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 2024-11-02.

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 6% 5% 4 5% 4 5% 7% 39%	101160
	Night	14% 9% 3 6% 4 4 4 3 5% 7% 41%	97780
Transparency	Day	42% 6% 11% 23% 15% 2	100959
	Night	42% 5% 10% 23% 17% 3	97651
Seeing	Day	17% 9% 23% 24% 18% 9%	15235
	Night	18% 8% 24% 30% 18% 2	24925

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% 14% 6% 9% 5% 5% 4 3 5% 4 29%	2527
	11th to 20th	Day	18% 10% 4 11% 6% 4 5% 2 3 4 31%	2657
	21st to end	Day	24% 13% 7% 6% 3 4 3 3 4 5% 28%	3266
February	1st to 10th	Day	18% 12% 4 8% 4 3 3 3 4 5% 34%	1900
	11th to 20th	Day	21% 9% 3 8% 5% 3 4 2 4 6% 34%	1848
	21st to end	Day	20% 10% 4 7% 4 3 5% 4 4 5% 34%	1570
March	1st to 10th	Day	25% 13% 3 7% 4 3 3 3 4 5% 32%	3120
	11th to 20th	Day	15% 7% 2 6% 3 3 3 3 5% 7% 46%	3379
	21st to end	Day	12% 7% 3 8% 5% 4 5% 3 5% 7% 40%	3941
April	1st to 10th	Day	13% 7% 3 7% 5% 4 4 4 5% 7% 42%	2280
	11th to 20th	Day	16% 8% 2 7% 5% 4 4 3 4 6% 41%	2254
	21st to end	Day	15% 8% 3 6% 5% 4 5% 4 6% 7% 38%	2387
May	1st to 10th	Day	20% 9% 2 7% 5% 5% 5% 4 5% 7% 31%	4082
	11th to 20th	Day	17% 8% 3 7% 4 4 4 3 5% 7% 37%	4081
	21st to end	Day	12% 7% 3 7% 5% 5% 6% 4 6% 8% 39%	4476
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 6% 7% 41%	2486
	11th to 20th	Day	6% 4 2 4 5% 5% 6% 5% 8% 11% 44%	2660
	21st to end	Day	7% 4 2 6% 5% 4 6% 5% 8% 11% 41%	2660
July	1st to 10th	Day	9% 5% 2 7% 6% 6% 6% 5% 7% 10% 37%	4440
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 4 8% 11% 42%	4347
	21st to end	Day	17% 10% 3 9% 7% 7% 6% 4 6% 9% 23%	4466
August	1st to 10th	Day	5% 4 2 4 4 4 4 5% 7% 11% 51%	4084
	11th to 20th	Day	8% 6% 2 6% 5% 5% 6% 5% 8% 11% 39%	3729
	21st to end	Day	5% 3 1 4 4 4 5% 5% 7% 8% 53%	4180
September	1st to 10th	Day	12% 7% 2 6% 5% 4 5% 4 6% 8% 41%	2227
	11th to 20th	Day	12% 6% 2 5% 4 5% 4 3 6% 7% 46%	2090
	21st to end	Day	13% 5% 2 5% 5% 4 3 3 4 7% 48%	2090
October	1st to 10th	Day	10% 5% 2 4 3 4 3 2 5% 7% 56%	2090
	11th to 20th	Day	13% 6% 2 5% 4 3 3 3 5% 6% 51%	2038
	21st to end	Day	19% 6% 3 5% 4 3 4 3 5% 5% 44%	1881
November	1st to 10th	Day	11% 6% 2 4 4 3 4 2 3 7% 54%	1681
	11th to 20th	Day	16% 6% 3 5% 3 4 3 2 5% 5% 48%	1710
	21st to end	Day	17% 8% 3 6% 3 4 3 3 4 5% 44%	1710
December	1st to 10th	Day	22% 11% 2 5% 4 3 4 3 5% 5% 35%	1710
	11th to 20th	Day	16% 12% 4 8% 5% 4 4 3 4 5% 35%	2153
	21st to end	Day	19% 15% 5% 6% 5% 5% 5% 3 5% 6% 27%	2960
January	1st to 10th	Night	17% 14% 4 7% 4 3 4 4 5% 6% 31%	4428
	11th to 20th	Night	19% 13% 4 10% 6% 5% 3 2 3 4 30%	4302
	21st to end	Night	24% 14% 4 6% 4 3 3 2 4 5% 32%	4375
February	1st to 10th	Night	21% 11% 4 10% 4 3 4 3 5% 5% 31%	2280
	11th to 20th	Night	21% 10% 3 7% 4 4 3 3 4 4 36%	2218
	21st to end	Night	22% 10% 4 8% 5% 4 5% 3 3 5% 32%	1884
March	1st to 10th	Night	23% 15% 3 7% 3 3 3 2 4 5% 32%	3733
	11th to 20th	Night	13% 7% 3 6% 4 3 3 3 4 6% 49%	3581
	21st to end	Night	14% 9% 3 6% 4 3 5% 3 5% 7% 40%	3705
April	1st to 10th	Night	12% 7% 2 6% 4 3 4 4 6% 7% 45%	1900
	11th to 20th	Night	16% 8% 2 6% 4 4 3 3 5% 6% 44%	1875
	21st to end	Night	14% 7% 3 7% 4 5% 4 5% 6% 6% 39%	1791
May	1st to 10th	Night	18% 9% 3 7% 5% 4 4 4 6% 6% 33%	2813
	11th to 20th	Night	15% 7% 3 6% 4 4 4 4 6% 8% 40%	2812
	21st to end	Night	7% 6% 2 7% 5% 4 5% 5% 7% 10% 42%	3079
June	1st to 10th	Night	10% 4 2 6% 4 4 4 4 6% 9% 46%	1687
	11th to 20th	Night	4 3 2 4 4 4 4 5% 7% 11% 52%	1520
	21st to end	Night	4 3 1 5% 4 5% 6% 5% 7% 11% 48%	1520
July	1st to 10th	Night	6% 5% 2 5% 6% 4 4 5% 8% 11% 44%	2530
	11th to 20th	Night	7% 4 2 5% 4 4 4 4 7% 10% 50%	2615
	21st to end	Night	11% 10% 4 10% 7% 5% 7% 4 7% 7% 27%	3087
August	1st to 10th	Night	6% 4 2 4 3 3 3 3 5% 9% 58%	2842
	11th to 20th	Night	5% 4 2 5% 4 4 5% 5% 7% 10% 47%	3100
	21st to end	Night	4 3 1 4 3 3 3 4 6% 9% 61%	3476
September	1st to 10th	Night	11% 5% 2 5% 3 5% 4 4 5% 7% 50%	1933
	11th to 20th	Night	10% 6% 2 6% 4 3 4 3 5% 8% 48%	2090
	21st to end	Night	12% 6% 2 5% 3 4 3 3 4 6% 53%	2090
October	1st to 10th	Night	9% 5% 2 4 3 3 2 2 4 5% 61%	2090
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 6% 52%	2139
	21st to end	Night	16% 8% 2 5% 3 3 3 3 4 5% 48%	2717
November	1st to 10th	Night	10% 7% 2 5% 4 4 3 3 3 5% 54%	2420
	11th to 20th	Night	14% 7% 2 5% 4 4 4 3 5% 5% 48%	2470
	21st to end	Night	17% 9% 3 5% 4 3 3 2 5% 6% 43%	2470
December	1st to 10th	Night	21% 12% 4 7% 4 4 3 3 5% 5% 33%	2470
	11th to 20th	Night	19% 10% 4 9% 4 3 3 3 4 6% 35%	3042
	21st to end	Night	17% 15% 5% 9% 6% 6% 5% 3 4 5% 25%	4696

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% 4 7% 20% 10% 1	2528
	11th to 20th	Day	58% 3 9% 20% 10% 1	2657
	21st to end	Day	59% 3 8% 22% 7% 1	3266
February	1st to 10th	Day	52% 4 9% 19% 14% 2	1900
	11th to 20th	Day	52% 4 8% 21% 12% 3	1858
	21st to end	Day	51% 5% 10% 15% 14% 5%	1570
March	1st to 10th	Day	56% 4 6% 18% 12% 5%	3120
	11th to 20th	Day	38% 5% 9% 28% 17% 3	3379
	21st to end	Day	42% 6% 11% 26% 14% 1	3941
April	1st to 10th	Day	41% 5% 10% 24% 17% 2	2280
	11th to 20th	Day	43% 5% 7% 22% 19% 3	2254
	21st to end	Day	43% 7% 9% 24% 13% 2	2387
May	1st to 10th	Day	50% 7% 12% 20% 10%	4120
	11th to 20th	Day	46% 7% 10% 23% 14%	4085
	21st to end	Day	40% 8% 11% 19% 20% 2	4489
June	1st to 10th	Day	39% 8% 11% 22% 18% 2	2486
	11th to 20th	Day	31% 8% 17% 24% 18% 2	2660
	21st to end	Day	34% 9% 16% 20% 18% 4	2660
July	1st to 10th	Day	39% 8% 16% 23% 12% 2	4371
	11th to 20th	Day	34% 8% 15% 31% 10% 2	4272
	21st to end	Day	56% 8% 12% 17% 6% 1	4324
August	1st to 10th	Day	25% 9% 15% 33% 17% 1	4071
	11th to 20th	Day	36% 8% 14% 25% 17% 1	3765
	21st to end	Day	26% 8% 11% 36% 18% 2	4179
September	1st to 10th	Day	40% 7% 12% 18% 18% 5%	2227
	11th to 20th	Day	38% 5% 9% 23% 22% 3	2090
	21st to end	Day	35% 6% 9% 24% 22% 4	2090
October	1st to 10th	Day	30% 5% 9% 20% 32% 4	2090
	11th to 20th	Day	34% 5% 7% 21% 27% 5%	2038
	21st to end	Day	40% 4 7% 23% 20% 5%	1881
November	1st to 10th	Day	33% 4 7% 27% 24% 5%	1681
	11th to 20th	Day	39% 3 8% 24% 21% 5%	1710
	21st to end	Day	44% 4 7% 24% 19% 2	1710
December	1st to 10th	Day	50% 4 10% 22% 12% 1	1710
	11th to 20th	Day	51% 4 10% 19% 14% 1	2150
	21st to end	Day	57% 6% 11% 18% 9%	2960
January	1st to 10th	Night	51% 4 9% 21% 13% 1	4428
	11th to 20th	Night	59% 4 6% 17% 11% 3	4302
	21st to end	Night	55% 4 8% 20% 12% 1	4375
February	1st to 10th	Night	55% 4 9% 18% 13% 1	2280
	11th to 20th	Night	52% 4 7% 19% 15% 3	2219
	21st to end	Night	56% 4 8% 15% 14% 4	1884
March	1st to 10th	Night	56% 4 7% 16% 14% 3	3733
	11th to 20th	Night	36% 5% 9% 28% 13% 9%	3581
	21st to end	Night	42% 5% 11% 25% 16% 1	3705
April	1st to 10th	Night	36% 6% 10% 24% 20% 3	1900
	11th to 20th	Night	42% 3 8% 17% 23% 6%	1875
	21st to end	Night	43% 7% 8% 24% 16% 2	1791
May	1st to 10th	Night	48% 8% 11% 22% 9% 2	2840
	11th to 20th	Night	42% 8% 13% 23% 15%	2813
	21st to end	Night	33% 11% 14% 22% 18% 3	3087
June	1st to 10th	Night	33% 8% 11% 27% 16% 4	1687
	11th to 20th	Night	25% 6% 16% 27% 23% 3	1520
	21st to end	Night	27% 9% 18% 22% 18% 6%	1520
July	1st to 10th	Night	32% 8% 16% 29% 13% 2	2490
	11th to 20th	Night	29% 7% 14% 35% 13% 3	2567
	21st to end	Night	53% 9% 11% 17% 9% 1	2988
August	1st to 10th	Night	23% 6% 12% 37% 21% 1	2831
	11th to 20th	Night	29% 8% 17% 29% 16% 1	3130
	21st to end	Night	19% 7% 12% 36% 23% 3	3476
September	1st to 10th	Night	34% 6% 9% 22% 23% 5%	1933
	11th to 20th	Night	34% 6% 10% 24% 22% 4	2090
	21st to end	Night	33% 5% 8% 24% 25% 6%	2090
October	1st to 10th	Night	26% 4 8% 23% 32% 6%	2090
	11th to 20th	Night	35% 4 8% 21% 27% 6%	2139
	21st to end	Night	38% 4 7% 22% 24% 5%	2717
November	1st to 10th	Night	34% 3 7% 25% 25% 6%	2420
	11th to 20th	Night	37% 4 7% 22% 22% 8%	2470
	21st to end	Night	42% 4 7% 24% 19% 3	2470
December	1st to 10th	Night	53% 4 9% 20% 11% 2	2470
	11th to 20th	Night	50% 4 8% 19% 17% 3	3044
	21st to end	Night	59% 5% 10% 16% 9% 1	4696

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	24% 17% 31% 21% 6% 1	270
	11th to 20th	Day	30% 21% 31% 14% 5%	270
	21st to end	Day	22% 22% 40% 13% 3	297
February	1st to 10th	Day	28% 20% 34% 14% 3 1	270
	11th to 20th	Day	33% 18% 34% 10% 5%	270
	21st to end	Day	36% 16% 35% 10% 3	225
March	1st to 10th	Day	24% 19% 37% 16% 3 1	270
	11th to 20th	Day	24% 17% 37% 14% 6% 1	398
	21st to end	Day	27% 16% 32% 18% 6% 1	506
April	1st to 10th	Day	19% 17% 28% 25% 10% 1	460
	11th to 20th	Day	20% 16% 25% 23% 14% 2	452
	21st to end	Day	20% 13% 32% 22% 9% 4	460
May	1st to 10th	Day	22% 11% 29% 22% 11% 4	463
	11th to 20th	Day	17% 9% 22% 29% 15% 7%	487
	21st to end	Day	15% 5% 19% 28% 19% 15%	529
June	1st to 10th	Day	13% 5% 17% 25% 27% 13%	506
	11th to 20th	Day	6% 2 19% 31% 26% 14%	680
	21st to end	Day	8% 3 21% 31% 24% 12%	680
July	1st to 10th	Day	10% 3 15% 25% 27% 20%	671
	11th to 20th	Day	8% 4 16% 26% 28% 19%	614
	21st to end	Day	13% 3 13% 27% 26% 18%	532
August	1st to 10th	Day	9% 4 13% 24% 31% 19%	486
	11th to 20th	Day	11% 4 16% 32% 27% 11%	479
	21st to end	Day	10% 2 8% 25% 32% 23%	539
September	1st to 10th	Day	14% 2 11% 27% 30% 15%	490
	11th to 20th	Day	13% 3 13% 23% 35% 14%	490
	21st to end	Day	17% 6% 18% 25% 23% 12%	490
October	1st to 10th	Day	11% 5% 17% 30% 28% 9%	490
	11th to 20th	Day	16% 12% 26% 26% 16% 5%	481
	21st to end	Day	24% 12% 28% 26% 9% 1	330
November	1st to 10th	Day	16% 8% 29% 29% 15% 3	273
	11th to 20th	Day	17% 15% 33% 26% 9%	270
	21st to end	Day	23% 11% 30% 22% 12% 1	270
December	1st to 10th	Day	26% 14% 31% 19% 9% 1	270
	11th to 20th	Day	25% 14% 31% 23% 8%	270
	21st to end	Day	27% 17% 34% 17% 5%	297
January	1st to 10th	Night	23% 14% 33% 25% 4	950
	11th to 20th	Night	29% 14% 32% 21% 4	864
	21st to end	Night	22% 15% 39% 22% 2	836
February	1st to 10th	Night	28% 11% 36% 22% 4	760
	11th to 20th	Night	28% 13% 36% 20% 2	743
	21st to end	Night	28% 13% 36% 21% 2	628
March	1st to 10th	Night	23% 13% 33% 26% 5%	760
	11th to 20th	Night	21% 13% 33% 26% 6%	760
	21st to end	Night	23% 12% 28% 30% 6%	775
April	1st to 10th	Night	15% 13% 31% 31% 9% 1	570
	11th to 20th	Night	21% 9% 31% 26% 12% 1	563
	21st to end	Night	17% 8% 32% 32% 9% 1	570
May	1st to 10th	Night	18% 6% 28% 31% 15% 2	570
	11th to 20th	Night	12% 6% 21% 37% 20% 3	561
	21st to end	Night	6% 2 17% 37% 32% 6%	617
June	1st to 10th	Night	11% 4 15% 37% 30% 4	570
	11th to 20th	Night	6% 2 13% 41% 35% 4	570
	21st to end	Night	5% 2 13% 42% 33% 5%	570
July	1st to 10th	Night	10% 2 8% 29% 43% 8%	555
	11th to 20th	Night	9% 1 8% 30% 45% 7%	552
	21st to end	Night	10% 3 9% 36% 35% 7%	624
August	1st to 10th	Night	10% 2 7% 31% 44% 6%	567
	11th to 20th	Night	8% 1 12% 38% 36% 5%	564
	21st to end	Night	7% 1 5% 32% 47% 8%	627
September	1st to 10th	Night	14% 1 11% 32% 38% 5%	603
	11th to 20th	Night	12% 3 12% 31% 38% 5%	760
	21st to end	Night	14% 4 17% 31% 30% 4	760
October	1st to 10th	Night	11% 4 16% 37% 28% 4	760
	11th to 20th	Night	18% 6% 22% 33% 18% 2	760
	21st to end	Night	18% 7% 32% 28% 14% 1	836
November	1st to 10th	Night	14% 7% 25% 35% 17% 2	745
	11th to 20th	Night	16% 11% 30% 31% 11% 1	760
	21st to end	Night	21% 11% 24% 32% 11% 1	760
December	1st to 10th	Night	27% 10% 28% 28% 7%	760
	11th to 20th	Night	23% 9% 33% 27% 7% 1	760
	21st to end	Night	28% 13% 28% 27% 4	935

Page generated at 2024-10-30 00:22:58. Version ac07

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