U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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acus03 kwns 200727 
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Storm Prediction Center ac 200726 


Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0226 am CDT Fri Jul 20 2018 


Valid 221200z - 231200z 


..there is a marginal risk of severe thunderstorms Sunday afternoon 
and evening across parts of the eastern Gulf and South Atlantic 
coast region...as well as portions of the northern plains... 


... 
Strong thunderstorms may impact parts of the southeast and northern 
plains Sunday afternoon and evening, accompanied by at least some 
risk for severe weather. 


... 
Models indicate that a subtropical high will remain prominent across 
much of the southwestern and south central U.S. During this period, 
but the center of highest mid-level heights is forecast to shift 
westward/northwestward from the southern High Plains into the 
southern rockies. It appears that troughing within the mid-latitude 
westerlies to the north of this feature will broaden, with one or 
two embedded impulses forecast to progress across the 
Saskatchewan/Manitoba/northwest Ontario vicinity. This likely will 
be accompanied by the southeastward progression of a weak surface 
front through the northern U.S. Plains. 


At the same time, near/east of the Mississippi Valley through the 
Atlantic Seaboard, upper troughing is forecast to linger between the 
aforementioned subtropical high and another over the western 
Atlantic. Some southward elongation of the trough through the 
eastern Gulf Coast may occur, in response to another significant 
embedded digging perturbation. Seasonably high moisture content 
characterized by precipitable water of 2+ inches may linger near 
southern and mid Atlantic coastal areas, while spreading northward 
through coastal New England. At the same time, this moisture may 
become increasingly suppressed southward into areas near/south of 
the eastern Gulf Coast, though fairly moist air will probably linger 
beneath the upper trough across the lower Ohio Valley into western 
slopes of the Appalachians. 


... 
Stronger surface heating coinciding with higher lingering boundary 
layer moisture, supportive of the development of moderate to large 
cape, appears likely to become increasingly confined to near the 
base of the elongating upper trough, across portions of northern 
Florida into the Carolinas. This is where mid-level forcing for 
ascent ahead of the digging short wave impulse, coupled with 
momentum/shear associated with 30-40+ kt flow in the 850-500 mb 
layer, could contribute to an environment conducive to organized 
strong to severe storm development. Uncertain sub-synoptic scale 
developments through this time period, though, preclude anything 
more than 5 percent severe probabilities at the present time. 


..northern plains... 
Stronger mid-level forcing for ascent appears likely to remain 
generally north of the international border through this period. 
This contributes to uncertainty concerning the extent of potential 
convective coverage ahead of the southeastward advancing cold front. 
However, instability will probably be sufficient to contribute to at 
least some severe weather potential with storms that do form Sunday 
afternoon and evening. 


.Kerr.. 07/20/2018 


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