SPC AC 272036

   Day 1 Convective Outlook RESENT 3
   NWS Storm Prediction Center Norman OK
   0336 PM CDT Tue Jun 27 2017

   Valid 272000Z - 281200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF NEBRASKA AND SOUTHERN SOUTH DAKOTA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   NORTH-CENTRAL PLAINS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   NORTH-CENTRAL HIGH PLAINS TO THE UPPER MIDWEST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   NORTHEAST STATES/NEW ENGLAND...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   FLORIDA PENINSULA...

   ...SUMMARY...
   Severe thunderstorms capable of large hail, damaging winds and a
   tornado or two are expected over much of Nebraska and South Dakota
   late this afternoon and evening, with the potential for significant
   wind gusts. Other strong to severe thunderstorms will be possible
   across parts of the Northeast States as well as the Florida
   Peninsula.

   ...Wyoming/Colorado High Plains eastward to southwestern Minnesota
   and Iowa...
   Recent satellite/radar observations and objective analyses indicate
   convection developing on the western edge of an increasingly
   unstable airmass advancing northward in portions of the
   central/northern Plains.  Observations and high-res guidance
   continue to indicate that storms will gradually increase in
   intensity and coverage, with one or two forward-propagating linear
   segments eventually developing across western portions of South
   Dakota and Nebraska.  Widespread damaging wind gusts and hail are
   likely with this activity, with perhaps an isolated tornado threat
   also evolving especially within the enhanced risk area as low-level
   shear profiles increase attendant to a strengthening low-level jet
   near/after dark.  Portions of the slight risk have been expanded
   into western Iowa and southwestern Minnesota as recent
   high-resolution guidance suggest that at least some lingering severe
   threat will exist in that region after sunset as convection
   develops/migrates into that area.

   A small part of northeastern Kansas has been added to marginal
   wind/hail probabilities as a result of a localized, persistent
   cluster of storms in that area.

   ...Portions of the Northeast...
   Scattered thunderstorms are ongoing across the marginal risk area,
   with an isolated threat of hail, wind damage, and perhaps a tornado.
   This threat should persist for the remainder of the afternoon before
   waning some after sunset.

   ..Cook/Peters.. 06/27/2017

   .PREV DISCUSSION... /ISSUED 1141 AM CDT Tue Jun 27 2017/

   ...Central/northern High Plains to middle MO Valley...
   A shortwave trough and related mid/high-level speed max are readily
   evident across the eastern ID/southwest MT/western WY vicinity and
   adjacent Great Basin per water vapor imagery and 12Z upper-air
   analysis. This eastward-progressive shortwave trough will reach the
   Dakotas and middle MO valley by this evening amid a steadily
   strengthening belt of mid-level westerlies.

   An initial increase in widely scattered strong thunderstorm
   development should occur this afternoon across interior WY (and far
   southern MT), where modest moisture/buoyancy will support some
   potential for severe hail and severe-caliber wind gusts. As forcing
   for ascent spreads eastward, additional development should occur by
   late afternoon in vicinity of the north/south-oriented lee trough,
   particularly across eastern WY/NE Panhandle and Black Hills
   vicinity. Large hail and damaging gusts will be possible for the
   first few hours, although very steep lapse rates and a relatively
   well-mixed environment should result in an upscale-growing and
   eastward-accelerating complex primarily across NE this evening. As
   mentioned in the prior outlook discussion, localized hurricane-force
   thunderstorm gusts are possible from the most intense surges of
   convection this evening.

   ...Northeast States/New England...
   Aided by a northeast-moving shortwave trough, scattered low-topped
   thunderstorms will continue to increase and spread
   east/northeastward across the region this afternoon. Relatively
   steep lapse rates, accentuated by cool mid-level temperatures (near
   -20C at 500 mb) will support stronger low-topped storms capable of
   hail, with a few low-topped supercells possible across southern New
   England where deep-layer shear will be somewhat stronger. For
   additional short-term information, see Mesoscale Discussion 1160.
   Convection should weaken as it moves eastward over either land-based
   evening diabatic cooling and/or the Atlantic marine layer.

   ...Florida...
   Ample insolation and a moist environment will lead to moderate
   buoyancy this afternoon across the FL Peninsula near and south of a
   stalled front. A few thunderstorms could produce strong/locally
   severe-caliber downdrafts this afternoon within a weak deep-layer
   shear environment.

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