Severe Thunderstorm Warning 170, NWS Aberdeen, SD

AREA FORECAST DISCUSSION FOR CENTRAL/N-EAST SD AND W-CENTRAL MN
NATIONAL WEATHER SERVICE ABERDEEN SD
235 AM CDT TUE AUG 20 2002

MAJOR CONCERN WITH TODAYS FORECAST AS ETA AND AVN HAVE DIVERGED IN
THEIR SOLUTIONS SOMEWHAT WRT LOCATION AND AMOUNT OF PCPN AS LEADING
SHORT WAVES EJECT ENE FROM WEST COAST SYSTEM INTO THE PLAINS LATE
THIS AFTERNOON THROUGH THURSDAY.

INITIALLY AVN APPEARS TO HAVE A SLIGHTLY BETTER HANDLE ON UPPER LOW
POSITION AT 06 UTC AS IT DIGS SE TOWARD THE UPPER OREGON COAST WHILE
ETA KEEPS THE LOW A BIT FARTHER NORTH. BOTH APPEAR TO HAVE CAPTURED
SHORT WAVE/VORT LOBE EJECTING OUT OF THE SWRN U.S. IN MONSOON FLOW.
WATER VAPOR IMAGERY ALSO DEPICTS RATHER DEEP MSTR FLOWING ENE OUT OF
THE SW INTO THE CENTRAL ROCKIES NOW.

AVN CONTINUES TO DIG THE UPPER LOW FARTHER SE INTO SE OREGON BOTH
AFTERNOON WHILE LEADING SHORT WVES RIDE INTO THE CENTRAL ROCKIES AND
MONSOON BECOMES ORINETED A BIT MORE SW-NE. THIS SEEMS A BIT ODD
GIVEN A DIGGING LOW. ONE WOULD EXPECT SOME STRONGER INDUCED RIDGING
DOWNSTREAM AND A LESS PROGRESSIVE PATTERN. BOTH ETA AND AVN APPEAR
TO HAVE CONVECTIVE FEEDBACK ISSUES AS WELL BY EARLY THIS EVENING AS
BOTH TAKE ON A MORE BULLSEYE TYPE PATTERN WITH UPPER DIVERGENCE/MID
LVL OMEGA AND VORTICITY PATTERNS/RAINFALL. OVERALL JET STRENGTHENING
ALSO NOTED BY THIS EVENING...BUT THIS MAY ALSO BE A BYPRODUCT OF
INCREASED WAA ALOFT WITH CONVECTIVE FEEDBACK PROBLEM.

NONETHELESS...BELIEVE AVN HAS A SLIGHTLY BETTER IDEA AND WILL TREND
CLOSER TO ITS SOLUTION. PWATS SEEM TO INCREASE TOO FAST...BUT TIME
SECTIONS INDICATE THIS IS MAINLY DUE TO INCREASED MID LEVEL MSTR
COMING OUT OF THE SWRN U.S. AND OVER THE ROCKIES. WILL EASE BACK ON
THIS MSTR RETURN BY A FEW HOURS ALLOWING THE TEMPS TO RISE ABOVE MAV
GUIDANCE...AND DELAYING START OF PCPN AS WELL. BEST CHANCES FOR
HEAVY PCPN SHOULD BE CONFINED TO THE EASTERN SECTIONS OF THE CWA
TONIGHT WHERE HIGHEST POPS WILL ALSO EXIST. WILL MENTION HEAVY RAIN
POTENTIAL THERE.

WITH PASSAGE OF INITIAL SHORT WAVES TO THE EAST BY WEDNESDAY MRNG
WILL SEE A PERIOD OF LOW POPS. WILL NOT REMOVE POPS ALTOGETHER AS
ENOUGH MID LVL FORCING LEFT OVER TO GENERATE ELEVATED ACTIVITY
WEDNESDAY INTO WEDNESDAY NIGHT. BREAK LOOKS LIKE THURSDAY DURING THE
DAY AS INDUCED SHORT WAVE RIDGE RIDES OVER THE REGION AND SFC
BOUNDARY IS SUPPRESSED TO THE SOUTH. WITH LESS CLOUDS THURSDAY
SHOULD BE THE WARMEST DAY OF THE SHORT TERM PORTION OF THE FORECAST
AS WELL. ANOTHER MID LVL WAVE APPROACHES THURSDAY NIGHT AND LLJ
TRIES TO STRENGTHEN. THIS SHOULD PRODUCE AT LEAST A CHANCE FOR PCPN
THURSDAY NIGHT MOST AREAS.

.ABR...NONE.

FAUCETTE