Severe Thunderstorm Warning 89, 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 WED JUL 19 2000

AT 18Z...CD FNT ALLIGNED ROUGHLY FM GFK TO JMS...THEN WEST TO NEAR
BIS...AND SW INTO SFC LOW NEAR MT-ND-SD INTERSECTION. EASTERN PORTION
OF FNT MAKING STEADY PROGRESS S AND E...BUT WESTERN END OF FNT
MOVING MORE SLOWLY...NRLY STNY FOR NOW...AS SFC LOW TO WEST
DEVELOPS. MODELS IN VERY GOOD AGREEMENT ON STRENGTH AND TIMING OF
MAJOR FEATURES THIS FCST PD. 5H HTS...85H TEMPS...AND MSLP IN
ETA/NGM/AVN ALL PLACE CD FNT JUST S OF ND/SD BORDER AT 00Z. MSAS
ANALYSIS SHOWS LI'S LOWERING TO 0 TO -4C NORTHWESTERN COUNTIES AT THIS
TIME UNDER INFLUENCE OF SFC HEATING AS STUBBORN LOW CLOUDINESS
FINALLY BEGINS TO CLEAR IN ADVANCE OF CD FNT. FOLLOWED ETA FOR MAIN
DETAILS AS IT SEEMS TO BE HANDLING CURRENT SITUATION WELL. THAT
SAID...CD FNT WILL PRESS ACROSS ND/SD BORDER AND LOOKS TO BE THROUGH
ENTIRE ABR COUNTY WARNING AREA BEFORE 12Z THURSDAY. BASED ON TIMING
OF CD FNT...AS WELL AS ETA FCST LI'S AND CAPES...WHICH ARE NOT OVERLY
IMPRESSIVE AS SYSTEM MOVES THROUGH...INDICATED MOSTLY EVENING
THUNDERSTORM ACTIVITY WEST AND NORTH...WITH A MIXTURE OF SHOWERS AND
THUNDERSTORMS FURTHER EAST. ETA DOES INDICATE A WELL DEFINED
THETA-E RIDGE AT 5H/7H WITH POS THETA-E ADVECTION ALONG AND IN
ADVANCE OF FNT...ALONG WITH WEAK TO MODERATE DIVERGENCE AT 3H/25H.
BEST MOISTURE...7H UPWARD OMEGA...AND 5H PVA WILL BE IN EASTERN
PORTION OF AREA...WHILE LOWEST STABILITY WILL BE OVER WESTERN
PORTION OF AREA. BASED ON THIS...PUT HIGHEST POPS EAST...LOWER POPS
WEST...BUT EMPHASIZED THUNDERSTORMS WEST. FOR THU...AS COOL CANADIAN
HIGH BUILDS IN FROM NORTH...COMBINATION OF L/L MOISTURE AND CAA
SHOULD RESULT IN MSTLY CLOUDY CONDITIONS WITH ST/SC CLOUD DECK
THROUGH THE MORNING...BUT 1000-850 MB AVE RH SHOWS DRYING BY
AFTN...AND BEST CAA SHOULD SHIFT SOUTHWARD...SO TRENDED TO PTLY CLDY
BY AFTN ALL AREAS. FRIDAY A BIT IN DOUBT IN THIS POINT. UPPER RIDGE
BUILDS SHARPLY TO WEST...BUT AVN SUGGESTS MOISTURE WILL AGAIN
INCREASE UNDER INFLUENCE OF RETURN FLOW ON WESTERN SIDE OF SFC HIGH.
THIS COMBINDED WITH A SERIES OF WEAK U/L VORT CENTERS MOVING ACROSS
AREA...AND POSSIBLY A WEAK INVERTED SFC TROUGH OVER SW-S CNTL SD...
INFLUENTIAL IN ADDING SMALL POP...20 PERCENT...FOR PIR AREA FRIDAY.
OTHERWISE...PTLY CLDY CONDITIONS EXPECTED. GUIDANCE TEMPS IN GOOD
AGREEMENT MOST AREAS...EXCEPTION IS PIR AREA THURSDAY...WHERE FWC
SEEMS A BIT COOL AND FAN APPEARS TOO WARM. OZF OUT SHORTLY.

...EXTENDED DISCUSSION...
LIKE THE LAST FEW DAYS...MRF CONTINUES TO BE THE MOST AGRESSIVE WITH
BUILDING THE 500MB RIDGE ACROSS THE WESTERN UNITED STATES DURING THE
PERIOD. NORTHWEST FLOW ALOFT WILL CONTINUE ACROSS THE CWA WITH
MODELS IN DECENT AGREEMENT BRINGING 500MB SHORTWAVE THROUGH SATURDAY
NIGHT INTO SUNDAY. WILL ADD A CHANCE OF THUNDERSTORMS AS THIS
FEATURE MOVES THROUGH LATE SATURDAY NIGHT INTO SUNDAY.
OTHERWISE...500MB HEIGHTS AND 850MB TEMPERATURES RISE THROUGH THE
PERIOD. THIS WILL BRING MOST OF THE CWA A GRADUAL WARMING TREND.
WILL FOLLOW FMR/MEX DATA FOR HIGHS AND LOWS.

.ABR...NONE.
LORENS/ECKBERG