SPC AC 051246

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0746 AM CDT Thu Jul 05 2018

   Valid 051300Z - 061200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE GREATER SOUTHERN GREAT LAKES REGION INTO NEW
   ENGLAND...NORTHERN GULF COAST...AND CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Marginally severe thunderstorms with hail and strong wind gusts will
   be possible across portions of the central High Plains and across
   the greater southern Great Lakes region into New England.  A few
   strong wind gusts may also occur across the northern Gulf Coast.

   ...Synopsis...

   In the mid-levels, a seasonably strong short-wave trough will skirt
   across the northern Great Lakes today, eventually ending up poised
   to sweep across the Northeast on Friday. Large-scale ascent
   associated with this trough will begin to lower heights across the
   Northeast. At the same time, strong southerly flow around a
   high-amplitude trough and cyclone along the Pacific coast will help
   raise heights across the Intermountain West. The result will be
   earnest westward building of the persistent, zonally-elongated ridge
   across the eastern United States, culminating in 500-millibar
   heights flirting with 600 decameters across the central Rocky
   Mountains this evening. 

   At the surface, a cold front will move eastward across the
   north-central United States and into the Great Lakes region. An
   anticyclone is found off the Mid-Atlantic coast, and the flow around
   this feature will maintain a very moist airmass to the south and
   east of the aforementioned front, with dewpoints in excess of 70F
   common.

   ...Greater Southern Great Lakes Vicinity into New England...

   The combination of large-scale ascent from the mid-level trough
   skirting the northern Great Lakes, modest low-level convergence
   along the front, and a very moist (precipitable water around two
   inches) and weakly capped environment will support isolated showers
   and thunderstorms today. Deep-layer shear will be weak as the best
   mid-level flow will remain north of the Great Lakes. The result will
   be poorly-to-loosely organized cellular and multicell clusters, the
   strongest of which may be capable of producing marginally severe
   hail or wind.

   ...Central High Plains...

   Despite rising heights through the day, continued moist low-level
   upslope on the nose of southeasterly low-level winds, and aided by a
   residual front in the vicinity, will support thunderstorms this
   afternoon and evening atop the favored terrain areas. These
   thunderstorms will be loath to move off the terrain initially, but
   with time, sufficient cold-pool development could eventually allow a
   few to move into the plains east of the Rockies. Additionally,
   strong diurnal heating to the south of the front -- and potentially
   on residual outflow boundaries -- may allow isolated thunderstorms
   to develop east of the terrain. With both possible areas of
   convection, mid-level lapse rates will remain somewhat muted -- only
   in the 6-7 C/km range -- but should be sufficient to support a
   marginal severe hail risk. Low-level lapse rates should be somewhat
   better and may support a marginal damaging wind threat as well.

   ...Northern Gulf Coast...

   This area remains south of the mid-level anticyclone across the
   central of the United States. As such, deep easterly flow will
   persist today. Embedded within the tropical easterlies will be
   several troughs. The first of these is currently located across far
   southern Texas and will move westward into northern Mexico through
   today. Another such trough is currently over the northeast Gulf of
   Mexico and will also move west through the day. Ascent with this
   wave will combine with strong diurnal heating of a very moist
   (precipitable water approaching two inches), weakly capped
   environment to allow numerous showers and thunderstorms. Given the
   expected degree of instability (mixed-layer CAPE between 1500-2500
   J/kg) and modest deep-layer shear (between 20-30 knots)
   thunderstorms may organize into multicell clusters, posing a
   marginal risk for wet microbursts this afternoon and evening. A
   modestly more substantive damaging-wind threat will be possible with
   any westward moving multicell cluster that can grow upscale into
   small bowing segments.

   ..Marsh/Edwards.. 07/05/2018

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