SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
850 AM PST THU FEB 24 2005

.SHORT TERM...SLOW MOVING REX BLOCK UPPER LOW STILL BEING A PEST, LEAVING ENOUGH RESIDUAL MOISTURE AND INSTABILITY TO WARRANT A SMALL CHANCE OF CONVECTIVE ACTIVITY TODAY. SORT OF A RANDOM SMATTERING OF LOW CLOUDS THIS MORNING, WITH INTERIOR SLO COUNTY, THE SANTA YNEZ VALLEY, AND SRN LA COUNTY ALL SOCKED IN WITH MOSTLY CLEAR SKIES ELSEWHERE. WITH AFTERNOON HEATING AND LOW LVL MOISTURE SKIES WILL BE PARTLY CLOUDY EVERYWHERE TODAY. WILL HAVE TO WATCH FOR POSSIBLE SEVERE WEATHER AGAIN THIS AFTERNOON AS CAPES RISE TO ABOUT 800 IN LA COUNTY. SIMILAR AGAIN FRIDAY, THOUGH CONDITIONS AREN'T QUITE AS FAVORABLE.

WITH THE UPPER LOW FINALLY MOVING FAR ENOUGH EAST BY SATURDAY, ALL CONVECTIVE CHANCES SHOULD BE GONE, LEAVING JUST PARTLY CLOUDY SKIES AND A SLIGHTLY WARMER DAY.

300 AM PST THU FEB 24 2005

.SHORT TERM...
PLENTY OF LOW LVL MOISTURE ACRS THE AREA EARLY THIS MORNING...AND SOME LOW CLOUDS AND FOG HAVE DEVELOPED. WILL START THE DAY WITH MOSTLY CLDY SKIES N OF PT CONCEPTION...AND ACRS AT LEAST CSTL SXNS OF L.A. COUNTY WHERE CLOUDS WERE MOST WDSPRD. ALSO...SOME FOG WILL LIKELY BE DENSE IN SPOTS THROUGH MID MORNING...ESPECIALLY IN THE VLYS...AND N OF PT CONCEPTION. THE CENTER OF THE RELENTLESS UPPER LVL LOW HAS FINALLY PUSHED TO THE E OF THE AREA...BUT IT HAS ONCE AGAIN BECOME NEARLY STATIONARY OVER WESTERN ARIZONA. MODELS SHOW A VORT LOBE WRAPPING BACK INTO THE FCST AREA TODAY...WHICH WILL PROVIDE SOME MODEST LIFT THIS AFTERNOON AND EVENING...MAINLY ACRS L.A. AND VTU COUNTIES. IN ADDITION...WITH 500 MB TEMPS NEAR -24C TODAY...SFC HEATING AND RESIDUAL LOW LVL MSTR WILL CAUSE THE ATMOSPHERE TO BECOME INCREASINGLY UNSTABLE. ALL MODELS SHOW LIFTED INDEX VALUES -1 TO -3 ACROSS SRN SXNS OF THE FCST AREA TODAY...WITH THE NAM INDICATING LIFTED INDEX VALUES NEAR -5 ACROSS L.A. COUNTY. THEREFORE...THE SLIGHT CHANCE OF SHOWERS AND TSTMS FOR L.A. COUNTY AND THE MTNS AND VLYS OF VTU COUNTY FOR THIS AFTERNOON AND EVENING LOOKS GOOD.

THE UPPER LOW IS FCST TO MOVE LITTLE TONIGHT AND FRIDAY...AND ANOTHER VORT WILL SPIRAL INTO THE AREA ON FRIDAY. WITH SOMEWHAT MORE IN THE WAY OF MSTR AT 850 AND 700 MB ON FRIDAY...THERE MAY BE SOMEWHAT MORE IN THE WAY OF CLOUDS...AT LEAST ACRS L.A./VTU...AND THINGS DO NOT LOOK AS UNSTABLE. STILL...THERE DOES APPEAR TO BE A SLIGHT CHANCE OF SHOWERS FRIDAY AFTERNOON AND FRIDAY EVENING...ESPECIALLY ACRS L.A./ERN VTU COUNTIES. LATER SHIFTS MAY WANT TO ADD THUNDERSTORMS IF INSTABILITY LOOKS SUFFICIENT.

IT IS IMPORTANT TO NOTE THAT ANY SHOWER OR THUNDERSTORM ACTIVITY THAT DOES DEVELOP TODAY AND FRIDAY SHOULD BE VERY SCATTERED IN NATURE...AND MOST AREAS OF THE SOUTHLAND WILL RECEIVE NO RAIN AT ALL THROUGH FRI. HOWEVER...ANY AREAS THAT DO RECEIVE CONVECTIVE ACTIVITY COULD SEE BRIEF HEAVY RAINFALL.

THE UPPER LOW WILL MOVE SLOWLY EWD FRI NIGHT AND SAT AS A RIDGE BUILDS INTO THE AREA. XPCT MORE SUNSHINE ON SAT ACRS THE AREA... WITH A BIT OF WARMING IN MOST AREA.