Mesoscale Discussion 0458
NWS Storm Prediction Center Norman OK
1246 PM CDT Thu Apr 17 2025
Areas affected...parts of nwrn IA...adjacent sern SD...swrn into
cntrl MN
Concerning...Severe potential...Watch possible
Valid 171746Z - 172015Z
Probability of Watch Issuance...60 percent
SUMMARY...Strong to severe thunderstorm development, accompanied by
a risk for severe hail and wind, appears increasingly likely by the
2-4 PM CDT time frame. A severe weather watch seems probable,
though timing remains a little uncertain.
DISCUSSION...Low-level moisture return (characterized by surface dew
points increasing into the mid/upper 50s F) is ongoing in a narrow
corridor northeast of Norfolk NE, across and northeast of the
Redwood Falls MN vicinity. This is focused along modestly deep
surface troughing, south through east of an initial surface low
center now near Brookings SD, where it appears that further
insolation and low-level warm advection may contribute to
mixed-layer CAPE in excess of 1500 J/kg within the next few hours.
This instability axis remains capped by an initially warm, dry layer
between 850-500 mb, beneath large-scale mid/upper ridging. At upper
levels, it appears that flow may remain anticyclonic through
mid/late afternoon. However, models suggest that subtle mid-level
height falls, beneath increasingly difluent upper flow near the exit
region of a strong jet streak in the 300-250 layer, will be
accompanied sufficient large-scale forcing for ascent to erode the
mid-level inhibition. Based on various short-term model output, it
appears that this may support the initiation of boundary-layer based
thunderstorm development, perhaps as early as 19Z, with increasingly
likelihood through 21-22Z.
It appears that deep-layer shear will become conducive to organizing
convection, including a couple of supercells initially, posing a
risk for severe wind and hail.
..Kerr/Smith.. 04/17/2025
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MPX...DMX...FSD...
LAT...LON 45259496 45339379 44569317 42699537 43039671 44529554
45259496
MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
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