ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 170858
   SPC AC 170858

   Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0358 AM CDT Fri May 17 2024

   Valid 201200Z - 251200Z

   ...DISCUSSION...
   ...Day 4/Mon-Day 5/Tue -- Central/Southern Plains to the Midwest...

   Increasing southwesterly deep-layer flow will overspread much of the
   southern/central Plains by Monday afternoon/evening ahead of a
   deepening upper trough across the western U.S. Subtle lead shortwave
   impulses will eject across the KS/NE vicinity after 21-00z Monday
   night as a surface front drops southeast across the northern Plains.
   Rich boundary-layer moisture will spread northward across OK/KS as
   at least weak surface cyclogenesis occurs over the central High
   Plains. This overall pattern will support some severe potential
   somewhere from NE/KS/OK to the Lower MO Valley into early Tuesday.
   However, uncertainty remains given the subtle nature of ejecting
   shortwave impulses and the potential for ongoing convection Monday
   morning, leaving some questions over smaller-scale details.
   Nevertheless, enough consistency exists to introduce a 15 percent
   severe probability for Monday evening/overnight ahead of the surface
   front across portions of the central Plains vicinity. Given
   uncertainty, this area may shift in the coming days.

   On Tuesday, the upper trough is expected to eject east/northeast
   across the Plains to the Mid/Upper MS Valley. A deepening surface
   cyclone will lift northeast from KS to the Upper Midwest as the
   trough ejects over the region, and a cold front will push
   east/southeast. A very moist/unstable and favorably sheared
   environment will exist from eastern KS/OK to the upper Great Lakes
   ahead of the surface low and upper trough. Organized convection is
   expected across a broad area. This area likely will change some in
   coming days given mesoscale uncertainties tied to likely convection
   in the Day 4/Mon time frame continuing into Day 5/Tue.

   ...Day 6/Wed -- Ohio Valley to the Mid-South...

   By Wednesday the upper trough is forecast to lift northeast from the
   Mid/Upper MS Valley to Ontario/Quebec. Large-scale ascent will
   quickly shunt north of the international border. The surface cold
   front is expected to become more diffuse as the surface cyclone also
   shift north into Canada. Still, moderate deep-layer southwesterly
   flow will overspread a moist boundary layer across the Ohio Valley,
   and some severe potential may persist. Confidence is too low to
   include probabilities at this time, but may be needed in subsequent
   outlooks.

   With southward extent into the Mid-South vicinity, some severe
   potential could also persist given an expected moist/unstable
   airmass and potentially ongoing morning MCS. However, upper-level
   support will not be as favorable heading into the afternoon hours,
   and confidence is too low for severe probabilities at this time. 

   ...Days 7-8/Thu-Fri...

   Forecast guidance is not in as good agreement by the end of the
   forecast period. The overall pattern may become less amplified and
   more quasi-zonal. However, some guidance does indicate at least some
   weak shortwave impulses migrating through westerly flow,
   particularly across the southern Plains vicinity. Trends will be
   monitored as a potential area of interest could develop across
   portions of the southern Plains around Day 7/Thu.

   ..Leitman.. 05/17/2024

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