Wintry mix early Friday morning?

After a truly arctic day, temps will drop once again into the single digits tonight. Both IAD and BWI broke daily low records and records for the lowest highs for the day. DCA did not break any daily temperature records. IAD had a low of 1 and  high of 18 while BWI had a low of 3 and a high of 16. DCA had a low of 8 and a high of 21 and the coldest mean temperature since 1996.

Iced over Potomac River on 1/7/14

Wednesday will feature highs in the upper 20s and lows int the lower 20s Southerly flow helps with the moderation of temperatures for the rest of the week into next week as the polar vortex lifts out. Thursday night into Friday morning is the next threat for wintry precipitation possibly starting out as snow and changing to light freezing rain. The storm's track and strength is still up in the air but it is likely that any precip will be light.

70 Hr Forecast by the CMC shows snow over the Midatlantic at 5AM Friday. 

Note the 1032 isobar (an isobar is just a line in delineating a certain air pressure and 1032 is a high pressure) jutting out over the region. This indicates possible cold air damming (CAD). Lows on Thursday night will be in the mid 20s while highs on Friday will rise above freezing to around 40. The light precip and nonexistent low pressure will work to prevent any major effects. However, this is only one solution and the actual outcome could be very different from what is depicted here. As the time frame draws closer, the details should begin to become clearer. At this point, all we know is that there is a threat for ice. Following that, a storm strengthens to our west, bringing temperatures into the 50s and heavy rain. A wet week after this one is supported by almost all model runs. However, the American Models (GFS and NAM) have had initialization errors for the past few days, meaning that their initial scenario does not match what is actually going on. This will lead to large errors for medium to long range forecasts. The NWS recommended that the runs be ignored outside of short term.

The 110 Hr forecast by the CMC shows a major rainstorm for the East Coast. The CMC is the weather model run by Canada.