SoCalGas: Upstream Constraints Drive Curtailment Risk in Southern California
On May 1, SoCalGas complied with ALJ Ormond's April 16 ruling in A.26-01-009 by providing information on outages and concerning events that occurred outside of SoCalGas's service territory over the past decade. Related coverage is available at the following links.
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BACKGROUND
SoCalGas notes that California imports more than 95% of its natural gas from out-of-state sources. The SoCalGas system sits at the terminus of several interstate pipelines, making it the last node in the western gas network. When upstream conditions tighten (freeze-offs in producing basins, compressor failures, infrastructure outages, or continental cold that diverts supply to higher-priced markets) California has no meaningful alternatives. Local underground storage, led by the Aliso Canyon facility, absorbs the shortfall. Reliability risk is driven outside California, not within it.
WEATHER EVENTS
SoCalGas documents eight discrete upstream disruption events from 2017 through January 2026. A recurring pattern emerges: upstream stress reduces Receipt Point Utilization (RPU) below normal levels, which forces large storage withdrawals, and this triggers Operational Flow Orders and curtailment watches.
- January - February 2017: Atmospheric River Events. Three back-to-back atmospheric river events, combined with cold Rockies temperatures, reduced system RPU to 68% during the most intense period. SoCalGas withdrew 14 Bcf from storage across the full January - February window and declared 18 Low OFOs. A system-wide curtailment watch ran January 23 - 26. No curtailments were required.
- January 2018: Arctic Outbreak. A widespread arctic air mass covering the western, central, and eastern U.S. from late December 2017 through mid-January 2018 caused well freeze-offs and interstate pipeline operational failures. System RPU fell to 72% during the peak period of January 1 - 9, with 1.2 Bcf withdrawn from storage. SoCalGas declared 14 Low OFOs.
- January - February 2019: Polar Vortex. A major polar vortex displacement drove arctic air into the central U.S., constraining national markets and east-west gas flexibility. Southern California temperatures were relatively mild, but upstream pipeline operators experienced constrained flow rates and lost supply to price-insensitive Midwest demand. System RPU fell to 88% during the peak period, with 7.3 Bcf withdrawn across the full event. SoCalGas implemented a curtailment for electric generation customers under Rule 23 from February 6 - 8, 2019 (the only end-use curtailment documented in the external outage record). A system-wide curtailment watch ran concurrently.
- February 2021: Winter Storm Uri. Uri was the most operationally severe weather event in the filing. Arctic air moving into the central and southern U.S. beginning February 10 produced freeze-offs eliminating approximately 5 Bcfd of Permian Basin supply (20 Bcf over four days) caused widespread Texas power failures, and knocked out compressor stations along upstream interstate pipelines. System RPU fell to 46% during the February 14 - 19 peak, the lowest system-wide reading to that point in the record, with the Northern Zone reaching 26%. SoCalGas withdrew 4.4 Bcf from storage. A Southern System curtailment watch ran February 14 - 19.
- December 2022: Winter Storm Elliott. An extreme arctic outbreak simultaneously affecting nearly all U.S. regions produced well freeze-offs, electric system failures, and pipeline stress. System RPU fell to 65% during the December 22 - 25 peak, with 1.2 Bcf withdrawn from storage. Core procurement costs reached an unprecedented $34/Dth, more than 300% above the prior year. A Southern System curtailment watch preceded the storm from December 13 - 17.
- January 2024: Winter Storm Heather. A cross-continental storm originating as an extratropical cyclone in the northeastern Pacific made landfall in the Pacific Northwest before driving extreme cold and elevated heating demand across the South and Southeast. Southern California was not directly affected by cold, but upstream demand diverted supply eastward. System RPU fell to 36% during the January 14 - 17 peak (the Northern Zone reached 19%, and 5.8 Bcf was withdrawn from storage). This was the first winter event since 2016 in which SoCalGas operated without Aliso Canyon restrictions. A system-wide curtailment watch ran January 15 - 17.
- January 2025: Western Arctic Events. A month-long North American cold wave produced multiple arctic intrusions over a four-week period rather than a single cold snap. The duration, not the magnitude, was the critical factor. System RPU fell to 36% during the January 19 - 26 peak, with the Northern Zone reaching 16%, and 8 Bcf was withdrawn from storage. Concerns intensified when the Honor Rancho Storage Field was temporarily shut January 22 - 24 due to its proximity to the Hughes Wildfire. Eight Low OFOs were declared across the event.
- January 2026: Winter Storm Fern. A multi-day arctic outbreak affecting approximately 230 million people across Northern Mexico, the South, Plains, and eastern U.S. produced heavy snowfall, widespread ice accumulation, more than one million electric customer outages, and over 10,000 flight cancellations. System RPU fell to 25% during the January 24 - 26 peak — the lowest system-wide reading in the filing, with the Northern Zone reaching 9%. SoCalGas withdrew 8.2 Bcf across the January 22 - 28 window. Fern coincided with a pre-existing infrastructure constraint: a December 27, 2025 landslide had ruptured Transmission Line 225, reducing Wheeler Ridge receipt capacity by 650 MMcfd to 115 MMcfd. A system-wide curtailment watch ran January 26 - 28.
CURTAILMENT RECORD
Fifteen curtailment watches are documented between December 2016 and January 2026, ranging from one day to 19 days in duration. Several summer 2021 and 2022 watches on the Southern System ran for weeks, driven by El Paso Natural Gas constraints, which were compounded by heat-driven demand. The sole actual end-use curtailment (electric generation customers under Rule 23) ran February 6 - 8, 2019.
NON-WEATHER INFRASTRUCTURE RISKS
- EPNG Line 2000. A force majeure outage beginning August 15, 2021 removed approximately 600 MDthd of supply capacity (about 20% of combined SoCalGas and SDG&E average daily winter demand) and was not resolved until February 14, 2023, an 18-month duration. Additional EPNG maintenance reductions on the North Main Line and at Cadiszou and Ehrenberg from November 2022 through January 2023 compounded the constraint, with reductions ranging from 194 to 739 MDthd across the affected points.
- Energía Costa Azul LNG Terminal. SoCalGas's filing identifies Energía Costa Azul (ECA) as a forward-looking structural risk that the CPUC's current reliability modeling does not capture. ECA's expected export capacity of up to 425 MMcfd would reduce available supply to the Southern System from 1,210 MMcfd to 785 MMcfd (65% of nominal Southern System capacity). The CPUC's Biennial Assessment assumes an 85% RPU floor. SoCalGas argues the gap between that assumption and the ECA-constrained reality would require increased reliance on Aliso Canyon withdrawals to maintain Southern System reliability, since Aliso Canyon cannot physically serve the Southern System directly but preserves Northern System supplies that can be redirected southward.
INSTANT ANALYSIS
SoCalGas is building its case to defend Aliso Canyon. The quantitative record assembled here (RPU lows, storage withdrawal volumes, OFO counts, curtailment watch durations across eight events) is designed to resist any proposal to further restrict storage operations or reduce capacity targets. The near-miss argument runs through every event: in most cases, Southern California was not experiencing unusual cold, yet national demand and upstream constraints pushed the system toward curtailment anyway. The filing states that a coincidence of upstream stress, local cold, low storage inventories, and high electric generation demand has not yet occurred simultaneously. The implication is that it will.
The ECA section warrants particular attention from intervenors in both this proceeding and any future Southern System infrastructure docket. If SoCalGas's supply compression numbers hold up, the CPUC's reliability baseline is understated and the case for maintaining Aliso Canyon strengthens into the next decision cycle.