Severe Thunderstorm Warning 11, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
317 PM CDT MON MAY 6 2002

...FORECAST CHALLENGE TO BE TEMPERATURES AND SVR CHANCES ON TUESDAY...

CURRENT SCENARIO HAS A COUPLE OF BOUNDARIES...ONE ACROSS KANSAS AND
ANOTHER COLDER BOUNDARY ACROSS EXTREME NORTH CENTRAL NEBRASKA.
TEMPERATURES VARY WIDELY ACROSS THE NRN BOUNDARY WITH TEMPS IN THE
40S OVER SOUTH DAKOTA...WITH TEMPS IN THE 70S FARTHER SOUTH OVER SRN
AND WRN NEBR. TRICK TO THE FCST WILL BE ESTIMATING THE POSITIONING
OF THE SFC...AS WELL AS UPPER LEVEL BOUNDARIES FOR THE FIRST 60 HRS.
THIS WILL BE KEY TO POSITIONING OF CONVECTION FOR THE PERIOD.

TONIGHT...COULD SEE ATM DESTABILIZE AFTER SUNSET OVER THE SW AND W.
SFC BASED CAPE INCREASES BY DAWN AND ELEVATED PARAMETERS BEGIN TO
COME TOGETHER. HIGH H85 TO H7 LAPSE RATES AND GOOD NEGATIVE LIS
ABOVE H800 ARE INDICATING DEEPENING INSTABILITY. LL MOISTURE WILL BE
THE LIMITING FACTOR HOWEVER AS H85 DEW POINTS CONTINUE TO REMAIN
VERY MARGINAL. FIREWORKS SHOULD HOLD OFF TIL TUESDAY. WITH
INCREASING CLOUDINESS...ESPECIALLY NORTH...TEMPS SHOULD BE MILD.

TUESDAY AND TUESDAY NIGHT...THIS COULD BE INTERESTING. ETA MODEL DEVELOPING
GOOD CONVECTION AND PRECIP SIGNATURE DURING THE DAY
TOMORROW...ESPECIALLY OVER THE CENTRAL AND NERN COUNTIES. BEST MID
LEVEL INSTABILITY EXISTS FROM THE SW TO THE NERN CWA PER LOW NEG
ELEVATED LIS AND STEEP MID LEVEL LAPSE RATES. LL MOISTURE WHICH IS
LACKING TONIGHT...SHOULD BE WELL ESTABLISHED BY TOMORROW AS ERLY LL
FLOW REESTABLISHES ITSELF. WILL NEED TO INITIATE POPS TOMORROW WITH
THE HIGHEST ALONG AND E OF A LBF TO MERRIMAN LINE. BY WEDNESDAY
NIGHT PRECIP THREAT BEGINS TO EXIT CWA BY EARLY EVENING BUT A
SECONDARY H7 SHORT WAVE TAKES AIM ON THE NRN ZONES. GOOD H3
DIVERGENCE SHOULD SUPPORT TSRA DEVELOPMENT IN THESE AREAS. FARTHER
SOUTH AND WEST...LAPSE RATES CONTINUE TO INDICATE DEEP MID LEVEL
INSTABILITY...AND MOISTURE WILL CONTINUE TO BE IN PLACE PER H85 DEW
POINTS AT OR NEAR 10C. WE SHOULD SEE SOME BREAKS IN THE CLOUDS BY
AFTN ACROSS THE SW...AND ANY LIMITED SUN WHICH OCCURS WILL HELP
DESTABILIZE THE SITUATION.

WEDNESDAY AND WEDNESDAY NIGHT...SFC LOW MOVES FARTHER SOUTH INTO SW
KANSAS. THIS WILL ALLOW FRONT STALLED OUT OVER SD NE BORDER TO CRASH
SOUTH. AM NOT BUYING GUIDANCE NUMBERS AS OF YET. NGM MOS WAY TOO
WARM WHILE THE MAV GUIDANCE SEEMS A LITTLE COOL. WILL USE H85 TEMPS
FOR GUIDANCE WITH A LITTLE UPWARD MODIFICATION. SHOULD SEE FAIRLY
PERSISTENT CLOUD COVER FURTHER HOLDING TEMPS BACK. SURFACE AS WELL
AS MID LEVEL LIS BEGIN TO SHOW STABILIZATION BY MID DAY. AM
THINKING AT THIS JUNCTURE THAT BULK OF PRECIP WILL BE IN THE AM WITH
CLOUDS PERSISTING INTO THE AFTN. H5 UPPER WAVE PULLS EWD BY THURSDAY
AM AND PLACES CWA IN AREA OF GOOD SUBSIDENCE. WITH GRADUAL CLEARING
AND SFC HIGH MOVG INTO ERN WYOMING...IT IS SHAPING UP TO BE A COLD
NIGHT. H85 TEMPS DIP TO -6C IN MOST OF THE CWA. WITH RESIDUAL
MOISTURE IN THE LOWER LEVELS IN PLACE...MEX NUMBERS MAY BE A LITTLE
LOW. WILL ADJUST THESE UP A BIT.

THURSDAY...AFTER A COLD START...AND WITH HIGH PRESSURE
OVERHEAD...SHOULD REMAIN CHILLY. AVN BEGINS TO USHER WARMER AIR IN
BY AFTN BUT IT WILL BE SLOW IN GETTING HERE. JUDGING BY H85
TEMPS...SHOULD BE A DAY WITH TEMPS MAINLY IN THE 50S. WE MAY CRACK
60 IN THE FAR SW.

.DAYS 4 THROUGH 7....
FRIDAY THROUGH MONDAY...
AFTER A COLD CLEAR START ON FRIDAY MORNING...TEMPS SHOULD REBOUND
QUICKLY. NEW MRF TRENDING TOWARD MORE ZONAL ECMWF SOLN. FROPA ON
FRIDAY NIGHT CONTINUES TO WARRANT MENTION OF PCPN SO WILL KEEP IN
FCST. WITH ZONAL PATTERN ALOFT THROUGH THE WEEKEND...STATIONARY
FRONT SHOULD CONTINUE TO STAY PUT AND LIFT NWD LITTLE. LOOKS TO BE
FAIRLY DRY IN OUR NEIGHBORHOOD WITH THE NEXT SLIGHT CHANCE OF PCPN
BEING ON SUNDAY EVENING WITH THE APPROACH OF THE NEXT H5 WAVE. AS
FOR TEMPERATURES...WITH A MORE ZONAL PATTERN AND FRONTAL BOUNDARY S
OF THE AREA...SEASONAL TEMPS IN THE MID 60S TO LOWER 70S SEEM IN
ORDER.

.LBF...NONE.

CLB