Amos
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Amos clear sky chart from 2005-11-06 to 2025-09-04.

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	17% 13% 4 10% 6% 5% 5% 4 5% 6% 26%	126561
	Night	16% 14% 6% 12% 6% 5% 5% 4 5% 5% 23%	122238
Transparency	Day	58% 5% 10% 18% 8% 1	130015
	Night	63% 5% 9% 15% 7% 1	126861
Seeing	Day	24% 15% 33% 19% 7% 2	16170
	Night	25% 13% 30% 23% 8% 1	24952

By Month

Percentage Cloud Cover NE (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	10% 24% 10% 20% 7% 8% 6% 4 4 3 6%	3158
	11th to 20th	Day	9% 17% 8% 18% 10% 5% 6% 5% 7% 5% 10%	3176
	21st to end	Day	9% 15% 7% 18% 6% 7% 7% 4 5% 5% 17%	4124
February	1st to 10th	Day	8% 15% 6% 13% 11% 8% 7% 4 6% 6% 16%	1800
	11th to 20th	Day	9% 19% 6% 15% 7% 6% 6% 5% 6% 5% 17%	1753
	21st to end	Day	12% 16% 7% 14% 7% 5% 4 5% 5% 6% 20%	1502
March	1st to 10th	Day	19% 16% 4 10% 7% 4 6% 3 4 4 22%	4702
	11th to 20th	Day	17% 16% 6% 14% 6% 4 3 2 3 4 24%	4980
	21st to end	Day	12% 16% 5% 14% 6% 6% 5% 3 3 4 26%	5592
April	1st to 10th	Day	19% 16% 5% 10% 5% 6% 4 3 4 5% 24%	2400
	11th to 20th	Day	21% 12% 4 9% 4 4 4 2 4 6% 30%	2482
	21st to end	Day	21% 14% 3 7% 5% 3 5% 3 4 5% 30%	2630
May	1st to 10th	Day	16% 11% 4 8% 5% 4 4 4 5% 6% 34%	6346
	11th to 20th	Day	14% 9% 3 8% 5% 5% 6% 4 6% 7% 32%	6318
	21st to end	Day	19% 11% 3 7% 4 4 4 3 4 6% 35%	6985
June	1st to 10th	Day	22% 8% 2 7% 5% 4 5% 4 6% 7% 29%	3000
	11th to 20th	Day	15% 8% 3 9% 5% 5% 5% 4 6% 7% 34%	3000
	21st to end	Day	21% 7% 3 6% 6% 4 5% 4 6% 7% 31%	3000
July	1st to 10th	Day	16% 7% 3 7% 5% 6% 6% 5% 7% 9% 29%	6819
	11th to 20th	Day	17% 6% 2 7% 5% 5% 5% 5% 7% 9% 34%	6820
	21st to end	Day	16% 8% 2 7% 5% 5% 5% 5% 6% 9% 32%	6977
August	1st to 10th	Day	16% 7% 2 7% 5% 5% 6% 5% 7% 9% 31%	4471
	11th to 20th	Day	18% 8% 3 7% 5% 4 5% 4 6% 7% 33%	4174
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	4524
September	1st to 10th	Day	20% 8% 3 7% 4 4 5% 5% 6% 6% 32%	2316
	11th to 20th	Day	21% 8% 3 7% 4 4 5% 4 6% 7% 31%	2272
	21st to end	Day	24% 11% 3 7% 5% 4 4 3 4 5% 30%	1987
October	1st to 10th	Day	22% 11% 3 7% 5% 4 4 3 5% 5% 30%	1900
	11th to 20th	Day	29% 21% 4 8% 4 3 3 3 3 4 18%	1900
	21st to end	Day	28% 17% 5% 9% 5% 5% 4 3 4 4 15%	1948
November	1st to 10th	Day	21% 21% 6% 10% 6% 4 4 3 3 5% 17%	1566
	11th to 20th	Day	21% 19% 8% 14% 6% 5% 3 3 4 4 13%	1600
	21st to end	Day	23% 27% 8% 12% 7% 4 3 2 3 3 7%	1600
December	1st to 10th	Day	14% 25% 12% 17% 7% 4 4 3 4 3 8%	2600
	11th to 20th	Day	13% 22% 7% 14% 9% 7% 4 4 3 3 14%	2663
	21st to end	Day	18% 21% 6% 17% 8% 6% 4 3 3 3 10%	3476
January	1st to 10th	Night	10% 21% 11% 21% 8% 5% 4 3 3 3 9%	6808
	11th to 20th	Night	9% 16% 8% 20% 10% 6% 6% 6% 5% 4 10%	6712
	21st to end	Night	7% 15% 10% 17% 7% 7% 7% 5% 5% 5% 14%	6830
February	1st to 10th	Night	9% 17% 5% 11% 10% 7% 7% 4 5% 7% 18%	2600
	11th to 20th	Night	12% 16% 7% 14% 9% 5% 5% 4 4 6% 18%	2533
	21st to end	Night	10% 16% 5% 13% 8% 7% 6% 5% 5% 5% 20%	2127
March	1st to 10th	Night	17% 17% 5% 11% 6% 5% 4 4 5% 4 22%	5134
	11th to 20th	Night	16% 19% 5% 14% 7% 6% 5% 3 4 4 17%	4979
	21st to end	Night	13% 13% 4 11% 6% 8% 5% 4 4 5% 26%	5340
April	1st to 10th	Night	20% 14% 4 11% 5% 4 3 2 4 5% 28%	2000
	11th to 20th	Night	18% 11% 4 8% 5% 4 5% 4 5% 6% 30%	1883
	21st to end	Night	19% 10% 4 8% 5% 3 4 3 4 5% 34%	1768
May	1st to 10th	Night	18% 9% 4 7% 5% 5% 4 4 5% 6% 34%	3594
	11th to 20th	Night	17% 9% 4 7% 4 4 4 4 5% 6% 37%	3575
	21st to end	Night	20% 8% 2 6% 4 4 4 4 6% 7% 33%	3887
June	1st to 10th	Night	20% 7% 4 7% 6% 5% 4 4 7% 7% 30%	1400
	11th to 20th	Night	17% 9% 3 6% 4 4 3 4 5% 6% 38%	1400
	21st to end	Night	15% 7% 2 7% 5% 6% 5% 4 6% 7% 36%	1400
July	1st to 10th	Night	18% 9% 3 6% 5% 4 5% 4 5% 8% 35%	3160
	11th to 20th	Night	18% 8% 4 7% 5% 4 5% 4 5% 7% 35%	3160
	21st to end	Night	14% 7% 3 6% 4 4 4 4 5% 8% 42%	3876
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 6% 5% 7% 7% 36%	2674
	11th to 20th	Night	15% 7% 3 7% 5% 5% 5% 4 5% 7% 37%	2875
	21st to end	Night	16% 7% 3 7% 4 5% 4 3 6% 7% 37%	3340
September	1st to 10th	Night	19% 9% 3 6% 5% 4 4 3 5% 6% 36%	1931
	11th to 20th	Night	21% 7% 2 6% 4 4 4 3 4 7% 37%	1905
	21st to end	Night	22% 9% 3 7% 4 3 4 2 5% 6% 35%	2192
October	1st to 10th	Night	21% 9% 3 8% 4 5% 5% 4 5% 6% 31%	2280
	11th to 20th	Night	26% 17% 5% 9% 5% 4 4 3 4 5% 19%	2280
	21st to end	Night	24% 19% 5% 9% 5% 4 4 3 4 5% 19%	2643
November	1st to 10th	Night	20% 18% 5% 10% 6% 6% 4 3 4 5% 19%	2732
	11th to 20th	Night	19% 18% 6% 13% 8% 5% 3 3 5% 5% 16%	2800
	21st to end	Night	21% 23% 7% 14% 7% 5% 4 3 4 3 10%	2800
December	1st to 10th	Night	14% 23% 9% 19% 9% 7% 4 3 3 3 7%	4580
	11th to 20th	Night	15% 20% 6% 14% 9% 9% 5% 4 4 4 11%	5538
	21st to end	Night	19% 20% 9% 16% 8% 5% 4 2 3 3 12%	7502

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	85% 3 6% 5% 1	3159
	11th to 20th	Day	74% 3 6% 11% 6%	3203
	21st to end	Day	69% 3 7% 16% 6%	4124
February	1st to 10th	Day	68% 4 6% 14% 7%	1800
	11th to 20th	Day	69% 4 8% 13% 5%	1762
	21st to end	Day	65% 3 8% 16% 6% 1	1502
March	1st to 10th	Day	66% 3 6% 14% 10% 1	4705
	11th to 20th	Day	66% 3 7% 16% 8% 1	4980
	21st to end	Day	64% 3 5% 19% 8% 1	5592
April	1st to 10th	Day	63% 4 8% 12% 11% 1	2400
	11th to 20th	Day	57% 4 7% 18% 12% 1	2482
	21st to end	Day	57% 4 8% 16% 13% 2	2630
May	1st to 10th	Day	50% 6% 7% 17% 17% 3	6357
	11th to 20th	Day	48% 7% 13% 20% 9% 2	6322
	21st to end	Day	51% 5% 8% 20% 15% 2	6985
June	1st to 10th	Day	52% 6% 10% 21% 10% 1	3000
	11th to 20th	Day	48% 6% 8% 23% 12% 2	3000
	21st to end	Day	51% 7% 10% 23% 9% 1	3000
July	1st to 10th	Day	48% 8% 14% 24% 6%	6746
	11th to 20th	Day	44% 7% 18% 23% 7%	6739
	21st to end	Day	48% 7% 12% 26% 7%	6778
August	1st to 10th	Day	47% 7% 16% 24% 4	4457
	11th to 20th	Day	49% 7% 14% 22% 8%	4213
	21st to end	Day	45% 6% 11% 29% 9%	4524
September	1st to 10th	Day	51% 7% 13% 21% 8% 1	2316
	11th to 20th	Day	52% 7% 16% 20% 5%	2272
	21st to end	Day	57% 5% 11% 20% 7%	1987
October	1st to 10th	Day	60% 4 10% 20% 5% 1	3160
	11th to 20th	Day	66% 4 12% 13% 5%	3140
	21st to end	Day	70% 5% 12% 8% 5%	3175
November	1st to 10th	Day	72% 4 12% 8% 4	1566
	11th to 20th	Day	77% 3 8% 9% 3	1600
	21st to end	Day	85% 3 7% 4 1	1600
December	1st to 10th	Day	83% 4 5% 7% 1	2600
	11th to 20th	Day	76% 3 5% 13% 3	2663
	21st to end	Day	81% 3 5% 8% 3	3476
January	1st to 10th	Night	81% 4 7% 5% 3	6808
	11th to 20th	Night	77% 4 6% 7% 7%	6760
	21st to end	Night	71% 4 5% 14% 6%	6830
February	1st to 10th	Night	66% 4 8% 13% 8%	2600
	11th to 20th	Night	68% 4 7% 13% 6%	2535
	21st to end	Night	66% 4 7% 15% 7% 1	2127
March	1st to 10th	Night	64% 3 6% 11% 12% 3	5144
	11th to 20th	Night	72% 4 7% 10% 6% 1	4980
	21st to end	Night	61% 4 6% 17% 10% 2	5340
April	1st to 10th	Night	61% 3 7% 15% 13% 1	2000
	11th to 20th	Night	53% 5% 8% 20% 12% 1	1883
	21st to end	Night	53% 4 7% 19% 15% 2	1768
May	1st to 10th	Night	49% 7% 8% 17% 17% 2	3600
	11th to 20th	Night	46% 7% 11% 21% 13% 2	3576
	21st to end	Night	48% 6% 11% 18% 14% 3	3888
June	1st to 10th	Night	52% 7% 7% 22% 12% 1	1400
	11th to 20th	Night	46% 7% 8% 22% 15% 3	1400
	21st to end	Night	46% 7% 12% 24% 11% 1	1400
July	1st to 10th	Night	48% 5% 12% 25% 9%	3125
	11th to 20th	Night	47% 6% 13% 25% 8%	3118
	21st to end	Night	42% 5% 17% 31% 5%	3761
August	1st to 10th	Night	43% 8% 16% 29% 5%	2664
	11th to 20th	Night	45% 7% 16% 25% 6%	2902
	21st to end	Night	45% 6% 14% 25% 9% 2	3340
September	1st to 10th	Night	48% 7% 14% 21% 9% 1	1931
	11th to 20th	Night	48% 6% 16% 23% 7%	1905
	21st to end	Night	51% 5% 12% 25% 7%	2192
October	1st to 10th	Night	54% 5% 13% 20% 7%	3800
	11th to 20th	Night	64% 4 10% 21% 2	3779
	21st to end	Night	64% 5% 14% 10% 6% 1	4354
November	1st to 10th	Night	67% 6% 13% 12% 2	2732
	11th to 20th	Night	72% 4 10% 11% 3	2800
	21st to end	Night	80% 4 8% 8% 1	2800
December	1st to 10th	Night	84% 3 6% 6% 1	4580
	11th to 20th	Night	78% 3 7% 10% 2	5537
	21st to end	Night	80% 2 5% 10% 3	7502

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	19% 22% 42% 12% 4 2	200
	11th to 20th	Day	22% 15% 37% 21% 5% 2	200
	21st to end	Day	14% 15% 42% 21% 7% 1	257
February	1st to 10th	Day	17% 27% 37% 15% 3 1	300
	11th to 20th	Day	21% 25% 37% 14% 3	300
	21st to end	Day	25% 21% 38% 12% 3	266
March	1st to 10th	Day	22% 19% 40% 14% 5%	500
	11th to 20th	Day	27% 18% 34% 16% 5%	500
	21st to end	Day	25% 18% 37% 13% 5% 1	550
April	1st to 10th	Day	25% 19% 32% 15% 8% 1	500
	11th to 20th	Day	28% 19% 28% 17% 6% 3	492
	21st to end	Day	30% 20% 28% 16% 5% 1	500
May	1st to 10th	Day	22% 16% 32% 22% 6% 2	503
	11th to 20th	Day	23% 16% 33% 18% 7% 2	527
	21st to end	Day	26% 15% 31% 20% 6% 1	583
June	1st to 10th	Day	26% 13% 34% 21% 6% 1	730
	11th to 20th	Day	21% 15% 35% 20% 6% 2	730
	21st to end	Day	22% 11% 34% 22% 10% 2	730
July	1st to 10th	Day	19% 12% 33% 25% 9% 1	721
	11th to 20th	Day	15% 15% 36% 23% 10% 1	718
	21st to end	Day	18% 10% 36% 23% 10% 2	601
August	1st to 10th	Day	21% 9% 29% 28% 9% 4	526
	11th to 20th	Day	17% 9% 29% 26% 13% 6%	519
	21st to end	Day	21% 13% 28% 22% 12% 5%	583
September	1st to 10th	Day	24% 12% 31% 21% 9% 4	502
	11th to 20th	Day	22% 10% 32% 22% 12% 2	490
	21st to end	Day	28% 13% 27% 18% 11% 2	490
October	1st to 10th	Day	28% 17% 27% 17% 9% 2	490
	11th to 20th	Day	37% 19% 27% 12% 4 1	490
	21st to end	Day	34% 17% 31% 15% 3 1	452
November	1st to 10th	Day	36% 22% 33% 9% 1	200
	11th to 20th	Day	31% 16% 37% 13% 3 1	200
	21st to end	Day	43% 18% 30% 7% 3 1	200
December	1st to 10th	Day	26% 17% 32% 19% 7% 1	200
	11th to 20th	Day	26% 15% 43% 10% 6% 1	200
	21st to end	Day	32% 14% 31% 15% 5% 2	220
January	1st to 10th	Night	26% 13% 36% 20% 5% 1	1000
	11th to 20th	Night	25% 14% 33% 22% 6%	979
	21st to end	Night	16% 12% 32% 27% 12% 1	880
February	1st to 10th	Night	17% 17% 35% 23% 6% 1	800
	11th to 20th	Night	22% 14% 35% 23% 6%	783
	21st to end	Night	18% 20% 37% 20% 5%	660
March	1st to 10th	Night	20% 19% 32% 22% 6% 1	800
	11th to 20th	Night	27% 19% 31% 20% 4 1	800
	21st to end	Night	21% 15% 37% 21% 5% 1	880
April	1st to 10th	Night	29% 15% 28% 21% 7%	800
	11th to 20th	Night	25% 17% 25% 25% 7% 1	699
	21st to end	Night	23% 14% 33% 24% 6% 1	568
May	1st to 10th	Night	21% 11% 35% 26% 8% 1	400
	11th to 20th	Night	24% 10% 29% 30% 7% 1	394
	21st to end	Night	25% 10% 31% 28% 6%	433
June	1st to 10th	Night	22% 9% 32% 28% 8% 1	400
	11th to 20th	Night	21% 10% 33% 28% 8% 1	400
	21st to end	Night	16% 8% 31% 32% 12% 1	400
July	1st to 10th	Night	21% 8% 29% 33% 9% 1	390
	11th to 20th	Night	16% 8% 27% 38% 11%	388
	21st to end	Night	15% 8% 26% 37% 15% 1	438
August	1st to 10th	Night	18% 6% 26% 29% 19% 2	447
	11th to 20th	Night	18% 7% 24% 30% 20% 1	594
	21st to end	Night	22% 8% 27% 26% 14% 2	725
September	1st to 10th	Night	24% 9% 28% 24% 12% 2	773
	11th to 20th	Night	25% 11% 27% 25% 12% 1	760
	21st to end	Night	26% 12% 23% 26% 12% 1	760
October	1st to 10th	Night	28% 13% 27% 24% 8% 1	760
	11th to 20th	Night	35% 14% 26% 18% 6% 1	760
	21st to end	Night	36% 11% 31% 17% 5%	836
November	1st to 10th	Night	30% 14% 34% 15% 6%	780
	11th to 20th	Night	30% 17% 31% 16% 7%	800
	21st to end	Night	33% 18% 30% 15% 3 1	800
December	1st to 10th	Night	31% 15% 30% 19% 6% 1	800
	11th to 20th	Night	27% 15% 32% 19% 6% 1	965
	21st to end	Night	31% 16% 27% 19% 6% 1	1100

Page generated at 2025-09-01 01:51:06. Version ac07

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