Winter is a month that causes much fear or anticipation and either moans & groans or shouts of joy. It's definitely not our grandparent's winters anymore though. Heck, as a barely millennial born in 1981, we don't get the winters of my childhood anymore either.
Minnesota in fact is one of the fastest, if not THE fastest warming state in winter of the lower 48. Alaska is warming faster because it has significant arctic territory and we know the arctic is warming at two to four times the rate as the rest of the planet. It is for a related reason that Minnesota is warming so fast. Our winter weather patterns are often driven by some of the coldest air on the continent, directly coming from the arctic. We're in a unique position: far from modifying affects of oceans or blocking of air from any mountains. Inevitably if the arctic is warming a lot & quickly, Minnesota's winters will be to some degree also.
Below: Winter Average temperature anomalies (difference from normal, i.e. zero) since 1981. Note a 2° warming in just 40 years.
It's not just that our average winter temperatures are warming so quickly. It's winter extremes too (both warm & cold).
Below: Top 10 warmest winters on record.
7 of the top 10 warmest winters are in my lifetime (1981). Four of the top 10 are just since 2000, despite the 2000s making up just 14% of our record (1873-present), they account for 40% of the top 10 warmest years. This alone tells you something is awry.
One of the seemingly counter-intuitive aspects of our warming climate is increased snowfall. Indeed a warmer atmosphere holds more water vapor and therefor has the potential for higher precipitation amounts. While Minnesota is warming rapidly, it's still cold enough most of the time for snow rather than rain.
The fact that this nearly 6" increase in snowfall has resulted in less average snow depth, however, tells you: something's up.
BELOW: Historical average snow depth (all years since 1873) compared to Normal (since 1991)
That something, is that, despite more snow, there's A LOT more variability & melting. Looking at the chart you see differences of about a 1/2" - which doesn't seem like a lot but when you're averaging many days over 148 years, that's a significant figure.
For example: We average almost no snow depth in November now. Historically, we averaged about 0.6" - again a meager amount, but it meant that many years we had some snow on the ground late in the month. Now? That's very, very rare.
And some of the biggest changes are at our peak: which is January 20th to February 5th, for snow depth. This is when the combination of cold & snow reaches its zenith.
Remember when it used to be COLD? Like real cold? Yeah, me either.
It's not just our imaginations. The coldest temp of winter, on average used to be about -27°. Now ? It's about -16°, but in more recent years, closer to about -14° to -15° (since 2000).
Below: Coldest night of winter:
One of the fascinating stats is the elusive -20° temperature. Before 1900, you could rely on several nights each winter dipping to -20° or colder in the Twin Cities. The historical average in fact is 3 per winter.
Below: Number of nights of -20° or colder per winter:
Now? We reach -20° on average, ONCE every OTHER winter. The last time we did this was 2019 (which means we're due in 2021-2022?). To be fair, some of this has to do with the urban heat island, which is, in itself climate change. We've altered the landscape with urban areas all over the world, but we cannot discount the trend in warmer nights overall, all over Minnesota. This is precisely in line with how a greenhouse works.
Remember: a greenhouse doesn't magnify heat or the sun's energy, or is a source of heat itself but rather it TRAPS heat from escaping so that it accumulates with time.
BELOW: The number of Subzero nights per winter.
We used to be able to rely on a month's worth of nights below zero at night ( or 1/3 of winter). That number has decreased by a third, to just about 3 weeks worth.
Our first & last subzero nights are shifting too. Historically, by December 10th we'd have our first subzero night, now it's almost two weeks later on December 23. The last subzero night used to be about February 28th, now it's February 15th. That's a 26 day shorter winter in one measure (80 versus 53 days of the potential subzero night season). We might think, well awesome... but for the flora & fauna of the state, that's evolved to long, brutal winters & hot, humid summers, this is a change happening too fast and that causes stress.
This past January (2021) for example had NO subzero nights at all. This has only happened three other times ever out of 148 years. EACH of the other three are just in the last few decades.
Below are a whole host of other charts, figures I've compiled on normal, average, and climate influence with a brief description:
Below: Average Ice-Out on Lake Osakis:
Below: Cold snaps getting shorter:
Below: NORMAL snow depth by date:
Below: CHANGE in snow depth (normal: 1991-2020) from historical average ( 1873-2021)
Note the increase in mid December snow pack (due to increasing December snowfall) but then an overall decrease January through mid February of snow pack. This is likely a result of warmer than normal January/February temperatures (since snowfall is increasing during this period). We used to be able to rely on January & the first half of February being below freezing, consistently (save for a little late January thaw?). Clearly there's much more thawing going on now than before, causing a decrease in the peak-season snow depth.
I'll continue to add graphics & stats here as winter progresses & new things pop in mind or are warranted....
Commentaires