Severe Thunderstorm Warning 134, NWS Aberdeen, SD

AREA FORECAST DISCUSSION FOR CENTRAL/NORTHCENTRAL AND NORTHEAST
SOUTH DAKOTA AND WEST CENTRAL MINNESOTA
NATIONAL WEATHER SERVICE ABERDEEN SD
215 PM CDT MON AUG 7 2000

...RETRANSMISSION TO INCLUDE EXTENDED FCST DISCUSSION...

LATEST SWOMCD FOCUSING ON CNTL AND N-CNTL SD FOR PSBL WATCH LATER
THIS AFTN. GOES AND MSAS LI'S...CAPES...AND PW'S POINT TOWARD
INCREASING POTENTIAL FOR CONVECTION ALONG INVERTED SFC TROUGH/WM FNT
APPROACHING FROM WEST...AND ALONG WM FNT TO EAST OF SFC LOW NOW
ALONG OR JUST NORTH OF SD-NE BORDER...ROUGHLY BETWEEN IEN AND VTN.
VIS AND IR SHOW CONVECTIVE CLOUDS STEADILY ON THE INCREASE WEST AND
SOUTHWEST...WITH A FEW AREAS OF CONVECTION ALSO DEVELOPING S CNTL
AND SE SOUTH DAKOTA. NORTHEAST STILL MOSTLY CLEAR...APPEARS THIS
AREA STILL CAPPED WTIH GOES CINH VALUES STILL IN THE 80-90 J/KG
RANGE...BUT DECREASING. SFC DEW POINT ANALYSIS SHOWS POOLING OF LOW
LEVEL MOISTURE ALONG AN AXIS ROUGHLY FROM YKN THROUGH BIS.
INSTABILITY CONSEQUENTLY GREATEST ALONG THIS SAME GENERAL AREA. WV
SHOWS S/W WRAPPING UP NICELY ATTM NW CORNER OF SD AND MOVING DUE
EAST. MODELS SEEM TO HAVE DECENT HANDLE ON OVERALL SITUATION...BUT
DO NOT SEEM TO HANDLE POSITION OF AFOREMENTIONED VORT MAX TOO WELL.
WILL FOLLOW ETA MOST CLOSELY...AS 18Z SFC PRESSURE FIT BEST WITH
MSAS ANALYIS...ESPECIALLY SFC LOW TO THE SOUTHWEST. DEPENDING ON
RADAR TRENDS...WILL GO WITH EITHER A 40-60 PERCENT POP RANGE...OR
JUST GO WITH SCT TSTMS WEST AND POPS EAST. WILL ALSO WAIT...OF
COURSE...ON SPC TO MENTION POSSIBLE SEVERE IN WESTERN ZONES. LOOKS
LIKE MOST ACTIVITY WILL BE THIS AFTN THROUGH ABOUT 06Z...THEN
TAPERING OFF. WILL LEAVE IN 20 POP EARLY FAR EASTERN ZONES...THEN
TREND TOWARD SUNNY AS ETA SHOWS DRY AIR AND STRONG SUBSIDENCE
DEVELOPING OVER MOST OF AREA. TUE NIGHT A QUESTION MARK OF
SORTS...WITH ETA AND AVN BOTH SHOWING AT LEAST MDT VERTICAL MOTION
AT 7H MOVING OVER AREA OVERNIGHT. 1000-500 MB AVE RH IS FAIRLY
LOW...AND LOW LEVEL MOISTURE NOT GREAT...BUT THEN LOW LEVEL MOISTURE
PROGS HAVE BEEN UNDERDOING MOISTURE LATELY. WILL PUT IN SMALL
POP...20 PERCENT...DURING OVERNIGHT PERIOD. GUIDANCE TEMPS IN FAIR
AGREEMENT EXCEPT FOR PIR AREA ON TUE...WHERE FWC SEEMS TOO COOL...IF
90 CAN BE CONSIDERED COOL. WILL TREND TOWARD MAV/FAN...AND
PERSISTENCE.

...EXTENDED DISCUSSION...
MODELS ARE IN DISARRAY FOR THIS EXTENDED PERIOD. THE MODELS DO AGREE
SOMEWHAT WITH UPPER LEVEL FEATURES AS 500MB RIDGE BUILDS ACROSS THE
PLAINS AND EASTERN ROCKIES. THE MAJOR DIFFERENCES ARE WITH THE
SURFACE FEATURES AND THE AMOUNT OF WARMING EXPECTED THROUGH THE
PERIOD. AT FIRST GLANCE...WITH RIDGE OVER THE CENTRAL UNITED
STATES...YOU WOULD EXPECT REALLY WARM TO HOT READINGS.
HOWEVER...LOOKING CLOSELY AT 850MB TEMPERATURES ON THE ECMWF...
NOGAPS...AND THE MRF AS WELL AS THE MRF BOUNDARY LAYER
TEMPERATURES...THE COUNTIES ALONG THE MINNESOTA BORDER WILL NOT GET
AS WARM AS YOU WOULD EXPECT. EAST TO SOUTHEAST FLOW AT THE SURFACE
AND 850MB COMBINED WITH 850MB TEMPERATURES WOULD SUPPORT
TEMPERATURES ONLY CLIMBING INTO THE UPPER 70S TO MID 80S WHILE
WARMING INTO THE 80S ON SATURDAY. THE WEST HAS THE BEEN CHANCE FOR
WARMING DURING THE PERIOD AS 850MB TEMPERATURES ARE SEVERAL DEGREES
WARMER THAN THE EAST AND WILL BE CLOSER TO THE RIDGE AXIS. THINK
MOBRIDGE AND PIERRE WILL HAVE THE BEST CHANCES FOR WARMING INTO THE
90S. THE SECOND CONCERN IS WITH A COLD FRONT EXPECTED TO PUSH
THROUGH THE REGION ALONG WITH THE ASSOCIATED CHANCES OF
THUNDERSTORMS. MRF IS SIGNIFICANTLY SLOWER WITH THIS FEATURE THAN
THE NOGAPS/CANADIAN MODEL. ECMWF LEANS TOWARD THE MRF. WILL TREND
TOWARD THE M=RF ON THIS ASPECT AND THINK THE CHANCES FOR
THUNDERSTORMS WILL BE ON SATURDAY.

.ABR...NONE.
LORENS