Alert archive / Iowa / Mesoscale Discussions in 2012

Mesoscale Discussion 2181

December 19, 201230 counties in Iowa; 10 counties in Nebraska

The Storm Prediction Center issued this mesoscale discussion at Dec 19, 2012, 9:32 PM CST for 30 counties in Iowa; 10 counties in Nebraska. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: Dec 19, 2012, 9:32 PM CST (03:32 UTC)
Expired: Dec 20, 2012, 3:00 AM CST
In force: 5 hr
Issued by: the Storm Prediction Center

All 40 counties

Adair County, IA, Adams County, IA, Audubon County, IA, Black Hawk County, IA, Boone County, IA, Bremer County, IA, Buchanan County, IA, Butler County, IA, Carroll County, IA, Cass County, IA, Chickasaw County, IA, Dallas County, IA, Fayette County, IA, Franklin County, IA, Fremont County, IA, Greene County, IA, Grundy County, IA, Guthrie County, IA, Hamilton County, IA, Hardin County, IA, Harrison County, IA, Madison County, IA, Marshall County, IA, Mills County, IA, Montgomery County, IA, Polk County, IA, Pottawattamie County, IA, Shelby County, IA, Story County, IA, Tama County, IA, Cass County, NE, Douglas County, NE, Johnson County, NE, Lancaster County, NE, Otoe County, NE, Saline County, NE, Sarpy County, NE, Saunders County, NE, Seward County, NE, Washington County, NE

The radar

The Des Moines radar (KDMX), 62 km from the middle of the area, began a volume at 03:30 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 nearest sounding before it

Omaha, NE (KOAX), launched 00:00Z, 3.5 hours before the alert went out and 163 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 472 m above ground
0-6 km bulk shear: 61 kt
0-1 km storm-relative helicity: 183 m²/s²
0-3 km storm-relative helicity: 888 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.

893 
ACUS11 KWNS 200332
SWOMCD
SPC MCD 200332 
IAZ000-MOZ000-NEZ000-200900-

MESOSCALE DISCUSSION 2181
NWS STORM PREDICTION CENTER NORMAN OK
0932 PM CST WED DEC 19 2012

AREAS AFFECTED...ERN NEB / W-CNTRL INTO NERN IA

CONCERNING...BLIZZARD 

VALID 200332Z - 200900Z

SUMMARY...BLIZZARD CONDITIONS ARE BEGINNING OVER PARTS OF E-CNTRL
NEB AND WILL COMMENCE FROM WSW-ENE FROM NEAR THE MISSOURI RIVER
/04-06 UTC/ TO CNTRL IA /07-09 UTC/.

DISCUSSION...WATER VAPOR IMAGERY SHOWS A VIGOROUS UPPER TROUGH
MOVING EWD FROM THE CNTRL PLAINS TOWARDS THE LOWER MO RIVER VALLEY. 
AS THIS OCCURS...00Z TOP RAOB SHOWED A MID LEVEL WARM NOSE AND THIS
EXTENDS INTO SRN IA/NRN MO EARLY THIS EVENING.  SURFACE MESOANALYSIS
SHOWS A DEEPENING 996 MB LOW OVER SERN KS THAT IS EXPECTED TO
DEVELOP ENEWD INTO W-CNTRL MO DURING THE OVERNIGHT.  A CONSISTENT
ENVELOPE OF WIND GUSTS AOA 35 MPH ENCOMPASSES E-CNTRL NEB SWWD INTO
THE WRN HALF OF KS...CREATING BLIZZARD CONDITIONS WHERE APPRECIABLE
SNOWFALL RATES/FRESHLY FALLEN SNOW ARE HINDERING VISIBILITIES.

MODEL GUIDANCE IS CONSISTENT IN SHOWING THE AXIS OF HEAVIEST
SNOWFALL RATES /1-1.5 INCH PER HR/ IN A SWATH NEAR THE MO RIVER AND
EVENTUALLY LATER OVER CNTRL AND NERN IA DURING THE 06-09 UTC PERIOD.
CONVECTIVE ENHANCEMENT TO PRECIP RATES OVER THE NEXT SEVERAL HOURS
IN IA /AS IMPLIED VIA OBSERVED LIGHTNING/ WILL ACT TO LOCALLY
AUGMENT RATES.  AS AN ASIDE...FORECAST SOUNDINGS SHOW THE COLUMN
COOLING 1-2 DEG C IN THE H8-H7 LAYER DURING THE 04-06 UTC TIME FRAME
NEAR DSM...TERMINATING MIXED P-TYPE /SNOW AND SLEET/ AND RESULTING
IN HEAVY SNOWFALL RATES.

MODEL DATA SHOW A TIME LAG ON THE ORDER OF SEVERAL HOURS FOR THE
HEAVIEST SNOWFALL RATES BEGINNING AND THE STRONGER WINDS
DEVELOPING...WHICH WILL LEAD TO INTERMITTENT BLIZZARD CONDITIONS
BECOMING MORE COMMON BY LATE TONIGHT.  TIMING OF BLIZZARD CONDITIONS
SEEMINGLY WILL OCCUR BY 06 UTC NEAR AND W OF THE MO RIVER...AND
APPROACH CNTRL IA BY 07-09 UTC.

..SMITH.. 12/20/2012

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

ATTN...WFO...DVN...ARX...DMX...EAX...OAX...

LAT...LON   43149231 43019179 42679168 42419180 41519341 40629567
            40309636 40309693 40529736 40979726 41429672 43149231

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 20, 3:12 AM CST	Mesoscale Discussion	SPC	Allamakee, Clayton, Winneshiek	4 hr
Dec 20, 7:49 AM CST	Mesoscale Discussion	SPC	Appanoose, Cedar, Davis, Des Moines, Henry, Jefferson and 10 more	4 hr
Dec 20, 10:52 AM CST	Mesoscale Discussion	SPC	Clinton, Des Moines, Scott	6 hr
Dec 19, 6:19 PM CST	Mesoscale Discussion	SPC	Adams, Buffalo, Clay, Fillmore, Franklin, Furnas and 15 more	4 hr

Nearby

Mesoscale Discussions in Iowa, 2012 Mesoscale Discussions in Nebraska, 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.