Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 270406
AREA FORECAST DISCUSSION
National Weather Service San Diego CA
900 PM PDT THU MAY 26 2016
A low pressure trough over Southern California will keep the marine
layer fairly deep through the holiday weekend. Temperatures will
remain below average for late May. Warmer next week with a shallower
marine layer as high pressure builds over the West.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
A solid deck of low clouds was moving into coastal areas of southern
San Diego County at 830 pm, but farther north in Orange County the
skies were mostly clear. Clouds will spread inland overnight and the
marine layer may be deep enough for patchy drizzle or mist late
tonight. The WRF is advertising 0.01" in coastal San Diego through
early Friday morning. If drizzle does in fact develop, the coverage
will be less widespread than it was Thursday morning.
There may be some changes to the forecast over the weekend. Both the
GFS and ECMWF model trends the last two days are a little deeper
with the trough that will settle over Southern California. On Friday
there will be enough midlevel moisture for cumulus to form over the
mountains in the afternoon with modest vertical growth. Then on
Saturday and Sunday an influx of greater midlevel moisture and
increasing instability could trigger isolated afternoon convection
over the mountains and high deserts. The best chances will be on
Sunday when a weak vort max rounds the base of the trough coincident
with a -15C 500 mb cold core. If the 00Z ECMWF continues this trend
of greater instability and moisture like the GFS, a chance of
afternoon thunderstorms may need to be added to the weekend
forecast. Coastal and Valley areas will likely remain dry with
marine layer clouds each night and morning with midday clearing.
Long range outlook: On Monday and Tuesday the upper trough is
forecast to move very slowly eastward over Arizona, and a high
amplitude ridge will build over the West Coast. This pattern will
bring warmer weather and a shallower marine layer next Wednesday
through Friday. Temperatures during this period will actually be
ABOVE (!) average in the Valley, Mountain and Desert zones. Only the
areas near the coast will still be near their averages due to the
shallow marine layer.
270310Z...Coast/Valleys...Areas of low clouds SCT-BKN with bases
around 2000 ft MSL and tops near 4000 ft MSL along the beaches this
evening. Expect low clouds to increase in coverage and spread 5-10
miles inland overnight, impacting coastal TAF sites after 04Z and
reaching the coastal slopes after 10Z. Reduced vis will occur where
terrain and clouds intersect, obscuring higher terrain. Risk of low
cloud bases tonight down to around 1500 feet MSL is moderate. Expect
clearing to the coast between 17Z and 20Z Fri.
Mountains/Deserts...West winds with gusts to 40 knots at times will
produce weak to moderate up/down drafts over and East of the
mountains through this evening.
810 PM...Wind gusts near 20 knots this evening over the outer
waters. Otherwise, no hazardous marine conditions are expected
Skywarn activation is not needed.