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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
230 PM PDT Sat Apr 25 2015

Synopsis...
a fast-moving cold front will continue to move through the area
this afternoon bringing windy and cool conditions with scattered
showers. A warming and drying trend is expected through early next
week as offshore flow develops and high pressure builds aloft. A
cooling trend is likely for the second half of next week.

&&

Short term (tonight-tue)...fast moving cold front continues to bring
scattered showers to portions of Ventura and Los Angeles counties this
afternoon...especially in the mountains. Highest rainfall totals today
have been across the northern coastal and foothill portions of slo
County...where amounts have ranged between .33 and .75 inches as of
2 PM. As the front moves eastward into Los Angeles County this
afternoon...there will be some cyclonic flow aloft that will help to
maintain scattered shower activity...especially in the San Gabriel Mountains
and adjacent foothills. By this evening...most of the shower activity
will be confined to north facing slopes of the mountains. Snow
levels will continue to range between 6000 and 7000 feet.

Main impact of this weather system will continue to be gusty winds.
Increasing southwest to west winds associated with the front this
afternoon as lax-Daggett gradient peaked at +8.2 mb. Winds have picked
up this afternoon across the mountains...Antelope Valley...and many
coastal areas. Wind advisories and high wind warnings have been
posted for several portions of the forecast area. The focus of the
strongest winds this afternoon into the early evening will likely be
the Antelope Valley...where there could be damaging wind gusts to 60
miles per hour along with areas of reduced visibilities in blowing dust. By
tonight...the flow will shift to a northwest direction behind the
front with stronger winds expanding to the Interstate 5 corridor and
the Santa Ynez range. The northerly winds will expand southward
overnight and impact portions of the Santa Clarita valley...San
Fernando Valley...and Santa Monica Mountains.

On Sunday...upper level trough shifts eastward into Four Corners area
while upper ridge of high pressure begins to build over eastern
Pacific. Substantial warming with lighter winds and more sunshine
expected on Sunday...with warmest valleys approaching 80 degrees.
Further warming expected on Monday...as most coastal and valley areas
soar well into the 80s under the influence of a quick burst of
offshore winds. While the offshore lax-Daggett pressure gradient is
not all that impressive with this upcoming event...there is descent
upper level wind support. In fact...latest 12z and 18z NAM models
now showing between 40 and 50 knot 850 mb winds late Sunday night
into early Monday morning. If this were to come anywhere close to
the solution...we could see a widespread Wind Advisory event across
Los Angeles and Ventura counties by Monday morning. In
addition...the associated warming temperatures and low humidities
will bring elevated fire danger to Southern California. While
offshore winds are expected to be significantly weaker on
Tuesday...it will continue to be very warm and dry.

Long term (wed-sat)...
weak upper trough will bring a return of onshore flow and marine layer
clouds during the extended period. Initially...the low clouds and fog
are expected to be confined to coastal areas...but should extend further
inland by Friday. There will be a gradual cooling trend through the
extended period.

&&

Aviation...25/1800z.

Middle/upper level trough of low pressure over the area will continue
moving east and a ridge of high pressure over the eastern Pacific
will approach the area. Upper level strong north winds will become
moderate north after 26/11z while middle level moderate to strong
northwest winds become moderate north after 26/19z. Middle/upper level
moisture will exit the area while areas of lower level moisture
lingers after 26/00z. Freezing level was approximately 8kft this
morning and will differ by plus 3kft Sunday morning.

Marine layer at lax at 1625z is none.

Klax...surface wind 27022g32kt likely between 25/21-26/05z.
Otherwise broken/overcast middle/upper level cloud field becoming
scattered after 26/00z.

Kbur...chance ceilings 025 at times between 25/18-25/20z otherwise
chance ceilings 035-040 through 26/00z and chance -ra at times between
25/20-26/00z.



Virtually certain - 95-100%
very likely - 80-95%
likely - 60-80%
chance - 30-60%
very unlikely - 20% or less

&&

Marine...25/200 PM...
it is likely northwest winds will continue to increase and gale
force gusts will exist from Piedras Blancas to San Clemente Island
late tonight through late Sunday night. The period with the peak
winds and most widespread is likely Sunday afternoon through Sunday
evening. Small Craft Advisory conditions will likely exist 0-10 nm slo County as well
as in Santa Barbara basin to San Pedro basin this afternoon through
Sunday evening. Steep combined seas will likely build to 9 to 12
feet in the outer waters and 6 to 8 feet in the near shore basins
this afternoon and subside Sunday night.

It is likely northwest winds will continue to increase and gale
force gusts will exist from Piedras Blancas to San Clemente Island
late tonight through late Sunday night. The period with the peak
winds and most widespread is likely Sunday afternoon through Sunday
evening. Small Craft Advisory conditions will likely exist 0-10 nm slo County as well
as in Santa Barbara basin to San Pedro basin this afternoon through
Sunday evening. Steep combined seas will likely build to 9 to 12
feet in the outer waters and 6 to 8 feet in the near shore basins
this afternoon and subside Sunday night.

&&

Lox watches/warnings/advisories...
High Wind Warning (see laxnpwlox).
Gale Warning (see laxmwwlox).
Small Craft Advisory (see laxmwwlox).

&&

$$

Public...gomberg
aviation/marine...30
synopsis...sukup

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