Why are these races all filling up?

It's got to be the snow. For the first time in nearly two decades, the Twin Cities are experiencing their third "good" snow year in a row. Assuming we don't have a total melt-down in the next couple of weeks (a rather fair assumption, given the snow depth and upcoming models) we should hit 70 days with good snow (3+") on the ground. That happened nine out of ten years in the 1970s, but only five times in the '80s and four times in each the '90s and '00s. The last time there were three such winters in a row was 1991-1993. Since then, 1995, 1996, 2001, 2004 and the last three winters.

So, since the early 1990s, people would have a good winter of skiing, get in to it, register for a couple races the next season, and be all pumped up and ready to go for a third when—it would be brown for months on end. For the serious skiers amongst us, we'll rollerski and run in December and January. Or drive to downhill areas. For many others—they'd sit inside and sulk. Like we probably wanted to (Trollhaugen is just not that fun day in and day out).

But the last three years, there's been good snow from early January through the first part of February. But take a look at recent winters:

The yellow-red lines are the generally mediocre winters from 2004-2007. The blue lines are the three most recent. Notice how, especially in January, especially, the recent winters far outperform the past ones. And notice how our current winter has pretty much outperformed the last five in snow depth; especially recently, when, even in good winters, the snow amounts have crashed. And when lines disappear off the bottom—no snow. We'll see if we get a nice March snowstorm this year, but in 2005-6 and 2006-7, most of the snow came from big storms in March. Which don't do too much good for skiing before then.

So it's good. Might it get a lot better?

Como and snow melting

I hit up Como again for some intervals (double pole then V2 uphill) and all around skiing. The conditions are very good, but it could use a groom. Coverage is full. The issues are that pole plants are soft in places, that the skate lane is getting pretty well packed (although better with warmer weather) and that someone ran a truck across a couple portions of the Glacier, which really needs a regroom. Hopefully they can take the machine across it before the weather turns too warm. Tonight would seem to be a good night for it, hint, hint.

As far as the snow melt goes, I'm actually less concerned now than I was yesterday for two reasons. First, the models are happier. They've backed up the huge, tropical rain storm idea and now just have us hovering in the mid-30s for daytime highs with very little moisture for a week, and then cooling back down. It's not ideal, but it should only take a couple inches off of our base if it comes to pass. As I mentioned earlier, we've dodged a bullet by having had an inversion lock in cold temperatures at the surface; it's still +10˚C at 3000 feet but 20 at the surface, and it never got near freezing today despite some sunshine. It looks like that pattern should continue, with a bit of warm-up but nothing worse than a few hours at 34˚. With January sun, we can handle that.

Second, I went in to the archives and looked at times that 8 or more inches of snow has been on the ground in January (about 40% of the time). I could find no cases where more than 10" of snow had melted in December or January, and only a couple times when 8" had. Here are some interesting analogs to make me less scared that the snow will disappear (although when February comes around, with its stronger sun and warmer temperatures, anything is possible). I can't think of a good way to graphically show this so:

2008: 8" on Jan 3, subsequent days 30/14, 37/19, 41/32, 37/27, 34/22, 31/13, 35/29, no rain or snow, melted to 4"
2005: 7" on Jan 22 melted to 0, but that took until Feb 6 and required highs of 35, 44, 33, and then later 33/28, 25/29, 26/31, 42/27, 50/31, 51/35. That was the City of Lakes Meltdown. We have four more inches of snow and those were extraordinarily high temperatures in February. In addition, there was far less snowcover that year to our south and west.
1993: 9" on the 30th melted to 5 on February 3, but only after 39/12, 45/34, 42/24, 38/22, 38/20 with no other moisture.
1992: 8" of snow on the 1st, aided by 0.8 inches but also hit with about 1/3" of rain, stuck around despite a week with highs around 34 and lows only around 31 (yes, for the first five days of the year the high was 37 and the low was 31). The snow barely melted despite a couple more days in the upper 30s. This seems like a worser-case scenario for our current situation.
1991: 8" on the 31st melted to 0 with temperatures of 43/8, 48/15, 42/35, 46/32; we are not expecting these types of temperatures and the sun was two weeks higher in the sky.
1989: 8" melted to 0 over two-plus weeks (the 8th to the 25th) with highs of 35, 37, 33, 37 (this took it from 6 to 2; it had settled from 8 to 6 already … our snow pack is rather dense so there won't be much settling) and then meted with highs of 39, 40, 40 and 35.
1986 may be the best analog: 12" on the 9th melted to 8" by the 20th, with temperatures of 42/28, 34/27, 44/24, 40/14, 22/6, 25/14, 34/11, 38/21, 39/29, 35/27, 33/28, 34/31 with no rain or snow. This would not be a bad outcome for us.
1976 went from 9 to 7 with a day at 41 and the next at 35.
1974 is another good analog. After a cold start to the month, 8" of snow on the 14th melted to 6 wth days at 39/16, 38/12, 41/24, 33/24, 34/12.
1973 melted 8" to 4" with 38/9, 46/24, 44/24, 36/25.
1952 melted 10" on the 30th to 5" with 42/30, 38/24, 37/21.

The one issue is that moisture would be a major wild card. There are only a couple of instances of a lot of rain falling on a lot of snow in January, and, while they are both a very long time ago, neither actually killed the snow pack. In 1946 melted 10" on the 4th to 4" on the sixth with temperatures of 38/25, 36/33 and 33/25, with 0.6 inches of rain on the middle day. Back in 1902, a December storm brought 0.75" of rain (and 3" of snow) but only depleted the snow pack from 10" to 4" despite 35/17, 34/15, 36/34 (with the rain and wet snow) and 36/28.

So the gist of what I'm saying is that to melt more than 10 inches of snow would require weather so extreme that we've never seen it before. A run-of-the-mill January thaw may eat away at half our base, but to lose more than 8" of snow in January is historically unheard of. Now that the three-inches-of-rain-with-embedded-thunder storm has worked its way off the models, it looks like we'll have a week in the 30s. That we can deal with.

The latest model run has significantly cooler weather in the next week—if it verifies I'd be surprised if we hit freezing more than two days, and then two warmer storms—with some rain or perhaps a lot of wet snow—the week after. So, who knows. If I had to predict, I'd say we have 6" of snow on the ground at the end of the month, with good skiing at most Metro locations and great skiing in Elk River (they are starting with more and they keep snow so damn well).

Ski on.

I can only get to two trails at most, on a good day! Check out all the trail reports at skinnyski.com

What does it take to melt a foot of snow?

This is a very pertinent question, given the current status of the weather. First of all, we are dodging a bullet for now, given the snow to our southwest and the massive inversion which kept temperatures yesterday in the teens and might keep us well below freezing most of today, even as temperatures aloft are well over 50 degrees! The chart below shows this; blue diagonal lines are temperatures gradients (in C) and the thick red line is the temperature at different levels of the atmosphere. Notice how it starts well below 0 but climbs, quickly, to above 10 (50F). (click the image to enlarge)

If it were going to be 50 for the next two weeks, well, bye bye snow. But it's not. According to the latest model run, the warmest air is in place right now through this afternoon—it's close to 60 (yes, 60 above) higher in the atmosphere, and it's probably 50-50 that it gets to freezing here at the surface today (the sky is still cloudy at 11:00 here in Saint Paul). And while it will remain rather warm for the next few weeks, this is by far the warmest day above, and by not mixing down those warm temperatures, we are really escaping the worst of it.

What happens beyond is a crapshoot. More sun would definitely aid in the depletion of the snow, as would more moisture. However, the models are being rather finicky on how much moisture is going to ride up in to the warm air. Last night, they were showing more than three inches of mostly-melted precipitation in the next two weeks. Now they are showing considerably less. And the most recent runs are showing a split flow with rather consistent temperatures topping our in the 30s for several days, but not skying towards 50 at any point (today would have been the day, but the inversion is helping us). And the temperatures, at least in the short term, should follow a nice diurnal pattern, so that lows will be around 18 around dawn, peak around freezing in the afternoon, and then fall off quickly. This is not a recipe for snow depth disaster.

In any case, back in December I ran the data to look at snow depth during the past 100 years in the Twin Cities. With the current situation, I am going to delve back in to that data and look at what it takes to melt snow in January. I'll look back to find Januaries with snow depths of at least 8 inches, and see what the weather was following. In other words, I want to know what it would take, weather-wise, to melt our base.

(Why just January? In January the sun is within a few degrees of the solstice, i.e. not very high. Come February and especially March, as the sun gets higher in the atmosphere its effect on snow melt increases dramatically, even if it is not reflected in the temperatures. Day lengths matter as well. Do data from past Februaries and Marches, when you can melt a foot of snow with two sunny, 50 degree days, is not particularly pertinent.)

23 megabytes of data have to be good for something, right?

Why I am not too, too concerned about the thaw next week

That's a map of snow cover this morning. The gradients are 0-2 (brown), 2-4, 4-8, 8-16, 16-24 and 24+ (light purple). Look at the snow cover to our southwest. There's at least 16 inches from northwest Missouri to northwest South Dakota. There's at least 8 inches from northwest Arkansas to northwest Nebraska. So any warm air, coming from the southwest, will have to cross hundreds of miles of cold, deep snow pack, moderating it dramatically (melting is endothermic, too, which can cool the air just above the snow). In addition, moisture released form melting snow may build a deck of stratus clouds, muting the ability of the sun to heat the air. This is why, despite 1000-500 mb thicknesses of 552, the air temperatures are not forecast to rise much past freezing. And although we don't have the snowpack in the Twin Cities that they have over the Buffalo Ridge in Southwest Minnesota, the snow down there should help to protect us, to some degree, from a total meltdown.

I hope.

More locally, check out the latest snow depth maps from the U.

That's more than 30" of snow over some of Southwest Minnesota (and, yes, not even a foot here in the Twin Cities), where the warm will come from. That's way more than normal—in the 99th percentile. In recent years, we've often seen a lot of snow over Northeast Minnesota (and, more interestingly, the north has often fallen in to high percentiles, with the south in lower ones), with little down south—a steep gradient which is often exacerbated by warm air which blows over the snow-free areas and eats in to the first snow it finds. This year, the southwest has more snow than up north, which should be good for snow for everyone.

I hope.

In any case, we are entering a dreaded split-flow situation, which brings warm, dry air to the area. We can only hope it is short-lived and does not do much to our base, and good, cold, moist weather returns soon.

That was the winter that was—weather

In the space of about 36 hours last week, we went from -4 to 50, and two days later we were close to 70. It melted all the snow this side of Duluth, it seems, and, looking at the weather charts for the next couple weeks to April (have we skied in April? Yeah, but it melts real quick), has pretty much put an end to the ski season. Today, I'll tackle the numbers, later I'll look at the ski season.

So how did it stack up? How does it compare to last year, and previous years. Was it warmer or colder? Was the snow better or worse? How was the skiing and grooming?

Well, there are a lot of ways to answer. First, we can look at the temperatures and snow (skiing will come later). "Meteorological Winter" runs from December to February—for which records are kept. March counts as spring. This coincides rather nicely with local ski season—there are some races in March but the big ones are done and the races are generally up north. Here's how it looks:

Month	Avg. High	Avg. Low	Mean	Max	Min	Hi >32	Lo <0
Dec.	23	4	13.5 (-5.2)	41	-13	6	12
Jan.	16.8	-0.2	8.3 (-4.8)	46	-22	1	15
Feb.	29.1	12.4	20.8 (+0.7)	47	-5	13	4

A few more tidbits: snowfall was about normal (17, 8 and 11 inches) as were below zero temperatures—about 30 for the winter. There were ten days below -10, and two below -20, the first time in five years. We had a month below freezing (December 30-January 30) and almost a calendar month until the temperature skied to 46 on the afternoon of the last day of January. We were running about five degrees colder than normal, February was about average.

The coldest day of the winter was January 15, which actually fell midweek and not during a race—what are the chances. Up north was down near -40; at the airport the high was -6, the low -22, meaning for the day it was 25 degrees below average. A lot of the 'burbs went to -30 or colder. March 11, however, with a high of 8 and a low of -3, was 27 degrees below average. The warmest day, and the only day not to fall below freezing, was during the mid-February, snow-eating meltdown when the high was 47 and low was 35, 23 degrees above normal. That was a bummer—at least it was post-Mora and post-City of Lakes and Birkie was pretty much spared.

Now, on to the meteorological, numerological and chartological fun. A guy called Charles Fisk has a great website chronicling Twin Cities weather back to the '20s. The 1820s. I'm not going to link his whole site—though I could—but he has taken a ton of data and presented it in great charts. For instance, here's the month of January, in temperature.

But then it gets cool. For this winter he has charted snowfall, against the average snowfall. It'll make more sense with a chart:
Okay, that's pretty cool. And he has charts going back to 1884 (for snow), for the year, with snowfall, snow depth, temperature and all else. Here's 2008, for example. And then he has some outrageously awesome charts, like this one, showing average temperature over the whole year, by hour. Uh, amazing? I could spend all day at this site.
No wonder I love early may—60s and dry. If that's not cool enough, he has charts about wind speeds and directions and even thunderstorm probabilities (most frequent just before dawn in July fwiw).

Anyway, what can we deduce from all this information? Well, it was a pretty normal winter. It was a little colder early on, and then normalised some. The snow never got deep, but it's not terribly frequent to have deep snow in the Twin Cities. Look at the average snow depths by day for Minneapolis. The median from Mid-January to Mid-February is about five inches of depth—which is about what we had this winter. And before New Years it is significantly less. So, I got to thinking, when did we build a real "base" of snow? When did we have a good, deep layer of snow on the ground—a foot or more—in January or February. It seems abnormal not to have it, although it is actually an aberration. The last time the snow depth was more than a foot in January or February for more than a couple days was in 2001, a good snow year; and before that 1997. Before that, you have to go back to even years in the early '08s: 1986, 1984 and 1982. Before that were six years from 1969, '70, '71 and '72, 1975 and 1979. Before that, it happened one other time in each the 1960s, 1950s, 1940s, and 1930s. So people remembering the big winters remember a seventeen year period from 1969 to 1986—since the advent of skating there have been two winters with real "base building."

What I mean by base building, is snow maps like (and these are from the Minnesota Climate Working Group at the U, going back to the mid-90s):
That's March 1, 2001. Most of Minnesota had had a foot of snow or more on the ground for a month, and more than 18 inches at the end of the month. I wasn't around, but that looks awesome. The best we mustered this year was mid-January, when most of the state had a foot. Not too shabby.

A couple more data points: A nice article from skinnyski.com (PDF) shows that the 1960s to 1980s were higher than average in snowfall but that we actually seem to be getting a bit more snow compared to the first half of the century(see pages six and seven). From Fisk's site, again comes:
(click to enlarge). Again, it shows the heyday of snow in the Twin Cities from about 1970-1985, but also it looks like snowfall has been increasing slightly. Does this mean the snow sticks around more? No, likely not—warming temperatures may preclude that, but they may well cancel each other out.

And, we might well be due for a nice, good winter with a foot and a half of snow on the ground where one warm spell doesn't kill the snow, as they seem to come once a decade or so (save for the '70s and '80s). Of course, we have snow-making now (and Wirth will probably get better at, you know, making enough snow) which helps, too. We paid dearly from 2001 to 2007—we'll explore that soon—but have done rather well this year and last, and hopefully will do better going forwards.

And stay tuned for a rough analysis, using Skinnyski.com trail reports, of conditions for every day back to 2002 (when Bruce's site started archiving).

(Oh, and take this all with a grain of salt. Despite some weather geekiness, IANAM—I am not a meteorologist.)