Temperatures in some locations this morning in eastern Iowa are hovering around freezing, but the rest of the state looks to miss out thanks to a slight southerly breeze and higher dew points. The featured chart presents a composite of air temperature and dewpoint for the 96 hours around the final sub 32F temperature measured at the Des Moines Airport. The plot perhaps indicates the importance of having low dew points for the period up until the cold temperature. The dry air helps the atmosphere to cool off efficiently, allowing temperatures to drop in the early morning hours (-6 to 0 hour). The moisture increase thereafter is probably showing the effect of having a high pressure system pass to the east and southerly flow returning.

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Tags:   freeze