Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
844 am PST Sat Feb 28 2015
Synopsis...low pressure moving south along the California coast
will will bring cooler weather and periods of showers into early
Tuesday...decreasing Tuesday afternoon. There will be strong gusty
west winds in the mountains and locally into the deserts into this
afternoon. Dry and warmer for the latter half of the week with
periods of locally gusty northeast winds at times.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Zone forecast updated to reduce cloud cover west of the mts today
and lower probability of precipitation slightly.
Satellite imagery this morning showed cloud bands moving onshore
from the coastal waters and concentrated over the mountains...
otherwise skies were partly cloudy. The strongest winds of 25-35 miles per hour
with gusts to around 45 miles per hour were confined to wind-prone areas of the
mountains. The 12z Miramar sounding had a 1500 feet saturated layer
topped by a weak inversion near 5700 feet. Westerly winds exceeded 40
knots above 9k feet. Precipitable water was 0.75 inch.
Through 8:30 am PST...radar had a smattering of showers drifting
east off the coastal waters. Precipitation amounts for the past 6 hours
were mostly under one-tenth of an inch. Amounts were greatest on the
Surface low pressure inland will weaken this evening as a broad...
positively tilted low pressure trough oriented from around Boise to
Morro Bay drifts south toward Point Conception. Mountain slope winds
will decrease by evening as the pressure gradient relaxes.
Scattered...mostly light showers are likely to continue as the low
approaches and cooler air aloft continues to destabilize the
Latest global models show the trough slowly weakening and becoming
more north-south oriented as it drifts south along the coast through
Monday. At the same time...another strong wave will drop south along
the coast...reinforcing the cold air aloft and possibly bringing
another round of showers and isolated thunderstorms Monday night into
Tuesday. Heights/thickness will gradually rise after Tuesday as the ridge
offshore builds back over California bringing a return of offshore flow and
fair...warmer weather for the latter half of the week.
Wind...a Wind Advisory will expire over the northern deserts by noon
today...and over the remainder of the mts/deserts by 4 PM. Gusts of
45 to 55 miles per hour will continue in wind-prone areas...mainly through the
San Gorgonio Pass and Desert Mountain slopes until then.
Precipitation...scattered...light showers today with an emphasis over the
coastal slopes due to upslope flow. The snow level was around 5500
feet this morning and should hold much of the day...then drop tonight
to around 5000 feet. An increase in the precipitation rate is likely late
tonight or on sun as colder air and better dynamics aloft develop.
However...it looks like the best organized lift will occur south of
the border...which may clip the tijuana River Valley. Showers will
become more numerous with heavier rainfall rates possible Sun night
through Tuesday morning as the colder air aloft overspreads the region.
We should also see the emphasis for consistently heavier precipitation
amounts move away from the mountains and toward the coastal areas with
All of extreme southern San Diego County has a chance to get more
rainfall than currently forecast if the moisture and energy forecast
to move over northern Baja California clips that region as indicated by the
latest GFS and wrfems runs.
Snowfall...a Winter Storm Warning is in effect above 5000 feet from
late this afternoon through Monday afternoon with the snow level
falling to 4800 to 5200 feet. The warning may be premature with the
latest hires models not indicating much precipitation overnight...but some
snow and freezing conditions are still likely. Heavier convective
snowfall looks like a better bet may be sun and Sun night. Latest
cips analogs for this type of system still favor 8 inch amounts in
the higher mts by late Tuesday.
Aviation...281600z...a mix of scattered-overcast cloud layers between 1500-
6000 feet will persist along and west of the mountains through the
overnight hours. Scattered showers will also occur today...with
brief visible reductions to 3 sm and ceilings as low as 1000 feet mean sea level in the
heaviest showers. Showers will become more numerous after 08z
Sunday. West winds will continue over the region...with strongest
winds over the mountain ridges and the deserts slopes through 00z.
Moderate uddfs/low level wind shear are possible over and east of the mountains winds
will gradually weaken this evening and overnight.
Marine...800 am...west-northwest winds 12-18 knots with gusts 18-25 knots
and steep seas seas will continue through early afternoon. Winds
will begin to weaken late this afternoon...with winds becoming 5-10
knots by Sunday morning. A short period swell at 4-6 feet and 7-9 seconds
will continue to produce choppy sea through tonight. A Small Craft
Advisory remains in effect until 1 PM this afternoon. Periods of
showers will occur through Monday night...with isolated
thunderstorms possible Sunday through Monday night. For forecast
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...Wind Advisory until 4 PM PST this afternoon for Coachella Valley-
Riverside County mountains-San Diego County deserts-San
Diego County mountains-San Gorgonio Pass near Banning.
Winter Storm Warning from 4 PM this afternoon to 4 PM PST Monday
for Riverside County mountains-San Bernardino County
mountains-San Diego County mountains above 5000 feet.
Wind Advisory until noon PST today for apple and Lucerne valleys.
Pz...Small Craft Advisory until 1 PM PST this afternoon 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.