Subj : MESO: Mesoscale Discussion 1712
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Jul 18 2025 23:04:12

ACUS11 KWNS 182303
SWOMCD
SPC MCD 182303=20
MNZ000-SDZ000-190100-

Mesoscale Discussion 1712
NWS Storm Prediction Center Norman OK
0603 PM CDT Fri Jul 18 2025

Areas affected...Eastern South Dakota...southwest Minnesota

Concerning...Severe potential...Watch possible=20

Valid 182303Z - 190100Z

Probability of Watch Issuance...60 percent

SUMMARY...Initial supercells will be capable of large hail, severe
winds, and perhaps a tornado or two. Timing of widely scattered to
scattered storm development is not clear, but should occur within
the next few hours. Eventual upscale growth will lead to a greater
wind threat with time. A watch is possible as convective trends
warrant.

DISCUSSION...Cloud cover has remained across eastern South Dakota
this afternoon. This has hindered surface heating and several models
are not handling this very well. Several CAM solutions from earlier
today depicted storms would already be ongoing. Recent HRRR/RRFS
runs suggest a more reasonable, later start. With a storm now having
developed in northeast South Dakota, a gradual increase in storm
coverage is probable over the next few hours. The 18Z OAX sounding
showed a capping layer near 800 mb which likely extends northward to
some extent. A subtle increase in mid-level ascent and a modest
low-level jet this evening are the likely forcing mechanisms to help
erode the modest capping.

Given effective shear of 40-50 kts and MLCAPE of 1500-2000 J/kg,
initial supercells will be capable of large hail and severe wind
gusts. The increase in 850 mb flow this evening will enlarge
low-level hodographs, but the overall tornado threat is less clear
given the less than ideal low-level thermodyamic profiles.
Convection is then expected to grow upscale by mid/late evening.
Severe wind gusts would be the primary hazard after this occurs.

...Wendt/Hart.. 07/18/2025

....Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj=
g!-HGJHGpSnOHYVf6txUPA1A_unjDne1NQ6c4257U6USOTXbTeCI3a5MnXAk63AY9yq4MYq-8YY=
xq1L6MNVo3qE_MotTs$  for graphic product...

ATTN...WFO...MPX...FSD...ABR...

LAT...LON   43859803 44189886 44349885 44639833 45309716 45519637
            45219550 44849479 44759469 44599467 44049491 43729546
            43519637 43589736 43859803=20

MOST PROBABLE PEAK TORNADO INTENSITY...85-115 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN


=3D =3D =3D
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