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.

February 8, 2011 Lake Erie Ice Cover, Image: NOAA

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.

January 11, 2011 Lake Erie Ice Cover, Image: NOAA

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.

To check out the forecast in places affected by the lake  freeze-over lull, take a look at Cleveland and Buffalo.

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.

February 2011 Blizzard, courtesy: NASA

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.

Gulf of Mexico Visible Satellite, courtesy: NOAA

Gulf of Mexico Infrared Satellite, courtesy: NOAA

Take a look at these two satellite images from the National Weather Service. The top image shows the visible satellite imagery of the Gulf of Mexico. You can also see the southern outline of Texas, Louisiana, Mississippi, Alabama and Florida in the image. I’m showing you both the visible (or daylight) satellite imagery and the infrared satellite because once the sun goes down, the visible image will be dark. Anyway, what I’m trying to show you is the stream of moisture headed toward Texas and Louisiana. See the bright yellow bands on the infrared imagery? That is cloud cover streaming over the Gulf of Mexico into the southern states. A southern stream of moisture like this usually tells us we’ll have cloudy skies and light rain across the area. It’s not a really unstable atmosphere, so we don’t expect a lot of fireworks with thunderstorms, etc.

What this image is not showing you is how cold it is at the surface. The winter storms that passed through the Midwest  left us with temperatures in the 30s today. Because it was so cold in the lower levels of the atmsphere, this warm and moist southerly flow of precipitation froze once it fell close tothe surface.

Granted, once it landed, it melted, because the air temperature was still above freezing. For snow to occur, you have to have freezing temperatures from the surface to the higher levels of the atmosphere. That’s why it’s tough for southern state to get snow. The tropics and the Gulf of Mexico like to send wam and tropical air masses in our direction. What’s fascinating about the weather pattern we have set up for the next 48-hours, though, is that it will give us a chance for wintry precipitation in the form of sleet or freezing rain because of the warm and tropical air mass.

Because so much warm air is overriding the arctic air mass near the surface, ice crystals that form high in the atmosphere will melt on their way down through the warm, tropical layer, and then freeze again close to the surface. Sleet is a form of precipitation known as ice pellets. It’s actually raindrops that freeze again before hitting the ground. Freezing rain or  black ice, is rain that freezes once it hits the ground.

Once more thing before I let you go.  Some of you may wonder why it will snow in Houston, but not in New Orleans or Mobile? Well, that has to do with the upper levels of the atmosphere. Texas is getting in on some colder air not just at the surface but through all levels of the atmosphere above it.

For the latest weather in your hometown, click on the link to your local TV station.

-Dawn Brown, FOX 8, New Orleans

Texas Snowfall Totals, Image: NOAA

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.

US Watches and Warnings, Image: NOAA

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.

Arctic Oscillation, Image: NOAA

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.

Forecasted Lows, Image: NOAA

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.

-Dawn Brown

Lake Effect Snow Event, Image: NOAA

The National Weather Service is predicting heavy snow from Upstate New York to Ohio as a cold artic airmass continues to descend across the country.

See my previous post on lake effect snow.

A quiet weather pattern will remain in place across portions of the Central Plains and Mid-Atlantic region until Saturday.

Expect heavy rain along the Gulf Coast this Friday into Saturday.

Along the West Coast, another storm system will be a rain event for the Bay Area and Los Angeles, a snow event for the Sierra.

-Dawn Brown

National Weather Warnings, Image: NOAA (Image is OLD!)

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.

National Satellite Map, Image: NOAA (Image is OLD!)

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.

-Dawn Brown

Friday - Saturday Snow Forecast, Image: NOAA

Friday – Saturday Snow Forecast, Image:  NOAA

Dallas TV forecasters are reporting freezing conditions overnight after a snow storm left more than an inch of the white stuff on the ground in the Big-D.

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.

-Dawn Brown