U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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acus02 kwns 221728 
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Storm Prediction Center ac 221727 


Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1227 PM CDT Friday Aug 22 2014 


Valid 231200z - 241200z 


..there is a slight risk of severe thunderstorms across eastern South Dakota...Southeastern ND and western 
Minnesota... 


... 
Scattered thunderstorms can be expected across parts of the northern 
plains and the upper Mississippi Valley on Saturday. The strongest 
storms may produce some hail...gusty winds...and a tornado threat. 


... 
A shortwave trough moving into the northern intermountain west...Great 
Basin and northern rockies today will shift eastward then northeastward during day 2 
with some deepening of this system as it takes on a negative tilt 
tracking toward the northern plains. A speed maximum rounding the base of 
the western trough today may phase with a shortwave trough...currently 
moving into The Four Corners region...as these features track north-northeastward 
across the Dakotas Saturday afternoon and through the northern Red River 
valley to south central Canada Saturday night. 


Concurrent with this evolution...an area of low pressure will track 
from northwestern Kansas/southwestern Nebraska at 23/12z through the northern plains to in 
vicinity of the northestern ND/Manitoba border. A warm front approaching 
the middle MO River Valley early Saturday morning will continue to 
advance poleward and should extend from central-eastern South Dakota into 
southwestern-south central Minnesota Saturday afternoon. Strong low-level warm air advection 
expected through day 2 along and north of the warm front and upward 
vertical motion attendant to middle-level impulses tracking northward through 
the northern plains will support an extended period of showers/thunderstorms north 
and northwest of the warm sector. 


..portions of the northern plains... 
Given some uncertainty in the motion of the surface low through South Dakota 
Saturday afternoon and its affect on the placement of the warm 
sector through peak heating...there is potential that more of eastern South Dakota 
will need to be in the slight risk. Despite some differences in the 
location of the surface low by 24/00z /00z European model (ecmwf) being the farthest 
south across south central SD/...models tend to agree with new 
convective development in eastern South Dakota near the southern periphery of the 
ongoing aforementioned area of warm air advection showers/tstms. And...new 
development may occur southward into north central-northestern Nebraska late Saturday 
afternoon...especially as a cold front advances eastward toward this 
region. These factors combined with the juxtaposition of moderate 
instability within the warm sector and effective bulk shear of 35-40 
knots suggest the southward expansion of the slight risk is warranted to 
include...at least...more of east central South Dakota. Given favorable deep 
layer shear and low-level shear for organized storms...including 
supercells...all severe hazards will be possible. The track of the 
shortwave trough and surface low into eastern ND Saturday night suggests 
strong-severe storms will move north-northeast toward the northern Red River valley 
and west-central/northwestern Minnesota. 


.Peters.. 08/22/2014