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Note: Back when this tutorial was originally written, the WxChallenge (formerly the National Collegiate Weather Forecasting Contest) had you forecast precip in categories, with each category specifying a range of precipitation amounts. In the present day, we forecast specific amounts. Category 0 stood for no precipitation during the period, and as you increased in category (up to Category 5), you increased in precip amounts.
Unlike Jackson, Mississippi, Rapid City is located in a mountainous part of the country. Western South Dakota features the Black Hills, home of Mount Rushmore. Rapid City is located at the eastern edge of the Black Hills. On a broader scale, Rapid City is in the upper Midwest, downstream from the Rocky Mountains. The general topographic slope is downward from west to east.
I decide to start with the current US surface map. I find that western South Dakota (the observation from RAP doesn't actually appear on this map) is near the center of a major cyclonic (counterclockwise) circulation. If the weather pattern moves east as usual, there will be a major change in the weather in store for Rapid City. Instead of the present southerlies, the wind will shift to the north or west and they will be getting a blast from the north.
Sure enough. The 4-panel surface forecast shows that during the day tomorrow (panels 2 and 3) Rapid City should be in the grip of strong northerlies and northwesterlies.
Tomorrow ought to be much colder than today. I say that not just because of the northwest winds, but also because of the thickness pattern. The colors on this map represent 1000-500 mb thickness: the total thickness of the layer of air between 1000 mb and 500 mb. Between these two (or any two) pressure surfaces, the temperature of the air is inversely proportional to the density of the air. If the layer of air is thick (tall), it's not very dense, and the mean temperature is high. If the layer of air is shallow (compacted), it is relatively dense, and the mean temperature is low. Simple rule: 1000-500 mb thickness is proportional to temperature: if the thickness is high, the temperature is high; if the thickness is low, the temperature is low.
Take another look at the 4-panel map. Notice that the thicknesses drop over Rapid City during the period. That means the airmass is getting colder. Notice too that the geostrophic wind is blowing from low thicknesses (cold temperatures) toward high thicknesses (warm temperatures). That's how the air gets colder at RAP: the cold air blows in from the northwest. This is called cold advection.
When will this major change in weather hit RAP? Look at the 4-panel maps again and decide when you think the northwest winds will begin.
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