Forecast Discussions mentioning ACARS, received at FSL on 03/04/00

MAIN FORECAST PROBLEMS THIS AFTERNOON ARE THE COVEREAGE, CHANCES AND TYPE OF PRECIPITATION ACROSS FORECAST AREA (FA) FOR TONIGHT.

MODELS CONTINUE TO BE QUITE SIMILAR AGAIN TODAY. UPPER LOW AND MOISTURE MOVE EAST INTO WEST KENTUCKY THEN DROP SOUTHEAST INTO TENNESSEE. THIS WILL KEEP GREATEST PART OF THE RAIN THAT IS NEAREST TO THE LOW OVER THE SOUTHWEST PARTS OF FA.

HOWEVER...DEFORMATION ZONE AS SEEN ON SATELLITE HAS BROUGHT A BAND OF LIGHT RAIN NORTH INTO THE NORTHERN PARTS OF FORECAST AREA. THIS IS FARTHER NORTH THAN INDICATED BY EARLIER MODEL RUNS OF RH...TIME SECTIONS OR ISENTROPIC LIFT. AVN AND 18Z RUC HAVE BEST HANDLE ON THIS FEATURE. AVN AND RUC HOLDS MOSTURE ALONG OHIO RIVER THROUGH EVENING THEN AVN DROPS TO SOUTH. WILL FOLLOW THIS THINKING IN WORDING FORECAST FOR NORTHERN HALF OF FA.

THE NEXT PROBLEMS IS TYPE. AIRCRAFT SOUNDING AROUND NOON SHOWS TEMPREATURES ONLY FEW DEGREES ABOVE ZERO IN LOWER LAYERS WITH SURFACE TEMPS IN THE UPPER 30S. THERE HAVE BEEN REPORTS OF SOME SLEET AND EVEN A LITTLE SNOW MIXED WITH THE RAIN. EXPECT LITTLE WARMER OR COOLER AIR ADDED AND WILL KEEP A LITTLE MIXTURE IN FORECAST.

PRECIPITATION TO THE SOUTH OF THE DEFORMATION ZONE...SOUTHERN TWO THIRDS OF FA...WILL HAVE SHOWERS WITH THE MOST NUMEROUS OVER THE SOUTHWEST PART. MOST PRECIPITATION WILL END BEFORE MORNING AS LOW DROPS SOUTHEAST INTO TENNESSEE.

AS SURFACE AND UPPER LOW CONTINUE TO THE SOUTHEAST ON SATURDAY...CLOUDS DECREASE RAPIDLY. HIGH PRESSURE BUILDING INTO KENTUCKY AND TENNESSE WILL BRING MOSTLY SUNNY SKIES FOR THE WEEKEND AND A RETURN TO UNSEASONABLY MILD TEMPRATURES BY SUNDAY.

HAVE MADE ONLY MINOR ADJUSTMENTS TO MOS TEMPERATURES.

.SDF...NONE.

SCHOLZ

...SYNOPSIS... A PACIFIC STORM MOVING ONSHORE ACROSS NORTHERN BAJA WILL CONTINUE TO BRING SHOWERS AND THUNDERSTORMS TO SOUTHWEST CALIFORNIA TODAY. A SECOND AND MORE POWERFUL STORM WILL FORM OFF THE COAST SUNDAY. THIS STORM IS EXPECTED TO BRING HEAVY RAIN AND SNOW LATE SUNDAY INTO MONDAY...WITH SNOW LEVELS FALLING BELOW 3000 FEET SUNDAY NIGHT AND MONDAY.

...DISCUSSION... MEAN MOTION OF LOW CENTER HAS BEEN SOUTH SOUTHEAST 7 KTS PAST 12 HOURS WHILE IMPULSES ROTATE ABOUT IT AT 15-25 KTS. NEXT IMPULSE ROUNDING THE BOTTOM OF THE LOW ALONG 119W AT 10Z SEEMS TO BE WELL INITIALIZED BY RUC MODEL. THIS IMPULSE WAS CARRIED FARTHER SOUTH AND ACROSS CENTRAL BAJA BY 04/00Z AVN MODEL WHILE EXTRAPOLATION FROM SATELLITE IMAGERY AND LATEST RUC WOULD SHOW A TRACK CLOSER TO THE SRN CA/N BAJA BORDER. ACARS SOUNDING OUT OF SAN AT 0645Z SHOWED SOUTHERLY WINDS 50-100 KT BETWEEN 15K-30K FT. THIS JET IMPULSE WAS NOT THAT WELL DEPICTED IN MODELS AND COULD HELP TO OFFSET THE SOUTHWARD MOMENTUM OF THE LOW. END RESULT WOULD BE TEMPORARY CLEARING THIS MORNING/AREAS OF DENSE FOG AS DIVERGENCE ALOFT/CIRRUS SHIELD ASSOCIATED WITH JET MAX PULLS AWAY. THEN DIURNAL HEATING COUPLED WITH ANOTHER 5 DEGREES CELSIUS COOLING IN MID LEVELS AND ARRIVAL OF IMPULSE SET OFF LATE MORNING/AFTERNOON THUNDERSTORMS. THIS IS A 180 DEGREES FLIP FROM CURRENT FORECAST...MAY TAKE THE EASY ROAD OUT AND DROP QUALIFIER OF DECREASING SHOWER ACTIVITY DURING THE AFTERNOON.

NEXT SYSTEM STILL ON TRACK THOUGH MODELS ARE TENDING TOWARDS A SLIGHTLY FARTHER WEST POSITION. AVN/MRF HAS LARGE AREA OF DIVERGENCE IN THE 500- 300 MB LAYER AND GREATEST UPWARD VERTICAL VELOCITIES AT 700 MB...-15 UBAR/SEC...MOVING OVER INNER WATERS SUNDAY AFTERNOON. THE FWCSAN HAS CATEGORY 5 QPF AMOUNTS FOR SUNDAY NIGHT. THIS IS GENERALLY ACCEPTED. WILL REWORD/DELAY ONSET OF PRECIPITATION SUNDAY FOR A LATER START TIME AND BEEF UP PRECIPITATION THREAT/COOLING FOR SUNDAY NIGHT/MONDAY TIME PERIODS. THE 500 MB HEIGHTS/TEMPS ASSOCIATED WITH THIS SYSTEM ARE 150 DECAMETERS/5 DEGREES CELSIUS LOWER THAN THE CURRENT LOW OFF THE COAST. THICKNESS FALLS OF 120 METERS ARE FORECAST BETWEEN SUNDAY AND MONDAY. SIMPLE RULE OF THUMB AND RELATIVE CHANGE WOULD SUPPORT SNOW LEVELS NEAR 2000 FEET...SINCE MAJOR EFFECTS IN THE PERIOD 4/5 TIME RANGE AND STILL POSSIBILITY THE STRONG THERMODYNAMICS MAY END UP BEING ELSEWHERE...ECMWF HAS LOW CENTER DEEPER AND FURTHER NORTHWEST...WILL HOLD OFF ISSUING WINTER STORM WATCH FOR NOW AND REISSUE SPECIAL WEATHER STATEMENT WITH HIGHER QPF/COLDER TEMPERATURES.

LOOKING FURTHER INTO THE MEDIUM RANGE PERIOD...THE MODELS ARE ALL IN GENERAL AGREEMENT OF DEVELOPING YET A THIRD CLOSED LOW OFF THE COAST...IT MUST BE SPRING TIME...WHICH IS CURRENTLY PROGGED TO MOVE ONSHORE THURSDAY. TWO AT A TIME IS ABOUT ALL I CAN HANDLE PLUS ITS OUTSIDE OF DAY 5. NCEP 6 TO 10 DAY DISCUSSION INDICATED MIXED CONFIDENCE

MIXED IN THIS SOLUTION...THOUGH SPLIT IN WESTERLIES WITH STRONGER SOUTHERN BRANCH IS SUPPORTED BY LONG WAVE THEORY/TELECONNECTIONS.

SAN 524

.SAN...MARINE WEATHER STATEMENT...SEE LAXMWSSAN. SPECIAL WEATHER STATEMENT...ISSUANCE AROUND 041300 UTC. BALFOUR