Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
125 PM PDT Tuesday Mar 31 2015
Synopsis... a series of low pressure troughs moving across
California will bring gusty west winds in the mountains and deserts
through Wednesday night. Marine layer clouds will spread into the
valleys each night. High pressure building aloft on Thursday will
bring warming along with gusty offshore winds to the mountains and
inland valleys through Friday. Over the weekend a low pressure
system will deepen along the West Coast bringing increasing onshore
flow and a cooling trend through early next week.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
An upper level trough will move across the northern Great Basin this
evening bringing a period of gusty winds to the mountains and
deserts tonight. The strongest winds will be in the deserts
where winds will be ramping up this afternoon as surface pressures
fall over southern Nevada. Onshore gradients will be strongest
between 00z-09z when a 1006 mb surface low deepens near Las
Vegas. The strongest winds will surface in the high deserts and
on the eastern slopes of the mountains and into the Coachella Valley
and the San Diego deserts. Gusts from 45 to 55 miles per hour are expected in
these areas with the strongest winds in the San Gorgonio Pass.
The marine layer clouds that retreated off the coast this
afternoon will return this evening. The marine layer will be a
few hundred feet deeper tonight due to the stronger onshore flow and
a developing Catalina eddy. Low clouds and fog will spread deeper
into the valleys Wednesday morning.
A second trough will move inland across south-central California
Wednesday bringing another round of gusty winds late Wednesday
afternoon and evening...but the winds will not be quite as strong.
The trough will move east Thursday and be followed by weak ridging
along the West Coast through Friday morning. This pattern will set
up a brief Santa Ana wind event with gusty offshore winds
surfacing across the mountains and into the inland valleys.
Initially the winds on Thursday will be aligned with the north-south
pressure gradient and mostly impact the Cajon Pass...the inland
Empire and the Santa Ana Mountains. The winds will then
shift from the north to the northeast Thursday night into
Friday morning with gusty winds in the San Diego mountains
and valleys. Downslope compressional warming will send coastal and
valley highs in the 80s to around 90 on Friday. The marine layer
will be forced out to sea.
Saturday through Monday...a low pressure trough will deepen along
the West Coast for gradual cooling and a slow increase in the marine
312014z...coast/valleys...through 01/0000 UTC...mostly unrestricted
visible and scattered clouds at or above 20000 feet mean sea level. 01/0000-1500 UTC...stratus
gradually developing 25-35 sm inland with bases 1300-1700 feet mean sea level and
tops 1800-2300 feet mean sea level. Local visible at or below 1 sm will be possible over the
central portions of the valleys...including in the inland Empire.
Forecast confidence of timing and ceiling heights/visible for
ksan...kcrq...ksna and kont tafs is moderate. Moderate-to-high
confidence that kont will get the stratus/fog. Stratus/fog clearing
to the coastal waters 01/1500-1800 UTC.
Deserts/mtns...unrestricted visible and scattered-few clouds at or above 20000 feet mean sea level
through Wednesday morning. West winds increasing...becoming 20-30 knots
with gusts around 40 knots by 01/0000 UTC over the mountain ridges...through
and below passes/canyons...along desert slopes and into adjacent
desert areas. This will result in moderate-strong uddfs/low level wind shear and possible
rotors over and east of the mountains
114 PM...steep seas of 10 feet and northwest wind gusts to 20 knots
will be possible on Thursday over the outer waters as a trough moves
inland north of the area. Forecast confidence is moderate.
Otherwise...no hazardous marine weather is expected through Saturday.
the moderate sized long-period south swell which brought widespread
4-6 foot surf and strong rip currents Sunday and Monday continues at
around 4 foot/14-15 seconds...resulting in 3-5 foot surf at the
beaches today...with some local 6 foot sets. These surf
conditions...along with a high risk of strong rip currents...will
continue through this evening as the swell lowers further.
Wave watch 3 indicates a building short-period west-northwest swell
today...peaking at 8 feet/11 seconds on Wednesday...with a 10
foot/11 second west-northwest swell then occurring on Thursday.
Although the period on these swells will be somewhat short...the
swell heights will be large enough to bring at least 4-6 foot surf
and an increased risk of rip currents.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Wind Advisory from 4 PM today to 3 am PDT Wednesday for
apple and Lucerne valleys-Coachella Valley-San Diego County
deserts-San Gorgonio Pass near Banning.