000 
fxus66 klox 181754 
afdlox 


Area forecast discussion...updated 
National Weather Service Los Angeles/Oxnard California 
954 am PST sun Feb 18 2018 


Synopsis...18/822 am. 


Light rain and mountain snow will fall across much of the region 
tonight and Monday with snow falling as low as 1500 feet Monday 
morning. Gusty winds and a blast of cold air will create very cold 
wind chill temperatures through Monday with frost or freezing 
conditions Tuesday and Wednesday mornings. Conditions will be dry 
but cool for the remainder of the week. 


&& 


Update... 
previous discussion handles the overall forecast well. Just a few 
minor tweaks to a few low temperatures for Tue night into Wed 
morning. Also, will be converting the freeze watch and hard freeze 
watch to warnings valid both Monday night into Tue morning and Tue 
night into Wed morning with the afternoon forecast package. 
Confidence is high that the cold air will persist both nights. 
Also will be adding the Santa Barbara County mountains and the 
Cuyama Valley to the Winter Weather Advisory. We are only 
expecting 1-2 inches of snow across the Santa Barbara County 
mountains including a dusting across the San Marcos Pass. Also 
around an inch or slightly less for people traveling across 
Highway 166 through the Cuyama Valley. The fact that it is a 
Holiday travel weekend, is the main reason for adding these zones 
to the Winter Weather Advisory. 


Not much change with precip with the latest 12z forecast but was a 
slight bit less then the earlier runs. Still, with the over-land trajectory 
of this incoming system tonight into Monday, precip amounts will 
be light. There could be some dusting of snow across the northwest 
foothills of the Antelope Valley as well. But best moisture 
parameters looks to be southern l.A. County tonight into Monday 
morning, and the northern mountain slopes of sba/Ventura and northwest 
l.A. County mountains through Tue morning. 


Again...very important for skiers, campers and hikers to take 
notice that these will be the coldest temperatures so far this 
winter. And with the increasing strong winds, wind chill 
temperatures will range between 10 degrees and -10 degrees in the 
higher elevations late tonight into Monday. Still remaining quite 
cold the following nights, but with less wind. 


***From previous discussion*** 


&& 


Short term (tdy-tue)...18/953 am. 


Low clouds were beginning to develop in coastal areas this morning. 
Clouds will probably remain confined to the coastal plain this 
morning. Otherwise, skies should be sunny today, possibly becoming 
partly cloudy by evening. 


Gradients will turn strongly onshore this afternoon. Expect gusty 
southwest winds in the Antelope Valley and through the Soledad Pass 
this afternoon, and have issued a Wind Advisory there. Northwest 
winds will also become gusty on the central coast but should remain 
just below advisory levels. Max temps will be down 6 to 12 degrees 
in most areas, today, generally down to near normal or slightly 
below normal levels. 


An upper low will move through the pac northwest today, then into the 
northern rockies tonight and Monday. The southern end of the 
trough will sharpen up and dig southward through the Great Basin. 
The WRF continues to show a rapid return of the low clouds to 
coastal sections of l.A. County this evening. Strong height falls 
and increasingly moist cyclonic flow should bring a chance of rain 
to l.A. County, especially southern and eastern areas where the low 
level flow will be most favorable. Developing moist northwest to 
north flow tonight will bring a chance of rain and snow to the 
northern slopes of the mtns of vtu County, to much of slo and sba 
counties, and to portions of the Antelope Valley foothills. The 
threat of rain and snow showers will linger through Monday morning, 
except into Monday evening across northern mtn slopes. 


Snow levels will plummet tonight, dropping from between 5000 and 
5500 feet this evening, to between 2500 and 3000 feet late 
tonight, and to 1500 to 2000 feet Monday morning. This could 
bring snow showers into foothills areas Monday morning. Little or no 
snow accumulation is expected in the foothills, but in the mountains 
above 2500 feet, snow accumulations of 2 to 4 inches are possible. 
A Winter Weather Advisory is in effect for the mtns of l.A. And 
vtu counties this evening through Monday night for the snow and 
advisory level northwest winds. 


Strong northwest winds will affect much of the region Monday into 
Monday evening, and wind advisories will likely be needed in many 
areas. It will be very cool on Monday, with highs only in the 50s 
in most coastal and Lower Valley areas, in the mid to upper 40s 
in the interior valleys, in the upper 30s to mid 40s in the lower 
mountains and the Antelope Valley and in the mid 20s to mid 30s at 
higher mountain locations. 


With the wind, it will feel much colder. In fact, wind chill values 
could drop to between 10 degrees and -10 degrees in the mountains 
late tonight and Monday. This is unusually cold for Southern 
California. People planning to hike, Camp, ski or snowboard in 
the mountains on the Holiday are urged to plan for the unusual 
cold and low wind chill values. 


Winds are expected to decrease rapidly Monday night. If winds drop 
off quickly enough as expected, it will be a very cold night 
across the region. A hard freeze watch has been issued for the 
central coast, the Santa Ynez and Cuyama valleys, and the 
interior valleys of Ventura County, especially for the Ojai 
Valley. In these areas, temperatures may drop to 28 degrees or 
lower for at least two hours Monday night. Some areas within the 
watch could have lows in the lower 20s. A freeze watch has been 
issued for Monday night for the South Coast of sba County, 
coastal sections of vtu County, and the vtu County coastal 
valleys. Temperatures in these areas could bottom out between 29 
and 32 degrees for at least two hours Monday night. It will also 
be very cold in the interior valleys of slo County and the 
Antelope Valley, with temps between 17 and 27 degrees there, but 
those locations have already experience two hard freezes this 
season. Frost is likely in the colder locations in the valleys of 
l.A. County Monday night, and a frost advisory will likely be 
needed for those areas. Tuesday will be sunny but it will continue 
to be very cool across the region. 


Long term (wed-sat)...18/533 am. 


The ec and GFS continue to show significant differences with the 
upper pattern Wed through Sat, so confidence in the forecast is low. 
It will most likely be very cool through the period, with a 
possible moderation in temps by Saturday. 


Both models show another short wave trough near the region Tue 
night and Wed. The GFS is sharper with this feature and takes it 
over the ocean, while the ec shows a broader system tracking 
through the region. It still looks very cold Tue night and Wed, 
and frost, freezes, and hard freezes are still a possibility. 
However, depending upon the track of the short wave trough, 
there may be some clouds. Therefore, at this time, did not have 
the confidence to have freeze watches for Tue night and early Wed, 
although they may well be needed. It will remain very cool on Wed. 


Another trough will drop southward through the pac northwest Wed night 
and Thu. The GFS shows this trough moving eastward into Arizona 
Thu night and Fri, while the ec is farther west and slower with 
it, tracking just to the northeast of the area Fri morning. The 
scenario indicated by the ec would bring a better chance of 
showers to the region late Thu through Fri, and pops may have to 
be added by later shifts. It will remain very cool Thu and Fri, 
with perhaps a bit of moderation in temps Sat. 


&& 


Aviation...18/1156z. 


At 1130z, the marine inversion at klax was based at 700 feet. The 
top of the inversion was 1200 feet with a temperature of 17 
degrees celsius. 


Overall, low confidence in 12z coastal/valley tafs and high 
confidence in desert tafs. Stratus/fog finally developing along 
coastal plain and could impact most, if not all, coastal 
airfields with IFR/LIFR conditions through the morning. Valley taf 
sites should remain VFR this morning, but only moderately 
confidence in that forecast. For tonight, low confidence in 
coastal/valley taf sites continues due to 50/50 nature of stratus 
developing. 


Across the deserts, gusty westerly winds are expected this 
afternoon and tonight which could result in reduced visibilities 
in blowing dust/sand. 


Klax...low confidence in 12z taf. There is a 40% chance conditions 
will remain VFR 12z-20z. For tonight, moderate confidence in 
return of MVFR conditions, but low confidence in timing (could be 
+/- 3 hours of current 03z forecast). Due to deepening marine 
inversion, some light showers/drizzle will be possible tonight. 


Kbur...moderate confidence in 12z taf. There is a 20% chance of 
IFR/LIFR conditions 13z-18z. For tonight, moderate confidence in 
return of MVFR conditions, but low confidence in timing (could be 
+/- 3 hours of current 03z forecast). Due to deepening marine 
inversion, some light showers/drizzle will be possible tonight. 


&& 


Marine...18/942 am. 


For the outer waters, high confidence in current forecast. Small 
Craft Advisory (sca) level winds will continue through this 
evening. From this evening through Monday evening, gale force 
winds are likely and a Gale Warning is in effect. Winds will 
diminish to Small Craft Advisory levels on Tuesday and will hover around Small Craft Advisory levels 
through Thursday. 


For the inner waters, moderate confidence in current forecast. For 
the waters north of Point Sal, high confidence in Small Craft Advisory level winds 
today and tonight and moderate confidence in gale force winds 
Monday afternoon/evening. For the waters south of Point 
Conception, moderate confidence in Small Craft Advisory level winds developing 
tonight and continuing through Monday night with a 30% chance of 
widespread gale force gusts Monday afternoon/evening. 


&& 


Lox watches/warnings/advisories... 
California...hard freeze warning in effect from 1 am to 9 am PST Tuesday 
for zones 34>36-38-44. (See laxnpwlox). 
Hard freeze warning in effect from 1 am to 9 am PST Wednesday 
for zones 34>36-38-44. (See laxnpwlox). 
Winter Weather Advisory in effect from 10 PM this evening to 
3 am PST Tuesday for zones 38-52. (See laxwswlox). 
Wind Advisory in effect from 8 PM this evening to 10 PM PST 
Monday for zones 39-52. (See laxnpwlox). 
Freeze warning in effect from 1 am to 9 am PST Tuesday for 
zones 39-40-45. (See laxnpwlox). 
Freeze warning in effect from 1 am to 9 am PST Wednesday for 
zones 39-40-45. (See laxnpwlox). 
Winter Weather Advisory in effect from 6 PM this evening to 3 
am PST Tuesday for zones 53-54. (See laxwswlox). 
Wind Advisory in effect until 10 PM PST Monday for zone 59. (See laxnpwlox). 
Pz...Small Craft Advisory in effect until 9 am PST Monday for zone 
645. (See laxmwwlox). 
Gale Warning in effect from 9 am to 9 PM PST Monday for zone 
645. (See laxmwwlox). 
Small Craft Advisory in effect from 9 PM this evening to 3 am 
PST Tuesday for zones 650-655. (See laxmwwlox). 
Small Craft Advisory in effect until 9 PM PST this evening 
for zones 670-673-676. (See laxmwwlox). 
Gale Warning in effect from 9 PM this evening to 3 am PST 
Tuesday for zones 670-673-676. (See laxmwwlox). 


&& 


Hazard potential outlook (tue-sat). 


It will be very cold during the late night through mid morning hours 
Monday night and through Wednesday, especially where the winds 
diminish. Hard freezes are possible on the central coast, and in the 
Santa Ynez, Cuyama and Ojai valleys Monday night. Freezes are 
possible across the South Coast of Santa Barbara County, the Ventura 
County coast and in the coastal valleys of Ventura counties. Frost 
is possible in the Los Angeles County valley. It could be just as 
cold Tuesday night, although that is less certain, since there may 
be some cloud cover. 


&& 


$$ 


Public...Kaplan/db 
aviation...rat 



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