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January 20-21, 2025 Winter Storm
A look at impacts across the Hill Country, Interstate 35 corridor, and Coastal Plains of south-central Texas
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Introduction
From the evening hours of January 20 to the morning of January 21, much of South-Central Texas was affected by a winter storm, with precipitation mainly occurring across the Coastal Plains, I-35 corridor, and portions of the Hill Country. Most areas received up to a trace of ice and a dusting to about an inch of snow and sleet. Higher snow accumulations occurred over the Coastal Plains, including Fayette, Gonzales, and Lavaca counties, with the highest report of 1.5" occurring in Gonzales.
San Antonio International Airport recorded 0.1" of snow, marking their first measurable snowfall since 2021 . Austin-Camp Mabry and Austin Bergstrom recorded 0.4" and 0.3" of snow, respectively, marking the first measurable snow in Austin since 2022. We recorded 0.3" of snow at our office in New Braunfels. For additional snowfall totals see the Snowfall Accumulation Map and County Accumulations below.
While wintry precipitation accumulations were generally light, they were enough to cause icy roads and several vehicle accidents overnight and in the morning rush hour, especially in the Austin area. Icy roads contributed to a multi-vehicle collision on Highway 57 in Zavala County just after midnight on January 21, killing five people and injuring seven others. The same winter storm would later go on to produce record-breaking snowfall along the Gulf coast.
Meteorological Synopsis
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300 mb upper-air analysis on January 19, showing an expansive longwave trough over the continental US
On January 18, two days before the event, a significant push of Arctic air made its way across the central United States, reaching the NWS Austin–San Antonio area that night. The cold Arctic air was expected to linger in our region for several days, bringing a stretch of below-average temperatures and freezing nights with hazardous wind chills.
This air was associated with a strong, slowly moving upper-level trough across the U.S., shunting the jet stream southward into our region. The combination of cold temperatures and the jet stream staying around our area meant that the office was on high alert for any possible disturbances that could develop along the jet stream, bringing in moisture and possibly leading to wintry precipitation.
While the general idea of cold weather in mid-January 2025 was well-forecast in weather models, less certain was whether or not an individual disturbance could be favorably timed and placed to give South-Central Texas wintry weather. By around January 15, some models had already started to show the possibility of winter weather over our area, but there was ample disagreement. Much of the uncertainty centered around whether a shortwave trough – a disturbance in the broader jet stream – would develop and strengthen over the Southwestern U.S. in the coming days. If this disturbance were to form, then it could both bring moisture and another shot of cold air: necessary ingredients for a winter storm in our area.
Whether or not models showed wintry precipitation for our area in the leadup to the event typically hinged on whether or not a trough would develop over the southwestern U.S. Representative illustrations based on WPC ensemble cluster analyses.
Models were roughly evenly split into two camps: those that showed very little development (or “amplification”) of the disturbance, and those that did. Eventually, models began to trend more towards the disturbance materializing, signaling an increased potential for a winter storm later on.
On January 19, a shortwave trough began to make its way southward over the Pacific Northwest, intensifying over the southwestern U.S. This caused the jet stream to accelerate over North Texas into the Ohio River Valley, causing moist and low-level Gulf air to ascend isentropically over Texas to feed the jet stream on the morning and afternoon of January 20. The onshore push of moisture was marked by the spread of a cloud deck about 5,000–10,000 ft high over much of the state. These clouds advanced inland a little faster than modeled, preventing the already cool temperatures near the surface from warming much during the day.
The January 20-21 winter storm was caused the subtle lift of humid Gulf air as a nearby jet stream strengthened ahead of an approaching upper-level disturbance
Low-level moisture early on January 20 produced an expanding cloud deck that helped to lower temperatures
By noon, radar began to show hints of rain droplets or ice crystals growing aloft, but these were not yet reaching the ground. While there was enough rising air to allow rain droplets and ice crystals to begin falling out of the cloud deck, the initially dry layer below the clouds caused these hydrometeors to evaporate or sublimate. However, over time, this caused the dry layer to cool and moisten, allowing the cloud deck to gradually descend and eventually allowing precipitation to make it all the way to the ground. Signals on radar continued to escalate over the next several hours.
Some light rain began falling in our southern counties shortly after 3 PM, but as temperatures fell and the shortwave trough came nearer, this quickly transitioned after 6 PM into freezing rain, sleet, and eventually light snow. The most distinct returns on radar were along a line from Pleasanton to Gonzales to La Grange, with radar also suggesting some light freezing drizzle possibly occurring as far west and south as Eagle Pass. Snowfall and sleet rates remained steady throughout the night, producing light accumulations. The area of wintry precipitation slowly moved east overnight, with most of the weather moving out of our area by noon on January 21. Above-freezing temperatures that afternoon melted most of the accumulated snow. More details on the chronology of the event can be found in the Timeline .
While a layer of dry air was initially present beneath the cloud deck on the afternoon of January 20, evaporative cooling caused that layer to moisten and cool throughout the day. Mean soundings from the 12Z January 20 HREF run shown.
Thinking About Snow Ratios
Leading up to this winter storm and in other events during the winter of 2024-2025, many attention-grabbing images spread quickly on social media showing weather model projections with large amounts of snow over South-Central Texas. Extreme caution should be used when looking at the output of any particular model, especially when it comes to snow totals. Models often produce very different results with each individual model run, and what you might see on a model snow map might not be accurately reflective of the atmospheric environment depicted in the model.
Snow is less dense than rain: ice itself is less dense than liquid water, and when snowflakes clump together as they descend to the ground, they leave air pockets that further decreases their density. That means it doesn't take a whole lot of water to produce a lot of snow. The ratio between the snow amount and the amount of liquid water stored in that snow is called the snow to liquid ratio (also known as SLR or simply "snow ratio"). High SLRs result in dry, powdery snows, while low SLRs produce more wet, clumpy snows.
Historically, a 10:1 SLR has been used as a rule of thumb. That would mean 10 inches of snow would be produced for every inch of liquid. However, snow ratios can vary greatly depending on weather conditions such as the air temperature and the wind, with the physics governing snow ratios occurring at small, microscopic scales.
Accurately modeling snow ratios at large scales is a tricky endeavor, so most models only simulate the amount of liquid-equivalent precipitation. Websites that show model outputs typically apply their own methods to this data to produce the model snow maps you often see. The 10:1 ratio is a common and popular method since it is easy to calculate, but it doesn't account for different weather conditions. Another popular method is the Kuchera method, which adjusts SLR based solely on what the maximum temperature is below where the air pressure is 500 mb (roughly from the surface to 18,000 ft up).
Neither of these methods were well-suited for the weather setup in January 2025, despite the broader details being well-captured in the models. The clouds that produced the sleet and snow were low-level clouds and likely composed entirely of supercooled liquid droplets rather than ice crystals. Data from aircraft passing through the cloud indicated that temperatures within the cloud were below freezing, but warmer than -10°C. At those temperatures, clouds are still more likely to be made of liquid than ice crystals . This made for lower SLRs and allowed for a mix of sleet and freezing rain, resulting in lower snow totals. The Cobb method ( Cobb 2011 ), a slightly more sophisticated method for estimating SLR, suggested ratios would be closer to 6:1, leading to snow totals far lower than what could often be found online. Our analysis of these facets in the leadup to the event allowed us to provide a more reasonable forecast of snow totals and the precipitation types observed.
Most websites will note the method used to estimate SLR. When you come across a model snow map, it's important to remember that common methods for estimating snow amounts don't apply equally well to all weather situations.
Timeline
Temperature and Precipitation Outlook Issued by the Climate Prediction Center on January 11 for the week of January 19-25
Social Media graphic posted by NWS Austin/San Antonio
Temperature and Precipitation Outlook Issued by the Climate Prediction Center
Social Media graphic posted by NWS Austin/San Antonio
Social Media graphic posted by NWS Austin/San Antonio
Social Media graphic posted by NWS Austin/San Antonio
Social Media graphic posted by NWS Austin/San Antonio
NWS Winter Storm Watch
NWS Total Snow and Sleet Accumulation Forecast
NWS Total Ice Accumulation from Freezing Rain Forecast
NWS Winter Storm Warning and Winter Weather Advisory
Social Media post by NWS Austin/San Antonio
Social Media post by NWS Austin/San Antonio
Storm Prediction Center Mesoscale Discussion Graphic
Social Media post by NWS Austin/San Antonio
Social Media post by NWS Austin/San Antonio
Video from NWS Austin/San Antonio office in New Braunfels
Social Media post by NWS Austin/San Antonio
Social Media post by NWS Austin/San Antonio
Social Media post by NWS Austin/San Antonio
Social Media post by Austin-Travis County EMS
Radar Loop
Radar Imagery of January 20th-21st Winter Weather Event Across South-Central Texas
Snowfall Map
Snowfall from the winter storm derived from the National Gridded Snowfall Analysis . Estimates may differ from local reports in some locations.
County Accumulations
Gulf Coast Snow Map
The storm system went on to produce snowfall along the Gulf coast and southeast Atlantic coast, including historic snowfall amounts in some areas southern Louisiana into the Panhandle of Florida.
National Snowfall Analysis from 6 AM CST Jan 20 to 6 AM CST Jan 23
SRH Winter Event Jan 20-22th 2025
Satellite
Snowpack from southeast Texas to eastern North Carolina as seen by GOES-East satellite the morning January 22nd
Snowpack from southeast Texas to Georgia as seen by GOES-East satellite the morning January 22nd