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SPC Moderate Risk for July 19, 2019

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  1. SPC AC 191236
  2.  
  3.    Day 1 Convective Outlook  
  4.    NWS Storm Prediction Center Norman OK
  5.    0736 AM CDT Fri Jul 19 2019
  6.  
  7.    Valid 191300Z - 201200Z
  8.  
  9.    ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS EAST-CENTRAL MN
  10.    AND NORTHERN WI...
  11.  
  12.    ...SUMMARY...
  13.    A regional outbreak of severe thunderstorms with strong tornadoes
  14.    and potentially widespread significant wind damage may occur from
  15.    central Minnesota across northern Wisconsin during the mid-afternoon
  16.    to evening.
  17.  
  18.    ...Upper Midwest/Great Lakes...
  19.    Upgrading to Moderate Risk this outlook for the potential threats of
  20.    multiple strong tornadoes and a derecho later this afternoon and
  21.    evening. CAPE/shear/SRH parameter space in this region is forecast
  22.    to be exceptionally rare for mid July amid a predominately zonal
  23.    flow regime across the northern states.
  24.  
  25.    A convective cluster is ongoing across north-central SD aided by
  26.    warm/moist advection around 700 mb along a pronounced baroclinic
  27.    zone. 00Z CAM guidance had a decent handle on this activity earlier
  28.    this morning and are consistent with a decaying trend through late
  29.    morning as advection shifts east amid pronounced MLCIN as sampled by
  30.    the 12Z Aberdeen sounding. There is a low confidence scenario that a
  31.    strong enough cold pool is becoming established with this early-day
  32.    cluster such that total decay does not occur. If this occurs, robust
  33.    boundary-layer heating downstream may be sufficient for an
  34.    increasing threat during the afternoon of strong to severe wind
  35.    gusts. This could still yield a scattered to widespread damaging
  36.    wind scenario, albeit in an earlier time frame than progged by
  37.    guidance.
  38.  
  39.    The more probable scenario is for an extremely unstable air mass
  40.    (MLCAPE > 4000 J/kg) to become established to from southeast SD
  41.    through central/southern WI as the elevated mixed-layer overspreads
  42.    surface dew points rising into the mid to upper 70s. A surface
  43.    cyclone over central SD should track towards the Twin Cities through
  44.    early evening. Strong low-level convergence near/northeast of this
  45.    cyclone along the warm front should sustain surface-based storm
  46.    development across central into east-central MN. Once initiation
  47.    occurs, intense supercells will develop rapidly, with an attendant
  48.    threat for all severe hazards including strong tornadoes amid 50-60
  49.    kt effective shear and 0-3 km SRH > 300 m2/s2. The very warm/moist
  50.    thermodynamic profiles will also support generation of strong cold
  51.    pools which should eventually yield a bowing, forward-propagating
  52.    MCS across northern WI into parts of northern Lower and Upper MI.
  53.    Strength of the vertical shear suggests the potential for intense
  54.    bowing segments capable of yielding a derecho with significant
  55.    severe wind gusts.
  56.  
  57.    ...Lower Great Lakes...
  58.    An MCV progressing east over the Lower Great Lakes this afternoon
  59.    should provide enough lift for scattered thunderstorms development.
  60.    Air mass over the region will be moderately to strongly unstable but
  61.    modestly sheared. Expectation is for predominantly multicellular,
  62.    outflow-dominant storms capable of isolated damaging wind gusts.
  63.  
  64.    ...SD tonight...
  65.    Another round of 700-mb warm/moist advection will occur tonight
  66.    within a tight baroclinic zone well north of a surface front arcing
  67.    across NE into northeast WY. Large elevated buoyancy and strong
  68.    effective shear will support a risk for isolated large hail. The
  69.    risk for severe wind will likely be tempered by a more stable
  70.    sub-cloud layer in the second convective round.
  71.  
  72.    ..Grams/Gleason.. 07/19/2019
  73.  
  74.    CLICK TO GET WUUS01 PTSDY1 PRODUCT
  75.  
  76.    NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
  77.    CURRENT UTC TIME: 1346Z (8:46AM), RELOAD THIS PAGE TO UPDATE THE TIME
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