Alert archive / Iowa / Tornado Warnings in 2004

Tornado Warning 12, NWS Sioux Falls, SD

May 21, 2004Plymouth County, Iowa

NWS Sioux Falls, SD issued this tornado warning at May 21, 2004, 8:56 PM CDT for Plymouth County, Iowa. It was in force for 49 min. 6 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: May 21, 2004, 8:56 PM CDT (01:56 UTC)
Expired: May 21, 2004, 9:45 PM CDT
In force: 49 min
Issued by: NWS Sioux Falls, SD
Area: Counties, with a storm outline in the text

County Plymouth County, IA

The radar

The Sioux Falls radar (KFSD), 96 km from the middle of the area, began a volume at 01:56 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 was reported inside it

Time	Report	Where
May 21, 9:01 PM CDT	HAIL 2.75	4 W Merrill, IA
May 21, 9:01 PM CDT	HAIL 2.75	4 W Merrill, IA
May 21, 9:01 PM CDT	HAIL 2.75	4 W Merrill, IA
May 21, 9:10 PM CDT	HAIL 0.75	Le Mars, IA
May 21, 9:10 PM CDT	HAIL 0.75	Le Mars, IA
May 21, 9:10 PM CDT	HAIL 0.75	Le Mars, IA

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Omaha, NE (KOAX), launched 00:00Z, 1.9 hours before the alert went out and 165 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: 2589 J/kg
Mixed-layer CIN: -33 J/kg
Mixed-layer LCL: 1462 m above ground
0-6 km bulk shear: 35 kt
0-1 km storm-relative helicity: 64 m²/s²
0-3 km storm-relative helicity: 166 m²/s²
Significant tornado parameter: 0.6
Supercell composite: 6.9

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

384 
WFUS53 KFSD 220156
TORFSD
IAC149-220245-

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE SIOUX FALLS SD
856 PM CDT FRI MAY 21 2004

THE NATIONAL WEATHER SERVICE IN SIOUX FALLS HAS ISSUED A

* TORNADO WARNING FOR...
  PLYMOUTH COUNTY IN NORTHWEST IOWA

* UNTIL 945 PM CDT

* AT 856 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
  SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO 5 MILES WEST OF
  MERRILL...OR ABOUT 10 MILES SOUTHWEST OF LE MARS...MOVING EAST AT
  25 MPH.

* THE TORNADO WILL BE NEAR...
  STRUBLE AROUND 905 PM CDT
  LE MARS AROUND 910 PM CDT
  REMSEN AROUND 930 PM CDT

THIS IS AN EXTREMELY DANGEROUS AND LIFE THREATENING SITUATION. TAKE 
COVER NOW. LARGE HAIL THE SIZE OF GOLFBALLS OR LARGER WILL OCCUR 
WITH THIS STORM.

THIS WARNING CONTINUES THE PREVIOUS TORNADO WARNING FOR PLYMOUTH 
COUNTY.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 100 AM CDT SATURDAY MORNING
FOR SOUTHEASTERN SOUTH DAKOTA. A TORNADO WATCH ALSO REMAINS IN EFFECT
UNTIL 1000 PM CDT FRIDAY EVENING FOR NORTHWEST IOWA.

LAT...LON 4291 9648 4264 9650 4262 9588 4291 9588

$$

JRM

The office that day

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

Issued	Product	Office	Counties	Lasted
May 21, 8:19 PM CDT	Tornado Warning	FSD	Plymouth	41 min
May 21, 8:37 PM CDT	Severe Thunderstorm Warning	FSD	Clay, O'Brien	23 min
May 21, 9:25 PM CDT	Severe Thunderstorm Warning	FSD	Cherokee	35 min
May 21, 9:33 PM CDT	Severe Thunderstorm Warning	FSD	Clay	27 min
May 21, 9:33 PM CDT	Severe Thunderstorm Warning	FSD	O'Brien	42 min
May 21, 9:59 PM CDT	Severe Thunderstorm Warning	FSD	Buena Vista, Cherokee, Woodbury	31 min
May 21, 10:12 PM CDT	Severe Thunderstorm Warning	FSD	Clay	33 min
May 21, 10:14 PM CDT	Severe Thunderstorm Warning	FSD	Plymouth	31 min
May 21, 10:29 PM CDT	Severe Thunderstorm Warning	FSD	Buena Vista	16 min
May 21, 11:07 PM CDT	Severe Thunderstorm Warning	FSD	Ida, Woodbury	23 min
May 21, 11:50 PM CDT	Severe Thunderstorm Warning	FSD	Woodbury	25 min
May 22, 12:03 AM CDT	Flash Flood Warning	FSD	Cherokee, Clay, O'Brien, Plymouth	87 min

Nearby

Tornado Warnings in Iowa, 2004 Every tornado warning in 2004 Tornadoes in 2004

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.