Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 191246
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
446 AM PST Wed Dec 19 2018

...Aviation and marine discussions updated...

.SYNOPSIS...19/131 AM.

Building high pressure and weak north to northeast winds will
bring a warming and drying trend through Thursday. For Friday and
Saturday, a cooling trend is anticipated. After a bit of a warmup
on Sunday, Monday and Christmas Day will be cooler. There will be
a chance of light precipitation on Christmas Day.

&&

.SHORT TERM (TDY-FRI)...19/130 AM.

Overall, 00Z models in good synoptic agreement through the period.
At upper levels, ridge will build over the area today then will
weaken Thursday/Friday as a trough moves across California. Near
the surface, weak north to northeast flow will prevail through
Thursday with weak onshore flow developing on Friday.

Forecast-wise, main issue in the short term will be north to
northeast winds. Currently, gusty north winds continue across the
area, but are beginning to weaken and shift to the northeast. So,
will let the WIND ADVISORY for southern Santa Barbara county
expire with forecast issuance. For the remainder of today through
Thursday, northeast winds will prevail with gusty winds in the
usual northeast wind-prone spots. Surface gradients do not get too
strong (NAM peaking at -3.5 mb LAX-DAG) and upper support is
minimal. So, northeast winds should generally remain below
advisory levels through Thursday.

As for temperatures, the combination of the ridge aloft and
offshore gradients will allow for most area to exhibit a warming
trend today and Thursday with most areas 5-10 degrees above normal
by Thursday. On Friday, noticeable cooling will occur as onshore
flow returns and ridge continues to weaken.

As for clouds, the weak offshore flow will keep skies mostly clear
through Thursday with the occasional bit of cirrus from time to
time. For Friday, expect an increase in high-level clouds as
trough moves across the state. Additionally, with the return of
weak onshore flow, some stratus could develop Friday morning
across the coastal plain.

.LONG TERM (SAT-TUE)...19/131 AM.

For the long-term, 00Z models continue to exhibit good synoptic
agreement. At upper levels, broad northwest flow pattern will
prevail across the West Coast. Near the surface, weak west to
northwest flow will prevail.

Forecast-wise, the northwest flow pattern aloft will allow for a
series of impulses to move across the West Coast. So, a decent
amount of mid and high level clouds is anticipated through the
middle of next week with some low clouds possible across the
coastal plain during the night/morning hours. Through Monday, the
various impulses will remain far enough north to prevent any rain
chances for the area. However on Christmas Day, both the GFS and
ECMWF indicate the potential for all areas to get some rain
although models differ in the details. So, will trend POPs upward
into the CHANCE category for all areas on Christmas Day. Rainfall
totals, if any, will not be too significant. Snow levels look to
drop to around 5000 feet on Christmas Day, so higher elevations
could receive some accumulating snowfall.

Otherwise, the cooling trend will continue on Saturday. However on
Sunday, some slight warming is anticipated as gradients turn
weakly offshore. However for Monday and Christmas Day, a cooling
trend will develop yet again.

&&

.AVIATION...19/1220Z.

At 11z at KLAX... there was a surface based inversion. The top of
the inversion was near 1200 feet with a temperature of about 15
degrees Celsius.

Overall... Moderate to high confidence in the TAFs. There is a
ten percent chance of MVFR patchy low clouds and fog along the
coast south of Point Conception 13z-16z. and at KPRB 14z-21z.
Otherwise and elsewhere VFR conditions will prevail.

KLAX... Moderate to high confidence in the TAF. There is a ten
percent chance of MVFR patchy low clouds and fog 13z-15z then
again after 20/12z-15z. Otherwise VFR conditions will prevail
throughout the forecast period. No east winds greater than eight
knots will occur during the forecast period.

KBUR... High confidence in the TAF. VFR conditions will prevail
throughout the forecast period.

&&

.MARINE...19/444 AM.

A large west to northwest swell will slowly subside today but will
continue to bring dangerous breaking waves to west to northwest
facing harbors, including Morro Bay. In addition, breaking waves
will be possible in shallower water areas outside the typical surf
zone. The swell will increase again on Thursday as another large
west to northwest swell moves into the area.

Small Craft Advisory (SCA) level hazardous seas will affect the
outer waters as well as the inner waters north of Point Sal
through early Friday morning. There is a sixty percent chance of SCA
level winds across the same area Friday night through Sunday.

For the inner waters south of Point Conception, conditions will
remain below SCA levels through Sunday.

&&

.BEACHES...19/430 AM.

Surf heights will continue to subside today then will increase
again on Thursday as another large west to northwest swell moves
across the coastal waters. High Surf Advisories are in effect
through midday Friday for most of the coast of southwestern
California with the exception of the Santa Barbara South Coast. A
Beach Hazards Statement is in effect for that area. The greatest
impact will be on west facing beaches.

Water may locally spill into normally dry beaches, beach parking
lots and harbor walkways. There is a risk of large breaking waves
across the Morro Bay Harbor entrance, which could capsize small
boats. Dangerous rip currents and sneaker waves will be present.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until noon PST Friday for zones
      34-35-40-41-87. (See LAXCFWLOX).
     Beach Hazards Statement in effect through Thursday evening
      for zone 39. (See LAXCFWLOX).
PZ...Small Craft Advisory for hazardous seas in effect until 3 AM
      PST Friday for zones 645-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

No significant hazards expected.

&&
$$

PUBLIC...Thompson
AVIATION...Kj
MARINE...Kj
BEACHES...Kj
SYNOPSIS...Thompson

weather.gov/losangeles


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