Mesoscale Discussion 1762

Issued

Sep 16, 2021, 7:15 PM CDT (00:15 UTC)

Expired

Sep 16, 2021, 9:15 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The North Platte radar (KLNX), 59 km from the middle of the area, began a volume at 00:16 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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• Severe Thunderstorm Watch 506Sep 16, 8:15 PM CDT

778 
ACUS11 KWNS 170016
SWOMCD
SPC MCD 170015 
SDZ000-NEZ000-170215-

Mesoscale Discussion 1762
NWS Storm Prediction Center Norman OK
0715 PM CDT Thu Sep 16 2021

Areas affected...Northern Nebraska and southeast South Dakota

Concerning...Severe potential...Watch possible 

Valid 170015Z - 170215Z

Probability of Watch Issuance...40 percent

SUMMARY...Strong to severe thunderstorms remain likely this evening
and into the overnight hours across northern Nebraska into southeast
South Dakota. Damaging winds and hail will be possible, and a watch
may be needed in the coming hours.

DISCUSSION...Latest GOES visible and IR imagery show some hints at
increasing lift in the vicinity of a surface low in western NE and
along a cold front draped across northern NE - mainly in the form of
cooling cloud tops within the stratus deck and increasing cloud
cover along the frontal zone. A few convective towers with transient
lightning have also been noted near Alliance, NE. Although sunset in
the coming hour will result in an increase in surface-based
inhibition through the evening, a strengthening low-level jet (the
onset of which is noted in recent KGLD VWP obs) impinging on the
frontal zone will maintain lift over the region and likely support
MU parcels reaching their LFCs. 1000-2000 J/kg MUCAPE and 35-45
knots of effective bulk shear will support the potential for
organized convection. Deep-layer shear vectors and initial storm
motions along and slightly behind the cold front will likely support
semi-discrete to linear storm modes. A severe hail/wind threat
appears likely, and may be augmented if 1) effective bulk shear
increases to near 60 knots - as suggested by some recent model runs,
or 2) if a storm can become rooted within the boundary layer on the
warm side of the front where weaker near-surface thermal inversions
may support a higher wind threat. A watch may be needed in the
coming hours to address this scenario as confidence in sustained
convective initiation increases.

..Moore/Edwards.. 09/17/2021

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

ATTN...WFO...FSD...OAX...LBF...UNR...CYS...

LAT...LON   41710041 41620137 41580227 41650307 42490319 42890268
            42910128 42980012 43269898 43619820 43309732 42619752
            42319822 42129883 41889960 41710041

Mesoscale Discussions in Nebraska, 2021Mesoscale Discussions in South Dakota, 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.