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Aug 24, 2017 0600 UTC Day 2 Convective Outlook
Updated: Thu Aug 24 04:50:04 UTC 2017 (Print Version | 20170824 0600Z Day 2 shapefile | 20170824 0600Z Day 2 KML)
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 Forecast Discussion

   SPC AC 240450

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1150 PM CDT Wed Aug 23 2017

   Valid 251200Z - 261200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY NIGHT
   ACROSS PARTS OF LOWER/MIDDLE TEXAS COASTAL AREAS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY EVENING
   ACROSS PARTS OF CENTRAL AND SOUTHERN SOUTH DAKOTA INTO NORTHERN
   NEBRASKA...

   ...SUMMARY...
   The circulation center of Harvey may reach the lower or middle Texas
   coast by late Friday night, accompanied by some risk for tornadoes. 
   Otherwise, a cluster of thunderstorms may develop across parts of
   the Black Hills and Badlands of South Dakota, into portions of the
   middle Missouri Valley, accompanied by at least some risk for severe
   weather Friday evening.

   ...Synopsis...
   Fairly sharp cyclonic mid-level flow is expected to linger either
   side of an axis extending across the Canadian Maritimes, southward
   through the southern Appalachians/southern Mid Atlantic Coast
   region, through this period.  However, models indicate that the
   significant upstream short wave trough, reaching the Canadian
   prairies by early Friday, will pivot northeastward into the
   Northwest Territories by late Friday night.  As it does, the
   stronger mid-latitude westerlies appear likely to retreat north of
   the western and central Canadian/U.S. border area, while subtropical
   ridging begins to build northward through the Southwest, and
   southern portions of the Great Basin, Rockies and Plains.  Within
   generally weak westerly/northwesterly mid and upper flow on the
   periphery of this ridging, at least one minor perturbation may
   progress east southeastward across parts of the Dakotas and mid
   Missouri Valley region.  Within/beneath the upper ridging, extending
   along an east/southeast axis into the Caribbean and Bahamas, it
   still appears that a significant tropical cyclone will migrate into
   the vicinity of the lower/middle Texas coast by late Friday night.

   ...Texas coastal areas...
   Harvey may reach hurricane intensity as it approaches lower/middle
   Texas coastal areas late Friday/Friday night.  As it does, sizable
   clockwise curved low-level hodographs may develop across coastal
   areas well in advance of its arrival, but until the near surface
   flow veers from northeasterly to more of an easterly or
   southeasterly component, to the right of its forward motion,
   relatively stable boundary layer air may minimize any tornado
   potential.  Appreciable boundary layer destabilization along coastal
   areas may not occur until late Friday evening, or later.  Once
   instability begins to increase, strong low-level shear will probably
   become supportive of at least some risk for tornadoes with
   convection associated with Harvey.  The extent of this risk remains
   unclear, and will strongly hinge on mesoscale developments which are
   still characterized by low predictability this far in advance.

   ...Parts of the northern Plains...
   Isolated to widely scattered strong thunderstorms may develop near
   the surface trough across the region during the late afternoon
   hours, perhaps aided by forcing associated with the minor short wave
   perturbation.  While westerly deep layer mean flow will be weak,
   sufficient veering of winds from lower through mid-levels may
   contribute to vertical shear marginally sufficient for organized
   convective development.  Any severe weather threat seems likely to
   remain rather isolated across most areas, but guidance appears
   increasingly suggestive that forcing associated with modest
   nocturnal low-level jet strengthening (to around 30+ kt at 850 mb)
   may enhance convective development spreading east of the Black
   Hills/Badlands area of South Dakota by Friday evening.  This is
   where a remnant zone of stronger differential surface heating,
   beneath at least modestly steep mid-level lapse rates supportive of
   CAPE on the order of 1000-2000 J/kg, may contribute to an
   environment conducive to an evolving cluster of storms accompanied
   by a risk for potentially damaging wind gusts.

   ..Kerr.. 08/24/2017

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z

        
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