Alert archive / Nebraska / Mesoscale Discussions in 2021
Mesoscale Discussion 1727
The Storm Prediction Center issued this mesoscale discussion at Sep 11, 2021, 4:23 PM MDT for 16 counties in Nebraska. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Sep 11, 2021, 4:23 PM MDT (22:23 UTC)
- Expired
- Sep 11, 2021, 6:30 PM MDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
Counties Arthur County, NE, Banner County, NE, Box Butte County, NE, Cheyenne County, NE, Dawes County, NE, Deuel County, NE, Garden County, NE, Grant County, NE, Hooker County, NE, Keith County, NE, Kimball County, NE, McPherson County, NE, Morrill County, NE, Scotts Bluff County, NE, Sheridan County, NE, Sioux County, NE
The radar
The Cheyenne radar (KCYS), 176 km from the middle of the area, began a volume at 22:22 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 nearest sounding before it
N. Platte/Lee Bi, NE (KLBF), launched 12:00Z, 10.4 hours before the alert went out and 227 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.
- Mixed-layer CAPE
- 2 J/kg
- Mixed-layer CIN
- -766 J/kg
- Mixed-layer LCL
- 3580 m above ground
- 0-6 km bulk shear
- 27 kt
- 0-1 km storm-relative helicity
- -165 m²/s²
- 0-3 km storm-relative helicity
- -96 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
830
ACUS11 KWNS 112223
SWOMCD
SPC MCD 112223
NEZ000-COZ000-WYZ000-120030-
Mesoscale Discussion 1727
NWS Storm Prediction Center Norman OK
0523 PM CDT Sat Sep 11 2021
Areas affected...Parts of far eastern Wyoming...northeastern
Colorado into parts of western and central Nebraska
Concerning...Severe potential...Watch unlikely
Valid 112223Z - 120030Z
Probability of Watch Issuance...5 percent
SUMMARY...Scattered strong storms may produce localized strong
downbursts through 7-9 PM CDT, but the evolution of an organized
severe wind threat currently appears low.
DISCUSSION...Widely scattered thunderstorm activity is initiating
along and east of the Colorado Front Range and Laramie Mountains
vicinity. This appears aided by mid/upper forcing for ascent
associated with one low amplitude impulse now crossing the higher
terrain, and forecast to progress into the adjacent high plains
through this evening.
The boundary layer has become hot and deeply mixed across the high
plains, with sufficient moisture in the presence of steep lapse
rates to support weak CAPE. Boundary-layer dew points and
mixed-layer CAPE gradually increase with eastward extent across the
high plains, and this could allow for slow further intensification
of high-based storms through early evening. Deep-layer shear is
strong, and westerly mean ambient flow within the convective layer
appears on the order of 30 kt, which may contribute to increasing
potential for locally severe down bursts in stronger storms, before
convection begins to wane after dark.
Due to weak low-level forcing for ascent, the potential for
substantive upscale growth currently appears low. This appears to
limit the risk for a broader, more organized severe wind threat.
..Kerr/Grams.. 09/11/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LBF...BOU...CYS...
LAT...LON 42740420 42840244 42230112 41240109 40700407 41730418
42740420Nearby
Mesoscale Discussions in Nebraska, 2021Every 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.