SPC AC 250603

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0103 AM CDT Tue Aug 25 2020

   Valid 261200Z - 271200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
   LOUISIANA AS WELL AS A PORTION OF THE GREAT LAKES AND OHIO VALLEY...

   ...SUMMARY...
   Threat for a few tornadoes will exist Wednesday and Wednesday night 
   primarily across a portion of Louisiana. Otherwise, a few strong to
   severe storms with damaging wind and marginally severe hail are
   possible over the Great Lakes and Ohio Valley regions. A few severe
   storms are possible from the northern Rockies through the northern
   Plains.

   ...Louisiana...

   Tropical Storm Laura is forecast by the National Hurricane Center to
   become a hurricane Tuesday before making landfall along the LA coast
   Wednesday evening. Outer rainbands associated with Laura will begin
   to affect LA Wednesday, while low-level shear and hodograph size
   also undergo a substantial increase during the afternoon and
   evening. The threat for a few tornadoes should therefore increase,
   and persist into the overnight based on current forecast track.

   ...Great Lakes and Ohio Valley regions...

   A stalled front will extend from the upper Great Lakes southeast
   into the Middle Atlantic region early Wednesday. Scattered elevated
   thunderstorms will likely be ongoing within the zone of isentropic
   ascent on the cool side of this boundary from parts of upper and
   lower MI into the OH Valley. Some of this activity might be capable
   of producing marginally severe hail, but overall severe threat is
   expected to remain marginal during the morning. Uncertainty exists
   regarding a more substantial severe threat. Early morning storms may
   weaken or dissipate. The front should begin to advance northeast as
   a warm front, especially during the evening and overnight as a
   westerly low-level jet strengthens in response to a progressive
   shortwave trough that will advance southeast through the Great Lakes
   overnight. Redevelopment of surface-based storms during the
   afternoon is uncertain given weak forcing aloft and weak frontal
   convergence. However, deeper forcing will increase later in the
   evening and overnight within frontal zone in association with
   shortwave trough and strengthening low-level jet, and additional
   storms may develop. These storms will initially be elevated, but
   some potential will exist for an MCS or two to develop and become
   forward propagating if a cold pool can become established. Overall
   threat appears conditional, but parameter space is sufficient for a
   damaging wind threat depending on how storms evolve.

   Other storms with a threat for a few strong to damaging wind gusts
   and hail might develop by late Wednesday afternoon or evening along
   a southeast-advancing cold front northern WI into the Upper
   Peninsula of MI.

   ...Northern Rockies through the northern Plains...

   A cold front will advance southward through the northern Plains
   during the day within a moderately unstable environment. However,
   the deeper forcing will remain in post-frontal zone with modest
   convergence along the front beneath a capping inversion. Though the
   shear/instability parameter space is sufficient for at least a SLGT
   risk, convective initiation is limited over much of this region in
   both the CAMs and parameterized models which lowers confidence in
   storm coverage.

   A better chance of scattered storms will evolve over the higher
   terrain of the northern Rockies where moisture and instability will
   be more limited. However, storms will be high-based with steep lapse
   rates and moderate shear supportive of both multicells and possibly
   a few supercells capable of a few damaging wind gusts and hail.

   ..Dial.. 08/25/2020

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