Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
400 am PST Sat Nov 28 2015
Synopsis... a cold upper low over the Great Basin will continue
to bring cool days and cold nights through this weekend.
Overnight lows may fall below freezing in the inland valleys and
the desert areas. It will be dry and warmer next week with weak
offshore flow persisting.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Notably quieter weather this morning with most of the upper level
support now shifted off to the northeast related to the cold upper
low. Some weaker shortwave energy is wrapping around the base of
the low and bringing some very light showers to the coastal waters
this morning. These are expected to remain just offshore during
the early morning hours given the trajectory and flow pattern.
Another slight chance of showers will present itself this evening
as another pocket of energy wraps around the low and shifts just
to the west and south of our area.
Temperatures will continue to be rather cold through Sunday for
much of our area. The temperature forecast presents the most
significant challenge for this forecast shift.
Temperatures at this time are not trending quite as cold as previously
thought...especially over the San Diego County deserts...where
considerable ground moisture is probably a factor in the slow
cooling that has taken place overnight. As the aforementioned
secondary shortwave energy may bring enough middle and high cloud
cover to keep temperatures from bottoming out late tonight.
However...other factors at play include the light broad offshore
flow developing today across Southern California...which will help
to dry out the lower levels of the atmosphere...and hence lower
dewpoint temperatures...allowing more a better potential for
radiational cooling conditions late tonight. Given these push-pull
thoughts...we decided to ride the freeze watch for this shift for
now...in effect for the high deserts and valley areas. Another
frost advisory will likely be needed again for the lower deserts
and the Coachella Valley for late tonight.
After Sunday...upper level height rises and continued broad but
generally light offshore flow will bring a gradual moderation in
temperatures...especially during the daytime...when abundant
sunshine should eventually push temperature to near normal early
next week...and then several degrees above normal into middle next
week. Overnight low temperatures will continue to be on the cool
side due to the dry air that will be in place.
A vigorous upper trough Thursday into Friday next week will likely be
moisture starved in Southern California...but may be strong enough
to squeeze out a few showers. Therefore a slight chance of showers
will remain in the forecast for mainly next Friday. No other
significant weather makers in the next 7 days.
281100z...few to scattered at or above 4000 feet mean sea level through Sunday morning.
Moderate confidence in a brief period of NE winds...with gusts to 15
knots...for kont between 18z Saturday and 00z Sunday. Otherwise light
winds will prevail across the region.
830 PM...no hazardous marine conditions are expected through Wednesday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...freeze watch from late tonight through Sunday morning for apple
and Lucerne valleys-San Bernardino and Riverside County
valleys-the inland Empire-San Diego County valleys.
Freeze warning until 8 am PST this morning for apple and Lucerne
valleys-San Bernardino and Riverside County valleys-the
Frost advisory until 8 am PST this morning for Coachella Valley-
San Diego County deserts-San Diego County valleys-San
Gorgonio Pass near Banning.