Heavy Rain in Galax (c) County, Virginia

The COOP site at Galax Water Plant (GAAV2) measured 4.50 inches in 24-hours ending at 700 AM local time on the 11th. This was the highest 24-hour rainfall during the month of October and 4th highest for any day, with complete records dating back to 2000 and a brief period from 1907-1910. This value falls into the 90 percent confidence interval (4.00-4.81 inches) for a 10-year recurrence interval event (.10 annual exceedance probability) per NOAA Atlas 2.

The remains of Hurricane Michael were preceded in parts of western Virginia by a so-called Predecessor Event (PRE) which brought moderate to heavy rainfall across several counties early on the 11th of October. A deep moisture plume surged north on the periphery of the subtropical ridge over the southeast with the very high precipitable water producing high rainfall rates. The heaviest rainfall from the PRE was concentrated in upper and middle portions of the New River basin and the far upper Dan basin where the amountsl ranged from 2 to 6 inches with isolated higher amounts in the 24 hours ending at 700 AM local time.