Mannford Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mannford Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	10% 6% 2 5% 4 4 4 3 5% 7% 50%	101597
	Night	10% 5% 2 5% 3 3 3 3 5% 6% 54%	98292
Transparency	Day	33% 4 10% 26% 21% 5%	105301
	Night	30% 3 10% 26% 24% 7%	102715
Seeing	Day	14% 10% 28% 28% 16% 4	15550
	Night	13% 10% 31% 32% 13% 1	25444

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	10% 9% 5% 8% 5% 5% 3 3 4 5% 43%	2847
	11th to 20th	Day	9% 6% 2 5% 5% 5% 4 3 4 5% 51%	2850
	21st to end	Day	20% 11% 3 5% 3 2 2 2 3 4 46%	3135
February	1st to 10th	Day	13% 11% 3 7% 4 3 4 3 4 6% 43%	1710
	11th to 20th	Day	12% 7% 3 6% 3 4 3 3 4 7% 47%	1830
	21st to end	Day	13% 9% 3 5% 3 3 4 3 4 6% 46%	1582
March	1st to 10th	Day	12% 7% 2 5% 3 3 3 2 4 5% 55%	3436
	11th to 20th	Day	10% 5% 2 4 4 4 3 3 5% 7% 53%	3480
	21st to end	Day	14% 11% 3 7% 5% 4 4 3 5% 6% 38%	3814
April	1st to 10th	Day	10% 6% 2 6% 4 4 3 4 6% 6% 49%	2090
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 6% 7% 44%	2239
	21st to end	Day	17% 7% 2 6% 3 4 4 3 4 6% 44%	2470
May	1st to 10th	Day	19% 8% 3 6% 4 4 3 3 4 5% 41%	4082
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 6% 7% 46%	4082
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 5% 6% 8% 38%	4477
June	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 4 7% 10% 49%	2470
	11th to 20th	Day	7% 4 2 4 4 5% 4 4 6% 8% 51%	2470
	21st to end	Day	5% 3 1 4 3 4 4 4 6% 8% 58%	2470
July	1st to 10th	Day	8% 5% 2 5% 5% 4 5% 4 8% 8% 47%	4120
	11th to 20th	Day	5% 4 2 5% 3 4 4 3 6% 9% 55%	4120
	21st to end	Day	5% 3 1 4 3 4 4 4 7% 10% 53%	4465
August	1st to 10th	Day	5% 3 2 4 3 3 4 4 7% 9% 57%	4104
	11th to 20th	Day	7% 4 2 5% 3 4 5% 4 7% 9% 50%	4041
	21st to end	Day	4 3 1 4 3 3 4 4 6% 7% 60%	4345
September	1st to 10th	Day	10% 5% 1 5% 4 3 3 3 5% 6% 54%	2093
	11th to 20th	Day	12% 4 2 5% 3 4 5% 4 6% 7% 48%	2090
	21st to end	Day	9% 3 2 5% 3 3 3 3 4 6% 59%	2090
October	1st to 10th	Day	8% 4 1 4 3 4 4 3 5% 6% 59%	1989
	11th to 20th	Day	11% 3 1 3 3 2 2 2 4 4 65%	1900
	21st to end	Day	13% 6% 2 4 3 3 2 3 3 4 57%	2090
November	1st to 10th	Day	10% 4 2 4 2 2 3 3 5% 6% 59%	1938
	11th to 20th	Day	10% 5% 1 3 2 2 3 2 4 6% 61%	1800
	21st to end	Day	13% 6% 2 3 3 2 2 2 5% 6% 55%	1800
December	1st to 10th	Day	12% 7% 2 6% 3 3 3 3 3 5% 52%	1782
	11th to 20th	Day	12% 8% 3 6% 4 4 3 2 4 5% 47%	2161
	21st to end	Day	14% 10% 4 10% 5% 5% 4 3 5% 5% 34%	3135
January	1st to 10th	Night	11% 8% 3 7% 4 4 3 3 5% 5% 48%	4108
	11th to 20th	Night	8% 5% 2 6% 4 7% 5% 3 4 6% 51%	4120
	21st to end	Night	20% 8% 2 4 3 2 2 2 4 4 49%	4532
February	1st to 10th	Night	14% 8% 2 7% 4 3 3 3 4 5% 47%	2470
	11th to 20th	Night	12% 7% 3 6% 3 2 4 2 4 5% 50%	2252
	21st to end	Night	12% 8% 2 6% 4 3 4 2 3 5% 51%	1870
March	1st to 10th	Night	12% 7% 2 6% 3 3 3 3 4 5% 52%	3419
	11th to 20th	Night	11% 5% 2 4 2 3 3 3 4 6% 59%	3480
	21st to end	Night	14% 6% 2 5% 4 4 4 4 5% 6% 48%	3817
April	1st to 10th	Night	10% 5% 2 4 3 3 3 3 5% 6% 55%	2090
	11th to 20th	Night	14% 5% 1 5% 3 3 3 3 4 6% 52%	1885
	21st to end	Night	14% 7% 2 5% 3 3 3 3 4 5% 50%	1710
May	1st to 10th	Night	15% 8% 2 5% 4 3 3 3 5% 7% 45%	2823
	11th to 20th	Night	15% 7% 2 6% 4 3 3 3 5% 6% 46%	2823
	21st to end	Night	9% 5% 2 5% 3 4 4 4 6% 9% 50%	3090
June	1st to 10th	Night	6% 3 2 5% 3 3 5% 4 6% 8% 57%	1710
	11th to 20th	Night	5% 3 1 4 3 3 4 4 7% 10% 56%	1710
	21st to end	Night	3 3 1 3 3 3 4 3 7% 9% 62%	1710
July	1st to 10th	Night	6% 5% 2 4 4 3 4 5% 7% 10% 51%	2850
	11th to 20th	Night	3 2 1 3 3 3 4 2 5% 10% 64%	2850
	21st to end	Night	6% 3 1 3 2 2 2 3 5% 8% 62%	3098
August	1st to 10th	Night	2 2 1 3 2 3 5% 4 6% 9% 63%	2836
	11th to 20th	Night	5% 3 2 5% 4 4 6% 5% 6% 8% 53%	2798
	21st to end	Night	3 2 1 3 3 2 3 4 5% 8% 66%	3316
September	1st to 10th	Night	8% 4 2 4 3 3 3 3 4 6% 59%	2082
	11th to 20th	Night	11% 5% 1 5% 4 4 4 4 4 6% 53%	2090
	21st to end	Night	7% 3 1 5% 3 3 3 3 4 6% 60%	2090
October	1st to 10th	Night	7% 4 2 3 3 3 4 3 4 5% 62%	2171
	11th to 20th	Night	11% 4 2 4 2 2 2 3 4 5% 62%	2280
	21st to end	Night	13% 5% 1 4 2 2 3 2 4 4 59%	2508
November	1st to 10th	Night	10% 5% 1 3 2 2 2 2 4 5% 63%	2355
	11th to 20th	Night	9% 5% 2 4 3 2 3 2 3 5% 60%	2600
	21st to end	Night	13% 6% 1 4 2 3 3 2 4 5% 57%	2600
December	1st to 10th	Night	12% 6% 2 4 3 3 3 3 4 6% 54%	2581
	11th to 20th	Night	12% 7% 3 5% 3 4 3 3 4 5% 51%	3036
	21st to end	Night	16% 8% 2 6% 3 3 3 3 5% 5% 45%	4532

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	43% 2 7% 24% 21% 2	2848
	11th to 20th	Day	32% 4 12% 26% 20% 6%	2850
	21st to end	Day	45% 2 7% 21% 23% 2	3135
February	1st to 10th	Day	45% 2 9% 23% 17% 4	1710
	11th to 20th	Day	39% 3 8% 28% 19% 4	1840
	21st to end	Day	41% 2 6% 23% 20% 8%	1582
March	1st to 10th	Day	33% 2 5% 23% 25% 11%	3436
	11th to 20th	Day	33% 3 12% 28% 21% 4	3480
	21st to end	Day	47% 4 9% 27% 11% 2	3814
April	1st to 10th	Day	35% 3 11% 24% 19% 7%	2090
	11th to 20th	Day	39% 5% 12% 22% 17% 6%	2239
	21st to end	Day	42% 4 9% 24% 18% 2	2470
May	1st to 10th	Day	48% 3 7% 22% 17% 4	4120
	11th to 20th	Day	38% 4 13% 24% 19% 1	4086
	21st to end	Day	44% 6% 11% 22% 14% 4	4489
June	1st to 10th	Day	30% 5% 17% 29% 16% 3	2470
	11th to 20th	Day	30% 5% 13% 29% 18% 4	2470
	21st to end	Day	24% 5% 14% 30% 22% 5%	2470
July	1st to 10th	Day	32% 5% 15% 27% 17% 3	4056
	11th to 20th	Day	25% 4 10% 34% 25% 2	4051
	21st to end	Day	24% 6% 18% 35% 17% 1	4325
August	1st to 10th	Day	24% 4 12% 28% 26% 6%	4090
	11th to 20th	Day	29% 5% 19% 28% 17% 2	4080
	21st to end	Day	23% 5% 13% 42% 14% 4	4344
September	1st to 10th	Day	31% 3 8% 25% 22% 10%	2093
	11th to 20th	Day	34% 5% 10% 23% 23% 5%	2090
	21st to end	Day	28% 4 7% 23% 30% 7%	2090
October	1st to 10th	Day	18% 2 8% 14% 44% 14%	3301
	11th to 20th	Day	16% 1 4 24% 39% 17%	3140
	21st to end	Day	27% 2 6% 28% 30% 7%	3428
November	1st to 10th	Day	27% 2 7% 28% 27% 9%	1938
	11th to 20th	Day	27% 2 8% 29% 25% 10%	1800
	21st to end	Day	30% 3 8% 27% 26% 6%	1800
December	1st to 10th	Day	36% 2 7% 30% 22% 2	1782
	11th to 20th	Day	40% 3 6% 23% 25% 4	2159
	21st to end	Day	48% 7% 7% 22% 13% 3	3135
January	1st to 10th	Night	38% 3 7% 27% 21% 4	4108
	11th to 20th	Night	32% 6% 12% 22% 25% 3	4120
	21st to end	Night	41% 2 8% 22% 23% 4	4532
February	1st to 10th	Night	41% 2 10% 23% 19% 5%	2470
	11th to 20th	Night	38% 2 7% 27% 19% 6%	2252
	21st to end	Night	38% 2 6% 20% 23% 10%	1870
March	1st to 10th	Night	37% 3 6% 21% 21% 13%	3419
	11th to 20th	Night	28% 2 9% 33% 22% 6%	3480
	21st to end	Night	37% 4 11% 33% 14% 2	3817
April	1st to 10th	Night	30% 4 9% 23% 23% 10%	2090
	11th to 20th	Night	34% 3 10% 25% 19% 9%	1885
	21st to end	Night	37% 3 9% 25% 22% 4	1710
May	1st to 10th	Night	40% 5% 10% 19% 21% 5%	2850
	11th to 20th	Night	39% 4 13% 26% 16% 2	2824
	21st to end	Night	31% 6% 14% 26% 20% 3	3099
June	1st to 10th	Night	25% 5% 17% 32% 19% 3	1710
	11th to 20th	Night	23% 4 15% 35% 19% 4	1710
	21st to end	Night	19% 3 14% 31% 26% 7%	1710
July	1st to 10th	Night	27% 6% 15% 31% 18% 4	2805
	11th to 20th	Night	17% 3 10% 38% 29% 3	2796
	21st to end	Night	20% 4 15% 37% 23% 1	2999
August	1st to 10th	Night	18% 3 13% 32% 26% 8%	2826
	11th to 20th	Night	28% 5% 15% 27% 21% 4	2825
	21st to end	Night	17% 5% 12% 43% 19% 5%	3316
September	1st to 10th	Night	27% 3 8% 26% 26% 10%	2082
	11th to 20th	Night	32% 4 9% 21% 27% 7%	2090
	21st to end	Night	26% 3 6% 25% 31% 8%	2090
October	1st to 10th	Night	15% 2 6% 15% 38% 25%	3626
	11th to 20th	Night	19% 2 4 20% 38% 18%	3779
	21st to end	Night	25% 3 6% 29% 28% 9%	4120
November	1st to 10th	Night	26% 2 8% 24% 30% 10%	2355
	11th to 20th	Night	28% 2 7% 24% 28% 10%	2600
	21st to end	Night	32% 2 7% 23% 29% 8%	2600
December	1st to 10th	Night	32% 3 9% 28% 22% 6%	2581
	11th to 20th	Night	36% 3 6% 22% 27% 5%	3037
	21st to end	Night	41% 4 7% 23% 20% 5%	4532

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	21% 19% 34% 22% 4	270
	11th to 20th	Day	24% 22% 39% 14% 1	270
	21st to end	Day	20% 20% 37% 17% 6%	297
February	1st to 10th	Day	23% 18% 43% 13% 3	270
	11th to 20th	Day	20% 24% 40% 15% 1	270
	21st to end	Day	30% 27% 32% 8% 3	225
March	1st to 10th	Day	23% 19% 37% 18% 2	270
	11th to 20th	Day	24% 20% 38% 16% 1	270
	21st to end	Day	25% 26% 33% 12% 4 1	297
April	1st to 10th	Day	23% 24% 32% 17% 4	270
	11th to 20th	Day	23% 21% 37% 16% 3	437
	21st to end	Day	24% 18% 34% 17% 7% 1	650
May	1st to 10th	Day	19% 14% 38% 23% 5% 1	653
	11th to 20th	Day	17% 11% 33% 27% 10% 2	675
	21st to end	Day	17% 7% 33% 23% 15% 5%	734
June	1st to 10th	Day	7% 4 24% 38% 21% 5%	680
	11th to 20th	Day	8% 3 30% 42% 15% 3	680
	21st to end	Day	5% 2 27% 40% 21% 5%	680
July	1st to 10th	Day	8% 3 14% 35% 30% 11%	671
	11th to 20th	Day	4 1 17% 40% 32% 6%	668
	21st to end	Day	7% 11% 38% 34% 10%	739
August	1st to 10th	Day	6% 2 15% 39% 33% 4	676
	11th to 20th	Day	8% 2 16% 38% 31% 5%	665
	21st to end	Day	5% 1 10% 38% 38% 8%	639
September	1st to 10th	Day	9% 2 16% 31% 33% 10%	303
	11th to 20th	Day	5% 1 20% 44% 25% 6%	300
	21st to end	Day	14% 4 20% 39% 17% 5%	300
October	1st to 10th	Day	9% 5% 36% 27% 18% 5%	300
	11th to 20th	Day	11% 13% 40% 26% 9% 1	300
	21st to end	Day	25% 13% 34% 21% 7% 2	330
November	1st to 10th	Day	17% 11% 44% 19% 8% 1	300
	11th to 20th	Day	17% 18% 33% 21% 9% 1	300
	21st to end	Day	24% 15% 39% 18% 4	300
December	1st to 10th	Day	18% 15% 40% 18% 7% 1	294
	11th to 20th	Day	23% 16% 38% 20% 4	270
	21st to end	Day	20% 23% 38% 18% 2	297
January	1st to 10th	Night	16% 14% 37% 27% 6% 1	950
	11th to 20th	Night	16% 17% 35% 27% 5%	950
	21st to end	Night	14% 15% 37% 28% 5%	1045
February	1st to 10th	Night	18% 15% 39% 24% 3	950
	11th to 20th	Night	19% 19% 36% 23% 3	778
	21st to end	Night	19% 17% 36% 24% 3	614
March	1st to 10th	Night	15% 14% 38% 29% 3	570
	11th to 20th	Night	22% 14% 35% 25% 4	570
	21st to end	Night	19% 16% 37% 23% 5%	627
April	1st to 10th	Night	16% 15% 41% 23% 4 1	570
	11th to 20th	Night	17% 15% 37% 25% 5%	563
	21st to end	Night	17% 12% 40% 23% 7% 1	570
May	1st to 10th	Night	16% 9% 39% 30% 6% 1	570
	11th to 20th	Night	16% 6% 32% 31% 14% 1	561
	21st to end	Night	9% 7% 31% 34% 17% 2	617
June	1st to 10th	Night	7% 3 23% 41% 24% 2	570
	11th to 20th	Night	5% 4 29% 44% 18% 1	570
	21st to end	Night	3 2 28% 47% 18% 2	570
July	1st to 10th	Night	4 1 15% 46% 30% 4	555
	11th to 20th	Night	4 1 17% 45% 29% 4	552
	21st to end	Night	7% 2 10% 43% 34% 4	624
August	1st to 10th	Night	3 1 16% 47% 31% 2	567
	11th to 20th	Night	5% 1 14% 44% 32% 3	564
	21st to end	Night	3 1 12% 42% 39% 4	627
September	1st to 10th	Night	10% 2 14% 40% 32% 1	570
	11th to 20th	Night	13% 1 21% 38% 23% 5%	570
	21st to end	Night	9% 2 23% 40% 22% 4	570
October	1st to 10th	Night	8% 4 29% 34% 22% 3	651
	11th to 20th	Night	13% 8% 38% 31% 9%	760
	21st to end	Night	17% 11% 31% 29% 11% 1	836
November	1st to 10th	Night	13% 9% 38% 29% 11% 1	795
	11th to 20th	Night	14% 13% 35% 30% 7% 1	1000
	21st to end	Night	17% 12% 37% 26% 8%	1000
December	1st to 10th	Night	17% 13% 35% 28% 6%	993
	11th to 20th	Night	20% 12% 36% 27% 6%	950
	21st to end	Night	17% 18% 33% 27% 5%	1045

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