Total Eclipse - April 8, 2024

Total eclipses are a rare occurrence for a particular location and a likely once in a lifetime event. Even though a total eclipse is so rare, they can be predicted decades or even hundreds of years in advance based on the orbital pattern on the moon in conjunction with the position of the earth and sun.

Although we knew it was coming for years in advance, the main question leading up to the eclipse would be the cloud cover and what the subsequent viewing conditions would be. On average South-Central Texas sees about a 40-60 percent sky cover during this time. Compared to the rest of the solar eclipse path of totality, South-Central Texas was the most likely area to not have clouds. However, April is one of our typical more rainy months of the year and, although climatology showed this area as more favorable compared to the rest of the country, it came down to nearly a 50/50 chance of seeing mostly clear skies vs mostly cloudy skies.

Leading up to April 8th, medium range ensemble weather model guidance latched onto a cloudy pattern early and never changed its predictions. This was in large part due to a slow moving upper-level low expected to be located across the southwestern United States. This location of an upper low leads to deep southwesterly flow aloft with a fetch extending from the eastern Pacific extending northeast into Texas and the Southern Plains. This allows for an abundance of mid and high level moisture that leads to clouds in these levels. With high confidence that this trough would be somewhere in this general vicinity, there was high confidence in the 7 to 10 days leading up to April 8th for cloud cover. 

Ultimately, observed sky conditions on the day of the eclipse was close to forecasted projections. This satellite image shows mostly cloudy skies over much of South-Central Texas, just before the eclipse began.

One other aspect with solar eclipses is the expected temperature drop due to decreasing solar insolation during the eclipse. The amount of drop expected is primarily caused by cloud cover and moisture at the surface. Drier air and clear skies could potentially lead to temperature drops near 10 degrees while cloudy conditions and moist air at the surface could see drops of 2-5 degrees. This 2-5 degree drop was typical for what occurred across South-Central Texas during the total eclipse. The official forecast from the National Weather Service in Austin/San Antonio leading up to April 8th accounted for this expected drop.

For additional eclipse satellite imagery check out this blog link below from Bill Line with the Regional and Mesoscale Meteorology Branch of NOAA/NESDIS/STAR:

Isolated showers and thunderstorms developed over the Coastal Plains in the late morning and early afternoon hours, and became scattered east of the I-35 corridor after the eclipse ended. Isolated showers also developed over the Hill Country after the eclipse ended.

Temperature drops of 2-5 degrees were common across south-central Texas leading up to and during eclipse totality. The temperatures drops would have been even greater, perhaps as much as 10 degrees, if conditions would have been clear and drier over the region.

A reduction and collapse of the cumulus cloud field was observed across northeast Texas. This was a result of the temporary loss of the sun's incoming shortwave radiation and loss of absorption by the earth's surface during the eclipse, which in turn resulted in a reduction of outgoing longwave thermal radiation, heating, and rising air in the low levels of the atmosphere needed to form cumulus clouds.

National Weather Service Doppler Radars can routinely detect biological targets, such as bats, birds, and butterfly migrations. In south-central Texas it is a common occurrence Spring through Fall to see at close radar ranges birds, such as Turkey Vultures and Swallows, take flight every morning as well as bats, such as the Mexican Free-Tailed Bat, emerge from caves around sunset and come back to roost around sunrise.

The radar returns associated with each are very identifiable each day, with reflectivity (dBZ) returns spreading out from a roosting point as from biological targets take flight and low correlation coefficients (CC) collocated with the dBZ returns.

During the eclipse totality our radars did not detect bats leaving their roosting caves. However, our radars did detect birds coming back to their roosting locations right at eclipse totality, then taking flight again just after eclipse totality. The comparisons below show what are likely Turkey Vultures and Sparrows taking flight after temporarily roosting during the eclipse totality!

Building off lessons learned from the 2017 total eclipse in portions of the northwest and central U.S., residents and visitors to Texas were encouraged to plan ahead, arrive early, and stay late to avoid traffic delays for people moving into and out of the path of totality.

Overall, traffic gridlock and delays were less than anticipated, potentially due to planning as well as cloud cover reducing the number of people wanting to move into the eclipse totality path. Nevertheless, some delays were seen on Interstate 10 leading into the eclipse path northwest of San Antonio as well as in smaller towns.

Early in 2023 NWS Austin/San Antonio began initial planning of Impact Based Decision Support Services (IDSS) for both the October 14, 2023 Annular Eclipse and April 8, 2024 Total Eclipse. NWS Austin/San Antonio also met with core emergency management partners and attended numerous planning meetings in 2023 and early 2024.

Starting over a week before each eclipse NWS Austin/San Antonio began detail IDSS forecasts and conference calls targeted at core emergency management partners that were actively managing the influx on visitors, traffic, and eclipse festivals in the area.

NWS Austin/San Antonio also posted eclipse climatology and safety information on social media weeks and months in advance of each eclipse. In the week ahead of each eclipse NWS Austin/San Antonio posted probabilistic forecast scenarios for cloud cover, rain chances, and the severe weather potential.