Amanda
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Amanda 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	15% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	120370
	Night	15% 11% 4 8% 5% 4 4 3 5% 7% 34%	118765
Transparency	Day	49% 5% 10% 21% 13% 2	124073
	Night	49% 5% 10% 21% 13% 2	123186
Seeing	Day	20% 13% 27% 21% 14% 6%	15779
	Night	19% 10% 27% 29% 14% 2	25858

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% 20% 9% 16% 8% 4 4 3 3 4 16%	4056
	11th to 20th	Day	13% 20% 7% 13% 7% 8% 4 3 4 3 17%	4060
	21st to end	Day	21% 15% 7% 10% 8% 6% 6% 3 4 4 17%	4466
February	1st to 10th	Day	21% 14% 5% 10% 6% 4 4 3 4 6% 24%	1800
	11th to 20th	Day	18% 14% 5% 13% 6% 4 4 3 5% 5% 25%	1925
	21st to end	Day	19% 15% 4 9% 5% 4 3 2 4 5% 29%	1650
March	1st to 10th	Day	16% 14% 6% 10% 5% 4 4 2 4 6% 28%	4709
	11th to 20th	Day	13% 8% 4 8% 5% 5% 5% 3 5% 6% 39%	4980
	21st to end	Day	19% 9% 4 9% 5% 4 4 3 4 6% 33%	5465
April	1st to 10th	Day	16% 12% 4 7% 6% 4 4 3 5% 6% 33%	2228
	11th to 20th	Day	17% 9% 3 7% 4 4 4 4 5% 6% 37%	2527
	21st to end	Day	18% 9% 3 6% 5% 4 5% 4 5% 7% 33%	2600
May	1st to 10th	Day	21% 10% 3 7% 5% 4 5% 4 6% 7% 28%	5862
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 4 6% 8% 31%	5861
	21st to end	Day	16% 6% 2 7% 5% 5% 6% 5% 7% 9% 33%	6433
June	1st to 10th	Day	12% 7% 2 6% 4 6% 5% 5% 7% 9% 38%	2600
	11th to 20th	Day	10% 6% 3 7% 6% 5% 6% 4 7% 9% 38%	2600
	21st to end	Day	11% 7% 2 5% 6% 5% 6% 4 8% 10% 36%	2600
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 4 4 6% 9% 40%	4250
	11th to 20th	Day	9% 5% 2 6% 4 4 6% 5% 7% 11% 41%	4250
	21st to end	Day	12% 7% 3 7% 5% 6% 6% 5% 7% 8% 34%	4466
August	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 5% 7% 10% 37%	4104
	11th to 20th	Day	9% 7% 2 6% 5% 5% 6% 5% 7% 9% 38%	4044
	21st to end	Day	6% 4 2 6% 4 5% 5% 4 7% 9% 49%	4450
September	1st to 10th	Day	14% 5% 2 4 3 3 5% 4 6% 8% 46%	2090
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 3 5% 8% 49%	2090
	21st to end	Day	19% 7% 3 6% 4 3 4 3 4 5% 42%	2090
October	1st to 10th	Day	12% 7% 3 6% 4 3 4 5% 6% 6% 44%	2031
	11th to 20th	Day	15% 7% 2 6% 5% 5% 3 3 5% 6% 43%	1900
	21st to end	Day	21% 8% 3 7% 4 3 3 3 4 6% 36%	2052
November	1st to 10th	Day	10% 7% 2 6% 5% 3 3 3 5% 5% 50%	1762
	11th to 20th	Day	16% 13% 5% 7% 4 4 4 3 4 6% 33%	1800
	21st to end	Day	18% 12% 4 9% 5% 4 4 3 4 7% 30%	1800
December	1st to 10th	Day	19% 12% 5% 13% 6% 4 4 3 4 5% 24%	2930
	11th to 20th	Day	23% 16% 6% 11% 5% 3 4 3 5% 6% 19%	3373
	21st to end	Day	19% 21% 6% 11% 6% 5% 5% 4 4 5% 15%	4466
January	1st to 10th	Night	14% 19% 8% 16% 7% 5% 3 3 4 4 18%	5889
	11th to 20th	Night	13% 18% 7% 16% 7% 6% 5% 3 4 4 17%	5900
	21st to end	Night	20% 13% 6% 10% 7% 4 3 3 3 4 27%	6490
February	1st to 10th	Night	21% 13% 4 10% 5% 5% 3 3 4 5% 29%	2600
	11th to 20th	Night	19% 15% 3 10% 5% 5% 4 4 4 6% 27%	2358
	21st to end	Night	19% 15% 5% 10% 4 4 4 3 3 5% 28%	1980
March	1st to 10th	Night	18% 12% 4 7% 4 4 3 3 4 6% 35%	5143
	11th to 20th	Night	13% 8% 3 5% 4 4 4 3 6% 8% 42%	4980
	21st to end	Night	17% 10% 4 8% 5% 4 4 3 5% 5% 34%	5467
April	1st to 10th	Night	17% 10% 4 6% 4 4 5% 4 5% 7% 36%	2190
	11th to 20th	Night	14% 8% 3 8% 5% 4 4 4 6% 7% 38%	1820
	21st to end	Night	15% 8% 3 7% 4 5% 4 3 6% 8% 37%	1800
May	1st to 10th	Night	23% 9% 3 7% 5% 4 4 4 6% 7% 27%	4033
	11th to 20th	Night	16% 8% 3 6% 4 4 4 4 7% 10% 35%	4032
	21st to end	Night	13% 7% 2 8% 4 4 4 4 6% 9% 37%	4421
June	1st to 10th	Night	9% 6% 2 5% 4 4 4 3 6% 9% 46%	1800
	11th to 20th	Night	9% 5% 3 5% 3 5% 5% 4 9% 10% 43%	1800
	21st to end	Night	9% 6% 2 5% 5% 3 5% 5% 6% 10% 44%	1800
July	1st to 10th	Night	11% 6% 3 6% 3 4 4 4 6% 7% 46%	2930
	11th to 20th	Night	8% 5% 2 5% 5% 5% 5% 4 7% 9% 46%	2930
	21st to end	Night	8% 6% 3 8% 6% 5% 5% 5% 8% 8% 38%	3087
August	1st to 10th	Night	6% 7% 3 8% 5% 5% 5% 5% 7% 10% 39%	2825
	11th to 20th	Night	9% 8% 3 8% 4 4 4 3 5% 7% 44%	2785
	21st to end	Night	4 3 2 5% 3 5% 5% 4 7% 10% 52%	3183
September	1st to 10th	Night	12% 5% 2 4 3 3 5% 3 5% 7% 52%	2076
	11th to 20th	Night	9% 4 2 5% 3 3 4 3 5% 7% 55%	2090
	21st to end	Night	14% 7% 2 5% 4 3 3 3 4 6% 47%	2090
October	1st to 10th	Night	10% 6% 3 5% 4 4 4 3 5% 7% 50%	2147
	11th to 20th	Night	15% 8% 2 6% 4 3 4 3 5% 6% 44%	2280
	21st to end	Night	20% 8% 2 6% 4 3 4 3 5% 6% 40%	2541
November	1st to 10th	Night	15% 7% 2 5% 4 3 3 2 4 6% 49%	2536
	11th to 20th	Night	17% 11% 3 8% 5% 4 4 3 5% 6% 35%	2600
	21st to end	Night	20% 13% 4 7% 5% 4 4 3 5% 6% 30%	2600
December	1st to 10th	Night	17% 13% 5% 10% 5% 4 4 3 5% 6% 28%	4250
	11th to 20th	Night	19% 17% 7% 10% 4 4 4 2 5% 5% 24%	4822
	21st to end	Night	20% 20% 6% 11% 6% 5% 4 3 4 5% 16%	6490

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	73% 4 8% 11% 4	4057
	11th to 20th	Day	72% 3 7% 9% 7% 1	4060
	21st to end	Day	71% 4 9% 10% 6% 1	4466
February	1st to 10th	Day	62% 4 10% 15% 9%	1800
	11th to 20th	Day	62% 4 9% 16% 9%	1935
	21st to end	Day	58% 3 11% 18% 8% 1	1650
March	1st to 10th	Day	58% 4 7% 22% 8% 2	4709
	11th to 20th	Day	44% 5% 9% 29% 11% 1	4980
	21st to end	Day	52% 4 10% 21% 11% 2	5465
April	1st to 10th	Day	53% 4 10% 20% 11% 2	2228
	11th to 20th	Day	48% 4 11% 21% 14% 3	2527
	21st to end	Day	50% 5% 10% 21% 12% 2	2600
May	1st to 10th	Day	54% 7% 9% 19% 10% 1	5897
	11th to 20th	Day	51% 6% 10% 21% 11% 1	5865
	21st to end	Day	45% 7% 13% 21% 13% 2	6447
June	1st to 10th	Day	42% 7% 11% 23% 16% 2	2600
	11th to 20th	Day	41% 8% 14% 21% 15% 1	2600
	21st to end	Day	42% 8% 13% 21% 14% 2	2600
July	1st to 10th	Day	42% 6% 11% 22% 17% 2	4185
	11th to 20th	Day	35% 7% 11% 30% 16% 1	4181
	21st to end	Day	45% 7% 11% 17% 17% 4	4324
August	1st to 10th	Day	39% 7% 14% 28% 10% 1	4091
	11th to 20th	Day	39% 6% 11% 29% 14% 1	4083
	21st to end	Day	31% 7% 14% 30% 15% 3	4450
September	1st to 10th	Day	35% 6% 10% 22% 22% 4	2090
	11th to 20th	Day	33% 5% 11% 26% 22% 3	2090
	21st to end	Day	45% 4 9% 21% 20% 1	2090
October	1st to 10th	Day	26% 4 8% 31% 29% 2	3369
	11th to 20th	Day	34% 3 10% 27% 22% 3	3140
	21st to end	Day	37% 3 10% 27% 20% 2	3366
November	1st to 10th	Day	36% 4 9% 29% 18% 3	1762
	11th to 20th	Day	52% 4 7% 20% 14% 3	1800
	21st to end	Day	55% 4 10% 20% 11% 1	1800
December	1st to 10th	Day	63% 3 11% 18% 5%	2930
	11th to 20th	Day	67% 3 9% 16% 5%	3370
	21st to end	Day	72% 5% 9% 10% 4	4466
January	1st to 10th	Night	71% 3 8% 14% 3	5889
	11th to 20th	Night	71% 3 9% 10% 6% 1	5900
	21st to end	Night	63% 2 10% 16% 7% 2	6490
February	1st to 10th	Night	59% 4 11% 18% 8% 1	2600
	11th to 20th	Night	60% 3 8% 17% 11% 1	2359
	21st to end	Night	60% 4 9% 16% 9% 2	1980
March	1st to 10th	Night	52% 4 6% 26% 10% 2	5143
	11th to 20th	Night	40% 5% 9% 31% 13% 1	4980
	21st to end	Night	51% 3 8% 23% 13% 2	5467
April	1st to 10th	Night	48% 5% 11% 20% 14% 2	2190
	11th to 20th	Night	43% 5% 11% 18% 18% 4	1820
	21st to end	Night	45% 5% 9% 23% 15% 2	1800
May	1st to 10th	Night	55% 7% 10% 17% 8% 4	4060
	11th to 20th	Night	44% 8% 11% 24% 12% 1	4033
	21st to end	Night	41% 7% 14% 26% 9% 3	4429
June	1st to 10th	Night	35% 7% 12% 23% 21% 2	1800
	11th to 20th	Night	33% 8% 16% 23% 18% 2	1800
	21st to end	Night	33% 8% 14% 23% 19% 3	1800
July	1st to 10th	Night	37% 5% 12% 24% 18% 5%	2885
	11th to 20th	Night	33% 7% 13% 30% 16% 1	2876
	21st to end	Night	41% 8% 12% 20% 14% 5%	2988
August	1st to 10th	Night	38% 8% 15% 26% 11% 1	2814
	11th to 20th	Night	39% 6% 10% 24% 21% 1	2812
	21st to end	Night	26% 7% 15% 29% 20% 3	3183
September	1st to 10th	Night	33% 4 12% 23% 22% 6%	2076
	11th to 20th	Night	29% 5% 11% 25% 26% 3	2090
	21st to end	Night	39% 4 9% 21% 26% 1	2090
October	1st to 10th	Night	28% 4 6% 28% 30% 3	3576
	11th to 20th	Night	31% 3 9% 27% 24% 6%	3779
	21st to end	Night	33% 3 8% 26% 25% 5%	4177
November	1st to 10th	Night	38% 3 11% 25% 20% 3	2536
	11th to 20th	Night	50% 3 8% 21% 15% 3	2600
	21st to end	Night	56% 4 10% 19% 10% 1	2600
December	1st to 10th	Night	57% 3 13% 21% 5%	4250
	11th to 20th	Night	64% 3 11% 17% 5%	4824
	21st to end	Night	70% 5% 9% 13% 4	6490

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	25% 24% 35% 12% 3 1	300
	11th to 20th	Day	28% 24% 37% 9% 2	300
	21st to end	Day	30% 22% 33% 11% 3	330
February	1st to 10th	Day	30% 22% 32% 13% 2	300
	11th to 20th	Day	33% 27% 29% 9% 2	300
	21st to end	Day	30% 25% 37% 7%	249
March	1st to 10th	Day	23% 26% 30% 18% 4	399
	11th to 20th	Day	26% 20% 33% 14% 7%	500
	21st to end	Day	31% 17% 32% 17% 4	550
April	1st to 10th	Day	24% 17% 33% 16% 9% 2	500
	11th to 20th	Day	25% 17% 30% 19% 7% 3	492
	21st to end	Day	22% 17% 31% 19% 10% 1	500
May	1st to 10th	Day	27% 17% 28% 16% 8% 3	503
	11th to 20th	Day	21% 12% 28% 21% 12% 5%	527
	21st to end	Day	14% 9% 25% 27% 18% 6%	573
June	1st to 10th	Day	13% 7% 26% 29% 18% 6%	530
	11th to 20th	Day	14% 7% 23% 30% 20% 6%	530
	21st to end	Day	12% 6% 27% 28% 18% 8%	530
July	1st to 10th	Day	16% 3 16% 23% 23% 20%	525
	11th to 20th	Day	11% 5% 20% 27% 27% 10%	524
	21st to end	Day	13% 4 17% 29% 23% 14%	532
August	1st to 10th	Day	11% 4 16% 28% 27% 13%	486
	11th to 20th	Day	13% 4 23% 29% 20% 11%	479
	21st to end	Day	9% 4 17% 28% 28% 14%	539
September	1st to 10th	Day	12% 7% 16% 26% 27% 13%	490
	11th to 20th	Day	11% 2 14% 26% 31% 15%	490
	21st to end	Day	24% 8% 18% 26% 20% 5%	490
October	1st to 10th	Day	12% 8% 26% 29% 18% 8%	490
	11th to 20th	Day	16% 14% 31% 22% 14% 3	490
	21st to end	Day	24% 15% 32% 20% 8% 1	501
November	1st to 10th	Day	15% 15% 38% 21% 9% 2	300
	11th to 20th	Day	28% 19% 27% 19% 7% 1	300
	21st to end	Day	25% 20% 35% 18% 3	300
December	1st to 10th	Day	25% 22% 34% 13% 4 2	300
	11th to 20th	Day	27% 23% 33% 11% 5%	300
	21st to end	Day	30% 21% 32% 15% 3	330
January	1st to 10th	Night	23% 21% 34% 18% 4	800
	11th to 20th	Night	27% 20% 31% 20% 2	800
	21st to end	Night	25% 16% 34% 23% 2	880
February	1st to 10th	Night	27% 14% 33% 24% 2	800
	11th to 20th	Night	28% 16% 35% 21% 1	783
	21st to end	Night	27% 15% 37% 20% 2	660
March	1st to 10th	Night	23% 15% 33% 24% 5%	800
	11th to 20th	Night	21% 16% 34% 23% 6%	800
	21st to end	Night	25% 14% 32% 23% 7%	880
April	1st to 10th	Night	21% 14% 34% 24% 6%	790
	11th to 20th	Night	18% 10% 37% 23% 11% 1	593
	21st to end	Night	18% 9% 40% 26% 7% 1	600
May	1st to 10th	Night	20% 10% 31% 26% 13%	600
	11th to 20th	Night	19% 7% 25% 31% 16% 1	591
	21st to end	Night	10% 3 24% 36% 25% 2	650
June	1st to 10th	Night	11% 2 26% 40% 20% 1	600
	11th to 20th	Night	10% 2 21% 42% 24% 1	600
	21st to end	Night	10% 4 21% 38% 24% 2	600
July	1st to 10th	Night	10% 3 16% 37% 28% 7%	585
	11th to 20th	Night	7% 2 15% 36% 35% 5%	582
	21st to end	Night	9% 3 13% 38% 35% 2	624
August	1st to 10th	Night	7% 2 13% 40% 34% 3	567
	11th to 20th	Night	9% 2 11% 42% 32% 4	564
	21st to end	Night	8% 1 15% 33% 36% 7%	627
September	1st to 10th	Night	14% 3 16% 37% 27% 4	746
	11th to 20th	Night	10% 2 13% 36% 33% 6%	760
	21st to end	Night	18% 6% 21% 32% 21% 2	760
October	1st to 10th	Night	11% 6% 24% 33% 22% 4	760
	11th to 20th	Night	18% 9% 29% 30% 12% 2	760
	21st to end	Night	24% 11% 26% 29% 10%	836
November	1st to 10th	Night	19% 9% 26% 30% 15% 1	780
	11th to 20th	Night	22% 15% 29% 26% 9% 1	800
	21st to end	Night	27% 11% 27% 29% 5% 1	800
December	1st to 10th	Night	30% 15% 27% 23% 5%	800
	11th to 20th	Night	27% 13% 32% 23% 5% 1	800
	21st to end	Night	28% 14% 31% 24% 3	880

Page generated at 2025-07-18 01:10:04. Version ac07

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