Alert archive / Iowa / Mesoscale Discussions in 2012

Mesoscale Discussion 1490

July 18, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Jul 18, 2012, 11:38 AM CDT for 4 states. It was in force for 67 min.

The area

The outline as issued.

The facts

Issued: Jul 18, 2012, 11:38 AM CDT (16:38 UTC)
Expired: Jul 18, 2012, 12:45 PM CDT
In force: 67 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 56 counties

Allamakee County, IA, Black Hawk County, IA, Bremer County, IA, Buchanan County, IA, Butler County, IA, Cerro Gordo County, IA, Chickasaw County, IA, Clayton County, IA, Clinton County, IA, Delaware County, IA, Dubuque County, IA, Fayette County, IA, Floyd County, IA, Franklin County, IA, Grundy County, IA, Hardin County, IA, Howard County, IA, Jackson County, IA, Jones County, IA, Linn County, IA, Mitchell County, IA, Winneshiek County, IA, Worth County, IA, Wright County, IA, Boone County, IL, Bureau County, IL, Carroll County, IL, DeKalb County, IL, DuPage County, IL, Grundy County, IL, Jo Daviess County, IL, Kane County, IL, Kendall County, IL, LaSalle County, IL, Lee County, IL, McHenry County, IL, Ogle County, IL, Stephenson County, IL, Whiteside County, IL, Will County, IL, Winnebago County, IL, Fillmore County, MN, Houston County, MN, Mower County, MN, Olmsted County, MN, Winona County, MN, Crawford County, WI, Dane County, WI, Grant County, WI, Green County, WI, Iowa County, WI, La Crosse County, WI, Lafayette County, WI, Richland County, WI, Rock County, WI, Vernon County, WI

The radar

The Quad Cities radar (KDVN), 99 km from the middle of the area, began a volume at 16:42 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.

Severe Thunderstorm Watch 493Jul 18, 1:00 PM CDT

The nearest sounding before it

Davenport, (KDVN), launched 12:00Z, 4.6 hours before the alert went out and 100 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: 1900 J/kg
Mixed-layer CIN: -67 J/kg
Mixed-layer LCL: 1674 m above ground
0-6 km bulk shear: 22 kt
0-1 km storm-relative helicity: 35 m²/s²
0-3 km storm-relative helicity: 44 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.

187 
ACUS11 KWNS 181639
SWOMCD
SPC MCD 181638
ILZ000-WIZ000-IAZ000-MNZ000-181745-

MESOSCALE DISCUSSION 1490
NWS STORM PREDICTION CENTER NORMAN OK
1138 AM CDT WED JUL 18 2012

AREAS AFFECTED...SRN MN...SWRN WI...NERN IA...NRN IL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 181638Z - 181745Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...DMGG WIND AND HAIL WILL BECOME POSSIBLE THIS
AFTERNOON...WITH A LOOSELY ORGANIZED CLUSTER PROGRESSING SEWD WITH
TIME. AREA IS BEING MONITORED FOR A POSSIBLE WW.

DISCUSSION...THE ONGOING ELEVATED THUNDERSTORMS ACROSS CNTRL/SRN MN
HAS LEFT AN OUTFLOW BOUNDARY...LOCATED JUST E OF FARIBAULT MN AND
EXTENDING SWWD THROUGH ALGONA IA. TWO SEPARATE BOUNDARIES ARE ALSO
ORIENTED NEAR MN/WI/IA/IL...INCLUDING BUT NOT LIMITED TO A
DIFFERENTIAL HEATING ZONE ACROSS CNTRL WI...AND A COLD FRONT
ORIENTED ACROSS NRN IA AND IL. WITH AMBIENT MOISTURE AND SURFACE
TEMPERATURES QUICKLY WARMING INTO THE 80S TO LOWER 90S F...MODIFIED
MPX AND DVN SOUNDINGS INDICATE ANY REMAINING CONVECTIVE INHIBITION
WILL BE ERODED SHORTLY. AS SUCH...EXPECT A GENERAL INCREASE IN
CONVECTION...PARTICULARLY NEAR THE OUTFLOW/COLD FRONT INTERSECTION
ACROSS SERN MN AND NERN IA. ALTHOUGH DEEP LAYER SHEAR IS WEAK...AS
THE EVOLVING CLUSTER OF STORMS PROGRESSES TOWARDS THE GREAT
LAKES...IT WILL ENCOUNTER LIGHT-MODEST NWLY FLOW ALOFT...SUPPORTING
MULTICELLULAR CLUSTERS CAPABLE OF DMGG WIND AND HAIL.

..HURLBUT/MEAD.. 07/18/2012

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

ATTN...WFO...LOT...MKX...DVN...ARX...MPX...DMX...

LAT...LON   42709397 44119258 44199143 43128941 42398833 41748764
            41288800 41108877 41609009 42309247 42459406 42709397

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 18, 12:58 PM CDT	Severe Thunderstorm Watch	SPC	Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 22 more	7 hr
Jul 18, 3:07 PM CDT	Mesoscale Discussion	SPC	Boone, Bureau, Carroll, DeKalb, DuPage, Grundy and 20 more	53 min
Jul 18, 6:56 PM CDT	Mesoscale Discussion	SPC	Boone, Cook, DeKalb, DuPage, Grundy, Jo Daviess and 8 more	94 min

Nearby

Mesoscale Discussions in Iowa, 2012 Mesoscale Discussions in Illinois, 2012 Mesoscale Discussions in Wisconsin, 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.