3:00 PM | The outlook for March - continued cold and snowy

Discussion

Overview It looks like our colder-than-normal weather pattern of recent months in the Mid-Atlantic region will continue on average right through the month of March. One signal that suggests cold weather will indeed continue in March in the eastern U.S. comes from a tropical disturbance known as the Madden Julian Oscillation (MJO). In addition, support for a colder-than-normal month of March comes from a NOAA seasonal climate forecast model called the Coupled Forecast System version 2 (CFSv2).

Background information on the Madden Julian Oscillation (MJO) 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. Furthermore, the MJO influences both precipitation and surface temperature patterns across the US. Specifically, one significant impact of the MJO over the U.S. during the northern hemisphere winter is an increase in the frequency and intensity of cold air outbreaks across the eastern US.

MJO Phases 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 diagram illustrates the progression of the MJO index through different phases, which generally coincide with locations along the equator around the globe. When the index is within the center circle, the MJO is considered weak, meaning it is difficult to discern. Outside of this circle, the index is stronger and will usually move in a counter-clockwise direction as the MJO moves from west to east. The very latest European model MJO index forecast (below) propagates the MJO from phase 8 in early March to phases 1, 2 and 3. All of these particular phases of the MJO (i.e., 8, 1, 2 and 3) typically result in a colder-than-normal temperature pattern for the eastern US (see “temperature composites” figure centered on February-March-April).

Euro_MJO_March_fcst

MJO_temps_FMA

CFSv2 The latest monthly forecast from NOAA’s Coupled Forecast Model (v2) strongly suggests the colder-than-normal weather pattern of recent months will continue (see below) throughout the eastern two-thirds of the nation. This model is updated on a daily basis and it has done a very good job in its temperature forecasts when reasonably close to event time as we are now with March only a few days away. As has been the case throughout the winter months, the core of the coldest air “relative to normal” will likely be centered from the Northern Plains to the Upper Midwest according to the model forecast, but an incredibly large area across much of Canada and the U.S. will be below-normal for the month of March.

CFSv2_March_fcst

How about snow As far as snow is concerned, the combination of the expected colder-than-normal temperatures along with a newly activated southern branch of the jet stream (e.g., California storms) will quite likely produce above-normal snowfall for the Mid-Atlantic region during the month of March. Philadelphia has actually had 3 straight months (December, January and February) featuring monthly snowfall totals in the top ten for the given month using records dating all the way back to the 1880’s. The 3 consecutive months of top ten monthly snowfall amounts has not happened in Philly since January-February-March of 1978. There has never been a winter with 4 consecutive months ending up in the top ten for that given month so if it happens in March - certainly a possibility given the overall pattern - it would be a first for Philadelphia. As far as seasonal totals are concerned, Philly is in 3rd place on their all-time list some 20 inches shy of the seasonal record set in the winter of 2009-2010 with 58.4 inches so far this season - this record of 78.7" is also within reach given the current overall pattern.