The featured chart presents a climatology of water vapor mixing ratio for Des Moines. This value is an expression of humidity, just like dew point and relative humidity is, but has a nice property of being on a linear scale so two values are easily comparable. For example, the difference between a 50 and 60 degree dew point is much different than the difference between 60 and 70 degrees. Anyway, this past weekend's surge in humidity shows up in the bottom graph as a large departure from climatology. The drought period during this year shows up as well during July and August with most of the departures drier than average. Very dry air is expected to arrive this weekend allowing for very chilly temperatures and highs well below freezing expected on Saturday!

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Tags:   mixingratio