Mammoth Cave National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mammoth Cave National Park clear sky chart from 2005-11-06 to 2026-09-14.

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% 4 4 5% 4 6% 8% 39%	148724
	Night	14% 8% 3 7% 4 4 4 3 5% 7% 40%	142463
Transparency	Day	42% 6% 11% 23% 15% 2	152390
	Night	42% 5% 10% 23% 17% 3	146871
Seeing	Day	17% 10% 24% 23% 17% 8%	17758
	Night	18% 8% 24% 30% 17% 2	27362

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% 11% 8% 10% 4 4 4 3 5% 5% 30%	4691
	11th to 20th	Day	13% 9% 4 11% 4 3 4 2 3 4 44%	4954
	21st to end	Day	21% 10% 5% 6% 4 4 4 3 4 5% 35%	6061
February	1st to 10th	Day	17% 12% 4 8% 4 3 3 3 4 5% 35%	2100
	11th to 20th	Day	21% 8% 3 9% 5% 3 4 2 4 7% 33%	2048
	21st to end	Day	19% 10% 4 8% 4 3 4 4 5% 5% 35%	1730
March	1st to 10th	Day	19% 12% 4 7% 4 4 3 3 4 5% 35%	4580
	11th to 20th	Day	14% 9% 3 6% 4 3 3 3 4 7% 45%	4944
	21st to end	Day	12% 7% 3 9% 5% 4 5% 3 5% 7% 41%	5770
April	1st to 10th	Day	13% 7% 2 7% 5% 4 4 4 5% 7% 43%	2520
	11th to 20th	Day	15% 8% 2 7% 4 4 4 3 4 7% 42%	2494
	21st to end	Day	15% 7% 3 6% 5% 4 5% 4 6% 7% 38%	2639
May	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 8% 31%	7616
	11th to 20th	Day	15% 8% 3 7% 4 5% 5% 4 6% 8% 37%	7626
	21st to end	Day	19% 9% 3 8% 5% 5% 5% 4 6% 7% 29%	8391
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 6% 7% 41%	2748
	11th to 20th	Day	7% 5% 2 5% 4 5% 6% 5% 7% 11% 43%	2940
	21st to end	Day	8% 4 2 6% 5% 4 6% 5% 8% 11% 41%	2940
July	1st to 10th	Day	9% 7% 3 7% 5% 5% 5% 4 7% 10% 37%	8280
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 5% 9% 12% 32%	8103
	21st to end	Day	11% 7% 2 8% 5% 6% 6% 5% 8% 12% 30%	8340
August	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 5% 7% 11% 44%	5993
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 41%	5486
	21st to end	Day	4 3 1 4 3 4 4 4 6% 8% 59%	6080
September	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 4 6% 8% 42%	2461
	11th to 20th	Day	12% 6% 2 5% 4 5% 3 3 6% 7% 46%	2233
	21st to end	Day	13% 5% 3 5% 4 4 3 3 4 7% 48%	2200
October	1st to 10th	Day	10% 5% 2 5% 3 4 3 2 5% 7% 56%	2200
	11th to 20th	Day	12% 6% 2 5% 4 3 3 3 4 6% 52%	2144
	21st to end	Day	20% 6% 3 5% 4 3 4 3 4 5% 44%	1980
November	1st to 10th	Day	11% 7% 3 4 4 3 4 3 4 7% 51%	1852
	11th to 20th	Day	16% 6% 3 5% 3 4 3 2 4 5% 47%	1890
	21st to end	Day	17% 10% 3 7% 3 4 3 3 4 5% 43%	1890
December	1st to 10th	Day	17% 9% 3 7% 4 3 4 3 4 5% 41%	3020
	11th to 20th	Day	20% 10% 5% 8% 5% 4 4 3 4 5% 32%	3463
	21st to end	Day	21% 15% 5% 8% 5% 5% 5% 3 4 5% 26%	4317
January	1st to 10th	Night	16% 13% 4 9% 4 3 3 3 5% 6% 33%	8232
	11th to 20th	Night	16% 11% 4 9% 5% 4 4 2 3 4 38%	8002
	21st to end	Night	19% 11% 4 8% 4 3 3 2 3 5% 38%	8105
February	1st to 10th	Night	21% 10% 4 10% 4 3 4 3 5% 5% 30%	2520
	11th to 20th	Night	23% 10% 3 7% 4 4 3 3 4 4 34%	2458
	21st to end	Night	22% 9% 3 8% 4 4 4 3 3 5% 34%	2076
March	1st to 10th	Night	19% 14% 3 7% 3 3 3 3 4 5% 34%	5493
	11th to 20th	Night	12% 6% 2 5% 4 3 4 4 5% 6% 48%	5236
	21st to end	Night	14% 8% 3 7% 5% 4 5% 4 6% 7% 37%	5431
April	1st to 10th	Night	13% 7% 2 6% 5% 3 4 4 6% 7% 44%	2100
	11th to 20th	Night	15% 7% 2 6% 4 4 3 3 5% 6% 44%	2075
	21st to end	Night	14% 7% 3 7% 4 4 4 4 6% 6% 39%	1979
May	1st to 10th	Night	17% 10% 3 8% 5% 4 5% 4 7% 7% 31%	5237
	11th to 20th	Night	13% 7% 3 8% 5% 5% 5% 4 6% 8% 35%	5234
	21st to end	Night	17% 9% 3 7% 5% 4 5% 4 6% 9% 31%	5761
June	1st to 10th	Night	10% 4 2 6% 4 4 5% 4 6% 9% 45%	1865
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 7% 10% 50%	1680
	21st to end	Night	5% 3 2 5% 4 5% 5% 5% 7% 11% 47%	1680
July	1st to 10th	Night	7% 5% 2 6% 5% 4 4 4 6% 9% 45%	4708
	11th to 20th	Night	9% 6% 2 6% 5% 5% 5% 5% 8% 11% 37%	4870
	21st to end	Night	8% 8% 3 8% 6% 5% 6% 5% 7% 11% 32%	5736
August	1st to 10th	Night	6% 6% 2 6% 4 4 4 4 6% 8% 49%	4152
	11th to 20th	Night	4 3 2 4 3 4 5% 4 7% 10% 53%	4560
	21st to end	Night	3 2 1 3 3 3 3 3 5% 9% 63%	5046
September	1st to 10th	Night	10% 5% 2 4 4 4 4 3 5% 7% 50%	2137
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 5% 8% 48%	2234
	21st to end	Night	12% 6% 2 5% 3 3 3 3 4 6% 52%	2200
October	1st to 10th	Night	9% 5% 2 4 3 2 3 2 4 5% 61%	2200
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 6% 53%	2252
	21st to end	Night	17% 8% 2 5% 3 3 3 3 4 5% 47%	2860
November	1st to 10th	Night	11% 7% 2 5% 4 4 3 3 3 5% 51%	2666
	11th to 20th	Night	14% 7% 2 5% 4 4 3 3 5% 5% 48%	2730
	21st to end	Night	17% 10% 3 5% 4 3 3 2 4 6% 42%	2730
December	1st to 10th	Night	19% 11% 3 8% 4 3 3 2 4 4 39%	4380
	11th to 20th	Night	23% 9% 3 7% 3 3 3 3 4 6% 36%	4952
	21st to end	Night	20% 14% 6% 10% 6% 5% 4 3 4 5% 23%	6886

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	57% 3 10% 20% 9% 1	4692
	11th to 20th	Day	46% 3 6% 25% 19% 2	4954
	21st to end	Day	52% 3 8% 21% 12% 4	6061
February	1st to 10th	Day	52% 3 10% 20% 14% 2	2100
	11th to 20th	Day	53% 4 8% 21% 11% 3	2058
	21st to end	Day	50% 5% 10% 17% 15% 5%	1730
March	1st to 10th	Day	52% 4 5% 17% 18% 5%	4580
	11th to 20th	Day	40% 4 9% 24% 20% 3	4944
	21st to end	Day	42% 5% 10% 28% 13% 1	5772
April	1st to 10th	Day	40% 5% 12% 24% 17% 2	2520
	11th to 20th	Day	43% 5% 8% 23% 18% 3	2494
	21st to end	Day	43% 7% 10% 24% 14% 2	2639
May	1st to 10th	Day	49% 6% 13% 21% 10% 1	7651
	11th to 20th	Day	45% 6% 12% 22% 14% 1	7630
	21st to end	Day	52% 7% 10% 17% 13% 2	8405
June	1st to 10th	Day	39% 8% 11% 22% 18% 2	2748
	11th to 20th	Day	32% 8% 16% 25% 17% 2	2940
	21st to end	Day	33% 9% 15% 22% 17% 3	2940
July	1st to 10th	Day	40% 8% 15% 24% 13% 1	8211
	11th to 20th	Day	40% 11% 18% 24% 6% 1	8028
	21st to end	Day	43% 8% 19% 21% 7% 1	8156
August	1st to 10th	Day	31% 9% 16% 28% 15% 1	5980
	11th to 20th	Day	34% 7% 18% 26% 14% 1	5522
	21st to end	Day	21% 6% 13% 39% 19% 2	6079
September	1st to 10th	Day	39% 7% 13% 19% 19% 4	2461
	11th to 20th	Day	37% 5% 9% 24% 22% 3	2233
	21st to end	Day	35% 6% 9% 23% 22% 4	2200
October	1st to 10th	Day	20% 3 6% 20% 47% 4	3590
	11th to 20th	Day	23% 3 8% 27% 32% 6%	3463
	21st to end	Day	30% 3 7% 28% 23% 8%	3180
November	1st to 10th	Day	35% 4 8% 26% 23% 5%	1852
	11th to 20th	Day	39% 3 8% 24% 21% 5%	1890
	21st to end	Day	45% 4 7% 23% 19% 2	1890
December	1st to 10th	Day	46% 3 7% 23% 20% 1	3020
	11th to 20th	Day	55% 3 9% 18% 13% 2	3460
	21st to end	Day	60% 5% 10% 18% 7%	4317
January	1st to 10th	Night	51% 4 12% 23% 9% 1	8233
	11th to 20th	Night	50% 4 5% 21% 17% 4	8002
	21st to end	Night	51% 3 7% 19% 17% 3	8105
February	1st to 10th	Night	55% 4 10% 18% 12% 1	2520
	11th to 20th	Night	54% 4 6% 20% 14% 3	2459
	21st to end	Night	54% 4 7% 17% 14% 3	2076
March	1st to 10th	Night	53% 3 6% 18% 16% 4	5493
	11th to 20th	Night	35% 5% 8% 25% 20% 7%	5236
	21st to end	Night	45% 5% 10% 25% 13% 1	5431
April	1st to 10th	Night	37% 6% 11% 23% 19% 3	2100
	11th to 20th	Night	41% 4 10% 19% 21% 5%	2075
	21st to end	Night	43% 6% 8% 24% 17% 2	1979
May	1st to 10th	Night	49% 6% 12% 22% 10% 1	5264
	11th to 20th	Night	46% 8% 12% 18% 16%	5235
	21st to end	Night	48% 8% 13% 19% 11% 1	5771
June	1st to 10th	Night	33% 8% 11% 27% 17% 4	1865
	11th to 20th	Night	27% 6% 15% 26% 23% 3	1680
	21st to end	Night	28% 9% 18% 22% 18% 5%	1680
July	1st to 10th	Night	35% 8% 14% 28% 14% 1	4670
	11th to 20th	Night	38% 10% 18% 25% 8% 1	4825
	21st to end	Night	43% 9% 18% 21% 8% 1	5606
August	1st to 10th	Night	30% 8% 13% 29% 18% 1	4141
	11th to 20th	Night	23% 7% 24% 32% 13% 1	4590
	21st to end	Night	17% 6% 12% 40% 24% 2	5046
September	1st to 10th	Night	33% 6% 9% 23% 23% 5%	2137
	11th to 20th	Night	34% 6% 9% 24% 23% 4	2234
	21st to end	Night	33% 5% 8% 23% 25% 6%	2200
October	1st to 10th	Night	19% 4 6% 19% 44% 8%	3590
	11th to 20th	Night	21% 3 6% 25% 36% 9%	3672
	21st to end	Night	28% 3 8% 21% 30% 9%	4610
November	1st to 10th	Night	36% 3 7% 25% 24% 5%	2666
	11th to 20th	Night	38% 4 6% 23% 21% 7%	2730
	21st to end	Night	44% 4 7% 24% 18% 3	2730
December	1st to 10th	Night	50% 3 7% 20% 18% 1	4380
	11th to 20th	Night	50% 4 8% 20% 16% 2	4954
	21st to end	Night	63% 4 8% 16% 7% 1	6886

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	25% 19% 31% 19% 5% 1	330
	11th to 20th	Day	30% 22% 32% 12% 4	330
	21st to end	Day	23% 24% 39% 11% 3	363
February	1st to 10th	Day	28% 21% 35% 13% 3 1	330
	11th to 20th	Day	34% 20% 32% 9% 4	330
	21st to end	Day	34% 16% 35% 13% 3	273
March	1st to 10th	Day	26% 20% 36% 15% 2 1	330
	11th to 20th	Day	25% 20% 36% 13% 5% 1	472
	21st to end	Day	26% 17% 35% 17% 5% 1	594
April	1st to 10th	Day	19% 18% 30% 23% 9% 1	540
	11th to 20th	Day	20% 18% 27% 22% 12% 2	532
	21st to end	Day	20% 14% 34% 21% 9% 4	540
May	1st to 10th	Day	23% 13% 31% 20% 10% 3	543
	11th to 20th	Day	18% 11% 24% 28% 14% 6%	567
	21st to end	Day	18% 6% 20% 26% 17% 12%	617
June	1st to 10th	Day	12% 5% 20% 26% 26% 11%	588
	11th to 20th	Day	8% 4 21% 30% 25% 13%	780
	21st to end	Day	8% 4 21% 30% 25% 13%	780
July	1st to 10th	Day	10% 4 15% 26% 28% 19%	771
	11th to 20th	Day	8% 4 16% 27% 28% 17%	708
	21st to end	Day	12% 3 14% 28% 27% 16%	620
August	1st to 10th	Day	10% 5% 12% 25% 30% 17%	566
	11th to 20th	Day	10% 4 16% 32% 28% 11%	559
	21st to end	Day	9% 3 10% 26% 33% 20%	627
September	1st to 10th	Day	13% 4 12% 27% 29% 15%	570
	11th to 20th	Day	12% 3 12% 23% 36% 14%	542
	21st to end	Day	17% 6% 18% 25% 23% 11%	530
October	1st to 10th	Day	11% 5% 17% 31% 27% 9%	530
	11th to 20th	Day	15% 11% 26% 27% 16% 5%	520
	21st to end	Day	24% 14% 27% 26% 8% 1	363
November	1st to 10th	Day	18% 10% 32% 26% 12% 3	330
	11th to 20th	Day	19% 17% 33% 23% 8%	330
	21st to end	Day	24% 14% 32% 19% 10% 1	330
December	1st to 10th	Day	26% 15% 34% 17% 7% 1	330
	11th to 20th	Day	26% 15% 31% 22% 7%	330
	21st to end	Day	29% 17% 33% 17% 4	363
January	1st to 10th	Night	23% 14% 34% 25% 4	1050
	11th to 20th	Night	28% 15% 32% 21% 4	954
	21st to end	Night	22% 15% 39% 22% 2	924
February	1st to 10th	Night	27% 11% 37% 22% 3	840
	11th to 20th	Night	30% 13% 35% 20% 2	823
	21st to end	Night	27% 12% 36% 23% 2	692
March	1st to 10th	Night	23% 14% 33% 25% 5%	840
	11th to 20th	Night	22% 14% 33% 25% 6%	840
	21st to end	Night	22% 14% 29% 29% 5%	857
April	1st to 10th	Night	16% 13% 32% 30% 9%	630
	11th to 20th	Night	19% 10% 32% 27% 11% 1	623
	21st to end	Night	17% 8% 32% 32% 10% 1	630
May	1st to 10th	Night	18% 7% 28% 31% 13% 2	630
	11th to 20th	Night	13% 7% 23% 36% 19% 3	621
	21st to end	Night	9% 3 17% 36% 29% 5%	683
June	1st to 10th	Night	11% 3 17% 37% 28% 3	630
	11th to 20th	Night	7% 3 14% 41% 33% 3	630
	21st to end	Night	6% 2 13% 41% 33% 4	630
July	1st to 10th	Night	10% 2 8% 28% 43% 9%	615
	11th to 20th	Night	9% 2 8% 30% 44% 7%	612
	21st to end	Night	10% 3 9% 36% 35% 7%	690
August	1st to 10th	Night	10% 2 8% 31% 43% 6%	627
	11th to 20th	Night	7% 1 12% 38% 37% 5%	624
	21st to end	Night	6% 1 6% 34% 45% 7%	693
September	1st to 10th	Night	13% 1 11% 32% 38% 5%	667
	11th to 20th	Night	11% 2 12% 32% 38% 5%	813
	21st to end	Night	14% 5% 17% 31% 30% 4	800
October	1st to 10th	Night	11% 4 16% 37% 29% 4	800
	11th to 20th	Night	17% 7% 22% 34% 18% 2	800
	21st to end	Night	19% 8% 31% 28% 13% 1	880
November	1st to 10th	Night	15% 8% 25% 34% 16% 2	820
	11th to 20th	Night	17% 13% 30% 31% 10%	840
	21st to end	Night	23% 11% 25% 31% 10%	840
December	1st to 10th	Night	27% 11% 29% 27% 6%	840
	11th to 20th	Night	24% 10% 34% 26% 6%	840
	21st to end	Night	29% 13% 29% 25% 4	1034

Page generated at 2026-09-11 03:11:55. Version ac07

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