Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
925 am PDT Friday Aug 1 2014
high pressure east of the region will keep temperatures above normal
through the weekend. Monsoonal moisture will bring a slight chance
of thunderstorms to the mountains and deserts through Saturday and
to most of l.A. County and the coastal waters Sunday. Night and
morning low clouds will affect much of the coast through the
Short term (today-sun)...low clouds have finally solidified up and
down the coast with a depth around 1300'. It's already cleared to
the beaches in most areas, but a little slower along the central
coast. Not expecting a whole lot of change today from yesterday.
Soundings are noticably drier than yesterday with precipitable waters down a
quarter inch and 850 dewpoints down from around 4c to -4c. Still
fairly unstable across the Ventura/la mountains so I expect we'll see
some more buildups like yesterday. Left in the small dollop of
slight chances for thunderstorms near the la/sbd County line, though with
less moisture to work with any precipitation is going to struggle to reach
the surface. Temperatures today probably a couple degrees cooler than
yesterday on average. Gradients are trending about 1 mb onshore from
yesterday and with more marine layer clouds this morning most areas
(except interior slo) are off to a slightly slower start.
Water vapor images this morning clearly show the demarcation of
monsoon air to our southeast and drier air to our northwest. This is
going to be a huge factor with this weekends weather as we continue
to be on the extreme western periphery of the monsoon surge from the
***From previous discussion***
Stratus tonight will be similar to today as the pressure gradients
and heights are unchanged.
The monsoon front pushes westward Saturday and skies will turn
partly cloudy (maybe even mostly cloudy over eastern l.A. County) a
slight chance of thunderstorms will develop over the la mountains and the Antelope
Valley. Big question mark is how much the cloud cover will inhibit
convective development. The cloud cover will produce a noticeable
drop in temperatures across the area but it will also push up humidities so
it will still be uncomfortable.
The marine stratus will likely be wiped out south of Point
Conception...but the low clouds will continue over the central coast
Saturday night. The big news is the large easterly wave that rotates
through la County overnight. The wave is certainly strong enough to
warrant a slight chance of thunderstorms across much of la County as well as
the adjacent coastal waters.
The monsoon continues Sunday. Partly to mostly cloudy skies will
prevail across the area. The slight chance of thunderstorms will move west into
the vta mountains enough moisture and instability as well as a little
synoptic lift will all contribute to a slight chance of thunderstorms across
l.A. County and the adjacent coastal waters. Maximum temperatures will fall
another degree or two due to the cloud cover.
Long term (mon-thu)...
on Monday the ridge pushes back to the east and a slight trough moves
closer to the West Coast. This will switch the monsoon off and
replace it with dry SW flow over the area.
Then it looks pretty dull all next week. The weak trough to the west
will increase the marine layer. Maximum temperatures inland will be very close
to normal. The slightly deeper than normal for August marine layer
will keep the coasts and valleys a few degrees below normal through the
north of Point Conception...moderate confidence with LIFR conds along
central coast 12z tafs. 20 percent chance that LIFR ceilings could reach
kprb by 11z this morning. 30 percent chance for ceilings to scour out
+/- 1 hours from taf. Similar timing for stratus once again tonight
with similar ceiling conds.
S of Point Conception...moderate confidence with coastal tafs.
Latest acars sounding was around 1400 feet this morning. Low clouds
have pushed into the San Gabriel valley. Expect low MVFR tafs for la
coastal tafs I.E. Klax/klgb...with IFR conds for koxr/kcma/ksba. 30
percent chance for stratus tonight although models indicate a
deeper marine layer influence with low MVFR ceilings after midnight.
However...increasing middle to high clouds expected across the
southern portion of the region might cause low cloud regime to
become chaotic tonight into Sat morning.
Klax...moderate confidence in the 12z taf through 06 this evening...hi
IFR to low MVFR ceilings will scour out between 15z-17z today. Lower
confidence with return timing of MVFR stratus. High clouds will
begin to move across the area by early Sat morning.
Kbur...hi confidence in the 12z taf with VFR conditions expected
through through this evening. 20 percent chance for LIFR/IFR ceilings between
13z-15z today. Moderate confidence for IFR ceilings after 10z Sat
Marine...01/900 am PDT
high confidence in no Small Craft Advisory conditions through at
least the weekend...except for local gusts to 25 knots near Point
Conception tonight. Moderate confidence in some southeast winds
south of Point Mugu including the San Pedro Channel each morning
through the weekend. A disturbance will rotate through the waters
south of Point Mugu on Sunday which may result in thunderstorm
development. Confidence is low on that however...as the disturbance
and instability is weak...and much weaker than what occurred last