Sometime when it rains the event lasts longer and the rain comes down heavier than our typical afternoon thunderstorm routine. This was the case through the deep south this weekend. When there is a “tropical connection” to a rain event, extreme or record rainfall often occurs. This happened back in September 2009 during the Atlanta Flood and what occurred this past weekend northwest of Jacksonville over parts of Tennessee, including Memphis.
This image shows a satellite‐derived precipitable water (PWAT) picture. It is better than using a water vapor image to track moisture transport because it can see moisture in the low levels of the sky. High pressure off the east coast has tapped tropical moisture from the eastern Pacific as well as the western Caribbean.
You can see from the image how PWAT values are nearly double normal levels and have resulted in a focus of moisture from the Gulf Coast northward into the Ohio Valley. This “efficient” rainfall resulted in very heavy rainfall over a fairly short period of time.
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