Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 042129
Area Forecast Discussion
National Weather Service San Diego CA
128 PM PST Sun Dec 4 2016
The sunny and mild weather today will give way to increasing clouds
and cooler conditions on Monday as winds turn back onshore and the
marine layer builds. The moist layer may get deep enough for a few
light showers or some drizzle on Tuesday. Warming begins on
Wednesday and continues through the end of the week as winds turn
back offshore under fair skies.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
It warmed up nicely this afternoon under the unfiltered December sun
with most areas west of the mts climbing into the 70s. Winds were
light as well which helped to make it feel even warmer. AT 1 PM PST
peak wind reports were under 20 MPH and had turned westerly. The sfc
pressure gradient was still offshore about 3 MBS from SW NV to
KSAN, but weakly onshore to the east.
After some temperatures in the 30s this morning, tonight will likley
not be as cold most areas as dewpoints begin to recover and some
higher clouds move over the region.
The prevailing offshore pattern is turning as the broad high
pressure area over the Great Basin collapses ahead of a sagging
Polar trough over the PacNW. A shortwave embedded in the trough
should guide it east across the Great Plains this week, but it will
be driving increasing onshore flow across SoCal through Tue before
cold sfc high pressure turns our flow back offshore later in the
week. Dry and mild Thu through Sun.
Clouds/Precip...High res model guidance suggests a return of coastal
low clouds and some fog by early Monday morning as a coastal eddy
develops. As the marine layer builds, look for more extensive low
cloud cover, and there may even be a few light showers or some
patchy drizzle west of the mts on Tue/Tue night. At this time,
precip does not look significant.
Wind...The surface high pressure center building south over the
Rockies this week is forecast to reach 1044 MBS or more by 12Z Thu
over Wyoming as arctic air surges south, east of the Rockies. The
ridge position (aligning with the cold arctic air east of the
Rockies) will help keep the sfc gradient farther SW more moderate.
With little additional support aloft, and the current forecast
position of the sfc high, offshore winds do not look to be near the
strength of the event late last week.
Temperatures...Coldest days Tue/Wed this week with max temps from 2
to 8 degrees F below average. Warmest days Thu/Fri with temps just
a few degrees F above average.
Looking ahead to next weekend...Not much discrepancy in the 500 MB
pattern between the 12Z GFS/ECMWF runs with largely a zonal flow
aloft. GEFSensemble looks pretty flat as well. This would mean fair
and mild weather. The outlier 12Z GEM run has a sharp trough
swinging through the SW for more wind and possible light precip. For
now, moderate confidence next weekend will be fair and dry.
042100Z...Coast/valleys...Mostly clear skies and unrestricted vis
will continue through late tonight. Stratus/fog could return to the
immediate coast sometime in the 11Z-15Z Mon time frame and could
impact KSAN and KCRQ and possibly KSNA. Timing and heights of
stratus are low confidence, but ceilings could be 600 ft MSL or less
before lifting rapidly by late morning Monday. Visibilities of less
than 3 miles are also possible along the coast early Monday morning,
with a slight chance of dense fog with vis 1/4 mile or less, most
likely over higher terrain. Timing of stratus clearing Mon is still
uncertain, with the possibility of SCT-BKN conditions along the
coast into Monday afternoon.
Mountains/Deserts...Mostly clear skies and unrestricted vis will
continue through Monday.
Wind gusts may exceed 20 knots near San Clemente Island late Tuesday
or Tuesday night. Otherwise, no hazardous marine weather is expected
Much weaker winds today are turning onshore this afternoon.
Midday...RH remained in the teens away from the immediate coast, but
should recover considerably later in the day, with continued
improvement through Tuesday as onshore flow strengthens. Another
round of gusty offshore winds and very dry conditions will develop
Wednesday morning and continue through Thursday, weakening Friday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.