SPC AC 161957

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0257 PM CDT Thu May 16 2019

   Valid 162000Z - 171200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE GREAT
   LAKES AND OHIO VALLEY THROUGH THE CENTRAL PLAINS AND NORTHERN
   ROCKIES...

   ...SUMMARY...
   Severe storms remain possible from the Great Lakes, Ohio Valley and
   westward through the central Plains and a portion of the northern
   Rockies.

   ...Discussion...

   Only minor adjustments have been made to previous outlook. MCS will
   continue southeast along instability gradient into southern IN and
   possibly northern KY where it should weaken. Will maintain SLGT risk
   area over the Great Lakes upstream from Ohio Valley MCS.
   Stabilization has occurred in the wake of this feature. However,
   moist advection associated with southwesterly winds  and diabatic
   warming will allow for the atmosphere to recover in pre-frontal warm
   sector from southern WI into MI where additional storms may develop
   by early evening with damaging wind and large hail possible. Farther
   west high-based storms are developing south of the stationary front
   over western NE and these may intensify as they continue northeast
   into zone of greater destabilization and higher surface dewpoints
   near the front. Other storms will develop tonight along and north of
   this boundary as the low-level jet strengthens and enhances
   isentropic ascent in frontal zone.

   ..Dial.. 05/16/2019

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Thu May 16 2019/

   ...Midwest...
   Considered increasing tornado probabilities and adding significant
   hail but low confidence exists in whether supercells can be
   sustained in the warm sector across IL/IN.

   A slowly decaying MCS is ongoing near the IL/WI border within a warm
   advection regime. Morning CAM guidance has poorly handled with most
   struggling to maintain any semblance of convection beyond
   initialization. The stratiform region across Lake MI should have an
   impact on downstream destabilization in Lower MI given that richer
   boundary-layer moisture characterized by low to mid 60s surface dew
   points is currently confined from IL west. It is possible that the
   MCS may not entirely dissipate as warm advection persists through
   the period. Renewed development on the upshear side would seemingly
   be most likely along trailing convective outflow. Along the eastern
   extent of the Great Plains elevated mixed layer at peak heating,
   robust upstream diabatic heating should result in large buoyancy
   with MLCAPE of 2000-3000 J/kg. Veering of the wind profile with
   height on the periphery of moderate mid-level northwesterlies will
   favor supercell structures. An evolution to another MCS with
   wind/hail risks appears probable tonight towards the OH Valley. 

   ...WY/NE/IA...
   Minimal change this outlook beyond adding low tornado probabilities
   across the northern/eastern WY vicinity.

   Easterly upslope flow will be maintained through the period on the
   cool side of the stalled front (just north of the lee cyclone), with
   the somewhat richer low-level moisture/buoyancy confined mainly to
   central NE east. Gradual height falls in advance of the expansive
   western trough will combine with the upslope flow and daytime
   heating in cloud breaks to support scattered thunderstorm
   development along the lee of the central Rockies during late
   afternoon, which will persist into this evening. The storm
   environment will support a few high-based supercells capable of
   mainly producing large hail and isolated severe wind gusts.
   Strengthening warm advection this evening yielding isentropic ascent
   along the largely west/east-oriented front across IA towards
   northern IL should result in scattered to widespread storms with a
   mix of isolated severe hail/wind amid a cluster convective mode.

   ...Northern Rockies...
   Have added a small Slight Risk for the expectation of a few
   supercells around peak heating.

   Increasing mid-level height falls and DCVA downstream of the
   expansive Pacific Coast trough will foster substantial ascent across
   the region at peak heating. With mid 40s to low 50s surface dew
   points prevalent, a corridor of modest buoyancy should develop where
   diabatic heating is greatest across northern ID into far western MT.
   Veering of the low-level wind profile with height beneath moderate
   mid-level southerlies should support a few supercell structures
   capable of mainly isolated severe hail.

   ...Eastern Great Basin...
   The zone of strongest forcing for ascent in advance of the mid-level
   trough and along the cold front will reach western UT and eastern ID
   later this afternoon through this evening. Though low-level moisture
   will be limited, weak buoyancy is expected ahead of the front.
   Thunderstorms will be capable of producing isolated
   strong/damaging gusts in an environment characterized by weak
   buoyancy, steep low-level lapse rates, and strong deep-layer
   southerly shear.

   ...Southeast NM and Far West TX...
   The surface lee trough will sharpen today in response to increasing
   southwest flow aloft over the southern Rockies. This area will lie
   along the northwest edge of the richer returning low-level moisture,
   which will likely be offset today by deep mixing. Still, some
   increase in deep-layer shear and sufficient buoyancy suggest that a
   couple of high-based supercells will be possible immediately east of
   the high terrain in the late afternoon and evening. Marginally
   severe hail and strong outflow gusts will be the main threats.

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