Confidence is increasing that an outbreak of severe thunderstorms will impact the Central Appalachians and Mid-Atlantic on Monday afternoon with widespread damaging winds posing the greatest threat.

The ingredients are coming together for more intense thunderstorms than usual to develop across the Appalachians from mid-afternoon through early evening. 

The Storm Prediction Center has issued a level 3 out of 5 risk for severe weather from the North Georgia Mountains all the way to Southern New York. 

A level 4 out of 5 risk has been issued from the Boone, NC area to the DC/Baltimore area with the mountains of Virginia and West Virginia included in this risk. A level 4 out of 5 risk is relatively rare for this region and indicates the threat of severe weather should be taken especially seriously.

The Setup

A powerful trough of low pressure by August standards is approaching the Mid-Atlantic from the west while a cold front will also approach this region at the surface. Strong winds aloft associated with this trough will contribute to high levels of wind shear (changes in wind speed and direction with height), which will support longer-lived, and in some cases, rotating thunderstorms.

Ahead of this trough, a warm and moist airmass is in place with dewpoints in the 60s across the higher terrain of the Appalachians and 70s across the adjacent lower elevations. This is “juicy” air and will contribute to high levels of instability to fuel thunderstorms as the trough approaches from the west.

Learn More → Dewpoint and Relative Humidity

Below: Forecast Dewpoint Temperatures for Early Monday Afternoon

High levels of moisture and instability, combined with wind shear profiles that feature significant changes in wind speed with height, will support thunderstorms developing into organized lines capable of producing damaging winds that could potentially knock over trees.

Possible Impacts:

Damaging straight-line winds are expected to be the most significant severe weather threat on a large scale. 

Areas in pink have the highest threat of experiencing thunderstorm wind gusts of 58 mph or higher, with the threat extending from North Georgia into Southeast Pennsylvania.

The hatched area indicates a higher probability of thunderstorm wind gusts exceeding 70 mph or higher. This area includes all mountainous terrain in West Virginia and Virginia, as well as Maryland, extreme NW North Carolina, and NE Tennessee.

While straight-line winds will pose the greatest threat for most, there is also a risk of tornadoes. Initially, semi-discrete (meaning standalone) thunderstorms could develop with a higher threat of rotating supercells that could produce tornadoes.

As the afternoon progresses, thunderstorms are expected to form into organized lines/clusters. Embedded supercells can still develop within these lines, which can also produce tornadoes. These types of twisters tend to be shorter-lived compared to those that occur with standalone supercells but can still produce significant damage.

As of early Monday afternoon, Tornado Watches (which indicate the potential for tornadoes over a longer period of time) have already been issued for portions of Tennessee, North Carolina, Kentucky, and West Virginia. More watches may be issued further east as the day progresses.

The highest threat for tornadoes is expected near and west of the Blue Ridge Crest from North Carolina to Maryland, with Virginia/West Virginia looking the most vulnerable.

Large hail up to 1” in diameter is also a threat with thunderstorms on Monday, though this appears to be more of an isolated threat.

Timing

Storms are already developing along the western side of the Appalachians from West Virginia to Tennessee as of early Monday afternoon.

The potential for severe thunderstorms will increase as the afternoon progresses, with most areas in the Appalachians seeing the highest threat from about 2pm to 7pm. East of the mountains, the timing window will be up to a couple of hours later. 

OpenSnow’s hourly point forecasts are a good resource to see when lightning potential is the highest, along with Current Radar and Forecast Radar maps. Also, when it comes to strong to severe thunderstorm setups such as this, be sure to give yourself an extra couple of hour’s margin for error on the hourly forecasts.

The potential for severe thunderstorms will increase as the afternoon progresses, with most areas in the Appalachians seeing the highest threat from about 2pm to 7pm. East of the mountains, the timing window will be up to a couple of hours later. 

Additional showers and thunderstorms are possible later Monday evening across the Appalachians behind the main round, but the threat of severe weather is expected to be lower.

OpenSnow’s hourly point forecasts are a good resource to see when lightning potential is the highest, along with Current Radar and Forecast Radar maps. Also, when it comes to strong to severe thunderstorm setups such as this, be sure to give yourself an extra couple of hours’ margin for error on the hourly forecasts.

Here is the hourly lightning forecast for Lewisburg, West Virginia on Monday:

And here is the hourly forecast for Shenandoah National Park in Virginia:

How To Prepare:

If you live in the highlighted risk areas, be sure to pay close attention to the forecast and have a plan to quickly retreat to a safe location in the event of severe weather. The safest place you can be is inside a building away from windows.

Also, have a way to receive severe weather alerts. You can enable your phone to receive Wireless Emergency Alerts, which will alert you if a significant severe weather warning (such as a Tornado Warning) is issued. 

You can also use follow your local National Weather Service office, via weather.gov or through Social Media to check for severe weather warnings as storms approach your area. In addition, local meteorologists on news stations will typically present live coverage for their area when severe weather is imminent. 

Outlook Beyond Monday:

Relatively cooler and drier air will move in behind this system on Tuesday and Wednesday. Lingering showers will be possible across some of the higher terrain in the Appalachians on Tuesday while further drying is expected for all areas into the day on Tuesday.

Another trough will approach during the second half of the week, with increasing shower and thunderstorm chances returning to the western side of the Appalachians on Wednesday night, and to the remainder of the Appalachians and Mid-Atlantic on Thursday.