Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
235 am PDT Monday Jul 14 2014
easterly flow will bring middle and high clouds and widely scattered
mainly light showers today. If enough breaks occur in the clouds
this afternoon over the inland areas...thunderstorms are possible
over the mountains...deserts...and inland valleys. Residual moisture
could continue a chance of showers and thunderstorms for the San
Bernardino County mountain and desert areas for late tonight through
Tuesday afternoon. Dry weather is then expected for Wednesday into
next weekend. The marine layer and onshore flow will bring areas of
night and coastal low clouds and fog...extending into the western
valleys for the middle and latter part of the week. High pressure
should bring inland warming next weekend.
Discussion...for extreme southwestern California including
Orange...San Diego...western Riverside and southwestern San
Short term (today through wednesday)...
precipitable water values increased slightly during the day Sunday.
This mostly brought some middle level clouds Sunday afternoon as the
moisture was too high...mainly 400 mb to 600 mb...and the
instability too limited...to support deeper convective development.
GPS integrated precipitable water sensors show only slight increases
in precipitable water values overnight so far. This is consistent
with model forecasts that show a greater influx of moisture this
morning from a little before sunrise through late morning with
precipitable water values in the lower deserts increasing to a
little greater than 2 inches.
An inverted trough of low pressure continues to move westward into
Southern California with widely scattered middle level showers...mainly
virga...moving into far southwestern California. This is expected to
continue overnight. As the lower level moisture increases toward
morning...the potential for accumulating rainfall should increase
during the morning. But even so...the organization is limited...and
any rainfall amounts this morning should be spotty and light...but
could extend to the coast. If the band band of convection over far
southwestern Arizona holds together...it could reach mountain and
desert areas of San Diego County around sunrise and areas farther
north after sunrise with greater prospects for accumulating rainfall
from showers and isolated thunderstorms. This band appears to be
supported by an upper vorticity center generated by an earlier
convective complex over Sonora. This vorticity center appears to
have been captured best by the 00z GFS.
There is still the question of whether there will be enough clearing
of higher level moisture from the east this afternoon to allow
enough heating in the mountains for thunderstorm development.
Current trends do not appear all that favorable for that. But if
enough heating does occur...thunderstorms that do develop would have
the potential for locally heavy rainfall and flash flooding. Higher
resolution models continue to show surface convergence boundaries
this afternoon over the mountains of Riverside and San Diego
counties nearly stationary and toward the coastal side of the
mountains...just inland of the inland valleys. For the San
Bernardino County mountains...the onshore flow and sea breeze should
allow any thunderstorms that develop over the mountains to move into
the adjacent upper desert areas. Otherwise...scattered mainly light
showers are possible almost anywhere across far southwestern
California today. After this evening...drying begins to spread into
the area from the south. This should increasingly limit any shower
and thunderstorm development to the San Bernardino County mountain
and desert areas for late tonight into early Tuesday evening.
Continued drying is then expected into Wednesday.
With the cloud cover and increase in lower level moisture
today...inland high temperatures will cool...then begin to slowly
warm for Tuesday and Wednesday as drying occurs.
For coastal areas...satellite imagery shows widespread stratus over
over the coastal waters extending locally inland. In the past two
days...sea surface temperatures near the coast have cooled a few
degrees...perhaps resulting in conditions a little more favorable
for stratus development. Higher resolution models show minor
deepening of the marine layer tonight with a little greater
deepening for Tuesday night into Wednesday morning. This should
allow stratus to return to the western valleys by Wednesday
Long term (thursday through sunday)...
drier conditions will prevail through Friday with the marine layer
and onshore flow continuing night and morning low clouds and fog
into the western valleys. Models have trended slower with any return
of monsoonal moisture. A slow return is possible during the
weekend...but any more substantial return should be delayed past
Sunday. Inland areas will begin to warm as high pressure aloft
begins to strengthen for late in the weekend into next week.
140915z...non-uniform scattered-bkn010-015 at the coastal airports through
16z...perhaps lingering at the beaches into the afternoon. Marine
layer clouds will be disrupted at times by broken-ovc100 middle level
clouds in the easterly monsoonal flow aloft. Scattered rain showers/thunderstorms and rain
over the mountains may drift west over the coastal and valley zones
Tonight...sct010-015 near the coast through 04z becoming
broken-ovc010-015 through 08z and spreading 10-15sm inland through 14z
Tuesday. Isolated evening thunderstorms becoming less widespread after
200 am...no hazardous marine weather conditions expected through
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.