EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 900 PM PDT SAT MAY 13 2000
...SYNOPSIS...
ONSHORE FLOW WILL CONTINUE THROUGH MONDAY AND BEYOND AS STRONG LOW
PRESSURE OVER THE EAST PACIFIC DRIFTS SLOWLY TOWARDS CALIFORNIA.
THIS WILL BRING A COOLING TREND TO THE COAST SUNDAY AND MONDAY AND
TO THE MOUNTAINS AND DESERTS MONDAY. THE MARINE LAYER WILL ALSO
DEVELOP...ESPECIALLY SUNDAY NIGHT. THE LOW PRESSURE SYSTEM WILL MOST
LIKELY MOVE BY TO OUR NORTH TUESDAY AND BRING A CHANCE OF SHOWERS
WITH AN ISOLATED THUNDERSTORM ALSO POSSIBLE. ABOVE NORMAL SURF IS
EXPECTED THROUGH SUNDAY AT THE BEACHES.
...DISCUSSION...
THE MODELS INITIALIZED THE SYSTEM NEAR 38N/135W PRETTY WELL THIS
EVENING...BOTH ON LOCATION AND STRENGTH. THE SYSTEM IS CURRENTLY
DIGGING SOUTHEAST DUE TO THE DECENT WINDS ON THE BACK SIDE...BUT THE
MODELS INDICATE THE SYSTEM WILL TURN MORE EAST OVERNIGHT...AND
SATELLITE INDICATES THIS IS THE CASE ALREADY. THE MOST DIFFICULT
THING WITH THIS SYSTEM IS THAT IT IS A VERY CLOSED LOW...AND THUS
THE MOVEMENT IS MORE DIFFICULT TO PREDICT.
OUR FLOW IS CONTINUING TO TREND ONSHORE WITH ABOUT A 6 MB GRADIENT
BETWEEN SAN DIEGO AND THE DESERTS. 00Z NKX SOUNDING AND ACARS
SOUNDINGS INDICATE AN INVERSION DEVELOPING AROUND 1000-1500 FEET
WHICH SHOULD INHIBIT DENSE FOG...AT LEAST AT THE IMMEDIATE COAST.
DEW POINTS ARE FAIRLY LOW GIVEN THE AMOUNT OF ONSHORE
FLOW...ESPECIALLY INLAND...AND THE NEAREST MARINE STRATUS IS NEARLY
200 MILES TO OUR WEST. THE MESAS ARE ABOUT THE ONLY LOCATION THAT
COULD RECEIVE ANY DENSE FOG TONIGHT. THEREFORE...EXPECT ONLY PATCHY
LOW CLOUDS AND FOG TONIGHT...WITH LATE FORMATION. LOOKING AT THE
LEVEL OF ONSHORE FLOW...THE 850 MB FLOW AND POSITIONING OF THE
THERMAL TROUGH...WE REALLY SHOULD NOT HAVE SIGNIFICANT DEEPENING OF
THE MARINE LAYER UNTIL MONDAY...SO SUNDAY NIGHT SHOULD HAVE LOW
CLOUDS AND/OR FOG IN THE NORMAL CLIMATOLOGICAL LOCATIONS GIVEN
MODERATE ONSHORE FLOW. 850 MB TEMPS MAINLY DECREASE MONDAY...SO THAT
IS WHEN THE COOLING FOR THE MTNS/DESERTS SHOULD OCCUR...BUT NOT
UNTIL THEN. W/SW WINDS ALOFT INCREASE QUITE A BIT MONDAY TO ABOUT 40
KT...SO EXPECT THE MTNS/DESERTS TO BE WINDY.
I HAVE LOOKED AT THE TUESDAY PROGS...INCLUDING THE 12Z ECM...AND IT
APPEARS THAT WHILE MOST OF THE ENERGY WILL STAY JUST TO OUR
NORTH...WE COULD STILL HAVE SOME SHOWERS DOWN HERE...PARTLY FROM THE
DEEP MARINE LAYER. 500 MB TEMPS DROP BELOW -20C...SO AN ISOLATED
TSTORM COULD OCCUR...MOST LIKELY THIS WOULD BE OVER THE
MTNS/NORTHERN DESERTS WHERE INSTABILITY WOULD BE BEST.
AN UPDATE...FOR NUMEROUS THINGS...ESPECIALLY LOW CLOUDS/FOG
WORDING...WILL BE ISSUED BY 930 PM.
SAN 0000
.SAN...MWS FOR ABOVE NORMAL SURF.
MAXWELL