Forecast Discussions mentioning ACARS, received at FSL on 04/18/00

...SYNOPSIS... A PACIFIC STORM WILL MOVE INLAND TODAY BRINGING SHOWERS AND A CHANCE OF THUNDERSTORMS TO SOUTHWEST CALIFORNIA THIS MORNING...DECREASING THIS AFTERNOON...AND ENDING TONIGHT. WARMER AND DRY FOR WEDNESDAY... THEN BREEZY AND A COOLER FOR THURSDAY AND FRIDAY WITH A CHANCE OF SHOWERS AS A WEAKER PACIFIC STORM MOVES ACROSS SOUTHERN CALIFORNIA. ...DISCUSSION... AVN/MRF/ECMWF MDLS OF CHOICE. SCT SHOWERS EXPECTED TO INCR IN COVERAGE AROUND DAYBREAK WITH POSSIBILITY OF THUNDERSTORMS AS WELL AS AXIS OF COLD POOL MOVES ACROSS SRN CA THIS MORNING. BEST CHANCE FOR THUNDERSTORMS FOR THE SGX FORECAST AREA WL BE ACROSS THE N HALF OF THE FORECAST AREA THRU MID MORNING...THEN MID LVL TEMPERATURES BEGIN TO WARM. WL RETAIN CHANCE POPS FOR THIS EVENING AS AVN BRINGS SECONDARY POCKET OF LWR LVL MSTR INTO SRN SXNS LATE AFTERNOON THRU EARLY EVENING. THIS MSTR...IN COMBINATION WITH ONSHR LOW LVL FLOW...SHOULD BE SUFFICIENT FOR SCT SHOWERS ALG AND W OF MTNS FOR SOUTHEAST HALF OF FORECAST AREA THRU EARLY TO MID EVENING.

MTNS...WL CONTINUE WINTER WEATER ADV IN MTNS THRU 2 PM. LATEST OBSERVATIONS FM RUNNING SPRINGS AND BIG BEAR LAKE HAVE TEMPERATURES IN THE 20S WITH IDYLLWILD NR 32. ACARS SOUNDINGS BETWEEN 06Z AND 10Z SHOW SNOW LVL AROUND 4000 FEET SBA COUNTY...5000 FEET LOS ANGELES/SBD/RIV COUNTIES...AND 5500 FEET SAN COUNTY. SNOW LVLS MAY LWR A LTL THRU MID MORNING AS AXIS OF COLDEST AIR MOVES ACROSS SRN CA...THEN BEGIN TO SLOWLY REBOUND THIS AFTERNOON. SNOW LVL COULD LWR BRIEFLY TO LVL OF CAJON PASS THIS MORNING IN HEAVIER SHOWERS AND THUNDERSTORMS...BUT ACCUMULATIONS OF SIGNIFICANCE LIKELY TO REMAIN 5000 TO 5500 FT AND ABV THRU EARLY AFTERNOON.

STRONGER AVN PREFERRED WITH NEXT (WKR) UPR LOW FOR WED NIGHT/THU INTO FRI. MDL MSTR FIELDS NOT OVERLY IMPRESSIVE WITH THIS STORM FOR THU INTO FRI...BUT MSTR AND INSTABILITY WARRANTS AT LEAST A CHANCE/SLIGHT CHANCE OF SHOWERS FOR THU AND FRI...ESPCIALLY NW HALF OF FORECAST AREA AND NR HIGHER TERRAIN. SAT LOOKS WARM AND DRY WITH SHORTWAVE RDGG BETWEEN SYSTEMS. LATEST MRF IS A LTL WKR WITH SUN/MON PAC STORM WITH EURO MDLS AND MRF NOW ADVERTISING A CNTRL RATHER THAN CNTRL AND SRN CA STORM. FORTUNATELY...SUN IS STILL BEYOND THE CURRENT EXTENDED.

SAN 730

.SAN...WINTER WEATHER ADVISORY (SEE LAXWSWSAN).

MARTIN



UPPER LOW FROM SUNDAY/S RAIN EVENT MOVING INTO THE CAROLINAS PER GOES WATER VAPORT IMAGERY...BUT 11-3.9 MICRON PICTURES SHOWING EXTENSIVE STRATUS BACK ACROSS THE GREAT LAKES AND UPPER MIDWEST. MAIN SHORT TERM CHALLENGE WILL BE DISSIPATION OF LOW CLOUDS OVER FORECAST AREA TODAY. FOCUS THEN SHIFTS TO PAIR OF SHORT WAVES MOVING THROUGH SPLIT FLOW...WHICH MODELS INDICATE COULD PROVIDE A REPEAT PERFORMANCE OF SATURDAY/S PNEUMONIA FRONTAL PASSAGE...ALBEIT WITHOUT GETTING VERY WARM AHEAD OF IT THIS TIME.

ACARS SOUNDING OUT OF ORD SHOWS BASE OF STRONG LOW LEVEL INVERSION AROUND 925 MB. NOT MUCH EROSION NOTED IN VISIBILE IMAGERY FROM MONDAY OVER IOWA...AND WITH SURFACE RIDGE AND SUBSIDENCE INVERSION MOVING ACROSS AREA THIS MORNING THINK IT WILL BE TOUGH TO SCATTER OUT UNTIL RIDGE WORKS EAST OF THE AREA THIS AFTERNOON. WILL CONTINUE DECREASING CLOUD FORECAST THIS AFTERNOON IN CURRENT ZFP. PREPER SLIGHTLY COOLER FWC MAXES FOR NORTHEASTERN PORTIONS OF FA TODAY.

LOOKING A LITTLE FARTHER AHEAD MODELS FAIRLY SIMILAR WITH LARGE SCALE FEATURES...BUT WILL TREND TOWARD ETA/S MORE AGRESSIVE HANDLING OF LOW LEVEL FEATURES. NORTHERN STREAM SHORT WAVE PUSHING EAST ACROSS SOUTHERN STREAM UPPER RIDGE AND INTO MANITOBA AT THIS TIME...WITH SURFACE LOW EAST OF LAKE WINNEPEG. 06Z SURFACE ANALYSIS SHOWS 3 MB PRESSURE RISES BEHIND TRAILING COLD FRONT DROPPING INTO MONTANA/NORTH DAKOTA. THIS LOW PROGGED TO BE NEAR JAMES BAY AT 00Z WED...WITH COLD FRONT FROM NORTHERN WISCONSIN TO NEBRASKA. FRONT PROGGED INTO SOUTHERN WISCONSIN BY 12Z WEDNESDAY MORNING...BUT AS WE VIVIDLY SAW SATURDAY WITH THESE SYSTEMS ACCELERATION OF BOUNDARY SOUTHWARD OVER LAKE MICHIGAN IS LIKELY. EXPECT WED TO BE A DAY OF WINDS OFF OF THE LAKE...WHICH FWC GUIDANCE IS BEGINING TO REFLECT.

2ND SHORT WAVE IS THE SOUTHERN STREAM UPPER LOW OFF THE CALIFORNIA COAST THIS MORNING. THIS SYSTEM IS FORECAST TO MOVE TO NE COLORADO BY 18Z WEDNESDAY...WITH 90-100 KNOT 250 MB JET MAX ROTATING NORTHEAST OVER THE TEXAS PANHANDLE. THIS INDUCES SURFACE CYCLOGENESIS OVER THE HIGH PLAINS BY 00Z WED. COLD FRONT FROM INITIAL WAVE EXPECTED TO STALL OUT OVER NORTHERN IL/IND...WITH GOOD PRECIP EVENT EXPECTED AS PLAINS LOW MOVES INTO IOWA WEDNESDAY WITH WAA ISENTROPIC LIFT AND MOIST 40-50 KNOT 850 FLOW OVER THE LOW LEVEL BOUNDARY. WILL LOOK AT BOOSTING POPS WED/WED NIGHT. .CHI...NONE

RATZER



WILD APRIL NIGHT ACROSS THE SRN CA AND ADJACENT CSTL WATERS. BAND AFTER BAND OF HEAVY SHOWERS AND THUNDERSTORMS HAS DEVELOPED IN THE SE QUADRANT OF THE UPPER LOW AND HAVE PUSHED INTO THE FCST AREA IN SWLY MID LVL FLOW. SAT PIX SHOW UPR LOW CENTERED JUST TO THE NW OF PT CONCEPTION THIS MORNING MOVING TOWARD THE CA CST. SEVERAL STRONG VORTS ROTATING AROUND THE SRN SIDE OF THIS LOW ALONG WITH GOOD UPR LVL DIFLUENCE AND DESTABILIZATION OF ATMOS DUE TO APCHG COLD POOL ALF HAVE WORKED TOGETHER TO PRODUCE ABUNDANT SHOWER AND TSTM ACTIVITY THIS MORNING. BETWEEN MIDNIGHT AND 1 AM...MANY SPOTTERS FROM THE BEVERLY HILLS/HOLLYWOOD AREA INTO THE SAN GABRIEL VLY REPORTED MARBLE SIZED HAIL AND VERY HEAVY RAIN. ALERT GAUGES INDICATED RAINFALL RATES OF MORE THAN ONE HALF INCH PER HOUR WITH MANY OF THE SHOWERS EARLIER THIS MORNING...AND SANTA BARBARA AIRPORT RECEIVED MORE THAN ONE HALF INCH OF RAIN IN A HEAVY TSTM.

WITH SO MUCH ACTIVITY ON RADAR...AND CURRENTLY A TSTM HERE AT THE OFFICE...WL EXTEND FLOOD ADVISORIES UNTIL 7 AM FOR SLO... SBA AND VTU COUNTIES. TEMPORARY LULL OF RAINFALL IN L.A. COUNTY WILL SOON END...SO WILL GO WITH FLOOD ADVISORY THERE UNTIL 8 AM. SNOW LEVELS HAVE DROPPED AND ACARS DATA WOULD SUGGEST SNOW LVLS LOCALLY DOWN TO 4000 FEET...WITH WDSPRD SNOW ABOVE 5000 FEET. PLENTY OF MSTR STREAMING INTO THE MTNS THIS MORNING...SO XPCT MANY AREA ABV 5000 FEET WL RECEIVE AT LEAST A FEW INCHES OF SNOW.

AS UPPER LOW MOVES INTO CENTRAL CA...SHOWER AND TSTM ACTIVITY WL DECREASE...FIRST ACRS SLO AND SBA COUNTIES BY MID MORNING.., THEN LATE THIS MORNING ACRS L.A, COUNTY. SHOULD BE SOME PARTIAL CLEARING THIS AFTERNOON IN MANY AREAS...BUT WL HAVE TO WAIT UNTIL LATE TONIGHT/WED MORNING FOR MORE COMPLETE CLRG. SHOULD BE FAIRLY NICE DAY IN MOST AREA WED...MOSTLY SUNNY AND A BIT WARMER. NEW MODELS ARE FASTER WITH NEXT SYSTEM...SHOWING IT APCHG THE W CST WED NIGHT...THE CLOSING IT OFF IN THE VICINITY OF THE FCST AREA THU. IT MUST BE EMPHASIZED THAT THIS STORM WL BE NOWHERE NEAR AS STRONG AS THIS PAST ONE...BUT ANY CLOSED LOW NEAR THE AREA IN SPRING COULD PRODUCE SHOWERS. WL BUMP UP TIMING OF GREATEST THREAT TO THU INTO EARLY FRIDAY BASED ON MED RANGE MODEL RUNS WHICH ARE IN GOOD AGREEMENT.

LAX +00. BRUNO.

.LAX...WINTER WEATHER ADVISORY (SEE LAXWSWLAX).