A RAPIDLY EVOLVING ENVIRONMENT WILL CHARACTERIZE THE ENH AND MDT
RISK AREAS -- I.E. THE MIDDLE MISSISSIPPI VALLEY AREA -- DURING THE
FIRST HALF OF THE PERIOD, AS THE UPPER SYSTEM CLOSES OFF AND THE
SURFACE LOW DEEPENS, AND EVENTUALLY OCCLUDES. EARLY-PERIOD
CONVECTION ACROSS THE RISK AREA IS FORECAST TO SHIFT NORTHEASTWARD
AND DISSIPATE, ALLOWING HEATING -- IN CONJUNCTION WITH RAPID
STEEPENING OF MID-LEVEL LAPSE RATES -- TO YIELD MODERATE
DESTABILIZATION. NEW STORM DEVELOPMENT IS FORECAST TO OCCUR DURING
THE MID AFTERNOON TIME FRAME IN THE FAR EASTERN IOWA/FAR
NORTHEASTERN MISSOURI/NORTHWESTERN ILLINOIS AREA, AND CELLULAR MODE
IS ANTICIPATED.
PRONOUNCED LOW-LEVEL VEERING IN THE WIND FIELD -- PARTICULARLY IN
THE VICINITY OF THE WARM FRONT OVER NORTHERN ILLINOIS -- IS
EXPECTED, WITH FLOW INCREASING TO SOUTHWESTERLY AT NEAR 100KT AT MID
LEVELS, AS THE UPPER SYSTEM APPROACHES. THE RESULTING SHEAR WILL BE
STRONGLY SUPPORTIVE OF STRONG UPDRAFT ROTATION -- AND THUS ATTENDANT
RISK FOR TORNADOES, A FEW OF WHICH COULD BE SIGNIFICANT. VERY LARGE
HAIL WILL ALSO BE POSSIBLE GIVEN UPDRAFT INTENSITY -- AIDED BY THE
VERY STEEP LAPSE RATES ALOFT AND STRENGTH OF THE SHEAR PROFILE.
LOCALLY DAMAGING DOWNBURST WINDS WILL ALSO BE POSSIBLE LOCALLY, WITH
THE STRONGER STORMS. PEAK TORNADO RISK THROUGH LATE AFTERNOON
SHOULD BEGIN TO GRADUALLY DIMINISH INTO THE EVENING, AS DIURNAL
COOLING BEGINS. STILL, SEVERE RISK -- INCLUDING POTENTIAL FOR LARGE
HAIL WITH ELEVATED STORMS NORTH OF THE WARM FRONT -- WILL LIKELY
CONTINUE THROUGH THE EVENING BEFORE DECREASING OVERNIGHT.