Updraft: July 6, 2009 Archive

Fireworks likely caused weekend pollution spike

Posted at 8:32 AM on July 6, 2009 by Paul Huttner (0 Comments)

Twin Cities Air Quality Index shows a dramatic spike in particulate matter over the 4th of July weekend.

Did you notice the smell of fireworks overnight Saturday night into Sunday morning? Many metro residents did. The smoke was so thick at the Weather Lab late Saturday night we had to close the windows.

Air pollution monitors in the Twin Cities detected a dramatic increase in fine particulate matter Sunday as light winds and stagnant air allowed pollutants to accumulate. The only reasonable explanation for the increase is smoke from fireworks displays on the 4th of July.

The boost in the MPCA's Air Quality Index (AQI) numbers Sunday was significant. From June 27th through July 2nd The Twin Cities enjoyed good air quality with AQI readings in the 30s and 40s.Then on July 3rd AQI readings rose to 51. They rose again to 81 on the 4th, followed by a spike to 124 on the 5th before improving to readings back into the 50s today.

Since vehicle emissions generally drop on the weekend, the only logical explanation for the pollution spike is municipal and home fireworks displays. Weather conditions featured light winds and stagnant air. Observations from Twin Cites Airport showed that many hours featured light winds less than 5 mph or calm air over the past 72 hours.

The good news is our air quality should continue to improve this week. The first in a series of bands of showers and thunderstorms is moving into the metro this morning. We can expect some "rain washed" air as the week goes on. The moisture will also be a welcome sight for many farmers and for the garden here at the Weather Lab.

PH

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Boundary Waters blowdown: Storm of the century?

Posted at 3:30 PM on July 6, 2009 by Paul Huttner (2 Comments)

Track of the July 4th, 1999 Derecheo across northern Minnesota. (Image courtesy Duluth NWS)

Ten years ago this week hurricane force winds devastated parts of the Boundary Waters. Today, that storm lives on as one of the biggest, baddest derecheos ever recorded on the planet. It figures the weather factory in the Upper Midwest would give birth to such a historic storm.

Stephanie Hemphill's piece last week paints a great picture of what things are like in the blowdown areas today near Ely. Meteorologists are still scratching our heads and studying the storm a decade later as well.

It started out as a cluster of thunderstorms near the Black Hills moving northeast. As the storm crossed North Dakota during the overnight hours, it morphed into something much more menacing and dangerous. Around 7 am west of Fargo, it exploded into what we meteorologists call a derecheo.

Derecheos are severe long lived damaging wind storms that can run for hundreds of miles.

Meteorologically speaking, derecheos are defined by three things.

-A path length of at least 250 miles.
-At least 3 reports of hurricane force (74 mph) winds separated by at least 40 miles.
-No more than 3 hours between damaging wind events.

There have been other accounts of so called "trans-continental derecheos" in the past. Some have travelled over 1,000 miles. This one travelled 6,000 miles. That may be the longest recorded path length for a derecheo.

The BWCAW Derecheo may hold another record. It is believed to be the first derecheo ever recorded to have spent over 24 hours over open ocean before returning to land to continue its damaging wind path.

The BWCAW Derecheo's path was amazing. It began in North Dakota then raced through Minnesota at speeds of approaching 100mph near Ely. It tracked into Canada and reentered the U.S., slamming New York and New England. Then it curved southeastward and eventually southwestward in the open Atlantic Ocean around the periphery of a large high pressure system. It re-entered the U.S. in South Carolina causing wind damage there before tracking southwest through the Gulf Coast States into the Gulf of Mexico.

The initial reports from the storm indicated damage in the BWCAW. It took a while to realize how widespread the damage was. It took years to realize how unique and monstrous this storm was on a bigger meteorological scale. We can thank weather satellite and researchers who study storms like this. It is because of them that we have a better understanding of these storms today.

PH

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