Heavy Rain — Galax (c), Virginia

2020-11-10 to 2020-11-13 · near Galax, Galax (c), Virginia

Event narrative

The Cooperative Weather Observer at Galax, VA (GAAV2) observed a 72-hour (ending 12Z on November 12th) precipitation amount of 5.76 inches. This was the highest 72-hour total for this station during the month of November. The 48-hour total (ending 12Z on November 12th) of 5.63 inches was also the highest 48-hour total for November and 7th highest all-time. The 24-hour total of 3.81 inches measured at 12Z on the 12th is the highest 24-hour measurement for November. These amounts are 10- to 25-year ARI events at the 48- and 72-hour durations, and 5- to 10-year events at the 24-hour duration per NOAA Atlas 14 point precipitation estimates. Records date back to May 1907.

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 → (36.6542, -80.9183)

Source: NOAA Storm Events Database, event_id 929643. Narrative written by the NWS forecast office that issued the report.