U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 180731 


Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0231 am CDT Thursday Sep 18 2014 


Valid 201200z - 211200z 


..no severe thunderstorm areas forecast... 


... 
thunderstorm development is expected on Saturday from the 
intermountain west eastward to the Great Plains and northeastward to 
the Great Lakes region. Some marginally severe wind gusts and hail 
will be possible with the stronger thunderstorms from the Central 
Plains northeastward to lower Michigan. Other storms are expected to 
develop across parts of the Gulf Coast states and along southern 
parts of the Atlantic Seaboard. 


..cntrl plains/middle to upper MS valley/Great Lakes... 
A low-amplitude upper-level trough is forecast to amplify across the 
upper MS valley on Saturday as a shortwave trough moves into the 
base of the larger-scale trough. At the surface...a cold front is 
forecast to advance southeastward across the Central Plains and upper MS 
valley. Ahead of the front...surface dewpoints should be in the middle to 
upper 60s f and moderate instability should be in place by late 
afternoon. Surface heating and increasing low-level convergence along 
the front should result in thunderstorm initiation by late 
afternoon. 


Forecast soundings at 00z/Sunday for Chicago Illinois and Alpena Michigan show 
0-6 shear of 45 to 50 knots and steep low-level lapse rates. 
However...model forecasts are in disagreement concerning the amount 
of instability that will be present. If moderate instability can 
develop as some models suggest...then a wind damage and hail threat 
would be possible late Saturday afternoon. Further to the southwest 
from NE Kansas into southeast Iowa...deep-layer shear is forecast to be less than 
in the Great Lakes region. In spite of this...stronger instability 
and higher surface dewpoints could help compensate for the weakness in 
shear...making a marginal wind damage threat possible as well. 


.Broyles.. 09/18/2014