Shelby
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shelby clear sky chart from 2005-11-06 to 2026-01-17.

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	7% 7% 3 7% 4 4 5% 4 6% 8% 46%	136419
	Night	6% 8% 3 7% 5% 5% 5% 4 6% 8% 44%	132589
Transparency	Day	34% 7% 15% 24% 15% 4	131071
	Night	36% 7% 16% 24% 13% 3	128944
Seeing	Day	12% 10% 26% 29% 18% 5%	16953
	Night	11% 9% 32% 34% 13% 1	26350

By Month

Percentage Cloud Cover SW (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	6% 13% 6% 12% 7% 6% 5% 3 5% 7% 29%	3249
	11th to 20th	Day	4 9% 5% 12% 7% 6% 7% 5% 6% 6% 33%	3337
	21st to end	Day	2 7% 4 9% 5% 5% 5% 4 6% 8% 46%	4004
February	1st to 10th	Day	7% 13% 5% 11% 6% 6% 4 5% 7% 8% 28%	1785
	11th to 20th	Day	6% 13% 6% 10% 6% 5% 5% 4 6% 9% 30%	1755
	21st to end	Day	4 10% 5% 11% 6% 5% 5% 5% 6% 6% 36%	1555
March	1st to 10th	Day	5% 8% 3 7% 5% 6% 5% 4 6% 11% 41%	4684
	11th to 20th	Day	3 6% 3 7% 6% 6% 6% 6% 7% 8% 42%	5000
	21st to end	Day	9% 16% 6% 16% 7% 5% 5% 4 5% 6% 21%	5486
April	1st to 10th	Day	7% 12% 4 9% 6% 5% 5% 4 6% 8% 34%	2401
	11th to 20th	Day	11% 13% 3 8% 5% 5% 5% 4 5% 7% 35%	2567
	21st to end	Day	11% 11% 3 7% 5% 4 4 4 6% 7% 38%	2600
May	1st to 10th	Day	13% 9% 3 7% 4 4 4 3 5% 7% 42%	5990
	11th to 20th	Day	11% 8% 3 8% 5% 5% 6% 5% 7% 8% 34%	6419
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 45%	7404
June	1st to 10th	Day	14% 5% 2 5% 6% 4 5% 4 7% 9% 39%	3000
	11th to 20th	Day	15% 6% 2 6% 6% 5% 5% 4 7% 7% 38%	3000
	21st to end	Day	6% 4 1 4 4 4 5% 4 6% 9% 53%	3000
July	1st to 10th	Day	4 2 1 4 3 4 5% 4 6% 8% 59%	6779
	11th to 20th	Day	5% 2 1 3 2 3 3 3 5% 8% 65%	6780
	21st to end	Day	4 3 1 3 2 3 3 3 5% 7% 67%	7168
August	1st to 10th	Day	7% 5% 2 5% 4 4 5% 4 8% 9% 48%	5849
	11th to 20th	Day	4 3 1 4 4 4 5% 4 7% 9% 56%	5798
	21st to end	Day	7% 4 1 4 3 3 3 3 5% 7% 62%	6468
September	1st to 10th	Day	9% 4 2 4 3 3 3 3 5% 7% 57%	2455
	11th to 20th	Day	9% 5% 2 6% 4 4 4 3 5% 6% 51%	2200
	21st to end	Day	10% 5% 2 5% 4 3 3 2 5% 6% 54%	2200
October	1st to 10th	Day	7% 6% 2 6% 4 3 4 4 6% 8% 51%	3350
	11th to 20th	Day	5% 6% 2 6% 4 4 5% 4 7% 7% 51%	3250
	21st to end	Day	6% 8% 3 7% 4 4 5% 4 6% 8% 46%	3205
November	1st to 10th	Day	10% 11% 3 8% 4 5% 5% 4 6% 8% 37%	1703
	11th to 20th	Day	4 8% 3 9% 6% 5% 5% 5% 9% 8% 37%	1680
	21st to end	Day	6% 12% 3 8% 3 4 4 4 6% 10% 39%	1648
December	1st to 10th	Day	2 8% 3 7% 5% 6% 5% 5% 9% 11% 37%	2360
	11th to 20th	Day	3 9% 5% 10% 5% 6% 6% 5% 7% 8% 37%	2715
	21st to end	Day	4 10% 4 9% 5% 5% 5% 5% 7% 6% 39%	3575
January	1st to 10th	Night	5% 11% 4 12% 6% 6% 6% 5% 6% 8% 30%	6916
	11th to 20th	Night	4 10% 4 9% 7% 7% 6% 4 6% 7% 36%	6800
	21st to end	Night	3 9% 4 9% 4 5% 5% 3 5% 8% 44%	6952
February	1st to 10th	Night	8% 11% 5% 11% 6% 4 4 4 6% 7% 33%	2615
	11th to 20th	Night	5% 14% 4 11% 6% 7% 5% 6% 6% 7% 30%	2532
	21st to end	Night	4 11% 4 11% 6% 5% 6% 4 6% 7% 35%	2073
March	1st to 10th	Night	2 7% 3 9% 7% 6% 6% 4 7% 11% 38%	5210
	11th to 20th	Night	3 7% 3 8% 5% 5% 5% 4 7% 9% 45%	5000
	21st to end	Night	11% 16% 6% 12% 5% 5% 5% 4 6% 9% 22%	5489
April	1st to 10th	Night	8% 11% 3 7% 5% 5% 5% 4 6% 8% 37%	1993
	11th to 20th	Night	11% 10% 3 7% 6% 6% 6% 4 7% 7% 36%	1781
	21st to end	Night	10% 8% 3 7% 6% 4 5% 4 6% 6% 40%	1800
May	1st to 10th	Night	13% 10% 2 5% 4 4 5% 4 5% 7% 40%	3990
	11th to 20th	Night	9% 6% 3 7% 6% 6% 7% 5% 8% 9% 34%	3487
	21st to end	Night	11% 6% 2 6% 4 4 4 3 5% 6% 48%	3470
June	1st to 10th	Night	11% 7% 2 5% 3 3 4 4 7% 9% 45%	1400
	11th to 20th	Night	12% 7% 2 5% 4 4 4 4 5% 9% 44%	1400
	21st to end	Night	6% 3 2 4 3 3 5% 3 7% 8% 57%	1400
July	1st to 10th	Night	5% 2 1 4 3 3 3 4 5% 7% 63%	3180
	11th to 20th	Night	6% 2 1 2 2 2 3 2 4 7% 69%	3180
	21st to end	Night	4 3 1 4 3 3 3 3 5% 7% 65%	3666
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 5% 8% 48%	3960
	11th to 20th	Night	4 2 1 4 4 4 5% 4 8% 10% 54%	4051
	21st to end	Night	9% 4 2 4 3 2 3 3 4 6% 60%	4509
September	1st to 10th	Night	9% 4 2 3 2 4 4 3 6% 7% 56%	1942
	11th to 20th	Night	9% 7% 3 5% 3 3 3 3 5% 8% 52%	2200
	21st to end	Night	11% 4 2 5% 3 3 4 3 5% 7% 54%	2200
October	1st to 10th	Night	7% 5% 2 6% 4 3 3 3 5% 6% 56%	3841
	11th to 20th	Night	6% 7% 3 5% 4 4 4 3 5% 7% 52%	3898
	21st to end	Night	4 6% 3 5% 4 4 5% 4 6% 8% 52%	4592
November	1st to 10th	Night	9% 12% 4 7% 4 5% 4 3 6% 8% 37%	2794
	11th to 20th	Night	4 8% 3 7% 5% 5% 6% 6% 6% 9% 41%	2940
	21st to end	Night	5% 11% 4 7% 5% 5% 4 5% 6% 8% 40%	2969
December	1st to 10th	Night	3 8% 3 7% 5% 6% 6% 6% 7% 9% 40%	5040
	11th to 20th	Night	5% 10% 4 10% 5% 5% 6% 4 6% 8% 36%	5696
	21st to end	Night	4 11% 4 7% 4 4 5% 4 7% 9% 41%	7623

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	52% 7% 14% 22% 5% 1	3249
	11th to 20th	Day	47% 8% 15% 15% 12% 2	3337
	21st to end	Day	34% 8% 19% 28% 11%	4004
February	1st to 10th	Day	50% 9% 17% 16% 8% 1	1785
	11th to 20th	Day	50% 9% 16% 18% 7% 1	1764
	21st to end	Day	44% 9% 16% 19% 10% 1	1555
March	1st to 10th	Day	33% 7% 17% 26% 16% 1	4684
	11th to 20th	Day	33% 10% 20% 25% 11% 1	5000
	21st to end	Day	60% 10% 13% 12% 4	5486
April	1st to 10th	Day	46% 8% 15% 21% 8% 1	2401
	11th to 20th	Day	46% 8% 13% 22% 9% 1	2570
	21st to end	Day	41% 9% 16% 23% 10% 1	2600
May	1st to 10th	Day	41% 6% 12% 22% 14% 5%	5990
	11th to 20th	Day	39% 10% 16% 23% 9% 2	6423
	21st to end	Day	33% 9% 15% 27% 16% 1	7406
June	1st to 10th	Day	39% 9% 18% 22% 12% 1	3000
	11th to 20th	Day	42% 9% 12% 18% 16% 3	3000
	21st to end	Day	26% 6% 16% 33% 17% 2	3000
July	1st to 10th	Day	22% 5% 14% 25% 23% 12%	6706
	11th to 20th	Day	18% 5% 13% 22% 28% 14%	6699
	21st to end	Day	16% 4 11% 24% 28% 16%	6960
August	1st to 10th	Day	26% 7% 14% 23% 24% 7%	4252
	11th to 20th	Day	23% 7% 14% 35% 19% 3	4197
	21st to end	Day	21% 5% 10% 32% 26% 6%	4663
September	1st to 10th	Day	25% 6% 12% 28% 19% 10%	2455
	11th to 20th	Day	33% 7% 13% 26% 16% 4	2200
	21st to end	Day	30% 5% 13% 29% 17% 5%	2200
October	1st to 10th	Day	29% 5% 12% 33% 18% 3	3350
	11th to 20th	Day	29% 7% 15% 31% 16% 2	3250
	21st to end	Day	35% 8% 11% 30% 15% 2	3205
November	1st to 10th	Day	43% 9% 16% 21% 9% 3	1703
	11th to 20th	Day	39% 9% 19% 23% 9% 1	1680
	21st to end	Day	39% 9% 20% 22% 9% 2	1648
December	1st to 10th	Day	37% 9% 21% 27% 6% 1	2360
	11th to 20th	Day	41% 11% 23% 19% 4 1	2714
	21st to end	Day	41% 7% 14% 21% 15% 2	3575
January	1st to 10th	Night	47% 9% 16% 21% 7% 1	6916
	11th to 20th	Night	45% 7% 17% 17% 13% 1	6800
	21st to end	Night	35% 8% 17% 28% 11% 1	6952
February	1st to 10th	Night	49% 7% 17% 17% 10% 1	2615
	11th to 20th	Night	49% 8% 16% 18% 8% 1	2533
	21st to end	Night	44% 9% 18% 19% 9% 2	2073
March	1st to 10th	Night	35% 9% 17% 26% 12% 2	5210
	11th to 20th	Night	33% 9% 19% 29% 11%	5000
	21st to end	Night	57% 8% 16% 13% 6%	5489
April	1st to 10th	Night	42% 9% 16% 24% 8%	1993
	11th to 20th	Night	44% 9% 13% 23% 10% 1	1781
	21st to end	Night	40% 9% 16% 26% 9% 1	1800
May	1st to 10th	Night	40% 7% 11% 26% 10% 5%	3987
	11th to 20th	Night	36% 12% 17% 25% 10% 1	3488
	21st to end	Night	33% 8% 15% 26% 16% 2	3470
June	1st to 10th	Night	35% 8% 18% 24% 14% 1	1400
	11th to 20th	Night	37% 8% 14% 24% 14% 3	1400
	21st to end	Night	22% 7% 16% 34% 17% 3	1400
July	1st to 10th	Night	19% 5% 13% 26% 27% 10%	3145
	11th to 20th	Night	17% 4 12% 30% 24% 13%	3138
	21st to end	Night	20% 4 13% 22% 25% 16%	3563
August	1st to 10th	Night	27% 5% 12% 23% 24% 9%	2882
	11th to 20th	Night	25% 6% 17% 30% 17% 5%	2928
	21st to end	Night	27% 5% 9% 29% 24% 7%	3245
September	1st to 10th	Night	26% 5% 13% 26% 18% 12%	1942
	11th to 20th	Night	31% 6% 14% 27% 17% 5%	2200
	21st to end	Night	30% 5% 13% 29% 19% 4	2200
October	1st to 10th	Night	29% 4 11% 33% 18% 4	3841
	11th to 20th	Night	31% 5% 11% 32% 18% 2	3898
	21st to end	Night	29% 7% 13% 31% 19% 1	4592
November	1st to 10th	Night	44% 7% 16% 21% 10% 2	2794
	11th to 20th	Night	36% 10% 19% 23% 11% 1	2940
	21st to end	Night	39% 8% 22% 21% 9% 2	2969
December	1st to 10th	Night	38% 8% 22% 20% 11% 1	5040
	11th to 20th	Night	45% 8% 24% 17% 6% 1	5697
	21st to end	Night	38% 6% 14% 24% 14% 4	7623

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	10% 10% 25% 33% 12% 9%	220
	11th to 20th	Day	13% 13% 25% 31% 14% 4	212
	21st to end	Day	7% 13% 33% 30% 15% 2	220
February	1st to 10th	Day	15% 12% 37% 26% 9% 1	293
	11th to 20th	Day	9% 13% 27% 34% 13% 4	300
	21st to end	Day	7% 16% 35% 29% 12% 1	319
March	1st to 10th	Day	9% 14% 32% 27% 13% 4	500
	11th to 20th	Day	10% 12% 29% 29% 14% 5%	500
	21st to end	Day	12% 16% 26% 31% 12% 4	550
April	1st to 10th	Day	15% 15% 31% 26% 12% 2	500
	11th to 20th	Day	13% 16% 32% 26% 11% 2	492
	21st to end	Day	17% 13% 29% 22% 16% 3	500
May	1st to 10th	Day	16% 10% 22% 28% 17% 7%	548
	11th to 20th	Day	19% 7% 21% 26% 20% 7%	725
	21st to end	Day	19% 7% 20% 27% 22% 7%	789
June	1st to 10th	Day	13% 11% 27% 24% 18% 6%	730
	11th to 20th	Day	17% 15% 29% 24% 13% 2	730
	21st to end	Day	8% 8% 27% 32% 20% 7%	730
July	1st to 10th	Day	5% 4 24% 34% 26% 7%	721
	11th to 20th	Day	6% 6% 24% 42% 19% 3	718
	21st to end	Day	4 3 22% 35% 28% 7%	707
August	1st to 10th	Day	7% 6% 20% 38% 23% 6%	527
	11th to 20th	Day	7% 4 17% 32% 28% 11%	517
	21st to end	Day	7% 5% 23% 33% 25% 7%	583
September	1st to 10th	Day	9% 9% 25% 28% 22% 8%	530
	11th to 20th	Day	10% 8% 24% 30% 21% 8%	530
	21st to end	Day	14% 11% 25% 29% 17% 5%	530
October	1st to 10th	Day	16% 7% 22% 27% 20% 7%	384
	11th to 20th	Day	14% 11% 25% 26% 17% 7%	330
	21st to end	Day	15% 16% 31% 23% 12% 2	363
November	1st to 10th	Day	25% 9% 26% 28% 12% 1	330
	11th to 20th	Day	9% 14% 34% 28% 14% 2	330
	21st to end	Day	9% 12% 31% 30% 13% 4	313
December	1st to 10th	Day	9% 12% 40% 22% 13% 4	220
	11th to 20th	Day	17% 14% 30% 26% 10% 3	220
	21st to end	Day	10% 10% 25% 34% 16% 5%	242
January	1st to 10th	Night	9% 12% 38% 30% 10% 1	1050
	11th to 20th	Night	10% 16% 39% 25% 10% 1	999
	21st to end	Night	8% 14% 37% 30% 9% 2	880
February	1st to 10th	Night	14% 11% 36% 29% 10% 2	800
	11th to 20th	Night	11% 11% 34% 32% 11% 1	784
	21st to end	Night	7% 9% 35% 31% 16% 1	660
March	1st to 10th	Night	7% 8% 36% 34% 13% 2	800
	11th to 20th	Night	7% 9% 33% 38% 12% 2	800
	21st to end	Night	15% 9% 32% 31% 13% 1	880
April	1st to 10th	Night	12% 11% 32% 33% 12%	693
	11th to 20th	Night	14% 10% 35% 30% 10%	593
	21st to end	Night	13% 9% 30% 34% 14%	600
May	1st to 10th	Night	14% 8% 27% 33% 19%	600
	11th to 20th	Night	12% 6% 23% 38% 19% 1	540
	21st to end	Night	21% 6% 21% 30% 19% 3	433
June	1st to 10th	Night	15% 6% 29% 33% 16% 1	400
	11th to 20th	Night	18% 8% 35% 28% 12% 1	400
	21st to end	Night	7% 3 27% 45% 18% 1	400
July	1st to 10th	Night	6% 3 23% 45% 23%	390
	11th to 20th	Night	6% 2 26% 51% 15%	388
	21st to end	Night	5% 2 21% 55% 17%	438
August	1st to 10th	Night	7% 3 24% 45% 21% 1	562
	11th to 20th	Night	6% 3 24% 45% 21% 2	594
	21st to end	Night	8% 5% 24% 44% 17% 1	660
September	1st to 10th	Night	12% 3 22% 43% 20% 2	622
	11th to 20th	Night	13% 3 21% 40% 22% 2	800
	21st to end	Night	13% 5% 26% 34% 19% 3	800
October	1st to 10th	Night	15% 5% 23% 37% 19% 1	800
	11th to 20th	Night	11% 11% 28% 34% 14% 2	800
	21st to end	Night	9% 11% 37% 31% 10% 1	880
November	1st to 10th	Night	15% 9% 37% 31% 7% 1	949
	11th to 20th	Night	9% 14% 39% 28% 9%	1050
	21st to end	Night	10% 11% 38% 33% 8% 1	1050
December	1st to 10th	Night	9% 14% 34% 31% 11% 2	1050
	11th to 20th	Night	9% 12% 36% 33% 9% 1	1050
	21st to end	Night	11% 10% 37% 31% 10% 1	1155

Page generated at 2026-01-13 23:14:25. Version ac07

Copyright © 2026 Attilla Danko.