An extremely complex weather system brought a unique double snowfall event to Central Alabama on February 11th and again on February 12-13th, 2014. The setup began as an Arctic cold front moved across the area on Monday, February 10th. The cold front brought temperatures from the 60s (previous weekend) down to near or just above freezing by Tuesday morning. As moisture from the Gulf of Mexico moved northward to coincide with the colder temperatures during the morning hours on Tuesday, most of Central Alabama experienced a cold rain, while areas along and just south of Hwy 278 saw a changeover to sleet and snow. Interestingly, a heavy band of snow formed right along Hwy 278, where several inches of snow fell across Marion and Winston Counties in the northwest and northern Blount, Etowah, and Cherokee in the northeast. The moisture from the first event quickly exited to the east into northern Georgia by the mid morning hours on Tuesday.
Meanwhile, a strong high pressure system was settling across Pennsylvania and New Jersey, which is a perfect setup for cold air damming along the East Coast and Southeast U.S. Cold air damming occurs when colder New England air settles and is essentially trapped in between the Smokey Mountains and the warmer waters of the Atlantic Ocean and Gulf of Mexico. This allows colder air to settle near the surface, while the air aloft oftentimes remains above freezing (think of cold dense air being heavy and settling close to the surface). Once again, on the heels of the Tuesday early morning storm system, another much stronger system was developing across the Southeastern CONUS. For the most part, at least early on, temperatures had warmed to just above freezing, and much of Central Alabama experienced just a cold rain. However, as the cold air damming strengthened Wednesday morning, many of the eastern counties went from a cold rain to an ice storm. Around a quarter-inch of ice or slightly less was seen from Cherokee County, southward into Cleburne, Randolph, Chambers, and Clay Counties. Cheaha State Park experienced the most ice, around one half inch, which knocked out power and brought down thousands of trees throughout the park. This system also led to the epic ice storm that impacted much of the East Coast.
This stronger second system wasn't quite done yet, as the upper level portion of the storm was still gaining strength across the Northern Gulf Coast. A strong deformation zone and TROWAL (Trough of Warm Air Aloft) set up over the northern half of Alabama. A TROWAL is formed by a maturing upper level storm system that pumps significant mid-level moisture around the northern side of the low center, while complex dynamic cooling takes place to quickly lower temperatures below freezing. From west to east (as seen on the snow map below), heavy bands of snow fell across most of the region north of Interstate 20. As the system progressed northeastward, it continued to gain strength. As a result, a heavy snowband setup across the northern half of Jefferson and Blount Counties, which led to locally maximized totals. Again, this is a very rare setup across the area where several non-unique weather events came together in just the right way to cause a prolonged winter weather event, thus creating a very difficult forecast.