Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
842 am PDT Friday Sep 19 2014
a low pressure trough moving slowly through central to Southern
California will continue to bring cooler weather and night and
morning stratus into the coast and valleys sections through Sunday.
Isolated thunderstorms may form over the mountains Saturday
afternoon due to a possible increase in moisture from the south. A
warming trend and shallower marine layer is expected for next Monday
through Wednesday as high pressure aloft expands into the region.
Then...another trough moving inland along the West Coast may bring
cooling...a deeper marine layer...and increasing onshore flow.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Visible satellite imagery shows a very deep marine layer this
morning...with overcast-to-broken clouds deep into the valleys...and
even into the Cajon Pass and san gorgonio/Banning pass. It appears
that there are multiple cloud layers...with some areas experiencing
a rather thick cloud layer resulting in some drizzle. In other
locations...the cloud layer is somewhat thin with some breaks in
between the clouds. The 12z Miramar sounding shows a weak marine
layer inversion at around 3500 feet...and recent pilot reports
indicate that tops have reached 4000 feet. Thus...the marine layer
is around 4000 feet deep this morning. There should be decent
clearing today due to the weak inversion and diminishing onshore
flow...with mostly sunny to partly clouds skies west of the
mountains late this morning through this afternoon. Cooling will
continue today as well...as water vapor satellite shows a southwest
to northeast oriented trough continuing to move south towards
Southern California from its current position over central
California. Day-time highs will likely be a few to several degrees
below normal for most areas. As the trough continues to move
south...a closed low will split out of it...and assume a position
just offshore of Point Conception late tonight. With weaker onshore
flow today...the stratus may come in slightly later this evening
than it did yesterday...but it should fill into the far inland
valleys again through early Saturday morning. Speaking of weakening
onshore flow...the onshore pressure gradients are down to 2.9
mb...whereas they were 4.8 mb at this time 24 hours ago.
Thus...winds have diminished somewhat in the mountains and
deserts...with mainly Guss in the 20s to 30s...so the Wind Advisory
for the Coachella Valley was allowed to expire at 6 am.
The low will move inland during the day Saturday...and the south
flow on the eastern edge of the circulation May Draw up enough
moisture to bring an afternoon thunderstorm or two to the mountains
and high deserts. However...it is a pretty slim chance...as the bulk
of the moisture remains to our east. The nam12 is particularly dry
for our area on Saturday. The low will be into Nevada by Sunday
morning...and some small rise in 850 mb temperatures may bring
slight warming that day...although day-time highs will still mostly
be below normal. Night and morning stratus will continue to move
into the valleys.
A ridge to the south is likely to expand into the region Monday
through Wednesday...resulting in a continued warming trend...with
day-time high temperatures reaching a few to several degrees above
normal. The marine layer will become much shallower as well...with
night and morning stratus/fog into the coastal sections and maybe
the western valleys at times. All models then show a deep trough
moving in along the West Coast Thursday into Friday which would
bring another cooling trend...with a deeper marine layer and gusty
onshore flow. Right now...models do not show US getting
precipitation from this system.
191513z...coast/valleys...marine stratus with multiple layers between
1500 and 3400 feet and tops 3500-4000 feet mean sea level will become scattered to
locally broken with unrestricted visible after 17z through 19z. Areas along
the foothills near the coastal slopes may be the last to clear. The
stratus layer will reform near the coast and spread rapidly inland
again after 00z through 06z this evening with bases 2000-2500 feet and
tops around 3000 feet.
Mountains/deserts...lower coastal slopes obscured below 4500 feet
through 20z...then ceilings will become scattered-locally broken for the
remainder of the day with local terrain obscuration into this
afternoon. Above 4000 feet and on the desert slopes...skies will be
clear and visible unrestricted through Sat morning.
830 am...no hazardous marine weather is expected through Tuesday.
from 235 am discussion...south-southwest swell will continue to
lower today. Local surf of 3 to 5 feet will occur on southwest
facing beaches along with strong rip currents.
spotter activation will not be needed today.