Alert archive / Iowa / Mesoscale Discussions in 2016

Mesoscale Discussion 769

May 28, 20165 counties in Illinois; 30 counties in Iowa; 6 counties in Missouri

The Storm Prediction Center issued this mesoscale discussion at May 28, 2016, 12:37 PM CDT for 5 counties in Illinois; 30 counties in Iowa; 6 counties in Missouri. It was in force for 113 min.

The area

The outline as issued.

The facts

Issued: May 28, 2016, 12:37 PM CDT (17:37 UTC)
Expired: May 28, 2016, 2:30 PM CDT
In force: 113 min
Issued by: the Storm Prediction Center
Chance of a watch: 60%

All 41 counties

Appanoose County, IA, Benton County, IA, Black Hawk County, IA, Buchanan County, IA, Cedar County, IA, Clayton County, IA, Clinton County, IA, Davis County, IA, Delaware County, IA, Des Moines County, IA, Dubuque County, IA, Henry County, IA, Iowa County, IA, Jackson County, IA, Jefferson County, IA, Johnson County, IA, Jones County, IA, Keokuk County, IA, Lee County, IA, Linn County, IA, Louisa County, IA, Mahaska County, IA, Monroe County, IA, Muscatine County, IA, Poweshiek County, IA, Scott County, IA, Tama County, IA, Van Buren County, IA, Wapello County, IA, Washington County, IA, Adams County, IL, Hancock County, IL, Henderson County, IL, Mercer County, IL, Rock Island County, IL, Adair County, MO, Clark County, MO, Knox County, MO, Lewis County, MO, Schuyler County, MO, Scotland County, MO

The radar

The Quad Cities radar (KDVN), 104 km from the middle of the area, began a volume at 17:36 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.

Severe Thunderstorm Watch 225May 28, 1:35 PM CDT

The nearest sounding before it

Davenport, (KDVN), launched 12:00Z, 5.6 hours before the alert went out and 111 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: 48 J/kg
Mixed-layer CIN: -32 J/kg
Mixed-layer LCL: 591 m above ground
0-6 km bulk shear: 38 kt
0-1 km storm-relative helicity: 78 m²/s²
0-3 km storm-relative helicity: 112 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

383 
ACUS11 KWNS 281738
SWOMCD
SPC MCD 281737 
ILZ000-WIZ000-IAZ000-MOZ000-281930-

MESOSCALE DISCUSSION 0769
NWS STORM PREDICTION CENTER NORMAN OK
1237 PM CDT SAT MAY 28 2016

AREAS AFFECTED...PARTS OF NERN MISSOURI/ERN IOWA AND ADJACENT AREAS
OF IL/WI

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 281737Z - 281930Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...THE RISK FOR SEVERE STORMS IS EXPECTED TO GRADUALLY
INCREASE THROUGH THE 20-22Z TIME FRAME.  TIMING REMAINS A BIT
UNCERTAIN...BUT A WATCH SEEMS PROBABLE AT SOME POINT THIS AFTERNOON.

DISCUSSION...AN AREA OF LARGE-SCALE ASCENT /PIVOTING AROUND THE
SOUTHEASTERN PERIPHERY OF THE MID-LEVEL CLOSED LOW OVER THE MID
MISSOURI VALLEY/ IS READILY APPARENT IN SATELLITE
IMAGERY...SPREADING NORTHEASTWARD ACROSS SOUTHERN IOWA AND NORTHERN
MISSOURI.  THIS IS ALREADY CONTRIBUTING TO SCATTERED DEEPENING
CONVECTIVE DEVELOPMENT...WHICH PROBABLY WILL CONTINUE TO GRADUALLY
INTENSIFY WHILE APPROACHING THE MISSISSIPPI RIVER THROUGH 20-22Z.

INSOLATION ACROSS NORTHEAST MISSOURI INTO EASTERN IOWA AND ADJACENT
PORTIONS OF THE MISSISSIPPI VALLEY IS CONTRIBUTING TO STEEPENING
LOW-LEVEL LAPSE RATES.  BOUNDARY LAYER INSTABILITY AS CHARACTERIZED
BY CAPE IS ALSO INCREASING DESPITE SOMEWHAT MODEST MID-LEVEL LAPSE
RATES...THOUGH DIFFERENTIAL UPWARD VERTICAL MOTION AND PERHAPS WEAK
MID-LEVEL COLD ADVECTION MAY CONTRIBUTE TO FURTHER STEEPENING
THROUGH LATE AFTERNOON.

GIVEN THESE TRENDS...IN THE PRESENCE OF SUFFICIENTLY STRONG DEEP
LAYER SHEAR FOR ORGANIZED CONVECTIVE DEVELOPMENT...AND MODEST
STRENGTHENING OF 850-700 MB FLOW TO 30-40+ KT...A GRADUAL INCREASE
IN SEVERE WEATHER POTENTIAL IS EXPECTED THROUGH THE AFTERNOON.  A
TORNADO OR TWO MAY NOT BE OUT OF THE QUESTION IN THE MORE DISCRETE
INITIAL STRONGER STORMS.  HOWEVER...THE RISK FOR MARGINALLY SEVERE
HAIL TRANSITIONING TO MORE GENERAL POTENTIALLY DAMAGING SURFACE
GUSTS APPEARS MORE PRONOUNCED...WITH UPSCALE CONVECTIVE GROWTH INTO
AN EVOLVING ORGANIZED CLUSTER OF STORMS BY LATE AFTERNOON.

..KERR/CORFIDI.. 05/28/2016

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

ATTN...WFO...MKX...LSX...DVN...ARX...DMX...EAX...

LAT...LON   42049291 42719227 43029103 42349021 41299037 39929115
            40049258 41199311 42049291

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 28, 1:37 PM CDT	Severe Thunderstorm Watch	SPC	Adams, Boone, Brown, Bureau, Carroll, DeKalb and 24 more	7 hr
May 28, 3:09 PM CDT	Mesoscale Discussion	SPC	Adams, Brown, Hancock, Pike, Schuyler	2 hr
May 28, 5:33 PM CDT	Mesoscale Discussion	SPC	Bureau, Carroll, Fulton, Hancock, Henderson, Henry and 15 more	57 min

Nearby

Mesoscale Discussions in Iowa, 2016 Mesoscale Discussions in Missouri, 2016 Mesoscale Discussions in Illinois, 2016 Every mesoscale discussion in 2016

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.