Alert archive / Nebraska / Severe Thunderstorm Watches in 2021

Severe Thunderstorm Watch 155

May 8, 20214 states

The Storm Prediction Center issued this severe thunderstorm watch at May 8, 2021, 6:42 PM CDT for 4 states. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: May 8, 2021, 6:42 PM CDT (23:42 UTC)
Expired: May 9, 2021, 12:24 AM CDT
In force: 6 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

All 22 counties

Fremont County, IA, Page County, IA, Atchison County, KS, Brown County, KS, Doniphan County, KS, Marshall County, KS, Nemaha County, KS, Andrew County, MO, Atchison County, MO, Holt County, MO, Nodaway County, MO, Cass County, NE, Gage County, NE, Jefferson County, NE, Johnson County, NE, Lancaster County, NE, Nemaha County, NE, Otoe County, NE, Pawnee County, NE, Richardson County, NE, Saline County, NE, Seward County, NE

The radar

The Omaha radar (KOAX), 93 km from the middle of the area, began a volume at 23:42 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.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 20%
One or more EF2 to EF5 tornadoes: 5%
Ten or more severe wind reports: 40%
One or more gusts of 65 knots or more: 20%
Ten or more severe hail reports: 60%
One or more hailstones of 2 inches or more: 30%
Six or more combined severe hail and wind reports: 90%

Warnings issued inside it

4 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
May 8, 7:58 PM CDT	Severe Thunderstorm Warning	OAX	Jefferson	47 min
May 8, 8:03 PM CDT	Severe Thunderstorm Warning	TOP	Marshall	42 min
May 8, 8:38 PM CDT	Severe Thunderstorm Warning	TOP	Marshall, Washington	52 min
May 8, 11:19 PM CDT	Severe Thunderstorm Warning	EAX	Atchison, Leavenworth, Wyandotte	41 min

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Omaha, NE (KOAX), launched 12:00Z, 11.7 hours before the alert went out and 93 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: 2218 m above ground
0-6 km bulk shear: 48 kt
0-1 km storm-relative helicity: 222 m²/s²
0-3 km storm-relative helicity: 383 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.7

Open this sounding in Storm Lab

The text

As transmitted.

827 
WWUS20 KWNS 082339
SEL5  
SPC WW 082339
IAZ000-KSZ000-MOZ000-NEZ000-090600-

URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 155
NWS Storm Prediction Center Norman OK
640 PM CDT Sat May 8 2021

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Southwest Iowa
  Northeast Kansas
  Northwest Missouri
  Southeast Nebraska

* Effective this Saturday night and Sunday morning from 640 PM
  until 100 AM CDT.

* Primary threats include...
  Scattered large hail likely with isolated very large hail events
    to 2 inches in diameter possible
  Scattered damaging wind gusts to 70 mph possible
  A tornado or two possible

SUMMARY...Thunderstorms will increase in coverage and intensity this
evening north of a warm front and across the watch area.  Large hail
and gusty/damaging winds are the main threats.

The severe thunderstorm watch area is approximately along and 45
statute miles north and south of a line from 35 miles west northwest
of Beatrice NE to 30 miles north northeast of Saint Joseph MO. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU5).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 153...WW 154...

AVIATION...A few severe thunderstorms with hail surface and aloft to
2 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
27035.

...Hart

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 8, 3:24 PM CDT	Mesoscale Discussion	SPC	Barton, Ellis, Ellsworth, Jewell, Lincoln, Mitchell and 7 more	2 hr
May 8, 4:00 PM CDT	Severe Thunderstorm Watch	SPC	Barton, Ellis, Ellsworth, Hodgeman, Jewell, Lincoln and 11 more	6 hr
May 8, 6:06 PM CDT	Mesoscale Discussion	SPC	Atchison, Barton, Brown, Clay, Cloud, Dickinson and 29 more	114 min
May 8, 6:30 PM CDT	Tornado Watch	SPC	Clay, Cloud, Dickinson, Douglas, Franklin, Geary and 12 more	7 hr

Nearby

Severe Thunderstorm Watches in Nebraska, 2021 Severe Thunderstorm Watches in Kansas, 2021 Severe Thunderstorm Watches in Missouri, 2021 Every severe thunderstorm watch 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.