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Meteorology (Weather)/Pattern of Storms over U,S

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I have been wondering for months now what is causing the repeating pattern of storm activity that moves west to east and spans almost the entire country. To give you an idea, on the radar it is a long band that moves west to east and will stretch from the top of the country down into the south (sometimes not all the way down). They are the major snow storms that we had over and over. Almost every other week it would be like the radar was on replay. Just last night ( April 19 2013) another one ended its roll through the country. I am not sure how common this is, but I can't recall something being so repetitive other than perhaps hurricane season, but even then they don't seem as repetitive as these strings of storms. I watch the weather every morning and have never heard them mention this, but its obvious to me. I havent found anything on the web, I would think that they would be sharing why this keeps happening or if it is normal for them to mention something like "here comes another country wide storm". Sorry for rambling, I'm just SUPER SUPER curious about this, and why no one mentions it!

Answer
Hi Violet,

For storms to form, you need three things:
1. Moisture
2. Instability
3. Lift

For the sake of this answer, I'm only going to talk about lift. This time of year, you'll usually see storm systems move down the West Coast and then eastward across the country. Ahead of the system is where you (typically) have the lift, but not always. We tend to refer to a storm system as deep if it sags south quite a bit. When the system is deep, you have a long band of rising motion to the east of the system and if the moisture and instability are sufficient, then thunderstorms begin to develop and eventually, they begin to form a solid line of storms.

I hope this helps!
David

Meteorology (Weather)

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David Moran

Expertise

I can answer questions about radar and large scale meteorology. If a question looks like homework, I won't answer it.

Experience

I have been a forecaster for many years with a specialty in severe weather.

Organizations
Full Member, American Meteorological Society

Education/Credentials
BS in Meteorology, University of Oklahoma BA in Mathematics, University of Oklahoma

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