Alert archive / Wisconsin / Mesoscale Discussions in 2012

Mesoscale Discussion 849

May 20, 2012Baraga County, Dickinson County, Iron County, Michigan; 24 counties in Wisconsin

The Storm Prediction Center issued this mesoscale discussion at May 20, 2012, 11:52 AM EDT for Baraga County, Dickinson County, Iron County, Michigan; 24 counties in Wisconsin. It was in force for 113 min.

The area

The outline as issued.

The facts

Issued: May 20, 2012, 11:52 AM EDT (15:52 UTC)
Expired: May 20, 2012, 1:45 PM EDT
In force: 113 min
Issued by: the Storm Prediction Center
Chance of a watch: 80%

All 27 counties

Baraga County, MI, Dickinson County, MI, Iron County, MI, Adams County, WI, Clark County, WI, Florence County, WI, Forest County, WI, Jackson County, WI, Juneau County, WI, La Crosse County, WI, Langlade County, WI, Lincoln County, WI, Marathon County, WI, Marquette County, WI, Menominee County, WI, Monroe County, WI, Oneida County, WI, Portage County, WI, Price County, WI, Shawano County, WI, Taylor County, WI, Vernon County, WI, Vilas County, WI, Waupaca County, WI, Waushara County, WI, Winnebago County, WI, Wood County, WI

The radar

The Green Bay radar (KGRB), 126 km from the middle of the area, began a volume at 15:52 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 285May 20, 1:25 PM EDT

The nearest sounding before it

Green Bay/Straub, WI (KGRB), launched 12:00Z, 3.9 hours before the alert went out and 128 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: 752 J/kg
Mixed-layer CIN: -121 J/kg
Mixed-layer LCL: 1614 m above ground
0-6 km bulk shear: 25 kt
0-1 km storm-relative helicity: 51 m²/s²
0-3 km storm-relative helicity: 31 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.

829 
ACUS11 KWNS 201553
SWOMCD
SPC MCD 201552
MIZ000-WIZ000-201745-

MESOSCALE DISCUSSION 0849
NWS STORM PREDICTION CENTER NORMAN OK
1052 AM CDT SUN MAY 20 2012

AREAS AFFECTED...CNTRL AND NRN WI THROUGH THE WRN UPPER PENINSULA OF
MI

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 201552Z - 201745Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...STORMS DEVELOPING ALONG AND JUST AHEAD OF THE COLD FRONT
SHOULD UNDERGO A GRADUAL INCREASE IN COVERAGE AND INTENSITY
INITIALLY FROM WRN THROUGH W CNTRL WI AND NWD INTO THE WRN UPPER
PENINSULA OF MI. DEVELOPING STORMS WILL EVENTUALLY POSE A THREAT OF
MAINLY DAMAGING WIND AND ISOLATED LARGE HAIL...BUT A COUPLE OF
TORNADOES CANNOT BE RULED OUT. A SEVERE THUNDERSTORM WATCH WILL
LIKELY BE NEEDED BY 17Z-18Z.

DISCUSSION...LATE THIS MORNING A COLD FRONT EXTENDS FROM LAKE
SUPERIOR SWWD TO A SURFACE LOW NEAR THE WI/MN BORDER THEN SWD
THROUGH SERN MN AND ERN IA. BOUNDARY LAYER DESTABILIZATION IS
OCCURRING IN THE PRE-FRONTAL WARM SECTOR WHERE UPPER 50S TO 60F
DEWPOINTS EXIST BENEATH 7-7.5 C/KM MID LEVEL LAPSE RATES. OBJECTIVE
ANALYSIS ALREADY SHOWS MLCAPE RANGING FROM 1000-1500 J/KG OVER MUCH
OF WI. STORMS CURRENTLY DEVELOPING WITHIN ZONE OF PRE-FRONTAL
CONFLUENCE AND ISENTROPIC ASCENT IN NWRN WI ARE AT LEAST SLIGHTLY
ELEVATED AND MAY POSE A NEAR TERM RISK FOR MARGINALLY SEVERE HAIL.

MODIFIED 12Z RAOBS SUGGEST SURFACE BASED CONVECTIVE INHIBITION WILL
WEAKEN SIGNIFICANTLY ONCE SURFACE TEMPERATURES REACH THE MID 80S.
ADDITIONAL STORMS WILL LIKELY DEVELOP AS PROGRESSIVE SHORTWAVE
TROUGH AUGMENTS DEEP ASCENT ALONG ADVANCING COLD FRONT. VERTICAL
SHEAR FROM 35-40 KT IN VICINITY OF BAROCLINIC ZONE WILL SUPPORT
ORGANIZED STORMS INCLUDING EMBEDDED SUPERCELL AND LEWP STRUCTURES.

..DIAL/WEISS.. 05/20/2012

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

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

LAT...LON   46468754 43888873 43409113 45109113 46858883 46468754

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 20, 1:24 PM EDT	Severe Thunderstorm Watch	SPC	Baraga, Dickinson, Gogebic, Houghton, Iron, Marquette and 2 more	7 hr
May 20, 3:57 PM EDT	Mesoscale Discussion	SPC	Baraga, Dickinson, Houghton, Iron, Marquette, Menominee	2 hr
May 20, 2:17 PM EDT	Mesoscale Discussion	SPC	Columbia, Dane, Dodge, Green, Jefferson, Kenosha and 4 more	118 min
May 20, 4:50 PM EDT	Mesoscale Discussion	SPC	Walworth, Waukesha	85 min

Nearby

Mesoscale Discussions in Wisconsin, 2012 Mesoscale Discussions in Michigan, 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.