Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
435 am PDT Friday Jul 25 2014
Updated aviation section
high pressure will remain anchored over the Desert Southwest through
the middle of next week. This will result in continued warm
temperatures across the area. Southerly flow around the high
pressure will bring in some high clouds this weekend...and the
slight possibility of some showers or thunderstorms over the Los
Angeles mountains by Sunday. Otherwise...some night and morning
stratus and fog can be expected across the coastal plain.
Short term (today-sun)...overall...00z models in good synoptic
agreement through the period. At upper levels...ridge will remain
centered around the 4-corners area through the weekend. Near the
surface...moderate onshore flow will prevail (with the strongest
onshore gradients today and saturday).
Forecast-wise...main challenges will be cloud cover and temperatures.
With the position of the upper ridge...the middle-level flow will
remain southeast to south through the weekend. This will open the
door for moisture to stream in from northern Mexico. So...will
expect varying amounts of middle/high level clouds through Sunday...which
will result in a general partly cloudy condition. With regard to any
threat of convective precipitation...models do not indicate any
great chances. There could be a mountain sprinkle or two this
afternoon or Saturday afternoon. On Sunday...models do indicate a
bit better instability...so will leave the slight chance probability of precipitation over
the San Gabriel Mountains.
With the return of the onshore flow...the marine layer stratus
should be able to get reestablished across the coastal plain through
the weekend. For today through Saturday...stratus/fog should impact
the central coast and the lax coastal plain. By Sunday morning...will
expect the stratus to extend a bit further north into Ventura
County. Of course...would not be surprised to see the marine
inversion have its own ideas...as it is the great humbler of the
As for temperatures...today will actually be several degrees cooler
(due to a switch to onshore flow)...but still a few degrees above
seasonal normals. On Saturday and Sunday...there will be minor
fluctuations in temperatures...but still most areas will remain a
few degrees above seasonal normals. Overall...very typical
As for winds...the return of moderate onshore gradients will produce
the typical gusty southwesterly winds across interior sections each
afternoon and evening. However...wind speeds should remain below
Long term (mon-thu)...for the extended...models remain on the same
synoptic Page...but differ in some details. At upper levels...ridge
will remain dominant feature over the southwest. The GFS keeps the
ridge centered over New Mexico while the European model (ecmwf) actually centers the
ridge over the California/Arizona border. Near the surface...weak to
moderate onshore flow will prevail.
Forecast-wise...nothing too exciting expected through the period. No
matter which model verifies with regard to the placement of the
upper ridge...the amount of middle-level clouds/moisture should
decrease through the period. So...no significant chances of any
convective precipitation through the period...and a general mostly clear
sky condition (outside of the marine layer stratus). With regard to
the stratus...will expect stratus/fog to continue to impact the
coastal plain each night/morning with minor day-to-day changes in
areal coverage. As for temperatures...only minor changes are
expected from day to day...with most areas remaining at or slightly
above seasonal normals.
stratus was widespread on the central coast and in the Santa Ynez
Valley...and across coastal sections of l.A. County. Expect stratus
to push into coastal sections of vtu County by daybreak. Conds will
be mostly low MVFR or high IFR. Expect skies to clear my middle or late
morning all sections. Expect similar low clouds coverage tonight/say
morning...but expect ceilings to arrive earlier in the night.
Klax...moderate confidence in taf. There is a 20 percent chance that
ceilings will slip into the IFR category for 1 to 3 hours through 16z.
There is a 10 to 20 percent chance that ceilings will linger until as
late as 19z. There is a 20 percent chance that east winds will reach
or exceed 9 knots between 13z and 16z.
Kbur...high confidence in VFR conditions through the forecast period.
Will be updated with 12z taf package.
Good confidence that Small Craft Advisory conds across the southern
two outer waters will decrease by middle morning. Otherwise...not
widespread significant hazards expected.
Fire weather...25/220 am...
elevated fire danger across interior sections of forecast area this
afternoon and evening due to combination of gusty onshore
winds...very warm temperatures...and low humidities. Onshore winds
gusting between 25 and 35 miles per hour will be common across the interior
valleys...mountains...and deserts...with local gusts as high as 45
miles per hour across the favored foothills of the Antelope Valley.
Meanwhile...many of these same areas will see humidities falling
into the teens during the afternoon hours...with isolated single
digit readings in the mountains and Antelope Valley. While brief
critical fire weather conditions will be possible in the mountains
and Antelope Valley today...there will not be a sufficiently
long duration to warrant a red flag warning.
Small Craft Advisory (see laxmwwlox).