Louisville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Louisville clear sky chart from 2005-11-06 to 2026-03-03.

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% 38%	130849
	Night	15% 9% 3 7% 4 4 4 3 5% 7% 39%	130445
Transparency	Day	44% 5% 11% 23% 15% 2	134492
	Night	44% 5% 10% 22% 16% 2	134874
Seeing	Day	17% 11% 25% 24% 16% 7%	17076
	Night	18% 8% 26% 30% 17% 2	26933

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	16% 12% 6% 9% 5% 4 4 3 5% 6% 29%	4691
	11th to 20th	Day	12% 10% 4 11% 5% 4 4 3 4 6% 36%	4783
	21st to end	Day	20% 13% 5% 8% 5% 5% 4 3 5% 6% 27%	5877
February	1st to 10th	Day	16% 12% 4 9% 4 4 3 3 4 8% 33%	2100
	11th to 20th	Day	18% 8% 4 7% 4 5% 4 4 5% 5% 35%	2048
	21st to end	Day	17% 11% 4 8% 6% 3 4 4 5% 6% 32%	1730
March	1st to 10th	Day	19% 12% 4 7% 4 3 3 2 3 5% 36%	4500
	11th to 20th	Day	13% 9% 3 6% 4 4 4 3 6% 8% 42%	4878
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	5598
April	1st to 10th	Day	15% 6% 3 7% 5% 5% 4 4 6% 7% 39%	2400
	11th to 20th	Day	16% 8% 3 7% 5% 5% 4 4 5% 6% 39%	2374
	21st to end	Day	16% 7% 2 6% 5% 4 5% 4 6% 7% 37%	2560
May	1st to 10th	Day	20% 8% 3 7% 5% 5% 6% 5% 8% 8% 25%	5862
	11th to 20th	Day	18% 8% 3 7% 5% 5% 4 4 5% 7% 35%	5861
	21st to end	Day	13% 6% 3 7% 6% 5% 6% 5% 8% 10% 32%	6433
June	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 4 6% 8% 44%	2680
	11th to 20th	Day	7% 4 2 6% 5% 6% 5% 4 7% 10% 44%	2800
	21st to end	Day	7% 5% 2 5% 5% 5% 5% 5% 8% 11% 44%	2800
July	1st to 10th	Day	10% 6% 2 5% 4 5% 5% 4 7% 10% 42%	6360
	11th to 20th	Day	8% 6% 3 5% 5% 5% 5% 5% 8% 11% 39%	6324
	21st to end	Day	10% 7% 4 9% 6% 6% 7% 6% 8% 10% 29%	6424
August	1st to 10th	Day	7% 5% 2 5% 4 4 5% 4 7% 11% 47%	4234
	11th to 20th	Day	7% 5% 2 6% 5% 6% 6% 5% 8% 9% 41%	3952
	21st to end	Day	4 4 1 4 4 4 5% 4 5% 10% 56%	4312
September	1st to 10th	Day	13% 5% 2 6% 3 4 4 4 6% 6% 47%	2335
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 6% 7% 49%	2200
	21st to end	Day	13% 5% 2 7% 4 3 4 3 5% 6% 48%	2200
October	1st to 10th	Day	10% 4 2 5% 4 3 3 3 4 6% 56%	2200
	11th to 20th	Day	12% 5% 2 5% 4 4 3 4 5% 8% 48%	2106
	21st to end	Day	18% 8% 2 5% 3 4 3 4 5% 6% 42%	1980
November	1st to 10th	Day	11% 6% 2 6% 4 3 3 3 5% 6% 51%	1852
	11th to 20th	Day	16% 10% 3 6% 3 3 4 3 5% 6% 42%	1890
	21st to end	Day	19% 10% 3 6% 3 4 4 3 5% 5% 38%	1890
December	1st to 10th	Day	18% 10% 3 7% 4 3 4 2 4 4 42%	3020
	11th to 20th	Day	15% 12% 5% 10% 6% 6% 4 3 4 6% 28%	3463
	21st to end	Day	22% 16% 3 9% 4 4 5% 4 4 6% 22%	4132
January	1st to 10th	Night	15% 13% 5% 10% 4 4 5% 3 4 5% 30%	8232
	11th to 20th	Night	14% 13% 5% 11% 5% 5% 4 3 4 5% 31%	8184
	21st to end	Night	18% 11% 3 8% 4 4 4 3 4 6% 35%	8302
February	1st to 10th	Night	21% 11% 4 8% 5% 4 4 3 5% 5% 29%	2520
	11th to 20th	Night	20% 9% 3 8% 5% 4 3 3 4 5% 36%	2458
	21st to end	Night	21% 11% 3 7% 5% 4 3 3 4 5% 33%	2076
March	1st to 10th	Night	21% 12% 2 6% 4 4 4 2 4 5% 36%	5398
	11th to 20th	Night	13% 6% 2 5% 4 4 4 3 5% 5% 48%	5082
	21st to end	Night	17% 8% 3 7% 5% 5% 5% 4 5% 6% 35%	5361
April	1st to 10th	Night	14% 7% 2 6% 4 4 5% 3 5% 8% 41%	2000
	11th to 20th	Night	15% 8% 2 6% 5% 3 3 3 5% 6% 43%	1975
	21st to end	Night	15% 7% 3 7% 5% 4 5% 4 5% 7% 39%	1840
May	1st to 10th	Night	19% 9% 3 8% 6% 5% 4 3 6% 8% 28%	4033
	11th to 20th	Night	16% 7% 3 8% 5% 4 6% 4 6% 8% 34%	4032
	21st to end	Night	12% 6% 2 7% 5% 5% 6% 5% 6% 9% 37%	4421
June	1st to 10th	Night	10% 4 2 4 5% 4 4 4 5% 9% 48%	1714
	11th to 20th	Night	7% 4 2 5% 4 4 5% 4 6% 10% 49%	1600
	21st to end	Night	5% 3 1 3 5% 4 5% 5% 7% 12% 50%	1600
July	1st to 10th	Night	8% 5% 2 7% 5% 5% 5% 4 5% 9% 47%	3618
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 4 7% 10% 46%	3648
	21st to end	Night	9% 5% 3 9% 6% 6% 6% 5% 8% 10% 33%	4427
August	1st to 10th	Night	6% 4 2 5% 3 3 4 4 6% 9% 54%	2915
	11th to 20th	Night	6% 5% 2 5% 4 4 6% 5% 7% 10% 46%	3094
	21st to end	Night	4 3 1 3 2 2 3 3 5% 10% 64%	3586
September	1st to 10th	Night	11% 4 2 5% 4 3 4 3 5% 8% 51%	2045
	11th to 20th	Night	9% 5% 2 6% 3 3 4 3 5% 8% 52%	2200
	21st to end	Night	13% 5% 2 6% 4 4 3 3 4 6% 51%	2200
October	1st to 10th	Night	8% 5% 2 5% 3 3 3 3 3 7% 58%	2200
	11th to 20th	Night	13% 5% 2 6% 4 3 4 3 4 6% 51%	2286
	21st to end	Night	18% 7% 2 5% 3 4 4 3 4 5% 46%	2860
November	1st to 10th	Night	13% 7% 2 5% 4 4 4 2 5% 5% 50%	2666
	11th to 20th	Night	14% 8% 3 5% 4 4 3 3 4 7% 45%	2730
	21st to end	Night	18% 11% 3 5% 5% 4 3 3 4 5% 39%	2730
December	1st to 10th	Night	18% 11% 3 7% 3 3 3 3 3 4 40%	4380
	11th to 20th	Night	20% 11% 4 6% 4 4 4 3 4 5% 35%	4952
	21st to end	Night	24% 16% 5% 9% 6% 5% 4 3 3 5% 21%	7080

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	56% 3 12% 21% 8% 1	4692
	11th to 20th	Day	50% 3 8% 21% 16% 2	4783
	21st to end	Day	59% 3 9% 18% 7% 4	5877
February	1st to 10th	Day	52% 4 10% 23% 10% 2	2100
	11th to 20th	Day	51% 5% 10% 21% 12% 2	2058
	21st to end	Day	53% 4 10% 20% 11% 3	1730
March	1st to 10th	Day	52% 3 5% 19% 16% 5%	4500
	11th to 20th	Day	41% 4 9% 27% 18% 1	4878
	21st to end	Day	46% 5% 12% 23% 12% 1	5600
April	1st to 10th	Day	43% 7% 11% 22% 16% 1	2400
	11th to 20th	Day	45% 5% 8% 23% 16% 3	2374
	21st to end	Day	46% 6% 10% 24% 12% 2	2560
May	1st to 10th	Day	53% 8% 12% 16% 10%	5897
	11th to 20th	Day	50% 5% 11% 22% 11%	5865
	21st to end	Day	44% 7% 14% 17% 16% 1	6447
June	1st to 10th	Day	37% 6% 11% 25% 17% 3	2680
	11th to 20th	Day	34% 9% 13% 24% 19% 2	2800
	21st to end	Day	33% 9% 14% 21% 19% 4	2800
July	1st to 10th	Day	38% 5% 13% 24% 20% 2	6291
	11th to 20th	Day	38% 6% 16% 28% 11% 1	6249
	21st to end	Day	49% 6% 16% 18% 10% 1	6240
August	1st to 10th	Day	30% 7% 14% 34% 14% 1	4221
	11th to 20th	Day	36% 6% 13% 29% 15% 1	3991
	21st to end	Day	25% 6% 12% 37% 17% 4	4311
September	1st to 10th	Day	36% 6% 11% 23% 19% 5%	2335
	11th to 20th	Day	32% 7% 11% 24% 22% 3	2200
	21st to end	Day	37% 5% 9% 22% 24% 3	2200
October	1st to 10th	Day	21% 4 5% 28% 39% 3	3590
	11th to 20th	Day	26% 5% 9% 26% 31% 3	3399
	21st to end	Day	33% 3 8% 29% 22% 5%	3180
November	1st to 10th	Day	35% 3 10% 28% 20% 4	1852
	11th to 20th	Day	44% 4 7% 24% 17% 4	1890
	21st to end	Day	49% 3 8% 23% 16% 1	1890
December	1st to 10th	Day	47% 2 10% 26% 14%	3020
	11th to 20th	Day	59% 3 9% 18% 9% 1	3460
	21st to end	Day	63% 4 13% 14% 6%	4132
January	1st to 10th	Night	56% 4 10% 21% 9%	8233
	11th to 20th	Night	56% 3 6% 17% 16% 3	8184
	21st to end	Night	52% 3 10% 21% 13% 1	8302
February	1st to 10th	Night	56% 5% 10% 19% 8% 1	2520
	11th to 20th	Night	52% 4 8% 21% 13% 1	2459
	21st to end	Night	54% 4 10% 17% 12% 3	2076
March	1st to 10th	Night	53% 3 6% 22% 13% 4	5398
	11th to 20th	Night	38% 4 9% 26% 21% 2	5082
	21st to end	Night	49% 4 9% 24% 13% 1	5361
April	1st to 10th	Night	41% 6% 11% 23% 16% 3	2000
	11th to 20th	Night	42% 4 9% 20% 18% 5%	1975
	21st to end	Night	45% 6% 9% 23% 13% 3	1840
May	1st to 10th	Night	53% 6% 11% 19% 9% 1	4060
	11th to 20th	Night	48% 7% 11% 23% 10% 1	4033
	21st to end	Night	42% 7% 14% 21% 13% 2	4429
June	1st to 10th	Night	32% 7% 11% 27% 20% 4	1714
	11th to 20th	Night	29% 8% 14% 23% 21% 5%	1600
	21st to end	Night	26% 8% 18% 23% 19% 6%	1600
July	1st to 10th	Night	36% 6% 10% 26% 20% 2	3580
	11th to 20th	Night	35% 6% 17% 28% 13% 2	3603
	21st to end	Night	45% 7% 15% 20% 13% 1	4297
August	1st to 10th	Night	26% 6% 15% 37% 14% 1	2904
	11th to 20th	Night	31% 7% 13% 30% 17% 1	3121
	21st to end	Night	18% 4 15% 35% 23% 4	3586
September	1st to 10th	Night	32% 5% 11% 23% 22% 6%	2045
	11th to 20th	Night	30% 6% 10% 26% 24% 5%	2200
	21st to end	Night	35% 4 8% 23% 26% 5%	2200
October	1st to 10th	Night	20% 4 6% 19% 47% 4	3590
	11th to 20th	Night	25% 5% 6% 23% 37% 4	3732
	21st to end	Night	32% 3 7% 22% 31% 6%	4610
November	1st to 10th	Night	37% 3 9% 24% 23% 4	2666
	11th to 20th	Night	41% 4 7% 22% 21% 5%	2730
	21st to end	Night	49% 4 9% 22% 16% 1	2730
December	1st to 10th	Night	50% 3 10% 22% 14%	4380
	11th to 20th	Night	51% 4 12% 21% 12% 1	4954
	21st to end	Night	68% 4 9% 14% 5%	7080

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% 18% 34% 18% 6%	330
	11th to 20th	Day	25% 24% 33% 14% 4	330
	21st to end	Day	23% 23% 37% 15% 2	363
February	1st to 10th	Day	22% 18% 41% 15% 4	330
	11th to 20th	Day	30% 22% 35% 10% 3 1	330
	21st to end	Day	29% 16% 38% 12% 4	273
March	1st to 10th	Day	23% 23% 33% 18% 3	306
	11th to 20th	Day	23% 16% 40% 14% 5% 2	450
	21st to end	Day	26% 18% 32% 17% 6% 1	550
April	1st to 10th	Day	21% 17% 30% 22% 10% 1	500
	11th to 20th	Day	22% 17% 24% 24% 10% 3	492
	21st to end	Day	18% 15% 34% 21% 9% 2	500
May	1st to 10th	Day	21% 15% 29% 23% 7% 5%	503
	11th to 20th	Day	19% 10% 25% 26% 14% 6%	527
	21st to end	Day	12% 7% 26% 25% 19% 11%	573
June	1st to 10th	Day	12% 7% 22% 28% 20% 10%	610
	11th to 20th	Day	6% 6% 19% 34% 24% 11%	730
	21st to end	Day	9% 5% 22% 30% 22% 12%	730
July	1st to 10th	Day	13% 3 16% 24% 24% 20%	721
	11th to 20th	Day	8% 4 17% 33% 26% 13%	708
	21st to end	Day	11% 2 14% 30% 29% 14%	576
August	1st to 10th	Day	11% 3 13% 28% 27% 18%	526
	11th to 20th	Day	12% 3 16% 30% 26% 12%	519
	21st to end	Day	9% 3 11% 27% 33% 17%	583
September	1st to 10th	Day	10% 3 16% 26% 33% 12%	530
	11th to 20th	Day	10% 2 14% 25% 34% 15%	530
	21st to end	Day	16% 7% 17% 27% 23% 10%	530
October	1st to 10th	Day	11% 5% 19% 34% 23% 8%	530
	11th to 20th	Day	13% 14% 28% 27% 13% 5%	520
	21st to end	Day	26% 15% 29% 23% 6% 1	363
November	1st to 10th	Day	15% 11% 35% 26% 10% 3	330
	11th to 20th	Day	23% 18% 29% 22% 6% 2	330
	21st to end	Day	25% 12% 35% 21% 7%	330
December	1st to 10th	Day	22% 22% 31% 19% 5% 1	330
	11th to 20th	Day	22% 16% 37% 18% 5% 1	330
	21st to end	Day	31% 19% 31% 15% 3	363
January	1st to 10th	Night	21% 16% 31% 27% 4	1050
	11th to 20th	Night	26% 15% 34% 21% 3	1019
	21st to end	Night	21% 15% 38% 24% 2	924
February	1st to 10th	Night	27% 10% 34% 26% 2	840
	11th to 20th	Night	24% 14% 37% 23% 2	823
	21st to end	Night	27% 12% 39% 21% 2	692
March	1st to 10th	Night	24% 13% 32% 27% 4	809
	11th to 20th	Night	23% 11% 35% 25% 7%	800
	21st to end	Night	23% 12% 29% 29% 6%	838
April	1st to 10th	Night	18% 10% 35% 28% 9%	600
	11th to 20th	Night	18% 11% 29% 30% 11% 1	593
	21st to end	Night	18% 6% 34% 32% 8% 1	600
May	1st to 10th	Night	19% 7% 32% 28% 14% 1	600
	11th to 20th	Night	16% 6% 18% 39% 18% 3	591
	21st to end	Night	9% 3 20% 38% 25% 5%	650
June	1st to 10th	Night	11% 2 20% 38% 26% 3	600
	11th to 20th	Night	8% 4 15% 40% 30% 3	600
	21st to end	Night	5% 1 17% 42% 32% 4	600
July	1st to 10th	Night	11% 2 10% 29% 39% 9%	585
	11th to 20th	Night	8% 3 10% 34% 39% 7%	582
	21st to end	Night	9% 2 11% 37% 35% 6%	657
August	1st to 10th	Night	9% 2 9% 32% 42% 5%	597
	11th to 20th	Night	7% 1 10% 39% 36% 6%	594
	21st to end	Night	7% 1 8% 35% 45% 5%	660
September	1st to 10th	Night	12% 2 10% 34% 37% 4	645
	11th to 20th	Night	9% 3 14% 30% 38% 5%	800
	21st to end	Night	14% 5% 19% 31% 28% 3	800
October	1st to 10th	Night	11% 4 17% 35% 28% 4	800
	11th to 20th	Night	15% 7% 25% 34% 17% 2	800
	21st to end	Night	22% 7% 31% 27% 12%	880
November	1st to 10th	Night	15% 8% 28% 33% 15% 1	820
	11th to 20th	Night	17% 12% 33% 28% 10%	840
	21st to end	Night	24% 11% 25% 30% 10%	840
December	1st to 10th	Night	26% 10% 32% 28% 5%	840
	11th to 20th	Night	24% 9% 34% 25% 6% 1	840
	21st to end	Night	29% 14% 31% 22% 4	1124

Page generated at 2026-02-28 01:40:22. Version ac07

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