000
ACUS11 KWNS 182359
SWOMCD
SPC MCD 182358
IAZ000-MNZ000-190100-

Mesoscale Discussion 1526
NWS Storm Prediction Center Norman OK
0658 PM CDT Fri Aug 18 2017

Areas affected...Portions of southern MN and northern/central IA

Concerning...Severe Thunderstorm Watch 456...

Valid 182358Z - 190100Z

The severe weather threat for Severe Thunderstorm Watch 456
continues.

SUMMARY...A risk for large hail and strong to locally damaging winds
should spread southeastward across WW 456 this evening.

DISCUSSION...Multiple instances of marginally severe hail and
estimated severe winds have occurred over the past several hours
across southwestern MN in association with a small cluster of
thunderstorms, and a MCV appears to have formed recently on the
northern extent of the cluster. This convection is occurring beneath
an upper trough and in the presence of seasonably cold mid-level
temperatures (around -12 to -14 degrees C at 500 mb). The ongoing
cluster should continue to pose a threat for strong to damaging wind
as it moves southeastward along an instability gradient noted on 23Z
RAP mesoanalysis into northern/central IA over the next several
hours. Strengthening west-northwesterly winds with height noted on
area VWPs and RAP forecast soundings are supporting 30-40 kt of
effective bulk shear and continued storm organization. In addition
to the convective wind threat, isolated large hail may also occur
with embedded supercell structures within the cluster of storms.

..Gleason.. 08/18/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...MPX...DMX...FSD...

LAT...LON   44099640 44309589 44719545 44189340 43579308 42929306
            42309238 41179246 41209476 41589503 41879503 42319537
            42949584 44099640