SPC AC 271959

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0259 PM CDT Sun May 27 2018

   Valid 272000Z - 281200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   SOUTHWEST NEBRASKA...FAR EASTERN COLORADO...WESTERN KANSAS AND THE
   OKLAHOMA PANHANDLE...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE HIGH PLAINS AND NORTHERN ROCKIES...

   ...SUMMARY...
   Severe storms with large hail and wind damage are possible late this
   afternoon into this evening across parts of the high Plains. A few
   tornadoes may occur across the Florida Peninsula.

   ...DISCUSSION...
   Several changes have been made to the outlook for this issuance. The
   first change to the outlook is to add an enhanced risk area to parts
   of far eastern Colorado, southwest Nebraska, western Kansas and the
   Oklahoma Panhandle. Confidence has increased that storms will be
   numerous enough to warrant adding a narrow corridor for 30 percent
   hail coverage where the storms are expected to interact with strong
   instability late this afternoon. The second change to the outlook is
   to expand the slight risk area westward across west-central Wyoming
   where strong to severe storms are ongoing. The third change to the
   outlook is to expand the marginal risk area across lower Michigan
   northward to a cold front where several severe storms are also
   ongoing.

   ..Broyles.. 05/27/2018

   .PREV DISCUSSION... /ISSUED 1125 AM CDT Sun May 27 2018/

   ...WY/SD/NE...
   A large upper low is positioned over NV today, with multiple
   shortwave troughs rotating around the trough into the central
   Rockies.  Models are very consistent in the development of a band of
   thunderstorms this afternoon across southern WY arcing into
   northeast CO.  These storms are expected to spread northward through
   the evening into parts of western SD and western NE.  Easterly
   low-level winds and favorable thermodynamics may support a few
   supercells in this regime, but it appears likely that congealing
   outflows will lead to multiple bowing line segments across the risk
   area.  Damaging winds and hail are the main threats, with isolated
   tornadoes possible early in the convective evolution.

   ...West TX into eastern CO/western KS...
   Mid level height falls are spreading into the central High Plains,
   where strong heating and rapid destabilization is occurring.  This
   will lead to scattered thunderstorms throughout the region later
   today.  Deep boundary-layer mixing and steep low-level lapse rates
   will promote strong outflows in the storms, with damaging winds and
   hail being the main threats.

   ...FL and coastal GA/SC...
   Relatively strong low-level winds are present today across most of
   the FL peninsula, although veering/weakening is occurring across
   southwest FL behind Alberto.  Visible satellite shows broken clouds
   across the region, providing some potential for daytime
   heating/destabilization.  This may lead to a few rotating cells
   later this afternoon with a risk of isolated tornadoes.  Based on
   12z model solutions, am extending low tornado probabilities into
   coastal sections of GA/SC for late tonight.

   ...PA/MD/VA...
   Visible satellite imagery shows a pocket of strong heating occurring
   over parts of southern PA into northern VA.  Meanwhile, a back-door
   cold front is surging southward into the region.  Given the
   moist/unstable air mass in this region, have added a MRGL risk for
   afternoon thunderstorms spreading east-southeastward as an weak
   upper trough grazes the area.  Locally gusty winds and hail are
   possible with the strongest cells.

   ...Eastern Lower MI...
   12z CAM solutions are consistent that a cluster of thunderstorms
   will form this afternoon over southeast Lower MI ahead of a weak
   shortwave trough and in region of strong heating.  Forecast
   soundings show considerable CAPE and sufficient vertical shear for
   hail and gusty winds in the strongest cells.

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