6 takeaways from Debby’s effects on Virginia

Debby came and went pretty quickly last Thursday after a week of anticipatory buildup on what its overall impacts might be for Virginia.

Both sighs of relief and genuine gratitude for drought relief are warranted after the former Category 1 hurricane and recent tropical storm made a considerable but, on the whole, fairly mild pass through the commonwealth almost a week ago. There appear to have been no fatalities, no severely damaged homes, and no lingering disaster impacts in Virginia from Debby, which delivered a lot of rain to catch up on deficits going back many months in much of Virginia while producing only scattered, mostly minor flooding in our state.

In Debby’s wake, we have a week of near- to slightly-below normal temperatures — lots of 70s-80s highs, 50s-60s lows — with very little rain expected until increasing again by Friday and Saturday.

As we catch our breath in this relatively calm week before whatever the next big weather story becomes, let’s take a quick look back at Debby and its effects on Virginia.

1. Primarily, it was a beneficial rain.

In my early years working at The Roanoke Times shortly after the turn of the century, while we were experiencing a major regionwide drought over multiple years with dried-up reservoirs and water restrictions, it was sometimes spoken among my newspaper colleagues that we needed a “small but tasteful hurricane” to relieve the drought.

With Debby that’s essentially what we got.

On my weather-related social media, the number of people rooting for this rain to happen outnumbered those absolutely not wanting it. Overall, it threaded the needle between opposing interest groups far better than any politician could, with enough rain to provide a good soaking over a wide area (excluding many areas west of Interstate 77) while only producing scattered reports of some small stream flooding, a few closed roads, and a small number of rivers barely going over their banks.

Amounts of 2-6 inches were fairly widespread between Interstate 95 on the east and the New River then up the Virginia-West Virginia line on the west, with a few bigger amounts, mostly along some Blue Ridge high points.

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2.  Here’s why it didn’t flood too badly.

On Wednesday, the National Weather Service office in Blacksburg issued a flood warning for the Roanoke River at its Walnut Street gauge in downtown Roanoke warning of a potential 15.5-foot crest. That would be 5.5 feet above flood stage and the 10 ^th highest crest on record going back to the early 1900s.

The actual crest: 4.31 feet, more than 5½ feet below flood stage.

In fairness, the weather service modified the forecast crest downward in subsequent hours as more information became available. The Roanoke River never threatened to flood at Roanoke. One key factor was that more widespread 8- to 12-inch rains did not develop along the Blue Ridge south of Roanoke, as some models suggested could happen, but rather mostly stayed in the 3- to 6-inch range with a few bigger amounts and a much less pronounced upslope-enhanced stripe than we sometimes see.

On a broader scale, across our region and really the whole state, two factors worked together to keep extreme flash flooding or widespread major river flooding from occurring.

• Torrential rainfall rates of 1-2 inches per hour did not train over locations for multiple hours. Most extended rainfall rates were under an inch per hour, with the heavier downpours generally moving through quickly rather than stalling or training over the same locations repeatedly.

• Dry soils and vegetation absorbed an enormous amount of rainfall before it could run off into creeks and streams, limiting flooding potential considerably. Heavier rain for longer or more saturated soils would have allowed more runoff.

One area that seemed to have a higher chance of flooding was Southside Virginia, because of heavy rains that fell in the week before, but that area mainly got 2-4 inches of rain spread out over time. Danville got a little less in three days of Debby, 3.29 inches, than in a single thunderstorm deluge the previous week — 3.45, mostly in a couple of hours, on Aug. 2.

3.  Southwest corner got left out.

Reminiscent of a coastal snowstorm, tracking where the western edge of Debby’s rain shield would end up was difficult, and it actually landed a little east of the general forecast consensus, not making it far past the I-77 corridor.

Rather than gradually reducing by a few tenths of an inch over many miles, rainfall amounts dropped off quickly at the western edge.

Wytheville’s official gauge collected 1.11 from Debby’s influence over a couple of days. Less than an hour’s drive west at Saltville, there was exactly an inch less, 0.11. Abingdon managed 0.02, while the Tri-Cities Airport just over the Tennessee line from Bristol got zilch from Debby.

For the most part, the Southwest counties west of Interstate 77 got more rain than most of Virginia during the prior two weeks of occasional storminess, so much so that most of Lee County was removed from dryness in last week’s U.S. Drought Monitor map and most of the counties just east were only in the weakest “abnormally dry” category. There is a spot in and around Tazewell County that was in moderate drought prior to Debby and mostly missed the storm’s soaking rain that may continue to show darker shades once this week’s drought map is issued on Thursday .

4.  Tornadoes almost skipped Virginia.

North Carolina has had at least seven confirmed tornadoes from Debby, including one that was as strong as EF-3 on the 0 to 5 Enhanced Fujita Scale, an unusual intensity for twisters spawned by tropical systems.

There were a few tornado warnings issued in central and eastern Virginia, as tight circulation was detected in some rain bands, but as of this writing, only two tornadoes been confirmed in the commonwealth from Debby, EF-1 tornadoes affecting Stafford, Loudoun and Clarke counties in Northern Virginia , leaving damage almost entirely limited to trees.

While it is possible there was a brief spin-up along the surface somewhere else, Virginia mostly caught Debby at a time when its strongest circulating winds had died down some and instability was not particularly strong without much daytime heating.

5.  Wind damage warns of what a hurricane could do.

Easterly winds north of the storm center got quite gusty, in the 35-45 mph range in some areas along and east of the Blue Ridge. The result was many trees downed and scattered power outages in the middle part of Virginia. The Lynchburg area particularly experienced a concentration of wind damage and power outage reports.

We saw similar power outages and tree damage with a similar geographic pattern — even a fatality with one falling tree in Campbell County — when diminishing Hurricane Ian slid inland on a somewhat similar trajectory on the first day of October in 2022.

We rarely think much about wind damage from tropical systems this far inland, but Debby and Ian are reminders that a stronger hurricane making a quick move inland from a Carolinas landfall could deal considerable damage and widespread outages this far inland. With trees that are braced against more common westerly winds and less flexible than many coastal varieties, gusty easterly winds north of a tropical storm center often seem to do more tree damage than do similar winds at the coast or blowing from a westerly trajectory here behind a winter cold front.

Hurricane Hazel of 1954 and Hurricane Hugo of 1989 are among the powerful hurricanes that made Carolinas landfalls and quickly moved toward Virginia with wind gusts still near hurricane force in parts of the state. Hurricane Isabel in 2003, which came ashore in the Outer Banks of North Carolina before tracking northwest, was both a wind-damage and flooding menace over most of the state except for most of the region covered by Cardinal News — remember, Virginia Tech and Texas A&M played football through some breezy rain that barely broke an inch that night in Blacksburg.

6.  Priming the pump, or backsliding into drought?

Where we go from here is the subject of considerable conjecture.

When the new drought map is issued Thursday, all the colors won’t be washed away by Debby. A big chunk of the state will probably still be in the yellow “abnormally dry” tone and some areas in western and northwestern parts of Virginia that were in severe to extreme drought may even cling to the beige “moderate drought.” One storm doesn’t end a long-term drought.

A few weeks of mostly dry weather would return much of the state into darker shades of drought, leading us toward fall wildfire season.

But that may not happen if the current pattern of eastern U.S. troughing brings fronts through regularly, such as this weekend, when showers and storms are expected to increase in coverage over our region.

Also, Debby may not be our last dance with tropical cyclones. While Hurricane Ernesto is expected to make a hard turn north into the open Atlantic after its scrape with Puerto Rico, there are other systems lined up behind it that may eventually become tropical cyclones.

Debby is somewhat reminiscent of the remnant circulation of Hurricane Frances in early September of 2004. Frances produced similar rainfall amounts as Debby over much of Virginia but only mild flooding. However, Ivan followed at mid-month with moderately heavy rain and many tornadoes, and then in late September, Jeanne tracked almost exactly like Frances with close to the same rainfall range, and it spawned deep flooding of many creeks and rivers because its rain came atop the wet soils of the other two storms.

There is no guarantee Virginia will be directly affected by any other tropical systems in the weeks and months ahead, but the more there are in what is projected to be a near-record Atlantic hurricane season, the better chance we will have for a sequel, perhaps a more consequential one.

Journalist Kevin Myatt has been writing about weather for 20 years. His weekly column, appearing on Wednesdays, is sponsored by Oakey’s, a family-run, locally owned funeral home with locations throughout the Roanoke Valley.

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