EF0 tornado in Allegheny County, Pennsylvania

A damage survey confirmed that a brief tornado occurred in and

near the Mount Nebo Pointe shopping center. Damage at the Target

store included broken glass in the entry doors (which were sucked

outward by the wind), as well as damage to a sign on the west-

facing side of the store. Minor tree damage and tall grass

blowdown was noted on the eastern side of the shopping center and

tree damage was noted at the base of the hill on the western

side. The circulation lifted very soon after as it reached a

small gully to the east. Damage indicators were consistent with a

maximum wind speed of 70 MPH during this brief event.

A broken line of supercells, which formed along a front, moved quickly through the Ohio River Valley the evening of October 21st and spun off several tornadoes. The number of tornadoes, time of year, and intensity (one long track EF2 tornado) will mark this event as very rare and significant for this region.

Prior to tornado development, surface temperatures warmed into the low-mid 60s; dew points topped out near 60F. Forecast soundings indicated modest levels of mean layer CAPE, and a relatively straight hodograph yielding marginal but sufficient storm relative helicity. The overall quick track of the broken line and eastward propagation helped cells sustain rotating updrafts.