Hey everyone! I apologize for the scant number of posts during the past 9 months (zero as a matter of fact!), but Philaburbia is back for the rest of the winter season.

With a strong El Niño present, it’s been a very warm winter so far, with temperatures in Philadelphia running 13.7 degrees above normal in December. So far in January we are running around 2 degrees above normal. However, with El Niño beginning to weaken (see below) and arctic air starting to creep in, we are in for a stormy and colder February and March.

Ocean Temperatures:

It’s been a very quiet winter so far with no major coastal system running up the coast. This, however, will change Friday and Saturday as a coastal system with abundant moisture will strengthen off of the Atlantic coast. I’ve explained to friends and colleagues, our warm December and January has resulted in extremely warm ocean temperatures off the coast. With warmer ocean temperatures, a low pressure system can strengthen quicker through sources of evaporation (this is why we primarily see hurricanes during the summer months, when the oceans are warm). As you can see from the map below, ocean temperatures have been nearly 3 degrees above normal:

Teleconnections:

Additionally, projected teleconnections have signaled the likelihood of a large disturbance. Both the NAO and AO (atlantic and arctic oscillations) are both headed toward a neutral position, with the AO doing so rapidly, following the storm.

Atmospheric Setup: 

The atmospheric setup is also favorable in the days leading up to the storm. All models are projecting a Canadian high moving in to provide cold air aloft while the low pressure moves into a benchmark position off the coast. Where the uncertainty lies so far is the location of the storm formation in the southeast. This aspect of forecasting is extremely difficult, since we do not possess the instruments necessarily to accurately predict the location of storm initialization. This brings us to our two scenarios:

Two Scenarios:

1. GFS, Canadian: Storm moves exits coast at Virginia, follows up the benchmark and stays close to the coast. In this scenario, areas in Maryland would receive the most snow with other areas like Philly, NYC, and Boston all receiving over a foot of snow as well. This solution is shown below:

2. EUROPEAN: Instead of exiting the coast off of Virginia, the storm will slide further south and strengthen more quickly than anticipated before moving Northeast, away from land. While this scenario still projects a strong nor’easter, most of the heavy precipitation will be located off the coast. In the Philadelphia region, we would still receive a plowable snowfall, but nothing close to the 1-2 feet projected in scenario 1. The european is pictured below, courtesy of Accuweather:

Timing:

For both scenarios, the timing will be from Friday night into early Sunday morning. The major snowfall will occur during the day on Saturday. If scenario 1 plays out, we could see a prolonged period of 1-2 inch/hour snowfall rates Saturday afternoon. By midnight on Sunday, most of the snow should be finished with some scattered snow showers moving out by 3 AM on Sunday.

Regardless of which scenario is correct, this storm will be disruptive. I would advise against traveling at all from Friday night to Sunday morning until roads are cleared.

More updates coming with a final forecast on Thursday. It’s nice to be back.