ICON and ECMWF AIFS held today's expected 36 degrees within the accuracy margin continuously from 6 days ahead. UKMO was only 0.5 degrees out one day ahead.
We compared 7 forecast models at 3 weather stations in the United Kingdom, using 552 observation hours across 23 complete station-days.
On 13 August 2026, Heathrow has already reached 36 degrees, possibly the hottest temperature of the summer. The day is still in progress: the station has reported 20 of 24 hours, and this comparison provisionally uses 36 degrees. The result will be updated after the day ends.
The earliest continuous accurate forecast was 6 days ahead, from ICON and ECMWF AIFS. One day ahead, ICON forecast 36.4 degrees. The highest measured temperature in the completed period was 34 degrees on 29 July 2026.
At 9 days ahead, no model was within 2 degrees of the expected 36. Forecasts ranged from 26.2 to 33.1 degrees. Even one day ahead, the furthest forecast was 38.0 degrees from GFS.
| Notice | ICON Germany | ECMWF AIFS Europe, AI | Foreca Finland, commercial | GFS United States | UKMO United Kingdom | Apple Weather United States, commercial | ECMWF IFS Europe |
|---|---|---|---|---|---|---|---|
| 9 days ahead | Not available | 33.1-2.9 | Not available | 30.5-5.5 | Not available | Not available | 26.2-9.8 |
| 8 days ahead | Not available | 34.2-1.8 | Not available | 32.9-3.1 | Not available | Not available | 26.2-9.8 |
| 7 days ahead | Not available | 33.2-2.8 | Not available | 35.7-0.3 | Not available | Not available | 30.2-5.8 |
| 6 days ahead | 35.4-0.6 | 34.2-1.8 | 32.4-3.6 | 32.5-3.5 | 34.0-2.0 | 31.6-4.4 | 34.6-1.4 |
| 5 days ahead | 35.2-0.8 | 34.0-2.0 | 34.0-2.0 | 36.5+0.5 | 32.8-3.2 | 33.2-2.8 | 32.9-3.1 |
| 4 days ahead | 35.6-0.4 | 34.0-2.0 | 35.1-0.9 | 36.7+0.7 | 36.1+0.1 | 34.4-1.6 | 34.1-1.9 |
| 3 days ahead | 35.6-0.4 | 34.7-1.3 | 35.3-0.8 | 37.0+1.0 | 35.1-0.9 | 34.4-1.6 | 34.3-1.7 |
| 2 days ahead | 36.1+0.1 | 34.9-1.1 | 36.0+0.0 | 36.8+0.8 | 35.7-0.3 | 34.9-1.1 | 34.7-1.3 |
| 1 day ahead | 36.4+0.4 | 35.2-0.8 | 36.4+0.4 | 38.0+2.0 | 36.5+0.5 | 35.1-0.9 | 34.9-1.1 |
| Inside 2 degrees from | 6 days ahead | 6 days ahead | 5 days ahead | 5 days ahead | 4 days ahead | 4 days ahead | 4 days ahead |
Apple Weather and Foreca are included alongside the public models. As neither has a public archive, VeriSky uses forecasts it collected itself: Apple Weather since 7 August 2026 and Foreca since 7 August 2026. An empty cell means no forecast was stored for that lead time. The event table normally uses the snapshot nearest 6 a.m. local time. If that snapshot stops before the afternoon, it uses a later snapshot from the same notice date that reaches the daytime maximum window and marks the partial hour count.
Temperature and wind, day by day
Across 23 complete station-days at Fairford, Heathrow, and Sumburgh, ICON had the highest temperature score at 92.8, with a typical error of 1.09 degrees. UKMO led for wind at 76.0, with a typical error of 5.14 km/h.
UKMO ranked 4th of 7 for temperature and 1st for wind. This result applies only to Fairford, Heathrow, and Sumburgh during 1 July to 12 August; it does not show how the model performs across the United Kingdom.
ECMWF AIFS is trained on historical weather and works differently from the physics-based models. It ranked 6th of 7 for temperature and 6th for wind.
For the hot day, it was within the margin from 6 days ahead. One day ahead it forecast 35.2 degrees, compared with 36 on the day itself. Strong average performance does not automatically produce the best forecast for an extreme.
| Model | Temperature score | Typical error | Wind score | Typical error |
|---|---|---|---|---|
| ICON Germany | 1.09 °C | 5.52 km/h | ||
| Apple Weather United States, commercial | 0.96 °C | 5.74 km/h | ||
| Foreca Finland, commercial | 0.91 °C | 6.25 km/h | ||
| UKMO United Kingdom | 1.11 °C | 5.14 km/h | ||
| ECMWF IFS Europe | 0.97 °C | 4.75 km/h | ||
| ECMWF AIFS Europe, AI | 1.30 °C | 6.16 km/h | ||
| GFS United States | 1.34 °C | 7.90 km/h |
Distance separates the models
The chart shows how accuracy changes as forecasts look further ahead, using the same stations throughout. A line stops below 95 percent coverage, or when the national model's own forecast ends.
View the chart values as a table
| Model | Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6 |
|---|---|---|---|---|---|---|
| ICON | 92.8 552 h | 90.7 552 h | 89.1 552 h | 89.3 552 h | Not available | Not available |
| Apple Weather | 92.6 552 h | 91.5 528 h | Not available | Not available | Not available | Not available |
| Foreca | 92.5 552 h | 90.1 528 h | Not available | Not available | Not available | Not available |
| UKMO | 91.6 552 h | 87.3 532 h | Not available | Not available | Not available | Not available |
| ECMWF IFS | 91.5 552 h | 91.3 552 h | 90.5 552 h | 86.2 552 h | 77.4 552 h | Not available |
| ECMWF AIFS | 82.4 552 h | 80.4 552 h | 80.4 552 h | 87.1 552 h | 80.7 552 h | 81.5 552 h |
| GFS | 81.0 552 h | 80.2 552 h | 75.6 552 h | 72.8 552 h | 70.9 552 h | 73.9 552 h |
The sample, not just the score
The results are based on the stations and periods below, showing the true size of the sample.
| Station | Days | Hours | First included | Last included |
|---|---|---|---|---|
| Fairford EGVA | 3 | 72 | 9 August 2026 | 11 August 2026 |
| Heathrow EGLL | 5 | 120 | 8 August 2026 | 12 August 2026 |
| Sumburgh EGPB | 15 | 360 | 28 July 2026 | 12 August 2026 |
What to take from this
At 6 days ahead, ECMWF AIFS has the best score across the full sample at 81.5. That is 11.3 points below the best one-day forecast. Accuracy declines clearly as the forecast range increases.
The 7 models on this page were selected in advance. Another 20 models were scored over the same hours and are listed in the accompanying dataset.
The next edition covers the rest of August. Rain will be added once enough independent radar data is available.
About this comparison
Temperature and wind come from NOAA Aviation Weather Center METAR station observations at Fairford, Heathrow, and Sumburgh. Only reports within 20 minutes of a whole hour and days with all 24 hours are included.
The heat section covers 13 August 2026, outside the scored period. As the day is still in progress, the comparison provisionally uses the expected 36 degrees. At the time of writing, 20 of 24 hours had been reported at Heathrow; the highest reading was 36 degrees. The measured maximum will follow after the day ends.
Because the heat day is still in progress, it was selected manually for this edition. The highest temperature in the completed period was 34 degrees on 29 July. The comparison uses Heathrow's record, the public models' 00 UTC runs and the commercial forecast selected from that notice date as described below.
Selection and coverage
For Apple Weather and Foreca, VeriSky normally uses the station forecast collected nearest 6 a.m. local time. For an event maximum, if that snapshot ends before the afternoon, a later snapshot from the same notice date may be used when it reaches the daytime maximum window; the table prints its partial hour count. Collection began on 7 August 2026 and 7 August 2026; the later date sets the start of the common sample. Commercial forecasts are newer than the public models' 00 UTC runs.
Only models with at least 95 percent coverage qualify. Each row is then scored over the same 552 available hours.
AccuWeather is excluded because its terms prohibit ranked comparisons. Other commercial services and VeriSky's own blend are also omitted. The remaining 20 scored models are listed in the dataset.
Limits and sources
This edition covers only Fairford, Heathrow, and Sumburgh during 1 July to 12 August. The results are not a verdict on the whole of the United Kingdom or on long-term performance.
We compare archived model output with independent station observations. Data is at data.json, the full method at methodology and corrections at corrections.
The live version of this report is an app
After The Forecast comes out on a schedule. VeriSky keeps the rolling scores current for the places you care about and shows how models change with forecast distance.
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