Tropical Cyclone Herman has upgraded to Tropical Storm status and currently sits in the Eastern Indian Ocean, approximately 1600 km from the coast of Western Australia. It has been measured to produce gusts up to 55 mph. As of yet, the storm poses no threat to human populations and is not forecast to make landfall. However, its outer rainbands could bring heavy precipitation to Indonesian islands Sumatra and Java.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (above) include an overlay of GLM Flash Extent Density — and showed the distinct circulation of a middle-tropospheric closed low (400 hPa analysis) as it moved northeastward across Illinois and Indiana into southern Lower Michigan on 25 March 2023. Isolated clusters of brief lightning activity were seen across the region, but there were no reports of thundersnow. A number of locations in Iowa, Illinois and Wisconsin received heavy snowfall, with several new daily records being set.

The corresponding 1-minue GOES-16 “Clean” Infrared Window (10.3 µm) images below helped to highlight areas of mesoscale banding where precipitation rates were enhanced (some sites reported snowfall rates of 1 to 2 inches per hour).

Later in the day, as clouds cleared along the back edge of the storm system, much of the southwest-to-northeast swath of fresh snow cover was revealed in GOES-16 Day Snow-Fog RGB images (darker shades of red) and Day Cloud Phase Distinction RGB images (brighter shades of green).

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Microwave estimates of snowfall rate (SFR) are available at this website, and imagery during the day on the 25th are shown below. The heavy band of snow is apparent early in the morning of 25 March; by afternoon, it has shifted eastward to hug the Lake Michigan shoreline in Wisconsin.

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Severe thunderstorms traveled across the Southeast United States on Friday 2023-03-24. In Mississippi, at least 25 people were killed by tornado outbreak. Notable damage was experienced in Rolling Fork and Silver City, MS. The governor issued a state of emergency on Saturday, the following day.

NOAA’s Storm Prediction Center (SPC) issued a total of 32 tornado reports for the area on 2023-03-24. The Weather Forecast Office in Jackson, Mississippi warns of continued severe weather for the remainder of this week, through 2023-03-31.

RealEarth allows users to layer weather data products over one another, allowing you to view multiple weather products for a specific event. Here, we look at NEXRAD Radar Reflectivity with ProbSevere. ProbSevere is a product developed at UW – Madison CIMSS and aims to assist forecasters in determining areas that may experience severe weather, such as tornadoes. ProbSevere uses a combination of satellite data, ground-based data, and numerical weather models. It can be thought of as a probability of severe weather. Note the area of severity over Rolling Fork, MS at the 1:00 UTC timestamp in the animation below. A bright magenta outline surrounds the Rolling Fork area. This corresponds to when a tornado was spotted from the ground, around 8:00pm local time.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) images (above) include plots of time-matched (+/- 3 minutes) SPC Storm Reports during an outbreak of deadly tornadoes across parts of Mississippi, Alabama and Tennessee late in the day on 24 March 2023. The coldest thunderstorm tops exhibited infrared brightness temperatures around -70ºC (darker black enhancement).

A closer view of 1-minute GOES-16 Infrared images — with and without an overlay of GLM Flash Extent Density (above) — showed the supercell thunderstorm which produced a fatal EF4-rated long track tornado across far western Mississippi (with devastating effects in the cities of Rolling Fork and Silver City) from 0047-0208 UTC. The default infrared image enhancement was modified — setting the coldest end of the brightness temperature range at -92ºC — to help highlight the pulsing overshooting tops prior to and during the life cycle of this tornado-producing thunderstorm. The GLM Flash Extent Density also revealed a notable lightning jump (denoted by clusters of brighter white pixels) just prior to the development of the tornado. Lightning jumps frequently coincide with an increase in thunderstorm updraft intensity and/or updraft volume, preceding the onset of severe weather.

As the lightning jump was beginning, a toggle between GOES-16 GLM Flash Extent Density (FED) and Minimum Flash Area (MFA) at 0049 UTC (below) showed a maximum FED (bright white pixels) coincident with a minimum MFA (yellow pixels) along the Missouri/Mississippi border — the increasing number of lightning flashes within a smaller area was an indicator of the increasing potential of that thunderstorm producing severe weather.

A 2-panel animation of FED and MFA is shown below.

In a comparison of 1-minute GOES-16 Infrared images with the corresponding Cloud Top Temperature (CTT) derived product (below), the coldest CTT was -75ºC over the Louisiana/Mississippi border at 0047 UTC (the coldest 10.3 µm infrared brightness temperature during that time period was -73ºC).

According to a plot of Jackson, Mississippi rawinsonde data at 0000 UTC on 25 March (source), the coldest -75ºC Cloud Top Temperature value closely corresponded to an altitude near that of the calculated Most Unstable (MU) Maximum Parcel Level (MPL), which was 14 km (below).  

GOES-16 Total Precipitable Water, Lifted Index and Convective Available Potential Energy (CAPE) derived products (below) displayed a corridor of moisture and instability that extended north-northeastward across the Mississippi Valley ahead of an approaching cold front — which helped to create a favorable environment for the development of severe thunderstorms.

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