July rates high for rainfall, and month isn’t over yet
Tuesday, July 16, 2013
A historic hour of deluge vaulted Roanoke’s monthly rainfall to the top of the heap for July after only 10 days.
But the soggy pursuit of history isn’t over.
Another fast deluge of more than an inch Tuesday evening at the official rain gauge at the Roanoke Regional Airport pushed July’s rain total very close to a foot — 11.99 inches — making July the fifth wettest month at any time of year, dating to the start of official weather records in 1912.
Merely normal rainfall over the last 15 days of the month — which is 1.95 inches — would move July 2013 easily into second place on the list at 13.94 inches.
As we’ve seen more than once, just one precisely placed thunderstorm could accomplish that.
Second place is currently held by an infamous month in Roanoke weather history, November 1985, when 12.36 inches of rain fell. More than 10 inches of that fell in the first five days, triggering the deadly and destructive Flood of ’85.
The top spot is held by August 1940 at 16.71 inches. A tropical system, another organized “monsoon”-type wet pattern like we had in early July or a couple more localized thunderstorm downpours at the airport could put that in play.
While there are no obvious signs of extreme wetness on the horizon, scattered showers and storms — typical for mid-July — will be possible just about any day in the next week.
Of course, the main reason this is a historic rainfall month for Roanoke boils down not only to getting 3.35 inches of rain between 3 and 4 p.m. on July 10 — estimated to be between a 200-year and 500-year deluge — but also that downpour having happened right over the official rain gauge at the airport.
Other parts of the Roanoke Valley did not get nearly as much rain that day — and many more parts of the valley entirely missed Tuesday night’s 1.15-inch downpour. Virtually all of Southwest Virginia is significantly above normal on rainfall this month, but not all of the region is at the same extreme level as the Roanoke official total.
Blacksburg, at 5.61 inches over the first 15 days of the month, has just barely moved into its top 10 list for wet Julys. Blacksburg’s period of record dates only to 1952, so it includes about 40 fewer years than Roanoke’s.
The day after the flash flooding deluge in north Roanoke, much of Lynchburg was inundated by a downpour. Rain totals exceeded 3 inches at gauges in downtown, but the official rain gauge at the Lynchburg airport south of town was outside the cloudburst and only got eight-hundredths of an inch. So that’s what went in the books for Lynchburg.
There is an element of chance to Roanoke’s record July rainfall … and still a good chance that the record will grow even more.
Weather Journal runs on Wednesdays.
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THE ROANOKE TIMES
