Alert archive / Nebraska / Mesoscale Discussions in 2012

Mesoscale Discussion 840

May 19, 201216 counties in Iowa; 20 counties in Kansas; 26 counties in Nebraska

The Storm Prediction Center issued this mesoscale discussion at May 19, 2012, 5:41 PM CDT for 16 counties in Iowa; 20 counties in Kansas; 26 counties in Nebraska. It was in force for 64 min.

The area

The outline as issued.

The facts

Issued: May 19, 2012, 5:41 PM CDT (22:41 UTC)
Expired: May 19, 2012, 6:45 PM CDT
In force: 64 min
Issued by: the Storm Prediction Center

All 62 counties

Buena Vista County, IA, Cherokee County, IA, Clay County, IA, Crawford County, IA, Harrison County, IA, Ida County, IA, Mills County, IA, Monona County, IA, O'Brien County, IA, Palo Alto County, IA, Plymouth County, IA, Pocahontas County, IA, Pottawattamie County, IA, Sac County, IA, Shelby County, IA, Woodbury County, IA, Butler County, KS, Chase County, KS, Clay County, KS, Cloud County, KS, Dickinson County, KS, Geary County, KS, Harvey County, KS, Kingman County, KS, Marion County, KS, Marshall County, KS, McPherson County, KS, Morris County, KS, Ottawa County, KS, Pottawatomie County, KS, Reno County, KS, Republic County, KS, Riley County, KS, Saline County, KS, Sedgwick County, KS, Washington County, KS, Burt County, NE, Butler County, NE, Cass County, NE, Colfax County, NE, Cuming County, NE, Dakota County, NE, Dodge County, NE, Douglas County, NE, Fillmore County, NE, Gage County, NE, Jefferson County, NE, Johnson County, NE, Lancaster County, NE, Nemaha County, NE, Nuckolls County, NE, Otoe County, NE, Pawnee County, NE, Polk County, NE, Saline County, NE, Sarpy County, NE, Saunders County, NE, Seward County, NE, Thayer County, NE, Thurston County, NE, Washington County, NE, York County, NE

The radar

The Omaha radar (KOAX), 81 km from the middle of the area, began a volume at 22:43 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.

The nearest sounding before it

Omaha, NE (KOAX), launched 12:00Z, 10.7 hours before the alert went out and 80 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: 438 J/kg
Mixed-layer CIN: -453 J/kg
Mixed-layer LCL: 1205 m above ground
0-6 km bulk shear: 24 kt
0-1 km storm-relative helicity: 348 m²/s²
0-3 km storm-relative helicity: 455 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.

887 
ACUS11 KWNS 192241
SWOMCD
SPC MCD 192241 
IAZ000-MOZ000-NEZ000-KSZ000-SDZ000-192345-

MESOSCALE DISCUSSION 0840
NWS STORM PREDICTION CENTER NORMAN OK
0541 PM CDT SAT MAY 19 2012

AREAS AFFECTED...ERN NEB...CNTRL KS...WRN IA

CONCERNING...SEVERE THUNDERSTORM WATCH 281...

VALID 192241Z - 192345Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 281
CONTINUES.

SUMMARY...PRIMARILY LARGE HAIL AND ISOLATED DAMAGING WIND RISKS
SHOULD BE PEAKING THROUGH THE NEXT FEW HOURS...WITH A MARGINAL
SEVERE THREAT LIKELY TO DEVELOP NE OF WW 281 IN NWRN IA. THIS AREA
IS BEING MONITORED FOR A POSSIBLE WW.

DISCUSSION...BROKEN LINE OF CONVECTION WITH SEVERAL EMBEDDED
SUPERCELL STRUCTURES WERE PRESENT ALONG A COLD FRONT THAT EXTENDED
FROM NEAR OLU SWWD TO A SURFACE LOW IN NUCKOLLS COUNTY NEB...AND
THEN SWD TO AROUND 20 NE P28. NUMEROUS REPORTS OF LARGE HAIL /SOME
SIGNIFICANT/ HAVE ALREADY OCCURRED WITH THESE SUPERCELLS. BUT WITH
CELL MERGERS/UPSCALE GROWTH RESULTING IN DISRUPTIVE INTERFERENCE OF
UPDRAFTS...ALONG WITH RELATIVELY LARGE SURFACE DEW POINT DEPRESSIONS
AND COMPOSITE OUTFLOW/EFFECTIVE FRONT SURGING AHEAD OF THE
CONVECTION...OVERALL SEVERE THREAT SHOULD BE AT/NEAR PEAK...LIKELY
WANING AFTER SUNSET. THE AFOREMENTIONED REASONING SHOULD CONTINUE TO
MITIGATE A MORE ROBUST TORNADO THREAT...BEYOND WEAK/BRIEF TOUCHDOWNS
MOST PROBABLE JUST E/NE OF THE SURFACE LOW IN SERN NEB.

AN MCS CLUSTER MAY DEVELOP NEWD ALONG THE FRONT INTO NWRN IA...WHICH
IS GENERALLY SUPPORTED BY CONVECTION-ALLOWING MODEL GUIDANCE. THE
SEVERE THREAT MAY BE MORE TEMPERED BY THE TIME CONVECTION FORMS NE
OF WW 281...BREEDING UNCERTAINTY IN THE NECESSITY OF A DOWNSTREAM
WW.

..GRAMS.. 05/19/2012

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

ATTN...WFO...DMX...EAX...FSD...OAX...TOP...ICT...GID...

LAT...LON   41339760 42839626 43349573 43369511 43069448 42719451
            41229541 40239591 37529666 37289797 37329823 37939822
            39849811 40189818 41339760

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 19, 2:36 PM CDT	Mesoscale Discussion	SPC	Fremont, Harrison, Mills, Pottawattamie	84 min
May 19, 3:25 PM CDT	Severe Thunderstorm Watch	SPC	Fremont, Harrison, Mills, Monona, Pottawattamie, Shelby	7 hr
May 19, 6:52 PM CDT	Severe Thunderstorm Watch	SPC	Adair, Audubon, Buena Vista, Calhoun, Carroll, Cass and 17 more	5 hr
May 19, 1:37 PM CDT	Mesoscale Discussion	SPC	Cheyenne, Decatur, Gove, Greeley, Hamilton, Kearny and 9 more	113 min
May 19, 12:51 AM CDT	Mesoscale Discussion	SPC	Brown, Keya Paha	84 min

Nearby

Mesoscale Discussions in Nebraska, 2012 Mesoscale Discussions in Kansas, 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.