The National Weather Service has issued a severe thunderstorm watch for the entire DC metropolitan area until 9pm this evening.

Thunderstorms are increasing in coverage across the eastern slopes of the Appalachians, and

will move slowly into increasingly unstable air this afternoon.

What is most impressive however, is that the noon air sounding from the area recorded a lifted index at 500mb of around -4 degrees, which means that if a parcel of air is risen to 500mb (the middle layers of the atmosphere), it will be 4 degrees warmer than its environment and thus, continue to rise. As a result, cloud tops of over 55,000 feet will be possible in stronger storms.

It is likely that stronger complexes of storms will form bow echos this afternoon, so damaging winds appears to be the biggest risk with any storm that does form.

I think that the storms will be able to move into the immediate DC area from west to east between 5-7pm, although storms will be possible before then particularly south and west.