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 2024-11-25.

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% 45%	105648
	Night	6% 8% 3 7% 5% 5% 5% 4 6% 8% 44%	102497
Transparency	Day	34% 8% 15% 24% 15% 4	105373
	Night	36% 8% 16% 24% 13% 3	102362
Seeing	Day	12% 10% 26% 29% 18% 5%	15513
	Night	11% 9% 32% 34% 13% 1	24787

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	4 11% 5% 10% 6% 6% 5% 4 7% 9% 33%	2219
	11th to 20th	Day	5% 10% 5% 12% 7% 7% 8% 6% 6% 6% 28%	2293
	21st to end	Day	2 8% 4 9% 5% 6% 5% 4 6% 9% 42%	2794
February	1st to 10th	Day	7% 13% 5% 11% 6% 6% 4 5% 7% 9% 28%	1695
	11th to 20th	Day	6% 14% 5% 10% 6% 6% 5% 4 5% 9% 31%	1665
	21st to end	Day	5% 11% 5% 11% 6% 5% 5% 5% 6% 6% 35%	1479
March	1st to 10th	Day	4 8% 4 8% 6% 7% 6% 4 6% 11% 38%	3252
	11th to 20th	Day	4 7% 2 6% 5% 5% 5% 5% 7% 9% 46%	3490
	21st to end	Day	10% 16% 6% 17% 7% 5% 4 4 5% 6% 21%	3825
April	1st to 10th	Day	8% 13% 4 9% 6% 5% 5% 4 6% 8% 33%	2280
	11th to 20th	Day	11% 14% 3 8% 5% 5% 5% 4 5% 7% 35%	2437
	21st to end	Day	11% 11% 3 7% 5% 4 4 4 6% 7% 37%	2470
May	1st to 10th	Day	18% 12% 4 8% 4 4 4 3 5% 6% 32%	4192
	11th to 20th	Day	9% 6% 2 8% 4 5% 6% 6% 7% 9% 38%	4470
	21st to end	Day	14% 7% 2 6% 5% 5% 6% 4 7% 8% 36%	5161
June	1st to 10th	Day	14% 5% 2 6% 6% 4 5% 4 6% 9% 39%	2850
	11th to 20th	Day	15% 6% 2 6% 6% 5% 5% 4 7% 6% 38%	2850
	21st to end	Day	6% 3 1 4 4 5% 5% 4 6% 9% 53%	2850
July	1st to 10th	Day	3 2 1 4 4 5% 5% 4 6% 7% 59%	4740
	11th to 20th	Day	2 2 1 3 2 2 3 3 5% 7% 71%	4740
	21st to end	Day	2 1 1 2 2 3 3 3 5% 7% 72%	4994
August	1st to 10th	Day	7% 4 1 4 3 4 4 4 7% 8% 52%	4136
	11th to 20th	Day	5% 3 1 4 4 4 5% 4 7% 9% 55%	4028
	21st to end	Day	5% 3 1 4 3 4 3 3 5% 7% 61%	4521
September	1st to 10th	Day	9% 4 2 4 3 3 3 3 5% 6% 57%	2332
	11th to 20th	Day	10% 6% 2 6% 4 4 4 3 5% 6% 50%	2090
	21st to end	Day	11% 5% 3 5% 4 3 3 2 5% 6% 53%	2090
October	1st to 10th	Day	7% 6% 2 6% 4 4 4 4 6% 8% 51%	3248
	11th to 20th	Day	4 6% 2 5% 4 4 5% 4 7% 7% 51%	3150
	21st to end	Day	6% 8% 3 7% 4 4 5% 4 6% 8% 45%	3106
November	1st to 10th	Day	10% 11% 3 8% 4 4 5% 4 5% 8% 37%	1620
	11th to 20th	Day	4 8% 3 9% 7% 4 5% 5% 9% 8% 38%	1600
	21st to end	Day	5% 12% 3 8% 3 4 4 4 6% 10% 40%	1524
December	1st to 10th	Day	3 11% 4 10% 6% 7% 6% 4 6% 7% 36%	1330
	11th to 20th	Day	4 10% 5% 10% 5% 5% 6% 5% 6% 8% 36%	1685
	21st to end	Day	4 9% 4 8% 4 4 5% 5% 7% 7% 44%	2442
January	1st to 10th	Night	3 8% 4 10% 6% 6% 6% 6% 7% 9% 34%	4726
	11th to 20th	Night	5% 12% 5% 10% 6% 6% 6% 4 5% 6% 34%	4697
	21st to end	Night	4 9% 4 10% 5% 5% 5% 4 6% 9% 41%	4862
February	1st to 10th	Night	8% 11% 5% 11% 6% 4 4 4 6% 7% 34%	2485
	11th to 20th	Night	5% 14% 4 10% 6% 7% 5% 6% 6% 7% 30%	2402
	21st to end	Night	4 11% 4 12% 7% 5% 5% 4 6% 7% 35%	1973
March	1st to 10th	Night	2 8% 4 11% 8% 7% 6% 5% 7% 9% 34%	3622
	11th to 20th	Night	3 7% 2 5% 4 5% 4 4 7% 9% 50%	3490
	21st to end	Night	11% 19% 6% 14% 6% 5% 4 4 5% 6% 21%	3828
April	1st to 10th	Night	8% 11% 3 8% 5% 5% 5% 4 6% 8% 36%	1894
	11th to 20th	Night	11% 10% 3 7% 5% 6% 5% 4 6% 6% 35%	1691
	21st to end	Night	10% 9% 3 7% 6% 4 5% 4 6% 6% 39%	1710
May	1st to 10th	Night	15% 13% 3 7% 4 4 5% 4 5% 6% 33%	2778
	11th to 20th	Night	8% 4 2 5% 5% 5% 6% 4 7% 9% 43%	2429
	21st to end	Night	15% 8% 3 7% 5% 4 5% 4 6% 7% 36%	2414
June	1st to 10th	Night	11% 7% 2 5% 4 3 4 4 7% 8% 45%	1330
	11th to 20th	Night	13% 7% 3 5% 4 4 4 4 5% 9% 43%	1330
	21st to end	Night	6% 3 2 4 2 3 5% 3 7% 8% 58%	1330
July	1st to 10th	Night	3 3 1 4 3 3 4 5% 6% 7% 60%	2220
	11th to 20th	Night	2 2 1 3 2 2 3 3 4 6% 73%	2220
	21st to end	Night	3 2 1 3 3 2 2 3 4 5% 72%	2555
August	1st to 10th	Night	8% 4 2 4 3 4 3 3 4 7% 57%	2802
	11th to 20th	Night	4 3 1 5% 5% 4 5% 5% 8% 10% 50%	2811
	21st to end	Night	9% 4 2 5% 3 3 3 3 4 6% 59%	3146
September	1st to 10th	Night	10% 4 2 3 2 4 4 3 6% 6% 55%	1845
	11th to 20th	Night	10% 7% 2 5% 3 3 3 3 5% 8% 52%	2090
	21st to end	Night	12% 4 2 4 4 3 4 3 5% 7% 52%	2090
October	1st to 10th	Night	7% 5% 2 6% 4 4 3 3 5% 6% 55%	3724
	11th to 20th	Night	6% 7% 3 5% 4 4 4 3 5% 7% 53%	3778
	21st to end	Night	4 7% 3 6% 4 4 5% 4 6% 8% 51%	4449
November	1st to 10th	Night	9% 12% 3 7% 4 5% 4 3 6% 8% 37%	2658
	11th to 20th	Night	4 8% 3 7% 5% 5% 6% 6% 6% 9% 41%	2800
	21st to end	Night	5% 11% 3 7% 5% 4 4 5% 6% 8% 41%	2748
December	1st to 10th	Night	4 11% 3 9% 7% 6% 6% 4 6% 8% 35%	2850
	11th to 20th	Night	4 10% 4 10% 5% 5% 5% 5% 6% 8% 39%	3506
	21st to end	Night	4 9% 3 7% 4 4 5% 4 7% 8% 45%	5214

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	43% 9% 19% 22% 6% 1	2219
	11th to 20th	Day	50% 11% 14% 11% 11% 3	2293
	21st to end	Day	35% 10% 24% 25% 5%	2794
February	1st to 10th	Day	50% 9% 17% 16% 7%	1695
	11th to 20th	Day	50% 9% 16% 17% 6% 1	1674
	21st to end	Day	46% 9% 16% 19% 9% 1	1479
March	1st to 10th	Day	35% 9% 20% 23% 12%	3252
	11th to 20th	Day	28% 12% 26% 26% 7%	3490
	21st to end	Day	60% 11% 13% 12% 4	3825
April	1st to 10th	Day	47% 9% 16% 20% 8% 1	2280
	11th to 20th	Day	47% 9% 13% 21% 9% 1	2440
	21st to end	Day	42% 9% 17% 22% 9% 1	2470
May	1st to 10th	Day	50% 7% 13% 23% 6% 1	4192
	11th to 20th	Day	33% 12% 18% 24% 11% 2	4474
	21st to end	Day	39% 12% 17% 22% 10%	5162
June	1st to 10th	Day	39% 9% 19% 21% 11% 1	2850
	11th to 20th	Day	42% 9% 12% 18% 15% 3	2850
	21st to end	Day	25% 6% 17% 33% 16% 3	2850
July	1st to 10th	Day	21% 6% 12% 28% 23% 10%	4666
	11th to 20th	Day	14% 4 8% 23% 32% 20%	4659
	21st to end	Day	12% 3 8% 22% 33% 23%	4836
August	1st to 10th	Day	26% 7% 13% 23% 24% 7%	4120
	11th to 20th	Day	23% 7% 14% 35% 19% 3	4067
	21st to end	Day	21% 5% 10% 32% 26% 6%	4520
September	1st to 10th	Day	26% 6% 12% 26% 19% 11%	2332
	11th to 20th	Day	34% 7% 13% 25% 16% 5%	2090
	21st to end	Day	31% 6% 13% 29% 16% 5%	2090
October	1st to 10th	Day	29% 5% 12% 32% 19% 3	3248
	11th to 20th	Day	28% 7% 15% 31% 17% 2	3150
	21st to end	Day	35% 8% 11% 29% 15% 2	3106
November	1st to 10th	Day	43% 9% 16% 21% 8% 3	1620
	11th to 20th	Day	39% 9% 19% 23% 9% 1	1600
	21st to end	Day	39% 8% 20% 21% 9% 2	1524
December	1st to 10th	Day	45% 8% 16% 22% 7% 2	1330
	11th to 20th	Day	41% 12% 24% 18% 4 1	1684
	21st to end	Day	34% 8% 16% 23% 15% 3	2442
January	1st to 10th	Night	39% 12% 20% 22% 7% 1	4726
	11th to 20th	Night	49% 7% 14% 16% 12% 2	4697
	21st to end	Night	36% 10% 20% 26% 8%	4862
February	1st to 10th	Night	48% 7% 17% 17% 9% 1	2485
	11th to 20th	Night	48% 9% 16% 18% 8%	2403
	21st to end	Night	44% 9% 17% 19% 9% 2	1973
March	1st to 10th	Night	39% 11% 18% 23% 9%	3622
	11th to 20th	Night	26% 11% 25% 31% 7%	3490
	21st to end	Night	61% 10% 14% 10% 4	3828
April	1st to 10th	Night	44% 10% 16% 23% 8%	1894
	11th to 20th	Night	44% 9% 13% 22% 10% 1	1691
	21st to end	Night	41% 9% 16% 25% 8% 1	1710
May	1st to 10th	Night	49% 9% 13% 23% 6% 1	2778
	11th to 20th	Night	26% 14% 18% 28% 13% 1	2430
	21st to end	Night	42% 10% 15% 23% 8%	2414
June	1st to 10th	Night	35% 9% 19% 24% 12% 1	1330
	11th to 20th	Night	37% 8% 14% 24% 14% 2	1330
	21st to end	Night	22% 7% 17% 33% 18% 3	1330
July	1st to 10th	Night	21% 6% 12% 28% 26% 7%	2185
	11th to 20th	Night	12% 4 7% 27% 30% 19%	2178
	21st to end	Night	14% 3 7% 22% 30% 23%	2475
August	1st to 10th	Night	26% 5% 12% 24% 25% 9%	2794
	11th to 20th	Night	26% 6% 17% 29% 17% 5%	2838
	21st to end	Night	27% 5% 9% 30% 24% 7%	3146
September	1st to 10th	Night	27% 5% 13% 25% 17% 12%	1845
	11th to 20th	Night	31% 6% 14% 27% 17% 5%	2090
	21st to end	Night	31% 5% 13% 29% 17% 4	2090
October	1st to 10th	Night	29% 4 11% 33% 19% 4	3724
	11th to 20th	Night	31% 5% 12% 32% 18% 2	3778
	21st to end	Night	29% 7% 13% 31% 19% 1	4449
November	1st to 10th	Night	44% 8% 16% 21% 10% 2	2658
	11th to 20th	Night	36% 11% 19% 23% 12% 1	2800
	21st to end	Night	39% 8% 21% 21% 9% 2	2748
December	1st to 10th	Night	42% 10% 17% 21% 8% 2	2850
	11th to 20th	Night	39% 11% 24% 21% 4 1	3507
	21st to end	Night	33% 8% 16% 24% 14% 6%	5214

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	8% 8% 28% 31% 14% 11%	180
	11th to 20th	Day	12% 11% 26% 31% 16% 5%	180
	21st to end	Day	7% 12% 32% 31% 15% 3	198
February	1st to 10th	Day	15% 13% 38% 25% 8% 1	263
	11th to 20th	Day	10% 14% 29% 30% 13% 4	270
	21st to end	Day	7% 15% 34% 31% 13% 1	291
March	1st to 10th	Day	10% 13% 32% 29% 13% 3	460
	11th to 20th	Day	11% 11% 28% 29% 15% 5%	460
	21st to end	Day	11% 15% 27% 30% 12% 4	506
April	1st to 10th	Day	15% 15% 32% 27% 10% 1	460
	11th to 20th	Day	13% 15% 33% 26% 12% 2	452
	21st to end	Day	18% 14% 28% 21% 16% 3	460
May	1st to 10th	Day	16% 10% 22% 28% 16% 7%	506
	11th to 20th	Day	19% 7% 20% 26% 20% 7%	675
	21st to end	Day	20% 7% 20% 25% 21% 7%	734
June	1st to 10th	Day	14% 11% 27% 25% 18% 6%	680
	11th to 20th	Day	17% 15% 29% 24% 13% 2	680
	21st to end	Day	7% 7% 26% 32% 20% 7%	680
July	1st to 10th	Day	5% 4 23% 35% 26% 7%	671
	11th to 20th	Day	5% 6% 25% 43% 19% 3	668
	21st to end	Day	4 3 23% 36% 27% 7%	657
August	1st to 10th	Day	7% 6% 21% 36% 24% 6%	487
	11th to 20th	Day	8% 5% 17% 32% 28% 12%	477
	21st to end	Day	6% 6% 24% 32% 24% 7%	539
September	1st to 10th	Day	10% 9% 26% 27% 20% 8%	490
	11th to 20th	Day	10% 8% 25% 30% 20% 7%	490
	21st to end	Day	15% 11% 24% 28% 16% 5%	490
October	1st to 10th	Day	16% 7% 23% 27% 20% 7%	352
	11th to 20th	Day	12% 10% 26% 26% 19% 7%	300
	21st to end	Day	14% 16% 31% 24% 12% 3	330
November	1st to 10th	Day	24% 9% 25% 28% 13% 1	300
	11th to 20th	Day	10% 13% 35% 29% 12% 1	300
	21st to end	Day	8% 13% 33% 28% 13% 4	269
December	1st to 10th	Day	11% 9% 40% 23% 13% 4	180
	11th to 20th	Day	17% 13% 29% 26% 11% 3	180
	21st to end	Day	11% 8% 24% 35% 17% 6%	198
January	1st to 10th	Night	9% 12% 39% 29% 10% 1	950
	11th to 20th	Night	10% 14% 39% 25% 10% 1	920
	21st to end	Night	8% 14% 37% 30% 9% 2	836
February	1st to 10th	Night	13% 11% 36% 28% 9% 2	760
	11th to 20th	Night	11% 11% 35% 31% 10% 1	744
	21st to end	Night	7% 9% 35% 30% 17% 1	628
March	1st to 10th	Night	7% 8% 37% 34% 13% 2	760
	11th to 20th	Night	8% 8% 33% 37% 13% 2	760
	21st to end	Night	14% 8% 32% 31% 13% 1	836
April	1st to 10th	Night	12% 11% 33% 33% 11%	659
	11th to 20th	Night	15% 10% 35% 30% 10%	563
	21st to end	Night	14% 9% 30% 33% 14%	570
May	1st to 10th	Night	14% 8% 26% 33% 18%	570
	11th to 20th	Night	12% 5% 22% 39% 20% 2	513
	21st to end	Night	22% 6% 21% 29% 19% 2	411
June	1st to 10th	Night	15% 6% 29% 32% 16% 1	380
	11th to 20th	Night	18% 8% 35% 26% 12% 1	380
	21st to end	Night	6% 3 27% 44% 19% 1	380
July	1st to 10th	Night	6% 4 22% 45% 23%	370
	11th to 20th	Night	6% 2 26% 50% 15%	368
	21st to end	Night	4 2 21% 55% 17%	416
August	1st to 10th	Night	6% 3 24% 45% 21% 1	534
	11th to 20th	Night	7% 3 23% 44% 22% 2	564
	21st to end	Night	8% 6% 25% 43% 18% 1	627
September	1st to 10th	Night	12% 3 23% 42% 19% 2	591
	11th to 20th	Night	13% 3 21% 40% 21% 2	760
	21st to end	Night	14% 6% 26% 33% 18% 3	760
October	1st to 10th	Night	15% 5% 24% 37% 19% 1	760
	11th to 20th	Night	11% 10% 28% 34% 14% 2	760
	21st to end	Night	9% 11% 37% 31% 10% 1	836
November	1st to 10th	Night	15% 9% 36% 31% 7% 1	903
	11th to 20th	Night	9% 14% 40% 28% 9% 1	1000
	21st to end	Night	10% 10% 39% 32% 8% 1	973
December	1st to 10th	Night	9% 13% 33% 31% 12% 2	950
	11th to 20th	Night	8% 12% 36% 34% 9% 1	950
	21st to end	Night	12% 10% 36% 31% 10% 1	1045

Page generated at 2024-11-22 06:02:30. Version ac07

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