Earlier in the week, I interviewed Keith Stellman for a forthcoming episode of the Weather Geeks podcast, which I host for the Weather Channel. Stellman is the Meteorologist-in-Charge for the National Weather Service – Atlanta office. As we bantered about the inner workings of a National Weather Service office, I recall him saying that it was going to be a busy week. He was mostly referring to the severe weather threat facing Georgia on Thursday, but the weekend also brought a credible snowstorm for that part of the country. What was up with the Georgia’s rollercoaster weather week?
Snow in metropolitan Atlanta area culminates a week of wild weather mood swings.
To the public, the weather this week in Georgia probably seemed like a bad case of “weather mood swings,” but from a meteorological perspective, they are oddly related. A Tweet on February 5th by the National Weather Service – Atlanta noted, “The risk for strong to severe thunderstorms increases tonight across west GA and pushes east through the day Thursday.” These storms were associated with the passage of a strong cold front and produced several severe storm and tornado warnings throughout the state. Many students were literally standing at bus stops as tornado warnings buzzed phones throughout the metropolitan Atlanta area on Thursday.
As if the severe weather threat was not enough, the National Weather Service office was also concerned about the flooding potential associated with the same storm system. They tweeted, “Widespread rainfall totals of 2-4 inches with locally higher amounts up to 6 inches will likely cause flooding issues.” The basic weather set-up was detailed in the February 5th weather discussion issued by the National Weather Service below:
Active forecast period on tap as rather high amplitude upper trough approaches the area from the west allowing for ample Gulf moisture transport and a developing surface frontal system set to bring rounds of heavy rainfall and increase thunderstorm chances mainly this evening through Thursday.
A cold front
The cold air nudging relatively warm, moist air is the “calling card” of a cold front. Thunderstorms (graphic above) are typically associated with strong cold fronts because the cold air behind the front is denser than the warmer air being lifted. As I monitored the situation Thursday morning, strong supercell thunderstorms were moving into Georgia ahead of the squall-line associated with the approaching front. After the round of storms and flooding, the cold air behind the front became the story. It allowed for a few lingering snow flurries on Friday morning, but Saturday morning would be Georgia’s real taste of a winter wonderland.
Surface map on February 7th, 2020
A little ripple in the atmosphere called a “short wave” moved through the Southeast and generated enough lift in the atmosphere to produce a decent little snowstorm for Georgia. With temperatures hovering just near or above 32 degrees F, the morning snowfall featured very large snowflakes. The size and shape of snowflakes are determined by the temperature of the atmosphere. MLive Chief Meteorologist Mark Torregrossa has a nice discussion below:
At temperatures near freezing, the individual flakes are small and called needles. As the temperature goes down to between -10 degrees celsius and -18 degrees celsius, the classic pretty snowflakes called dendrites form. As it continues to get colder, plates are formed. Plates are very thin and take a long time to stack up for accumulations. Finally, at real cold temperatures below -30 celsius, columnar snowflakes form. Those flakes can fall all day and only amount to an inch.
Throughout Georgia, pictures were posted on social media of houses, decks, and kids playing in snow. However, the fun gave way to danger as several accidents were reported in Georgia and other parts of the Southeast. The snowfall was enough to warrant Winter Storm Warnings and Winter Weather Advisories throughout North Georgia and the metropolitan Atlanta area. Unfortunately the region is not out of danger as temperatures in affected areas are expected to drop below freezing Saturday night. This could lead to the dangerous “black ice,” which is all too familiar to Southerners.
If you are wondering how “normal” or “rare” it is to get snow in Georgia in February, The Weather Atlas website has your answer. According to the site, Atlanta, Georgia averages 2.1 snowfall days and about 2.9 inches of snowfall per year. January is typically the snowiest month in Atlanta. February typically averages 0.6 snowfall days and slightly under 0.5 inches of accumulated snowfall. While people in much of Atlanta and southern metropolitan counties were left to experience the snow through Facebook or Instagram posts of others, northern suburbs and the mountains of Georgia received anywhere from 1 to 5 inches of snowfall.
By the way, kudos to the National Weather Service meteorologists who sniffed this out Friday and pretty much nailed the timing.
Winter storm and advisory warnings in Georgia on Saturday February 8th, 2020
NWS Atlanta Source