EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 930 PM PDT WED SEP 1 1999
...SYNOPSIS...
LOW PRESSURE ALOFT WILL BE AT ITS STRONGEST THURSDAY AND THEN WEAKEN
GRADUALLY FROM FRIDAY THROUGH THE WEEKEND. TEMPERATURES WILL REMAIN
UNSEASONABLY COOL THROUGH FRIDAY. NIGHT AND MORNING LOW CLOUDS WILL
OCCUR NEAR THE COAST AND IN MOST INLAND VALLEYS...AND EVEN SOME
LOCAL DRIZZLE IS EXPECTED THURSDAY MORNING.
...DISCUSSION...
00Z ETA IS IN ONLY THROUGH 36 HOURS DUE TO NCEP PROBLEMS...AND THE
00Z NGM IS COMPLETE. BOTH MODELS INDICATE THE TROUGH AXIS/HIGHER
VORTICITY AXIS...NOW ORIENTED NE-SW NEAR SAN FRANCISCO...TO MOVE
THROUGH OUR AREA LATE THURSDAY AFTERNOON. WITH INCREASING CYCLONIC
FLOW...EXPECT THE MARINE LAYER TO DEEPEN...POSSIBLY TO A DEPTH
AROUND 3500 FEET BY THURSDAY. THE NKX SOUNDING SHOWED THE INVERSION
AROUND 2500 FEET THIS AFTERNOON WITH A SECONDARY INVERSION NEAR 5500
FEET. ACARS SOUNDINGS FROM LAX AND SAN ARE KIND OF MIXED
TONIGHT...BUT IT APPEARS THE INVERSION IS SOMEWHERE AROUND 3000
FEET. AN AIRCRAFT AT 830 PM SHOWED A TEMPERATURE OF 51 DEGREES AT
2000 FEET OVER LINDBERGH FIELD...QUITE COLD. THUS...WE COULD BE A
BIT UNSTABLE UNDER THE INVERSION...AND WITH THE CYCLONIC FLOW AND
ABUNDANTLY DEVELOPING LOW CLOUDS...THERE COULD BE SOME DRIZZLE BY
THURSDAY MORNING.
ONSHORE FLOW IS QUITE STRONG THIS EVENING...ABOUT +7 MB FROM SAN
DIEGO TO THE DESERTS AND +10 TO DESERT ROCK. THIS PRODUCED WIND
GUSTS OF AROUND 30 KNOTS AT PALM SPRINGS AND IN THE UPPER DESERTS.
EXPECT SIMILAR GRADIENT/WIND CONDITIONS THURSDAY BEFORE A DECREASE
FRIDAY. TEMPS SHOULD BE AT THEIR LOWEST ON THURSDAY ALSO. THE SLIGHT
INCREASE ON FRIDAY WILL MAINLY OCCUR NEAR THE COAST DUE TO WEAKER
ONSHORE FLOW. THE TEMPS ALOFT CHANGE LITTLE THAT DAY.
AN RER WAS ISSUED EARLIER THIS EVENING FOR 2 NEW RECORD LOW MAXIMUMS
AND 2 TIES. AN UPDATE WILL BE ISSUED TO LOWER SOME TEMPS...MAINLY
FOR THURSDAY...TO ADD LOCAL DRIZZLE TO SOME ZONES FOR THURSDAY
MORNING AND TO EMPHASIZE SLIGHTLY MORE WIDESPREAD WINDS IN THE
MTNS/DESERTS.
SAN 0000
.SAN...NONE.
MAXWELL