Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Diego California
853 PM PDT Friday Apr 18 2014

weak low pressure aloft will exit the region on Saturday...but leave
behind some moisture and instability...keeping a chance of isolated
showers over the mountains in the afternoon. Onshore flow will
continue through the marine layer clouds will return
each night...with clearing expected each day. It will be warmer
through Monday...then breezy and sharply cooler Tuesday and
Wednesday as a low pressure trough swings through the state.
Slightly warmer to end the week ahead of another Pacific storm
system for California next weekend.


Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino

We got an early taste of the Summer monsoon today as thunderstorms
erupted over the mountains. Numerous lightning strikes were observed
along with pockets of small hail and heavy downpours. Remote rain
gage reports indicated up to 0.42 inch...but radar estimates showed
amounts approaching and even exceeding one inch in spots in the
Santa Rosa and San Ysidro Mountains of Riverside and San Diego counties.
The activity has long since died off with the setting sun. Outflow
clouds and sprinkles from the activity fanned out into the Coachella
Valley late in the day with accumulating rain reported near the
foothills on the valley floor.

Satellite imagery shows areas of low clouds west of the mountains...
and higher clouds well inland across the deserts. The 00z Miramar
sounding still had a precipitable water of 0.75 inch...and a weak 3 degree c
inversion based near 3k feet. Surface pressure gradients were running
3-5 mbs onshore at 03z.

The weak upper low responsible for our thunderstorms today will move
slowly east through Sat. Lingering moisture and instability in
northerly flow around the west side of this system will continue a
threat of afternoon showers in the mountains. West of the
mountains...marine clouds should thicken overnight...then burn off
by late morning...leaving sunny and mild conditions on Sat. Warmer
on sun/Mon...especially the marine layer thins under a
weak ridging aloft. Any threat for mountain showers diminishes
further under increasing stability aloft.

Models have keyed in on a Sharp Ridge to approach the coast Monday
night and pass through California Tuesday. Onshore gradients will increase as a
997 mb surface low develops over NV/UT. This will result in strong
westerly winds/gusts over the mountains and into the deserts...a rapidly
deepening marine layer...and much cooler days Tue/Wed. Westerly wind
gusts could well exceed 55 miles per hour by Tuesday afternoon across portions of
the High Desert.

The trough will slide east for the latter half of the week as
another deep trough develops over the eastpac. In the interim...
heights/ thickness will rebound modestly for slightly warmer days.
There is fair agreement from recent global model runs in the
extended period with the yet-to-develop eastpac trough. If later
model solutions for next weekend remain could be a
significant late-season precipitation producer across much of the state.


190330z...coast/valleys/mtn coastal slopes...stratus scattered-bkn020-030
slowly filling in and becoming broken-ovc020-030 tops 035 over the
coastal basin through 15z Saturday. Clearing of stratus between

Above the marine layer scattered-bkn150-250 through 18z...becoming
sct150-250 after 18z.

Mountains and deserts...sct-bkn080-150 between 18z-24z Saturday with slt
chance of high based showers and virga with brief downdraft winds.


no significant marine weather conditions through Monday.

Increasing southwest winds Tuesday ahead of a strong trough of low
pressure. The winds will peak Tuesday afternoon through evening with
peak gusts of 25 knots over the outer Waters. Peak gusts over the inner
waters of 20 knots. These strong winds combined with an 8-10 foot
short-period swell will be potentially hazardous for small craft
over the outer waters. Confidence is moderate to high.

Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


Sgx watches/warnings/advisories...none.