Severe Thunderstorm Watch 557

Issued

Aug 4, 2012, 10:50 AM CDT (15:50 UTC)

Expired

Aug 4, 2012, 3:58 PM CDT

In force

5 hr

Issued by

the Storm Prediction Center

Largest hail expected

2 in

Strongest gust expected

60 kt

The Quad Cities radar (KDVN), 103 km from the middle of the area, began a volume at 15:50 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

20%

One or more EF2 to EF5 tornadoes

5%

Ten or more severe wind reports

60%

One or more gusts of 65 knots or more

30%

Ten or more severe hail reports

30%

One or more hailstones of 2 inches or more

20%

Six or more combined severe hail and wind reports

80%

• Mesoscale Discussion 1698Aug 4, 10:26 AM CDT
• Mesoscale Discussion 1699Aug 4, 1:09 PM CDT

742 
WWUS20 KWNS 041552
SEL7
SPC WW 041552
IAZ000-ILZ000-042200-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 557
NWS STORM PREDICTION CENTER NORMAN OK
1055 AM CDT SAT AUG 4 2012

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

       EAST CENTRAL AND SOUTHEAST IOWA
       NORTHWEST ILLINOIS

EFFECTIVE THIS SATURDAY MORNING AND AFTERNOON FROM 1055 AM UNTIL
500 PM CDT.

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

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 65
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 20 MILES NORTH
NORTHWEST OF KNOXVILLE IOWA TO 45 MILES EAST OF MOLINE ILLINOIS.
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU7).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...A LINE OF STORMS ACROSS CENTRAL IA ALONG THE SURFACE
COLD FRONT WILL LIKELY INTENSIFY THIS AFTERNOON WHILE SPREADING EWD
ACROSS THE MS RIVER.  STRONG SURFACE HEATING ACROSS SE IA/NW IL WILL
CONTRIBUTE TO MODERATE-STRONG INSTABILITY TO SUPPORT THE
INTENSIFYING STORMS...WHILE DEEP-LAYER VERTICAL SHEAR WILL BE
SUFFICIENT FOR BOTH ORGANIZED LINE SEGMENTS/BOWS AND PERHAPS SOME
EMBEDDED SUPERCELL STRUCTURES.  LARGE HAIL WILL BE POSSIBLE WITH THE
STRONGEST STORMS...THOUGH THE PRIMARY THREAT SHOULD BE DAMAGING
WINDS THROUGH THE AFTERNOON.

AVIATION...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 550. MEAN STORM
MOTION VECTOR 27035.


...THOMPSON

Severe Thunderstorm Watches in Iowa, 2012Severe Thunderstorm Watches in Illinois, 2012Every severe thunderstorm watch in 2012

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.