SPC AC 190556

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1256 AM CDT Sat May 19 2018

   Valid 191200Z - 201200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS FAR
   SOUTHEAST NE...NORTHWEST MO...AND EASTERN KS AND ACROSS NORTHWEST TX
   AND SOUTHWEST OK...

   ...SUMMARY...
   Severe thunderstorms will develop across the central Plains into the
   lower Missouri Valley Saturday. Very large hail and damaging winds
   are the primary threats. A few strong storms are also possible from
   eastern Ohio and Kentucky into western Pennsylvania and West
   Virginia.

   ...Synopsis...
   Numerous, predominantly low-amplitude, shortwave troughs currently
   exists within weak upper flow pattern in place across the CONUS.
   Each of these perturbations is expected to move east/northeastward
   throughout the day, with the convectively induced vorticity maximum
   currently over the central Plains and the shortwave trough currently
   moving through NM as the primary features of interest. Farther east,
   the upper low currently over IL will open up and become move
   progressive, moving quickly eastward across the OH Valley and into
   the Northeast. 

   Complex surface pattern is anticipated across the Plains with an
   outflow boundary from the ongoing MCS, an approaching cold front,
   and well-defined dryline all expected by the early afternoon. These
   boundaries, particularly the MCS outflow, will play a major role in
   delineating the severe thunderstorm threat across the central
   Plains.

   ...Southern/Central Plains into the Mid MS Valley...
   Despite the widespread convection ongoing across a large portion of
   the central Plains, steep mid-level lapse rates advected in by
   southwesterly mid-level flow atop dewpoints in the mid-60s will
   result in moderate to strong instability across the region by the
   mid to late afternoon. Convergence along the remnant outflow
   boundary as well as along the approaching cold front combined with
   modest large-scale forcing for ascent will result in convective
   initiation during the mid afternoon. 

   Linear nature of the forcing for ascent coupled with relatively weak
   mid-level flow suggest a predominately linear convective mode across
   much KS. An initially cellular mode is more possible across
   northwest MO and adjacent portions of northeast KS and far southeast
   NE. Additionally, the low-level flow will likely be a bit more
   backed in this region, contributing to more favorable low-level
   shear for tornadogenesis. As such, a narrow window, both spatial and
   temporally, may exist for a tornado or two before a transition to a
   more linear mode occurs. Given the amount of instability
   anticipated, some very large hail is possible, particularly in the
   early stages of convection.

   Farther south, a more deeply mixed airmass is expected but steep
   mid-level lapse rates, strong diurnal heating, and convergence along
   the dryline should result in thunderstorms across the eastern TX
   Panhandle and far western OK by the late afternoon. Dry mid-levels
   suggest these storm will likely produce strong outflow, resulting in
   quick transition to a linear structure as well as an enhanced
   potential for damaging wind gusts. Increasing low-level jet may
   result in storm maintenance into portions of central OK and
   north-central TX. 

   ...OH Valley into the Lower Great Lakes...
   Generally moist profiles are anticipated across the region with the
   resulting modest instability precluding robust updrafts. Even so, a
   few bowing segments capable of damaging wind gusts are possible,
   particularly across eastern OH and western PA. Cell mergers may also
   contribute to brief updraft intensification and isolated hail.

   ..Mosier/Cook.. 05/19/2018

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