Wednesday 2 January 2013

Looking Ahead Into February and March


For my February analog set i looked for years with a similar temperature trend to this year as well as a similar 500mb setup. I put less focus into the ENSO trend with these years because of the weak signal this year but most of my years are central/west based el nino's. First lets start off by taking a look at what this december looked like to try and match it up with previous years. Take note of the above normal temperature departures that take over much of the lower 48 states as well as eastern canada. Very cold air is locked up across NW canada including northern B.C. A tongue of cold extends into the prairie provinces with much warmer temperatures dominating further SE.
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500mb height field shows a strong trough in the west with a ridge upstream across eastern canada and blocking towards greenland. Notice the strong ridge across the bering sea which causing energy to dump into the west promoting an eastern ridge most of the time. Another key feature is the trough centered west of hawaii which promotes a ridge in the bering sea and a trough in the west. For eastern cold we like to see the trough east of hawaii to pump a western ridge and an eastern trough.
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Now lets look at some past years with a similar match to december 2012 so that we can try and get a better handle on what might occur down the road. Taking a look at surface temperatures we can see the warmth dominating over much of the u.s extending up towards eastern canada and greenland. All of the cold air is locked up further NW which is very similar to this years december pattern.
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On the 500mb height field we notice a ridge in the bering sea as well as a trough west of hawaii which is very similar to this year and is a key player for the north american weather pattern. A trough is centered along the west coast and gulf of alaska with ridging further east across the central and eastern u.s. Blocking is found across hudson bay and greenland although weaker then this year.
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Lets take a look at what february and march looked like in these years. 
I like what the february analogs look like and believe that a broad based trough across the nation makes sense. The -PNA regime will probably continue but cold will be able to penetrate the east with more blocking over the top. With the SSW event taking place, it should drive the cold air south for the end of january and much of february. An active storm track will set up for the first half of the month in the eastern great lakes, quebec and the northeast.
500mb setup shows the trough retrograding off the east coast and another broad trough across the continents midsection:
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Surface Temperatures are pretty inline with my thinking but i think the coldest anomalies will be focused further NW across the prairies, northern plains as well as NW canada with the tongue of cold extending into the northeast. A SE ridge may get going later in the month:
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Heading into march we can see the warmth is confined to the southern u.s with the cold air locked up much further north with a positive NAO. March is still pretty far out and is a low confidence forecast at the moment but I do believe that the southern u.s will average warmer then normal with temps being held back across the great lakes, northern plains and west coast. How much colder then normal is still uncertain right now but i feel the most confident along the west coast within the negative PDO regime. A late start to spring is likely along the west coast with an early start to spring in the SE, midwest and mississippi valleys.
2m Temps:
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500mb heights:
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