The Shoals
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Shoals clear sky chart from 2005-11-06 to 2025-07-21.

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	12% 7% 3 7% 5% 4 5% 4 6% 7% 41%	120190
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	118958
Transparency	Day	40% 5% 10% 22% 18% 4	123954
	Night	38% 4 10% 22% 20% 6%	123336
Seeing	Day	14% 7% 21% 24% 22% 13%	16019
	Night	15% 5% 22% 32% 22% 4	25679

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% 9% 4 9% 4 3 2 3 3 5% 41%	3617
	11th to 20th	Day	16% 6% 3 8% 4 4 3 2 4 5% 46%	3961
	21st to end	Day	18% 10% 3 6% 4 3 3 3 5% 6% 38%	4972
February	1st to 10th	Day	19% 10% 4 7% 4 3 3 3 4 6% 38%	2000
	11th to 20th	Day	19% 9% 3 7% 5% 4 4 3 4 5% 38%	1948
	21st to end	Day	20% 9% 3 6% 4 3 4 3 4 6% 39%	1650
March	1st to 10th	Day	17% 10% 4 9% 4 4 4 3 5% 5% 34%	4480
	11th to 20th	Day	12% 7% 3 6% 4 4 4 3 5% 6% 46%	4651
	21st to end	Day	12% 7% 3 7% 4 4 5% 3 5% 6% 42%	5962
April	1st to 10th	Day	12% 6% 3 5% 4 4 4 4 6% 7% 45%	2400
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 46%	2374
	21st to end	Day	11% 6% 3 6% 4 4 4 4 6% 9% 44%	2400
May	1st to 10th	Day	16% 6% 3 7% 5% 5% 5% 5% 7% 9% 32%	5716
	11th to 20th	Day	15% 7% 3 8% 5% 5% 5% 5% 7% 8% 30%	5861
	21st to end	Day	16% 7% 3 7% 4 4 4 3 6% 8% 38%	6433
June	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 5% 8% 9% 41%	2602
	11th to 20th	Day	5% 4 2 5% 5% 6% 7% 5% 7% 10% 44%	2800
	21st to end	Day	5% 4 2 5% 5% 6% 6% 6% 8% 11% 43%	2800
July	1st to 10th	Day	6% 5% 2 7% 7% 7% 7% 6% 9% 11% 34%	4580
	11th to 20th	Day	8% 5% 2 6% 5% 6% 6% 6% 9% 12% 34%	4496
	21st to end	Day	13% 9% 4 9% 7% 6% 5% 5% 7% 8% 26%	4319
August	1st to 10th	Day	3 2 1 4 4 4 6% 4 7% 10% 55%	3785
	11th to 20th	Day	5% 5% 2 7% 5% 4 5% 4 6% 10% 47%	3729
	21st to end	Day	6% 4 2 6% 4 5% 5% 4 5% 7% 51%	4180
September	1st to 10th	Day	10% 5% 2 6% 6% 5% 6% 4 5% 8% 44%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 43%	2100
	21st to end	Day	10% 5% 2 4 4 4 4 4 5% 7% 51%	2090
October	1st to 10th	Day	9% 5% 2 5% 3 4 4 3 5% 6% 55%	2090
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 5% 6% 55%	2000
	21st to end	Day	14% 6% 2 5% 2 3 4 3 4 5% 51%	1981
November	1st to 10th	Day	12% 4 2 5% 3 3 4 4 4 5% 54%	1762
	11th to 20th	Day	12% 6% 1 5% 4 4 3 3 5% 6% 52%	1800
	21st to end	Day	14% 7% 2 6% 4 4 4 5% 5% 5% 44%	1800
December	1st to 10th	Day	15% 8% 3 7% 4 4 3 3 4 5% 45%	2930
	11th to 20th	Day	20% 10% 3 7% 4 3 3 3 4 4 39%	3373
	21st to end	Day	16% 9% 3 7% 5% 4 5% 4 5% 8% 35%	4268
January	1st to 10th	Night	17% 9% 4 9% 3 3 4 3 4 5% 39%	6348
	11th to 20th	Night	17% 8% 4 7% 3 2 2 2 3 5% 47%	5976
	21st to end	Night	19% 10% 2 5% 4 3 3 3 5% 5% 41%	5984
February	1st to 10th	Night	17% 9% 3 7% 4 4 3 3 4 5% 40%	2400
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 3 4 4 39%	2338
	21st to end	Night	22% 7% 3 6% 4 3 4 3 4 5% 39%	1980
March	1st to 10th	Night	21% 8% 2 7% 5% 4 4 3 4 6% 35%	5373
	11th to 20th	Night	11% 6% 2 5% 4 3 4 3 5% 7% 50%	5307
	21st to end	Night	17% 6% 3 7% 5% 4 3 3 4 5% 44%	5008
April	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 5% 8% 47%	2000
	11th to 20th	Night	13% 5% 2 4 3 4 4 4 5% 7% 49%	1975
	21st to end	Night	11% 6% 3 5% 4 4 4 4 6% 8% 46%	2000
May	1st to 10th	Night	14% 9% 3 7% 5% 4 4 3 6% 8% 37%	4179
	11th to 20th	Night	16% 8% 3 9% 5% 5% 5% 3 5% 7% 33%	4032
	21st to end	Night	11% 7% 3 7% 5% 5% 5% 4 6% 9% 39%	4421
June	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 4 6% 10% 45%	1790
	11th to 20th	Night	3 3 2 3 4 4 5% 5% 7% 11% 53%	1600
	21st to end	Night	4 4 1 6% 4 4 4 4 8% 12% 50%	1600
July	1st to 10th	Night	6% 4 2 6% 5% 6% 6% 6% 9% 12% 37%	2610
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 4 8% 12% 42%	2674
	21st to end	Night	9% 10% 4 10% 7% 6% 6% 5% 6% 9% 27%	3230
August	1st to 10th	Night	2 2 1 4 4 4 4 4 6% 9% 60%	3144
	11th to 20th	Night	4 3 1 5% 4 4 5% 4 7% 10% 54%	3100
	21st to end	Night	5% 3 2 5% 4 4 4 3 6% 8% 57%	3476
September	1st to 10th	Night	9% 4 2 4 3 4 5% 3 6% 9% 50%	1900
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 5% 8% 46%	2060
	21st to end	Night	9% 5% 2 4 4 4 3 3 4 6% 56%	2090
October	1st to 10th	Night	8% 3 1 5% 3 3 3 3 4 5% 62%	2090
	11th to 20th	Night	11% 6% 2 6% 3 4 3 2 4 5% 55%	2175
	21st to end	Night	14% 6% 2 5% 3 3 3 2 4 5% 53%	2616
November	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 5% 6% 52%	2536
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 5% 6% 51%	2600
	21st to end	Night	16% 6% 2 5% 4 3 3 3 5% 5% 49%	2600
December	1st to 10th	Night	19% 8% 2 4 3 3 3 3 4 5% 46%	4250
	11th to 20th	Night	23% 7% 2 5% 3 2 3 3 4 5% 43%	4822
	21st to end	Night	18% 9% 3 7% 5% 4 4 4 5% 7% 34%	6674

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	46% 3 7% 25% 18% 2	3618
	11th to 20th	Day	41% 4 5% 23% 25% 2	3961
	21st to end	Day	47% 3 6% 21% 20% 3	4972
February	1st to 10th	Day	49% 3 7% 20% 18% 4	2000
	11th to 20th	Day	50% 3 6% 20% 16% 5%	1958
	21st to end	Day	47% 2 8% 15% 20% 7%	1650
March	1st to 10th	Day	52% 4 6% 14% 16% 9%	4480
	11th to 20th	Day	38% 4 7% 21% 20% 10%	4651
	21st to end	Day	43% 4 9% 24% 19% 1	5964
April	1st to 10th	Day	38% 5% 10% 25% 18% 6%	2400
	11th to 20th	Day	37% 4 7% 23% 23% 7%	2374
	21st to end	Day	37% 5% 10% 28% 18% 2	2400
May	1st to 10th	Day	45% 7% 15% 21% 11% 2	5752
	11th to 20th	Day	50% 6% 16% 20% 9%	5865
	21st to end	Day	45% 4 10% 22% 16% 2	6447
June	1st to 10th	Day	37% 6% 15% 22% 17% 3	2602
	11th to 20th	Day	31% 8% 14% 25% 19% 2	2800
	21st to end	Day	31% 9% 17% 23% 17% 4	2800
July	1st to 10th	Day	39% 9% 20% 23% 7% 1	4511
	11th to 20th	Day	38% 8% 22% 26% 6% 1	4421
	21st to end	Day	54% 7% 13% 19% 6%	4181
August	1st to 10th	Day	23% 7% 14% 36% 19% 1	3773
	11th to 20th	Day	32% 6% 16% 27% 16% 3	3765
	21st to end	Day	31% 6% 11% 22% 25% 4	4179
September	1st to 10th	Day	38% 7% 13% 19% 18% 4	2280
	11th to 20th	Day	39% 6% 12% 18% 22% 4	2100
	21st to end	Day	33% 5% 9% 25% 22% 7%	2090
October	1st to 10th	Day	20% 3 5% 16% 37% 18%	3480
	11th to 20th	Day	21% 2 5% 20% 34% 18%	3305
	21st to end	Day	26% 4 5% 22% 34% 9%	3245
November	1st to 10th	Day	32% 4 8% 19% 28% 8%	1762
	11th to 20th	Day	35% 4 6% 19% 29% 7%	1800
	21st to end	Day	41% 3 7% 22% 22% 5%	1800
December	1st to 10th	Day	42% 3 5% 25% 21% 3	2930
	11th to 20th	Day	50% 3 5% 22% 15% 5%	3370
	21st to end	Day	46% 4 10% 25% 13% 2	4268
January	1st to 10th	Night	48% 3 8% 19% 19% 3	6348
	11th to 20th	Night	43% 3 5% 20% 25% 6%	5976
	21st to end	Night	46% 3 4 20% 20% 7%	5984
February	1st to 10th	Night	47% 3 7% 20% 19% 4	2400
	11th to 20th	Night	50% 3 7% 17% 17% 6%	2339
	21st to end	Night	48% 3 6% 17% 19% 7%	1980
March	1st to 10th	Night	50% 4 6% 16% 17% 7%	5373
	11th to 20th	Night	34% 4 7% 18% 21% 16%	5307
	21st to end	Night	44% 3 7% 21% 21% 4	5008
April	1st to 10th	Night	36% 4 11% 24% 20% 5%	2000
	11th to 20th	Night	34% 4 8% 21% 23% 9%	1975
	21st to end	Night	35% 4 13% 25% 20% 3	2000
May	1st to 10th	Night	45% 5% 13% 21% 14% 1	4208
	11th to 20th	Night	51% 5% 14% 19% 10% 1	4033
	21st to end	Night	40% 7% 13% 24% 15% 2	4429
June	1st to 10th	Night	33% 6% 15% 23% 20% 3	1790
	11th to 20th	Night	23% 7% 18% 29% 21% 3	1600
	21st to end	Night	26% 8% 15% 30% 18% 4	1600
July	1st to 10th	Night	35% 10% 22% 23% 7% 2	2570
	11th to 20th	Night	32% 7% 26% 27% 7% 2	2626
	21st to end	Night	51% 8% 15% 18% 8%	3127
August	1st to 10th	Night	18% 7% 13% 38% 22% 2	3132
	11th to 20th	Night	23% 7% 24% 27% 16% 2	3130
	21st to end	Night	25% 5% 15% 23% 27% 4	3476
September	1st to 10th	Night	31% 7% 14% 23% 19% 5%	1900
	11th to 20th	Night	36% 6% 13% 17% 24% 4	2060
	21st to end	Night	29% 4 8% 27% 22% 9%	2090
October	1st to 10th	Night	18% 4 5% 18% 36% 20%	3480
	11th to 20th	Night	20% 2 4 16% 35% 23%	3609
	21st to end	Night	24% 3 4 27% 27% 15%	4302
November	1st to 10th	Night	34% 4 7% 21% 24% 11%	2536
	11th to 20th	Night	34% 3 7% 19% 27% 10%	2600
	21st to end	Night	38% 3 7% 22% 24% 7%	2600
December	1st to 10th	Night	42% 3 6% 24% 24% 2	4250
	11th to 20th	Night	45% 3 5% 21% 23% 3	4824
	21st to end	Night	49% 5% 7% 26% 12% 2	6674

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	22% 16% 36% 20% 6%	300
	11th to 20th	Day	24% 14% 41% 14% 5% 2	300
	21st to end	Day	19% 15% 42% 20% 5%	330
February	1st to 10th	Day	21% 13% 36% 22% 6% 2	300
	11th to 20th	Day	31% 17% 32% 16% 2 2	300
	21st to end	Day	30% 13% 37% 14% 6%	249
March	1st to 10th	Day	23% 15% 31% 22% 7% 1	300
	11th to 20th	Day	19% 16% 35% 23% 6% 1	353
	21st to end	Day	21% 14% 31% 24% 10%	550
April	1st to 10th	Day	19% 13% 28% 26% 13% 1	500
	11th to 20th	Day	16% 13% 29% 26% 14% 2	492
	21st to end	Day	13% 9% 25% 31% 16% 5%	500
May	1st to 10th	Day	15% 11% 23% 28% 15% 7%	503
	11th to 20th	Day	12% 5% 22% 29% 19% 13%	527
	21st to end	Day	12% 4 18% 26% 23% 18%	573
June	1st to 10th	Day	11% 4 13% 25% 25% 23%	532
	11th to 20th	Day	5% 2 14% 25% 31% 22%	730
	21st to end	Day	6% 2 13% 25% 33% 21%	730
July	1st to 10th	Day	7% 1 9% 28% 30% 25%	721
	11th to 20th	Day	8% 3 8% 20% 29% 33%	673
	21st to end	Day	8% 1 7% 21% 33% 30%	532
August	1st to 10th	Day	6% 2 8% 22% 36% 27%	486
	11th to 20th	Day	9% 1 9% 20% 42% 18%	479
	21st to end	Day	12% 2 7% 17% 35% 27%	539
September	1st to 10th	Day	9% 1 12% 18% 39% 21%	490
	11th to 20th	Day	12% 1 10% 21% 33% 23%	490
	21st to end	Day	13% 2 13% 25% 34% 13%	490
October	1st to 10th	Day	10% 1 14% 31% 30% 14%	490
	11th to 20th	Day	9% 7% 27% 34% 19% 5%	400
	21st to end	Day	18% 10% 22% 28% 18% 5%	330
November	1st to 10th	Day	18% 8% 24% 25% 19% 5%	300
	11th to 20th	Day	12% 10% 35% 30% 12% 2	300
	21st to end	Day	15% 14% 29% 23% 15% 4	300
December	1st to 10th	Day	22% 18% 30% 22% 8% 1	300
	11th to 20th	Day	20% 14% 33% 22% 10% 1	300
	21st to end	Day	21% 15% 34% 21% 9%	330
January	1st to 10th	Night	22% 10% 34% 29% 6%	1000
	11th to 20th	Night	23% 10% 34% 27% 7%	937
	21st to end	Night	19% 8% 40% 31% 3	880
February	1st to 10th	Night	21% 10% 32% 32% 6%	800
	11th to 20th	Night	26% 12% 29% 30% 3	783
	21st to end	Night	25% 11% 35% 27% 2	660
March	1st to 10th	Night	20% 10% 31% 34% 5%	800
	11th to 20th	Night	20% 8% 34% 30% 8% 1	800
	21st to end	Night	16% 8% 33% 32% 12%	680
April	1st to 10th	Night	14% 9% 31% 33% 13%	600
	11th to 20th	Night	13% 6% 29% 37% 13% 2	593
	21st to end	Night	13% 6% 26% 40% 16% 1	600
May	1st to 10th	Night	12% 3 25% 38% 20% 2	600
	11th to 20th	Night	12% 4 17% 37% 25% 5%	591
	21st to end	Night	8% 2 12% 38% 34% 6%	650
June	1st to 10th	Night	7% 2 10% 38% 38% 7%	600
	11th to 20th	Night	4 8% 33% 47% 8%	600
	21st to end	Night	4 1 6% 32% 45% 11%	600
July	1st to 10th	Night	9% 1 6% 25% 46% 14%	585
	11th to 20th	Night	7% 1 4 24% 51% 14%	582
	21st to end	Night	7% 7% 26% 44% 16%	624
August	1st to 10th	Night	4 1 4 22% 55% 14%	567
	11th to 20th	Night	6% 1 4 29% 51% 9%	564
	21st to end	Night	10% 1 5% 23% 51% 10%	627
September	1st to 10th	Night	11% 2 8% 26% 46% 7%	570
	11th to 20th	Night	13% 2 10% 28% 40% 6%	730
	21st to end	Night	12% 2 12% 31% 39% 4	760
October	1st to 10th	Night	9% 2 12% 37% 35% 6%	760
	11th to 20th	Night	13% 4 19% 40% 21% 3	760
	21st to end	Night	17% 4 19% 37% 22% 2	836
November	1st to 10th	Night	13% 4 21% 39% 21% 2	780
	11th to 20th	Night	14% 5% 30% 37% 14% 1	800
	21st to end	Night	18% 8% 24% 37% 12% 1	800
December	1st to 10th	Night	22% 9% 28% 32% 9%	800
	11th to 20th	Night	22% 6% 29% 33% 10%	800
	21st to end	Night	25% 8% 29% 32% 6%	960

Page generated at 2025-07-18 00:09:58. Version ac07

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