Jun 21, 2018 1730 UTC Day 2 Convective Outlook
Updated: Thu Jun 21 17:31:05 UTC 2018 (20180621 1730Z Day 2 shapefile | 20180621 1730Z Day 2 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180621 1730 UTC Day 2 Outlook Graphic
Day 2 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 147,132 7,037,381 Birmingham, AL...Jackson, MS...Huntsville, AL...Chattanooga, TN...Greeley, CO...
MARGINAL 422,430 46,446,880 Columbus, OH...Memphis, TN...Charlotte, NC...Oklahoma City, OK...Nashville, TN...
Probabilistic Graphic
20180621 1730 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
SIG SEVERE 34,021 199,493 Liberal, KS...Pampa, TX...Woodward, OK...Guymon, OK...Lamar, CO...
15 % 147,503 7,018,914 Birmingham, AL...Jackson, MS...Huntsville, AL...Chattanooga, TN...Greeley, CO...
5 % 425,266 46,821,593 Columbus, OH...Memphis, TN...Charlotte, NC...Oklahoma City, OK...Nashville, TN...
   SPC AC 211731

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1231 PM CDT Thu Jun 21 2018

   Valid 221200Z - 231200Z


   Scattered severe storms will be possible across parts of the
   central/southern Plains and southeast US on Friday.

   ...Central/Southern Plains...
   Initial mid-level ridging over the High Plains will yield to an
   upstream trough, characterized by several embedded impulses, which
   will overspread the region during peak heating. Broad forcing for
   ascent will support a deepening surface low over the southern High
   Plains, with increasing upslope flow over Colorado and surface
   convergence southward into the Texas/Oklahoma Panhandles. Surface
   dew points rising into the 50s/lower 60s and strong heating (once
   low-level cloud cover dissipates) should support at least 1000-1500
   J/kg of MLCAPE, with much of this buoyancy residing in the favored
   -10 to -30 C zone for hail growth. Combined with ample veering of
   flow with height, this thermodynamic environment will be supportive
   of initial supercells capable of very large hail, damaging winds,
   and perhaps a tornado or two. 

   Through the evening hours, an amplifying low-level jet will likely
   foster upscale growth into one or more east/southeastward-moving
   convective systems, with damaging winds becoming the primary threat.
   Although surface-based inhibition will rise given nocturnal cooling,
   residual steep mid-level lapse rates and dry air aloft may allow a
   mature convective system (characterized by a well-established cold
   pool) to make farther eastward progress than would be expected of
   individual cells alone. As such, continued adjustments to the
   outlook will likely be needed.

   ...Southeast US to the Ohio Valley...
   500mb flow will be anomalously strong over much of the Southeast
   Friday (based on sounding climo for various sites), such that
   pockets of storms will exhibit more organization than what would be
   otherwise expected for mid/late June here. Still, the potential for
   early-day convection and related cloud cover/overturning/outflow
   lends considerable spatial uncertainty with regards to
   destabilization and convective initiation during peak heating.
   Across the lower Mississippi Valley, strong storms may be ongoing
   Friday morning, given a lobe of ascent dropping southeast along the
   periphery of a closed low centered over the Midwest. To the
   west/southwest of these storms, heating through the day should yield
   at least moderate instability. However, increasing subsidence aloft
   and southward-advancing outflow may: (a) Decouple new development
   from stronger flow aloft and (b) Cause cells to become elevated atop
   outflow relatively quickly. Still, a conditional threat will exist
   for large hail, damaging winds, and perhaps a tornado or two, and no
   change is made to the ongoing slight risk here.

   Farther east, downstream cloud cover from the aforementioned
   convection may slow destabilization over parts of Mississippi and
   Alabama, and a relative minimum in storm coverage may be realized in
   some areas. Nonetheless, where heating does occur, enhanced
   unidirectional flow will likely encourage small linear segments with
   an attendant damaging wind threat, as they move east during the
   afternoon and evening. An embedded tornado or two may be possible as
   well. This risk should extend farther northeast towards Kentucky and
   Virginia, and the marginal risk has been expanded accordingly. Some
   of these areas may require an upgrade to slight risk, pending
   greater confidence in the focus of destabilization and convective

   Tornado:   5%     - Slight
   Wind:     15%     - Slight
   Hail:     15% SIG - Slight

   ..Picca.. 06/21/2018