Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
440 PM PDT Friday Jul 11 2014
..updated aviation discussion...
Weak low pressure off the coast will keep a deep marine layer in
place through Friday...with slightly below normal temperatures. High
pressure will expand west again over the weekend...resulting in a
significant warming trend for inland areas. Monsoonal flow will
return by Sunday...bringing a slight chance of thunderstorms for the
mountains and deserts through at least Thursday.
Short term (today-mon)...made minor changes through the period.
Guidance initialized a long wave ridge centered over the Great Basin
and trough over the eastern Pacific reasonably well. And guidance
was consistent between suites as well as with previous runs through
the period. The ridge down stream will likely propagate west over
the area and the marine layer's inland-reach will shrink each night.
Temperatures over the entire area will rise through the period. This
morning's temperatures in the lower elevations were 5 to 10 degrees
above seasonal normal and they differed plus or minus 3 degrees from
normal in the higher elevations. Saturday morning's low temperatures
will differ from this morning by minus 4 degrees in the lower
elevations to plus 3-6 degrees inland and in the higher elevations
and temperatures will likely be 3-6 degrees above normal over the
entire area Saturday morning. Afternoon temperatures will differ by
approximately plus 3-6 degrees each day from the previous day
through Sunday and likely be 5 to 10 degrees above normal by Sunday
excluding the beaches along the central coast. A dry modified air
mass currently over the area will become moist tropical as the ridge
shifts west over the area. As the air mass changes temperatures will
differ by minus 2-3 degrees on Monday from Sunday. As the moisture
gradually propagates north over the area the chance of thunderstorms
will spread north. Will continue with a slight chance of
thunderstorms over the San Gabriel Mountains Sunday and then over
the desert and Ventura County mountains Monday.
Long term (tue-fri)...made minor changes through the period.
Guidance was consistent with previous runs and the long wave ridge
continues to shift west over the eastern Pacific through the period.
The bulk of the tropical moisture and steepest lapse rates are
centered over the area Tuesday. Will continue with a chance of
thunderstorms Tuesday afternoon and evening and slight chance each
afternoon Wednesday through Thursday. A slight cooling trend will
continue through Wednesday and temperatures will differ by minus 2-3
degrees each day from the previous day. Little temperature change is
expected Thursday through Friday and temperatures may range from 3
degrees below normal in the lower elevations to 2 degrees above
normal inland and the higher elevations.
marine layer depth expected to shrink somewhat overnight...most likely
in the 1500 foot range. Satellite imagery showing a good burnoff of low
clouds this afternoon. As a result...have backed off onset of ceilings across
most coastal areas south of Point Conception. With marine layer depth
expected to lower...higher probability of IFR ceilings across coastal and
coastal valley locations overnight into Saturday morning...with localized
LIFR conditions possible at ksmx and kbur. Due to the shallower marine
layer...only about 50 percent chance of brief ceilings reaching kbur and
ksba...and 30 percent at kvny.
Klax...due to good burnoff of low clouds off the coast...have delayed
onset of ceilings in current 00z taf package until 06z...but there is a chance
of even later arrival. Higher probability of IFR conditions if ceilings
do develop tonight.
Kbur...moderate confidence in brief IFR or LIFR conditions at kbur
early Saturday morning. Rapid burnoff expected.
small craft advisories have been extended through Sunday night
for outer waters due to increased confidence in prolonged period
of increasing winds.
Inner waters... locally gusty west to northwest winds across the
western portion of the inner waters with a thirty percent chance for
gusts to 25 knots this afternoon and evening and again Saturday
afternoon and evening and through the weekend.
Small Craft Advisory (see laxmwwlox).
Beach hazards statement (see laxcfwlox).