Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
930 am PST Friday Feb 27 2015
a low pressure system from the north will bring cooler weather with
periods of showers for tonight through Tuesday. There will be strong
gusty west winds in the mountains and deserts for tonight and
Saturday...decreasing Saturday night. Fair weather with seasonal
temperatures will follow later Wednesday and Thursday.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Mostly cloudy skies resulted this morning from a rapidly deepening
marine layer. Some clouds will stay with US all day today as a
winter storm drops down the coast. This low pressure trough contains
some cold Continental air although the track of the trough is over
water. It is not the wettest system we have seen...but we will get
some showers that will accumulate to decent precipitation totals before we
are done. Expect the showers to begin mainly in mountains this
evening and become more widespread overnight. Showers will continue
Saturday. Strong winds will develop mostly in the mountains and
deserts this evening along the front edge of the trough and will
continue Saturday before subsiding Saturday night. There are not
really any clear frontal bands or bands of moisture that would make
for steady heavy precipitation...but there does seem to be a wave or band
of moisture that would increase coverage and intensity Saturday
night into Sunday morning.
coast and valleys: 0.50 to 1.25 inch
mountains: 1.50 to 3 inches
deserts: up to 0.65 inch.
Snow showers will fall mainly above 5000 feet through Saturday.
Colder air arrives Sunday morning...dropping the snow level to 4000
feet. Snowfall totals above 5000 feet will be 4 to 12 inches. The
cold air will also destabilize our atmosphere so that a few
thunderstorms become possible Saturday night and Sunday.
Initially...thunderstorms are most likely in Orange County...but
then the chance spreads across the entire region Sunday night and
continues Monday. Of course rainfall amounts will vary greatly
between the tstorm haves and have nots. The trough takes its time
slowly moving through our region. On Monday an additional shortwave
zips down the backside of the trough to basically prolong the
showers and keep the snow levels low and instability sufficient for
a few thunderstorms. Models begin to differ on Tuesday. The GFS and
its ensembles move the trough out Monday night and end the precipitation
then. The Euro model hangs on to the trough for another day for
showers until Tuesday night. Either way by midweek fair...dry and
warmer weather will take over. For details on snow...see our Winter
Storm Watch laxwswsgx. For details on wind...see our Wind Advisory
271616z...patchy stratus over the coast...valleys and along the
coastal slopes...with bases 2500-3000 feet mean sea level...tops 3000-4000 feet mean sea level
and mountain obscuration due to clouds...will partially clear through
2300 UTC. 2300-28/1500 UTC...stratus redeveloping over the
coast...valleys and mountains...with bases 2500-3500 feet mean sea level and tops
5000-6000 feet mean sea level. Isolated showers will begin over and west of the
mountains after 28/0300 UTC...with showers becoming scattered after
28/0900 UTC...producing local visible below 3 sm. Mountain obscuration
will occur due to clouds and showers. Deserts will continue to have
unrestricted visible through Saturday morning.
After 2100 UTC...west winds strengthening...becoming 20-35 knots with
gusts 40-50 knots over mountain ridges...through and below
canyons/passes...along desert slopes and into adjacent desert
areas...resulting in strong-severe uddfs/llws/rotors over and east of the
mountains continuing into Saturday morning.
816 am...winds and seas will increase this afternoon through
Saturday afternoon with an approaching storm system. West-northwest
wind gusts 25 to 30 knots are likely over the coastal waters during
that time period...with short-period seas increasing to 6-9
feet...resulting in hazardous conditions for small craft. A Small
Craft Advisory GOES into effect this afternoon. Winds and seas will
lower Saturday night into Sunday...although another round of briefer
gusty northwest winds may occur on Tuesday due to another
disturbance moving through the region.
Also with this storm system...periods of showers will occur this
weekend...with thunderstorms possible Sunday into Monday.
Thunderstorms may produce small hail...gusty and erratic
winds...heavy rains and waterspouts. For forecast details...see
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Wind Advisory from 6 PM this evening to 3 am PST Sunday for
Coachella Valley-Riverside County mountains-San Diego
County deserts-San Diego County mountains.
Winter Storm Watch from Saturday afternoon through Monday
afternoon for Riverside County mountains-San Bernardino
County mountains-San Diego County mountains above 5000 feet.
Wind Advisory from 6 PM this evening to 4 PM PST Saturday for
apple and Lucerne valleys-San Bernardino County mountains-
San Gorgonio Pass near Banning.
Pz...Small Craft Advisory from 2 PM this afternoon to 1 PM PST
Saturday for coastal waters from San Mateo Point to the
Mexican border and out to 30 nm-waters from San Mateo Point
to the Mexican border extending 30 to 60 nm out including
San Clemente Island.