Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
833 PM PDT Monday Sep 15 2014
moisture from Hurricane Odile will spread northward overnight
through Wednesday...elevating the chance for showers and
thunderstorms across Southern California. Some of the storms will
produce heavy rainfall and there will be a threat of flash
flooding...especially afternoons and evenings near the mountains.
There will not be much relief from the heat and humidity until
Thursday when a trough of low pressure brings cooling and drying
from the northwest. Isolated showers and thunderstorms are still
possible into Friday over the mountains and deserts...then partly
cloudy weather with seasonal temperatures next weekend.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
No major changes to the forecast. Slightly higher daytime
temperatures for coastal areas Tue/Wed.
It was another hot day across the region with many sites tying or
setting record high minimums. Even a few record maximum temperatures
were tied/set. The nearshore buoys all continue to indicate sea
temperatures in the lower to middle 70s. This will likely result in more
record high minimums over the next few days. At 8 PM PDT...
temperatures were still in the 80s and 90s. The 00z Miramar sounding
still had northwest flow around 10 knots below 5k feet...but aloft...a deeper
layer of 10-20 knots easterly winds had developed up through 22k feet. Precipitable water
was just below 1.5 inch. At 7 PM PDT...the Gulf surge was underway
as the wind at Yuma turned southerly 15kt with a large dewpoint jump.
Tropical cyclone Odile is indeed weakening this evening as it drifts
northward along the Baja California peninsula. The storm has fallen below
hurricane strength and will continue to wind down through Tuesday as it
navigates the mountains of the Baja California peninsula on a northwest course...then
turns east into the northern Gulf of California Wednesday. Ahead of this
storm...a surge of low-level moisture is forecast to ride northward
through the lower Colorado River valley. The surge may generate southeast
winds of 15-20kt and result in low clouds into the Coachella Valley
by morning. Depending on the depth of the moisture...it may be able
to fuel thunderstorm development along and east of the mountains on
Tuesday. Deeper moisture will follow into the middle-levels on Wednesday when the
chance of thunderstorms looks greatest.
The high pressure ridge aloft over the region will build northward
into the Great Basin through Wednesday as a longwave trough swings NE off
the Pacific toward central California. The models have been indicating a
slight increase in the offshore gradient over the region Tue/Wed.
This will have implications for coastal areas if it materializes
with some additional warming spreading westward. The inland areas
may have peaked and will stay warm with increasing humidity...and
overnight minimums will remain well above average.
Forecast confidence is lower for the next couple of days as Odile
gets closer. Indirect circulations around the storm may influence
our weather in ways not properly modeled. For example surface
pressure...moisture...and Omega fields...mesoscale convective system development...or
unexpected warming in some areas. The 18z nam12 guidance did
indicate some warming along the coast Tuesday/Wednesday with increased
offshore flow...however it also had increasing instability and
rainfall over coastal areas on Thursday morning. The rain is not expected
or indicated on other global models...but with the large amount of
moisture from an anomalous feature like Odile entering
the domain...and an approaching upper trough...it cannot be ruled
For now we are expecting thunderstorms to become more numerous
Tuesday...and peak on Wednesday before drier air sweeps in from the northwest with
the approaching Pacific trough. Ahead of the trough...steering
currents are moderate easterly...so expect some activity west of the
mountains by late Thursday into Friday...the trough should clear any shower
threat from the coast...but the mountains/deserts may still have enough
moisture and instability to get scattered showers/thunderstorms through Friday
afternoon. The marine layer will deepen and cool areas west of the
mountains into the weekend.
160300z...there is a small chance that low clouds and fog could form
within 5 sm of the coast between 09z and 15z...but confidence is too
low to include in the tafs. Otherwise...mostly clear with
unrestricted visible through Tuesday morning.
Between 18z Tuesday and 03z Wednesday...sct-bkn clouds layered from 8000 feet
mean sea level to 35000 feet with isolated thunderstorms/showers over the
mountains...deserts...eastern San Diego valleys and the inland
Empire. Kont...kpsp and ktrm may be impacted...but confidence is low.
800 PM...no hazardous marine weather expected through Saturday.
Skywarn activation may be needed on Tuesday afternoon and will
likely be needed on Wednesday.
California...heat advisory until 7 PM PDT Tuesday for the Orange County
coastal areas...San Bernardino and Riverside County
valleys-the inland Empire...San Diego County valleys...
Santa Ana Mountains and foothills.