739 
FXUS66 KSGX 142101
AFDSAN
EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
200 PM PDT MON AUG 14 2000

                             ...SYNOPSIS...
STRONG HIGH PRESSURE CENTERED OVER THE CENTRAL AND SOUTHERN ROCKIES 
WILL CONTINUE THE HOT INLAND TEMPERATURES FOR SOUTHWEST CALIFORNIA 
THROUGH WEDNESDAY. A COASTAL EDDY WILL BRING NIGHT AND MORNING LOW 
CLOUDS TO THE COAST THE NEXT FEW DAYS. THERE WILL ALSO BE A SLIGHT 
CHANCE OF AFTERNOON THUNDERSTORMS OVER THE MOUNTAINS AND DESERTS.

                             ...DISCUSSION...

VISIBLE SATELLITE LOOP THIS MORNING SHOWS GOOD EDDY CIRCULATION 
DROPPING SOUTH OF SAN NICOLAS ISLAND. THE BROAD CIRCULATION IS HAVING 
AN EFFECT ON THE COASTS WITH PATCHY LOW CLOUDS REMAINING AT SOME 
BEACHES MUCH OF THE DAY AND COOLER CONDITIONS INLAND. ELSEWHERE MID
AND UPPER LEVEL CLOUDS HAVE BEEN PREVALENT OVER THE MOUNTAINS AND 
DESERTS. RAWS SITES IN THE UPPER DESERTS AND MOUNTIANS HAVE SHOWN 
SUBSTANTIAL RISES IN DEW POINTS. SOME LARGE BUILD UPS HAVE DEVELOPED 
OVER THE NORTHERN MOUNTAINS BUT UP THROUGH 2 PM NO THUNDER REPORTED.

12Z ETA AND AVN MODELS DIFFER BEYOND 48 HOURS. THE AVN DEVELOPS A 
WEAK WAVE NEAR 26N 123W...INTO ENOUGH OF A TROUGH BY WEDNESDAY 
EVENING TO TURN OUR UPPER-LEVEL FLOW SW. THE ETA CONTINUES TO HOLD 
THE RIDGE OVER US WITH SE FLOW ALOFT. IN THE NEAR TERM THE AVN HAS 
BACKED OFF ON THE EASTERLY WAVE FROM PREVIOUS RUNS...NOW STEERING 
MOST OF THE ENERGY UP THROUGH SW AZ. MODEL CROSS SECTIONS DO 
ADVERTISE AN INCREASE IN RH INTO WEDNESDAY...AND IF AVN IS CORRECT 
UPPER LEVEL RIDGE AXIS WILL BE FORCED NORTH FOR BETTER DYNAMICS 
HERE. BOUNDARY LAYER TEMPS AND THICKNESS SHOW LITTLE VARIATION 
DESPITE INCREASING 500 MB HEIGHTS.

COASTS...MESO SCALE MODELS CONTINUE AN EDDY THROUGH TUESDAY...
THOUGH NOT AS WELL DEVLOPED. WILL FORECAST PERSISTENCE AT LEAST 
THROUGH TOMORROW. BUT WE COULD SEE SOME WARMING ALONG THE 
COAST...DEPENDING ON THE STRENGTH AND POSITION OF THE EDDY.

MOUNTAINS/DESERTS...BASED ON CONTINUED SE FLOW ALOFT AND INCREASING 
MOISTURE PROFILES FEEL THUNDERSTORM THREAT INCREASING. ETA K-F SHOWS 
CONVECTIVE RAIN BLOSSOMING TUESDAY. DYNAMICS STILL VERY WEAK BUT 
SHOULD IMPROVE IF AVN MODEL VERIFIES. AVN MODEL LOOKS REASONABLE 
AND WILL BE FOLLOWED. DAYTIME TEMPERATURES MAY INCREASE A BIT DUE TO 
INCREASING 500 MB HEIGHTS. NIGHTTIME INCREASE DUE TO INCREASE IN RH 
AND CLOUDS.

VALLEYS...SOME INCREASE IN NIGHTTIME MINIMUMS DUE TO HIGHER RH AND 
CLOUDS. MAYBE SOME THUNDER NEAR THE FOOTHILLS IF STORMS DEVELOP OVER 
THE MOUNTAINS.

LOOKING AHEAD...UKMO...ECMWF...AND MRF ALL CONTINUE TO ADVERTISE A 
SHIFT IN THE MASSIVE HIGH TO THE EAST...WHICH ALLOWS A SIGNIFICANT 
TROUGH TO DEVELOP ALONG THE WEST COAST STARTING FRIDAY. THIS SHOULD 
PROVIDE COOLER AND DRY WEATHER THIS WEEKEND. THE HIGH REBUILDS AGAIN 
NEXT WEEK OVER THE SW. SO SHOULD THE COOLING MATERIALIZE THIS WEEKEND
...IT LIKELY WILL NOT LAST LONG.     
   
SAN 000

.SAN...NONE.

JAD