U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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acus02 kwns 210417 
swody2 
Storm Prediction Center ac 210416 


Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1116 PM CDT sun may 20 2018 


Valid 221200z - 231200z 


..there is a marginal risk of severe thunderstorms across parts of 
the High Plains and Ohio Valley... 


... 
Isolated strong thunderstorms are expected across portions of the 
High Plains from West Texas into southeast Montana. A few strong 
storms may also develop across the Ohio Valley. 


..High Plains... 


Strong mid-level jet will round the base of Southern California trough 
during the day1 period before ejecting into The Four Corners region 
and weakening Tuesday. As stronger flow aloft translates into Colorado/nm 
downstream upper ridge should be nudged east and the Prospect for 
scattered deep convection will increase in the Lee of The Rockies 
from West Texas into southeast Montana. Even so, deep-layer shear will be 
seasonally weak but likely adequate for the maintenance of a few 
robust updrafts, especially given the expected steep lapse rates. 
Latest guidance continues to suggest an early-day disturbance 
(possibly related to late day1 convection) will eject into West Texas 
and convection may be ongoing at the beginning of the period. 
Renewed development may take place if sufficient heating can 
materialize in the wake of this activity. 


Farther north, weak large-scale forcing for ascent should spread 
into southwest Wyoming during the afternoon which should contribute to an 
easterly boundary-layer component across the plains. This should aid 
scattered thunderstorm development that could grow upscale into the 
Black Hills region after dark, especially as low level jet increases across 
western NE. 




..OH valley... 


Mid-level heights are expected to fall across the lower Great Lakes 
region during the day2 period along the southwestern flank of a 
trough that will dig toward New England. Associated surface front 
should progress into western Ohio/southern in by 18z and a corridor of 
pre-frontal boundary-layer heating is expected to contribute to 
instability that will support a few robust thunderstorms. This 
activity will be strongly diurnal in nature and gusty winds and 
perhaps marginally severe hail are the primary threats. 


..maximum risk by hazard... 
Tornado: 2% - marginal 
wind: 5% - marginal 
hail: 5% - marginal 


.Darrow.. 05/21/2018 


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