U.S. Severe Weather Forecast (Convective Outlook)

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 

.Jewell.. 09/20/2018