Area Forecast Discussion
Issued by NWS San Diego, CA
FXUS66 KSGX 212038
Area Forecast Discussion
National Weather Service San Diego CA
138 PM PDT Fri Oct 21 2016
Hot and dry weather will continue this afternoon, with the hottest
conditions occurring over the inland valleys and lower deserts.
Temperatures will return to near average values by early next
week. The potential for showers and/or thunderstorms will arrive
Sunday and Monday over the entire region. Drier and sunnier
conditions are expected during the middle next week, as attention
turns towards the next potential weather maker along the CA coast
late Thursday into Saturday.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
At 130 PM, ridging remained in control over SoCal with
subsidence and offshore flow from the past two days having
produced a very dry atmosphere over the region. As such, skies
were clear and the marine layer inversion was absent.
For the rest of today and tonight, clears skies, weak subsidence
and low RH will keep conditions warm through the afternoon.
Highest temperatures should be found over the inland valleys and
lower deserts, where afternoon highs will be in the 90s. Along
the coast, a weak sea breeze will limit temperatures. Continued
low RH, clear skies and cooling below 800 mb should help
temperatures drop this evening and overnight. No significant
marine layer fog or stratus is expected through Saturday morning.
The ridge that dominated our weather for the past 3-4 days
will shift eastward over the weekend as a deep trough develops
off the West Coast. As this occurs moderate southwest flow will
develop and draw sub-tropical moisture northward over SoCal by
Sunday. Light showers or virga will be possible Sunday for all
areas, with light shower activity possible Monday as a sub 700 mb
dry layer becomes less pronounced. Isentropic lift and/or a weak
shortwave may help produce a small amount of elevated CAPE during
this period, potentially resulting in a few lightning strikes.
However, widespread thunderstorm activity is not expected at this
time. Precipitation totals should be light with this event, with
most locations seeing only a trace to 0.15 inches, local amounts
to 0.60 inches are possible in the mountains where evaporation
due to low level dry air should be less pronounced.
An amplified ridge is forecast to develop during the middle of
next week over the Four Corners. This will bring minor warming
Tuesday-Wednesday, but allow onshore flow to continue. After
Wednesday the forecast becomes more uncertain with good
continuity between the 12Z ECMWF and GFS deterministic runs
contradicted by spread in their respective ensembles. This makes
it difficult to determine the likely timing and impact of the
next progged storm system along the West Coast. At this point the
only thing that can be said with any confidence is that a
significant plume of sub-tropical to tropical moisture will
impact the CA coast between Thursday and Saturday of next week.
211941Z...Slight chance for dense fog within 5 sm of the coast
during the 22/0300-1500 UTC time-frame, possibly impacting KSAN,
KCRQ and KSNA. However, confidence in this occurring is low at the
moment. Otherwise, unrestricted vis through Saturday morning, with
SKC becoming FEW clouds AOA 20000 ft msl late tonight.
An upper level disturbance and surge of mid-level moisture will
create some showers and possibly some thunderstorms over the coastal
waters at times Sunday into Monday. Otherwise, no hazardous marine
weather is expected through Thursday.
Skywarn activation will not be needed today.