SPC MD 2180

SPC MD 2180


Mesoscale Discussion 2180
NWS Storm Prediction Center Norman OK
0937 AM CDT Sat Sep 23 2023

Areas affected…Northeast/East-Central NE…Northwest/West-Central

Concerning…Severe potential…Watch possible

Valid 231437Z – 231630Z

Probability of Watch Issuance…40 percent

SUMMARY…Isolated large hail and/or damaging gust are possible over
the next few hours across northeast/east-central Nebraska and
northwest/west-central Iowa.

DISCUSSION…Organized convective line continues to push
eastward/northeastward across northeast NE at around 30-35 kt. Based
on a recent surface analysis, this line is just to the northeast of
a surface low centered near GRI (in south-central NE). The warm
frontal zone associated with this low is fairly diffuse, but some
interaction between this warm front and the ongoing convective line
has likely contributed to stronger gusts reaching the surface. OFK
recently gusted to 53 kt and recent OAX radar imagery shows
strengthening inbound velocities in Colfax and Stanton Counties. The
downstream air mass is cool, moist, and modestly buoyant.

12Z OAX sounding sampled very steep mid-level lapse rates, supported
by 500 mb temperatures around -13 to -14 deg C. These conditions are
still in place, with a mesoanalysis estimating a pocket of 8 to 8.5
deg C 700 to 500 mb lapse rates ahead of the line. These lapse rates
are supporting modest buoyancy, with recent mesoanalysis estimating
MLCAPE around 1000 J/kg, most of which is above 700 mb. Strong
vertical shear is in place as well, and the overall expectation is
that the line will maintain its intensity for at least the next few
hours as it continues northeastward.

Low-level stable layer will likely limit the amount and strength of
the downdrafts reaching the surface. It is not entirely out of the
question for additional strengthening of this line, which could
intensify the rear-inflow jet enough for it to reach the surface.
However, that appears to be a low-probability scenario at this
point. Given the steep lapse rates, large hail appears possible
within this line as well. Overall severe coverage will likely remain
isolated, but convective trends will be monitored closely.

..Mosier/Guyer.. 09/23/2023

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


LAT…LON 42419744 42839701 42979554 42279499 41739498 41169568
41039734 42419744

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