Sunday, December 25, 2016

Christmas Thaw... Plus Thunder!

One week ago today, here in Minneapolis, we woke up to temperatures of -20 F (-29 C), with wind chills around -35 F (-37 C).  And we had upwards of a foot of fluffy snow, which was blowing and drifting in the wind.  Now, lest you dismiss this as being normal for Minnesota, in the third week of December, you are mistaken; it is not!  This was the Polar Vortex, that shifting of super-cold air from around the north pole, pushed southward, with the jet-stream, by temperatures in the Arctic Circle, which have been hovering right around freezing for several weeks, a departure from normal polar temps of  -25 to -35 F. (-32 to -37 C).  In other words, as counterintuitive as it may seem, the shift of the polar vortex southward into North America and Siberia is the effect of global warming in the polar region.  See my December 2016 blog:

Now, on Christmas day (and for the last several days), with the Polar Vortex past, we are experiencing unusually warm temperatures for late-December and our once-fluffy snow is melting fast.  Right now, at noon, I am looking out my window at wind-blown steady rain, with the air temperature hovering just above freezing. Thunderstorms and temperatures in the 40s are predicted for later in the day, with upwards to an inch of rain, and it's likely that most of our snow cover will be gone by tomorrow.

Thunderstorms on Christmas Day in Minnesota?  No one can remember this happening before, but it serves as a very good example of what winter-protecting your roses is all about, if you live some place where winter (and especially the Polar Vortex these days) affects your garden.  Last week at this time, my roses were frozen solid, probably at least a foot or more below the surface (it doesn't take long for that to happen at -20 F (-29 C).  Now, with temperatures well above freezing and rain coming down, the ground surface will start to thaw after the snow melts, but I know my roses will stay frozen solid because they are mounded with dirt and insulated with leaves and/or marsh hay.  Likewise, tomorrow morning, when temperatures fall and the surface re-freezes, they will be unaffected, because they did not thaw.

Now, for example, if you live near St. Louis, Detroit, Indianapolis, Louisville, Boston or New York, and your ground and roses were certainly not frozen before the Polar Vortex came through last week, but you had at least mounded them and your bud unions are planted several inches below the ground, it is very unlikely that they froze from that short blast of polar temperatures (which we may see again in January or February). So, like mine, they are just fine for exactly the same reason: they were winter-protected from freezing and thawing.  The only difference is that mine didn't thaw and yours didn't freeze; so no problem either way.  If you haven't already seen it, please read my recent blog: "Five Important Steps to Winter-Protecting Your Roses".  Here is that address: .

As I have said repeatedly in the last few years, you can debate why global warming is happening but the facts clearly demonstrate that it is; the Polar Vortex notwithstanding.  As mentioned earlier, the Polar Vortex is caused by extreme warming of the polar regions pushing cold air southward into Siberia or North America (or both this year), via the jet-stream. And because it is still unusually warm in the Arctic, we can expect the Polar Vortex to re-emerge in any winter going forward, particularly in January or February (December was a surprise).  Please see my March 2014 blog "What the Heck Was Wrong with this Winter": ,
as well as my October 2014 blog: "Winter-Protecting Roses in a Climate-Change Environment".

Bottom line?  If you live in any zone where winter comes along at some point each year, do something to winter-protect your roses, even if it's only planting your bud unions several inches below ground and providing some mounding with mulch or dirt around your plants each fall, because we can now say, with a fairly high degree of certainty, that the Polar Vortex will strike again in North America, in any year going forward.

Jack Falker

Wednesday, December 14, 2016

Here Comes the Polar Vortex... Again!

The last time the dreaded Polar Vortex invaded the lower 48 states was nearly three years ago, in January 2014, and it was pretty rough, especially for rosarians in parts of the country who aren't used to deep cold, as we are here in the Upper Midwest.  I remember writing back then that we would probably see a vortex invasion again, because it's something that's always circulating up there at the north pole, and it would be just a matter of time before it found its way south again, especially with the weather anomalies we are experiencing on a regular basis these days.  I also cautioned readers in my previous blog "Five Important Steps for Winterizing Your Roses": "Don't forget the Polar Vortex of a couple of years ago (and act accordingly)!"

Well, I hope you did, because here it comes again!  However, for those in zones 6 and 7, If you didn't get all your winter work done, you may have a few more days to protect your roses from the effects of freezing and thawing.  See the animated map below to see when the vortex will strike your area.

The good news is that this particular polar vortex incursion isn't going to last too long.  Obviously, we can't know for sure, but there seems to be a pretty good chance that the vortex will not repeat itself in January, when the the polar air is considerably colder

This is all from my friend Paul Douglas' blog, which I read daily:

What Is The Polar Vortex? NOAA has a very good explainer, separating fact from hype: "...The polar vortex is a large area of low pressure and cold air surrounding both of the Earth’s poles. It ALWAYS exists near the poles, but weakens in summer and strengthens in winter. The term "vortex" refers to the counter-clockwise flow of air that helps keep the colder air near the Poles. Many times during winter in the northern hemisphere, the polar vortex will expand, sending cold air southward with the jet stream (see graphic above). This occurs fairly regularly during wintertime and is often associated with large outbreaks of Arctic air in the United States. The one that occurred January 2014 is similar to many other cold outbreaks that have occurred in the past, including several notable colder outbreaks in 1977, 1982, 1985 and 1989. There are several things the polar vortex is NOT. Polar vortexes are not something new. The term “polar vortex” has only recently been popularized, bringing attention to a weather feature that has always been present..."

Here's the full description:

And here is an excellent,timely article from the New York Times: "Feeling a Chill? Blame the Polar Vortex. And Global Warming".

And here is Paul Douglas' take on the odds of this happening again this winter:

Late-Month Moderation. I want to see a few more model runs, but GFS 500 mb predicted winds looking out 2 weeks suggests a more zonal flow for the USA with temperatures at or above average for late December. The question is not: will we endure more arctic fronts. We will. The question is how pervasive will bitter air be east of the Rockies? Will the polar vortex weaken and break down, allowing subzero air to consistently flood south? I'm still not convinced it's going to be nearly as numbing as it was 3 years ago.

Thank Heaven! But it's better to be safe than sorry.

The map below tracks the polar vortex incursion through the end of December: