An arctic blast set the stage for a rare Winter snowstorm across the Gulf Coast and Southeast, bringing at least 4″ of snow from Texas to South Carolina, including over 8″ in four states: Alabama, Louisiana, Florida, and North Carolina. New Orleans set a new all-time single day snowfall record of 8.0″, smashing the old record of 2.7″ set back on December 31, 1963. The cold air flooded the U.S. starting back on 17 January 2025, when a strong cold front associated with a low pressure system across the Upper Midwest pushed into the nation’s midsection. Blizzard warnings were posted for Western Minnesota and Eastern North Dakota, and the GOES-East Blowing Snow RGB confirmed the low visibility conditions as mentioned in Bill Line’s latest blog.
That same cold front cleared most of the Gulf Coast by 19 January 2025 and by 20 January at 2300 UTC, the NWS Weather Prediction Center (WPC) Winter Storm Severity Index (WSSI) highlighted ‘Major Impacts’ from Houston to New Orleans, with ‘Moderate Impacts’ across the Florida Panhandle and eastern North Carolina through 1900 UTC 23 January. NWS WPC shared Key Messages to their social media, including at 2230 UTC 20 January 2025, mentioning “Historic snowfall possible for the Gulf Coast”.
The CIRA Advected Layered Precipitable Water (ALPW) from 0900 UTC 21 January to 0500 UTC 22 January 2025 showed where moisture was available for snow to reach the ground as the low pressure in the Gulf pushed east, with elevated low-level moisture stretching from Texas to southeast Virginia, and a surge of 700-500 hPa moisture in the second half of the period from Florida’s Panhandle to eastern North Carolina. You’ll note very dry conditions to the north in an arctic air mass, helping to explain why cities like Washington, D.C., just missed out on the snow.
There was just enough instability to yield thundersnow across Louisiana late in the morning on 21 January 2025. LightningCast had probabilities as high as 50% that the GLM would observe lightning in the next hour, providing about 20 minutes of lead time before the GLM Flash Extent Density (FED) indeed confirmed lightning in south-central Louisiana. LightningCast probabilities were also elevated just offshore of Louisiana, paired with glaciating clouds and thick clouds with ice particles as seen in the Day Cloud Phase Distinction (DCPD) RGB (greenish-yellow colors), though no lightning occurred.
The NESDIS Snowfall Rate (SFR) Product provided a look at the snow falling in the clouds across the western and central Gulf Coasts at 1535 UTC 21 January 2025, derived from the Metop-C Microwave Humidity Sounding (MHS) instrument than can penetrate cloud cover, with liquid-equivalent SFRs above 3 mm/hr. There can often be a lag between the snow observed by the NESDIS SFR, depicting snow through the atmospheric column, and snow that reaches the ground, but according to Sheldon Kusselson from CIRA, about an hour after this product output, Mobile, AL, was nearing 2″ of snowfall. The NESDIS SFR uses direct broadcast satellite data and is updated with 15-minute latency on the UMD SFR Website. There’s also the Radar-Satellite Merged SFR Product that incorporates MRMS data.
As the system pushed off the Eastern Seaborad on 22 January 2025, a fresh snowpack can be seen in the GOES-East Geocolor imagery from Houston to southern Delmarva. The contrast between snow and clouds is even easier to see in the Day Snow Fog RGB, with red-orange colors representing snowpack, found both over the Gulf Coast and Southeast Coast, but also in the Ohio Valley and Mid-Atlantic, while shades of yellow and pink represent water and ice clouds, which are seen pushing off the North Carolian Coast while also enveloping Florida with a cold northeast flow in place.
Luckily for those wanting warmer temperatures, by Tuesday, highs are expected to return to the 50s and 60s across much of the Gulf Coast and Southeast.
