Yamada Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yamada Observatory clear sky chart from 2005-11-06 to 2024-12-24.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	6% 3 1 3 2 2 3 2 4 5% 68%	105366
	Night	8% 4 1 3 2 2 2 2 4 5% 65%	103486
Transparency	Day	19% 5% 8% 17% 25% 26%	105114
	Night	21% 5% 9% 19% 24% 22%	103327
Seeing	Day	8% 6% 23% 35% 22% 5%	15425
	Night	9% 2 14% 39% 32% 4	25014

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	12% 9% 4 7% 5% 4 5% 4 5% 7% 37%	2539
	11th to 20th	Day	12% 7% 3 9% 6% 6% 6% 4 7% 7% 33%	2714
	21st to end	Day	18% 7% 3 6% 5% 4 6% 4 6% 9% 34%	3146
February	1st to 10th	Day	14% 7% 2 3 3 3 4 3 5% 6% 50%	1837
	11th to 20th	Day	13% 7% 2 5% 3 4 3 4 5% 7% 48%	1850
	21st to end	Day	16% 8% 2 5% 5% 3 4 3 6% 6% 43%	1570
March	1st to 10th	Day	14% 9% 2 8% 4 4 5% 4 7% 8% 35%	3138
	11th to 20th	Day	8% 5% 1 4 3 3 3 3 4 7% 59%	3384
	21st to end	Day	17% 7% 2 5% 4 4 5% 4 5% 8% 40%	4120
April	1st to 10th	Day	10% 5% 1 4 3 3 3 3 5% 7% 55%	2280
	11th to 20th	Day	11% 4 1 4 3 3 3 3 5% 6% 56%	2249
	21st to end	Day	8% 4 1 3 3 3 3 2 5% 7% 61%	2280
May	1st to 10th	Day	4 2 1 2 1 2 2 2 4 5% 74%	3918
	11th to 20th	Day	2 1 1 2 1 2 2 2 3 5% 79%	4071
	21st to end	Day	4 1 1 2 1 2 1 2 3 4 80%	4751
June	1st to 10th	Day	3 2 1 3 2 3 3 2 5% 7% 70%	2660
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 87%	2660
	21st to end	Day	1 1 2 2 1 1 2 2 2 86%	2660
July	1st to 10th	Day	1 1 1 1 2 2 92%	4420
	11th to 20th	Day	1 1 1 1 1 2 2 3 3 85%	4420
	21st to end	Day	1 1 1 1 1 1 1 1 2 3 86%	4559
August	1st to 10th	Day	1 1 1 1 1 1 1 2 3 87%	3827
	11th to 20th	Day	1 1 1 1 1 1 1 2 92%	3724
	21st to end	Day	1 1 1 1 1 1 1 2 2 90%	4180
September	1st to 10th	Day	2 1 1 1 1 1 1 1 2 3 86%	2280
	11th to 20th	Day	1 1 1 1 2 2 2 1 3 4 83%	2213
	21st to end	Day	2 1 1 2 2 2 2 2 3 4 82%	2090
October	1st to 10th	Day	2 2 1 3 2 2 2 2 4 5% 76%	3349
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 3 78%	3161
	21st to end	Day	4 3 1 3 2 3 3 4 5% 7% 64%	3396
November	1st to 10th	Day	7% 4 1 4 3 3 4 3 5% 6% 59%	1764
	11th to 20th	Day	7% 3 1 3 3 3 3 3 5% 8% 61%	1800
	21st to end	Day	9% 5% 1 3 3 4 4 3 5% 6% 58%	1800
December	1st to 10th	Day	11% 5% 2 4 3 3 4 3 5% 7% 54%	1730
	11th to 20th	Day	19% 8% 2 7% 5% 5% 4 3 5% 6% 37%	2008
	21st to end	Day	13% 8% 3 7% 6% 5% 5% 4 6% 8% 35%	2818
January	1st to 10th	Night	15% 9% 3 6% 5% 4 3 3 4 6% 41%	4406
	11th to 20th	Night	16% 9% 3 7% 4 4 4 3 6% 7% 37%	4237
	21st to end	Night	20% 7% 2 5% 4 3 4 3 6% 8% 38%	4521
February	1st to 10th	Night	16% 6% 1 4 3 3 2 3 4 7% 51%	2341
	11th to 20th	Night	13% 4 1 3 3 3 3 3 4 7% 56%	2218
	21st to end	Night	17% 5% 2 4 3 2 3 3 4 6% 50%	1884
March	1st to 10th	Night	18% 6% 2 6% 4 3 3 4 6% 8% 41%	3736
	11th to 20th	Night	9% 4 1 3 2 3 3 3 5% 6% 61%	3593
	21st to end	Night	19% 6% 2 6% 3 3 4 3 5% 5% 44%	3533
April	1st to 10th	Night	10% 4 1 3 4 2 3 2 4 6% 61%	1900
	11th to 20th	Night	8% 3 1 3 3 3 3 3 3 6% 64%	1879
	21st to end	Night	6% 4 1 3 3 2 3 2 4 6% 67%	1900
May	1st to 10th	Night	6% 2 1 2 2 1 1 2 3 5% 76%	3057
	11th to 20th	Night	3 1 1 1 1 2 2 3 4 81%	2834
	21st to end	Night	3 1 1 1 1 1 2 1 2 3 84%	2808
June	1st to 10th	Night	4 1 1 2 2 1 2 2 3 6% 76%	1520
	11th to 20th	Night	1 1 1 2 1 1 1 2 3 87%	1520
	21st to end	Night	1 1 1 1 1 1 1 2 2 89%	1520
July	1st to 10th	Night	1 1 1 1 3 93%	2540
	11th to 20th	Night	1 2 1 2 1 2 2 2 2 3 82%	2540
	21st to end	Night	1 1 1 1 2 1 2 2 3 3 85%	2997
August	1st to 10th	Night	1 1 1 2 1 1 2 1 3 3 83%	3119
	11th to 20th	Night	1 1 1 1 1 2 2 92%	3126
	21st to end	Night	1 1 1 1 1 1 1 1 2 90%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 90%	1900
	11th to 20th	Night	1 2 1 2 1 1 2 2 2 3 84%	1966
	21st to end	Night	2 1 1 1 1 1 2 3 4 83%	2090
October	1st to 10th	Night	2 1 1 1 1 2 1 3 4 83%	3627
	11th to 20th	Night	2 1 1 1 2 2 2 3 4 81%	3777
	21st to end	Night	3 2 1 2 2 2 2 2 3 5% 77%	4171
November	1st to 10th	Night	7% 4 1 2 2 3 2 2 4 5% 67%	2535
	11th to 20th	Night	6% 3 1 3 2 3 3 3 5% 6% 66%	2600
	21st to end	Night	9% 4 2 4 3 3 3 3 5% 6% 58%	2600
December	1st to 10th	Night	12% 5% 2 5% 3 4 3 3 4 6% 54%	2667
	11th to 20th	Night	20% 6% 2 5% 3 3 4 4 6% 7% 40%	3416
	21st to end	Night	12% 7% 3 7% 6% 5% 5% 4 6% 8% 37%	4910

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	42% 10% 20% 19% 9% 2	2539
	11th to 20th	Day	43% 13% 14% 14% 9% 7%	2714
	21st to end	Day	44% 9% 16% 17% 10% 3	3146
February	1st to 10th	Day	33% 7% 10% 24% 19% 6%	1837
	11th to 20th	Day	34% 6% 11% 22% 18% 7%	1860
	21st to end	Day	41% 8% 11% 24% 15% 1	1570
March	1st to 10th	Day	40% 11% 14% 18% 15% 2	3138
	11th to 20th	Day	23% 7% 15% 33% 15% 7%	3384
	21st to end	Day	37% 10% 16% 21% 13% 2	4120
April	1st to 10th	Day	27% 6% 13% 29% 20% 5%	2280
	11th to 20th	Day	27% 6% 12% 26% 21% 8%	2252
	21st to end	Day	21% 7% 11% 29% 27% 5%	2280
May	1st to 10th	Day	12% 4 8% 28% 34% 13%	3918
	11th to 20th	Day	9% 3 7% 26% 43% 12%	4074
	21st to end	Day	10% 3 5% 30% 43% 9%	4751
June	1st to 10th	Day	13% 4 9% 21% 35% 17%	2660
	11th to 20th	Day	5% 2 5% 15% 42% 31%	2660
	21st to end	Day	7% 1 2 8% 32% 49%	2660
July	1st to 10th	Day	3 1 1 4 14% 76%	4351
	11th to 20th	Day	7% 1 3 5% 18% 66%	4345
	21st to end	Day	5% 2 3 7% 29% 54%	4415
August	1st to 10th	Day	7% 1 2 5% 32% 52%	3812
	11th to 20th	Day	3 1 1 6% 28% 61%	3760
	21st to end	Day	5% 1 3 7% 29% 56%	4179
September	1st to 10th	Day	6% 1 3 6% 32% 51%	2280
	11th to 20th	Day	7% 3 3 18% 39% 29%	2213
	21st to end	Day	9% 1 4 16% 38% 32%	2090
October	1st to 10th	Day	12% 3 3 10% 23% 49%	3349
	11th to 20th	Day	12% 3 5% 23% 36% 21%	3161
	21st to end	Day	20% 3 6% 15% 36% 20%	3396
November	1st to 10th	Day	23% 6% 10% 22% 24% 15%	1764
	11th to 20th	Day	21% 5% 15% 25% 25% 9%	1800
	21st to end	Day	27% 5% 11% 19% 25% 12%	1800
December	1st to 10th	Day	29% 6% 14% 21% 21% 9%	1730
	11th to 20th	Day	47% 7% 12% 15% 13% 6%	2008
	21st to end	Day	43% 10% 17% 18% 9% 3	2818
January	1st to 10th	Night	37% 12% 16% 22% 11% 2	4406
	11th to 20th	Night	43% 10% 17% 15% 9% 6%	4237
	21st to end	Night	41% 8% 14% 21% 12% 4	4521
February	1st to 10th	Night	34% 5% 10% 25% 19% 7%	2341
	11th to 20th	Night	27% 6% 11% 26% 22% 7%	2219
	21st to end	Night	34% 6% 14% 27% 16% 3	1884
March	1st to 10th	Night	36% 9% 15% 20% 18% 3	3736
	11th to 20th	Night	22% 6% 15% 35% 15% 7%	3593
	21st to end	Night	38% 8% 16% 22% 13% 3	3533
April	1st to 10th	Night	25% 5% 13% 30% 20% 7%	1900
	11th to 20th	Night	23% 4 11% 31% 23% 8%	1879
	21st to end	Night	19% 5% 13% 29% 31% 3	1900
May	1st to 10th	Night	13% 4 7% 31% 35% 11%	3057
	11th to 20th	Night	8% 2 6% 26% 44% 13%	2835
	21st to end	Night	9% 2 6% 27% 47% 9%	2808
June	1st to 10th	Night	12% 3 8% 24% 33% 19%	1520
	11th to 20th	Night	5% 3 4 16% 39% 34%	1520
	21st to end	Night	4 1 2 8% 33% 52%	1520
July	1st to 10th	Night	2 1 3 15% 78%	2500
	11th to 20th	Night	9% 1 2 6% 16% 65%	2492
	21st to end	Night	6% 2 2 6% 26% 58%	2903
August	1st to 10th	Night	9% 1 1 7% 30% 52%	3110
	11th to 20th	Night	3 1 1 5% 21% 69%	3156
	21st to end	Night	6% 1 1 7% 28% 58%	3498
September	1st to 10th	Night	5% 2 2 8% 26% 58%	1900
	11th to 20th	Night	8% 3 3 13% 43% 30%	1966
	21st to end	Night	7% 1 4 16% 38% 34%	2090
October	1st to 10th	Night	9% 2 4 9% 25% 51%	3627
	11th to 20th	Night	10% 2 5% 21% 42% 20%	3777
	21st to end	Night	12% 2 4 21% 40% 21%	4171
November	1st to 10th	Night	20% 5% 11% 24% 25% 16%	2535
	11th to 20th	Night	18% 5% 14% 24% 26% 14%	2600
	21st to end	Night	28% 4 10% 19% 28% 11%	2600
December	1st to 10th	Night	31% 5% 12% 21% 18% 12%	2667
	11th to 20th	Night	42% 7% 13% 18% 15% 6%	3416
	21st to end	Night	40% 11% 16% 21% 9% 3	4910

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	29% 6% 26% 23% 13% 3	180
	11th to 20th	Day	16% 8% 23% 31% 16% 5%	289
	21st to end	Day	15% 7% 24% 33% 19% 3	407
February	1st to 10th	Day	17% 7% 27% 28% 15% 6%	430
	11th to 20th	Day	16% 9% 32% 27% 13% 1	455
	21st to end	Day	17% 9% 33% 29% 11% 1	382
March	1st to 10th	Day	18% 10% 31% 31% 10% 1	460
	11th to 20th	Day	14% 11% 32% 26% 15% 2	460
	21st to end	Day	16% 13% 32% 28% 10% 1	506
April	1st to 10th	Day	13% 13% 30% 27% 15% 2	460
	11th to 20th	Day	14% 13% 27% 32% 13% 1	452
	21st to end	Day	6% 13% 27% 33% 16% 5%	460
May	1st to 10th	Day	5% 14% 37% 26% 15% 3	463
	11th to 20th	Day	6% 7% 29% 35% 18% 5%	488
	21st to end	Day	8% 8% 21% 36% 22% 5%	529
June	1st to 10th	Day	2 7% 24% 34% 27% 7%	490
	11th to 20th	Day	2 7% 23% 38% 23% 7%	490
	21st to end	Day	1 4 18% 41% 28% 8%	490
July	1st to 10th	Day	1 14% 42% 33% 9%	486
	11th to 20th	Day	1 7% 41% 37% 14%	484
	21st to end	Day	2 1 10% 38% 37% 11%	531
August	1st to 10th	Day	3 2 17% 45% 22% 11%	487
	11th to 20th	Day	1 2 14% 42% 29% 11%	477
	21st to end	Day	1 1 12% 42% 34% 10%	539
September	1st to 10th	Day	3 2 15% 44% 30% 8%	490
	11th to 20th	Day	2 6% 22% 40% 25% 4	490
	21st to end	Day	2 6% 19% 38% 32% 4	490
October	1st to 10th	Day	2 4 23% 38% 32% 2	490
	11th to 20th	Day	4 5% 20% 42% 25% 4	490
	21st to end	Day	5% 5% 20% 38% 28% 4	511
November	1st to 10th	Day	7% 7% 25% 30% 27% 4	300
	11th to 20th	Day	6% 4 25% 36% 23% 5%	300
	21st to end	Day	14% 4 24% 33% 21% 4	300
December	1st to 10th	Day	15% 3 25% 35% 19% 3	265
	11th to 20th	Day	17% 6% 24% 29% 19% 6%	200
	21st to end	Day	24% 3 24% 29% 16% 4	204
January	1st to 10th	Night	20% 2 16% 33% 24% 5%	760
	11th to 20th	Night	13% 3 14% 43% 23% 4	760
	21st to end	Night	20% 2 16% 36% 24% 3	836
February	1st to 10th	Night	18% 3 16% 38% 22% 4	760
	11th to 20th	Night	14% 4 18% 37% 24% 3	744
	21st to end	Night	19% 3 19% 41% 16% 2	628
March	1st to 10th	Night	16% 4 18% 41% 18% 3	760
	11th to 20th	Night	14% 3 19% 33% 28% 4	760
	21st to end	Night	16% 4 18% 39% 23% 1	836
April	1st to 10th	Night	11% 3 20% 44% 21% 1	760
	11th to 20th	Night	9% 5% 20% 38% 28% 1	751
	21st to end	Night	7% 3 18% 41% 29% 3	760
May	1st to 10th	Night	5% 2 20% 43% 28% 1	689
	11th to 20th	Night	6% 1 16% 42% 34% 1	561
	21st to end	Night	5% 4 18% 40% 32% 2	445
June	1st to 10th	Night	5% 1 12% 45% 35% 3	380
	11th to 20th	Night	1 15% 47% 35% 3	380
	21st to end	Night	1 1 10% 42% 43% 3	380
July	1st to 10th	Night	5% 39% 53% 4	370
	11th to 20th	Night	2 2 38% 51% 7%	368
	21st to end	Night	1 4 28% 57% 9%	551
August	1st to 10th	Night	2 5% 36% 50% 6%	721
	11th to 20th	Night	1 4 36% 54% 6%	752
	21st to end	Night	2 4 28% 59% 8%	836
September	1st to 10th	Night	1 1 5% 34% 54% 5%	760
	11th to 20th	Night	2 1 11% 41% 39% 6%	760
	21st to end	Night	2 1 9% 42% 43% 4	760
October	1st to 10th	Night	4 1 11% 48% 32% 5%	760
	11th to 20th	Night	4 2 13% 41% 35% 6%	760
	21st to end	Night	5% 1 14% 36% 33% 10%	836
November	1st to 10th	Night	9% 2 14% 35% 32% 8%	780
	11th to 20th	Night	7% 2 17% 39% 29% 6%	800
	21st to end	Night	11% 2 17% 40% 24% 6%	800
December	1st to 10th	Night	15% 2 16% 40% 22% 6%	800
	11th to 20th	Night	18% 1 18% 39% 20% 4	800
	21st to end	Night	19% 3 18% 39% 18% 4	850

Page generated at 2024-12-21 01:13:47. Version ac07

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