May 19th, 1998 Large Hail/Downburst

This day was characterized by large values of CAPE (Convective Available Potential Energy) and weak disturbances aloft. The image below shows a modified sounding based on conditions at 19z May 19th, 1998.

 19Z KDVN Modified Sounding

Notice the B+ (CAPE) was 5549 J/KG with LI's to -14.  Very unstable. Storms were not widespread, however, because we had a weak cap in place around 750mb as seen above. Thunderstorms developed around 17z along a cold front in northeast Iowa. Below is the 1km visible satellite image of these thunderstorms at 1815z.

May 19th, 1998 1815Z

These storms weakened and collapsed within an hour or so and produced a strong outflow boundary. The beginnings of the boundary are depicted here in a mesoanalysis performed at 19Z.

An outflow boundary is usually a cold pool of air produced by a thunderstorm that rushes out from the storm. This outflow boundary produced 25-40 MPH wind gusts as it moved from Highway 20 to Interstate 80. It then hit very unstable air depicted in the sounding at the beginning of this document. Explosive thunderstorm development resulted. Below you can see the 1km satellite image. The yellow line is drawn just behind the outflow boundary. The boundary is moving south. Notice how the wind changes direction behind the line and notice the puffy clouds developing ahead of the boundary.

May 19th, 1998 2030Z Outflow Boundary

Check out the radar image of the initial development below. There is a Composite Reflectivity (CR) image in the center and a Reflectivity Cross Section (RCS) of the left. The RCS was taken through the storm just to the east of the radar site. On the left is a scale of return strength for the CR image.

Composite Reflectivity ScaleMay 19th, 1998 2112Z Composite ReflectivityMay 19th, 1998 2112Z Reflectivity Cross Section

Check out the following sequence of satellite images to see the explosive thunderstorm development: 2100z, 2130z, 2145z, 2215z, 2245z, and 2315z.

The storm over entering Henry County, IL produced a good swath of large hail and some damaging wind. Details follow:

PRELIMINARY LOCAL STORM REPORT...UPDATED FOR REPORTS AND DETAIL
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
115 PM CDT WED MAY 20 1998
...UPDATED FOR REPORTS AND DETAIL FOR /MAY 19TH 1998/...
TIME(CDT)  .....CITY LOCATION.....   ST   ...EVENT/REMARKS...
DATE(CDT) ....COUNTY LOCATION....
0408 PM    PORT BYRON                			IL   1.75 SIZE HAIL
05/19/98 ROCK ISLAND GOLF BALL SIZED HAIL
0425 PM    CONESVILLE               			 IA   1.75 INCH HAIL
05/19/98 MUSCATINE GOLF BALL SIZED HAIL
0430 PM    4 NW GENESEO              IL   1.75 INCH HAIL
05/19/98 HENRY GOLF BALL SIZED HAIL
0432 PM    2 N GENESEO               IL   0.75 INCH HAIL
05/19/98 HENRY DIME SIZED HAIL
0445 PM    GENESEO HILLS             IL   2.75 INCH HAIL
05/19/98 HENRY BASEBALL SIZED HAIL
0446 PM    2 SW LETTS                IA   1.75 INCH HAIL
05/19/98 LOUISA GOLFBALL SIZED HAIL
0455 PM    ATKINSON                  IL   60 MPH WINDS
05/19/98 HENRY NUMEROUS TREES DAMAGED
0500 PM    ANNAWAN                   IL   WIND DAMAGE
05/19/98 HENRY NUMEROUS LARGE TREE BRANCHES
DOWN
 
0500 PM ANNAWAN IL 1.75 INCH HAIL
05/19/98 HENRY GOLFBALL SIZED HAIL
WIND DRIVEN HAIL CAUSED
DAMAGE TO SIDING AND ROOFS
0510 PM    MINERAL                   IL   1.00 INCH HAIL
05/19/98 BUREAU
0515 PM    KEWANEE                   IL   WIND DAMAGE
05/19/98 HENRY TREES DOWN
0515 PM    GALVA                     IL   WIND DAMAGE
05/19/98 HENRY TREES DOWN
0516 PM    JUST SOUTH OF RARITAN     IL   FUNNEL DROPPING DOWN
05/19/98 HENDERSON
0524 PM    3 1/2 N BLANDINSVILLE     IL   FUNNEL
05/19/98 MC DONOUGH
0525 PM    JUST S OF STRONGHURST     IL   FUNNEL
05/19/98 HENDERSON
0525 PM    TERRA HAUTE               IL   FUNNEL
05/19/98 HENDERSON
0526 PM    4 E LA HARPE              IL   TORNADO
05/19/98 MC DONOUGH
0550 PM    2 SE BLANDINSVILLE        IL   1.25 INCH HAIL
05/19/98 MC DONOUGH
0615 PM    1 N MAGNOLIA              IL   WIND DAMAGE
05/19/98 PUTNAM TREES DOWN
DOWN

 


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.