SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
330 AM PDT SUN JUL 17 2005

.SHORT TERM... MARINE LAYER BECOME A BIT MORE SHALLOW DURING THE PAST 24 HOURS... WITH THE BASE OF THE MARINE INVERSION NOW DOWN TO AROUND 1000 FEET.  LOW CLOUDS HAVE PUSHED ACROSS MOST COASTAL ZONES... BUT WITH THE EXCEPTION OF SOME PATCHY FOG EARLY THIS MORNING... THE VALLEYS SHOULD REMAIN CLEAR.  CLOUDS SHOULD CLEAR QUICKLY THIS MORNING... EXCEPT NEAR THE IMMEDIATE COAST... WHERE THE VERY STRONG MARINE INVERSION MAY ALLOW SOME CLOUDS TO LINGER INTO THE AFTERNOON.

WEAK UPPER LOW OFF THE COAST WAS BEGINNING TO DRIFT WESTWARD AS A STRONG UPPER HIGH OVER ARIZONA WAS STARTING TO BUILD WESTWARD... ALL THE WHILE STRENGTHENING.  MODELS SHOW SOME SMALL RISES IN HEIGHTS AND THICKNESSES TODAY ACROSS THE AREA... WHICH SHOULD LEAD TO A COUPLE OF MORE DEGREES OF WARMING IN THE MOUNTAINS AND DESERTS.  THE MOST SIGNIFICANT WARMING TODAY IS EXPECTED TO OCCUR IN THE VALLEYS... AS 950 MB TEMPS RISE SEVERAL DEGREES THANKS TO A SHARP DECREASE IN MARINE INFLUENCE...  AND TEMPS SHOULD BE BACK TO NEAR OR OVER 100 DEGREES MANY OF THE WARMER VALLEY LOCATIONS.  HEAT INDEX VALUES... THE APPARENT "FEELS LIKE" TEMPERATURE RESULTING FROM THE COMBINATION OF HEAT AND HUMIDITY WILL COME CLOSE TO EXCESSIVE HEAT WARNING LEVELS TODAY ACROSS THE INTERIOR VALLEYS... AND THE LOWER ELEVATIONS IN THE MOUNTAINS.  HOWEVER... BLV DEW POINTS WILL BE JUST LOW ENOUGH TO KEEP MOST AREAS BELOW SUCH LEVELS TODAY.  TEMPS ON THE COASTAL PLAIN WILL LIKELY WARM A FEW DEGREES... BUT WITH A STRONG MARINE PRESENCE SHOULD REMAIN REASONABLY COMFORTABLE FOR MOST PEOPLE.

THE HEAT WILL BUILD ACROSS THE AREA MONDAY... AND CONTINUE TUESDAY AS A VERY STRONG UPPER LEVEL HIGH PRESSURE SYSTEM ANCHORS ITSELF ACROSS THE FORECAST AREA. THE NAM INDICATES 950 MB TEMPERATURES OF 44 DEGREES CELSIUS IN THE ANTELOPE VALLEY... AND OVER 40 DEGREES CELSIUS IN THE INTERIOR VALLEYS OF LOS ANGELES... VENTURA... SANTA BARBARA... AND SAN LUIS OBISPO VALLEYS... RIDICULOUSLY HIGH LEVELS.  IF THIS VERIFIES... MANY DAILY HIGH TEMPERATURE RECORDS WILL LIKELY FALL ACROSS THE INTERIOR VALLEYS... THE MOUNTAINS AND THE ANTELOPE VALLEY... AND SOME LOCATIONS COULD APPROACH ALL TIME HIGH TEMPERATURE RECORDS. EXCESSIVE HEAT WARNING WILL LIKELY BE NEEDED FOR THE LOWER ELEVATIONS IN THE MOUNTAINS... AND ACROSS MUCH OF THE VALLEYS.  THE ANTELOPE VALLEY... WITH HIGHER CRITERIA MAY NOT QUITE MAKE IT... BUT IT WILL BE CLOSE.  AREAS OF NIGHT THROUGH MORNING LOW CLOUDS AND FOG SHOULD CONTINUE ACROSS THE COASTAL PLAIN THROUGH TUESDAY... AND THE MARINE INFLUENCE WILL CONTINUE TO MODERATE TEMPERATURES FROM THE EXCESSIVELY HOT CONDITIONS ABOVE THE INVERSION. HOWEVER... THERE MAY BE ENOUGH WARMING TO ALLOW DOWNTOWN LOS ANGELES TO REACH 90 DEGREES FOR THE FIRST TIME SINCE SEPTEMBER 23 2004.. NEARLY TEN MONTHS AGO... ONE OF THE LONGEST STRETCHES BETWEEN 90 DEGREE DAYS EVER.