SPC AC 191952

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0252 PM CDT Thu Sep 19 2024

   Valid 192000Z - 201200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE UPPER MIDWEST INTO EASTERN KANSAS...WESTERN MISSOURI...AND FAR
   NORTHEAST OKLAHOMA...

   ...SUMMARY...
   Scattered severe thunderstorms are possible this afternoon and
   evening across central/eastern Minnesota, Iowa, and western
   Wisconsin. A couple of tornadoes, large hail, and damaging winds may
   occur across this region. Farther south, an area of locally severe
   wind gusts and hail may also develop over parts of eastern Kansas,
   southwest Missouri, and northeast Oklahoma.

   ...20Z Update...
   The 18Z observed Minneapolis sounding showed steep mid-level lapse
   rates in addition to a long and predominantly straight hodograph.
   The expectation remains that a few supercells may initially develop
   from north-central Iowa into east-central Minnesota over the next
   2-3 hours. These storms would pose the greatest risk for
   large/very-large hail. Given weak low-level shear evident on area
   VAD data in combination with linear forcing from the cold front,
   upscale growth should still occur quickly with a transition to more
   of a damaging wind threat. As this is in line with the thinking of
   the previous forecast, no changes have been made other than minor
   changes to the general thunderstorm area.

   See the previous discussion for further details.

   ..Wendt.. 09/19/2024

   .PREV DISCUSSION... /ISSUED 1126 AM CDT Thu Sep 19 2024/

   ...Minnesota/Wisconsin/Iowa...
   Widely spaced and mainly elevated thunderstorms ongoing late this
   morning across parts of IA into eastern MN and western WI should
   continue to diminish in coverage over the next couple of hours. In
   their wake, daytime heating of a seasonably moist low-level airmass
   (surface dewpoints generally in the 60s) and somewhat steep
   mid-level lapse rates will contribute to at least moderate
   instability by mid afternoon along/ahead of a cold front extending
   north to south from western MN into eastern NE and western IA. An
   upper low over northern ND and southeast SK/southwest MB will
   continue to advance slowly northeastward across south-central Canada
   through the period. A belt of 35-50 kt mid-level west-southwesterly
   winds on the southern periphery of the upper low will spread
   eastward from the northern Plains into the Upper Midwest through
   this evening. A veering/strengthening wind profile with height
   through mid levels will support around 30-40 kt of deep-layer shear
   across the warm sector. This shear will be sufficient for organized
   thunderstorms, including the potential for a few supercells.

   Current expectations are that scattered thunderstorms will develop
   by mid to late afternoon across central/eastern MN into
   northern/central IA along or just ahead of the eastward-advancing
   cold front. A rather favorable thermodynamic environment will foster
   robust updrafts, and any initial supercells should pose a threat for
   large to very large hail (around 1.5-2.5 inches in diameter). But, a
   fairly quick transition to more linear structures should occur given
   the presence of the cold front, with a potentially greater damaging
   wind threat evolving with eastward extent through the evening before
   convection eventually weakens. South-southwesterly low-level flow
   and related shear ahead of the front is not forecast to be overly
   strong by most guidance this afternoon. But, some threat for a
   couple of tornadoes remains apparent, especially with any sustained
   supercells across east-central/southern MN into northern IA late
   this afternoon/early evening.

   ...Eastern Kansas into Missouri and Northeast Oklahoma...
   An upper ridge, with rather warm mid-level temperatures, will remain
   centered over the southern Plains today. The surface cold front is
   forecast to continue moving east-southeastward across the mid MO
   Valley and central Plains through late this afternoon. A surface
   trough extending southward from this front across the southern High
   Plains should also mix eastward through peak daytime heating. Given
   weak large-scale ascent and rather warm mid-level temperatures
   across this area, there is still a fair amount of uncertainty
   regarding how many additional thunderstorms will develop later
   today, notwithstanding the ongoing (mainly elevated) convection over
   eastern KS and far northwest MO. Still, other surface-based
   thunderstorms may develop later this afternoon along/near the
   front/dryline intersection in south-central KS/north-central OK, and
   along the cold front in eastern KS. While low/mid-level flow should
   remain fairly modest, steepened low-level lapse rates and moderate
   instability should support a risk for mainly severe/damaging
   downdrafts as convection spreads east-southeastward into western MO
   and northeast OK through this evening.

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