GOES-16 Upper-level water vapor infrared imagery for the 15 hours ending at 2011 UTC on 21 January 2025, above, shows the development of cold cloud tops (white and green in the enhancement used) especially after 1100 UTC over east Texas and Louisiana in response to the eastward propagation of a digging shortwave indicated by yellow (warmer brightness temperatures) moving across northern Mexico into west Texas at the end of the animation. The combination of this storm and an unusually cold and dry airmass over the deep south (and the rest of the country east of the Rockies) has resulted in a near-unprecedented snowstorm over the Gulf Coast states.

GOES-16 Day Cloud Phase Distinction from 1816-1951 UTC, below, shows the strengthening storm. You can use the cloud texture over Louisiana to infer regions where precipitation is occurring (all in the form of snow!). Day Cloud Phase Distinction also highlights — in green — snow that is on the ground in Kansas and Oklahoma, and also in southeast Texas that becomes apparent as the deeper clouds (orange/yellow in this RGB) pull away. That snow on the ground in southeast Texas is inhibiting the development of cumulus clouds (white/cyan).

The toggle below includes annotations highighting regions of snow and low clouds.

A zoomed-in Day Cloud Phase Distinction RGB over Louisiana at 2001 UTC, below, shows how one might use this RGB, both the color and texture, to infer regions where precipitation is occurring.

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A closer look at the Gulf Coast — from Bay City, Texas across Louisiana to Gulfport-Biloxi, Mississippi — using GOES-16 Infrared (10.3 µm) images (above) showed the eastward progression of snow observations (occasionally moderate to heavy at some sites) during the 16.5 hours ending at 2201 UTC. Cloud-top infrared brightness temperatures became increasingly colder (-40s to -50s C, shades of green to yellow) as snowfall rates increased across the region. A corresponding animation with overlays of Winter Watches, Warnings and Advisories is available here — which included the first-ever Blizzard Warning issued by the NWS Lake Charles forecast office (that extended all the way to the coast).

NWS Lake Charles has issued it's first ever Blizzard Warning for Jefferson and Orange counties as well as Cameron, Calcasieu, Jeff Davis, Acadia, Vermilion and Lafayette parishes until noon today. pic.twitter.com/JlyJpIxRcw

— NWS Lake Charles (@NWSLakeCharles) January 21, 2025

Two features of note occurred during that time period: a brief cluster of GOES-16 GLM Flash Extent Density pixels over southwest Louisiana at 1511 UTC (above), suggesting that thundersnow may have occurred (none of the 3 nearby METAR sites explicitly reported lightning or thundersnow, although the southernmost site was reporting heavy snow) — and a Ship Report of moderate to heavy freezing rain off the coast of Louisiana at 1800 UTC (below); there was quite a difference between that ship report air temperature (32ºF) the sea surface temperature (61ºF)!

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This is an ongoing storm, and this blog post will be amended later.

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While Wisconsin endures a very cold airmass without the brightening benefit of snow, various satellites continue to take spectacular imagery.  The GOES-16 True Color imagery above, from the CSPP Geosphere site, shows a clear scene and snowless features over southern Wisconsin (except over Racine and Kenosha counties in far southeast WI where lake-effect snow fell earlier this month).  The resolution of the GOES-16 Visible channel (Band 2, 0.64 µm) is 0.5 km at the sub-satellite point, meaning an effective resolution of around 1 km over Wisconsin.  NOAA-20 overflew Wisconsin on 19 January and the scene below, from the VIIRS Today website, shows a similar view, but with nominally better resolution:  the visible channels (M03, M04, M05) used to create true-color imagery have 750-m resolution.  The ‘true color’ views do not look the same because of the different wavelengths that are used to create them.

Even better resolution imagery occurred when Sentinel-2A overflew Wisconsin on 17 January 2025 (link; to reproduce the imagery below, change the date at the website that opens; this site also allows a user to view southern California and the effects of recent fires).  The MSI (Multi-Spectral Imager) on Sentinel-2A has 10-m resolution at 0.49, 0.56 and 0.67 micrometers), so it can produce pictures with far higher resolution, but its temporal coverage is restricted.  Madison was lucky on the 17th: full coverage on a clear day. It really is that brown in Wisconsin without snowcover! Your blogger also finds the ice patterns on the lakes fascinating.

A zoomed-in view over Madison’s isthmus, below, includes the UW-Madison campus and the State Capitol.

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Thermal signatures of the still-unfrozen water of Lake Oahe reservoir (along the Missouri River, in central South Dakota) were evident in GOES-16 (GOES-East) Infrared, Low-level Water Vapor and Mid-level Water Vapor images on 19th January 2025 (above). As a result of cold arctic air (morning low temperatures across western/central SD were generally in the -10 to -20F range) flowing across the open water of Lake Oahe, there were also 2 brief periods of light lake effect snow at Pierre (KPIR), each which reduced the surface visibility to 2.5 miles (below).

With a cold/dry arctic air mass in place over the region, the GOES-16 Mid-level Water Vapor (Band 09) and Low-level Water Vapor (Band 10) weighting functions peaked at lower than normal altitudes (below) — with significant amounts of radiation from the surface reaching the satellite detectors (thereby enabling a signature of Lake Oahe in the Water Vapor imagery).

In fact, the Total Precipitable Water value derived from 1200 UTC Rapid City rawinsonde data (0.03 in) (above) was a record low value for 1200 UTC soundings on 19 January (below).

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) Visible images (above) revealed horizontal Convective Roll (HCR) clouds that are often associated with areas where blowing snow is occurring — such as was the case across parts of eastern North Dakota and western Minnesota on 17th January 2025. With strong N-NW winds (in the wake of an arctic cold front) gusting as high as 67 mph in ND and 65 mph in MN, widespread blowing snow was reducing the surface visibility to near zero at some locations. Interstate 29 was closed from Grand Forks (KGFK) to the Canadian border.

1-minute GOES-16 Blowing Snow RGB images created using Geo2Grid (below) provided a clearer depiction of where the HCRs coincided with blowing snow. Existing snow cover appeared as darker shades of red in the RGB imagery, while bare ground appeared as brighter shades of green; supercooled water droplet clouds appeared as brighter shades of white, with mixed phase or glaciating clouds taking on pale shades of green.

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