Weather-Normalized Utility Sales: Separating Load Growth From Weather

Weather-normalized utility sales estimate electricity or natural-gas sales after adjusting for the effect of weather that differs from a defined normal level.

The metric helps investors separate underlying load trends from temporary heating and cooling effects.

Why utilities normalize for weather

Electricity and gas usage can move sharply with temperature.

Hot summers can raise air-conditioning demand, while cold winters can increase electric or gas heating demand. Comparing raw year-over-year sales can therefore make structural demand growth look stronger or weaker than it really is.

A weather-normalized estimate asks a different question:

What would sales have looked like if weather had been closer to normal?

Simplified framework

There is no universal formula, but the concept is generally:

1Reported Sales
2- Estimated Effect of Abnormal Weather
3= Weather-Normalized Sales

Utilities typically use statistical relationships between temperature measures and historical usage.

Southern Company states that its weather-adjusted kWh sales use statistical models of the historical relationship between temperatures and energy sales and remove estimated deviations from normal temperature conditions.

Weather-normalized sales are estimates

Weather normalization is model-based, not directly observed.

Results depend on:

• the historical period used to define normal weather;
• customer class;
• geography;
• heating and cooling degree-day assumptions;
• statistical model specification; and
• changes in customer behavior, efficiency, and technology.

That makes weather-normalized sales useful for trend analysis but not a standardized GAAP measure.

What the metric can reveal

After weather effects are removed, changes may better reflect:

• customer growth;
• data-center or industrial load additions;
• economic activity;
• electrification;
• energy efficiency;
• distributed generation; and
• changes in average customer usage.

Southern Company's 2025 Form 10-K, for example, discusses weather-adjusted commercial sales growth driven partly by new and existing data centers.

It is not a demand forecast

Weather-normalized historical growth does not automatically predict future load growth.

Future demand can change because of new customers, plant closures, efficiency, pricing, distributed generation, economic conditions, or large-project timing.

Management guidance for future weather-normalized growth should therefore be distinguished from the historical normalization itself.

Relationship to revenue decoupling

Where Revenue Decoupling applies, distribution revenue may be less sensitive to short-term changes in sales volume.

Weather-normalized sales can still matter for infrastructure needs, peak demand, capital planning, and long-term load growth even if immediate distribution margin is partly insulated.

Raw sales versus normalized sales

Investors should preserve both values.

Raw sales tell you what physically occurred. Normalized sales help estimate the underlying trend after removing weather effects.

Neither should silently replace the other.

A utility that reports strong normalized growth during a mild year may still have weak reported sales, while a utility with unusually hot weather may show strong reported sales but modest normalized growth.

Real-world filing context

Southern Company's 2025 Form 10-K reports both total retail kWh growth and weather-adjusted growth by customer class. CMS Energy also presents weather-normalized electric deliveries, while Pinnacle West uses weather-normalized retail electricity sales growth in earnings guidance.

Sources:

• Southern Company 2025 Form 10-K
• CMS Energy 2025 annual report
• Pinnacle West 2025 earnings materials filed with the SEC

Bottom line

Weather-normalized utility sales are modeled estimates that remove the effect of abnormal weather from reported usage. They help investors evaluate underlying load trends, but they are not GAAP sales, directly observed values, or forecasts and should be interpreted alongside raw sales, customer growth, economic activity, and the utility's regulatory structure.

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