Spring is Here (Meteorologically Speaking)

Mon 3/3:

Weather-wise, March is such an interesting month, with huge temperature contrasts and extreme weather events possible. Some of the biggest storms the East Coast has ever seen have come in the month of March. The March Superstorm of 1993 being just one example of many strong storms that have developed thanks to the seasonal battle that rages between winter and spring.

Meteorologically speaking, winter (Dec. Jan. Feb.) is now officially over - another one come and gone - and its time to think spring. This is reflected well in the daily/monthly averages. We are well past the climatological low point of the year and the daily averages start to climb rather quickly through the month here on the Cape. Compare January and February temperatures to that of March. Notice January and February's high temperatures remain rather steady in the mid 30s - the lowest point of the year. However, come March, average highs jump from 40°F at the start of the month to 48°F by month's end. That 48 represents the highest daily mean since the last week of November.

The increasing warmth is a direct result of increasing sunshine in the Northern Hemisphere (places such as Barrow, Alaska are gaining 4 to 5 minutes of daylight a day - thats approx. 30 minutes a week!) which is limiting the ability for cold air masses generate or to strengthen. Actually, at this point in the year, the cold is more a "leftover" from mid-winter. That said, its still plenty cold up near the Arctic Circle, where temperatures this morning in Northern Canada and Alaska are a toasty -30°F to -40°F. Therein lies the problem with March - winter is still holding strong across parts of the Northern Hemisphere, but spring is trying to push its way northward - creating huge contrasts in temperature.

So what forces will win out this week? Well for much of the Eastern Seaboard, the next seven days will be a great representation of March as a whole - with both winter and spring making an appearance. The week will start mild with spring-like rains and will end cold and potentially stormy.

A storm system developing over the Lower Mississippi River Valley will strengthen and lift northeastward up the Appalachian Mountains Monday and Tuesday, before cutting through New England on Wednesday. As has been the case many times this winter, this track places much of the Eastern Seaboard on the warm side of the storm, sparing the I-95 Corridor from a major snow/ice event. For those down south, this storm will be a major severe weather producer as spring surges northward in advance of the storm and interacts with winter cold trying to move eastward. Locally, for us here on the Cape, this system will spell a period of milder temperatures Monday through Wednesday and will bring another decent shot of rain.

Our rain will actually come from the merging of two weather systems. Before the heaviest rain arrives Tuesday night and Wednesday morning from the aforementioned storm center, a cold front will sag through New England on Tuesday, sending a line of showers southward through the six state region. This band of light showers is destined to reach our area during the second half of Tuesday, leaving us with a gray and damp afternoon, but with only light to moderate rain showers scattered about the area.

While the cold air behind the front will try and sneak through New England, the advancing storm will not allow it to sink this far south. In fact, the storm will actually send this same cold front back to the north as a warm front Tuesday night and Wednesday. So after Tuesday afternoon/evening showers, the front will return to our north, probably shutting down any organized precipitation for a time and also sending our temperatures sky-rocketing into the 50s. When the actual storm center approaches later Tuesday Night and Wednesday morning, a second round of rain will develop, and thanks to the mild air, some of the showers that cross through the region could be briefly heavy. All told, another 1/2 inch of rainfall is likely on average across the Cape. Strong gusty south winds will also develop for several hours while we remain in the warm sector, with gusts over 40 mph possible for a time. Eventually cooler and drier air will push in Wednesday afternoon and into Thursday as the storm passes our latitude.

One of the factors driving the early week storm is a big contrast (in typical March fashion) in air masses over the eastern half of the nation. Cold arctic air is diving southward across the Plains and Upper Midwest while mild air builds up the east coast. Now, while we might normally expect cold air to rush eastward behind the departing storm, this go-around the colder air will only slowly filter eastward towards New England as the upper trough axis remains positioned to our west - holding the deepest and coldest air back. While this will mean a nice day Thursday, it does raise some concern for the Friday / Saturday time frame for another storm to develop.

Eventually, the trough axis will shift eastward, allowing colder air to build into New England (in fact, by later next weekend temperatures could be well below normal). The big question lies in how this transition takes place. Will the cold be marked by a simple cold frontal passage or will a bigger storm take shape? This will be highly dependent on the timing of upper level energy diving through the trough and forcing the trough axis eastward. It's way too early to know. Minimally, a period of showers (rain to snow?) is possible Friday and Saturday as a frontal zone moves eastward. But we will be watching through the week as there is a window open for a far stormier situation.