First Alert: Biggest Snow of Winter 2017 Coming Our Way Next Week? | NBC 10 Philadelphia
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NBC10 First Alert Severe Weather Central

First Alert: Biggest Snow of Winter 2017 Coming Our Way Next Week?

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    NEWSLETTERS

    First Alert: Biggest Snow of Winter 2017 Coming Our Way Next Week?

    UPDATE: Timing and expected totals for Tuesday's storm HERE


     

    FRIDAY WAS JUST THE APPETIZER

    As is often the case in March, the snow that fell Friday melted on the roads, but stuck on the trees. It looked beautiful (the common “winter wonderland” comment was likely a frequent expression). But it wasn’t much of a storm, with the highest amounts in our area only reaching 4-6 inches. Most places got 1-3 inches.

    But now that we’re getting past the 10th of March, we enter a week when we’ve had some big snowstorms in the past. The 12th is the anniversary of the famous “Blizzard of ‘88”. What, you don’t remember the storm from 1988? That’s because it was the Blizzard of 1888! The Philadelphia snow total: 10.5”. New York City and New England were hardest hit, with snow totals of 20 to 60 inches (yes, 60!). And drifts got as high as 50 feet! It was known as “The Great White Hurricane”. It was responsible for NYC deciding to build subways and underground communications systems so future storms wouldn’t cripple the city like that one did. One storm did that.

    Another historic storm hit the East Coast on March 13, 1993. We got 12.0” of snow that day in Philadelphia. But the storm became famous for the extent of brutal weather. The National Climatic Data Center reported that 40% of the country’s population felt impacts from the storm-from Florida to Maine. Below is the snowfall map. Everything in light blue was in the 10-20” category.

    Another big one hit on March 20, 1958. This one was really wild. While Philadelphia got 11.4”, Morgantown, PA got an unbelievable 50”! That’s the red area west of Philadelphia in the map below:

    The one thing common about all three storms was that the Philadelphia area did not get an “all-snow” storm. Either rain, sleet, or both cut down the snow totals. Areas N&W of Philadelphia got much more snow in the ’93 and ’58 storms. Keep that in mind as we talk about storm scenarios with the one next Tuesday. It’s hard to get an “all-snow” storm in March near the coast.

    WHAT DOES THE OCEAN LOOK LIKE?

    You can’t make an accurate forecast of a March winter storm without checking on the ocean temperatures-both at the coast and offshore. The latest water temperature at Atlantic City is 44 degrees. The higher that temperature is, the more likely it is for warmer air to change snow to rain. That is, unless the wind direction isn’t coming from the ocean at any part of the storm. Since intense storms like the one Tuesday are Nor’easters, and by definition, the wind is coming from the Northeast, the wind will surely come from the ocean at some point.

    Now, a 44 degree ocean temperature isn’t that warm for March. Most “all-snow” storms in the Philadelphia area have come with ocean temperatures in the 30s, so we’re not that far off. But it’s still 44, which favors a change to rain at some point.

    But a warm ocean also helps intensify Nor’easters, and brings more moisture into the storm. If the atmosphere is cold enough for snow, that extra moisture can turn a big snowstorm into a bigger snowstorm. I have discussed this impact on our monster snowstorms in recent years. The 2nd, 3rd, and 4th biggest snows in Philadelphia’s recorded history (since 1874) have occurred in 2010, 2009, and 2016 respectively. In each case, unusually high “precipitable water” was offshore ahead of the storms. We will certainly be following this factor.

    The overall pattern shows unusually warm water over much of the Western Atlantic. The red areas show the biggest warm “anomalies”. This would help add moisture to any coming Nor’easter. 

    THE COMPUTER MODELS VARY-AN UNCERTAIN TRACK

    As is often the case, the track of the coming storm will be crucial in determining snow amounts in our area. A track closer to the coast would bring warmer air up from the south and east, and surely turn any snow to rain well inland. A track far offshore would suggest even the shore could get all snow, and areas N&W of Philadelphia would see less precipitation overall. This is a typical forecast challenge with winter storms.

    The American model, the GFS, has been tracking the storm right up the coast, which would severely limit snow totals from Philadelphia to the shore. But it would slam areas N&W of Philly with the biggest snow totals-and I mean BIG. (I refuse to mention or show specific amounts this far in advance-even from multiple models. The numbers usually change back and forth, and people tend to only remember the highest numbers). Here is their map:

    The LOW pressure center is close to Cape May 7am Tuesday, with heavy rain or even thunderstorms along the coast (red), rain to Philly (green), and heavy snow in much of eastern PA (dark blue).

    The Canadian model shows a strong storm, but the LOW is centered way offshore. As a result, the heavier snow is near the Delaware Beaches and Jersey Shore, with lighter snows in eastern Pennsylvania.

    A solution between the two above models would lead to the biggest snows in our area overall. And guess what the European model (the world’s best overall) shows? Yup-an ideal track and strength for a big snowstorm. And what I have called “the best of the best”, the European “ensembles” shows the same thing. This caused many forecasters to raise their eyebrows Friday.

    But how will the models change over the next couple of days? Will the European stay consistent, or flip-flop as it has done at times in the recent past? The computer models overall vary enough that it’s clearly too early for absolute forecasts. But what they all agree on-a Nor’easter with lots of moisture will affect our area Monday night and Tuesday. And some part of our area is likely to be slammed with snow as a result. Stay tuned over the weekend, so there won’t be surprises when you get up Monday morning and hear the forecast.