Area Forecast Discussion
Issued by NWS San Diego, CA

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796
FXUS66 KSGX 160530
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PST Sun Jan 15 2017

.EVENING UPDATE...
Partly cloudy skies across the area this evening with some high
clouds drifting through the region. Clouds will thicken up west of
the mountains later tonight and Monday morning as the coastal eddy
spins up some renewed onshore flow and deepens the marine layer. An
upper level ridge will be slow to move across the region Monday
through Wednesday. This feature will bring a slight boost in daytime
temperatures and keep fair conditions across our region. The first
in a series of winter storms will develop late Wednesday night and
move across the area on Thursday. Forecaster confidence has gotten a
boost today with much better agreement in our medium range models.
Timing is still somewhat troubling but in general the brunt of the
first storm will come during the day Thursday, with the brunt of the
second, stronger and colder storm, likely occurring Friday afternoon
and evening. Have increased our pops and QPF during this timeframe.
No other significant changes to the forecast this evening.

$$

.SYNOPSIS...
A coastal eddy will drive clouds inland this evening and may
produce a few sprinkles before diminishing Monday morning. For
Monday through Wednesday...high pressure aloft over California and
surface high pressure over the Great Basin will bring fair, dry and
warmer weather, with weak offshore flow. A moist and unsettled flow
off the Pacific returns for the latter half of the week, with periods
of rain, gusty winds, and mountain snow.

&&

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

Low clouds returned to coastal areas today, thanks to a coastal eddy
swirling offshore. some thin, cirrus clouds were present as well,
thanks to a weak trough dropping south off the coast. Winds
have picked up along the coast from the S-SE and become gusty to
around 25 MPH in some areas, due to the eddy. Surface pressure
gradients were largely weak to the deserts, so inland, winds were
generally light except near the wind-prone passes.

The clouds will linger into the night and may leak a few light
sprinkles or showers, mainly along the foothills. This is based on
the latest hires models, so small POPS have been added for the
evening, but accumulations, if any, should be minimal.

Weak ridging over the EastPac early this week will shut-off the
moisture spigot over CA briefly. This will allow several days of
fair, dry, and warmer weather with daytime temperatures approaching
average for mid-January.

For the latter half of the week, the main belt of westerlies will
become reestablished at a lower latitude across the central and
EastPac. This will set the stage for an extended cool and wet period
over CA through the middle of next week as disturbances drive Pacific
moisture inland.

The first system is slated to arrive here on Thu, with a period of
moderate rain and mountain snow. The second is forecast to arrive
on Fri. This one looks to have better jet dynamics, and a PW near one
inch to work with. Overall precip should be heavier, with higher
convective rainfall rates possible.

The 12Z ECMWF/GFS operational runs have come into alignment with
timing and intensity of these events, which boosts confidence. So
POPS were raised to the likley category Thu/Fri. Both models then
indicate a reprieve of sorts next weekend, although the ECMWF is
tending to hold onto periods of light precip along and west of the
mts.

Confidence is lower early next week as the operational model
solutions diverge in timing of what may be the most substantial
event of them all. Once again, the ECMWF is the most aggressive
dynamically, developing a closed low along the West Coast, while the
GFS keeps the system more progressive and holds off closing off and
deepening the upper low until it moves east of CA. Despite the weaker
dynamics over SoCal, the GFS develops more precip on Mon as the PW
approaches 1.5 inch. Looks like we need a few more model runs to
build any confidence for amounts and timing next week, but by next
Sunday, count on having several more inches of rain under our belts,
with more snow to brighten the mountain tops.

&&

.AVIATION...
160530Z...Mostly BKN clouds with bases 2500-3500 ft MSL with tops to
6000 ft MSL will continue through 10Z from the coastal mountain
slopes west to the coast, then gradually dissipate 10Z-16Z Mon.
There is a chance that some CIGS could lower to below 2000 ft MSL.
Some mountain terrain will be obscured through 10Z. Most vis will
remain above 5 miles below the cloud bases. After 16Z Mon, skies
will be mostly clear.

&&

.MARINE...
No hazardous marine weather conditions are expected through
Wednesday. Another Pacific storm will bring rain, strong west to
northwest winds gusting 25 kt and large seas of 7-10 feet on
Thursday, mainly in the outer waters. These conditions would be
hazardous to small craft. The storm system that follows late Friday
into Saturday has the potential for winds reaching gale-force at
times in the inner and outer waters, in addition to combined seas
reaching near 14 ft.

&&

.BEACHES...
A moderate sized long-period west-northwest swell from around 285
degrees will peaking Monday at 5-6 ft/17-18 seconds, and lowering on
Tuesday. The swell will create surf of around 3-6 ft with local 7 ft
sets and strong rip currents on Monday. However, widespread high
surf is not expected.

From Thursday through next weekend, a couple short to moderate
period large west-northwest swells will impact the coast. The
highest surf will occur over the weekend when a very large short-
period WNW swell combines with a moderate sized WNW long-period
swell.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

Update...JMB
PUBLIC...JAD
AVIATION/MARINE/BEACHES...Maxwell



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