Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 061640
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
940 AM PDT FRI MAY 6 2016
A slow-moving low pressure system will bring cool weather to the
region through the weekend, with scattered to isolated showers and
thunderstorms through Saturday. A ridge of high pressure will
build over the area next week, resulting in a gradual warming
trend, with slightly above normal temperatures by mid-week.
An unseasonably cold upper level low pressure system (558 DM with
temps around -22 at 500 mb) was centered over L.A. County this
morning. Plenty of moisture lingered over the forecast area this
morning with lots of cloud cover and a few showers at mid morning,
altho breaks in the clouds were noted over parts of SLO/SBA Counties
and over the Antelope Valley. Mostly cloudy skies overall will
prevail across the forecast area thru this afternoon, and with
continued instability (12Z NAM sfc-based CAPE as low as 1257 J/KG
over SBA County mtns), cold 500 mb temps, cyclonic flow aloft, and
strong early May sunshine, the threat of showers and isolated
thunderstorms will continue especially for the mtns and deserts,
altho with weak steering flow out of the nw some of this activity
could drift to the vlys and coast mainly over VTU/L.A. Counties this
afternoon. PWAT values today will be around 0.85 inch which is above
normal for this time of year. Any thunderstorms that develop will
not move very fast, and there is the threat of heavy rain which
could lead to a flash flooding threat. As a result, a FLASH FLOOD
WATCH is in effect from noon thru 8 PM for the Cuyama Vly, mtns of
SBA/VTU/L.A. Counties,and the Antelope Vly. Please see the latest
FLASH FLOOD WATCH statement (LAXFFALOX) for further details. Any
thunderstorms today could also produce small hail, dangerous cloud-
to-ground lightning and gusty winds. In addition, snow levels will
be around 6000 to 6500 feet thru today, with a possibility of some
light accumulating snow fall above 6500 feet.
The upper level low will elongate to the w off the coast tonight,
then extend from the Great basin into far srn CA on Sat. This system
will then move e across the southern Great Basin Sat night and Sun
as upper level ridging builds off the CA coast.
A slight chance to chance of showers will linger across the forecast
area tonight and Sat, altho showers will be likely in the mtns this
evening and again Sat afternoon. A slight chance of thunderstorms
can also be expected Sat afternoon mainly over the mtns and Antelope
Vly thanks to lingering moisture and slight instability.
Additional rainfall amounts today thru Sat will be highly variable
due to the convective nature of this weather system. Most areas
across the coast and vlys should receive 0.15 inch or less. In the
mtns, about 0.20 to 0.33 inch is expected with local higher amounts
of around 0.50 inch in the VTU County mtns. However, where any
thunderstorms occur today, isolated precip amounts up to an inch
cannot be ruled out.
Snow levels of 6500 to 7000 feet are expected tonight thru Sat.
Additional accumulating snow is possible where showers and
thunderstorms occur in the higher mtns, with local totals of 4 to 6
inches possible thru Sat above 7000 feet for VTU County, and locally
up to 2 to 4 inches possible above 7000 feet for L.A. County.
A slight chance to chance of showers will persist Sat evening in all
areas, with a slight chance of thunderstorms mainly in the mtns and
Antelope Vly. A slight chance of showers will then linger later Sat
night for the mtns and deserts. By Sun, the NAM/GFS were indicating
no measurable rain for the forecast area on Sun, with a much more
stable air mass moving in. There may be some cu buildups in the mtns
on Sun, otherwise partly to mostly cloudy skies should prevail
across the region as some moisture will linger over the area.
Temps will be much cooler than normal across the area today thru
Sun, with highs ranging from 7 to 16 deg below normal for today,
from about 3 to 13 deg below normal overall for Sat, and 2 to 12 deg
below normal for Sun. Hi temps for the cst and vlys will be
generally in the 60s today, then warm slightly into the mid 60s to
low 70s for Sat, and upper 60s to lower 70s for Sun.
***FROM PREVIOUS DISCUSSION***
EC/GFS continue to be in good agreement Mon thru Thu.
Upper level ridging will build off the California coast Monday
and become amplified by Tue. This ridge will then shift over
California Wednesday and Thursday. Expect dry and warmer
conditions through the extended period. Some night and morning
marine layer low clouds and fog should affect some coastal and
coastal valley areas at times, otherwise clear to partly cloudy
skies can be expected across the region for Mon thru Thu. High
temps will be around normal by next Tue and Wed, and then warmer
than normal for many areas by Thursday, with the warmest vlys
reaching the mid 80s.
At 12Z...There was no marine inversion at KLAX.
Low to moderate confidence in the current forecast. Ceilings at
or below 5000 feet will be prevalent across the region. Periods of
MVFR conditions are possible in rain/showers. There is a chance of
IFR conditions in heavier rain/showers. There is a slight chance
of thunderstorms east of KNSI-KSBA-KPRB line.
KLAX and KBUR...Low to moderate confidence in the current
forecast. Ceilings at or below 5000 feet will be prevalent.
Period of MVFR conditions are possible in rain/showers, mainly
between 16Z and 22Z. There is a 20 percent chance of
thunderstorms and a 30 percent chance of IFR conditions during
unstable air will bring isolated thunderstorms to the coastal
waters south of point conception today. these storms will be
slow moving...and could produce localized gusty winds and
waterspouts. otherwise...high confidence in generally light winds
under 20 kt and mild sea conditions through the weekend.
CA...Flash Flood Watch in effect until 8 PM PDT this evening For
zones 38-52>54-59. (See LAXFFALOX).