Saturday, January 9, 2010

Arrival of Mild January Weather

Cold weather is expected to persist for the remainder of the weekend.  A strong area of Arctic High pressure is holding across the nations midsection allowing a cold blast from the Arctic to penetrate deep into the eastern half of the United States.  Temperatures for our area will be about 10 degrees below average, but a deep freeze is crippling the Gulf states and Florida in particular.  This deep freeze is expected to possibly damage or kill a significant portion of the citrus crop across the south. 

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A significant change in the atmospheric flow will signal a noticeable chance in our weather pattern by the middle of the week.  This deep trough in the jet stream will lift back into Canada and the atmospheric flow will become more zonal.  (Flow from the west to the east)  This will allow for milder Pacific air to return to the region instead of the cold Arctic air that has dominated through the month of January thus far.  This "split flow" in the jet stream will bring milder weather by the middle of the week and is more typical of what we would expect during an El Nino winter.  Under this scenario the northern branch of the jet stream stays north in Canada limiting the Arctic air that invades the United States.  The southern branch of the jet stream will bring active and wet weather back to the southern tier of the country bringing storms to the California coast and across the Gulf Coast and into Florida.  For our area we remain mild and dry with Pacific air in place.

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Other atmospheric signals called teleconnections (AO -Arctic Oscillation & NAO - North Atlantic Oscillation)  indicate that the middle and possibly end of January may have temperatures near or above average.