000
ACUS11 KWNS 182031
SWOMCD
SPC MCD 182031
SDZ000-MTZ000-WYZ000-182130-

MESOSCALE DISCUSSION 0677
NWS STORM PREDICTION CENTER NORMAN OK
0331 PM CDT SAT MAY 18 2013

AREAS AFFECTED...WRN/CNTRL SD...NERN WY

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 182031Z - 182130Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...TSTM COVERAGE IS EXPECTED TO INCREASE IN COVERAGE THROUGH
THE REMAINDER OF THE AFTERNOON...WITH A PRIMARY THREAT OF LARGE HAIL
AND DAMAGING WINDS. AREA IS BEING MONITORED FOR A POSSIBLE WW.

DISCUSSION...SLOW-MOVING SUPERCELL THUNDERSTORMS HAVE BEEN ONGOING
FOR THE LAST 1-2 HOURS ACROSS THE BLACK HILLS...WITH MODERATE MLCAPE
OF 1000-2000 J/KG AND EFFECTIVE SHEAR OF 35-45 KTS SUPPORTING A
LARGE HAIL RISK. ADDITIONAL ATTEMPTS AT INITIATION ARE UNDERWAY
NORTH OF THE ONGOING SUPERCELLS...AND ALSO FURTHER EAST NEAR PIR
ALONG A DIFFUSE SLOW-MOVING WARM FRONT. MULTIPLE EMBEDDED VORTICITY
MAXIMA WITHIN BROAD SWLY MIDLEVEL FLOW WILL CONTINUE TO SUPPORT TSTM
DEVELOPMENT...WITH SUFFICIENT INSTABILITY/SHEAR FOR ORGANIZED STORM
STRUCTURES.

SPLITTING SUPERCELLS WILL BE THE PRIMARY MODE FOR THE NEXT 2-3
HOURS...WITH A THREAT OF LARGE HAIL AND PERHAPS AN ISOLATED
TORNADO...ESPECIALLY WITH ANY STORMS INTERACTING WITH THE WARM
FRONT. UPSCALE GROWTH INTO ONE OR MORE CLUSTERS IS POSSIBLE EARLY
THIS EVENING...WHICH WOULD LEAD TO INCREASE IN SEVERE WIND RISK. IF
THE UPWARD TREND IN TSTM COVERAGE CONTINUES...WW ISSUANCE WILL BE
POSSIBLE.

..DEAN/KERR.. 05/18/2013

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

ATTN...WFO...FSD...ABR...UNR...CYS...BYZ...

LAT...LON   43490430 44130510 45020508 45630337 45730190 45590035
            45139934 44469890 43909877 43549887 43369958 43100010
            43040042 43050199 43010293 43030356 43070388 43330414
            43490430