Freezing Rain: The NUCAPS Perspective
A major winter storm was brewing over most of the eastern continental United States over the weekend of 24-25 January 2026. At one point during the weekend, 185 million people were under some kind of National Weather Service-issued winter weather alert, with warnings for winter storms, ice storms, extreme cold, and others. A quick look at the map of NWS active warnings for the night of Saturday 24 Jan shows just how extensive this winter storm was:
One of the most challenging winter weather phenomena to address is freezing rain, which can cause problems ranging from widespread vehicle accidents to extensive power outages. Pinpointing where freezing rain is going to occur can be difficult, as it requires knowledge of weather conditions throughout the lower atmosphere: you have to know that the air is moist enough to support precipitation reaching the surface, that there is a deep enough layer of warm air (that is, air above freezing) to melt falling snowflakes, but surface conditions have to be below freezing to force the melted water to refreeze upon contact. While radiosondes may be ideal for this, the sparse cadence of launches makes it difficult to monitor how conditions are changing.
This is an arena where NUCAPS can be very useful. These thermodynamic profiles from polar orbiting satellites can help fill in those gaps and inform where to expect elevated moist layers. Because the NUCAPS profiles are spatially dense, it’s possible to extract surfaces from the retrieved data, like temperature at a particular level. Take a look at this plot, which shows the 850 mb temperature (shaded, in Celsius) and the surface weather conditions (station plot, in Fahrenheit). The color mapping for the NUCAPS has been changed to a NEXRAD velocity plot as that makes it easy to identify positive or negative locations. In this case, temperature below freezing are shaded as greens and blues while temperatures above freezing are shaded as reds, pinks, and oranges.
This image shows that the 850 mb temperature is above freezing for large parts of the south. However, take a look at northeast Texas / northwest Louisiana / southwest Arkansas. The Ark-la-tex (as that region is commonly called) has 850 mb temperatures above freezing but surface temperatures at or below freezing. That’s an ideal setup for freezing rain, and in fact local media in Shreveport, LA; Texarkana, TX/AR; and other places reported freezing rain throughout the region.
One thing to keep in mind with using NUCAPS profiles is the data quality. In AWIPS and in other systems, that’s given by a simple traffic light code: green means both the infrared and microwave observations produced a valid thermodynamic retrieval, yellow means that due to cloud cover only the microwave sounder was able to contribute to the retrieval, and red means that the retrieval didn’t converge and the data are of suspect quality. The data quality plot shows mostly yellow due to all the cloud coverage, but has a large swatch of red where the precipitation rates are so intense that the microwave radiometer can’t penetrate through. This means that the 850 mb temperatures from eastern Louisiana to western Tennessee shouldn’t be trusted. Regardless, there’s a large region where the NUCAPS observations are providing additional value and helping to inform about the state of the atmosphere away from the surface.
