post tropical storm debby causes flooding, wind damage and tornadoes

Now that Debby has passed, this will be a fairly brief summary of the impact she delivered across the central portions of the state from Thursday into Friday.

Rainfall wise, a widespread 3-5" fell generally along and west of the I-95 corridor especially across Montgomery, Howard, Carroll, and Frederick counties which is where multiple bands of rain with rates of 3-4" per hour occurred. Unfortunately, this resulted in numerous instances of flash flooding, including at my house which has only happened on 2 other occasions in the 3 years living here. Further east, some areas saw as little as just a quarter inch of rain, but most saw 1-2" along the I-95 and just east. The lowest amounts were along the bay shore. 

As far as wind gusts go, most areas saw winds in the 30-40mph range, with a few 50+mph gusts being recorded along the bay where there is less friction. Because these winds were from the SSE, they also produced significant coastal flooding that exceeded the expectations of most forecasts, with 3-5 foot tidal anomalies (above normal) being observed. Inland, the combination of heavily saturated soils, drought stress, and wind gusts of 30-40mph produced scattered instances of wind damage to trees as well as several thousand power outages.

Thankfully, we had no confirmed tornadoes in Maryland, however almost every downpour had rotation in it thanks to copious amounts of wind shear. Hence the long duration tornado watch (nearly 18 hours in some areas). This may have been the longest duration tornado watch in our area on record. However, several tornadoes did occur nearby from Debby, including 2 in northern VA, 1 in the WV panhandle, one in northern DE, and one in Harrisburg PA. 

There was a swath of minor tree damage in the southern portion of Mount Airy along Florence Road and Mullinix Mill Road, north to Watersville Road where a few dead trees were downed and branches were broken off. This lined up with where a weak velocity couplet tracked and a tornado warning was in effect. However after a good discussion with the NWS in Sterling VA, it was determined that this damage was due to strong straight line winds combined with heavily saturated soils loosening the root balls and weakening the trees. While sheltering in my basement, I peeked at our storm camera (we use this camera to watch storms from our shelter) and saw a rotating funnel cloud passing over our neighborhood here in Mount Airy. Luckily it never touched down but that was WAY too close for comfort. The image below was taken outside of my neighborhood consisting of a downed tree and  few small branches.

Senior Forecaster Jack