Alert archive / Nebraska / Mesoscale Discussions in 2021

Mesoscale Discussion 1657

August 31, 20214 states

The Storm Prediction Center issued this mesoscale discussion at Aug 31, 2021, 3:02 AM CDT for 4 states. It was in force for 118 min.

The area

The outline as issued.

The facts

Issued
Aug 31, 2021, 3:02 AM CDT (08:02 UTC)
Expired
Aug 31, 2021, 5:00 AM CDT
In force
118 min
Issued by
the Storm Prediction Center
Concerning
Severe thunderstorm watch 479
All 54 counties

Adams County, IA, Cass County, IA, Fremont County, IA, Harrison County, IA, Mills County, IA, Montgomery County, IA, Page County, IA, Pottawattamie County, IA, Ringgold County, IA, Shelby County, IA, Taylor County, IA, Atchison County, MO, Holt County, MO, Nodaway County, MO, Worth County, MO, Antelope County, NE, Boone County, NE, Boyd County, NE, Brown County, NE, Burt County, NE, Butler County, NE, Cass County, NE, Colfax County, NE, Cuming County, NE, Dodge County, NE, Douglas County, NE, Garfield County, NE, Greeley County, NE, Holt County, NE, Johnson County, NE, Keya Paha County, NE, Knox County, NE, Lancaster County, NE, Madison County, NE, Merrick County, NE, Nance County, NE, Nemaha County, NE, Otoe County, NE, Pawnee County, NE, Pierce County, NE, Platte County, NE, Polk County, NE, Richardson County, NE, Rock County, NE, Sarpy County, NE, Saunders County, NE, Seward County, NE, Stanton County, NE, Thurston County, NE, Washington County, NE, Wayne County, NE, Wheeler County, NE, York County, NE, Gregory County, SD

The radar

The Omaha radar (KOAX), 94 km from the middle of the area, began a volume at 08:04 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

Omaha, NE (KOAX), launched 00:00Z, 8.0 hours before the alert went out and 94 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-pSkew-T log-p diagram, Omaha, NE at 00:00Z on 2021-08-31Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1443 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Omaha, NE at 00:00Z on 2021-08-31The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 4 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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
1443 J/kg
Mixed-layer CIN
-31 J/kg
Mixed-layer LCL
1305 m above ground
0-6 km bulk shear
35 kt
0-1 km storm-relative helicity
4 m²/s²
0-3 km storm-relative helicity
143 m²/s²
Significant tornado parameter
0.3
Supercell composite
3.5

Open this sounding in Storm Lab

The text

As transmitted.

123 
ACUS11 KWNS 310802
SWOMCD
SPC MCD 310802 
MOZ000-IAZ000-NEZ000-SDZ000-311000-

Mesoscale Discussion 1657
NWS Storm Prediction Center Norman OK
0302 AM CDT Tue Aug 31 2021

Areas affected...Far Southern South Dakota...Northern and Eastern
Nebraska...Southwest Iowa...Far Northwest Missouri

Concerning...Severe Thunderstorm Watch 479...

Valid 310802Z - 311000Z

The severe weather threat for Severe Thunderstorm Watch 479
continues.

SUMMARY...An isolated severe threat is likely to continue for a few
more hours, mainly across northern and eastern Nebraska
southeastward into southwest Iowa and far northwest Missouri. New
weather watch issuance is not expected beyond the 10Z expiration
time of WW 479.

DISCUSSION...The latest radar imagery shows a MCS extending from
southern sections of the northern Plains southeastward into the
lower Missouri Valley. This large area of thunderstorms is located
along a northwest-to-southeast corridor of moderate instability. The
RAP is estimating MLCAPE along this corridor in the 1500 to 2000
J/kg range. Most of the instability is located above 850 mb with
forecast soundings showing a boundary layer temperature inversion.
In spite of this, effective shear is estimated to be in the 30 to 35
kt range. This combined with 700-500 mb lapse rates near 7.0 C/km
should be enough for a isolated large hail threat with the stronger
rotating cells. An isolated wind-damage threat will also be
possible. However, the severe threat should become more isolated
with time over the next few hours and should be too marginal for the
issuance of another watch after 10Z.

..Broyles.. 08/31/2021

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

ATTN...WFO...DMX...EAX...FSD...OAX...GID...LBF...UNR...

LAT...LON   43129857 43299944 43230047 42750076 42200026 41649875
            40679736 40149647 40009545 40219460 40489414 40879407
            41659510 42219660 43129857

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Aug 30, 11:35 PM CDTMesoscale DiscussionSPCHarrison85 min
Aug 31, 7:59 AM CDTMesoscale DiscussionSPCAndrew, Buchanan, Clay, Clinton, DeKalb, Holt and 2 more61 min
Aug 30, 7:25 PM CDTMesoscale DiscussionSPCAntelope, Boyd, Brown, Cedar, Cherry, Holt and 5 more3 hr
Aug 30, 9:57 PM CDTSevere Thunderstorm WatchSPCAntelope, Boone, Boyd, Brown, Burt, Butler and 24 more7 hr

Nearby

Mesoscale Discussions in Nebraska, 2021Mesoscale Discussions in Iowa, 2021Mesoscale Discussions in Missouri, 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.