Summer Sub-Seasonal Forecast Success in Europe

A successful long-lead forecast for the recent, significant pattern change over Europe provided early insight on conditions. The sub-seasonal forecast successfully predicted the change from warm, calm weather patterns of June to cooler, wetter windier conditions in early July — three weeks in advance.

Understanding developing weather patterns

In mid-June, some customers were unsure how the first half of the July pattern would evolve. DTN meteorologists used the World Climate Service analog tool to identify previous June weather patterns over Europe, like June 2020. They assessed global weather patterns and sea surface temperature anomalies. Using this insight, they created several sets of analog forecasts for July, based on similar years in the historical data.

The conclusion was that the pattern in June — high pressure over Scandinavia and low wind over Germany and the UK — would suddenly change to a stronger westerly by early July. As a result, it would allow a windier pattern over the UK and Germany, as the high-pressure area shifted to south and southwest Europe. These early and accurate reports to customers ensured that they were prepared for weather patterns in July.

Using statistical analogs to fine-tune analysis

In addition to computer models, DTN meteorologists use statistical analogs to aid with sub-seasonal forecasts. These are created by analyzing climatology records for years with similar local and global conditions to current patterns. This approach helps build confidence in forecast accuracy — especially where computer models struggle with a particular scenario.

Conflicting raw model forecasts from the ECMWF and CFSv2 models for the expected pattern, and weak to non-existent signals for precipitation and wind over Europe at 3-4 weeks presented a challenge.

However, the analog analysis allowed the meteorologists to put much more trust in the ECMWF pressure pattern – a trough over northwest Europe – and apply plenty of forecast impact detail in the report to customers. It summarized conditions as wet, windy, and less warm in the north, with a warmer, drier, and sunnier pattern in south and southwest Europe. This weather pattern in early to mid-July has verified.

Sub-seasonal forecasting for summer in Europe, especially 3-4 weeks ahead, can be a challenge. However, DTN meteorologists consistently predicted the weather going into July, calling the significant pattern changes at range. Confidence in this pattern change increased with the DTN forecast analysis methodology and the use of the WCS analysis tools.