12:20 PM | Could be a wild and interesting beginning to spring
Paul Dorian
Discussion
Spring will begin officially get underway tomorrow, but there is no spring-like weather pattern in sight for the Mid-Atlantic region. In fact, the overall weather pattern may actually get colder and stormier before it gets better.
Last week we talked about the development of an impressive “omega-shaped” blocking pattern in the upper atmosphere to our north and that process is now well underway. Specifically, “omega-shaped” blocking refers to strong winds in the upper atmosphere that take on the shape of the Greek letter “omega” with large southward dips and northward bulges. This type of upper atmospheric blocking pattern will affect the temperature pattern in the Mid-Atlantic region in a couple of ways. First, it will act to force additional cold air masses into the central and eastern US from northern Canada and secondly, it will prevent any of the warm air building up in the southwest US from expanding into the northeastern US – at least not on any kind of consistent basis – through the rest of the month of March and perhaps right into early April.
Two forecast indices that can provide clues about this “omega-shaped” blocking pattern in the upper atmosphere include the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO). These index values are related to the “oscillation” between the pressure differences in the North Atlantic and when they are consistently in negative territory, atmospheric blocking patterns often form in the northern hemisphere. In fact, both of these indices have been dropping sharply in the last few days into deep negative territory not seen in months.
The colder-than-normal temperature pattern will continue to be quite active as well which is not surprising given the developing northern hemisphere blocking pattern and indeed, there are growing signs for significant coastal storms next week. Last night’s 00Z European model run not only features a “threatening-looking” coastal storm early next week that bears watching, but it also generates a second storm late in the week - exactly how far north they go in this blocking environment is still to be determined. The GFS computer forecast model has also been generating a coastal storm threat in its forecast for early next week.
Stay tuned…the beginning of spring could be quite wild and interesting in the Mid-Atlantic region. On the positive side, there is one definite sign of spring - Opening Day is now less than two weeks away.