SPC AC 302000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Sun Jun 30 2019

   Valid 302000Z - 011200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF
   THE MIDDLE TO UPPER MISSISSIPPI VALLEY INTO THE CENTRAL AND NORTHERN
   HIGH PLAINS...

   ...SUMMARY...
   Strong to severe storms will persist into the early evening from
   southern Minnesota through central Illinois and Indiana. Other
   severe storms remain possible over a portion of the central through
   northern Plains this evening and tonight. Damaging wind and hail are
   the primary threats.

   ...Discussion...

   Have made modest adjustments to SLGT risk area over the Midwest
   region based on latest convective and mesoscale trends, including
   expansion of the SLGT southeast into west central IN ahead of a
   strong to severe MCS that is expected to continue developing
   southeast into early evening with a risk for damaging wind. Western
   extension of an upstream MCS will also pose a severe risk from
   southeast MN into eastern IA. Otherwise previous forecast appears
   generally on track with additional storms expected to develop over
   the higher terrain of the central and northern Rockies and spread
   east through northern NE and SD tonight.

   ..Dial.. 06/30/2019

   .PREV DISCUSSION... /ISSUED 1124 AM CDT Sun Jun 30 2019/

   ...Upper Mississippi Valley...
   Two MCSs are ongoing. The lead one has largely been decaying, but is
   maintaining a near-term threat for strong gusts and small hail in
   its core across far south-central WI. There is potential for
   intensification this afternoon as the downstream air mass continues
   to become strongly unstable. However, weak warm advection at the
   base of the elevated mixed layer and perhaps more importantly weak
   deep-layer shear ahead of the MCS may preclude a more organized MCS.
   Nevertheless, will maintain Slight Risk for a predominant threat of
   strong wind gusts across most of IL. 

   An upstream MCS has developed across central MN into far northwest
   WI with low-level warm advection atop the surface-based cold dome.
   Rather steep mid-level lapse rates near 8.5 C/km as sampled by 12Z
   BIS/ABR/MPX soundings along with moderate speed shear through the
   cloud-bearing layer may support a severe hail risk. Although linear
   convective mode should temper hail magnitudes. There is potential
   for this MCS to continue south-southeast, but would likely remain
   elevated given that outflow continues to surge south and west
   (currently into far northeast IA to southwest MN) from the lead MCS.
   This renders uncertainty over the degree of damaging wind potential,
   especially in the near-term. However, cloud decay is occurring in
   the wake of the lead MCS and erosion of the surface cold dome is
   underway. Will maintain Slight Risk for wind given some potential
   for this MCS to intensify. 

   ...Northern/central High Plains to SD...
   East-northeasterly post-frontal upslope flow will aid in late
   afternoon scattered thunderstorm development. More pervasive cloud
   coverage in association with an MCV over central WY shifting towards
   the Black Hills should confine stronger boundary-layer heating to
   its south across southeast WY/NE Panhandle. Effective shear will be
   greater with northwest extent as mid-level flow weakens with
   southeast extent. Potential will exist for several supercells with a
   risk of mainly large hail and isolated severe wind gusts. Multiple
   clusters may develop this evening across SD as a southerly low-level
   jet intensifies atop the quasi-stationary surface front. Activity
   would likely impinge on a more buoyant air mass with eastern extent,
   yielding a persistent risk for severe wind/hail into tonight perhaps
   as far east as southwest MN.

   ...Southeast NY to southern New England...
   Scattered showers and isolated thunderstorms have begun developing
   ahead of a mid-level vorticity lobe rotating through the base of a
   shortwave trough. While boundary-layer temperatures are relatively
   cool and northwest surface flow dominates, cold mid-level
   temperatures should permit small hail growth. Locally strong wind
   gusts might accompany a few cells over the next few hours.

   ...VA/NC to KY/TN...
   Robust boundary-layer heating is occurring ahead of a weak
   southward-sagging front. This boundary should be the focus for
   scattered thunderstorms this afternoon. Activity with western extent
   should be predominantly pulse. The fringe of modest mid-level
   west-northwesterlies east of the Appalachians could foster a few
   multicell clusters with locally damaging winds as the primary
   hazard.

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