An End to Our Mild Fall Weather

November 2, 2016

Milwaukee – Much of the United States and southern Canada have enjoyed mild temperatures since September.  Yes, there have been a few brief shots of cold and light snow east of the Rockies, but not many.  Many Canadian cities enjoyed the mild temperatures in October, too.  The only cities east of the Rockies to experience colder than average temperatures were Calgary and Edmonton.  Here is a chart of the October warmth:

City October 2016 Temp (°C) Normal October Temp (°C) Departure from Normal
Calgary 3.0 5.2 -2.2
Edmonton 1.2 3.8 -2.6
Montreal 9.7 8.5 1.2
Ottawa 8.6 8.0 .6
Quebec City 7.1 6.6 .5
Toronto 11.9 9.5 2.4
Winnipeg 6.6 5.0 1.6

 

In the United States, if you live outside of the northern Rockies and Pacific Northwest, you saw above average temperatures – in some places, near record warmth for the month.

Pacific Ocean Affects Keeping Weather Mild

The reason the United States and most of southern Canada has experienced this mild weather is a persistent flow off the Pacific Ocean.  Some of the energy in this flow has contained remnants of tropical systems from eastern Pacific typhoons.  The remnants of typhoon Songda was an example of this energy, when it hit the Pacific Northwest on October 13th.  You can read about that storm in this CNN article.

When the flow comes off the Pacific Ocean into North America, it transports two characteristics – mild air and plenty of moisture.  It results in impressive rain and snow for northern California, Oregon, Washington and British Columbia.  Quite a bit of the moisture is captured as snowpack by the Cascades and Rockies. However, the mild temperatures continue to push east across the continent.  This pattern that transports pacific warmth and moisture looks like it is going to change.

Now, this isn’t going to happen right away.  In fact, this morning we are still in a pattern of mild, wet weather coming off the Pacific Ocean.  Here is the GFS model 500mb forecast/ analysis for early morning November 2nd.

Cold Air Locked in Northern Canada

Fig. 1 6Z 11/2/16 GFS 500MB

If you have never seen a map like this, it can be a little confusing.  The green arrow is over the Pacific Ocean and it represents the flow moving into Washington and British Columbia.  The text ‘wet’ is over Washington, Alberta and British Columbia.  The text ‘cold air’ is over Nunavut and the Northwest Territories of very northern Canada.  The text ‘warm to very warm’ is over the Plains, Midwest and Great Lakes of the United States.  So, now that we have our bearings, this 500mb analysis shows cold air locked in northern Canada and Greenland.  To the south, the mild pattern continues.  In fact, the North American Ensemble Forecast System has most of North America very mild through mid-November.  Figure 2 shows temperature probabilities through November 17th for all of North America.

Above Avg Temps till Mid-november

Fig. 2 8 to 14 Day Temp Probabilities

                  The areas in dark red are near 100% confidence of above average temperatures between November 10th and 17th.  So, when is this mild weather pattern change going to happen and what can we expect?  Good rhetorical question.

Weather Models Point to Cold Coming Soon

Over the last several days, global forecast models – the GFS, Euro, CMC – and more importantly the Ensembles that run off of these computer models are showing a significant pattern change.  And when many or all of the trusted models are forecasting a similar event, at a similar time for several days consecutively, a forecaster has a high degree of confidence that event will verify.  So, what am I talking about?

I have two ensembles from two different models – the North American Ensemble Forecast System (NAEFS) and the Global Ensemble Forecast System (GEFS).  They are very effective at signaling changes in weather patterns.  These models excel at mid to longer range, larger events.  They do not excel with short term or mesoscale events – thunderstorms, rain, snowstorms.  Looking at forecast patterns out a week to 16 days is in their wheelhouse.

Fig. 3 NAEFS 500mb Analysis 00z 11/16/16           Fig. 4 GEFS 500mb Analysis 06z 11/16/16

If you compare figures 3 and 4 to the map in figure one, you can see some subtle changes that should have significant impacts in the weather by the middle of November.  The big change: the mean flow off the Pacific shifts well north into British Columbia.  In fig. 3, there is a ridge of high pressure along the Pacific coast that extends into Alaska.  To the east, a trough extends from the Canadian Prairies into the United States and east to the Atlantic Ocean.  This setup allows cold air in the northern latitudes to shift south.  In fig. 4, the amplitude of the western ridge and eastern trough are more pronounced.  If fig. 4 verifies, the intensity of the cold in the east increases.  What can we expect around November 15th and 16th?  As the western ridge builds, a cold front or clipper, will move south from Canada into the United States.  This first clipper will drop the above average temperatures to normal.  The longer the western ridge holds, the more clippers or cold fronts will drop south from Canada.  Each front will reinforce the cold air.  At this point, it is too early to know if this lasts 3 days or two weeks.  From November 16th through the 18th, the Canadian prairie cities of Edmonton, Calgary and Winnipeg can expect strong winds, snow and a drop in temperatures.  In the United States, Minneapolis, Milwaukee, Chicago, Detroit, Cleveland and Buffalo can expect strong winds, a drop in temperatures and possible Lake Effect Snow.  The large cities of the east – Toronto, Montreal, Ottawa, Boston, Philadelphia, New York City and Quebec City – can expect rain, gusty winds and temps dropping to normal and slightly below normal.

It may not feel like it, but winter is coming.  Don’t be surprised that many areas east of the Rockies experience a significant change in the weather mid-November.  For some areas, this means snow and Lake Effect Snow.  It is still too early to predict how long this pattern sticks around.  Could it linger through Thanksgiving?  It is possible, but again, it is too early to predict.  In the meantime, do you have salt, shovels?  How is your snow blower running?  Do you have your snow removal contractor lined up for the winter?

Meteorologist Mark McGinnis is on Facebook, LinkedIn and Twitter @fairskiesconsul