Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 240058
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
558 PM PDT Mon May 23 2022

Updated Aviation and Synopsis Sections

.SYNOPSIS...23/556 PM.

Warmer conditions expected through at least the middle of the
week under developing high pressure. The marine layer will
continue to impact coastal areas and nearby valley areas, most
expansive after Tuesday. Gusty winds will affect the mountains
and interior valleys each afternoon and evening after Tuesday.

&&

.SHORT TERM (TDY-THU)...23/225 PM.

Today, temperatures continue on the upward trend, warming 3-8
degrees. Interior areas will experience the hottest temperatures
today with highs in the 90s, and onshore flow will limit warming
at the coasts. Otherwise, it should be a relatively quiet day with
stubborn marine layer clouds lingering over the waters and for
the coasts south of Point Conception. Low clouds and fog will
return tonight and Tuesday night, covering similar areas as last
night, but should be somewhat shallower in depth. By Wednesday
night, heights start to rise. This combined with stronger onshore
flow will lead to a deeper more extensive marine layer clouds.

Some sub-advisory level gusty northerly winds will start off the
day Tuesday for the interior mountains. Winds will shift to the
northeast through the day, with gusty conditions shifting to the
Antelope Valley. The combination of ridging and northeast winds
over the region Tuesday will allow further heating throughout the
area, with the Antelope Valley and interior portions of San Luis
Obispo County pushing the mid to upper 90s. Fortunately, these hot
temperatures will be limited to the daytime hours from 10 AM to 4
PM.

Stronger onshore flow develops Wednesday afternoon with an
onshore LAX-DAG gradient of around 7-8 mb will support west winds
of 25 to 35 mph, with gusts to 45 mph over the Antelope Valley.

Minor edits were made to account for lingering marine layer
clouds this afternoon and increase cloud coverage this evening
into Tuesday morning. Otherwise, the forecast looked on track.


***From Previous Discussion***

Overall, 00Z models in good synoptic agreement through the short
term period. At upper levels, ridge will build over the eastern
Pacific today/Tuesday then will be pushed eastward as a trough
approaches the West Coast. Near the surface, moderate onshore flow
will persist.

Forecast-wise, main challenge will be the marine layer stratus.
Currently, AMDAR soundings indicate marine inversion around 1300
feet deep. With onshore gradients and eddy over the Bight, stratus
and fog should become widespread across the coastal plain south of
Point Conception, but could struggle getting into the coastal
valleys (based on latest satellite trends). North of Point
Conception, stratus/fog will remain confined to the west coast of
SBA county (mainly Lompoc and Vandenberg area) this morning.
Stratus should dissipate by late morning all areas. For
tonight/Tuesday, rising H5 heights will help squash the inversion
a bit, but areal coverage will be very similar to this morning
(with a little more penetration into the lower coastal valleys).
For Tuesday night/Wednesday, high resolution models indicate a
"southerly surge" which will combine with slightly lower H5
heights to allow for more widespread stratus coverage across the
coastal plain, reaching up to the SLO county coast (with a bit
more coverage across the lower coastal valleys). Other than the
stratus/fog, skies should remain mostly clear through Wednesday.

Secondary issue will be the temperatures. Given the overall
pattern, will expect a general warming trend for the area through
Wednesday. In fact by Wednesday, coastal areas will generally be
4-8 degrees above normal with inland areas 6-12 degrees above
normal. However, there is a chance that the coastal plain could be
a little bit cooler on Wednesday due to the southerly surge
increasing the marine influence.

As for winds, moderate onshore gradients will continue to generate
some gusty southwesterly winds each afternoon/evening across
interior sections. However, any advisory-level gusts will be very
localized in the usual `wind tunnels" such as Lake Palmdale.

.LONG TERM (FRI-MON)...23/224 PM.

For the extended, models continue to exhibit decent synoptic
agreement through the period. At upper levels, ridging gradually
slips eastward Thursday as a trough passes Friday. Near the
surface, onshore flow will prevail to the east with an increase in
northerly offshore flow over the weekend.
Forecast-wise, Thursday and Friday look similar with the
continuation of strong onshore flow. The LAX-DAG onshore gradient
is forecast to peak Thursday near 8-9 mb. The combo of continued
onshore flow and cyclonic flow aloft will allow for a bit more
widespread stratus/fog, reaching into the coastal valleys, with
mostly clear/partly cloudy skies elsewhere (due to high clouds
drifting overhead). Temperatures through Friday will exhibit a
cooling trend.

From Friday night through Sunday, things get a little more
interesting, mainly due to increasing northerly winds. Models
indicate northerly gradients will gradually increase through the
weekend, peaking Saturday night/Sunday morning. Looking at the
NBM probabilities, there is generally a 75-85% chance of northerly
gusts 45-50 MPH Saturday night and Sunday night across the Santa
Ynez Range and the Interstate 5 Corridor. With this increased
northerly flow, areal coverage of marine layer stratus will
noticeably diminish through the weekend. Additionally, the lesser
marine influence and northerly offshore winds will allow for a
warming trend for the area (with the best warming west of the
mountains).

&&

.AVIATION...24/0020Z.

At 23Z at KLAX, the marine layer was 1600 feet deep. The
inversion top as at 3800 feet and 23 degrees Celsius.

The next 24 hours should see a similar marine layer stratus
evolution expected as last 24 hours. 30 percent chance of LIFE
conditions at KSMX. OVC006-012 chances at at KSBA (80%) KOXR
(100%) KCMA (90%) KSMO (100%) KLAX (100%) KLGB (90%) KBUR (50%)
KVNY (30%). Moderate confidence in timing by +/- 3 hours. High
confidence in VFR at KPRB KSBP KWJF KPMD. High confidence in
gusty onshore winds typical for this time of the year.

KLAX...High confidence in low clouds for majority of tonight.
Random breaks are possible 01-08Z but less likely than last night.
Moderate confidence in CIGS staying above OVC010, with a chance of
dipping just below 06-12Z. High confidence in and east winds
staying well under 8 knots.

KBUR...High confidence in VFR through at least 06Z. 50 percent
chance of OVC006-010 09-17Z.

&&

.MARINE...23/159 PM.

No changes to the marine forecast this afternoon.

High confidence in Gale Force winds affecting the outer waters
north of Point Sal through tonight, except for a brief break
this morning. The Gale Warning continues for this area (see
MWWLOX for details). Moderate confidence that those Gale winds
will also extend to the outer waters northwest of San Miguel
Island, but high confidence they will stay at least 30 miles from
the nearest shore (northwest portion of zone PZZ670). These winds
will also create Small Craft Advisory conditions for the nearshore
waters of the Central Coast and outer waters down to San Nicolas
Island, for winds 20-30 knots and/or choppy seas. The rest of the
area should have fairly benign and seasonal conditions, with
Southeast morning winds 5-10 knots, and typical seabreezes.

For Wednesday through Thursday afternoon, southerly winds will
push up to Monterey County and shove the seasonal coastal jet well
offshore. Local south to southeast winds of 10-15 knots are likely
near all coasts in the morning hours, especially Wednesday. More
significantly, seas will fall to nearly lake-like conditions by
Thursday, with only 2-4 feet total waves everywhere including the
Central Coast. The coastal jet should reform quickly Thursday
Night into Friday, with Gale Force (focused outer waters to
Central Coast) and widespread choppy seas returning for the
weekend.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
      for zone 645. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Tuesday for zones
      670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zone 676. (See LAXMWWLOX).

&&

$$

PUBLIC...Phillips/Thompson
AVIATION...Kittell
MARINE...Sweet/Munroe/Kittell
SYNOPSIS...Kittell

weather.gov/losangeles

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


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