After The Forecast 14 August to 23 August

Rain check · 14 August to 23 August 2026

For tomorrow at Lakenheath, GFS wins; ECMWF AIFS saw the wet week from 6 days ahead.

Rainfall totals and rain timing are different tests. This report checks the models on both.

Edition No. 4 · The United Kingdom · 10 days of hourly rain at Lakenheath

From 17 August 2026 to 23 August 2026, Lakenheath recorded 22.2 millimetres of rain. At least one millimetre fell on 4 days; 21 August 2026 was the wettest with 13.5 millimetres.

For the question of whether it will rain tomorrow, GFS scored best over the whole test period at 66.5. Further out, ECMWF AIFS was the most consistent: from 6 days ahead, its weekly estimate stayed within a factor of two. One day ahead it expected 19.9 millimetres.

At 9 days ahead, GFS forecast 14.8 millimetres against 22.2 measured. It was the only model whose run covered the whole week at that distance. One day ahead, estimates still ranged from 2.7 by GFS to 19.9 by ECMWF AIFS.

17 August 2026 to 23 August 2026, 22.2 millimetresFig. 1 · forecast rainfall over the whole spell

Forecast rainfall for 17 August 2026 to 23 August 2026, by notice
Notice	ECMWF AIFS Europe, AI	ECMWF IFS Europe	GFS United States	ICON Germany	UKMO United Kingdom
9 days ahead	9.0139 h · to 23 August	0.4139 h · to 23 August	14.82 wet days	Not available	Not available
8 days ahead	23.35 wet days	18.32 wet days	5.92 wet days	Not available	Not available
7 days ahead	7.81 wet day	15.94 wet days	10.31 wet day	0.014 h · to 17 August	0.02 h · to 17 August
6 days ahead	40.36 wet days	15.35 wet days	4.82 wet days	2.338 h · to 18 August	2.526 h · to 18 August
5 days ahead	27.04 wet days	23.07 wet days	17.34 wet days	0.162 h · to 19 August	2.250 h · to 19 August
4 days ahead	14.03 wet days	22.73 wet days	1.51 wet day	3.485 h · to 20 August	0.373 h · to 20 August
3 days ahead	12.65 wet days	7.62 wet days	6.41 wet day	4.0103 h · to 21 August	2.491 h · to 21 August
2 days ahead	23.87 wet days	10.83 wet days	13.63 wet days	5.4127 h · to 22 August	7.4115 h · to 22 August
1 day ahead	19.96 wet days	9.54 wet days	2.71 wet day	18.5150 h · to 23 August	14.9139 h · to 23 August
Within a factor of 2 from	6 days ahead	never	never	does not reach	does not reach

Each cell shows the forecast total for the 160 readable hours at Lakenheath; the gauge measured 22.2 millimetres. Coloured cells fall between 11.1 and 44.5 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 21 August 2026, Lakenheath measured 13.5 millimetres across 10 of the 23 hours. ECMWF AIFS was the most useful at short range: one day ahead it caught 9 of those 10 wet hours with 2 false alarms.

21 August 2026, 13.5 millimetresFig. 2 · wet hours caught, by notice

Wet hours correctly forecast on 21 August 2026, by notice
Notice	ECMWF AIFS Europe, AI	ECMWF IFS Europe	GFS United States	ICON Germany	UKMO United Kingdom
7 days ahead	9+2 false	0+0 false	1+2 false	beyond horizon	beyond horizon
6 days ahead	10+7 false	7+2 false	3+4 false	0+0 false	6+0 false
5 days ahead	10+7 false	8+0 false	0+0 false	9+7 false	4+0 false
4 days ahead	10+7 false	4+0 false	0+3 false	6+0 false	1+5 false
3 days ahead	10+7 false	6+1 false	3+0 false	3+0 false	4+2 false
2 days ahead	10+7 false	8+0 false	0+0 false	8+0 false	4+0 false
1 day ahead	9+2 false	6+0 false	6+0 false	5+1 false	2+0 false

The gauge at Lakenheath measured 13.5 millimetres on 21 August 2026, with at least a tenth of a millimetre in 10 of the 23 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 timed tomorrow's rain best?

Across all 10 days, GFS offered the best balance between missed rain and false alarms, with a score of 66.5. ECMWF AIFS followed closely at 65.9. UKMO finished last at 30.5: it found many wet hours but raised 9 false alarms. For rain at Lakenheath one day ahead, GFS is therefore the best choice in this test.

Rain, 14 August to 23 AugustFig. 3 · one day ahead

Rain standings, one day ahead
Model	Rain score	Caught	Missed	False alarm	Hours called wet
GFS United States	66.5	22	20	2	22
ECMWF AIFS Europe, AI	65.9	34	8	44	99
ECMWF IFS Europe	62.4	23	19	11	40
ICON Germany	48.0	15	27	4	15
UKMO United Kingdom	30.5	9	33	9	19

Scores for one-day-ahead forecasts across 231 readable hours at Lakenheath; 42 of them were wet. The score rewards hits and penalises misses and false alarms. The gauge has no reading for 9 hours (15 August 06:00, 19 August 16:00, 20 August 15:00, 20 August 20:00 to 21 August 00:00, and 23 August 07:00); 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, 21 August 2026 with 13.5 millimetres. Forecasts come from the public models' 00 UTC runs and are compared with the gauge at Lakenheath.

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 Lakenheath, not a verdict on a whole country.

At Lakenheath, the scheduled METAR at 55 minutes past the hour carries a P group for rain during the preceding hour. It is compared with the model hour ending five minutes later. No P group in a scheduled report means dry; no scheduled report means unknown, and that hour is left out.

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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