Mesoscale Discussion 511

Issued

Apr 21, 2025, 12:47 PM EDT (16:47 UTC)

Expired

Apr 21, 2025, 3:15 PM EDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

Counties Cattaraugus County, NY, Chautauqua County, NY, Erie County, NY, Carroll County, OH, Columbiana County, OH, Mahoning County, OH, Portage County, OH, Stark County, OH, Trumbull County, OH, Beaver County, PA, Butler County, PA, Crawford County, PA, Erie County, PA, Forest County, PA, Lawrence County, PA, Mercer County, PA, Venango County, PA, Warren County, PA

The Pittsburgh radar (KPBZ), 143 km from the middle of the area, began a volume at 16:47 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

425 
ACUS11 KWNS 211647
SWOMCD
SPC MCD 211647 
NYZ000-PAZ000-WVZ000-OHZ000-211915-

Mesoscale Discussion 0511
NWS Storm Prediction Center Norman OK
1147 AM CDT Mon Apr 21 2025

Areas affected...parts of nern OH...nwrn PA...swrn NY State

Concerning...Severe potential...Watch unlikely 

Valid 211647Z - 211915Z

Probability of Watch Issuance...20 percent

SUMMARY...Strengthening low-topped thunderstorm development appears
probable by 3-5 PM EDT, including isolated to widely scattered
supercells accompanied by small to marginally severe hail and at
least some risk for a tornado.  It is not clear that a severe
weather watch will be needed, but trends are being monitored.

DISCUSSION...Within the warm sector of an occluding cyclone
migrating northeastward across the upper peninsula of Michigan,
boundary-layer destabilization is ongoing within at least a narrow
corridor across eastern Ohio into the lower Great Lakes vicinity. 
Closely trailing an initial band of weak mid-level warm advection
driven convection, which has contributed to saturation of initially
dry lower/mid-tropospheric profiles, boundary-layer moisture
characterized by dew points near 60f, is rapidly advecting
northeastward.  This is occurring beneath the leading edge of a
mid-level dry slot, which is allowing for increasing insolation. 
The NAM and Rapid Refresh suggest that this will contribute to
mixed-layer CAPE on the order of 500 J/kg, prior to the passage of
the cold front.

This is also occurring beneath a 30-50 kt south-southwesterly 850 mb
jet axis, where forecast soundings indicate enlarged low-level
hodographs may include modest clockwise curvature of the shear
vector with height by peak destabilization.  As mid/upper forcing
for ascent (downstream of the base of a negatively tilted short wave
advancing toward the region) supports deepening convective
development, there appears a window of opportunity for scattered
low-topped supercell development by 19-21Z.  This may be accompanied
by a risk for small to marginally severe hail, locally strong
surface gusts, and at least potential for a tornado or two.

..Kerr/Hart.. 04/21/2025

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...BUF...CTP...PBZ...CLE...

LAT...LON   42887905 42497783 41857867 40827995 40408114 40938153
            41898069 42887905 

MOST PROBABLE PEAK TORNADO INTENSITY...85-115 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.