The following is provided by DC Severe Winter Weather:

We continue to close in on what is shaping up to be a major snowstorm with widespread traffic delays and possible power outages. Despite this, a significant amount of uncertainty still exists, especially regarding the rain/snow line.

Timing:

Monday-Tuesday

6-9 PM: Snow, possibly mixed with rain, overspreads the area. Temperatures 32-36.

9PM-2AM: Moderate to heavy snow. Temperatures 28-34.

2AM-7AM: Heavy snow, mixing with sleet and possibly rain along I-95 and southeast. Temperatures 28-34

7AM-9AM: Snow continues, temperatures drop, areas that were mixing transition back to snow. Temperatures 27-33

9AM-7PM: Period light-to-moderate snow. Little additional accumulation. Temperatures 28-36

7PM-10PM: Snow exits the area, temperatures plunge into the teens

Impacts: Roads will become snow covered and slippery. Expect widespread cancellations Tuesday and possibly into Wednesday. Montgomery county will almost certainly cancel. Another concern is power outages. Near the mix/snow line where the snow is wetter, snow will stick to and accumulate on trees and power lines. Be prepared for possible power outages after the storm.

The main uncertainty exists in the position of the rain/snow line. Our snow map reflects our thoughts that the DC-Baltimore corridor will briefly mix with sleet, but not rain. If it looks colder than expected tomorrow afternoon we will have to increase our snow forecast. If it looks warmer and like rain is more likely, we will have to lower it.

We will continue to update you as the situation changes. Expect a final call tomorrow afternoon before the snow starts.