MESOSCALE DISCUSSION 0456
NWS STORM PREDICTION CENTER NORMAN OK
0149 PM CDT TUE APR 04 2023
AREAS AFFECTED...PORTIONS OF CENTRAL/SOUTHERN IA...NORTHWEST IL AND
NORTHERN MO
CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY
VALID 041849Z - 042045Z
PROBABILITY OF WATCH ISSUANCE...95 PERCENT
SUMMARY...SUPERCELL THUNDERSTORMS ARE EXPECTED TO DEVELOP BY 22Z/5
PM CDT AND SHIFT EAST ACROSS CENTRAL/SOUTHERN IOWA, NORTHERN
MISSOURI AND NORTHWEST ILLINOIS THROUGH THE EVENING. THESE STORMS
WILL BE CAPABLE OF PRODUCING VERY LARGE HAIL, TORNADOES (SOME
STRONG) AND DAMAGING GUSTS. A TORNADO WATCH WILL LIKELY BE ISSUED IN
THE NEXT COUPLE OF HOURS.
DISCUSSION...NORTHWARD TRANSPORT OF LOW-LEVEL MOISTURE CONTINUES
EARLY THIS AFTERNOON. DEWPOINTS ACROSS SOUTHERN IL/NORTHERN MO INTO
NORTHWEST IL HAVE INCREASED 8 DEGREES F OVER THE PAST 3 HOURS.
STRONG HEATING TO THE SOUTH OF A WARM FRONT HAS RESULTING IN
TEMPERATURES INTO THE LOW/MID 80S F AMID LOW/MID 60S F SURFACE
DEWPOINTS. SOME MIDLEVEL DRY AIR IS EVIDENT IN FORECAST AND OBSERVED
SOUNDINGS, AND MAY RESULT IN SOME MIXING OF BOUNDARY-LAYER MOISTURE.
FORECAST GUIDANCE SUGGEST AN INCREASING LOW-LEVEL JET WILL NOSE
INTO THE EASTERN IA/NORTHWEST IL LATER THIS AFTERNOON AND SUPPORT
OPEN WARM SECTOR STORMS NEAR THE WARM FRONT. ADDITIONAL STORMS ARE
EXPECTED TO DEVELOP NEAR THE SURFACE LOW, SOUTHWARD ALONG THE
EASTWARD-ADVANCING DRYLINE/COLD FRONT. WHILE MIXING MAY RESULT IN
SOMEWHAT HIGHER LCLS, VERY STEEP MIDLEVEL LAPSE RATES AND STRONG
VERTICAL SHEAR WILL SUPPORT SUPERCELLS CAPABLE OF VERY LARGE HAIL
(GREATER THAN 3 INCH IN DIAMETER) AND DAMAGING GUSTS. FURTHERMORE,
FORECAST SOUNDINGS INDICATED FAVORABLE LOW-LEVEL SHEAR AND 0-1 KM
SRH INCREASING TO AROUND 250 M2/S2, SUPPORTING TORNADO POTENTIAL.
INCREASING CUMULUS IS NOTED IN LATEST VISIBLE SATELLITE IMAGERY BOTH
ALONG THE WARM FRONT AND AHEAD OF THE DRYLINE AS OF 1830Z. A COUPLE
OF ELEVATED CELLS HAVE EVEN STARTED TO DEVELOP SOUTHWARD INTO
WEST-CENTRAL MO. WHILE CAPPING REMAINS OVER THE REGION, THIS MAY BE
AN INDICATION OF SOME INCREASED FORCING BEGINNING TO IMPINGE ON THE
AREA. CONTINUED LOW-LEVEL WARM/MOIST ADVECTION BENEATH THE CAP,
COUPLED WITH HEATING AND GRADUAL INCREASING ASCENT SHOULD RESULT IN
GREATER CONVECTIVE INITIATION/COVERAGE BY AROUND 22Z. A TORNADO
WATCH WILL BE LIKELY IN THE NEXT COUPLE OF HOURS.
..LEITMAN/HART.. 04/04/2023
