SPC AC 101300

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0800 AM CDT Wed Jun 10 2020

   Valid 101300Z - 111200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF LOWER MICHIGAN...NORTHEAST INDIANA...AND NORTHERN OHIO...

   ...SUMMARY...
   Widespread severe thunderstorms are expected across portions of the
   Midwest and Ohio Valley today and tonight. Damaging thunderstorm
   wind gusts are the main threat, although a few tornadoes and severe
   hail are also possible.

   ...Midwest/Great Lakes/Ohio Valley...
   No major changes to the prior outlook and associated reasoning with
   this update cycle (13z). A regional outbreak of severe
   thunderstorms, primarily in the form of widespread damaging winds,
   are expected across Lower Michigan and eastern Indiana into Ohio
   mainly this afternoon and evening.

   Morning water vapor imagery features a relatively compact mid-level
   shortwave trough centered near the Kansas City area in the predawn
   hours. As it ejects northeastward and takes on a negative tilt, this
   shortwave trough will increasingly phase with the remnants of
   Cristobal and a broad trough over northern Ontario/Lake Superior
   vicinity.

   The now extratropical remnants of Cristobal have contributed to a
   very moist air mass across the region, with lower 70s F surface
   dewpoints prevalent (as far north as northern Lower Michigan) to the
   east of an east-northeastward moving cold front. This advancing cold
   front will spread across Lower Michigan/Indiana and western
   Ohio/east-central Kentucky through peak heating/early evening.

   Mid-level height falls between 120-150m will overspread the region
   and large-scale forcing for ascent will encourage an upward-evolving
   pre-frontal convective corridor. Moderate pre-frontal buoyancy with
   2000+ J/kg MLCAPE will ensure robust updrafts that should remain
   organized within the strongly sheared regime. Near the front,
   increasing bands of storms are already noted just after sunrise
   across east-central/northeast Illinois. These storms are likely
   incipient signs of increasingly organized/intense storms that are
   expected to evolve east-northeastward through early afternoon into
   Indiana/Lower Michigan. 

   With a tendency for strengthening but backing (south-southwesterly)
   winds through much of the lower/mid-troposphere, aside from more of
   a westerly mid-level component along/south of the Ohio River, it
   appears a mixed storm mode will evolve with initial supercells
   giving way to more prevalent fast-moving line segments/clusters and
   evolving bowing segments. Mean storm motions around 45 kt/50+ mph
   are expected with these storms. 

   Widespread damaging winds are likely to be the most common impact
   from the fast-moving storms, particularly as they merge/evolve into
   northeastward-racing bands and bows this afternoon through early
   evening. Isolated large hail will also be possible, particularly
   within the first couple of hours of surface-based initiation when
   storms may be in more of a semi-discrete supercellular form. A few
   tornadoes could also occur regionally.

   ...Northeast States/north-central Appalachians...
   A lead/weak belt of ascent and strong heating across the region will
   contribute to scattered thunderstorm development by early afternoon
   well ahead of the upstream upper trough and synoptic cold front.
   This activity will not be robustly forced, but moderate
   destabilization in the presence of 30-40 kt effective shear, which
   will be maximized across Pennsylvania and northern Maryland/southern
   New York, will allow for some risk for storms capable of isolated
   severe wind and possibly some hail.

   ...Tennessee Valley/southern Appalachians/Deep South...
   Multiple bands of showers and thunderstorms will occur in areas
   along and east of the east/southeastward-advancing cold front today.
   An intensification of storms is probable into the afternoon as the
   very moist air mass preceding the front diurnal destabilizes,
   particularly if cloud breaks become more prevalent. Only modest
   deep-layer shear (25-35 kt) will exist over the region, relatively
   strongest over the Tennessee Valley where a few supercells could
   occur. That said, multicells will be most common across the region
   with isolated damaging winds the most probable severe risk. Severe
   hail potential will tend to be limited by aforementioned modest
   deep-layer shear and weak mid-level lapse rates.

   ..Guyer/Leitman.. 06/10/2020

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