Severe Thunderstorm Warning 146, NWS Aberdeen, SD

AREA FORECAST DISCUSSION FOR CENTRAL/N-EAST SD AND W-CENTRAL MN
NATIONAL WEATHER SERVICE ABERDEEN SD...CORRECTED
325 PM CDT FRI AUG 9 2002

OBVIOUSLY A DECENT S/W IS LIFTING OUT OF WESTERN HIGH PLAINS
TROF...AND INDUCING STRONG UPWARD MOTION ACROSS CENTRAL AND EASTERN
SOUTH DAKOTA.  S/W EXPECTED TO CROSS SOUTH DAKOTA AND EXIT CWA
SHORTLY AFTER 06Z AND THEREFORE WILL TAPER PCPN FROM WEST TO EAST IN
ACCORDANCE WITH THIS.  STILL SOME POTENTIAL FOR SVR TSRA OVER
EASTERN 1/4 OF CWA WHERE SFC BASED CAPES A BIT BETTER DUE TO MORE
INSOLATION.  MOST ACTIVITY SHOULD BE OFF INTO MN BY 06Z.  HAVE
PULLED ALL POPS FROM SATURDAY FORECAST AS MODELS HAVE ALL COME INTO
GOOD AGREEMENT ON MOVEMENT AND INTENSITY OF MID LEVEL LOW CROSSING
DAKOTAS.  UPPER LOW PROGGED TO TAKE A MORE NORTHERLY TRACK WITH LESS
CHANCE OF WRAPAROUND INTO NORTHERN CWA.  ALSO LAPSE RATES ONLY
MARGINALLY SUPPORTIVE OF AFTERNOON INSTABILITY SHOWERS SO WILL LEAVE
OUT FOR NOW.  NEXT CHANCE OF PCPN COMES SUNDAY AS MOISTURE RETURNS
SWIFTLY TO THE EASTERN CWA VIA STRONG LLJ AHEAD OF NEXT S/W AND SFC
FRONT.  FOR NOW WILL ONLY CARRY SCT AFTERNOON POPS BUT LATER SHIFTS
WILL HAVE TO MONITOR.  TEMPS ON SUNDAY SOMEWHAT OF A QUANDRY WITH
MOS LOOKING TOO COOL BASED ON ETA 8H TEMPS.  AVN A BIT COOLER BUT
STILL SUGGESTS WARMER THAN MOS READINGS.  MONDAY COULD BRING SOME
EARLY SHOWERS OTHERWISE LOOKS BENIGN.

TDK

.EXTENDED DISCUSSION...
TRANSITION TO MIDWEST TROF CONTINUES INTO THE EXTENDED PORTION OF
THE FORECAST WITH ALL MODELS SHOWING THIS SHIFT TO VARYING DEGREES.
ENSEMBLES ALSO SHOWING RATHER LARGE SPREADS WRT POSITION AND DEPTH
OF THE TROF. AS TROF AXIS SLIDES EAST OF THE CWA WE SHOULD END BEST
CHANCES FOR PCPN WITH ONE EXCEPTION. EXTENDED AVN...AND ENSEMBLES TO
SOME EXTENT...DROP A SFC BOUNDARY SOUTH THROUGH THE AREA WEDNESDAY.
THIS SHOULD MAINLY SUPPORT ADDITIONAL COOL AIR ADVECTION AND
CLOUDS...BUT WITH BOUNDARY SLIDING THROUGH SOME PCPN IS POSSIBLE. SO
WILL ADD A CHANCE OF SHOWERS TO THE WEDNESDAY FORECAST. DISAGREEMENT
IN THE ENSEMBLES ARE ENOUGH TO CAUSE ME TO LEAVE ANY MENTION OF PCPN
BEYOND WEDNESDAY OUT OF THE FORECAST FOR NOW. SOME HINT OF RETURN TO
MORE ZONAL FLOW BY FRIDAY WITH BEST CYCLONIC FLOW ALOFT SLIDING
EAST. UNDER COOLER MID LVL AND LOW LVL TEMPS AND CYCLONIC FLOW ALOFT
SHOULD SEE MORE CLOUDS THURSDAY THEN DECREASING FRIDAY. WILL GO NEAR
MEX GUIDANCE TEMPS FOR THE PERIOD...WELL BELOW NORMAL HIGHS.

MLF

.ABR...NONE.