Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
148 PM PST Friday Nov 27 2015
a cold low pressure system centered over the Great Basin...will
keep the weather very cool or downright cold through the Holiday
weekend. Scattered showers will continue through early evening
mainly for San Diego County...with showers tapering off towards late
evening. 1 to 3 inches of new snowfall may occur in the mountains
around 4500 feet or higher...mainly in the San Diego and Riverside
County mountains. The nights will be very cold this weekend with
below freezing temperatures likely in portions of the valleys and
desert areas. Dry and warmer next week as low pressure drifts east
with weak offshore surface flow.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
A strong vorticity maximum is currently rotating around the Great Basin
trough and swooping down through Southern California...according to
water vapor satellite. Also...on visible satellite a circulation is
evident which is slowly making its way toward the San Diego County
coast. Isolated to scattered showers associated with the these
features are continuing...mainly over San Diego County...although
a pop-up stationary heavy shower in southern Orange County produced
some pea size hail and 0.38 inches of rain in 10 minutes. There are
also some isolated showers evident in the southern inland Empire
and some light snow showers in the San Bernardino County mountains.
Rainfall amounts from most of the showers today has been mainly on
the order of 0.03-0.10 inches with local 0.20-0.30 inch amounts
under the heavier cells. Taking a look at web-cams and temperatures
in the mountains...snow levels are currently at around 4500-5000
feet. As the vorticity maximum continues to move through the region...latest
hrrr now shows scattered light to moderate showers
continuing...mainly over and west of the San Diego County
mountains...through early evening...with showers gradually
dissipating in the middle to late evening. Snow levels currently at
4500-5000 feet this afternoon will likely drop to 4000-4500 feet
this evening...with additional snow accumulations of 1-3 inches
possible in the Riverside and San Diego County mountains...mainly
above 4500 foot elevation. Considering what the hrrr shows...have
extended the Winter Weather Advisory through 7 PM for the San Diego
and Riverside County mountains. Additional precipitation amounts
over the Riverside County mountains and over and west of the San
Diego County mountains look to be generally about 0.05-0.20
inches...with a trace to a tenth of an inch elsewhere over and west
of the mountains. Temperatures currently are several degrees lower
than at this time yesterday...and day-time highs will be 10-20
degrees below normal.
Saturday and Sunday...the trough will gradually move off to the east
with mainly zonal flow aloft for most of next week. Meanwhile...weak
offshore flow kicking in tonight through most of next week will
bring drying and very gradual warming through that period...with day-
time highs reaching back above normal by Wednesday.
However...overnight lows the next few nights will be below freezing
for many inland valley due to the lingering cold air mass...drier
air...light winds and mostly clear skies. A freeze warning GOES into
effect late tonight for the high deserts and central/eastern inland
Empire...with a freeze watch remaining in effect for overnight
Saturday night. The inland Empire was a little bit of a question
mark as to if temperatures would get low enough for a freeze...but
local WRF shows that there should be enough drying...and MOS
guidance shows lows reaching the 29-32 degree range.
Meanwhile...with lingering moisture in the area...does not look
likely that the San Diego County valleys will reach below freezing
for late tonight/Saturday morning...so have opted for a frost
advisory...although freeze conditions look more likely for overnight
Saturday night due to increased drying...so the freeze watch remains
in effect for that time period. In addition...some of the colder
portions of the lower deserts may also get cold enough...in the 33
to 36 degree range...for frost conditions...so a frost advisory has
been issued for those areas for overnight tonight. Similarly cold
conditions are likely in these areas overnight Sunday night as well.
By overnight Monday...temperatures may be high enough where frost
and freeze will no longer be a concern.
In the extended...onshore flow looks like it will return
Thursday...with a trough moving through Southern California on
Friday. The European model (ecmwf) spits out some precipitation with this
trough...while the GFS is mostly dry. A slight chance of showers has
been added for portions of the area for Friday.
272100z...coast/valleys/mtns...sct/bkn clouds...with bases 4500 to
6000 feet mean sea level and tops near 9000 feet mean sea level...will continue through this
afternoon. Skies this evening will become skc-sct...with greatest
cloud coverage near the mountains -shra will be possible through this
afternoon...with greatest coverage in San Diego County. Above 4000
feet mean sea level...scattered snow showers and clouds intersecting terrain will
reduce surface visible to less than 1 sm at times today.
Deserts...few-bkn at or above 10000 feet mean sea level with unrestricted visible
through Sat morning.
100 PM...scattered showers will continue through this afternoon. No
hazardous marine conditions are expected Saturday through Wednesday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Winter Weather Advisory until 7 PM PST this evening for
Riverside County mountains-San Diego County mountains.
Freeze warning from 1 am to 8 am PST Saturday for apple and
Lucerne valleys-San Bernardino and Riverside County valleys-
the inland Empire.
Frost advisory from 1 am to 8 am PST Saturday for Coachella
Valley-San Diego County deserts-San Diego County valleys-
San Gorgonio Pass near Banning.
Freeze watch from late Saturday night through Sunday morning for
apple and Lucerne valleys-San Bernardino and Riverside
County valleys-the inland Empire-San Diego County valleys.