U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 160559 
Storm Prediction Center ac 160558 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1258 am CDT Mon Jul 16 2018 

Valid 161200z - 171200z 

..there is a slight risk of severe thunderstorms across parts of 
Wyoming into the central/northern High Plains area... 

Locally severe storms are expected this afternoon and tonight from 
portions of the intermountain west into the central/northern High 
Plains area, where potential for damaging winds and possibly hail 
will exist. A marginal threat for locally damaging winds is also 
apparent across portions of the Great Lakes area. 

Modest flow aloft will continue to prevail over the southern half of 
the U.S., Where upper ridging will persist. Meanwhile farther 
north, a short-wave trough crossing the intermountain west and a 
second/larger trough expanding across eastern Canada and the 
northeast quarter of the U.S. Will allow modestly stronger westerly 
flow to evolve across portions of the northern half of the country. 

At the surface, a cold front is forecast to move slowly east across 
the Great Lakes region, while sagging southeastward across the 
Midwest/Ohio Valley and southward across the Ozarks and Oklahoma 
through the daylight hours. By Tuesday morning, the front should 
extend in an arc from central Quebec southwest across the lower 
Great Lakes and upper Ohio Valley into the mid south, westward 
across Arkansas and Oklahoma, and then northwestward across the High 

..parts of the Idaho vicinity eastward across Wyoming into western 
Nebraska and surrounding areas... 
as a mid-level short-wave trough moves gradually eastward out of the 
northwestern U.S. Into the Idaho/Wyoming vicinity, modest mid-level 
cooling atop a diurnally warming boundary layer will result in 
moderate afternoon destabilization. Instability will become most 
pronounced across central/eastern Wyoming and into the High Plains, 
where a more moist boundary layer is anticipated in the vicinity of 
the northwest-to-southeast frontal zone. 

Storm development is expected during the afternoon aided by 
increasing large-scale ascent, with a few stronger cells possibly 
evolving as far west as the southern Idaho/northwest Nevada region, 
but likely more numerous farther east into Wyoming. With 
enhanced/30-40 kt mid-level westerlies spreading across the area 
atop a low-level easterly component, shear sufficient for 
organized/possibly rotating storms should evolve. As such, 
potential for locally damaging winds and possibly hail will likely 
accompany stronger cells. 

As a southerly low-level jet evolves over the High Plains during the 
evening, most cam output suggests varying degrees of 
congealing/upscale growth of convection, possibly resulting in an 
mesoscale convective system shifting east-southeast out of eastern Wyoming into the 
southwest South Dakota/western Nebraska and possibly northeast 
Colorado area through the evening and into the overnight hours. 
Presuming this evolution manifests, potential for damaging winds may 
extend into the overnight hours. 

..the eastern upper Great Lakes and lower Great Lakes area... 
Modest destabilization ahead of the slowly advancing cold front will 
support considerable shower/thunderstorm development across parts of 
the eastern upper Great Lakes/Midwest region during the afternoon. 
Though stronger mid-level cyclonic flow will remain farther north 
across Ontario and Quebec, 25 to 30 kt mid-level westerlies should 
overspread the warm sector north of the Ohio River valley, 
supporting potential for locally stronger/organized storms. With 
both cape and shear expected to remain sub-optimal for a more 
widespread severe risk, will maintain only marginal/5% severe 
probability across areas in the vicinity of the Great Lakes, mainly 
for gusty/locally damaging wind potential. Storms -- and limited 
wind potential -- will spread eastward with time in conjunction with 
the slow frontal advance, affecting portions of Pennsylvania and New 
York through the evening and possibly into the overnight hours. 

.Goss/squitieri.. 07/16/2018 


Mesoscale Discussion

acus11 kwns 150130 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 150130 

Mesoscale discussion 1057 
National Weather Service Storm Prediction Center Norman OK 
0830 PM CDT Sat Jul 14 2018 

Areas affected...northeastern North Dakota into far northwestern 

Concerning...Severe Thunderstorm Watch 277... 

Valid 150130z - 150300z 

The severe weather threat for Severe Thunderstorm Watch 277 

Summary...storms, mainly across northeastern North Dakota, may 
continue to pose some severe weather potential into late evening 
before diminishing. An additional weather watch now appears 

Discussion...forcing for ascent and shear associated with the 
vigorous short wave impulse progressing east of the Canadian 
prairies has provided support for the evolution of a broken squall 
line across southern Manitoba into the vicinity of international 
border area. This includes an evolving cluster of storms straddling 
the eastern North Dakota/Manitoba border, and additional cells as 
far south as areas near/west of Devils Lake. Pre-frontal 
instability, to the east of the axis of stronger daytime heating, 
appears sufficient to maintain this activity eastward across the 
remainder of northeastern North Dakota (mainly northwest through 
north of grand forks) through the 03-5z time frame. This will 
probably be accompanied by at least some risk for strong surface 
gusts before activity diminishes as it begins to ingest drier more 
stable air to the east. 

Farther south, isolated ongoing vigorous thunderstorms to the south 
of Bismarck, seems likely to diminish within the next hour or two, 
in the presence of waning boundary layer instability and weaker 
shear/forcing for ascent. 

.Kerr.. 07/15/2018 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 49449651 48969660 48439763 47889940 48259994 48999898 
49569781 49449651