SPC AC 091957

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0257 PM CDT Thu Jul 09 2020

   Valid 092000Z - 101200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON AND EVENING ACROSS PARTS OF THE UPPER MISSISSIPPI
   VALLEY...THE SOUTHERN GREAT PLAINS AND TO THE LEE OF THE FRONT
   RANGE...

   ...SUMMARY...
   A few strong to severe storms remain possible into this evening
   across parts the upper Mississippi Valley, the southern Great Plains
   into lower Mississippi Valley, and to the lee of the Front Range.

   ...20Z Outlook Update...
   A number of adjustments have been made to categorical and
   probabilistic lines in an attempt to better account for the gradual
   progression of synoptic and sub-synoptic features, and trends
   concerning destabilization, which will impact convective potential
   through the remainder of the period.

   A zone of strong differential surface heating, near a
   stalling/weakening outflow boundary across central through
   northwestern Oklahoma, will remain a potential focus for the
   initiation of isolated to widely scattered thunderstorm activity
   late this afternoon and evening.  Mid-level inhibition may be
   sizable beneath warm mid-level air, but thermodynamic profiles
   characterized by steep mid-level lapse rates, seasonably high
   boundary-layer moisture content and large CAPE are supportive of
   intense storms if sustained deep convection can initiate.  Veering
   winds with height beneath modest northwesterly mid-level flow is
   also contributing to sufficient shear for supercells capable of
   producing severe hail and strong wind gusts.

   ..Kerr.. 07/09/2020

   .PREV DISCUSSION... /ISSUED 1154 AM CDT Thu Jul 09 2020/

   ...Upper Mississippi Valley/Upper Midwest...
   A prominent MCV over Iowa will continue to influence strong/severe
   thunderstorm development this afternoon, particularly near/south of
   an outflow-reinforced boundary that extends east-northeastward
   across southeast Minnesota into Wisconsin. Other storms should also
   develop south-southeastward this afternoon across eastern Iowa into
   northern Illinois near/east of the cold front. Damaging winds should
   be the primary concern, but some severe hail is possible, and some
   tornado threat may exist as well.

   ...Ozarks/Mid-South...
   The remnants of a long-lived bowing MCS that moved out of the
   central Plains persists at late morning across far east-central
   Oklahoma/northwest Arkansas. This may continue to pose an isolated
   damaging wind threat into the early afternoon, although its exact
   disposition is not certain. A destabilizing downstream air mass
   across the Mid-South region suggests some concern for a persistent
   and semi-organized damaging wind risk this afternoon; however, upper
   heights are tending to rise with some mid-level warming in
   conjunction with weakening deep-layer winds aside from the MCS
   itself. Regardless, isolated damaging thunderstorm winds will at
   least be some concern across the region this afternoon.

   ...South-central Plains including Oklahoma/southern Kansas...
   MCS-peripheral outflow is expected to gradually modify/decay and
   possibly gradually develop northward through late afternoon/early
   evening. Along/south of this outflow, a very unstable environment is
   expected particularly across northern Oklahoma and far southern
   Kansas. Severe potential is conditional along this boundary, but
   least isolated but intense severe thunderstorm develop is plausible
   late this afternoon and early evening. Relatively maximized
   low-level shear near and north of the residual boundary also may
   encourage supercell characteristics, with all severe hazards a
   possibility if/where storms do form.

   ...Central High Plains...
   Isolated to widely scattered thunderstorms should form this
   afternoon over the High Plains/near the higher terrain, as heating
   of relatively high terrain preferentially removes MLCINH. Despite
   generally rising heights over the region, the environment will
   include steep low/middle-level lapse rates, adequate residual
   moisture for convection, and areas of relatively backed/upslope
   low-level flow related to the front and MCS-outflow trajectories.  A
   few supercells are possible, with attendant wind/hail threat atop a
   deep/well-mixed subcloud layer. Forecast soundings show modest winds
   below about 600 mb, but strong veering of wind direction with
   height, contributing to favorable deep shear and elongated, nearly
   straight-line hodographs. As such, splitting supercells may occur.
   Strong upper/anvil-level flow will aid in ventilation and
   cloud-layer shear as well. The moist axis expected to exist by
   afternoon, from central Kansas northwestward across southwestern
   Nebraska to near the Nebraska/Wyoming line, will support peak MLCAPE
   ranging from 1500-2000 J/kg, locally higher. Upscale organization of
   some of this activity into a small evening/overnight MCS with
   continued wind/hail potential is possible.

   ...Coastal Mid-Atlantic States...
   Regarding a low off the coast of North Carolina, whose development
   is being monitored by the National Hurricane Center, it appears that
   the inland potential for weak supercells and/or thunderstorm-related
   gusty winds will remain low. Even under a scenario of increasing
   strength/organization, it is likely that the strongest low-level
   winds will remain offshore with limited surface-rooted buoyancy
   expected in coastal areas.

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