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 2026-07-01.

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	14% 8% 3 7% 5% 4 5% 4 6% 8% 37%	137535
	Night	14% 9% 3 7% 4 4 4 3 5% 7% 39%	134847
Transparency	Day	45% 5% 11% 23% 15% 2	141248
	Night	44% 4 10% 23% 16% 3	139205
Seeing	Day	20% 10% 23% 23% 16% 8%	16862
	Night	19% 8% 22% 30% 18% 3	26902

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	17% 15% 7% 11% 4 4 4 4 4 5% 26%	5258
	11th to 20th	Day	15% 11% 6% 12% 4 4 3 2 3 4 38%	5280
	21st to end	Day	21% 11% 3 7% 6% 3 4 4 5% 6% 31%	5813
February	1st to 10th	Day	18% 12% 4 8% 4 4 4 3 4 6% 32%	2100
	11th to 20th	Day	23% 10% 4 9% 5% 3 3 3 3 6% 31%	2048
	21st to end	Day	18% 12% 4 9% 4 3 3 3 4 5% 34%	1730
March	1st to 10th	Day	19% 11% 4 6% 4 4 4 3 4 6% 34%	4615
	11th to 20th	Day	13% 8% 3 6% 4 4 4 3 4 6% 45%	5090
	21st to end	Day	14% 8% 3 6% 5% 4 4 3 6% 7% 40%	5586
April	1st to 10th	Day	13% 7% 2 7% 5% 4 5% 3 6% 7% 41%	2474
	11th to 20th	Day	14% 8% 2 7% 4 4 4 4 5% 6% 42%	2494
	21st to end	Day	15% 7% 2 7% 5% 4 5% 4 6% 8% 38%	2720
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	7616
	11th to 20th	Day	13% 7% 3 8% 5% 5% 6% 4 6% 7% 36%	7626
	21st to end	Day	18% 8% 3 8% 6% 5% 5% 4 7% 8% 27%	8391
June	1st to 10th	Day	10% 6% 3 7% 4 5% 5% 5% 7% 10% 38%	2730
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 10% 43%	2730
	21st to end	Day	8% 5% 1 5% 5% 6% 6% 5% 7% 11% 40%	2730
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 7% 5% 7% 10% 40%	5900
	11th to 20th	Day	8% 6% 3 7% 5% 6% 6% 5% 8% 11% 34%	5900
	21st to end	Day	15% 8% 3 8% 6% 5% 6% 5% 8% 10% 26%	6424
August	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 10% 42%	4234
	11th to 20th	Day	9% 5% 2 6% 5% 5% 7% 5% 8% 11% 36%	4019
	21st to end	Day	6% 4 2 4 4 4 4 4 6% 9% 54%	4312
September	1st to 10th	Day	15% 6% 2 7% 5% 5% 5% 4 5% 7% 40%	2270
	11th to 20th	Day	14% 5% 2 5% 4 4 4 3 6% 7% 46%	2200
	21st to end	Day	15% 5% 2 5% 4 3 4 3 5% 7% 46%	2200
October	1st to 10th	Day	12% 4 1 4 4 3 3 3 5% 7% 54%	2200
	11th to 20th	Day	13% 6% 2 5% 4 3 2 3 4 6% 53%	2080
	21st to end	Day	18% 7% 2 5% 3 3 3 3 5% 7% 44%	2085
November	1st to 10th	Day	13% 6% 2 4 3 4 3 3 5% 6% 51%	1852
	11th to 20th	Day	15% 9% 2 5% 3 3 4 4 4 7% 44%	1890
	21st to end	Day	16% 10% 4 6% 4 4 3 3 5% 5% 40%	1890
December	1st to 10th	Day	17% 11% 3 8% 4 4 3 3 5% 4 37%	3020
	11th to 20th	Day	19% 15% 6% 8% 5% 4 4 3 4 6% 27%	3463
	21st to end	Day	18% 13% 5% 9% 6% 4 5% 4 5% 6% 24%	4565
January	1st to 10th	Night	15% 14% 5% 11% 4 4 3 3 4 5% 32%	7635
	11th to 20th	Night	16% 12% 4 8% 5% 4 3 2 3 4 38%	7680
	21st to end	Night	18% 13% 4 8% 4 3 3 2 3 4 36%	8364
February	1st to 10th	Night	20% 10% 4 9% 4 4 4 4 5% 6% 30%	2520
	11th to 20th	Night	22% 10% 4 9% 4 4 4 3 3 4 33%	2458
	21st to end	Night	21% 12% 3 8% 4 5% 3 3 5% 4 31%	2076
March	1st to 10th	Night	19% 13% 3 7% 5% 4 4 3 4 5% 35%	5457
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 5% 7% 48%	5090
	21st to end	Night	13% 8% 3 8% 5% 5% 5% 4 6% 7% 36%	5588
April	1st to 10th	Night	13% 7% 1 6% 4 4 4 3 6% 7% 43%	2163
	11th to 20th	Night	16% 6% 2 4 4 4 3 3 5% 7% 44%	2075
	21st to end	Night	14% 6% 2 6% 4 5% 5% 3 5% 8% 40%	1898
May	1st to 10th	Night	17% 8% 3 8% 5% 5% 4 4 7% 8% 31%	5237
	11th to 20th	Night	14% 7% 3 8% 5% 5% 5% 4 6% 7% 36%	5234
	21st to end	Night	17% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	5761
June	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 7% 10% 43%	1890
	11th to 20th	Night	5% 4 2 6% 5% 4 5% 4 6% 10% 49%	1890
	21st to end	Night	7% 4 2 5% 5% 5% 5% 6% 8% 12% 41%	1890
July	1st to 10th	Night	7% 5% 2 6% 5% 5% 5% 5% 8% 10% 43%	4058
	11th to 20th	Night	8% 6% 2 6% 5% 5% 5% 5% 8% 12% 39%	4057
	21st to end	Night	10% 7% 3 8% 7% 6% 6% 5% 8% 11% 28%	4427
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 9% 47%	2915
	11th to 20th	Night	8% 5% 2 7% 4 5% 6% 4 7% 8% 43%	3026
	21st to end	Night	5% 2 1 3 3 3 4 4 5% 8% 62%	3586
September	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 3 6% 8% 47%	2110
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 6% 8% 47%	2200
	21st to end	Night	13% 5% 2 5% 3 3 4 3 4 6% 51%	2200
October	1st to 10th	Night	11% 4 1 4 3 2 3 2 4 6% 59%	2200
	11th to 20th	Night	15% 5% 2 4 4 3 3 3 4 6% 51%	2320
	21st to end	Night	17% 7% 2 5% 3 3 4 3 4 7% 46%	2751
November	1st to 10th	Night	12% 7% 3 6% 3 3 3 3 4 5% 51%	2666
	11th to 20th	Night	15% 8% 2 4 4 3 4 2 4 6% 47%	2730
	21st to end	Night	17% 10% 3 6% 4 3 3 3 3 5% 43%	2730
December	1st to 10th	Night	18% 13% 4 10% 4 3 3 2 3 4 36%	4380
	11th to 20th	Night	22% 11% 5% 8% 3 3 3 3 3 5% 34%	4952
	21st to end	Night	16% 13% 5% 9% 6% 6% 6% 5% 5% 6% 24%	6633

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	61% 3 7% 19% 8% 1	5259
	11th to 20th	Day	53% 2 5% 21% 18% 2	5280
	21st to end	Day	54% 3 7% 24% 11% 2	5813
February	1st to 10th	Day	54% 3 7% 20% 14% 1	2100
	11th to 20th	Day	56% 3 7% 21% 10% 2	2058
	21st to end	Day	54% 3 8% 18% 14% 4	1730
March	1st to 10th	Day	52% 3 6% 15% 19% 6%	4615
	11th to 20th	Day	41% 3 7% 23% 21% 5%	5090
	21st to end	Day	44% 3 9% 30% 13% 1	5586
April	1st to 10th	Day	41% 5% 11% 26% 15% 3	2474
	11th to 20th	Day	43% 3 9% 23% 20% 4	2494
	21st to end	Day	44% 4 10% 27% 13% 2	2720
May	1st to 10th	Day	50% 5% 12% 23% 10% 1	7651
	11th to 20th	Day	47% 6% 13% 21% 13% 1	7630
	21st to end	Day	53% 6% 11% 16% 11% 2	8405
June	1st to 10th	Day	40% 5% 13% 23% 16% 2	2730
	11th to 20th	Day	34% 7% 17% 24% 17% 1	2730
	21st to end	Day	36% 7% 17% 21% 17% 3	2730
July	1st to 10th	Day	37% 7% 17% 24% 14% 1	5835
	11th to 20th	Day	40% 9% 19% 25% 6% 1	5831
	21st to end	Day	50% 9% 15% 21% 5% 1	6240
August	1st to 10th	Day	34% 6% 17% 29% 13%	4221
	11th to 20th	Day	37% 8% 14% 26% 14% 1	4058
	21st to end	Day	26% 5% 12% 39% 16% 2	4311
September	1st to 10th	Day	43% 5% 11% 20% 17% 4	2270
	11th to 20th	Day	37% 4 10% 26% 21% 2	2200
	21st to end	Day	37% 4 9% 25% 21% 3	2200
October	1st to 10th	Day	24% 3 6% 23% 41% 3	3590
	11th to 20th	Day	25% 2 9% 26% 31% 8%	3372
	21st to end	Day	31% 3 7% 29% 21% 10%	3348
November	1st to 10th	Day	35% 3 9% 24% 25% 4	1852
	11th to 20th	Day	40% 3 6% 26% 20% 5%	1890
	21st to end	Day	47% 2 8% 22% 18% 3	1890
December	1st to 10th	Day	50% 3 5% 20% 20% 1	3020
	11th to 20th	Day	60% 3 7% 19% 10% 2	3460
	21st to end	Day	59% 4 10% 20% 6% 1	4565
January	1st to 10th	Night	56% 4 11% 22% 7% 1	7636
	11th to 20th	Night	51% 3 4 20% 19% 3	7680
	21st to end	Night	54% 2 7% 18% 17% 3	8364
February	1st to 10th	Night	55% 3 10% 18% 13% 1	2520
	11th to 20th	Night	57% 2 6% 19% 13% 3	2459
	21st to end	Night	56% 2 7% 16% 15% 3	2076
March	1st to 10th	Night	53% 2 7% 20% 14% 5%	5457
	11th to 20th	Night	36% 3 8% 27% 20% 7%	5090
	21st to end	Night	48% 4 10% 25% 13% 1	5588
April	1st to 10th	Night	40% 3 11% 24% 18% 4	2163
	11th to 20th	Night	40% 3 10% 21% 21% 4	2075
	21st to end	Night	43% 4 10% 27% 14% 1	1898
May	1st to 10th	Night	51% 4 11% 22% 10% 1	5264
	11th to 20th	Night	47% 5% 14% 20% 13%	5235
	21st to end	Night	49% 7% 12% 20% 11% 1	5771
June	1st to 10th	Night	35% 5% 14% 27% 15% 3	1890
	11th to 20th	Night	30% 6% 17% 26% 19% 2	1890
	21st to end	Night	33% 8% 17% 23% 15% 4	1890
July	1st to 10th	Night	35% 7% 16% 25% 15% 1	4015
	11th to 20th	Night	35% 8% 21% 25% 8% 2	4006
	21st to end	Night	47% 8% 17% 20% 7%	4297
August	1st to 10th	Night	33% 6% 13% 30% 17% 1	2904
	11th to 20th	Night	35% 6% 17% 29% 13% 1	3053
	21st to end	Night	20% 5% 12% 40% 21% 2	3586
September	1st to 10th	Night	35% 6% 14% 20% 20% 5%	2110
	11th to 20th	Night	36% 4 9% 26% 22% 2	2200
	21st to end	Night	35% 4 8% 23% 25% 4	2200
October	1st to 10th	Night	25% 3 7% 23% 36% 6%	3590
	11th to 20th	Night	24% 2 6% 26% 31% 11%	3767
	21st to end	Night	28% 2 7% 24% 28% 10%	4438
November	1st to 10th	Night	36% 3 6% 25% 23% 6%	2666
	11th to 20th	Night	39% 3 7% 22% 23% 6%	2730
	21st to end	Night	45% 3 6% 25% 18% 3	2730
December	1st to 10th	Night	55% 2 6% 19% 17% 1	4380
	11th to 20th	Night	54% 3 7% 21% 14% 1	4954
	21st to end	Night	60% 4 9% 18% 8%	6633

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% 34% 16% 4 1	330
	11th to 20th	Day	34% 23% 30% 9% 3	330
	21st to end	Day	27% 23% 33% 13% 3	363
February	1st to 10th	Day	27% 21% 34% 15% 3	330
	11th to 20th	Day	39% 19% 31% 8% 2	330
	21st to end	Day	32% 16% 38% 12% 1	273
March	1st to 10th	Day	32% 18% 31% 13% 5%	339
	11th to 20th	Day	27% 18% 32% 18% 6%	540
	21st to end	Day	27% 14% 34% 18% 6% 1	594
April	1st to 10th	Day	24% 15% 28% 24% 8% 2	540
	11th to 20th	Day	23% 15% 28% 20% 12% 2	532
	21st to end	Day	21% 13% 30% 22% 10% 4	540
May	1st to 10th	Day	21% 15% 30% 21% 10% 3	543
	11th to 20th	Day	17% 11% 25% 25% 15% 7%	567
	21st to end	Day	18% 6% 21% 23% 19% 13%	617
June	1st to 10th	Day	14% 3 20% 30% 20% 13%	570
	11th to 20th	Day	8% 5% 18% 30% 26% 12%	570
	21st to end	Day	10% 3 20% 28% 22% 17%	570
July	1st to 10th	Day	13% 2 11% 28% 20% 25%	525
	11th to 20th	Day	10% 1 12% 30% 28% 19%	524
	21st to end	Day	15% 3 9% 27% 28% 17%	576
August	1st to 10th	Day	14% 3 12% 27% 28% 16%	526
	11th to 20th	Day	13% 2 11% 31% 29% 13%	519
	21st to end	Day	12% 2 9% 24% 33% 21%	583
September	1st to 10th	Day	16% 3 12% 22% 31% 17%	530
	11th to 20th	Day	14% 2 11% 22% 34% 16%	530
	21st to end	Day	18% 5% 17% 25% 25% 10%	530
October	1st to 10th	Day	14% 4 16% 30% 26% 10%	530
	11th to 20th	Day	15% 9% 25% 28% 16% 6%	530
	21st to end	Day	25% 9% 25% 28% 10% 3	468
November	1st to 10th	Day	22% 7% 30% 26% 12% 4	330
	11th to 20th	Day	20% 17% 33% 24% 5%	330
	21st to end	Day	25% 12% 35% 15% 11% 1	330
December	1st to 10th	Day	30% 16% 31% 16% 7% 1	330
	11th to 20th	Day	27% 15% 31% 20% 7% 1	330
	21st to end	Day	28% 18% 30% 19% 6%	363
January	1st to 10th	Night	25% 17% 28% 26% 4	840
	11th to 20th	Night	30% 15% 29% 22% 4	840
	21st to end	Night	24% 15% 36% 23% 2	924
February	1st to 10th	Night	27% 11% 33% 26% 3	840
	11th to 20th	Night	30% 15% 33% 21% 2	823
	21st to end	Night	30% 13% 34% 21% 2	692
March	1st to 10th	Night	25% 12% 30% 28% 5%	840
	11th to 20th	Night	24% 11% 33% 26% 6% 1	840
	21st to end	Night	21% 11% 32% 30% 6%	924
April	1st to 10th	Night	18% 10% 30% 32% 10%	693
	11th to 20th	Night	20% 8% 30% 30% 12%	623
	21st to end	Night	19% 6% 30% 34% 11% 1	630
May	1st to 10th	Night	18% 6% 26% 33% 16% 2	630
	11th to 20th	Night	15% 5% 19% 36% 22% 3	621
	21st to end	Night	10% 3 16% 36% 28% 7%	683
June	1st to 10th	Night	9% 2 13% 41% 30% 4	630
	11th to 20th	Night	7% 2 13% 39% 32% 7%	630
	21st to end	Night	8% 2 10% 39% 33% 7%	630
July	1st to 10th	Night	11% 2 7% 31% 40% 9%	585
	11th to 20th	Night	9% 1 7% 29% 47% 8%	582
	21st to end	Night	9% 3 7% 32% 42% 8%	657
August	1st to 10th	Night	11% 2 5% 29% 44% 9%	597
	11th to 20th	Night	10% 1 6% 39% 36% 8%	594
	21st to end	Night	9% 2 5% 31% 42% 11%	660
September	1st to 10th	Night	13% 3 9% 29% 42% 5%	710
	11th to 20th	Night	14% 3 10% 29% 39% 6%	800
	21st to end	Night	16% 4 14% 31% 30% 5%	800
October	1st to 10th	Night	13% 4 15% 31% 31% 7%	800
	11th to 20th	Night	17% 6% 20% 35% 20% 2	800
	21st to end	Night	20% 8% 26% 29% 16% 1	880
November	1st to 10th	Night	16% 8% 23% 34% 18% 2	820
	11th to 20th	Night	19% 12% 26% 33% 10% 1	840
	21st to end	Night	24% 12% 23% 29% 11%	840
December	1st to 10th	Night	30% 13% 25% 26% 6%	840
	11th to 20th	Night	26% 10% 31% 27% 6% 1	840
	21st to end	Night	28% 14% 25% 29% 4	924

Page generated at 2026-06-28 02:10:47. Version ac07

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