Trying to find a pattern - Analyzing North Atlantic Oscillation and Norfolk, VA Snow

Does the NAO Really Matter for Local Snowfall?

One of the most common winter questions is whether large-scale indices like the North Atlantic Oscillation (NAO) can tell us something meaningful about local snowfall. The chart below compares NAO values with snowfall at NRFK, and while the relationship is often assumed to be strong, the data tells a different story.

The regression line slopes slightly negative, but the fit is extremely weak—NAO explains only about 1% of the snowfall variability in this dataset. Big snow events occur during negative, neutral, and even positive NAO phases. In short, NAO alone does not control snowfall totals here.

Why This Matters Right Now

This becomes especially relevant when looking at the current pattern, which has featured:

• Periods of blocking or near-blocking signals
• Fluctuations between negative and neutral NAO
• A generally active but inconsistent storm track

It’s tempting in setups like this to assume that a negative or trending-negative NAO automatically favors significant snowfall. But this dataset shows that assumption doesn’t hold up well on its own.

Forecast Takeaway: What the NAO Can Tell Us in This Pattern

In the current regime, NAO is useful for context, not conclusions.

A negative or neutral NAO can suggest:

• Slower or more amplified flow
• Increased chances for cold air to linger
• A background environment that can support wintry outcomes

But it does not guarantee:

• That storms will track favorably
• That cold air arrives at the right time
• That precipitation intensity overlaps with sub-freezing thermals

Those details are being driven right now by shortwave timing, phasing, and thermal profiles, not by the NAO index itself.

Why Snowfall Still Comes Down to Storm-Scale Details

Looking at the current setup, snowfall outcomes will hinge on:

• Whether individual waves phase or shear out
• How far north warm air intrudes ahead of systems
• The placement of deformation zones and banding
• Boundary-layer temperatures during peak precipitation

All of those factors can overwhelm whatever background signal the NAO is providing.

Bottom Line for the Current Pattern

This analysis reinforces a critical forecasting lesson:

The NAO can help frame the pattern—but it won’t solve the snowfall forecast.

Even in a block-leaning or colder-looking regime, snowfall remains a storm-by-storm problem. The best forecasts right now will come from focusing on:

• Synoptic evolution inside 5–7 days
• Thermal structure and precipitation timing
• High-resolution guidance as events approach

NAO may help explain why the pattern looks the way it does—but it won’t tell you how much snow is going to fall.