SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

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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