Alert archive / Iowa / Mesoscale Discussions in 2012

Mesoscale Discussion 1908

September 6, 201231 counties in Iowa

The Storm Prediction Center issued this mesoscale discussion at Sep 6, 2012, 9:33 PM CDT for 31 counties in Iowa. It was in force for 117 min.

The area

The outline as issued.

The facts

Issued: Sep 6, 2012, 9:33 PM CDT (02:33 UTC)
Expired: Sep 6, 2012, 11:30 PM CDT
In force: 117 min
Issued by: the Storm Prediction Center
Chance of a watch: 60%

All 31 counties

Audubon County, IA, Boone County, IA, Buena Vista County, IA, Butler County, IA, Calhoun County, IA, Carroll County, IA, Cerro Gordo 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, Jasper County, IA, Kossuth County, IA, Marshall County, IA, O'Brien County, IA, Palo Alto County, IA, Pocahontas County, IA, Polk County, IA, Sac County, IA, Story County, IA, Webster County, IA, Wright County, IA

The nearest sounding before it

Omaha, NE (KOAX), launched 00:00Z, 2.6 hours before the alert went out and 197 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.

876 
ACUS11 KWNS 070233
SWOMCD
SPC MCD 070233 
IAZ000-070430-

MESOSCALE DISCUSSION 1908
NWS STORM PREDICTION CENTER NORMAN OK
0933 PM CDT THU SEP 06 2012

AREAS AFFECTED...PORTIONS OF IA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 070233Z - 070430Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...POTENTIAL FOR AT LEAST ISOLATED SEVERE HAIL/PERHAPS
DAMAGING WINDS SHOULD CONTINUE TO INCREASE THROUGH LATE EVENING
ACROSS NORTHWEST/CENTRAL IA. WHILE THE EXTENT/MAGNITUDE OF THE
SEVERE POTENTIAL THIS EVENING INTO THE OVERNIGHT IS A BIT
UNCERTAIN...DEVELOPMENTAL TRENDS WILL BE CLOSELY MONITORED FOR A
POSSIBLE WATCH.

DISCUSSION...MASS RESPONSE APPEARS TO BE QUICKLY OCCURRING ACROSS
THE MIDDLE MO VALLEY/IA VICINITY OWING TO UPSTREAM HEIGHT FALLS
JET/APPROACHING UPPER JET STREAK...WITH A RECENT /SINCE 0115Z/
DEVELOPMENT AND QUICK INCREASE OF A STRONG/SEVERE TSTM ACROSS
NORTHWEST IA. THIS ACTIVITY IS OCCURRING ATOP A DRY/STABLE BOUNDARY
LAYER TO THE NORTH-NORTHEAST OF A SURFACE LOW/WARM FRONT. IN TANDEM
WITH THE WARM FRONT...A MOIST INFLUX WILL CONTINUE TO OCCUR
NEAR/ABOVE THE SURFACE...ALTHOUGH THE IMMEDIATE SOURCE REGION
AIRMASS /AT LEAST INITIALLY/ IS NOT ROBUSTLY MOIST...REFERENCE 9
G/KG MEAN MIXING RATIO PER THE 00Z OMAHA OBSERVED SOUNDING. 

NONETHELESS...WITH AN INCREASING LOW LEVEL JET/DEEP LAYER FORCING
FOR ASCENT...FACTORS SUCH AS THE AFOREMENTIONED MOIST INFLUX...EDGE
OF THE ELEVATED MIXED LAYER...AND A STRONGLY SHEARED ENVIRONMENT MAY
ACCOUNT FOR A SUSTENANCE/ADDITIONAL INTENSIFICATION OF THIS INITIAL
DEVELOPMENT...WHILE LIKELY LEADING TO ADDITIONAL TSTMS BY LATE
EVENING/OVERNIGHT ACROSS NORTHWEST/CENTRAL IA. AT LEAST AN
ISOLATED/MARGINAL SEVERE HAIL THREAT WILL LIKELY BE THE PRIMARY
HAZARD GIVEN THE ELEVATED NATURE OF THESE STORMS. HOWEVER...DAMAGING
WINDS CANNOT BE DISCOUNTED LATER THIS EVENING/OVERNIGHT ESPECIALLY
NEAR/JUST NORTHEAST OF THE WARM FRONT GIVEN STEADY LOW-LEVEL
MOISTENING AND INCREASINGLY STRONG MEAN WESTERLY FLOW.

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

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

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

LAT...LON   42119579 43389589 43319362 42859257 41729291 41359342
            41519502 42119579

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 6, 11:56 PM CDT	Mesoscale Discussion	SPC	Audubon, Black Hawk, Boone, Buena Vista, Calhoun, Carroll and 33 more	2 hr

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.