U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 181731 
Storm Prediction Center ac 181730 

Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1230 PM CDT Wed Jul 18 2018 

Valid 191200z - 201200z 

..there is a slight risk of severe thunderstorms for portions of 
eastern Iowa...northeast MO...western Illinois... 

Severe thunderstorms will be possible on Thursday across parts of 
the Mississippi Valley and Central Plains. 

A seasonably strong shortwave trough and associated surface low are 
expected to progress southeastward from the eastern Dakotas into the 
upper Midwest on Thursday. A weak mid/upper-level trough will remain 
in place over portions of the Ohio Valley and southeast, with a 
surface boundary expected to arc from portions of the southeast 
northwestward into the upper Midwest surface low. 

..mid-upper Mississippi Valley... 
The potential for one or more early day thunderstorm clusters 
complicates the forecast scenario on Thursday. Any such cluster may 
present a localized severe wind risk early in the day, especially 
across portions of MO. For areas that can recover from any early-day 
convection, modest heating amidst rich low-level moisture will allow 
moderate instability to develop, with MLCAPE of 1500-2500 j/kg 
possible to the south and east of the shortwave trough and 
associated surface low. The strongest flow aloft will be within the 
largely subsident region southwest of the trough, so storm coverage 
may be quite limited where the strongest shear resides. However, 
sufficient midlevel shear across portions of central and eastern 
Iowa/northeast MO/western Illinois will support the potential for organized 
storms, including a few supercells or organized clusters. Some 
threat of large hail, damaging wind, and perhaps a tornado or two 
will exist in this area. 

Further south down the Mississippi Valley, a more conditional severe 
risk will be present. Any early day thunderstorm cluster that 
survives may rejuvenate across portions of southern MO/northern Arkansas 
during the afternoon. Later-day storms that initiate further north 
may also merge into a cluster that moves southeastward into this 
region. Some damaging wind risk would be possible in either 
scenario, with some marginal hail risk associated with any more 
discrete convection that may develop. 

..northeast Kansas...Northwest MO...southeast NE... 
large-scale subsidence should limit convective coverage during the 
day across portions of northern KS, northwest MO, and southeast NE, 
where an otherwise quite favorable environment of strong instability 
(mlcape of 2500-3500 j/kg) and moderate-to-strong effective shear 
(40-50 kt) will reside during the afternoon and evening. However, a 
conditional risk for isolated supercell development will exist along 
a southeastward-moving surface trough. In addition, several href 
members and some larger-scale guidance show potential for elevated 
thunderstorm development late Thursday night, possibly related to 
another lobe of ascent and associated midlevel moistening. Any such 
activity would present a risk of large hail and perhaps locally 
damaging wind. The marginal risk has been expanded into these areas 
to cover these scenarios. 

..southwest Kansas... 
While large-scale ascent will generally be weak across this region, 
strong heating/mixing may support the development of isolated 
thunderstorms across southwest Kansas on Thursday afternoon. Weak 
low-level flow will likely result in outflow-dominant storms, but 
midlevel northwesterly flow will be sufficient for some storm 
organization, with a corresponding risk of severe wind gusts and 
perhaps hail. 

..maximum risk by hazard... 
Tornado: 2% - marginal 
wind: 15% - slight 
hail: 15% - slight 

.Dean/dial.. 07/18/2018