Area Forecast Discussion
Issued by NWS San Diego, CA

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677
FXUS66 KSGX 192127
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
127 PM PST Sun Feb 19 2017

.SYNOPSIS...
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.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

NWS 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-NV 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 MPH 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 NW. That will be ending
overnight. However another string of disturbances aloft will brush
NW portions of the CWA 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 SE 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 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 NW 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.

&&

.AVIATION...
192056Z...Through 20/0900 UTC, isolated showers dissipating, with
clouds BKN-OVC clouds becoming SCT-BKN in the 2500-6000 ft msl
layer, mountain obscuration continuing, and otherwise vis P6SM
prevailing. 20/0900-1500 UTC, SCT-BKN cloud decks within the 5000-
15000 ft msl layer developing, with mountain obscuration of higher
slopes, a slight chance of isolated showers in Orange and San
Bernardino counties, and otherwise P6SM vis prevailing.

&&

.MARINE...
At 12 pm, buoy observations indicated 11 foot seas in the outer
waters and 8-10 foot seas in the inner waters. A Small Craft
Advisory continues through this evening for the large combined seas.
Seas should lower below 10 feet over the entire area by late this
evening, if not before that.

Another storm system may create more hazardous marine weather
conditions late Wednesday into Thursday, with northwest winds of 25-
30 kt possible and seas near or above 10 feet.

&&

.BEACHES...
Latest buoy and surf observations indicate that seas and surf
continue to trend down, with surf heights well below Warning levels,
and swell will continue to gradually lower through the day. Thus,
the High Surf Warning has been downgraded to a High Surf Advisory.
Nevertheless, high surf of 5-10 feet will continue today, with
strong rip currents as well, resulting in dangerous swimming
conditions.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...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.

&&

$$

PUBLIC...JAD
AVIATION/MARINE/BEACHES...Harrison



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