It's so hard to get these kinds of forecasts into 2 minutes and 45 seconds of our full weather. I think the best way to break this forecast down is by county & coverage area, so that's what I'm going to do! We'll start with the most affected areas and work our way south.
Frederick, Clarke, Hardy & Grant Counties: You are all under Winter Storm Watches for tonight into Tuesday Morning. Expect high temperatures to struggle today, and only get into the mid to upper 40's. The first area of precipitation should approach around the evening commute (3:30-5ish) as rain - though it may get the to the western slopes of the Highlands a little earlier. Cold air will quickly move south and change precip into a sleet/snow mixture by 7pm and all snow by 9pm (might be a little sooner in the Highland). Banding will occur with this event - it will likely form in a E-W orientation, though I think it will be just a touch to our north along I-68. However, 3-5" of snow/sleet cannot be ruled out in these areas, of course with highest amounts the farther north you go.
Shenandoah, Warren & Page Counties: You may be wondering why you're not under Winter Storm Watches if Hardy & Grant are. Well, it's mainly because Hardy & Grant are going to rob a lot of the moisture and heaviest bands from you. I do think you'll be under Winter Weather Advisories tonight. High temperatures today will likely be around 50-55º under mostly cloudy skies. Precipitation should enter the region around 4-5:30, during the evening commute in the form of rain. Rain will changeover to sleet from north to south by 8pm, with another changeover to a sleet/snow mix (and all snow in northern areas) by 10pm. Highest amounts will be in northern Shenandoah County where up to 2" may fall. Isolated areas of 3" possible but most amounts should stay within 1-2".
Pendleton & Rockingham Counties: High temperatures Monday will be rather warm, likely crossing the 60º mark in most areas. The farther south you go, the warmer it will be. Precipitation should close in on the area just around or after the evening commute, starting as rain and changing over to sleet/snow mix around 10pm and may stay that way for the entirety of the night. Some areas may change over to complete snow however, it depends on the structure of the atmosphere. The mix of snow and sleet will hold down any accumulation, with up to an inch possible in the northern portions of the counties, with <.50" possible at the southern end.
Highland & Augusta Counties: Temperatures will likely hit the 60's and even the 70's in some areas, especially southern Augusta county. Precipitation will close in on the area around or just after the evening commute. It will take time for temperatures to fall, therefore most precipitation will fall as rain until 11pm/Midnight when we may see a rain/sleet mix. Higher elevations of Highland county have a better chance of seeing a sleet/snow mix but accumulation will be limited due to the warmer air Monday afternoon. Less than .50" precipitation is expected, with most areas in the southern portions of these counties seeing little to no wintry precipitation.
All precipitation should end before sunrise on Tuesday morning, however at this point, all areas in the Valley will likely be below freezing. Therefore any leftover moisture may freeze, leading to black ice in some areas.
As I mentioned this is a complicated forecast because of the gradients from north to south with this system. Feel free to ask questions and I'll try to update later as more model information comes in.