It happens that the Pittsburgh radar, as well as the Phoenix radar, is an early test site for dual polarization. Not long after the Pittsburgh upgrade there was flash flooding in an area about 30 miles southeast of the radar. There were no fatalities, unlike a later event in Pittsburgh.
The image above is at 12:35 PM local daylight time. Thunderstorms by then were organized along two lines: one old, the other newly developed. The older, solid line of thunderstorms was oriented east-west and had been moving slowly to the south, reaching a position generally along highway I-70 (the thin red line in the background map generated by NOAA/NCDC's Weather and Climate Toolkit). The brown lines in the background map crudely approximate county boundaries, with the meandering brown line segments being where the county boundaries coincide with the Monongahela River. The flood reports (Donora, Allens Crossroads, Fayette City) were within a few miles of the point where I-70 crosses the river/county boundary. By this time a new, broken line of thunderstorm cells had formed in an area elongated west-southwest to east-northeast (from the southwest quadrant of the image toward the middle), with cell movement toward just slightly north of east. The severe flooding occurred where cells of the new line met and merged with the older line.
The differential reflectivity was higher at the western end of the old line and for most of the cells in the new line. It was lower in the area affected by flooding. It would be nice to think that the new information available after the dual-polarization upgrade would contribute to improved automated estimates of rainfall. But it would also be nice to think that the new information would better enable human forecasters to confidently, quickly, precisely and accurately communicate a flood threat.
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