- Day Three
acus02 kwns 201718
Storm Prediction Center ac 201717
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1217 PM CDT Thu Sep 20 2018
Valid 211200z - 221200z
..there is a slight risk of severe thunderstorms across much of
Ohio...Pennsylvania...New York and Vermont...
Scattered thunderstorms capable of damaging wind gusts may affect
the Ohio Valley into parts of the northeast on Friday.
An upper high will remain situated over the mid Atlantic, but
heights will lower across the northeast as a shortwave trough moves
out of the Great Lakes during the day. Despite height falls aloft,
midlevel temperatures will be quite warm, and will limit
instability, especially across New England where surface
temperatures will be cool. A low will pivot from eastern Ontario
across Quebec, with a cold front extending from southwest Ontario
into the Ohio Valley by 21z. The main push with this front will
clear New England overnight, reaching coastal areas by 12z Saturday.
Immediately ahead of the front, a moist air mass with mid to upper
60s f dewpoints will exist, with the moist axis from the Ohio Valley
into western New York by afternoon. The combination of sufficient
instability and southwesterly 850 mb winds of 40-50 kt will likely
result in thunderstorms capable of locally damaging wind gusts in
association with the cold front, mainly during the day, with a
lessening threat overnight and with eastward extent.
..Ohio Valley into the northeast...
Storms are expected to form along the front by midday, from
southeast lower Michigan into Indiana, and will then develop
eastward across Ohio, Pennsylvania, and New York. The greatest risk
of damaging wind gusts will be coincident with the instability axis
which will be from the Ohio River into western Pennsylvania and New
York during the afternoon. A storm or two may acquire rotation as
well, from northwest Pennsylvania into western New York where
low-level shear will be favorable coincident with the stronger
While the front will continue east during the evening and overnight,
the threat of severe weather should decrease owing to very little
instability. Winds just off the surface will remain strong with 50
kt 850 mb flow, however, it is likely to be decoupled from the
near-surface layer, with only weak downdraft potential.
..maximum risk by hazard...
Tornado: 2% - marginal
wind: 15% - slight
hail: <5% - none