MESOSCALE DISCUSSION 0021
   NWS STORM PREDICTION CENTER NORMAN OK
   0150 AM CST TUE JAN 17 2012
   
   AREAS AFFECTED...SW THRU E CNTRL MISSOURI...INTO CNTRL IL INTO NRN
   AND CNTRL INDIANA
   
   CONCERNING...TORNADO WATCH 1...
   
   VALID 170750Z - 170915Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 1 CONTINUES.
   
   SEVERE THREAT IS DIMINISHING ACROSS SOUTHWEST AND SOUTH CENTRAL
   MISSOURI.  TRENDS ARE BEING MONITORED FOR THE POSSIBILITY OF AN
   ADDITIONAL WW EAST OF WW 0001.
   
   VIGOROUS CONVECTIVE DEVELOPMENT APPEARS GENERALLY ASSOCIATED WITH
   DEEP LAYER UPWARD VERTICAL MOTION...SUBSTANTIALLY FORCED BY A SHORT
   WAVE IMPULSE/MID-LEVEL JET STREAK NOW TURNING EASTWARD ACROSS THE
   CENTRAL PLAINS.  THROUGH THE 09-12Z TIME FRAME...MODELS SUGGEST THAT
   THIS STRONGER LIFT WILL RAPIDLY SHIFT EAST OF THE ST. LOUIS
   AREA...ACROSS CENTRAL ILLINOIS...INTO NORTH CENTRAL INDIANA.  EVEN
   WITH A 40-60 KT WEST SOUTHWESTERLY 850 MB JET AIDING THE TRANSPORT
   OF INCREASINGLY MOIST LOW-LEVEL AIR INTO THIS REGION...THE EVOLVING
   MESOSCALE CONVECTIVE SYSTEM WILL PROBABLY BEGIN OUTRUNNING MORE
   FAVORABLE WARM SECTOR NEAR SURFACE INSTABILITY.  WHEN THIS
   OCCURS...ACTIVITY SHOULD BECOME INCREASINGLY ELEVATED IN
   NATURE...WITH A DIMINISHING SEVERE THREAT...ALTHOUGH MORE HIGHLY
   LOCALIZED STRONG SURFACE GUSTS ASSOCIATED WITH THE DOWNWARD
   TRANSPORT OF HIGHER MOMENTUM AIR MAY STILL NOT BE OUT OF THE
   QUESTION.  GIVEN THE CURRENT 50 KT STORM MOTION...AND UNCERTAIN
   TIMING OF WEAKENING TRENDS...IT MAY BE THAT THE SEVERE THREAT
   REMAINS HIGH ENOUGH TO REQUIRE AN ADDITIONAL WW ALONG THE INTERSTATE
   70 CORRIDOR OF ILLINOIS AND INDIANA EARLY THIS MORNING.
   
   ..KERR.. 01/17/2012
   
   
   ATTN...WFO...ILN...LMK...IWX...IND...PAH...LOT...ILX...LSX...
   
   LAT...LON   40168892 41098709 41028498 39768483 38228706 37559015
               37979130 38948975 40168892