Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
145 PM PST Wednesday Dec 24 2014
cooler conditions will develop for Christmas day...as a trough of
low pressure moves inland across northern California and into the
Great Basin. Gusty west winds will develop in our mountains and
deserts late this afternoon and evening...with a few light showers
will possible for areas along the west of the mountains late tonight
and on Christmas morning. As this system shifts east...periods of
gusty northeast winds will return to the coastal slopes of the
mountains into adjacent coastal foothill areas through Saturday.
Although some minor warming may occur this Holiday weekend...cool
conditions will continue to prevail...with even cooler conditions
possible for the first part of next week.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Water vapor imagery continues to show a trough of low pressure
moving inland across the Pacific northwest and northern California
this afternoon...squashing the ridge of Southern California. As a
result...plenty of high clouds are spilling into the region this
afternoon...and temperatures are running several degrees cooler than
this time yesterday. The surface pressure gradients have also
turned onshore...and will increase through this evening...with gusty
west winds developing across our mountains and deserts. The upper
level wind support will increase this evening to between 35 and 45
knots at 850 mbs...so some isolated gusts up to 65 miles per hour in the favored
locations is not out of the question. Current wind advisories look
on track for this evening through tonight.
Models are showing that the marine layer will return late
this afternoon and evening to the coastal areas...rapidly deepening
and spreading inland overnight. For this reason...think some light
showers will be possible...mainly along and west of the mountains
late tonight and for Christmas morning. Amounts will be
light...mainly less than a tenth of an inch along the coast upwards
of a quarter inch along the coastal mountain slopes. Even a dusting
of new snow will be possible above 5000 feet in the mountains...but
not much more than that.
As this system quickly shifts east during the day...drier conditions
will develop across the Southland by Christmas afternoon. Gusty
offshore winds will develop once again...with north to northeast
winds possible across mainly the coastal slopes of the mountains and
adjacent coastal foothills areas in Orange and southwestern San
Bernardino counties on Thursday...before becoming more northeasterly
and spreading into San Diego and western Riverside counties by
Friday. Although a minor warming trend will develop for the weekend
under weak ridging...cool conditions will continue to prevail. The
12z models are continuing to hint at a potentially impressive dry
back door cold front spreading into Southern California early next
week...sometime between Monday and Wednesday. There are still a few
timing differences...with the GFS timing a little faster with the
initial surge of cold air...but both models are showing a surge of
very cold air for Tuesday and Wednesday. Given the trajectory of
this system...believe that dry conditions will prevail.
However...very gusty north to northeast winds will probably be in
store for these days as well.
242100z...coast/valleys...skc conds with unrestricted visible and light
winds through this afternoon. Low coastal stratus will move inland
between 24/0300z-0600z this evening. Bases will start around 1000
feet...possibly lower...then will raise to above 3000 feet by middle
morning. Light showers west of the mountains possible tonight into
Thursday morning with local visible 3-5sm. Rain chances diminish after 25/1500z
with low clouds scattering out.
Deserts/mts...SW-W winds with surface gusts 45-55 knots developing along
the mountain ridges and desert slopes...and adjacent desert foothills
this evening through Thursday morning with strong uddfs and low level wind shear over and
east of the mountains
130 PM...brief patchy dense fog may form late this afternoon over
the coastal waters. A trough of low pressure moving inland tonight
into early Thursday will bring gusty west-northwest winds to the coastal
waters. Wind gusts of 25 knots...locally higher...are likely over the
coastal waters late tonight through midday Thursday. Combined seas near
10 feet are also possible for a short time early Thursday over the outer
coastal waters. Winds will weaken gradually Thursday afternoon/evening. A
Small Craft Advisory is in effect for the inner and outer coastal
waters this evening through Thursday afternoon.
130 am...a long-period west-northwest will continue elevated
surf of 3-5 feet...with occasional sets to 7 feet...and strong rip
currents at the San Diego and Orange County beaches through Friday.
Swell and surf will subside over the weekend.
Fire weather (from previous discussion)...
gusty onshore flow will develop this afternoon and evening...with
strong and gusty west winds possible in the mountains and deserts.
Higher humidities will also briefly return tonight into early
Thursday. However...periods of strong gusty northeast winds will
redevelop for Thursday through Saturday...with cool and dry
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Wind Advisory from 9 PM this evening to 6 am PST Thursday for
the Coachella Valley...Riverside County mountains...San Diego
County deserts...San Diego County mountains.
Wind Advisory from 6 PM this evening to 3 am PST Thursday for
the apple and Lucerne valleys...San Bernardino County
Pz...Small Craft Advisory from 10 PM this evening to 2 PM PST
Thursday for the coastal waters from San Mateo Point to the
Mexican border and out 30 nm...waters from San Mateo Point
to the Mexican border extending 30 to 60 nm out including
San Clemente Island.