Clayton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clayton clear sky chart from 2005-11-06 to 2024-12-09.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	100846
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	98899
Transparency	Day	39% 5% 12% 21% 18% 5%	104493
	Night	39% 5% 10% 20% 19% 6%	103392
Seeing	Day	16% 8% 22% 26% 19% 9%	15468
	Night	16% 6% 24% 33% 18% 2	25847

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	18% 5% 2 5% 4 3 3 3 3 4 51%	2836
	11th to 20th	Day	13% 6% 3 6% 3 3 3 2 4 5% 52%	2840
	21st to end	Day	17% 10% 2 6% 4 3 4 3 4 5% 43%	3124
February	1st to 10th	Day	15% 6% 3 5% 4 4 4 3 5% 7% 44%	1710
	11th to 20th	Day	20% 7% 2 5% 3 3 3 3 3 5% 46%	1705
	21st to end	Day	17% 8% 3 6% 4 4 4 3 4 5% 42%	1684
March	1st to 10th	Day	23% 8% 3 5% 3 3 4 3 5% 6% 36%	3435
	11th to 20th	Day	10% 5% 2 5% 3 3 3 3 5% 6% 55%	3480
	21st to end	Day	19% 7% 2 5% 4 3 4 3 5% 5% 43%	3815
April	1st to 10th	Day	11% 4 1 4 4 3 3 3 5% 8% 54%	2228
	11th to 20th	Day	11% 5% 3 5% 4 4 4 4 5% 8% 49%	2254
	21st to end	Day	13% 5% 2 6% 4 3 4 4 6% 7% 46%	2280
May	1st to 10th	Day	9% 7% 3 8% 6% 6% 6% 5% 7% 9% 35%	3974
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	4081
	21st to end	Day	7% 4 2 6% 4 5% 4 5% 7% 10% 47%	4476
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 10% 38%	2470
	11th to 20th	Day	9% 4 2 5% 5% 4 5% 5% 8% 10% 43%	2470
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 9% 10% 38%	2470
July	1st to 10th	Day	6% 5% 3 8% 6% 6% 6% 6% 8% 11% 35%	4120
	11th to 20th	Day	11% 7% 3 7% 6% 5% 6% 5% 8% 11% 29%	4120
	21st to end	Day	11% 8% 3 8% 6% 6% 6% 6% 8% 10% 28%	4466
August	1st to 10th	Day	20% 10% 4 8% 5% 5% 6% 5% 7% 10% 21%	4104
	11th to 20th	Day	9% 6% 3 8% 6% 6% 7% 5% 8% 10% 33%	3863
	21st to end	Day	6% 5% 2 6% 4 4 5% 4 7% 10% 47%	4180
September	1st to 10th	Day	9% 5% 2 6% 4 4 5% 5% 6% 9% 45%	2280
	11th to 20th	Day	15% 5% 2 7% 4 5% 4 4 6% 8% 41%	2191
	21st to end	Day	19% 8% 2 6% 4 4 4 3 5% 7% 37%	2028
October	1st to 10th	Day	14% 6% 2 6% 4 3 4 3 4 6% 48%	1900
	11th to 20th	Day	12% 5% 2 4 3 3 3 3 3 5% 56%	1900
	21st to end	Day	12% 4 2 5% 3 2 3 3 4 5% 57%	2090
November	1st to 10th	Day	13% 6% 2 5% 3 3 3 2 4 6% 53%	1957
	11th to 20th	Day	14% 6% 2 5% 3 3 3 2 5% 7% 51%	2000
	21st to end	Day	14% 5% 2 5% 3 3 4 3 4 7% 51%	1656
December	1st to 10th	Day	17% 6% 2 5% 4 4 3 4 5% 6% 43%	1584
	11th to 20th	Day	16% 5% 2 5% 2 2 2 2 4 5% 56%	1951
	21st to end	Day	16% 7% 2 6% 4 4 3 4 5% 7% 42%	3124
January	1st to 10th	Night	15% 7% 2 5% 3 3 4 3 5% 6% 47%	4109
	11th to 20th	Night	14% 8% 3 7% 4 4 4 3 4 5% 45%	4120
	21st to end	Night	18% 7% 2 6% 4 3 3 3 4 5% 44%	4532
February	1st to 10th	Night	17% 6% 2 5% 4 3 4 4 5% 5% 45%	2470
	11th to 20th	Night	19% 7% 2 6% 3 3 4 3 5% 5% 42%	2361
	21st to end	Night	16% 6% 2 5% 3 4 4 4 5% 6% 47%	1765
March	1st to 10th	Night	23% 10% 3 8% 4 4 4 2 4 4 34%	3418
	11th to 20th	Night	13% 7% 2 5% 3 3 3 4 4 6% 51%	3480
	21st to end	Night	17% 5% 2 4 3 4 4 3 4 5% 50%	3817
April	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 8% 48%	1951
	11th to 20th	Night	12% 6% 2 5% 4 4 4 4 4 7% 49%	1875
	21st to end	Night	10% 5% 1 5% 4 4 5% 4 6% 7% 48%	1900
May	1st to 10th	Night	10% 8% 2 9% 5% 4 4 4 6% 8% 39%	2948
	11th to 20th	Night	17% 8% 3 8% 5% 5% 4 3 4 6% 36%	2812
	21st to end	Night	9% 4 2 5% 4 5% 5% 4 7% 9% 46%	3079
June	1st to 10th	Night	10% 5% 2 6% 5% 6% 6% 5% 8% 9% 39%	1710
	11th to 20th	Night	10% 7% 2 6% 5% 5% 5% 4 7% 8% 41%	1710
	21st to end	Night	7% 7% 3 6% 5% 5% 6% 5% 9% 10% 38%	1710
July	1st to 10th	Night	8% 6% 3 8% 5% 4 6% 5% 9% 12% 34%	2840
	11th to 20th	Night	13% 8% 3 7% 5% 4 5% 5% 8% 11% 30%	2840
	21st to end	Night	18% 9% 3 8% 6% 5% 5% 4 7% 8% 28%	3087
August	1st to 10th	Night	22% 9% 3 8% 5% 5% 6% 4 6% 8% 24%	2825
	11th to 20th	Night	8% 6% 3 8% 6% 6% 6% 5% 8% 10% 34%	2934
	21st to end	Night	6% 4 2 5% 4 4 5% 4 8% 11% 46%	3476
September	1st to 10th	Night	11% 6% 2 5% 4 4 5% 5% 5% 9% 44%	1900
	11th to 20th	Night	13% 5% 3 7% 5% 5% 4 3 5% 7% 43%	1985
	21st to end	Night	19% 7% 3 8% 4 4 5% 3 4 6% 36%	2152
October	1st to 10th	Night	14% 5% 3 6% 3 3 3 3 5% 6% 49%	2280
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 6% 54%	2280
	21st to end	Night	11% 4 2 5% 3 3 2 3 4 6% 57%	2508
November	1st to 10th	Night	14% 6% 2 5% 3 2 3 3 4 5% 52%	2341
	11th to 20th	Night	14% 5% 2 5% 4 3 4 3 5% 6% 50%	2400
	21st to end	Night	13% 5% 2 5% 4 3 3 3 5% 7% 51%	2734
December	1st to 10th	Night	18% 6% 2 7% 4 4 3 3 5% 4 43%	2779
	11th to 20th	Night	17% 7% 2 5% 3 3 3 3 4 6% 48%	3239
	21st to end	Night	16% 7% 2 5% 4 3 3 2 5% 6% 47%	4532

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	38% 3 5% 24% 23% 6%	2837
	11th to 20th	Day	36% 3 6% 17% 31% 6%	2840
	21st to end	Day	45% 4 6% 17% 19% 8%	3124
February	1st to 10th	Day	40% 4 10% 21% 20% 5%	1710
	11th to 20th	Day	42% 3 6% 19% 23% 7%	1714
	21st to end	Day	45% 4 8% 17% 20% 6%	1684
March	1st to 10th	Day	49% 4 8% 17% 14% 8%	3435
	11th to 20th	Day	30% 4 8% 19% 25% 13%	3480
	21st to end	Day	43% 4 7% 22% 19% 5%	3815
April	1st to 10th	Day	30% 4 10% 24% 25% 7%	2228
	11th to 20th	Day	34% 4 10% 23% 22% 7%	2254
	21st to end	Day	36% 6% 12% 23% 18% 4	2280
May	1st to 10th	Day	43% 7% 18% 18% 12% 2	4010
	11th to 20th	Day	47% 6% 12% 22% 12% 1	4085
	21st to end	Day	30% 7% 16% 23% 19% 4	4489
June	1st to 10th	Day	39% 7% 16% 21% 16% 1	2470
	11th to 20th	Day	33% 9% 16% 25% 15% 2	2470
	21st to end	Day	36% 10% 16% 21% 14% 2	2470
July	1st to 10th	Day	39% 8% 20% 19% 12% 2	4055
	11th to 20th	Day	47% 7% 25% 15% 4 1	4051
	21st to end	Day	48% 8% 17% 16% 11% 1	4324
August	1st to 10th	Day	57% 6% 18% 13% 5%	4091
	11th to 20th	Day	43% 7% 16% 24% 9% 1	3902
	21st to end	Day	31% 5% 14% 32% 16% 1	4180
September	1st to 10th	Day	35% 8% 15% 19% 19% 4	2280
	11th to 20th	Day	41% 6% 9% 19% 20% 4	2191
	21st to end	Day	46% 6% 10% 19% 14% 4	2028
October	1st to 10th	Day	35% 4 8% 22% 24% 7%	3160
	11th to 20th	Day	21% 2 6% 19% 26% 26%	3140
	21st to end	Day	26% 2 5% 26% 25% 17%	3428
November	1st to 10th	Day	35% 3 7% 23% 26% 6%	1957
	11th to 20th	Day	35% 3 9% 20% 26% 7%	2000
	21st to end	Day	34% 4 7% 23% 25% 7%	1656
December	1st to 10th	Day	42% 3 11% 21% 18% 5%	1584
	11th to 20th	Day	34% 2 7% 25% 24% 8%	1947
	21st to end	Day	41% 5% 9% 22% 21% 2	3124
January	1st to 10th	Night	37% 4 6% 22% 26% 5%	4109
	11th to 20th	Night	42% 3 8% 17% 24% 6%	4120
	21st to end	Night	43% 4 6% 19% 22% 7%	4532
February	1st to 10th	Night	41% 4 8% 20% 21% 6%	2470
	11th to 20th	Night	45% 4 8% 16% 21% 7%	2363
	21st to end	Night	38% 4 9% 20% 21% 8%	1765
March	1st to 10th	Night	56% 4 7% 13% 15% 6%	3418
	11th to 20th	Night	35% 5% 7% 12% 24% 17%	3480
	21st to end	Night	37% 4 8% 24% 21% 6%	3817
April	1st to 10th	Night	36% 4 10% 17% 24% 9%	1951
	11th to 20th	Night	35% 5% 10% 22% 21% 7%	1875
	21st to end	Night	34% 6% 12% 26% 18% 5%	1900
May	1st to 10th	Night	41% 6% 16% 22% 12% 2	2978
	11th to 20th	Night	48% 6% 10% 19% 16% 1	2813
	21st to end	Night	31% 8% 16% 24% 19% 2	3087
June	1st to 10th	Night	38% 9% 17% 20% 14% 2	1710
	11th to 20th	Night	38% 7% 17% 20% 15% 2	1710
	21st to end	Night	37% 12% 16% 20% 13% 2	1710
July	1st to 10th	Night	40% 10% 21% 17% 10% 1	2795
	11th to 20th	Night	46% 10% 25% 14% 5% 1	2786
	21st to end	Night	54% 8% 13% 15% 10%	2988
August	1st to 10th	Night	58% 6% 18% 14% 4 1	2814
	11th to 20th	Night	43% 7% 20% 22% 7% 1	2961
	21st to end	Night	31% 6% 13% 30% 18% 2	3476
September	1st to 10th	Night	35% 10% 14% 20% 16% 5%	1900
	11th to 20th	Night	40% 7% 12% 19% 20% 3	1985
	21st to end	Night	49% 6% 11% 16% 15% 3	2152
October	1st to 10th	Night	38% 3 7% 21% 25% 6%	3800
	11th to 20th	Night	24% 3 5% 17% 27% 23%	3779
	21st to end	Night	22% 2 7% 29% 23% 17%	4120
November	1st to 10th	Night	35% 4 7% 19% 28% 8%	2341
	11th to 20th	Night	36% 4 8% 16% 25% 11%	2400
	21st to end	Night	33% 3 8% 23% 26% 8%	2734
December	1st to 10th	Night	44% 4 8% 20% 19% 5%	2779
	11th to 20th	Night	38% 4 8% 19% 23% 8%	3242
	21st to end	Night	39% 3 6% 25% 23% 3	4532

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	21% 19% 35% 19% 5%	270
	11th to 20th	Day	21% 23% 33% 16% 7%	270
	21st to end	Day	19% 19% 39% 19% 4	297
February	1st to 10th	Day	18% 17% 37% 22% 5% 1	270
	11th to 20th	Day	34% 13% 35% 16% 3	312
	21st to end	Day	24% 18% 32% 20% 6%	382
March	1st to 10th	Day	22% 13% 31% 26% 7%	460
	11th to 20th	Day	20% 16% 37% 20% 6% 1	460
	21st to end	Day	21% 13% 35% 24% 6% 2	506
April	1st to 10th	Day	18% 15% 31% 23% 10% 2	460
	11th to 20th	Day	15% 14% 27% 25% 16% 4	452
	21st to end	Day	17% 10% 26% 25% 20% 2	460
May	1st to 10th	Day	13% 12% 30% 24% 15% 6%	463
	11th to 20th	Day	16% 6% 18% 30% 21% 9%	487
	21st to end	Day	18% 5% 15% 27% 21% 15%	529
June	1st to 10th	Day	11% 4 16% 33% 25% 12%	490
	11th to 20th	Day	10% 3 17% 29% 24% 17%	490
	21st to end	Day	9% 3 15% 29% 30% 14%	490
July	1st to 10th	Day	9% 2 7% 26% 34% 22%	485
	11th to 20th	Day	8% 2 7% 25% 35% 23%	484
	21st to end	Day	10% 2 10% 29% 33% 17%	532
August	1st to 10th	Day	14% 4 12% 23% 31% 15%	486
	11th to 20th	Day	12% 3 8% 25% 32% 20%	479
	21st to end	Day	11% 2 8% 28% 28% 22%	539
September	1st to 10th	Day	13% 2 14% 25% 25% 21%	490
	11th to 20th	Day	18% 2 10% 27% 28% 14%	490
	21st to end	Day	24% 5% 19% 26% 19% 7%	490
October	1st to 10th	Day	16% 4 21% 24% 24% 10%	490
	11th to 20th	Day	12% 9% 22% 32% 19% 7%	490
	21st to end	Day	12% 8% 22% 31% 21% 6%	539
November	1st to 10th	Day	18% 6% 26% 30% 16% 4	495
	11th to 20th	Day	17% 9% 32% 28% 12% 2	500
	21st to end	Day	18% 10% 28% 27% 15% 3	245
December	1st to 10th	Day	19% 12% 37% 25% 6% 2	196
	11th to 20th	Day	21% 7% 35% 23% 12% 1	193
	21st to end	Day	24% 11% 33% 20% 10% 2	297
January	1st to 10th	Night	21% 11% 34% 27% 6% 1	760
	11th to 20th	Night	19% 11% 33% 30% 7%	760
	21st to end	Night	20% 9% 37% 29% 5%	836
February	1st to 10th	Night	20% 8% 39% 29% 4	760
	11th to 20th	Night	24% 11% 41% 22% 2	743
	21st to end	Night	19% 12% 36% 29% 4	628
March	1st to 10th	Night	16% 13% 33% 33% 5%	760
	11th to 20th	Night	20% 9% 37% 27% 6% 1	760
	21st to end	Night	17% 9% 36% 32% 6%	836
April	1st to 10th	Night	18% 12% 33% 29% 7%	760
	11th to 20th	Night	16% 10% 30% 32% 12% 1	751
	21st to end	Night	14% 6% 32% 38% 10%	760
May	1st to 10th	Night	10% 9% 31% 37% 13%	656
	11th to 20th	Night	18% 3 20% 42% 15% 1	561
	21st to end	Night	12% 2 14% 39% 31% 2	617
June	1st to 10th	Night	13% 2 14% 44% 26% 2	570
	11th to 20th	Night	12% 3 14% 36% 30% 4	570
	21st to end	Night	8% 4 12% 40% 33% 4	570
July	1st to 10th	Night	9% 2 8% 38% 39% 4	555
	11th to 20th	Night	8% 3 7% 37% 38% 7%	552
	21st to end	Night	10% 3 10% 36% 39% 3	624
August	1st to 10th	Night	12% 2 8% 40% 34% 4	567
	11th to 20th	Night	11% 3 9% 35% 37% 5%	648
	21st to end	Night	12% 3 8% 32% 38% 8%	836
September	1st to 10th	Night	13% 2 8% 33% 38% 6%	760
	11th to 20th	Night	16% 3 10% 33% 35% 3	760
	21st to end	Night	23% 4 15% 31% 26% 2	760
October	1st to 10th	Night	16% 4 17% 32% 27% 4	760
	11th to 20th	Night	15% 6% 22% 34% 21% 2	760
	21st to end	Night	13% 5% 26% 32% 21% 2	836
November	1st to 10th	Night	18% 4 24% 35% 16% 3	780
	11th to 20th	Night	17% 7% 27% 35% 14% 1	800
	21st to end	Night	15% 7% 29% 33% 15% 1	800
December	1st to 10th	Night	22% 9% 30% 33% 6%	795
	11th to 20th	Night	19% 7% 30% 36% 9%	760
	21st to end	Night	19% 9% 29% 33% 9%	836

Page generated at 2024-12-06 03:54:51. Version ac07

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