IT'S UNCERTAIN HOW MUCH CONVECTIVE FEEDBACK THE 00Z NAM INCORPORATES INTO THE DEVELOPMENT OF A SURFACE LOW THAT TRACKS FROM SOUTH-CENTRAL NE INTO SOUTHEAST MN BY LATE AFTERNOON. HOWEVER, IF A SHARP BAROCLINIC ZONE EVOLVES, A CORRIDOR OF GREATER INSTABILITY/SHEAR WILL EXIST ACROSS PORTIONS OF IA INTO SOUTHERN WI SUCH THAT MORE SUBSTANTIAL, ORGANIZED CONVECTION IS POSSIBLE. IF THE EARLY-DAY MCS IS DOMINANT THEN THE PRIMARY CONCERN FOR ORGANIZED SEVERE WILL BE ALONG THE LEADING EDGE OF THE LARGER COMPLEX. THIS ACTIVITY WILL SPREAD TOWARD LAKE MI BY LATE AFTERNOON. TRAILING FLANK OF THE MCS SHOULD EXTEND SOUTHWEST ACROSS IA WHERE FRONTAL INTERACTION MAY ENCOURAGE ORGANIZED SEVERE. THE MAIN SEVERE THREAT WITH THE MCS SHOULD BE DAMAGING WINDS, ALTHOUGH HAIL MAY ALSO BE NOTED WITH CONVECTION THAT EVOLVES WITHIN THE MORE BUOYANT AIR MASS LATER IN THE DAY. IF SUPERCELLS CAN DEVELOP THERE IS ALSO SOME THREAT FOR TORNADOES GIVEN THE FORECAST SHEAR; HOWEVER, MUCH UNCERTAINTY EXISTS REGARDING THE MCS AND POTENTIAL STORM MODE.

Storm relative flow should be quite strong, and the environment will support ingestion of mainly streamwise vorticity with initial convection. This is particularly concentrated between the Hwy. 30 and Hwy. 20 corridors, and are based on RAP and HRRR soundings sampled near Fort Dodge. Recent HRRR runs also are showing stronger UH tracks across this area, which makes sense with the low- level hodograph structure seen in soundings. Soundings and hodographs sampled closer to the Des Moines metro after 20z also have decent turning, but SRH values for both mean wind moving storms and right moving storms are not nearly as high. But, should a supercell develop, it will continue to move into a supportive environment. Supercells if they develop will be capable of all hazards. The discrete supercell threat will not be long lived through. As 00z approaches, there continues to be a strong signal for a robust LLJ development ahead of the initiating boundary over the buoyant warm sector. Any discrete development will congeal as this kicks in. The severe threat will continue though, as the kinematic fields will still be able to foster the development of a RIJ and could provide a bowing convective mode to the complex. Low- level lapse rates may still be steep, especially as a complex moves into eastern and southeastern Iowa where the air has destabilized and remained mostly unpolluted from morning convection. This will continue the threat for damaging wind swathes. With low-level lapse rates remaining steep, the surface may not quickly become cut-off from the complex. Further, 0-3 km bulk shear may reach as high as 50 kts as the LLJ strengthens. In this setup, it will not be hard achieve 30 kt line-normal shear to the complex, which could lead to the development of mesovortices along the leading edge, and the dreaded nighttime QLCS tornado threat. Depending on the how the cold pool dynamics would play out, balance with the ambient environment may be achieved through eastern portions of the forecast area. The one factor that may end a QLCS tornado threat though is if a convective cluster releases a strong outflow and it rapidly propagates ahead of the system, cutting off surface based inflow. But, will still be looking at a damaging wind threat through the evening.

DISCUSSION...A supercell thunderstorm in Calhoun County has recently had a tornado reported with it. A newer storm to the east in Hamilton County has also shown supercell structure with a weak TDS signature on the 0.5 degree KDMX 2109Z scan. These storms are interacting favorably with outflow from a convective complex that moved through the region earlier today. This favorable mesoscale environment will continue to support supercell storms with tornadic potential this afternoon.

At 505 PM CDT, a severe thunderstorm capable of producing a tornado was located near Roland, or 14 miles north of Nevada, moving northeast at 35 mph. HAZARD...Tornado. SOURCE...Radar indicated rotation. This storm continues to exhibit strong rotation and a wall cloud.