Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
945 PM PDT Thursday Jul 30 2015
Synopsis... thunderstorms are still possible over the mountains and
deserts on Friday and Saturday. Drier weather with near normal
temperatures Sunday through early next week as high pressure builds
aloft. Night/morning low clouds along the coast and breezy westerly
wind through mountain passes and along Desert Mountain slopes
through the period.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Thunderstorms wound down this evening with heavy rain and flash
flooding at several locations including Idyllwild...Calimesa and
Cherry Valley. Still a lot of moisture in the atmosphere this
evening with a precipitable water of 1.63" on the 00z nkx sounding...and a weak
inverted trough slides across the region tonight...so scattered
showers and thunderstorms may form at times in the mountains and deserts.
But boundary layer cooling will keep them from getting too strong or
..from previous discussion...
On Friday...flow will shift from southeast to more southerly...advecting
drier air into the region. This will create less of a flash flood
threat and lower the coverage of afternoon thunderstorms compared to
today. Models are trending drier for the weekend into early next
week as the aforementioned upper-level ridge builds to the southeast.
Therefore...have lowered probability of precipitation to slight chance for mountain and High
Desert areas on Saturday...with a dry forecast for Sunday through
Tuesday. The 30/1200 GFS brings moisture back into the region next
Wednesday as it pulls the high back north...while the European model (ecmwf)
maintains dry southwesterly flow aloft. A slight chance of afternoon
thunderstorms has been added to mountain and desert areas Wednesday
and Thursday. Building heights aloft will help raise high
temperatures to near normal...and maintain a shallow marine layer
with patchy night/morning low clouds/fog along the coast and coastal
valleys. Normal onshore pressure gradients will create breezy
westerly winds through mountain passes and along Desert Mountain
slopes in the afternoons/evenings through the period.
Aviation...310330...coast/valleys...low clouds are back along the
coast at most locations with ksna likely to follow. Convection debris
is slowly dissipating and mostly high clouds at or above 7000 feet
mean sea level or higher. Less convection expected on Friday as the airmass
dries some and will continue the trend into the weekend. Low marine
stratus will continue around the coastal areas overnight and into
the morning hours per local model guidance. Forecast confidence is
moderate to high.
Mtns/deserts...thunderstorms and associated east winds are causing
some local dust and wind forecast problems in the kpsp...ktrm and
nearby desert areas...including East San Diego County areas. This
should be over by 310600z. This will just leave some high clouds
around as precipitation ends overnight. Friday a few thunderstorms
may pop up again in the mountains and nearby deserts. Thunderstorm
bases will generally be at or above 8000 feet mean sea level with tops to 35000 feet mean sea level.
The main threats from these storms will be brief heavy rain and
frequent cloud-to-cloud and cloud-to-ground lightning.
Marine... 8 PM...showers and thunderstorms chances over the inner
coastal waters is ending. No hazardous marine weather is expected
Beaches... 8 PM...the elevated surf is subsiding and the risk of
thunderstorms all the way to the coast is decreasing as well.
Therefore the beach hazards statement will be allowed to expire. The
slow downward trend in the swell will continue through the weekend.
Skywarn... Skywarn activation is not requested. However weather
spotters are encouraged to report significant weather conditions.