Category Archives: PHL Climate Forecasts


I’m often asked around this time of year whether we’ll get a lot of snow in the coming winter. My response over the past two to three winters has been that I don’t see any pattern evolving that would give us a greater likelihood for large snowfalls.

All I would say is that large temperature swings would be something to expect. The last three winters have been light on large snowfalls with large swings in temperatures every few weeks.

The large swings in temperature are likely to continue this winter.

In years where I see a pattern evolving, I usually wait until the first week of December to make the call. But this year, I’m chiming in early.

Let me cut to the chase— The jet pattern I’ve seen develop over the past month hasn’t been seen in several past winters. If it continues, it translates into more frequent coastal storm development with higher snowfall amounts this winter for our area.

The jet stream pattern forecast for this weekend captures the setup—

NAEFS forecast jet stream (250 mb winds) for Saturday. Plunging jet stream in central Canada with strong southern stream jet flow converging. This is a very different setup than we saw much of last winter where the plunge of cold air was much further into eastern Canada.

Climate forecasts are tough and even the experts at the NWS Climate Center have not always done well. Climate forecasts and weather forecasts, while they may appear on the surface to somewhat similar, are very different sciences. Climatologists even have their own models.

I’m more knowledgeable about weather compared to climate, but I’ve been looking at the maps these past few weeks and I wanted to share what I see in them a bit earlier in the season than usual.

While I’m at it, we need to keep an eye on Thanksgiving weekend, especially next Friday night into Saturday. Our first taste of either light snow or a mix is possible.


…Update added Arctic Temperature Anomaly chart below.

When temperatures reach into the 60s this weekend (the Canadian model has us near 70!), it’s appropriate to wonder where’s the snow this winter?   I don’t have any good answers, but I have some interesting observations.

Taking last year as an example, we would have jet stream configurations and air mass positions that would suggest the possibility of coastal storm development and snow.  Most of the times last year, these model forecasts of snowstorm development would fall apart just a few days before the forecast event.  But there were possibilities.

What’s fascinating about this year’s weather pattern is that the models haven’t even projected a potential storm for us. I haven’t seen any instance of southern and northern jet stream phasing over the western Atlantic in a way that would allow a coastal low to form near the Carolinas or Virginia.

The jet stream, which really represents the “air river valley” at the periphery of cold air masses sagging southward has been broad in shape instead of a sharp dip in most cases.  Where there have been some sharp dips, they have occurred in the Western and Central US. Where there was any sort of dip, the shape was positively tilted instead of negatively tilted (tilted back westward), which induces deep storm formation and slower movement.

There has been no large blocking North Atlantic high pressure that results in these sharp dips along the coast.

Not only have there been no sharp dips along the east coast in any model projections during December or the first week in January, the current GFS which forecasts 16 days in advance shows no potential snowstorms through January 24th.

Things could change, but the Climate Prediction Center shows our area with above normal temperatures and precipitation through the spring and summer.

One more thing —the amount of cold air dropping south is dependent upon the amount of cold air that accumulates in the arctic.  Here’s December’s temperature anomaly for the arctic:

Arctic air temperature departure Dec 2019 at 925 mb height

There’s simply less cold air pooling in the arctic circle.