Alert archive / Illinois / Severe Thunderstorm Warnings in 2003

Severe Thunderstorm Warning 139, NWS Chicago, IL

July 20, 2003Lee County, Illinois

NWS Chicago, IL issued this severe thunderstorm warning at Jul 20, 2003, 5:57 PM CDT for Lee County, Illinois. It was in force for 48 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
Jul 20, 2003, 5:57 PM CDT (22:57 UTC)
Expired
Jul 20, 2003, 6:45 PM CDT
In force
48 min
Issued by
NWS Chicago, IL
Area
Counties, with a storm outline in the text

County Lee County, IL

The radar

The Chicago radar (KLOT), 102 km from the middle of the area, began a volume at 22:58 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 nearest sounding before it

Lincoln, IL (KILX), launched 12:00Z, 11.0 hours before the alert went out and 187 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, Lincoln, IL at 12:00Z on 2003-07-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 649 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, Lincoln, IL at 12:00Z on 2003-07-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 74 square meters per square second.1939Sfc1 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
649 J/kg
Mixed-layer CIN
-220 J/kg
Mixed-layer LCL
888 m above ground
0-6 km bulk shear
26 kt
0-1 km storm-relative helicity
74 m²/s²
0-3 km storm-relative helicity
115 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.2

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 Jul 20, 3:15 PM CDT, 2 hours 42 minutes earlier.

Area forecast discussion, Jul 20, 3:15 PM CDT, 2 hours 42 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
315 PM CDT SUN JUL 20 2003

PUBLIC DISCUSSION AFTERNOON ZONES/GRIDS:

MAIN PROBLEM THIS EVENING IS WITH TSTM FCST.  SPC HAS LOWERED REGION
INTO SLIGHT RISK AS LO LEVEL FEATURES ARE AS YET POORLY DEFINED. SFC
DEW POINTS HAVE RISEN INTO LOER 70S BUT MOISTURE CONVERGENCE REMAINS
QUITE NEBULOUS ACROSS MOST OF MIDWEST.  CONVECTIVE DEBRIS HAS
CONTRIBUTED TO RELATIVE STABILIZATION COMPARED TO AREAS TO OUR W AND
S WHERE LIFTED INDEX VALUES ARE NOW RUNNING AOB -10.  BASED ON
THIS...BELIEVE DYNAMIC FORCING WILL BE REQUIRED TO GENERATE
CONVECTION.  VIGOROUS, DIGGING S/W TROF NOW ROTG SSEWD ACROSS WRN
ONTARIO WITH VORT TAIL ARCING SWWD INTO ND ATTM BASED ON AFTN SATLT
LOOPS.  EXPECT THIS TO TRIGGER MORE ORGANIZED CONVECTION NXT FEW HRS
WELL TO OUR NW WITH THESE STORMS MAINTAINING THEMSELVES OVERNIGHT
DUE TO MORE FAVORABLE DYNAMICS.  AS A RESULT WILL KEEP LIKELY POPS
GOING IN FCST BUT WILL MENTION THIS AS AN OVERNIGHT EVENT.  THIS IS
ALSO SUPPORTED BY MOS AND ALL MODELS CONCUR IN BRINGING OMEGA MAX
ACROSS FA OVERNIGHT.  SOME PRECIP WILL LIKELY LINGER INTO MONDAY
MORNING.  REMAINDER OF FCST CHANGED LTL FROM GUID WITH ETA AND GFS
IN FAIRLY GOOD AGREEMENT ON STRENGTH OF COLD AVDECTION THRU ERLY
PART OF UPCOMING WEEK.   WILL KEEP MOSTLY CLOUDY CONDS AT LEAST THRU
MONDAY DUE TO SHARP CYCLONINC TURNING IN MID/UPR LVL FLOW AND ASSD
COLD ADVECTION.  SKIES SHOULD CLEAR TUES NIGHT AS H5 TROF AXIS
SHIFTS EWD AND SFC HI PRES BUILDS SEWD INTO FA.

.CHI...NONE
MERZLOCK
Hazardous weather outlook, Jul 20, 4:20 PM CDT, 1 hour 37 minutes before
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The office that day

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

IssuedProductOfficeCountiesLasted
Jul 20, 5:06 PM CDTSevere Thunderstorm WarningLOTLee54 min
Jul 20, 5:45 PM CDTSpecial Marine WarningLOT90 min
Jul 20, 5:45 PM CDTSpecial Marine WarningLOT90 min
Jul 20, 5:45 PM CDTSpecial Marine WarningLOT90 min
Jul 20, 6:01 PM CDTSevere Thunderstorm WarningLOTCook19 min

Nearby

Severe Thunderstorm Warnings in Illinois, 2003Every severe thunderstorm warning in 2003

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.