Alert archive / Illinois / Severe Thunderstorm Warnings in 2013

Severe Thunderstorm Warning 18, NWS Chicago, IL

May 20, 20134 counties in Illinois

NWS Chicago, IL issued this severe thunderstorm warning at May 20, 2013, 9:58 PM CDT for 4 counties in Illinois. It was in force for 62 min. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued: May 20, 2013, 9:58 PM CDT (02:58 UTC)
Expired: May 20, 2013, 11:00 PM CDT
In force: 62 min
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Hail: 0.75 in
Wind: 60.0 mph

Counties Cook County, IL, DuPage County, IL, Kendall County, IL, Will County, IL

The radar

The Chicago radar (KLOT), 11 km from the middle of the area, began a volume at 03:00 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 watch it was issued in

The SPC watch in force over the same counties when this warning went out.

Issued	Product	Office	Lasted
May 20, 7:48 PM CDT	Severe Thunderstorm Watch	SPC	6 hr

The nearest sounding before it

Lincoln, IL (KILX), launched 00:00Z, 3.0 hours before the alert went out and 178 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: 1540 J/kg
Mixed-layer CIN: -5 J/kg
Mixed-layer LCL: 1320 m above ground
0-6 km bulk shear: 36 kt
0-1 km storm-relative helicity: 31 m²/s²
0-3 km storm-relative helicity: 173 m²/s²
Significant tornado parameter: 0.8
Supercell composite: 6.7

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Chicago, IL wrote its last area forecast discussion before this severe thunderstorm warning went out at May 20, 8:08 PM CDT, 1 hour 50 minutes earlier.

Area forecast discussion, May 20, 8:08 PM CDT, 1 hour 50 minutes before

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Hazardous weather outlook, May 20, 8:54 PM CDT, 1 hour 4 minutes before

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
854 PM CDT MON MAY 20 2013

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
220200-
WINNEBAGO-BOONE-MCHENRY-LAKE ILLINOIS-OGLE-LEE-DE KALB-KANE-
DUPAGE-COOK-LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-
IROQUOIS-FORD-LAKE INDIANA-PORTER-NEWTON-JASPER-BENTON-
854 PM CDT MON MAY 20 2013 /954 PM EDT MON MAY 20 2013/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL ILLINOIS...
NORTHEAST ILLINOIS AND NORTHWEST INDIANA.

.DAY ONE...TONIGHT.

 WEATHER HAZARDS EXPECTED:

  THUNDERSTORMS...THE STRONGEST COULD PRODUCE:
    HAIL TO THE SIZE OF HALF DOLLARS.
    WIND GUSTS OVER 60 MPH.
    FREQUENT CLOUD TO GROUND LIGHTNING.
    AND HEAVY RAIN.

  AREAS AFFECTED AND TIMING:

  THUNDERSTORMS WILL CONTINUE TO MOVE NORTHEASTWARD INTO NORTHERN
  ILLINOIS THIS EVENING AND EVENTUALLY INTO NORTHWEST INDIANA LATE
  THIS EVENING OR OVERNIGHT. WAVES OF THUNDERSTORMS ARE EXPECTED
  TO CONTINUE THROUGH THE WEE HOURS OF TUESDAY MORNING. THE MAIN
  SEVERE THREAT WILL BE PRIOR TO 3 AM CDT.

  DISCUSSION:

  A MOISTENING ATMOSPHERE WILL SUPPORT THE EXPANSION OF SHOWERS
  AND THUNDERSTORMS INTO NORTHERN ILLINOIS...WITH NORTHWEST
  INDIANA SEEING ACTIVITY LATER THIS EVENING OR EARLY TONIGHT. THE
  MAIN THREAT WILL BE DAMAGING WIND GUSTS BUT SOME HAIL IS ALSO
  POSSIBLE. WITH ACTIVITY LINED UP BACK INTO CENTRAL MISSOURI
  SEVERAL HOURS OF RAIN AND THUNDERSTORMS ARE POSSIBLE LEADING TO
  THE POTENTIAL FOR HEAVY RAINFALL AND LOCALIZED FLOODING. THE
  THUNDERSTORM ACTIVITY IS EXPECTED TO MOVE EAST OF THE AREA EARLY
  TUESDAY MORNING.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.

SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE TUESDAY WITH A
HIGHER CHANCE TUESDAY EVENING AND TUESDAY NIGHT. SOME STORMS MAY
BECOME SEVERE WITH DAMAGING WINDS AND LARGE HAIL THE MAIN
THREATS. HEAVY RAINFALL IS ALSO POSSIBLE...ESPECIALLY TUESDAY
NIGHT.

ADDITIONAL THUNDERSTORMS ARE POSSIBLE WEDNESDAY AND AGAIN
SATURDAY THROUGH MONDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS SHOULD REPORT SEVERE WEATHER.

&&

LMZ740>745-220200-
WINTHROP HARBOR TO WILMETTE HARBOR-
WILMETTE HARBOR TO NORTHERLY ISLAND-
NORTHERLY ISLAND TO CALUMET HARBOR-CALUMET HARBOR TO GARY-
GARY TO BURNS HARBOR-BURNS HARBOR TO MICHIGAN CITY-
854 PM CDT MON MAY 20 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS NEARSHORE
WATERS OF LAKE MICHIGAN AND THE INDIANA NEARSHORE WATERS OF LAKE
MICHIGAN.

.DAY ONE...TONIGHT.

STRONG WINDS WILL LEAD TO HAZARDOUS CONDITIONS FOR SMALL CRAFT
THROUGH MID EVENING.

THUNDERSTORMS ARE LIKELY LATE THIS EVENING INTO THE OVERNIGHT
HOURS...SOME MAY BE SEVERE WITH WIND GUSTS WELL OVER 35 KNOTS
POSSIBLE.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.

SCATTERED THUNDERSTORMS WILL BE POSSIBLE TUESDAY THROUGH
WEDNESDAY WITH THE POTENTIAL FOR SEVERE WEATHER TUESDAY AND
TUESDAY NIGHT. THE MAIN SEVERE WEATHER THREATS WILL BE WIND GUSTS
GREATER THAN 35 KNOTS AND LARGE HAIL.

STRONG WINDS AND HIGH WAVES MAY CREATE HAZARDOUS CONDITIONS FOR
SMALL CRAFT WEDNESDAY NIGHT THROUGH FRIDAY.

&&

LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868-
870-872-874-876-878-220200-
LAKE MICHIGAN FROM MICHIGAN CITY IN TO ST. JOSEPH MI 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM SEUL CHOIX POINT TO ROCK ISLAND PASSAGE 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN SOUTH OF A LINE FROM SEUL CHOIX POINT TO THE
MACKINAC BRIDGE AND NORTH OF A LINE FROM CHARLEVOIX MI TO SOUTH
FOX ISLAND 5 NM OFFSHORE-
LAKE MICHIGAN FROM CHARLEVOIX TO POINT BETSIE MI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM POINT BETSIE TO MANISTEE MI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM ROCK ISLAND PASSAGE TO STURGEON BAY WI-
LAKE MICHIGAN FROM STURGEON BAY TO TWO RIVERS WI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM TWO RIVERS TO SHEBOYGAN WI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM SHEBOYGAN TO PORT WASHINGTON WI 5 NM OFFSHORE
TO MID LAKE-
LAKE MICHIGAN FROM PORT WASHINGTON TO NORTH POINT LIGHT WI 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM NORTH POINT LIGHT TO WIND POINT WI 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM WIND POINT WI TO WINTHROP HARBOR IL 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM WINTHROP HARBOR TO WILMETTE HARBOR IL 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM WILMETTE HARBOR IL TO MICHIGAN CITY IN 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM PENTWATER TO MANISTEE MI 5 NM OFFSHORE TO MID
LAKE-
LAKE MICHIGAN FROM WHITEHALL TO PENTWATER MI 5 NM OFFSHORE TO MID
LAKE-
LAKE MICHIGAN FROM GRAND HAVEN TO WHITEHALL MI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM HOLLAND TO GRAND HAVEN MI 5 NM OFFSHORE TO MID
LAKE-
LAKE MICHIGAN FROM SOUTH HAVEN TO HOLLAND MI 5 NM OFFSHORE TO MID
LAKE-
LAKE MICHIGAN FROM ST. JOSEPH TO SOUTH HAVEN MI 5 NM OFFSHORE TO
MID LAKE-
854 PM CDT MON MAY 20 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE OPEN WATERS OF LAKE
MICHIGAN.

.DAY ONE...TONIGHT.

PATCHY DENSE FOG WILL BE POSSIBLE ACROSS THE ENTIRE LAKE.

THUNDERSTORMS ARE LIKELY...SOME MAY BE SEVERE.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.

AREAS OF DENSE FOG WILL BE POSSIBLE TUESDAY ACROSS THE ENTIRE
LAKE.

SCATTERED THUNDERSTORMS WILL BE POSSIBLE TUESDAY THROUGH
WEDNESDAY WITH THE POTENTIAL FOR SEVERE WEATHER TUESDAY AND
TUESDAY NIGHT. THE MAIN SEVERE WEATHER THREATS WILL BE WIND GUSTS
GREATER THAN 35 KNOTS AND LARGE HAIL. ADDITIONAL THUNDERSTORMS
ARE POSSIBLE SATURDAY THROUGH MONDAY.

&&

MDB

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO

In the hours before

Special weather statement, May 20, 8:21 PM CDT, 1 hour 37 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
821 PM CDT MON MAY 20 2013

ILZ010-019-032-210155-
LA SALLE IL-LEE IL-LIVINGSTON IL-
821 PM CDT MON MAY 20 2013

...SIGNIFICANT WEATHER ALERT TIL 855 PM FOR WESTERN
LIVINGSTON...LASALLE...AND SOUTHERN LEE COUNTIES...

AT 820 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 21 MILES SOUTHWEST
OF AMBOY TO TONICA TO 17 MILES SOUTHWEST OF FLANAGAN...MOVING
NORTHEAST AT 55 MPH.

ONE HALF INCH DIAMETER HAIL AND WINDS TO 50 MPH ARE POSSIBLE WITH
THESE STORMS.

CITIES AND TOWNS AFFECTED...TONICA...RUTLAND...AND CEDAR POINT AROUND
825 PM...PERU...OGLESBY...AND LEONORE AROUND 830 PM...UTICA AND LONG
POINT AROUND 835 PM.

OTHER LOCATIONS AFFECTED...
BUFFALO ROCK STATE PARK...ILLINOIS VALLEY COMMUNITY COLLEGE...
MATTHIESSEN STATE PARK...STARVED ROCK STATE PARK...TRI-COUNTY
FAIRGROUNDS...

&&

LAT...LON 4175 8928 4139 8880 4079 8877 4075 8884
      4075 8894 4092 8894 4093 8905 4110 8905
      4111 8917 4158 8917 4158 8952
TIME...MOT...LOC 0120Z 226DEG 48KT 4146 8953 4113 8908
          4072 8909

IZZI

Local storm report, May 20, 9:13 PM CDT, 45 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
913 PM CDT MON MAY 20 2013

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0911 PM     HAIL             MARSEILLES              41.33N 88.69W
05/20/2013  E1.00 INCH       LA SALLE           IL   TRAINED SPOTTER

            NEAR INTERSTATE 80. FREQUENT STRONG WIND GUSTS.

&&

RC

Special weather statement, May 20, 9:28 PM CDT, 30 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
928 PM CDT MON MAY 20 2013

ILZ011>014-019>022-210300-
COOK IL-DE KALB IL-DUPAGE IL-GRUNDY IL-KANE IL-KENDALL IL-LA SALLE
IL-
WILL IL-
928 PM CDT MON MAY 20 2013

...SPECIAL WEATHER STATEMENT...

AT 928 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM NEWARK TO 10 MILES
SOUTHEAST OF NEWARK...MOVING NORTHEAST AT 45 MPH.

UP TO PENNY SIZE HAIL...WINDS TO 50 MPH...ARE POSSIBLE WITH THESE
STORMS.

CITIES AND TOWNS AFFECTED...YORKVILLE AROUND 935 PM...SUGAR GROVE...
AND SHOREWOOD AROUND 940 PM...OSWEGO...MONTGOMERY...AND BOULDER HILL
AROUND 945 PM...NORTH AURORA AND PLAINFIELD AROUND 950 PM.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

GUSTY WINDS MAY CAUSE SMALL BRANCHES TO BE BLOWN DOWN...AND LOOSE
OBJECTS TO BLOW AROUND.  SEEK SHELTER IN A STURDY STRUCTURE UNTIL
THESE STORMS HAVE PASSED.

&&

LAT...LON 4195 8821 4166 8795 4147 8826 4146 8848
      4146 8859 4168 8861
TIME...MOT...LOC 0228Z 226DEG 38KT 4161 8851 4146 8840

IZZI

The office that day

Everything else NWS Chicago, IL issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 20, 8:21 PM CDT	Special Weather Statement	LOT	LaSalle	34 min
May 20, 8:55 PM CDT	Severe Thunderstorm Warning	LOT	Grundy, Kendall, LaSalle	35 min
May 20, 9:12 PM CDT	Severe Thunderstorm Warning	LOT	Grundy, LaSalle, Livingston	78 min
May 20, 9:28 PM CDT	Special Weather Statement	LOT	Kendall	32 min
May 20, 9:46 PM CDT	Special Marine Warning	LOT		119 min
May 20, 10:22 PM CDT	Flash Flood Warning	LOT	Cook	4 hr
May 20, 10:54 PM CDT	Severe Thunderstorm Warning	LOT	Cook, DuPage, Ford, Grundy, Iroquois, Kankakee and 2 more	66 min
May 20, 10:58 PM CDT	Special Marine Warning	LOT		107 min
May 21, 5:22 AM CDT	River Flood Advisory	LOT	Will	16 hr
May 21, 10:01 AM CDT	Small Craft Advisory	LOT		10 hr
May 21, 3:05 PM CDT	Gale Watch	LOT		23 hr
May 20, 11:26 PM CDT	Severe Thunderstorm Warning	LOT	Lake, Porter	79 min

Nearby

Severe Thunderstorm Warnings in Illinois, 2013 Every severe thunderstorm warning in 2013

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.