Scientific Forecaster Discussion
fxus66 klox 210315
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
815 PM PDT Fri Jul 20 2018
Temperatures will remain hot across the region for at least another
week with excessive heat in many areas Tuesday through Thursday.
Overnight and morning low clouds will bring some relief along the
coast. There is a slight chance of isolated thunderstorms this
Short term (fri-mon)...20/813 PM.
High temps trended down a few degrees along the coast with 3-7
degrees of cooling across inland areas S of Point Conception this
afternoon. The upper ridge centered over nrn Texas extending to
the socal coast did not move much over the past 24 hours. The
upper level flow turned more southerly which benefited areas to
the east with best moisture influx and instability as seen by
thunderstorms that developed over the Barstow area and the debris
anvil clouds were blowing straight to the north. A weak upper low
sitting just off the central coast helped to keep 500 mb heights
around 591 decameters (dm) over the forecast area. Although models
were advertising best instability across the Ventura and Santa
Barbara County mtns today, moisture was lacking, and the cumulus
field that developed could net get any vertical growth. There will
continue to be a similar night through morning low clouds and
patchy fog across coastal zones and could filter into a few
coastal valleys of Ventura and l.A. County before sunrise.
High temps are expected to climb slightly tomorrow as onshore flow
weakens a bit and humidity levels lower slightly. There will be
some cu buildups across some mountain locations, but not expecting
any shower or thunderstorm activity over the next few days.
Otherwise not much change expected tomorrow. The NAM-WRF 00z
models were starting to come in, but not seeing any major changes
with the forecast over the next few days. The upper pattern will
begin to change as a strong ridge aloft begins to strengthen and
with the increasing northerly wind gradients, very hot
temperaturesand the beginning of a heat wave will on Sunday
***from previous discussion***
The long-advertised heat wave beginning Sunday and lasting much of
next week still looks on track with essentially no changes made to
the forecast. Temps will increase a few degrees Sunday but the big
jump will take place Monday as northerly flow increases. Sunday
night will be the first of 3 or 4 evenings of hot and gusty
sundowner winds, the strongest now appears to be back to Monday.
Advisory level winds possible any or all of those nights. Monday
temps expected to jump into the 80s for coastal zones and locally
into the 90s across southern sb County with the sundowners
providing the extra temperature boost there. Valleys and Lower
Mountain locations will see their first of several triple digit
days Monday. The excessive heat watch in effect for areas south of
pt Conception will be converted to a warning as confidence is high
that most of that area will experience warning level heat,
particularly Tue-Thu. The only part of that area that's somewhat
less certain would be the immediate coast where a continued
onshore flow might keep temps more in the advisory level, but that
can be addressed as we get closer. This won't be another July 6-8
heat wave when coastal areas were over 100 and valleys 110+. This
event should be 5-10 degrees cooler than that due to a weaker
northerly push but still significant.
Areas north of pt Conception will remain under a watch as temps
there won't reach criteria until at least Tuesday and coastal
areas likely will only see advisory level temps at best.
Long term (tue-fri)...20/141 PM.
Hot temps will be the story next week. Monday will be the start of
it but it looks like the peak will be Tue/Wed as the nearly 600dm high
shifts west. Onshore gradients are also weakest those days so the
combo of a delayed/weak sea breeze and an extremely warm air mass
will drive temps to near record levels. As mentioned in the short
term discussion hot and gusty sundowners that will begin Sunday
evening across southern sb County will continue through Wednesday
evening at least with advisory level winds possible any or all of
those nights. The north push is not as strong with this event as
the last so winds won't be as strong and temps not quite as hot.
But still a potentially dangerous fire weather situation.
Marine layer expected to be shrinking and possibly gone entirely
by Tuesday, especially south of pt Conception. Gradients start
trending onshore Thursday and Friday so some cooling expected for
coast, but less so for inland areas. Some consideration will need
to be given towards extending heat advisories/warnings into
Friday, especially la/Ventura inland areas, however the onshore
flow should keep coastal areas cooler.
At 0012z at klax, the marine inversion was around 1000 ft deep.
The top of the inversion was around 2500 feet with a temperature
near 21 degrees celsius.
North of Point Conception...high confidence for VFR conds at kprb,
with moderate confidence for vlifr/LIFR conds for ksbp and ksmx
from between 07z and 11z and continuing into mid morning. 30%
chance for IFR conds after 14z. Otherwise high confidence after
18z with VFR conds. Expect a similar return of the marine layer
stratus once again Sat eve into Sunday morning.
S of Point Conception...moderate confidence with IFR to low MVFR
cigs as early as 03z to 06z for coastal areas through mid morning
Sat. 30% chance for IFR to low MVFR cigs to develop after 09z for
coastal valleys.Otherwise, hi confidence in VFR conditions at the
rest of the airfields thru Sat morning.
Klax...moderate confidence overall in the 00z taf. Low clouds
with MVFR cigs are expected at the airfield from about 05z-17z
Sat. Otherwise, VFR conditions can be expected thru Sat afternoon.
The timing of the onset and dissipation of the low clouds may be
off +/- an hour or two.
Kbur...hi confidence in the 00z taf with VFR conditions expected
thru Sat morning. 20% chance for IFR/low MVFR cigs after 10z Sat
Generally good to moderate confidence in the current forecast.
For the outer waters, Small Craft Advisory (sca) winds are not
forecast thru Sun morning, then there is a 40%-50% chance of Small Craft Advisory
winds for much of the area Sun afternoon through Mon night, and a
30%-40% chance of these conditions Tue and Wed.
For the inner waters north of Point Conception, Small Craft Advisory conditions are not
expected thru Sun night, then there is a 30%-40% chance of Small Craft Advisory
winds Mon thru Wed.
For the inner waters S of Point Conception, Small Craft Advisory winds are not
expected for pzz655 tonight thru Wed, while in pzz650 there is a
30%-40% chance of Small Craft Advisory winds at times expected for Sun night and
Mon night thru Wed.
A long-period southerly swell originating from the southern
hemisphere is expected to move into the coastal waters early next
week, with up to 3 ft swell possible, but may be as high as 4 ft
Choppy short-period seas will persist across much of the waters
through the weekend.
California...excessive heat watch in effect from Tuesday morning through
Thursday evening for zones 34>38-51. (See laxnpwlox).
Excessive heat warning in effect from 10 am Monday to 8 PM
PDT Thursday for zones 39>41-44>46-52>54-59-88-547. (See laxnpwlox).
Hazard potential outlook (mon-fri).
An extended heat wave is expected Monday through at least
Thursday of next week, especially for inland areas. Elevated fire
weather conditions due to the extended period of hot and dry
conditions, especially southern Santa Barbara County where gusty
sundowner winds will add to the threat. A long period southerly
swell will also bring elevated surf and strong rip current
potential early next week across south facing beaches coinciding
with the heat wave.