Backdoor cold front season is here, what’s the deal?

Each spring we emerge from a long cold winter with aspirations of 70 degree temperatures, a cool breeze and plenty of sun.  It rarely works out that way. Whether it be an upper level low, a stalled cold front, or a backdoor frontal boundary there are plenty of meteorological events that could be to blame for a colder and damp spring in this area. The fact of the matter is, our location during a transition season (fall, spring) is a difficult place to be. The changing and morphing wavelengths of the mid and upper level ridges and troughs mean the potential for cutoff lows, and the colder ocean waters this time of year especially will wreak havoc on any warmup.

This time around, we have a significant low pressure system moving through the Central United States. Meteorology tells us that a warm front should be surging north from the Mid Atlantic states into New England as this low pressure moves towards the Great Lakes, with southerly winds ramping up warm air south of the warm front. But where is the warm front, and why hasn’t it made progress north? The answer lies in the setup both aloft and at the surface, and it leads to the development of a backdoor front which pushed the warm air back to our south. While maybe not a classic backdoor cold front, which often sweeps out very warm air and brings low clouds and fog with it, the warm front at the end of this week is stuck well back to our south as cold, marine air is entrenched over New England.

An illustration of a backdoor cold front, showing the colder marine air moving southwest from New England.

An illustration of a backdoor cold front, showing the colder marine air moving southwest from New England.

A glance at the mid levels shows us part of the reason why the front was forced to strengthen/redevelop south of us. With a significant shortwave and disturbance in the mid levels over the Central US (more specifically the Northern Mississippi Valley), the mid level heights out ahead of it are pumped up. In essence, a developing mid level ridge. In most cases, as discussed above, this would be the first sign of warmer weather to come for our area — in the warm sector ahead of a cold front. But upon further inspection, it’s not hard to see the mid level trough which is hanging around over Northern New England. This compresses the mid level ridge axis which is developing ahead of the Central US storm system, and keeps colder air to our north.

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At the surface, a high pressure system develops on the periphery of the mid level ridge. But with the troughing to our north over New England, the high pressure noses its way down into Central New England. The flow around this high pressure turns the wind direction east/northeasterly — and that is bad news for anybody in the area. The cold, marine air over New England and essentially from the Gulf of Maine to the Northwest Atlantic then has the ability to surge southward into the Northern Mid Atlantic states. Meanwhile, the warm front strengthens over the Mid-Atlantic but cannot make a push northward due to the compressed surface and mid level flow to its north.

We can see this exact feature on todays forecast models. The warm front is situated well to our south over the Mid Atlantic, despite the fact that yesterday (And even the days before that) our area saw temperatures in the mid to upper 60’s. The warm front was able to redevelop and strengthen over this area to our south as a result of the push of colder, marine air from New England — owing to the setup in the low and mid levels of the atmosphere.

 

HRRR surface temperature forecast for Friday afternoon, showing the warm front well to our south.

HRRR surface temperature forecast for Friday afternoon, showing the warm front well to our south.

As the season draws on, the warm air tends to gain traction — and the colder ocean waters will have less of an influence as they inevitably warm up. Plenty of times later this spring and into the summer, our area will benefit from changing wavelengths and troughs which are forced much farther north, therefore leading to thermal boundaries moving north as well. This often keeps the backdoor cold fronts over New England, while our area is able to sit under the warm sun.

But for now, we’ll have to deal with the raw and cool conditions knowing that warm air is just a few hundred miles to our south.

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