When Winter Arrives At Once

MetSwift Claros · European windstorm

Our lowest call in fourteen winters.

Every August, before the season starts, we forecast whether Europe’s winter storms will arrive spread through the season or all at once. For the winter now beginning, the call sits below all thirteen we have scored.

September 2026

the thirteen calls we have scored 2013/14 2014/15 2015/16 2016/17 2017/18 2018/19 2019/20 2020/21 2021/22 2022/23 2023/24 2024/25 2025/26 2018/19 2022/23 2026/27, the winter now starting 2026/27 quieter, less bunched busier, more bunched

We are not expecting another February 2022. What follows is the record that call is scored against.

2 of 2
the two winters we called highest were the two most concentrated of the thirteen
4 of 5
of the five we called highest, four finished in the five most concentrated
46%
of the variation in how bunched a winter is, explained by an August forecast
0.1%
explained by the long-run historical trend

What we forecast

Not how much bad weather is coming. Whether it arrives together. A second call, issued in October, asks the other question: how severe the storms themselves will be.

Oct Nov Dec Jan Feb Mar Spread 8 bad days Bunched 8 bad days one week

Same amount of severe weather, and two completely different winters for an aggregate, a reinstatement or an hours clause. February 2022 is the reference case: Dudley, Eunice and Franklin inside a single week, and PERILS settled the series at €3,851m.

Nothing else tells you this

Every other way of guessing, measured on the same thirteen winters.

agreement with how bunched the winter turned out · 0 is none, 1 is perfect -0.5 +0.5 0 Our August forecast issued before the season Our August forecast: +0.68 +0.68 The long-run trend the whole record The long-run trend: -0.03 -0.03 How windy the winter was known only afterwards How windy the winter was: -0.04 -0.04 Last winter’s outcome known before the season Last winter’s outcome: -0.39 -0.39 The season’s storm severity known only afterwards The season’s storm severity: -0.48 -0.48

Knowing, with hindsight, how windy a winter was or how severe its storms were tells you nothing about how concentrated it was.

How it was built

The relationships were found in the observed record first, then tested as forecasts.

Found in the recordAcross 53 winters of station observations, rain days track storm clustering at +0.59 and warm days at +0.53. Across 41 winters, wind activity tracks our independent storm catalogue at +0.62.
Then forecastOnly after those links held were the same instruments used to make a forward call. Thirteen August forecasts later, that call tracks how concentrated the winter turned out at +0.68.
Pointed at the right wintersRun the concentration measure back across the 53-year record and 1989/90 sits with 2018/19 and 2021/22 at the top: the winter of Daria, Vivian and Wiebke.

The record

Thirteen winters, each called in August before the season and never revised. Ordered by what we said, strongest at the top.

What we said in August before the season started How bunched the winter actually was the share of the winter’s bad weather that landed in its worst single week, as a multiple of an evenly spread season quieter call more bunched call 2.5× 3.5× 4.0× a typical winter, 2.93× rank 2018/19 2018/19: our August call ranked 1st of thirteen 2018/19: worst week carried 3.90 times an even spread, 2nd of thirteen. Week of 2019-03-09. 3.90× 2nd 2021/22 2021/22: our August call ranked 2nd of thirteen 2021/22: worst week carried 4.04 times an even spread, 1st of thirteen. Week of 2022-02-16. 4.04× 1st 2023/24 2023/24: our August call ranked 3rd of thirteen 2023/24: worst week carried 3.00 times an even spread, 4th of thirteen. Week of 2024-01-20. 3.00× 4th 2013/14 2013/14: our August call ranked 4th of thirteen 2013/14: worst week carried 2.51 times an even spread, 13th of thirteen. Week of 2013-12-21. 2.51× 13th 2014/15 2014/15: our August call ranked 5th of thirteen 2014/15: worst week carried 3.55 times an even spread, 3rd of thirteen. Week of 2015-01-09. 3.55× 3rd 2019/20 2019/20: our August call ranked 6th of thirteen 2019/20: worst week carried 2.93 times an even spread, 7th of thirteen. Week of 2020-02-15. 2.93× 7th 2025/26 2025/26: our August call ranked 7th of thirteen 2025/26: worst week carried 2.83 times an even spread, 11th of thirteen. Week of 2025-10-22. 2.83× 11th 2017/18 2017/18: our August call ranked 8th of thirteen 2017/18: worst week carried 2.86 times an even spread, 8th of thirteen. Week of 2017-12-29. 2.86× 8th 2024/25 2024/25: our August call ranked 9th of thirteen 2024/25: worst week carried 2.83 times an even spread, 10th of thirteen. Week of 2024-11-18. 2.83× 10th 2015/16 2015/16: our August call ranked 10th of thirteen 2015/16: worst week carried 2.93 times an even spread, 6th of thirteen. Week of 2015-11-12. 2.93× 6th 2016/17 2016/17: our August call ranked 11th of thirteen 2016/17: worst week carried 2.85 times an even spread, 9th of thirteen. Week of 2017-02-21. 2.85× 9th 2020/21 2020/21: our August call ranked 12th of thirteen 2020/21: worst week carried 2.97 times an even spread, 5th of thirteen. Week of 2021-03-09. 2.97× 5th 2022/23 2022/23: our August call ranked 13th of thirteen 2022/23: worst week carried 2.66 times an even spread, 12th of thirteen. Week of 2023-01-10. 2.66× 12th

Four of the five winters we called highest finished among the five most concentrated. Concentration is the share of a winter’s severe weather that landed in its single worst week, as a multiple of an evenly spread season, and the worst week is found from station records rather than from a storm list.

Two alarms, thirteen winters

Two alarms on top, what the winter actually did underneath. Reading down a column gives one winter.

alarm fired did not fire the winter delivered it did not no catalogue reading yet THE ALARMS WHAT THE WINTER DELIVERED Concentration · August run will it arrive together? fired 5 times 2013/14: yes 2014/15: yes 2015/16: no 2016/17: no 2017/18: no 2018/19: yes 2019/20: no 2020/21: no 2021/22: yes 2022/23: no 2023/24: yes 2024/25: no 2025/26: no Extremity · October run will it be an extreme season? fired 4 times 2013/14: no 2014/15: no 2015/16: yes 2016/17: no 2017/18: no 2018/19: yes 2019/20: yes 2020/21: yes 2021/22: no 2022/23: the storm catalogue has no reading for this winter yet 2023/24: no 2024/25: no 2025/26: the storm catalogue has no reading for this winter yet Did it arrive together? the five most concentrated of thirteen 5 of 13 winters 2013/14: no 2014/15: yes 2015/16: no 2016/17: no 2017/18: no 2018/19: yes 2019/20: no 2020/21: yes 2021/22: yes 2022/23: no 2023/24: yes 2024/25: no 2025/26: no Was it an extreme season? the four most extreme of the eleven with a reading 4 of 11 winters 2013/14: yes 2014/15: no 2015/16: yes 2016/17: no 2017/18: no 2018/19: no 2019/20: yes 2020/21: no 2021/22: no 2022/23: the storm catalogue has no reading for this winter yet 2023/24: yes 2024/25: no 2025/26: the storm catalogue has no reading for this winter yet 2013/14 2014/15 2015/16 2016/17 2017/18 2018/19 2019/20 2020/21 2021/22 2022/23 2023/24 2024/25 2025/26

An alarm fired in eight of the thirteen winters, and all eight were bad on at least one measure. The five quiet winters were bad on neither. In six of the eight the alarm that fired was the one that came in. In two, 2013/14 and 2020/21, the other measure was the one that went: a warning delivered rather than a call proven. Concentration scores 4 right, 1 false and 1 missed; extremity 2, 2 and 2. An alarm here fires when the call comes in above its own long-run average, which is a placeholder rather than a calibrated level. Concentration is the August index; extremity is the three October measures averaged. A bad winter is one of the five most concentrated of the thirteen, or one of the four most extreme in our storm catalogue. The catalogue has no reading yet for 2022/23 or 2025/26, so extremity is scored on eleven winters.

February 2022, found from the weather alone

The worst week of each winter is identified from station records with no reference to a storm list. For 2021/22 it lands exactly where the market remembers.

16–22 Feb 2022
Dudley, Eunice, Franklin
Concentration
4.04× an even season
Rank of thirteen
1st
Stations hit hard that week
59%
PERILS industry loss
€3,851m
Our August 2021 call
2nd highest of thirteen
Seasonal storm severity
bottom quarter of 75 years
Seasonal wind total
barely above average
Flagged by an activity screen
no

A thin season on every conventional measure, and one of the costliest weeks on record inside it.

And where

What we expected on the left, what arrived on the right.

Built fromWeather station records and our own reanalysis catalogue. No loss data is used anywhere in building, fitting or scoring the forecast.
Scored onThirteen winters, 2013/14 to 2025/26. Each call issued in August, before the season, and never revised.
What it isA view on the shape of a season, for northwest Europe. Not a loss estimate, not a date, and regional rather than local.

MetSwift Claros, European windstorm concentration signal. September 2026. Full method, station selection, reference periods and validation are set out in the technical report, available on request.