U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 281638 
Storm Prediction Center ac 281636 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1136 am CDT Wed Jun 28 2017 

Valid 281630z - 291200z 

..there is an enhanced risk of severe thunderstorms from far 
southeast NE into northern Illinois/southern WI... 

..there is a slight risk of severe thunderstorms from the Central 
High plains to the middle/upper MS River Valley... 

..there is a marginal risk of severe thunderstorms from the 
northern rockies to the Great Lakes... 

Severe thunderstorms with large hail, wind damage and a few 
tornadoes are expected across the middle Missouri Valley 
northeastward into the middle and upper Mississippi Valley. Other 
more isolated severe storms may occur in the Central Plains and 
northern rockies. 

..middle MO River Valley to middle/upper MS River Valley... 
Related to last night's MCS, scattered showers/thunderstorms and 
related prevalent cloud cover continue to progress eastward across 
eastern portions of Minnesota/Iowa into WI/northern Illinois late this morning. 
This is just ahead of an eastward-moving shortwave trough over Minnesota, 
with a few other convectively related disturbances/mcvs noted 
farther south, embedded within a belt of moderately strong mid-level 
westerlies. A surface low analyzed at 15z near the Minnesota/SD/ND border 
vicinity will continue to spread eastward across central Minnesota toward 
northern WI and the Western Upper Peninsula of Michigan through this 
evening, while a cold front spreads southeastward across MN/IA/WI. 

Near and ahead of this cold front, low-level moistening and general 
air mass recovery will steadily occur this afternoon in the wake of 
the lingering early-day precipitation and cloud cover, particularly 
given relatively steep mid-level lapse rates and ample low-level 
moisture sampled in source-region 12z observed soundings from Omaha 
NE and Topeka Kansas. Increasingly prevalent mid/upper 60s f surface 
dewpoints will support upwards of 2000-3000 j/kg MLCAPE particularly 
from southeast NE/northern Kansas into IA, with somewhat more modest 
(and uncertain) degree of pre-frontal destabilization farther north 
into WI/eastern Minnesota owing to early-day cloud cover and some 
regenerative precipitation this morning across northern Iowa. 

While the aforementioned cloud cover/precipitation lingering into 
midday still casts some uncertainty, it seems most likely that 
surface-based storms will redevelop just ahead of the front 
semi-focused along outflow and zones of differential heating across 
southern/eastern Iowa and nearby far northern MO and northern Illinois. 
Pending adequate destabilization, other potentially severe 
development may occur by late afternoon in closer proximity to the 
surface low/front from far eastern Minnesota into western/central WI. 
Around 40-45 kt of effective shear will support some initial 
supercells capable of large hail, with a few tornadoes possible as 
well given the strength of 2-3 km above ground level southwesterly winds and 
related 150-250 m2/s2 0-1 km srh (with prospective surface-based 
convection). Eastward-moving clusters should evolve by evening with 
a related increase in damaging wind potential particularly across 
southern Iowa/northern MO into northern Illinois. 

..co/Wyoming Front Range to northern Kansas/southern NE... 
Within a modestly moist environment, widely scattered thunderstorms 
should develop and spread eastward across the region by late 
afternoon into evening, including some potential for at least 
small-scale mesoscale convective system development this evening. Modest buoyancy and ample 
vertical shear will support the possibility of sporadic large hail 
and locally damaging winds into this evening. 

..northern rockies... 
Ahead of an amplifying shortwave trough over the northern 
intermountain region, modest moisture and a strengthening belt of 
west-southwesterly mid-level winds should contribute to the 
possibility of isolated strong to severe storms spanning parts of 
Wyoming/southern Montana and eastern Idaho/northern Utah. 

.Guyer/Dean.. 06/28/2017 


Mesoscale Discussion

acus11 kwns 280434 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 280433 

Mesoscale discussion 1167 
National Weather Service Storm Prediction Center Norman OK 
1133 PM CDT Tue Jun 27 2017 

Areas affected...eastern NE and western Iowa 

Concerning...severe potential...watch unlikely 

Valid 280433z - 280530z 

Probability of watch issuance...20 percent 

Summary...a local watch extension-in-area could be utilized to 
address some remaining risk for severe gusts in the eastern 
NE/western Iowa region but the overall severe risk appears to be 
decreasing. A new Severe Thunderstorm Watch will likely not be 
issued to the east of Severe Thunderstorm Watch 374. 

Discussion...radar mosaic at 0430z shows a mature squall line from 
Antelope County south-southwestward into Kearney County with east 
movement of the line of 35-40 kt. Grand Island recently 
observed/measured a gust of 54 kt at 0421z. The 00z oax raob showed 
a 7.9 degrees c/km 700-500 mb lapse rate and the koax VAD shows 50+ 
kt southerly flow in the 925-850 mb layer as of 0430,z with a strong 
low level jet. However, despite the eastward migration of a shortwave trough 
into the middle MO valley late tonight, the 00z oax raob exhibited 
large mlcinh with over -200 j/kg noted. While strong/localized 
severe gusts may continue east of the eastern edge of the Severe 
Thunderstorm Watch, the severe risk may lessen as the squall line 
moves into an environment less supportive for intense downdrafts to 
reach the surface. 

.Smith/Hart.. 06/28/2017 

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


Latitude...Lon 42229664 42239528 40409519 40489685 42229664