SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook AMEND 1 NWS Storm Prediction Center Norman OK 0334 PM CDT Tue Jul 27 2021 Valid 272000Z - 281200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF NEW YORK INTO SOUTHERN NEW ENGLAND...AND ADJACENT PARTS OF MINNESOTA...IOWA...AND WISCONSIN... AMENDED TO ADD MORE OF SOUTHERN NEW ENGLAND TO SLGT. ...SUMMARY... Severe thunderstorms are possible today from central New York across parts of southern New England, and mainly tonight over portions of the upper Mississippi Valley region. ...Southern New England... Line of thunderstorms along the PA/NY border is building farther south than earlier anticipated, and could affect areas from southeast NY into CT/RI and Long Island. Therefore have adjusted outlook to encompass this risk. ..Hart.. 07/27/2021 .PREV DISCUSSION... /ISSUED 1108 AM CDT Tue Jul 27 2021/ ...NY into New England... A long-lived MCV that affected MN last evening is now over southeast Ontario. A line of thunderstorms associated with the MCV is moving into western NY at over 45 knots. The air mass ahead of the activity is warming rapidly, with dewpoints in the low/mid 60s leading to afternoon MLCAPE values of 1000-1500 J/kg. This will result in intensification of the storms this afternoon over NY with an increasing risk of damaging winds. Storms are likely persist into central New England later this afternoon and evening before weakening. There is also some potential for re-development of storms over western NY and northern PA later today, but confidence of this scenario is lower. ...MN/WI/IA... A surface baroclinic zone is forecast to strengthen this afternoon over MN/WI, with hot/humid conditions over southern MN and northerly winds developing over northern WI. Increasing convergence along the boundary will lead to at least isolated thunderstorm development late this afternoon or evening. Sufficient deep-layer shear will promote supercell storm structures capable of large hail. Storms may congeal during the evening with an increasing risk of damaging wind gusts over southern WI.
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