SPC AC 191251

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0751 AM CDT Thu Sep 19 2024

   Valid 191300Z - 201200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM
   MINNESOTA...IOWA AND WESTERN WISCONSIN SOUTHWARD INTO EASTERN KANSAS
   AND WESTERN MISSOURI...

   ...SUMMARY...
   Scattered severe thunderstorms are possible across central/eastern
   Minnesota, Iowa, and western Wisconsin. A couple tornadoes, isolated
   large hail, and damaging winds may occur. An area of locally severe
   gusts and hail may also develop over parts of eastern Kansas,
   southwest Missouri, and into northeast Oklahoma.

   ...Synopsis...
   Early morning water-vapor imagery shows a slow-moving mid- to
   upper-level low near the SK/MB/Dakotas border.  A negatively tilted
   shortwave trough will move across the Dakotas and MN through the
   day.  A belt of strong (40-50 kt) 500mb flow will extend through the
   base of the trough from NE wrapping cyclonically through the Upper
   MS Valley into western ON and to the northwest of a flattening ridge
   over the mid MS Valley/southwest Great Lakes.  Farther south, weaker
   west to northwest winds will encompass an area around a southern
   Plains upper high from KS/OK into MO and AR.  In the high levels,
   flow will be strongest across the central Plains, with weakening
   winds over the northern Plains/upper MS Valley.

   In the low levels, a cyclone will develop northeastward from
   southeast SK into central MB by early Friday morning, while a cold
   front moves into MN/western IA by mid afternoon, with frontolysis
   expected during the latter part of the period.  A wind shift/surface
   trough will also extend southward across eastern KS and into
   northern OK.  Ahead of the aforementioned boundaries, southerly flow
   will maintain a plume of mid to upper 60s F dewpoints.

   ...MN/IA/WI...
   Scattered weak, elevated storms from the lower MO Valley northward
   into MN/WI will gradually move east this morning and likely
   dissipate by midday.  Cloud breaks and clearing in their wake will
   contribute to appreciable heating and moderate to strong buoyancy
   developing from near the MO River in western IA northward into MN. 
   Forecast soundings show 2500-3000 J/kg MLCAPE with a veering and
   strengthening wind profile into the mid levels.  A broken band of
   quasi-discrete storms (including supercells) is forecast to develop
   from MN southward into at least northern IA.  The risk for a couple
   of tornadoes may be highest from MN into northern IA where effective
   SRH may exceed 200 m2/s2.  A couple of stronger supercells may also
   develop into western/southwest IA per recent HRRR model trends. 
   Given the northward lifting of the shortwave trough, and increasing
   inhibition east of the MS River, the primary threat should remain
   relatively narrow.

   ...Eastern KS into western MO and into OK...
   Widely scattered thunderstorms are ongoing this morning from
   south-central into northeast KS.  Much of this activity will likely
   dissipate but a few residual storms may continue or regenerate on
   outflow over parts of western MO later this afternoon.  Strong
   heating and the steepening of 0-3 km lapse rates will favor the
   development of other isolated to widely scattered storms later this
   afternoon near the wind shift.  12 UTC regional raobs sampled warm
   mid-level temperatures (around -1 deg C at 525 mb at Norman, OK). 
   These warm midlevel temperatures will limit the overall magnitude of
   instability.  However, lengthy mid to upper level hodographs will
   support storm organization with any robust/established updraft.  The
   stronger storms will potentially be capable of a risk for severe
   gusts and perhaps large hail.

   ..Smith/Mosier.. 09/19/2024

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