U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 161955 
Storm Prediction Center ac 161953 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0253 PM CDT Mon Jul 16 2018 

Valid 162000z - 171200z 

..there is a slight risk of severe thunderstorms across portions of 
Wyoming and the Central High plains... 

Scattered severe storms are expected across parts of Wyoming into 
the Central High plains and Black Hills regions from late afternoon 
into tonight. Large hail and strong to severe wind gusts should be 
the main hazards. 

Only minor changes have been made to the previous outlook. The 
northern portion of the marginal risk area across northern lower Michigan 
has been trimmed to account for the progression of the primary 
convective band. See mesoscale discussion 1058 for additional details regarding this 
region. The marginal risk area across northeast OK/southeast Kansas into 
the Ozarks has been adjusted to account for ongoing convective 
trends. See mesoscale discussion 1059 for more information regarding this area. 

Elsewhere, the previous forecast, including the slight risk over Wyoming 
into the Central High plains, remains unchanged. See the previous 
discussion below for more details. 

.Dean/Peters.. 07/16/2018 

Previous discussion... /issued 1130 am CDT Mon Jul 16 2018/ 

..intermountain West/Wyoming to Central High plans... 
A perturbation embedded within a low-amplitude shortwave trough over 
the Pacific northwest will move east from southern Idaho towards the 
Central High plains through this evening with a subtle disturbance 
or two preceding this more discernible mid-level impulse. Related 
weak large-scale ascent in conjunction with a moist air mass, with 
prevalent 60s f surface dewpoints across the High Plains, will lead 
to widely scattered storm development by mid/late afternoon. Such 
development is likely to initially occur over the intermountain west 
to interior Wyoming, and potentially as far east as the Black Hills 
vicinity and southwest/south-central South Dakota by late afternoon. 

Semi-elongated hodographs (aided by 40+ kt high-level winds at 7+ km 
agl) are anticipated to overlap with the eastern periphery of the 
elevated mixed-layer characterized by steep mid-level lapse rates. A 
moderately buoyant air mass is expected mainly from east-central/far 
southeast Wyoming into southern South Dakota and much of 
west/central Nebraska. The setup should favor a few discrete 
supercells, the most sustained of which may be those that move 
south-southeast from western/southern South Dakota into the Nebraska Panhandle 
and/or northern Nebraska. Large hail along with isolated severe wind 
gusts should be the primary hazards. 

During the evening, this activity will likely grow upscale as 
moderate low-level southerlies strengthen to around 30 kt over the 
Central High plains. This should result in a 
south/southeastward-propagating cluster with mainly a strong to 
isolated severe wind risk in western Nebraska before weakening 
overnight in the northwest Kansas/northeast Colorado vicinity. 

..eastern Great Lakes... 
In advance of an eastward-moving front, scattered thunderstorm 
development is expected this afternoon across lower Michigan to the 
Lee of lakes Erie/Ontario. Convergence is generally weak and 
stronger mid-level westerlies will lag behind the surface cold 
front, although brief overlap of the warm sector with modest 
effective shear values may support some sustained/briefly organized 
storms. With weak mid-level lapse rates and unfavorable nocturnal 
timing of frontal impingement east of the lower lakes, the overall 
setup is expected to only yield localized strong gusts capable of 
tree damage. 

..southeast Kansas/northeast Oklahoma to the Ozarks... 
Small-scale cold pools and zones of differential heating will likely 
influence additional storm development and intensification across 
the region within a very moist and diurnally destabilizing boundary 
layer. Given the degree of heating/moisture and resultant buoyancy, 
it is conceivable that a couple of the wet microbursts could produce 
localized wind damage this afternoon. 


Mesoscale Discussion

acus11 kwns 162052 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 162052 

Mesoscale discussion 1061 
National Weather Service Storm Prediction Center Norman OK 
0352 PM CDT Mon Jul 16 2018 

Areas affected...parts of south-central and southwestern South 
Dakota...Nebraska Panhandle into north-central Nebraska 

Concerning...severe potential...watch possible 

Valid 162052z - 162245z 

Probability of watch issuance...60 percent 

Summary...cumulus clouds have become increasingly agitated within 
the discussion area. A conditional threat exists for large hail and 
severe wind gusts, with storm initiation/evolution uncertain. 
Convective trends will be monitored for a possible ww issuance later 
this afternoon. 

Discussion...cumulus clouds across south-central and southwestern 
South Dakota along and near a Theta-east gradient and over the Black 
Hills. Afternoon heating across the area, with low- to mid-60s 
dewpoints in place, has lead to MLCAPE values of 1500-2500 j/kg. 
With continued heating and approaching mid-level ascent, some cams 
develop a cluster of storms in South Dakota and move them 
south/southeastward into Nebraska. However, given upstream mid-level 
ridging, uncertainty exists with regard to if storms will initiate 
and how much coverage there will be. The greatest threat for severe 
hail will be with any initial storms, should they develop, in South 
Dakota as effective bulk shear of 30-40 kts will favor storm 
organization. Any storms that do develop will also pose a risk of 
severe wind gusts given the steep low-level lapse rates and high 
surface temperature/dewpoint spreads. 

Additional storms may also move out of Wyoming into southwest South 
Dakota and the Nebraska Panhandle later this evening. These storms 
will primarily pose a severe wind gust risk given the expected 
linear/cluster storm Mode. Given the overall uncertainty in the 
exact evolution of this event, convective trends will continue to be 
monitored for the possible issuance of a ww. 

.Wendt/guyer.. 07/16/2018 

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


Latitude...Lon 44590375 44870285 44770180 44640107 44350068 43800030 
42750006 41740010 40990137 41070214 41060327 42050367 
43460386 44590375