Heaven's Plateau
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heaven's Plateau clear sky chart from 2005-11-06 to 2025-04-26.

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	9% 5% 1 3 2 2 2 2 3 5% 64%	117619
	Night	11% 5% 1 3 2 2 3 2 4 5% 60%	119875
Transparency	Day	24% 3 7% 17% 25% 24%	117369
	Night	27% 3 7% 18% 23% 21%	119714
Seeing	Day	13% 12% 31% 29% 12% 4	15731
	Night	13% 4 16% 36% 25% 6%	25229

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	17% 8% 1 3 2 2 3 3 3 6% 51%	3639
	11th to 20th	Day	15% 6% 2 4 3 3 3 2 3 3 56%	3934
	21st to end	Day	17% 8% 2 5% 3 3 4 2 4 5% 47%	4510
February	1st to 10th	Day	21% 9% 2 4 2 3 3 2 4 5% 46%	1800
	11th to 20th	Day	14% 10% 2 4 3 3 3 3 4 7% 46%	1940
	21st to end	Day	19% 11% 2 4 3 3 3 2 4 4 45%	1650
March	1st to 10th	Day	16% 15% 3 7% 4 4 4 3 5% 6% 33%	4553
	11th to 20th	Day	17% 11% 2 4 3 2 3 2 3 5% 48%	5000
	21st to end	Day	19% 11% 2 5% 4 4 4 3 5% 6% 38%	5780
April	1st to 10th	Day	14% 8% 1 4 3 3 5% 3 5% 7% 47%	2400
	11th to 20th	Day	12% 6% 2 5% 3 2 3 2 5% 5% 55%	2369
	21st to end	Day	11% 4 1 4 3 2 3 3 4 6% 60%	2342
May	1st to 10th	Day	8% 4 1 2 2 2 2 2 4 4 70%	3879
	11th to 20th	Day	4 3 1 2 1 2 2 2 2 5% 77%	4310
	21st to end	Day	6% 3 1 2 2 2 2 2 3 5% 73%	4813
June	1st to 10th	Day	6% 3 1 4 3 2 2 3 4 6% 66%	2660
	11th to 20th	Day	2 1 1 2 2 2 2 2 4 4 80%	2660
	21st to end	Day	2 2 1 2 1 2 2 2 3 2 83%	2660
July	1st to 10th	Day	1 1 1 1 1 2 93%	4420
	11th to 20th	Day	2 1 1 2 1 1 2 2 2 3 84%	4420
	21st to end	Day	1 1 1 1 1 1 1 1 2 3 88%	4528
August	1st to 10th	Day	2 1 1 2 2 1 2 2 3 4 81%	4061
	11th to 20th	Day	1 1 1 1 1 3 3 88%	3724
	21st to end	Day	2 1 2 1 1 1 1 2 2 88%	4180
September	1st to 10th	Day	2 1 1 1 1 1 2 3 88%	2280
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 5% 76%	2271
	21st to end	Day	4 2 1 2 2 1 1 1 3 4 80%	2085
October	1st to 10th	Day	3 2 1 3 2 2 2 3 4 5% 74%	3180
	11th to 20th	Day	5% 2 1 2 1 2 2 2 3 4 77%	3161
	21st to end	Day	6% 3 1 4 2 3 3 3 5% 6% 66%	3448
November	1st to 10th	Day	11% 6% 1 4 3 3 3 3 4 8% 53%	1770
	11th to 20th	Day	12% 4 1 4 3 3 4 3 4 7% 55%	1800
	21st to end	Day	13% 7% 1 4 3 3 2 3 4 6% 54%	1740
December	1st to 10th	Day	9% 4 1 3 3 4 4 2 4 7% 59%	2620
	11th to 20th	Day	26% 9% 2 5% 3 3 3 3 5% 6% 36%	3028
	21st to end	Day	21% 8% 2 5% 4 4 5% 4 6% 7% 33%	4004
January	1st to 10th	Night	12% 8% 2 4 3 3 3 3 6% 8% 50%	6306
	11th to 20th	Night	16% 5% 1 4 3 3 3 3 3 4 54%	6037
	21st to end	Night	16% 8% 2 5% 4 4 3 3 4 5% 48%	6468
February	1st to 10th	Night	19% 8% 2 4 4 2 2 3 4 5% 48%	2600
	11th to 20th	Night	16% 8% 2 4 3 3 3 3 5% 7% 46%	2347
	21st to end	Night	17% 9% 2 4 2 3 3 2 4 5% 50%	1980
March	1st to 10th	Night	18% 15% 3 4 3 3 3 3 4 6% 38%	5337
	11th to 20th	Night	18% 11% 2 3 2 2 2 2 3 5% 49%	5000
	21st to end	Night	22% 11% 1 4 3 3 4 3 4 7% 38%	5193
April	1st to 10th	Night	14% 7% 1 5% 4 3 3 3 4 6% 51%	2000
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 4 6% 55%	1979
	21st to end	Night	10% 4 1 3 2 3 3 3 5% 6% 60%	1954
May	1st to 10th	Night	5% 6% 1 2 1 2 2 2 4 6% 71%	3095
	11th to 20th	Night	4 1 1 1 1 1 1 2 3 6% 77%	2580
	21st to end	Night	4 2 1 2 1 2 2 2 2 4 77%	2762
June	1st to 10th	Night	5% 3 1 3 2 2 2 3 4 6% 68%	1520
	11th to 20th	Night	1 1 2 1 1 2 1 4 3 83%	1520
	21st to end	Night	2 1 1 2 2 1 1 1 2 3 85%	1520
July	1st to 10th	Night	1 1 1 1 1 1 94%	2540
	11th to 20th	Night	3 2 1 2 2 2 3 2 3 4 78%	2540
	21st to end	Night	2 1 1 2 2 2 2 2 3 84%	3029
August	1st to 10th	Night	3 2 1 2 1 2 2 2 3 3 78%	2877
	11th to 20th	Night	1 1 1 1 1 2 1 3 2 87%	3126
	21st to end	Night	4 1 1 1 1 1 1 1 2 88%	3498
September	1st to 10th	Night	2 1 1 1 1 1 2 3 88%	1900
	11th to 20th	Night	4 2 1 2 1 2 2 1 3 3 80%	1907
	21st to end	Night	3 1 1 1 1 2 2 1 2 3 81%	2090
October	1st to 10th	Night	3 1 1 3 2 2 2 2 3 3 79%	3800
	11th to 20th	Night	3 1 1 2 1 2 1 2 3 4 80%	3777
	21st to end	Night	8% 2 1 3 3 3 3 2 3 5% 67%	4121
November	1st to 10th	Night	12% 5% 1 3 2 2 2 2 4 6% 60%	2527
	11th to 20th	Night	11% 4 2 4 3 2 3 3 4 7% 57%	2600
	21st to end	Night	13% 5% 1 4 3 3 3 3 4 6% 56%	2657
December	1st to 10th	Night	10% 4 1 3 2 3 3 3 4 6% 61%	4560
	11th to 20th	Night	25% 8% 2 4 3 3 4 4 7% 8% 32%	5176
	21st to end	Night	21% 9% 3 7% 4 5% 4 4 5% 6% 32%	6952

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	36% 3 12% 22% 17% 9%	3639
	11th to 20th	Day	35% 4 6% 12% 25% 17%	3934
	21st to end	Day	40% 5% 7% 14% 21% 14%	4510
February	1st to 10th	Day	42% 3 7% 20% 17% 11%	1800
	11th to 20th	Day	39% 4 8% 20% 23% 6%	1950
	21st to end	Day	43% 3 7% 22% 17% 7%	1650
March	1st to 10th	Day	50% 5% 10% 13% 16% 5%	4553
	11th to 20th	Day	39% 4 12% 28% 10% 7%	5000
	21st to end	Day	44% 7% 14% 22% 11% 2	5780
April	1st to 10th	Day	36% 5% 13% 24% 17% 5%	2400
	11th to 20th	Day	31% 4 13% 27% 18% 6%	2372
	21st to end	Day	25% 4 13% 31% 23% 3	2342
May	1st to 10th	Day	18% 4 10% 30% 25% 13%	3879
	11th to 20th	Day	13% 2 6% 26% 42% 10%	4313
	21st to end	Day	15% 3 9% 32% 35% 5%	4814
June	1st to 10th	Day	20% 4 10% 24% 30% 12%	2660
	11th to 20th	Day	10% 2 6% 23% 36% 23%	2660
	21st to end	Day	10% 2 2 12% 31% 43%	2660
July	1st to 10th	Day	3 1 5% 15% 75%	4351
	11th to 20th	Day	9% 1 2 6% 17% 65%	4345
	21st to end	Day	6% 1 1 5% 27% 59%	4385
August	1st to 10th	Day	10% 2 2 7% 24% 56%	4046
	11th to 20th	Day	5% 1 1 5% 35% 53%	3760
	21st to end	Day	7% 1 2 7% 40% 43%	4179
September	1st to 10th	Day	6% 1 2 8% 32% 51%	2280
	11th to 20th	Day	13% 2 5% 20% 38% 21%	2271
	21st to end	Day	12% 2 4 18% 37% 27%	2085
October	1st to 10th	Day	14% 2 4 11% 26% 43%	3180
	11th to 20th	Day	14% 2 4 18% 40% 21%	3161
	21st to end	Day	21% 3 5% 19% 37% 16%	3448
November	1st to 10th	Day	31% 3 8% 21% 22% 15%	1770
	11th to 20th	Day	29% 5% 8% 20% 26% 12%	1800
	21st to end	Day	31% 4 6% 19% 26% 14%	1740
December	1st to 10th	Day	27% 3 6% 22% 26% 16%	2620
	11th to 20th	Day	50% 3 7% 14% 17% 9%	3028
	21st to end	Day	46% 7% 13% 19% 9% 5%	4004
January	1st to 10th	Night	32% 4 15% 23% 16% 10%	6306
	11th to 20th	Night	34% 4 7% 13% 26% 16%	6037
	21st to end	Night	38% 5% 6% 13% 17% 20%	6468
February	1st to 10th	Night	40% 3 6% 18% 20% 13%	2600
	11th to 20th	Night	37% 4 7% 23% 20% 9%	2348
	21st to end	Night	38% 3 9% 23% 19% 8%	1980
March	1st to 10th	Night	48% 5% 7% 18% 14% 8%	5337
	11th to 20th	Night	40% 4 9% 24% 16% 8%	5000
	21st to end	Night	46% 6% 13% 22% 11% 3	5193
April	1st to 10th	Night	34% 5% 15% 21% 20% 6%	2000
	11th to 20th	Night	30% 5% 12% 27% 16% 9%	1979
	21st to end	Night	24% 5% 11% 35% 19% 6%	1954
May	1st to 10th	Night	17% 3 12% 28% 24% 15%	3095
	11th to 20th	Night	11% 2 9% 26% 36% 16%	2580
	21st to end	Night	12% 3 8% 40% 30% 6%	2762
June	1st to 10th	Night	17% 5% 13% 23% 29% 13%	1520
	11th to 20th	Night	7% 3 6% 25% 34% 24%	1520
	21st to end	Night	9% 1 2 13% 33% 42%	1520
July	1st to 10th	Night	3 1 5% 15% 75%	2500
	11th to 20th	Night	13% 2 2 7% 13% 62%	2492
	21st to end	Night	9% 1 1 5% 23% 61%	2934
August	1st to 10th	Night	12% 1 1 7% 23% 55%	2868
	11th to 20th	Night	5% 2 1 6% 32% 53%	3156
	21st to end	Night	8% 1 1 10% 37% 44%	3498
September	1st to 10th	Night	5% 2 2 7% 34% 51%	1900
	11th to 20th	Night	12% 2 3 19% 40% 25%	1907
	21st to end	Night	11% 2 2 20% 36% 29%	2090
October	1st to 10th	Night	13% 2 3 10% 25% 46%	3800
	11th to 20th	Night	11% 2 4 25% 36% 23%	3777
	21st to end	Night	21% 3 3 18% 35% 20%	4121
November	1st to 10th	Night	26% 4 8% 21% 22% 19%	2527
	11th to 20th	Night	27% 4 7% 22% 27% 13%	2600
	21st to end	Night	31% 4 6% 19% 25% 16%	2657
December	1st to 10th	Night	25% 2 6% 22% 26% 19%	4560
	11th to 20th	Night	49% 4 6% 14% 21% 7%	5176
	21st to end	Night	50% 7% 10% 18% 9% 6%	6952

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	31% 12% 26% 19% 10% 3	200
	11th to 20th	Day	21% 8% 25% 32% 11% 3	325
	21st to end	Day	21% 9% 28% 23% 15% 3	440
February	1st to 10th	Day	31% 12% 23% 22% 11% 3	400
	11th to 20th	Day	22% 16% 33% 21% 8% 1	490
	21st to end	Day	22% 16% 32% 21% 8%	414
March	1st to 10th	Day	28% 21% 25% 19% 5% 1	500
	11th to 20th	Day	29% 18% 24% 17% 9% 2	500
	21st to end	Day	24% 18% 31% 21% 6%	550
April	1st to 10th	Day	20% 17% 34% 20% 8% 1	500
	11th to 20th	Day	18% 23% 27% 24% 7% 1	492
	21st to end	Day	10% 18% 32% 25% 12% 3	481
May	1st to 10th	Day	12% 20% 33% 24% 8% 3	463
	11th to 20th	Day	13% 16% 30% 23% 13% 5%	488
	21st to end	Day	12% 14% 24% 32% 13% 5%	529
June	1st to 10th	Day	7% 12% 32% 30% 10% 8%	490
	11th to 20th	Day	5% 16% 34% 31% 9% 5%	490
	21st to end	Day	3 7% 38% 32% 12% 8%	490
July	1st to 10th	Day	1 5% 40% 35% 12% 7%	486
	11th to 20th	Day	2 3 33% 42% 12% 8%	484
	21st to end	Day	2 2 35% 39% 14% 8%	531
August	1st to 10th	Day	3 6% 38% 35% 13% 5%	487
	11th to 20th	Day	1 6% 39% 35% 13% 5%	477
	21st to end	Day	2 5% 35% 39% 15% 4	539
September	1st to 10th	Day	3 7% 40% 35% 13% 2	490
	11th to 20th	Day	5% 12% 34% 35% 13% 1	490
	21st to end	Day	4 10% 34% 39% 10% 2	490
October	1st to 10th	Day	5% 12% 32% 34% 14% 3	490
	11th to 20th	Day	7% 11% 28% 34% 16% 4	490
	21st to end	Day	11% 11% 28% 31% 16% 4	539
November	1st to 10th	Day	16% 10% 22% 27% 18% 7%	306
	11th to 20th	Day	15% 9% 20% 33% 17% 7%	300
	21st to end	Day	20% 10% 19% 29% 19% 4	270
December	1st to 10th	Day	18% 7% 24% 25% 18% 9%	200
	11th to 20th	Day	21% 9% 27% 27% 12% 6%	200
	21st to end	Day	26% 15% 22% 20% 12% 5%	220
January	1st to 10th	Night	23% 6% 24% 25% 17% 6%	800
	11th to 20th	Night	17% 6% 21% 38% 14% 4	800
	21st to end	Night	21% 5% 21% 29% 18% 4	880
February	1st to 10th	Night	22% 5% 21% 31% 18% 3	800
	11th to 20th	Night	20% 7% 20% 31% 17% 5%	784
	21st to end	Night	21% 8% 21% 34% 13% 2	660
March	1st to 10th	Night	26% 7% 19% 31% 14% 3	800
	11th to 20th	Night	22% 8% 17% 29% 19% 5%	800
	21st to end	Night	23% 8% 19% 30% 18% 2	880
April	1st to 10th	Night	17% 4 19% 40% 18% 2	800
	11th to 20th	Night	15% 7% 20% 37% 18% 3	791
	21st to end	Night	11% 3 18% 40% 23% 5%	782
May	1st to 10th	Night	10% 5% 20% 39% 22% 4	714
	11th to 20th	Night	8% 4 12% 39% 34% 3	412
	21st to end	Night	7% 2 13% 37% 36% 5%	411
June	1st to 10th	Night	6% 3 10% 37% 38% 6%	380
	11th to 20th	Night	1 1 12% 45% 36% 5%	380
	21st to end	Night	2 9% 44% 40% 5%	380
July	1st to 10th	Night	1 3 44% 46% 6%	370
	11th to 20th	Night	2 7% 38% 46% 7%	368
	21st to end	Night	3 1 5% 32% 46% 13%	570
August	1st to 10th	Night	3 1 5% 42% 41% 8%	583
	11th to 20th	Night	1 1 9% 45% 36% 8%	752
	21st to end	Night	1 6% 42% 46% 4	836
September	1st to 10th	Night	2 6% 47% 38% 6%	760
	11th to 20th	Night	4 2 10% 37% 37% 10%	760
	21st to end	Night	4 2 14% 40% 31% 9%	760
October	1st to 10th	Night	6% 4 13% 44% 25% 7%	760
	11th to 20th	Night	8% 3 13% 41% 30% 5%	760
	21st to end	Night	7% 4 18% 35% 24% 12%	836
November	1st to 10th	Night	14% 3 14% 36% 25% 8%	780
	11th to 20th	Night	13% 4 20% 37% 20% 6%	800
	21st to end	Night	16% 6% 22% 32% 18% 6%	800
December	1st to 10th	Night	21% 4 20% 34% 16% 5%	800
	11th to 20th	Night	27% 4 20% 30% 16% 4	800
	21st to end	Night	25% 7% 22% 28% 15% 3	880

Page generated at 2025-04-23 06:25:08. Version ac07

Copyright © 2025 Attilla Danko.