ADAS depiction of the nocturnal inversion in complex terrain

The early morning hours of October 16, 2010 were clear with calm winds over the Southern Appalachian region, providing an ideal set up for radiative cooling. The ADAS objective analysis of temperatures revealed some interesting temperature profiles that reflected the nocturnal inversion across the complex terrain of East Tennessee and southwest North Carolina.

Topographic image of the Cumberland Plateau, Great Tennessee Valley, and southern Appalachian Mountains, with 09Z suface observations plotted.

ADAS objective analysis of temperature at 09Z October 16, 2010.

The ADAS temperature analysis  at 09Z (image above) shows surface temperatures in the Great Tennessee Valley (about 800-1200 ft MSL) mainly  in the lower 40s. In the foothills of the Great Smoky Mountains and the sheltered valleys of southwest North Carolina (about 1200-1800 ft MSL), the temperatures drop to between 34 and 40 degrees, matching very closely to observations. These lower temperatures at the base of the mountains reflect colder, more dense air sinking down the mountainsides and collecting in the elevated sheltered valleys.

As we move toward higher elevations, temperatures begin increasing sharply at around 2 kft MSL. ADAS temperatures in this warm layer are between 43 and 48 degrees. This creates the appearance of a “ring” of higher temperatures around the Great Smoky Mountains in the image above. Also note how the higher temperatures across the northern Cumberland Plateau correlate very well to the higher terrain of that area (the highest elevations in this area are below 3000 ft MSL).

As we continue above 3000 ft MSL, temperatures decrease to between 43 and 39 degrees. The difference from the ADAS valley temperatures to the higher “mountainside” temperatures is about 10 degrees. This temperature pattern can also be seen by overlaying the ADAS temperature contours with the topography image (image below).

ADAS temperature contoursat 09Z overlaid on a topography image, zoomed in on the Great Smoky Mountains and southwest North Carolina.

The RUC sounding at that same time (image below) showed a strong temperature inversion, with maximum temperatures in the warm nose of 54 degrees, and a surface temperature of 44 degrees. Temperatures in the sounding begin to drop off at about 2800 ft, very close to the same level as shown by ADAS. Though actual temperature values between the RUC and ADAS differ, the temperature difference from the surface to the warm nose is about 10 degrees – the same as show by ADAS.

09Z RUC sounding at TYS. The maximum temperature value at the nose of the inversion is 54 degrees at about 2500 ft MSL.

Some observations of minimum temperatures that morning from across the region reflected this temperature inversion:

McGee-Tyson Airport (TYS) @ 981 ft MSL – 41

Sugarland Center @ 1600 ft MSL – 36

Cades Cove @ 1900 ft MSL – 43

Newfound Gap @ 5000 ft MSL – 36

The benefits of using the ADAS temperature analysis are even more striking when we compare it to the LAPS objective analysis of temperature in the image below.

09Z LAPS objective analysis of temperature.

A Frost Advisory was also in effect on this morning, and ADAS temperature analysis helped to get a better idea of which areas may have received a frost or a freeze.

2 thoughts on “ADAS depiction of the nocturnal inversion in complex terrain

  1. Great post Doug. The highly complex terrain of New Mexico allows for nocturnal inversion development nearly every night. The strength of the inversion obviously depend on the type of air mass in place. The ADAS network could benefit us out here, in particular for fire weather applications, however the data cuts off around 100W. Unfortunately this may be an artifact of our relatively data sparse region. I completed an inversion study back in January of 2008 to provide some measure of our inversions. We found in some very shallow strong cases the lapse rate can be as strong as 63 C/km within the Rio Grande Valley.

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