How Rare Was The Severe Winter Weather That Struck Texas This Week?
February 19, 2021
As Texas and the Deep South thaws out from an extraordinary stretch of severe winter weather, many questions are circulating related to the severity and rarity of this event.
In light of the energy and water crisis that struck the region, particularly Texas, the essence of these questions tries to determine the frequency of these events, while glancing in the rearview mirror and asking if the severity of this event should have been reasonably expected.
The Answer: We don’t know yet. These questions are quite complex and will take weeks to months of analysis to respond to them.
THE COMPLEXITY BEHIND DETERMINING THE FREQUENCY OF THIS EVENT
Low frequency, high magnitude weather events are responsible for most fatalities and financial losses. These rare events claim a disproportional amount of losses because they blindside us and catch us unprepared.
Climate scientists analyze data and run models to determine the return frequency of these events. A return frequency, sometimes called a return period, is the amount of time we should expect to pass, on average, between extreme conditions reaching or exceeding some threshold.
Return frequencies are used to describe everything from flood levels to drought conditions to the probability that a citrus crop will endure a hard freeze. A common return frequency that many people are familiar with is the level of the 100-year flood. This is a flood level so rare that the water should only reach or exceed this level, on average, once every 100 years. The probability of this event occurring is 1% annually. FEMA often refers to this water level as the Base Flood Elevation (BFE).
Return frequency analysis must answer a specific question. Some questions in climate science are less complex because they only relate to one hazard impacting one geographic point at one moment in time. For example, what is the return frequency of four inches of rain falling in my front yard in one hour? This is a simplistic question because it involves one process (heavy rain) at one location (my yard) in a specific time frame (one hour). The answer to this question provides guidance about the design criteria for drainage infrastructure on my street.
Understanding the frequency of the severe weather event in Texas and the Deep South this week is complex because there are so many angles to it. I’ve listed a few of them below:
- Understanding the frequency of the extreme cold temperatures. How cold did it get and how rare was this?
- Understanding the duration of cold temperatures. Not only should we look at how cold it got, but how long did it stay cold? A common way to analyze this for cold weather is by analyzing continuous hours below freezing.
- Understanding the spatial extent of the cold. This severe weather event impacted both energy consumers and producers. The impacts to energy production affected natural gas production and transmission, as well as solar and wind. An analysis of impacts on gas production, for example, would have to take into account locations of gas wells, transmission lines and generation stations. So not only must we understand how cold the temperature dropped and for how long it lasted, but we must also understand the spatial dimension of the event. Perhaps previous events produced colder extreme temperatures but for less duration. Or perhaps this event produced less cold extremes, but the cold weather covered a larger area.
- This severe weather event produced so many impacts because it not only inflicted extremely low temperatures, but also several rounds of wintry precipitation, including snow, sleet and freezing rain. This combination exacerbated impacts on both energy production and the ability of the public to be mobile to relocate or obtain adequate supplies.
A thorough analysis considering these factors will take weeks to months to complete. However, given the high-impact of this weather event, we should expect to see multiple studies emerge that consider factors related to climate science, energy production and societal decisions/ behavior choices.
THE VALUE OF ANALYZING CLIMATE DATA WITH DEEP HISTORY
Most energy within Texas is managed by the Electricity Reliability Council of Texas (ERCOT). Every autumn, ERCOT releases a prediction of forecasted energy capacity and demand, including a range of potential risks. Included in those range of risks is the forecasted season peak load for the winter season.
The report for winter 2020-2021 utilizes a severe cold weather event from 2011 as the baseline for forecasting extreme demand this winter. During the 2011 event, ERCOT lost 210 power generating units due to extreme cold weather. Adjustments are made from this baseline, such as revised economic growth forecasts, that could be used to equate a similar weather event with energy demand.
From a climate perspective, much thought will be put into assessing if the 2011 cold weather event was an appropriate baseline or if it was too short-sided. That event produced extremely cold weather in the southwestern states, including New Mexico and Texas. El Paso, Texas, observed 78 consecutive hours below freezing, which was unusual, but not unprecedented.
The FERC/NERC Staff Report summarizes the impacts of this event on the energy system. The report states that the 2011 storm was, “not without precedent. There were prior severe cold weather events in the Southwest in 1983, 1989, 2003, 2006, 2008, and 2010. The worst of these was in 1989, the prior event most comparable to 2011.”
At a first glance, something that concerns me about the statement in the FERC/NERC report is that all of these cold weather events occurred within the past 40 years. While this timeframe is long by human standards, it is short when considering climate science.
One of the biggest problems I come across as a climate data and natural hazards scientist is people using a timeline that is too short when considering the potential for extreme events. I often hear people say things like, “I’ve lived here for 25 years and my street never floods.” Yet, the local archives provide evidence of a storm perhaps 50 or 100 years ago that inundated their street with several feet of water.
With this perspective in mind, I looked back in the weather archive for Galveston, Texas, the city where I live, to get a perspective on how severe this cold weather event was compared to past events. Galveston is a great place to consider because the energy and water crisis severely impacted us this week, and we also have the longest continuous weather records west of the Mississippi River, starting in 1871. I personally lost electricity for 47 hours, lost water for at least three days, and kept my kitchen above freezing by boiling water. My bedroom windows were encased in ice on the inside.
Take this quick analysis with a grain of salt, however, in the context of what I previously shared about the need to consider the spatial extent of this event and the coupling of the cold weather with snow and ice, especially inland.
A brief review of Galveston’s weather history revealed at least six cold weather events that were more formidable than the current outbreak we endured this week. Our low temperature this week dropped to 21F Sunday night and 20F Monday night, and we only rebounded to 29F during the day on Monday. We observed around 35 consecutive hours below freezing (hourly obs were briefly discontinued at the airport on Tue Feb 16).
Our temperature started slightly above freezing on Mon Feb 15 and ended at 44F at 11:59PM Tue Feb 16, so in the climate record, Galveston will not even have one calendar day with a sub-freezing maximum temperature. Inland locations observed longer-duration cold.
Nonetheless, this event produced severe impacts in Galveston. However, a review of Galveston’s weather history revealed six events that appear more formidable:
January 8-9, 1886: The low temperature dropped to 11F on Jan 8 and 15F on Jan 9. The high temperature on January 9 reached 31F. According to local historian Casey Greene, Galveston Bay froze over in 1886.
February 7-8, 1895: The low temperature reached 15F on both dates, and the high only reached 25 on Feb 7 and 27 on Feb 8. The heaviest snowfall on record in Galveston occurred in this storm, as 15.4 inches fell on the city, according to Casey Greene.
January 26-28, 1897: The high temperature only reached 30F on January 26 and 32F on January 27. Low temps reached 21F on January 27 and 25F on January 28.
February 12-13, 1899: This was the coldest winter event in Galveston’s history. The low temperature on Feb 12 reached 8F, followed by 10F on Feb 13. The high temperature on Feb 12 only reached 25F, tying the lowest all-time maximum temperature, set just two years earlier.
February 1-2, 1951: The high temperature reached only 27F on Feb 1 and 31F on Feb 2. Both mornings started in the teens, with temperatures of 17 and 18, respectively. Stan Blazyk stated that this event produced more than 80 consecutive hours of freezing weather at Galveston in his exceptional book chronicling the city’s weather during the 20th Century.
January 10-11, 1962: The high temperature only reached 26F on January 10 and 28F on January 11. The low on January 10 dropped to 18. Stan Blazyk tabulated 67 consecutive hours below freezing, and numerous water breaks and natural gas shortages in the region.
HISTORICAL PERSPECTIVE ON THE RECENT SEVERE WINTER WEATHER – SUMMARY AND CONCLUSION
The 2021 severe winter weather outbreak in Texas and the Deep South inflicted exceptional impacts, as failure of the energy grid left millions of people in the dark. Powerless homes quickly became frigid, leading to massive plumbing problems and broken water lines.
Analyzing the frequency of this severe weather event from a climatological perspective is complex, because we must consider the magnitude of cold temperatures, as well the the duration and spatial extent of the cold. We also must consider that multiple snow and ice events impacted the region.
Due to the high-profile impacts of this event, numerous analyses will likely scrutinize choices made by ERCOT to prepare for this event. Climatologically, that will include assessing the choice of the 2011 cold weather event as a baseline for a potential cold weather outbreak this winter.
A quick review of cold weather events in Galveston, a coastal location with the longest continuous weather records west of the Mississippi River, reveals at least six historic severe cold events more formidable than this year’s outbreak. Importantly, four of these six events occurred in the late 1800s, and the most recent event occurred in 1962.
In summary, we have been blindsided by a cold weather event that may have been less severe than prior events because we have forgotten our climate history. Our species continuously makes this mistake with other hazards, including hurricanes, earthquakes and tsunamis. A more thorough analysis of past cold weather events and models of potential future events in the region will provide important perspectives to prevent a week like this one from happening again.