Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
430 PM PDT Wednesday Jul 1 2015
..updated aviation discussion...
The monsoonal moisture will bring a chance of showers and
thunderstorms...mainly in the mountains and deserts...into Friday.
Temperatures will remain normal through Friday. But the approach of
a low system by Saturday will deepen the overnight marine layer and
cool coastal areas into next week.
Short term (today-sat)...lots of clouds but not much else so far in
our area. Radar and satellite show some showers and storms
associated with a vorticity maximum moving northwest through the southern San
Joaquin Valley and just clipping the far north portion of slo
County. Elsewhere, just random sprinkles with no reports of
measurable rain yet. Temperatures running cooler due to the cloud cover
with changes from yesterday running anywhere from just a couple
degrees at the coast to as much as 20 degrees inland. The Winner is
Saddleback Butte which is 26 degrees cooler than this time Tuesday.
The southeast flow aloft will leave the door open for moisture to
come through the area through Friday, however models show only one
last push tonight into early Thursday associated with some upper
level energy moving in from southern Arizona before the air mass starts to dry
out for the end of the week. Small probability of precipitation were added overnight for all
areas to account for the possibility of more sprinkles or light
showers with this next (and likely last) push, though again it's
likely most areas will just see a few drops and not actually
measure. Models show just a little bit of instability aloft so
there's a non-zero chance of a very isolated storm tonight with that
moisture, but not high enough to include in the forecast. Mostly
just a lot clouds and maybe a sprinkle or two. Another warm and
humid night with overnight lows well above normal.
As mentioned, the air mass is expected to slowly dry out Thursday
into Friday with precipitable waters dropping from 1.5-2" currently to around an
inch or lower Thursday afternoon and Friday. As a result, Thursday
and Friday should be much sunnier with just some clouds and a small
chance of afternoon convection over the mountains and Antelope Valley.
Temperatures should rebound most of what was lost today due to cloud cover,
though coastal areas probably won't gain as much ground with the
onshore flow returning.
Long term (sun-wed)...weather returning to more typical early
Summer conditions as a trough sets up across northern California and the 4
corners high shifts east. By middle week there is a fair amount of
model disagreement with the European model (ecmwf) now showing the trough deepening
across the West Coast while the the GFS shows the ridge expanding
west again with a significant warming trend. This is a reversal of
roles from yesterday when the ec was the much warmer model for the
latter half of next week. Either way, there's no indication of
monsoon flow returning next week.
At 2300z...the marine inversion at klax was based at 650 feet. The
top of the inversion was 2600 feet with a temperature of 26 degrees.
Overall...low to moderate confidence in the 18z taf package. All taf
sites will likely remain VFR for most of the next 24+ hours...but
there is a chance for IFR/LIFR conditions for coastal sites tonight.
The best chance for IFR/LIFR conditions are from 10-14z...but the
formation of the stratus deck will likely be spotty and random due
to the middle and high-level clouds. Isolated showers and sprinkles
will continue through Thursday morning. There is a very slight
chance (less than 10%) of thunderstorms at kpmd or kwjf this evening.
Klax...moderate confidence in 18z taf. There is a 30 percent chance
of IFR/LIFR ceilings tonight from 10-14z.
Kbur...moderate to high confidence in 18z taf. There is a 10 percent
chance of IFR/LIFR ceilings tonight from 10-14z.
High confidence that winds and seas will remain below Small Craft
Advisory (sca) criteria through the early afternoon on Thursday.
There is a chance for some local Small Craft Advisory conditions around Point
Conception and in the vicinity of The Channel islands late Thursday
afternoon and Thursday night...but likely not widespread enough to
issue a Small Craft Advisory. There is a better chance for Small Craft Advisory conditions by Friday
afternoon and Friday night for the areas mentioned above.
The threat of thunderstorms has been removed from the forecast for
the remainder of today...but there could still be some isolated
sprinkles and showers.