Alert archive / Nebraska / Mesoscale Discussions in 2012

Mesoscale Discussion 654

May 1, 20127 counties in Iowa; 47 counties in Nebraska

The Storm Prediction Center issued this mesoscale discussion at May 1, 2012, 7:30 PM CDT for 7 counties in Iowa; 47 counties in Nebraska. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: May 1, 2012, 7:30 PM CDT (00:30 UTC)
Expired: May 1, 2012, 9:30 PM CDT
In force: 2 hr
Issued by: the Storm Prediction Center

All 54 counties

Buena Vista County, IA, Cherokee County, IA, Harrison County, IA, Ida County, IA, Monona County, IA, Plymouth County, IA, Woodbury County, IA, Adams County, NE, Antelope County, NE, Boone County, NE, Buffalo County, NE, Burt County, NE, Butler County, NE, Cedar County, NE, Clay County, NE, Colfax County, NE, Cuming County, NE, Custer County, NE, Dakota County, NE, Dawson County, NE, Dixon County, NE, Dodge County, NE, Douglas County, NE, Fillmore County, NE, Franklin County, NE, Garfield County, NE, Gosper County, NE, Greeley County, NE, Hall County, NE, Hamilton County, NE, Holt County, NE, Howard County, NE, Kearney County, NE, Knox County, NE, Loup County, NE, Madison County, NE, Merrick County, NE, Nance County, NE, Nuckolls County, NE, Phelps County, NE, Pierce County, NE, Platte County, NE, Polk County, NE, Saunders County, NE, Seward County, NE, Sherman County, NE, Stanton County, NE, Thurston County, NE, Valley County, NE, Washington County, NE, Wayne County, NE, Webster County, NE, Wheeler County, NE, York County, NE

The radar

The Omaha radar (KOAX), 148 km from the middle of the area, began a volume at 00:31 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 watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 224May 1, 9:30 PM CDT

The nearest sounding before it

Omaha, NE (KOAX), launched 00:00Z, 0.5 hours before the alert went out and 148 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: 1502 J/kg
Mixed-layer CIN: -30 J/kg
Mixed-layer LCL: 1477 m above ground
0-6 km bulk shear: 36 kt
0-1 km storm-relative helicity: 75 m²/s²
0-3 km storm-relative helicity: 122 m²/s²
Significant tornado parameter: 0.4
Supercell composite: 5.2

Open this sounding in Storm Lab

The text

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

192 
ACUS11 KWNS 020030
SWOMCD
SPC MCD 020030 
IAZ000-NEZ000-SDZ000-020230-

MESOSCALE DISCUSSION 0654
NWS STORM PREDICTION CENTER NORMAN OK
0730 PM CDT TUE MAY 01 2012

AREAS AFFECTED...PORTIONS SERN SD...CENTRAL/NERN NEB...NWRN IA.

CONCERNING...SEVERE THUNDERSTORM WATCH 221...

VALID 020030Z - 020230Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 221
CONTINUES.

SUMMARY...WW MAY BE CLEARED BEHIND PRIMARY BAND OF CONVECTION AND
RELATED SFC COLD FRONT OVER NRN NEB AND SERN SD.  ADDITIONAL WW
ISSUANCE MAY BE REQUIRED DURING NEXT COUPLE HOURS OVER PORTIONS OF
CORRIDOR FROM S-CENTRAL NEB TO NWRN IA.  DAMAGING GUSTS AND SVR HAIL
REMAIN PRIMARY CONCERNS.

DISCUSSION...AT 00Z...MAIN TSTM BAND WAS LOCATED FROM FSD AREA SWWD
OVER EXTREME ERN BOYD COUNTY NEB...EXTRAPOLATING SWD TO ISOLATED SVR
TSTMS OVER ROCK COUNTY NEB.  THIS ACTIVITY WILL CONTINUE TO SHIFT
GENERALLY EWD ACROSS NERN NEB/SERN SD/NWRN IA REGION.  SFC
STREAMLINE ANALYSIS REVEALED QUASISTATIONARY AND PREFRONTAL
CONFLUENCE LINE FROM NEAR YKN SSWWD BETWEEN HSI-EAR...THEN
INTERSECTING DRYLINE BULGE AND WEAK MESOLOW INVOF HLC.  ISOLATED
TSTM HAS DEVELOPED WHERE THIS CONFLUENCE LINE JUXTAPOSES WITH SFC
THERMAL AXIS...ACCORDINGLY MAXIMIZING BOUNDARY-LAYER LIFT.  35-45 KT
EFFECTIVE SHEAR VECTORS ALIGNED NEARLY PARALLEL WITH ZONES OF
ENHANCED LOW-LEVEL FORCING SUPPORT EVENTUAL QUASI-LINEAR
ORGANIZATION...ALTHOUGH EML-RELATED CINH SHOULD FOSTER SOME DISCRETE
CELLS BEFORE SUCH UPSCALE DEVELOPMENT/GROWTH.  MODIFIED FCST
SOUNDINGS SUGGEST MLCAPE AROUND 1500-2000 J/KG...WHICH SHOULD CHANGE
LITTLE THROUGH ABOUT 02Z BEFORE SLOW NOCTURNAL DECREASE.  LLJ IS
EXPECTED TO STRENGTHEN CONTERMINOUSLY OVER THIS
REGION...HOWEVER...OFFERING ENHANCED STORM-RELATIVE INFLOW AND
MOISTURE TRANSPORT FOR TSTMS EITHER BACKBUILDING FROM MN/SD MCS OR
DEVELOPING ANEW ACROSS NEB.

..EDWARDS.. 05/02/2012

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

ATTN...WFO...DMX...FSD...OAX...GID...LBF...

LAT...LON   41520005 43209815 42809827 42839671 42859486 41389603
            40209776 40059876 40610009 41520005

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 1, 9:18 PM CDT	Severe Thunderstorm Watch	SPC	Adair, Adams, Audubon, Black Hawk, Boone, Buena Vista and 54 more	7 hr
May 1, 11:08 PM CDT	Mesoscale Discussion	SPC	Adair, Adams, Audubon, Black Hawk, Boone, Bremer and 47 more	2 hr
May 2, 2:02 AM CDT	Mesoscale Discussion	SPC	Adair, Adams, Audubon, Boone, Carroll, Cass and 22 more	58 min
May 2, 3:34 PM CDT	Mesoscale Discussion	SPC	Clay, Dickinson, Emmet, Lyon, O'Brien, Osceola and 2 more	86 min

Nearby

Mesoscale Discussions in Nebraska, 2012 Mesoscale Discussions in Iowa, 2012 Every mesoscale discussion in 2012

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.