On Monday morning, the low temperature for Waterloo was -16 while just a few miles east at Oelwein it was 8 degrees warmer at -8. The featured chart looks at differences in morning low temperature between the two sites over the course of a year (top plot) and against the average wind speed at Waterloo. The difference in temperature is due to micro climate effects are that are much more common during low wind conditions. Near surface winds help to mix the lower atmosphere and keep temperatures more evenly distributed. When winds relax, local effects happen and rapid cooling may occur at night time. The lower plot clearly shows the difference are most noticeable at low wind speeds. As wind speed increases, the average difference in low temperature approaches zero. This creates a forecasting issue when local weather stations can have large differences in low temperature as compared with their nearby neighbors.

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Tags:   lows