Alert archive / Missouri / Tornado Watches in 2002

Tornado Watch 786

December 18, 200214 counties in Illinois; 20 counties in Missouri

The Storm Prediction Center issued this tornado watch at Dec 18, 2002, 4:35 PM CST for 14 counties in Illinois; 20 counties in Missouri. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: Dec 18, 2002, 4:35 PM CST (22:35 UTC)
Expired: Dec 18, 2002, 10:00 PM CST
In force: 5 hr
Issued by: the Storm Prediction Center

All 34 counties

Calhoun County, IL, Cass County, IL, Christian County, IL, DeWitt County, IL, Greene County, IL, Jersey County, IL, Logan County, IL, Macon County, IL, Macoupin County, IL, Mason County, IL, Menard County, IL, Morgan County, IL, Sangamon County, IL, Scott County, IL, City of Saint Louis, MO, Crawford County, MO, Dent County, MO, Franklin County, MO, Gasconade County, MO, Jefferson County, MO, Laclede County, MO, Lincoln County, MO, Maries County, MO, Montgomery County, MO, Osage County, MO, Phelps County, MO, Pulaski County, MO, Saint Charles County, MO, Saint Louis County, MO, Texas County, MO, Warren County, MO, Washington County, MO, Webster County, MO, Wright County, MO

The radar

The St Louis radar (KLSX), 67 km from the middle of the area, began a volume at 22:39 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.

Warnings issued inside it

3 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Dec 18, 4:39 PM CST	Tornado Warning	LSX	Franklin, Gasconade	21 min
Dec 18, 4:44 PM CST	Severe Thunderstorm Warning	ILX	Morgan, Scott	46 min
Dec 18, 4:47 PM CST	Tornado Warning	LSX	Greene	28 min

The nearest sounding before it

Springfield, MO (KSGF), launched 12:00Z, 10.6 hours before the alert went out and 272 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: 894 J/kg
Mixed-layer CIN: -3 J/kg
Mixed-layer LCL: 549 m above ground
0-6 km bulk shear: 69 kt
0-1 km storm-relative helicity: 425 m²/s²
0-3 km storm-relative helicity: 449 m²/s²
Significant tornado parameter: 2.4
Supercell composite: 8.2

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

000 
WWUS20 KWNS 182237
SEL6  
SPC WW 182235
ILZ000-MOZ000-190400-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 786
STORM PREDICTION CENTER NORMAN OK
435 PM CST WED DEC 18 2002

THE STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

   WESTERN AND CENTRAL ILLINOIS                           
   CENTRAL AND EASTERN MISSOURI                           

EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 435 PM UNTIL
1000 PM CST.

TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS
TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE TORNADO WATCH AREA IS ALONG AND 45 STATUTE MILES EAST AND WEST
OF A LINE FROM 55 MILES SOUTH SOUTHWEST OF FORT LEONARD WOOD
MISSOURI TO 15 MILES WEST OF BLOOMINGTON ILLINOIS.

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. 
PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING
WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE
WARNINGS.

OTHER WATCH INFORMATION...  CONTINUE...WW 784...WW 785...

DISCUSSION...SUPERCELLS HAVE DEVELOPED IN PARTS OF SRN/CNTRL/ERN MO
ALONG CONVERGENCE ZONE ORIENTED PARALLEL TO 80+ KT 500 MB SWLY JET.
SURFACE PRESSURE RISE/FALL COUPLET AND PRESENCE OF INSTABILITY AXIS
AHEAD OF CONVERGENCE ZONE SUGGEST THAT STORMS WILL REMAIN ACTIVE
ALONG THIS NARROW CORRIDOR FOR A FEW MORE HOURS...WITH THREAT FOR
LARGE HAIL AND POSSIBLE TORNADOES.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2 INCHES.  EXTREME TURBULENCE AND SURFACE WIND
GUSTS TO 60 KNOTS.  A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. 
MEAN STORM MOTION VECTOR 23055.

...CORFIDI

402,0882 370,0914 370,0931 402,0900

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 17, 10:40 PM CST	Tornado Watch	SPC	Calhoun, Cass, Greene, Jersey, Macoupin, Madison and 7 more	5 hr
Dec 18, 2:15 AM CST	Severe Thunderstorm Watch	SPC	Adams, Hancock, Henderson	6 hr
Dec 18, 3:30 AM CST	Tornado Watch	SPC	Calhoun, Greene, Jersey, Macoupin, Madison, Monroe and 3 more	5 hr
Dec 18, 9:30 AM CST	Tornado Watch	SPC	Adams	6 hr
Dec 17, 7:35 PM CST	Tornado Watch	SPC	Adair, Audrain, Barry, Barton, Bates, Benton and 51 more	5 hr
Dec 18, 7:20 AM CST	Tornado Watch	SPC	Christian, Dent, Douglas, Howell, Iron, Laclede and 12 more	6 hr
Dec 18, 2:30 PM CST	Tornado Watch	SPC	Butler, Carter, Dunklin, Howell, Mississippi, New Madrid and 4 more	7 hr
Dec 18, 5:50 PM CST	Tornado Watch	SPC	Dunklin, Pemiscot	3 hr

Nearby

Tornado Watches in Missouri, 2002 Tornado Watches in Illinois, 2002 Every tornado watch in 2002

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.