Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
139 PM PST Thursday Feb 26 2015
onshore flow will strengthen through Saturday as a cold storm
drops south along the California coast. Strong winds in the
mountains and deserts...and periods of rain and mountain snow is
expected from late Friday through Monday. Showers may become heavy
at times with a thunderstorm or two possible Saturday night and
Sunday. Scattered showers could linger through early Wednesday as
a few more systems move across the area.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
At 1 PM PST...water vapor satellite imagery displayed an upper-
level trough off the coast of southwest British Columbia and an
upper-level ridge off of the West Coast. Visible satellite showed
some high clouds over portions of the coast and valleys. The
26/1200 UTC European model (ecmwf) and GFS are in relatively good agreement through
the mid-term...and slightly differ in the long term.
Upper-level ridging will remain off the coast through early
tomorrow. Lowering heights from an approaching upper-level trough
will help deepen the marine layer tonight and develop low clouds
and patchy fog into the inland valleys. A cooling trend will begin
Friday as heights aloft continue to lower and onshore flow
strengthens with the trough approaching from the northwest. Gusty
westerly winds will develop in the mountains and deserts by Friday
The trough digging along the Pacific northwest Friday will continue
south and deepen...arriving over southwest California by late Sunday. Light
to moderate precipitation may begin as early as Friday evening and
continue through Monday over SW California...with greatest
chances...heaviest precipitation and coldest weather Saturday and
Sunday. Snow levels will begin around 7000 feet Friday evening...drop to
around 5500 feet Saturday morning...and bottom out at near 4000 feet
Sunday morning. H500 temperatures of -26 degree c will create the possibility
of thunderstorms Saturday night and Sunday...which could generate
locally higher precipitation amounts where they develop. Strong
westerly winds will develop from the system...with strongest wind
gusts of 55 to 65 miles per hour over mountain peaks...and gusts to 50 miles per hour
possible in the deserts Saturday. A Winter Storm Watch remains in
effect for the mountains above 5000 feet for Saturday afternoon
through Monday afternoon.
..forecast storm total precipitation amounts Friday afternoon - Monday morning...
Deserts.....0.25 to 0.50 inches
coast.......0.50 to 1.00 inches
valleys.....0.75 to 1.50 inches
mountains...1.50 to 2.75 inches
..forecast storm total snowfall amounts Friday afternoon - Monday morning...
4000 to 5000 feet...1 to 4 inches
5000 to 6000 feet...4 to 10 inches
6000 to 7000 feet...6 to 12 inches
above 7000 feet.....10 to 16 inches...local amounts to 18 inches
Another trough will quickly follow the weekend storm and continue
the possibility of precipitation...mainly over and west of the mountains
later Monday through early Wednesday. This system will keep snow
levels low...around 4500 feet through middle next week. Light to
moderate precipitation amounts are possible with this trough...as
well. Models then disagree for Wednesday as the European model (ecmwf) digs a
trough along SW California...and the GFS develops northwest flow over the
area. Models have varied in the solution from run to run
recently...so will keep the forecast dry for Wednesday afternoon.
Dry northwest flow aloft is forecast for next Thursday. High
temperatures will warm to near normal by the middle of next week.
262105z...coast/valleys...through 27/0000 UTC...scattered clouds at or above 20000
feet mean sea level and unrestricted visible. 27/0000-1500 UTC...stratus gradually
developing within 25-50 sm of the coast with bases around 1400-1800
feet mean sea level...tops 2200-2500 feet mean sea level...areas of 3-5 sm visible...and local visible
at or below 1sm for the Central Valley areas. Forecast confidence in timing
is moderate...confidence in ceiling/visible is moderate-to-high...and
confidence in stratus occurrence is high. Slow and partial clearing
of stratus 27/1500-2000 UTC.
Mtns/deserts...unrestricted visible and few-scattered clouds at or above 20000 feet mean sea level
through Friday morning.
105 PM...winds and seas will increase Friday evening 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. Winds and
seas will lower Saturday night into Sunday.
Also with this storm system...periods of showers will occur this
weekend...with thunderstorms possible Sunday. Thunderstorms may
produce small hail...gusty and erratic winds...heavy rains and
waterspouts. For forecast details...see laxcwfsgx.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Winter Storm Watch from Saturday afternoon through Monday
afternoon for Riverside County mountains-San Bernardino
County mountains-San Diego County mountains.