Flood — Roanoke (c), Virginia

2020-11-12 · near Roanoke, Roanoke (c), Virginia

Event narrative

The Roanoke River at Roanoke, VA (RONV2) was above flood stage (10 feet) on November 12th, and crested at the moderate flood stage of 14.07 feet (14,000 cfs) at 12:35 PM EST on November 12th, the 13th highest crest on record for this gauge. This was between a 5- and 10-year Average Return Interval per the USGS StreamStats website.

Wider weather episode

One of the most significant flooding events in years occurred during November 11th and 12th, given both the amounts of rainfall and the footprint where flooding occurred. In the wake of high pressure passing east off the mid-Atlantic coast, a plume of deep tropical moisture was rapidly carried inland to the central Appalachians ahead of a slow-moving cold front. Though this plume was of tropical origin, it was not directly related to Tropical Storm Eta, which was off the coast of southern Florida. Precipitable Water values were in the extremely high range of 1.9 to 2.2 inches with this airmass, around the 99th percentile for mid-November. In addition, evapotranspiration was significantly lower than during the previous few months given lower daytime heating and the fact that most vegetation had become dormant for the upcoming winter months. Despite dry conditions for almost two weeks leading up to the event, numerous instances of flooding and flash flooding occurred as 4 to 6 inches of rain fell across portions of the Piedmont on the 11th, followed by an additional 1 to 3 inches on the 12th. Some of the activity was convective in nature, producing locally 2 to 4 inch per hour rainfall rates. The rainfall produces numerous instances of flooding and flash flooding, followed shortly by river flooding.

View location on OpenStreetMap → (37.2576, -79.9083)

Source: NOAA Storm Events Database, event_id 929975. Narrative written by the NWS forecast office that issued the report.