SPC AC 281725

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1225 PM CDT Tue Jul 28 2020

   Valid 291200Z - 301200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM
   NORTHEASTERN OHIO INTO WESTERN NEW YORK...ACROSS THE HIGH
   PLAINS...AND IN OREGON...

   ...SUMMARY...
   Strong thunderstorms may impact parts of lower Great Lakes region,
   portions of the High Plains, and parts of central Oregon Wednesday
   afternoon and evening, accompanied by at least some risk for severe
   weather.

   ...Synopsis...
   Several mid-level synoptic features will foster an isolated severe
   weather risk across portions of the Northeast, High Plains, and
   Oregon.  The first is a long-wave trough centered over
   Ontario/Quebec that will spread a belt of enhanced mid-level flow
   across the Great Lakes and adjacent northeast States.  Another
   series of weaker, shorter-wave troughs will migrate southeastward
   across the central Plains and Ozarks.  Another shortwave trough will
   migrate northward along the California coast, and spread enhanced
   mid-level flow over Oregon late in the period - particularly after
   00Z or so.  At the surface, convection should be ongoing across
   areas of Kansas/Oklahoma early, which should impact subsequent
   destabilization across much of the central Plains and downstream
   areas of the mid-Mississippi Valley.  In areas that aren't affected
   by prior convection, diurnal surface heating amidst a moist airmass
   will result in destabilization and ultimately areas of scattered
   thunderstorms - especially south of a front located from South
   Dakota into lower Michigan.  

   ...Central High Plains...
   Upstream of morning convection over eastern Kansas/Missouri, surface
   heating amidst a moist airmass (containing 50s to 60s F dewpoints)
   will foster strong instability beneath an EML plume containing 7-8
   C/km mid-level lapse rates.  Lift/forcing associated with the
   shortwave centered near the region and weak southeasterly upslope
   flow will result in scattered to numerous thunderstorms along an
   axis from eastern Wyoming south-southeastward to western Kansas. 
   Low-level shear will be weak, though areas of enhanced mid-level
   flow will likely aid in forward-propagation and upscale growth into
   clusters that will migrate southeastward over the course of the
   evening.  Some enhancement of low-level flow across west Texas will
   likely help to maintain any ongoing clusters from southwest Kansas
   into northern Oklahoma overnight, with a marginal hail/wind threat. 
   An isolated tornado cannot be completely ruled out in this regime -
   especially where any remnant outflow boundaries can favorably
   interact with newer convective development in the afternoon/early
   evening.  Isolated hail/damaging wind gusts are the most likely
   threats with this activity.

   ...Northeastern Ohio into western New York...
   Weak to moderate instability will develop in the afternoon in
   response to surface heating within a moist airmass characterized by
   low to mid-60s F dewpoints.  Though mid-level lapse rates are
   appreciably weaker compared to areas west, strong shear and
   sufficient buoyancy will allow for areas of organized convection,
   including a mix of cells and linear segments.  Long/straight
   hodographs may favor updraft rotation in cellular storms, though
   weak low-level shear should promote mostly outflow-dominant storms. 
   An isolated wind/hail risk will exist with the strongest activity,
   with storms weakening overnight with nocturnal stabilization of the
   boundary layer.

   ...Oregon...
   Isolated storms are expected to develop in the afternoon/evening
   across central Oregon downstream of the advancing shortwave along
   the California coastline.  These storms will exist in a strongly
   sheared environment as a mid-level jet impinges upon the region. 
   Weak to moderate instability and steep low-level lapse rates will
   foster a risk of isolated damaging wind gusts and hail, though
   convective coverage is expected to be limited until mid-level
   forcing can arrive - possibly after 00Z or so within the Marginal
   Risk area.

   ...Eastern Nebraska/western Iowa/southeastern South Dakota...
   Though mid-level winds will be weak, a few models indicate strong
   instability developing by afternoon as a moist low-level airmass
   resides beneath steep mid-level lapse rates (exceeding 7.5 deg
   C/km).  A lingering uncertainty within this convective regime
   involves downstream convection and cloud debris over
   Kansas/Missouri, which could limit afternoon destabilization.  If
   these storms do not limit destabilization as currently expected,
   isolated damaging wind gusts and hail may develop with any afternoon
   convection.  This scenario will be revisited for possible low severe
   probabilities in later outlooks.

   ...Missouri/western Kentucky and vicinity...
   Some enhancement of mid-level flow may occur in tandem with an
   approaching shortwave and any ongoing convective organization from
   morning through afternoon.  Though mid-level lapse rates are modest
   and shear is weak, any organized convection/MCS that can persist
   eastward during the afternoon may foster an isolated wind-gust
   threat in the afternoon/early evening.  A possible addition of
   low/Marginal severe probabilities may be needed in later outlooks
   pending convective trends.

   ..Cook.. 07/28/2020

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