Flash Flood in California, May 29, 2019

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
201 PM PDT Wed May 29 2019

.SYNOPSIS...29/1218 PM.

Mostly sunny skies will cover the area today with temperatures
a few degrees warmer than earlier this week. There will be a
slight chance of thunderstorms over the interior mountains this
afternoon and subsequent afternoons through the week. Overnight
and morning coastal marine layer clouds will also continue.

&&

.SHORT TERM (TDY-SAT)...29/148 PM.

Convection a little slower to start than expected but clouds now
finally starting to show some significant vertical development
over the mountains, at least across Ventura County. Still
expecting a pretty active afternoon and would not be surprised if
one or more of these storms causes some local flooding in the back
country as steering flow is very light, especially the western
ranges.

Not too much change in the overall pattern next few days and
really into early next week. The current trough over the west
coast will evolve into a semi-cutoff upper low over southern
California by Friday which will then move very little through at
least Monday. So while the low isn't particularly cold aloft it
will destabilize the air mass enough to create a threat of
afternoon thunderstorms over the mountains pretty much every day
for the next week. Models are slightly less excited about
tomorrow's thunderstorm prospects but ramp the instability back
up for Friday and Saturday.

Elsewhere, expecting the marine layer to expand tonight to cover
more of the coast/valleys south of Pt Conception at least by
sunrise Thursday and then continue with that theme into the
weekend leading to some cooling there after temps had bounced back
into the 80s in some of the valleys the last couple days.

.LONG TERM (SUN-WED)...29/158 PM.

Not much change in the pattern into next week as the upper low
will still be sitting pretty much right over us until at least
early Tuesday. However it will be weakening and
heights/thicknesses actually start climbing Monday. There's enough
moisture and instability around to justify convective chances over
the mountains through Tuesday, and with the flow shifting to
northeast as the upper low moves to our southeast there'd be some
concern for those storms to move over the the ridges and into the
coast and valley areas. A little too early to make that call but
something to keep in mind.

Otherwise expect similar marine layer coverage through early next
week. Temperatures expected to warm up inland with the higher
heights/thicknesses but a moderate onshore flow and the marine
layer will keep temps from warming up too much across
coast/valleys.

&&

.AVIATION...29/1823Z.

At 1719Z at KLAX, the marine layer was 1900 feet deep. The top of
the inversion was around 4000 feet with a temp of 16C.

Skies will be mostly clear on the Central Coast and in the Santa
Ynez and Salinas Valleys this afternoon. However, widespread low
clouds and patchy dense fog should return to these areas tonight
into Thursday morning, with mostly LIFR to VLIFR conds.

S of Pt Conception, widespread low clouds expected in all coastal
areas tonight, with MVFR to IFR conds. IFR cigs should spread
into most valley areas late tonight.

KLAX...Moderate to high confidence in the 18z TAF. There is a 20%
chance that cigs could arrive as early as 03Z this evening. There
is a 20% chance that cigs tonight will be in the IFR category, at
least initially. There is a 20 percent chance of east winds of 7
knots or more late tonight into Thursday morning.

KBUR...High confidence in the 18Z TAF through early tonight, with
clear skies and VFR conds expected. There is a 20-30% chance that
skies will remain clear tonight and conds will remain VFR.

&&

.MARINE...29/1254 PM.

For the outer waters, high confidence in forecast. NW winds will
remain at Small Craft Advisory (SCA) levels much of the time thru
Thu evening, then conds should remain below SCA levels thru Sun.

For the inner waters north of Pt. Sal, moderate confidence in
forecast. SCA conds are expected this afternoon and evening, but
there is a 30% chance winds will remain below SCA levels. After
this evening, there is a 30% chance of SCA winds Thu afternoon
and evening, then conds should remain below SCA levels thru Sun.

For the inner waters south of Pt. Conception, moderate to high
confidence in forecast. SCA conds are not expected thru Sun.
However, there is a 20-30% chance of SCA level winds across
western portions of the SBA Channel this afternoon and evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
      for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PDT Thursday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

Showers and thunderstorms are possible over the mountains each day
through Tuesday with a possibility of heavy rainfall and isolated
flash flooding.

&&

PUBLIC...MW
AVIATION...Sweet/DB
MARINE...Sweet
SYNOPSIS...Stewart

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