AREA FORECAST DISCUSSION

FXUS66 KLOX 172249
AFDLOX
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
230 PM PST THU MAR 17 2005

.SHORT TERM...SATELLITE IMAGERY SHOWING A WELL DEFINED NEGATIVELY TILTED UPPER TROUGH IN EASTERN PACIFIC TAKING AIM AT THE CALIFORNIA COAST FOR FRIDAY. A LARGE AREA OF SUBTROPICAL MOISTURE BEING ENTRAINED INTO THIS SYSTEM...WITH PW VALUES ANALYZED OVER 1.5 INCHES SOUTH OF 30N. WHILE MAIN UPPER LOW CENTER IS PROGGED TO TRACK TO THE NORTHEAST OVER TIME...A BROAD MOIST SOUTHWEST FLOW PATTERN WILL ESTABLISH OVER CENTRAL AND SOUTHERN CALIFORNIA. THE MAIN HIGHLIGHT WITH THIS SYSTEM WILL BE THE LONG DURATION OF THE EVENT...WITH PERIODS OF RAIN EXPECTED FRIDAY THROUGH SATURDAY...WITH SOME LINGERING SHOWERS POSSIBLE SATURDAY NIGHT INTO EARLY SUNDAY. IT APPEARS THAT THE PEAK RAINFALL INTENSITIES WILL OCCUR FRIDAY NIGHT WHEN A 110 KNOT JET CORE DEVELOPS TO OUR SOUTHWEST...LEAVING OUR REGION UNDER THE FAVORABLE LEFT FRONT QUADRANT. DURING THIS TIME...IT WILL BE INTERACTING WITH A FAIRLY MOIST AIR MASS...WITH LATEST MODEL RUNS SHOWING PW VALUES AS HIGH AS 1.3 INCHES OFF THE COAST.

INITIALLY...MODEL CROSS SECTIONS SHOWING SOME 25-35 KNOT SOUTHERLY LOW LEVEL FLOW ON FRIDAY AFTERNOON AND EVENING...BECOMING SOUTHWEST LATER FRIDAY NIGHT INTO SATURDAY. THIS TYPE OF FLOW PATTERN WILL HELP PROVIDE SOME OROGRAPHIC ENHANCEMENT TO SOUTH AND SOUTHWEST FACING SLOPES. RAINFALL INTENSITIES IN THESE FAVORED AREAS WILL LIKELY BE ONE QUARTER TO ONE THIRD OF AN INCH PER HOUR...BUT WE COULD SEE LOCAL RATES AS HIGH AS ONE HALF INCH PER HOUR.

OVERALL RAINFALL TOATLS FROM FRIDAY THROUGH SUNDAY ARE NOW EXPECTED TO RANGE BETWEEN ONE HALF AND ONE AND ONE HALF INCHES...WITH FOOTHILL AND MOUNTAIN AREAS EXPECTED TO RECEIVE BETWEEN ONE AND ONE HALF INCHES AND THREE INCHES OF RAIN. LOCAL AMOUNTS OVER FOUR INCHES WILL BE POSSIBLE ACROSS FAVORED SOUTH AND SOUTHWEST FACING MOUNTAIN SLOPES. THE SNOW LEVELS WILL REMAIN QUITE HIGH WITH THIS SYSTEM...GENERALLY 7000 TO 8000 FEET...SO WINTER WEATHER CONCERNS SHOULD BE MINIMAL EXCEPT AT THE HIGHEST PEAKS.

.LONG TERM...ANOTHER UPPER TROUGH IS EXPECTED TO DEVELOP DURING THE EXTENDED PERIOD. LONG RANGE MODELS DIFFER SOMEWHAT IN THE TIMING OF THIS NEXT SYSTEM...BUT IT APPEARS THAT RAINFALL COULD FALL SOMETIME BETWEEN MONDAY NIGHT AND WEDNESDAY.



&&



.LOX WATCHES/WARNINGS/ADVISORIES...

SMALL CRAFT ADVISORY (SEE LAXCWFLOX).

SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX).



&&








GOMBERG