JMA announcements vs. observations
Announcements and observations for August 12, 2026 to November 2, 2026
We record JMA's prefectural forecasts and one-week forecasts every day and set them beside that day's observations.
By days ahead
| Days ahead | High error (°C) | Low error (°C) | Rain / no rain agreement |
|---|---|---|---|
| 1 day ahead | 1.0 | 0.8 | 69% |
| 2 days ahead | 1.2 | 1.0 | 83% |
| 3 days ahead | 1.4 | 1.1 | 79% |
| 4 days ahead | 1.5 | 1.1 | 77% |
| 5 days ahead | 1.6 | 1.2 | 75% |
| 6 days ahead | 1.7 | 1.3 | 72% |
| 7 days ahead | 1.9 | 1.5 | 69% |
The error is the average size of the difference between the announced and the observed temperature. Temperatures are compared only on days when the observed low came between 0:00 and 9:00 and the high between 9:00 and 18:00. Rain / no rain agreement is the share of days on which whether the announced weather included rain or snow matched whether it actually rained or snowed.
Error in the high by region (°C)
| Region | Days ahead | ||||||
|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
| Hokkaido | 1.0 | 1.3 | 1.5 | 1.5 | 1.7 | 1.8 | 1.9 |
| Tohoku | 1.1 | 1.5 | 1.7 | 1.8 | 2.0 | 2.0 | 2.2 |
| Kanto Koshin | 1.0 | 1.3 | 1.5 | 1.6 | 1.7 | 1.8 | 1.9 |
| Tokai | 1.1 | 1.3 | 1.4 | 1.7 | 1.9 | 2.0 | 2.0 |
| Hokuriku | 1.0 | 1.3 | 1.3 | 1.4 | 1.6 | 1.9 | 2.0 |
| Kinki | 1.0 | 1.2 | 1.2 | 1.5 | 1.5 | 1.7 | 1.8 |
| Chugoku | 1.0 | 1.3 | 1.5 | 1.6 | 1.8 | 2.0 | 2.1 |
| Shikoku | 1.0 | 1.1 | 1.2 | 1.4 | 1.5 | 1.7 | 1.8 |
| Northern Kyushu | 1.0 | 1.2 | 1.4 | 1.4 | 1.7 | 1.8 | 2.0 |
| Southern Kyushu and Amami | 0.8 | 0.9 | 0.9 | 1.0 | 1.0 | 1.0 | 1.1 |
| Okinawa | 0.6 | 0.7 | 0.7 | 0.8 | 0.8 | 0.8 | 0.8 |
Error in the low by region (°C)
| Region | Days ahead | ||||||
|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
| Hokkaido | 1.0 | 1.2 | 1.3 | 1.3 | 1.5 | 1.6 | 1.9 |
| Tohoku | 0.9 | 1.1 | 1.2 | 1.3 | 1.3 | 1.4 | 1.6 |
| Kanto Koshin | 0.8 | 1.0 | 1.1 | 1.1 | 1.2 | 1.3 | 1.4 |
| Tokai | 0.7 | 0.8 | 0.8 | 0.9 | 1.0 | 1.1 | 1.1 |
| Hokuriku | 0.8 | 0.9 | 1.0 | 1.0 | 1.1 | 1.2 | 1.4 |
| Kinki | 0.7 | 1.0 | 1.0 | 1.1 | 1.2 | 1.2 | 1.4 |
| Chugoku | 0.9 | 0.9 | 1.1 | 1.2 | 1.3 | 1.4 | 1.5 |
| Shikoku | 0.8 | 1.1 | 1.1 | 1.2 | 1.3 | 1.4 | 1.5 |
| Northern Kyushu | 0.9 | 0.9 | 1.1 | 1.2 | 1.3 | 1.4 | 1.5 |
| Southern Kyushu and Amami | 0.7 | 0.8 | 1.0 | 1.1 | 1.1 | 1.3 | 1.4 |
| Okinawa | 0.7 | 0.9 | 1.0 | 1.0 | 1.0 | 1.1 | 1.1 |
Probability of precipitation vs. how often it rained
| Announced probability of precipitation | Share of days with rain or snow |
|---|---|
| 0% | 0% |
| 10% | 1% |
| 20% | 6% |
| 30% | 16% |
| 40% | 35% |
| 50% | 60% |
| 60% | 70% |
| 70% | 84% |
| 80% | 91% |
| 90% | 95% |
| 100% | 100% |
Daily probability of precipitation for 2 to 7 days ahead.
Announced weather vs. how often it rained
| Announced weather | Share of days with rain or snow |
|---|---|
| Includes rain or snow | 64% |
| No rain or snow | 17% |
By reliability (3 or more days ahead)
| Reliability | Rain / no rain agreement | High error (°C) |
|---|---|---|
| A | 91% | 1.2 |
| B | 72% | 1.7 |
| C | 62% | 2.0 |
Reliability is one of 3 levels, A / B / C, that JMA gives one-week forecasts for 3 or more days ahead.
Error by month (°C)
| Month | 1 day ahead | 7 days ahead | ||
|---|---|---|---|---|
| High | Low | High | Low | |
| August 2026 | 1.0 | 0.7 | 2.1 | 1.3 |
| September 2026 | 1.1 | 0.8 | 2.0 | 1.4 |
| October 2026 | 0.9 | 0.9 | 1.7 | 1.6 |
| November 2026 | 1.1 | 0.9 | 1.6 | 1.4 |
Days with the largest gap between announcement and observation
| Date | Station | Announced | Observed |
|---|---|---|---|
| Oct 21, 2026 | Nagano Kanto Koshin High, 7 days ahead | 18.0°C | 31.0°C |
| Aug 25, 2026 | Abashiri Hokkaido High, 5 days ahead | 29.0°C | 17.9°C |
| Aug 29, 2026 | Wakamatsu Tohoku High, 5 days ahead | 31.0°C | 20.4°C |
| Oct 21, 2026 | Kofu Kanto Koshin High, 4 days ahead | 23.0°C | 33.5°C |
| Oct 21, 2026 | Toyama Hokuriku High, 7 days ahead | 20.0°C | 30.4°C |
| Aug 31, 2026 | Miyako Tohoku High, 7 days ahead | 31.0°C | 20.9°C |
| Oct 21, 2026 | Yamagata Tohoku High, 7 days ahead | 18.0°C | 28.0°C |
| Aug 31, 2026 | Kumagaya Kanto Koshin High, 3 days ahead | 37.0°C | 27.3°C |
| Oct 21, 2026 | Fukui Hokuriku High, 7 days ahead | 20.0°C | 29.7°C |
| Aug 30, 2026 | Yamagata Tohoku High, 6 days ahead | 30.0°C | 20.4°C |