Chance of a Thunderstorm in the DC Area this afternoon

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12:20 pm – Early showers and storms are coming

Some showers and storms have developed earlier than planned and are moving rapidly into the Route 15 corridor (from Leesburg to Warrenton). They are generally not severe, so expect some brief showers and maybe a bit of lightning with this activity as it extends eastward for the next 60 or 90 minutes. However, activity could intensify a bit, especially after crossing Interstate 95 around 1 p.m.

This activity can consume some of the available energy from the atmosphere by reducing the chances of additional storms later.

We will re-evaluate the storm threat late in the afternoon after these pass.

Original article of the morning

Crazy air is spreading across the Washington region, displacing the little moisture we enjoyed on July 4th. The arrival of this warm, humid air sets the stage for possibly intense storms from Tuesday afternoon until early evening.

The National Weather Service’s Storm Prediction Center has placed our region in a level 2 out of 5 risk zone for severe storms, pointing out the potential for “damaging gusts” and “large isolated hail”.

Any storm affecting the area should pass quickly, reducing the risk of flooding. However, some of the areas that were flooded Saturday night (i.e., saturated soils in the northern part of the district and south of Montgomery and northern Prince George’s counties) could fight back with the high water if strong storms passed.

As the flood rains flooded the district and northern suburbs Saturday night

Short-range computer models suggest that the best chance of storms is between 3 and 6 p.m., with sweeping rainfall from west to east.

In the late hours of the morning, showers and storms were present from the Ohio Valley to West Virginia, and generally headed from east to southeast in a general direction in the Washington region.

Storm time: Although subject to change, storms should arrive in and out of the following areas in the following windows:

  • Interstate 81 (Hagerstown to Front Royal): 2 to 4 p.m.
  • Route 15 (Frederick to Leesburg to Warrenton): 14:45 to 16:45
  • Interstate 95 (Baltimore to DC to Fredericksburg): 3:30 to 5:30 p.m.
  • Route 301 (Bowie to La Plata): 4:15 to 6:15 p.m.

Storms should move quickly, lasting in any area about 30 to 45 minutes. Keep in mind that some very scattered showers and storms are possible after the initial round, but they should decrease coverage and intensity after dark.

Storm cover: Patchy light: any individual area has approximately a 60 percent chance of measurable rainfall.

  • Probably: torrential rain, lightning, gusty winds (up to 30-40 mph)
  • Possible: harmful winds (up to 60-70 mph), small hail
  • Very small possibility: big hail, floods, tornado

Rain potential: In storm-affected areas, it is most likely 0.25 to 0.5 inches, with isolated totals of up to 1 to 2 inches.

Today’s potentially severe weather setting features a warm front that moves across the region (as shown in the map below), resulting in a wetter air mass in southerly winds. In addition, a higher-level disturbance in the flow of the jet stream will move to the mid-Atlantic from the Ohio Valley.

This disturbance has been organizing scattered showers and storms in West Virginia, and these may remain solid or broken by cloud cover around the DC region during the first and a half afternoons.

The degree of severity of the storm will depend on how much the atmosphere is destabilized over the next few hours. Any persistent rupture of the clouds will allow sunlight to increase surface temperatures, which is key to destabilization.

Perfect weather for a spectacular fireworks show in Washington

There is enough wind shear (increase in wind speed with altitude) to help make storm cells more intense, in case they bloom, and organize the cells into groups and lines of inclination.

The set of high-resolution models suggests that storms are triggered earlier (between 1pm and 2pm) on the Blue Ridge, and these storms spread by meters as early as the middle or last hour of the afternoon.

As shown in the simulated radar fields below, the line travels through the DC region. The warm front boundary can help organize and intensify this complex.

With these types of fast-moving complexes, there is potential for a range of harmful gusts of wind, and this is likely to be the greatest risk of severe weather this afternoon and early evening.

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