Severe Storm Outlook Narrative (AC)
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123
ACUS11 KWNS 201904
SWOMCD
SPC MCD 201903
NYZ000-PAZ000-202030-

Mesoscale Discussion 1363
NWS Storm Prediction Center Norman OK
0203 PM CDT Thu Jul 20 2017

Areas affected...Portions of southern NY and northeastern PA

Concerning...Severe Thunderstorm Watch 424...

Valid 201903Z - 202030Z

The severe weather threat for Severe Thunderstorm Watch 424
continues.

SUMMARY...The severe weather threat continues for Watch 424, with
the greatest threat now shifting to south-central NY and
northeastern PA as outlined in the MCD graphic.

DISCUSSION...A cluster of thunderstorms continues to move south and
east over the area within a corridor of overlapping 1000-2000 J/kg
of MUCAPE and 50 kt of bulk 0-6 km vertical wind shear.  Thick
cirrus associated with convective outflow and a jet streak moving
over the area has stabilized the northern third of the Watch area,
leaving the greatest severe threat near and ahead of the ongoing
cluster of thunderstorms from Allegheny to Seneca Counties.

The greatest threat continues to be severe wind gusts associated
with the strongest outflows and rotation within transient supercell
structures, as observed earlier and presently in a path from Hamburg
to southern Steuben County. The brief tornado threat should continue
to remain localized to areas where surface winds locally back to a
south or south-southeast direction, as was observed earlier in the
day over southern Erie County, and has occurred recently at the
Addison mesonet site ahead of the rotating cell.

..Coniglio/Cohen.. 07/20/2017

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

ATTN...WFO...ALY...PHI...BGM...BUF...CTP...

LAT...LON   43327674 43197591 42907509 42397444 41977452 41507479
            41137544 41177615 41587725 42007785 42347818 42887784
            43327674




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