Why Did(n’t) My Power Go Out Last Sunday?

The Big Storm that hit the Manchester Area was a multi-state affair.

We had a long, severe thunderstorm last Sunday.  It hit most of the lower peninsula.  At it’s largest it stretched from Arkansas here to Michigan.

(View an animation of the storm here: http://wxug.us/1a4us)

Clearly, from the animation above, you see a large storm covering most of the state.  But we all know that the results were not the same throughout the state.  The western part of the state had a far higher percentage of power outages than the eastern part of the state.  In Washtenaw County, for example, Chelsea had more widespread outages than Manchester, even though they are only separated by a few miles.

Here in Manchester there were areas of several square blocks inside the Village that lost power.  There were outages three blocks to the east of my own house and outages to the south too.  But my house, luckily, never lost power.

So, why do storms do that?  From the radar you can see orange and yellow and red covering large parts of the state, yet the damage varied from block to block, neighborhood to neighborhood.  Why?

The answer is that the storms we had last Sunday are very hard to predict.  And they are harder to predict the smaller the area you choose.

Thunderstorms and tornadoes are fickle.  We can know hours in advance that either of these things can happen in, say, a whole county or large metropolitan area.  But all we really know is that that area is only MORE LIKELY to have thunderstorms or tornadoes.

Lots of small variables can cause a storm to hit a certain area, or cause a regular thunderstorm to spit out a tornado.  Passing over a lake or a large parking lot can cause a significant change in the path and nature of a thunderstorm by changing the temperature, humidity, or wind.  All of these little variables make precise, street-by-street forecasting impossible.  Even with powerful radar and supercomputers to map out all the data, we still can’t say where on a map the wind will be the worst, or where the tornadoes will touch down. So when you look on the map, and there is a uniform line of red and yellow, remember, local conditions vary, and a cool forest or a hot factory roof can change wind speeds considerably.

Weather is an inexact science.  In physics, a person can tell me precisely where a planet will be in the sky decades from now.  And it will be there.  Weather can’t do that.  There’s too much going on and we understand too little of it.

The next time the sky darkens or sirens go off, remember this: Even good weather forecasts are about probability, not certainty.  A good weather forecast can tell you that it’s slightly or very likely to rain.  It can tell you within a dozen miles where it’s more likely to rain.  But we still can’t say whose block will get it the worst, or which side of the street will lose power.

Be kind to the weatherman.  He doesn’t always know either.

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by News News