As the Spring gets closer, the first month of the year has not been particularly calm regarding weather activity. On one hand we have had considerable storm activity all across the state of Georgia, and on the other hand we have reached temperatures as low as 15°F, which is not usual. Last weekend, from Jan. 26th to Jan. 28, Atlanta residents received multiple warnings for severe weather activity and flooding. However, it turned out not to be that severe, receiving rain mostly on Saturday Jan. 27, 2024. By looking back at different meteorological data, we can obtain more about what was happening in the southeast region.
One of the most common types of satellite images is the infrared (IR) image and they are helpful to identify storm activity based on their ability to measure differences in temperature. Figure 1 shows an animation of the IR images from Jan. 27 01:00 UTC to Jan. 28 05:00 UTC. The color scale is associated with different temperatures; the red colors correspond to colder temperatures and the blue colors to warmer temperatures. Since the temperature decreases with height, colder clouds are an indication of clouds at higher altitudes, which are typically associated with stronger convection and storm activity. We can observe how the storm system originates in the Gulf of Mexico and extends northeast, with strong activity in Luisiana that later moves up to Georgia and the East coast.
Figure 1. Series of IR Longwave Window images from Jan. 27 01:00 UTC to Jan. 28 05:00 UTC, showcasing the development of the storm system and its transition over Georgia. Yellow tones indicate colder temperatures, whereas blue and gray tones indicate warmer temperatures Source: RAMMB-CIRA of NOAA/NESDIS.
Radar imaging is another useful tool to obtain valuable weather data. In contrast with satellite, radar sensors are located on the Earth’s surface, and they are particularly useful to obtain more information about precipitation, storm severity, and even cloud speeds. Figure 2 and Figure 3 show two types of radar images, corresponding to composite reflectivity and quantitative precipitation estimation (QPE), respectively. Figure 2 is helpful to determine the storm intensity and track its process over time. Radars work by sending a signal to the environment and reading how much of the energy is reflected back at them (the name for this quantity is reflectivity). Clouds reflect more or less signal depending on how dense they are, which is also related to storm activity. Therefore, higher reflectivity values are correlated with more intense activity. In the animation, we can observe how the storm activity had more intense storms in the western coast of Florida and then advanced northeast, reaching Virginia and Pennsylvania. It can be noted how there is clear cyclonic activity by the end of Jan. 27, in the region North of Tennessee, part of the same storm system. Regarding precipitation, radars have the capability of integrating measurements over one-hour periods, resulting in estimation of precipitation rates, as it is shown in Figure 3. The darker blue regions show the locations that received more rain, coinciding with the reflectivity and IR imaging information. As mentioned, southern Georgia received more precipitation.
Figure 2. Composite reflectivity radar imagery from Jan. 27 09:00 UTC to Jan. 28 02:00 UTC. Source: Multi-Radar Multi-Sensor, NSSL-NOA. Yellow tones indicate the highest reflectivity values, whereas blue and gray tones indicate small reflectivity values.
Figure 3. Q3 Radar Quantitative Precipitation Estimation (QPE) radar imagery from Jan. 27 09:00 UTC to Jan. 28 02:00 UTC. Stronger blue shades indicate precipitation rates in the order of 0.2 – 0.4 in/hr, and the lightest blue shades 0.01 in/hr. Source: Multi-Radar Multi-Sensor, NSSL-NOA.
As its name indicates, surface weather maps give valuable information about what is happening at the surface level, something that can is challenging to obtain from satellite and radar images. Figure depicts two surface weather maps corresponding to before and after the storm system moved over Georgia. Here we can see how the cold front advanced to the East, extending from the Gulf of Mexico to the coast of North Carolina, coinciding with the cloud formation seen in satellite and radar images. Multiple low-pressure points are also observed before the storm system developed over Georgia, indicating strong points of convection activity that contributed to the heavy storm development that occurred later.
The combination of multiple weather imagery products allows us to obtain a clearer understanding of weather phenomena that we experience on a daily basis, and also to predict future events.
Figure 4. Surface weather maps measured before the storm system passed over Georgia (top image) and after the storm passed (bottom image). Source: WPC-NOAA.