Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
142 PM PDT Thursday Jul 30 2015
warm and humid today with isolated to numerous showers and
thunderstorms over the area. Flash Flood Watch for
mountains/deserts/inland Empire through this evening. Drier...with
near normal high temperatures...this weekend into 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
At 1 PM PDT...water vapor satellite imagery displayed a broad
upper-level ridge stretching from the lower Mississippi Valley to
central Nevada...and a weak upper-level low around 200 miles south-southwest
of San Diego. Composite radar imagery showed scattered showers and
thunderstorms...mainly over the Riverside County and San
Bernardino County mountains. With high precipitable water
values...diurnal heating and cooling aloft...convective activity
is expected to strengthen and increase through this
afternoon...mainly over the inland valleys...mountains and
deserts. Given the middle and upper-level winds...most storms are
moving around 15 to 20 miles per hour. However...if any of these storms
become stationary or train over a location...there is a good
potential for flash flooding. The Flash Flood Watch for the
mountains...deserts and inland Empire remains in effect through 8
PM PDT this evening. A weak upper-level wave moving across the
region tonight will create the possibility of an isolated
shower/thunderstorm over the mountains and deserts.
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
302015z...coast/valleys...low clouds are persisting
over the coastal waters and hovering just off the coast. There is a
slight chance of showers and thunderstorms through this evening
across the entire region...though the mountains will be favored.
However...confidence on timing is low so will monitor for thunderstorms in the vicinity
inclusion in the tafs. Stratus with bases near 1500 feet mean sea level and tops
2000 feet mean sea level will push back inland after 31/0200z.
Mtns/deserts...a chance of showers and thunderstorms continues
through this evening across the mts and deserts. Thunderstorm bases
will generally be at or above 8000 feet mean sea level with tops to 40000 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.
115 PM...there is a slight chance of showers and
thunderstorms over the inner coastal waters through this evening.
Otherwise...no hazardous marine weather is expected through Sunday.
115 PM...the elevated surf will subside today as the
swell declines to around 2 feet at 14-15 second...but the risk of strong
rip currents and lightning will persist through the evening.
Therefore the beach hazards statement will continue through this
evening. The slow downward trend in the swell will continue through
Skywarn activation is requested for San Diego...western Riverside
and southwestern San Bernardino counties.
California...Flash Flood Watch until 8 PM PDT this evening for apple and
Lucerne valleys-Coachella Valley-Riverside County mountains-
San Bernardino County mountains-San Bernardino and
Riverside County valleys-the inland Empire-San Diego County
deserts-San Diego County mountains-San Gorgonio Pass near
Beach hazards statement until 8 PM PDT this evening for Orange
County coastal areas-San Diego County coastal areas.