Link to NWS Louisville Science and Technology Homepage WSR-88D Images from the April 28, 1999 Large Hail Event
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During the afternoon of April 28, 1999, numerous thunderstorms affected central Kentucky and south-central Indiana. Although the atmosphere was not conducive for a major severe weather outbreak nor tornadoes, warm, moist air at the surface combined with cold, relatively dry air aloft made large hail producing storms likely.  Numerous cases of dime (3/4 inch diameter) and larger size hail were reported to the National Weather Service (NWS) in Louisville. One of these storms occurred at the NWS office, just south of downtown Louisville. The hail coated the ground with continuous hail for around 10 minutes. Initially, the hail was pea to marble size, then increased in diameter to dime to quarter (1 inch) size. Near the end of the storm, numerous larger, odd-shaped pieces of hail fell, with the length of some pieces around 2.5 inches and a width around 1 inch. The storm moved north across downtown Louisville and gradually weakened thereafter. The following images show the storm at its maximum intensity, as well as examples of hail that fell from the storm.
WSR-88D Image 1: April 28, 1999 Severe Weather Event This is a low-level base reflectivity image of the severe thunderstorm over the NWS office in south-central Jefferson county, Kentucky, just south of Louisville. Very heavy rain and large hail were occurring within the dark red colors on the southwestern flank of the storm. Rain, but no hail, was occurring in the yellow and green areas to the north and east of the severe portion of the storm.  
WSR-88D Image 2: April 28, 1999 Severe Weather Event This reflectivity image shows the same storm at the same time as above, but higher up in the storm, i.e., in the middle-levels. Note that very high reflectivity values (65-70 dBZ; pink and small purple colors) are evident in the southwestern part of the convective cell. This indicates that very large hail was being suspended aloft in the storm by the updraft. Velocity data, not shown, revealed weak rotation in the updraft aloft, which enhances its potential to suspend large particles, but no rotation near the ground. As this elevated hail core descended, reported hail size increased from dime size to well over one inch, as shown below.
WSR-88D Image 3: April 28, 1999 Severe Weather Event This reflectivity vertical cross-section shows a separate severe storm that produced around one inch diameter hail just southeast of the Jefferson county storm above. The storm shown at left exhibits vertical tilt and a high reflectivity core (65-70 dBZ; pink color) suspended aloft. The storm top is not particularly high (about 30,000 ft), but this can be misleading in assessing severe storm potential. On this day, the atmosphere precluded tall storms, but supported severe pulse storms, as exhibited in this cross-section.
April 28, 1999 Severe Weather Event: Hail on Ground Image 1 This picture, taken outside the NWS Louisville office, shows a hail pile accumulating during the storm as hail fell from off the roof and congregated at this location on the ground. Note the falling hail in the upper left portion of the image. This image was taken before pieces of very large hail began falling. 
April 28, 1999 Severe Weather Event: Hail on Ground Image 2 Marble and dime size hail began to coat the sidewalk, gravel area, and grass outside the NWS office during the storm, before larger hail pieces began to fall. Some other storms across central Kentucky and southern Indiana on this day also caused hail to coat or cover the ground. 
April 28, 1999 Severe Weather Event: Hail Displayed in Hands These are examples of some of the odd-shaped pieces of large hail that fell near the NWS Louisville office during the height of the storm. Initially, the smaller hail that fell was circular in shape. However, note that none of these very large pieces were circular shaped. Hail shape and size are a function of atmospheric conditions, and internal dynamics and physics within a thunderstorm. It appears that pieces of smaller hail may have froze together into larger pieces within this storm, thereby producing the clumps of hail shown here.  
April 28, 1999 Severe Weather Event: Hail Size Measured by a Ruler This large hail piece measured up as one of the longest that fell during the storm. Note that it has a length of nearly 2.5 inches, i.e., just smaller than baseball size (2.75 inch diameter). However, the width of the piece shown here is only about one inch.
April 28, 1999 Severe Weather Event: Hail Size Measured by a Ruler Another measurement shows 2 of the larger hail pieces that fell. The piece on the left is the same as in the picture above. The hail piece on the right has a length of at least 2.75 inches, although again the width is smaller. Fortunately, there was little hail damage from the storm at the NWS office.

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