Weekend scenario(s) One way to get a significant snowstorm in the Mid-Atlantic region is to have a wave of upper-atmosphere energy in the northern branch of the jet stream “phase” together at just the right time with a wave of energy in the southern branch of the jet stream to generate a strong storm along the Mid-Atlantic coastline (of course, cold air is needed as well). Even though there will be two systems to deal with this weekend – one riding along the southern branch of the jet stream and the other in the northern branch – they appear to be separated by about 24-hours or so. The southern system will arrive on the scene in the Mid-Atlantic region on Saturday while the northern system will move in on Sunday.
In this particular weekend setup, there are still two other ways to get significant snowfall around here – neither of which seems likely at the moment - but still cannot be ruled out completely. The first way would be if the southern system generates on its own a strong storm along the coast. Indeed, it does like a strong low pressure system will form along the Mid-Atlantic coastline by Saturday, but – at least for the moment – its heaviest precipitation shield is just a bit too far to the southeast of the I-95 corridor to create any substantial snowfall around here. The second possibility would be if the northern system on Sunday intensifies rapidly on its own as it reaches the relatively warm waters of the western Atlantic Ocean. While this scenario does not currently seem likely, the upper-level trough associated with the northern system does become “negatively-tilted” as it approaches the east coast and this sometimes signals rapid intensification is about to occur along the Northeast US coastline.
The bottom line: both systems still bear watching. The first system (southern) on Saturday has to be monitored to see if its heaviest precipitation area shifts to the northwest and into the I-95 corridor. The second (northern) system has to be monitored to see if it could experience quick intensification along the Mid-Atlantic coastline on Sunday. If neither happens, then the most likely result would be nothing more than a "light-to-moderate" snowfall with either system. Stay tuned.
12Z NAM The latest 12Z NAM computer forecast model run shows (above) the southern wave of energy in the upper atmosphere (500 mb) on Saturday morning well ahead of the northern wave. This southern wave does not phase together with the northern wave, but it does generate quite a strong storm off the Mid-Atlantic coastline that needs to be monitored. The northern wave of energy takes on a “negative-tilt” by Sunday and it could intensify quickly upon reaching the coastal waters. More details available on the 12Z NAM model run in the video discussion (below).
Looking ahead The overall cold weather pattern looks like it will continue in the Mid-Atlantic region for the foreseeable future through much of February. The active nature to the weather pattern also looks like it will continue with another storm threat coming around the middle of next week.