Will Cold Air Return After the Late February Warmth?

The stubborn southeast ridge threw a wrench in our winter temperature and snow outlook for Cleveland and the Ohio Valley (more on that next week). We anticipated it to stay further east It has remained very strong throughout winter driving many panhandle low type storms along with temperatures recently to levels only reached a few times since record keeping began in 1871.

The stretch of warmth in Cleveland will more than likely end up being the warmest 11 day winter stretch ever!  This February stretch is similar to a warm February stretch back in 1976 and 2000. Notice the widespread nature of the warmth back in those years.

Looks similar to this stretch...

Yet California keeps getting pounded with heavy rain/snow as the very strong Pacific jet stream continues. Reanalysis of vector wind anomalies at 300 mB since December 1st (3 day running average). Pacific jet is through the roof strong. No sign of the ominous western ridge which was dominant over the last several winters.

The MJO strength increased significantly since early February to very high amplitudes into Phase 6,7 and 8 territory.

Phase 7 and phase 8 in February with high amplitudes tend to favor warmth east. Yet look at Phase 8. It tends to favor cooler temperatures east (middle chart below). So even with a very strong MJO the temperatures can be highly variable. What I find interesting is that the Phase 1 temperature composite (far right map below) looks very similar to the overall pattern since this current warm up began.

The chances of this February finishing out as the warmest ever in Cleveland is climbing fast.

Will colder air return?  If so, how strong?

To answer this we look at the Pacific teleconnections to start March. I reference my quick cheat sheet so that I can visualize the pressure regions in question.

PNA is heading sharply negative
EPO is heading positive/neutral
WPO is heading negative (strongly negative)

Strongly negative WPO during the first week of March

What do these teleconnection levels mean for our sensible weather?  Historic temperature composites for each of these indices (PNA,WPO,EPO) in March mean below normal temperatures across the northern states centered over the Corn Belt and High Plains. The Computer models are also depicting colder air (see graphic below, lower left) centered across the upper midwest/west to start March with above normal temperatures across the eastern US and deep south.

While we should anticipate short-lived cool intrusions across the Great Lakes, temperatures overall will average out near the 30 year average (see lower right graphic) for the first week of March.  For Cleveland, daytime average high temperatures for March are in the lower 40s. 

Long range teleconnections for the middle of March show some colder signs centered central US and west. Something to watch over the next week.

The South Oscillation Index (SOI)--changes in the pressure patterns in the tropical Pacific Ocean (click here for more on the SOI and here)--shows rising pressure in the central US March 10-13th after the central US trough slides east March 7-9th.

Will the weak trough be a more permanent feature over the Great Lakes or will a warmer ridge develop by the 3rd week of March?  The answer will be apparent in both the SOI changes. The teleconnections will reflect the changes by the end of next week.

Outlook For The Rest Of Winter? Written January 19th/Updated Feb 9th

Yes. It's a catchy title that probably evokes many suspect responses.  Let me explain my self:

Big cool down late this month/first week of February followed by a warm up by mid month February per the Bering Sea Rule which dictates ridge over the Bering Sea correlates well to eastern US ridge roughly 16-18 days in the future.





The GFS shows this ridge evolution quite well.

February 9th Update:

BSR verification (forecast left panel with actual heights right) for the period above looks pretty good.

This warm up may be the final nail in the coffin shutting down arctic cold for good this winter. Why? Check this out...how much snowfall did we get from 3rd week of February to start of spring in 10 historically cold winters in Cleveland? Not much...

Current US Snow Cover vs Last Winter & Others

Quick look at the progression of US snow cover shows many ups and downs. The first graph shows the snow cover during two cold winters nationally starting December 15 through mid May. Interestingly, the peaks and valleys in these two winters (2013-14 and 2010-11) match up with the exception of mid January.

The numbered peaks correspond to large scale cold periods. See the US temperature anomalies below for each peak.

#1

#2

#3

#4

The graph below shows snow cover over the same period with the two cold winters above along with the El Nino winter 2015-16 added in red. A spike in late December and two smaller ones in January preceded a steady decline from late January through the end of the winter.

The yellow line shows this winter's snow cover through December 27th now at 41%.

Expect this number to steadily climb through the first two weeks of January 2017 north of 65% given the colder long range outlook below.

Conditions Far Different This December vs December 2015

The conditions over the higher latitudes at 10mB (65-70,000 feet) are much warmer recently than last November/December...

Hat tip: Peter Mullinax

 ...which translates to higher heights aloft at 10 mB.

Pressure pattern completely the opposite of the polar conditions in early December last year where heights were much lower. Polar vortex was very stable probably influenced by the El Nino.

 Temperatures last December were well above normal across the eastern 2/3 of the US

In fact, over the last 6 Decembers, only 2013 and 2010 were below normal east and/or north.

So far, temperatures in early December through the 5th were above average.

Based on the high latitude conditions at 10 mb (65 and 70,000 feet) mentioned above and the higher than normal Eurasian snow cover which has driven skyrocketing high pressure across Russia, this first shot of colder air across North America was not a surprise.

Nearly Record Setting High Pressure Across Asia in late November

Graphic courtesy Greg Carbin, SPC

In fact, we mentioned this in our winter weather outlook issued back on October 27th and in subsequent tweets on November 22nd and Dec 2nd emphasizing a significant lake effect snow event a week in advance:

The CPC painted its first below normal temperature outlook across ALL of North America for the first time since December 2013. Hat tip: Brian Brettschneider

We haven't had a December with temperatures at least one degree below normal in Cleveland since 2010.

A few days ago (December 6) I retweeted a post from late November highlighting the shifting jet stream position across the middle of the US allowing more frequent storm systems.

Our 8day forecast issued on December 7th and 8th shows these individual systems with high snow potential for northern Ohio through December 16th and beyond.

Anticipate below normal temperatures, overall, the rest of December 2016. 80% Chance for a white Christmas for northern Ohio!

Historically Does US Warmth In Fall Connect to Higher Eurasian Snow Cover?

Eurasian Snow Cover - November 12 (2015 vs 2016)

The snow cover across northern Asia is now 3rd highest since record keeping began in the mid 1960s for early November.

The northern Pacific jet has been very strong and stable with little "waviness" until the last few days. The low over the Aleutian Islands is locked in place as the strong northern Pacific jet undercuts the low pumping up the ridge across North America locking in abnormally warm temperatures.

November temperatures vs normal

Is the high snow cover across Asia influencing the strong jet stream?  Is there a history of this in early November in very high/very low Eurasian snow cover years?

I examined the 500 mb vector wind, sea surface temperature anomaly and US surface temperature anomalies (Oct 15 through Nov 15) for the years (top 10) with greatest Eurasian snow cover in week 44 (early November): These are: 1976, 72, 2016, 1969, 2015, 2012, 1973, 2009, 2014 and 1966.

While this year's cool pool in the northern Pacific has expanded recently, three of the top four years had significantly larger and colder cool pools (reanalysis is in Kelvin). Interestingly, widespread US warmth from mid October to mid November only occurred in 2016, 2015, 2014, 2012 and 2009.

1976

1972

2016

1969

2015

2012

1973

2009

2014

1966

What about the years with very low Eurasian snow cover (bottom 10) since 1966? 10th lowest to all-time lowest? The 500 mB jet seems consistently stronger in years with lower Eurasian snow cover. The northern Pacific water temperatures seem cooler overall. Only 1975, 83 and 2007 has widespread above normal temperatures in late October and early November.

1997

2007

1974

1983

1980

1979

1981

1975

1982

1988

Comparing high and low Eurasian snow cover to the ENSO state shows a blend to either side--cool and warm. 8 of the 20 years occurred during a strong ENSO state. Overall, there doesn't seem to be an overall trend which suggests that other factors are at play aside from ENSO.

Thoughts?