Think this winter’s been bad in the South? Well imagine over 100 inches of snow… every year! Places like the Great Lakes see it, routinely. You know when you hear about those Christmas or New Year’s reports of 35 inches of snow snarling holiday travel in places like Buffalo, New York? Well, typically that’s caused by a phenomenon known as lake-effect snow. Lake-effect snow is caused by an unstable atmosphere (similar to the atmosphere during a thunderstorm.) In the case of thunderstorms, you have an atmosphere with lots of humidity, warm ground, and a cool upper atmosphere. Lake-effect snow is caused by cold, arctic air rushing in on cold winds out of the northwest over the relatively warmer (and of course, moist) Great Lakes waters. Now, of course, you need “water” to get lake-effect snow going. If there’s ice covering the lake, the water vapor needed for lake-effect snow is not available and the lake basically “shuts down” for the production of lake-effect snow.
The Great Lakes, as you may know, are very big: hundreds of miles long, tens of miles wide, and hundreds of feet deep, so it’s not likely they’ll all entirely freeze over for any significant amount of time, although it is, on rare occasion, possible that they’ll mostly freeze over, like during the very cold winters of 1976-1977, 1977-1978, and 1978-1979. Most years, though, most locales on the lakes don’t get a break and get inundated with lake snow all winter long.
In several areas, though: far western New York, northwestern Pennsylvania, and northern Ohio, folks do get a break! During the coldest months of the winter; it’s typical during many winters, the shallowest of all the lakes, Lake Erie, will nearly entirely freeze over and this nearly closes down the heavy snow machine along its shoreline.
In the latest February image of Lake Erie taken via satellite above, you can see there’s lots of white over the lake. That’s actually a sheet of ice. The darker black area, in fact, is the area of the lake that has been left uncovered and unfrozen. By far, there’s more ice than water. Therefore, it’s tough to get much more than lake-effect flurries going. Earlier in the season, though, before it really gets cold, it’s a totally different story.
In the satellite photo above, you can see just a month ago, before the long duration of cold… the lake is wide open with plenty of water and water vapor to work with! This is the season where we see the blizzards along the lake shore.
On a side note, take a look at the imagery again and focus on the upper right. That’s Lake Ontario. It’s over 10 times deeper than Lake Erie. You can see, between both photos, there’s not much change in the amount of white on the lake. Lake Ontario, since its much deeper and contains a larger volume of water, has a much harder time cooling off and, therefore, has a much harder time freezing. In places like Rochester and Watertown, New York, there’s nary a respite from the lake snow onslaught.
Click on the image above twice for a high resolution picture.
Calling it one of the largest storms since the 1950s, NASA turned its cameras toward the Midwestern States Tuesday to capture a winter storm stretching across 30 states. Chicago and Oklahoma City were two of the hardest hit cities. Chicago came to a standstill with its 3rd highest snowfall on record, 20. 2″ of snow fell during the blizzard. Blizzard warnings are issued when winds are expected to reach 35 miles per hour. That is one of the reasons this storm was so dangerous. The other reason was ice on the roadways. Warmer air in the upper atmosphere can support other types of wintry precipitation, such as sleet or freezing rain. Freezing rain is rain that freezes on contact with the surface or roadways.
If you want more information on sleet versus freezing rain, read my previous blog entry on wintry precipitation.
A lot of excitement here in New Orleans, Louisiana, as sleet began falling shortly before noon in our viewing area. The mighty Midwest storm yesterday was a rain and wind event for us, with a line of heavy thunderstorms crossing before the arctic cold front blasted us with freezing temperatures overnight.
It’s snowing again in Texas! Snow showers have been falling all day in the Lone Star State. Dallas, Texas has very few accumulations (snow on the ground), but hill country areas such as Waco have 3 inches of snow on the ground.
The National Weather Service has issued Winter Storm Warnings for Texas, California, New York and other parts of the Northeast.
Two weather patterns are colliding over the United States this winter to produce storm after storm for the southern Gulf Coast and the Northeast. The El Nino Southern Oscillation is a weather pattern that causes a warming of the Pacific Ocean off the coast of Central America. This winter, El Nino is being credited with the surge of moisture and added rainfall/snow events in California, Arizona, New Mexico, Texas, and the Gulf Coast. At the same time El Nino is occurring, scientists are also examining the effects of a Negative Arctic Oscillation. The NAO is associated with cold winters across the Northern Hemisphere, as more cold air descends from the Arctic to the nearby continents of North America, Europe and Asia.
The above graphic is data taken from the entire month of December 2009. What this graphic shows is average temperatures across Asia, Europe and North America have been substantially cooler than normal, whereas temperatures in the Arctic, Africa and parts of the Mid-East have been warmer.
Take a look at the large dip of cold air across Minnesota, Iowa and the Dakotas. Once again, folks in Minneapolis will be waking up to below freezing temperatures. Look at the forecast lows across Louisiana… below freezing. If you add the extra moisture coming in from the Pacific due to El Nino and the cold air due to the Arctic Oscillation, you have the perfect recipe for snow.
TV forecasters in Shreveport and New Orleans, Louisiana are reporting once again on the unusual snowfall events. In the Northeast, where snow has caused massive transportation problems, another round this week is expected.
See my previous post on lake effect snow.
Expect heavy rain along the Gulf Coast this Friday into Saturday.
Click for the latest weather warnings across the US.
A large and potent storm begins its march across the US this week.
Parts of southeast Utah, southwest Colorado, Arizona and New Mexico are under blizzard warning this Monday as a large winter storm envelopes the Southwestern United States. This large and potent storm system could dump up to 3′ of snow in resort areas such as Crested Butte, Colorado.
Click for the latest satellite image.
These warnings will continue through Tuesday until the storm system begins to move East, dumping heavy rain and snow in parts of Arkansas, Missouri and Tennessee before landing in the Northeast. By the time the storm system makes it to D.C., South Jersey, and New York it will most likely be a heavy rainmaker.
The computer model image above shows where precipitation may fall Friday night into Saturday morning. I drew in the “snow line”, snow is forecast to fall in areas above the line. In this model, it is not forecast to snow as far south as New Orleans. However, these models update every few hours, and temperature changes in the storm itself Friday night may cause snow to fall and possibly accumulate. Watch the previous TV link for the latest forecast in Southeast Louisiana.
Snow is forecast across the Southern States in the next several days as a Gulf low develops. It’s very difficult to forecast snow, for several reasons. You need freezing temperatures in all levels of the atmosphere for snow to occur. (It can be above freezing at the surface, but the snow may not stick.) You also need ample moisture in all levels of the atmosphere. And, third, you need a lifting mechanism, in the form of low pressure, for air to rise and continually cool.
In New Orleans, where snowfall rarely sticks, there’s a slight chance for a rare early snow event. If it did snow in New Orleans, it would beat last years record event, which was the earliest snowfall in the city’s recorded history. Click here for the latest TV forecast in New Orleans.
Currently, winter storm watches are in effect North and West of Southeast Lousiana, where 1-3 inches of snow accummulations are expected, beginning late Friday evening.
This storm system will then track through the Mid-Atlantic region and then out to sea.