Sunday, March 31, 2013

Long Range Chatter - March 30, 2013

Temperature anomalies from the last week show the lack of spring continuing throughout nearly every region of the nation, save the Southwest. Temperature anomalies, shown in Kelvin, dropped as low as 10 degrees below normal in the Dakotas, with even the Gulf of Mexico experiencing some of this cool weather. This cold weather has been provoked by prominent high pressure over the Arctic Circle and Greenland, as this reanalysis image from March 25th shows:

500mb height anomalies are placed on the left, where warm colors depict high pressure
and cool colors indicate low pressure. Mean sea level pressure contour lines, as well as cloud
cover are shown on the right half of the image.
In response to this extreme high pressure over the Arctic and Greenland, low pressure has been provoked to develop over the central and eastern US, more-so over the latter region. As long as we see that high pressure area over the upper latitudes, chances are more than likely that the tendency for cooler weather will continue to fall upon the central and eastern US. With the cold weather, we also expect a tendency for low pressure in very similar regions, so storm systems moving into the eastern US could be more commonplace than instances of above-normal temperatures.

European ensembles predict that this high pressure will remain stagnant over the Arctic and Greenland from now until at least 10 days away. Consequential low pressure will also stay in place north of the Canadian Maritimes and into eastern Canada. New England will also be affected by this relatively stagnant body of low pressure, and these effects may range from below normal temperatures to unusually cloudy days (both of which I consider likely). High pressure attempting to develop over the Western US will enhance cold weather potential south of Canada, possibly encompassing millions east of the Mississippi.

European model temperature anomalies 5000 feet above ground display this cold weather trend, clearer than day in the Northeast. Below normal temperature anomalies resonate well into Canada, sideswiping the Great Lakes and Upper Midwest. Warmer than normal temperatures will assist the skiing season in coming to a close in regions where resorts remain open. This forecast, valid for forecast days 6-10, is pretty likely to turn out when you look at what has been experienced and comparing it to what is being forecast. High pressure will remain favorably positioned over the Arctic to allow cold weather to hit regions of the US previously hit by the cold, and also spread eastward.

Next 10 days look to remain below normal in temperatures for the central and eastern regions of the United States. Warmer than normal temperatures should persist in the Western US. I feel that best chances for storm systems will be in the northern Gulf Coast (TN/AL/MS/GA) and north, along the Eastern Seaboard and into the New England area. Probably will not see any significant Nor'easters in this timeframe, although a wayward storm system well offshore may allow coastal cities to get a quick bout of precipitation.


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