Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1100 am PDT Monday Aug 31 2015
..new aviation discussion...
Synopsis...a broad upper level trough will persist over the West
Coast this week...bringing below normal temperatures to most of the
region...with areas of night through morning low clouds and fog west
of the mountains. Slight warming is possible next weekend as the
trough of low pressure shifts east and onshore flow weakens.
Short term (today-wed)...marine layer depth around 1000' up
north and up to around 2000' in the south thanks to an eddy
circulation, though coverage mostly confined to Ventura/la counties.
Profilers and soundings all showing cooling, and despite a slightly
weaker onshore flow to start off most locations should see highs off
by a few degrees from yesterday. Forecast looks good for cooling today
and Tuesday with better night/morning low clouds and fog coverage
for coast/valleys. Wednesday temperatures will be similar or perhaps
slightly cooler than Tuesday.
***From previous discussion***
An upper low will move into southwestern Canada Tuesday through Wednesday...which will
maintain a broad trough along the West Coast. The models indicate a
fair amount of night through morning low clouds and patchy fog
across the coastal plain (including the sba County S coast once
winds diminish late this evening)...and in many valley locations
tonight/Tuesday morning...and again Tuesday night/Wednesday morning. The WRF
actually indicates little clearing at some beaches on Tuesday.
However...the unusually warm ocean water may tend to keep the
stratus field somewhat disorganized...so confidence on the clouds
forecast is below average. There may be a couple of more degrees of
cooling on Tuesday...with little change on Wednesday. Maximum temperatures will generally
be several degrees below normal across the region...except will
likely remain near to slightly above normal near the coast as the
warmish water will keep seabreeze from being as cool as normal.
Long term (thu-sun)...another upper low will drop southward through western
Canada into the Pacific northwest Thursday and Friday...maintaining the broad upper
trough along the West Coast...with mostly minor changes in night
through morning stratus and maximum temperatures. As the upper low moves into
the northern rockies over the weekend...heights across the region
will rise...so there may be a few degrees of warming.
At 1555z...the marine inversion at klax was around 2200 feet deep. The
top of the inversion was around 2600 feet with a temperature of 21
North of Point Conception...patchy fog was clearing this morning and
patchy to areas of low clouds and fog are expected tonight into
Tuesday morning. Good confidence in the forecast.
S of Point Conception...areas of low clouds and fog were clearing
this morning and areas to widespread low clouds and fog are expected
tonight into Tuesday morning with areas of low clouds even spreading
into the La Valley taf sites. Good confidence in the forecast.
Klax...good confidence in the 18z taf. There is a 30 percent chance
of the arrival time of low clouds and MVFR conditions will vary more
than plus or minus two hours from the forecast.
Kbur...good confidence in the 18z taf. There is a 30 percent chance
of the arrival time of low clouds and IFR to MVFR conditions will
vary more than plus or minus two hours from the forecast.
Outer waters...good confidence in Small Craft Advisory level winds
north of San Nicolas Island lasting until early Tuesday morning.
Inner waters...good confidence in the inner waters forecast. There
will be local small craft gusts across the western third of the sba
channel and in western portions of the inner waters adjacent to the
central coast later this afternoon and evening.
Small Craft Advisory (see laxmwwlox).