Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 051223
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
423 AM PST Mon Dec 5 2016
An upper low will move into the Pacific Northwest today then drop into
the Great Basin Tuesday, bring onshore flow and a cooling trend to the
area. Gusty northwest winds will affect portions of the region late
Tuesday and Tuesday night. Winds will turn northeasterly on Wednesday,
bringing warmer weather. Moist westerly flow will develop across northern
and central Thursday and persist into the weekend. There will be a slight
chance of rain north of Point Conception at times from Thursday through
Sunday, with partly cloudy skies and seasonable temperatures elsewhere.
Areas of low clouds have developed on the SBA County Central Coast
and the Santa Ynez Valley this morning, and across coastal sections
of L.A. County. The marine inversion was very low, around 300 feet,
so there was a fair amount of dense fog across the L.A. County
Coast. Have issued a dense fog advisory for this area through mid
morning. There will be local dense fog on the Central Coast and in
the Santa Ynez and Salinas Valleys, but not widespread enough for
Heights and thicknesses will lower across the region today.
Gradients were already more that 3 mb onshore between KLAX and
KDAG. The WRF was handling this poorly, showing neutral gradients
at this time. With increasing onshore flow and cooling at 850 and
950 mb, expect several degrees of cooling in all areas today.
A trough moving through the Pac NW will drop into the Great Basin
tonight and Tue, with cyclonic northwesterly flow aloft developing
across the forecast area. The WRF continues to show a deepening
marine layer tonight, with an eddy circulation across the inner
coastal waters, and plenty of night through morning low clouds in
coastal and valley areas of L.A. and VTU Counties. In fact clouds
could push into coastal areas as early as late this afternoon or
evening. There will also be some low level lift across L.A. and
VTU Counties, so there may be some drizzle there late tonight and
Tue morning, especially in the foothills. Clouds may hang on
stubbornly near the L.A. and VTU coast into Tue afternoon.
Increasing N-S gradients across SLO and SBA Counties tonight may
be strong enough for some locally gusty north winds through and
below passes and canyons of the Santa Ynez Range into the S Coast
of SBA County, and that should keep skies mostly clear there.
Gusty winds may also develop across the Interstate 5 corridor
tonight. Strong west winds will affect the Antelope Valley
Tuesday afternoon, possibly strong enough to warrant wind
advisories. There will likely be a couple of degrees of
additional cooling in most areas Tue.
Gusty nw-n winds may require advisories across the Santa Ynez
Range and adjacent south coast of SBA County Tue night, and across
the I-5 Corridor as well. Low level flow will turn northeasterly
by early Wed, producing some locally gusty NE winds across L.A.
and VTU Counties, possibly close to advisory levels. Skies should
be mostly clear. Max temps will likely rise several degrees on
Wed, especially west of the mountains.
Heights will rise across the region on Thu. All models continue
to show abundant moisture and rainfall pushing into the West
Coast to the north of the forecast area Thu. The WRF is farthest
south with rain associated with a weak warm front on Thu, bringing
light rain into SLO and most of SBA Counties as early as Thu
morning. Have gone with slight chance pops there all day Thu.
Elsewhere, skies will be partly cloudy, and temps will near or
possibly slightly above normal.
General zonal flow pattern will persist across CA Fri through the
weekend, with a couple of weak impulses rippling through the flow
and enhancing rainfall at times across northern and central CA.
While most of the significant rain will remain north of the
region, there will be at least a slight chance of rain in areas
north of Pt Conception Fri through Sun, depending upon which model
is correct. For now, will keep the slight chance pops in the
forecast for SLO and SBA Counties through the period, even though
it will likely be dry for much of that time. South of Pt
Conception, expect partly cloudy skies with near to slightly above
normal temps Fri through Sun.
At 1130Z at KLAX, the marine layer was near 300 feet deep. The top
of the inversion was at 1300 feet with a temperature of 13 degrees
Good confidence in TAFs other than KSMO, KLAX and KLGB through
02Z. Low confidence in coastal TAFs after 02Z with timing and hgt
uncertainties of low clouds return. There is a 30 percent chc of
IFR cigs. Cigs could develop anytime from 02Z-08z.
Low confidence in the LA cstl TAFs due to timing and hgt of
clouds and vis this morning and then again after 02Z. Dense fog
could linger until 17Z and IFR conds could linger until 20Z. There
is a 30 percent chc of IFR cigs. Cigs could develop anytime from
KLAX...Moderate confidence in TAF. There is a 30 percent chc vis
less than a half mile will persist to 17Z. There is a 30 percent
chc of IFR cigs 03Z-14Z. There is a 40 percent chc of MVFR cigs
KBUR...Very good confidence in 12Z TAF.
Outer Waters...High confidence in SCA winds lasting through early
Wednesday. The SCA winds will likely continue into Wednesday in
zones 673 and 676. There will be local Gale Force gusts during
the afternoon and evening hours through Tuesday.
Inner Water...Good confidence in Todays forecast. Fair confidence
in Tuesdays forecast with a 30 percent chc of SCA winds across the
western third of the area.
CA...High Surf Advisory in effect until 4 PM PST this afternoon
for zones 34-35. (See LAXCFWLOX).
Dense Fog Advisory in effect until 9 AM PST this morning for
zone 41. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 PM PST Wednesday for
zones 670-673-676. (See LAXMWWLOX).
.HAZARD POTENTIAL OUTLOOK...(WED-SUN)
No significant hazards expected.