SPC AC 171958

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0258 PM CDT Wed Apr 17 2024

   Valid 172000Z - 181200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   THE OH VALLEY AND THE CENTRAL PLAINS...

   ...SUMMARY...
   Scattered thunderstorms capable of producing damaging winds, large
   hail, and a few tornadoes remain possible across parts of the Ohio
   Valley and Lower Great Lakes this afternoon. Thunderstorms with
   mainly a large hail threat may still occur tonight over parts of the
   central Plains.

   ...20Z Update...
   Primary changes to the outlook have been to: 1) Add 5 percent wind
   and hail probabilities to portions of the TX Hill Country to parts
   of northwestern TX. 2) Remove the Marginal Risk from the Southeast.
   3) Add 5 percent wind probabilities to portions of central NE. 4)
   Clear probabilities behind the main band of storms over the OH
   Valley. 

   Though confidence is still not overly high in organized thunderstorm
   development across central into northern TX this afternoon, agitated
   cumulus over central TX has recently developed, suggesting that a
   sparse storm or two is possible. Given adequate buoyancy and shear
   over central TX, any storms that can develop and mature into
   supercells may be accompanied by a severe wind and hail threat,
   warranting the introduction of 5 percent wind/hail probabilities.
   Please see MCD #475 for more information. Storms have percolated in
   intensity across AL, but have not yet become overly robust. A strong
   wind gust or instance of small hail cannot be completely ruled out,
   but current thinking is that the severe threat will be too sparse to
   warrant categorical highlights. A well-mixed boundary layer is
   becoming established across central NE, where storms are expected to
   develop later today. Given the mixed boundary layer, 5 percent wind
   probabilities have been added to account for the possibility of a
   severe gust or two. Otherwise, the rest of the outlook remains on
   track, with severe probabilities maintained in eastern parts of the
   OH Valley ahead of ongoing storms.

   ..Squitieri.. 04/17/2024

   .PREV DISCUSSION... /ISSUED 1144 AM CDT Wed Apr 17 2024/

   ...Synopsis...
   Satellite imagery continues to show a negatively tilted upper trough
   extending from the Upper Midwest into the OH Valley. Surface low
   associated with this trough is currently over northeast WI. An
   occluded front extends southwestward from this low to a triple point
   in the southern Lake Michigan vicinity. From this triple point, a
   warm front extends east-southeastward across southern Lower MI into
   northeast OH and a cold front extends south-southwestward across
   western IN and southern IL. Strong to severe thunderstorms are
   anticipated along and ahead of the cold front as it moves across the
   OH Valley and Lower MI today and tonight. This cold front then
   becomes stationary as it becomes more east-west orientated over AR
   before transitioning to a warm front OK. 

   ...Lower Michigan into the Ohio/Tennessee Valleys...
   As mentioned in recently issued MCDs #469 and #470, the showers and
   isolated thunderstorms currently ongoing along and ahead of the cold
   front are expected to gradually intensify as the downstream air mass
   diurnally destabilizes. Stronger forcing for ascent is anticipated
   across Lower MI, which will favor quicker upscale growth into one or
   more bowing segments. As such, primary severe risk over Lower MI is
   expected to be damaging gusts from 45 to 65 mph.

   Farther south, less forcing for ascent and generally modest buoyancy
   should favor less storm coverage than areas farther north, with a
   more cellular storm mode anticipated as well. This region will be
   displaced north of the stronger upper-level flow, but the enhanced
   mid-level flow in place should still be sufficient for updraft
   organization and the potential for a few supercells.  Primary risk
   with these storms will be hail around 1" and damaging gusts from 45
   to 65 mph, but low-level flow is expected to be strong enough to
   support some tornado potential as well.

   Continued development along and ahead of the front could lead foster
   a transition to a more linear mode with eastern extent this evening.
   Damaging gusts and line-embedded tornadoes will still be possible.

   ...Eastern KS into the Mid/Lower MO Valley...
   An upper-level trough will move eastward across the north-central
   CONUS tonight. Isolated thunderstorms are possible later this
   evening in central NE. Expectation is for these storms to be
   elevated, but some hail is possible.

   A 40-45 kt southerly low-level jet will develop this evening across
   parts of the southern/central Plains in response to the approaching
   trough. Thunderstorms should eventually initiate near the northern
   edge of the low-level jet late this evening from central KS into far
   southeast NE. Ample buoyancy, and strong shear in the cloud-bearing
   layer should support some threat for large hail with this mainly
   elevated convection. If convection can grow upscale into a small
   bowing cluster, then isolated damaging winds may also occur.

   ...Mid-Atlantic...
   Across the Mid-Atlantic, filtered daytime heating will contribute to
   a well-mixed boundary layer and steep low-level lapse rates,
   resulting in modest buoyancy this afternoon. A few thunderstorms may
   move into the region off the higher terrain, with occasionally
   damaging gusts possible. Given the limited instability, the overall
   severe wind threat will likely remain isolated.

   ...Texas Hill Country into Northwest TX...
   Isolated thunderstorms may develop late this afternoon and early
   evening across parts of south-central into central TX along the
   dryline. If any convection can be sustained, it could produce severe
   winds and hail, but the threat currently appears too uncertain to
   introduce any severe probabilities.

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