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 2024-11-30.

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 8% 5% 4 4 3 5% 6% 28%	102030
	Night	21% 12% 4 9% 5% 4 4 3 4 6% 28%	97623
Transparency	Day	57% 3 10% 19% 9% 1	105616
	Night	58% 3 10% 19% 9% 1	102127
Seeing	Day	30% 17% 31% 16% 5% 1	17475
	Night	28% 15% 30% 21% 5%	25016

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	14% 15% 6% 13% 7% 5% 4 3 4 4 25%	2526
	11th to 20th	Day	14% 16% 5% 18% 8% 5% 5% 3 3 5% 17%	2573
	21st to end	Day	17% 12% 6% 11% 8% 4 4 3 5% 5% 24%	3124
February	1st to 10th	Day	19% 15% 5% 10% 7% 6% 5% 3 5% 4 20%	1710
	11th to 20th	Day	17% 17% 5% 12% 6% 4 4 3 4 5% 22%	1663
	21st to end	Day	12% 17% 5% 7% 7% 5% 4 2 3 7% 30%	1456
March	1st to 10th	Day	25% 16% 4 8% 4 6% 3 2 4 4 25%	3386
	11th to 20th	Day	13% 23% 7% 10% 5% 4 4 3 4 5% 22%	3480
	21st to end	Day	31% 16% 4 9% 5% 4 4 2 3 3 20%	3837
April	1st to 10th	Day	24% 18% 5% 8% 5% 4 3 2 4 5% 24%	2280
	11th to 20th	Day	20% 13% 3 7% 4 4 4 4 5% 6% 30%	2298
	21st to end	Day	23% 14% 3 7% 4 3 4 3 5% 5% 27%	2470
May	1st to 10th	Day	26% 17% 4 8% 4 3 4 3 5% 6% 20%	4252
	11th to 20th	Day	22% 12% 3 8% 4 4 3 3 5% 6% 30%	4398
	21st to end	Day	19% 10% 3 7% 4 4 5% 4 6% 8% 29%	4836
June	1st to 10th	Day	27% 12% 3 6% 5% 5% 4 4 5% 6% 23%	2660
	11th to 20th	Day	23% 9% 3 7% 4 4 4 3 6% 5% 32%	2666
	21st to end	Day	29% 10% 3 7% 5% 4 4 4 4 6% 25%	2850
July	1st to 10th	Day	21% 10% 3 7% 5% 4 4 4 6% 7% 29%	4482
	11th to 20th	Day	14% 10% 4 9% 6% 6% 5% 4 6% 8% 30%	4440
	21st to end	Day	17% 10% 3 7% 5% 5% 4 4 6% 8% 31%	4728
August	1st to 10th	Day	23% 10% 4 8% 5% 5% 4 4 5% 7% 25%	4105
	11th to 20th	Day	17% 8% 3 8% 5% 6% 5% 4 6% 8% 31%	4045
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 44%	4319
September	1st to 10th	Day	18% 7% 2 5% 5% 3 4 3 5% 8% 38%	2280
	11th to 20th	Day	20% 7% 2 5% 4 3 4 3 4 7% 40%	2235
	21st to end	Day	19% 8% 3 6% 3 3 4 3 5% 6% 40%	2011
October	1st to 10th	Day	19% 7% 4 5% 5% 4 5% 4 5% 7% 36%	1900
	11th to 20th	Day	19% 10% 3 6% 4 4 4 4 6% 7% 33%	1900
	21st to end	Day	22% 10% 3 7% 5% 4 4 4 4 6% 30%	2085
November	1st to 10th	Day	23% 12% 4 9% 5% 5% 4 3 4 6% 28%	1627
	11th to 20th	Day	23% 17% 5% 7% 4 4 4 3 5% 5% 25%	1600
	21st to end	Day	19% 15% 6% 8% 6% 5% 5% 4 5% 5% 23%	1599
December	1st to 10th	Day	24% 17% 5% 9% 5% 4 4 3 4 5% 20%	1520
	11th to 20th	Day	30% 15% 5% 10% 5% 3 4 3 3 5% 16%	1906
	21st to end	Day	24% 12% 9% 13% 4 3 3 3 4 6% 20%	2783
January	1st to 10th	Night	15% 13% 7% 13% 8% 4 4 3 4 5% 24%	4429
	11th to 20th	Night	19% 14% 4 18% 7% 5% 4 3 4 4 18%	4394
	21st to end	Night	17% 12% 5% 14% 7% 6% 5% 4 4 6% 21%	4532
February	1st to 10th	Night	20% 13% 4 10% 8% 6% 5% 4 5% 5% 19%	2470
	11th to 20th	Night	18% 15% 5% 10% 7% 5% 4 4 6% 6% 21%	2403
	21st to end	Night	12% 14% 5% 11% 7% 5% 4 4 5% 6% 27%	1998
March	1st to 10th	Night	23% 14% 5% 11% 7% 4 4 3 4 4 22%	3450
	11th to 20th	Night	20% 18% 8% 8% 4 4 4 3 4 6% 23%	3479
	21st to end	Night	30% 12% 5% 11% 4 3 2 2 2 3 24%	3795
April	1st to 10th	Night	23% 14% 3 7% 4 4 4 3 4 5% 28%	1900
	11th to 20th	Night	22% 12% 3 8% 4 3 4 2 4 6% 32%	1830
	21st to end	Night	23% 13% 3 7% 4 4 4 3 5% 4 30%	1710
May	1st to 10th	Night	24% 19% 4 7% 4 4 3 3 5% 6% 23%	2690
	11th to 20th	Night	22% 10% 3 7% 4 4 4 4 5% 7% 30%	2506
	21st to end	Night	20% 11% 4 7% 5% 4 4 5% 5% 7% 27%	2749
June	1st to 10th	Night	28% 12% 3 6% 4 3 3 3 4 6% 28%	1520
	11th to 20th	Night	22% 9% 3 6% 4 4 3 3 4 6% 36%	1520
	21st to end	Night	26% 10% 3 8% 6% 5% 4 4 5% 6% 24%	1331
July	1st to 10th	Night	18% 9% 3 10% 6% 6% 5% 4 6% 7% 26%	2431
	11th to 20th	Night	16% 9% 3 8% 5% 4 5% 3 7% 9% 32%	2530
	21st to end	Night	19% 8% 2 6% 4 4 4 3 5% 7% 39%	2830
August	1st to 10th	Night	22% 9% 3 7% 4 3 3 3 5% 6% 34%	2825
	11th to 20th	Night	15% 9% 3 8% 4 4 5% 3 6% 9% 34%	2782
	21st to end	Night	12% 6% 2 5% 3 3 3 3 5% 7% 51%	3335
September	1st to 10th	Night	16% 7% 2 6% 3 3 4 3 5% 7% 44%	1900
	11th to 20th	Night	19% 7% 2 5% 3 3 3 3 4 6% 45%	1943
	21st to end	Night	20% 7% 3 6% 4 4 4 3 4 6% 39%	2168
October	1st to 10th	Night	19% 8% 2 6% 4 4 4 3 5% 6% 40%	2280
	11th to 20th	Night	20% 7% 3 6% 4 4 4 3 5% 7% 38%	2280
	21st to end	Night	25% 10% 2 6% 5% 3 4 3 4 6% 32%	2513
November	1st to 10th	Night	20% 11% 3 8% 5% 4 4 3 4 6% 32%	2666
	11th to 20th	Night	21% 14% 3 8% 5% 5% 4 3 5% 6% 26%	2800
	21st to end	Night	21% 15% 4 7% 5% 5% 4 3 5% 6% 25%	2797
December	1st to 10th	Night	24% 14% 4 10% 6% 5% 5% 4 3 5% 20%	2660
	11th to 20th	Night	32% 12% 4 11% 5% 4 3 3 4 3 20%	3293
	21st to end	Night	26% 12% 6% 11% 4 4 3 3 4 4 23%	4884

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	63% 3 14% 13% 6% 1	2527
	11th to 20th	Day	71% 3 6% 16% 5%	2573
	21st to end	Day	63% 2 8% 14% 13%	3124
February	1st to 10th	Day	67% 3 8% 12% 9% 1	1710
	11th to 20th	Day	65% 4 8% 15% 7% 1	1671
	21st to end	Day	57% 2 9% 17% 11% 3	1456
March	1st to 10th	Day	66% 1 7% 16% 8% 2	3390
	11th to 20th	Day	67% 1 7% 16% 8% 1	3480
	21st to end	Day	72% 1 5% 13% 8% 1	3837
April	1st to 10th	Day	66% 2 6% 13% 11% 3	2280
	11th to 20th	Day	55% 3 7% 21% 13% 1	2298
	21st to end	Day	59% 2 8% 17% 11% 2	2470
May	1st to 10th	Day	67% 1 9% 16% 6% 1	4266
	11th to 20th	Day	58% 2 12% 20% 7%	4402
	21st to end	Day	54% 3 15% 19% 9% 1	4836
June	1st to 10th	Day	61% 3 11% 18% 6% 1	2660
	11th to 20th	Day	53% 3 11% 21% 10% 1	2666
	21st to end	Day	61% 4 11% 15% 9%	2850
July	1st to 10th	Day	54% 4 12% 18% 11% 1	4412
	11th to 20th	Day	52% 5% 14% 21% 8%	4364
	21st to end	Day	51% 5% 14% 20% 9%	4577
August	1st to 10th	Day	59% 4 11% 18% 6%	4092
	11th to 20th	Day	50% 5% 13% 25% 7%	4084
	21st to end	Day	37% 4 12% 29% 17% 1	4319
September	1st to 10th	Day	45% 3 11% 26% 13% 2	2280
	11th to 20th	Day	45% 3 11% 25% 15% 1	2235
	21st to end	Day	46% 3 9% 26% 16%	2011
October	1st to 10th	Day	48% 5% 10% 25% 12%	3160
	11th to 20th	Day	45% 4 9% 27% 15%	3140
	21st to end	Day	47% 3 14% 23% 12% 1	3412
November	1st to 10th	Day	59% 4 8% 21% 8% 1	1627
	11th to 20th	Day	62% 4 10% 16% 8% 1	1600
	21st to end	Day	63% 5% 10% 15% 7%	1599
December	1st to 10th	Day	66% 4 9% 16% 5%	1520
	11th to 20th	Day	71% 3 7% 14% 4 1	1905
	21st to end	Day	68% 2 14% 12% 5%	2783
January	1st to 10th	Night	63% 3 11% 21% 3	4429
	11th to 20th	Night	70% 4 7% 13% 6%	4394
	21st to end	Night	66% 3 8% 15% 7% 1	4532
February	1st to 10th	Night	66% 4 8% 13% 8% 1	2470
	11th to 20th	Night	64% 3 9% 15% 7% 1	2406
	21st to end	Night	59% 4 9% 18% 9% 1	1998
March	1st to 10th	Night	67% 2 6% 16% 8% 1	3459
	11th to 20th	Night	66% 2 7% 16% 8% 1	3480
	21st to end	Night	69% 1 6% 15% 8% 1	3795
April	1st to 10th	Night	61% 3 8% 15% 11% 3	1900
	11th to 20th	Night	56% 2 7% 20% 14% 1	1830
	21st to end	Night	57% 3 9% 17% 12% 2	1710
May	1st to 10th	Night	65% 1 11% 15% 8% 1	2696
	11th to 20th	Night	57% 1 11% 22% 8%	2507
	21st to end	Night	58% 3 15% 19% 5% 1	2750
June	1st to 10th	Night	59% 2 11% 20% 7%	1520
	11th to 20th	Night	52% 2 11% 23% 12% 1	1520
	21st to end	Night	62% 3 11% 17% 7% 1	1331
July	1st to 10th	Night	56% 5% 13% 17% 8% 1	2392
	11th to 20th	Night	50% 6% 17% 18% 9%	2482
	21st to end	Night	46% 4 14% 23% 12% 1	2741
August	1st to 10th	Night	53% 4 14% 25% 5%	2813
	11th to 20th	Night	48% 6% 16% 24% 6%	2809
	21st to end	Night	34% 4 16% 29% 16% 1	3334
September	1st to 10th	Night	41% 3 12% 27% 15% 2	1900
	11th to 20th	Night	42% 3 10% 30% 14% 1	1943
	21st to end	Night	48% 3 8% 27% 13% 1	2168
October	1st to 10th	Night	51% 3 11% 24% 11%	3800
	11th to 20th	Night	42% 3 11% 28% 16%	3779
	21st to end	Night	45% 3 13% 23% 16%	4137
November	1st to 10th	Night	54% 4 11% 20% 10% 1	2666
	11th to 20th	Night	59% 4 10% 17% 9%	2800
	21st to end	Night	60% 3 13% 16% 6%	2797
December	1st to 10th	Night	66% 4 9% 16% 4	2660
	11th to 20th	Night	70% 4 6% 13% 7%	3295
	21st to end	Night	66% 2 10% 16% 5%	4884

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	31% 20% 34% 14% 1	370
	11th to 20th	Day	33% 19% 31% 13% 4	370
	21st to end	Day	25% 22% 37% 12% 3	407
February	1st to 10th	Day	33% 23% 28% 13% 3	370
	11th to 20th	Day	36% 25% 26% 11% 2	366
	21st to end	Day	29% 24% 30% 13% 4 1	307
March	1st to 10th	Day	31% 24% 32% 10% 2	445
	11th to 20th	Day	28% 27% 31% 10% 3 1	460
	21st to end	Day	35% 25% 26% 10% 3 1	506
April	1st to 10th	Day	42% 22% 24% 9% 2	460
	11th to 20th	Day	32% 25% 29% 12% 2	452
	21st to end	Day	32% 21% 29% 12% 5% 1	460
May	1st to 10th	Day	37% 21% 28% 10% 3 1	544
	11th to 20th	Day	29% 17% 29% 20% 4 1	674
	21st to end	Day	30% 14% 36% 15% 4	735
June	1st to 10th	Day	37% 15% 27% 17% 4	680
	11th to 20th	Day	28% 14% 34% 18% 5% 1	680
	21st to end	Day	36% 10% 29% 19% 5% 1	680
July	1st to 10th	Day	23% 10% 37% 21% 9% 1	670
	11th to 20th	Day	22% 8% 34% 25% 9% 1	668
	21st to end	Day	27% 8% 34% 24% 8% 1	689
August	1st to 10th	Day	19% 9% 38% 25% 7% 2	486
	11th to 20th	Day	24% 9% 33% 21% 10% 3	479
	21st to end	Day	20% 13% 29% 25% 9% 4	539
September	1st to 10th	Day	22% 13% 32% 24% 7% 1	490
	11th to 20th	Day	26% 15% 29% 16% 11% 2	490
	21st to end	Day	24% 15% 29% 20% 10% 2	447
October	1st to 10th	Day	23% 13% 33% 20% 10% 2	390
	11th to 20th	Day	25% 21% 29% 15% 8% 2	390
	21st to end	Day	29% 21% 29% 14% 5% 1	429
November	1st to 10th	Day	30% 16% 31% 16% 6% 1	395
	11th to 20th	Day	37% 20% 25% 14% 5% 1	400
	21st to end	Day	37% 23% 27% 9% 4 1	400
December	1st to 10th	Day	38% 17% 29% 12% 3	370
	11th to 20th	Day	42% 23% 25% 9% 1	370
	21st to end	Day	31% 24% 30% 11% 3 1	407
January	1st to 10th	Night	30% 20% 32% 17% 2	850
	11th to 20th	Night	33% 21% 27% 16% 3	835
	21st to end	Night	26% 22% 33% 17% 3	836
February	1st to 10th	Night	30% 19% 30% 19% 2	760
	11th to 20th	Night	32% 25% 27% 15% 1	743
	21st to end	Night	23% 20% 33% 20% 4	628
March	1st to 10th	Night	27% 23% 33% 15% 3	760
	11th to 20th	Night	27% 19% 31% 19% 5%	760
	21st to end	Night	31% 19% 29% 18% 3	827
April	1st to 10th	Night	33% 18% 28% 18% 3	570
	11th to 20th	Night	30% 19% 31% 16% 4	564
	21st to end	Night	31% 15% 32% 17% 3 1	570
May	1st to 10th	Night	33% 13% 33% 16% 5% 1	570
	11th to 20th	Night	28% 14% 29% 23% 6%	562
	21st to end	Night	22% 13% 42% 19% 3	616
June	1st to 10th	Night	36% 10% 32% 18% 3	570
	11th to 20th	Night	26% 9% 38% 23% 4	570
	21st to end	Night	30% 5% 31% 26% 8%	381
July	1st to 10th	Night	20% 5% 37% 31% 7%	496
	11th to 20th	Night	21% 4 36% 32% 7%	552
	21st to end	Night	21% 5% 31% 34% 9%	623
August	1st to 10th	Night	20% 4 32% 32% 11% 1	568
	11th to 20th	Night	19% 6% 28% 35% 12% 1	562
	21st to end	Night	18% 7% 28% 34% 12%	627
September	1st to 10th	Night	18% 7% 34% 31% 9% 1	570
	11th to 20th	Night	24% 9% 26% 29% 11% 1	613
	21st to end	Night	26% 10% 29% 25% 9% 1	760
October	1st to 10th	Night	23% 11% 28% 29% 8% 1	760
	11th to 20th	Night	25% 14% 32% 19% 9% 1	760
	21st to end	Night	33% 16% 28% 17% 5%	839
November	1st to 10th	Night	30% 14% 29% 21% 5% 1	880
	11th to 20th	Night	32% 18% 25% 19% 5%	900
	21st to end	Night	33% 20% 26% 18% 4	899
December	1st to 10th	Night	35% 17% 31% 13% 4	850
	11th to 20th	Night	36% 20% 30% 12% 2	850
	21st to end	Night	30% 23% 28% 16% 3	935

Page generated at 2024-11-27 18:30:51. Version ac07

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