Learning Corner

Ms. Katherine Raz has written with some fascinating weather questions. All of you who want to know more about the mysterious and exciting world of contemporary American weather, read on.

1.) What's going on with the tidal wave in New Orleans? I heard something small about it on the news. Seems pretty freaky - you'd think they'd cover it more. Does that wave have to do with tectonic shift, or is it hurricaine-related?

In a kick-ass exciting world there would be a huge tidal wave heading right towards our favorite southern metropolis caused by a massive tectonic shift and intensified by a force 5 hurricane, and we would be getting cool enhanced infrared images of the Gulf of Mexico and then news footage of a 200 foot high breaking wave towering over suburban bungalows with people running around and screaming in the foreground. But given that we just live in a sucky moderately interesting world, here is what is going on:

There is no tidal wave, just a storm surge. A storm surge is exactly what it sounds like: a big surge of water caused by a hurricane or tropical storm that pushes the water away from itself. The National Weather Service is expecting a pretty big surge to hit the coast today, and given the fact that most of New Orleans is below sea level and that it is heavily populated one can expect quite a bit of damage. At the worst they are predicting flooding up to two stories high in houses near the coast. Because this isn't as exciting as a tidal wave, and it is generally what people expect in hurricane prone areas, we don't hear too much about it.

Here is a nice little graphic that the NY Times put together.

2.) Can you explain "lake effect" snow? I'm from Grand Rapids, Mich., which got a lot of lake effect. Does Chicago get it? How does the lake effect snowfall in Chicago, and how does that differ from a place like GR or Buffalo, New York, for instance?

Lake effect snow is the result of cold dry winter air flowing over the warmer, wetter air above a lake. Other conditions (those necessary for any precipitation) have to be satisfied for actual snowfall to occur, but cold winds and lakes provide most of what is needed. Precipitation is a complicated thing, but basically to get any you want warmer wetter air to be lifted over dryer colder air, and the warm wet air will cool down as it rises and condensation will occur and that condensation will get heavy and fall and then you have yourself some precipitation. So when cold air blows across the lake and the conditions are right for that lake air to be lifted over and in front of the cold air then snow is created on the leeward side of the lake.

Because the prevailing winds in these parts are from west to east, places on the eastern sides of the Great Lakes get the most lake effect snow. Occasionally if the winds shift or if we are on the northern part of a cyclonic storm system we will get lake effect snow here in Chicago. A little more snowfall falls here than on those podunks west of us, but we don't get nearly as much as our friends in Michigan or Buffalo.

Katherine, I hope this 'clears up' your 'foggy' weather notions.

Please folks! Don't remain in the dark about the weather that affects your life.
Write in to the Chicago Weather Learning Corner and watch the skies clear!

Love,
Adrienne