[MCD] SWOMCD

[MCD at goshenarc.org]

ACUS11 KWNS 231754
SWOMCD
SPC MCD 231754 
MNZ000-SDZ000-NDZ000-232000-

MESOSCALE DISCUSSION 2254
NWS STORM PREDICTION CENTER NORMAN OK
1254 PM CDT THU SEP 23 2004

AREAS AFFECTED...PORTION NERN SD...EXTREME SERN ND...EXTREME
W-CENTRAL/SWRN MN

CONCERNING...SEVERE THUNDERSTORM POTENTIAL 

VALID 231754Z - 232000Z

CONDITIONAL TORNADO POTENTIAL DEVELOPING N THROUGH NE OF DEEP-LAYER
CYCLONE OVER THIS AREA.  WW MAY BE NEEDED OVER SOME PART OF THIS
REGION.

PRIMARY CONCERN IS WITH THIN ARC OF CONVECTION -- EVIDENT AT 1730Z
FROM JUST E OF PIR TO SPINK COUNTY SD THEN SEWD TOWARD PIPESTONE
COUNTY MN.  THIS CORRESPONDS WELL TO LOCATION OF OCCLUDED/COLD
FRONT...E OF SFC LOW.  THIS ACTIVITY SHOULD LIFT NEWD ACROSS AREA
NEAR MN/DAKOTAS BORDERS...AS WELL AS ABR REGION...THROUGH 19-20Z
TIME FRAME AND INTO SERN ND LATER THIS AFTERNOON.  ASSOCIATED NARROW
CORRIDOR OF FAVORABLE VERTICAL SHEAR WAS NOT WELL SAMPLED BY 12Z
RAOBS...HOWEVER VWP DATA AND FCST MODEL SOUNDINGS INDICATES 0-3 KM
SHEAR 30-35 KT AND 40-50 KT 0-6 KM SHEAR WITH THIS ARC.  VWP SHOWED
90-100 KT 5-8 KM AGL SPEED MAX OVER FSD DURING PAST 2 HOURS -- AT
LEAST 20-30 KT MORE THAN FCST BY ETA/RUC 500 MB PROGS. THIS
INDICATES EVEN STRONGER DEEP-LAYER SHEAR IS POSSIBLE THAN PROGGED. 
IN FACT...SHEAR MAY BE TOO STRONG TO SUSTAIN DISTINCT UPDRAFTS FOR
VERY LONG GIVEN WEAK BUOYANCY.

MAIN CAVEAT IS PRESENCE OF...AT MOST...VERY MARGINAL
INSTABILITY...BECAUSE OF LIMITED SFC HEATING IN PROSPECTIVE INFLOW
REGION OF CONVECTION.  MODIFIED RUC SOUNDINGS INDICATE MLCAPES BELOW
300 J/KG...BUT ALSO LITTLE OR NO CINH FOR SFC-BASED PARCEL BECAUSE
OF RELATIVELY COLD AIR ALOFT.  THOUGH CONVECTIVE ELEMENTS WILL
STRUGGLE TO REMAIN INTACT AND DISCRETE...ANY SUSTAINED CELL COULD
ROTATE AND PRODUCE A TORNADO IN SUCH A FAVORABLY SHEARED PROFILE.

..EDWARDS.. 09/23/2004

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MPX...FGF...FSD...ABR...BIS...

44619943 45039978 45459981 45989911 46289831 46289704
45969624 44689550 43939581 44419674 44909776 44929880
44779945 

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