Updraft: October 23, 2009 Archive

Odd Climate Pattern in 2009 Continues

Posted at 10:48 AM on October 23, 2009 by Mark Seeley (1 Comments)

The oddity of our 2009 climate pattern across Minnesota is evident when we examine the historical rankings of temperature and precipitation quantities over the past several months.

First off, the summer months, June through August, were quite cool, ranking as the 7th coolest summer on a statewide basis, and the coolest since that of 2004. Dry weather was a dominant climate signature of this summer as well. On a statewide basis it ranked 23rd driest, with many eastern counties designated to be in severe or extreme drought at times.

The summer was followed by the 6th warmest month of September in state history, and the warmest since that of 1998. This proved to be an advantage for Minnesota crops, as most were allowed to mature before a hard freeze came.

The unusually warm September has been followed by a rare wet and cold October. So far this month ranks as the 5th coldest October in history on a statewide basis, with a low of 11 degrees F reported at Brimson. In addition it is the 9th wettest October in history with some areas reporting over 7 inches of precipitation so far.

What will November bring? A reversal or a continuation......let's hope for a reversal in our weather pattern and an Indian Summer.

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Giant snowflakes fall in the Twin Cities

Posted at 3:35 PM on October 23, 2009 by Paul Huttner

Extreme close up of a stellar dendrite. All photos by Dr. Kenneth Libbrecht at Cal Tech.

Remember the old Dave Letterman joke about hail the size of canned hams?

Well it wasn't that extreme, but there were some pretty big snowflakes at times today in the Twin Cities. Here at the Huttner Weather Lab I observed snow "clumps" about two inches in diameter falling to earth. MPR staffer Chris Worthington reports large snowflakes also fell in downtown St. Paul today. Atmoshperic conditions were just right in the Twin Cities for big flakes today.

Stellar plate

Giant snowflakes as big as dinner plates have been reported in weather lore. The most credible observations from reliable observers of unusually large snowflakes report a diameter between 2 and 6 inches. William Pike, who is an observer in the British Royal Meteorological service, witnessed 2 to 3 inch diameter flakes in Vancouver, British Columbia. He documented 11 credible reports of giant snowflakes in the Journal of Meteorology in January of 1988. There is a great article in The New York Times about his observations.

Hollow column

The average snowflake is made up of one or many individual snow crystals. According to snowflake guru Dr. Ken Libbrecht at Cal Tech, the biggest snow crystals in nature are about the size of a pea. Ken is a North Dakota native who has made a career out of his fascination with snowflakes. His work has even been featured on USPS stamps. You can see his amazing images of snow crystals at snowcrystals.com.

Capped column

It turns out it takes just the right atmospheric conditions to produce big snowflake clusters. The best conditions occur when temperatures in the lowest mile of the atmosphere are just near or above freezing, and winds are relatively light. It may also help to have a slight updraft higher up.

Here's how it works. Normal snow crystals form several thousand feet up. Light updrafts keep them aloft, where they bump into each other and stick together. As they grow, smaller crystals continue to stick to them and they get bigger. Then the weight of the cluster overcomes the updraft and they begin to fall to earth.

The bigger flakes are now falling faster than the tiny snow crystals. As they fall through the slower moving snow crystals they gain mass as the crystals stick, growing even bigger. If the winds are light enough the giant flimsy puffballs can reach the ground intact.

It's amazing what nature can do under just the right conditions.

PH