Scientific Forecaster Discussion
fxus66 klox 221720
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
920 am PST Wed Feb 22 2017
A low will bring gusty winds and possible precipitation to the
mountains into Thursday morning. Elsewhere the clouds will
decrease into Friday and temperatures should stay below normal
into Tuesday. One low will arrive from the north on Saturday and
spread precipitation to Los Angeles that night and into Sunday.
Then another low on Monday will continue the precipitation into
Morning temperatures are running five to ten degrees cooler in
most locations. Not surprising as the mostly clear skies allowed
for radiational cooling last night. The afternoon temperatures
will be more of a mixed bag however as an increasing northerly
flow will bring a cooler airmass to the region. Locations to the
north and on the north side of the larger mountain ranges will
have temperatures peak early and cooler than the temps of
yesterday. Locations to the south and closer to the coastline with
likely be a few degrees warmer than yesterday.
More impactful will be the gusty winds that will develop over the
mountains and adjacent valleys. Wind advisories in place beginning
this afternoon and continuing into the evening for some and into
Thursday morning for others look to be on track. Areas below
passes and canyons may get a period of stronger gusts late this
evening. It is also possible that showers may develop at the
higher elevations and a little snow could fall down to 6000 feet
in the evening and down to 4500 feet overnight. Precipitation
amounts will be low but travelers should be watchful for wet
roadways in addition to preparing for the gusty winds.
Still Head scratching a bit regards the weekend storm. Timing wise
it seems to be settling into a mostly Sunday timeframe and probably
Sunday afternoon and evening for the heaviest rainfall. However
there continues to be a fair amount of waffling regards how much
rain may fall. Will expect it to be generally wet but pinning down
the amounts will most likely take another day or two or three.
The overall forecast package looks good and not much change is
expected to the when and where... mostly will be tinkering with
the how strong and how much.
Drying westerly flow is over the area now. To the west there is a
very weak cold front. This front will move over the area today. It
will likely not bring rain but it will usher in a northerly wind
event. This mornings sky forecast will be tricky as the all the
high clouds have left the area reveling a landscape of random low
clouds. The afternoon will be partly cloudy or perhaps even
mostly sunny. The only exception will be the north slopes where
north winds will pile up the clouds and generate a chc of showers.
The bigger news is the winds. North flow and cool air advection
behind the front will combine to produce advisory level wind gusts
later this afternoon across the mtns... the sba South Coast...the
Antelope Vly and the central coast. A little bit later the winds
will work their way into the Santa Clarita Vly. In addition to the
advisory areas there will be local gusts to 35 mph a few miles
either side of the la/vta County line. The winds will peak
overnight. Clouds and a chance of showers will persist over the
north slopes as well as spilling into the Cuyama Vly.
Cool and dry northwest flow aloft is on tap for Thursday. The day will
be mostly sunny except for the lingering clouds and chc of
showers on the north slopes. Enough cool air will be in place to
lower the snow level to the pass level and the Grapevine will
likely see a dusting of snow. The advisory level winds will end by
There will be another little burst of I-5 corridor winds Thursday
evening. Perhaps it will be worthy of a low end advisory.
The dry northwest flow flattens to dry westerly flow as a cold upper low
pushes out of British Columbia and down off the Washington coast.
With all of the cool air filtering into the area Max temps across
the coasts and vlys will range from 58 to 64 all three days or
about 4 to 8 degrees blo normal.
Both the ec and the GFS agree that the westerly flow aloft will
continue into Saturday. The day will be quite similar to Friday
except there will be a slow ramp up in mid and high level clouds
due to the slow approach of an upper low. Max temps will be a
degree or two cooler as hgts slowly fall and clouds slowly
Both the ec and the GFS agree that rain will develop over the area
sometime Saturday evening or perhaps early Sunday before dawn.
Both mdls further agree that it will rain most everywhere and for
most of the day on Sunday. The rain will turn to showers Sunday
night in the wake of the front. The shower activity will continue
through the day on Monday aided by the passage of a secondary
The big question is how big a storm this is going to be. The GFS
is much more bullish than the ec. It forecasts a fully cut off low
that has a more westerly over water trajectory. The ec brings an
open trof through the area with a slightly more easterly (and
hence drier) trajectory. If the GFS comes to pass this will be a 1
to 3 inch rain producer if the ec is correct then it will be a
half inch local one inch storm. Both mdls have been tenaciously
holding on to their solutions so will have to take a wait and see
approach to the forecast for now.
Dry northwest flow and cool air advection will make Tuesday a partly
cloudy...cool and breezy day.
At 1030z, there was no marine inversion at klax.
Overall, moderate confidence in 12z taf package. Through 20z, low
confidence in coastal/valley taf sites as MVFR to LIFR cigs and
vsbys will continue to form and dissipate haphazardly. After 20z,
high confidence in taf package as developing northerly flow should
keep all sites VFR through tonight.
Klax...overall, moderate confidence in 12z taf. Low confidence in
forecast through 20z as there is a 50% chance of IFR/MVFR cigs and
vsbys developing. After 20z, high confidence in VFR conditions
prevailing. This evening, after 02z, there will likely be some
northerly cross winds with a 30% chance of cross winds exceeding
Kbur...overall, moderate confidence in 12z taf. Through 20z,
moderate confidence in VFR conditions (30% chance of IFR/MVFR cigs
and vsbys developing). After 20z, high confidence in VFR
conditions. There is a 30% chance of light turbulence/low level wind shear
developing after 02z.
For the outer waters, high confidence in current forecast.
Northwest winds will increase today, reaching Small Craft Advisory
(sca) levels, with the Small Craft Advisory level winds continuing through Thursday
night. Winds and seas will diminish on Friday, but southerly winds
will increase on Saturday/Sunday with a high likelihood of Small Craft Advisory
For the inner waters, high confidence in current forecast. West to
northwest winds will increase today, reaching Small Craft Advisory levels, with the
Small Craft Advisory level winds continuing through Thursday evening. On Friday,
winds and seas will diminish below Small Craft Advisory levels. However on
Saturday, southerly winds will increase to Small Craft Advisory levels north of
Point Sal with southeasterly winds increasing to Small Craft Advisory levels south
of Point Conception on Sunday.
California...high surf advisory in effect until 3 PM PST this afternoon
for zones 34-35. (See laxcfwlox).
Wind Advisory in effect from 2 PM this afternoon to 9 PM PST
this evening for zones 34-35. (See laxnpwlox).
Wind Advisory in effect from 3 PM this afternoon to 10 am PST
Thursday for zones 39-52>54. (See laxnpwlox).
High surf advisory in effect until 9 PM PST Thursday for
zones 40-41-87. (See laxcfwlox).
Wind Advisory in effect from 3 PM this afternoon to 3 am PST
Thursday for zones 59-88. (See laxnpwlox).
Pz...Small Craft Advisory in effect until 3 PM PST Thursday for
zones 645-670-673-676. (See laxmwwlox).
Small Craft Advisory in effect from 2 PM this afternoon to 3
am PST Thursday for zones 650-655. (See laxmwwlox).
Hazard potential outlook...(fri-tue)
more rain and wind is expected over the weekend.