Tag Archives: Snow

PHL Climate Forecasts

WINTER 2022-2023 SNOW OUTLOOK

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.

Winter Storm Outlook

WINTER WEATHER UPDATE 11:45 PM

As often happens with the afternoon “off-hour” runs of the models, the forecast can be pushed off course.  Such was the case with this afternoon’s NAM. One of these days, I’ll stop looking at them.

Tonight’s latest NAM and GFS models have become available. The trend is towards colder temperatures and higher QPF values.

The NAM has a QPF of 0.89 inches water and the GFS has 0.73.

If this were a straight forward forecast, this would be a 7-10 inch snowfall, even for Philadelphia.  However, there’s a few glitches.

The temperatures at critical levels of the upper atmosphere are a bit warm for snow. We’ve had similar data where we have had snow but other times, there was significant sleet and rain in the mix, making the snowstorm forecast a bust.

Here’s my take. Having seen the new NBM correctly predict precipitation type, I’m leaning on it heavily for this forecast, along with NAM thermal profiles.

A mix of rain sleet and snow will begin about 3-5 PM The mix will continue, leaning towards a shift to more sleet and rain between 7 and and 11pm in the area south of the white line in graphic below.

Transition line snow – sleet rain

Areas northwest of this white line will be all snow. Total snow accumulation In those areas about 5-8 inches by daybreak Monday.

Areas south of this white line will have a considerable amount of sleet and rain in the mix for at least 1/3 of the total storm QPF, during the heaviest precipitation time. This will significantly reduce total snow accumulations. The sleet line moves back south after midnight, as shown in my earlier afternoon post.

It’s an educated guess but the area from the Delaware river north to that white line may have 2-4 heavy inches. I think the warmer temperatures aloft will play a big role in keeping those numbers lower than they would be otherwise as a result of the sleet rain mix.  Very cold temperatures follow later Monday.

I will update again with tomorrow morning’s data.