• MESO: Mesoscale Discussion 1319

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Tue Jul 20 17:04:13 2021
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    ACUS11 KWNS 201704
    SPC MCD 201703=20

    Mesoscale Discussion 1319
    NWS Storm Prediction Center Norman OK
    1203 PM CDT Tue Jul 20 2021

    Areas affected...Parts of Upstate New York and adjacent portions of

    Concerning...Severe potential...Watch possible=20

    Valid 201703Z - 201930Z

    Probability of Watch Issuance...60 percent

    SUMMARY...An organizing cluster of thunderstorms over parts of
    southern Ontario likely will begin impacting the upper St. Lawrence
    Valley and Lake Ontario vicinity by 3-5 PM EDT, accompanied by
    increasing potential for damaging wind gusts.

    DISCUSSION...Associated with larger-scale mid/upper troughing
    digging in the St. Lawrence Valley/lower Great Lakes region, forcing
    for ascent with a lead speed maximum (30-50 kts in the 500-300 mb
    layer) appears to be providing support for an ongoing, well
    organized cluster of thunderstorms across southeastern Ontario.=20
    Perhaps aided by an associated strengthening surface cold pool, this
    activity has accelerated some (up to 40 kt) over the past couple of
    hours, and may reach the Ottawa vicinity by around 19Z.

    Along trailing outflow into the vicinity of its intersection with a
    southward advancing cold front, additional thunderstorm development
    and intensification is now also well underway. Supported by
    moderate southeasterly low-level inflow of moist air characterized
    by CAPE of 1000-2000 J/kg, this seems likely to continue with the
    evolution of another upscale growing and organizing cluster/segment
    possible. This may begin impacting the Ontario shores of Lake
    Ontario into the Watertown vicinity as early as 20-21Z, perhaps a
    bit earlier and more substantively than suggested by the latest
    Rapid Refresh.

    Although low-level wind fields are generally weak, the effective
    downward mixing of higher momentum air aloft, associated with the
    well developed/maturing organized convective system and associated
    surface cold pools, probably will be accompanied by increasing
    potential for strong gusts at least approaching severe limits.

    ..Kerr/Hart.. 07/20/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!qhrpl1vp-uifcNoysCi16b77wNBtxzpofvp5kpwbpvc5b6kvlN3Beab7IWw_uzCyGhxJowIr$=
    for graphic product...


    LAT...LON 44618000 44557856 44917736 45307677 45407578 44937319
    44477329 44107422 43797486 43407580 43167760 43377902
    44238068 44618000=20

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