SPC AC 120606

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0106 AM CDT Mon Jun 12 2017

   Valid 121200Z - 131200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   EASTERN WYOMING..NEBRASKA PANHANDLE...AND SOUTHWEST SOUTH DAKOTA...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
   NORTH-CENTRAL HIGH PLAINS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
   ROCKIES TO THE UPPER MIDWEST...

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

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MAINE...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS WEST
   TEXAS...

   ...SUMMARY...
   Severe thunderstorms are likely this afternoon into tonight across
   the north-central High Plains. Other severe thunderstorms are
   expected from parts of the northern Rockies to the Upper Midwest,
   with other strong storms possible across Maine and west Texas this
   afternoon into evening.

   ...MT/WY/CO Front Range and North-central High Plains...
   The overall setup appears very favorable for a corridor of locally
   intense severe thunderstorms including supercells across the region
   later this afternoon into evening, especially across eastern WY into
   SD and parts of the NE panhandle. An amplifying upper trough over
   the Great Basin will begin to eject more east-northeastward today,
   with ample height falls and considerably strengthening
   mid/high-level southwesterly winds overspreading CO/WY into the
   north-central High Plains through into this evening. In concert with
   this large-scale scenario, relatively rich low-level moisture will
   continue to develop west-northwestward in concert with
   east-southeasterly low-level upslope flow to the north of a
   sharpening/northward shifting surface cyclone.  Regarding this
   relatively rich moisture, Sunday evening's 00Z observed soundings
   from Dodge City, Amarillo, North Platte, and Denver all featured
   precipitable water values in the upper 10-20th percentile for daily
   climatological values. 

   Given the timing/degree of forcing for ascent and moisture, storms
   should steadily increase initially across the northern Rockies
   vicinity including parts of ID/southern MT into WY, with other
   potentially more intense development expected by mid/late afternoon
   near and just east of the WY/northeast CO Front Range vicinity this
   afternoon. As storm increase into the High Plains, strong deep-layer
   shear with ample low-level veering and very steep lapse
   rates/moderate buoyancy will support supercells capable of very
   large hail and some tornadoes, especially across eastern WY into NE
   Panhandle/southwest SD and possibly northeast CO. It seems likely
   that storms will merge and grow upscale and spread
   east-northeastward toward the Black Hills vicinity/northwest NE into
   other parts of SD/possible far northern NEB this evening with an
   increase in severe-caliber wind potential.

   ...Middle MO Valley/Upper Midwest to Lake MI vicinity...
   At the very least, there appears to be an appreciable conditional
   severe risk across the region this afternoon into tonight. While
   upper-level heights may gradually rise in most areas, a potentially
   unstable air mass will exist along a roughly west-east frontal
   corridor, with the possibility of at least isolated deep convective
   development by late afternoon into evening owing to sufficient
   near-boundary convergence/warm advection. A near-boundary maximized
   corridor of moderate to strong buoyancy and 30-40 kt effective shear
   would support severe storms including a few supercells capable of
   large hail and damaging winds.

   ...Maine...
   A weak mid-level disturbance/MCV, potentially related to upstream
   convection over the Great Lakes early this morning, should approach
   the region later today as an influx of somewhat richer low-level
   moisture develops into the region. It appears that the
   aforementioned forcing for ascent will be relatively well-timed with
   which could be a moderately destabilized air mass this afternoon, in
   the presence of relatively strong effective shear. At least some
   hail/damaging wind potential appears possible.

   ...West TX...
   Although very warm mid-level temperatures will exist across the
   region, the influence of weak height falls in conjunction with ample
   near-dryline mixing should be sufficient to develop a few
   thunderstorms late this afternoon into early evening. While
   low/mid-tropospheric winds will be weak with only 25-30 kt of
   effective shear, steep lapse rates/deeply mixed boundary layers and
   moderate buoyancy will conditionally support some potential for hail
   and stronger downdraft winds.

   ..Guyer/Gleason.. 06/12/2017

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