Another Round of Winter
2016-04-26 14:10:42.000 – Michael Wessler, Summit Intern
As a lover of all things snow-related, wandering onto the deck this morning to find a fresh coat of light, relatively low density snow draped over the landscape was quite the treat. While thoughts of warm, summer days are not far off in the future, and a few warm days are under our belt already, winter has a way of overstaying its welcome in New England and especially up on the Rockpile.
This time of year, changes occur that can lead to a highly amplified trough-wave pattern in the upper troposphere. This often leads to the strong high and low pressure systems that drive highly variable weather for us at the surface in the spring. The arctic circle is coming out of a long winter of darkness, and the newly introduced solar radiation means that there is a shift in the patterns of heat flux across the hemisphere. The April sun provides much more energy to the surface and lower atmosphere, as the arc of the sun is at a higher angle allows for more focused solar radiation. Temperature gradients between the land and ocean surface begin to shift, with the oceans just beginning to rebound from the coldest temperatures of the year and the land surface warming quickly under the late April sun. Snowpack (the little there was this winter) is retreating further to the north, and causes the cold arctic air masses to shrink and retreat to the pole, and no longer has a strong influence on storm tracks through the central US. With everything in such a dynamic state, anything can happen, including cold air outbreaks and snow across New England in April and May.
Today’s snow event is the result of a fairly interesting, and I think, pretty neat setup. A strong anticyclone (winds counterclockwise around high pressure) over interior Canada and another off the coast of the southeastern US have led to the development of a stationary frontal boundary in the northeast. A stationary front occurs when two competing air masses stall in place, neither strong enough to cut into the other. Often, weak disturbances are able to propagate along these stationary fronts and produce steady, sometimes heavy, precipitation over a long period of time. In today’s case, the strong high to the north is driving cold air southward, and the strong high to the south driving warm air northward. The warm air is able to rise above the cold air mass stalled in New England and produce precipitation. The front has set up far enough south that the result is much of northern New England is seeing the precipitation fall as snow today! So far, we have received 5.6” of snow at the summit, and what a treat it has been. Eventually, atmospheric conditions on one side of the front or another must change enough so that the front can transition to a warm front or cold font, and begin to move out. It seems for us today, the high to the north will win out, and we will see a few more days of below average temperatures this week as a cold front develops and pushes south.
Michael Wessler, Summit Intern