Severe Thunderstorm Warning 224, NWS Sioux Falls, SD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
945 PM CDT WED AUG 12 2009

.DISCUSSION...
BOTH THE NEW SHORT RANGE MODELS...THE RUC AND NAM12...AND CURNT
COMPLEX MOVG BODILY INTO WRN FCST AREA NEAR INSTBLTY AXIS...POINT TO
INCREASED TSTM CHANCE OVER MOST OF FCST AREA TNGT...XCP LTL CHANGE
FAR SE WHERE POPS WERE HIEST ANYWAY...AND NOT MUCH BETTER CHC FAR NE
WHERE STORMS MAY NOT REACH. ABV MODELS ALSO HANG LLJ FRTHR WWD AS
FAR AS POINTING TO NEW DVLPMNT...BUT IN ANY EVENT LOOKS LIKE CURNT
COMPLEX WILL RULE THE ROOST FOR TNGT. WNDS AND LOW TEMPS LOOK
OK...OF COURSE HRLY TEMPS AND WNDS WILL BE AFFECTED BY TSTMS.

&&

.AVIATION...
VFR OVERALL THRU 00Z FRI. HOWEVER...TSTMS WILL CAUSE LCL LWRG TO
MVFR CIGS AND VERY BRIEF VSBYS BLO 3SM...ALONG WITH LCL GUSTY WNDS.
ASIDE FROM STORMS...PATCHY MVFR VSBYS IN BR ALSO POSSIBLE FM 08Z TO
14Z.

&&

.PREV DISCUSSION...
DEEPER LOW LVL MOISTURE ADVECTION WILL CONTINUE FROM THE SOUTH
TNGT...AS MOISTURE TDA INITIALLY ON THE SHALLOW SIDE. AS WEAK MID
LVL WAVE AND SOME MID LVL COOLING START TO MOVE EWD FM HIGH
PLAINS...SFC CONVECTIVE TEMP SHOULD BE REACHED ENUF FOR SCT TSTMS
TO DVLP NR MISSOURI VALLEY ARND 00Z OR SO...WITH SOME POTENTIAL FOR
LARGE HAIL AND DOWNBURST WINDS DUE TO EVAP COOLING FM DRY MID LVLS.
ANY TSTMS SHOULD TRY TO DVLP ENEWD AS AN MCS IN BEST LOWER LVL
CONVERGENCE ZONE ALG AND SOUTH OF I90 TNGT...REINFORCED BY CONTINUED
WARM ADVECTION FROM THE WEST. SOME CAPPING AND LACK OF FOCUS MAY
LIMIT COVERAGE...SO JUST WENT 20 TO 40 POPS FOR NOW...WITH THE LEAST
POPS NORTH. RAISED LOWS AND ESP DEWPOINTS SOME ALSO FROM PREV FCST.

MAIN STORY THE NEXT FEW DAYS WILL BE THE HEAT AND HUMIDITY AS THE
UPPER RIDGE HOLDS OVER THE AREA THROUGH SATURDAY. TEMPERATURES WILL
GENERALLY RISE INTO THE 90S DURING THE DAY AND ONLY DROP INTO THE
MID 60S TO NEAR 70 AT NIGHT. HEAT INDEX WILL REACH HIGH VALUES BUT
SHOULD REMAIN BELOW THE 105 MARK NEEDED TO CONSIDER A HEAT ADVISORY.
ONLY CHANCE FOR THUNDERSTORMS THE NEXT FEW DAYS WILL BE OVER SW MN
AND NW IA TOMORROW MORNING NEAR THE NOSE OF THE LOW LEVEL JET...
OTHERWISE A CAP SHOULD HOLD UNTIL FRI NIGHT WHEN A S/WV MOVING
ACROSS THE AREA MAY POP SOME THUNDERSTORMS. HIGHEST CHANCES FOR
THUNDERSTORMS WILL BE SAT NIGHT AND SUNDAY WITH THE MAIN UPPER
TROUGH AND FROPA. EXTENDED MODELS HAVE CONTINUE TO BECOME MORE
PROGRESSIVE WITH FROPA SAT NIGHT AND SUN. FASTER SOLUTIONS HAVE LED
TO THE REMOVAL OF POPS FOR MONDAY AS COOL HIGH PRESSURE SETTLES IN.
SOME QUESTIONS REMAIN TOWARDS THE MIDDLE OF THE WEEK...AS TO WHETHER
OR NOT RETURN FLOW WILL BRING ANOTHER ROUND OF THUNDERSTORMS TO THE
AREA.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.

WILLIAMS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1127 AM CDT WED AUG 12 2009

SDZ038>040-050-052>071-MNZ071-072-080-081-089-090-097-098-
IAZ001>003-012>014-020>022-031-032-NEZ013-014-131200-
AURORA-BEADLE-BON HOMME-BROOKINGS-BRULE-BUENA VISTA IA-
CHARLES MIX-CHEROKEE IA-CLAY-CLAY IA-COTTONWOOD MN-DAKOTA NE-
DAVISON-DICKINSON IA-DIXON NE-DOUGLAS-GREGORY-HANSON-HUTCHINSON-
IDA IA-JACKSON MN-JERAULD-KINGSBURY-LAKE-LINCOLN-LINCOLN MN-
LYON IA-LYON MN-MCCOOK-MINER-MINNEHAHA-MOODY-MURRAY MN-NOBLES MN-
OBRIEN IA-OSCEOLA IA-PIPESTONE MN-PLYMOUTH IA-ROCK MN-SANBORN-
SIOUX IA-TURNER-UNION-WOODBURY IA-YANKTON-
1127 AM CDT WED AUG 12 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST SOUTH DAKOTA...
SOUTHWEST MINNESOTA...NORTHWEST IOWA...AND NORTHEAST NEBRASKA.

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS...
SCATTERED THUNDERSTORMS SHOULD DEVELOP NEAR THE MISSOURI RIVER
VALLEY LATE THIS AFTERNOON AND EARLY EVENING...THEN SPREAD EAST
AND NORTHEAST INTO THE AREA TONIGHT...ESPECIALLY ALONG AND SOUTH
OF INTERSTATE 90. A FEW SEVERE STORMS WITH HAIL UP TO THE SIZE OF
HALF DOLLARS AND WIND GUSTS TO 60 MPH ARE POSSIBLE SOUTHWEST OF A
LINE FROM CHAMBERLAIN TO MITCHELL TO SIOUX CITY INTO THE EVENING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THERE IS A CHANCE OF THUNDERSTORMS ACROSS THE REGION THIS
WEEKEND.  SOME OF THE STRONGER STORMS MAY BE CAPABLE OF PRODUCING
LARGE HAIL AND WIND GUSTS TO AROUND 60 MPH.  SOME AREAS OF VERY
HEAVY RAINFALL ARE ALSO POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL BE POSSIBLE AFTER 5 PM CDT SOUTHWEST OF A
LINE FROM CHAMBERLAIN TO MITCHELL TO SIOUX CITY.

&&

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT
WWW.WEATHER.GOV/SIOUXFALLS. THIS INCLUDES THE GRAPHICAL HAZARDOUS
WEATHER OUTLOOK.

RSR

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