SWODY1
SPC AC 201628
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1128 AM CDT THU SEP 20 2007
VALID 201630Z - 211200Z
..THERE IS A SLGT RISK OF SVR TSTMS TODAY THROUGH TONIGHT ACROSS
THE ERN DAKOTAS AND MN...
..MN/DAKOTAS TODAY THROUGH TONIGHT...
A LARGE CLUSTER OF ELEVATED THUNDERSTORMS IS ONGOING OVER W CENTRAL
MN IN ASSOCIATION WITH STRONG LOW-LEVEL WAA ON THE NOSE OF A 40-50
KT LLJ...AND A SUBTLE MID LEVEL SPEED MAX. THIS SYSTEM SHOULD
DEVELOP SLOWLY EWD ACROSS CENTRAL MN DURING THE DAY...WITH OTHER
ELEVATED THUNDERSTORM DEVELOPMENT EXPECTED FARTHER NW. THE INITIAL
ACTIVITY APPEARS TO BE ROOTED IN THE 850-700 MB LAYER...WHERE MUCAPE
OF 1000-2000 J/KG AND EFFECTIVE BULK SHEAR OF 40-50 KT WILL SUPPORT
SOME SUPERCELL STRUCTURES TO LOCALLY ENHANCE THE LARGE HAIL THREAT.
THE SURFACE WARM FRONT WILL LIFT NEWD ACROSS ERN SD/SW MN AS THE
BOUNDARY LAYER DESTABILIZES NEWD INTO THE ZONE OF STORM GENERATION
ACROSS W CENTRAL/SW MN. LOW-LEVEL CONVERGENCE WILL BE FOCUSED ALONG
THE WARM FRONT/OUTFLOW BOUNDARY...WITH WAA ABOVE THE GROUND TO THE
NE OF THE FRONT. SW OF THIS BOUNDARY...THERE DOES NOT APPEAR TO BE
ANY CLEAR FOCUS FOR WARM SECTOR DEVELOPMENT THIS AFTERNOON...WHERE A
RELATIVELY WARM ELEVATED MIXED LAYER MAY PROVIDE A CAP. A POSSIBLE
EXCEPTION WILL BE ALONG THE REMNANT LEE TROUGH ACROSS NRN NEB/SRN
SD...WHERE STRONG SURFACE HEATING MAY SUFFICIENTLY WEAKEN THE CAP.
THERE IS SOME UNCERTAINTY REGARDING THE POTENTIAL FOR SURFACE-BASED
STORMS ALONG THE WARM FRONT/OUTFLOW THIS AFTERNOON/EVENING IN MN.
IF SUCH DEVELOPMENT OCCURS...MLCAPE NEAR 2500 J/KG AND STRONG
LOW-LEVEL SHEAR WILL BE SUPPORTIVE OF SUPERCELLS WITH VERY LARGE
HAIL AND A FEW TORNADOES.
MEANWHILE...A STRONG NRN STREAM SHORTWAVE TROUGH OVER SRN BC WILL
AMPLIFY ESEWD TOWARD THE NRN HIGH PLAINS. CYCLOGENESIS IS EXPECTED
ACROSS THE SE MT AREA EARLY TONIGHT IN ADVANCE OF THIS MID LEVEL
WAVE...AND THE SURFACE CYCLONE IS FORECAST TO DEVELOP EWD INVOF THE
ND/SD BORDER THROUGH 21/12Z. STRONG FORCING FOR ASCENT WILL
ACCOMPANY THIS DEEPENING CYCLONE AND MID LEVEL TROUGH ACROSS
CENTRAL/ERN ND LATE TONIGHT...WHERE STEEP MID LEVEL LAPSE RATES AND
SLIGHTLY ELEVATED INSTABILITY ARE FORECAST TO PERSIST. ANY
CONVECTION THAT DEVELOPS THIS AREA OVERNIGHT WILL HAVE THE POTENTIAL
TO PRODUCE LARGE HAIL...AND POTENTIALLY DAMAGING GUSTS.
.THOMPSON/JEWELL.. 09/20/2007
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