Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
900 am PDT Sat Apr 25 2015
The final of the series of weather disturbances will quickly move
through southeast California today and tonight. This will bring
additional showers and windy conditions to the mountains and desert
slopes. Behind the system the wind will shift to offshore and much
drier air will filter across Southern California on Sunday and
Monday. Lighter winds and a warming trend for the first half of next
week. A return to onshore flow and increasing marine layer starting
middle week and continuing into late week as an upper level trough
passes by well to the north.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Short term (today through monday)...
the first portion of the main short wave trough...now located in
central California and moving southeast...is now passing across
southwest California. It is evident in the bands of middle level clouds
and also allow the deep low level moisture in place to produce areas
of drizzle on the coast and scattered light showers inland. As this
passes through later this morning the drizzle and cloud cover will
decrease but low level moisture will remain.
The main weather system and short wave trough is due to arrive this
afternoon and evening between 21 and 03 UTC. This is the period
where mountain and desert winds will increase notably and also
showers will increase...especially for the mountains and west slopes
and all of San Diego County and southern Riverside County coast and
valleys. During this period free air winds aloft reach 50 knots at
700 mb as a rather strong short wave trough cuts across eastern San
Bernardino and Riverside County. Historically this type of wave and
resultant strong downsloping wind occurs in March and April which we
have seen the past 3 years. This west to northwest flow should bring
winds as strong as 65 to 70 for wind prone areas and widespread 40
to 55 miles per hour in the desert passes and desert floors. The strong wind
flow continues 03 to 08 UTC just behind the short wave trough axis
and the winds shift to northerly direction. Will have to consider
upgrading to a warning for desert floor areas where local gusts to
60 miles per hour are possible in this pattern. BUFKIT soundings depict momentum
Transfer of 40 knots to the floor. The lower Coachella Valley and
Borrego desert appears to be the best potential where forecast peak
winds are now 45 to 55 miles per hour. Finally, for snow in this event The
Levels are high...above 7500 feet as the coldest 700 mb temperatures
are during precipitation is -1c.
Subsidence takes over by 06 UTC Saturday night and precipitation
should rapidly end...last in San Diego County mountains. The wind
shift to offshore flow increases on Sunday so the inland Empire
region near Cajon and Banning pass...and parts of the High Desert
will experience increasing north to northeast wind gusts of 40 to 50
miles per hour in the wind prone areas...and isolated 60 miles per hour. Low level
moisture will decrease allowing for partly cloudy skies...except
clear in deserts.
On Monday the upper level heights rise and the wind flow will
decrease in the afternoon with sunny skies. Temperatures will
moderate closer to normal. The warming trend continues on Tuesday
and Wednesday for all areas.
Long term (tuesday through friday)...
cooling will begin near the coast on Wednesday and spread inland
into next weekend as onshore flow returns in response to an broad
upper level trough moving across far northern California. Night
and morning coastal low clouds and fog will return and spread
farther inland late in the
251530z...coast/valleys...sct clouds based around 3000 feet mean sea level
with tops around 5000 feet mean sea level. Locally broken clouds lowering to
2000-3000 feet mean sea level and local visibilities around 5sm in -shra.
After 26/00z this afternoon clouds broken-overcast 2000-3000 feet mean sea level
spreading over the area with tops gradually increasing to 12000 feet
mean sea level. Visibilities 3-5sm in -ra at times. West winds increasing to
15-20 knots with gust to 25 knots at times as well...then winds decreasing
06z-10z Sun morning.
Mtns/deserts...coastal slopes and ridges obscured in clouds and occasional
rw-...increasing in coverage after 00z sun. Areas of layered clouds with
tops increasing to fl120 by late evening. Westerly winds 15-25 knots
increasing over the ridges and onto the deserts slopes. West winds
35 to 40 knots by late afternoon with local gusts to near 50 knots through
and below wind prone passes through Sat night. East of the mountain
crests expect scattered clouds at or above fl080 with strong uddfs and wind shear at
times. Visible generally unresricted...except locally at or below 3sm in bldu in
830 am PDT...northwest winds will increase to 20 to 25 knots this
afternoon over the coastal waters...with higher gusts over the outer
waters. A large short-period wind swell will develop by evening. The
wind and rough seas will continue through tonight creating a hazard
to small craft. The winds and seas will diminish Sun morning...but
some gusts over 20 knots will continue over the outer waters through
Sun afternoon. A Small Craft Advisory has been issued beginning this
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Wind Advisory from noon today to 10 PM PDT this evening for
Riverside County mountains-San Bernardino County mountains.
Wind Advisory until 10 PM PDT this evening for apple and Lucerne
valleys-Coachella Valley-San Diego County deserts-San Diego
County mountains-San Gorgonio Pass near Banning.
Pz...Small Craft Advisory from 2 PM this afternoon to 10 PM PDT
Sunday for waters from San Mateo Point to the Mexican
border extending 30 to 60 nm out including San Clemente
Small Craft Advisory from 2 PM this afternoon to 5 am PDT Sunday
for coastal waters from San Mateo Point to the Mexican
border and out to 30 nm.