Friday, December 11, 2015

What's Happening to Winter?

The United States has just experienced its warmest autumn in history. In Minneapolis-St. Paul, temperatures in December are running about 20 degrees (f) above average; an average already pulled much warmer over 50-plus years. December in the Twin Cities is when our miriad of shallow ponds freeze, with our deeper lakes not far behind.  Not this year; what ice had accumulated has all but disappeared and what would normally be a deepening snow pack is all in the form of rain or slush.  Golf courses are open and my greening lawn looks like it could use a cutting.  And we're expecting up to an inch of rain over the weekend (which would be a foot or more of snow, if it were about five degrees colder)!

In his December 12th weather blog, my friend Paul Douglas, founder of Aeris Weather and WeatherNation says:  "... What makes our current stretch of (irrational) warmth unusual is the sheer persistence of the mild signal: day after day, week after week, month after month.... Since September 1, over 80 percent of the days have been warmer than average, according to (Minnesota state climatologist) Mark Seeley. Further, if you add in the first 10 days of December, the stretch of days from September 1, 2015 to December 10th is the warmest in state history, a remarkable run of warmth."

And here is a Climate Central map that Paul published:

Here is the address of Paul's weather blog, in case you would like to read more:

Something is going on here.  It looks like we could have a St. Louis winter (USDA Zone 7) in the Twin Cities (i.e. not below zero). And in St. Louis?  How about an Atlanta winter, and so on.  For the last several years, I have been developing and analyzing extreme minimum temperature trend lines, extending over the last 55 years, for Midwest cities, and my conclusion has been that the upper Midwest is warming faster than any other area of the country and that winters would become warmer still over the next several years.  I just didn't think it would happen quite this soon.

As a long-time, cold-zone rose gardener, I have been lightening up on my winter protection a little each year.  This year, anticipating a massive, climate-change-driven El Nino, I decided to use only compost-mounding, with no insulating leaves; a process that I might have used in Detroit (Zone 6), 40 years ago.  For several years, I have been writing that using the Minnesota-Tip winter protection procedure in the Twin Cities is a lot of unnecessary hard work and a horiticulturally unsound practice, given the trend of our winters (see my blog: "No Tipping Please").

What surprises (and amuses) me is how many people around the Twin Cities still tip their roses.  Even the University of Minnesota Landscape Arboretum still tips their roses (courtesy of the strong backs of the Minnesota Rose Society).  The reason for this, I believe, is that, in order to effectively use the "tip" method, the bud unions of hybrid tea roses must be grown at or above ground level, which, in itself, is a horticulturally unsound practice (wherever you live). So, in order to get out from under the "tip" method, you have to re-plant your bud unions deeper, which is a simple, one-time procedure (I know, I did it).  Also, old habits (and fears) die hard, but people just need to stop and recognize what's happening around them, and trust the statistical evidence.

I am also amused by articles written in local rose newsletters this past year referring to our brutally cold Zone 4 winters.  The extreme minimum temperature last winter (2014-15) was -11, only one degree shy of being in Zone 6.  Our coldest winter in many years, 2013-14 (with the horrible polar-vortex effect) had only one night falling a few degrees into Zone 4, at -23. All other night-time temps were Zone 5 or Zone 6. People who dispute these facts are probably thinking about wind chills, which have nothing whatsoever to do with plants.  See my blog "Don't Sweat the Wind Chill":

The Statistical Facts

The mathematical study of statistics focuses on the probabilities that certain events will happen (or not).  Put another way, statistical analysis can be predictive.  So, when we perform valid statistical analysis on regional winter weather, over many years, and we can see very clear trends developing, we are positioned to make predictions about future winters.  As cold-climate rose gardeners, this is pretty important because it allows us to make informed decisions about which roses to plant and how to winter-protect them most effectively.

For several years now, I have been doing 50-plus year statistical analysis on Minneapolis-St. Paul winters and comparing them with winters in other upper-Midwest cities.  The results are pretty amazing in that we can see very distinct warming trends developing. And it has become much easier to predict that these trends will continue and that we will see warmer winters going forward.  The meteorological winter of 2015-16 began on December 1st and what we are now seeing is exactly what the trend line shows we should expect: temperatures are much warmer than average, an average which itself has been pulled significantly upward over the last 55 years.  Below is my chart for the 55 winters beginning in 1961, through 2015, in the Twin Cities. What it shows is that since year 2000, all but three of our winters have been in USDA Zone 5 or higher, even though the USDA continues to rate MSP as Zone 4 (based on data that is now 10 years old).  What's most important here is the upward slope of the trend-line, which, as mentioned above, is predictive.  What the trend-line shows, if you extend it, is that MSP will be firmly in Zone 6 within the next three or four years.  Right now, based on what we are seeing, I believe we will see a Zone 6 winter in 2016, for the second time in history, and there is a distinct possibility that it could be Zone 7, i.e. not below zero at all, which would be a first.

Below is the 55 year trend line for Chicago.  Note that while Chicago has moved firmly into Zone 6, the slope of the trend line is shallower than the MSP line. In other words, while Chicago is warming, it is warming more slowly than MSP.  Interesting that Chicago's 2015 low temperature was -10, right at the      lower edge of Zone 6, while MSP's low was -11, right at the upper edge of  Zone 5; virtually no difference.

And below is the 55 year EMT trend line for St. Louis to give us some idea of what a Zone 7 winter might look like.

The differing slope of these trend lines is born out in Climate Central's chart below.  Note that the MSP area and points north along the Minnesota/Wisconsin border, as well as the Red River Valley in Northwestern Minnesota, have warmed more than any other area in the country.

Finally, let's look at NOAA's Winter Outlook for 2015-2016 and note that most of Minnesota is projected to be 50-60% warmer than average this winter. In the short term, this is attributed to El Nino ("the child"), but it is important to recognize that the phenomenon of El Nino is itself the "child" of long-term climate change. In other words, it is becoming impossible to differentiate short-term from long-term effects.  If you go back and look at all of these graphs and charts together, there is a great deal of similarity in the pace of warming in the northern tier of states.  And this is exactly what the trend lines above are pointing toward.

(credit: NOAA)

There is growing evidence that, with the extreme warming of the oceans, El Nino could become a long-term phenomenon.  Here is another snippet from Paul Douglas' weather blog, quoting a climatologist at NASA's Jet Propulsion Laboratory:

"Monster" El Nino Could Usher In Decade of More and Stronger Events. A sign of things to come?  "...While El Nino oscillates on a more or less yearly cycle, another dynamic in Pacific Ocean water temperatures, known as the Pacific Decadal Oscillation (PDO), has the potential to accelerate global warming and increase the severity of El Nino episodes, scientists said. The last time the PDO was, as it may be now, in a prolonged positive, or "warm" phase, it corresponded with two of the strongest El Ninos on record. "When you really have a monster El Nino, it could be enough to flip the PDO into a new phase for a decade or so," said William Patzert, a climatologist at NASA's Jet Propulsion Laboratory in California. "Keep your eyeballs peeled because maybe we're in for a decadal shift..." 

While this may be good news for rose gardeners, it is very bad news for our planet.  In the meantime, my advice to upper-Midwest gardeners is to plant your bud unions a couple of inches below ground and forget about uprooting and tipping your roses.  For northern-gardeners, like myself, who keep our roses firmly planted and mounded in the winter, it may be time to lighten up a little, but winter cover will still be important.  It still gets cold in Zone 6 and freezing and thawing (the roses' winter enemy) is an even bigger problem in a warmer winter environment.

Jack Falker
December 12, 2015


  1. Freezing and thawing killed many zone 4 hardy perennials, mulched hardy shrub roses, and many tender roses mulched and covered by insulated construction blankets at Munsinger and Clemens Gardens in St Cloud, MN during our unusually warm, snowless winter of 2014/2015. With no promise of snow cover due to the warm winters, planting bud unions 2 to 3 inches below ground level and mulching roses heavily over the crown and extending the mulch out the drip line to fully cover the root zone is especially important. Snow is a wonderful insulator when we have it. When we don't have snow, it means plants experience the full effect of freezing and thawing.

  2. The hot weather is not welcomed by us as it takes away various privileges like sun bath and partying with the friends on the beach.