The night that San Antonio dropped down to zero

San Antonio is far enough north of the equator where bitter-cold temperatures and snowfall are not out of the realm of possibility. But we also sit close enough to the Gulf of Mexico that significant winter weather doesn’t happen very often. So, to see San Antonio’s all-time record low temperature is shocking, even to a meteorologist. Zero. Yes, San Antonio dropped all the way down to zero degrees on the morning of January 31, 1949. As you would expect, it took a rare combination of events to get the mercury that low.

First, a little perspective. Here are San Antonio’s coldest readings, since records have been kept. Notice that January 30, 1949, the day prior, also ranks in the top 3.

It takes a powerfully cold airmass to surge deep into South Texas. That was the case as a massive front blew through just days before. Take a look at this archived weather map from January 30th, 1949, courtesy of NOAA.

You can see a cold front which has pushed all the way into central Mexico. But even the coldest of airmasses wouldn’t be enough to cause temperatures to plummet to zero in South Texas. It took another component: snow. The cold air behind it would coincide with an overrunning pattern producing widespread snow for Central and South Texas. Austin received 5-7 inches, while San Antonio reported 4 inches on the ground. The pictures below show a blanket of snow over San Antonio.

Just like in the northern part of the country, snow on the ground often acts to bring temperatures even lower. The snow releases any energy or heat into the atmosphere, causing rapid cooling. That’s what happened the morning of January 31, 1949. It caused San Antonio to be colder than many places in the nation, including locations well to our north. As for other sites nearby, it was also a record-setting day.

It has not been since December 23, 1989 that San Antonio has even dropped below 9°, making 1949′s rare arctic reading all that much more impressive.