We interrupt this program to bring you important weather information...

Quite some weather we've had these past couple days. First, nice 70 degree weather, then thunderstorms, hail, and tornadoes, then cool rain, now cold snow. Hmmm.... if it had stopped before the snow I would have been a lot happier.

So what in the world is going on?

Well, since you asked...
*everyone starts slinking away*

Here we have a current surface map of the US. The circles with tails sticking out of them are weather reports from individual stations. The tails point in the direction from which the wind is blowing, and the circle is filled based on how much cloud cover there is at the station. So, it looks like we have a nice, friendly mid-latitude cyclone meandering across the midwest, bringing rain, hail, drizzle, snow, thunderstorms, and tornadoes to everything in its way!
















You can see the mid-latitude cyclone on this next map which shows isobars - lines that connect places of constant pressure. The big L (representing an area of low pressure) is the mid-latitude cyclone. Air travels from areas of high pressure to areas of low pressure, so you would expect to see a lot of air converging on the center of the low pressure area. Because of the rotation of the Earth, however, in the northern hemisphere, the air tends to spiral towards the center of the low in a counterclockwise direction. You can see that on the previous map.

This is just a radar map showing precipitation. As you can see, the precipitation reflects the counter-clockwise spiral of the air around the low pressure.
















In this satellite image, you can see the clouds also reflecting the counter-clockwise spiral around the low pressure system.

This detailed weather map shows the low pressure center currently dousing Denver. The heavy blue line is a cold front; the red line is a warm front, but what I really want to talk about is the purple line. This is what is called an occluded front. Occluded fronts happen when the fast-moving cold front catches up to the slower-moving warm front. When this happens, the air between the two fronts is forced upward, and when air rises, it cools, becomes saturated, and usually dumps all of its moisture. Thus, the rain we're getting. The cold front shown is what gave us thunderstorms and tornadoes yesterday; it looks like a particularly agressive and severe cold front. You can see some of the effects of it in the south if you look back at the first weather map.

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This is an enhanced infared satellite image. That is, it shows the clouds, but also includes information about the temperature of the clouds. This can be helpful because it can give you clues as to the height of the cloud tops because the higher the cloud tops, the colder they are. The blue sections on the map show where the clouds are the coldest, and thus, the highest. This helps to explain why maybe the eastern plains got such big hail yesterday. The taller the clouds in a thunderstorm, the more distance the hailstones have to fall before reaching the ground. As they fall, they run into lots of water droplets in the cloud and grow larger and larger. Also, if the thunderstorm has very powerful updrafts, the hailstones can be carried back up to the top of the cloud and grow even more. Golf-ball sized hail? That's why.

This is what is called a meteogram. It shows the weather for the past 25 hours. The first graph shows the temperature and dew point (the temperature at which air becomes saturated and its moisture condenses).What is especially interesting to note is how the temperature (the top line) rises until it drops off suddenly. If you look right under the graph, you can see some funny symbols. The symbol right under the drop in temperature is the symbol for thunderstorms. According to this map, it looks like the cold front came through around 3 pm yesterday when the thunderstorms and tornadoes happened, and there was a corresponding drop in pressure (the bottom graph) which often signals the passage of a front. Also, you can see that the temperatures have steadily decreased, which is another indication that the front was a cold front. The numbers directly above the wind symbols are showing wind speed (in knots) of gusts. It is interesting to note that there were a lot of gusts right around the time of the thunderstorm. Usually, there will be a sudden shift in wind dirction with the passage of a front, but the wind directions are all over the place in the graph, so it's hard to discern any general shift in direction. After the wind has stabilized a little, though (towards the right of the graph), we can see that the wind has shifted slightly counterclockwise which indicates that perhaps the low pressure center is moving slightly to the south. (?) That's just a guess, though. The graph second to the bottom shows cloud ceiling and cover which I'm really not quite sure how to read. :) Back up with the weather symbols, we can see to the right that we've had two-dot and three-dot rain which indicates continuous rain. You can see an explanation of the weather symbols at this link: http://www.srh.noaa.gov/jetstream//synoptic/sfc_plot_symbols.htm#ww

This is just a close-up surface map of the midwest area. You can see the wind moving in the counterclockwise spiral. I wish I had gotten this map off the website last night because last night, the cold front was very obvious. There was a definite line where the wind basically turned all the way around. No wonder we had such sever weather! It's not quite so obvious now, but you can still kind of see it over eastern Texas where the wind coming from the Gulf of Mexico is blowing in the opposite direction from the wind over western Texas. The cold front is where the wind changes direction.

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This map is an upper-air data map. This information is recorded by balloons and satellites at the heights in the atmosphere where the air pressure is 250 millibars. On this map as well, the tails coming off the dots point in the direction from which the wind is blowing. The more lines are on the tail, the stronger the wind is. This 250 mb upper-air map is useful because it shows the jet stream which moves around during the year. The areas shaded blue are the core of the jet stream, the places where the winds are the highest. Knowing where the jet stream is and what it's doing is important because often, mid-latitude cyclones follow the jet stream. Right now, it looks like the jet stream is kind of all over the place and doesn't really follow any strong path. Especially around Colorado where our current low pressure system decided to call home, the upper-level winds are all over the place, so it looks like our friendly, neighborhood mid-latitude cyclone is around to stay for a while. Yep, the weather stays rainy at least over the weekend according to the forcast. So, just relax and enjoy it, and try not to think about the snow that's coming down and stacking rather quickly. Or about all the flowers that are going to be frosted. Or about all the fruit trees that were just getting ready to bloom.

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If this lecture fascinated you (I can tell you all were engrossed), you can find all these great maps on these sites: http://www.srh.noaa.gov/ffc/?n=mapslast

http://weather.unisys.com/index.html

But if you'd rather back away slowly, oh well. I tried.

I'm afraid that mine is soon to join the ranks of boring blogs crowding the great expanse of blogger.

By the way, when do you think Google's going to start buying car brands? I can just see it-introducing the new Toyota Google... comes in four bright colors with the speed and precision that has characterized our search engine for years... more powerful engine than ever...