414
ACUS11 KWNS 221555
SWOMCD
SPC MCD 221555
NYZ000-PAZ000-221830-

Mesoscale Discussion 1548
NWS Storm Prediction Center Norman OK
1055 AM CDT Tue Aug 22 2017

Areas affected...Portions of NY and northern PA

Concerning...Severe potential...Tornado Watch likely

Valid 221555Z - 221830Z

Probability of Watch Issuance...95 percent

SUMMARY...The risk for severe thunderstorms with damaging winds and
tornadoes is increasing, and the severe risk will continue through
the afternoon. The issuance of a Tornado Watch will be forthcoming
within the next couple of hours.

DISCUSSION...Large-scale forcing for ascent continues atop a
relatively moist boundary layer characterized by upper 60s to lower
70s surface dewpoints. Pockets of at least modest insolation will
continue to enhance buoyancy, with MLCAPE forecast to increase to
1000-1500 J/kg ahead of a pre-frontal trough/effective boundary
crossing the Great Lakes region. Thunderstorms will continue to
increase in coverage and intensity from western NY to western PA and
spread eastward and northeastward through the afternoon, amidst weak
capping. The presence of 30-40 kt of effective shear accompanying a
mid-level speed maximum will promote organized convective
structures, including quasi-linear segments and perhaps a few
transient supercells. Moderate low-level shear in the warm sector
associated with a low-level jet, enhanced by a trough-related deep
cyclone north of the area, will support some tornado risk with cells
and with meso-vortices embedded in lines, given 150-300 m2/s2 of
effective SRH. Otherwise, damaging wind gusts will be likely --
enhanced with small, line-accompanying rear-inflow jets. A Tornado
Watch will be issued.

..Cohen/Grams.. 08/22/2017

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

ATTN...WFO...BTV...ALY...BGM...BUF...CTP...

LAT...LON   41977890 42457876 43497729 44267593 44987461 44337377
            42617468 41507582 41207677 41187778 41497853 41977890