Alert archive / Nebraska / Mesoscale Discussions in 2011

Mesoscale Discussion 2011

August 18, 20114 states

The Storm Prediction Center issued this mesoscale discussion at Aug 18, 2011, 6:18 PM CDT for 4 states. It was in force for 27 min.

The area

The outline as issued.

The facts

Issued: Aug 18, 2011, 6:18 PM CDT (23:18 UTC)
Expired: Aug 18, 2011, 6:45 PM CDT
In force: 27 min
Issued by: the Storm Prediction Center

All 64 counties

Fremont County, IA, Harrison County, IA, Mills County, IA, Monona County, IA, Montgomery County, IA, Page County, IA, Pottawattamie County, IA, Woodbury County, IA, Atchison County, MO, Holt County, MO, Antelope County, NE, Blaine County, NE, Boone County, NE, Boyd County, NE, Brown County, NE, Burt County, NE, Butler County, NE, Cass County, NE, Cedar County, NE, Cherry County, NE, Clay County, NE, Colfax County, NE, Cuming County, NE, Dakota County, NE, Dixon County, NE, Dodge County, NE, Douglas County, NE, Fillmore County, NE, Gage County, NE, Garfield County, NE, Greeley County, NE, Hall County, NE, Hamilton County, NE, Holt County, NE, Howard County, NE, Johnson County, NE, Keya Paha County, NE, Knox County, NE, Lancaster County, NE, Loup County, NE, Madison County, NE, Merrick County, NE, Nance County, NE, Nemaha County, NE, Otoe County, NE, Pawnee County, NE, Pierce County, NE, Platte County, NE, Polk County, NE, Richardson County, NE, Rock County, NE, Saline County, NE, Sarpy 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, Wheeler County, NE, York County, NE, Union County, SD

The radar

The Omaha radar (KOAX), 144 km from the middle of the area, began a volume at 23:18 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.

Tornado Watch 787Aug 18, 6:40 PM CDT

The nearest sounding before it

Omaha, NE (KOAX), launched 12:00Z, 11.3 hours before the alert went out and 143 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: 1181 J/kg
Mixed-layer CIN: -126 J/kg
Mixed-layer LCL: 683 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 234 m²/s²
0-3 km storm-relative helicity: 385 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 11.7

Open this sounding in Storm Lab

The text

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

313 
ACUS11 KWNS 182319
SWOMCD
SPC MCD 182318
MOZ000-IAZ000-NEZ000-SDZ000-182345-

MESOSCALE DISCUSSION 2011
NWS STORM PREDICTION CENTER NORMAN OK
0618 PM CDT THU AUG 18 2011

AREAS AFFECTED...PARTS OF CENTRAL/ERN NEB...FAR WRN IA...AND FAR
NWRN MO

CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY

VALID 182318Z - 182345Z

THREAT FOR ADDITIONAL TORNADOES SHOULD INCREASE THIS EVENING ACROSS
FAR WRN IA...ERN NEB INTO NRN NEB.  A TORNADO WATCH WILL LIKELY BE
ISSUED TO REPLACE PART OF WW 785...AND INCLUDE AREAS NWWD INTO NRN
NEB.

EARLY EVENING SURFACE ANALYSIS SHOWED A WARM FRONT EXTENDING FROM
SWRN SD ESEWD THROUGH NRN NEB /JUST S OF ANW/ TO SERN HOLT
COUNTY...WITH THIS BOUNDARY THEN EXTENDING SEWD INTO SERN NEB AND
FAR ERN KS.  HIGH THETAE AIR MASS EXISTS INVOF OF THIS WARM FRONT
WITH SURFACE DEWPOINTS IN THE LOWER 70S EXTENDING FROM THE ERN HALF
OF NEB INTO NORTH CENTRAL NEB.  AREA WIND PROFILER DATA SHOWED A
STRENGTHENING SLY LLJ ACROSS THE ERN HALF OF NEB WITH SUBSEQUENT
INCREASE IN LOW LEVEL SHEAR /EFFECTIVE SRH 100-300 M2 PER S2/ WHICH
WILL CONTINUE TO SUPPORT A THREAT FOR A FEW TORNADOES.  THIS THREAT
EXTENDS NWWD INTO NORTH CENTRAL NEB AS A STRONG TO SEVERE STORM
TRACKS SEWD FROM BENNETT COUNTY SD /SRN EXTENT OF WW 786/ INTO NRN
NEB.

..PETERS.. 08/18/2011

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

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

LAT...LON   42250106 42650153 43020188 43049945 42969792 42829640
            42059555 41109505 40189502 40039532 40079636 40289749
            40539836 42250106

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 18, 12:31 PM CDT	Mesoscale Discussion	SPC	Crawford, Harrison, Ida, Mills, Monona, Plymouth and 3 more	89 min
Aug 18, 1:27 PM CDT	Severe Thunderstorm Watch	SPC	Adair, Adams, Audubon, Carroll, Cass, Cherokee and 17 more	8 hr
Aug 18, 2:51 PM CDT	Mesoscale Discussion	SPC	Adair, Adams, Audubon, Cass, Fremont, Guthrie and 9 more	84 min
Aug 18, 6:38 PM CDT	Tornado Watch	SPC	Fremont, Mills, Page	5 hr
Aug 18, 7:41 AM CDT	Mesoscale Discussion	SPC	Douglas, Howell, Oregon, Ozark, Ripley	3 hr
Aug 18, 2:40 PM CDT	Mesoscale Discussion	SPC	Bollinger, Cape Girardeau, Madison, Mississippi, Perry, Scott and 2 more	2 hr
Aug 18, 6:00 PM CDT	Mesoscale Discussion	SPC	Andrew, Atchison, Bates, Benton, Buchanan, Caldwell and 21 more	60 min
Aug 17, 9:18 PM CDT	Mesoscale Discussion	SPC	Blaine, Brown, Chase, Cherry, Dundy, Frontier and 10 more	57 min
Aug 18, 3:43 PM CDT	Mesoscale Discussion	SPC	Beadle, Brookings, Brown, Campbell, Clark, Codington and 20 more	92 min
Aug 18, 4:45 PM CDT	Severe Thunderstorm Watch	SPC	Bennett, Brown, Buffalo, Campbell, Corson, Dewey and 22 more	4 hr

Nearby

Mesoscale Discussions in Nebraska, 2011 Mesoscale Discussions in Iowa, 2011 Mesoscale Discussions in Missouri, 2011 Every mesoscale discussion in 2011

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.