Alert archive / Iowa / Tornado Warnings in 2021

Tornado Warning 7, NWS Sioux Falls, SD

August 27, 2021Sioux County, Iowa

NWS Sioux Falls, SD issued this tornado warning at Aug 27, 2021, 1:04 AM CDT for Sioux County, Iowa. It was in force for 26 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Aug 27, 2021, 1:04 AM CDT (06:04 UTC)
Expired: Aug 27, 2021, 1:30 AM CDT
In force: 26 min
Issued by: NWS Sioux Falls, SD
Area: Storm-based polygon
Tornado: Radar indicated
Hail: 0.75 in

County Sioux County, IA

The radar

The Sioux Falls radar (KFSD), 72 km from the middle of the area, began a volume at 06:05 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 watch it was issued in

The SPC watch in force over the same counties when this warning went out.

Issued	Product	Office	Lasted
Aug 26, 8:03 PM CDT	Severe Thunderstorm Watch	SPC	7 hr

The nearest sounding before it

Omaha, NE (KOAX), launched 00:00Z, 6.1 hours before the alert went out and 204 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: 5342 J/kg
Mixed-layer CIN: -16 J/kg
Mixed-layer LCL: 1163 m above ground
0-6 km bulk shear: 27 kt
0-1 km storm-relative helicity: 111 m²/s²
0-3 km storm-relative helicity: 199 m²/s²
Significant tornado parameter: 3.8
Supercell composite: 24.0

Open this sounding in Storm Lab

The text

As transmitted.

691 
WFUS53 KFSD 270604
TORFSD
IAC167-270630-
/O.NEW.KFSD.TO.W.0007.210827T0604Z-210827T0630Z/

BULLETIN - EAS ACTIVATION REQUESTED
Tornado Warning
National Weather Service Sioux Falls SD
104 AM CDT Fri Aug 27 2021

The National Weather Service in Sioux Falls has issued a

* Tornado Warning for...
  Northeastern Sioux County in northwestern Iowa...

* Until 130 AM CDT.

* At 104 AM CDT, severe thunderstorms capable of producing both
  tornadoes and extensive straight line wind damage were located over
  Sioux Center, moving east at 45 mph.

  HAZARD...Tornado.

  SOURCE...Radar indicated rotation.

  IMPACT...Flying debris will be dangerous to those caught without 
           shelter. Mobile homes will be damaged or destroyed. 
           Damage to roofs, windows, and vehicles will occur.  Tree 
           damage is likely.

* These dangerous storms will be near...
  Boyden around 120 AM CDT.

Other locations in the path of this tornadic thunderstorm include
Sheldon.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW! Move to a basement or an interior room on the lowest
floor of a sturdy building. Avoid windows. If you are outdoors, in a
mobile home, or in a vehicle, move to the closest substantial shelter
and protect yourself from flying debris.

This cluster of thunderstorms is capable of producing tornadoes and
widespread significant wind damage. Do not wait to see or hear the
tornado. For your protection move to an interior room on the lowest
floor of a building.

Torrential rainfall is occurring with this storm, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 4312 9632 4325 9587 4323 9586 4309 9587
      4306 9628
TIME...MOT...LOC 0604Z 251DEG 39KT 4311 9619 

TORNADO...RADAR INDICATED
MAX HAIL SIZE...<.75 IN

$$

SG

2 follow-up statements

293 
WWUS53 KFSD 270611
SVSFSD

Severe Weather Statement
National Weather Service Sioux Falls SD
111 AM CDT Fri Aug 27 2021

IAC167-270630-
/O.CON.KFSD.TO.W.0007.000000T0000Z-210827T0630Z/
Sioux IA-
111 AM CDT Fri Aug 27 2021

...A TORNADO WARNING REMAINS IN EFFECT UNTIL 130 AM CDT FOR
NORTHEASTERN SIOUX COUNTY...

At 111 AM CDT, a severe squall line capable of producing both
tornadoes and extensive straight line wind damage was located near
Hull, or near Sioux Center, moving east at 45 mph.

HAZARD...Tornado.

SOURCE...Radar indicated rotation.

IMPACT...Flying debris will be dangerous to those caught without 
         shelter. Mobile homes will be damaged or destroyed. Damage 
         to roofs, windows, and vehicles will occur.  Tree damage is 
         likely.

These dangerous storms will be near...
  Boyden around 120 AM CDT.

Other locations in the path of this tornadic thunderstorm include
Sheldon.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW! Move to a basement or an interior room on the lowest
floor of a sturdy building. Avoid windows. If you are outdoors, in a
mobile home, or in a vehicle, move to the closest substantial shelter
and protect yourself from flying debris.

This cluster of thunderstorms is capable of producing tornadoes and
widespread significant wind damage. Do not wait to see or hear the
tornado. For your protection move to an interior room on the lowest
floor of a building.

Torrential rainfall is occurring with this storm, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 4325 9587 4323 9586 4309 9587 4307 9614
      4315 9620
TIME...MOT...LOC 0611Z 251DEG 39KT 4313 9609 

TORNADO...RADAR INDICATED
MAX HAIL SIZE...<.75 IN

$$

SG

307 
WWUS53 KFSD 270622
SVSFSD

Severe Weather Statement
National Weather Service Sioux Falls SD
122 AM CDT Fri Aug 27 2021

IAC167-270631-
/O.EXP.KFSD.TO.W.0007.000000T0000Z-210827T0630Z/
Sioux IA-
122 AM CDT Fri Aug 27 2021

...THE TORNADO WARNING FOR NORTHEASTERN SIOUX COUNTY WILL EXPIRE AT
130 AM CDT...
    
The tornado threat has diminished and the Tornado Warning has been 
cancelled. However, damaging winds remain likely and a Severe 
Thunderstorm Warning remains in effect for the area.  However gusty 
winds are still possible with this thunderstorm.

A Severe Thunderstorm Watch remains in effect until 300 AM CDT for
northwestern Iowa.

Remember, a Severe Thunderstorm Warning still remains in effect for
Sioux County until 200 AM CDT.

LAT...LON 4325 9587 4323 9586 4309 9587 4307 9614
      4315 9620
TIME...MOT...LOC 0621Z 250DEG 38KT 4315 9599 

$$

SG

The office that day

Everything else NWS Sioux Falls, SD issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 27, 12:17 AM CDT	Severe Thunderstorm Warning	FSD	Lyon, Sioux	28 min
Aug 27, 12:34 AM CDT	Severe Thunderstorm Warning Considerable damage threat	FSD	Plymouth, Sioux	41 min
Aug 27, 1:09 AM CDT	Severe Thunderstorm Warning Considerable damage threat	FSD	Cherokee, Lyon, O'Brien, Osceola, Plymouth, Sioux	51 min
Aug 27, 1:25 AM CDT	Severe Thunderstorm Warning Considerable damage threat	FSD	Cherokee, Ida, Plymouth, Woodbury	50 min
Aug 27, 1:52 AM CDT	Severe Thunderstorm Warning	FSD	Buena Vista, Cherokee, Clay, Dickinson, O'Brien, Osceola	68 min
Aug 27, 2:00 AM CDT	Severe Thunderstorm Warning	FSD	Buena Vista	60 min

Nearby

Tornado Warnings in Iowa, 2021 Every tornado warning in 2021 Tornadoes 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.