I HOPE YOU DON’T HAVE TRAVEL PLANS TUESDAY
This is going to be nasty-at best. We only had one significant snow last winter, and it was a whopper -- 22.4 inches in Philadelphia. That was the equivalent of an average winter snow in the city for an entire winter! This coming storm shouldn’t be quite as big, but a lot of us are going to get more than a foot of snow.
The snow will start Monday evening (between 10 p.m. to midnight) and quickly accumulate. Remember, the roads are cold this time after this bitter cold weekend. Snow will immediately stick to untreated surfaces throughout the area. And by morning, what should be the a.m. rush won’t be one. Heavy snow, with very poor visibility, and gusty winds will make travel hazardous. And in areas that see the snow change to heavy sleet or rain (with possible thunderstorms), it will be a huge mess.
THE LATEST ON THE STORM
Big winter storms in this part of the country have been studied for hundreds of years. Benjamin Franklin is credited with discovering "nor’easters," where the LOW pressure center tracks TO the northeast, but the wind is blowing FROM the northeast. He managed to figure it out, without sophisticated satellites, radar, or even a network of observations. Pretty impressive!
This storm is going to become a classic Nor’easter. But, as usual, the storm track is crucial. It’s that nearby Atlantic Ocean that causes the difficulty (of course, if there was no ocean there, the storm wouldn’t form in the first place). A track too close to the coast allows warmer air to move in, changing snow to rain. Tracks too far offshore lead to less precipitation. Miss the track forecast by a mere 50 miles and there can be a difference between 2 inches and 10 inches or even more.
Computer models were in pretty good agreement last Thursday for the storm, but started to diverge by Saturday. Snow projections for Philadelphia from one model gave us a mere 2 inches, while another one was up to 24 inches! Yes, at the same time. With the same atmosphere. Wonder why winter storm forecasting is hard on the East Coast?
Here are three models from Sunday that are valid at 8 a.m. Tuesday. These models disagreed a good bit 24 hours earlier, but are very similar now. All three have a strong LOW along or just off the mid-Atlantic coast. The NAM, GFS, and Canadian all show major winter storms affecting our area, with a lot of rain near the coast and a lot of snow well inland.
The dark blue represents the heaviest snow, which would fall at 1 to 2 inches per hour (or even more for the darkest blue). This is likely the peak of the storm-the heaviest snow inland, heaviest sleet and rain near the coast, and the strongest winds at the coast. Unfortunately, this is close to the time of high tide in South Jersey. Very heavy rain along with 60 mph gusts, and high tide add up to possible significant flooding at the Jersey Shore.
The one thing preventing many 20-inch-plus snows this time is the speed of the storm. Below is the forecast map for a mere 12 hours after the above maps:
The LOW is now off the coast of Maine. That means the storm is moving more than 35 mph. The faster the storm moves, the fewer hours of snow will fall. And the biggest snowstorms here move much slower than this one will. Some storms in the past have stalled. The famous Blizzard of 1888 actually moved from well offshore back toward the coast, leading to many more hours of heavy snow.
Some snow could fall later Tuesday and even Tuesday night, but the bulk of the accumulation will come between 10 p.m. Monday and 1 p.m. Tuesday.
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