Mesoscale Discussion 1765

Issued

Sep 17, 2021, 12:53 AM CDT (05:53 UTC)

Expired

Sep 17, 2021, 2:00 AM CDT

In force

67 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The Minneapolis radar (KMPX), 103 km from the middle of the area, began a volume at 05:54 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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508 
ACUS11 KWNS 170553
SWOMCD
SPC MCD 170553 
MNZ000-IAZ000-170700-

Mesoscale Discussion 1765
NWS Storm Prediction Center Norman OK
1253 AM CDT Fri Sep 17 2021

Areas affected...southern MN...northwest IA

Concerning...Severe potential...Watch possible 

Valid 170553Z - 170700Z

Probability of Watch Issuance...40 percent

SUMMARY...Strong to locally severe gusts are possible as a squall
line moves east across southern MN.

DISCUSSION...Latest surface mesoanalysis places a pre-frontal
boundary oriented from southwest MN northeastward into parts of
central MN ahead of a squall line advancing east.  The surface wind
shift will probably continue to serve as a focus area for the
northern periphery of stronger outflow winds.  South of the
boundary, surface temperatures are warmer with low-mid 70s observed.
The Sioux Falls, SD 88D VAD showed a strong southwesterly LLJ this
evening (50+ kt) beneath a weakness in flow evident in the hodograph
in the 3-6 km AGL layer, surmounted by stronger flow above (50-65 kt
in the 6-9 km layer).  This wind profile undoubtedly favors a squall
line mode.  It appears the orientation of the squall line is at
least marginally favorable with respect to the mean flow in the 1-6
km layer.  So despite appreciable convective inhibition from a
slow-to-cool boundary layer, the strength of the wind field may
continue to enable localized severe gusts with the squall line.  A
plethora of surface observations during the past hour seem support
this notion (e.g., KFSD, KPQN, KBKX) with gusts ranging mainly in
the 40-45 kt range.

..Smith/Guyer.. 09/17/2021

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

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

LAT...LON   45259369 44569570 43659589 42819651 43079496 43499342
            44169286 45029294 45259369

Mesoscale Discussions in Minnesota, 2021Mesoscale Discussions in Iowa, 2021Every mesoscale discussion in 2021

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.