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