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Jun 25, 2018 1730 UTC Day 2 Convective Outlook
Updated: Mon Jun 25 17:30:03 UTC 2018 (Print Version | 20180625 1730Z Day 2 shapefile | 20180625 1730Z Day 2 KML)
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 Forecast Discussion

   SPC AC 251730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Mon Jun 25 2018

   Valid 261200Z - 271200Z


   Severe storms are possible across the lower Missouri and middle
   Mississippi Valley region Tuesday afternoon into Tuesday night.  One
   or two larger clusters of storms may eventually evolve, accompanied
   by the risk for potentially damaging wind gusts and some hail. 
   Other strong to severe storms are possible across parts of the
   southern Appalachians into southern Mid Atlantic coast, as well as
   across parts of the northern Plains.

   A significant short wave trough, now progressing inland of the
   Pacific coast, is forecast to continue pivoting northeast of the
   international border through the Canadian Prairies during this
   period.  In its wake, a seasonably strong and zonal belt of
   mid-latitude westerlies appears likely to gradually nose across the
   northern U.S. Rockies into the northern Plains.  Downstream flow
   will remain split, with models indicating that a compact closed low,
   within broader scale southern stream troughing, will continue
   migrating east/northeast of the middle/lower Missouri Valley region
   into the Great Lakes region by 12Z Wednesday.  As this occurs,
   subtropical ridging may become an increasing influence across parts
   of the southern Plains into the Southwest, with an increasingly
   prominent embedded high center near the southern Rockies. 
   Downstream, it appears that subtropical ridging may become at least
   somewhat suppressed across parts of the Tennessee Valley and
   southern Appalachians into southern Mid Atlantic coast region.

   ...Lower Missouri/middle Mississippi Valley region...
   Considerable uncertainty lingers concerning the potential convective
   evolution for Tuesday through Tuesday night.  Much will probably
   depend on the evolution of convection across this same region
   between now and 12Z Tuesday.  Widespread convective cloud cover may
   be present, at least initially, with convective outflow possibly
   impacting a large portion of at least central and southern Missouri
   at the outset of the period.  This may have at least some impact on
   potential destabilization through the day, as a warm frontal zone
   begins to advance northeast of the middle Mississippi Valley.

   At least some warming at mid-levels is forecast during the day
   across much of the region, but perhaps not prohibitive to convective
   development, as a seasonably moist boundary layer attempts to warm
   and destabilize through late afternoon.  South and southwest of the
   mid-level closed low, models indicate that clearing skies may allow
   for stronger heating that could support moderate to strong boundary
   layer destabilization along an axis across central Kansas through
   northern Missouri, and perhaps northern Illinois.  This seems most
   likely to provide the primary focus for renewed convective
   development, aided by forcing near the mid-level cyclonic vorticity
   center across northern Missouri into northern Illinois, and within a
   zone of low/mid-level warm advection in its wake, across east
   central Kansas/west central Missouri.

   Given the possible large potential instability (CAPE of 2000-3000+
   J/kg), and shear associated with a belt of 30-40 kt westerly 850-500
   mb flow, discrete supercells are possible initially, but upscale
   convective growth may be fairly quick, with one or two larger
   convective clusters possibly evolving through Tuesday evening.  East
   of the middle Mississippi Valley, the tendency should be for
   activity to propagate eastward, while veering mid-level flow to the
   west supports a southeastward propagation of convection toward the
   Ozark Plateau.  After an initial hail and, perhaps, isolated tornado
   risk, damaging wind gusts probably will become the more prominent
   severe weather hazard.

   ...Southern Appalachians into southern Mid Atlantic coast...
   Beneath at least modestly steep lower/mid tropospheric lapse rates,
   moderately large CAPE is expected to support scattered vigorous
   thunderstorm development Tuesday afternoon and evening.  This may be
   focused initially near a stalled frontal zone, and across the higher
   terrain, with a gradual consolidation into one or more clusters. 
   These may be accompanied by a risk for potentially damaging wind
   gusts as they propagate southeastward through Tuesday evening.

   ...Black Hills and western Dakotas...
   Generally well south of the vigorous short wave trough migrating
   across Saskatchewan/Manitoba, thunderstorm coverage remains unclear.
   However, an environment characterized by steep lower/mid
   tropospheric lapse rates supportive of at least modest CAPE may
   promote isolated severe storm development late Tuesday afternoon
   into Tuesday night, in the presence of strengthening deep layer
   shear associated with the westerlies.

   Tornado:   5%     - Slight
   Wind:     15%     - Slight
   Hail:     15%     - Slight

   ..Kerr.. 06/25/2018



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