Alert archive / Nebraska / Mesoscale Discussions in 2021

Mesoscale Discussion 1760

September 16, 20215 counties in Colorado; 7 counties in Nebraska

The Storm Prediction Center issued this mesoscale discussion at Sep 16, 2021, 3:46 PM MDT for 5 counties in Colorado; 7 counties in Nebraska. It was in force for 119 min.

The area

The outline as issued.

The facts

Issued: Sep 16, 2021, 3:46 PM MDT (21:46 UTC)
Expired: Sep 16, 2021, 5:45 PM MDT
In force: 119 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

Counties Logan County, CO, Phillips County, CO, Sedgwick County, CO, Washington County, CO, Yuma County, CO, Arthur County, NE, Chase County, NE, Deuel County, NE, Dundy County, NE, Hayes County, NE, Keith County, NE, Perkins County, NE

The radar

The Goodland radar (KGLD), 130 km from the middle of the area, began a volume at 21:48 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 506Sep 16, 7:15 PM MDT

The nearest sounding before it

Denver, CO (KDNR), launched 12:00Z, 9.8 hours before the alert went out and 96 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 4076 m above ground
0-6 km bulk shear: 16 kt
0-1 km storm-relative helicity: -31 m²/s²
0-3 km storm-relative helicity: 44 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

308 
ACUS11 KWNS 162147
SWOMCD
SPC MCD 162146 
NEZ000-KSZ000-COZ000-162345-

Mesoscale Discussion 1760
NWS Storm Prediction Center Norman OK
0446 PM CDT Thu Sep 16 2021

Areas affected...Northeast Colorado into southwest Nebraska

Concerning...Severe potential...Watch unlikely 

Valid 162146Z - 162345Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated to scattered thunderstorms may pose a downburst
wind threat over the next 1-2 hours across northeast Colorado. The
potential for severe hail and wind may increase as storms move into
southwest Nebraska this evening.

DISCUSSION...Latest radar and IR satellite imagery show a few robust
convective towers developing along a surface trough across northeast
CO. RAP forecast soundings from this region, as well as mesoanalysis
and GOES CAPE estimates, suggest that MLCAPE is meager (around
250-500 J/kg). However, this instability is situated atop a deep,
well-mixed boundary layer with low-level lapse rates approaching 10
C/km. Nearly 50 F dewpoint depressions are noted in recent surface
obs in the vicinity of the developing convection, which supports
recent analyses. This environment will support the potential for
strong to severe downbursts as storms continue to mature across
northeast CO over the next 1-2 hours.

This activity will likely propagate into southwest NE into the
evening hours where higher quality boundary-layer moisture and
stronger effective shear may support a general intensification trend
with an attendant increase in severe wind/hail potential. Additional
convection is possible along the southward-moving cold front later
this evening/tonight, which may pose a similar wind/hail threat. In
general, confidence in the longevity and coverage of these storms is
low and a watch is not currently anticipated. However, trends will
continue to be monitored.

..Moore/Edwards.. 09/16/2021

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

ATTN...WFO...LBF...GLD...BOU...CYS...

LAT...LON   40490327 41160281 41680222 41880158 41590116 41280091
            40590083 40150119 39820180 39570237 39380300 39300343
            39320373 39570378 40490327

Nearby

Mesoscale Discussions in Nebraska, 2021 Mesoscale Discussions in Colorado, 2021 Every mesoscale discussion in 2021

Sources

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.