The Netherlands All editions · No. 3 ENNL

After The Forecast

The weather forecast, reviewed after the weather.

Published by VeriSky

Rain check · 26 July to 24 August 2026

For tomorrow at De Bilt, KNMI Harmonie NL wins; ECMWF AIFS saw the wet week from 8 days ahead.

The best forecast for tomorrow did not come from the model that gave the earliest steady signal for this wet week.

Edition No. 3 · The Netherlands · 30 days of hourly rain at De Bilt

From 17 August 2026 to 23 August 2026, De Bilt recorded 30.3 millimetres of rain. At least one millimetre fell on 5 days; 18 August 2026 was the wettest with 13.5 millimetres.

For the question of whether it will rain tomorrow, KNMI Harmonie NL scored best over the whole test period at 58.4. Further out, ECMWF AIFS was the most consistent: from 8 days ahead, its weekly estimate stayed within a factor of two. One day ahead it expected 39.6 millimetres.

At 9 days ahead, GFS forecast 30.0 millimetres against 30.3 measured. It was the only model whose run covered the whole week at that distance. One day ahead, estimates still ranged from 15.9 by GFS to 39.6 by ECMWF AIFS.

17 August 2026 to 23 August 2026, 30.3 millimetresFig. 1 · forecast rainfall over the whole spell
NoticeECMWF AIFS Europe, AIApple Weather United States, commercialECMWF IFS EuropeGFS United StatesForeca Finland, commercialICON GermanyKNMI Harmonie NL Netherlands
9 days ahead3.6141 h · to 23 August3.332 h · to 18 August3.2141 h · to 23 August30.04 wet daysNot availableNot availableNot available
8 days ahead22.85 wet days0.056 h · to 19 August14.03 wet days14.21 wet daysNot availableNot availableNot available
7 days ahead16.23 wet days4.480 h · to 20 August6.61 wet days18.52 wet days0.25 h · to 17 August0.115 h · to 17 AugustNot available
6 days ahead37.24 wet days17.898 h · to 21 August14.04 wet days7.82 wet days6.830 h · to 18 August5.139 h · to 18 AugustNot available
5 days ahead33.35 wet days17.7122 h · to 22 August26.24 wet days23.45 wet days14.354 h · to 19 August2.563 h · to 19 AugustNot available
4 days ahead21.65 wet days20.1146 h · to 23 August11.13 wet days3.61 wet days3.878 h · to 20 August0.987 h · to 20 AugustNot available
3 days ahead23.47 wet days23.55 wet days15.74 wet days5.42 wet days16.697 h · to 21 August5.6105 h · to 21 AugustNot available
2 days ahead35.47 wet days24.85 wet days50.66 wet days31.84 wet days17.1121 h · to 22 August7.3129 h · to 22 August0.115 h · to 17 August
1 day ahead39.67 wet days23.55 wet days21.86 wet days15.94 wet days44.9145 h · to 23 August11.2153 h · to 23 August5.539 h · to 18 August
Within a factor of 2 from8 days ahead3 days ahead3 days ahead2 days aheaddoes not reachdoes not reachdoes not reach
Each cell shows the forecast total for the 162 readable hours at De Bilt; the gauge measured 30.3 millimetres. Coloured cells fall between 15.1 and 60.6 millimetres. A partial run does not cover the whole week and is not counted.

The wettest day, hour by hour

A good weekly total does not mean the showers fell in the right hours. On 18 August 2026, De Bilt measured 13.5 millimetres across 8 of the 24 hours. ICON was the most useful at short range: one day ahead it caught all 8 wet hours with 0 false alarms.

18 August 2026, 13.5 millimetresFig. 2 · wet hours caught, by notice
NoticeICON GermanyKNMI Harmonie NL NetherlandsECMWF AIFS Europe, AIGFS United StatesECMWF IFS Europe
7 days aheadbeyond horizonbeyond horizon8+13 false6+3 false0+0 false
6 days ahead6+0 falsebeyond horizon8+13 false1+4 false7+12 false
5 days ahead0+0 falsebeyond horizon7+9 false0+0 false1+7 false
4 days ahead7+0 falsebeyond horizon8+10 false7+3 false1+1 false
3 days ahead7+0 falsebeyond horizon8+10 false4+2 false8+7 false
2 days ahead8+0 falsebeyond horizon8+10 false5+5 false6+4 false
1 day ahead8+0 false8+1 false8+10 false7+9 false6+8 false
The gauge at De Bilt measured 13.5 millimetres on 18 August 2026, with at least a tenth of a millimetre in 8 of the 24 hours it could be read. Each cell is how many of those hours the run caught, allowing an hour either side, with the false alarms it raised beside it.

Which model for tomorrow?

Across all 30 days, KNMI Harmonie NL offered the best balance between missed rain and false alarms, with a score of 58.4. ICON followed closely at 56.9. ECMWF AIFS finished last at 44.0: it found many wet hours but raised 168 false alarms. For rain at De Bilt one day ahead, KNMI Harmonie NL is therefore the best choice in this test.

Rain, 26 July to 24 AugustFig. 3 · one day ahead
Model Rain score Caught Missed False alarm Hours called wet
KNMI Harmonie NL Netherlands
58.4
 23 16 16 38
ICON Germany
56.9
 20 19 13 36
GFS United States
52.2
 29 10 55 92
ECMWF IFS Europe
52.0
 31 8 65 106
ECMWF AIFS Europe, AI
44.0
 39 0 168 234
Scores for one-day-ahead forecasts across 712 readable hours at De Bilt; 39 of them were wet. The score rewards hits and penalises misses and false alarms. The gauge has no reading for 8 hours (30 July 13:00 to 30 July 14:00 and 20 August 21:00 to 21 August 02:00); those hours are left out for every model.

About this comparison

The selected wet week runs from 17 August 2026 to 23 August 2026. The hourly comparison uses its wettest day, 18 August 2026 with 13.5 millimetres. Forecasts come from the public models' 00 UTC runs and are compared with the gauge at De Bilt.

How rain is judged

An hour counts as wet from 0.1 millimetres. A forecast may be 1 hour early or late; when the gauge has no reading, that hour is left out for every model. This is a test at one gauge in De Bilt, not a verdict on a whole country.

Selection and coverage

Apple Weather and Foreca have no public archive. Their columns come from forecasts VeriSky has stored since 16 July 2026 and 24 July 2026; a different time convention means they are not scored hour by hour.

We compare archived model output with independent station observations. Data is at data.json, the full method at methodology and corrections at corrections.

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