Another Cold And Snowy Winter For The Eastern United States?


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CPC's winter temperature forecast.  Courtesy of NOAA

CPC’s winter temperature forecast. Image courtesy of NOAA.

Any long-range weather forecast should be considered an educated guesstimate. On October 16, the Climate Prediction Center (CPC, part of NOAA) issued a winter forecast that is even more suspect than usual.

Inconsistencies riddle the report, many of which the CPC acknowledges, but dismisses.

2014 Winter Temperature Forecast

The CPC couched its forecast in statistical gobbledegook, i.e. percentages. In simple terms, the forecast is as follows:

  • Well above normal: The entire west coast.
  • Above normal: The intermountain west, the desert southwest, the northern Rockies, the northern plains, the northeast, and Alaska.
  • Below normal: all of the south northward to Arkansas and Tennessee.
  • Normal: An arc from the mid-Atlantic through the midwest, the central plains, and the southern Rockies

This forecast presumes what meteorologists call a ‘split in the westerlies.’ This term describes a division of the jet stream into two branches: One branch takes a route across southern Canada, and a second flows from Mexico through the southern states.

Relying Too Much On El Niño

The CPC report admits that it bases much of  the forecast on the expectation that an El Niño will develop. Yet it acknowledges several things: In the last few months, the conditions that anticipate an El Niño have leveled off and even declined a bit; It is unusually late in the season for an El Niño to develop; Conditions have been close to qualifying for an El Niño for some time; and the expected El Niño will be a weak one.

At the same time the report also acknowledges that the sea surface temperature (SST) anomaly over the eastern Pacific and the Gulf of Alaska persists. This SST anomaly has been part of the reason that a jet stream ridge has wielded such pronounced influence over the weather of the west coast. The forecast for warm temperatures in Alaska and the states of the west coast reflects a belief that the nearby waters will continue to be warmer than normal.

Jet stream undulations tend to have a characteristic wavelength; the corollary to the ridge on the west coast is a trough (dip) over the central and eastern US. It would be unusual to see any other result.

The warm temperature forecast for the northern plains and midwest is simply inconsistent with a warm west coast.

The Decoded Temperature Forecast

While NOAA still insists that there is a 65% chance of an El Niño, Decoded Science puts the odds at less than 35% and falling daily. Our forecast, therefore, calls for a repeat of the pattern of last year, but less pronounced. The effects of the nascent El Niño, even if it doesn’t meet the technical standard, will moderate the temperatures in the central and eastern U.S., but they will still be below normal.

This Winter’s Precipitation Forecast

CPC's winter precipitation forecast. Courtesy of NOAA

CPC’s winter precipitation forecast. Image courtesy of NOAA.

The CPC’s precipitation forecast mirrors the temperature forecast in that it based the forecast primarily on the expectation of an El Niño. The result is a prediction of wet across the south under the influence of the southern branch of the jet stream, and dry in parts of the north.

Decoded Science believes the precipitation pattern this winter will mirror last winter’s: Dry on the west coast and wet in the midwest, east and much of the south.

Winter 2014: Bottom Line

The position of the jet stream will control the weather this winter as it does every winter. The trend has been for the jet stream to push farther equatorward in recent years, with larger undulations. SSTs seem to control much of the placement of the vortices in the jet stream.

Last winter, a polar vortex was displaced far to the south over the eastern US. With the climate changing in ways that meteorologists are struggling to understand, long-range prediction is more precarious than ever. Decoded Science stipulates that its forecast is an educated guesstimate. But we feel it is much more consistent than the CPCs.

Check back with Decoded Science in the spring when we look back on the winter. We can compare the Decoded forecast with that of the CPC. I’m bettin’ on us.

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