Jul 21, 2017 0600 UTC Day 2 Convective Outlook
Updated: Fri Jul 21 06:03:14 UTC 2017 (20170721 0600Z Day 2 shapefile | 20170721 0600Z Day 2 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170721 0600 UTC Day 2 Outlook Graphic
Day 2 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 305,137 83,281,414 New York, NY...Chicago, IL...Philadelphia, PA...Detroit, MI...Indianapolis, IN...
MARGINAL 255,977 28,522,053 Phoenix, AZ...Tucson, AZ...Mesa, AZ...Virginia Beach, VA...Minneapolis, MN...
Probabilistic Graphic
20170721 0600 UTC Day Probabilitic Graphic
Probability of severe weather within 25 miles of a point.
Hatched Area: 10% or greater probability of significant severe within 25 miles of a point.
Day 2 Prob. Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 305,078 83,278,184 New York, NY...Chicago, IL...Philadelphia, PA...Detroit, MI...Indianapolis, IN...
5 % 256,191 28,527,774 Phoenix, AZ...Tucson, AZ...Mesa, AZ...Virginia Beach, VA...Minneapolis, MN...
   SPC AC 210603

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0103 AM CDT Fri Jul 21 2017

   Valid 221200Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MIDWEST
   AND EXTENDING EAST ACROSS THE CENTRAL APPALACHIANS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE UPPER
   MISSISSIPPI VALLEY AREA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   NORTH CENTRAL AND NORTHEAST U.S. SLIGHT RISK AREAS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   SOUTHERN ARIZONA...

   ...SUMMARY...
   A broad area of severe weather risk is apparent from portions of the
   northern and central Plains east across the Midwest to the mid
   Atlantic region.  A few severe storms may also occur across portions
   of southern Arizona.

   ...Synopsis...
   Moderately strong west-northwesterly flow aloft is forecast to
   persist across the northern tier of the U.S. this period, with
   numerous small-scale disturbances embedded therein.  A stronger
   short-wave trough/low is forecast to move out of south-central
   Canada and across the north-central U.S. with time.

   At the surface, a migratory low is forecast to move along a
   pre-existing front across the Midwest states, eventually reaching
   the mid-Atlantic/southern New England coast.  A weaker low/frontal
   system is expected to shift across the upper Mississippi Valley
   region.

   ...Midwest to the mid Atlantic...
   A large area of convection is forecast to be ongoing over the
   southern Great Lakes area and vicinity early in the period, which
   should shift east-southeast with time.  While some severe risk may
   persist with the ongoing convection, new storm development is
   forecast on the southern and western flank of this convection, as
   afternoon heating of a very moist boundary layer supports
   mixed-layer CAPE values in the 2500 to 3500 J/kg range across much
   of the Midwest and into the central Appalachians.  Multiple
   bands/clusters of storms will likely traverse the area through the
   afternoon and evening, before convection diminishes in coverage and
   intensity late in the period.  In the mean time, risk for damaging
   winds and hail will exist with stronger storms/storm clusters moving
   quickly east-southeast across the region.

   ...Upper Mississippi Valley vicinity...
   In the wake of overnight/early-period convection, some
   heating/destabilization is forecast across the upper Mississippi
   Valley area in advance of the compact upper low/short-wave trough
   progged to be shifting east-southeast out of the Canadian Prairies. 
   Ascent -- focused near a weak surface frontal system -- should
   support scattered storm development during the afternoon and
   evening, spreading east toward the western upper Great Lakes area
   with time.  Enhanced mid-level westerly flow -- sufficient for
   updraft organization -- suggests potential for locally damaging
   winds and hail with stronger cells, lingering well into the evening
   hours.

   ...Southern Arizona...
   Daytime heating of a moist boundary layer progged to reside over
   southern Arizona will support airmass destabilization, with ample
   high-based CAPE to support fairly widespread storm development over
   the higher terrain.  With mid-level ridging to gradually strengthen
   over the Great Basin, some enhancement of northeast mid-level flow
   could eventually allow storms to organize/congeal, and spread off
   the rim into the lower deserts.  As such, evaporatively enhanced
   downdrafts could result in locally damaging winds from late
   afternoon through the evening, and possibly into the overnight hours
   before convection slowly diminishes.

   ..Goss.. 07/21/2017

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z