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 2024-01-16.

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	5% 5% 2 4 4 3 4 5% 5% 7% 56%	74686
	Night	5% 4 2 4 4 2 4 4 5% 7% 59%	75106
Transparency	Day	24% 5% 9% 16% 26% 19%	74414
	Night	24% 5% 8% 16% 27% 21%	74900
Seeing	Day	10% 18% 28% 25% 15% 4	13547
	Night	8% 13% 26% 31% 19% 3	23900

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	4 8% 2 5% 3 2 2 4 5% 5% 58%	1708
	11th to 20th	Day	6% 5% 2 4 3 2 3 3 5% 6% 62%	1665
	21st to end	Day	8% 7% 3 3 3 2 3 3 4 5% 58%	1782
February	1st to 10th	Day	5% 6% 1 3 3 2 3 3 3 6% 65%	1762
	11th to 20th	Day	8% 6% 3 4 4 2 3 3 5% 6% 57%	1749
	21st to end	Day	5% 6% 2 4 4 2 3 3 3 5% 65%	1480
March	1st to 10th	Day	8% 8% 3 4 4 2 4 4 4 7% 54%	1900
	11th to 20th	Day	6% 7% 2 5% 3 2 3 3 3 6% 59%	1980
	21st to end	Day	4 5% 2 4 4 2 4 3 4 7% 61%	2254
April	1st to 10th	Day	3 3 1 3 3 2 4 4 5% 7% 64%	2160
	11th to 20th	Day	4 4 2 3 3 2 2 2 3 5% 70%	2131
	21st to end	Day	4 3 1 3 2 2 3 3 4 5% 70%	2160
May	1st to 10th	Day	3 3 1 4 3 2 3 3 3 6% 69%	2160
	11th to 20th	Day	3 3 2 3 4 3 4 5% 5% 7% 60%	2125
	21st to end	Day	3 2 1 2 3 1 3 3 4 7% 71%	2447
June	1st to 10th	Day	3 3 1 2 3 2 4 5% 6% 8% 62%	2520
	11th to 20th	Day	3 2 1 2 3 2 3 4 5% 7% 68%	2520
	21st to end	Day	4 4 2 5% 5% 4 5% 7% 8% 10% 46%	2425
July	1st to 10th	Day	8% 5% 2 7% 8% 5% 7% 7% 9% 10% 33%	2340
	11th to 20th	Day	4 5% 2 5% 8% 5% 8% 8% 9% 12% 34%	2340
	21st to end	Day	8% 4 3 7% 7% 5% 9% 10% 11% 11% 26%	2537
August	1st to 10th	Day	7% 4 2 7% 7% 6% 7% 9% 9% 10% 33%	2149
	11th to 20th	Day	7% 5% 3 7% 8% 5% 8% 7% 9% 10% 32%	2123
	21st to end	Day	6% 5% 3 7% 8% 4 8% 8% 8% 10% 35%	2376
September	1st to 10th	Day	9% 6% 2 7% 7% 3 6% 5% 6% 8% 41%	2160
	11th to 20th	Day	9% 4 2 4 6% 3 5% 5% 6% 6% 50%	2160
	21st to end	Day	5% 3 2 3 4 2 3 5% 6% 6% 61%	1985
October	1st to 10th	Day	6% 4 2 5% 4 3 3 4 5% 7% 58%	1802
	11th to 20th	Day	4 5% 1 3 3 1 2 3 4 5% 69%	1800
	21st to end	Day	3 2 2 2 3 1 3 3 4 5% 73%	1980
November	1st to 10th	Day	2 5% 2 3 3 2 2 3 3 6% 69%	1859
	11th to 20th	Day	4 3 2 3 3 2 4 4 4 6% 66%	1758
	21st to end	Day	6% 5% 2 3 4 3 4 4 5% 6% 58%	1710
December	1st to 10th	Day	7% 6% 2 3 4 2 3 4 5% 7% 58%	1710
	11th to 20th	Day	6% 7% 3 6% 4 2 3 5% 4 7% 53%	1969
	21st to end	Day	5% 8% 2 3 3 2 3 3 4 5% 63%	3000
January	1st to 10th	Night	4 7% 2 4 4 3 4 3 4 5% 60%	2457
	11th to 20th	Night	5% 6% 2 3 4 2 3 4 4 5% 62%	2405
	21st to end	Night	7% 6% 2 4 4 3 3 4 4 6% 57%	2574
February	1st to 10th	Night	4 7% 2 3 4 1 3 3 5% 7% 62%	2196
	11th to 20th	Night	9% 5% 1 3 4 2 3 3 4 5% 58%	2098
	21st to end	Night	5% 7% 2 3 3 2 4 4 4 5% 60%	1776
March	1st to 10th	Night	7% 5% 2 5% 3 3 3 4 4 7% 56%	2056
	11th to 20th	Night	8% 5% 3 4 2 2 3 3 6% 5% 59%	1980
	21st to end	Night	5% 5% 1 4 3 2 4 3 4 6% 64%	2102
April	1st to 10th	Night	3 3 2 4 3 3 4 4 4 6% 65%	1800
	11th to 20th	Night	6% 4 2 4 3 2 3 3 4 6% 63%	1777
	21st to end	Night	5% 3 2 3 3 2 3 3 4 5% 68%	1800
May	1st to 10th	Night	4 4 1 3 2 2 3 3 4 6% 68%	1800
	11th to 20th	Night	3 3 2 3 2 3 4 4 5% 6% 65%	1770
	21st to end	Night	2 3 1 3 2 2 4 4 5% 5% 69%	1817
June	1st to 10th	Night	2 3 2 5% 6% 3 4 5% 5% 8% 55%	1440
	11th to 20th	Night	3 1 1 3 3 2 3 4 5% 8% 67%	1440
	21st to end	Night	3 4 3 6% 6% 4 5% 7% 7% 9% 46%	1526
July	1st to 10th	Night	5% 4 2 5% 5% 4 6% 5% 7% 11% 44%	1620
	11th to 20th	Night	4 3 2 5% 5% 3 7% 7% 8% 13% 44%	1620
	21st to end	Night	3 4 2 4 5% 4 7% 8% 10% 14% 39%	1777
August	1st to 10th	Night	4 4 2 5% 6% 3 6% 8% 10% 15% 37%	1790
	11th to 20th	Night	6% 3 2 5% 6% 4 5% 8% 10% 12% 41%	1778
	21st to end	Night	4 4 2 5% 6% 4 6% 6% 8% 10% 46%	1980
September	1st to 10th	Night	6% 4 2 5% 5% 3 6% 6% 7% 7% 48%	1800
	11th to 20th	Night	8% 3 2 5% 4 3 4 5% 6% 6% 55%	1800
	21st to end	Night	4 3 1 3 4 2 4 5% 4 7% 63%	1975
October	1st to 10th	Night	6% 3 2 4 3 2 3 4 6% 8% 58%	2153
	11th to 20th	Night	4 4 1 3 3 1 2 3 3 5% 71%	2160
	21st to end	Night	5% 3 1 3 3 2 2 2 2 4 73%	2376
November	1st to 10th	Night	4 3 2 3 3 2 3 3 4 7% 68%	2220
	11th to 20th	Night	3 2 1 2 3 2 4 4 4 6% 68%	2399
	21st to end	Night	7% 4 2 4 3 3 3 3 4 6% 59%	2470
December	1st to 10th	Night	8% 5% 2 3 4 2 3 4 5% 7% 57%	2470
	11th to 20th	Night	5% 6% 3 6% 6% 2 4 4 4 7% 54%	3223
	21st to end	Night	6% 7% 2 4 4 2 3 3 3 5% 61%	4681

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	26% 4 8% 15% 31% 16%	1709
	11th to 20th	Day	21% 3 6% 16% 35% 19%	1665
	21st to end	Day	28% 3 5% 14% 29% 19%	1782
February	1st to 10th	Day	22% 3 5% 17% 27% 25%	1762
	11th to 20th	Day	28% 3 5% 15% 27% 22%	1759
	21st to end	Day	23% 1 4 9% 31% 32%	1480
March	1st to 10th	Day	28% 4 7% 12% 30% 20%	1900
	11th to 20th	Day	26% 3 5% 12% 29% 24%	1980
	21st to end	Day	21% 4 5% 14% 34% 22%	2254
April	1st to 10th	Day	18% 4 5% 15% 33% 25%	2160
	11th to 20th	Day	18% 2 4 11% 30% 34%	2134
	21st to end	Day	16% 3 5% 13% 33% 29%	2160
May	1st to 10th	Day	17% 3 6% 10% 29% 35%	2160
	11th to 20th	Day	20% 7% 8% 13% 28% 24%	2128
	21st to end	Day	13% 3 5% 18% 28% 32%	2447
June	1st to 10th	Day	17% 5% 10% 19% 27% 22%	2520
	11th to 20th	Day	14% 3 6% 13% 24% 39%	2520
	21st to end	Day	26% 8% 11% 16% 21% 17%	2425
July	1st to 10th	Day	37% 11% 15% 16% 14% 7%	2276
	11th to 20th	Day	32% 12% 18% 20% 14% 4	2271
	21st to end	Day	36% 17% 22% 17% 8% 1	2396
August	1st to 10th	Day	35% 12% 17% 25% 8% 3	2136
	11th to 20th	Day	37% 12% 16% 18% 12% 4	2123
	21st to end	Day	35% 12% 16% 19% 16% 2	2376
September	1st to 10th	Day	36% 7% 12% 16% 18% 10%	2160
	11th to 20th	Day	30% 6% 9% 19% 26% 10%	2160
	21st to end	Day	20% 5% 8% 22% 32% 13%	1985
October	1st to 10th	Day	24% 5% 10% 18% 25% 19%	1802
	11th to 20th	Day	19% 3 5% 14% 30% 30%	1800
	21st to end	Day	15% 3 5% 19% 34% 24%	1980
November	1st to 10th	Day	18% 3 4 21% 31% 23%	1859
	11th to 20th	Day	18% 3 7% 20% 28% 25%	1758
	21st to end	Day	24% 5% 6% 16% 30% 19%	1710
December	1st to 10th	Day	25% 3 6% 21% 30% 15%	1710
	11th to 20th	Day	30% 4 9% 16% 28% 14%	1967
	21st to end	Day	23% 2 5% 17% 30% 23%	3000
January	1st to 10th	Night	25% 4 7% 15% 30% 20%	2457
	11th to 20th	Night	24% 4 5% 13% 37% 18%	2405
	21st to end	Night	27% 3 6% 14% 30% 20%	2574
February	1st to 10th	Night	22% 3 7% 14% 26% 28%	2196
	11th to 20th	Night	27% 3 6% 13% 29% 22%	2098
	21st to end	Night	24% 3 5% 9% 29% 31%	1776
March	1st to 10th	Night	27% 3 5% 13% 28% 24%	2056
	11th to 20th	Night	25% 3 6% 11% 33% 22%	1980
	21st to end	Night	21% 4 5% 15% 34% 22%	2102
April	1st to 10th	Night	20% 3 5% 12% 37% 24%	1800
	11th to 20th	Night	22% 3 6% 11% 28% 30%	1777
	21st to end	Night	18% 4 4 15% 33% 26%	1800
May	1st to 10th	Night	17% 3 4 11% 32% 34%	1800
	11th to 20th	Night	18% 5% 8% 18% 25% 26%	1771
	21st to end	Night	15% 4 7% 15% 26% 32%	1818
June	1st to 10th	Night	24% 5% 9% 17% 21% 24%	1440
	11th to 20th	Night	16% 3 5% 13% 23% 40%	1440
	21st to end	Night	29% 8% 13% 16% 15% 19%	1526
July	1st to 10th	Night	30% 8% 16% 21% 19% 7%	1575
	11th to 20th	Night	26% 9% 15% 26% 17% 5%	1566
	21st to end	Night	27% 14% 22% 23% 12% 2	1678
August	1st to 10th	Night	29% 12% 19% 26% 10% 4	1779
	11th to 20th	Night	29% 11% 19% 25% 13% 3	1778
	21st to end	Night	29% 10% 15% 25% 18% 3	1980
September	1st to 10th	Night	30% 7% 14% 16% 20% 13%	1800
	11th to 20th	Night	27% 6% 11% 18% 25% 13%	1800
	21st to end	Night	20% 5% 10% 18% 32% 14%	1975
October	1st to 10th	Night	23% 5% 9% 17% 27% 19%	2153
	11th to 20th	Night	18% 4 4 14% 27% 33%	2160
	21st to end	Night	18% 2 3 16% 33% 27%	2376
November	1st to 10th	Night	17% 3 4 17% 34% 25%	2220
	11th to 20th	Night	16% 3 6% 17% 33% 26%	2399
	21st to end	Night	26% 3 6% 15% 31% 20%	2470
December	1st to 10th	Night	26% 4 6% 17% 28% 19%	2470
	11th to 20th	Night	29% 3 9% 16% 24% 18%	3224
	21st to end	Night	25% 3 7% 13% 30% 22%	4681

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	17% 30% 26% 23% 4	270
	11th to 20th	Day	16% 29% 27% 21% 5% 2	255
	21st to end	Day	9% 34% 29% 18% 9% 1	264
February	1st to 10th	Day	13% 27% 28% 23% 8% 1	240
	11th to 20th	Day	20% 33% 30% 13% 3	240
	21st to end	Day	23% 38% 22% 13% 4 1	198
March	1st to 10th	Day	18% 30% 36% 12% 3 1	340
	11th to 20th	Day	21% 25% 33% 14% 5% 2	420
	21st to end	Day	17% 37% 33% 10% 2 1	462
April	1st to 10th	Day	11% 35% 36% 13% 3 1	420
	11th to 20th	Day	14% 39% 33% 12% 3	412
	21st to end	Day	13% 37% 32% 15% 3 1	420
May	1st to 10th	Day	7% 28% 45% 16% 3 1	423
	11th to 20th	Day	4 23% 44% 21% 6% 1	448
	21st to end	Day	4 20% 47% 21% 6% 1	525
June	1st to 10th	Day	4 9% 30% 37% 17% 3	630
	11th to 20th	Day	3 9% 32% 34% 20% 3	630
	21st to end	Day	4 5% 29% 34% 25% 4	535
July	1st to 10th	Day	7% 3 15% 37% 29% 9%	446
	11th to 20th	Day	5% 2 8% 35% 39% 10%	444
	21st to end	Day	5% 2 8% 31% 43% 11%	487
August	1st to 10th	Day	4 2 9% 34% 39% 12%	447
	11th to 20th	Day	6% 5% 13% 38% 28% 9%	437
	21st to end	Day	7% 2 11% 34% 37% 9%	495
September	1st to 10th	Day	10% 4 18% 38% 24% 7%	450
	11th to 20th	Day	8% 3 25% 41% 18% 6%	450
	21st to end	Day	6% 8% 31% 35% 13% 6%	275
October	1st to 10th	Day	11% 9% 31% 29% 16% 3	270
	11th to 20th	Day	9% 14% 32% 29% 13% 4	270
	21st to end	Day	10% 18% 29% 24% 15% 4	297
November	1st to 10th	Day	9% 29% 34% 16% 10% 3	270
	11th to 20th	Day	6% 18% 31% 28% 13% 3	270
	21st to end	Day	14% 32% 26% 19% 9%	270
December	1st to 10th	Day	18% 25% 26% 23% 7% 1	270
	11th to 20th	Day	11% 36% 30% 18% 5%	270
	21st to end	Day	21% 30% 28% 16% 5%	297
January	1st to 10th	Night	10% 13% 30% 31% 13% 3	760
	11th to 20th	Night	10% 16% 30% 29% 13% 3	740
	21st to end	Night	10% 18% 28% 27% 15% 2	792
February	1st to 10th	Night	9% 17% 29% 29% 13% 3	720
	11th to 20th	Night	13% 20% 34% 24% 8% 1	704
	21st to end	Night	10% 27% 38% 20% 5% 1	592
March	1st to 10th	Night	11% 24% 28% 27% 8% 1	720
	11th to 20th	Night	12% 16% 27% 30% 13% 1	720
	21st to end	Night	8% 23% 33% 26% 9% 1	716
April	1st to 10th	Night	5% 26% 39% 23% 7%	540
	11th to 20th	Night	10% 25% 32% 26% 6%	533
	21st to end	Night	8% 22% 38% 25% 7%	540
May	1st to 10th	Night	7% 18% 35% 31% 9%	540
	11th to 20th	Night	4 13% 32% 34% 16% 1	531
	21st to end	Night	4 12% 36% 37% 10% 1	584
June	1st to 10th	Night	3 8% 26% 43% 19% 1	540
	11th to 20th	Night	4 7% 29% 39% 19% 2	540
	21st to end	Night	4 6% 21% 42% 24% 3	540
July	1st to 10th	Night	5% 3 18% 41% 30% 3	525
	11th to 20th	Night	4 1 12% 37% 40% 6%	522
	21st to end	Night	5% 2 13% 33% 37% 10%	591
August	1st to 10th	Night	4 1 8% 29% 45% 12%	537
	11th to 20th	Night	5% 3 11% 28% 41% 11%	534
	21st to end	Night	4 3 13% 31% 41% 8%	594
September	1st to 10th	Night	6% 3 15% 34% 35% 7%	540
	11th to 20th	Night	7% 2 15% 42% 29% 4	540
	21st to end	Night	5% 7% 21% 37% 27% 4	540
October	1st to 10th	Night	7% 7% 26% 37% 19% 3	713
	11th to 20th	Night	7% 7% 27% 34% 22% 4	720
	21st to end	Night	7% 12% 22% 28% 25% 7%	792
November	1st to 10th	Night	6% 13% 25% 28% 23% 6%	740
	11th to 20th	Night	5% 10% 24% 36% 21% 3	879
	21st to end	Night	11% 15% 25% 27% 17% 5%	950
December	1st to 10th	Night	12% 16% 24% 31% 15% 2	950
	11th to 20th	Night	12% 18% 33% 24% 12% 1	950
	21st to end	Night	14% 17% 29% 29% 10% 2	931

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