Environmental Factors
Due to its large geographic territory, the ReliabilityFirst (RF) footprint is exposed to a wide range of environmental risks, including extreme high and low temperatures, severe storms, tornadoes, and hurricanes. Extreme weather events can influence the reliability and resilience of the Bulk Power System (BPS) and cause adverse impacts on customer demand, resource performance, and transmission availability. For the 2025-26 RRA, RF rated environmental factors with a high risk score.
As reported in NERC’s 2025 State of Reliability Report, twenty-seven weather related disasters occurred in the United States in 2024 with losses exceeding one-billion dollars in damage per event. Nine of those events were identified by NERC as large transmission events, but none of them caused significant outages on the BPS.
Figure 3. Billion-dollar Weather and Climate Disasters in RF Footprint (2020-2025)
Figure 3. Billion-dollar Weather and Climate Disasters in RF Footprint (2020-2025)
Figure 3 displays the increasing trend of billion-dollar weather disasters across the RF footprint between 2020 and 2025, according to the National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Environmental Information. The number of confirmed billion-dollar weather disasters increased from one event in 2020 to five events in 2025. As costly weather events become more prevalent, greater resources will be required for emergency preparedness and maintaining BPS reliability.
Cold weather events
Since the 2014 Polar Vortex, the RF footprint has faced recurring extreme cold weather events, with some, including Winter Storms Uri and Elliott, causing widespread generation resource unavailability that led to customer outages. In 2022, Winter Storm Elliott jeopardized grid reliability, resulting in 90.5 GW of coincident unplanned generating unit outages, derates, and failures to start. At one point, PJM had 47 GW of generation capacity on forced outages but was able to maintain system reliability by implementing multiple emergency procedures and appealing for reductions in energy use. MISO also went into emergency procedures but there were no customer interruptions, as MISO consistently exported nearly 5 GW to its southern neighbors.
More recently, cold weather events like Winter Storm Fern stressed the natural gas and electric systems but did not result in widespread impacts. This event demonstrated how industry efforts to enhance winterization, operator preparedness, and coordination between the gas and electricity sectors can strengthen BPS performance during extreme weather events. It also reaffirmed the critical role of dispatchable generation during winter peaks and the importance of effective interregional transfer capability.
Collectively, these severe weather events demonstrate the need for a continued focus on fuel assurance, transmission expansion, infrastructure hardening, and planning for prolonged extreme weather impacts to enhance overall BPS resilience.
Cold Weather Standards
Some of the NERC Reliability Standards that address cold weather issues, such as EOP-012-3 (Extreme Cold Weather Preparedness and Operations), EOP-011-4 (Emergency Operations), and TOP-002-5 (Operations Planning), were recently updated to improve reliability during cold weather events. RF plans to monitor metrics from its Compliance Monitoring and Enforcement Program (CMEP) to measure compliance with these updates.
RF plant winterization visits
RF conducts a Cold Weather Winterization (CWW) outreach program, separate from its compliance monitoring activities, to educate generation facilities on cold weather risks and promote winterization best practices. This voluntary program occurs annually, beginning with a winter readiness survey and followed by site visits to selected generation facilities.
Since 2014, RF has completed over 110 CWW assist visits and developed a comprehensive set of winterization lessons learned and best practices. During site visits, RF staff share lessons learned and best practices that are augmented with other observations as needed. RF also provides winterization lessons learned and best practices in other outreach forums such as RF Tech Talks. The effectiveness of RF’s CWW site visits are measurable. RF staff observed statistically significant results for improved generating unit performance among program participants.
Weather impacts on generation
RF utilizes NERC Generating Availability Data System (GADS) data to better understand weather impacts on generation assets. As shown in Figure 4, wet coal (which causes fuel shortages) was the most frequent cause of weather-related outages for conventional fossil-based generation between 2020 and 2025.
However, environmental-related coal outages have declined over time, which could be related to the increase in coal plant retirements in RF’s territory. Severe storm and lightning-related outages showed year-over-year increases between 2020 and 2025, aligning with the rise in extreme weather events. Separately, RF staff analysis of GADS data has observed that natural gas resources exhibit less availability in winter months when compared to summer months.
Figure 4. Environmental-related Outages in RF Footprint (2020-2025)
Figure 4. Environmental-related Outages in RF Footprint (2020-2025)
Weather impacts on transmission
RF utilizes NERC Transmission Availability Data System (TADS) data to evaluate environmental-related outages on transmission elements, which accounted for 28% of transmission outages within the RF footprint from 2020-2025. As shown in Figure 5, the most common environmental outage types were lightning, weather (non-lightning), and vegetation. Since 2020, the overall trend in vegetation outages increased, while lightning and non-lighting weather-related outages decreased.
Within RF’s footprint, 100–199 kV transmission facilities, a voltage level range typically not covered by NERC Reliability Standard FAC-003-5, represented the largest share of vegetation-related outages. Because the average height of towers within this voltage level range is lower and rights-of-way tend to be narrower, transmission is more susceptible to vegetation growth issues (e.g., vegetation fall-ins from outside the rights-of-way). NERC recently held a Wildfire Mitigation Workshop where a recommendation was made to expand FAC-003-5 (Transmission Vegetation Management) applicability to transmission facilities 100 kV and above.
Figure 5. Transmission and Transformer Outage Cause in RF Footprint (2020-2025)
Figure 5. Transmission and Transformer Outage Cause in RF Footprint (2020-2025)
After RF shared its concerns about narrow right-of-ways causing outages in a previous iteration of the RF Regional Risk Assessment, RF performed outreach with Registered Entities that had more frequent vegetation outages on 100-199 kV facilities. While RF observed some improvements at 100-100 kV facilities, vegetation-related outages increased between 2022 and 2024. RF plans to engage with Transmission Owners that experience recurring vegetation outages.
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