EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 300 AM PDT TUE AUG 3 1999
...SYNOPSIS...
A WEAK TROUGH OF LOW PRESSURE OFF THE WEST COAST THIS WEEK WILL
RESULT IN WEAK SOUTHWESTERLY FLOW ALOFT AND WEAK ONSHORE LOW LEVEL
FLOW FOR SOUTHERN CALIFORNIA. SEASONAL TEMPERATURES WILL CONTINUE
WITH MONSOONAL MOISTURE AND AFTERNOON THUNDERSTORMS REMAINING EAST
OF SOUTHERN CALIFORNIA. PATCHY DENSE FOG IS POSSIBLE NEAR THE COAST
THIS MORNING.
...DISCUSSION...
MAIN FORECAST CONCERN THIS MORNING IS THE POTENTIAL FOR DENSE FOG
ALG THE CST EARLY THIS MORNING. MON EVENING ACARS SOUNDINGS SHOWED THE
BASE OF A STRONG SHALLOW MARINE INVERSION AROUND 500 FT AT
LAX/SNA/LGB WITH THE INVERSION BASE IN THE 00Z NKX RAOB BLO 1000 FT.
HIGH RESOLUTION MDLS DEVELOP A WK CSTL EDDY BY MORNING. WOULD EXPECT
AREAS OF LOW CLOUDS AND LOCALLY DENSE FOG TO DEVELOP ALG THE SAN
COUNTY CST BY MORNING SPREADING LCLLY INLD INTO THE LWR CSTL VLYS OF
SAN COUNTY AND LCLLY N ALG THE ORANGE COUNTY CST AROUND SUNRISE. AS
WITH MON...CLEARING TO THE CST SHOULD BE RAPID THIS MORNING. AS THE UPR
TROUGH OFF THE WEST CST EDGES CLOSER FOR WED WITH A SLIGHT LWRG OF
HEIGHTS ALF AND SLIGHT INCR IN THE WK ONSHR FLOW FOR TONIGHT... CSTL
STRATUS SHOULD FORM A LTL SOONER TONIGHT...BE MORE EXTENSIVE BY WED
MORNING...AND EXTEND A LTL FARTHER INLAND AS THE MARINE LYR DEEPENS
SLIGHTLY.
SECOND FORECAST ISSUE IS THE POTENTIAL FOR AFTERNOON THUNDERSTORMS
OVR THE MTNS AND DESERTS. PREFERRED ETA SHOWS SLY TO SSELY FLOW
CONTINING NEXT TWO DAYS BLO 500 MB WITH A GRADUAL DRYING OF MID LVL
MSTR. DRY SWLY FLOW CONTINUES ABV 500 MB. THE GREATER MSTR MON
AFTERNOON WAS INSUFFICIENT FOR THUNDERSTORM DEVELOPMENT OVR THE
MTNS. THOUGH AFTERNOON TEMPERATURES WL BE HIGHER THIS AFTERNOON THAN
MON AFTERNOON OVR THE MTNS AND DESERTS DUE TO REDUCED CLOUD COVER
AND DECRD LOW LVL MSTR...THE DECR IN MID LVL MSTR SHOULD BE
SUFFICIENT TO PRECLUDE THUNDERSTORM DEVELOPMENT. HENCE...WL TRIM
BACK TO "PARTLY CLOUDY AFTERNOON" WORDING FOR THE MTNS/DESERTS TODAY.
EXTENDED...PERSISTENCE OF THE WK TROUGH OFF THE W CST SHOULD ALLOW
ONLY MINOR INTRUSIONS OF MONSOONAL MSTR...AT MOST...INTO THE MTNS
AND DESERTS OF SWRN CA THRU THE WEEKEND.
SAN 000
.SAN...NONE.
MARTIN