Alert archive / Iowa / Mesoscale Discussions in 2003

Mesoscale Discussion 421

April 6, 200343 counties in Iowa; 9 counties in Nebraska; Clay County, Union County, South Dakota

The Storm Prediction Center issued this mesoscale discussion at Apr 6, 2003, 5:41 PM CDT for 43 counties in Iowa; 9 counties in Nebraska; Clay County, Union County, South Dakota. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: Apr 6, 2003, 5:41 PM CDT (22:41 UTC)
Expired: Apr 6, 2003, 10:45 PM CDT
In force: 5 hr
Issued by: the Storm Prediction Center

All 54 counties

Audubon County, IA, Benton County, IA, Black Hawk County, IA, Boone County, IA, Bremer County, IA, Buena Vista County, IA, Butler County, IA, Calhoun County, IA, Carroll County, IA, Cerro Gordo County, IA, Cherokee County, IA, Chickasaw County, IA, Clay County, IA, Crawford County, IA, Dickinson County, IA, Emmet County, IA, Floyd County, IA, Franklin County, IA, Greene County, IA, Grundy County, IA, Guthrie County, IA, Hamilton County, IA, Hancock County, IA, Hardin County, IA, Harrison County, IA, Humboldt County, IA, Ida County, IA, Kossuth County, IA, Marshall County, IA, Monona County, IA, O'Brien County, IA, Osceola County, IA, Palo Alto County, IA, Plymouth County, IA, Pocahontas County, IA, Sac County, IA, Shelby County, IA, Sioux County, IA, Story County, IA, Tama County, IA, Webster County, IA, Woodbury County, IA, Wright County, IA, Burt County, NE, Cedar County, NE, Cuming County, NE, Dakota County, NE, Dixon County, NE, Pierce County, NE, Stanton County, NE, Thurston County, NE, Wayne County, NE, Clay County, SD, Union County, SD

The radar

The Des Moines radar (KDMX), 121 km from the middle of the area, began a volume at 22:40 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 12:00Z, 10.7 hours before the alert went out and 184 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: 1035 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 57 m²/s²
0-3 km storm-relative helicity: 136 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

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

619 
ACUS11 KWNS 062241
SWOMCD
SPC MCD 062241 
IAZ000-NEZ000-SDZ000-070345-

MESOSCALE DISCUSSION 0421
NWS STORM PREDICTION CENTER NORMAN OK
0541 PM CDT SUN APR 06 2003

AREAS AFFECTED...CENTRAL AND NRN IA...AND NERN NEB

CONCERNING...HEAVY SNOW 

VALID 062241Z - 070345Z

MODERATE TO OCCASIONALLY HEAVY SNOW/THUNDERSNOW WILL TRANSLATE
FROM NERN NEB EWD ACROSS NWRN AND N-CENTRAL IA THROUGH THIS
EVENING AND INTO THE OVERNIGHT PERIOD. SNOWFALL RATES OF 1/HR
ARE LIKELY ALONG AN E-W AXIS EXTENDING FROM OFK TO FOD TO
ALO...WITH THE HEAVY SNOW DEVELOPING EWD ACROSS THIS REGION
BETWEEN 00-09Z.



A STRONG/CLOSED 700MB LOW ACROSS CENTRAL NEB WILL BECOME NEARLY
STATIONARY DURING THE NEXT 6-12 HOURS. STRONG MID-LEVEL PVA IS
EXPECTED TO ROTATES NEWD ON THE EAST SIDE OF THE LOW AND ACROSS
WRN/CENTRAL IA THIS EVENING...RESULTING IN AN INCREASE IN
LARGE-SCALE PRECIPITATION COVERAGE. THIS IS SUPPORTED BY RADAR
TRENDS AT 2225Z INDICATING AN INCREASE IN PRECIPITATION ECHOES
ACROSS ERN NEB/SWRN IA/WRN IA. DESPITE SFC TEMPERATURES IN THE
MID TO UPPER 30S ACROSS N-CENTRAL IA...DYNAMIC AND EVAPORATIVE
COOLING WILL QUICKLY ALLOW TEMPERATURES TO DROP TO NEAR FREEZING
AS PRECIPITATION INTENSIFIES IN THE NEXT FEW HOURS. 



ON THE MESOSCALE...STRONG 700MB DEFORMATION IS ALSO EXPECTED TO
BECOME ESTABLISHED ALONG AN E-W FRONTAL BOUNDARY AT THAT LEVEL
ACROSS CENTRAL IA BY 06Z. MODEL SOUNDINGS INDICATE CAPE VALUES
AROUND 100 J/KG FOR PARCELS LIFTED FROM 650MB ACROSS CENTRAL IA
AROUND 06Z...SUGGESTING CONVECTIVE NATURE TO SNOWFALL AND THE
POSSIBILITY OF A FEW LIGHTNING STRIKES ACROSS CENTRAL/N-CENTRAL
IA LATER TONIGHT. LIGHTNING DATA AT 06/22Z HAS INDICATED
SCATTERED CLOUD-TO-GROUND STRIKES ACROSS MUCH OF ERN NEB DURING
THE PAST FEW HOURS. GIVEN THESE CONDITIONS...THE POSSIBILITY
EXISTS FOR MULTIPLE E-W MESOSCALE BANDS PRODUCING OCCASIONAL
HEAVY SNOW ACROSS MUCH OF NWRN/N-CENTRAL/NERN IA AS FORCING
SHIFTS EWD THIS EVENING AND OVERNIGHT. 

..BANACOS.. 04/06/2003

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...DVN...ARX...DMX...FSD...OAX...

43279209 43439545 43169675 42379792 41629731 41659521
41699427 41869201

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 6, 6:40 AM CDT	Mesoscale Discussion	SPC	Adams, Blaine, Boone, Buffalo, Butler, Cass and 54 more	5 hr

Nearby

Mesoscale Discussions in Iowa, 2003 Mesoscale Discussions in Nebraska, 2003 Mesoscale Discussions in South Dakota, 2003 Every mesoscale discussion in 2003

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.