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 2024-05-13.

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% 6% 2 5% 4 4 4 4 5% 7% 55%	83823
	Night	5% 5% 2 5% 3 3 4 3 5% 7% 58%	85765
Transparency	Day	25% 5% 9% 16% 26% 19%	83551
	Night	24% 4 9% 16% 28% 19%	85559
Seeing	Day	10% 19% 28% 25% 15% 4	13971
	Night	8% 13% 26% 31% 19% 3	24328

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 11% 4 7% 3 3 3 3 6% 5% 53%	2858
	11th to 20th	Day	3 5% 2 5% 3 2 3 2 4 5% 67%	2860
	21st to end	Day	8% 13% 4 5% 3 3 4 5% 5% 5% 45%	3146
February	1st to 10th	Day	5% 7% 1 4 2 3 3 2 4 6% 63%	1860
	11th to 20th	Day	7% 7% 2 4 4 3 3 2 5% 5% 58%	1849
	21st to end	Day	5% 7% 2 4 4 2 3 2 3 5% 64%	1570
March	1st to 10th	Day	4 8% 2 5% 3 3 3 3 3 6% 59%	3314
	11th to 20th	Day	4 7% 2 6% 3 3 3 3 4 6% 58%	3490
	21st to end	Day	2 10% 3 7% 5% 4 4 4 5% 7% 50%	3965
April	1st to 10th	Day	3 4 1 4 3 3 4 3 5% 6% 64%	2280
	11th to 20th	Day	3 4 2 4 3 2 2 2 3 5% 70%	2251
	21st to end	Day	3 3 1 3 2 2 2 3 4 5% 71%	2280
May	1st to 10th	Day	2 3 1 5% 3 3 3 3 3 5% 70%	2280
	11th to 20th	Day	2 4 2 4 4 4 4 4 5% 7% 60%	2150
	21st to end	Day	2 2 1 3 2 2 2 3 4 7% 71%	2447
June	1st to 10th	Day	3 3 1 3 3 3 4 4 6% 9% 61%	2520
	11th to 20th	Day	3 2 1 2 2 3 3 4 6% 6% 67%	2520
	21st to end	Day	4 4 2 5% 5% 5% 6% 6% 8% 9% 46%	2425
July	1st to 10th	Day	8% 5% 2 8% 7% 7% 6% 6% 9% 10% 32%	2340
	11th to 20th	Day	4 5% 2 7% 7% 7% 8% 7% 9% 11% 34%	2340
	21st to end	Day	8% 5% 3 8% 6% 7% 8% 9% 11% 10% 26%	2537
August	1st to 10th	Day	7% 4 2 8% 5% 7% 7% 7% 9% 10% 32%	2149
	11th to 20th	Day	7% 5% 2 8% 7% 7% 7% 6% 9% 9% 32%	2123
	21st to end	Day	6% 5% 2 8% 6% 5% 8% 6% 9% 9% 35%	2376
September	1st to 10th	Day	9% 6% 2 8% 5% 5% 6% 4 6% 8% 41%	2160
	11th to 20th	Day	9% 4 2 6% 5% 4 5% 4 6% 6% 50%	2160
	21st to end	Day	5% 3 2 4 3 3 4 4 6% 6% 61%	1985
October	1st to 10th	Day	6% 4 1 6% 3 4 3 3 5% 6% 58%	1802
	11th to 20th	Day	4 5% 1 4 3 2 2 3 4 4 69%	1800
	21st to end	Day	3 3 1 3 3 2 3 2 3 5% 73%	1980
November	1st to 10th	Day	2 5% 2 4 2 2 2 3 4 6% 68%	1859
	11th to 20th	Day	4 3 2 3 2 3 4 3 5% 6% 66%	1758
	21st to end	Day	6% 6% 1 4 3 4 4 3 6% 6% 57%	1710
December	1st to 10th	Day	7% 7% 2 3 3 3 3 3 5% 7% 58%	1710
	11th to 20th	Day	6% 7% 3 7% 3 3 4 4 4 7% 52%	1969
	21st to end	Day	4 8% 2 3 3 3 3 3 4 5% 62%	3000
January	1st to 10th	Night	3 8% 3 7% 4 3 4 3 4 5% 57%	4097
	11th to 20th	Night	3 5% 1 3 3 4 4 2 3 5% 67%	4110
	21st to end	Night	7% 11% 2 7% 4 4 5% 4 5% 5% 45%	4521
February	1st to 10th	Night	4 8% 2 3 4 2 2 3 5% 6% 60%	2318
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 4 6% 59%	2218
	21st to end	Night	5% 8% 2 4 2 3 4 3 5% 5% 60%	1884
March	1st to 10th	Night	4 6% 2 5% 3 2 3 3 4 6% 61%	3552
	11th to 20th	Night	8% 8% 2 5% 3 3 5% 3 5% 6% 53%	3490
	21st to end	Night	3 9% 2 7% 4 3 4 3 6% 8% 52%	3683
April	1st to 10th	Night	3 4 2 4 3 4 3 3 4 6% 65%	1900
	11th to 20th	Night	5% 4 2 4 3 3 3 3 4 6% 63%	1877
	21st to end	Night	4 3 1 4 2 2 3 2 4 5% 69%	1900
May	1st to 10th	Night	3 4 1 3 2 2 3 3 4 6% 69%	1900
	11th to 20th	Night	3 4 1 3 2 4 4 3 5% 5% 65%	1800
	21st to end	Night	2 3 1 3 2 3 4 3 5% 6% 68%	1817
June	1st to 10th	Night	2 3 2 5% 6% 4 4 4 7% 7% 55%	1440
	11th to 20th	Night	3 2 1 3 2 3 3 3 5% 8% 67%	1440
	21st to end	Night	3 5% 2 7% 6% 6% 4 6% 7% 9% 46%	1526
July	1st to 10th	Night	5% 5% 2 6% 5% 5% 5% 5% 7% 11% 44%	1620
	11th to 20th	Night	4 3 2 6% 5% 4 7% 6% 8% 13% 44%	1620
	21st to end	Night	3 5% 2 5% 5% 5% 7% 7% 10% 14% 38%	1777
August	1st to 10th	Night	4 4 2 6% 5% 4 7% 6% 10% 15% 37%	1790
	11th to 20th	Night	6% 4 2 6% 5% 5% 5% 6% 9% 12% 41%	1778
	21st to end	Night	4 4 2 6% 5% 5% 7% 4 8% 10% 45%	1980
September	1st to 10th	Night	6% 5% 2 6% 5% 5% 6% 5% 6% 8% 48%	1800
	11th to 20th	Night	8% 3 2 5% 4 4 3 4 6% 6% 55%	1800
	21st to end	Night	4 3 1 4 3 3 4 4 4 7% 63%	1975
October	1st to 10th	Night	6% 4 2 4 3 3 3 3 6% 7% 58%	2153
	11th to 20th	Night	4 4 1 4 3 2 2 2 3 5% 71%	2160
	21st to end	Night	5% 3 1 4 3 3 2 2 2 4 73%	2376
November	1st to 10th	Night	4 3 2 3 2 2 3 2 5% 6% 68%	2220
	11th to 20th	Night	3 2 1 3 2 3 3 4 4 6% 68%	2399
	21st to end	Night	7% 5% 2 5% 3 3 3 3 4 6% 59%	2470
December	1st to 10th	Night	8% 5% 2 4 3 3 3 4 5% 7% 56%	2470
	11th to 20th	Night	5% 6% 3 7% 5% 3 4 3 4 6% 54%	3223
	21st to end	Night	6% 7% 1 5% 3 3 3 2 4 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	28% 2 11% 10% 35% 14%	2859
	11th to 20th	Day	18% 3 6% 18% 40% 15%	2860
	21st to end	Day	35% 3 10% 17% 24% 11%	3146
February	1st to 10th	Day	23% 3 5% 17% 27% 25%	1860
	11th to 20th	Day	27% 3 5% 15% 27% 23%	1859
	21st to end	Day	24% 1 4 9% 31% 31%	1570
March	1st to 10th	Day	24% 2 7% 8% 35% 23%	3314
	11th to 20th	Day	24% 4 7% 20% 29% 16%	3490
	21st to end	Day	29% 4 7% 13% 30% 18%	3965
April	1st to 10th	Day	18% 3 6% 15% 32% 26%	2280
	11th to 20th	Day	17% 2 5% 11% 30% 36%	2254
	21st to end	Day	16% 3 5% 13% 33% 30%	2280
May	1st to 10th	Day	16% 3 5% 10% 29% 37%	2280
	11th to 20th	Day	20% 7% 8% 13% 28% 24%	2153
	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	26% 2 10% 12% 33% 17%	4097
	11th to 20th	Night	19% 3 6% 14% 44% 13%	4110
	21st to end	Night	37% 3 9% 14% 26% 11%	4521
February	1st to 10th	Night	23% 3 7% 14% 26% 27%	2318
	11th to 20th	Night	26% 3 6% 13% 30% 23%	2218
	21st to end	Night	24% 3 5% 9% 28% 30%	1884
March	1st to 10th	Night	23% 2 6% 11% 35% 23%	3552
	11th to 20th	Night	27% 5% 9% 15% 29% 15%	3490
	21st to end	Night	26% 3 9% 13% 31% 17%	3683
April	1st to 10th	Night	20% 3 5% 11% 37% 24%	1900
	11th to 20th	Night	21% 3 6% 11% 27% 32%	1877
	21st to end	Night	17% 4 4 14% 33% 27%	1900
May	1st to 10th	Night	16% 3 4 10% 31% 36%	1900
	11th to 20th	Night	18% 5% 7% 18% 25% 26%	1801
	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	17% 28% 28% 21% 4 1	270
	21st to end	Day	11% 32% 30% 19% 8% 1	297
February	1st to 10th	Day	17% 26% 28% 21% 7% 1	270
	11th to 20th	Day	18% 33% 31% 14% 3	270
	21st to end	Day	25% 38% 21% 12% 3	225
March	1st to 10th	Day	19% 31% 35% 12% 3 1	376
	11th to 20th	Day	21% 28% 32% 13% 4 2	460
	21st to end	Day	19% 37% 32% 9% 2 1	506
April	1st to 10th	Day	13% 35% 35% 12% 2 2	460
	11th to 20th	Day	14% 39% 33% 11% 2	452
	21st to end	Day	13% 35% 33% 15% 2 1	460
May	1st to 10th	Day	8% 29% 45% 15% 3 1	463
	11th to 20th	Day	5% 23% 44% 21% 6% 1	457
	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% 29% 29% 13% 3	760
	21st to end	Night	11% 18% 28% 27% 14% 2	836
February	1st to 10th	Night	11% 17% 29% 28% 12% 3	760
	11th to 20th	Night	12% 21% 34% 25% 8% 1	744
	21st to end	Night	11% 27% 38% 19% 4 1	628
March	1st to 10th	Night	11% 25% 27% 27% 8% 1	760
	11th to 20th	Night	13% 17% 28% 29% 13% 1	760
	21st to end	Night	8% 24% 33% 25% 9% 1	755
April	1st to 10th	Night	6% 26% 38% 23% 7%	570
	11th to 20th	Night	10% 25% 33% 25% 6%	563
	21st to end	Night	8% 22% 37% 26% 7%	570
May	1st to 10th	Night	7% 18% 35% 31% 8%	570
	11th to 20th	Night	4 14% 32% 34% 16% 1	540
	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

Page generated at 2024-05-10 10:39:05. Version ac07

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