Mill Springs
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mill Springs clear sky chart from 2005-11-06 to 2025-02-25.

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	15% 8% 3 7% 4 4 5% 4 5% 7% 38%	108995
	Night	15% 9% 3 7% 4 4 4 3 5% 6% 40%	109713
Transparency	Day	44% 4 10% 24% 15% 2	112752
	Night	44% 4 9% 23% 17% 3	114094
Seeing	Day	20% 9% 22% 23% 17% 9%	15047
	Night	19% 8% 22% 30% 19% 3	25183

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	15% 16% 7% 11% 4 4 5% 3 5% 5% 25%	4056
	11th to 20th	Day	16% 13% 7% 12% 3 4 3 2 3 4 34%	4060
	21st to end	Day	21% 11% 3 6% 4 3 3 4 5% 6% 34%	4485
February	1st to 10th	Day	18% 13% 4 8% 4 4 4 3 4 6% 32%	2000
	11th to 20th	Day	22% 10% 4 9% 5% 3 3 3 3 6% 30%	1948
	21st to end	Day	19% 12% 4 9% 4 3 3 3 4 5% 33%	1610
March	1st to 10th	Day	25% 11% 3 6% 4 3 4 3 4 6% 31%	3141
	11th to 20th	Day	16% 7% 2 5% 4 4 3 3 4 6% 47%	3480
	21st to end	Day	15% 9% 2 6% 5% 4 4 3 5% 7% 40%	3815
April	1st to 10th	Day	13% 7% 2 7% 5% 3 5% 4 6% 7% 41%	2238
	11th to 20th	Day	15% 8% 2 7% 4 4 4 4 5% 5% 42%	2254
	21st to end	Day	16% 7% 2 7% 5% 4 5% 4 6% 7% 38%	2460
May	1st to 10th	Day	19% 9% 3 7% 5% 5% 4 4 6% 7% 32%	4082
	11th to 20th	Day	18% 8% 3 8% 5% 5% 4 3 5% 6% 35%	4081
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 5% 7% 8% 38%	4476
June	1st to 10th	Day	11% 6% 2 7% 4 5% 5% 5% 7% 10% 38%	2470
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 5% 7% 10% 44%	2470
	21st to end	Day	8% 5% 1 5% 6% 6% 6% 5% 7% 11% 40%	2470
July	1st to 10th	Day	8% 5% 2 7% 5% 6% 7% 5% 8% 10% 38%	4120
	11th to 20th	Day	8% 5% 2 7% 5% 6% 5% 5% 7% 10% 41%	4120
	21st to end	Day	19% 10% 4 9% 6% 5% 6% 5% 6% 7% 22%	4466
August	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 43%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 5% 7% 5% 8% 11% 36%	3894
	21st to end	Day	6% 4 1 4 3 4 4 4 6% 9% 54%	4180
September	1st to 10th	Day	14% 6% 3 7% 5% 4 5% 4 5% 7% 41%	2157
	11th to 20th	Day	15% 5% 2 5% 4 4 4 3 6% 7% 45%	2090
	21st to end	Day	16% 5% 2 4 4 3 4 3 5% 7% 47%	2090
October	1st to 10th	Day	12% 4 1 4 4 3 3 3 5% 7% 54%	2090
	11th to 20th	Day	14% 6% 2 5% 4 3 2 3 4 6% 51%	1976
	21st to end	Day	18% 7% 2 5% 3 3 4 3 5% 7% 45%	1981
November	1st to 10th	Day	13% 6% 2 4 3 4 3 3 4 6% 52%	1762
	11th to 20th	Day	15% 9% 2 5% 3 3 4 4 4 7% 44%	1800
	21st to end	Day	16% 10% 4 6% 4 4 3 3 5% 5% 40%	1800
December	1st to 10th	Day	17% 11% 3 8% 4 4 4 3 5% 4 37%	2930
	11th to 20th	Day	19% 15% 6% 8% 5% 4 4 3 4 6% 27%	3373
	21st to end	Day	18% 14% 5% 8% 5% 4 5% 4 5% 6% 25%	4466
January	1st to 10th	Night	15% 16% 6% 13% 5% 4 4 3 4 5% 27%	5889
	11th to 20th	Night	19% 13% 4 8% 6% 4 3 2 3 3 34%	5900
	21st to end	Night	18% 12% 3 7% 4 3 3 2 3 5% 39%	6467
February	1st to 10th	Night	21% 11% 4 9% 4 4 4 4 5% 6% 30%	2400
	11th to 20th	Night	23% 10% 4 9% 4 4 4 3 3 4 33%	2338
	21st to end	Night	22% 12% 3 8% 4 5% 3 3 5% 4 31%	1939
March	1st to 10th	Night	23% 12% 3 6% 5% 4 4 3 4 5% 32%	3711
	11th to 20th	Night	14% 6% 2 4 4 3 4 3 5% 6% 48%	3480
	21st to end	Night	14% 8% 2 7% 5% 5% 4 4 6% 6% 39%	3817
April	1st to 10th	Night	13% 7% 1 6% 4 4 4 4 6% 8% 44%	1957
	11th to 20th	Night	18% 6% 2 4 4 4 3 3 5% 6% 44%	1875
	21st to end	Night	15% 6% 2 6% 4 5% 5% 3 5% 7% 40%	1718
May	1st to 10th	Night	18% 7% 3 9% 5% 5% 5% 3 5% 7% 33%	2813
	11th to 20th	Night	19% 7% 2 7% 5% 4 4 4 5% 7% 37%	2812
	21st to end	Night	8% 5% 2 6% 5% 4 5% 4 7% 10% 44%	3079
June	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 6% 10% 43%	1710
	11th to 20th	Night	4 4 2 5% 5% 4 5% 4 6% 11% 50%	1710
	21st to end	Night	7% 4 2 5% 5% 5% 5% 6% 8% 11% 41%	1710
July	1st to 10th	Night	7% 4 2 6% 5% 5% 5% 5% 8% 11% 41%	2840
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 6% 10% 48%	2840
	21st to end	Night	13% 9% 4 9% 7% 7% 5% 5% 7% 9% 26%	3087
August	1st to 10th	Night	9% 4 2 6% 4 4 4 4 6% 9% 47%	2825
	11th to 20th	Night	8% 5% 2 7% 5% 5% 6% 4 7% 8% 44%	2931
	21st to end	Night	5% 2 1 3 3 3 4 3 5% 8% 62%	3476
September	1st to 10th	Night	12% 5% 2 6% 4 4 5% 3 5% 8% 47%	2004
	11th to 20th	Night	13% 5% 2 6% 4 4 4 3 6% 8% 46%	2090
	21st to end	Night	13% 5% 2 5% 3 3 4 4 4 6% 52%	2090
October	1st to 10th	Night	11% 4 1 4 3 2 3 2 4 6% 58%	2090
	11th to 20th	Night	16% 5% 2 5% 4 3 3 2 4 6% 51%	2204
	21st to end	Night	16% 7% 2 5% 3 3 4 3 4 7% 46%	2613
November	1st to 10th	Night	12% 7% 3 6% 3 3 3 3 4 5% 51%	2536
	11th to 20th	Night	15% 8% 2 4 4 3 4 2 4 7% 47%	2600
	21st to end	Night	17% 9% 3 6% 4 3 3 3 3 5% 43%	2600
December	1st to 10th	Night	18% 13% 4 10% 4 3 3 2 3 4 36%	4250
	11th to 20th	Night	22% 11% 5% 8% 3 3 3 3 3 5% 34%	4822
	21st to end	Night	16% 13% 5% 9% 6% 6% 6% 5% 5% 6% 24%	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	62% 3 7% 19% 9% 1	4057
	11th to 20th	Day	57% 2 5% 18% 17% 1	4060
	21st to end	Day	52% 2 7% 25% 13% 2	4485
February	1st to 10th	Day	54% 3 7% 19% 14% 2	2000
	11th to 20th	Day	57% 3 7% 20% 10% 2	1958
	21st to end	Day	54% 3 8% 18% 13% 5%	1610
March	1st to 10th	Day	56% 2 6% 18% 13% 4	3141
	11th to 20th	Day	40% 3 9% 27% 18% 4	3480
	21st to end	Day	45% 3 9% 30% 12% 1	3815
April	1st to 10th	Day	41% 4 10% 25% 16% 4	2238
	11th to 20th	Day	43% 3 8% 22% 20% 4	2254
	21st to end	Day	44% 4 10% 27% 13% 2	2460
May	1st to 10th	Day	52% 4 11% 23% 9% 1	4120
	11th to 20th	Day	50% 4 10% 23% 12% 1	4085
	21st to end	Day	42% 6% 12% 20% 17% 2	4489
June	1st to 10th	Day	40% 5% 13% 24% 15% 2	2470
	11th to 20th	Day	32% 7% 18% 24% 18% 2	2470
	21st to end	Day	36% 7% 16% 20% 17% 3	2470
July	1st to 10th	Day	38% 7% 20% 22% 11% 1	4055
	11th to 20th	Day	37% 6% 16% 31% 8% 2	4051
	21st to end	Day	59% 6% 12% 16% 7% 1	4324
August	1st to 10th	Day	34% 6% 17% 30% 13%	4091
	11th to 20th	Day	37% 7% 14% 26% 15% 1	3933
	21st to end	Day	27% 4 13% 40% 15% 2	4179
September	1st to 10th	Day	43% 5% 11% 19% 17% 4	2157
	11th to 20th	Day	38% 4 11% 25% 20% 2	2090
	21st to end	Day	37% 4 9% 26% 21% 3	2090
October	1st to 10th	Day	24% 3 6% 22% 41% 3	3480
	11th to 20th	Day	25% 2 9% 25% 31% 7%	3268
	21st to end	Day	30% 2 7% 29% 21% 10%	3244
November	1st to 10th	Day	34% 2 9% 24% 25% 4	1762
	11th to 20th	Day	41% 3 6% 26% 20% 5%	1800
	21st to end	Day	46% 3 8% 22% 18% 4	1800
December	1st to 10th	Day	50% 3 5% 20% 21% 1	2930
	11th to 20th	Day	60% 2 7% 19% 9% 2	3370
	21st to end	Day	59% 4 10% 20% 6% 1	4466
January	1st to 10th	Night	61% 3 7% 19% 9% 1	5889
	11th to 20th	Night	56% 3 4 17% 16% 4	5900
	21st to end	Night	51% 2 7% 19% 19% 3	6467
February	1st to 10th	Night	55% 3 10% 18% 13% 1	2400
	11th to 20th	Night	57% 2 6% 18% 13% 3	2339
	21st to end	Night	57% 3 7% 16% 14% 3	1939
March	1st to 10th	Night	57% 2 7% 18% 14% 2	3711
	11th to 20th	Night	37% 3 9% 31% 14% 8%	3480
	21st to end	Night	46% 3 10% 25% 15% 1	3817
April	1st to 10th	Night	39% 3 10% 25% 19% 4	1957
	11th to 20th	Night	42% 2 9% 19% 23% 5%	1875
	21st to end	Night	43% 4 10% 26% 14% 2	1718
May	1st to 10th	Night	51% 4 11% 24% 8% 2	2840
	11th to 20th	Night	47% 4 12% 24% 11%	2813
	21st to end	Night	33% 6% 13% 27% 18% 2	3087
June	1st to 10th	Night	35% 5% 14% 28% 15% 3	1710
	11th to 20th	Night	28% 6% 18% 26% 20% 2	1710
	21st to end	Night	33% 8% 17% 22% 15% 5%	1710
July	1st to 10th	Night	34% 8% 19% 27% 11% 1	2795
	11th to 20th	Night	31% 5% 17% 33% 12% 3	2786
	21st to end	Night	53% 7% 14% 17% 8% 1	2988
August	1st to 10th	Night	33% 6% 13% 30% 17% 1	2814
	11th to 20th	Night	35% 6% 16% 29% 13% 1	2958
	21st to end	Night	20% 5% 12% 41% 20% 2	3476
September	1st to 10th	Night	35% 6% 14% 20% 20% 6%	2004
	11th to 20th	Night	37% 4 9% 26% 21% 3	2090
	21st to end	Night	34% 4 7% 24% 25% 5%	2090
October	1st to 10th	Night	25% 3 7% 22% 36% 6%	3480
	11th to 20th	Night	24% 3 6% 26% 31% 11%	3651
	21st to end	Night	27% 2 8% 25% 28% 10%	4300
November	1st to 10th	Night	36% 3 6% 24% 24% 6%	2536
	11th to 20th	Night	39% 3 7% 21% 24% 6%	2600
	21st to end	Night	44% 3 6% 25% 18% 3	2600
December	1st to 10th	Night	55% 2 6% 19% 17% 1	4250
	11th to 20th	Night	54% 3 7% 21% 13% 1	4824
	21st to end	Night	60% 4 9% 19% 8%	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	28% 17% 33% 17% 3 1	300
	11th to 20th	Day	34% 23% 30% 10% 4	300
	21st to end	Day	25% 23% 34% 14% 3	330
February	1st to 10th	Day	26% 21% 34% 15% 4	300
	11th to 20th	Day	39% 19% 31% 8% 3	300
	21st to end	Day	33% 15% 39% 11% 2	237
March	1st to 10th	Day	32% 17% 33% 13% 5%	278
	11th to 20th	Day	25% 17% 32% 20% 6%	460
	21st to end	Day	28% 13% 32% 19% 7% 1	506
April	1st to 10th	Day	24% 15% 25% 25% 9% 2	460
	11th to 20th	Day	22% 13% 28% 21% 14% 2	452
	21st to end	Day	21% 13% 29% 23% 10% 4	460
May	1st to 10th	Day	20% 12% 30% 23% 12% 4	463
	11th to 20th	Day	18% 8% 24% 26% 16% 8%	487
	21st to end	Day	15% 4 19% 25% 22% 15%	529
June	1st to 10th	Day	15% 2 18% 30% 21% 13%	490
	11th to 20th	Day	8% 3 17% 30% 28% 14%	490
	21st to end	Day	11% 2 21% 28% 21% 16%	490
July	1st to 10th	Day	14% 3 11% 27% 20% 26%	485
	11th to 20th	Day	10% 1 12% 29% 29% 20%	484
	21st to end	Day	16% 3 9% 28% 28% 17%	532
August	1st to 10th	Day	13% 2 12% 28% 28% 17%	486
	11th to 20th	Day	13% 2 11% 32% 29% 12%	479
	21st to end	Day	12% 1 7% 24% 34% 22%	539
September	1st to 10th	Day	16% 2 10% 22% 32% 17%	490
	11th to 20th	Day	16% 3 11% 22% 32% 16%	490
	21st to end	Day	19% 5% 16% 24% 27% 10%	490
October	1st to 10th	Day	14% 4 16% 31% 26% 10%	490
	11th to 20th	Day	16% 10% 25% 28% 16% 6%	490
	21st to end	Day	22% 9% 26% 29% 11% 3	430
November	1st to 10th	Day	21% 6% 29% 27% 13% 4	300
	11th to 20th	Day	20% 15% 34% 25% 6%	300
	21st to end	Day	24% 11% 35% 17% 12% 1	300
December	1st to 10th	Day	30% 16% 29% 17% 8% 1	300
	11th to 20th	Day	27% 14% 31% 20% 8% 1	300
	21st to end	Day	28% 16% 30% 20% 6%	330
January	1st to 10th	Night	25% 17% 28% 26% 4	800
	11th to 20th	Night	31% 14% 29% 23% 4	800
	21st to end	Night	23% 15% 37% 23% 2	880
February	1st to 10th	Night	28% 11% 33% 25% 3	800
	11th to 20th	Night	29% 14% 34% 20% 2	783
	21st to end	Night	30% 13% 34% 21% 2	647
March	1st to 10th	Night	25% 12% 29% 29% 5%	760
	11th to 20th	Night	24% 10% 32% 26% 7% 1	760
	21st to end	Night	21% 9% 30% 32% 7%	836
April	1st to 10th	Night	17% 10% 30% 32% 11%	627
	11th to 20th	Night	22% 8% 28% 30% 13% 1	563
	21st to end	Night	19% 4 31% 34% 11% 1	570
May	1st to 10th	Night	18% 5% 24% 33% 18% 2	570
	11th to 20th	Night	15% 4 19% 35% 24% 3	561
	21st to end	Night	8% 2 15% 37% 30% 7%	617
June	1st to 10th	Night	10% 2 12% 41% 31% 4	570
	11th to 20th	Night	6% 2 12% 39% 34% 8%	570
	21st to end	Night	8% 2 11% 40% 33% 6%	570
July	1st to 10th	Night	11% 2 7% 31% 40% 9%	555
	11th to 20th	Night	9% 1 7% 28% 47% 8%	552
	21st to end	Night	10% 3 7% 33% 40% 8%	624
August	1st to 10th	Night	11% 2 5% 29% 44% 10%	567
	11th to 20th	Night	10% 1 6% 39% 36% 7%	564
	21st to end	Night	9% 2 4 30% 44% 12%	627
September	1st to 10th	Night	13% 3 8% 28% 43% 5%	674
	11th to 20th	Night	14% 3 10% 29% 39% 6%	760
	21st to end	Night	16% 3 14% 30% 31% 5%	760
October	1st to 10th	Night	13% 4 15% 31% 30% 7%	760
	11th to 20th	Night	18% 5% 20% 34% 20% 2	760
	21st to end	Night	19% 7% 26% 30% 17% 1	836
November	1st to 10th	Night	16% 7% 22% 34% 19% 2	780
	11th to 20th	Night	18% 12% 26% 33% 10% 1	800
	21st to end	Night	23% 12% 23% 30% 12% 1	800
December	1st to 10th	Night	31% 13% 24% 26% 7%	800
	11th to 20th	Night	25% 11% 31% 27% 6% 1	800
	21st to end	Night	28% 13% 24% 30% 4	880

Page generated at 2025-02-22 06:51:37. Version ac07

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