SPC AC 171239

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0739 AM CDT Fri Apr 17 2026

   Valid 171300Z - 181200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
   THE UPPER AND MID MISSISSIPPI VALLEY SOUTHWESTWARD INTO KANSAS AND
   OKLAHOMA...

   ...SUMMARY...
   Numerous severe thunderstorms are likely this afternoon into tonight
   across parts of the Upper Midwest southward across the lower
   Missouri Valley into central Great Plains.  Initially this may be
   accompanied by a risk for large to giant hail and a few strong
   tornadoes, before severe wind gusts 60 to 90 mph become the
   most prominent hazard by this evening.

   ...Synopsis...
   Surface analysis this morning depicts a front bisecting MN north to
   south to a low near the NE-IA-SD border, with the front extending
   southwestward into the central High Plains.  Water-vapor imagery
   shows a prominent upper trough near the MT-ND border
   south-southwestward into eastern UT.  A belt of increasingly strong
   southwesterly 500-mb flow will overspread a destabilizing warm
   sector today as the upper trough eventually reaches the Upper
   Midwest and central Great Plains late tonight.  Concurrently, the
   aforementioned cyclone will develop northeast to Lake Superior as a
   warm front over IA advances northward into the western Great Lakes. 
   Meanwhile, the cold front will sweep southeast reaching the central
   Great Lakes southwestward into the southern Great Plains by early
   Saturday. 

   ...Upper and Mid Mississippi Valley...
   A northward expanding warm/moist sector on the nose of a 50+ kt
   southerly LLJ will continue to destabilize as large-scale ascent
   approaches from the west.  A large-hail threat may develop this
   morning with developing convection across southern MN (see
   forthcoming MCD #472 for short-term details).  Heating and advection
   of 60s deg F surface dewpoints beneath steep mid-level lapse rates
   will support the development of a moderately to very unstable
   airmass from IA-IL northward into the upper MS Valley to the east of
   the front and southeast of the low.  Upwards of 1500-3000 J/kg
   MLCAPE is forecast immediately ahead of the front with strengthening
   flow aloft, strongly favoring organized storms, including
   supercells.  Recent model guidance continues to show the development
   of discrete supercells later this afternoon ahead of the front over
   parts of central/northern WI near the low, and farther south in the
   vicinity of eastern IA into adjacent portions of WI/northwest IL. 
   All hazards will be possible with this potential activity, including
   the possibility for an intense tornado.  Large to giant hail will be
   possible with supercells.  Other storms likely to evolve quickly
   into a band of severe thunderstorms will develop farther west and
   push east coincident with the front.  Damaging wind gusts will tend
   to become more prevalent during the evening with linear storm modes.
   Some tornado risk may continue into the evening as maturing bands of
   storms yield a threat for bowing segments and embedded mesovortices,
   before this activity gradually diminishes late as it moves east into
   IN/Lower MI late.

   ...KS-OK eastward into the lower MO Valley...
   Continued moistening and heating of an airmass to the east of a
   dryline/cold front and associated triple point will lead to a very
   unstable airmass from OK into KS by early to mid afternoon.  A
   capping inversion will likely inhibit storm development until mid
   afternoon near the front.  Initial storm development will likely be
   supercellular near the triple point before a more extensive band of
   cellular storms develops along the boundary.  Both a supercell and
   QLCS tornado risk is apparent given the appreciably large
   CAPE/shear.  A coalescing of cold pools and intensification of a
   squall line with embedded surges and bowing segments may result in
   focused swaths of more intense severe gusts (i.e., locally 75-90
   mph) from south-central and eastern KS into west-central MO. 
   Farther south, a more conditional setup south of the triple point
   along the dryline is expected.  Large to giant hail could accompany
   any mature/sustained supercell along with a tornado risk. 
   Eventually the front will sweep southeastward with a convective line
   yielding a risk for wind/hail.

   ..Smith/Dean.. 04/17/2026

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z