This activity can use up some of the atmosphere’s available energy, reducing the chances of new storms later on.
We will reassess the late afternoon thunderstorm threat after it comes through.
Original article from late morning
The balmy air is spreading across the Washington region, displacing the low humidity we enjoyed on July 4. The arrival of this warm, moist air sets the stage for potentially intense thunderstorms Tuesday afternoon into early evening.
The National Weather Service Storm Prediction Center has placed our region in a Level 2 out of 5 risk zone for severe storms, pointing to the potential for “damaging wind gusts” and “isolated large hail.”
Any storms that hit the area should pass quickly, reducing the risk of flooding. However, some of the areas flooded Saturday night (i.e. saturated ground in the northern part of the district and southern Montgomery and northern Prince George counties) could experience high water again if severe storms pass.
Short-range computer models suggest the best chance of storms is between about 3 and 6 p.m., with precipitation moving from west to east.
As of late morning showers and storms were present from the Ohio Valley into West Virginia and drifted generally east to southeast in the general direction of the Washington region.
Storm time: While subject to change, storms should arrive and leave the following areas in the following windows:
- Interstate 81 (Hagerstown to Front Royal): 2 to 4 hours
- Route 15 (Frederick to Leesburg to Warrenton): 2:45 PM to 4:45 PM
- Interstate 95 (Baltimore to DC to Fredericksburg): 3:30 PM to 5:30 PM
- Route 301 (Bowie to La Plata): 4:15 PM to 6:15 PM
Storms should move quickly and last about 30 to 45 minutes in a given area. Please note that some widespread showers and storms are possible after the first round, but should decrease in coverage and intensity after dark.
Storm cover: Scattered — each individual area has about a 60 percent chance of measurable rain.
- Likely: torrential rain, lightning, gusts (up to 30-40 mph)
- Possible: Harmful winds (up to 60-70 mph), small hail
- Very small chance: large hail, flood, tornado
Rain potential: In storm-hit areas, 0.25 to 0.5 inches is most likely, with isolated totals up to 1 to 2 inches.
Today’s potential lineup of severe weather features a warm front moving through the region (as shown in the map below), ushering in a more humid air mass with southerly winds. In addition, an upper-level disturbance in the jet stream will travel from the Ohio Valley to the Mid-Atlantic.
That disruption has caused scattered showers and thunderstorms across West Virginia, which could remain solid through the early and afternoon hours into broken clouds around the DC region.
The storm’s severity will depend on the degree to which the atmosphere becomes destabilized in the coming hours. Any continued break in the clouds will allow the sunshine to push up surface temperatures, which is key to destabilization.
There is enough wind shear (increase in wind speed with height) to make storm cells more intense, should they bloom, and organize the cells into clusters and curving lines.
The series of high-resolution models all suggest that storms in the Blue Ridge are generated fairly early (1:00 p.m. to 2:00 p.m.), with those storms then raging through the subways mid-to-late afternoon.
As the simulated radar fields below show, the line marches through the DC area. The warm frontal boundary can help organize and intensify this complex.
With these kinds of fast-moving complexes, there’s the potential for a range of damaging wind gusts – and that’s probably the biggest risk of severe weather this afternoon and early evening.
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