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Apr 30, 2017 1730 UTC Day 2 Convective Outlook
Updated: Sun Apr 30 17:35:15 UTC 2017 (Print Version | 20170430 1730Z Day 2 shapefile | 20170430 1730Z Day 2 KML)
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 Forecast Discussion

   SPC AC 301735

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1235 PM CDT Sun Apr 30 2017

   Valid 011200Z - 021200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
   WESTERN NEW YORK AND CENTRAL PENNSYLVANIA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   THE LOWER GREAT LAKES SOUTHWARD INTO EASTERN WEST VIRGINIA AND
   VIRGINIA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK AND INCLUDING PARTS OF THE CAROLINAS INTO SOUTHERN
   GEORGIA...

   ...SUMMARY...
   Scattered to numerous severe thunderstorms will be possible from
   portions of western New York southward into parts of West Virginia
   and Virginia.  Isolated strong to severe thunderstorms may occur in
   the Carolinas and Georgia.

   ...Synopsis...
   A closed 500-mb low is forecast to move from the middle MS Valley
   into the northern Great Lakes during the period.  Midday Sunday
   water-vapor imagery showed a well-defined mid-level vorticity lobe
   over OK/TX and this feature is forecast to shear northeastward and
   reach the upper OH Valley by midday Monday.  An occluded low over
   northeast IA will develop northeast through northern Michigan.  A
   cold front will extend from the OH Valley through the southern
   Appalachians and northeast Gulf Coast Monday morning and sweep
   eastward and into the western Atlantic from the Mid-Atlantic states
   south into northern FL.

   ...Much of western and central NY/PA southward into VA/eastern WV...

   The latest model guidance continues to indicate most of the region
   is expected to remain free of precipitation through the early
   afternoon.  A band of convection may be ongoing along the front
   Monday morning but modest mid-level lapse rates coupled with a
   destabilizing boundary layer (i.e., surface heating and dew points
   in the lower 60s) is forecast to result in weak buoyancy ahead of a
   potent mid- to upper-level trough/cold front by early afternoon. 
   Despite this somewhat marginal thermodynamic environment, intense
   low/mid-level wind fields veering with height will result in
   enlarged low-level hodographs yielding 300-500 m2/s2 0-1 km SRH. 
   The overall severe risk will be somewhat dependent on the magnitude
   of buoyancy (MLCAPE most probable ranging from 200-800
   J/kg)---yielding highly nonlinear effects on updraft strength and
   convective mode.  A cellular mode will be favored by the wind
   profile but the strength of mid-upper forcing for ascent (DCVA and
   associated 60-120 m 12 hr height falls) and initial storm
   development probably on the front casts considerable uncertainty
   whether cellular storms over the Enhanced Risk will form.  The most
   likely scenario is a mix mode of a few cells/linear segments with a
   transition to primarily linear bands of storms evolving towards
   evening.  If the boundary layer can destabilize more than currently
   projected, in turn promoting the development of a few pre-line
   supercells, a greater tornado risk may develop.  Nonetheless,
   convection will likely organize into small bands/bowing structures
   and it appears a corridor of higher potential for 50-70 mph gusts
   and associated wind damage will occur during the mature phase of
   broken linear segments across PA/NY as 50-60 kt 700-mb flow
   overspreads the warm sector.  Farther south over MD/VA/WV, slightly
   richer low-level moisture with dewpoints in the middle 60s is
   forecast.  A strong wind profile will support storm organization
   with the stronger updrafts and scattered damaging winds, marginally
   severe hail, and a tornado are possible with this activity before
   weakening during the evening hours.

   ...Carolinas and southern GA...
   While mid-level flow and forcing for ascent will be weaker farther
   south, richer low-level moisture (surface dew points in the
   mid/upper 60s) will yield more substantive MLCAPE (upwards of 1000
   J/kg) by afternoon/early evening. Convection will likely intensify
   within pockets of heating amidst remnant cloud cover from overnight
   convection to the west. As it does so, effective shear of 30-40 kt
   will likely yield at least a few stronger storms, capable of
   isolated severe hail and strong/damaging gusts during the afternoon
   and evening hours.

   ..Smith.. 04/30/2017

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

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

        
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