Scientific Forecaster Discussion
fxus66 klox 262038
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
138 PM PDT Mon Jun 26 2017
an upper level trough off the California coast will weaken high
pressure aloft starting this afternoon and bring a cooling trend
as onshore flow strengthens. One more day of very warm
temperatures expected inland before cooling down to more normal
highs for this time of year by midweek. Expect low clouds and fog
to redevelop after today and continue through the week.
Temps were off to a fast start today and definitely warmed up
above what models were showing yesterday but so far at least we
haven't seen that west wind arrive to help really push the temps
up in the San Fernando Valley. Could still happen through mid to
late afternoon though. Otherwise, the forecast for the rest of the
week is virtually unchanged. Very minimal low cloud development
expected tonight south of pt Conception but there should be some
along the central coast later on. Then increasing coverage Tuesday
night into Wed as a weak eddy develops and troughing along the
West Coast helps increase onshore flow and deepen the marine lyr.
Temps will respond accordingly. Cooler Tuesday (but still above
normal) with a more typical afternoon sea breeze, then additional
cooling Wed bringing highs down to near normal or even slightly
below normal in some areas. Little change Thu with again clouds
pushing into the coastal valleys overnight.
Still a decent northwest gradients across the Santa Ynez range the
next couple night but minimal support aloft. So for the most part
winds should remain below advisory levels. The northwest flow and
warm air mass will help keep South Coast temps in the 80s Tuesday
and possibly even near 90 in some isolated spots.
A Little Ridge will pop up Friday to help push temps up a few
degrees in most areas but the warm up will be brief as weak
troughing returns for the weekend. Still a little uncertainty with
this though as models have sort of been bouncing around with the
weak trough/ridge scenario. Probably not a huge difference either
way as temps should remain within a few degrees of normal through
early next week.
At 17z at klax...there was a 300 ft marine layer. The inversion
top was 2800 ft with a temperature of 31 degrees celsius.
High confidence in VFR conditions everywhere through 03z today,
with very hot conditions stronger than usual west winds. Kvny
likely to have rare west wind again today. 70 percent chance of
LIFR/IFR ceiling at ksmx tonight, 40 percent chance at ksbp kprb, 20
percent chance at klgb klax ksmo. Moderate confidence in VFR
conditions everywhere else through Tuesday.
Klax...high confidence in VFR conditions through 08z, with a 20
percent chance of IFR conditions mainly from 10-17z Tuesday. West
wind gusts between 20 and 30 knots likely this afternoon. No
significant east winds expected through Tuesday.
Kbur...high confidence in VFR conditions through at least
Tuesday. 40 percent chance for the same rare west wind today as
that occurred yesterday. If wind does not occur, temperatures will
top out around 100. If wind does occur, 110 is possible.
High confidence in Small Craft Advisory (sca) conditions from the
central coast to San Nicolas Island through at least Thursday.
The strongest winds of the period will be today and tonight.
Moderate confidence in low end scy conditions over the Santa
Barbara Channel and Santa Monica basin through tonight...with
similar but slightly weaker winds on Tuesday. The stronger winds
will generally be over the western portions of these areas, but
the winds should be fairly widespread through this evening.
There will be lulls each morning within 10 miles from the coast,
but the scy will extend through those lulls to highlight the
extended period of gusty afternoon and night winds.
Two distinct wave types will be observable over the waters, with a
long period (13-15 seconds) south to southwest swell through
Tuesday, and a short period (6-8 second) west swell and/or wind
wave. The buoys will likely highlight the long period swell, but
the short period swell will be most noticeable and will be
highlighted in the forecast. By the middle to end of the week, the
short-period west swell will dominate as the south swell fades.
Fire weather...26/130 PM.
Red flag conditions reported at about a dozen reporting sites
within the warning area as of 1 PM PDT this afternoon. Widespread
single digit relative humidities run from all across the Antelope
Valley, into the western two thirds of the la County mountains,
and extending northwestward into the Santa babara County
mountains. Along with this warm and very dry air are areas with
west and southwest winds gusting between 30 and 40 mph, including
at Lake Palmdale, ozena, and Lancaster. The highest gust reported
thus far has been 47 mph at Mill Creek. These winds will remain
around this intensity through the afternoon before decreasing over
the course of the evening. Thus the current expiration time of 9
PM looks good for rfw over Antelope Valley, la County mountains,
and Santa Clarita. The only wildcard will be if duration criteria
will be met. Elsewhere outside of the rfw there is still an
elevated fire weather concern across the Ventura and Santa Barbara
County mountains and across the higher elevations of the Santa
Barbara South Coast where rufigio is reporting 18% relative humidity and winds
gusting in the 20-28 mph range.
Expecting a light sundowner event along the western portion of
the Santa Barbara South Coast. Sba-smx pressure gradient peaks out
at -4.0 tonight. With continued dry air in place and winds
expected to gust around 35 to 40 mph, primarily in the passes and
canyons from Gaviota to Goleta, elevated fire weather conditions
are expected over that area this evening and again on Tuesday
Fire weather conditions improve a bit Tuesday all areas with the
upper level ridge beginning to weaken, bringing cooler temperatures
and slightly higher minimum relative humidities. The single digit
relative humidities will be restricted to far eastern Antelope
Valley, although min rh's in the lower teens will reappear across
all interior sections. Winds, however, will not be as strong as
today's, but still breezy in spots in the afternoon to warrant
The upper ridge changes little through the week as temps cool some
around midweek before a possible bump up again by Friday. Overall
expect fire weather conditions to be below elevated Wednesday-Fri.
California...heat advisory in effect until 9 PM PDT this evening for zones
53-54-88-547. (See laxnpwlox).
Red flag warning in effect until 9 PM PDT this evening for
zones 254-259-288. (See laxrfwlox).
Pz...Small Craft Advisory in effect until 3 am PDT Wednesday for
zones 645-650-670-673-676. (See laxmwwlox).
Small Craft Advisory in effect until 3 am PDT Tuesday for
zone 655. (See laxmwwlox).
Hazard potential outlook...(thu-mon)
no significant hazards expected.