Mesoscale Discussion 663

Issued

May 2, 2012, 3:34 PM CDT (20:34 UTC)

Expired

May 2, 2012, 5:00 PM CDT

In force

86 min

Issued by

the Storm Prediction Center

Chance of a watch

60%

The Sioux Falls radar (KFSD), 94 km from the middle of the area, began a volume at 20:35 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

• Severe Thunderstorm Watch 225May 2, 5:30 PM CDT

305 
ACUS11 KWNS 022035
SWOMCD
SPC MCD 022034
MNZ000-IAZ000-NEZ000-SDZ000-022200-

MESOSCALE DISCUSSION 0663
NWS STORM PREDICTION CENTER NORMAN OK
0334 PM CDT WED MAY 02 2012

AREAS AFFECTED...NE...SD...MN...IA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 022034Z - 022200Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...TSTM DEVELOPMENT APPEARS POSSIBLE OVER THE NEXT FEW HOURS
FROM PORTIONS OF NERN NEB ACROSS SERN SD TO SRN MN AND NWRN IA. IF
THIS POTENTIAL BECOMES INCREASINGLY LIKELY...A WATCH IS POSSIBLE.

DISCUSSION...VERY UNSTABLE CONDITIONS HAVE DEVELOPED IN THE VICINITY
OF NUMEROUS AND SUBTLE SMALL SCALE BOUNDARIES FROM THE MIDDLE
MISSOURI RIVER VALLEY INTO THE UPPER MS VALLEY THIS AFTERNOON.
RESIDUAL OUTFLOW BOUNDARY APPEARS TO HAVE MERGED WITH WEAK SURFACE
INVERTED TROUGH AXIS OVER NERN NEB WHERE RECENT SATL IMAGERY WAS
SHOWING CU CONGESTUS INCREASING. THE CU ALSO CONTINUE TO BUILD ALONG
NERN SEGMENT OF THIS TROUGH AXIS INTO PORTIONS OF SCNTRL MN. IT ALSO
APPEARS THAT A WARM FRONT IS BEGINNING TO TAKE FORM ACROSS SRN MN
WHERE AIRMASS CONTINUES TO DESTABILIZE AND CONVECTIVE INHIBITION HAS
LIKELY WEAKENED. THE ENTIRE REGION LIES BENEATH A BELT OF
ANTICYCLONICALLY CURVED SWLY MID LEVEL FLOW AROUND 50KT THAT IS
SUPPORTING EFFECTIVE VERTICAL SHEAR ON THE ORDER OF 45-55KT.

WHILE LATEST CALIBRATED ENSEMBLE GUIDANCE INDICATES A HIGH
PROBABILITY OF SEVERE STORMS TO FORM OVER THE NEXT FEW HOURS IN THIS
GENERAL AREA...DETAILS OF INITIATION AND SUBSEQUENT STORM EVOLUTION
REMAIN COMPLEX AND UNCERTAIN. LATEST 18Z NAM-WRF SHOWS LIMITED QPF
SIGNAL ON THE MISSOURI RIVER WITH MORE ROBUST POTENTIAL EAST ALONG
THE WARM FRONT INTO MN/WI THIS EVENING. MOST LIKELY REASON FOR THESE
VARIOUS SCENARIOS IS THE LACK OF MORE PRONOUNCED LARGE SCALE FORCING
FOR ASCENT ACROSS THE AREA UNTIL LATER THIS EVENING WHEN A SHORT
WAVE TROUGH NOW ACROSS MT BEGINS TO INFLUENCE THE REGION.

IF PERSISTENT MESOSCALE FORCING IN THE ABSENCE OF STRONGER FORCING
ALONG THE BOUNDARIES CAN PROMOTE STORM DEVELOPMENT IN THE NEXT
COUPLE OF HOURS...MAGNITUDE OF CAPE AND SHEAR IN PLACE WOULD
CONTRIBUTE TO POSSIBLE SUPERCELLS WITH THE THREAT OF VERY LARGE HAIL
AND LOCALLY DAMAGING WINDS. WHILE WEAK LOW LEVEL WINDS OVER MOST OF
THE AREA SHOULD NEGATE GREATER TORNADO THREAT...ENHANCED SHEAR NEAR
BOUNDARY/FRONT/TROUGH INTERSECTIONS...COINCIDENT WITH STORM
DEVELOPMENT IN SUCH AN UNSTABLE REGIME...MIGHT RESULT IN A HIGHER
CHANCE FOR A TORNADO OR TWO.

THE REGION WILL CONTINUE TO BE MONITORED AND A WATCH IS POSSIBLE IF
THIS DEVELOPMENT BEGINS TO OCCUR.

..CARBIN.. 05/02/2012

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

ATTN...WFO...ARX...MPX...DMX...FSD...OAX...GID...LBF...

LAT...LON   42349639 40879786 40729851 41079867 42649801 43519752
            43969702 44309643 44609527 44749466 44759388 44629319
            44529301 44119245 43749272 43339395 42789580 42349639

Mesoscale Discussions in Minnesota, 2012Mesoscale Discussions in Nebraska, 2012Mesoscale Discussions in Iowa, 2012Every mesoscale discussion in 2012

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.