SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
300 AM PDT MON SEP 6 2004
.SHORT TERM...HOT TEMPERATURES CONTINUE TO BE MAIN FORECAST STORY FOR THE AREA IN THE SHORT TERM. SUNDAY WAS BRUTALLY HOT EVERYWHERE ESPECIALLY COASTAL ZONES WHERE READING IN THE UPPER 90S TO LOW 100S WERE COMMON.
00Z MODELS INDICATE LITTLE...IF ANY...RELIEF FOR THE NEXT THREE DAYS. THICKNESSES DO NOT EXHIBIT ANY DOWNWARD TREND THROUGH WEDNESDAY. THEREFORE...WILL EXPECT NEAR PERSISTENT TEMPS FOR INLAND AREAS THROUGH WEDNESDAY. AS FOR COASTAL ZONES...THESE AREAS WILL BE AT THE WHIM OF THE GRADIENTS AND BOUNDARY LAYER TEMPS NEXT THREE DAYS (PRODUCING PLENTY OF FORECAST BUST POTENTIAL). CURRENT GRADIENTS SHOWS SOME VERY WEAK ONSHORE TRENDS. SO...EXPECT SOME SLIGHT COOLING FOR COASTAL ZONES TODAY...BUT STILL PLENTY OF 90+ READINGS TODAY. FOR TUESDAY/WEDNESDAY...FORECAST IS QUITE TRICKY AS BOUNDARY LAYER TEMPS RISE SLIGHTLY...BUT SURFACE GRADIENTS SHOW VARYING DEGREES OF ONSHORE OR OFFSHORE TRENDS. THEREFORE...DEPENDING ON EXACT NATURE OF THE GRADIENTS...COULD HAVE SLIGHT WARMING OR MORE COOLING FOR COASTAL AREAS TUESDAY/WEDNESDAY. WILL INDICATE SLIGHT COOLING TREND FOR NOW WITH CAVEAT THAT ACTUAL TEMPS COULD BE VASTLY DIFFERENT THAN MY CURRENT FORECAST.
CLOUD COVER WILL BE A NON-ISSUE THROUGH WEDNESDAY AS MOISTURE FROM HOWARD DISSIPATES AND OFFSHORE GRADIENTS KEEP MARINE LAYER AT BAY.
ON THE FIRE WEATHER FRONT...THE COMBINATION OF HOT TEMPERATURES AND DRY CONDITIONS WILL CONTINUE TO PRODUCE A VERY HIGH FIRE DANGER
SHORT TERM...VERY HOT DAY TODAY WITH SEVERAL RECORDS BROKEN. MAIN CULPRIT WAS PERSISTENT OFFSHORE FLOW THROUGH THE ENTIRE DAY. IN FACT...LAX-DAGGETT GRADIENT STILL REMAINING AT -1.9 MB. WEAK OFFSHORE FLOW PATTERN EXPECTED NEXT COUPLE OF MORNINGS...TURNING NEARLY NEUTRAL IN THE AFTERNOON HOURS. THIS COMBINED WITH WARMING BOUNDARY LAYER TEMPERATURES WILL RESULT IN MANY TRIPLE DIGIT READINGS NEXT COUPLE OF DAYS ACROSS THE SOUTHLAND. IN FACT...WOULD NOT BE SURPRISED TO SEE EVEN A FEW DEGREES OF WARMING ON MONDAY ACROSS THE VALLEYS...WITH HOTTEST LOCATIONS EXPECTED TO REACH 108 DEGREES. HOWEVER...THIS IS NOT UNUSUAL...AS THE FIRST WEEK OF SEPTEMBER OFTEN BRINGS SOME OF THE HOTTEST WEATHER OF THE YEAR.
MAIN SHORT TERM CONCERN WILL BE FIRE WEATHER SITUATION. A RED FLAG WARNING WAS ISSUED FOR VERY LOW HUMIDITIES MONDAY THROUGH TUESDAY
IN ADDITION TO THE VERY HOT AND DRY CONDITIONS...WEAK OFFSHORE FLOW WILL CONTINUE TO BRING NORTHEAST TO EAST WINDS OF 10 TO 20 MPH WITH LOCALLY HIGHER GUSTS THROUGH FAVORED MOUNTAIN PASSES...MAINLY DURING THE LATE NIGHT AND MORNING HOURS. THE COMBINATION OF VERY LOW HUMIDITY VALUES...OFFSHORE WINDS...AND CRITICALLY DRY FUEL CONDITIONS HAS PROMPTED THE ISSUANCE OF A RED FLAG WARNING
SHORT TERM...MODELS IN GOOD AGREEMENT WITH SYNOPTIC CONDITIONS FOR NEXT THREE DAYS. AT UPPER LEVELS...RIDGE BUILDS OVER THE AREA TODAY AND REMAINS THROUGH TUESDAY. NEAR THE SURFACE...OFFSHORE GRADEINTS PEAK TODAY...THEN WEAKEN SLIGHTLY MONDAY/TUESDAY. OVERALL...VERY LITTLE...IF ANY...SIGNIFICANT CHANGES INDICATED BY MODELS THROUGH TUESDAY.
WITH THE ABOVE SCENARIO...EXPECT SEVERAL DAYS OF HOT TEMPERATURES ACROSS THE ENTIRE AREA.
FOR TODAY...MODELS INDICATE WARMER BOUNDARY LAYER TEMPS...HIGHER THICKNESSES...AND OFFSHORE GRADIENTS WHICH WILL RESULT IN MUCH WARMER TEMPS THAN SATURDAY WITH MANY VALLEY AREAS REACHING OVER 100 DEGREES.
ON MONDAY...MODELS CONTINUE TO INDICATE SLIGHT INCREASES IN BOUNDARY LAYER TEMPS AND THICKNESSES. SO...INLAND AREAS WILL ACTUALLY BE A DEGREE OR TWO WARMER THAN TODAY. ALSO... SINCE COASTAL AREAS WILL BE STARTING MONDAY MORNING MUCH WARMER THAN THIS MORNING...WILL EXPECT SOME SLIGHT WARMING COASTAL ZONES DESPITE WEAK ONSHORE FLOW MONDAY AFTERNOON. ON TUESDAY...PATTERN REMAINS VERY PERSISTENT...SO PERSISTENT TEMP FORECAST WILL GENERALLY BE FOLLOWED ALTHOUGH IMMEDIATE COASTAL ZONES SHOULD COOL A DEGREE OR TWO.
OTHER THAN SOME SCATTERED MID/HIGH CLOUDS FROM THE REMNANTS OF HOWARD
SKIES WILL REMAIN CLEAR THROUGH TUESDAY AS OFFSHORE GRADIENTS KEEP MARINE LAYER
NON-EXISTENT.
SHORT TERM...
OFFSHORE GRADIENTS TAKING OVER TODAY AS EXPECTED, THOUGH UPPER SUPPORT IS TOO
WEAK TO GENERATE MUCH WIND. DID GET SOME GUSTS INTO THE LOW 40S AT A COUPLE OF
THE MORE WIND EXPOSED LOCATIONS IN THE LA COUNTY MOUNTAINS THIS MORNING BUT THAT
WILL PROBABLY BE ABOUT IT. EXPECT A LARGE JUMP IN TEMPERATURES THIS AFTERNOON
OVER FRIDAY'S NUMBERS, ESPECIALLY IN THE VALLEYS AND INLAND COASTAL PLAIN. ABOVE
THE INVERION HOWEVER, TEMPERATURES ARE ACTUALLY RUNNING A LITTLE COLDER THAN
YESTERDAY SO MOUNTAINS AND DESERTS WILL SEE CONSIDERABLY LESS WARMING THAN OTHER
AREAS TODAY.
ANOTHER BIG JUMP IN HIGHS SUNDAY AS WEAK OFFSHORE FLOW CONTINUES AND AIRMASS CONTINUES TO WARM UP. THE 12Z ETA NOW INDICATES WARM WEATHER WILL CONTINUE AT LEAST THROUGH MONDAY, THOUGH GRADIENTS WILL BE TRENDING ONSHORE BY THAT TIME SO THE BEACHES MAY START TO COOL OFF A TAD. OTHERWISE, EXPECT ANOTHER DAY OF TRIPLE DIGIT HIGHS IN THE VALLEYS AND LOW TO MID 90S DOWNTOWN LA AND OTHER INLAND COASTAL PLAIN LOCATIONS.
SHORT TERM...MARINE INVERSION THIS EVENING RANGES FROM NEAR 500 FT AT VBG TO NEAR 1900 FT AT LAX. EXPECT THE INVERSION OVER LAX TO LOWER OVERNIGHT AS GRADIENTS TREND OFFSHORE AND SOME SUBSIDENCE BEGINS TO MOVE INTO THE REGION WITH A NORTHEAST FLOW DEVELOPING. ONLY LOW CLOUDS OVER SOCAL BIGHT EXTENDING FROM CATALINA ISLAND TO THE S ORANGE COUNTY COAST AND SOUTHWARD...WITH LITTLE NORTHWARD MOVEMENT THIS EVENING. LOOKS LIKE THE LOW CLOUDS MAY HAVE A DIFFICULT TIME PUSHING N IN THE ABSENCE OF AN EDDY SO PATCHY LOW CLOUDS LOOKS FINE FOR L.A. COAST LATER TONIGHT. MOSTLY CLEAR ELSEWHERE OVERNIGHT ALTHO PATCHY LOW CLOUDS AND FOG NOT OUT OF THE QUESTION LATER TONIGHT ALONG THE CENTRAL COAST.
BROAD UPPER TROF OVR SRN CA WILL MOVE INTO THE GREAT BASIN THRU SAT...THEN IS LOOKS LIKE SW CA WILL BE UNDER A COL REGION BETWEEN TWO UPPER HIGHS ON SUN AND MON. AT THE SURFACE THE MODELS PUSH A THERMAL TROF TO THE COAST OR SLIGHTLY OFF EACH MORNING THRU MON. SOME OFFSHORE FLOW WILL AFFECT THE REGION LATE NIGHT AND MORNING HOURS DURING THE PERIOD...BUT MOST ESPECIALLY SAT AND SUN MORNINGS WITH SOME GUSTY CANYON WINDS POSSIBLE. AT THIS TIME DOES NOT APPEAR WE WILL SEE EVEN ADVISORY LEVEL WINDS OVER THE REGION. THE OFFSHORE FLOW WILL HELP TO SHRINK THE MARINE LAYER DOWN TO 500 FT OR LOWER WITH LITTLE IN THE WAY OF MARINE LAYER CLOUDS BY SUN MORNING. TEMPS WILL WARM UP CONSIDERABLY ON SAT AND EVEN MORE ON SUN...WITH READINGS TOPPING THE CENTURY MARK AGAIN OVER INLAND AREAS. EVEN THE COAST SHOULD HAVE TEMPS ABOVE NORMAL FOR THE MOST PART. TEMPS MON SHOULD ONLY DROP SLIGHTLY WITH A SOMEWHAT WEAKER OFFSHORE GRADIENT IN THE MORNING.
IT LOOK LIKE VERY LOW HUMIDITIES OF LESS THAN 10 PERCENT WILL AFFECT INTERIOR PORTIONS OF SW CA FOR A PROLONGED PERIOD SUN. AS A RESULT A FIRE WEATHER WATCH IS IN EFFECT FOR THE MOUNTAINS AND INTERIOR VALLEYS OF SLO/SBA/L.A. COUNTIES (SEE LAXRFWLOX FOR DETAILS).