Weather.com

by Jonathan Erdman, weather.com Sr. Meteorologist

The snow season "that largely wasn't" in the Northeast will be "bookended" by two destructive winter storms.

A heavy, wet snowstorm in 2011 downed trees and powerlines, knocking out power to over 3 million customers in the Northeast just before Halloweeen 2011, in a storm dubbed "Snowtober".

Snowtober 2011: Photos | A record-setter | #1 winter storm of 2011-2012

Unfortunately, another "Snowtober"-type destructive snowstorm will wreak havoc in parts of the Northeast kicking off this week. Let's get to the critical details.

Heavy, wet snow

Low pressure will intensify as it moves up the Eastern Seaboard from North Carolina later Sunday into the interior Northeast Monday. In concert with this surface low, a powerful dip in the jet stream and just enough cold air near the surface will team up to produce heavy, wet snow.

The areas of concern are western New York, western Pennsylvania, extreme eastern Ohio, parts of northern West Virginia and extreme western Maryland. The timing of the changeover to snow is shown by the model forecast loop below (denoted by white shadings). Snowfall rates may exceed 1" per hour Sunday night into early Monday, accompanied by thunder and lightning!

Forecast model timing: Animation from 12am Monday through 6am Tuesday illustrating when and where the heaviest snow will fall (denoted in white shading). Heaviest rain shows up in green, yellow, and orange shading.

How much snow? Below is our storm total snowfall forecast. No, you're not seeing things. It may be late April, but we're expecting significant accumulations in both Buffalo and Pittsburgh, and at least a foot of snow in the Allegheny Plateau and Appalachians!

City forecasts: Buffalo | Pittsburgh | State College | Bradford | Your location

Storm total snowfall forecasts: Heaviest snow, 1 foot or more, is denoted by the dark purple shading. | Enlarge snow forecast

This would be a noteworthy storm enough, but there's another factor that will likely make this spring snow destructive!

Thanks to the intensifying low, strong winds will develop in these same areas late Sunday night, persisting through much of Monday, before slackening off Tuesday.

Wind forecast Monday: Strongest sustained winds shown by darker blue shadings. Occasional wind gusts topping 50 mph will be likely, as well.

These winds will combine with heavy snow to reduce visibilities, leading to hazardous driving conditions late Sunday night into Monday from western New York to northern West Virginia.

However. these reduced visibilities will pale in comparison to the storm's most significant impact....

One side-effect of the record warmest March for the Lower 48 States was the early green-up of foliage in the Northeast, in some areas 3-4 weeks ahead of schedule.

Read article: Record warmest March

The weight of heavy, wet snow, plus the additional force from high winds acting on trees with leaves will likely lead to widespread downed trees and powerlines, leading to numerous power outages, possibly for several days from western New York to northern West Virginia! These downed trees may make roads impassable in some areas!

Tree Density Map: Darker green shadings show more dense tree cover in the Northeast. Some of the densest tree cover areas (boxed yellow) will be impacted by this April snowstorm. Source: whrc.org

Also important to note: once power outages begin, temperatures may hold in the 30s through Tuesday morning, and may only rise into the 40s, at best, Tuesday and Wednesday afternoons!

Forecast maps: Mon highs | Tue lows | Wed lows

Bottom line: The time to prepare for a power outage is now! Click on this video for tips on how to prepare.
WeatherREADY: Prepare for a power outage

So, you may rightly ask...how unusual is this heavy a snowstorm so late in the season in this area?

While accumulating snow has fallen well into the month of May in many locations from western New York to West Virginia, snowfall this heavy, so late in the season is rare, but not unprecedented.

For instance, in Buffalo, N.Y. there have been 10 calendar days of 1"+ snow after April 22, according to the National Weather Service. However, dating to 1884, there have been only 3 calendar days after April 22 with at least 4" of snow, there, only one of which is since 1909!

Similarly, in Pittsburgh, dating to 1880, there have been only 2 calendar days after April 22 with at least 3" of snow, the last of which occurred almost 46 years ago!

What about higher elevations, those that could see a foot or more of total snow? In Warren, Pa. (elev. 1200'), dating to 1893, there have been only 2 calendar days after April 22 with at least 6" of snow, the last of which occurred 45 years ago!

Northeast storm tracker maps: Rain, snow, wind, travel delays

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