ACUS11 KWNS 210201
SWOMCD
SPC MCD 210201
KSZ000-COZ000-210400-

Mesoscale Discussion 2320
NWS Storm Prediction Center Norman OK
0901 PM CDT Sun Sep 20 2026

Areas affected...portions of eastern Colorado and western Kansas

Concerning...Severe Thunderstorm Watch 673...

Valid 210201Z - 210400Z

The severe weather threat for Severe Thunderstorm Watch 673
continues.

SUMMARY...The initial severe threat has come to an end across the
area. However, the region is being monitored for additional
thunderstorm development, such as that suggested by latest numerical
models. A new watch or the extension in space or time of the
existing watch may become necessary before Severe Thunderstorm Watch
#673 expires at 9:00 PM MDT.

DISCUSSION...The long-track supercell that moved southeast across
the Plains of Colorado this evening has dissipated bringing an end
to the initial severe threat. This evolution was handled very well
by high-resolution guidance.

Attention is now focused on areas to the north where high-resolution
guidance is indicating additional thunderstorm development is likely
in the next 60-90 minutes. This scenario seems plausible given the
persistent moist, easterly flow into the foothills expected this
evening. Initial development may already be underway across portions
of the Denver and Fort Collins metro areas based on MRMS CREF
imagery.

The overall environment will remain conducive for supercells with
MUCAPE values in excess of 1000 J/kg, especially south and east of
the Denver metro. Effective-layer shear remains more than sufficient
for updraft rotation, with shear values between 40-55 knots across
the Colorado Plains. Large hail and strong thunderstorm outflows
will be possible with any sustained supercell this evening and
overnight.

Severe Thunderstorm Watch #673 is scheduled to expire at 9 PM MDT.
The area will continue to be monitored for additional thunderstorm
initiation and intensification. If it becomes apparent that
additional severe thunderstorms are probable this evening, the
region will either need a new Severe Thunderstorm Watch or an
extension of Severe Thunderstorm Watch #673. A decision will be made
regarding the need for a new watch, an extension of the existing
watch, or cancellation of the existing watch within the hour.

..Marsh.. 09/21/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fjg!9QWcc_41h-Yx50U4pji1EUGl59LOHQ9W5krpFovvguNkAEpoIVR7Q3yzoCoxch9CFMC103B-W_ZjH96-JsT1M51Kl1c$ for graphic product...

ATTN...WFO...DDC...GLD...PUB...BOU...

LAT...LON 37620267 38560409 39030494 39620532 40110518 40290471
40250355 40110245 39960193 39750156 39360106 38750079
37890098 37630143 37620267

MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN


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--- scorpsmtpd
* Origin: capitolcityonline.net * KY, USA (1:2320/107)