High Wind in California, March 14, 2023

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
444 AM PDT Tue Mar 14 2023

.SYNOPSIS...14/310 AM.

A powerful storm will bring widespread moderate to heavy rain to
the region through early Wednesday, possibly resulting in flooding
and gusty winds at times. Dry but cool weather is expected for
Thursday, then a weaker storm system is expected for Friday into
the weekend. A cool and unsettled weather pattern could linger
into late next week.

&&

.SHORT TERM (TDY-THU)...14/443 AM.

The latest radar mosaic shows mainly light rainfall moving over
the northern areas this morning as a pseudo-warm frontal feature
moves over the region. The heaviest rainfall still sits offshore
and will move towards the Central Coast of California through
late morning. Infrared imagery shows cooling cloud tops to -60
degrees Celsius off the Central Coast as the system matures. This
places cloud tops closer to 34000 feet, highlighting the amount of
lift and dynamics taking place with this system. Deterministic
model solutions show the surface low and the 850 and 700 mb
centers deepening as the storm moves ashore through this afternoon
and this evening. NAM-WRF solutions specifically suggest the
central pressure of the surface low dropping by 8 mb (over 18
hours) as the surface low approaches the San Francisco Bay area.
All this indicates that the storm system is strengthening and
undergoing a lot of changes right now. While some 00Z model
solutions backed off the QPF amounts, sometimes up to about half
of the current forecast, the most recent runs are starting to come
back into the current and consistent forecast. Fundamentally, the
overall pattern has not changed and with the atmospheric river
parameters coming into play and the intensification of the storm
system taking place. It made sense not to change away from the
forecast and remain consistent. 850 mb mixing ratios increase to
between 8 and 9 g/kg, or about 4 to 5 standard deviations above
the mean for this time of year, and IVT values range closer to 7
to 8 standard deviations above the mean.

Rainfall amounts between 2 and 4 inches of rainfall are expected
across the coastal and valley areas with up to 4 to 8 inches
possible in the foothills and mountains. Peak rainfall rates are
still advertised to range between 0.50 and 1.00 inch. Thunderstorm
chances are non-zero for today and tonight, but the convective
parameters are marginal. 1000-500 mb lapse rates approach 7
degrees Celsius per km and K-index values exceed 30.

Snow levels will remain high, above 7500 feet with this storm
system, keeping most of the precipitation type rain, except for
snow on the highest peaks through late tonight. By Wednesday
morning, 700 mb temperatures fall to -4 degrees Celsius, which
should lower snow levels down to between 6000 and 7000 feet.
Snowfall amounts will be minimal with a dusting to 2 inches
possible on Wednesday morning.

High Wind Warnings remain in effect for the coastal ranges north
of Point Conception and the interior valleys of San Luis Obispo
through late this evening as there is a very high likelihood of
damaging wind gusts in these areas. Elsewhere, wind advisories
remain in effect for the Central Coast, the remaining valley
areas north of Point Conception, and most of remaining Transverse
mountains and into the Antelope Valley from this morning or
midday through at least this evening. 850 mb winds increase to
between 50 and 60 knots over San Luis Obispo and Santa Barbara
County. Downed powerlines and trees will be of concern,
especially as the day progresses and the stronger winds along the
system's cold front push in.

Rain will taper off to showers from north to south late tonight
or Wednesday morning as the front pushes south and east across
the region. The frontal boundary should exit Los Angeles County
around or just slightly after daybreak on Wednesday morning.

A zonal flow pattern will develop for Thursday as shortwave
ridging aloft slowly builds in from the west. A dry weather
pattern should commence on Thursday, but temperatures will remain
on the cooler side of normal across the area.

.LONG TERM (FRI-MON)...14/440 AM.

EPS, GEFS, and CMC ensemble members all favor another storm
system between Friday and Sunday, albeit much weaker than the
current one. This storm system will likely be drier and colder
than today's storm. Rainfall amounts with this system should
amount to a quarter to half inch, possibly less than that for
areas south of Point Conception, if GFS deterministic solutions
play out as advertised.

A dry pattern should start off the work week next week, but still
another storm system will likely move into the region toward the
middle portion of the next week. Ensemble members indicate this
storm to be a little wetter and deterministic solutions show this
to be an atmospheric river type system, a Pacific storm system
with a decent subtropical tap. This could potentially be the last
gasp for the rain season as much longer range ensemble members
bring only two more system over the next month amounting to much
less rainfall.

&&

.AVIATION...14/1052Z.

At 0900Z, the marine inversion at KLAX was based at 1400 feet.
The top of the inversion was 3100 feet with a temperature of 11
degrees Celsius.

Overall, moderate confidence in 12Z TAF package. High confidence
in widespread rain developing with CIG/VSBY restrictions ranging
from MVFR to LIFR. However, only moderate confidence in timing of
category changes through the period.

KLAX...Moderate confidence in 12Z TAF. There is a 30% chance of
IFR/MVFR conditions through 04Z. There is a 60% chance of
easterly winds (100-110 degrees) up to 10 knots 14Z-20Z.

KBUR...Moderate confidence in 12Z TAF. High confidence in moderate
to heavy rainfall after 15z, but low confidence in timing of
category changes through the period.

&&

.MARINE...14/352 AM.

For the Outer Waters, moderate to high confidence in current
forecast. For today, high confidence in Gale force southerly
winds developing across PZZ670/673 and a GALE WARNING remains in
effect for those areas while SMALL CRAFT ADVISORY remains in
effect for PZZ676 (with a 30% chance of low end Gales in this
zone). Winds will shift to the west to northwest tonight with SCA
level winds and seas expected tonight through Wednesday night.
For Thursday through the weekend, high confidence in winds and
seas remaining below SCA levels.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. For today, gale force southerly
winds will develop and a GALE WARNING remains in effect. By this
evening, winds will diminish to SCA levels and continue through
tonight. For Wednesday and Wednesday night, there is a 40% chance
of SCA level winds. For Thursday through the weekend, high
confidence in winds and seas remaining below SCA levels.

For the Inner Waters south of Point Conception, high confidence in
current forecast. For today, SCA level southerly winds will
develop, continuing through tonight. On Wednesday and Wednesday
night, there is a 50-60% chance of SCA level westerly winds. For
Thursday through the weekend, high confidence in winds and seas
remaining below SCA levels.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 10 PM PDT this evening for
      zones 38-340-341-343-346>349. (See LAXNPWLOX).
     Flood Watch in effect through late tonight for zones
      38-346>353. (See LAXFFALOX).
     Flood Watch in effect from 2 PM PDT this afternoon through
      Wednesday morning for zones
      88-362-366>368-370>373-379-380-548. (See LAXFFALOX).
     Flood Watch in effect through this evening for zones 340>345. (See LAXFFALOX).
     High Surf Advisory in effect from noon today to 6 AM PDT
      Thursday for zones 340-346. (See LAXCFWLOX).
     High Wind Warning in effect until 10 PM PDT this evening for
      zones 342-344-345-353. (See LAXNPWLOX).
     Flood Watch in effect from 11 AM PDT this morning through
      Wednesday morning for zones 354>358-369-374>376. (See LAXFFALOX).
     High Surf Advisory in effect from 6 PM this evening to 6 AM
      PDT Thursday for zone 354. (See LAXCFWLOX).
     Wind Advisory in effect until 5 AM PDT Wednesday for zones
      377>379-381. (See LAXNPWLOX).
     Wind Advisory in effect until 8 PM PDT Wednesday for zones
      380-382. (See LAXNPWLOX).
     Wind Advisory in effect from noon today to 10 PM PDT this
      evening for zone 383. (See LAXNPWLOX).
PZ...Gale Warning in effect until 6 PM PDT this evening for zones
      645-670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 4 AM PDT Wednesday for
      zones 650-676. (See LAXMWWLOX).
     Small Craft Advisory in effect from noon today to 4 AM PDT
      Wednesday for zone 655. (See LAXMWWLOX).

&&

PUBLIC...Hall
AVIATION...RAT
MARINE...RAT
SYNOPSIS...Hall

weather.gov/losangeles

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