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 2024-07-03.

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 4 4 6% 7% 38%	89483
	Night	15% 9% 3 6% 4 4 4 3 5% 7% 40%	89693
Transparency	Day	44% 6% 11% 22% 15% 2	89247
	Night	44% 6% 10% 22% 15% 3	89534
Seeing	Day	17% 10% 25% 24% 16% 7%	14863
	Night	18% 8% 26% 30% 17% 2	24674

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	14% 15% 5% 9% 5% 4 4 3 5% 6% 29%	2527
	11th to 20th	Day	18% 10% 4 12% 6% 6% 5% 2 4 4 28%	2564
	21st to end	Day	27% 16% 6% 7% 4 3 3 3 4 5% 22%	3165
February	1st to 10th	Day	17% 12% 4 9% 5% 4 3 3 4 7% 32%	1900
	11th to 20th	Day	17% 8% 4 7% 4 5% 4 4 5% 6% 36%	1848
	21st to end	Day	18% 11% 4 8% 6% 3 4 4 4 6% 30%	1570
March	1st to 10th	Day	24% 14% 3 7% 4 3 3 2 3 5% 31%	3120
	11th to 20th	Day	13% 7% 2 6% 4 3 4 3 5% 8% 44%	3406
	21st to end	Day	13% 8% 3 7% 5% 4 5% 4 6% 7% 37%	3908
April	1st to 10th	Day	14% 6% 3 7% 5% 5% 4 4 7% 7% 39%	2280
	11th to 20th	Day	16% 8% 3 7% 5% 5% 4 3 5% 6% 40%	2254
	21st to end	Day	16% 7% 2 6% 5% 4 5% 4 6% 7% 37%	2432
May	1st to 10th	Day	20% 8% 3 6% 5% 5% 5% 5% 7% 8% 29%	4082
	11th to 20th	Day	18% 8% 3 6% 4 4 4 3 5% 7% 39%	4081
	21st to end	Day	10% 6% 3 7% 6% 5% 6% 4 7% 8% 37%	4476
June	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 6% 8% 44%	2546
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 7% 10% 46%	2660
	21st to end	Day	7% 5% 2 5% 5% 5% 5% 5% 8% 11% 43%	2660
July	1st to 10th	Day	12% 7% 2 6% 5% 5% 6% 5% 7% 10% 36%	2549
	11th to 20th	Day	8% 6% 2 5% 5% 5% 5% 5% 8% 10% 43%	2512
	21st to end	Day	9% 5% 3 5% 5% 4 5% 5% 7% 10% 42%	2547
August	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 5% 8% 11% 42%	2327
	11th to 20th	Day	8% 6% 3 7% 5% 5% 5% 5% 7% 8% 41%	2186
	21st to end	Day	7% 6% 2 6% 4 4 6% 4 5% 9% 47%	2376
September	1st to 10th	Day	14% 6% 2 7% 3 3 4 4 6% 6% 46%	2102
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 7% 48%	1980
	21st to end	Day	12% 5% 1 6% 4 3 4 3 5% 6% 50%	1980
October	1st to 10th	Day	11% 4 2 5% 4 3 4 3 4 7% 54%	1980
	11th to 20th	Day	13% 6% 2 6% 4 4 3 4 5% 7% 46%	1897
	21st to end	Day	17% 8% 2 6% 4 4 4 4 5% 6% 41%	1782
November	1st to 10th	Day	11% 6% 1 6% 3 2 3 3 5% 6% 53%	1672
	11th to 20th	Day	15% 10% 3 6% 3 3 3 3 5% 6% 42%	1710
	21st to end	Day	18% 9% 3 6% 3 4 3 3 5% 5% 40%	1710
December	1st to 10th	Day	21% 13% 3 7% 5% 3 4 2 4 5% 33%	1710
	11th to 20th	Day	14% 12% 5% 10% 6% 5% 3 3 4 6% 32%	2153
	21st to end	Day	21% 17% 3 8% 4 5% 5% 3 5% 6% 23%	2831
January	1st to 10th	Night	17% 15% 4 9% 5% 5% 4 4 5% 5% 27%	4428
	11th to 20th	Night	16% 14% 5% 11% 7% 4 4 3 4 4 28%	4400
	21st to end	Night	25% 15% 4 7% 4 3 3 3 4 6% 27%	4489
February	1st to 10th	Night	22% 11% 4 8% 5% 4 4 3 5% 5% 29%	2280
	11th to 20th	Night	18% 9% 4 8% 5% 4 3 3 4 5% 37%	2218
	21st to end	Night	22% 12% 3 7% 5% 4 3 3 4 5% 31%	1884
March	1st to 10th	Night	24% 12% 3 6% 4 4 3 2 4 4 33%	3733
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 5% 5% 49%	3554
	21st to end	Night	15% 8% 3 7% 4 4 4 3 4 5% 41%	3739
April	1st to 10th	Night	12% 7% 2 7% 4 4 5% 3 5% 9% 42%	1900
	11th to 20th	Night	15% 8% 2 6% 5% 3 3 3 5% 6% 42%	1875
	21st to end	Night	15% 7% 3 6% 5% 4 4 3 5% 7% 40%	1748
May	1st to 10th	Night	18% 9% 3 9% 6% 5% 4 4 6% 7% 30%	2813
	11th to 20th	Night	16% 6% 2 6% 4 3 5% 3 5% 8% 42%	2812
	21st to end	Night	9% 5% 2 6% 5% 5% 6% 5% 7% 9% 42%	3079
June	1st to 10th	Night	10% 4 2 4 4 4 5% 4 5% 9% 48%	1629
	11th to 20th	Night	6% 3 2 5% 3 4 5% 4 6% 10% 51%	1520
	21st to end	Night	5% 3 1 3 5% 4 5% 5% 7% 12% 50%	1520
July	1st to 10th	Night	9% 5% 2 7% 5% 4 4 4 6% 9% 45%	1456
	11th to 20th	Night	6% 4 2 4 4 4 4 3 7% 10% 51%	1445
	21st to end	Night	8% 4 2 6% 4 5% 4 4 6% 9% 48%	1771
August	1st to 10th	Night	7% 4 2 5% 3 4 5% 4 6% 10% 50%	1611
	11th to 20th	Night	6% 4 2 5% 5% 4 6% 6% 7% 10% 45%	1712
	21st to end	Night	6% 4 1 4 3 3 3 3 7% 10% 55%	1980
September	1st to 10th	Night	12% 4 2 5% 4 3 4 3 5% 8% 50%	1840
	11th to 20th	Night	9% 5% 2 6% 3 3 4 3 5% 8% 52%	1980
	21st to end	Night	11% 5% 2 6% 3 4 3 3 4 7% 53%	1980
October	1st to 10th	Night	9% 5% 2 5% 3 3 4 3 4 7% 57%	1980
	11th to 20th	Night	14% 6% 2 6% 4 3 4 3 4 6% 48%	2056
	21st to end	Night	18% 7% 2 6% 3 4 4 3 4 5% 45%	2574
November	1st to 10th	Night	12% 7% 2 5% 4 4 4 2 4 5% 51%	2406
	11th to 20th	Night	14% 8% 3 6% 4 4 3 3 4 7% 44%	2470
	21st to end	Night	18% 10% 3 5% 5% 4 3 3 4 6% 40%	2470
December	1st to 10th	Night	21% 11% 3 6% 4 4 4 3 4 5% 35%	2470
	11th to 20th	Night	19% 11% 4 6% 5% 4 4 3 4 5% 35%	3042
	21st to end	Night	20% 16% 4 9% 6% 5% 5% 4 3 5% 22%	4829

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% 5% 11% 19% 9% 1	2528
	11th to 20th	Day	59% 4 10% 18% 8% 1	2564
	21st to end	Day	64% 4 8% 19% 4 1	3165
February	1st to 10th	Day	53% 4 9% 22% 11% 2	1900
	11th to 20th	Day	49% 5% 10% 22% 12% 2	1858
	21st to end	Day	54% 4 10% 19% 10% 3	1570
March	1st to 10th	Day	57% 3 6% 19% 10% 4	3120
	11th to 20th	Day	39% 5% 10% 27% 17% 2	3406
	21st to end	Day	44% 7% 13% 23% 13% 1	3908
April	1st to 10th	Day	42% 7% 11% 23% 16% 1	2280
	11th to 20th	Day	46% 5% 8% 22% 17% 3	2254
	21st to end	Day	45% 6% 10% 24% 12% 3	2432
May	1st to 10th	Day	50% 9% 13% 18% 9% 1	4120
	11th to 20th	Day	47% 7% 10% 23% 13% 1	4085
	21st to end	Day	41% 9% 12% 16% 20% 1	4489
June	1st to 10th	Day	36% 7% 11% 26% 17% 3	2546
	11th to 20th	Day	32% 9% 13% 24% 19% 2	2660
	21st to end	Day	33% 10% 14% 20% 18% 4	2660
July	1st to 10th	Day	41% 9% 13% 20% 14% 3	2480
	11th to 20th	Day	34% 9% 15% 23% 15% 4	2437
	21st to end	Day	35% 9% 15% 24% 14% 2	2405
August	1st to 10th	Day	34% 10% 15% 24% 16% 2	2314
	11th to 20th	Day	37% 8% 13% 25% 15% 2	2186
	21st to end	Day	32% 8% 13% 24% 17% 6%	2376
September	1st to 10th	Day	38% 6% 11% 23% 17% 5%	2102
	11th to 20th	Day	33% 7% 11% 23% 21% 3	1980
	21st to end	Day	34% 5% 9% 24% 25% 3	1980
October	1st to 10th	Day	32% 5% 9% 25% 25% 4	1980
	11th to 20th	Day	37% 5% 7% 25% 22% 4	1897
	21st to end	Day	43% 5% 9% 25% 14% 3	1782
November	1st to 10th	Day	33% 4 10% 28% 20% 5%	1672
	11th to 20th	Day	43% 4 7% 23% 18% 5%	1710
	21st to end	Day	46% 3 8% 24% 17% 1	1710
December	1st to 10th	Day	55% 3 11% 20% 10% 1	1710
	11th to 20th	Day	55% 4 8% 20% 12% 1	2150
	21st to end	Day	61% 5% 11% 15% 7%	2831
January	1st to 10th	Night	56% 6% 11% 16% 11% 1	4428
	11th to 20th	Night	61% 4 8% 17% 9% 1	4400
	21st to end	Night	60% 5% 8% 18% 10% 1	4489
February	1st to 10th	Night	56% 5% 10% 19% 8% 1	2280
	11th to 20th	Night	51% 4 9% 21% 14% 1	2219
	21st to end	Night	56% 5% 10% 15% 11% 3	1884
March	1st to 10th	Night	56% 3 7% 21% 11% 2	3733
	11th to 20th	Night	37% 5% 10% 26% 19% 3	3554
	21st to end	Night	44% 5% 10% 25% 14% 1	3739
April	1st to 10th	Night	40% 6% 11% 23% 17% 3	1900
	11th to 20th	Night	43% 4 9% 19% 19% 6%	1875
	21st to end	Night	45% 6% 9% 23% 13% 3	1748
May	1st to 10th	Night	52% 8% 11% 20% 8% 2	2840
	11th to 20th	Night	40% 8% 13% 26% 11% 1	2813
	21st to end	Night	34% 10% 13% 23% 17% 3	3087
June	1st to 10th	Night	31% 7% 11% 27% 19% 4	1629
	11th to 20th	Night	28% 7% 15% 23% 22% 5%	1520
	21st to end	Night	26% 8% 18% 23% 19% 7%	1520
July	1st to 10th	Night	35% 9% 12% 23% 17% 4	1416
	11th to 20th	Night	28% 7% 15% 26% 19% 5%	1397
	21st to end	Night	32% 9% 13% 29% 16% 2	1672
August	1st to 10th	Night	28% 8% 17% 27% 17% 3	1600
	11th to 20th	Night	30% 11% 14% 26% 17% 2	1712
	21st to end	Night	24% 6% 18% 27% 20% 5%	1980
September	1st to 10th	Night	33% 6% 12% 23% 20% 6%	1840
	11th to 20th	Night	31% 6% 10% 26% 23% 5%	1980
	21st to end	Night	32% 5% 7% 25% 26% 5%	1980
October	1st to 10th	Night	28% 5% 11% 24% 27% 5%	1980
	11th to 20th	Night	37% 6% 7% 23% 23% 4	2056
	21st to end	Night	42% 4 8% 22% 20% 4	2574
November	1st to 10th	Night	37% 3 9% 23% 23% 5%	2406
	11th to 20th	Night	41% 4 7% 21% 21% 5%	2470
	21st to end	Night	47% 4 9% 22% 17% 1	2470
December	1st to 10th	Night	51% 5% 11% 20% 12% 1	2470
	11th to 20th	Night	51% 5% 9% 20% 13% 2	3044
	21st to end	Night	65% 5% 10% 13% 7% 1	4829

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% 17% 33% 19% 6%	270
	11th to 20th	Day	26% 23% 33% 14% 4	270
	21st to end	Day	24% 22% 36% 15% 3	297
February	1st to 10th	Day	23% 19% 41% 14% 3	270
	11th to 20th	Day	28% 22% 36% 10% 3 1	270
	21st to end	Day	32% 15% 38% 12% 4	225
March	1st to 10th	Day	23% 23% 34% 17% 3	270
	11th to 20th	Day	23% 16% 40% 15% 6% 1	412
	21st to end	Day	25% 17% 32% 18% 7% 1	506
April	1st to 10th	Day	20% 17% 29% 23% 10% 1	460
	11th to 20th	Day	23% 16% 24% 24% 10% 3	452
	21st to end	Day	19% 15% 35% 21% 9% 2	460
May	1st to 10th	Day	20% 16% 30% 23% 7% 5%	463
	11th to 20th	Day	20% 10% 23% 26% 15% 6%	487
	21st to end	Day	12% 6% 25% 26% 20% 12%	529
June	1st to 10th	Day	11% 7% 22% 28% 21% 11%	566
	11th to 20th	Day	6% 5% 19% 35% 24% 11%	680
	21st to end	Day	10% 5% 23% 30% 21% 11%	680
July	1st to 10th	Day	14% 2 16% 23% 24% 22%	632
	11th to 20th	Day	8% 4 16% 32% 26% 14%	610
	21st to end	Day	11% 2 14% 29% 30% 15%	488
August	1st to 10th	Day	12% 3 12% 28% 28% 17%	446
	11th to 20th	Day	13% 3 16% 29% 26% 13%	439
	21st to end	Day	10% 3 11% 26% 33% 17%	495
September	1st to 10th	Day	11% 3 15% 26% 34% 10%	450
	11th to 20th	Day	10% 3 15% 25% 34% 13%	450
	21st to end	Day	14% 7% 18% 25% 25% 11%	450
October	1st to 10th	Day	11% 4 21% 36% 21% 7%	450
	11th to 20th	Day	14% 14% 31% 26% 11% 3	442
	21st to end	Day	25% 15% 29% 23% 7%	297
November	1st to 10th	Day	14% 10% 33% 28% 12% 4	270
	11th to 20th	Day	22% 16% 30% 24% 6% 2	270
	21st to end	Day	23% 11% 35% 23% 8%	270
December	1st to 10th	Day	23% 22% 27% 20% 7% 1	270
	11th to 20th	Day	22% 16% 36% 19% 6% 1	270
	21st to end	Day	30% 20% 31% 15% 3	297
January	1st to 10th	Night	21% 17% 31% 27% 4	950
	11th to 20th	Night	27% 15% 33% 22% 4	923
	21st to end	Night	22% 15% 36% 25% 2	836
February	1st to 10th	Night	28% 10% 34% 26% 3	760
	11th to 20th	Night	22% 14% 38% 24% 2	743
	21st to end	Night	28% 13% 39% 19% 2	628
March	1st to 10th	Night	24% 13% 33% 26% 4	760
	11th to 20th	Night	23% 11% 36% 24% 7%	760
	21st to end	Night	23% 12% 29% 30% 7%	796
April	1st to 10th	Night	16% 10% 35% 29% 9%	570
	11th to 20th	Night	18% 10% 29% 29% 12% 1	563
	21st to end	Night	19% 6% 35% 31% 8% 1	570
May	1st to 10th	Night	17% 7% 32% 28% 15% 1	570
	11th to 20th	Night	16% 6% 17% 39% 19% 4	561
	21st to end	Night	8% 3 19% 39% 26% 6%	617
June	1st to 10th	Night	11% 2 19% 38% 26% 3	570
	11th to 20th	Night	7% 4 15% 42% 29% 3	570
	21st to end	Night	5% 1 18% 42% 30% 4	570
July	1st to 10th	Night	11% 2 10% 28% 39% 10%	531
	11th to 20th	Night	6% 3 9% 34% 41% 7%	522
	21st to end	Night	9% 2 11% 37% 35% 6%	591
August	1st to 10th	Night	9% 1 8% 34% 43% 5%	537
	11th to 20th	Night	6% 1 11% 39% 36% 7%	534
	21st to end	Night	7% 1 8% 34% 45% 5%	594
September	1st to 10th	Night	13% 1 10% 34% 37% 5%	580
	11th to 20th	Night	10% 4 15% 29% 37% 5%	720
	21st to end	Night	12% 5% 21% 30% 29% 3	720
October	1st to 10th	Night	11% 4 19% 35% 26% 5%	720
	11th to 20th	Night	16% 7% 26% 33% 16% 2	720
	21st to end	Night	22% 7% 31% 28% 12%	792
November	1st to 10th	Night	14% 8% 27% 33% 16% 1	740
	11th to 20th	Night	17% 11% 33% 28% 11%	760
	21st to end	Night	23% 10% 25% 31% 11%	760
December	1st to 10th	Night	26% 10% 32% 27% 5%	760
	11th to 20th	Night	24% 9% 34% 26% 7% 1	760
	21st to end	Night	29% 14% 31% 22% 4	1016

Page generated at 2024-06-29 22:08:56. Version ac07

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