NWS Los Angeles, CA wrote its last area forecast discussion before the first event at Jan 21, 8:20 PM PST, 4 hours 50 minutes earlier.
Area forecast discussion, Jan 21, 8:20 PM PST, 4 hours 50 minutes before
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
820 PM PST Tue Jan 21 2025
.SYNOPSIS...21/726 PM.
Light to moderate Santa Ana winds will continue through Wednesday
afternoon across Ventura and Los Angeles Counties. There will be
another increase in northeast winds Wednesday night into
Thursday. Daytime temperatures will warm up each day, peaking
Thursday with highs in the 70s and lower 80s along with continued
very low humidities. Freezing temperatures are likely in wind
sheltered areas tonight and Wednesday night. Friday will be cooler
with a return to onshore flow. An upper low will bring very cool
conditions and a chance of showers this weekend.
&&
.SHORT TERM (TUE-FRI)...21/819 PM.
***UPDATE***
Northeast winds are for the most part weakening and diminishing in
coverage across the offshore wind-prone areas of LA and Ventura
Counties this evening. However, some of the hot spots continue to
gust near Advisory thresholds, including in the Santa Susana
Mountains, near Porter Ranch and in the Santa Lucias. While
surface pressure gradients remain moderate (LAX to Daggett
currently -5.8 MB) the upper level support has weakened. The high
resolution models, and the NAM12, show some increase in wind
speeds between 4AM to 10AM Wednesday, but expect overall speeds to
peak around 30 mph, with isolated gusts to 50 mph possible in the
most wind-prone locations. The more significant wind increase
will not occur until late Wednesday night into early Thursday.
With the very dry airmass in place across SW California, expect to
see many chilly to cold overnight temperatures tonight and
Wednesday night. The Antelope Valley has a Freeze Warning in
effect for lows in the mid teens, and upper 20s are expected for
the Ojai Valley.
Highs on Wednesday will be considerably warmer than today, with
increases of 10 to 15 degrees in the valleys and even some coastal
areas. The deserts will see around 2 to 10 degrees of warming,
with the least across interior SLO county.
***From Previous Discussion***
The next round of Santa Ana winds is expected to arrive Wednesday
night into Thursday. This one doesn't have the support aloft to
generate the 80 mph winds that occurred early in the previous
event, but a -10mb LAX-DAG gradient should be be able to produce
isolated gusts to 60 in the mountains and foothills of LA/Ventura
Counties and 30-50 mph in most other areas that fall under a
traditional Santa Ana event. Winds are expected to drop off below
advisory levels Thursday afternoon and evening.
With the colder air shifting east and high pressure aloft building
over the California, high temperatures Wed/Thu will be climbing.
Warmest highs today have been at the coast which is typical during
Santa Ana events with good cold air advection. Now that the whole
airmass is warming temperatures will warm up everywhere with not
much difference between coast and valleys. Looking for highs Wed
in the mid to upper 70s and by Thursday getting into the low to
mid 80s in the warmest areas (mainly LA/Ventura Counties).
Some lingering northeast flow aloft Friday and moderate -5mb
morning LAX-DAG gradient will keep some offshore breezes going
over the higher valleys and mountains into Friday morning,
otherwise the area will quickly transitioning to a much cooler
onshore pattern with highs dropping back into the 60s to lower
70s.
.LONG TERM (SAT-TUE)...21/238 PM.
A tricky forecast this weekend into early next week as we
transition from dry and gusty Santa Ana winds to a slow moving and cold
upper low with a chance of showers. The good news is that the
models are in pretty good agreement on the trajectory of the low,
dropping south through California and arriving in southern
California Saturday afternoon and evening. Naturally with this
sort of track PW's are lower than a traditional winter storm in
this area with ensembles averaging around .5". However, 500mb
temperatures are expected to drop to around -25c by Sunday morning
so there is a small chance of a thunderstorm with this system.
Overall amounts will be on the lighter side, mostly under a half
inch, but since it's slow moving and lingering through early
Monday, can't rule out rain amounts approaching an inch. Given the
location of the low creating the best upslope conditions over the
eastern San Gabriels, and potential for 48 hours of off and on
showers, that area has the highest potential for rain amounts
exceeding a half inch. Chances for heavy rain remain low and
mostly associated with convection, the chances of which remain
small but zero. Thus, rain rates overall expected to be under a
quarter inch per hour which is well below debris flow thresholds.
With the upper low moving overhead, snow levels will be lowering
through the weekend, reaching as low as 3500-4000 feet by early
Sunday. Not expecting enough accumulation to create any
significant issues on the Grapevine but some higher mountain areas
above 5000 feet could see a few inches of snow this weekend.
Most solutions have the upper low exiting the area by Monday
morning but a few keep it around through the day, so light precip
chances still possible on Monday, mainly LA County and areas east
and south. Some light offshore flow develops behind it through
next Tuesday but so far not expecting any significant Santa Ana
events next week.
&&
.AVIATION...21/2337Z.
At 2302Z at KLAX, there was no marine layer nor inversion.
High confidence in VFR conditions at all sites, except KPRB. There
is a 30% chance for IFR to MVFR vsbys at KPRB between 12Z and
17Z. Gusty E to NE winds will remain at KCMA and KVNY through
most of the period. Winds will ramp back up and expand to KBUR and
KOXR after 18Z. After 18Z, light to moderate LLWS and turbulence
may occur, especially near the Los Angeles and Ventura county
mountains and foothills. Maximum wind gusts after 18Z may be off
by 10 kts at KOXR, KCMA, KBUR, and KVNY.
KLAX...High confidence in TAF. High confidence in VFR conds
through the period. There is a 40% chance of an east wind
component reaching 8 kts between 07Z and 16Z.
KBUR...High confidence in TAF. High confidence in VFR conds
through the period. NE winds will reestablish after 18Z and
continue to strengthen after 00Z Thursday. Light to moderate LLWS
and turbulence may occur near the airfield, with best chances
after 18Z near mountains and foothills.
&&
.MARINE...21/710 PM.
For the Outer Waters, Small Craft Advisory (SCA) level winds are
likely for zones PZZ670 and PZZ673 this evening thru around noon
on Wednesday (50-60% chance), with higher chances for the central
zone. Thursday and Friday look fairly quiet north of the Channel
Islands. SCA level winds near the Channel Islands are likely
late Wednesday into Thursday afternoon (PZZ676 and PZZ673), with
best chances of winds being strongest south of the Channel
Islands. There is also a 30-40% chance for Gales during this
period. There is a 20-30% chance of SCA level winds extending into
early Friday morning before dropping off in this area.
For the Inner Waters along the Central Coast (PZZ645), there is a
70-80% chance of SCA level winds tonight through at least mid-
day Wednesday, especially from Cayucos to Morro Bay. There is a
30% chance for these NE SCA level winds to continue into late
Wednesday night. Thursday and Friday look to be sub advisory.
For the Inner Waters South of Point Conception, the SCAs were
extended through Wednesday afternoon, with the SCA for the Santa
Barbara Channel starting overnight. There are currently SCA level
wind gusts being recorded nearshore from Point Mugu to Malibu, and
many gusts within a few knots of SCA thresholds. Brief lulls are
possible late tonight/early Wednesday morning. A Gale Watch
(50-60% chance of Gales) has been issued for Wednesday afternoon
through Thursday afternoon. The strongest winds, again, will be
focused nearshore from Ventura to Malibu, and out to the Channel
Islands. Winds across the San Pedro Channel and out to Catalina
Island will be sub-advisory until Wednesday afternoon. Then there
is a 20-30% chance for SCA level winds from Wednesday afternoon
through Thursday for Avalon Harbor. East facing harbors may be
exposed to breaking waves, but confidence in the Wednesday through
Thursday event being weaker than the most recent event is fairly
high. Friday looks to be a relatively quiet day across the inner
water south of Point Conception.
Across the entirety of the Coastal Waters, winds and seas will
rapidly increase early Saturday as a storm system enters the
area.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Freeze Warning in effect from midnight tonight to 9 AM PST
Wednesday for zone 357. (See LAXNPWLOX).
Freeze Warning in effect until 9 AM PST Wednesday for zone
383. (See LAXNPWLOX).
Red Flag Warning in effect until 8 PM PST Thursday for zones
288-354-355-358-362-369>380. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until noon PST Wednesday for
zones 645-670. (See LAXMWWLOX).
Small Craft Advisory in effect from 3 AM to 4 PM PST
Wednesday for zone 650. (See LAXMWWLOX).
Gale Watch in effect from Wednesday afternoon through
Thursday afternoon for zones 650-655. (See LAXMWWLOX).
Small Craft Advisory in effect until 4 PM PST Wednesday for
zone 655. (See LAXMWWLOX).
Small Craft Advisory in effect until 9 AM PST Wednesday for
zone 673. (See LAXMWWLOX).
Small Craft Advisory in effect from 3 PM Wednesday to 9 PM
PST Thursday for zone 676. (See LAXMWWLOX).
&&
PUBLIC...MW/Ciliberti
AVIATION...Lewis
MARINE...Lewis
SYNOPSIS...MW/DB/Smith
weather.gov/losangeles
Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox