Dense overcast sits over the region and will continue to thicken to the east as a cold front approaches from the west. Radar imagery from the NWS Doppler radar in Sterling, VA shows light showers breaking out across western Maryland and the Shenandoah Valley. As the cold front nears by late this afternoon/evening, expect showers to become more numerous. Also of importance is the drought the DC area has experienced, with most locations reporting a 3" deficit in rainfall for the month.

While the showers from this frontal passage may drop a quarter to half an inch of rainfall on the region, it won't be enough to make much of a difference in the rainfall deficit.

The next chance for (a possibly) more significant rain-event moves into the area during the day Thursday. There is some model discrepancy (as can be expected at three days out), with the GFS model pushing the cold front through early Thursday, with the NAM (formerly the ETA) holding it back until Thursday evening.

Also, depending on the amount of sunshine we see Thursday, we may have a small chance of some convection bubbling up (assuming the NAM model is correct), due to the strong low level jet over the Mid Atlantic in excess of 30kts at about 15,000 feet. This then increases to near 100kts at 20,000 feet or so, which displays a large amount of speed shear is present in the atmosphere. Speed shear is simply the change of wind speed with height--the higher the winds in the upper levels of the atmosphere, the stronger the wind shear. This helps sustain thunderstorm updrafts and is one key element forecasters look for in severe weather situations.

Granted, I can't see a large severe weather event for Thursday afternoon at this time--while the extreme wind shear is conducive for strong thunderstorms, there doesn't seem to be enough instability to initiate severe storms.

There is one thing I am certain about, though, and that is a cold Canadian High Pressure system will slide in behind the aforementioned cold front and deliver some "chilly" air to the region. Some models show low temperatures Friday morning dipping into the 30s out west in the mountains, and into the upper 40s-lower 50s near the metropolitan centers.

It would seem that autumn really has arrived...