Special Weather Statement, NWS Los Angeles, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
451 PM PDT Tue Aug 1 2017

.SYNOPSIS...
Monsoonal moisture will bring a chance of showers and
thunderstorms to the area through at least Wednesday night. It
will be warm and humid with mostly above normal temperatures this
week. The weekend looks to be dry and only slightly cooler.

&&

.SHORT TERM...(TDY-FRI)

It's a pretty quiet day so far with minimal convective activity
but still plenty of afternoon heating to go, especially where the
clouds have cleared across LA/Ventura Counties. At this point the
best threat of any thunderstorms would be over the mountains and
Antelope Valley, though a storm could drift off the mountains and
into the valleys. Coastal areas are likely safe from any
convection until later tonight when the next wave and batch of
moisture arrives.

Speaking of which, the NAM is the only model currently showing a
decent easterly wave moving through the area Wednesday. All
models show a pretty good slug of mid and upper level moisture
coming in later tonight and if the NAM is correct with that wave
then we could be in for a decent outbreak of showers and
thunderstorms by early Wednesday. But confidence not particularly
high with this and will keep pops where the are for now (20-30
percent).

Steering flow decreases by 10-15 kt Wednesday and precipitable
waters increase from their current levels of 1.25-1.5" to as much
as 2" Wednesday. So the potential for flash flooding Wednesday is
higher than today.

Temperatures will continue to be problematic with the cloud cover
though dewpoints will be higher so any decrease in ambient
temperature should be offset by the added humidity. Today
dewpoints were actually unchanged at lower elevations but much
higher in the mountains.

Thursday and Friday could turn out to be the warmest day of the
week (at least for coast/valleys) as there should be less cloud
cover but still weak onshore flow and a very warm air mass in
place. Still fairly unstable but any convection should be limited
to the mountains and deserts.

.LONG TERM...(SAT-TUE)

Drier southwest flow will develop over the weekend so no
thunderstorms expected through early next week. Cooling will be
most pronounced at the coast where an eddy circulation is expected
to spin up a marine lyr. Still seasonably warm inland but less
humid.

&&

.AVIATION...01/2350Z.

At 2310Z at KLAX, the marine layer was around 900 ft deep. The
top of the marine inversion was around 2300 ft with a temperature
of 31 degrees Celsius.

Expect only patchy low clouds overnight into Wed morning, confined
mainly to the Central Coast. Expect any cigs to be in the LIFR
category.

Otherwise, monsoonal moisture will bring a chance of showers and
a slight chance of thunderstorms to the entire region overnight
and Wed. Any thunderstorm could produce very heavy rainfall with
brief vsbys restrictions to 1 nm or less, and gusty erratic
winds.

KLAX and KBUR...Generally good confidence in the 00Z TAFS. VFR
conditions are expected through the period. However, there is a 20
to 30% chance of showers or thunderstorms through the period,
with vsbys possibly briefly down to 1 nm or less, and gusty
erratic winds.

&&

.MARINE...01/200 PM.

The SCA winds in 673/676 have not yet decreased, so the SCA for
those zones has been extended until 9 pm this evening.

A long-period southerly swell will continue across the coastal
waters through Thursday and possibly into Friday.

There is a slight chance of showers and thunderstorms across the
far southern portion of the coastal waters spreading northward
across PZZ655 later today...and into PZZ650 this evening. The
thunderstorm chances may spread to the Central Coast waters
Wednesday afternoon and evening.

&&

.BEACHES...01/200 PM.

There is a slight chance of showers and thunderstorms at the
beaches for the next couple of days, with deadly lightning the
primary concern. When thunder roars, go indoors. There is also a
continued threat of elevated surf and high risk of rip currents
through Thursday. Always swim near a lifeguard.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect until 10 PM PDT this evening for
      zones 37-51>54-88. (See LAXNPWLOX).
     Beach Hazards Statement in effect through Wednesday morning
      for zones 40-41-87. (See LAXCFWLOX).
     Flash Flood Watch in effect through Wednesday evening for
      zones 53-54-59. (See LAXFFALOX).
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
      for zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(FRI-TUE)
Elevated surf and strong rip currents will continue through the
week. There will be a slight chance of afternoon thunderstorms in
the mountains and Antelope Valley Friday.

&&

PUBLIC...MW
AVIATION...DB
MARINE...Sweet
BEACHES...Sweet
SYNOPSIS...B

weather.gov/losangeles

Special Weather Statement
National Weather Service OXNARD CA
511 PM PDT TUE AUG 1 2017

CAZ041-054-059-548-020130-
Los Angeles County San Gabriel Valley CA-Antelope Valley CA-
Los Angeles County Mountains excluding the Santa Monica Range CA-
Los Angeles County Coast including Downtown Los Angeles CA-
511 PM PDT TUE AUG 1 2017

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN LOS ANGELES COUNTY UNTIL
630 PM PDT...

At 500 PM PDT, Doppler radar was tracking a line of strong
thunderstorms approaching eastern Los Angeles County.
These storms were moving northwest at around 15 mph and will
become more widespread during the evening rush hour across
the Long Beach metro area extending northward into the
eastern San Gabriel Valley and eastern portions of the
Antelope Valley.

Dime size hail and wind gusts in excess of 40 mph will be possible
with these storms. In addition, frequent lightning and heavy downpours
can be expected with some of these storms, capable of producing localized
flash flooding. A Flash Flood Watch is in effect for the Los Angeles
County mountains and Antelope Valley.

Locations impacted include...
Long Beach...Lake Los Angeles...Wrightwood...Pomona...San Dimas...
Glendora...West Covina...Mount Wilson...Whittier...and Pearblossom.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3402 11773 3400 11779 3395 11779 3395 11797
      3390 11798 3384 11806 3376 11809 3374 11812
      3376 11820 3372 11818 3372 11820 3382 11830
      3482 11789 3482 11767 3429 11765
TIME...MOT...LOC 0001Z 239DEG 49KT 3427 11768

Gomberg/Bruno