IEM Daily Feature
Thursday, 25 May 2023

May Precipitable Water + Rain

Posted: 25 May 2023 05:20 AM

The NWS office near Omaha launches a weather balloon at 7 AM and 7 PM each day to sample the troposphere for weather variables like temperature, humidity, pressure, and wind speed. This vertical profile can be evaluated for the amount of water vapor present and is expressed as a liquid water depth called precipitable water. Rewording, if you condensed all the water vapor in a column of air, what depth of water would that equate to. This metric is very useful for a number of weather forecasting needs as it can ballpark potential rainfall rates. The featured chart compares the 7 PM sounding for May precipitable water against the following twelve hours of accumulated precipitation for Omaha. The dots represent the combination of those two and the line is an estimate of the percentage of days with precipitation. The chart nicely shows the usefulness of this metric for precipitation forecasting. It is very difficult for a dry (low precipitable water) atmosphere to produce precipitation and higher precipitable water amounts allow for larger precipitation totals. The red dots show the 2023 values.

Good = 11
Bad = 0

Tags:   precipitablewater   sounding