Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
130 PM PST Thursday Dec 12 2013
upper level low will gradually move east tonight...with a few light
wrap around showers lingering over the the deserts and mountains
through late this afternoon. An inside slider will then dive across
California on Friday...continuing the trend for cooler weather. Dry
and warmer conditions will develop for this weekend and early next
week though...as high pressure rebuilds over California. Moderate
to locally strong and gusty northeast and east winds will also
develop early Saturday morning and continue through Sunday...with
weaker...but still locally moderate offshore winds continuing into
Monday. A gradual cooling trend will then develop by midweek.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Water vapor imagery continues to show an upper level low moving
slowly inland across Southern California this afternoon. At this
time...a few light wrap around showers are continuing to spread into
the Coachella Valley and the High Desert as well as into the
mountains of Riverside and San Bernardino counties...but this will
come to an end by this evening. Precipitation reports have been
light...with just a few hundredths have been reported here and
there. Otherwise...skies are predominately sunny...with
temperatures running similar to or a few degrees cooler than this
This upper level low will continue to move east over the next 24
hours...as the system moving into the Pacific northwest currently
dives across the northern California and into the Desert Southwest
during the day on Friday. All of the local models are showing the
marine layer redeveloping this evening and overnight tonight...ahead
of this next system. However...given that there are only a few low
clouds over the coastal waters right now...think it might be a
little slower to return than the current models are showing.
Otherwise...expect slightly cooler conditions to prevail through
Friday...with locally gusty onshore winds developing across the
mountains and deserts.
The main concern for this forecast period though will be with the
developing offshore wind event for this weekend and early next
week...as high pressure rebuilds over the region. The 12z models
are split the difference between a moderate and a strong event. For
now... the 12z NAM is showing the San Diego to Tonopah and the San
Diego to Daggett gradients peaking between 15 and 16 mbs and around
8 mbs respectively on Saturday morning. Upper level wind support
varies between the models...but the 12z NAM shows 30 to 35
kts...while the 12z WRF shows 40 to 45 kts. Our in house guidance
also backed off a bit with the 12z runs...showing local gusts around
55 miles per hour in the favored areas of San Bernardino and Orange counties.
Therefore...thinking that these offshore winds will primarily gust
to between 40 and 50 miles per hour...with just the favored locations like
Freemont canyon and Highland Spring topping out around 60 miles per hour.
Although the gradients relax ever so slightly for Saturday
afternoon...these winds will turn easterly and spread south into San
Diego County. There will also be a secondary peak in the gradients
Sunday morning...with locally strong winds continuing at the favored
locations. This will likely be when San Diego County sees its
strongest wind gusts.
Besides the winds...much warmer conditions will also develop across
the Southland for Saturday through Monday. Sunday and Monday will
likely be the warmest days of the week...as temperatures across the
inland valleys pushing into upper 70s and the lower 80s. Even the
coastal areas will see some warmer conditions these days. That
being said...this ridge of high pressure will gradually weaken by
the middle of the work week...with cooler conditions developing.
The extended models are also hinting that the marine layer will
return to the coastal areas as early as Wednesday morning...with low
clouds and fog possible during the late night and early morning
122100z...unrestricted visible will continue through this evening...with
broken-scattered cloud layers at or above fl150...becoming few-scattered overnight. A shallow
marine layer is expected to return tonight...with areas of low
clouds 500-1000 feet mean sea level developing along the coast after 13/06z.
Confidence in stratus bases is low-mod. Any stratus is expected to
clear the coast by 16-18z Friday morning. Gusty west winds 15-30 knots
will result in moderate uddfs over and east of the mts through Friday
a moderate northwest swell generated by a storm over the
north-central Pacific is expected to arrive in the coastal waters
Saturday...peaking at 6 feet/16 seconds south of San Clemente Island
Monday evening...lowering Tuesday. This swell will likely bring
elevated surf conditions and strong rip currents to exposed west
facing beaches Monday into early Tuesday.
moderate to locally strong offshore winds will develop early
Saturday morning...with northeast winds gusts up to 55 miles per hour through
and below the favored canyons and passes. These moderate to locally
strong winds will spread south into San Diego County by Saturday
afternoon...and turn more easterly as well. These moderate to
locally strong winds will continue into Sunday as well...with a
secondary peak on Sunday morning.
These moderate to locally strong northeast and east winds will also
combine with humidity values less than 15 percent on Saturday
afternoon through Sunday evening to elevate the wildfire danger.
Therefore...a Fire Weather Watch has been issues for the inland
areas of Orange County as well as the Santa Ana foothills and
mountains...the San Bernardino County mountains...the inland
Empire...the Riverside County mountains...the San Diego County
mountains...and the San Diego County valleys.
Skywarn activation is not requested. However...weather spotters are
encouraged to report significant weather conditions.
California...Fire Weather Watch from Saturday afternoon through Sunday
afternoon for the Orange County coastal areas...Riverside
County mountains-including the San Jacinto Ranger district
of the San Bernardino National Forest...San Bernardino and
Riverside County valleys-the inland Empire...San Bernardino
County mountains-including the mountain top and front
country Ranger districts of the San Bernardino National
Forest...San Diego County inland valleys...San Diego County
mountains-including the Palomar and Descanso Ranger
districts of the Cleveland National Forest...Santa Ana
Mountains-including the Trabuco Ranger district of the
Cleveland National Forest.