Showing posts with label eastern US. Show all posts
Showing posts with label eastern US. Show all posts

Tuesday, April 21, 2015

HUGE Winter 2014-15 Recap: Reasons for Arctic Cold, Snow, Records



I hesitated to post the final details on this past winter until I was pretty darn certain we were finished with snow. Historically, we have always used April 15th (Tax Day) as this magical, non-scientific date that signifies the demarcation between snow and spring.  If you can make it to the 15th, 99 times out of 100 you're good to go.  This winter worked out great in this regard.


Here are the final winter numbers. See my early March post on the metrics we typically use and why we used them.  Many of these graphics compare this winter to last winter and the COLDEST winter ever (1976-77) in northern Ohio.


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Our winter outlook was created by analyzing the global sea surface temperatures in these regions.


Pacific warm and cool pools have shifted since last winter (2013-14). Yet the result was the same:  COLD EAST, MILDER WEST.

The pressure pattern over the Pacific Ocean and North American continent reflected the sea surface temperature pattern:  This pressure configuration was a strong -EPO, -WPO, +PNA set up. It stood firm all winter which locked in the ridge west and trough east for the most part.


Image courtesy: Larry Cosgrove


Negative EPO favors eastern cold. Eastern US Cold periods circled in red
Positive PNA favors eastern cold. Cold periods circled in blue
-WPO favors eastern cold. Cold periods circled in red


Last summer (2014), talk of a strong El Nino faded as a central based El Nino developed called a "Modoki". These central based weak El Nino come in many different flavors. The current El Nino is circled at the top of the graphic below.


These favor below normal temperatures across the eastern US and above normal temperatures across the west.  Ridge west, trough east. 

Our winter forecast was created with weighting certain years in our analog set. Our forecast matched up very close to the overall average temperatures across the US from December through February.



We started off very cold in November partially driven by the Typhoon in the Pacific. It boosted the Gulf of Alaska low which boosted the ridge of warmth in the west which in turn drove cold south across the eastern US.  I wrote about the Typhoon Rule back in November and how we uses that to forecast the November cold.



Overall temperatures across the continental US on November 18th were the coldest since 1976!

The high of 18 degrees on the 18th was the coldest November day since 1958; 4th coldest high temperature in November since the 1870s.  
 
US temperatures rebounded in December after the cold November. We had one SNOWFALL in December which was under an inch. The 3rd lowest total since 1893; lowest since 1931.


By New Year Day, people were wondering where this cold winter was we had outlined in our outlook back in late October. I kept telling people on Facebook and Twitter to be patient. The cold is coming and when it does, it will harsh and similar to the year before.  Guess what happened in January?  The slow turnaround toward ARCTIC COLD began across the eastern US.


By February, the arctic floodgates had opened across the eastern 1/2 of North America. It was ALL-TIME COLDEST February in Cleveland since weather records began in 1871.

Rome, Ohio in the heart of Ashtabula County, due to cold air drainage down the surrounding terrain had a low of -39 degrees!

As the winds dropped, so did the temperatures. The next day, temperatures jumped 65 degrees in 30 hours!


February 14th through the 20th was 5th coldest 7 day stretch in 145 years in Cleveland coming close to matching the arctic cold of 1994.

Remember back a few winter ago when the ski resorts were having a tough time staying open because of the lack of snow and cold? Look at the winter 2012-13 temperature ranks vs the last two winters.

Add caption
Coldest winter since 1977-78
Less days above 40...
More days below freezing
 

Arctic cold and clear/calm skies produced huge ranges of temperature.



 Very cold late season morning lows we haven't seen since the early 1960s!







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 We had much more snow in 2013-14 vs this past winter...hard to believe.  If December snowfall would have been closer to average, the last two winter snow totals would have very close.
Days with snow cover of at least ONE INCH. Last winter we had more.


 Peak Lake Erie Ice Cover and Dates.









Tuesday, December 02, 2014

Signs of Colder Air Returning Before Christmas

You live by your long range outlook sword and die by it.

This past summer and fall, we hinted that the variables present across the globe were conducive for a colder/snowier winter ahead. November big start out of the gate was a big sign that winter will be cold and snowier than average.

This brings me to the present "break" in the arctic air.

High temps across the eastern US trend slightly above normal by the weekend. Typically when November temperatures average as cold as last month did, bounce-backs are not that uncommon in December.

What has me concerned is the Typhoon in the eastern Pacific. Two models have it recurving back to the northeast next week with it eventually getting absorbed into the Alaskan low which boosts the western ridge making eastern US troughs/colder intrusions that much easier.


The American Model also shows the recurvature by December 10th


 The European is the only outlier with a more westerly track.

Remember the old Typhoon Rule? It states that when Typhoons recurve north and east near Japan, this signifies the overall pattern is conducive for below normal temperatures across the eastern US. See my post a few weeks back on this HERE.

The PNA pattern is showing a strong tendency toward positive which indicated the ridge is rebuilding in the west which drops the trough/colder air east.

I ran a composite of all December years where the PNA index was PLUS ONE OR HIGHER and MINUS ONE OR LOWER. You can see how these correlate strongly to extreme temperatures cold and warm.

PNA at -1 or Below correlates to MILDER EAST

PNA at +1 or Higher correlates to COLDER EAST
Sure enough, the European and Canadian models both develop the beginnings of an eastern trough by December 16-17.



So unless the typhoon tracks further west and doesn't recurve and the PNA pattern (which has trended colder across the US for a while now does a complete 180 degree flip), I would expect temperatures to trend colder the week before Christmas with higher chances of lake effect snow.