Weather Wednesday: When the Great Lakes Freeze

Satellite image of Great Lakes February 2015. NOAA.

 

As of February 25, 2015, the Great Lakes are over 85% ice covered and the coverage is growing weekly.  glsea_curOther than the obvious impact to shipping, what does this really mean?

When the Great Lakes experience heavy ice cover as they have in the winters of 2014 and 2015 there are a multitude of impacts.  Some are beneficial and some are problematic and some are both.

For example, evaporation takes place over open water even in the winter time.  At least partially because evaporation was inhibited in the winter of 2014-15, Lake Michigan water levels last summer increased dramatically over the summer of 2013.  Some of the impacts included reduced usable recreational beach areas. On the positive side, the higher water levels mitigated some of the need to dredge channels and harbor entrances especially along the eastern shore of the lake.  As of February 25, the water level on Lake Michigan was a whopping 21-inches higher than a year earlier and was 8 inches higher than the long term average.  Snow melt and rainfall also are a factor, but the reduced evaporation plays a role. lighthouse

Snowfall amounts are also affected when the lakes freeze.  Lake Effect Snow basically shuts down once the lakes freeze over, a welcomed break for motorists in the Great Lakes snow belt areas.

Heavy ice cover also tends to influence spring and even summer weather in areas close to the lakes.  The temperatures in communities near Lake Michigan were noticeably cooler than inland communities in the spring and summer of 2014, far cooler than the usually welcomed moderating effect of the lake.  One benefit of the late spring is to fruit growers.  The cooler weather delays the blossoming of fruit trees to the extent that the threat of frost damage from isolated cold snaps is mitigated.  And the normal micro-climate of shoreline communities is more pronounced in years when the lakes are ice-covered.

Arcadia, MI. Cool summer of 2014. Author.

Long lasting ice cover also affects the water temperature of the Great Lakes.   Even the normally more moderate lakes remained quite cool for swimming and other warm weather recreation in the summer of 2014.  It is worth noting that there was still visible ice on Lake Superior into June of 2014 and some water temperatures in Lake Michigan were still in the upper-30 degree range on Memorial Day weekend!!  The reduced water temperatures impact how anglers approach their prey.  And the development of algae can also be affected.

It is likely that the ice cover of the lakes will continue to expand for at least a few more weeks this year.

Weather Wednesday: Just what the heck is going on with this winter?

first snow 2013 003The wild winter weather continues this week with snow and ice stretching all the way down into the Deep South.  Brutal wind chills have been common in many areas of the north.  Here in Champaign, we’ve had a fresh snow pack and because of that, little wind and clear skies, our overnight temperature fell to 12-below, 10 degrees below the forecast and 10-degrees below the previous record low for this date in late February.  So what’s going on?

Meteorologist Tom Skilling and his staff at WGN-TV in Chicago have been researching the topic and posted a rather extensive article, the link to which is here.

Skilling’s Facebook posts are always informative and, if you are a weather fan, you may want to like him on Facebook even if you’re not from the Chicago area.

Weather Wednesday: Freezing Rain, Ice Storms and Black Ice

precip_types
NOAA graphic

Winter weather certainly has remained in the news this post-Valentine’s Day week. It’s been another major snow event in the Northeast, heavy snow from southern Illinois and Missouri to the south into Kentucky and adjacent states and freezing rain and ice, especially in Georgia, North Carolina and other states in the southeast. Multiple highway fatalities have occurred and over 100,000 people have lost power, mostly due to ice. Bitterly cold temperatures are plunging far into the south on the date this is posted, February 18, 2015.

We’ve written about heavy snow several times and we’ll revisit the topic of how climate change may affect that snowfall, but today we’ll focus on freezing rain, ice storms and “black ice,” all of which are being experienced in parts of the south and southeast this week.

According to the National Weather Service freezing rain and sleet occur when raindrops in a layer of warm air well above the surface fall into a layer of freezing air at and near ground level. Whether the liquid ends up as freezing rain or sleet is determined by the thickness of the layer of freezing air. When that layer is thin, the raindrops don’t have time to freeze so the water freezes on contact with the surface, coating streets, sidewalks, power lines, tree limbs and whatever else is exposed and below freezing. Complicating the situation this week is bitter cold temperatures to follow the snow and ice.

A freezing rain event is escalated to an Ice Storm Warning when ice accumulations of ¼ inch or more are expected. The National Weather Service considers ice storms to be high impact events and if you’ve lived through one or more, you know that to be true. Ice storms can occur across a wide area of the United States and can be very devastating. The single most destructive weather event ever to occur here in Champaign-Urbana, Illinois was the Valentine’s Day ice storm of 1990. The 25th anniversary of the event passed largely unobserved last weekend. Seemingly no one wants to relive that week.

The storm began during a home basketball game at the University of Illinois and ice quickly accumulated. The lights in the Assembly Hall flickered, but stayed on. I was the public address announcer that night and I vividly recall being handed a series of announcements to be read if the main power went off. The final announcement I did read was that game attendees should expect that many traffic signals would be out of commission across town after the game. When I left the Hall I could see the flashes and hear the explosions as electrical transformers failed.

I drove the few blocks to the radio station where I worked at the time. It was operating on generator power. We started to cover the event and things just got worse during the overnight. At one point around 2:00AM I decided to go check on my family and home. I followed a snowplow down a main street as it pushed trees and branches out of the road so emergency vehicles could get through. I turned down my street as limbs were falling behind me and decided to just keep going back to work before the street was completely blocked. Some areas of town were without power for a week. Damage to utility infrastructure, trees, traffic signs and signals and buildings and homes reached into the millions of dollars not counting the loss of productivity and dumpster loads of ruined refrigerated and frozen food.

I relate that account not because it was unusual, but rather because it is typical of major ice events. They can be extremely destructive and expensive.

Finally today I want to mention “black ice.”

Black Ice accident

Black ice can be every bit as dangerous as a heavy snow or ice storm. It is a very thin layer of ice that is nearly transparent. It frequently forms on bridges and overpasses because that pavement temperature may be colder as the cold air circulates above and below the pavement. Black ice often occurs when snow melts during the day and then the water refreezes at night. Or the temperature drops below freezing after a rainy day. Unlike during an ice storm, black ice is a much greater threat to pedestrians and vehicles than to structures. Multi-vehicle accidents are common when the pavement refreezes and emergency rooms are kept busy treating pedestrians who slip and fall.

Ice storm threats include: