Scientific Forecaster Discussion
fxus66 klox 181643
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
943 am PDT sun Aug 18 2019
Near normal temperatures today will warm into midweek then cool
again into next weekend. Many locations will have triple digit
temperatures Wednesday and Thursday. Overnight and morning low
clouds and fog will diminish in area a bit each day through
Thursday then expand again beginning Friday.
Short term (tdy-tue)...18/858 am.
The marine inversion this morning ranged from near 2100 ft deep at
vbg to around 3000 ft deep at lax. Low clouds were quite widespread
this morning, extending from the coast well into the vlys, and even
into some lower coastal slopes across sba/slo counties. The low
clouds are forecast to clear back to the coast by midday with low
clouds probably lingering at some of the beaches thru the afternoon
thanks to good onshore gradients, which are expected to be around
+7.9 mb lax-dag at 00z according to the latest NAM. Otherwise,
mostly sunny skies will prevail across the region thru the
The good onshore gradients will promote gusty S to west winds across
much of the foothills, mtns and deserts this afternoon. Temps will
continue to be several degrees cooler-than-normal today across the
forecast area as well, with highs expected to reach only into the
80s in the warmer vlys and lower mtns, altho the Antelope Vly should
still warm into the 90s this afternoon. Temps overall across the
region today will be 6-15 deg below normal for this time of year.
An upper level trof will persist along and off the California coast thru
today, with 500 mb heights in the 586-588 dm range. A large upper level
high centered over southern Texas today will start to slowly expand
west and into srn California tonight thru Tue, with 500 mb heights expected to
increase to 589-591 dm for Mon afternoon and 591-593 dm for Tue
afternoon. A dry SW flow aloft will prevail thru the period.
The marine inversion is expected to shrink to about 1800-2200 ft or
so tonight into Mon morning, and probably down to 1000-1500 ft for
Mon night into Tue morning. Plenty of night and morning low clouds
and fog will affect the coastal areas into portions of the adjacent
vlys tonight and Mon, then be confined mainly to the central coast,
Santa Ynez Vly and the l.A. County coast Mon night into Tue morning,
altho some low clouds could move into the vtu County coast early Tue
morning as well. Low clouds and fog will also likely affect the
Salinas river Vly for the late night and morning hours tonight thru
Tue morning. Otherwise, mostly clear skies will continue across swrn
California thru Tue afternoon.
The onshore flow will slowly decrease thru the period, with the lax-
dag forecast gradient (nam) expected to be about +7.5 mb Mon
afternoon and +6.5 mb Tue afternoon. Some gusty S-west afternoon and
evening winds will continue for the foothills, mtns and deserts
especially thru Mon afternoon. Some gusty northwest winds are also forecast
for the central coast during the period.
Temps are expected to warm slightly to about 2-7 deg below normal
for Mon. On Tue, temps will continue to warm up, with highs ranging
from slightly below normal along the coast to about 2-8 deg above
normal inland. The warmest vlys and lower mtns should reach the mid
80s to lower 90s Mon, and 90s to near 100 on Tue.
Long term (wed-sat)...18/321 am.
Wednesday will be the warmest of the next 7. 594 dm hgts should
develop. The offshore flow from the north will peak perhaps as
high a -3 mb. The flow to the east will be very weak. There will
only be limited (and perhaps non existent) low cloud coverage. Max
temps will rise another 3 to 6 degrees. The interior will be about
10 degrees above normal and could meet heat advisory criteria. The
vlys will be about 5 degrees above normal.
The ridge begins to break down on Thursday. There will be a degree
or two cooler but overall it will be very similar to Wednesday.
Where once there was a broad trof for Friday and weekend there is
now very weak non descript flow which will morph in to a broad
upper high over the weekend. The once forecast cooling trend will
now be weaker except at the coast where onshore flow and the
marine layer will make a slow comeback.
The ec and the GFS which at one time agreed on the tropical system
off of baja now disagree. Will have to keep an eye on it as it
could pump some moisture into the area early next week.
At 1615z, the marine inversion at klax was based at 2800 feet.
The top of the inversion was 4600 feet with a temperature
of 21 degrees celsius.
Overall, moderate confidence in 18z coastal/valley tafs and high
confidence in desert tafs. Current MVFR cigs are expected to
dissipate early this afternoon. For tonight, high confidence in
return of MVFR/IFR cigs to all coastal/valley sites, but only
moderate confidence in timing.
Klax...overall, moderate confidence in 18z taf. There is a 40%
chance that current MVFR cigs may not dissipate until 21z. For
tonight, high confidence in return of MVFR cigs, but only moderate
confidence in timing (could be +/- 2 hours of current 03z
Kbur...overall, moderate confidence in 18z taf. High confidence in
return of IFR cigs tonight, but only moderate confidence in timing
(could be +/- 2 hours of current 08z forecast).
For the outer waters, moderate to high confidence in current
forecast. High confidence in winds and seas remaining below Small
Craft Advisory (sca) levels through Monday morning. There is a 50%
chance of Small Craft Advisory level winds Monday afternoon. From Monday evening
through Thursday, Small Craft Advisory level winds are likely.
For the inner waters north of Point Sal, moderate to high
confidence in current forecast. High confidence in winds and seas
remaining below Small Craft Advisory levels through Monday. For Tuesday through
Thursday, there is a 70% chance of Small Craft Advisory level winds during the
afternoon and evening hours.
For the inner waters south of Point Conception, moderate to high
confidence in current forecast. And evening. Through Thursday,
high confidence in winds and seas remaining below Small Craft Advisory levels for a
majority of the area. The only exception will be the western half
of the Santa Barbara Channel where there will be a 30% chance of
Small Craft Advisory level winds during the late afternoon and evening hours on
Tuesday and Wednesday.
Hazard potential outlook (tue-sat).
Hot temperatures could lead to heat advisories for some inland
areas Wednesday and possibly Thursday. Otherwise, no significant
hazards are expected through the period.