Shelbyville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shelbyville clear sky chart from 2005-11-06 to 2025-01-07.

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% 9% 3 7% 4 4 4 4 6% 8% 37%	104872
	Night	15% 10% 3 7% 4 4 4 3 5% 6% 37%	104203
Transparency	Day	44% 6% 12% 23% 14% 2	108542
	Night	45% 6% 11% 22% 15% 2	108674
Seeing	Day	16% 9% 25% 25% 18% 8%	15709
	Night	18% 7% 27% 31% 15% 2	25589

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% 16% 8% 10% 5% 5% 4 3 5% 6% 23%	2575
	11th to 20th	Day	17% 13% 6% 14% 5% 8% 7% 4 4 3 19%	2530
	21st to end	Day	27% 19% 10% 8% 4 4 3 2 3 5% 16%	2999
February	1st to 10th	Day	18% 15% 5% 9% 6% 5% 3 3 4 6% 26%	1885
	11th to 20th	Day	16% 12% 3 10% 6% 5% 4 3 6% 7% 29%	1848
	21st to end	Day	18% 13% 5% 10% 5% 3 4 3 4 5% 31%	1570
March	1st to 10th	Day	22% 16% 4 7% 5% 4 3 2 4 5% 27%	3120
	11th to 20th	Day	14% 8% 3 6% 4 4 4 4 6% 6% 42%	3400
	21st to end	Day	15% 10% 4 8% 5% 4 5% 4 6% 7% 31%	3931
April	1st to 10th	Day	14% 12% 4 8% 5% 4 4 3 5% 7% 34%	2280
	11th to 20th	Day	17% 8% 3 6% 5% 4 4 4 5% 6% 38%	2254
	21st to end	Day	20% 7% 3 7% 5% 4 4 4 6% 7% 34%	2456
May	1st to 10th	Day	19% 9% 4 8% 5% 5% 5% 4 6% 8% 29%	4082
	11th to 20th	Day	20% 7% 2 6% 4 4 4 3 6% 6% 38%	4081
	21st to end	Day	10% 6% 2 8% 5% 4 5% 5% 7% 10% 37%	4476
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 6% 8% 42%	2655
	11th to 20th	Day	9% 5% 2 5% 4 5% 4 4 7% 8% 46%	2660
	21st to end	Day	9% 6% 2 6% 4 5% 5% 5% 7% 9% 41%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 7% 11% 38%	4440
	11th to 20th	Day	7% 4 2 5% 3 4 4 5% 8% 11% 48%	4440
	21st to end	Day	10% 7% 2 7% 5% 6% 6% 5% 7% 10% 34%	4592
August	1st to 10th	Day	7% 5% 2 5% 4 4 5% 4 8% 10% 46%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 4 8% 11% 41%	3898
	21st to end	Day	5% 4 2 5% 4 4 4 4 5% 9% 54%	4180
September	1st to 10th	Day	12% 5% 2 5% 5% 4 5% 4 6% 6% 47%	2228
	11th to 20th	Day	10% 5% 1 6% 4 4 4 3 6% 8% 48%	2090
	21st to end	Day	14% 6% 2 6% 4 3 4 2 5% 7% 48%	2090
October	1st to 10th	Day	12% 5% 1 6% 4 4 4 3 4 7% 50%	2090
	11th to 20th	Day	13% 7% 2 6% 3 4 5% 4 5% 7% 46%	1957
	21st to end	Day	20% 9% 3 7% 4 4 4 3 5% 6% 36%	1881
November	1st to 10th	Day	8% 7% 2 6% 3 4 5% 3 4 7% 51%	1762
	11th to 20th	Day	15% 12% 3 7% 4 3 4 4 6% 6% 36%	1800
	21st to end	Day	19% 13% 4 7% 4 3 3 4 4 6% 34%	1800
December	1st to 10th	Day	16% 12% 4 7% 4 3 3 2 4 5% 40%	2930
	11th to 20th	Day	16% 15% 5% 11% 5% 5% 5% 3 4 5% 25%	3146
	21st to end	Day	25% 18% 6% 9% 5% 5% 4 3 5% 5% 15%	3982
January	1st to 10th	Night	18% 17% 6% 11% 5% 4 3 3 5% 4 24%	4513
	11th to 20th	Night	15% 19% 6% 13% 6% 5% 4 3 4 5% 21%	4440
	21st to end	Night	26% 17% 6% 8% 4 4 3 2 3 4 23%	4659
February	1st to 10th	Night	20% 12% 4 9% 6% 4 4 3 5% 4 28%	2291
	11th to 20th	Night	14% 11% 4 9% 5% 5% 5% 3 5% 6% 32%	2218
	21st to end	Night	21% 11% 5% 7% 5% 4 3 4 5% 5% 30%	1884
March	1st to 10th	Night	21% 14% 3 6% 4 4 3 3 4 5% 34%	3733
	11th to 20th	Night	13% 7% 2 7% 4 4 4 3 5% 7% 46%	3558
	21st to end	Night	17% 8% 3 6% 5% 4 3 3 5% 6% 39%	3727
April	1st to 10th	Night	14% 9% 2 6% 5% 4 4 4 6% 7% 38%	1900
	11th to 20th	Night	15% 8% 3 6% 5% 4 3 4 5% 7% 40%	1875
	21st to end	Night	17% 8% 2 6% 5% 4 4 4 6% 7% 36%	1722
May	1st to 10th	Night	18% 10% 3 8% 5% 5% 5% 4 6% 7% 28%	2813
	11th to 20th	Night	18% 8% 2 6% 4 3 4 3 5% 7% 41%	2812
	21st to end	Night	10% 5% 2 6% 5% 4 5% 4 7% 9% 44%	3079
June	1st to 10th	Night	8% 6% 2 7% 5% 4 4 4 6% 8% 47%	1520
	11th to 20th	Night	9% 6% 2 5% 4 4 4 5% 7% 9% 47%	1520
	21st to end	Night	7% 4 1 5% 4 4 5% 4 7% 11% 48%	1520
July	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 5% 7% 48%	2530
	11th to 20th	Night	6% 3 1 4 4 3 4 4 7% 8% 55%	2530
	21st to end	Night	10% 7% 2 7% 4 4 5% 4 7% 10% 39%	2960
August	1st to 10th	Night	8% 5% 2 7% 4 4 4 3 5% 8% 50%	2825
	11th to 20th	Night	7% 5% 2 7% 4 5% 6% 4 6% 8% 46%	2928
	21st to end	Night	4 4 2 5% 4 4 4 4 6% 8% 56%	3476
September	1st to 10th	Night	10% 5% 2 6% 3 5% 5% 3 4 8% 49%	1931
	11th to 20th	Night	7% 4 1 5% 3 3 4 4 5% 8% 55%	2090
	21st to end	Night	13% 6% 2 6% 4 4 3 3 4 7% 49%	2090
October	1st to 10th	Night	9% 4 2 5% 4 3 3 3 4 6% 56%	2090
	11th to 20th	Night	15% 7% 2 6% 3 4 4 3 5% 5% 46%	2218
	21st to end	Night	18% 7% 2 7% 4 3 4 3 5% 7% 40%	2717
November	1st to 10th	Night	12% 7% 3 5% 4 4 3 3 4 6% 48%	2536
	11th to 20th	Night	15% 9% 3 6% 4 4 4 4 5% 7% 40%	2600
	21st to end	Night	19% 12% 4 8% 5% 4 4 3 4 6% 32%	2600
December	1st to 10th	Night	17% 11% 3 7% 4 4 3 3 4 5% 39%	4250
	11th to 20th	Night	19% 14% 5% 10% 5% 4 4 3 4 5% 27%	5052
	21st to end	Night	27% 18% 5% 10% 5% 4 4 3 4 4 17%	6996

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	61% 5% 8% 19% 7%	2576
	11th to 20th	Day	68% 4 12% 13% 4	2530
	21st to end	Day	73% 3 7% 14% 3 1	2999
February	1st to 10th	Day	59% 4 10% 17% 10% 1	1885
	11th to 20th	Day	53% 5% 10% 21% 10% 1	1858
	21st to end	Day	54% 5% 9% 21% 8% 2	1570
March	1st to 10th	Day	60% 4 8% 17% 10% 1	3120
	11th to 20th	Day	41% 5% 12% 27% 14% 1	3400
	21st to end	Day	51% 6% 12% 23% 7%	3931
April	1st to 10th	Day	48% 6% 11% 20% 13% 1	2280
	11th to 20th	Day	46% 5% 12% 22% 12% 3	2254
	21st to end	Day	49% 5% 11% 21% 11% 2	2456
May	1st to 10th	Day	50% 9% 12% 23% 6%	4120
	11th to 20th	Day	46% 6% 12% 25% 11%	4085
	21st to end	Day	38% 9% 14% 20% 17% 2	4489
June	1st to 10th	Day	39% 7% 12% 24% 16% 3	2655
	11th to 20th	Day	34% 8% 11% 25% 20% 2	2660
	21st to end	Day	37% 9% 15% 20% 15% 4	2660
July	1st to 10th	Day	39% 7% 13% 21% 18% 2	4371
	11th to 20th	Day	27% 8% 15% 30% 18% 1	4365
	21st to end	Day	41% 10% 15% 16% 14% 3	4447
August	1st to 10th	Day	29% 9% 17% 30% 13% 1	4091
	11th to 20th	Day	33% 9% 13% 30% 14% 1	3937
	21st to end	Day	26% 7% 14% 31% 18% 4	4179
September	1st to 10th	Day	37% 6% 11% 24% 17% 5%	2228
	11th to 20th	Day	33% 6% 11% 25% 20% 4	2090
	21st to end	Day	37% 5% 10% 24% 24% 2	2090
October	1st to 10th	Day	23% 4 8% 31% 32% 2	3480
	11th to 20th	Day	30% 6% 9% 27% 26% 2	3238
	21st to end	Day	39% 4 10% 23% 22% 2	3081
November	1st to 10th	Day	34% 5% 11% 29% 17% 4	1762
	11th to 20th	Day	47% 4 10% 21% 14% 4	1800
	21st to end	Day	52% 4 8% 23% 12% 1	1800
December	1st to 10th	Day	48% 3 9% 27% 12%	2930
	11th to 20th	Day	61% 5% 8% 17% 8%	3143
	21st to end	Day	69% 5% 10% 10% 5%	3982
January	1st to 10th	Night	61% 5% 12% 14% 7%	4513
	11th to 20th	Night	67% 4 10% 13% 6%	4440
	21st to end	Night	65% 4 8% 15% 7%	4659
February	1st to 10th	Night	59% 4 11% 17% 8% 1	2291
	11th to 20th	Night	51% 5% 12% 19% 12% 1	2219
	21st to end	Night	55% 5% 10% 17% 10% 2	1884
March	1st to 10th	Night	53% 5% 7% 23% 10% 1	3733
	11th to 20th	Night	37% 6% 12% 24% 19% 2	3558
	21st to end	Night	45% 5% 10% 29% 9% 1	3727
April	1st to 10th	Night	44% 5% 11% 25% 13% 2	1900
	11th to 20th	Night	43% 5% 10% 19% 17% 5%	1875
	21st to end	Night	44% 7% 11% 22% 13% 3	1722
May	1st to 10th	Night	54% 9% 10% 19% 7% 2	2840
	11th to 20th	Night	43% 7% 13% 26% 11% 1	2813
	21st to end	Night	33% 10% 16% 23% 15% 4	3087
June	1st to 10th	Night	33% 7% 12% 24% 21% 3	1520
	11th to 20th	Night	32% 8% 11% 23% 22% 4	1520
	21st to end	Night	29% 9% 15% 24% 19% 4	1520
July	1st to 10th	Night	35% 7% 10% 26% 18% 5%	2490
	11th to 20th	Night	24% 8% 15% 30% 21% 2	2482
	21st to end	Night	38% 9% 13% 23% 14% 4	2866
August	1st to 10th	Night	32% 7% 14% 33% 12% 1	2814
	11th to 20th	Night	32% 8% 13% 28% 18% 1	2955
	21st to end	Night	25% 7% 13% 28% 23% 4	3476
September	1st to 10th	Night	32% 7% 11% 23% 19% 7%	1931
	11th to 20th	Night	26% 7% 11% 27% 26% 4	2090
	21st to end	Night	36% 6% 10% 22% 23% 3	2090
October	1st to 10th	Night	20% 4 7% 24% 42% 3	3480
	11th to 20th	Night	28% 4 8% 24% 35% 2	3676
	21st to end	Night	35% 4 8% 24% 25% 4	4467
November	1st to 10th	Night	38% 5% 10% 23% 22% 3	2536
	11th to 20th	Night	43% 4 10% 21% 18% 4	2600
	21st to end	Night	54% 5% 10% 20% 11% 1	2600
December	1st to 10th	Night	48% 4 11% 25% 11%	4250
	11th to 20th	Night	59% 4 10% 16% 10% 1	5054
	21st to end	Night	71% 5% 9% 11% 4	6996

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	20% 17% 34% 23% 5% 1	288
	11th to 20th	Day	26% 16% 31% 21% 6%	270
	21st to end	Day	31% 11% 32% 21% 5%	297
February	1st to 10th	Day	28% 12% 33% 22% 5%	270
	11th to 20th	Day	22% 16% 36% 21% 6%	270
	21st to end	Day	27% 11% 41% 17% 3	225
March	1st to 10th	Day	21% 20% 36% 18% 4	270
	11th to 20th	Day	25% 13% 35% 18% 7% 1	406
	21st to end	Day	28% 14% 31% 19% 7% 1	506
April	1st to 10th	Day	18% 16% 31% 24% 9% 2	460
	11th to 20th	Day	19% 13% 29% 24% 11% 4	452
	21st to end	Day	21% 13% 36% 19% 9% 3	460
May	1st to 10th	Day	20% 13% 29% 24% 10% 4	463
	11th to 20th	Day	21% 7% 25% 25% 16% 7%	487
	21st to end	Day	12% 5% 25% 26% 19% 14%	529
June	1st to 10th	Day	11% 7% 23% 30% 21% 8%	675
	11th to 20th	Day	11% 3 21% 31% 24% 10%	680
	21st to end	Day	12% 4 25% 28% 23% 9%	680
July	1st to 10th	Day	11% 3 13% 27% 24% 21%	671
	11th to 20th	Day	8% 3 15% 32% 28% 15%	668
	21st to end	Day	11% 2 12% 29% 30% 15%	606
August	1st to 10th	Day	8% 3 12% 26% 32% 20%	486
	11th to 20th	Day	14% 3 13% 27% 29% 13%	479
	21st to end	Day	8% 3 11% 23% 36% 19%	539
September	1st to 10th	Day	9% 3 16% 26% 34% 12%	490
	11th to 20th	Day	9% 3 12% 27% 30% 19%	490
	21st to end	Day	16% 6% 21% 21% 23% 12%	490
October	1st to 10th	Day	10% 5% 22% 35% 20% 8%	490
	11th to 20th	Day	11% 13% 32% 27% 14% 3	452
	21st to end	Day	27% 10% 35% 21% 6% 1	330
November	1st to 10th	Day	13% 13% 31% 26% 13% 4	300
	11th to 20th	Day	19% 17% 30% 20% 12% 2	300
	21st to end	Day	23% 11% 35% 25% 6% 1	300
December	1st to 10th	Day	19% 17% 36% 20% 7% 2	300
	11th to 20th	Day	20% 13% 39% 21% 6% 1	300
	21st to end	Day	28% 16% 33% 18% 5%	330
January	1st to 10th	Night	23% 12% 33% 27% 5%	981
	11th to 20th	Night	25% 12% 36% 24% 4	950
	21st to end	Night	23% 11% 34% 28% 4	911
February	1st to 10th	Night	27% 9% 35% 27% 3	760
	11th to 20th	Night	21% 12% 39% 26% 3	743
	21st to end	Night	25% 10% 38% 24% 2	628
March	1st to 10th	Night	21% 11% 35% 27% 6%	760
	11th to 20th	Night	19% 12% 36% 26% 7% 1	760
	21st to end	Night	23% 7% 34% 30% 5% 1	784
April	1st to 10th	Night	17% 10% 38% 28% 8%	570
	11th to 20th	Night	17% 9% 33% 30% 10% 1	563
	21st to end	Night	22% 5% 38% 26% 8% 1	570
May	1st to 10th	Night	21% 6% 32% 30% 10% 1	570
	11th to 20th	Night	17% 6% 23% 32% 19% 2	561
	21st to end	Night	9% 3 23% 36% 27% 2	617
June	1st to 10th	Night	9% 3 21% 43% 22% 1	570
	11th to 20th	Night	10% 4 18% 42% 24% 2	570
	21st to end	Night	8% 1 19% 41% 30% 2	570
July	1st to 10th	Night	9% 2 10% 35% 35% 8%	555
	11th to 20th	Night	7% 3 11% 38% 35% 5%	552
	21st to end	Night	9% 3 12% 40% 33% 4	624
August	1st to 10th	Night	8% 2 11% 37% 38% 4	567
	11th to 20th	Night	7% 2 11% 41% 34% 5%	564
	21st to end	Night	5% 2 11% 35% 42% 5%	627
September	1st to 10th	Night	12% 3 10% 35% 35% 5%	601
	11th to 20th	Night	8% 3 12% 35% 36% 5%	760
	21st to end	Night	15% 5% 18% 34% 25% 3	760
October	1st to 10th	Night	11% 5% 21% 35% 25% 4	760
	11th to 20th	Night	17% 8% 28% 30% 16% 2	760
	21st to end	Night	21% 8% 32% 29% 9%	836
November	1st to 10th	Night	15% 8% 32% 29% 15% 1	780
	11th to 20th	Night	19% 12% 33% 26% 10% 1	800
	21st to end	Night	24% 11% 29% 30% 6% 1	800
December	1st to 10th	Night	22% 10% 38% 24% 6%	800
	11th to 20th	Night	26% 7% 34% 26% 6% 1	905
	21st to end	Night	30% 12% 31% 23% 3	1100

Page generated at 2025-01-04 03:23:59. Version ac07

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