Alert archive / Iowa / Mesoscale Discussions in 2012

Mesoscale Discussion 1909

September 6, 201239 counties in Iowa

The Storm Prediction Center issued this mesoscale discussion at Sep 6, 2012, 11:56 PM CDT for 39 counties in Iowa. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Sep 6, 2012, 11:56 PM CDT (04:56 UTC)
Expired: Sep 7, 2012, 2:00 AM CDT
In force: 2 hr
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 39 counties

Audubon County, IA, Black Hawk County, IA, Boone County, IA, Buena Vista County, IA, Calhoun County, IA, Carroll County, IA, Cherokee County, IA, Clay County, IA, Crawford County, IA, Dallas County, IA, Franklin County, IA, Greene County, IA, Grundy County, IA, Guthrie County, IA, Hamilton County, IA, Hancock County, IA, Hardin County, IA, Humboldt County, IA, Ida County, IA, Iowa County, IA, Jasper County, IA, Keokuk County, IA, Lucas County, IA, Madison County, IA, Mahaska County, IA, Marion County, IA, Marshall County, IA, Monroe County, IA, O'Brien County, IA, Palo Alto County, IA, Pocahontas County, IA, Polk County, IA, Poweshiek County, IA, Sac County, IA, Story County, IA, Tama County, IA, Warren County, IA, Webster County, IA, Wright County, IA

The nearest sounding before it

Omaha, NE (KOAX), launched 00:00Z, 4.9 hours before the alert went out and 202 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: 275 J/kg
Mixed-layer CIN: -320 J/kg
Mixed-layer LCL: 2527 m above ground
0-6 km bulk shear: 45 kt
0-1 km storm-relative helicity: 140 m²/s²
0-3 km storm-relative helicity: 305 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.2

Open this sounding in Storm Lab

The text

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

856 
ACUS11 KWNS 070456
SWOMCD
SPC MCD 070456 
IAZ000-070700-

MESOSCALE DISCUSSION 1909
NWS STORM PREDICTION CENTER NORMAN OK
1156 PM CDT THU SEP 06 2012

AREAS AFFECTED...PORTIONS OF IA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 070456Z - 070700Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...POTENTIAL FOR AT LEAST ISOLATED SEVERE HAIL AND PERHAPS
DAMAGING WINDS WILL EXIST OVERNIGHT ACROSS PORTIONS OF
IA...INCLUDING NORTHWEST-MUCH OF CENTRAL-SOUTHEAST IA. WHILE THE
EXTENT/MAGNITUDE OF THE SEVERE POTENTIAL REMAINS
UNCLEAR...DEVELOPMENTAL TRENDS ARE STILL BEING MONITORED FOR A
POSSIBLE WATCH.

DISCUSSION...UPDATING EARLIER MESOSCALE DISCUSSION 1908...TSTMS
CONTINUE TO STEADILY INCREASE IN COVERAGE ACROSS NORTHWEST/CENTRAL
PORTIONS OF IA EARLY IN THE OVERNIGHT. THESE TSTMS ARE OCCURRING TO
THE NORTHEAST OF A SURFACE LOW WARM FRONT LOCATED ACROSS FAR EASTERN
NEB/WESTERN IA. WHILE UPDRAFTS HAVE NOT BEEN PARTICULARLY
ROBUST/SUSTAINED OVER THE PAST FEW HOURS...CURRENT CLUSTER ACROSS
NORTH-CENTRAL IA HAS A HISTORY OF 1-1.75 INCH HAIL IN NORTHWEST
IA...AND A SIMILAR THREAT WILL LIKELY CONTINUE OVER THE FEW HOURS AT
LEAST ON A SPORADIC BASIS WITH AID OF A MODERATE LOW LEVEL JET
/REFERENCE 30 KT PER OMAHA AND TOPEKA WSR-88D VWPS/.

AS A WARM/MOIST INFLUX CONTINUES TO OCCUR NEAR/ABOVE THE
SURFACE...ADDITIONAL STORM DEVELOPMENT/POSSIBLE INTENSIFICATION
SHOULD OCCUR ACROSS IA.  WHILE SEVERE HAIL SHOULD BE THE PRIMARY
HAZARD AS THE BOUNDARY LAYER IS RELATIVELY STABLE...POTENTIAL FOR
EVENTUAL UPSCALE GROWTH/CONTINUALLY STRENGTHENING WESTERLY MEAN FLOW
SUGGESTS THAT SOME DAMAGING WIND THREAT CANNOT BE ENTIRELY
DISCOUNTED OVERNIGHT.

..GUYER/HART.. 09/07/2012

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

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

LAT...LON   42119579 43269588 43179368 42429215 41209191 40909304
            41519502 42119579

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 6, 9:33 PM CDT	Mesoscale Discussion	SPC	Audubon, Boone, Buena Vista, Butler, Calhoun, Carroll and 25 more	117 min

Nearby

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.