New Mesoscale Discussion issued by the SPC

MESOSCALE DISCUSSION 1119
NWS STORM PREDICTION CENTER NORMAN OK
0122 PM CDT MON JUN 22 2015

AREAS AFFECTED...CENTRAL AND SOUTHERN IOWA...NORTHERN MISSOURI...AND WESTERN ILLINOIS

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 221822Z - 222015Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...ONGOING CONVECTION CONTINUES ACROSS THE DISCUSSION AREA...WITH HAIL THE PRIMARY THREAT. REDEVELOPMENT ALONG/SOUTH OF AN OUTFLOW BOUNDARY AND ALONG/AHEAD OF A COLD FRONT WILL POSE A GREATER THREAT LATER THIS AFTERNOON...WITH LARGE HAIL...DAMAGING WINDS AND A FEW TORNADOES POSSIBLE. WW ISSUANCE MAY BE NEEDED LATER THIS AFTERNOON. DISCUSSION...STRONG TO SEVERE THUNDERSTORMS CONTAINING LARGE HAIL ARE ONGOING ACROSS EASTERN IOWA. THESE STORMS WERE ELEVATED ATOP A COLD POOL LEFT BEHIND FROM AN EARLIER MCS...WITH STEEP LAPSE RATES/INSTABILITY ALOFT CONTRIBUTING TO A CONTINUED HAIL THREAT. ADDITIONAL SHOWERS AND STORMS WERE DEVELOPING SOUTH OF AN OUTFLOW BOUNDARY ACROSS SOUTHERN/SOUTHWESTERN IOWA...BUT THESE STORMS WERE LIKELY ROOTED ABOVE A STRONG CAP AT AROUND 750 MB.

THESE STORMS MAY ALSO YIELD A SMALL HAIL THREAT THIS AFTERNOON....BUT SHOULD REMAIN LARGELY SUB-SEVERE UNLESS THEY CAN BECOME SURFACE BASED THIS AFTERNOON. LATER THIS AFTERNOON...STORMS ARE EXPECTED GRADUALLY BECOME MORE SURFACE BASED WITH DEVELOPMENT EXPECTED ALONG A SEWD-MOVING COLD FRONT IN IOWA...AND ADDITIONAL DEVELOPMENT POSSIBLE ALONG NEARLY STATIONARY OUTFLOW BOUNDARY LOCATED ACROSS CENTRAL IOWA AND WESTERN ILLINOIS. RECENT HI-RES GUIDANCE SUGGESTS THE GREATEST LIKELIHOOD WITH THIS DEVELOPMENT IS ACROSS CENTRAL/EASTERN IOWA NEAR AND NORTHEAST OF DES MOINES. WITH STRONG INSTABILITY /I.E. 3000-4000 J/KG MLCAPE/ AND DEEP LAYER SHEAR IN EXCESS OF 45 KNOTS EXPECTED...AN APPRECIABLE SEVERE THREAT WILL EXIST WITH LARGE HAIL AND DAMAGING WIND GUSTS POSSIBLE.

ADDITIONALLY...ANY STORMS DEVELOPING ALONG OR NEAR THE REMNANT OUTFLOW BOUNDARY MAY POSE A TORNADO THREAT...ESPECIALLY IF STORMS CAN REMAIN ISOLATED RELATIVELY EARLY IN THEIR EVOLUTION. GIVEN THE EXPECTED THREAT THIS AFTERNOON...A WW MAY BE NEEDED BEFORE 21Z. ..COOK/GOSS..