UMD Buoys

An update on lake temperatures, in an unusually cold year: the western portion of the lake has finally reached the "magic" 39F threshold beyond which the lake can start forming a warm surface layer- this is as late as this has occurred- almost a month later than average- in the last 42 years! Right now, the western arm is about 25F cooler than it was this time last year. The other two Lake Superior sites are still colder.

Following up on the last post- it turns out that a very useful measure of whether the lake is having a cold or warm year is to determine the date on which the lake surface temperature reaches 4C, or about 39F (when this happens depends on where you are in the lake- shallow water reaches this date earlier than deep water). This is the date when the lake can start to form a warm upper layer- sort of the beginning of "summer" for the lake. Comparing the last 41 years shows that there is a noisy but significant trend towards earlier onset of summer- about 3 days earlier every decade, which is a consequence of warmer winters. The red dot is UMDBuoy's estimate for this year- we're still a week or two away! Note 2014- the polar vortex winter, had a late onset, and 2012 (after a very warm winter) had very early onset. Last winter was fairly chilly, so this year's onset is relatively late.

Brr- it's been chilly in Duluth the last few days, as wind is blowing off the lake. It's worth keeping in mind that the surface water temperature at our offshore site (~50mi S of Grand Marais) is still about 38F. In this season, when the water temperature is below about 39F, water in the deep areas of the lake can take ~20 days to warm 1F! Once the surface reaches 39F, a shallow surface layer can form and warm much more quickly.

I was going to do a post about the incredible heat last Monday- when I do posts like that, I usually show daily average temperatures. It turns out that the daily average temperature last Monday wasn't terribly out of line- high, but not in any record breaking sense. However, what was unusual was the range of temperature- the Harbor air temp rocketed from 48F to 94F in just a few hours- the third-largest daily range in the last 20 years! The greatest was on January 29, 2008, when it dropped from 38F to -14F over the course of a single day. Brr!

Our data streams are finally set up! You can access our buoy data at d.umn.edu/buoys, and get tweets every other hour from one of our coastal buoys at twitter.com/UMDbuoys !

The R/V Blue Heron heads off to do some early season work through the ice pack, following the tug Helen. Stay warm!
Photo credit: Michael Jacob.

Here's a great example of an unusual phenomenon called finger rafting. Long, artificial looking features form when two very thin plates of ice interact. This image was taken by a drone about 150m above the lake surface. The long, straight features in the center of the image are naturally occurring. Weird! Thanks to Craig Hill for drone support.

We wrapped up our surface meteorology program for the year yesterday! we recovered two surface meteorology buoys, two small subsurface moorings in place to fine-tune our surface wave estimations, and deployed an over-winter (under-ice) mooring to continue to expand our large collection of winter data. We'll head back out in the spring to recover it!

How unusual was this weekend's warm weather? Pretty unusual! This is a graph of daily-averaged air temperature from the Duluth Harbor. The grey area is the observed range (2004-2020) the blue is the average daily temperature over that range, and red is this year. The weekend air temperatures were warmer than anything we've seen in the ENTIRE month of September! In fact, daily average temperature has run significantly above average for most of the year. The one real exception to this all year was the early February cold snap, which set records of its own.