Forecast Discussions mentioning ACARS, received at FSL on 05/03/01

...SYNOPSIS... DEVELOPING SURFACE HIGH PRESSURE OVER NORTHERN NEVADA WILL ALLOW OFFSHORE FLOW TO DEVELOP LATE TONIGHT AND THURSDAY MORNING. STRONG GUSTY WINDS WILL OCCUR BELOW SOME PASSES AND CANYONS...MAINLY NORTH OF SAN DIEGO COUNTY. MOST OF THE COASTAL LOW CLOUDS WILL CLEAR OUT THURSDAY TO BRING WARMER WEATHER THERE. A RETURN TO ONSHORE FLOW AND WEST FLOW ALOFT WILL BRING SEASONABLE TEMPERATURES WITH AREAS OF COASTAL LOW CLOUDS AND FOG BY THE WEEKEND.

...DISCUSSION... EROSION OF THE LOW CLOUDS IS FINALLY OCCURRING OVER NORTHERN AREAS AS THE INVERSION CONTINUES TO WEAKEN. THE LATEST ACARS SOUNDING FROM ONT SHOWS THAT INVERSION STRENGTH IS ONLY ABOUT 3 DEG C. NE WINDS NOW EXTEND DOWN TO ABOUT 3500 FEET IN THAT SOUNDING. THE MAIN REASON THAT THE OFFSHORE FLOW STALLED EARLIER THIS EVENING WAS DUE TO NOT ENOUGH SUBSIDENCE...BOTH FROM A LACK OF DYNAMICS AND A LACK OF COLD AIR ADVECTION ABOVE ABOUT 800 MB. THE WINDS ABOVE 800 MB WILL BECOME MORE N-NE AFTER 06Z WHICH WILL GET THE CAA GOING AND THUS INCREASE THE SUBSIDENCE...THOUGH THE WINDS DO NOT LOOK LIKE THEY WILL BE QUITE AS STRONG AS EARLIER PROGS SUGGESTED...SO IN THE UPDATE...I TOOK OFF 5 MPH FROM WINDS IN ZONES 48/61 WHERE THE WAD IS IN EFFECT. ALSO...IVORY'S WIND PROGRAM INDICATES SOME DECREASE IN THE 00Z MODELS THAN 12 HOURS BEFORE. AFTER ABOUT 18Z THU...THE WINDS SHOULD REALLY DECREASE...AND IN FACT A FAIRLY VIGOROUS SEA BREEZE SHOULD DEVELOP...BOTH WITH THE ONSHORE AFTERNOON GRADIENTS TO THE SURFACE LOW OVER W NEW MEXICO AND THE TIGHT DENSITY GRADIENTS EXPECTED NEAR THE COAST DUE TO WARMING OF THE VALLEYS RELATIVE TO THE SST VALUES AVERAGING AROUND 60.

NO CHANGES HAVE BEEN MADE FOR FRIDAY OR THE EXTENDED AS ONSHORE FLOW OCCURS AS THE UPPER LOW STARTS TO DRIFT TO THE EAST FROM ITS CURRENT-AND-THURSDAY UTAH LOCATION. SO...AS MENTIONED ABOVE...NEAR SEASONABLE WEATHER IS EXPECTED FOR THE WEEKEND.

THE ZONE UPDATE WAS ISSUED AT 9 PM.

SAN 0000

.SAN...WIND ADVISORY...SEE LAXNPWSAN. ABOVE NORMAL SURF...SEE LAXMWSSAN.

MAXWELL



UPDATE CONCERN IS CLOUD/TEMP TRENDS

A PARTLY TO MOSTLY SUNNY DAY TO THIS POINT WITH ONLY SCT MID-HIGH CLOUDS OVRHEAD AS FA IS IN BTWN SHRTWVS. UPSTREAM...NEXT AREA OF PRECIPITATION IS EDGING INTO SRN MN/SW WI ASSOCIATED WITH MCS THAT DEVELOPED OVR IA LATE LAST EVENING. CONVECTIVELY INDUCED SHRTWV OVR WRN IA HAS SPREAD AS/AC AS FAR NORTH AS STC/PKF THIS MORNING...WITH CIRRUS STREAMING OVR WRN UPR MI ATTM. CI IS AIDED BY RRQ DIVERGENCE OF 120KT JET STREAK OVR SW ONTARIO PER ACARS ANALYSIS AND WV LOOP. 12Z SOUNDINGS FM MPX AND GRB SHOW SHARP MOISTURE GRADIENT IN PLACE WITH DRY PROFILE BLO H7 AT MPX AND NEARLY MOIST PROFILE FOUND AT GRB THRU H6. GRB PROFILE IS REPRESENTATIVE OF MOIST AIRMASS PRESENT ALONG H85 BAROCLINIC ZONE STRETCHING FM IA INTO NRN LOWER MI.

AS ONTARIO JET TEMPORARILY SHIFTS NWRD SUPPORT FOR UPR LEVEL CIRRUS WILL BEGIN TO DIMINISH AND MID-LEVEL AC/AS ADVANCING FM SW WILL HAVE A HARD TIME AS IT APPROACHES DUE TO MID-LEVEL FLW BECOMING INCREASINGLY CONFLUENT. RUC/ETA ALSO DEPICT CONVECTIVE VORT TO DIMINISH AS IT PRESSES NORTH INTO MN...WHICH WILL FURTHER HAMPER CLOUD COVERAGE...ESPECIALLY ACROSS CNTRL ZONES. INVESTIGATION OF ISENTROPIC 295K SFC (H8-H7) SHOWS THAT BULK OF MID CLOUDS SHOULDN/T MAKE IT INTO WRN ZONES UNTIL AFT 19Z...AND INTO CNTRL ZONES UNTIL AFT 21Z. THIS TIMING MORE IN LINE WHEN LIFT FM PRIMARY SHRTWV (ATTM OVR CNTRL NEB) BEGINS TO AFFECT FA AS WAVE MOVES TO SERN MN. WITH LITTLE CU DEVELOPMENT EXPECTED DUE TO INCREASINGLY DRY AIRMASS (SFC DWPTS IN 30S)...WILL GO MORE OPTIMISTIC ON SUNSHINE UNTIL LATE AFTN WHEN AC ARRIVES. MORE SUNSHINE EXPECTED THRU AT LEAST MID AFTN SHOULD ALLOW PREVELANT MIXING TO OCCUR. THEREFORE HAVE ALSO NUDGED MAX TEMPS UP AWAY FM LAKE SUPERIOR. OTHERWISE GOING FCST LOOKS FINE AND FEW ADDITIONAL CHANGES MADE.

.MQT...NONE.

JLA