Weather Service Report

FXUS66 KLOX 260406

906 PM PDT Tue Oct 25 2016

An overnight marine layer will linger into Wednesday with near
normal temperatures. A low will arrive Thursday, and with
subtropical moisture should bring a slight chance of thunderstorms
and peak precipitation amounts from Thursday night into Friday.
Another low will bring possible precipitation for early next week
with below normal temperatures.



The marine inversion this evening ranged from near 800 ft deep at
KLAX to near 1100 ft deep at KVBG. Clear skies covered the forecast
area this evening. Low clouds have developed along and off the coast
around Point Conception. Additional low clouds are forecast to
develop over the SoCal bight thru tonight, with some low clouds
moving into the coast both n and s of Point Conception. However, 00Z
NAM boundary layer moisture would suggest patchy low clouds at the
coast later tonight, especially further s. Otherwise, mostly clear
skies will prevail across the forecast area thru the night.

Upper level ridging over srn CA this evening will persist thru Wed,
with a broad sw flow aloft. A deep upper level trof will develop
over the e Pac well off the CA coast on Wed, with an upper low at
the base of the upper trof near 30N/132W by late Wed night. The
upper low is forecast to track ne toward CA Thu and Thu night. The
00Z NAM is much slower with the movement of the upper low than the
12Z EC and 18Z GFS, with the EC the fastest moving the system inland
over CA Thu evening, and the GFS in the middle with the system
moving into the CA coast late Thu night. The 00Z NAM moves the
system inland Fri morning. There will be a decent cold front with
this storm system, which is expected to push across the region
sometime between Thu night and Fri morning. There is not a lot of
confidence in the exact timing of the system, however, there is good
confidence that a storm with significant rainfall will affect swrn
CA between Thu afternoon and Fri. This storm system will tap into
plenty of subtropical moisture, with PWAT values much above
normal all the way up to near 1.80 inches according to the 00Z NAM.

Generally quiet wx will prevail across the region Wed and Wed night,
with mostly sunny skies most areas Wed giving way to increasing
clouds Wed night. 

Warm frontal rain out ahead of the main storm system should begin to
push mainly into SLO/SBA Counties by Thu afternoon. The rain will
spread into VTU/L.A. Counties Thu night. The most significant rains
will arrive with the cold front Wed night along the Central Coast.
The front will slide eastward thru the forecast area late Thu Night
and Fri morning before moving e of the region by early Fri
afternoon, with a few leftover showers Fri afternoon into into Fri
evening. There are also indications that enough instability may
accompany the Pacific storm (e.g., most unstable CAPE up to 500
j/kg) for the development of a few thunderstorms with the main front
as it passes thru the region Thu night.

Gusty south winds possibly to advisory levels will prevail over
higher terrain ahead the front Thu night and early Fri, with
orographic pcpn enhancement expected. Rainfall amounts with this
storm system are expected to be 0.5-1.00 inch across most areas with
0.25-0.5 inch in the deserts. However, the foothills and mountains
will likely see 1-2 inches, and the favored coastal hills in San
Luis Obispo County could see up to 2-4 inches.

Significant rainfall rates of 0.50 inch per hour or higher will be
possible with the storm front, especially in any thunderstorms, so
the threat of flash flooding and debris flows in recent burn areas
can be expected across the forecast area. It looks like flash flood
watches for the recent burn areas will be needed, likely issued
either tonight or sometime on Wednesday. 

Temps across the region are expected to be near to slightly above
normal across the region Wed, from near to slightly below normal
north to several degrees above normal south on Thu, and several
degrees below normal in all areas on Fri.



A Gulf of Alaska low pressure trough reinforces southwest flow
aloft over California over the weekend. Another cold front will
remain north of our region Saturday, but some cloud cover is
likely across the central coast and overall temperatures do not
warm that much. This front slides across southwest California late
Saturday night and Sunday with the focus for any rain staying
mostly north of Point Conception. For now have low chance
probabilities of rain for western SBA and SLO Counties then. A
mixture of clouds will be found across the rest of the area with
another coolish day. 

For early next week it looks like a weak ridge will build overhead
on Halloween for a dry day and moderating temperatures. There is
quite a bit of uncertainty in the medium range models beyond
Monday, but another weak trough could bring more rain to the
central coast to start the month of November on the right path. 



At 2302Z, the marine inversion at KLAX was at 1400 feet deep.
The top of the inversion was at 2600 ft with a temp of 18 deg C.

Moderate confidence overall in the 00Z TAFs. Low clouds and IFR/LIFR
conditions are expected to develop at the coastal and some vly
airfields. However, there is uncertainty in the onset times of the
low clouds which could be off +/- 2 hours. There is also uncertainty
in the extent of the low clouds with some airfields having minimal
low cloud coverage thru Wed morning. The low clouds are forecast to
develop between 09Z-11Z tonight and persist until late Wed morning
to early Wed afternoon. For KPRB, there is a 50 percent chance of
IFR vsbys and cigs late tonight and early Wed. For KBUR, scattered
low clouds and MVFR vsbys are forecast late tonight into Wed
morning, with a 40 percent chance IFR cigs could develop. Otherwise,
VFR conditions will prevail at the airfields thru Wed afternoon.

KLAX...Moderate confidence overall in the 00Z TAF. Low clouds and
LIFR conditions are expected to develop by 09Z, improve to IFR by
14Z, MVFR by 18Z, and VFR by 20Z, with VFR conditions expected thru
Wed evening. The timing of the development of the low clouds could
be off +/- 2 hours or so. 

KBUR...Generally hi confidence in the 00Z TAF. VFR conditions are
expected at the airfield for the most part thru Wed afternoon,
except for a period of MVFR vsbys 12Z-16Z. However, there is a 40
percent chance that LIFR cigs could develop at the airfield late
tonight into early Wed morning.


.MARINE...25/900 PM

There is high confidence that winds and seas will remain below
SCA levels through at least Thu. South to southeast winds will
likely reach SCA levels by Thursday night for the outer waters as
the next Pacific storm moves into the region. Patchy dense fog
with vsbys 1 nm or less will be possible over the coastal waters
tonight through Wednesday morning.






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Western Regional Climate Center,