Area forecast discussion
National Weather Service San Diego California
110 PM PDT Sat may 18 2013
Synopsis...
high pressure will gradually build over the eastern Pacific through
Monday...bringing much drier and warmer conditions to Southern
California as well as a shallower marine layer. A period of light
to moderate offshore winds will also develop along the coastal
foothills late Sunday night into Monday morning...with local gusts
up to 35 miles per hour possible in the favored spots. Another trough of low
pressure will move into the Pacific northwest on Tuesday...and
deepen over the West Coast for the remainder for the work week.
Therefore...expect a gradual cooling trend to develop...the marine
layer to deepen...and the onshore to increase...with locally gusty
west winds in the mountains and deserts.
&&
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
counties...
Water vapor imagery continues to show California under northwesterly
flow aloft...as a trough of low pressure shifts to the east across
the Great Basin and high pressure builds over the eastern Pacific.
As a result...skies are predominately sunny this afternoon...with
temperatures running similar to or up to 6 degrees warmer than this
time yesterday. However...visible imagery shows some stubborn low
over the northern San Diego County and up into Orange County.
Although these low clouds have decreased in areal coverage today...a
few low clouds may linger over portions of Orange County through
this evening. Otherwise...expect a relatively pleasant afternoon
and evening across the Southland. A weak eddy will reform later
tonight...bringing less extensive low clouds and a shallower marine
layer back inland to the coastal areas and valleys...with some
patchy fog possible by morning.
High pressure will continue to build over the eastern Pacific
through Monday...with even warmer conditions developing for Sunday
and Monday. At this point in time...Monday looks as though it will
be the warmest day...as 850 mb temperatures warm back into the lower
20s. This means that inland areas will likely see temperatures 5 to
15 degrees above normal. However...a shallow marine layer will
linger along the coast...helping moderate temperatures in these
areas. In fact...some of the beaches may not see much in any
sunshine on these days...as the inversion strengthens.
Although high pressure will remain over the region...a disturbance
will pass through the Great Basin...bringing a period of weak to
moderate offshore winds to the coastal foothills possible late
Sunday night and Monday morning. At this time...the surface
gradients do not look that impressive...but there is a bit of upper
level support at 850 mbs and within the 30 above ground level level. For this
reason...think that the majority of the wind gusts will be around 30
miles per hour...and will likely not be strong enough to reach the coastal
areas. However...some of the favored windy spots through and below
the passes and canyons may see some gusts as high as 40 miles per hour...and
potentially flirt with advisory type winds.
A trough of low pressure will then move into the Pacific northwest
on Tuesday...flattening the ridge. Therefore...expect some minor
cooling across mainly areas west of the mountains to start on
Tuesday...even though inland areas will still be quite warm. A more
significant cooling trend will develop on Wednesday through Saturday
though...as this trough deepens over the west. The marine layer
will also deepen during this time...with more extensive low clouds
and fog possible each night west of the mountains. The marine layer
may even deepen enough for some drizzle Thursday night and Friday
night...although any real chances of precipitation will stay well to
our north. The onshore flow will strengthen during this time as
well...with locally gusty west winds in the mountains and deserts
each afternoon and evening.
&&
Aviation...
182001z...coast/valleys...few-sct clouds 2500-3500 feet mean sea level will linger
through 19/0500 UTC. 19/0500-0900 UTC...bkn-ovc stratus moving
inland 10-15 sm...with bases 900-1200 feet mean sea level and tops 1800-2000 feet
mean sea level. Stratus likely not reaching kont...although visible may lower to
5sm by 19/1200 UTC. Clearing of stratus 19/1500-1800 UTC.
Mtns/deserts...unrestricted visible and sky clear through Sunday morning. West to
northwest wind gusts of 25-35 knots along and east of Mountain Ridge-tops will
continue to create moderate-strong uddfs.
&&
Marine...
a 3 feet/17-18 second southwest swell will arrive tomorrow and
continue through Wednesday...bringing elevated surf and strong rip
currents to south and southwest facing beaches.
&&
Fire weather...
much warmer and drier conditions will develop over the Southland on
Sunday and Monday...with daytime temperatures rising 5 to 15 degrees
above normal by Monday. Daytime relative humidity values will also
fall into the lower teens and single digits on Monday...following
moderate to locally poor overnight recoveries.
There is also the potential for some moderate and gusty northeast
winds to develop over the coastal foothills of the San Bernardino
Mountains...the Santa Ana Mountains...and the Riverside County
mountains late Sunday night into Monday morning. Although
widespread gusts appear to remain around 30 miles per hour at this time...some
of the favored windy spots through and below the canyons and passes
may see local gusts up to 40 miles per hour. The duration of these northeast
winds will be relatively short lived...so no highlights are
anticipated at this time. However...these gusty winds will combine
with the very warm and dry conditions on Monday to elevate the
wildfire danger across portions of San Bernardino...Orange...and
Riverside counties.
&&
Sgx watches/warnings/advisories...none.
&&
$$
Public/fire...Palmer
aviation/marine...Harrison
