Updated forecast: Severe thunderstorm risk ends as squall line passes D.C. area (2024)

And yep — D.C. did manage its sixth wet weekend in a row, if sneakily.

This is the final update. Our new forecast will be published at 5 a.m. More storms are likely on the way Monday afternoon and evening.

10:20 p.m. — Warning canceled early as storms enter Fairfax County

The Weather Service dropped the severe thunderstorm warning over southwestern suburbs early as activity is weakening on approach to the immediate area.

Although the potential for damaging wind gusts has diminished with the storms at present, some isolated strong gusts remain possible. Showers and storms will move inside the beltway over the next 30-60 minutes.

9:53 p.m. — Storms arriving in southwest suburbs

With storms beginning to enter southwestern parts of the area, a severe thunderstorm warning was issued through 10:45 p.m. for parts of Loudoun, Fauquier, Prince William and Fairfax counties.

Winds gusting upwards of 60 mph are the main severe weather threat. There are fewer wind damage reports with the line lately.

8:54 p.m. — Severe thunderstorm watch has been issued until midnight; approaching storms have a history of producing wind damage

The National Weather Service Storm Prediction Center has placed much of the D.C. area under a severe thunderstorm watch until midnight. All counties but those along the Chesapeake Bay are included in the watch. A watch means conditions are favorable for severe storms in the region. If warnings are issued for your location, it means the storms are imminent.

A line of storms with a history of producing damaging winds is approaching the region.

Storms recently passed Charlottesville and stretch from central Virginia into western Maryland. They are on target to reach the the close-in D.C. area between about 10 p.m. and midnight, arriving first in our southwest suburbs.

Here’s an approximate arrival timeline for different locations:

These storms have a long history of producing wind damage and may end up characterized as a derecho in areas west of the Appalachians. While the storms may weaken some by the time they reach Interstate 95, they have produced widespread downed trees around Charlottesville.

We’ll post another update around 10 p.m.

Please see the more detailed two-part severe weather briefing at the bottom of this report.

Original forecast from this afternoon

Storms are possible into this evening, especially around the Chesapeake Bay and secondarily perhaps nearer elevated terrains. Later tonight, we could see a stronger round of storms — and some may be severe.

Memorial Day has the relatively highest severe weather threat, and storms may be most widespread from about noon to 9 p.m. Wind damage, large hail, a couple of tornadoes and flooding downpours are possible.

This humid, unstable air mass persists until the instigating strong cold front clears out Monday night.

Through tonight: The highest chances (around 50 percent) of strong storms may come in the late evening into the overnight hours. Otherwise, it’s mostly cloudy. Low temperatures will drop close to the uncomfortable dew points in the mid-60s to around 70. With this potential 100 percent relative humidity, we may see patchy fog near sunrise.

Memorial Day (Monday): A lot of filtered sunshine and clouds are possible. Morning showers and storms are possible, but strong storms with prolonged downpours don’t appear to be too likely. Most eyes are on the afternoon and evening for organized, widespread, potentially damaging storms.

Wind gusts from the south-southwest may get to around 25 mph, even outside of storms, offering some relief from sticky temperatures in the low to mid-80s. By midnight, most showers, storms and breezes should be over as the energetic cold front passes. Temperatures will bottom out in the low to mid-60s by sunrise.

Part 1, tonight: Vigorous storms like last night’s are possible, perhaps strongest after 10 p.m.

We’ll have to look toward the Ohio Valley tonight as a potential complex of storms moves toward the Appalachians well ahead of tomorrow night’s cold front. This complex is likely to weaken as it approaches our area, but it’s typically best to stay a bit cautious given the atmospheric setup. Here is one potential forecast of how radar will look from 8 p.m. Sunday to 6 a.m. Monday:

The storms could travel through central Virginia and the Interstate 64 corridor late tonight. The National Weather Service has some limit to the concern, though, with the overall severe threat appearing “to be marginal at best due to modest instability and shear.”

Part 2, tomorrow: Widespread storms from about noon to 9 p.m. may be very organized and potent.

From our severe storm expert, Jeff Halverson: “A combination of an approaching cold front, upper level disturbance, unstable atmosphere and strong winds aloft will trigger numerous thunderstorms” — perhaps in waves of strong thunderstorm cells or lines of cells. “Some storms may be locally severe and necessitate a severe thunderstorm watch.”

Many threats are on the table, but damaging wind gusts of at least 58 mph are the primary threat. Lightning, hail and a couple of tornadoes are also possible. Torrential downpours may be brief, thanks to the quick movement of storms, limiting flooding concerns. A simulated radar for tomorrow looks active from noon to 9 p.m.:

Halverson said the ingredients could all come together for thunderstorms to form over our region. Clouds are one unknown variable: More clouds tomorrow could mean fewer thunderstorms. However, high levels of convective potential energy and wind shear — shifting winds at different heights in the atmosphere — may allow for large thunderstorm “supercells” to develop, along with one or two tornadoes.

Stay tuned. Our next severe weather update is currently expected tomorrow morning, as we assess the latest data for this potentially hazardous weather. If you’re heading outside during the holiday tomorrow, keep weather-aware! We’ll discuss storms and go over the shortened workweek’s weather in tomorrow’s Holiday Monday Sunset Live Q&A on YouTube, Facebook, Instagram and X! Our 20-minute chat will start at 8:25 p.m.

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Jason Samenow contributed to this report