MAC-Hunter Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MAC-Hunter Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 43%	127030
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	123683
Transparency	Day	38% 7% 12% 19% 18% 6%	130663
	Night	38% 7% 11% 18% 20% 7%	128119
Seeing	Day	14% 7% 23% 25% 21% 10%	16877
	Night	15% 6% 24% 33% 20% 2	26945

By Month

Percentage Cloud Cover SE (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	14% 5% 2 5% 2 2 2 2 3 5% 56%	4056
	11th to 20th	Day	12% 5% 1 4 3 3 3 2 3 4 59%	4060
	21st to end	Day	15% 7% 3 6% 4 4 4 3 4 5% 45%	4466
February	1st to 10th	Day	15% 8% 2 6% 4 3 3 3 5% 6% 43%	1800
	11th to 20th	Day	21% 6% 2 7% 3 3 4 2 4 5% 45%	1894
	21st to end	Day	18% 6% 2 6% 4 4 4 3 4 5% 44%	1754
March	1st to 10th	Day	21% 7% 2 7% 4 3 3 3 5% 5% 39%	4935
	11th to 20th	Day	9% 4 2 6% 4 3 3 3 5% 6% 54%	4980
	21st to end	Day	14% 6% 2 7% 4 4 3 3 4 5% 48%	5465
April	1st to 10th	Day	9% 4 2 4 3 3 5% 4 6% 8% 51%	2221
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 3 6% 7% 49%	2374
	21st to end	Day	9% 5% 2 5% 4 4 4 4 5% 7% 51%	2460
May	1st to 10th	Day	9% 7% 2 7% 5% 5% 5% 5% 7% 10% 38%	5862
	11th to 20th	Day	18% 7% 3 7% 5% 5% 5% 4 7% 9% 31%	5861
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 6% 8% 45%	6433
June	1st to 10th	Day	9% 6% 2 7% 6% 5% 5% 5% 8% 11% 36%	2600
	11th to 20th	Day	7% 5% 2 5% 5% 5% 6% 5% 9% 12% 41%	2600
	21st to end	Day	7% 4 2 7% 5% 4 6% 5% 8% 12% 40%	2600
July	1st to 10th	Day	11% 6% 3 8% 6% 7% 7% 6% 8% 10% 28%	5900
	11th to 20th	Day	6% 5% 2 7% 5% 6% 8% 6% 9% 14% 30%	5900
	21st to end	Day	8% 6% 3 9% 6% 6% 7% 6% 8% 12% 29%	6424
August	1st to 10th	Day	24% 7% 3 7% 5% 5% 6% 5% 9% 9% 21%	4234
	11th to 20th	Day	12% 6% 2 7% 5% 5% 6% 5% 6% 11% 36%	4148
	21st to end	Day	7% 4 1 5% 3 4 5% 5% 8% 10% 48%	4312
September	1st to 10th	Day	8% 4 2 6% 5% 5% 6% 5% 6% 9% 45%	2280
	11th to 20th	Day	13% 7% 2 6% 4 5% 5% 4 5% 8% 41%	2200
	21st to end	Day	17% 6% 2 7% 4 4 3 3 5% 6% 42%	2200
October	1st to 10th	Day	14% 6% 2 5% 4 4 3 3 4 6% 49%	2045
	11th to 20th	Day	11% 4 1 5% 3 3 4 2 4 5% 58%	2000
	21st to end	Day	13% 4 1 4 3 4 3 2 4 5% 57%	2200
November	1st to 10th	Day	12% 5% 2 4 3 3 3 2 4 4 56%	2057
	11th to 20th	Day	14% 5% 2 4 3 2 3 2 4 6% 55%	2032
	21st to end	Day	13% 6% 2 4 4 3 3 3 5% 6% 51%	1890
December	1st to 10th	Day	12% 5% 2 6% 4 3 3 3 4 5% 51%	2948
	11th to 20th	Day	16% 5% 2 6% 3 4 4 2 5% 5% 47%	3373
	21st to end	Day	20% 7% 2 4 3 3 3 3 4 5% 46%	4466
January	1st to 10th	Night	12% 4 2 4 3 3 3 3 4 5% 57%	5889
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 6% 52%	5900
	21st to end	Night	14% 9% 2 6% 4 4 3 3 4 5% 46%	6490
February	1st to 10th	Night	16% 5% 2 6% 3 3 5% 4 5% 6% 45%	2600
	11th to 20th	Night	19% 7% 2 6% 4 4 3 3 4 4 43%	2389
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 6% 47%	1875
March	1st to 10th	Night	19% 7% 3 6% 4 4 4 3 5% 5% 40%	4918
	11th to 20th	Night	11% 4 1 4 3 3 3 4 5% 7% 54%	4980
	21st to end	Night	14% 4 2 5% 4 4 4 3 5% 6% 49%	5467
April	1st to 10th	Night	12% 5% 2 5% 3 4 3 4 6% 6% 50%	2177
	11th to 20th	Night	10% 5% 2 5% 3 4 3 3 4 7% 54%	1975
	21st to end	Night	10% 4 2 5% 3 4 4 4 6% 8% 51%	1955
May	1st to 10th	Night	11% 6% 2 6% 4 5% 4 4 7% 9% 41%	4033
	11th to 20th	Night	18% 7% 2 7% 4 5% 4 4 7% 9% 34%	4032
	21st to end	Night	12% 6% 2 6% 4 5% 5% 4 7% 9% 42%	4421
June	1st to 10th	Night	11% 6% 3 7% 4 5% 6% 6% 7% 9% 35%	1800
	11th to 20th	Night	9% 7% 3 5% 5% 6% 5% 6% 8% 10% 36%	1800
	21st to end	Night	7% 5% 3 7% 4 4 7% 6% 8% 12% 38%	1800
July	1st to 10th	Night	12% 7% 3 9% 7% 6% 6% 5% 8% 10% 26%	4058
	11th to 20th	Night	9% 6% 2 7% 6% 6% 7% 7% 11% 14% 25%	4057
	21st to end	Night	12% 9% 4 10% 7% 6% 7% 5% 8% 10% 23%	4427
August	1st to 10th	Night	25% 6% 3 7% 5% 5% 5% 4 8% 8% 23%	2915
	11th to 20th	Night	11% 6% 2 8% 5% 6% 6% 4 8% 10% 33%	2875
	21st to end	Night	6% 4 2 5% 4 4 5% 4 7% 11% 49%	3577
September	1st to 10th	Night	9% 5% 2 7% 5% 4 5% 5% 7% 9% 42%	2115
	11th to 20th	Night	13% 7% 3 6% 5% 5% 5% 3 5% 7% 41%	2200
	21st to end	Night	16% 7% 3 7% 5% 4 4 4 4 6% 42%	2200
October	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 4 6% 52%	2353
	11th to 20th	Night	13% 5% 2 4 3 3 2 3 4 5% 56%	2400
	21st to end	Night	10% 5% 2 4 2 3 3 3 4 5% 57%	2640
November	1st to 10th	Night	13% 5% 2 5% 3 3 3 3 3 5% 55%	2461
	11th to 20th	Night	13% 6% 2 4 3 3 3 2 4 5% 54%	2585
	21st to end	Night	13% 5% 1 5% 3 3 4 3 6% 6% 50%	2730
December	1st to 10th	Night	13% 6% 2 5% 3 2 3 2 4 4 54%	4277
	11th to 20th	Night	17% 7% 3 7% 4 3 3 3 4 6% 44%	4822
	21st to end	Night	19% 7% 2 5% 3 4 3 3 4 6% 44%	6490

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	32% 3 5% 20% 33% 8%	4057
	11th to 20th	Day	31% 3 4 15% 36% 11%	4060
	21st to end	Day	42% 3 4 18% 22% 11%	4466
February	1st to 10th	Day	42% 4 9% 20% 19% 5%	1800
	11th to 20th	Day	43% 4 5% 17% 24% 6%	1904
	21st to end	Day	42% 5% 8% 15% 21% 8%	1754
March	1st to 10th	Day	48% 4 6% 12% 20% 10%	4935
	11th to 20th	Day	30% 5% 8% 15% 26% 17%	4980
	21st to end	Day	40% 4 6% 20% 21% 8%	5465
April	1st to 10th	Day	30% 6% 11% 21% 26% 6%	2221
	11th to 20th	Day	32% 6% 10% 21% 21% 10%	2374
	21st to end	Day	32% 6% 12% 24% 22% 4	2460
May	1st to 10th	Day	38% 9% 17% 24% 11% 1	5897
	11th to 20th	Day	48% 7% 15% 18% 12% 1	5865
	21st to end	Day	36% 8% 13% 19% 20% 3	6447
June	1st to 10th	Day	37% 10% 17% 23% 10% 2	2600
	11th to 20th	Day	32% 11% 20% 22% 14% 1	2600
	21st to end	Day	32% 12% 20% 23% 13% 1	2600
July	1st to 10th	Day	46% 12% 17% 17% 6% 1	5835
	11th to 20th	Day	38% 15% 32% 11% 3 1	5831
	21st to end	Day	43% 13% 18% 19% 7%	6240
August	1st to 10th	Day	55% 11% 18% 11% 5%	4221
	11th to 20th	Day	40% 10% 17% 20% 12%	4187
	21st to end	Day	28% 9% 16% 31% 15% 1	4312
September	1st to 10th	Day	35% 9% 15% 19% 18% 4	2280
	11th to 20th	Day	40% 8% 11% 17% 21% 3	2200
	21st to end	Day	43% 6% 10% 21% 15% 6%	2200
October	1st to 10th	Day	33% 4 8% 19% 28% 8%	3331
	11th to 20th	Day	19% 4 4 17% 27% 28%	3240
	21st to end	Day	26% 3 5% 21% 27% 17%	3538
November	1st to 10th	Day	31% 4 6% 19% 28% 12%	2057
	11th to 20th	Day	32% 4 7% 19% 27% 10%	2032
	21st to end	Day	35% 4 8% 21% 24% 9%	1890
December	1st to 10th	Day	35% 4 6% 17% 27% 10%	2948
	11th to 20th	Day	39% 4 12% 20% 19% 6%	3370
	21st to end	Day	40% 4 7% 22% 24% 2	4466
January	1st to 10th	Night	30% 4 5% 16% 37% 7%	5889
	11th to 20th	Night	34% 4 6% 15% 33% 8%	5900
	21st to end	Night	41% 4 4 14% 28% 9%	6490
February	1st to 10th	Night	39% 5% 8% 20% 20% 8%	2600
	11th to 20th	Night	45% 4 7% 15% 22% 7%	2390
	21st to end	Night	38% 5% 9% 17% 21% 11%	1875
March	1st to 10th	Night	45% 6% 6% 11% 25% 7%	4918
	11th to 20th	Night	29% 5% 7% 12% 27% 20%	4980
	21st to end	Night	36% 4 8% 20% 21% 10%	5467
April	1st to 10th	Night	33% 6% 10% 20% 23% 9%	2177
	11th to 20th	Night	31% 5% 9% 23% 21% 11%	1975
	21st to end	Night	31% 6% 12% 24% 21% 5%	1955
May	1st to 10th	Night	37% 8% 15% 23% 15% 2	4060
	11th to 20th	Night	46% 7% 17% 18% 12% 1	4033
	21st to end	Night	36% 8% 13% 23% 17% 2	4429
June	1st to 10th	Night	41% 11% 14% 22% 10% 2	1800
	11th to 20th	Night	38% 12% 19% 19% 12% 2	1800
	21st to end	Night	34% 14% 19% 21% 10% 2	1800
July	1st to 10th	Night	49% 13% 20% 13% 5% 1	4015
	11th to 20th	Night	44% 17% 28% 8% 3 1	4006
	21st to end	Night	52% 11% 17% 15% 5%	4297
August	1st to 10th	Night	55% 10% 17% 14% 3 1	2904
	11th to 20th	Night	42% 12% 21% 19% 6% 1	2902
	21st to end	Night	28% 8% 15% 30% 17% 3	3577
September	1st to 10th	Night	36% 10% 15% 20% 13% 6%	2115
	11th to 20th	Night	42% 8% 12% 17% 18% 3	2200
	21st to end	Night	44% 7% 12% 18% 15% 4	2200
October	1st to 10th	Night	34% 6% 9% 19% 25% 7%	3847
	11th to 20th	Night	21% 3 5% 15% 28% 28%	3899
	21st to end	Night	26% 4 6% 20% 27% 18%	4252
November	1st to 10th	Night	33% 4 7% 15% 27% 13%	2461
	11th to 20th	Night	33% 4 6% 17% 28% 12%	2585
	21st to end	Night	33% 5% 8% 20% 24% 9%	2730
December	1st to 10th	Night	34% 4 7% 16% 29% 10%	4277
	11th to 20th	Night	42% 4 10% 16% 18% 9%	4824
	21st to end	Night	42% 4 7% 22% 22% 3	6490

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	19% 13% 45% 18% 5%	300
	11th to 20th	Day	14% 15% 41% 22% 7%	300
	21st to end	Day	21% 18% 37% 18% 6%	330
February	1st to 10th	Day	16% 14% 41% 22% 7%	300
	11th to 20th	Day	32% 12% 37% 16% 3	300
	21st to end	Day	20% 16% 38% 22% 4 1	353
March	1st to 10th	Day	19% 13% 34% 25% 9%	500
	11th to 20th	Day	16% 14% 39% 24% 6% 1	500
	21st to end	Day	15% 14% 36% 24% 9% 1	550
April	1st to 10th	Day	14% 14% 34% 24% 13% 1	500
	11th to 20th	Day	10% 9% 31% 28% 17% 6%	492
	21st to end	Day	12% 7% 25% 28% 23% 6%	500
May	1st to 10th	Day	8% 11% 33% 24% 18% 6%	503
	11th to 20th	Day	17% 3 19% 26% 23% 12%	527
	21st to end	Day	15% 4 16% 23% 24% 18%	573
June	1st to 10th	Day	10% 3 14% 31% 27% 15%	530
	11th to 20th	Day	9% 2 15% 28% 26% 20%	530
	21st to end	Day	8% 2 10% 28% 33% 19%	530
July	1st to 10th	Day	9% 2 6% 23% 31% 29%	525
	11th to 20th	Day	9% 2 6% 19% 37% 27%	524
	21st to end	Day	6% 3 8% 23% 38% 23%	576
August	1st to 10th	Day	17% 3 10% 24% 26% 21%	526
	11th to 20th	Day	12% 2 7% 23% 32% 24%	519
	21st to end	Day	12% 2 12% 22% 32% 21%	583
September	1st to 10th	Day	10% 2 11% 28% 32% 17%	530
	11th to 20th	Day	15% 3 13% 24% 31% 14%	530
	21st to end	Day	19% 2 15% 29% 23% 11%	530
October	1st to 10th	Day	15% 4 19% 29% 23% 10%	530
	11th to 20th	Day	11% 5% 23% 29% 23% 8%	530
	21st to end	Day	13% 5% 25% 26% 23% 7%	583
November	1st to 10th	Day	16% 5% 27% 31% 17% 5%	535
	11th to 20th	Day	19% 8% 32% 27% 12% 2	472
	21st to end	Day	12% 11% 35% 26% 14% 2	330
December	1st to 10th	Day	20% 15% 36% 20% 8% 1	306
	11th to 20th	Day	22% 5% 34% 25% 11% 2	300
	21st to end	Day	22% 13% 37% 16% 9% 3	330
January	1st to 10th	Night	19% 10% 37% 26% 7%	800
	11th to 20th	Night	16% 11% 35% 31% 7%	800
	21st to end	Night	19% 7% 38% 33% 3	880
February	1st to 10th	Night	18% 10% 34% 32% 6%	800
	11th to 20th	Night	22% 12% 37% 27% 2	783
	21st to end	Night	16% 13% 38% 29% 5%	660
March	1st to 10th	Night	18% 10% 33% 33% 6%	800
	11th to 20th	Night	17% 10% 35% 30% 8% 1	800
	21st to end	Night	16% 8% 37% 31% 7%	880
April	1st to 10th	Night	14% 13% 35% 29% 9%	800
	11th to 20th	Night	11% 11% 31% 32% 14%	791
	21st to end	Night	11% 6% 27% 43% 13%	755
May	1st to 10th	Night	12% 7% 27% 41% 14%	600
	11th to 20th	Night	14% 5% 23% 39% 18% 1	591
	21st to end	Night	11% 3 14% 34% 35% 3	650
June	1st to 10th	Night	12% 4 13% 40% 29% 3	600
	11th to 20th	Night	10% 2 13% 36% 31% 7%	600
	21st to end	Night	8% 2 10% 42% 32% 8%	600
July	1st to 10th	Night	8% 3 8% 34% 42% 6%	585
	11th to 20th	Night	10% 1 5% 28% 49% 7%	582
	21st to end	Night	7% 3 7% 33% 44% 5%	657
August	1st to 10th	Night	17% 2 6% 26% 42% 7%	597
	11th to 20th	Night	13% 2 7% 31% 40% 7%	594
	21st to end	Night	12% 2 8% 31% 41% 5%	871
September	1st to 10th	Night	8% 2 11% 32% 41% 6%	800
	11th to 20th	Night	16% 2 11% 30% 36% 4	800
	21st to end	Night	20% 2 14% 33% 29% 2	800
October	1st to 10th	Night	15% 3 18% 31% 28% 5%	800
	11th to 20th	Night	16% 4 22% 33% 24% 2	800
	21st to end	Night	12% 7% 23% 33% 22% 2	880
November	1st to 10th	Night	15% 5% 25% 34% 18% 3	820
	11th to 20th	Night	15% 9% 28% 35% 12% 1	840
	21st to end	Night	15% 7% 30% 32% 15% 1	840
December	1st to 10th	Night	20% 8% 29% 34% 8% 1	809
	11th to 20th	Night	18% 6% 29% 35% 11% 1	800
	21st to end	Night	23% 9% 26% 33% 9%	880

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