weather is expected through Friday.
830 am...The long period south swell will continue to decrease, but
3-5 foot surf will continue on the southwest facing beaches today.
The surf will lower to 2 to 4 feet Tuesday. Another long-period
south swell from 200 degrees will bring 4-7 foot surf to southwest
facing beaches late Wednesday and Thursday along with dangerous rip
Slight chance of dry lightning over the mountains and portions of
the valleys this afternoon and evening, as an easterly wave moves
through the region. Drying will take place Tuesday through
Wednesday, with maybe just enough moisture leftover on Tuesday to
produce isolated afternoon thunderstorms over the mountains.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
CA...Heat Advisory until 8 PM PDT Wednesday for Apple and Lucerne
Valleys-Coachella Valley-Riverside County Mountains-San
Bernardino County Mountains-San Bernardino and Riverside
County Valleys-The Inland Empire-San Diego County Deserts-
San Diego County Mountains-San Gorgonio Pass Near Banning.