Apache Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Apache Point clear sky chart from 2005-11-06 to 2025-11-03.

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	4 5% 2 5% 3 4 4 4 6% 7% 57%	134120
	Night	4 5% 2 4 3 3 4 3 5% 7% 60%	133357
Transparency	Day	23% 6% 9% 16% 26% 20%	129207
	Night	22% 4 8% 16% 28% 22%	129274
Seeing	Day	11% 18% 28% 25% 14% 3	15971
	Night	8% 14% 26% 31% 18% 3	26194

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	2 13% 5% 6% 3 3 3 3 5% 5% 53%	4098
	11th to 20th	Day	2 4 2 4 3 2 2 2 4 4 71%	4100
	21st to end	Day	5% 10% 3 5% 3 2 4 4 4 5% 56%	4510
February	1st to 10th	Day	5% 7% 1 4 2 3 3 2 4 6% 63%	1958
	11th to 20th	Day	7% 7% 2 5% 4 3 3 2 5% 5% 58%	1949
	21st to end	Day	4 7% 2 4 4 2 3 2 3 5% 64%	1650
March	1st to 10th	Day	4 7% 2 4 3 3 3 3 4 5% 62%	4768
	11th to 20th	Day	3 7% 3 6% 3 3 3 3 4 5% 61%	5000
	21st to end	Day	3 10% 3 6% 4 3 3 3 4 7% 54%	5678
April	1st to 10th	Day	3 5% 2 4 3 3 4 3 5% 6% 63%	2400
	11th to 20th	Day	3 4 2 4 2 2 2 2 3 5% 70%	2371
	21st to end	Day	3 3 1 3 2 2 2 3 5% 5% 71%	2400
May	1st to 10th	Day	3 3 1 3 2 2 2 2 3 4 74%	5440
	11th to 20th	Day	3 3 1 3 3 3 3 3 4 6% 69%	5405
	21st to end	Day	1 2 1 2 2 2 3 2 4 6% 76%	6228
June	1st to 10th	Day	3 4 1 3 3 3 4 4 6% 8% 61%	2800
	11th to 20th	Day	3 2 1 2 2 3 3 3 5% 6% 69%	2800
	21st to end	Day	5% 5% 2 6% 5% 5% 6% 6% 8% 9% 44%	2693
July	1st to 10th	Day	7% 4 2 6% 5% 6% 6% 5% 8% 11% 40%	5879
	11th to 20th	Day	2 3 1 5% 5% 7% 8% 7% 10% 13% 40%	5880
	21st to end	Day	6% 4 2 7% 6% 8% 8% 7% 11% 11% 29%	6368
August	1st to 10th	Day	4 3 1 6% 4 6% 7% 6% 9% 10% 43%	5348
	11th to 20th	Day	4 4 2 7% 5% 7% 8% 6% 9% 11% 37%	5366
	21st to end	Day	5% 4 2 7% 6% 5% 7% 6% 8% 10% 41%	5984
September	1st to 10th	Day	9% 6% 2 8% 5% 5% 6% 4 6% 8% 41%	2400
	11th to 20th	Day	9% 4 2 5% 5% 4 5% 4 6% 6% 51%	2400
	21st to end	Day	5% 3 2 4 3 2 3 4 6% 6% 62%	2205
October	1st to 10th	Day	4 4 2 5% 2 3 2 2 4 6% 66%	3272
	11th to 20th	Day	4 4 2 4 3 2 3 3 4 6% 65%	3250
	21st to end	Day	2 2 1 2 2 1 2 1 2 3 82%	3548
November	1st to 10th	Day	2 5% 2 4 2 2 2 3 4 6% 68%	1979
	11th to 20th	Day	4 3 2 3 2 3 4 3 4 6% 66%	1850
	21st to end	Day	6% 5% 1 4 3 4 4 3 6% 6% 57%	1800
December	1st to 10th	Day	6% 7% 1 3 2 2 2 2 4 6% 64%	2940
	11th to 20th	Day	4 5% 3 6% 3 2 3 3 4 7% 60%	3095
	21st to end	Day	3 5% 2 3 2 3 3 2 4 8% 65%	4308
January	1st to 10th	Night	2 9% 3 7% 3 3 4 3 5% 6% 55%	5867
	11th to 20th	Night	2 4 1 2 2 3 3 2 3 4 73%	5880
	21st to end	Night	5% 9% 2 5% 3 3 4 3 5% 6% 54%	6468
February	1st to 10th	Night	4 8% 2 3 3 2 3 3 5% 6% 61%	2439
	11th to 20th	Night	8% 5% 2 4 3 3 3 3 4 6% 58%	2338
	21st to end	Night	5% 7% 2 4 2 3 4 3 5% 5% 60%	1980
March	1st to 10th	Night	3 6% 2 5% 3 3 3 3 4 5% 63%	5114
	11th to 20th	Night	5% 8% 3 5% 3 3 4 3 4 6% 58%	5000
	21st to end	Night	3 7% 2 6% 4 3 3 2 5% 7% 59%	5288
April	1st to 10th	Night	3 4 2 4 3 4 3 3 4 6% 65%	2000
	11th to 20th	Night	5% 4 2 4 2 3 3 3 4 6% 64%	1977
	21st to end	Night	4 3 1 3 2 2 3 2 4 5% 70%	2000
May	1st to 10th	Night	3 3 1 3 2 2 3 2 3 5% 73%	4540
	11th to 20th	Night	2 3 1 3 3 3 4 3 5% 6% 67%	4510
	21st to end	Night	1 2 1 2 2 2 3 2 4 3 79%	4630
June	1st to 10th	Night	2 3 2 5% 5% 4 4 4 6% 7% 57%	1600
	11th to 20th	Night	3 2 1 3 2 3 3 3 5% 8% 67%	1600
	21st to end	Night	4 5% 2 7% 6% 5% 4 5% 7% 9% 45%	1696
July	1st to 10th	Night	4 5% 2 6% 5% 5% 6% 5% 7% 9% 48%	4100
	11th to 20th	Night	2 2 1 5% 5% 5% 7% 6% 8% 12% 48%	4100
	21st to end	Night	5% 4 2 5% 4 6% 7% 7% 10% 14% 35%	4501
August	1st to 10th	Night	2 2 1 4 4 4 5% 5% 8% 15% 51%	4464
	11th to 20th	Night	4 3 1 5% 4 5% 5% 5% 8% 14% 44%	4483
	21st to end	Night	3 3 2 6% 5% 5% 6% 5% 8% 11% 46%	4993
September	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 5% 6% 7% 48%	2000
	11th to 20th	Night	8% 3 2 5% 3 4 4 4 6% 6% 55%	2000
	21st to end	Night	4 3 1 4 4 3 4 4 4 6% 63%	2195
October	1st to 10th	Night	3 2 1 3 2 2 2 2 4 5% 73%	3913
	11th to 20th	Night	11% 4 1 3 2 2 2 2 3 4 65%	3898
	21st to end	Night	4 2 1 3 2 2 2 2 3 4 76%	4252
November	1st to 10th	Night	4 3 2 3 2 2 3 2 5% 7% 68%	2364
	11th to 20th	Night	3 2 1 3 2 3 3 3 5% 6% 68%	2526
	21st to end	Night	7% 5% 2 5% 3 4 3 3 4 6% 59%	2600
December	1st to 10th	Night	5% 4 1 3 2 2 3 3 4 6% 67%	4250
	11th to 20th	Night	3 4 2 5% 4 3 4 3 4 6% 61%	5107
	21st to end	Night	4 5% 1 4 2 3 3 2 4 7% 63%	6684

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	31% 2 8% 9% 35% 15%	4099
	11th to 20th	Day	15% 3 5% 13% 44% 20%	4100
	21st to end	Day	27% 3 7% 14% 25% 24%	4510
February	1st to 10th	Day	23% 3 5% 16% 27% 26%	1958
	11th to 20th	Day	27% 3 5% 16% 26% 22%	1959
	21st to end	Day	24% 1 4 8% 30% 33%	1650
March	1st to 10th	Day	22% 3 5% 6% 31% 33%	4768
	11th to 20th	Day	23% 4 5% 15% 32% 21%	5000
	21st to end	Day	27% 4 5% 12% 34% 18%	5678
April	1st to 10th	Day	19% 3 6% 14% 32% 26%	2400
	11th to 20th	Day	17% 2 4 11% 30% 35%	2374
	21st to end	Day	15% 3 5% 13% 33% 31%	2400
May	1st to 10th	Day	14% 3 4 14% 28% 36%	5440
	11th to 20th	Day	16% 4 6% 12% 31% 33%	5408
	21st to end	Day	10% 3 6% 11% 19% 51%	6229
June	1st to 10th	Day	17% 5% 9% 19% 27% 23%	2800
	11th to 20th	Day	13% 3 6% 13% 25% 40%	2800
	21st to end	Day	28% 8% 12% 16% 19% 16%	2693
July	1st to 10th	Day	31% 9% 20% 19% 14% 7%	5816
	11th to 20th	Day	26% 13% 25% 19% 14% 4	5811
	21st to end	Day	36% 16% 21% 17% 8% 1	6184
August	1st to 10th	Day	28% 12% 17% 31% 10% 2	3892
	11th to 20th	Day	28% 13% 16% 26% 15% 2	3882
	21st to end	Day	34% 12% 19% 24% 10% 1	4311
September	1st to 10th	Day	37% 7% 12% 16% 19% 10%	2400
	11th to 20th	Day	29% 6% 9% 20% 27% 10%	2400
	21st to end	Day	20% 5% 8% 21% 32% 13%	2205
October	1st to 10th	Day	18% 4 6% 15% 33% 23%	3272
	11th to 20th	Day	20% 4 7% 18% 32% 19%	3250
	21st to end	Day	9% 2 3 20% 37% 30%	3548
November	1st to 10th	Day	18% 3 4 21% 30% 24%	1979
	11th to 20th	Day	18% 2 6% 19% 27% 27%	1850
	21st to end	Day	24% 4 7% 16% 29% 19%	1800
December	1st to 10th	Day	22% 2 4 16% 35% 20%	2940
	11th to 20th	Day	24% 3 5% 11% 39% 17%	3093
	21st to end	Day	19% 2 4 17% 36% 22%	4308
January	1st to 10th	Night	27% 3 7% 10% 40% 13%	5867
	11th to 20th	Night	15% 3 4 11% 42% 26%	5880
	21st to end	Night	29% 3 6% 11% 27% 24%	6468
February	1st to 10th	Night	22% 3 7% 14% 26% 29%	2439
	11th to 20th	Night	26% 3 6% 14% 29% 22%	2338
	21st to end	Night	24% 3 5% 9% 28% 31%	1980
March	1st to 10th	Night	21% 4 4 8% 33% 30%	5114
	11th to 20th	Night	24% 5% 6% 12% 30% 23%	5000
	21st to end	Night	24% 3 7% 14% 37% 17%	5288
April	1st to 10th	Night	21% 3 5% 11% 37% 24%	2000
	11th to 20th	Night	20% 3 6% 12% 28% 31%	1977
	21st to end	Night	16% 4 4 14% 32% 30%	2000
May	1st to 10th	Night	15% 3 3 15% 25% 38%	4537
	11th to 20th	Night	17% 4 8% 12% 28% 31%	4511
	21st to end	Night	10% 2 5% 8% 18% 56%	4631
June	1st to 10th	Night	23% 5% 8% 17% 21% 25%	1600
	11th to 20th	Night	15% 4 5% 13% 23% 40%	1600
	21st to end	Night	30% 8% 13% 18% 15% 17%	1696
July	1st to 10th	Night	31% 7% 17% 27% 14% 5%	4055
	11th to 20th	Night	25% 7% 25% 24% 15% 4	4046
	21st to end	Night	34% 11% 24% 20% 10% 1	4373
August	1st to 10th	Night	21% 9% 16% 33% 17% 3	3244
	11th to 20th	Night	21% 8% 13% 36% 19% 2	3243
	21st to end	Night	33% 9% 19% 25% 12% 2	3597
September	1st to 10th	Night	31% 7% 13% 16% 20% 13%	2000
	11th to 20th	Night	27% 6% 11% 18% 26% 13%	2000
	21st to end	Night	21% 5% 10% 18% 32% 15%	2195
October	1st to 10th	Night	14% 3 6% 13% 35% 29%	3913
	11th to 20th	Night	24% 3 5% 13% 35% 20%	3898
	21st to end	Night	14% 2 2 18% 31% 32%	4252
November	1st to 10th	Night	17% 3 4 17% 34% 25%	2364
	11th to 20th	Night	16% 3 6% 16% 32% 27%	2526
	21st to end	Night	26% 4 6% 15% 30% 20%	2600
December	1st to 10th	Night	18% 4 4 18% 40% 16%	4250
	11th to 20th	Night	24% 3 6% 11% 33% 23%	5108
	21st to end	Night	20% 3 5% 16% 34% 22%	6684

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	18% 32% 25% 21% 4	300
	11th to 20th	Day	18% 29% 28% 20% 4 1	300
	21st to end	Day	15% 31% 28% 17% 8% 1	330
February	1st to 10th	Day	19% 25% 28% 19% 7% 1	300
	11th to 20th	Day	21% 32% 30% 13% 3	300
	21st to end	Day	25% 37% 21% 12% 4	249
March	1st to 10th	Day	22% 30% 34% 11% 3	412
	11th to 20th	Day	25% 27% 30% 12% 4 2	500
	21st to end	Day	19% 36% 33% 9% 2 1	550
April	1st to 10th	Day	15% 34% 36% 12% 2 1	500
	11th to 20th	Day	17% 38% 32% 11% 2	492
	21st to end	Day	15% 35% 33% 14% 2 1	500
May	1st to 10th	Day	9% 29% 45% 14% 3 1	503
	11th to 20th	Day	9% 23% 42% 20% 5% 1	528
	21st to end	Day	6% 21% 47% 20% 6%	618
June	1st to 10th	Day	5% 10% 31% 35% 16% 3	730
	11th to 20th	Day	3 10% 33% 33% 18% 2	730
	21st to end	Day	6% 5% 28% 33% 25% 4	623
July	1st to 10th	Day	7% 4 16% 39% 27% 8%	526
	11th to 20th	Day	5% 2 11% 38% 36% 9%	524
	21st to end	Day	6% 2 10% 33% 40% 10%	575
August	1st to 10th	Day	3 2 11% 35% 37% 11%	527
	11th to 20th	Day	5% 5% 13% 41% 28% 9%	517
	21st to end	Day	6% 3 13% 35% 34% 9%	583
September	1st to 10th	Day	11% 5% 20% 37% 22% 6%	530
	11th to 20th	Day	8% 4 27% 39% 16% 5%	530
	21st to end	Day	7% 8% 33% 34% 13% 5%	335
October	1st to 10th	Day	11% 10% 32% 29% 15% 3	330
	11th to 20th	Day	11% 16% 33% 25% 11% 4	330
	21st to end	Day	10% 20% 31% 21% 13% 4	363
November	1st to 10th	Day	12% 28% 33% 15% 9% 3	306
	11th to 20th	Day	10% 18% 32% 25% 12% 3	300
	21st to end	Day	16% 31% 27% 18% 8%	300
December	1st to 10th	Day	20% 25% 27% 22% 6% 1	300
	11th to 20th	Day	12% 33% 29% 19% 6%	300
	21st to end	Day	23% 28% 28% 15% 4	330
January	1st to 10th	Night	10% 13% 31% 30% 12% 3	800
	11th to 20th	Night	11% 16% 30% 28% 13% 3	800
	21st to end	Night	10% 20% 28% 26% 14% 2	880
February	1st to 10th	Night	11% 18% 30% 28% 12% 3	800
	11th to 20th	Night	13% 21% 34% 24% 7% 1	784
	21st to end	Night	11% 26% 38% 20% 4 1	660
March	1st to 10th	Night	13% 25% 27% 26% 8% 1	800
	11th to 20th	Night	15% 17% 27% 28% 12% 1	800
	21st to end	Night	8% 24% 33% 26% 9% 1	795
April	1st to 10th	Night	7% 26% 37% 23% 7%	600
	11th to 20th	Night	11% 25% 33% 25% 6%	593
	21st to end	Night	8% 21% 37% 27% 7%	600
May	1st to 10th	Night	7% 19% 34% 31% 8%	600
	11th to 20th	Night	6% 14% 31% 34% 14% 1	591
	21st to end	Night	5% 12% 36% 36% 10% 1	650
June	1st to 10th	Night	3 8% 28% 42% 18% 1	600
	11th to 20th	Night	4 7% 29% 40% 18% 2	600
	21st to end	Night	5% 7% 21% 41% 24% 3	600
July	1st to 10th	Night	5% 4 19% 41% 29% 2	585
	11th to 20th	Night	4 1 15% 37% 37% 5%	582
	21st to end	Night	6% 3 13% 33% 36% 9%	657
August	1st to 10th	Night	4 2 10% 30% 44% 11%	597
	11th to 20th	Night	6% 3 13% 29% 39% 10%	594
	21st to end	Night	4 4 14% 31% 39% 8%	660
September	1st to 10th	Night	6% 5% 17% 33% 33% 6%	600
	11th to 20th	Night	7% 2 18% 42% 27% 4	600
	21st to end	Night	5% 8% 22% 37% 26% 3	600
October	1st to 10th	Night	7% 8% 26% 36% 20% 3	793
	11th to 20th	Night	9% 8% 27% 32% 21% 4	800
	21st to end	Night	7% 12% 23% 29% 23% 6%	880
November	1st to 10th	Night	7% 14% 25% 26% 22% 5%	788
	11th to 20th	Night	5% 11% 25% 35% 20% 3	926
	21st to end	Night	11% 16% 25% 27% 16% 4	1000
December	1st to 10th	Night	11% 16% 25% 32% 14% 2	1000
	11th to 20th	Night	12% 18% 33% 24% 12% 1	1000
	21st to end	Night	14% 17% 29% 29% 10% 2	979

Page generated at 2025-10-31 00:02:36. Version ac07

Copyright © 2025 Attilla Danko.