The SI Weather
28Jan/13Mon

1:00 PM | In addition to the stratospheric warming event, there is a tropical signal suggesting the cold weather pattern continues into February

Discussion

There are currently two atmospheric phenomena that are suggesting colder-than-normal weather conditions continue here in the Mid-Atlantic region during the first part of February despite the flirtation with spring coming on Tuesday and Wednesday. We’ve talked in detail about the first phenomenon which took place recently in the stratosphere over the middle and high latitudes (i.e. sudden and major warming). The second phenomenon is called the Madden-Julian Oscillation (MJO) and it takes place in the tropics and is described in detail below.

The MJO is a tropical disturbance that propagates eastward around the global tropics with a cycle on the order of 30-60 days. It is a large-scale coupling between atmospheric circulation and tropical deep convection. The MJO has wide ranging impacts on the patterns of tropical and extratropical precipitation, atmospheric circulation, and surface temperature around the global tropics and subtropics. Rather than a standing pattern like El Nino and La Nina, the MJO is a traveling pattern, propagating eastwards at about 5 m/s through the portion of the Indian and Pacific oceans where the sea surface is warm. There is evidence that the MJO influences the El Nino/La Nina cycle. While it does not cause El Nino or La Nina, it can contribute to the speed of development and intensity of El Nino and La Nina episodes. The MJO influences both precipitation and surface temperature patterns across the US. The two most significant impacts over the US during the northern hemisphere winter are an increase in the frequency and intensity of heavy precipitation events along the US west coast, and an increase in the frequency and intensity of cold air outbreaks across the eastern US. The MJO also influences tropical cyclone activity in both the eastern Pacific and Atlantic basins during the northern hemisphere summer.

Research has found that the location of the MJO, or phase, is linked with certain temperature and precipitation patterns around the world. The MJO phase is tracked by an index value that illustrates the progression of the MJO on a phase diagram that generally coincides with locations along the equator around the globe. The index will usually move in a counter-clockwise direction as the MJO moves from west-to-east through the possible 8 phases. The very latest MJO forecast propagates the MJO into phase 8 come early February and this is one of the coldest phases possible for the eastern US. To view the current MJO phase diagram and forecast go to: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/foroper.shtml
and to view the impact on US temperatures for the different phases go here: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/Composites/Temperature/ .

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