Major Pattern Change On The Way

Mark SpencerNational, Seasonal Predictions, US, Weather NewsLeave a Comment

While winter hasn’t officially started yet – meteorological winter starts December 1st and astronomical winter starts December 21st  – this is typically the time of year when we begin to turn colder and we start seeing some snow.  While we’ve seen little bits of this, it hasn’t been able to really stick around in any one location for very long.  However, that does look to begin to change here as we head through December.

We’ve been monitoring a fairly strong pattern change for about the past week and a half and this looks to occur around the December 10th time frame.  Strong low pressure from Canada will help drive colder air and possibly snow into the eastern United States.  Temperatures will be well below average during this time period as well.  How much snow could we see?  It’s just way too soon to say where or even how much snow could fall just yet.  However, it is looking more likely that we could see a shot of some decent snowfall somewhere during this time period.


Areas of blue and green are areas of low pressure, while areas of orange and red are areas of high pressure. This is the projected pressure anomaly at 500mb (approx. 18,000 feet) for December 10, 2017.


Similarly, these are the projected temperature anomalies for December 10, 2017. Areas in blue and purple are below average and areas in orange and red are above average. Green represents near average temperatures.



We’ll see another reinforcing shot of cold air around December 15th and low pressure moves across the Northern Plains and into the Great Lakes.  This will also bring much colder air to a good portion of the Great Lakes, Plains, and Midwest.  Some snow is certainly possible somewhere in these regions too.


A reinforcing shot of cold air is likely for a large portion of the United States around December 15th as this area of low pressure moves through.


Some very cold air is possible with this system as temperatures look to be 10-15 degrees below average across parts of the Western Great Lakes and Midwest.


As we approach Christmas, things tend to quiet down and warm up.  For Christmas Day, the latest EPS Weeklies suggest much of the country will see above to well above average temperatures with parts of the Gulf Coast seeing below average temperatures.  That will likely be associated with a low pressure system tracking across the area.


It looks to be much quieter by Christmas across a large portion of the country. Low pressure looks to possibly track across the Gulf Coast states, which will lead to cooler temperatures and unsettled weather.


Temperatures look to be well above average across the Plains and parts of the Northeast US. Cooler temperatures will prevail along the Gulf Coast.


Looking Into 2018

Further out, as we head into 2018, we do begin to enter what looks to be a more active pattern with a big shot of warm air for the eastern United States just after the New Year, with very cold air for the western United States.  After that, colder air and a more active pattern look to settle in for the first part of January.

A word of caution: these are just model projections and are subject to change.  These are not an official forecast however, these projections to help us determine what the overall weather pattern may do in the coming weeks.  They give us a “heads up” as to what to watch for and approximately around what time to watch for it.  We use these to help with our long range forecasting and to compare to our seasonal outlooks to see if adjustments are needed or if the outlook is still accurate. They are just one tool in a meteorologist’s tool box.




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