SPC AC 281636

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1136 AM CDT Wed Jun 28 2017

   Valid 281630Z - 291200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM FAR
   SOUTHEAST NE INTO NORTHERN IL/SOUTHERN WI...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
   HIGH PLAINS TO THE MIDDLE/UPPER MS RIVER VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   NORTHERN ROCKIES TO THE GREAT LAKES...

   ...SUMMARY...
   Severe thunderstorms with large hail, wind damage and a few
   tornadoes are expected across the middle Missouri Valley
   northeastward into the middle and upper Mississippi Valley. Other
   more isolated severe storms may occur in the central Plains and
   northern Rockies.

   ...Middle MO River Valley to middle/upper MS River Valley...
   Related to last night's MCS, scattered showers/thunderstorms and
   related prevalent cloud cover continue to progress eastward across
   eastern portions of MN/IA into WI/northern IL late this morning.
   This is just ahead of an eastward-moving shortwave trough over MN,
   with a few other convectively related disturbances/MCVs noted
   farther south, embedded within a belt of moderately strong mid-level
   westerlies. A surface low analyzed at 15Z near the MN/SD/ND border
   vicinity will continue to spread eastward across central MN toward
   northern WI and the western Upper Peninsula of MI through this
   evening, while a cold front spreads southeastward across MN/IA/WI. 

   Near and ahead of this cold front, low-level moistening and general
   air mass recovery will steadily occur this afternoon in the wake of
   the lingering early-day precipitation and cloud cover, particularly
   given relatively steep mid-level lapse rates and ample low-level
   moisture sampled in source-region 12Z observed soundings from Omaha
   NE and Topeka KS. Increasingly prevalent mid/upper 60s F surface
   dewpoints will support upwards of 2000-3000 J/kg MLCAPE particularly
   from southeast NE/northern KS into IA, with somewhat more modest
   (and uncertain) degree of pre-frontal destabilization farther north
   into WI/eastern MN owing to early-day cloud cover and some
   regenerative precipitation this morning across northern IA.

   While the aforementioned cloud cover/precipitation lingering into
   midday still casts some uncertainty, it seems most likely that
   surface-based storms will redevelop just ahead of the front
   semi-focused along outflow and zones of differential heating across
   southern/eastern IA and nearby far northern MO and northern IL.
   Pending adequate destabilization, other potentially severe
   development may occur by late afternoon in closer proximity to the
   surface low/front from far eastern MN into western/central WI. 
   Around 40-45 kt of effective shear will support some initial
   supercells capable of large hail, with a few tornadoes possible as
   well given the strength of 2-3 km AGL southwesterly winds and
   related 150-250 m2/s2 0-1 km SRH (with prospective surface-based
   convection). Eastward-moving clusters should evolve by evening with
   a related increase in damaging wind potential particularly across
   southern IA/northern MO into northern IL.
    
   ...CO/WY Front Range to northern KS/southern NE...
   Within a modestly moist environment, widely scattered thunderstorms
   should develop and spread eastward across the region by late
   afternoon into evening, including some potential for at least
   small-scale MCS development this evening. Modest buoyancy and ample
   vertical shear will support the possibility of sporadic large hail
   and locally damaging winds into this evening.

   ...Northern Rockies...
   Ahead of an amplifying shortwave trough over the northern
   Intermountain region, modest moisture and a strengthening belt of
   west-southwesterly mid-level winds should contribute to the
   possibility of isolated strong to severe storms spanning parts of
   WY/southern MT and eastern ID/northern UT.

   ..Guyer/Dean.. 06/28/2017

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