Mesoscale Discussion 1128

Issued

Jun 30, 2021, 11:04 AM EDT (15:04 UTC)

Expired

Jun 30, 2021, 1:00 PM EDT

In force

116 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...severe thunderstorm watch likely

Chance of a watch

80%

The Burlington radar (KCXX), 122 km from the middle of the area, began a volume at 15:07 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.

• Severe Thunderstorm Watch 326Jun 30, 11:45 AM EDT
• Severe Thunderstorm Watch 327Jun 30, 12:05 PM EDT
• Severe Thunderstorm Watch 328Jun 30, 12:45 PM EDT

311 
ACUS11 KWNS 301505
SWOMCD
SPC MCD 301504 
MEZ000-NHZ000-VTZ000-MAZ000-NYZ000-PAZ000-301700-

Mesoscale Discussion 1128
NWS Storm Prediction Center Norman OK
1004 AM CDT Wed Jun 30 2021

Areas affected...Portions of far northern PA into much of NY...far
western MA...VT...NH...and southern/central ME

Concerning...Severe potential...Severe Thunderstorm Watch likely 

Valid 301504Z - 301700Z

Probability of Watch Issuance...80 percent

SUMMARY...The threat for scattered severe/damaging wind gusts and
isolated marginally severe hail will increase late this morning into
the afternoon. One or more Severe Thunderstorm Watches will likely
be needed.

DISCUSSION...40-50 kt of mid-level west-southwesterly flow
associated with an upper trough centered over Ontario/Quebec and the
Great Lakes will remain over much of the Northeast today. With the
lack of an appreciable surface front, low-level convergence should
remain fairly weak across this region. Still, a zone of differential
heating between morning clouds/precipitation and partly to mostly
clear conditions to the south, as well as some convergence off of
Lakes Erie/Ontario, will probably serve as foci for storm
development. As surface temperatures generally warm into the upper
80s and low 90s over the next couple of hours, convective
temperatures will likely be reached as 1000-2000 J/kg of MLCAPE
develops.

Around 30-40 kt of effective bulk shear should prove favorable for a
mix of small clusters/multicells and supercells as storms form and
then move eastward across NY and New England. Steep low-level lapse
rates and strengthening flow with height through low/mid levels
suggest that scattered damaging wind gusts will likely be the main
severe threat. With some supercell potential given the mostly
long/straight hodographs expected, isolated marginally severe hail
may also occur. But, modest mid-level lapse rates will probably
limit a greater hail threat. Current expectations are for robust
storm development to occur by 16-17Z (Noon - 1 PM EDT), and multiple
Severe Thunderstorm Watches will likely be issued to address this
increasing severe threat.

..Gleason/Thompson.. 06/30/2021

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

ATTN...WFO...CAR...GYX...BTV...ALY...BGM...BUF...

LAT...LON   43007067 42747134 42777303 42237338 42017395 41787480
            42017693 42047831 42387844 42947751 43557587 44047524
            44457389 44817215 45157102 45586995 45626747 45226712
            44776688 44056854 43766954 43457022 43007067

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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.