Glenn's Blog: Sunday Spring Snowstorm | NBC 10 Philadelphia

Glenn's Blog: Sunday Spring Snowstorm

Will our area ring in the first day of spring with snow? NBC10 First Alert Weather meteorologist Sheena Parveen has more on what could be a snowy Sunday and when we can expect the comfortable spring temperatures to return. (Published Friday, March 18, 2016)

Does history repeat itself in weather? YES!

The year was 2006, and we had a rather warm and snow-free January. There were 5 days with temperatures above 60. Then February started unseasonably warm, with 60s on the 3rd and 4th. But merely a week later, a foot of snow had fallen in Philadelphia.

The similarity with the current pattern goes beyond those numbers. Researchers are now able to compare different weather patterns in detail to see which ones the current situation looks like. They’re called “Analogs”. One of the analogs to the current pattern is February 2006. Other analogs show smaller snow amounts in Philadelphia with more N&W of the city. They even can create maps that show probabilities of snow amounts of 4” or more based on an average of the top analogs. In this case:

That’s about an 80% chance of 4”+ in the Poconos; 60% in most other areas N&W of Phila, ranging down to less than 30% at the Jersey Shore. This is similar to my latest thinking on which areas are likely to see the most snow from the storm. So we now have history “on-board”, along with the most reliable computer models.

The latest models:

The “best of the best”, as we’ve mentioned many times before, is the Ensemble average of the European model. It’s run 51 times with slightly different initial conditions, and scores the highest overall. Here are the maps for Sunday 8am and Monday 8am:

Photo credit: Levi Cowan - tropicaltidbits.com

Photo credit: Levi Cowan - tropicaltidbits.com

A couple of things stand out to me here. First, the track is pretty close to the East Coast-this storm clearly is NOT moving out to sea. And second, that’s a pretty intense storm by Monday morning when you consider that it’s the average of 51 solutions!

The GFS model from the U.S. has a weaker track farther east, while the Canadian model has an intense, closer track to the coast, suggesting more rain than snow. So the European is the compromise track, but is clearly stronger and snowier than other models.

Factors to consider:

1. It takes a temperature below 30 and/or rather heavy snow to stick on roads during the daytime hours this late in the season. So there could be a lot of melting during the day, which would cut down snow totals.

2. While the atmosphere overall will be cold enough for snow, the layer right near the ground may be warm enough to melt snow into rain on the way down during the day. That is, if the snow is light. As snow gets heavier, a light rain can change to a heavy snow in minutes.

3. While much of the snow could melt on roads in some areas, it would still stick to trees and power lines. With a “wet” snow like this, it can weigh a lot. If enough snow falls, tree limbs can start coming down, leading to power outages. This will need to be watched closely.

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