Severe Thunderstorm Warning 11, NWS Aberdeen, SD

AREA FORECAST DISCUSSION FOR CENTRAL/N-EAST SD AND W-CENTRAL MN
NATIONAL WEATHER SERVICE ABERDEEN SD
350 PM CDT SAT JUN 8 2002

CONTINUED FOCUS FOR THIS FORECAST WILL BE CHANCES FOR CONVECTION AND
SEVERE WEATHER THROUGH MONDAY AFTERNOON.  WATER VAPOR IMAGERY THIS
AFTERNOON NICELY SHOWING UPPER LEVEL JET BEGINNING TO ROUND BASE OF
BROAD UPPER TROUGH.  CANADIAN AND AVN IN GOOD AGREEMENT IN TERMS OF
UPPER WAVE EVOLUTION THAT IS SLOWER THAN ETA.  WILL BASE FORECAST
MORE ON THIS SLOWER SOLUTION WITH THE THINKING THAT ETA IS EJECTING
UPPER HEIGHT MINIMUM NORTHWARD TOO QUICKLY GIVEN UPPER JET STREAK
UPSTREAM OF UPPER TROUGH AXIS.

SHORT TERM CONCERNS WILL BE SEVERE WEATHER AND HEAVY RAIN TONIGHT.
19Z ANALYSIS INDICATES WEAK SLP TROUGH EXTENDS FROM WESTERN SOUTH
DAKOTA NORTHEAST INTO WEST CENTRAL MINNESOTA.  DEW POINTS HAVE RISEN
INTO MID 60S THIS AFTERNOON ACROSS SOUTHERN CWA...WITH MID 50S
ACROSS NORTHERN CWA.  EXPECT SOUTHEAST FLOW IN LOW LEVELS TO
CONTINUE INCREASING LOW LEVEL MOISTURE EARLY THIS EVENING.  A FEW
FEATURES OF INTEREST FOR TONIGHT WHICH WILL LIKELY FOCUS
CONVECTION.  ETA AND AVN BOTH SHOWING MID LEVEL SPEED MAX AND 700
HPA VORTICITY MAX WORKING INTO CWA EARLY THIS EVENING.  MESOETA EVEN
TRIES TO GENERATE CONVECTIVE COMPLEX IN ASSOCIATION WITH THIS
FEATURE ACROSS CENTRAL CWA.  UPPER LEVEL VORTICITY MAXIMUM ALSO
APPROACHING WESTERN CWA.  ETA AND AVN BOTH DEVELOP NOCTURNAL JET BY
06Z WITH ETA 850 HPA WIND SPEEDS OF 60 KNOTS.  WIND PROFILES STILL
LOOK FAVORABLE FOR ANY CONVECTION THAT DOES DEVELOP TO TURN SEVERE
QUICKLY WITH LARGE HAIL BEING MAIN THREAT.  12Z ETA SUGGESTING 0-3
KM SHEAR MAGNITUDES IN THE 40-50 KNOT RANGE ACROSS NORTH CENTRAL CWA
TONIGHT...WITH SURFACE BASED CAPE VALUES BETWEEN 2000 AND 3000
J/KG.  HOWEVER...BEST LOW LEVEL CONVERGENCE ASSOCIATED WITH LOW
LEVEL JET AND MAIN AREA OF UPPER DIVERGENCE WILL BE LOCATED OVER
NORTHWEST CWA THIS EVENING...AND THEN MIGRATE NORTH OF CWA.
THUS...FEEL THAT NORTHWEST CWA WILL HAVE BEST POTENTIAL FOR HEAVY
RAINFALL.  WITH BEST UPPER FORCING AND LOW LEVEL CONVERGENCE MOVING
NORTH OF CWA LATE THIS EVENING...WILL OPT NOT TOO ISSUE FLASH FLOOD
WATCH BUT NEXT SHIFT WILL HAVE TO MONITOR THIS AREA FOR HEAVY RAIN
POTENTIAL.

FOR SUNDAY...POSSIBLY ANOTHER ACTIVE EVENING SHAPING UP.  DURING
AFTERNOON WILL LIKELY HAVE A TOUGH TIME INITIATING CONVECTION WITH
WARMING MID LEVEL TEMPERATURES.  FEEL THAT BEST CHANCE OF CONVECTION
WILL BE ACROSS NORTHWEST IN BETTER PROXIMITY OF STRONG LOW LEVEL
FRONTOGENESIS AND UPPER LEVEL DIVERGENCE WHICH MAY HELP TO ERODE
CAP.  SUFFICIENT INSTABILITY IN MODEL FORECAST SOUNDINGS FOR
TOMORROW...WITH SHEAR PROFILES NOT AS IMPRESSIVE AS THIS EVENING.
FEEL THAT FWC AND MAV GUIDANCE ARE NOT QUITE WARM ENOUGH TOMORROW
AFTERNOON...AND FAVORED WARMER ETA 2-METER TEMPERATURES.

IN GOING WITH SLOWER AVN...WILL KEEP CHANCE OF CONVECTION GOING
THROUGH MONDAY AFTERNOON ACROSS EASTERN CWA...AND END CHANCE MENTION
ACROSS THE WEST.  MONDAY AND TUESDAY LOOK MUCH COOLER WITH 850 HPA
TEMPERATURES FALLING BACK INTO THE 8-12 DEGREE CELSIUS RANGE.

NDM

.EXTENDED DISCUSSION...

00Z AVN AND 12Z FRI ECMWF IN PRETTY GOOD AGREEMENT ON THE EVOLUTION
OF THE CONUS WAVETRAIN THROUGH THE EXTENDED.  AND THE 12Z RUNS
APPEAR FAIRLY SUPPORTIVE.  WE WILL TRANSITION FROM A WEST CONUS TROF
TO A ROCKIES RIDGE/EASTERN CONUS TROF DURING THIS PERIOD.  NORTHWEST
MID LEVEL FLOW WILL PREDOMINATE FROM WED THROUGH SATURDAY AND THIS
IN ITSELF CAN PRESENT SOME PROBLEMS THIS TIME OF YEAR.  AT THIS
POINT WILL MAINTAIN DRY FORECAST FROM WED THROUGH SAT WITH THE
ACKNOWLEDGMENT THAT ISOLD/SCT ACTIVITY COULD OCCUR WITH JUST ABOUT
ANY S/W THAT TRACKS SOUTHEAST OVER THE REGION.  AT THIS TIME RANGE
MODEL ACCURACY WITH INDIVIDUAL WAVES VERY SUSPECT AND HATE TO
INTRODUCE PCPN TIMING THAT WILL SURELY GET FLIP FLOPPED.  TEMPS WERE
BASED ON AVN 8H TEMPS AND MEX GUIDANCE.

TDK

.ABR...NONE