SPC AC 061726

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1126 AM CST Mon Feb 06 2017

   Valid 071200Z - 081200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OH VALLEY
   TO THE CENTRAL GULF COAST STATES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK AREA...

   ...SUMMARY...
   Showers and scattered thunderstorms are forecast to affect the mid
   Mississippi, Ohio, and Tennessee Valleys and central Gulf Coast
   States Tuesday, eventually spreading eastward across the
   Appalachians.  Isolated strong to severe thunderstorms will be
   possible across these areas.

   ...Synopsis...
   Within broadly cyclonic flow across the CONUS, a lead shortwave
   trough is forecast to be located over the upper Midwest to lower MS
   Valley at the start of the period (12Z Tuesday). This trough will
   advance quickly eastward across the OH/TN Valleys and the central
   Gulf Coast States through Tuesday evening, before continuing to move
   across the East Coast and into Quebec overnight. At the surface, a
   low initially over northern IL should develop northeastward across
   the lower Great Lakes while deepening, before moving into Canada
   late Tuesday evening. A trailing cold front will shift
   eastward/southeastward across the OH/TN Valleys into the Southeast,
   as low-level moisture return ahead of the front supports some
   convective risk across these regions.

   ...OH Valley to the Southeast...
   Confidence in the evolution of the severe threat Tuesday is lower
   than usual for a Day 2 forecast given a wide range of possible
   scenarios regarding convective development through the latter
   portion of the Day 1 period (Monday). At this time, it appears that
   mainly elevated thunderstorms posing an isolated large hail threat
   may be ongoing Tuesday morning from the OH Valley to the Mid-South
   in association with a southwesterly low-level jet and the previously
   mentioned mid-level shortwave trough. This convection, if it
   develops, would shift quickly eastward across much of the
   Marginal/Slight Risk area by early Tuesday afternoon. It is possible
   that with time and modest diurnal heating this activity could pose
   some strong to locally damaging wind threat if it can become surface
   based. Better low-level moisture and corresponding instability will
   be in place across the lower MS Valley into the central Gulf Coast
   States Tuesday morning, although stronger large-scale forcing for
   ascent should become increasingly displaced farther to the north
   with time.

   Behind the morning/early afternoon activity, thunderstorm
   development along the surface cold front appears highly
   uncertain/conditional. The lead shortwave trough and its associated
   ascent will be departing the OH/TN Valleys and Southeast by Tuesday
   afternoon. Most guidance suggests little in the way of convective
   redevelopment given the nebulous forcing for ascent and perhaps even
   some subsidence behind the initial shortwave trough. However, if any
   isolated thunderstorms were able to form along or just ahead of the
   front Tuesday afternoon/evening, they would pose a severe risk given
   steep mid-level lapse rates and the forecast combination of
   instability and shear.

   ..Gleason.. 02/06/2017

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