BUST! Although locations from Long Island into much of southeastern New England are seeing or will soon see a crippling blizzard into the day Tuesday, the corridor from eastern Pennsylvania –including Philadelphia– to New York City will not see anywhere near the projected snowfall. After putting hours and hours into forecasting this storm late last week, this weekend and even on Monday, it is extremely disappointing to see the forecast go so badly for such a large area.
I owe it to you…and myself…to determine where the forecast went wrong. First a little bit of background information: This type of Nor’ Easter is called a “Miller B” storm. These types of storms involve a clipper system that drops through the Midwest and Great Lakes or Ohio Valley and then re-develops into a Nor’ Easter off of the East Coast. These storms typically drop their heaviest snow on New England. New York City is far enough northeast to get in on the “action” from Miller B’s when the pattern is right (if they move off the coast far enough south). Philadelphia is much trickier…they have seen over a foot of snow from Miller B’s before, but have also been completely screwed out of snow by Miller B’s, even when significant amounts are predicted the day of the storm…much like what occurred this go-around. I mentioned my concerns about Philadelphia seeing heavy snow multiple times and did keep the highest totals northeast of Philly, despite what the Euro and NAM showed at times, but was still WAY too high there. If the upper level portion of the storm developed like the Euro and NAM showed, Philly would’ve gotten heavy snow, but that didn’t occur, which I’ll explain below.
Typically, the Mid-Atlantic needs a -AO and -NAO to get a major snow storm. New England can get by with neutral or even positive values in the right setup. The NAO and AO were both close to neutral for this storm. Last week I was worried that this storm wouldn’t be major for anyone due to those lackluster indices, and mentioned in my long discussion blog post leading up to this storm that the AO and NAO weren’t optimal, which gave me some pause about the Mid Atlantic snowfall projections. However, a piece of the “polar vortex” was expected to be in a favorable position…near 50N, 50W (known as a 50/50 low) for a Mid Atlantic snow storm, which gave me enough justification, in my mind, to forecast heavy snows for parts of the eastern Mid Atlantic. This is where the forecast went wrong.
After comparing last night’s extremely snowy Euro run to the actual observations this evening, it appears as though the polar vortex was a little farther northeast than expected. The polar vortex probably moved away a little bit due to a lack of a -NAO. This gave our storm more room to swing out to the northeast before stalling out and really intensifying, which pulled the heaviest snows away from the Mid Atlantic and even New York City. The Euro absolutely nailed the location of the “shortwave” moving off of the East Coast Monday evening, which is why many, including myself, were reluctant to pull the heavy snows east of the Mid Atlantic.
In reflection…snowfall climatology in the Mid Atlantic suggests a favorable NAO and especially AO are needed for significant storms…with just a few exceptions. Unless the models are in unanimous agreement (which they weren’t for this storm) that a storm will buck this strong trend, it is not wise to forecast heavy snows in the Mid Atlantic from Miller B low pressures especially. This is the Euro’s worst bust with a Nor’ Easter in quite some time…it is normally extremely solid with Nor’ Easter forecasts…but this goes to show that not even “the king” isn’t infallible. Miller B’s will continue to give Mid Atlantic forecasters fits due to their known boom or bust nature in the region. Typically with Miller B’s, unless the AO and NAO are strongly negative, you have to be farther north to get the heaviest snows.