SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NWS LOS ANGELES/OXNARD CA
AFDLOX 945 PM PST TUE FEB 19 2002
SOME RISIDUAL LOW LEVEL MOISTURE ALONG THE CENTRAL COAST THIS EVENING
IN THE FORM OF LOW CLOUDS. S OF POINT CONCEPTION...ACARS SOUNDINGS
SHOWING A WEAK INVERSION ABOUT 3500 FEET OVER LAX...AND ONE SOUNDING
INCLUDING THE DEWPOINT WAS SHOWING A MOIST LAYER UP TO ABOUT 2000
FEET. A FEW LOW CLOUDS ALREADY DEVELOPING ALONG THE L.A. COUNTY COAST
THIS EVENING. SOME LINGERING ONSHORE LOW LEVEL FLOW AND PERHAPS A WEAK
EDDY IS EXPECTED TO CONTINUE DEVELOPING LOW CLOUDS INTO THIS AREA
OVERNITE...AND POSSIBLY INTO THE L.A. VALLEYS LATER TONIGHT. LOW
CLOUDS ALSO EXTEND FROM THE SOUTHERN SAN JOAQUIN VALLEY INTO THE
SLO/VTU/L.A. COUNTY MOUNTAINS...AND INTO THE CUYAMA VALLEY. LOW CLOUDS
CLEARED AWAY FROM MOST OF THE SLO COUNTY INTERIOR VALLEYS.
DURING THE NEXT 48 HOURS...A FAIRLY STRONG UPPER LEVEL RIDGE IS
FORECAST TO BUILD OFF THE CA COAST THRU WED...THEN INTO THE STATE ON
THU. THERE WILL BE A NORTHERLY FLOW OVER THE DISTRICT THRU THU...THEN
AS HIGH PRESSURE BUILDS INTO THE GREAT BASIN...OFFSHORE FLOW
IS EXPECTED TO DEVELOP ACROSS THE REGION WED NITE AND THU. AT THIS
TIME IT APPEARS ONLY MODERATE NORTHEAST CANYON WINDS CAN BE EXPECTED
THU MORNING AS UPPER LEVEL AND THERMAL SUPPORT FOR STRONG WINDS ARE
NOT FORECAST BY THE MODELS. THICKNESSES AND BOUNDARY LAYER TEMPS WARM
UP SIGNIFICANTLY FOR THU...WITH LOWER 80S POSSIBLE OVER PORTIONS OF
THE VALLEYS AND EVEN COAST OF L.A. AND VTU COUNTIES. TEMPS THURSDAY IN
THE CURRENT ZONES ARE NOT WARM ENOUGH...AND WILL ADJUST THEM UP WITH
A ZONE UPDATE.
THE UPPER HIGH CENTER STAYS JUST SOUTH OF THE DISTRICT FRI...THEN AN
UPPER TROF IS FORECAST TO MOVE INTO NORTHERN CA SAT TO WEAKEN THE
RIDGE AND GIVE THE DISTRICT INCREASING ONSHORE FLOW BY AFTERNOON. THE
LATEST AVN SHOWS ANOTHER UPPER RIDGE BUILDING JUST OFF THE W COAST FOR
SUN. DRY WEATHER WILL CONTINUE THRU SUN...WITH WELL ABOVE NORMAL TEMPS
FRI...THEN COOLER SAT...THEN SLIGHTLY WARMER AGAIN SUN.
WILL UPDATE ZONES BY 1015 PM TO ADJUST LOW CLOUD WORDING IN THE FIRST
PERIOD SEVERAL ZONES...AND TO RAISE HI TEMPS THU FOR MOST AREAS.
LAX 0000. SIRARD.
.LOX...NONE.
EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 840 PM PST TUE FEB 19 2002
.SYNOPSIS...THE MARINE LAYER AND ONSHORE FLOW WILL CAUSE AREAS OF NIGHT
AND MORNING COASTAL LOW CLOUDS AND FOG...DECREASING THURSDAY.
OTHERWISE...BUILDING HIGH PRESSURE ALOFT WILL KEEP THE WEATHER FAIR
WITH A WARMING TREND INTO FRIDAY. IT WILL BE COOLER WITH MORE CLOUDS
THIS WEEKEND AS UPPER LEVEL LOW PRESSURE MOVES PAST TO THE NORTH
FOLLOWED BY OFFSHORE FLOW EARLY NEXT WEEK.
.DISCUSSION...LOW CLOUDS ARE A BIT SLOW TO FORM THIS EVENING...BUT
THE RH IS RATHER HIGH WEST OF THE MOUNTAINS...AND THERE IS EASTWARD
EXPANSION OF THE LOW CLOUDS OUT NEAR THE ISLANDS. SO...AREAS OF LOW
CLOUDS SHOULD FORM LATE TONIGHT. THE 1500-3500 FOOT LAYER HAS BEEN
NEARLY ISOTHERMAL...THOUGH AN ACARS SOUNDING FROM ABOUT AN HOUR AGO
SHOWED AN INVERSION FORMING AT AROUND 1400 FEET. THUS...MOST OF THE
LOW CLOUDS SHOULD FORM NEAR THE COAST.
ALL OF THE MODELS SHOW STRONG HIGH PRESSURE ALOFT BY THU...SO WE
SHOULD SEE A GOOD WARMUP. THE INVERSION STRENGTH WILL INCREASE
RAPIDLY WITH 850 MB TEMPS APPROACHING 15 DEG C BY WED PM...THOUGH A
REALLY STRONG INVERSION SHOULD NOT FORM SINCE SOON AFTER THAT WE GET
SOME OFFSHORE FLOW. THUS...WHILE LOW CLOUDS SHOULD CLEAR IN A TIMELY
MANNER WED AM...THE COAST WILL NEVERTHELESS SEE A SLOWER JUMP IN
TEMPS THAN INLAND AREAS AND ESPECIALLY MTNS. WITH THE OFFSHORE FLOW
THU...TEMPS WILL SOAR IN THE VALLEYS AND EVEN ALMOST TO THE COAST.
THE OFFSHORE FLOW WILL CONTINUE TO BRING A WARM DAY FRIDAY BEFORE A
WEAK TROUGH BY TO THE NORTH OVER THE WEEKEND TO BRING ONSHORE FLOW
HERE. SINCE THE JET STREAM IS TOO FAR NORTH FOR US...AS HAS BEEN
TYPICAL MUCH OF THE WINTER...THE PRECIP SHOULD STAY WITH IT.
THE CURRENT ZONES LOOK GOOD...SO NO UPDATE WILL BE ISSUED THIS
EVENING.
.SAN...NONE.
MAXWELL