Rainy Weather in the Mid-State and a Glance at New Rainfall Estimation Technology

The end of June and the first week of July was a rainy period in Middle Tennessee. Many areas saw rain virtually
every day. Lawns were green and lush, and creeks and streams received new infusions of water on a routine basis.
Most of the Mid-State picked up between 2 and 4 inches, and some sections received average rainfall amounts of
4 to 6 inches. A few spots were deluged by between 6 and 6 1/2 inches of rain.

Some of the greatest 7-day rain amounts included:

Elmwood (Smith Co)  . . . . . . . . . . . . . . .  6.40 inches
Portland (Sumner Co.). . . . . . . . . . . . . .   6.01    "
Carthage (Smith Co.) . . . . . . . . . . . . . .    5.61    "
Winchester (Franklin Co.). . . . . . . . . . . .  5.56    "
Celina (Clay Co.). . . . . . . . . . . . . . . . . .   5.45    "
Big Sandy (Benton Co.). . . . . . . . . . . . .   5.29    "
Cookeville (Putman Co.). . . . . . . . . . . . .  5.28    "
Livingston (Overton Co.). . . . . . . . . . . . .   5.12    "
Clarkrange (Fentress Co.). . . . . . . . . . . .  5.12    "
Rockvale (Rutherford Co.). . . . . . . . . . . .  5.12    "
Shelbyville (Bedford Co.). . . . . . . . . . . . . 4.98    "
 
There were four sections of the Mid-State that saw the heaviest rainfall, with each showing average amounts
between 4 and 6 inches:

Area 1:  In the northwest, including parts of Stewart, Houston and Humphreys
            Counties.

Area 2:  In the southeast, including parts of Bedford, Coffee, Cannon and Rutherford
            Counties.

Area 3:  In the northeast, including parts of Macon, Trousdale, Putnam, Jackson,
            Overton, Fentress, Clay and Pickett Counties.

Area 4:  In the north-central, in the Portland area.

One of the newest rainfall-estimation software packages used by the National Weather
Service was created to utilize data from multiple radars and hydrologic sensors to
produce detailed color graphics. This software is part of a broader computer system that
combines data streams not only from radars, but also from satellites, surface observations,
lightning reports, rain gauges and numerical weather prediction models. This computer
system is known as "Multiple Radar/Multiple Sensor"--or, MRMS, for short. It was created
by the National Severe Storms Laboratory, in cooperation with the Cooperative
Institute for Mesoscale Meteorological Studies (CIMMS) and the University of Oklahoma.

The rainfall estimates provided by MRMS can aid in forecasting flash floods, as
well as coastal and inland flooding associated with tropical storms and hurricanes.
In addition, the data output can help forecasters analyze the potential impacts of developing
snow, hail and tornado events.

So, how can we gauge the accuracy of computer-generated rainfall estimates? One way is
to compare a map of estimated values to one that shows the observed values.

In the image below, you will find two maps--one showing the observed 7-day rainfall
in Middle Tennessee for the period extending from 7 am, June 30th to 7 am July 7th
(on the left), and the other showing MRMS-estimated rainfall for the same time period
(on the right).



As you can see from these two images, the map of computer-estimated rainfall (on the right) clearly shows the same
4 "bulls-eye" areas mentioned earlier (as revealed by the image on the left). Even though there is a certain amount of point-to-point
variation between the two maps, the general solutions are strikingly similar. The colors on the two maps differ a bit simply because
a different color scale was used to produce each map. In addition, the image resolution of the estimated rainfall is likely superior
to the observed data, at least in part, due to a limited rainfall observation network.