Alert archive / Iowa / Severe Thunderstorm Warnings in 1998

Severe Thunderstorm Warning 91, NWS Des Moines, IA

May 20, 19984 counties in Iowa

NWS Des Moines, IA issued this severe thunderstorm warning at May 20, 1998, 5:20 AM CDT for 4 counties in Iowa. It was in force for 60 min. 2 reports came from inside the area while it was in force.

The area

The counties it named, with what was reported inside it.

The facts

Issued: May 20, 1998, 5:20 AM CDT (10:20 UTC)
Expired: May 20, 1998, 6:20 AM CDT
In force: 60 min
Issued by: NWS Des Moines, IA
Area: Whole counties

Counties Dallas County, IA, Madison County, IA, Polk County, IA, Warren County, IA

The radar

The Des Moines radar (KDMX), 25 km from the middle of the area, began a volume at 10:21 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	Remark
May 20, 5:40 AM CDT	Thunderstorm Wind 55	Cumming, IA
May 20, 5:55 AM CDT	Thunderstorm Wind 52	Des Moines Arpt, IA

NCEI Storm Data entries that began inside the alert's area while it was in force. Before 2003 the local storm report archive is thin, so this is the record of what happened rather than what was phoned in.

The watch it was issued in

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

Issued	Product	Office	Lasted
May 20, 1:45 AM CDT	Severe Thunderstorm Watch	SPC	6 hr

The nearest sounding before it

Omaha, NE (KOAX), launched 00:00Z, 10.3 hours before the alert went out and 216 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: 2454 J/kg
Mixed-layer CIN: -8 J/kg
Mixed-layer LCL: 1962 m above ground
0-6 km bulk shear: 36 kt
0-1 km storm-relative helicity: 21 m²/s²
0-3 km storm-relative helicity: 64 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 3.4

Open this sounding in Storm Lab

The text

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

000 
TTAA00 KDSM 201020 RRA
SVRDSM
IAC049-121-153-181-201120-

BULLETIN - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE DES MOINES IA
520 AM CDT WED MAY 20 1998

THE NATIONAL WEATHER SERVICE IN DES MOINES HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
  EASTERN DALLAS COUNTY IN CENTRAL IOWA
  EASTERN MADISON COUNTY IN SOUTH CENTRAL IOWA
  POLK COUNTY IN CENTRAL IOWA
  WARREN COUNTY IN SOUTH CENTRAL IOWA

* UNTIL 620 AM CDT

* AT 517 AM CDT... DOPPLER RADAR INDICATED A LINE OF SEVERE
  THUNDERSTORMS 19 MILES WEST SOUTHWEST OF DES MOINES OR 1 MILE WEST
  OF VAN METER MOVING EAST AT 35 MPH.

* THIS STORM CAN BE EXPECTED NEAR...
   ADEL               BY 522 AM CDT
   DALLAS CENTER      BY 522 AM CDT
   WINTERSET          BY 524 AM CDT
   WAUKEE             BY 525 AM CDT
   WEST DES MOINES    BY 540 AM CDT
   NORWALK            BY 541 AM CDT
   URBANDALE          BY 541 AM CDT
   INDIANOLA          BY 549 AM CDT
   DES MOI`NES         BY 549 AM CDT
   ANKENY             BY 552 AM CDT
   CARLISLE           BY 557 AM CDT

DAMAGING WINDS AND HEAVY RAIN ARE LIKELY. GO INSIDE A STURDY
BUILDING AND STAY AWAY FROM WINDOWS!

COGIL

The office that day

Everything else NWS Des Moines, IA issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 19, 7:23 PM CDT	Severe Thunderstorm Warning	DMX	Appanoose	47 min
May 19, 7:31 PM CDT	Severe Thunderstorm Warning	DMX	Warren	34 min
May 19, 7:59 PM CDT	Severe Thunderstorm Warning	DMX	Lucas	36 min
May 20, 3:46 AM CDT	Severe Thunderstorm Warning	DMX	Crawford	49 min
May 20, 3:53 AM CDT	Severe Thunderstorm Warning	DMX	Audubon, Cass	62 min
May 20, 4:31 AM CDT	Severe Thunderstorm Warning	DMX	Carroll	49 min
May 20, 5:47 AM CDT	Severe Thunderstorm Warning	DMX	Jasper, Marion	48 min
May 20, 10:19 AM CDT	Severe Thunderstorm Warning	DMX	Marion	36 min
May 20, 10:21 AM CDT	Severe Thunderstorm Warning	DMX	Marion	34 min
May 20, 10:50 AM CDT	Severe Thunderstorm Warning	DMX	Monroe	35 min
May 20, 11:05 AM CDT	Severe Thunderstorm Warning	DMX	Wapello	35 min
May 20, 11:45 AM CDT	Severe Thunderstorm Warning	DMX	Mahaska	20 min

Nearby

Severe Thunderstorm Warnings in Iowa, 1998 Every severe thunderstorm warning in 1998

Sources

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