Happy Spring! (Yes, spring! Meteorologists count March 1 as the start of spring.)
I don’t know about you, but I sure am ready for “real spring” to arrive. Not false spring. Those of us who grew up or live in the northern half of the U.S. know all about false spring. A week or two of warm weather teases us, charms us with its warm sun and puffy clouds and maybe even a slight whiff of moisture in the air, only to shatter our dreams when winter returns.
We need moisture with our warm weather here in Nebraska and across Iowa toward the upper Midwest and Great Lakes. Warm winters are often dry winters in this part of the country, and outside of a very snowy couple of weeks in January, we have struggled to get much moisture. The last time we had a really dry and warm late winter to early spring in this area was 2012, and it wasn’t a great harbinger for the rest of the year as we baked in a summer drought. I hope the patterns are different in 2024.
Bring on the spring showers and thunderstorms. Bring on a good soaking rain. And then let the sun shine down and turn the landscape green. And if winter has any last gasps, let’s get those out of the way now so we can have spring uninterrupted!
Of course, weather isn’t made to order, and the transition seasons (spring and fall) always bring wild weather swings. Buckle up, pay attention, and get ready for it! Keep your weather alerts open in this season of thunderstorms, wildfires, snow, and ice, sometimes in the same storm system. Protect tender early plants from freezes. And if you ever have any questions about the weather around you, send them my way!
What’s Wrong with Warm Late Winters?
We’ve already talked about how warm the winter has been in the heartland, save for a few weeks of cold weather in January. The longer it goes on, the more worried I get.
But why would I be worried? Isn’t it nice to have pleasant weather and maybe spend a little less on home heating? Yes, both of those are true. But my concerns are bigger than me and my personal comfort. I’m worried about buds.
Tracking Winter Severity
About a decade ago, I got interested in putting a number on how severe a winter is. I wanted to be able to put a number on how severe the Long Winter of Laura Ingalls Wilder’s books actually was, compared to other winters in the same area. (The origin story is much longer but one I’ll save for another time!) Working with my colleague Dr. Steve Hilberg at the Midwestern Regional Climate Center, we created the Accumulated Winter Season Severity Index, or AWSSI (rhymes with “bossy”) for short. Using daily temperature, snowfall, and snow depth information from the onset of winter to the end, the AWSSI tallies points to count how severe or mild the winter was.
On the AWSSI map above, each category is color-coded, from Mild to Extreme, by ranking all the winters from mildest to most extreme and then dividing them up evenly into five categories. The Mild category includes the lowest 20% of scores on record for that site, while the Extreme category includes the highest 20% of scores. Red dots are locations in the mildest 20% of winters, and red diamonds mark record mildest winters.
The map is not final, as “winter” conditions are still possible in at least some parts of the country. Some sites may drop or rise a category before it’s all done. But it would take unprecedented late-spring extreme winter weather to budge those red diamonds in the northern U.S. out of the Mild category. And that swath of red is extensive - comparable to the final AWSSI for the winter of 2011-2012, another year with a very mild late winter.
Early Green-Up
Warm weather in the late winter to early spring entices trees, flowers, and fruit to bud prematurely. Early-budding fruit trees can handle a cold snap, but they grow vulnerable to a freeze kill quickly once buds swell and take on their green or flowery colors. Take, for example, apple trees. Apple trees can tolerate temperatures in the teens when the first nubbins of buds emerge, but when the buds start to separate and green leaves poke out, they can only tolerate the mid-20s before kills ramp up. Tart cherry buds follow a similar temperature profile. Peaches are even more vulnerable, with kills ramping up rapidly with temperatures in the 20s once the first pink flushes on the buds. (Want more detail? Here’s a great chart!)
All of this early warming means that buds will emerge early. When that happens, it doesn’t even take a late freeze to kill the emerging buds. It’s not the calendar that matters to the plants, after all - it’s the bud stage, which depends on the accumulation of growing degree days (what’s a growing degree day? Click here for more!). Warmer temperatures at the end of winter and early spring mean more accumulated growing degree days by a given calendar day, when compared to a normal or cold late winter to early spring season.
That’s exactly what happened in the Easter Freeze of 2007 across a wide swath from the central Plains to the Southeast. Record March warmth led to early bud and plant growth. But winter wasn’t quite done, as a deep freeze struck in early April. The blast of cold brought low temperatures in the upper teens to lower 20s for several consecutive days, with gusty winds that enhanced the heat loss from the vegetation. The result was a two-billion-dollar disaster, with serious damage to apple, peach, cherry, and other fruit orchards, as well as winter wheat, alfalfa, and other forage crops.
Then, it happened again just a few years later. Extreme warm temperatures in the late winter to early spring of 2012 broke records, especially from the central and northern Plains through the Midwest. The freeze in Michigan destroyed 97% of the tart cherry crop in 2012, as well as significant losses to apple and peach trees, and caused hundreds of millions of dollars in losses.
While our winter-weary eyes might delight at the sight of buds bursting on branches, there is such thing as “too early” for the buds to be safe.
Tracking Spring in Your Backyard
The U.S. National Phenology Network keeps track of spring leaf and bud emergence nationwide, as well as the seasonal arrival and bloom of a whole bunch of specific plants and animals, from lilacs to mayflies and monarchs to sugar maples. Some of their maps use temperature data to track emergence, while other projects rely on observations from any willing volunteer who wants to step outside and pay just a little closer attention to their backyard and landscape.
The latest green-up map has a lot of red on it, too, showing areas that are greening up as much as two weeks or more ahead of schedule. The early green-up puts buds at risk of a freeze, even if the freeze isn’t technically “late” compared to averages over many decades. It would nip the seedlings from ambitious backyard gardeners who got a little spring fever and put their seeds in the soil too early, and it could bite nurseries that set out tender vegetation too soon.
So, while I love spring and can’t wait for it to really arrive, I’m also uneasy. I’m paying attention to what starts budding and sprouting in my own yard and neighborhood. I’m watchful for signs of spring freezes still to come. I’m not ready to start my garden seeds early. And I’m hopeful that the orchard growers get lucky and avoid a costly freeze after the fruit trees sprout their tender buds.
This Month in Wilder Weather History
March 13, 1937: Laura Ingalls Wilder wrote in a letter to her daughter, Rose Wilder Lane, ““But! Dust settled over us again yesterday.” It was the midst of the Dust Bowl, and though the worst of the drought was in states to their west, like Oklahoma, Kansas, Colorado, New Mexico, and Texas, the dust from those states blew across the country. March and April 1937 were especially dusty, sending dust streaking from the origin area in the High Plains all the way to the Atlantic coast. The Wilders likely saw quite a bit of dust in the spring of 1937 at their Rocky Ridge farm in Mansfield, Missouri.
You are so stinkin' smart, friend! This was a fun (and educational!) read! <3
I totally agree! I had no idea there was such a thing as a “green-up” map! As a Southern California container gardener I pay attention to the Sierra Nevada snowpack, since it’s an indicator of future drought status. But I do watch the buds, too!