Alert archive / Wisconsin / Mesoscale Discussions in 2012

Mesoscale Discussion 1879

September 4, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Sep 4, 2012, 1:33 PM CDT for 4 states. It was in force for 117 min.

The area

The outline as issued.

The facts

Issued
Sep 4, 2012, 1:33 PM CDT (18:33 UTC)
Expired
Sep 4, 2012, 3:30 PM CDT
In force
117 min
Issued by
the Storm Prediction Center
Chance of a watch
80%
All 53 counties

Allamakee County, IA, Bremer County, IA, Chickasaw County, IA, Clayton County, IA, Delaware County, IA, Fayette County, IA, Howard County, IA, Winneshiek County, IA, Gogebic County, MI, Fillmore County, MN, Goodhue County, MN, Houston County, MN, Mower County, MN, Olmsted County, MN, Wabasha County, MN, Winona County, MN, Adams County, WI, Ashland County, WI, Barron County, WI, Bayfield County, WI, Buffalo County, WI, Burnett County, WI, Chippewa County, WI, Clark County, WI, Crawford County, WI, Douglas County, WI, Dunn County, WI, Eau Claire County, WI, Grant County, WI, Iowa County, WI, Iron County, WI, Jackson County, WI, Juneau County, WI, La Crosse County, WI, Lafayette County, WI, Lincoln County, WI, Marathon County, WI, Monroe County, WI, Pepin County, WI, Pierce County, WI, Polk County, WI, Portage County, WI, Price County, WI, Richland County, WI, Rusk County, WI, Saint Croix County, WI, Sauk County, WI, Sawyer County, WI, Taylor County, WI, Trempealeau County, WI, Vernon County, WI, Washburn County, WI, Wood County, WI

The radar

The La Crosse radar (KARX), 125 km from the middle of the area, began a volume at 18:36 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

Minneapolis, MN (KMPX), launched 12:00Z, 6.6 hours before the alert went out and 198 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-pSkew-T log-p diagram, Minneapolis, MN at 12:00Z on 2012-09-04Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1446 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Minneapolis, MN at 12:00Z on 2012-09-04The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 172 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
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
1446 J/kg
Mixed-layer CIN
-171 J/kg
Mixed-layer LCL
1471 m above ground
0-6 km bulk shear
28 kt
0-1 km storm-relative helicity
172 m²/s²
0-3 km storm-relative helicity
221 m²/s²
Significant tornado parameter
0.0
Supercell composite
7.8

Open this sounding in Storm Lab

The text

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

010 
ACUS11 KWNS 041834
SWOMCD
SPC MCD 041833
MIZ000-WIZ000-IAZ000-MNZ000-042030-

MESOSCALE DISCUSSION 1879
NWS STORM PREDICTION CENTER NORMAN OK
0133 PM CDT TUE SEP 04 2012

AREAS AFFECTED...CNTRL AND WRN WI...NERN IA...SERN MN

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 041833Z - 042030Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...STORMS ARE EXPECTED TO DEVELOP PRIOR BY 20-21Z WITH VERY
LARGE HAIL AND DAMAGING WINDS.

DISCUSSION...A COLD FRONT CONTINUES TO PROGRESS EWD TOWARD THE MS
RIVER AND TRAILING SWWD INTO NWRN IA. STRONG HEATING PERSISTS AND CU
FIELDS ARE BEGINNING TO FORM. MODIFIED SOUNDINGS SUGGEST
TEMPERATURES IN THE MOD TO UPPER 80S F WILL ERODE ALL CIN...AND SFC
CONVERGENCE SHOULD BE ENOUGH TO INITIATE STORMS ALONG THE FRONT.
LAPSE RATES ALOFT ARE QUITE STEEP...AND WILL SUPPORT RAPID STORM
DEVELOPMENT. WHILE LOW LEVEL FLOW IS WEAK...MID TO UPPER LEVEL FLOW
IS SUBSTANTIAL AND SHOULD SUPPORT LONG LIVED SEVERE STORMS INCLUDING
SUPERCELLS. AS SUCH...VERY LARGE HAIL WILL BE POSSIBLE. DAMAGING
WINDS WILL ALSO BE A THREAT AS STORMS PRODUCE SIGNIFICANT COLD
DOWNDRAFTS AND BEGIN TO EXPAND AND FORWARD PROPAGATE LATER TODAY.

..JEWELL/CORFIDI.. 09/04/2012

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

ATTN...WFO...MQT...GRB...MKX...DVN...DLH...ARX...MPX...DMX...

LAT...LON   44678941 43668944 42698981 42459130 42739231 43699281
            45009283 46029275 46549270 46879217 47049079 46868993
            46358961 44678941

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 4, 3:27 PM CDTSevere Thunderstorm WatchSPCAllamakee, Black Hawk, Bremer, Buchanan, Butler, Chickasaw and 9 more8 hr
Sep 4, 5:08 PM CDTMesoscale DiscussionSPCHarrison, Monona97 min
Sep 4, 6:39 PM CDTMesoscale DiscussionSPCAllamakee, Black Hawk, Bremer, Buchanan, Butler, Chickasaw and 9 more66 min

Nearby

Mesoscale Discussions in Wisconsin, 2012Mesoscale Discussions in Iowa, 2012Mesoscale Discussions in Minnesota, 2012Every 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.