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No severe weather was expected at all this morning, but several isolated
thunderstorm cells
developed over the western half of Pennsylvania. Even though they were
isolated (and at
night!), they were very strong. The two that appeared the most severe on
radar, was the one in
Westmoreland county, and the one in Somerset county, but strangely enough, the
worst damage was
done in Beaver county.
As you can see on the 0615Z (2:15 am) regional radar summary, thunderstorms were developing across western PA, ahead of the solid line of severe thunderstorms just entering western Ohio (which had a long history of wind damage). A short while ago, there was absolutely nothing in PA, with clear skies. Note that radar indicated HAIL with the storms in PA. Still, no warnings were issued. The thunderstorms started to really intensify around 0630Z (2:30 am), virtually out of no where. If I was in charge at the NWS, I would have put out a warning about now for southern Somerset county. Notice the 66 dbz! Keep in mind that this is in the middle of the night (not to mention in PA). Very unusual. I waited for several minutes, wondering why a severe thunderstorm warning had not been issued yet. Finally, at 2:47 am (0647Z), the State College NWS office issued a severe thunderstorm warning for Somerset county. As seen on this 0700Z (3 am) radar image, the storms intensified some more, now reaching 69 dbz! 6 minutes later, I couldn't believe what the radar showed - 71 dbz!! 2 minutes later, the NWS in Pittsburgh issued a severe thunderstorm warning for Westmoreland county. The Infrared satellite at 0715Z (3:15 am) showed the storms in PA nicely. Notice the bright white clouds over western PA and northern West Virginia... and then notice the clear skies over the rest of PA. The bright white clouds show where the highest cloud tops are, thus showing thunderstorms, since they grow very high into our atmosphere. Nickel size hail (.88") was reported in sections of Westmoreland, Fayette, and Somerset counties, and quarter size hail (1.0") fell from Beaver Falls to Beaver... in Beaver county. It is likely that even larger hail, maybe up to golf ball size, fell in isolated locations but went unreported because of the time of night. Half dollar size hail was reported as the severe thunderstorm moved into northern West Virginia... still in the NWS-PIT CWA. The only reported wind damage occurred in Beaver county, near the town of Beaver Falls. For some reason, no severe thunderstorm warning was issued for Beaver county. The damage occurred around 520 am, and was due to a microburst from a thunderstorm. Many trees were snapped or uprooted, two telephone poles were snapped, power lines were downed, a few roof shingles were ripped off a couple houses, and a porch was torn right off a house. Maximum winds were around 80 mph at the microbursts peak intensity, but around 70 mph for most of the time. The width of this microburst was 350 yards (1050 ft) and the length 700 yards (2100 ft). Due to the torrential rain associated with the thunderstorms, flash flooding started. A few flash flood warnings were issued by both the CTP (state college) and PIT (Pittsburgh) offices. A mudslide occurred in Westmoreland county due to heavy rain. Also, streams were out of their banks, with some evacuations needed. Many basements were flooded, and roads were closed.
Click here to see the warnings issued with
this event by the
CTP & PIT offices Go here for a complete listing of all images/text available for this event.
Email: BowEchoCPA@suscom.net |
