Damaging Winds in South Dakota, July 26 to 27, 2002

AREA FORECAST DISCUSSION FOR CENTRAL/N-EAST SD AND W-CENTRAL MN
NATIONAL WEATHER SERVICE ABERDEEN SD
335 PM CDT FRI JUL 26 2002

S/W LIFTING ACROSS C AND NE SD THROUGH THIS EVENING NOT BRINGING
MUCH AS FAR AS PRECIP TO THE CWA THIS AFTN...ONLY MID AND HIGH LEVEL
CLOUDS. THERE ARE SOME SHRAS ACROSS NC SD THIS AFTN AND THERE MAY BE
MORE SHRAS YET TO DEVELOP ACROSS NE SD AND WC MN THIS EVENING BEFORE
THE S/W EXITS THE AREA. MID LEVEL LAPSE RATES ARE PRETTY STABLE SO
DONT EXPECT MUCH AS FAR AS TSRAS WITH THIS S/W. NEXT MORE
SIGNIFICANT S/W OVER WY WILL MOVE EAST ACROSS SD THROUGH THE NIGHT
ALONG WITH A SFC TROUGH. DWPTS ARE NOT ALL THAT IMPRESSIVE ACROSS
THE CWA LATE THIS AFTN ALONG WITH LIS BUT...AS THIS SECOND WAVE
MOVES IN...STEEPER MID LEVEL LAPSE RATES WILL OCCUR. THIS WAVE WAS
ALREADY BRINGING SOME SCT TSRAS TO WY LATE THIS AFTN. THEREFORE...AS
THIS SECOND WAVE AND SFC TROUGH MOVES ACROSS TONIGHT...SCT TSRAS ARE
EXPECTED TO DEVELOP AND MOVE EAST ACROSS THE CWA...ENDING SAT MRNG
ACROSS NE SD AND WC MN. THE WINDS WILL BECOME WEST BEHIND SFC TROUGH
THROUGH SAT MRNG. SAT SHOULD BE MOSTLY A DRY DAY ACROSS THE CWA WITH
M/S SKIES AND W TO NW WINDS AT 10 TO 20 MPH. THE AVN AND ETA BOTH
SHOW SOME S/W ENERGY SLIDING ACROSS THE UPPER MIDWEST ALONG WITH
SOME QPF FOR SAT NIGHT AND SUNDAY. ALTHOUGH THE AVN WANTS TO PUSH A
STRONGER COLD FRONT THROUGH THE CWA WHILE THE ETA PUSHES A WEAKER
COLD FRONT THROUGH. THEREFORE...WILL GO WITH A 30 POP FOR SHRAS AND
TSRAS SAT NIGHT AND SUN. SUN NIGHT THROUGH MON NIGHT LOOKS TO BE DRY
ACROSS THE CWA.

.EXTENDED DISCUSSION...

RATHER SUBSTANTIAL SHIFT IN 00Z AVN RUN IN TERMS OF UPPER FLOW
PATTERN ACROSS WESTERN AND CENTRAL US FOR THE MIDDLE OF NEXT WEEK.
AVN NOW MORE INLINE WITH ECMWF IN DEVELOPING CUT-OFF LOW IN EAST
CENTRAL PACIFIC AND TRENDING TOWARD MORE PROGRESSIVE AND LESS
AMPLIFIED EVOLUTION WITH NORTHERN PORTION OF TROUGH.  THIS EVOLUTION
RESULTS IN MUCH LESS AMPLIFIED UPPER RIDGE ACROSS WESTERN US FOR THE
BEGINNING OF NEXT WEEK AS ADVERTISED BY PREVIOUS FEW AVN RUNS.
LITTLE IN THE WAY OF SIGNIFICANT SHORT WAVES THROUGH WEDNESDAY.
SEVERAL WEAK SHORT WAVES WILL DROP SOUTHWARD FROM GULF OF ALASKA IN
THE WEDNESDAY TO FRIDAY TIME FRAME WHICH WILL ACT TO LOWER HEIGHTS
ACROSS PACIFIC NORTHWEST WHILE MAINTAINING WEAK RIDGING ACROSS CWA.
THIS WILL ALLOW WEAK SHORT WAVES TO APPROACH THE DAKOTAS IN
SOUTHWEST UPPER LEVEL FLOW ON THURSDAY AND FRIDAY BUT FEEL THAT MID
LEVEL BAROCLINIC ZONE AND BEST UPPER FORCING WILL STILL BE NORTH OF
CWA FOR THIS TIME PERIOD AND WILL KEEP PERIOD DRY AT THIS TIME.
ACCEPTING THIS MORE ZONAL PATTERN WILL GO WITH TEMPERATURES RIGHT
AROUND SEASONAL LEVELS THROUGHOUT THE PERIOD WITH LITTLE IN THE WAY
OF DAY TO DAY VARIATIONS.

.ABR...NONE

MOHR/MARSILI