Tornado Watch 620

Issued

Jul 19, 2006, 3:49 PM CDT (20:49 UTC)

Expired

Jul 19, 2006, 9:47 PM CDT

In force

6 hr

Issued by

the Storm Prediction Center

Largest hail expected

3 in

Strongest gust expected

70 kt

The Sioux Falls radar (KFSD), 123 km from the middle of the area, began a volume at 20:50 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.

Two or more tornadoes

60%

One or more EF2 to EF5 tornadoes

30%

Ten or more severe wind reports

40%

One or more gusts of 65 knots or more

30%

Ten or more severe hail reports

70%

One or more hailstones of 2 inches or more

60%

Six or more combined severe hail and wind reports

90%

• Mesoscale Discussion 1565Jul 19, 3:31 PM CDT
• Mesoscale Discussion 1572Jul 19, 7:57 PM CDT

000 
WWUS20 KWNS 192053
SEL0  
SPC WW 192053
IAZ000-NEZ000-SDZ000-200400-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 620
NWS STORM PREDICTION CENTER NORMAN OK
350 PM CDT WED JUL 19 2006

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

       NORTH CENTRAL AND NORTHWEST IOWA
       EXTREME NORTHEAST NEBRASKA
       EXTREME SOUTHEAST SOUTH DAKOTA

EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 350 PM UNTIL
1100 PM CDT.

TORNADOES...HAIL TO 3 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 80 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 45 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 45 MILES NORTHWEST OF SIOUX
CITY IOWA TO 35 MILES SOUTH OF MASON CITY IOWA.  FOR A COMPLETE
DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE
(WOUS64 KWNS WOU0).

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 617...WW 618...WW 619...

DISCUSSION...AN OUTFLOW BOUNDARY FROM MORNING CONVECTION HAS STALLED
ACROSS NW IA...WHILE A REINFORCING SURGE PUSHES WWD ACROSS CENTRAL
IA FROM THE ONGOING IL MCS.  ALONG AND S/W OF THESE OUTFLOWS...THE
LOW LEVELS HAVE BECOME QUITE MOIST AND UNSTABLE...WITH MLCAPE VALUES
NOW EXCEEDING 4000 J/KG.  FARTHER W...STRONG SURFACE HEATING HAS
ERODED THE CAP AND BOUNDARY LAYER CUMULUS ARE DEVELOPING ENEWD
ACROSS NE NEB. PRESENT INDICATIONS ARE THAT THUNDERSTORM INITIATION
WILL OCCUR BY ROUGHLY 22-23Z NEAR THE INTERSECTION OF
IA/NEB/SD...WITH RAPID INTENSIFICATION OF THE STORMS EXPECTED. THE
EXTREME INSTABILITY...ALONG WITH EFFECTIVE BULK SHEAR IN EXCESS OF
40 KT AND 0-1 KM SRH IN EXCESS OF 150 M2/S2 ALONG THE OUTFLOW
BOUNDARY...WILL SUPPORT INTENSE SUPERCELLS CAPABLE OF PRODUCING VERY
LARGE HAIL AND A FEW TORNADOES.  CONVECTION MAY EVENTUALLY GROW
UPSCALE INTO AN MCS ACROSS IA BY EARLY TONIGHT...WITH AN INCREASING
THREAT FOR DAMAGING WINDS.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 70 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
600. MEAN STORM MOTION VECTOR 29025.


...THOMPSON

Tornado Watches in Iowa, 2006Tornado Watches in Nebraska, 2006Tornado Watches in South Dakota, 2006Every tornado watch in 2006

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.