Kevin Myatt is The Roanoke Times' weather columnist.

kevin.myatt
@roanoke.com
981-3341

Weather with Kevin Myatt

Recent columns

• We got graupel, but not on official record
• Moisture could get caught up in cold blast
• Forecast for Weather Journal: Partly print, with frequent Internet
• Column archive

Read the Weather Journal blog

• Sprinkles or flurries possible Tuesday, but maybe something bigger for the weekend?
• For now, it looks like a quiet, mostly mild week ahead for SW Virginia
• Coldest morning of winter so far likely across much of Southwest Virginia; Tuesday precipitation looking doubtful
• Weather Journal blog

#swvawx on Twitter

@KevinMyattWx

• Follow Kevin on Twitter at @KevinMyattWx

Yes, you can have a flood and a drought at the same time.

It's possible today. The remnants of Tropical Storm Fay may bring localized flooding to Southwest Virginia, but yet the system is unlikely to entirely eliminate the long-term drought we've been having.

The rainfall that began Tuesday is forecast to total 2 to 5 inches across most of the area when it ends Thursday. But National Weather Service hydrologist Peter Corrigan said Monday that it would take 6 to 10 inches to truly relieve the drought.

That kind of rainfall is not impossible, but not likely today as Fay's old circulation center passes to our west. The cost of widespread 6- to 10-inch rainfall amounts would probably be some damaging floods.

We're on that strange precipice between getting desperately needed rain and getting too much of a good thing. It would be better to have a few inches of rain slowly soaking the soil than it would to have several inches running off the hard, dry ground in a few minutes.

Phil Hysell, a meteorologist at the National Weather Service in Blacksburg, said the biggest flooding concern today would be localized downpours that could overflow small streams and inundate urban roadways.

Tropical systems tend to spawn bands of heavy rain that move over the same locations repeatedly. Some places under those bands could see up to 8 inches.

"Many of the rivers are running near record low levels, so it will take a lot of rain to get them out of their banks," said Hysell, who coordinates warning systems for the Blacksburg office. "The 2 to 5 inches of rain that we expect, we don't anticipate that amount of rain to bring main stem rivers out of their banks.

Hysell, however, added that widespread rainfall of 5 to 6 inches might be enough to start pushing some rivers a little past their banks.

Looking at recent history, that rings true for the Roanoke River, even in dry spells.

The remnants of Hurricane Frances, which arrived in early September 2004 after four dry weeks, dumped 5 inches of rain in about 12 hours and pushed the Roanoke River barely out of its banks. Frances' deluge helped set up a much worse flood caused by similar rainfall amounts with the remnants of Hurricane Jeanne later that month.

With drought expanding across the area in late June 2006, Roanoke received nearly 7 inches of rain over 3 days as a low off the South Carolina coast pumped in copious tropical moisture. It was enough to push the Roanoke River into a partly demolished Victory Stadium one last time.

Tropical systems have often played an important role in easing or at least interrupting drought in Southwest Virginia.

In September 1999, Carvins Cove reached its record low mark of 29.2 feet below the spillway. Tropical Storm Dennis, pushing into the Carolinas, hurled a band of rain westward that dumped 3 to 5 inches and started refilling the reservoir, raising it 3 feet in a couple of days.

Not quite a quarter-inch of rain fell in September 2005, but Tropical Storm Tammy just off the East Coast spun in 4 inches of rain over four days in early October.

"If you look at past events where we've been in periods of well below-normal precipitation, it takes a tropical system like a Fay or some of the systems in the past not only to bring the amount of rain to reduce the deficit, but the duration of rain," Hysell said.

Unless unexpected historic flooding occurs, today's rain should benefit almost everyone in Southwest Virginia.

But it's probably only a break in the drought, not a drought-breaker.