The low temperature this morning in Alamosa in south central Colorado ("Hub of the San Luis Valley" and "Gateway to the Great Sand Dunes") dropped down to at least -2 F, which is the first sub-zero temperature there since last winter. The forecast for Wednesday's low temperature is in the same neighborhood, so let's forecast Tmin and see if it gets below 0 F again.
Question of the Day: Of our more than 800 non-Alaskan contest sites, Alamosa has the lowest forecasted Tmin for Wednesday, lower than sites much farther north such as International Falls, MN. And the coldest air in the southern plains is to the east of Colorado. So why would Alamosa be the coldest?
The night was calm and clear, so perfect conditions for nocturnal cooling, and the actual Tmin was 4 F, in the middle of the range of MOS forecasts (-2 to +8 F).
Answer: Alamosa's elevation is about 7500 feet above sea level, almost the highest of all of the contest sites, and high elevation sites are generally colder. Also, despite the high elevation, Alamosa is in a valley, so cold air draining down into the valley from the surrounding mountains at night will often drop the temperature even further. The result is that Alamosa is sometimes listed as the coldest city in the conterminous U.S., based on the number of nights below 32 F or the number of nights below 0 F.
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