Scientific Forecaster Discussion
fxus66 ksgx 200535 aaa
Area forecast discussion
National Weather Service San Diego California
935 PM PST sun Feb 19 2017
scattered, light showers will linger, mainly along the coastal slopes
of the mountains into the night. Light showers may redevelop over
Orange, San Bernardino, and northwest sections of Riverside County at
times into Tuesday as weather systems move through northern portions
of the state, but San Diego and most of Riverside counties should be
warmer with a bit more sun. Breezy and cooler again by midweek as a
trough passes with a period of showers possible. Even cooler by next
weekend with another chance of rain and mountain snow.
Scattered light showers will continue to build southeast overnight from the
Los Angeles basin and will likely affect the northern sections of
our area, including Orange County, and SW San Bernardino County. Any
precip amounts will generally only be a few hundredths of an inch
overnight and Monday morning. With the ridge quite weak through
Monday, additional weak disturbances in the northwest flow aloft will
continue to drop into socal and could bring additional light
precipitation into our northern areas through Monday night. No
significant changes were needed to the ongoing forecast database
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
National Weather Service radar showed coverage and intensity of echoes decreasing early
this afternoon. Over the past hour ending at 1 PM PST, the only
rain gages showing any accumulation were on the coastal slopes. Based
on the latest hires models a few more light showers are possible
through this evening before decreasing.
At midday...satellite imagery showed mostly cloudy skies along
and west of the mountains. Some clouds were over the lower deserts,
but the High Desert was mostly clear and sunny. An eddy circulation
was evident as well, centered NE of San Clemente isl. Some clearing
was occurring along the coast. Surface pressure gradients were
running around 8 mbs onshore ksan-Nevada and 4 mbs onshore to the lower
deserts. At midday, peak wind gusts were mostly under 20 mph, except
in wind-prone Mountain Pass and canyon areas where westerly gusts of
25-35 miles per hour were reported.
The clouds and showers were surprisingly stubborn today, even under
ridging aloft. The deep saturated layer was being lifted by weak
disturbances riding the ridge from the northwest. That will be ending
overnight. However another string of disturbances aloft will brush
northwest portions of the County Warning Area Mon/Tue, keeping a small chance of precip over
those areas. With any sunshine farther to the south, it will be
considerably warmer as heights/thickness will be quite high. Tue
looks to be the warmest day of the week when daytime Max temps could
easily top the 70 degree mark in many areas.
For the midweek period, the large trough over the eastpac, ejecting
the disturbances moving over the state early in the week, will drift
inland. This will force a stronger shortwave southeast across the region Wed
evening. As it moves through, onshore flow will increase and westerly
winds will become gusty over the mts/deserts and coastal waters.
There will also be a chance of mostly light showers along and west of
the mts. It will be dry and cooler for Wed through Fri, with Max
temps expected to be from 4 to 8 degrees below average.
Looking ahead to next weekend, it could be even cooler and possibly
wet. The global models have been advertising a large hemispheric
longwave adjustment. The cold trough over the eastpac is replaced
by a strong ridge along 150w longitude. This favors a return of
troughing to the conus along with wintry conditions there. The West
Coast will lie in the transition zone, where shortwaves topping the
eastpac ridge can amplify/dig as they drop south.
Ensemble and deterministic global model spread during this period
is unusually high, resulting in a low-confidence forecast blend
after Friday. The 12z Canadian and GFS runs are in lock-step,
bringing a cold storm system across socal Sat night, while the
00z/12z European model (ecmwf) deterministic solutions will have none of it, keeping
the wave shallow and inside. Given the sharpness of the forecast
ridge to the west, well into the Arctic on Thu, dismissing the more
aggressive 12z GFS/CMC solutions here next weekend would be folly.
Therefor we have some chance pops and low snow levels in the forecast
for Sat night.
The drier northwest flow pattern persists through the first half of next
week. This should give much of the state a period of limited precip
and cool weather.
200530z...areas of broken-overcast cigs 2000-4000 ft mean sea level will continue from
the mountains west to the coast through 18z Mon with some rise in
cigs to mostly 3500-5000 ft mean sea level after 18z Mon. Higher terrain,
especially in the mountains, will be obscured at times through Mon.
Local vis 2-4 mi will occur in fog and isolated -shra through Mon
morning. Desert areas will mostly have clouds above 6000 ft mean sea level and
seas have diminished to less than 10 feet in all areas this evening,
so the Small Craft Advisory will be allowed to expire at 10 PM.
Another system may create hazardous marine weather conditions late
Wednesday into Thursday, with northwest winds of 25-30 kt possible
and seas near or above 10 feet.
high surf advisory will be allowed to expire at 10 PM as the
westerly swell continues to diminish. High surf could return
Wednesday as a new west swell around 10 feet/14 seconds/280 degrees
will move into the coastal waters.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...high surf advisory until 10 PM PST this evening for Orange
County coastal areas-San Diego County coastal areas.
Pz...Small Craft Advisory until 10 PM PST this evening 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.