EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 900 PM PST MON JAN 10 2000
...SYNOPSIS...
ONSHORE FLOW WILL BRING AREAS OF COASTAL LOW CLOUDS AND DENSE FOG.
LOCALLY BREEZY IN THE MOUNTAINS AND DESERTS AT TIMES. OTHERWISE...DRY
WESTERLY FLOW ALOFT WILL KEEP THE WEATHER FAIR.
...DISCUSSION...
IN THE SHORT TERM INCREASING ONSHORE WILL MOISTEN AIR MASS AND MODIFY
TEMPERATURES AT LOWER ELEVATIONS. 24 HOUR CHANGES SHOW DEWPOINTS UP
ANOTHER 2 TO 10 DEGREES. QUITE A FEW INLAND LOCATIONS REPORTING MVFR
CONDITIONS AND EVEN HAD A MEDIA REPORT OF HAZE IN THE COACHELLA VALLEY
OBSCURING MOUNTAINS...ALTHOUGH METARS THERE DID NOT REPORT REDUCED
VISIBILITY AND/OR MENTION HAZE. ALONG THE COAST ALREADY GETTING REPORTS
OF DENSE FOG AND LOW CEILINGS. ALOFT THE FLOW HAS BACKED TO WESTERLY AND
REMAINS STRONG. ACARS REPORTS SHOW WIND SPEEDS 40 KTS OR HIGHER FROM
10000 FEET UP...ABOUT 10 KTS HIGHER THAN ETA 700 MB MODEL. CURRENT
FORECASTS ONLY MENTION WIND GUSTS TO 25 MPH ACROSS HIGHER MOUNTAINS AND
APPLE/YUCCA VALLEYS. AFTERNOON AND EARLY EVENING RAWS AND AWS
OBSERVATIONS INDICATE WIND GUSTS CLOSER TO 35 MPH IN HIGHER VALLEYS OF
SAN BERNARDINO COUNTY AND AROUND 45 MPH ACROSS HIGHER MOUNTAINS....BUT
INSIGNIFICANT OVER SAN DIEGO MOUNTAINS. WITH BOTH NGM AND ETA 700 MB
WIND SPEEDS INCREASING 10-15 KT BY TUE AFTERNOON AS THE BAROCLINIC ZONE
CURRENTLY OVER OREGON/N CALIFORNIA SAGS INTO CENTRAL CALIFORNIA...WIND
GUSTS SHOULD BE EVEN HIGHER OVER THIS SAME TERRAIN...SO WILL ISSUE AN
UPDATE AROUND 930 PM TO INCREASE.
FOR THE REMAINDER OF THE FORECAST A STEADY INCREASE IN RELATIVE HUMIDITY
AT ALL LEVELS AND WESTERLY FLOW THROUGH WEDNESDAY EXPECTED. LATER SHIFTS
MAY NEED TO REVISE MOSTLY SUNNY/CLEAR SKY COVER FORECAST AS BAROCLINIC
ZONE NEARS SW CALIFORNIA...ALTHOUGH BY THURSDAY A TEMPORARY RETREAT
NORTHWARD IS POSSIBLE. ALL THE MEDIUM RANGE MODELS ARE IN AGREEMENT IN
BUCKLING THE STRONG ZONAL FLOW AND DIGGING A TROUGH ALONG 135/140W
THROUGH FRIDAY.
THERE HAS ALSO BEEN A SIGNIFICANT INCREASE IN CONVECTION IN THE TROPICS
CENTERED NEAR 10N/135W. THIS WILL HAVE TO BE CLOSELY MONITORED FOR SIGNS
OF MOISTURE ENTRAINING INTO THE BASE OF THE DIGGING TROUGH. THE LATEST
RUN OF THE MRF AND THE NOGAPS FILLS IN THE BOTTOM OF THE TROUGH FRIDAY
NIGHT AND MOVES IT ONSHORE WHILE THE UKMET/ECMWF KEEP THE TROUGH OFF THE
CALIFORNIA COAST. THE LATER SOLUTION WOULD MAINTAIN THE FRONTAL ZONE
OVER CENTRAL CALIFORNIA COAST WITH A TROPICAL CONNECTION FOR SIGNIFICANT
RAINFALL. WILL NEED TO CONTINUE TO ASSESS MODELS WITH EACH OTHER...BUT
AT THIS TIME UKMET/ECMWF FAVORED.
SAN 000
.SAN...NONE ATTM. WIND ADVISORIES MAY BE NEEDED FOR TUE OVER SAN
BERNARDINO ZONES.
BALFOUR