SPC AC 251725

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1225 PM CDT Sun Aug 25 2024

   Valid 261200Z - 271200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
   OF FAR NORTHERN NEBRASKA...EXTREME NORTHWEST IOWA...EASTERN SOUTH
   DAKOTA...SOUTHERN/CENTRAL MINNESOTA...AND FAR WESTERN WISCONSIN...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   SOUTHERN NEW ENGLAND...

   ...SUMMARY...
   Severe storms are expected to evolve within a zone extending from
   the northern/central High Plains eastward to Wisconsin Monday
   afternoon into the nighttime hours. Large to very large hail, and
   swaths of severe, potentially damaging, gusts are expected,
   especially across South Dakota into Minnesota.  A few severe storms
   producing strong gusts and hail are also expected across southern
   New England.

   ...South Dakota into MN/WI and vicinity...

   An upper shortwave trough will develop east/northeast from the
   Intermountain West to the Dakotas on Monday. This will flatten the
   upper ridge over the Upper Midwest and a belt of enhanced
   southwesterly mid/upper flow (50-60 kt at 500 mb) will overspread
   the region. By late afternoon, 700 mb flow is expected to increase
   to around 40-50 kt. Vertical wind profiles, and effective shear
   magnitudes increasing to greater than 40 kt, will support supercell
   thunderstorms. 

   At the surface, a cold front will extend from northern MN
   southwestward into western SD during the morning. The front will
   develop southeast through the day and into the evening, becoming
   positioned from western WI/IA to the NE/KS border by Tuesday
   morning. Ahead of the front, a very moist airmass (upper 60s to mid
   70s F dewpoints) will be in place across portions of MN/WI/IA and
   eastern SD, while a dryslot will be oriented over NE nosing into far
   southeast SD/western IA. With increasing ascent through the day, and
   persistent low-level warm advection, MLCIN should gradually erode.
   MLCAPE values across warm/moist sector are forecast as high as
   3000-5000 J/kg, decreasing with southwest extent into the drier
   airmass. Steep midlevel lapse rates will within the strong to
   extremely unstable airmass will support robust updrafts, and initial
   supercell thunderstorms are expected to develop along the cold front
   from SD into MN. Large to very large (isolated stones greater than 2
   inches diameter) will be possible. While damaging gusts will also be
   possible with cellular activity, one or more bowing segments/MCSs
   are expected to develop into the evening hours as convection shifts
   northeast across eastern SD/MN and eventually WI. As this occurs,
   potential for severe/damaging wind swaths will increase and a few
   gusts greater than 65 kt/75 mph are possible. Tornado potential is a
   bit more uncertain, but would likely be locally increased near and
   east of the surface low where low-level flow will remain more
   southeasterly. This will enhance low-level SRH and frontal
   convergence and a few tornadoes are possible with either supercells
   or within mesovortex formation along bowing segments.

   ...Northern/Central High Plains...

   Within the drier boundary-layer across southeast MT/eastern WY
   southward into eastern CO/western KS/western NE, scattered
   thunderstorms are expected to develop as the main upper trough
   overspreads the area during the afternoon. High-based thunderstorms 
   amid steep low-level lapse rates will pose a risk for
   strong/isolated severe outflow winds. Isolated large hail also is
   possible, mainly from eastern WY into western SD/NE.

   ...New England and portions of the Upper OH Valley/Mid-Atlantic...

   Modestly enhanced deep-layer northwesterly flow on the back side of
   an upper trough will overspread the region. Pockets of 60 F
   dewpoints and cool temperatures aloft will support modest
   destabilization during the afternoon and thunderstorm bands/clusters
   are expected. Locally strong gusts will be possible with the
   activity. Isolated large hail also may be possible, especially over
   southern New England where forecast hodographs show more favorable
   vertical shear and elongated/straight hodographs.

   ..Leitman.. 08/25/2024

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