Updraft: December 16, 2008 Archive

Always something

Posted at 7:32 AM on December 16, 2008 by Craig Edwards

Just when you thought it was safe to take to the highways, along comes the dreaded black ice, known for its transparency, You see black pavement and believe it to be good to go, when suddenly there is a thin layer of clear ice. YIKES!

Here's the definition I found on Wikipedia.

Black ice, also known as "glare ice" or "clear ice," typically refers to a thin coating of glazed ice on a surface, often a roadway. While not truly black, it is transparent, allowing the usually-black asphalt/macadam roadway to be seen through it, hence the term. It is unusually slick compared to other forms of roadway ice.

Because it contains relatively little entrapped air in the form of bubbles, black ice is transparent and thus very difficult to see (as compared to snow, frozen slush). In addition, it often is interleaved with wet road, which is identical in appearance. For this reason it is especially hazardous when driving or walking because it is both hard to see and unexpectedly slick.

Bridges and overpasses can be especially dangerous. Black ice forms first on bridges and overpasses because air can circulate both above and below the surface of the elevated roadway, causing the pavement temperature to drop more rapidly. This is often indicated with "Bridge May Be Icy" warning signs.

Black ice may form even when the ambient temperature is several degrees above the NTP freezing point of water 32°F (0°C) if the air warms suddenly after a prolonged cold spell that leaves the surface of the roadway well below the freezing point temperature.

The term black ice is sometimes used to describe any type of ice that forms on roadways, even when standing water on roads turns to ice as the temperature falls below freezing. However, this use of the term black ice is not included in the American Meteorological Society Glossary of Meteorology.

CE
naturesmessenger.com

MINNESOTA'S REPUTATION FOR COLD IS ALREADY SOLIDIFIED THIS MONTH!

Posted at 2:07 PM on December 16, 2008 by Mark Seeley (3 Comments)

One measure of the degree of cold we have been experiencing this month is a relative comparison of low temperature reports from the 48 contiguous states. Over the period from December 1-16, Minnesota has reported the lowest temperature on ten days. That's a very large fraction from all national reports. Here are the nation's lowest temperatures (outside of Alaska) that have come from Minnesota so far this month.....

December 2nd -7 degrees F at Embarrass
December 3rd 3 degrees F at Grand Marais
December 6th -5 degrees F at Embarrass
December 7th -23 degrees F at Embarrass
December 8th -23 degrees F at Embarrass
December 10th -18 degrees F at Orr
December 11th -16 degrees F at Embarrass
December 12th -32 degrees F at Embarrass
December 13th -32 degrees F at Embarrass
December 16th -35 degrees F at Longville and Babbitt

The readings of -35 degrees F this morning are not far below the all-time state record for December 16th which is -39 degrees F at Pokegama Dam way back in 1903.

Embarrass has clearly had a very cold month so far, and they are on track to record their 2nd coldest December in history there. But several other Minnesota communities have already been -30 degrees F or colder this month. In addition to Embarrass and Longville, Babbitt, Orr, Eveleth, Cook, and Hibbing have all been below -30 degrees F.

You can track morning low temperatures from nearly any climate station by using the commercial web site known as Anything Weather.

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Life in a snow globe

Posted at 3:56 PM on December 16, 2008 by Paul Huttner

Snow slows traffic at 494 & 169 in the southwest metro today

Here we go again. Another slow slippery commute in the metro.

The jet stream is sending snow impulses our way every 48 hours or so these days. It's starting to add up to a pile in many areas. Snow cover is impressive around much of the Midwest for mid-December. There is snow on the ground all the way south into New Mexico and Arkansas.

Current snow cover in North America

Our latest shot this evening will bring 1" to 3" to the metro. Mankato, Owatonna and the I-90 corridor may see 2" to 4" with this system.

Twin Cities radar loop

We are keeping an eye on another system for Thursday that could bring heavy snow to southern Minnesota, Iowa, and Wisconsin.

Stay tuned, and enjoy the view out the window!

PH