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12:20 PM — Early blooming showers and storms are already arriving
Some showers and storms have developed ahead of schedule and are quickly moving into the Route 15 corridor (Leesburg to Warrenton). These are generally not serious, so mainly expect some brief showers and maybe some lightning with this activity as it moves east over the next 60 to 90 minutes. However, activity can pick up a bit — especially after crossing Interstate 95 around 1 p.m.
This activity can use up some of the atmosphere’s available energy, reducing the chances of additional storms later.
We will reassess the storm threat in the late afternoon as they develop.
Original article from Late Morning
Sultry air is spreading over the Washington area, displacing the low humidity we enjoyed on the Fourth of July. The arrival of this warm and moist air sets the stage for possible intense thunderstorms Tuesday afternoon into early evening.
The National Weather Service’s Storm Prediction Center has placed our region in a Level 2 out of 5 severe storm risk area, noting the potential for “damaging gusts” and “isolated large hail.”
Any storms that affect the area should pass quickly, reducing the risk of flooding. However, some of the areas that were flooded Saturday night (i.e., saturated ground in the northern part of the county and southern Montgomery and northern Prince George’s counties) may again contend with high water if strong storms move through them .
How torrential rain inundated the area and the northern suburbs on Saturday night
Short-range computer models suggest the best chance for storms is between about 3 and 6 p.m., with precipitation moving from west to east.
By late morning there were showers and storms from the Ohio Valley to West Virginia and generally moving east-southeast in the general direction of the Washington area.
Storm Time: Although subject to change, storms should arrive and exit the following areas in the following windows:
- Interstate 81 (Hagerstown to Front Royal): 2:00 p.m. to 4:00 p.m.
- Route 15 (Frederick to Leesburg to Warrenton): 2:45 to 4:45 p.m.
- Interstate 95 (Baltimore to DC to Fredericksburg): 3:30 to 5:30 p.m.
- Route 301 (Bowie to La Plata): 4:15 p.m. to 6:15 p.m
Storms should move quickly, lasting about 30 to 45 minutes in any one area. Note that some scattered showers and storms are possible after the initial round, but should decrease in coverage and intensity after nightfall.
Storm coverage: Scattered — Each individual area has about a 60 percent chance of measurable rain.
- Likely: Heavy rain, lightning, gusty winds (up to 30-40 mph)
- Possible: Damaging winds (up to 60-70 mph), small hail
- Very Low Chance: Large Hail, Flood, Tornado
Rain Potential: In areas affected by storms, 0.25 to 0.5 inches is most likely, with isolated amounts of up to 1 to 2 inches.
Today’s potential severe weather setup includes a warm front moving through the region (as shown on the map below), bringing a wetter air mass with southerly winds. Additionally, an upper-level disturbance in the jet stream flow will move into the Mid-Atlantic from the Ohio Valley.
This disturbance is organizing scattered showers and thunderstorms across West Virginia, and they may retain solid to scattered clouds around the DC area through the early to mid-afternoon.
The strength of the storm will depend on how much the atmosphere destabilizes over the next few hours. Any persistent cloud breaks will allow sunshine to raise surface temperatures, which is key to destabilization.
Picture-perfect weather for a spectacular fireworks display in Washington
There is enough wind shear (increase in wind speed with altitude) to help storm cells become more intense if they develop and to organize the cells into clusters and meandering lines.
The high-resolution model suite suggests fairly early (1 to 2 p.m.) triggering of storms in the Blue Ridge, with these storms then moving across the metro as early as mid to late afternoon.
As the simulated radar fields below show, the line passes through the DC area. A warm frontal border can help organize and strengthen this complex.
With these types of fast-moving complexes, there is the potential for a series of damaging wind gusts — and that will likely be the biggest risk of severe weather this afternoon and early evening.
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