Tropical system, blocking will lead to forecasting headache
It has been a while since the meteorological community has had the chance to analyze the potential for higher latitude blocking. It has also been a while since we’ve had the opportunity to analyze a synoptic heavy rain event. Both of those look to come to fruition, in multiple facets, over the next five to seven days. A dramatic pattern change will unfold across North America this week, with anomalously strong ridging and surface high pressure building into Canada and the Northwestern Atlantic Ocean. Precariously timed with the formation of a tropical cyclone, this blocking high pressure will lead to a forecasting headache — and the potential for heavy rains and impacts from a Tropical Storm along the East Coast.
For those without a technical background, high latitude blocking is a broad term for higher then normal pressures/heights in the higher latitudes. These “blocking” ridges of high pressure to our north, sometimes over Canada and the Atlantic and sometimes as far north as parts of Greenland, slow down the weather pattern closer to our area. The slower weather pattern can allow disturbances to interact and phase — forming much larger, more powerful storms that otherwise would have continued on their own way if the pattern was moving at a normal progressive speed.
This week, forecast models are in agreement that higher latitude blocking will develop over much of Canada into the Northern Atlantic Ocean. Ridging builds into these areas in the mid levels of the atmosphere, and a very strong surface high pressure builds east and southeast into Canada and even parts of New England. This is one important piece to the forecast headache, and one reason why meteorologists are slightly more concerned than normal at this range: The tropical system, or storm system that forms, cannot simply escape north or northeast. The blocking will slow down the pattern considerably.