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000
FXUS66 KLOX 060251
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
751 PM PDT Sun Apr 5 2020

.SYNOPSIS...05/207 PM.

Significant rain and mountain snow will move across the region
through Monday with lingering showers possible through Thursday.
There is a slight chance of thunderstorms tonight through Tuesday
including across the coastal waters and some snow will fall on the
major passes by Tuesday morning. Dry and warmer weather can then
be expected Friday through Sunday.

&&

.SHORT TERM (SUN-WED)...05/750 PM.

***UPDATE***

At 730 pm a prefrontal band of rain was over eastern VTA county
and the main frontal band was over SLO county. The 1003 MB SFC
low was 60 miles SW of Eureka. An unseasonably cold 536 DM upper
low was 250 miles west of Monterey.

Steady light to moderate rain covers SLO and SBA counties. VTA has
some scattered light rain. As was expected the rainfall totals
over the coastal slopes and foothills are over performing. Most
of the csts/vlys of SLO and SBA county have seen a quarter inch to
a half inch xcp only a tenth of less in and around the city of
SBA. The coastal slopes on the other hand have so far received 1
to inches of rain with local amounts near three inches. In a stark
example of this: The beaches near SBA city college so far have .01
of an inch; A little north of the Old SBA mission about a quarter
inch of rain has fallen; further north half way the Santa Ynez
range .90 inches has fallen and at the top of the Santa Ynez 1.44
inches has fallen.

The heaviest rain is currently over SLO and SBA counties; by mid
morning over VTA county. The heaviest rain will enter LA county a
few hours before dawn. The steady rain

The rain will turn to showers just before dawn across SLO and nrn
SBA counties. The heaviest rain will move over southern SBA
county by mid evening, then into VTA county around midnight. The
steady rain will exit LA county around noon.

There is enough low level lift, jet dynamics and upper level
diffluence to create a slight chc of TSTMs just ahead of and with
the front. The TSTM threat will then continue in the unstable air
behind the front.

***From Previous Discussion***

We remain on track for significant and unseasonable amounts of pcpn
over the next few days. In fact, there is the potential for many
areas to recieve rainfall far exceeding what we normally see for the
entire month of April, including downtown L.A. where the normal
April rainfall is 0.91 inch. This should help to go a long way to
bringing seasonal rainfall totals for many areas closer to normal or
possibly even above normal in some locations.

Rainfall totals through Tue are expected to generally range from
1.00-2.00 inches for the coastal/valley areas with 1.50-3.00 inches
in the foothills and mountains. Local rain totals to 4.00 inches or
more will be possible in some mountain areas. Rainfall rates of 0.25-
0.50 inches/hour are expected with local rates up to 0.75 inches per
hour. With any thunderstorm activity, hourly rainfall rates could
even be higher. With these rainfall totals, there will likely be
widespread nuisance urban flooding as well as the potential for
minor mud and debris flows near the recent burn areas.

Additional rainfall Tue night and Wed should be around 0.10 to
0.33 inch or so for the coast and vlys, and 0.25 to 0.75 inch in
the mtns, except possibly up to 1.25 inches in the eastern San
Gabriel mtns.

Snow levels will continue near 6000 feet through Mon morning then
drop to 5000-5500 feet Monday afternoon, and to 4000-4500 feet Mon
night and Tue morning. There will likely be significant snow
accumulations, especially above 6000 feet. With the heavy snow and
strong gusty winds expected, a WINTER STORM WARNING is in effect for
the Ventura/LA county mountains from this evening through Tuesday
afternoon. Wind gusts up to 45 to 55 mph are expected in the high
mountains tonight and Mon. Snow accumulations of 15 to 30 inches
or more will be possible above 6000 feet, and about 4 to 12
inches between 4500 and 6000 feet. In addition, lower snow levels
late Mon night into Tue morning will likely result in travel
delays along Interstate 5 over the Grapevine. Please see the
latest Winter Weather Message (LAXWSWLOX) for further details.

More snow is expected above 5000 to 5500 feet Tue night and Wed,
with 3 to 6 inches or more possible especially above 5500 feet.
This should prolong wintry travel conditions in the higher mtn
elevations thru mid week.

Needless to say, temperatures will remain significantly below normal
in most areas Mon thru Wed. Highs for the coast and vlys should
reach only into the mid 50s to lower 60s.

.LONG TERM (THU-SUN)...05/204 PM.

The EC and GFS continue to differ on the speed of the upper low
moving E and out of the area. The EC stalls the upper low near Las
Vegas thru Thu before tracking slowly SE across AZ Thu night and
Fri. The GFS continues to be more progressive and moves it well E
and into New Mexico on Thu then starts to build upper level ridging
into srn CA by Fri. The NBM continues to keep some POPs over the
area thru Thu reflecting a lean toward the EC solution, so a slight
chance to chance of showers and mountain snow showers will linger
Thu, mainly for VTU/L.A. Counties. However, there is only moderate
confidence in the pcpn forecast for Thu. The EC does keep some
showers over the region Thu night but will lean more dry by then.
Otherwise, dry and warmer weather is expected Fri thru Sun as some
mainly flat upper level ridging moves into area.

Temps will continue to be a few degrees below normal Thu, then warm
to slightly below normal for many areas Fri, and near normal to
slightly above normal for Sat and Sun.

&&

.AVIATION...05/1748Z.

At 1539Z, there was no marine inversion at KLAX. However, there
was a moist layer up to 5000 feet.

Overall, low to moderate confidence in 18Z TAFs. Steady rain
will spread over the region from northwest to southeast, but low
confidence in timing of rain and associated flight categories.
Cigs/vis will most likely be MVFR, but there is a 40% chance of
IFR conditions, especially in heavier rainfall. There will be a
slight chance of thunderstorms for all sites this evening through
Monday morning.

KLAX...Low to moderate confidence in 18Z TAF. MVFR cigs
continuing into the early afternoon with occasional IFR conditions
afterward. Steady rain will most likely develop in the evening,
but low confidence in timing (could be +/- 2 hours of current
forecast). Southeast winds in excess of 10 kt are expected after
10z.

KBUR...Low to moderate confidence in 18Z TAF. MVFR cigs
continuing into the early afternoon with occasional IFR conditions
afterward. Steady rain will most likely develop in the evening,
but low confidence in timing (could be +/- 2 hours of current
forecast).

&&

.MARINE...05/937 AM.

Overall, moderate to high confidence in current forecast. A storm
system moving south along the California coast will push a cold
front into the region today, bringing gusty south winds. High
confidence in Small Craft Advisory (SCA) level winds developing
this morning into this afternoon along the waters along the
Central Coast southward to San Nicolas Island. Less confidence in
exact timing, but SCA level winds will generally develop from
north to south, potentially reaching Point Conception around noon.
The cold front will move quickly, so winds will likely drop off
below SCA level pretty quickly late tonight from north to south.
There is a 60% chance of SCA level winds developing within the
Santa Barbara Channel this afternoon and evening. By late
tonight, moderate confidence in SCA level winds reaching the
waters inside the Southern California Bight lasting through Monday
late morning or early afternoon. These winds will likely produce
steep, short-period choppy seas today and into early Monday. For
all the coastal waters, thunderstorms will be possible from this
evening through Tuesday evening. Any thunderstorms will be capable
of producing brief heavy rain, small hail, rough seas, and
possibly waterspouts.

High confidence that winds and seas will remain below SCA level
from Monday afternoon through next week.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning in effect until 5 PM PDT Tuesday for
      zone 53. (See LAXWSWLOX).
     Winter Storm Warning in effect from 11 PM this evening to 5
      PM PDT Tuesday for zone 54. (See LAXWSWLOX).
PZ...Small Craft Advisory in effect until 11 PM PDT this evening
      for zones 645-670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Monday for
      zones 650-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect from 11 PM this evening to 3
      PM PDT Monday for zone 655. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

Numerous rain and mountain snow showers are expected Wednesday.
Showers will decrease on Thursday. Impacts will include minor
urban flooding and difficult mountain travel.

&&

$$

PUBLIC...Sirard/Rorke
AVIATION...Sweet/Stewart
MARINE...Sweet/Stewart
SYNOPSIS...Kj

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