How Accurate is the Weather Forecast in Japan?

Japan Meteorological Agency publishes the result of their weather forecasts. It is the percentage of right forecasting cases. 

The below is the average percentage of the right forecasts which predicted a chance of rain (data in 1992 - 2013). If a forecast says that there is a chance of rain, we will have rain with a probability of 83%.

Table : Percentage of right forecasting cases by region (%)

Annual average	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Nationwide Average
Tomorrow's forecast	78	84	85	84	84	78	83
2 days after	74	80	81	80	81	75	79
3 days after	70	75	76	75	75	71	74
4 days after	67	73	73	73	73	69	71
5 days after	66	71	71	70	71	67	69
6 days after	64	70	69	69	69	66	68
7 days after	62	69	68	67	68	65	66
3 - 7 days after, average	66	72	72	71	71	67	70

January	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	71	90	85	83	81	78	82
2 days after	68	87	83	80	77	75	80
3 days after	68	84	81	80	75	69	77
4 days after	66	83	79	76	72	68	75
5 days after	64	80	76	73	70	66	73
6 days after	64	80	75	72	68	64	71
7 days after	63	79	74	70	68	62	70
3 - 7 days after, average	65	81	77	74	71	66	73

February	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	73	88	86	84	84	80	83
2 days after	70	85	82	81	82	78	80
3 days after	66	81	79	77	77	73	76
4 days after	65	79	77	73	74	70	73
5 days after	64	79	75	71	71	68	72
6 days after	63	77	74	70	69	66	70
7 days after	62	76	72	68	68	64	68
3 - 7 days after, average	64	78	75	72	72	68	72

March	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	75	86	86	84	86	81	83
2 days after	71	81	83	81	83	78	79
3 days after	67	77	79	77	79	72	75
4 days after	66	75	76	74	73	70	72
5 days after	64	72	71	69	70	68	69
6 days after	63	71	69	69	69	66	67
7 days after	61	68	67	64	68	64	65
3 - 7 days after average	64	73	73	70	72	68	69

April	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	79	85	88	87	88	78	85
2 days after	76	83	84	83	84	74	81
3 days after	71	76	78	76	79	71	75
4 days after	69	74	74	74	75	67	72
5 days after	67	72	73	73	73	67	71
6 days after	65	69	69	70	70	66	68
7 days after	63	67	66	67	67	65	65
3 - 7 days after, average	67	72	72	72	73	67	70

May	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	82	85	87	87	88	79	85
2 days after	78	80	83	83	84	75	81
3 days after	72	75	78	77	78	69	76
4 days after	70	72	74	73	75	66	72
5 days after	68	69	72	72	74	65	70
6 days after	66	66	69	70	71	61	68
7 days after	65	65	68	69	70	60	66
3 - 7 days after, average	68	69	72	72	74	64	71

June	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	83	79	82	83	83	79	82
2 days after	79	72	77	77	76	75	76
3 days after	73	66	68	68	69	73	69
4 days after	71	62	66	66	66	71	66
5 days after	70	59	61	60	61	71	63
6 days after	68	56	59	59	60	72	61
7 days after	67	56	55	55	58	72	59
3 - 7 days after, average	70	60	62	61	63	72	64

July	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	80	77	80	80	81	78	79
2 days after	75	72	76	76	77	74	75
3 days after	68	65	68	69	69	72	68
4 days after	65	63	65	68	68	70	66
5 days after	65	61	64	68	67	69	65
6 days after	63	61	65	68	66	68	64
7 days after	63	61	63	67	66	67	64
3 - 7 days after, average	65	62	65	68	67	69	66

August	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	80	78	79	80	79	74	79
2 days after	76	74	76	76	74	70	75
3 days after	69	68	70	71	68	66	69
4 days after	67	67	68	69	66	65	67
5 days after	65	65	67	68	66	65	65
6 days after	63	65	66	67	64	64	64
7 days after	62	64	65	66	62	63	63
3 - 7 days after, average	65	66	67	68	65	65	66

September	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	81	82	83	82	84	76	81
2 days after	76	78	79	77	80	73	77
3 days after	70	70	71	71	75	68	71
4 days after	66	66	68	68	73	65	67
5 days after	63	65	65	67	71	64	66
6 days after	62	63	64	66	71	64	64
7 days after	60	61	62	65	71	64	63
3 - 7 days after, average	64	65	66	67	72	65	66

October	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	80	85	87	87	87	77	84
2 days after	77	80	83	83	84	74	81
3 days after	71	77	78	78	82	70	76
4 days after	69	75	76	77	81	69	74
5 days after	65	73	75	74	78	68	72
6 days after	63	72	74	73	78	68	71
7 days after	60	71	72	71	76	67	69
3 - 7 days after, average	66	73	75	75	79	68	72

November	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	78	88	88	86	86	80	84
2 days after	74	84	85	83	85	75	81
3 days after	71	81	81	79	78	71	77
4 days after	70	78	79	76	75	68	74
5 days after	67	77	76	74	72	67	72
6 days after	65	75	75	73	72	66	71
7 days after	62	74	74	71	70	64	69
3 - 7 days after, average	67	77	77	75	73	67	73

December	Sapporo	Tokyo	Nagoya	Osaka	Fukuoka	Okinawa	Average
Tomorrow	75	89	86	84	84	81	83
2 days after	71	87	83	80	80	78	80
3 days after	70	84	81	78	77	73	77
4 days after	67	84	79	76	75	72	76
5 days after	65	82	77	73	74	69	73
6 days after	64	82	75	72	73	68	73
7 days after	62	82	76	72	74	66	72
3 - 7 days after, average	65	83	78	74	74	69	74

Source is Japan Meteorological Agency. 降水の有無の適中率の例年値

www.data.jma.go.jp/fcd/yoho/kensho/reinen.html

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