Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 241758 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1058 AM PDT Sun Mar 24 2024

...updated aviation discussion...

.SYNOPSIS...23/914 PM.

A lingering storm system will continue a cold and unsettled
weather pattern into Sunday. Scattered showers with isolated
thunderstorms are possible with snow levels lowering to as low as
3500 feet. West to northwest winds will continue to
strengthen through Sunday evening as a tight northerly pressure
difference develops across the state. Warmer and drier weather is
expected for early week, than another storm system, potentially
heavy rainfall, is possible for next weekend.

&&

.SHORT TERM (TDY-TUE)...24/944 AM.

***UPDATE***

The latest short range ensemble guidance (HREF) showed a slight
uptick in instability with modest values of 400-700 J/kg (local
values may approach 1000 J/kg), highest near the LA Basin this
afternoon. Surface convergence associated with strong northwest
flow or downstream of the mountains in coastal valleys of Los
Angeles and Ventura Counties supports a small (5-10 percent)
chance of a somewhat long duration supercell thunderstorm or two
with the greatest threat of damaging wind, frequent lightning, and
hail, although a brief tornado cannot be completely ruled out
(very small chance). Storm movement may be quite fast up to around
40 mph towards the south or southeast, meaning that any
thunderstorms that do form may approach with limited warning.

The very cold air mass for this time of year is supporting snow
levels already down to between 3000 and 4000 feet per the
Vandenberg radar with snow also reported at the Sandberg (4500 ft
elevation) sensor in the northwest LA mountains with a
temperature of 34 degrees. The current Winter Weather Advisory
across the interior mountains looks well placed for the time
being as this is where we have the highest confidence in advisory
snow amounts - although isolated advisory level snows are possible
elsewhere above 4-5 feet where training of heavier showers or
thunderstorms occur.

This evening into tonight gusty north winds are likely with a
20-40 percent chance of warning level gusts across prone interior
mountains of Ventura County, far northwest LA county mountains and
possibly extending into the eastern Santa Ynez Range of Santa
Barbara County.

***From Previous Discussion***

Overall, 00Z models in good synoptic agreement through the short
term period. At upper levels, trough will remain over the West
Coast through tonight then a ridge will build over the Eastern
Pacific Monday and Tuesday. Near the surface, moderate to strong
northwesterly flow will continue through Tuesday.

Forecast-wise, main concern is the chances of showers and
thunderstorms across the area through early Monday morning. All
models indicate a couple of vorticity maxes will rotate around the
upper trough and across the area through tonight. With plenty of
cold air filtering in (500 mb temperatures around -28 degrees C)
and high resolution ensembles indicating CAPE values greater than
500 J/kg, showers and thunderstorms will continue to be a threat.
With the morning forecast, will indicate chance to likely POPs for
showers and a slight chance of thunderstorms. Any thunderstorms
that develop will be capable of producing brief heavy rain, gusty
winds and hail. Rainfall total today through tonight will be
highly variable, generally ranging around 0.25 inches or less for
most areas. However across the northern mountain slopes, rain
totals up to near one inch will be possible.

With the cold air moving in, snow levels will drop to the
3500-4000 foot range this morning, but will slowly rise to the
4000-4500 foot range this afternoon and tonight. In any thunderstorm
activity, snow levels could briefly drop to around 3000 feet
through this evening. Given the forecast QPF amounts across the
Interstate 5 Corridor, Ventura Mountains and the interior Santa
Barbara county mountains, snowfall totals of several inches will
be likely through tonight (4-10" above 5500 feet and 1-4" between
3500 and 5500 feet). So with these expected snow totals and gusty
northwest winds, WINTER WEATHER ADVISORIES have been issued for
these areas through tonight. Given these conditions, travel
through the Grapevine could be problematic and travelers should be
prepared.

Along with the rain and snow, strong and gusty northwesterly winds
are expected through early Monday morning. Wind gusts between 35
and 55 MPH are expected across the coastal plain as well as the
mountains. WIND ADVISORIES remain in effect for coastal areas as
well as the Santa Clarita Valley and the western San Gabriel
Mountains.

For Monday and Tuesday, dry conditions are anticipated as the
ridge builds offshore. A warming trend can be expected Monday and
Tuesday. There will continue to be some gusty northwesterly winds
across the mountains at times, but any advisory-level winds are
expected to be localized.

.LONG TERM (WED-SAT)...24/233 AM.

For the extended, no major changes to previous thinking. On
Wednesday, the warm and dry conditions will continue across the
area. On Thursday, the tail end of a weak system will clip the
area. There will be the chance of some light rain across San Luis
Obispo county with amounts, if any, likely under 0.10 inches.
Elsewhere on Thursday, partly to mostly cloudy, but dry,
conditions can be expected with some slightly cooler temperatures.

For Friday through the weekend, another period of wet and
unsettled weather is expected. Deterministic models all have an
rather strong upper low dropping south along the coast, but differ
greatly in the exact track of the upper low. So, ensembles are the
way to go with the forecast. To that end, ensemble solutions
indicate the potential for a significant storm with high
confidence in a 1-3 inch rain event with potential for even higher
amounts. Given the time of year and cold air associated with the
upper low (thicknesses around 540 dm), significant mountain snow
is likely along with the chances of thunderstorms for all areas.
No doubt that the forecast details for next weekend will likely
change from day-to-day, but at this time there is relatively high
confidence in a significant late season storm. Stay tuned through
the week.

&&

.AVIATION...24/1756Z.

At 17Z at KLAX, there was no marine layer nor inversion.

Moderate confidence in the 18z TAFs due to strong gusty winds,
scattered/isolated showers, and potential (15% chance) for
thunderstorms through 03Z. Generally VFR conditions are expected
except MVFR to locally IFR near convective showers this afternoon
to early evening, ending sooner N of Point Conception.

KLAX...Moderate confidence in the 18Z TAF. VFR conditions are
expected to prevail except 20% chance of BKN025 to brief BKN015
conds in showers/slight chc thunderstorms this afternoon to early
evening. Lower confidence start and end times of stronger gusty
winds. There is a 20% chance of an east wind component of 06 kt or
more with any thunderstorm that may form near the TAF site.

KBUR...Moderate confidence in the 18Z TAF. VFR conds are expected
for most of the fcst period. However, best chances for
showers/thunderstorms and possible brief MVFR cigs will be from
20Z-00Z. Lower confidence start time of stronger gusty winds.

&&

.MARINE...24/829 AM.

Dangerous large seas and strong winds will continue through
Monday, especially today when widespread Gales are nearly
certain. Seas are expected to peak near 13 to 17 feet over the
outer waters, and 9 to 14 feet over the inner waters on this
evening/night. The strongest winds will be focused across all the
waters south of Point Sal, with winds dropping below Gale Force
at times northward of Point Sal. There is a 40 percent chance that
the current Gale Watches will need to be extended through Monday
for the waters south of Point Conception.

In addition to the winds, there is a 10 to 20 percent chance of
thunderstorms late this morning to evening with the potential for
brief heavy rainfall and/or hail, and dangerous cloud to surface
lightning. The combination of strong winds, high, choppy seas, and
potential for thunderstorms create dangerous conditions for
vessels. Boaters, especially small vessels should postpone
traveling the coastal waters at least until conditions improve
around Tuesday/Wednesday.

Conditions will improve Tuesday and Wednesday, but it will still
be hazardous to most small craft due to choppy seas. Winds and
seas will increase once again on Thursday and Friday with
widespread Gale Force Winds possible.

&&

.BEACHES...24/834 AM.

Large swells moving into the coastal waters will generate high
surf along all west and northwest facing beaches into Monday
morning. For the Central Coast, surf of 7 to 12 feet can be
expected. For west-facing beaches south of Point Conception, surf
of 7 to 10 feet is expected. The high surf will also generate
dangerous rip currents.

With the high surf, there is an increased risk for ocean
drowning. Rip currents can pull swimmers and surfers out to sea.
Large breaking waves can cause injury, wash people off beaches and
rocks, and capsize small boats near shore.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 9 AM PDT Monday for zones
      87-340-346-354-362-366. (See LAXCFWLOX).
     Wind Advisory in effect until 8 PM PDT this evening for zones
      87-340-341-346-347-354-355-362-366>368. (See LAXNPWLOX).
     Wind Advisory in effect from 4 PM this afternoon to 3 AM PDT
      Monday for zones 88-349>352-356-379. (See LAXNPWLOX).
     Winter Weather Advisory in effect until 6 AM PDT Monday for
      zones 353-376>378. (See LAXWSWLOX).
PZ...Gale Warning in effect until 3 AM PDT Monday for zones
      645-650-655-670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Munroe/Thompson
AVIATION...Sirard
MARINE...Lund/Sirard
BEACHES...Sirard
SYNOPSIS...Hall

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox


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