So, we have all probably noticed that it has been cold lately. Well, due to the ample snow cover over much of the U.S. at this time, the baroclinic zone is sharpening over the lower Mississippi and Ohio River Valleys this afternoon with the aid of shortwave energy coming out of a cutoff low located over the Southwest U.S. One of the Ocean Prediction Center forecasters, Tim Collins, noted the strong contrast in temperature on either side of this zone in the RGB Air Mass image from MODIS below.
Note the orange and purplish coloring to the north (above) of the moisture plume (cirrus, etc). This delineates the colder, drier air advancing south and east, while to the south (below) of the clouds there is a greenish coloring that denotes warmer mid-tropospheric air associated with a ridge of high pressure aloft over the Gulf of Mexico and Southwest Atlantic.
For contrast, the above image is the ~6.7 um water vapor channel from MODIS. Notice that north of the moisture plume you can see evidence of the lower tropopause and cold air by the relative smoothing noted in the image (lighter blue coloring due to the enhancement). To the south of the moisture plume, you can see the dry air at ~400-500 mb associated with the ridge over the Gulf of Mexico.
This baroclinic zone will continue to sharpen overnight and produce a significant snowstorm for many in the central and eastern US into tomorrow.
Thanks for reading!