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.


Two more rain storms forecast for this week –one Thursday (possibly missing us, staying to the south) and on Saturday.   The Saturday storm may be a nor’easter, but the lack of cold air makes this an atypical nor’easter for January.  It looks like rain!

The current weather pattern is quite anomalous for January.  There’s little evidence of deep intrusions of cold air into the  continental US for the first two to three weeks of January!

There will be short duration cold air intrusions  into the Northeastern US which will alternate with mild air and wet flows from the southwest.

The current climate model forecast captures this nicely:

CFS Forecast for the first week in January (areas in red/orange are above average upper air heights associated with above normal temperatures.)

What we need for winter to return is for the height contours (shown in black) to take the following configuration, (shown in blue.)

Blue line drawn shows typical configuration for cold air intrusion in January

Obviously, there  would have to be giant changes in the current weather pattern to support my early December climate forecast of significant cold weather and significant precipitation.  I’m not very confident about that forecast at this time.

So enjoy the relatively mild weather!

The current long range climate models show colder intrusions around the third to fourth week in January, a time when we usually get the “January Thaw”.