Update 3/13 8:00 AM: Confidence in a high-impact snowstorm has increased. Forecasted Snowfall accumulations have increased. The city of Ithaca can expect 14″, with surrounding towns in the 14-18″ range. The graphics below have been updated.

Update, 3/12 10:00 PM
: Graphics have been updated. The accumulation forecasts for the Ithaca area are still in the 10-14″ range. The forecast for the major Northeast cities has not substantially changed. Heavy snows are now expected throughout Vermont, New Hampshire, and Maine.

ITHACA, N.Y. — Be prepared for some a rough week ahead – a complex and potentially high-impact Nor’easter is set to pass through Ithaca and the Northeastern U.S. on Tuesday. Please note that this story will be regularly updated as the latest information becomes available.

Let’s highlight the word potentially. This is a very complex setup that requires two separate low pressure areas merging into one very powerful storm at just the right place and just the right time to create maximum impact. There is still some uncertainty. If the storms fail to align, or do so too far offshore, than the impacts on Ithaca will be limited. Unfortunately, the leading weather models, the European ECMWF and the American GFS, have been moving towards the major snowstorm outcome over the past few days.

As a result, the National Weather Service’s Binghamton Office has issued a Winter Storm Warning for Tompkins County. This is in effect from 8 PM Monday to 8 PM Wednesday.

The ensemble of model runs, which tweak the initial conditions a little bit to figure out the range of outcome, indicates Ithaca and Tompkins County could see as little as two inches over the course of the day Tuesday, to a potential of 18-20″. The consensus of those runs, meaning the most likely scenario, is 12-14″ throughout the area, with locally higher amounts in the hills, and in towns south and east of Ithaca.

Here’s the basic setup meteorologically – the first storm system is currently over the Northern Plains. It will pass over the Ohio River Valley, strengthening along the way. Meanwhile, storm system number two is forming off the coast of the Carolinas. It is likely to strengthen over the warm Gulf Stream current, developing a deep low-pressure core as it tracks up the Northeastern seaboard. The current forecast calls for the two storms of them to merge into one very powerful system off the coast north of Virginia Beach. As that happens, the storm is expected to rapidly strengthen further into a very powerful, very large Nor’easter. Tuesday and Wednesday, this very potent storm will track up the coast and into the Canadian Maritimes.

GFS model run for 18z (2 PM) Tuesday. Image courtesy Tropicaltidbits.com.

As it does, it will use its very large and strong circulation to pull vast amounts of moisture from the Atlantic, and large amounts of cold air to our north and east. This along with strong uplifting (destabilized air) will provide the ingredients needed for very deep snow accumulations. The system will likely unload snow at 1-2″/hour rates for several hours – late Tuesday, the moisture flow and wind will weaken as it pulls further away from the Southern Tier, resulting in lighter if still steady snowfall, before eventually tapering into snow showers over the course of Wednesday morning. Things should clear out from Wednesday afternoon on.

More specifically on timing – snow will likely start in Tompkins County around 2 AM, moving from southwest to northeast – so Dryden and Lansing will be about an hour later than Newfield. Expect widespread snowfall rates of 1-2″/hour through the morning commute, with wind gusts of 25 MPH – whiteouts will be possible during intense bands. If it looks as bad Tuesday morning as the models currently indicate, stay off the roads if at all possible.

If you have travel plans anywhere in the Northeast or Mid-Atlantic, expect delays and cancellations. There is increasing confidence that New York City, Boston, and Philadelphia will see as much as 18″, and DC could see a foot. Pretty much anywhere from Cleveland to Southern Maine, and the Adirondacks to Northern Virginia, could see 12″ or more. Travel will be hazardous, especially with gusty winds exceeding 40 MPH in locations closer to the storm. Blowing snow and drifting snow will be an issue Tuesday night, and some rural roads will likely be impassable.

Even friends and family in the south aren’t getting away from it. Although they won’t see snow except early on in higher elevations, because the storm’s circulation is going to be so large and pulling down so much cold air, there are major concerns that crops from Northern Florida through the Mississippi River Valley could see major freeze damage from prolonged sub-freezing temperatures. The crops are three weeks ahead of schedule in the growing season due to the warm February that the Eastern U.S. experienced, so they are tender and at risk.

Yes, it’s March and we’re all tired of winter. Unfortunately, March has hosted some of the area’s most severe blizzards – 1984 and 1993, for instance. If it’s any consolation, conditions are looking to improve next week, but it’s looking to be cooler than normal for at least the next two weeks. If you want sustained heat, a bubble of abnormally warm air is expected to persist over the Desert Southwest for the remainder of the month.

Brian Crandall

Brian Crandall reports on housing and development for the Ithaca Voice. He can be reached at bcrandall@ithacavoice.com.