Maple-Brook Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maple-Brook Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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	20% 12% 4 9% 5% 4 4 3 5% 6% 27%	131608
	Night	20% 12% 4 10% 5% 4 4 3 4 5% 27%	129357
Transparency	Day	58% 3 10% 19% 9% 1	135176
	Night	59% 3 10% 19% 9% 1	133877
Seeing	Day	30% 17% 31% 16% 5% 1	19093
	Night	28% 15% 30% 21% 5%	26729

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	13% 16% 7% 18% 9% 5% 4 3 3 4 18%	4690
	11th to 20th	Day	17% 17% 9% 19% 7% 4 4 3 3 4 13%	4776
	21st to end	Day	14% 11% 5% 12% 9% 7% 6% 4 5% 5% 23%	5781
February	1st to 10th	Day	18% 15% 6% 12% 7% 6% 4 3 4 4 19%	1890
	11th to 20th	Day	17% 17% 5% 13% 6% 4 4 3 4 5% 23%	1798
	21st to end	Day	12% 17% 5% 8% 7% 5% 4 3 3 7% 29%	1530
March	1st to 10th	Day	23% 15% 5% 12% 5% 5% 3 2 3 3 23%	4858
	11th to 20th	Day	14% 19% 6% 9% 4 4 4 3 4 5% 27%	4980
	21st to end	Day	27% 17% 4 10% 5% 4 4 3 4 4 20%	5501
April	1st to 10th	Day	25% 17% 5% 8% 5% 4 3 2 3 5% 24%	2400
	11th to 20th	Day	20% 14% 3 7% 4 4 4 4 5% 6% 29%	2421
	21st to end	Day	23% 14% 3 7% 4 3 4 3 5% 5% 27%	2600
May	1st to 10th	Day	28% 15% 4 7% 4 4 4 3 5% 6% 19%	6102
	11th to 20th	Day	23% 12% 3 9% 4 4 4 3 4 5% 28%	6318
	21st to end	Day	20% 12% 3 7% 4 4 5% 3 5% 7% 28%	6948
June	1st to 10th	Day	26% 11% 3 6% 5% 5% 4 4 5% 6% 24%	2800
	11th to 20th	Day	22% 9% 3 7% 4 4 4 3 6% 6% 32%	2807
	21st to end	Day	29% 10% 3 7% 4 3 4 4 5% 6% 26%	3000
July	1st to 10th	Day	19% 11% 3 8% 5% 5% 5% 5% 6% 9% 25%	6416
	11th to 20th	Day	14% 9% 3 9% 5% 5% 5% 4 6% 8% 32%	6360
	21st to end	Day	14% 8% 3 6% 5% 4 4 4 7% 9% 36%	6798
August	1st to 10th	Day	23% 10% 4 8% 5% 5% 4 4 5% 7% 26%	4235
	11th to 20th	Day	16% 8% 3 8% 5% 6% 5% 4 6% 8% 31%	4175
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 44%	4455
September	1st to 10th	Day	18% 8% 2 5% 5% 4 4 3 5% 8% 38%	2400
	11th to 20th	Day	19% 7% 2 5% 4 3 4 3 4 7% 41%	2352
	21st to end	Day	19% 8% 3 6% 3 3 4 3 5% 6% 41%	2117
October	1st to 10th	Day	18% 7% 4 6% 5% 4 5% 4 5% 7% 37%	2000
	11th to 20th	Day	18% 10% 3 6% 4 4 4 4 6% 7% 32%	2000
	21st to end	Day	22% 10% 4 7% 5% 4 4 4 4 6% 30%	2194
November	1st to 10th	Day	23% 12% 4 9% 5% 5% 4 3 4 6% 28%	1710
	11th to 20th	Day	23% 17% 6% 7% 4 4 3 3 5% 5% 24%	1680
	21st to end	Day	19% 15% 6% 9% 6% 5% 5% 4 5% 5% 23%	1680
December	1st to 10th	Day	19% 14% 6% 13% 6% 5% 4 3 5% 6% 18%	2690
	11th to 20th	Day	28% 12% 4 11% 5% 4 4 3 3 4 21%	3076
	21st to end	Day	20% 13% 8% 15% 4 3 3 2 3 5% 23%	4070
January	1st to 10th	Night	14% 15% 6% 15% 8% 5% 5% 3 4 5% 18%	8234
	11th to 20th	Night	21% 15% 6% 18% 6% 4 4 3 3 4 15%	8132
	21st to end	Night	12% 11% 4 15% 11% 9% 6% 4 5% 5% 19%	8400
February	1st to 10th	Night	19% 13% 5% 12% 8% 6% 5% 4 5% 5% 19%	2730
	11th to 20th	Night	18% 14% 5% 10% 7% 5% 4 4 6% 6% 22%	2599
	21st to end	Night	12% 14% 5% 11% 7% 5% 5% 4 4 6% 27%	2099
March	1st to 10th	Night	25% 13% 5% 12% 7% 4 4 2 4 3 21%	4964
	11th to 20th	Night	20% 16% 7% 7% 3 4 3 3 4 5% 28%	4979
	21st to end	Night	29% 14% 5% 11% 4 3 3 2 3 4 23%	5431
April	1st to 10th	Night	24% 14% 4 7% 4 4 4 3 4 5% 27%	2000
	11th to 20th	Night	22% 12% 4 8% 4 3 4 2 4 6% 31%	1927
	21st to end	Night	22% 13% 3 7% 4 4 4 3 5% 4 30%	1800
May	1st to 10th	Night	28% 18% 4 7% 4 4 3 3 4 5% 21%	3845
	11th to 20th	Night	25% 12% 3 6% 3 4 3 3 5% 6% 29%	3596
	21st to end	Night	18% 14% 4 7% 5% 4 4 4 5% 6% 28%	3948
June	1st to 10th	Night	27% 12% 3 6% 4 3 3 3 4 6% 29%	1600
	11th to 20th	Night	22% 9% 3 6% 4 4 3 3 5% 6% 36%	1600
	21st to end	Night	26% 9% 3 8% 6% 5% 4 3 5% 6% 24%	1401
July	1st to 10th	Night	16% 10% 4 11% 6% 6% 6% 4 6% 7% 25%	3479
	11th to 20th	Night	16% 10% 3 7% 4 4 4 3 6% 8% 36%	3620
	21st to end	Night	17% 7% 2 5% 4 4 4 4 6% 8% 39%	4067
August	1st to 10th	Night	22% 9% 3 7% 4 3 3 3 5% 6% 35%	2915
	11th to 20th	Night	15% 9% 3 8% 4 4 5% 3 6% 8% 34%	2872
	21st to end	Night	12% 6% 2 5% 3 3 3 4 5% 7% 50%	3441
September	1st to 10th	Night	16% 7% 2 6% 3 3 4 3 5% 7% 44%	2000
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 5% 6% 45%	2045
	21st to end	Night	20% 7% 3 6% 4 4 4 3 4 6% 40%	2282
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 4 6% 41%	2400
	11th to 20th	Night	20% 8% 3 6% 5% 4 4 3 5% 7% 37%	2400
	21st to end	Night	25% 10% 2 6% 5% 3 4 3 4 6% 31%	2645
November	1st to 10th	Night	20% 11% 3 8% 5% 4 4 3 4 6% 32%	2803
	11th to 20th	Night	21% 15% 3 8% 5% 5% 4 3 5% 6% 26%	2940
	21st to end	Night	20% 14% 4 8% 5% 5% 4 3 5% 6% 25%	2940
December	1st to 10th	Night	16% 11% 5% 16% 7% 5% 5% 3 4 6% 22%	4720
	11th to 20th	Night	26% 12% 3 10% 5% 4 3 3 3 4 26%	5353
	21st to end	Night	23% 13% 5% 11% 4 3 3 3 3 4 27%	7150

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	70% 3 10% 10% 6%	4691
	11th to 20th	Day	76% 3 6% 12% 3	4805
	21st to end	Day	62% 3 7% 13% 13% 3	5781
February	1st to 10th	Day	68% 3 7% 12% 9% 1	1890
	11th to 20th	Day	64% 4 8% 15% 7% 1	1806
	21st to end	Day	57% 3 10% 17% 11% 2	1530
March	1st to 10th	Day	68% 1 6% 13% 8% 4	4862
	11th to 20th	Day	61% 3 11% 19% 6% 1	4980
	21st to end	Day	70% 2 4 15% 8% 1	5501
April	1st to 10th	Day	66% 2 6% 13% 11% 3	2400
	11th to 20th	Day	56% 3 7% 20% 13% 1	2421
	21st to end	Day	59% 3 8% 18% 11% 2	2600
May	1st to 10th	Day	67% 2 10% 15% 6%	6113
	11th to 20th	Day	60% 3 10% 21% 6%	6322
	21st to end	Day	55% 3 12% 19% 10%	6948
June	1st to 10th	Day	60% 3 10% 19% 7% 1	2800
	11th to 20th	Day	53% 3 11% 21% 10% 1	2807
	21st to end	Day	60% 4 11% 16% 9% 1	3000
July	1st to 10th	Day	56% 5% 14% 17% 8%	6346
	11th to 20th	Day	49% 5% 13% 23% 9%	6284
	21st to end	Day	44% 6% 17% 24% 9%	6603
August	1st to 10th	Day	58% 4 11% 19% 8%	4222
	11th to 20th	Day	49% 5% 13% 25% 7%	4214
	21st to end	Day	37% 4 12% 29% 16% 1	4455
September	1st to 10th	Day	45% 3 11% 26% 13% 2	2400
	11th to 20th	Day	44% 3 11% 25% 15% 1	2352
	21st to end	Day	45% 3 9% 26% 17%	2117
October	1st to 10th	Day	48% 5% 10% 25% 12%	3260
	11th to 20th	Day	46% 4 9% 27% 14%	3240
	21st to end	Day	47% 3 14% 23% 12% 1	3521
November	1st to 10th	Day	59% 4 8% 21% 8% 1	1710
	11th to 20th	Day	63% 4 9% 16% 7% 1	1680
	21st to end	Day	63% 5% 11% 15% 6%	1680
December	1st to 10th	Day	64% 5% 8% 19% 3	2690
	11th to 20th	Day	67% 3 8% 15% 7%	3075
	21st to end	Day	66% 2 11% 15% 7%	4070
January	1st to 10th	Night	68% 3 8% 16% 4	8234
	11th to 20th	Night	73% 4 7% 12% 4	8178
	21st to end	Night	65% 5% 8% 13% 8% 1	8400
February	1st to 10th	Night	67% 4 8% 12% 8% 2	2730
	11th to 20th	Night	63% 3 9% 16% 7% 1	2602
	21st to end	Night	59% 4 8% 19% 9% 1	2099
March	1st to 10th	Night	69% 2 5% 12% 11% 1	4973
	11th to 20th	Night	60% 3 9% 19% 8% 1	4980
	21st to end	Night	68% 2 5% 17% 8% 1	5431
April	1st to 10th	Night	61% 3 8% 15% 12% 3	2000
	11th to 20th	Night	57% 2 6% 20% 13% 1	1927
	21st to end	Night	57% 3 10% 18% 11% 2	1800
May	1st to 10th	Night	67% 2 8% 14% 8% 1	3851
	11th to 20th	Night	58% 2 9% 22% 7% 1	3597
	21st to end	Night	57% 3 12% 20% 7%	3949
June	1st to 10th	Night	58% 2 10% 21% 7% 1	1600
	11th to 20th	Night	51% 2 11% 23% 12% 1	1600
	21st to end	Night	62% 3 11% 16% 7% 1	1401
July	1st to 10th	Night	58% 5% 13% 17% 7% 1	3440
	11th to 20th	Night	48% 5% 14% 22% 11% 1	3572
	21st to end	Night	43% 5% 16% 24% 11% 1	3948
August	1st to 10th	Night	52% 4 14% 25% 5%	2903
	11th to 20th	Night	47% 6% 16% 24% 6%	2899
	21st to end	Night	34% 4 15% 29% 16% 1	3440
September	1st to 10th	Night	41% 3 12% 27% 15% 2	2000
	11th to 20th	Night	42% 3 10% 31% 14% 1	2045
	21st to end	Night	47% 3 8% 28% 13% 1	2282
October	1st to 10th	Night	49% 4 11% 24% 12%	3920
	11th to 20th	Night	43% 3 10% 28% 16%	3899
	21st to end	Night	45% 3 13% 23% 15%	4269
November	1st to 10th	Night	54% 4 11% 20% 10% 1	2803
	11th to 20th	Night	60% 4 10% 17% 8%	2940
	21st to end	Night	60% 3 13% 16% 6% 1	2940
December	1st to 10th	Night	62% 4 10% 20% 3	4720
	11th to 20th	Night	63% 3 7% 17% 8% 1	5355
	21st to end	Night	62% 2 10% 17% 8%	7150

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	32% 22% 32% 14% 1	430
	11th to 20th	Day	35% 19% 29% 13% 4	430
	21st to end	Day	26% 23% 37% 11% 3	473
February	1st to 10th	Day	32% 23% 30% 13% 3	430
	11th to 20th	Day	37% 24% 27% 10% 2	411
	21st to end	Day	30% 23% 30% 13% 4 1	331
March	1st to 10th	Day	32% 25% 32% 10% 2	483
	11th to 20th	Day	28% 26% 31% 10% 3 1	500
	21st to end	Day	35% 26% 26% 10% 3 1	550
April	1st to 10th	Day	44% 23% 23% 8% 2	500
	11th to 20th	Day	34% 24% 28% 11% 2	492
	21st to end	Day	33% 23% 28% 11% 5% 1	500
May	1st to 10th	Day	37% 20% 29% 10% 3 1	589
	11th to 20th	Day	30% 17% 29% 19% 4 1	724
	21st to end	Day	31% 14% 36% 15% 3 1	790
June	1st to 10th	Day	36% 15% 27% 17% 4	730
	11th to 20th	Day	27% 15% 34% 18% 5% 1	730
	21st to end	Day	36% 11% 28% 18% 5% 1	730
July	1st to 10th	Day	23% 10% 36% 21% 8% 1	720
	11th to 20th	Day	22% 8% 34% 26% 9% 1	718
	21st to end	Day	26% 8% 35% 23% 7% 1	741
August	1st to 10th	Day	18% 9% 39% 24% 8% 2	526
	11th to 20th	Day	23% 10% 34% 21% 10% 3	519
	21st to end	Day	20% 14% 30% 24% 8% 4	583
September	1st to 10th	Day	21% 13% 33% 24% 8% 2	530
	11th to 20th	Day	25% 15% 30% 16% 11% 3	530
	21st to end	Day	22% 17% 29% 21% 9% 2	483
October	1st to 10th	Day	23% 13% 33% 20% 10% 2	420
	11th to 20th	Day	24% 20% 30% 15% 9% 2	420
	21st to end	Day	29% 21% 29% 14% 5% 1	462
November	1st to 10th	Day	32% 16% 30% 16% 6% 1	425
	11th to 20th	Day	37% 19% 25% 14% 5%	430
	21st to end	Day	37% 22% 27% 9% 4 1	430
December	1st to 10th	Day	38% 17% 30% 12% 3	430
	11th to 20th	Day	42% 23% 24% 10% 1	430
	21st to end	Day	30% 25% 30% 10% 3 1	473
January	1st to 10th	Night	30% 21% 32% 16% 2	950
	11th to 20th	Night	34% 20% 27% 16% 3	931
	21st to end	Night	26% 23% 32% 16% 2	924
February	1st to 10th	Night	29% 19% 30% 19% 3	840
	11th to 20th	Night	32% 24% 27% 15% 1	804
	21st to end	Night	23% 20% 33% 20% 4	660
March	1st to 10th	Night	28% 23% 32% 14% 3	800
	11th to 20th	Night	27% 18% 31% 19% 5%	800
	21st to end	Night	31% 19% 30% 18% 3	870
April	1st to 10th	Night	34% 18% 28% 17% 3	600
	11th to 20th	Night	31% 19% 31% 16% 3	594
	21st to end	Night	31% 15% 33% 18% 3 1	600
May	1st to 10th	Night	34% 13% 32% 16% 5% 1	600
	11th to 20th	Night	28% 14% 30% 22% 6%	592
	21st to end	Night	22% 13% 42% 19% 3	649
June	1st to 10th	Night	36% 10% 32% 19% 3	600
	11th to 20th	Night	27% 9% 38% 23% 4	600
	21st to end	Night	29% 5% 31% 26% 7%	401
July	1st to 10th	Night	20% 5% 37% 31% 7%	523
	11th to 20th	Night	21% 4 35% 33% 7%	582
	21st to end	Night	21% 5% 31% 34% 9%	656
August	1st to 10th	Night	20% 4 31% 34% 11% 1	598
	11th to 20th	Night	19% 6% 29% 35% 12% 1	592
	21st to end	Night	18% 7% 30% 34% 12%	660
September	1st to 10th	Night	19% 7% 33% 31% 10% 1	600
	11th to 20th	Night	24% 9% 26% 29% 11% 1	645
	21st to end	Night	26% 10% 29% 26% 9% 1	800
October	1st to 10th	Night	23% 12% 28% 29% 8% 1	800
	11th to 20th	Night	26% 13% 31% 20% 9% 1	800
	21st to end	Night	34% 16% 28% 17% 5%	883
November	1st to 10th	Night	31% 15% 29% 20% 4 1	930
	11th to 20th	Night	33% 17% 26% 19% 5%	950
	21st to end	Night	32% 20% 26% 18% 4	950
December	1st to 10th	Night	34% 17% 31% 14% 4	950
	11th to 20th	Night	36% 21% 29% 13% 1	950
	21st to end	Night	30% 23% 28% 16% 3	1045

Page generated at 2026-02-13 02:42:13. Version ac07

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