CAISO and Mid-C Winter Outlook: Storms Set the Price

Based on the Enverus Winter Power Market Outlook webinar for CAISO and Mid-C, presented by Rob Allerman, Sr. Director of Power Analytics.

A record El Niño is likely to bring a warm, wet winter across the West, and the two sides of the region may price it in opposite ways. In CAISO, frequent storms can suppress solar, raise net load and leave batteries charging into high-priced hours. In Mid-C, plentiful wind, hydro generation and lower carbon costs point the other way. Enverus Intelligence® Research (EIR) sees CAISO leaning bullish at times this winter and Mid-C leaning bearish.

A record El Niño sets up a warm, wet West

EIR’s analog years are 2015/16 and 2023/24, which average +1.6 on the Relative Oceanic Niño Index (RONI). The global climate model statistical average for December through February is +3.1, and the models show record-high El Niño conditions. We expect a warm, wet winter West-wide, and an especially wet one in California. A supercharged jet stream should keep wind above average.

In CAISO, the population-weighted SP-15 temperature averages 53°F in December, while our analog years show 58°F. We expect above-average temperatures and below-average load in December, with January near to above average. In the Northwest, Portland averages 41°F in December against 45°F in our analog years. January should come in near average, though the January 2024 analog included four days below freezing, and February should turn warm again.

CAISO batteries keep setting records

New PV-plus-storage and standalone battery projects have come online this year, including Ventasso Energy Storage and the Willow Springs 8-hour battery. Combined with new transfer capability from SunZia, these additions have pushed CAISO to new records for solar, wind and battery activity. Battery discharge hit a record 13.441 GW on Aug. 18, and charging hit 11.003 GW on Aug. 9. Local transmission bottlenecks mean solar buildout still slightly outpaces effective battery charging, so midday curtailment stays active.

SunZia came online in June and pushed CAISO wind to a record 7,122 MW. TransWest Express (3,000 MW, late 2027) and SWIP-North (targeting 2028) add more wind that produces in the evenings and overnight, which supports softer evening ramp prices in SP-15 and Mead.

Alamitos, Huntington Beach and Ormond Beach (about 2.9 GW of coastal gas) retire on Dec. 31, 2026. These units have been emergency-only resources in DWR’s Strategic Reliability Reserve since Jan. 2024. Their retirement doesn’t cut day-to-day supply, but it removes the emergency backstop and raises scarcity risk in extreme heat from 2027.

EDAM vs. Markets+: the West’s market choice is still open

Markets+ keeps adding members across the Desert Southwest, the Rockies and the Pacific Northwest. BPA is the wildcard. In a Sept. 3 letter, new Administrator Travis Kavulla said he’s reconsidering Bonneville’s 2025 choice of Markets+ over EDAM, citing EDAM’s much deeper market and governance improvements at its new oversight body, the ROWE. He plans a draft decision by year-end. Losing BPA would be a meaningful hit to Markets+’ scale.

On the EDAM side, Portland General Electric filed tariff revisions with FERC in Aug. 2026 to support its planned Oct. 1 entry, and the CPUC voted Sept. 10 to open a rulemaking that lets CAISO and California utilities participate in the ROWE.

The debate over EDAM congestion revenue is escalating. Powerex has again questioned how CAISO calculates and distributes congestion revenue across PACE and PACW. In June alone, total EDAM congestion revenues reached $37.9 million, while returns to PacifiCorp areas from CAISO congestion totaled $1.33 million.

CAISO price view: risks skew bullish

If frequent storms keep behind-the-meter and utility-scale solar low, EIR expects prices to clear toward its bullish scenario, with batteries recharging into high-priced hours while thermal units stay on. February is where we differ most from the market, which appears to be downplaying the extreme storm activity we expect.

Mid-C: hydro, wind and cheaper carbon

Utility load growth forecasts for 2025 through 2027 vary by state: +5.5% in Washington, +4.1% in Oregon, +1.5% in Idaho and +0.9% in Montana. Flows have also changed. Over the last four years, stronger flows have moved into Mid-C from CAISO because of higher Mid-C prices.

Carbon costs are moving in Mid-C’s favor. Washington’s September auction cleared at $39.50, down $25 from June and the first since the June 25 agreement to link Washington with the California-Québec market in 2027. That drop takes roughly $10/MWh out of Northwest gas bids, while California’s rise adds about $1.50/MWh. All else equal, that narrows Mid-C’s premium to SP-15 in gas-marginal hours.

Mid-C price view: leaning bearish

For December, EIR forecasts mild weather and strong wind, with building confidence in a wet, windy and warm pattern. January looks similar, with lower-than-average load and plenty of hydro generation. In February, EIR’s forecast sits above the market, but we aren’t bullish. If February is windy and warm all month, our bearish case could easily play out.

What to take into the winter

• The record El Niño and warm ocean temperatures point to a warm, wet winter West-wide, especially in California.

• New builds focus on batteries, but low solar during storms can make CAISO prices spiky and make midday charging harder.

• CAISO looks bullish at times this winter, while Mid-C should lean bearish with plentiful wind, hydro generation and lower carbon costs.

Want to stay ahead of how CAISO and Mid-C trade this winter? Learn more about our power trading solutions.