Severe Thunderstorm Warning 121, NWS Aberdeen, SD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
325 PM CDT SUN JUL 13 2003

.SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT
MDLS SHOW A COLD FRONTAL BOUNDARY DROPPING SE ACROSS THE CWA LATER
TONIGHT AFTER MIDNIGHT THROUGH 18Z MON. THE NGM WAS THE QUICKEST.
THERE WILL BE GOOD LL MOISTURE CONVERGENCE AND INSTABILITY ALONG THE
BOUNDARY AS IT MOVES SE LATER TONIGHT THROUGH MON MRNG ACROSS THE
CWA. THE MID LEVEL CAP REMAINS STRONG ACROSS THE CWA THROUGH THIS
EVENING. SOME TSRAS SHOULD DEVELOP ALONG THE BOUNDARY AFTER MIDNIGHT
ACROSS NC SD AS MID LEVEL TEMPS COOL. THERE SHOULD BE MORE TSRA
DEVELOPMENT INTO NE SD AND WC MN THROUGH MON MRNG ALONG THE
BOUNDARY. OTHERWISE FOR TONIGHT...SKIES WILL BE MOSTLY CLEAR WITH
SOUTH WINDS DECREASING BY SUNSET. TEMPS SHOULD ONLY FALL TO 65 TO
AROUND 70 BY MON MRNG. THERE MAY BE SOME AFTN TSRAS IN FAR NE SD AND
WC MN MON AFTN ALONG FRONT OTHERWISE...MON AFTN S/B DRY FOR THE CWA
WITH NW WINDS AND P/C SKIES. SFC HIGH PRES WILL BUILD ACROSS THE
REGION MON NIGHT THROUGH TUES. THUS...EXPECT CLEAR TO P/C
SKIES...LESS HUMIDITY...DRY CONDITIONS AND NOT MUCH WIND THROUGH
THIS TIME. TUES NIGHT THROUGH WED NIGHT BECOME MORE INTERESTING AS A
WARM FRONT RETURNS ALONG WITH A LLJ AND INCREASING MOISTURE.
ALSO...A WK S/W SHOULD SLIDE NE ACROSS THE CWA. WITH NO CAP IN
PLACE...EXPECT SOME TSRAS TO DEVELOP OUT WEST TUES NIGHT AND DEVELOP
INTO THE REST OF CWA INTO WED NIGHT. WILL GO WITH A 30 POP FOR NOW
FOR THIS TIME PERIOD. TEMPS WILL BE NEAR NORMAL THROUGH THE SHORT
TERM IN THE MID 80S TO THE LOWER 90S.

.LONG TERM...THURSDAY THROUGH SUNDAY
FUNDAMENTALLY DIFFERENT SOLUTIONS FROM MODELS FOR THE EXTENDED
PERIOD.  GFS CONTINUES TO HANG ONTO WELL AMPLIFIED TROUGH FROM
EASTERN PACIFIC TRACKING ACROSS SOUTHERN CANADA ON THURSDAY...TAKING
LOW LEVEL CONVERGENCE ZONE THROUGH AREA ON THURSDAY.  HOWEVER GFS
HAS BEEN TRENDING FURTHER NORTH WITH LESS AMPLITUDE WITH THIS SHORT
WAVE WHICH COMES MORE INLINE WITH TRENDS OF NOGAPS/CANADIAN AND NCEP
ENSEMBLE MEANS.  NCEP ENSEMBLE MEAN 500 HPA FIELD EVEN DEPICTING
MEAN UPPER RIDGE ACROSS SOUTHERN CANADA IN POSITION OF OPERATIONAL
TROUGH AXIS.  THUS HAVE PREPARED EXTENDED FORECAST UNDER THE
ASSUMPTION THAT THIS SLOWER FURTHER NORTH TREND OF GFS WILL CONTINUE
SO WILL KEEP THURSDAY DRY.  MORE AND MORE AM LIKING THE
NOGAPS/CANADIAN IDEA OF HOLDING BACK POSITIVELY TILTED UPPER TROUGH
ACROSS WEST COAST WITH WEAK RIDGING DOWNSTREAM OVER THE NORTHERN
PLAINS.  THIS SOLUTION ALSO GETTING SOME SUPPORT FROM LATER PERIODS
OF ETA.  MODELS ALSO SHOW WEAK VORT LOBES PASSING OVER ROCKIES INTO
NORTHERN PLAINS THROUGH UPPER RIDGE.  MID LEVEL TEMPS WILL LIKELY
REMAIN VERY WARM THROUGH PERIOD BUT GIVEN DRAMATIC MODEL DIFFERENCES
WILL NOT MAKE DRASTIC CHANGES TO POPS.  FOR NOW WILL JUST LOWER
FRIDAY POPS TO 20 AND THEN KEEP SATURDAY CHANCE POPS GOING AS WEST
COAST POSITIVELY TILTED TROUGH ALLOWS FOR POSSIBILITY OF SOME MID
LEVEL COOLING WITH RIDGE RIDER.  OVERALL HOWEVER TOUGH TO FAVOR ONE
PERIOD OVER ANOTHER POST FRIDAY.  GIVEN THIS UNCERTAINTY WILL KEEP
DAY 7 DRY FOR NOW.

.ABR...NONE

MOHR/MARSILI

MNZ039-046-SDZ003>011-015>023-033>037-045-048-051-141030-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ABERDEEN SD
532 AM CDT SUN JUL 13 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PARTS OF CENTRAL...
NORTH CENTRAL AND NORTHEAST SOUTH DAKOTA...AS WELL AS
BIG STONE AND TRAVERSE COUNTIES IN MINNESOTA.

.DAY ONE...TODAY AND TONIGHT

AN APPROACHING COLD FRONT MAY PRODUCE A FEW THUNDERSTORMS ACROSS
CENTRAL AND NORTHEAST SOUTH DAKOTA TONIGHT. THESE THUNDERSTORMS MAY
BECOME SEVERE.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED LATER TONIGHT.

DORN