000 
fxus66 klox 222129 
afdlox 


Area forecast discussion 
National Weather Service Los Angeles/Oxnard California 
229 PM PDT Tue may 22 2018 


Synopsis...22/121 PM. 


An upper level trough continues to move east of California 
bringing continued onshore flow and below normal temperatures 
throughout the week. Night to morning low clouds will continue 
through the weekend for the coast and valley areas. 


&& 


Short term (tdy-fri)...22/206 PM. 


Latest satellite imagery showed low clouds hanging tough across 
many coastal and valley areas south of Point Conception. It seems 
la County will hang onto the low clouds the longest. Low clouds 
off the central coast continue to stream in from the northwest. 
Isolated cumulus clouds have developed due to limited moisture and 
instability across the northern Ventura County mountains near 
Lockwood Valley and the San Gabriel Mountains in eastern la 
County. Can't completely rule out a few sprinkles or a shower with 
this development, however at this time vertical development of the 
clouds has been limited. 


A weak pop up ridge is expected over the region with 500 mb 
heights rising from around 571 dm today to around 578 dm by 
Wednesday afternoon. A piece of energy is expected to pinch off a 
trough of low pressure currently positioned over the Gulf of 
Alaska and move into central California Friday. Southwesterly flow 
aloft ahead of this feature Thursday will support a modest 
increase in onshore flow with lowering heights north of Point 
Conception. The increase in onshore flow will likely maintain low 
clouds well into Thursday afternoon for many coastal and valley 
areas. A 100+ knot jet streak at 300 mb may help provide enough 
lift for drizzle or a few light showers for coastal and valley 
areas north of Point Conception (especially slo county). Have 
opted to leave out of the forecast for now (tho did bump up pops) 
as there remains some uncertainty of the eventual track of the 
system. Drizzle can't be ruled out further south either, 
especially the climatologically favored foothills and lower 
coastal slopes of eastern la County. 


Temperatures will warm some, especially away from the marine layer 
through Wednesday before gradually cooling through Friday, first 
due to increasing onshore flow, then lowering 500 mb heights. 
Locally gusty onshore winds will continue for the foothills of the 
Antelope Valley each afternoon and early evening. 


Long term (sat-tue)...22/227 PM. 


Moderate confidence exists in the extended forecast mainly due to 
uncertainty with the exact position and associated impacts of a 
trough of low pressure expected to pass through the region. 


The fastest model solutions have trended the core of the upper 
level low closer to southwest California. Temperatures were 
trended downward slightly (and could be lowered further by future 
shifts) as a result of the low's proximity. This is unusually cold 
feature for this time of year. Night to morning low clouds may 
have trouble forming over the weekend as a result, especially 
north of Point Conception. Will also keep an eye on the potential 
for a few showers or thunderstorms over the mountains mainly 
Saturday due to the low's proximity. Advisory level sundowner 
winds are possible for western portions of the sba South Coast 
this weekend with gusty also possible in the la and vta mountains 
near the I-5 corridor. 


The trough of low pressure is expected to exit into The Four 
Corners by early next week. This will support increasing 500 mb 
heights and weakening onshore flow, especially from the south. The 
resulting lower marine layer and likely better clearing with 
support a gradual warming trend with widespread 80s away from the 
coast. 


&& 


Aviation...22/1728z. 


At 17z, there is a weak marine inversion at klax based at 4200 
feet. The top of the inversion was 5400 feet with a temperature 
of 12 degrees celsius. 


Overall, moderate confidence in coastal/valley tafs and high 
confidence in desert tafs. The trends in the marine inversion will 
be lowering through tonight with a shallower layer that is likely 
to burn off quicker Wednesday morning. Lingering MVFR cigs for 
portions of the central coast and valleys south of pt Conception 
this afternoon with some scattered between 22-04z. MVFR cigs with patchy 
IFR likely to return after 06z for all coastal and valley tafs. 


Klax...moderate confidence in 18z taf. Broken VFR conditions through 
21z then scattered-broken from 21-06z. MVFR cigs are likely to return 
07-17z Wednesday with a 20% chance of IFR cigs occurring. 


Kbur...moderate confidence in 18z taf. Broken VFR conditions through 
06z then MVFR cigs are likely to return 07-17z Wednesday with a 
50% chance of IFR cigs occurring. 


&& 


Marine...22/146 PM. 


For the outer waters, high confidence in current forecast. Winds 
and seas will remain below Small Craft Advisory (sca) levels 
through Thursday. By late Friday into Saturday, there is a 70% 
chance of Small Craft Advisory level northwest winds. There will be a mixed swell 
with shorter periods from the northwest and long periods from the S. 


For the inner waters, moderate to high confidence in current 
forecast. For the waters north of Point Sal, winds and seas will 
remain below Small Craft Advisory levels through Thursday then there is a 60% 
chance of Small Craft Advisory level winds beginning late Friday into Saturday. 
For the waters south of Point Conception, winds and seas will 
remain below Small Craft Advisory levels through Thursday. Late Friday into 
Saturday, there is a 50% chance of Small Craft Advisory level winds, especially 
across western sections. 


A long period southerly swell will continue to move across the 
coastal waters through Thursday. Locally rough conditions may 
occur at local Harbor entrances, especially those with southerly 
exposure. 


&& 


Lox watches/warnings/advisories... 
California...beach hazards statement in effect through Thursday evening 
for zones 40-41-87. (See laxcfwlox). 
Pz...none. 


&& 


Hazard potential outlook (fri-tue). 


Strong rip currents and elevated surf will linger at south-facing 
beaches across Los Angeles and Ventura counties through Thursday. 
Advisory level sundowner winds are possible for western portions 
of the sba South Coast this weekend. 


&& 


$$ 


Public...Munroe 
aviation...eb 



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