SPC MOD OTL 07/19/2019, 1630z

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  1.  SPC AC 191647
  3.    Day 1 Convective Outlook  
  4.    NWS Storm Prediction Center Norman OK
  5.    1147 AM CDT Fri Jul 19 2019
  7.    Valid 191630Z - 201200Z
  12.    ...SUMMARY...
  13.    A regional outbreak of severe thunderstorms with the possibility of
  14.    strong tornadoes and widespread significant wind damage is expected
  15.    from central Minnesota across northern Wisconsin during the mid/late
  16.    afternoon into tonight.
  18.    ...Upper Midwest/Great Lakes...
  19.    A regional outbreak of severe thunderstorms is expected later this
  20.    afternoon into tonight. That said, some specific uncertainties
  21.    remain with the timing details/exact sub-regional corridor of peak
  22.    severe-weather risk given capping/warm temperatures aloft and
  23.    uncertainty with the decay of the cloud shield from the earlier MCS
  24.    across South Dakota.
  26.    A very strong summertime belt of westerlies exists across the
  27.    northern tier of the CONUS, with 50-100 kt westerlies noted between
  28.    500/250 MB in 12Z upper-air data spanning Montana to the
  29.    Dakotas/Minnesota. Where storms develop/increase later today, this
  30.    very strong belt of winds aloft will be influential in storm
  31.    organization including supercells and potential evolution of a
  32.    fast-moving MCS (possible if not likely derecho) later
  33.    today/tonight.
  35.    Consult Mesoscale Discussion 1523 regarding midday details across
  36.    western Minnesota. Additional surface-based thunderstorm development
  37.    may emanate from the ascent/differential heating related to the MCS
  38.    remnants, focusing downstream surface-based severe potential across
  39.    central Minnesota. An extremely unstable air mass (MLCAPE >4000
  40.    J/kg) will continue to become established from southeast Southeast
  41.    South Dakota through central/southern Wisconsin as the elevated
  42.    mixed-layer overspreads surface dew points rising into the mid to
  43.    upper 70s. A surface cyclone over central South Dakotas should track
  44.    towards the Twin Cities through early evening. Strong low-level
  45.    convergence near/northeast of this cyclone along the warm front
  46.    should sustain surface-based storm development across central into
  47.    east-central Minnesota.
  49.    Intense supercells are likely to develop rapidly, with an attendant
  50.    threat for all severe hazards including the possibility of a strong
  51.    tornado or two amid 50-60 kt effective shear and 0-3 km SRH >300
  52.    m2/s2. The very warm/moist thermodynamic profiles will also support
  53.    generation of strong cold pools which should eventually yield a
  54.    bowing, forward-propagating MCS across northern Wisconsin into parts
  55.    of northern Lower and Upper Michigan. Strength of the vertical shear
  56.    suggests the potential for intense bowing segments capable of
  57.    yielding a derecho with significant/widespread severe wind gusts.
  59.    ...Lower Great Lakes/Northeast States...
  60.    Have upgraded parts of the region for thunderstorm-wind related
  61.    potential this afternoon into evening. This will be related to the
  62.    possible east-southeastward persistence of a complex of storms
  63.    across Ontario and additional scattered development that is expected
  64.    in the lee of the Lower Great Lakes. The ambient air mass will be
  65.    moderately to strongly unstable but the region will generally be
  66.    south of the stronger westerlies aloft. The overall expectation is
  67.    for predominantly multicellular, outflow-dominant storms capable of
  68.    isolated damaging wind gusts this afternoon and evening.
  70.    ...South Dakota tonight...
  71.    Another round of 700-mb warm/moist advection will occur tonight
  72.    within a tight baroclinic zone well north of a surface front arcing
  73.    across Nebraska into northeast Wyoming. Large elevated buoyancy and
  74.    strong effective shear will support a risk for isolated large hail.
  75.    While storms will generally tend to be elevated, there may be some
  76.    wind damage potential if upscale quasi-linear growth occurs late
  77.    tonight as storms progress east-southeastward across South Dakota.
  79.    ..Guyer/Wendt.. 07/19/2019
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