Figure 1: Photo by WSBTV News Staff, “Heavy rain causes wrecks, rescues across parts of metro Atlanta”. Image accessed through WSBTV website: https://www.wsbtv.com
The torrential downpour across Georgia impeded on Super Bowl Sunday and into Monday afternoon. This multi-day rain storm occurred for numerous reasons, first being the significant moisture being supplied by the Gulf. The loop below is from the GOES-16 satellite, this is a satellite that stays positioned over the Western Hemisphere to provide imagery for meteorologists and weather enthusiasts. This specific loop is on the infrared channel that detects water vapor in the upper atmosphere, where the cooler colors indicate high levels of moisture aloft. This loop cycles from February 10th at 7:00 am to February 12th at 2:00 pm so that it records the times with the most significant precipitation in regards to this case. In this loop, the majority of the water vapor begins over central Texas and it begins to quickly migrate east but notably slows down as it approaches the east coast. The moist conditions in combination with the stationary nature of this event lead to hazardous flash flooding across central and north Georgia
Figure 2: Upper-level 6.2 micron Visible satellite loop from the GOES-16 visible imager from 1200 UTC February 10, 2024 (7:00 am EST) to 1900 UTC February 12, 2024 (2:00 pm EST). Imagery loop downloaded from Colorado States satellite imagery website: https://rammb-slider.cira.colostate.edu/?sat=goes-16
The slowing down of the atmospheric moisture alludes to the next atmospheric condition that made this seemingly inconsequential amount of precipitation such a hazard for Georgia residents. The image below depicts a surface analysis recorded on February 12th at 1:00 pm. A surface analysis is useful in determining frontal patterns and viewing current weather conditions that are close to the surface. The solid lines represent isobars which are measurements of pressure at the surface. The red and blue patterned lines are stationary fronts, a stationary front is the boundary between a cool and warm air mass that is not moving significantly. This frontal boundary is important pertaining to the showers this weekend because the precipitation was able to gather over the state of Georgia and provide continuous rainfall for almost three days. If this frontal boundary had been a cold front, it would have moved much more quickly through the state and given the infrastructure in place a chance to drain all of the excess precipitation. This slow-moving front working jointly with the considerable amount of moisture in the atmosphere created a continuous downpour that led to flash flooding across the state.
Figure 3: Surface Analysis of the Southeast United States at 1800 UTC (1 pm EST) on February 12, 2024. Image accessed through the WPC Severe Weather Archive Page: https://www.wpc.ncep.noaa.gov/html/sfc-zoom.php
These two factors operated in tandem to produce a havoc-wreaking weather system. Below is a radar base reflectivity map. This type of meteorological product is helpful in determining the strength and location of rainfall. Radar works by emitting electromagnetic radiation in all directions from the radar site, the radiation waves deflect off of objects in the atmosphere. When the radar receives the deflected radiation it is able to determine the amount of energy returned and thus the type and intensity of precipitation in the atmosphere. The warmer yellow and orange colors depict stronger precipitation while cooler greens and blues signify weaker precipitation. This specific image shows rainfall covering almost all of Georgia at 1:00 pm on February 12th, a significant portion of this rainfall being moderate. The precipitation seems to halt abruptly where the stationary front was indicated in Figure 3, this is not abnormal as stationary fronts generate upward vertical motion on their western sides. The upward vertical motion causes divergence aloft which can lead to cloud formation, thus creating a likelihood of rain at the surface if there is enough moisture in the atmosphere.
Figure 4: Base reflectivity radar imagery from 1800 UTC February 12, 2024 (1:00 pm EST). Image accessed through NOAA NCEI Radar Mosaic: https://www.ncei.noaa.gov/maps/radar/
These key atmospheric conditions led to days of rainfall across the Southeastern United States and cost hundreds of thousands of dollars in damages. Although separately, these conditions may be unassuming, together they generate intense amounts of precipitation and work synchronously to generate rain at the surface. Fortunately, the only damages encountered were those to houses, cars, and other property. No one was harmed in a flash flooding event which is certainly in part to the forecasters that issued flood watches and warnings throughout the Southeast United States.