SPC AC 251716

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1216 PM CDT Tue Sep 25 2018

   Valid 261200Z - 271200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
   APPALACHIANS NORTHWARD INTO NEW ENGLAND...

   ...SUMMARY...
   Scattered thunderstorms associated with a wind damage threat are
   expected to develop on Wednesday from the central Appalachian
   mountains to the Northeast. A tornado threat will also be possible
   mainly from eastern Pennsylvania northeastward into New England.

   ...Synopsis...
   A longwave trough centered over Hudson Bay will result in fast,
   broadly cyclonic flow aloft across much of the Continental U.S.
   throughout the forecast period.  One significant shortwave will
   migrate through the trough across Ontario/Quebec during the
   afternoon, while another series of troughs will migrate
   southeastward across Oklahoma and New Mexico.  At the surface, a low
   centered over southwestern Quebec will continue to strengthen while
   migrating northeastward.  A trailing cold front will sweep eastward
   throughout the forecast period and extend from central New York
   state southwestward to the Mid-South and central Texas by 00Z. 
   Ahead of this front, a warm, humid airmass (characterized by upper
   60s and 70s F dewpoints) will persist, supporting scattered
   thunderstorms across much of the southern and eastern U.S.

   ...Portions of the Appalachians northward to the Northeast...
   Scattered storms may be ongoing along and ahead of the advancing
   front across portions of Ohio and Kentucky at around 12Z.  As
   surface heating commences ahead of the approaching front, models
   suggest that one or two bands of storms will organize and migrate
   northeastward through the discussion area within an environment
   characterized by weak to moderate surface-based instability
   (1000-1500 J/kg MUCAPE) and very strong shear (owing to 50-70 kt
   mid-level flow - strongest over portions of New York and northern
   New England).  Shear/instability parameters suggest a damaging wind
   threat with bands of storms migrating quickly northeast. 
   Supercellular structures may also develop and result in a few
   tornadoes - especially if isolated cells can materialize ahead of
   any lines (as hinted at in a few of the convection-allowing models).
    Instability will be a limiting factor for a higher severe-weather
   threat, although portions of region (particularly eastern New York
   and Vermont) may need to be upgraded in later outlooks.

   The  threat should shift eastward into New England and the
   mid-Atlantic Coast through the evening, with any lingering severe
   threat diminishing with time due to nocturnal boundary-layer
   stabilization.

   ...Tennessee and Alabama...
   Guidance suggests that a few forward-propagating bands of storms may
   develop during peak heating, although profiles suggest a more
   limited severe threat due to areas farther north given weaker shear.
    Isolated wind gusts should be the primary threat with diurnally
   driven convection in this area.

   ...New Mexico...
   Forcing aloft associated with a mid-level shortwave trough
   approaching the area will foster development of a few storms during
   the afternoon and early evening, with small hail and perhaps
   isolated damaging wind gusts beneath any storms that can develop. 
   This threat should be too sparse for even low probabilities,
   however, given weak instability profiles.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   5%     - Slight
   Wind:     15%     - Slight
   Hail:      5%     - Marginal

   ..Cook.. 09/25/2018

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z