Late Season Snowfall in Minnesota

photo by Nic McPhee via Flickr
photo by Nic McPhee via Flickr

A week ago today, the landscape in southern Minnesota was snowless. Our lawn was bare – covered only with brown grass (which I convinced myself was most definitely turning green by the hour) and the desiccated leaves of last autumn. I imagined myself getting to work in the garden, planting hardy seeds of kale and spinach. I threw the kids’ snowsuits down the stairs to wash and dry them to put in storage for next fall. As retribution for such thoughts and actions, we received 3.6 inches of snow on Sunday night and more is coming down even as I type. After nearly 30 years here, you’d think I would know better. In Minnesota, you must keep your dreams of spring in check until at least April, possibly May.

In the Twin Cities, the average snowfall for March is 10.2 inches, beating out all months besides December and January. In March of 1951, the Twin Cities received a whopping 40 inches of snow. (Tangent: They shoveled this by hand. No ‘snowblowing’. Although snow throwing machines were invented as early as the 1880s for clearing train tracks, the domestic use ‘walk behind’ machines were only just coming on the market in the early 1950s.) Calling March ‘spring’ here might be tempting fate. March is a month of extreme variability in Minnesota with a record high of 88°F and a record low of -50°F. That’s a 138 degree spread!

I’ve been reading meteorologist Mark Seeley’s informative Minnesota Weather Almanac this week. In this book, Seeley details Minnesota’s worst and most remarkable winter storms. I was surprised how many of them occurred in March. My surprise is probably due to my annual (and naive) belief that winter is over in March – a belief which is perpetually crushed. Do I learn? Of course not, I’m an optimist; we never do.

A few notable late season snow storms:

March 19-20, 1826: Like 1951, March of 1826 brought about 40 inches of snow, including 18 inches on these two days causing snowdrifts of 6 to 15 feet. This snowfall was followed by a further 8 inches in early April. Subsequently, a blast of cold air (4°F on April 10th) arrived further delaying the breakup of ice on the rivers. This sequence of events led to massive flooding carrying away low lying buildings at Fort Snelling and Fort Crawford as well as Chief Little Crow’s village at the site of modern day South Saint Paul. The river ultimately crested at 20 feet above low water.

April 5, 1933: A heavy snowfall struck the north shore, dumping 28 inches of snow in Cook County, a still standing record for 24 hour snowfall in April.

March 15-16, 1941: A blizzard hits western Minnesota. 85 mph winds were reported at Grand Forks and 75 mph winds were reported at Fargo-Moorhead. The wind chill bottomed out at -35°F. Although snowfall from this storm was light, a number of people died from exposure due to the extreme winds and temperatures. Before this storm, Minnesota only had observational weather services, but upset over the lack of warning and the resulting fatalities resulted in forecasting services being added by the National Weather Services.

May 2-3. 1954: Yes, you read that correctly, MAY. A huge storm moves across northern Minnesota. Dropping as much as 10-12 inches of snow across much of the northern half of the state. I would be pissed.

March 14-15, 2002: A storm of mixed precipitation, thunder, and lightning, brought 10-21 inches of snow.

March and April snowfalls aren’t the outliers I’d like the believe they are. They are, in fact, the norm. And while they are often minor interludes between luxuriously (to Minnesotans) sunny days in the mid-40s, they can also be severe, even dangerous. Huge winter storms can even arrive in May (as they did in 1954), but it’s uncommon.

Well, at least we have June, July, and August, because it sometimes snows in September too.

Advertisements

Why isn’t the Solstice the Coldest Day of the Year?

cold as ice by matthias klaiber via flickr
cold as ice by matthias klaiber via flickr

After I wrote about the winter solstice back in December, I got to wondering why the solstice isn’t typically the coldest day of the year. Since we get our heat from the sun and on the winter solstice we receive the fewest hours of sunlight, why does the coldest day on average occur almost a month later (at least here in Minnesota – this map shows average coldest day across the US.)? On January 21st, we receive almost forty more minutes of sunlight then we do on December 21st, so why is January 21st on average the colder of the two days?

The answer is actually quite straight forward. It takes awhile to warm up! Technically, this phenomenon is known as the lag of the seasons. There are a few forces at work. First, the oceans and ground absorb heat from the sun. They are still hanging onto (and releasing) some of the heat they gathered up over the hot summer months into December. As we move past the solstice, deeper into winter, the amount of residual heat has decreased, so even though we are getting more sunlight, the temperatures still continue to drop.

One apt analogy is a tea kettle on a stove top. When you place the tea kettle on the stove and light the burner, it takes awhile for the water to absorb the heat. The water won’t be hottest thirty seconds after you turn in on, even if you’ve turned the burner all the way up; it takes some time for the water to warm up. Inversely, if after you have heated the water all the way up (this would be July or August on Earth) and then you turn the burner down to low, the water won’t be immediately cool. It will take some time (until January) to cool down to the minimum temperature.

Since the ocean is efficient at retaining heat, this is why some places along the ocean experience less seasonal change than one might expect given their latitudes. For example, London (51 degrees N) is farther North than Minneapolis (44 degrees N), but the average temperature of London in the winter is much warmer than in land-locked Minneapolis. Additionally, the average monthly temperatures in Minneapolis vary by 61.7F, while in London monthly temperatures vary by only 24.3F. The North Atlantic Current brings warm water up to London from the Gulf of Mexico. This water retains much of its warmth during its long Tranatlantic voyage into northerly latitudes, thus keeping temperatures in London much warmer than one would expect given the city’s latitude.

Another factor that slows down warming in the winter is snow cover. When the solar heat emitted by the sun is retained by the Earth, it leads to greater warming. However, abundant snow cover reflects the solar heat back into space, so that we don’t feel its full warming effects. This is like wearing a white t-shirt on a hot day in an attempt to stay cool. So, in the months with the most snow cover (December – February), solar heat retention is reduced.

This year in Minneapolis, we may already have our coldest day behind us. We had a stretch of several sub-zero days at the beginning of January, with a low of -11F on January 5th. Now, we are in the midst of a warming trend. We enjoyed a balmy 37F, sunny day today and we broke out the sleds and skis. It can’t last though, February will bring more cold weather, but hopefully we’ve seen the bottom and are on a (slow) path toward spring weather.

The Moon Halo

Upon stepping outside this evening, I was greeted by an unexpected sight: a gibbous moon surrounded by a large ring of light. This phenomenon is referred to as a ‘moon halo’. The appearance of a moon halo is purely an optical effect. Moon halos may appear on nights when there are very high thin clouds (cirrus clouds) around 20,000 feet. These clouds are filled with tiny ice crystals. The ice crystals act like prisms refracting and reflecting the light, thereby creating the appearance of a halo around the moon.

There is a folkloric belief that a moon halo is a sign of an impending storm. This actually turns out to be mostly true. While cirrus clouds do not bring rain or snow themselves, they are often the forerunners of the low pressure systems that do bring precipitation. Another belief is that the number of stars within the halo indicates the number of days until the bad weather arrives, though this one doesn’t seem to hold much water, as you might imagine.

The moon halo was an unanticipated and beautiful sight. It is easy to get so involved in our days and busy lives that we miss these little gifts that are all about us if we just take the time to look around (or above in this case). Looking up at the shining halo around the moon tonight, I felt very fortunate to be there to see it and to have the time to stand out in the cold evening with my little son just gazing upward.

I took some bad pictures on my phone that I won’t make you suffer by posting. Fortunately, there are a number of better photos of moon rings available from Wikimedia Commons:

By Radoslaw Ziomber (Own work) [CC-BY-SA-3.0], via Wikimedia Commons
By Radoslaw Ziomber (Own work) [CC-BY-SA-3.0], via Wikimedia Commons
If you’d like to see some very impressive photos of both lunar and solar halos, visit:

http://earthsky.org/space/what-makes-a-halo-around-the-moon

When have you witnessed unexpected moments of beauty in nature?