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 2024-03-08.

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% 7% 3 6% 5% 3 5% 5% 5% 7% 38%	78968
	Night	15% 8% 3 6% 5% 3 4 4 5% 7% 40%	80596
Transparency	Day	44% 6% 11% 22% 15% 2	78681
	Night	43% 5% 10% 22% 17% 3	80403
Seeing	Day	17% 9% 23% 24% 18% 9%	14260
	Night	18% 8% 24% 30% 18% 2	24136

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% 13% 7% 8% 6% 3 5% 4 5% 5% 29%	2527
	11th to 20th	Day	19% 10% 4 10% 8% 3 6% 3 3 4 31%	2657
	21st to end	Day	24% 12% 8% 5% 4 2 3 4 3 5% 28%	3266
February	1st to 10th	Day	18% 11% 4 7% 5% 2 3 4 4 6% 34%	1900
	11th to 20th	Day	21% 8% 4 7% 7% 2 5% 3 4 7% 34%	1848
	21st to end	Day	20% 10% 4 7% 5% 2 4 5% 5% 5% 34%	1570
March	1st to 10th	Day	18% 9% 3 5% 5% 3 4 5% 4 6% 39%	1870
	11th to 20th	Day	22% 9% 4 6% 5% 2 4 4 4 6% 33%	1921
	21st to end	Day	17% 8% 4 9% 7% 3 5% 4 5% 6% 31%	2250
April	1st to 10th	Day	12% 6% 3 6% 5% 3 4 5% 5% 8% 44%	2160
	11th to 20th	Day	16% 7% 2 6% 6% 3 4 4 4 6% 41%	2134
	21st to end	Day	16% 7% 3 5% 5% 3 5% 5% 6% 7% 37%	2261
May	1st to 10th	Day	17% 6% 3 5% 5% 3 4 5% 5% 8% 38%	2340
	11th to 20th	Day	16% 8% 3 6% 5% 3 5% 4 5% 7% 36%	2301
	21st to end	Day	8% 5% 3 7% 7% 4 6% 6% 6% 10% 37%	2531
June	1st to 10th	Day	10% 5% 2 6% 6% 4 6% 6% 6% 7% 42%	2355
	11th to 20th	Day	6% 4 2 4 6% 4 6% 7% 8% 10% 45%	2520
	21st to end	Day	8% 3 2 5% 6% 3 6% 6% 8% 12% 41%	2520
July	1st to 10th	Day	10% 5% 3 6% 6% 5% 7% 6% 7% 10% 34%	2520
	11th to 20th	Day	8% 5% 2 6% 7% 4 6% 6% 8% 10% 38%	2469
	21st to end	Day	9% 5% 3 6% 6% 4 7% 7% 7% 12% 35%	2547
August	1st to 10th	Day	8% 6% 2 5% 6% 4 5% 7% 8% 11% 39%	2321
	11th to 20th	Day	9% 6% 3 6% 6% 4 6% 7% 7% 9% 37%	2125
	21st to end	Day	9% 4 2 5% 5% 4 6% 7% 7% 8% 43%	2376
September	1st to 10th	Day	13% 6% 3 5% 6% 3 5% 5% 6% 8% 40%	2110
	11th to 20th	Day	12% 6% 2 5% 5% 4 4 4 5% 7% 45%	1980
	21st to end	Day	12% 4 3 4 5% 3 4 4 4 7% 51%	1980
October	1st to 10th	Day	11% 5% 2 4 4 3 3 3 5% 7% 54%	1980
	11th to 20th	Day	14% 5% 2 5% 4 2 4 3 5% 6% 50%	1932
	21st to end	Day	20% 6% 3 4 4 2 4 4 5% 5% 43%	1782
November	1st to 10th	Day	11% 6% 3 4 4 2 3 4 3 7% 54%	1672
	11th to 20th	Day	17% 5% 3 4 4 3 4 3 4 5% 48%	1710
	21st to end	Day	18% 8% 3 6% 3 3 3 4 4 5% 44%	1710
December	1st to 10th	Day	22% 10% 3 5% 5% 2 3 4 5% 6% 35%	1710
	11th to 20th	Day	17% 11% 5% 7% 6% 2 5% 4 4 5% 35%	2153
	21st to end	Day	19% 15% 5% 6% 5% 4 5% 5% 5% 6% 27%	2960
January	1st to 10th	Night	18% 14% 4 6% 5% 3 4 5% 5% 6% 31%	4428
	11th to 20th	Night	19% 13% 5% 8% 7% 4 4 3 3 4 30%	4302
	21st to end	Night	24% 14% 4 6% 4 2 3 3 4 5% 32%	4375
February	1st to 10th	Night	22% 10% 4 8% 6% 2 4 4 5% 6% 31%	2280
	11th to 20th	Night	21% 9% 3 7% 5% 3 4 4 4 4 36%	2218
	21st to end	Night	23% 10% 4 7% 5% 3 5% 4 3 5% 32%	1884
March	1st to 10th	Night	17% 10% 3 5% 4 2 4 4 4 6% 41%	2251
	11th to 20th	Night	18% 9% 4 6% 6% 3 4 5% 4 6% 35%	2039
	21st to end	Night	18% 9% 3 6% 6% 2 4 4 5% 8% 35%	2121
April	1st to 10th	Night	12% 6% 2 5% 5% 2 4 5% 6% 8% 46%	1800
	11th to 20th	Night	16% 7% 2 5% 4 3 3 3 4 6% 44%	1775
	21st to end	Night	14% 7% 3 6% 5% 3 4 6% 6% 6% 39%	1697
May	1st to 10th	Night	15% 7% 3 5% 6% 3 5% 5% 6% 6% 39%	1620
	11th to 20th	Night	12% 6% 3 5% 6% 4 5% 6% 6% 9% 39%	1592
	21st to end	Night	5% 4 2 6% 6% 3 6% 6% 8% 12% 42%	1744
June	1st to 10th	Night	10% 4 3 5% 5% 3 5% 5% 6% 9% 46%	1599
	11th to 20th	Night	5% 3 2 3 5% 3 4 5% 7% 10% 53%	1440
	21st to end	Night	4 3 2 4 5% 3 7% 6% 7% 12% 48%	1440
July	1st to 10th	Night	8% 5% 2 4 6% 3 5% 6% 7% 10% 43%	1440
	11th to 20th	Night	8% 4 3 5% 5% 3 4 5% 6% 12% 46%	1486
	21st to end	Night	7% 4 2 5% 6% 2 6% 6% 8% 10% 43%	1771
August	1st to 10th	Night	7% 5% 2 4 5% 3 4 5% 6% 10% 50%	1614
	11th to 20th	Night	6% 5% 3 5% 5% 3 5% 7% 7% 9% 45%	1776
	21st to end	Night	6% 4 1 4 4 2 3 5% 6% 11% 52%	1980
September	1st to 10th	Night	11% 5% 2 4 4 3 4 5% 5% 8% 49%	1831
	11th to 20th	Night	10% 6% 2 5% 4 3 4 4 5% 8% 48%	1980
	21st to end	Night	10% 5% 2 4 4 2 3 3 4 6% 56%	1980
October	1st to 10th	Night	10% 5% 2 4 3 2 2 3 4 5% 60%	1980
	11th to 20th	Night	15% 7% 2 4 4 2 3 3 4 6% 49%	2025
	21st to end	Night	17% 8% 2 5% 4 2 3 4 4 6% 46%	2574
November	1st to 10th	Night	10% 7% 2 4 4 2 4 3 3 5% 54%	2406
	11th to 20th	Night	15% 6% 2 4 4 3 4 4 5% 5% 48%	2470
	21st to end	Night	17% 9% 3 5% 4 2 3 3 4 6% 43%	2470
December	1st to 10th	Night	21% 12% 4 6% 5% 3 4 3 5% 6% 33%	2470
	11th to 20th	Night	19% 9% 4 8% 4 2 3 4 4 6% 36%	3042
	21st to end	Night	17% 14% 5% 8% 7% 4 5% 4 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	46% 4 8% 22% 17% 2	1870
	11th to 20th	Day	53% 4 10% 19% 12% 2	1921
	21st to end	Day	53% 6% 9% 20% 10% 2	2250
April	1st to 10th	Day	39% 5% 11% 25% 17% 2	2160
	11th to 20th	Day	44% 5% 8% 21% 19% 3	2134
	21st to end	Day	44% 7% 9% 24% 13% 3	2261
May	1st to 10th	Day	45% 6% 11% 25% 12% 1	2340
	11th to 20th	Day	47% 6% 11% 22% 13% 1	2305
	21st to end	Day	40% 10% 14% 23% 12% 2	2531
June	1st to 10th	Day	38% 8% 11% 23% 18% 2	2355
	11th to 20th	Day	31% 8% 17% 24% 17% 2	2520
	21st to end	Day	34% 9% 15% 21% 17% 4	2520
July	1st to 10th	Day	41% 10% 14% 19% 13% 3	2451
	11th to 20th	Day	39% 9% 16% 19% 13% 3	2394
	21st to end	Day	37% 10% 16% 24% 11% 2	2405
August	1st to 10th	Day	36% 11% 15% 23% 14% 1	2308
	11th to 20th	Day	41% 9% 12% 21% 16% 2	2125
	21st to end	Day	35% 8% 12% 24% 16% 4	2376
September	1st to 10th	Day	41% 7% 13% 19% 17% 4	2110
	11th to 20th	Day	38% 6% 9% 23% 22% 3	1980
	21st to end	Day	33% 5% 9% 25% 23% 4	1980
October	1st to 10th	Day	31% 5% 9% 21% 30% 5%	1980
	11th to 20th	Day	35% 5% 7% 20% 27% 6%	1932
	21st to end	Day	42% 4 7% 23% 20% 4	1782
November	1st to 10th	Day	33% 4 7% 27% 24% 5%	1672
	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	46% 4 8% 18% 19% 5%	2251
	11th to 20th	Night	49% 5% 9% 22% 13% 2	2039
	21st to end	Night	48% 6% 11% 23% 11% 2	2121
April	1st to 10th	Night	35% 7% 10% 24% 21% 3	1800
	11th to 20th	Night	42% 4 8% 17% 22% 6%	1775
	21st to end	Night	43% 7% 8% 24% 16% 2	1697
May	1st to 10th	Night	43% 6% 11% 24% 13% 3	1620
	11th to 20th	Night	40% 9% 14% 21% 15% 1	1593
	21st to end	Night	32% 11% 16% 24% 14% 3	1745
June	1st to 10th	Night	33% 8% 11% 27% 17% 4	1599
	11th to 20th	Night	25% 6% 16% 28% 22% 3	1440
	21st to end	Night	27% 9% 19% 22% 17% 6%	1440
July	1st to 10th	Night	33% 9% 16% 24% 14% 3	1400
	11th to 20th	Night	31% 7% 16% 24% 17% 5%	1438
	21st to end	Night	31% 10% 15% 27% 15% 2	1672
August	1st to 10th	Night	30% 7% 15% 26% 19% 2	1603
	11th to 20th	Night	33% 9% 16% 24% 17% 2	1776
	21st to end	Night	26% 8% 14% 29% 18% 4	1980
September	1st to 10th	Night	35% 6% 10% 23% 21% 5%	1831
	11th to 20th	Night	34% 6% 10% 24% 22% 4	1980
	21st to end	Night	30% 4 7% 25% 26% 7%	1980
October	1st to 10th	Night	27% 4 8% 24% 30% 7%	1980
	11th to 20th	Night	37% 4 8% 20% 25% 6%	2025
	21st to end	Night	40% 4 7% 22% 23% 5%	2574
November	1st to 10th	Night	34% 3 7% 25% 25% 6%	2406
	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	23% 19% 38% 17% 3 1	261
	11th to 20th	Day	25% 17% 36% 14% 7% 1	361
	21st to end	Day	27% 16% 31% 19% 7% 1	462
April	1st to 10th	Day	17% 16% 29% 26% 11% 1	420
	11th to 20th	Day	20% 15% 24% 23% 15% 2	412
	21st to end	Day	22% 12% 32% 21% 9% 4	420
May	1st to 10th	Day	22% 10% 29% 23% 11% 4	423
	11th to 20th	Day	17% 10% 22% 29% 14% 7%	447
	21st to end	Day	14% 4 16% 30% 20% 16%	485
June	1st to 10th	Day	12% 4 15% 26% 29% 14%	465
	11th to 20th	Day	6% 2 19% 31% 27% 15%	630
	21st to end	Day	9% 3 20% 31% 25% 12%	630
July	1st to 10th	Day	10% 2 14% 24% 28% 21%	621
	11th to 20th	Day	8% 3 14% 25% 29% 20%	567
	21st to end	Day	10% 2 12% 29% 28% 19%	488
August	1st to 10th	Day	10% 4 12% 24% 31% 20%	446
	11th to 20th	Day	12% 3 14% 31% 29% 12%	439
	21st to end	Day	11% 3 8% 25% 32% 22%	495
September	1st to 10th	Day	15% 2 10% 26% 31% 16%	450
	11th to 20th	Day	13% 2 13% 22% 36% 15%	450
	21st to end	Day	15% 6% 18% 24% 24% 13%	450
October	1st to 10th	Day	12% 5% 18% 28% 27% 9%	450
	11th to 20th	Day	16% 11% 27% 28% 13% 4	442
	21st to end	Day	25% 13% 25% 27% 9% 1	297
November	1st to 10th	Day	16% 9% 29% 29% 14% 3	270
	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	22% 13% 33% 27% 5%	751
	11th to 20th	Night	22% 13% 32% 26% 7%	720
	21st to end	Night	23% 12% 27% 31% 6%	735
April	1st to 10th	Night	14% 12% 31% 32% 10% 1	540
	11th to 20th	Night	22% 8% 30% 26% 12% 1	533
	21st to end	Night	18% 7% 31% 32% 10% 1	540
May	1st to 10th	Night	18% 6% 28% 31% 15% 2	540
	11th to 20th	Night	13% 6% 21% 36% 20% 3	531
	21st to end	Night	6% 2 16% 37% 33% 6%	584
June	1st to 10th	Night	11% 3 15% 37% 30% 4	540
	11th to 20th	Night	5% 2 13% 41% 35% 4	540
	21st to end	Night	5% 2 13% 42% 34% 4	540
July	1st to 10th	Night	10% 2 8% 27% 44% 9%	525
	11th to 20th	Night	9% 1 8% 28% 46% 7%	522
	21st to end	Night	9% 2 8% 36% 37% 7%	591
August	1st to 10th	Night	11% 1 6% 31% 45% 6%	537
	11th to 20th	Night	8% 1 11% 37% 37% 5%	534
	21st to end	Night	8% 1 5% 32% 47% 7%	594
September	1st to 10th	Night	14% 1 10% 31% 39% 5%	571
	11th to 20th	Night	12% 2 12% 30% 38% 5%	720
	21st to end	Night	12% 4 17% 31% 32% 4	720
October	1st to 10th	Night	12% 4 16% 36% 28% 4	720
	11th to 20th	Night	19% 6% 22% 33% 17% 3	720
	21st to end	Night	19% 7% 31% 28% 13% 1	792
November	1st to 10th	Night	14% 7% 25% 35% 17% 2	740
	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 2024-03-05 06:24:05. Version ac07

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