A thick, Gulf-fed stream of moisture is parked over central Missouri this afternoon, and forecasters say any thunderstorm that taps into it could wring out rain in a hurry. The key number on their maps is precipitable water, a measure of how much moisture is stacked above us, and it is running unusually high for mid-June over Columbia and nearby counties.
What Precipitable Water Actually Measures
Precipitable water, often shortened to PWAT, is the depth of liquid you would get if every drop of water vapor in a column of air were condensed down to the ground. The National Weather Service notes that it represents the total water content of that column and gives forecasters a quick read on how much moisture a storm can tap. PWAT is listed in inches, which helps separate a dry atmosphere from one primed for intense, short-lived downpours.
How Forecasters Measure Moisture
Meteorologists map this vertical moisture with radiosondes, the instrument packages lofted by weather balloons that send back temperature, humidity and wind data as they climb. Those observations are plotted on Skew-T diagrams, where a saturated column jumps out: temperature and dew point lines running close together from the surface upward mean the air is loaded with moisture, and lines spreading apart signal a relatively dry column. Forecast tools and archives like the University of Wyoming upper-air archive supply the raw soundings forecasters work with in real time.
What This Means For Central Missouri Tonight
Local meteorologists report that steady, strong southwesterly winds have set up a direct pipeline pulling subtropical moisture out of the Gulf and into central Missouri. That feed has pushed PWAT into the 1.5 to more than 2 inch range this afternoon and evening, compared with typical comfortable-day values under about 0.5 inch. Any thunderstorm that taps into that juiced profile can turn into a hyper-efficient rainmaker, unloading heavy rain in minutes and boosting the odds of localized flash flooding, according to ABC 17 News.
Why High PWAT Raises Flood And Severe-Weather Risks
High PWAT alone does not guarantee rain. Storms still need a trigger and some instability to actually fire. But once a cell develops, that deep moisture gives it instant access to plenty of water, which can spike rainfall rates and the risk of flash flooding. As Weather.com explains, values above roughly 1.5 inches are considered quite moist, and readings over 2 inches are commonly tied to tropical or very humid air masses that can produce intense rain.
Safety Steps For Drivers And Neighbors
When storms can dump a lot of water in a short time, the main concern becomes sudden flooding on streets, low bridges and small creeks. The National Weather Service "Turn Around, Don't Drown" guidance reminds people not to drive into flooded roadways and to head for higher ground if flooding is observed.
Watch And Prepare
Keep an eye on local radar and forecasts this evening and plan a little extra time if your trip takes you through low spots or areas with poor drainage. For local context and more detailed commentary from area meteorologists, check out the ABC 17 News explainer and stay tuned to your county's weather alerts.
