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January 2012

The tropics, a possible polar low, and North American winter musings

   Posted by Levi at 12:47am on January 10, 2012

The global tropics are fairly quiet overall, with the only activity confined to the southern Indian Ocean, where the remnants of Tropical Cyclone Chanda are beginning to exit Madagascar, leaving much of the island drenched in over a foot of rain in some places. These remnants may get stuck north of a subtropical ridge and try to regenerate later, but for now they will cease to be an immediate threat after leaving Madagascar. An invest off of northwestern Australia may become a weak tropical storm over the next few days as it moves southwards towards the west Australian coastline, bringing rain to that area, but no models strengthen it beyond manageable intensity for now.

The video shows an interesting vertically-stacked low pressure area in the Sea of Okhotsk, which may become a polar low during the next 48-72 hours as it sits nearly stationary and strengthens, in part due to warm-core processes.

Back in North America, the forecast battle for the rest of the winter continues. Blocking is due to develop up through Alaska, Siberia, and over the north pole this week, sending the arctic oscillation negative and providing a tempting look to the pattern for snowlovers in the eastern United States. However, the arctic vortex over northern Baffin Bay is remaining strong, and the blocking over the pole will do little to it except squeeze it slightly more southward and allow the northern tier states of the U.S. to get in on some seasonal cold at times during the next 10 days or so. The southeast and central part of the country will get a day or two of cold as a trough rolls through in about 96 hours, but then normal temperatures will return in its wake.

The thing about the Alaskan blocking is that such blocks loves to build up and then cut-off into blocking highs that retrograde westward into northern Russia as they weaken. Heights then crash in their wake, and the arctic vortex loves to redevelop farther west into the void left by the exiting block. All of the ensemble sets are starting to see this in the 10-15 day forecast, and I show those in the video. This would make sense also because the troughing loves to be in western Canada when the PDO is negative and cold water exists along western North America, helping heights to lower. With the arctic vortex remaining intact and shifting westward during the next two weeks, it is going to be very hard to shut off the strong zonal flow over the U.S. and get true long-lasting cold air into the eastern half of the country. As the cold builds in western Canada, some may get into the northwest U.S. and midwest as time goes on, which is only natural in this kind of a winter, but for the east and southeast, don’t expect a big pattern flip going into the end of January.

We shall see what happens!