Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
136 PM PDT Wednesday Oct 1 2014
patchy stratus and fog may develop tonight mainly in the coastal
areas before offshore flow clears things out Thursday morning. A
building high pressure ridge aloft and offshore flow at the surface
will bring increasingly hotter and drier weather for Thursday
through Saturday...especially along and west of the Lower Mountain
slopes. Day-time highs are likely to reach 10 to 20 degrees above
normal in these areas. The offshore flow will also bring gusty
northeast to east winds at times for Thursday into
Saturday...strongest Thursday morning through and below the mountain
passes...canyons and into the coastal foothills. Weak onshore flow
and some weakening of the ridge is expected to bring slightly cooler
conditions for the coast on Sunday...but conditions will still be
quite hot elsewhere. Continued slow weakening of the ridge Monday
through Wednesday...resulting in continued gradual cooling...and a
return of night and morning low clouds and fog along the coast and
possibly into the western valleys.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
A weak coastal eddy developed last night which resulted in better
stratus coverage into the coastal and western valley areas of San
Diego County this morning. However...afternoon visible satellite
shows that almost all of the stratus has cleared out. The 12z
Miramar sounding shows a 3 degree marine layer inversion at around
1700 feet...with weak south flow at the surface from the eddy...and
west flow aloft. The eddy is expected to diminish soon...according
to local WRF and MOS guidance. Meanwhile...temperatures are actually
a bit lower today compared to 24 hours ago...likely due to coastal
eddy and maybe the shortwave-trough moving through the region.
Water vapor satellite currently shows a trough moving into the Great
Basin region. Surface high pressure is starting to build over that
area in the troughs wake...resulting in strengthening offshore
pressure gradients in our area. Latest offshore pressure gradients
are 6.3 mb from San Diego to Tonopah...compared to only 1.3 mb at
this time yesterday. Gusty offshore winds are likely to start in the
San Bernardino County mountains and Cajon Pass area by late this
afternoon...with winds increasing in coverage and strength tonight
though Thursday morning. Forecast models indicate offshore pressure
gradients about 1 mb stronger than previous runs were showing...at
around 10 mb from San Diego to Tonopah...and 12 mb from San Diego to
Salt Lake City. There is not much upper level support for
winds...with 850 mb winds only at around 15-25 knots according to local
WRF. However...cansac_wrf continues to show 25-35 miles per hour sustained with
possible northeast to east 45-50 miles per hour gusts through and below the
Cajon Pass and San Gorgonio Pass...along the Santa Ana
foothills...and along the coastal slopes of the San Diego County
valleys. A Wind Advisory has been issued for the inland Empire and
San Bernardino County mountains...mainly for the areas through and
below the Cajon Pass...through and west of the San Gorgonio
Pass...and near the Santa Ana foothills. Local WRF indicates stratus
moving in tonight through early Thursday morning...mainly along the
San Diego County coast where the offshore flow will not be as strong
and less will take a little longer for the stratus/fog to clear out.
Before the marine layer gets scoured out Thursday morning...it may
become shallow enough to produce some dense fog along the coast.
Orange County is unlikely to see much stratus/fog due to the better
offshore flow in that area. Offshore gradients will weaken later
Thursday and continue a slow weakening trend through
Saturday...although the previously mentioned favored areas may still
see northeast to east gusts to 35 miles per hour at times.
Meanwhile...the ridge mentioned earlier will continue to build over
the region Thursday into Saturday. This...in addition to the
offshore flow...will result in increasingly hotter days...with
day-time highs reaching 10-20 degrees above normal for Friday and
Saturday in the valleys...coast...Santa Ana Mountains/foothills and
Lower Mountain slopes. Saturday looks to be the hottest day
overall...although some coastal locations may experience their
hottest conditions on Friday due to the slightly better offshore
flow on that day. Expected day-time highs for Friday and Saturday
are as follows...low to middle 100s in the inland Empire...upper 90s to
low 100s in the San Diego valleys and inland Orange County...90s in
the lower elevations of the Santa Ana Mountains/foothills...and low
to middle 90s a few miles inland of the coast. A heat advisory has been
issued for Friday through Sunday for the valleys and the Santa Ana
Mountains/foothills. A heat advisory has also been issued for the
San Diego and Orange County coastal areas and the lower slopes of
the mountains for Friday through Saturday...with highest
temperatures occurring inland from the beaches. Slight cooling is
likely to occur at the coast Sunday due to possible weak onshore
flow and weakening of the upper level ridge.
The ridge will continue to slowly weaken Monday through
Wednesday...resulting in slow cooling each day...and gradually
increasing night and morning low clouds/fog along the coast and
western valley areas. Day-time high temperatures may finally reach
near normal by Wednesday.
012015z...coasts/valleys...clear through this evening. Patchy
stratus may push back into the coastal areas around 02/06z and up
to 10 Michigan inland overnight. Ceilings will likely begin around 1000-1500
feet mean sea level...lowering to 500-1000 feet late tonight as offshore flow
strengthens. Visible may locally drop to 1sm or less over higher coastal
terrain in San Diego County Thursday morning. Clearing will occur by
02/12z Thursday in Orange County...and 14-16z in San Diego County. Clear
with unrestricted visible beyond Thursday morning.
Northeast winds with surface gusts 25-35 knots...locally as high as 45
knots...will develop below the Cajon and Banning passes and Santa Ana
foothills late tonight...including near kont. Low level wind shear and moderate uddfs
possible near the coastal foothills of the San Bernardino and Santa
Ana Mountains with these winds. Winds will weaken early Thursday afternoon.
Mountains/deserts...clear with unrestricted visible through Thursday morning.
NE to east winds with surface gusts 35-45 knots developing through the
passes...canyons...and coastal slopes of the mountains as well as the far
north Coachella Valley by 02/12z...weakening by early Thursday afternoon.
115 PM...no hazardous marine weather is expected through Sunday.
a long period south-southwest swell arriving in the coastal waters
late Thursday will generate elevated surf early Friday morning
through at least late Sunday. Surf of 3 to 5 feet with sets to 6
feet is expected along south and southwest facing beaches of Orange
and San Diego counties. In addition to the surf...strong rip
currents and longshore currents will create hazardous swimming
conditions at most area beaches. A beach hazards statement has been
issued for the surf and rip currents...valid early Friday morning
through late Sunday night.
high pressure aloft and offshore flow with locally gusty northeast
winds will bring much warmer and drier conditions for Thursday
through Sunday. Strongest winds...with local gusts to around 40
miles per hour...are expected for late tonight into Thursday morning...followed
by gradual weakening Friday and Saturday. Friday and Saturday will
be the warmest days...especially inland where temperatures of 95 to
105 degrees are possible. Slow cooling may begin near the coast on
Sunday as weak onshore flow returns. Humidities will fall
Thursday...reaching the middle teens by late morning for inland areas.
Expect lowest daytime humidities of 5 to 10 percent for inland areas
Friday and Saturday with poor overnight recovery. Humidities are
expected to slowly recover for Sunday into early next week as weak
onshore flow returns. While more widespread areas meeting red flag
warning criteria is not expected...warning criteria will likely be
met in some locations on Thursday...mainly below the Cajon
Pass...west of the Banning pass...portions of the coastal foothills
of the Santa Ana Mountains...and portions of the San Diego
foothills. Regardless...there will be an elevated threat for
wildfires Thursday into Sunday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...beach hazards statement from late Thursday night through late
Sunday night for the Orange County coastal areas...San
Diego County coastal areas.
Heat advisory from 11 am Friday to 8 PM PDT Saturday for the
Orange County coastal areas...Riverside County mountains...
San Bernardino County mountains...San Diego County coastal
areas...San Diego County mountains.
Wind Advisory from 2 am to 2 PM PDT Thursday for the San
Bernardino County mountains...San Bernardino and Riverside
County valleys-the inland Empire.
Heat advisory from 11 am Friday to 8 PM PDT Sunday for the San
Bernardino and Riverside County valleys-the inland Empire...
San Diego County valleys...Santa Ana Mountains and