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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
138 PM PDT Wednesday Jul 29 2015

Synopsis...

Approaching high pressure will allow for southeasterly monsoonal
flow aloft through the Saturday. Thunderstorm potential will spread
northward across the area through Thursday. The possibility of
thunderstorms will linger until Saturday for the interior. By Monday
dry southwest winds will likely remove the thunderstorm threat.

&&

Short term (today-sat)...

Satellite and radar imagery this afternoon is showing a few
thunderstorms popping from eastern la County and points south and
east. So far just one cell that developed over the eastern san
Gabriels and moved northwestward across the eastern Antelope
Valley...producing a couple of lightning strikes. Storms seem to be
moving fairly quickly despite models showing weak southeast steering
winds...so likely will not have any flash flood issues today. Based
on satellite and radar trends...it looks like any thunderstorms that
develop today...will stayed confined to the la mountains and a.V.

Overall...it looks like tomorrow will be the most active with
regards to thunderstorms. Slight chance to chance threat of
thunderstorms will spread northwestward across the entire forecast
area tonight through tomorrow...reaching slo County by tomorrow
afternoon. The best chance for showers/T-storms for the
coastal/valley areas from la to sba County will be early tomorrow
morning through about noon...as a weak short-wave moves
northwestward across the area. The mountains and the a.V. Will have
the best chance of showers/T-storms...with 30-50% probability of precipitation tomorrow
afternoon and evening. The flash flood and debris flow threat for
the mountains and a.V. Looks greater tomorrow with precipitable waters peaking
around 1.8". However...models continue to show 15-20 knots southeast steering
winds...so decided to hold off on any flash flood watches...although
isolated flash flooding is possible.

Shower/T-storm activity should decrease tomorrow night into Friday
morning...especially for the coast/valley areas. In fact...only real
change made to the previous forecast was to decrease probability of precipitation for the
coastal/valley areas tomorrow evening and night. On Friday and
Saturday any thunderstorm activity will be confined to the
mountains...interior valleys...and desert...as southeast flow aloft shifts
to the south on Friday...then the SW on Saturday...resulting a
gradual drying trend.

Aside from the T-storm threat...only other significant forecast
uncertainties in the short-term are the coastal stratus tonight and
the maximum temperatures tomorrow. Visible satellite imagery shows low clouds
hanging tough at many beaches this afternoon...especially from
Ventura north. Most beaches should clear this afternoon. The low
cloud forecast tonight will be problematic with the middle-level
monsoon moisture moving in. Best chance for low clouds and fog
tonight and tomorrow morning will be on the central coast. Tomorrow
could end up being just as hot as today depending on how much middle
and high clouds there area. Overall...we are forecasting slightly
cooler conditions Thursday through Saturday as height/thickness
values fall somewhat...but with the added humidity...it won't feel
much cooler.

Long term (sun-wed)...

The thunderstorm threat will continue to diminish on Sunday and
Monday as dry SW flow aloft becomes more established...with a ridge
building over the western U.S. And a trough of low pressure off the
coast. On Sunday...a slight chance of T-storms will linger over the
eastern san Gabriels and eastern Antelope Valley. By
Monday...thunderstorms are no longer mentioned in the forecast. The
building ridge over the interior western U.S. Will result in a
gradual increase in height/thickness values over SW California
Sunday through Wednesday...bringing slight warmer conditions to the
region. At this point...it just looks like slightly above normal
temperatures.

&&

Aviation...29/1740z...

Marine layer around 014 this morning.

IFR/MVFR stratus should clear out of all airports by 19z. Moderate
confidence of similar IFR/LIFR cats at ksbp and ksmx when compared
to yesterday. Low confidence elsewhere as middle-level clouds will be
moving in from the south. Moderate confidence that this moisture
will bring thunderstorms to mountains and deserts this
afternoon/evening as well as Thursday. Low confidence for
thunderstorms elsewhere...with a 20 percent chance starting late
tonight over Los Angeles County...and starting elsewhere on
Thursday.

Klax...moderate confidence in VFR from 19z to 24z today. Ceilings near
012 should be near coastline...with a 30 percent chance of a ceiling
anytime today. Middle-level clouds will arrive this evening...bringing
a 20 percent chance of a shower or thunderstorm after 09z. Very low
confidence for MVFR/IFR ceilings tonight as middle-level clouds will
disrupt formation.

Kbur...high confidence in VFR from 19z to 06z today. There is a 20
percent chance of a ceilings after 06z tonight...but confidence is very
low as middle-level clouds will arrive this evening and disrupt
formation. There is a 20 percent chance of a shower or thunderstorm
after 09z.

&&

Marine...29/900 am.

High confidence in generally light winds for at least the next 36
hours. Fog with some visibilities near 1 mile will continue this
morning and may for again Thursday morning...especially north of
Point Conception. Moderate long period swell will continue to impact
the area through Thursday. Thunderstorms will be possible late
tonight through early Friday morning. The best chance will be
Thursday morning as a disturbance moves through the area from the
south.

&&

Lox watches/warnings/advisories...
high rip current risk (see laxsrflox).
Marine weather statement (see laxmwslox).
Special Weather Statement (see laxspslox).

&&

$$

Public...sukup
aviation/marine...kittell
synopsis...rm

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