Current SPC Activity Chart

Current Severe US Wx Maps

SPC Activity Chart
Hazard Wed (07/17) Thu (07/18) Fri (07/19) Sat (07/20) Sun (07/21) Mon (07/22) Tue (07/23) Wed (07/24)
Severe Slight Slight Marginal No Area No Area No Area No Area No Area
Fire Elevated Elevated No Area No Area No Area No Area No Area No Area

Forecast Discussion - Convective Outlook

   SPC AC 171950

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0250 PM CDT Wed Jul 17 2019

   Valid 172000Z - 181200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE UPPER MISSISSIPPI VALLEY...NORTHERN HIGH PLAINS...AND FROM
   EASTERN PENNSYLVANIA INTO SOUTHERN NEW ENGLAND...

   ...SUMMARY...
   Severe thunderstorms capable of severe wind gusts and large hail are
   expected across the northern High Plains and mid-to-upper
   Mississippi Valley through tonight. Storms capable of damaging wind
   gusts will be possible across portions of the Northeast this
   afternoon and evening.

   Little change was made to the previous outlook as multiple areas of
   potential continue to evolve.

   An MCS with near-severe wind gusts recently measured over southeast
   IA will continue southeastward across eastern MO and western IL,
   with a continued threat of strong to locally severe wind gusts as
   the storms propagate into a very unstable air mass.  While temporary
   stabilization has occurred behind this system, further development
   is expected this evening and overnight across the Upper MS Valley in
   association with a strengthening low-level jet. For more information
   see Mesoscale Discussion 1502.

   To the east, numerous small storms persist from PA into southern New
   England, where a very moist air mass exists. Good instability along
   with pockets of heating will continue to support localized
   downbursts.

   ..Jewell.. 07/17/2019

   .PREV DISCUSSION... /ISSUED 1154 AM CDT Wed Jul 17 2019/

   ...Iowa/northern Missouri to western Illinois...
   A quasi-linear cluster of storms will likely persist generally
   southeastward across the region as the downstream air mass continues
   to destabilize, with persistence aided by warm/moist advection
   focused in vicinity of a sharp surface-850 mb moisture/instability
   gradient across the region. A focused corridor of damaging winds
   could evolve and some severe hail is possible as well.

   ...Minnesota/eastern Dakotas to western Wisconsin...
   Although forecast confidence is not particularly high across the
   region, storm redevelopment is expected later today as the air mass
   and/or source region trajectories recover in the wake of early day
   convection and/or the earlier MCS across far southern Minnesota and
   Iowa. Such surface-based redevelopment could initially focus later
   this afternoon across eastern North Dakota and nearby northeast
   South Dakota/northwest Minnesota, and subsequently develop eastward
   through the evening. Other storms may develop farther south across
   central Minnesota, with overall intensity/surface-based likelihood
   depending on air mass recovery. Where the air mass does
   moderately/strongly destabilize, deep-layer shear will be more than
   adequate for supercells/organized multicells. Multiple sub-regional
   corridors of storms capable of hail/wind are possible across the
   region later this afternoon into tonight, and some tornado risk may
   exist as well, particularly as the low-level jet strengthens early
   this evening.

   ...Northern High Plains...
   A shortwave trough feature will move into Montana/Wyoming this
   afternoon, helping to develop scattered thunderstorms. Isolated
   severe thunderstorms including a few supercells capable of large
   hail and damaging winds will affect parts of the western Dakotas and
   nearby Wyoming/Nebraska later this afternoon and evening.

   ...NY/PA/NJ into southern New England...
   A moist and potentially very unstable air mass is in place across
   this region today, with dewpoints in the upper 60s to lower 70s and
   early visible satellite imagery is showing the potential for strong
   heating. Afternoon SBCAPE values of 2000-3000 J/kg are expected,
   with scattered thunderstorms forming by mid-afternoon.  Vertical
   shear profiles will not be particularly strong, but sufficient
   westerly steering flow will help organize outflows and pose a risk
   of locally damaging wind gusts in the strongest cells.  Coverage and
   intensity of storms will decrease farther south across the Delmarva
   region, but isolated strong convection is possible.

    

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z