Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 230522 CCA
Area Forecast Discussion
National Weather Service San Diego CA
930 PM PST Wed Feb 22 2017
Low pressure aloft will move east towards the Rockies, with fair but
very cool weather behind the low through Friday. Locally gusty winds
will occur in the mountains and deserts tonight through early
Thursday. Clouds will gradually increase Saturday with a chance of
rain Sunday as a storm system moves down from the north. A second
system will likely interact with more moisture Monday and bring more
significant rain with mountain snow. Fair weather will return by
late Tuesday and Wednesday.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
A few showers moved through the San Bernardino County Mountains and
the Inland Empire late this afternoon and early this evening, with
most precipitation amounts less than 0.10". A few flurries fell
above about 6500 feet in the SBD County Mtns. Partly to mostly
cloudy conditions prevailed at mid-evening. Due to the trough,
onshore pressure gradients were rather strong but weakening
slightly, with 6.6 MB onshore flow from San Diego to Thermal, so
wind gusts were in the 40s in parts of the mountains and deserts,
down a little from earlier today when Volcan Mountain in San Diego
County and Whitewater along I-10 in San Gorgonio Pass peaked at 61
and 60 MPH respectively. Tonight will be rather chilly, especially
as some of the clouds will decrease as well as the wind, so colder
valleys will have lows in the mid to upper 30s. Highs Thursday will
only be around 60 at lower elevations west of the mountains and in
the 60s in the lower deserts. Some frost could occur Thursday night
due to the cold air mass, with 850 MB temps in the 0-3 deg C range,
mostly clear skies and light winds. Only slight warming will occur
Friday and Saturday during the day, though the nights could get
progressively warmer due to increasing cloud cover.
Models have trended weaker with the first system for Sunday, mainly
because the subtropical moisture fetch to the south of that system
will not arrive until Monday. Thus, it appears we will just have
scattered showers Sunday, though a few inches of snow could fall in
the mountains due to a fairly cool air mass bringing the snow level
as low as 5000 feet. More substantial rainfall will occur Monday as
the moderately strong moisture fetch from the WSW will arrive. GFS
has around 0.9 inches of TPW with near saturation to a little over
700 MB. Some areas could get an inch of rain west of the mountains,
with locally higher amounts mainly on west-facing slopes due to the
more westerly versus southerly orientation of the flow, though the
flow will not be all that stronger until 700 MB versus 850 MB, so
orographic forcing of coastal-slope precip will not be all that
great. Moderate amounts of snow are likely in the mountains as the
snow level could be fairly low again, possibly below 5000 feet at
times. Current model guidance suggests the low will move to the east
Tuesday with drying aloft, so fair but continued cool weather is
likely late Tuesday through Wednesday under weakening cyclonic flow.
Surface offshore flow will be possible sometime around the middle of
next week after the low passes east.
220500Z...Coasts/Valleys...FEW/SCT clouds between 2500 and 5000 ft
msl will continue to clear through 10Z. After 10z, predominantly
SKC, unrestricted vis, and light winds will prevail though 06z
Friday. No impacts are expected at the TAF sites through 06Z Friday.
Mountains/Deserts...W/NW surface wind gusts of 30-55 kt will persist
through Thursday morning over the ridges and along the desert slopes
of the mountains. Mountain wave activity will also produce areas of
moderate to strong UDDFS and LLWS over and E of the mountains. Winds
will slowly diminish after 20z Thursday. Wind impacts at KPSP and
KTRM should diminish after 12z with predominantly SKC and
unrestricted vis Thursday afternoon.
NW winds gusting 20-30 kt and combined seas of 7-12 ft will continue
over the coastal waters through Thursday night. These conditions
will produce hazardous boating conditions, and a Small Craft
Advisory remains in effect through Thursday night. Combined seas and
winds will diminish some Friday and Saturday before another period
of unsettled weather arrives early next week. Additional choppy seas
and gusty winds are possible Sunday into Tuesday.
A westerly swell from 275-285 degrees will create high surf along
westerly-facing beaches through Thursday night. This will result in
surf of 4-8 ft with local sets to 10 ft. A High Surf Advisory
remains in effect through Thursday night for dangerous surf and
strong rip currents.
SKYWARN activation will not be needed through Saturday.
CA...Wind Advisory until 10 AM PST Thursday for Apple and Lucerne
Valleys-Riverside County Mountains-San Bernardino County
Mountains-San Diego County Deserts-San Diego County
Mountains-San Gorgonio Pass Near Banning.
High Surf Advisory until 2 AM PST Friday for Orange County
Coastal Areas-San Diego County Coastal Areas.
PZ...Small Craft Advisory until 2 AM PST Friday 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.