Maple's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maple's Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	6% 7% 2 6% 3 3 3 3 4 7% 55%	135537
	Night	8% 11% 3 8% 4 3 3 3 4 6% 48%	133286
Transparency	Day	23% 6% 10% 19% 25% 17%	130505
	Night	30% 8% 11% 17% 21% 13%	129301
Seeing	Day	7% 9% 24% 34% 20% 6%	16967
	Night	9% 4 14% 32% 31% 8%	26460

By Month

Percentage Cloud Cover SW (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% 6% 3 5% 3 3 3 3 4 8% 53%	3940
	11th to 20th	Day	10% 5% 2 6% 4 3 4 3 4 5% 55%	4100
	21st to end	Day	14% 8% 3 7% 5% 4 4 3 4 6% 43%	4510
February	1st to 10th	Day	14% 9% 3 4 4 3 4 3 5% 6% 47%	1800
	11th to 20th	Day	11% 9% 2 5% 4 3 5% 4 6% 7% 45%	1900
	21st to end	Day	11% 8% 3 5% 6% 4 3 3 5% 5% 46%	1650
March	1st to 10th	Day	12% 10% 3 7% 5% 6% 6% 6% 7% 8% 30%	4815
	11th to 20th	Day	11% 6% 2 6% 4 4 3 3 5% 7% 50%	5000
	21st to end	Day	10% 9% 3 7% 5% 5% 5% 4 6% 10% 37%	5612
April	1st to 10th	Day	9% 8% 2 6% 4 3 3 3 5% 6% 49%	2400
	11th to 20th	Day	8% 9% 2 6% 4 4 4 3 5% 6% 51%	2369
	21st to end	Day	7% 8% 3 5% 3 3 2 4 6% 7% 52%	2400
May	1st to 10th	Day	6% 4 1 3 2 2 2 2 3 6% 69%	5440
	11th to 20th	Day	4 6% 2 4 3 2 2 3 4 8% 62%	5930
	21st to end	Day	3 12% 4 6% 3 3 3 2 5% 7% 52%	6902
June	1st to 10th	Day	4 7% 2 6% 4 4 3 4 5% 8% 53%	2800
	11th to 20th	Day	3 4 2 3 3 3 3 2 4 8% 65%	2800
	21st to end	Day	2 5% 2 5% 3 2 3 2 4 7% 66%	2800
July	1st to 10th	Day	3 2 7% 3 3 2 2 3 6% 69%	6289
	11th to 20th	Day	1 3 3 9% 3 3 2 2 3 7% 63%	5880
	21st to end	Day	1 13% 6% 7% 4 3 3 2 4 9% 48%	6402
August	1st to 10th	Day	1 6% 3 7% 3 3 3 2 5% 9% 59%	5777
	11th to 20th	Day	2 6% 3 7% 2 2 3 2 4 7% 61%	5373
	21st to end	Day	4 1 6% 3 3 3 2 4 6% 67%	5984
September	1st to 10th	Day	1 4 2 3 2 2 2 2 3 6% 73%	2400
	11th to 20th	Day	4 7% 2 4 3 3 2 2 4 8% 61%	2400
	21st to end	Day	3 4 1 3 2 1 2 2 4 6% 71%	2142
October	1st to 10th	Day	2 3 1 3 2 2 2 3 3 5% 73%	3280
	11th to 20th	Day	3 7% 3 5% 3 2 3 2 3 6% 63%	3261
	21st to end	Day	4 4 2 4 3 3 3 3 5% 7% 62%	3558
November	1st to 10th	Day	6% 5% 1 4 3 4 3 3 4 7% 58%	2017
	11th to 20th	Day	8% 7% 2 6% 3 3 4 3 4 6% 53%	1890
	21st to end	Day	10% 5% 1 4 3 3 3 3 5% 7% 56%	1816
December	1st to 10th	Day	6% 5% 2 5% 4 4 3 3 5% 8% 56%	2700
	11th to 20th	Day	15% 9% 3 6% 4 4 4 4 6% 7% 40%	3108
	21st to end	Day	18% 10% 3 7% 5% 4 4 4 6% 8% 33%	4092
January	1st to 10th	Night	9% 7% 2 5% 3 3 3 3 5% 8% 53%	6038
	11th to 20th	Night	10% 6% 3 8% 4 3 4 3 4 6% 48%	5880
	21st to end	Night	14% 11% 4 7% 4 3 3 3 4 6% 42%	6468
February	1st to 10th	Night	14% 9% 2 5% 4 3 4 2 4 6% 48%	2600
	11th to 20th	Night	12% 9% 3 5% 3 3 5% 4 5% 7% 45%	2385
	21st to end	Night	10% 9% 2 5% 4 3 2 3 4 6% 51%	1980
March	1st to 10th	Night	18% 14% 3 7% 4 4 4 3 4 5% 33%	5074
	11th to 20th	Night	11% 9% 2 6% 4 4 4 3 4 5% 48%	5000
	21st to end	Night	15% 13% 3 7% 4 3 3 4 6% 7% 36%	5361
April	1st to 10th	Night	10% 8% 2 6% 4 3 4 3 7% 6% 47%	2000
	11th to 20th	Night	9% 10% 2 6% 3 3 3 3 4 7% 50%	1979
	21st to end	Night	7% 9% 3 5% 3 3 4 3 5% 7% 52%	2000
May	1st to 10th	Night	4 10% 3 6% 3 2 2 2 4 5% 58%	4560
	11th to 20th	Night	4 19% 4 10% 5% 3 2 2 4 4 44%	3960
	21st to end	Night	3 22% 4 7% 3 2 2 2 3 4 51%	3972
June	1st to 10th	Night	5% 14% 3 7% 4 2 3 3 5% 7% 48%	1600
	11th to 20th	Night	2 10% 3 6% 4 4 3 2 5% 6% 56%	1600
	21st to end	Night	2 9% 3 7% 4 3 2 2 4 7% 57%	1600
July	1st to 10th	Night	8% 5% 15% 6% 3 2 2 3 5% 51%	3640
	11th to 20th	Night	1 12% 8% 20% 5% 3 3 2 3 5% 40%	4100
	21st to end	Night	1 39% 7% 9% 4 3 2 2 3 5% 25%	4472
August	1st to 10th	Night	1 17% 4 18% 7% 4 3 3 3 6% 35%	4035
	11th to 20th	Night	3 16% 4 11% 4 2 2 1 2 4 50%	4496
	21st to end	Night	1 9% 3 14% 4 3 2 2 3 5% 54%	5015
September	1st to 10th	Night	3 6% 3 5% 3 3 3 2 4 6% 62%	2000
	11th to 20th	Night	5% 11% 4 6% 3 3 3 3 4 7% 54%	2000
	21st to end	Night	3 5% 2 5% 2 3 2 2 3 6% 66%	2252
October	1st to 10th	Night	3 3 1 4 3 3 2 2 3 5% 72%	3920
	11th to 20th	Night	4 16% 3 7% 3 3 3 2 3 4 53%	3897
	21st to end	Night	5% 9% 2 3 2 3 2 2 5% 6% 62%	4253
November	1st to 10th	Night	7% 7% 2 5% 2 3 3 2 4 6% 59%	2499
	11th to 20th	Night	9% 7% 2 6% 3 3 3 3 5% 8% 52%	2730
	21st to end	Night	8% 5% 2 4 3 4 3 3 4 7% 56%	2798
December	1st to 10th	Night	6% 4 2 4 3 3 3 4 4 6% 61%	4700
	11th to 20th	Night	16% 10% 3 6% 4 4 5% 4 7% 8% 35%	5316
	21st to end	Night	16% 11% 4 9% 6% 4 5% 4 6% 6% 29%	7106

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	31% 6% 16% 26% 18% 4	3940
	11th to 20th	Day	32% 6% 9% 13% 19% 22%	4100
	21st to end	Day	40% 6% 6% 13% 20% 13%	4510
February	1st to 10th	Day	38% 5% 8% 18% 19% 11%	1800
	11th to 20th	Day	36% 8% 11% 19% 19% 7%	1910
	21st to end	Day	38% 7% 8% 22% 19% 6%	1650
March	1st to 10th	Day	40% 15% 12% 14% 17% 2	4815
	11th to 20th	Day	31% 8% 13% 29% 12% 8%	5000
	21st to end	Day	37% 12% 16% 23% 10% 1	5612
April	1st to 10th	Day	34% 7% 13% 26% 16% 4	2400
	11th to 20th	Day	32% 6% 12% 26% 18% 6%	2372
	21st to end	Day	28% 6% 13% 29% 20% 4	2400
May	1st to 10th	Day	15% 5% 9% 29% 34% 8%	5440
	11th to 20th	Day	14% 6% 9% 33% 29% 9%	5933
	21st to end	Day	20% 7% 11% 26% 32% 4	6904
June	1st to 10th	Day	22% 8% 12% 23% 27% 7%	2800
	11th to 20th	Day	13% 4 10% 22% 34% 17%	2800
	21st to end	Day	13% 2 6% 13% 33% 31%	2800
July	1st to 10th	Day	8% 3 6% 9% 24% 50%	6221
	11th to 20th	Day	14% 2 9% 7% 22% 46%	5811
	21st to end	Day	18% 7% 9% 21% 25% 19%	6217
August	1st to 10th	Day	12% 4 8% 13% 33% 29%	4206
	11th to 20th	Day	8% 5% 6% 13% 41% 28%	3889
	21st to end	Day	12% 4 7% 12% 33% 32%	4311
September	1st to 10th	Day	11% 3 4 11% 29% 42%	2400
	11th to 20th	Day	17% 4 9% 21% 32% 17%	2400
	21st to end	Day	13% 3 6% 21% 37% 20%	2142
October	1st to 10th	Day	13% 4 6% 13% 30% 35%	3280
	11th to 20th	Day	19% 6% 9% 21% 29% 17%	3261
	21st to end	Day	18% 5% 7% 21% 33% 16%	3558
November	1st to 10th	Day	24% 6% 10% 21% 26% 13%	2017
	11th to 20th	Day	30% 5% 12% 20% 22% 10%	1890
	21st to end	Day	28% 5% 9% 18% 26% 14%	1816
December	1st to 10th	Day	25% 6% 8% 20% 33% 9%	2700
	11th to 20th	Day	41% 8% 11% 17% 14% 9%	3108
	21st to end	Day	46% 10% 14% 17% 10% 3	4092
January	1st to 10th	Night	29% 9% 16% 24% 18% 3	6038
	11th to 20th	Night	33% 10% 12% 11% 21% 12%	5880
	21st to end	Night	42% 8% 7% 12% 18% 13%	6468
February	1st to 10th	Night	38% 5% 10% 15% 20% 12%	2600
	11th to 20th	Night	37% 7% 12% 17% 21% 6%	2386
	21st to end	Night	36% 6% 11% 25% 16% 7%	1980
March	1st to 10th	Night	49% 10% 9% 16% 14% 2	5074
	11th to 20th	Night	34% 9% 13% 22% 15% 7%	5000
	21st to end	Night	43% 12% 15% 18% 10% 2	5361
April	1st to 10th	Night	34% 9% 13% 24% 15% 5%	2000
	11th to 20th	Night	32% 7% 14% 24% 17% 6%	1979
	21st to end	Night	27% 10% 14% 25% 20% 5%	2000
May	1st to 10th	Night	22% 10% 11% 19% 28% 9%	4557
	11th to 20th	Night	24% 17% 9% 20% 22% 9%	3961
	21st to end	Night	26% 11% 11% 20% 28% 4	3972
June	1st to 10th	Night	29% 8% 10% 20% 23% 10%	1600
	11th to 20th	Night	20% 5% 11% 16% 29% 19%	1600
	21st to end	Night	17% 4 5% 14% 29% 31%	1600
July	1st to 10th	Night	13% 8% 13% 7% 19% 40%	3600
	11th to 20th	Night	31% 5% 13% 8% 15% 28%	4046
	21st to end	Night	39% 12% 10% 11% 13% 14%	4345
August	1st to 10th	Night	19% 10% 23% 11% 19% 18%	2929
	11th to 20th	Night	15% 6% 7% 9% 36% 27%	3246
	21st to end	Night	18% 6% 8% 9% 35% 24%	3608
September	1st to 10th	Night	17% 5% 3 9% 25% 40%	2000
	11th to 20th	Night	21% 8% 6% 17% 28% 20%	2000
	21st to end	Night	16% 4 6% 16% 35% 22%	2252
October	1st to 10th	Night	13% 3 6% 15% 25% 38%	3920
	11th to 20th	Night	24% 12% 6% 17% 25% 15%	3897
	21st to end	Night	20% 5% 6% 22% 30% 16%	4253
November	1st to 10th	Night	25% 6% 9% 22% 23% 15%	2499
	11th to 20th	Night	30% 6% 11% 20% 23% 9%	2730
	21st to end	Night	27% 6% 10% 19% 24% 15%	2798
December	1st to 10th	Night	24% 5% 8% 25% 28% 11%	4700
	11th to 20th	Night	43% 8% 11% 15% 18% 6%	5316
	21st to end	Night	51% 12% 12% 13% 8% 4	7106

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% 13% 24% 27% 15% 2	326
	11th to 20th	Day	10% 10% 27% 32% 20% 2	400
	21st to end	Day	13% 9% 25% 32% 18% 3	440
February	1st to 10th	Day	14% 14% 27% 21% 20% 5%	400
	11th to 20th	Day	12% 17% 27% 29% 14% 1	470
	21st to end	Day	9% 14% 30% 30% 15% 1	414
March	1st to 10th	Day	15% 16% 31% 27% 9% 1	500
	11th to 20th	Day	15% 15% 30% 24% 13% 3	500
	21st to end	Day	11% 18% 35% 25% 10% 2	550
April	1st to 10th	Day	11% 15% 34% 23% 15% 2	500
	11th to 20th	Day	11% 18% 27% 27% 13% 4	492
	21st to end	Day	6% 16% 30% 29% 12% 7%	500
May	1st to 10th	Day	8% 12% 32% 31% 13% 4	503
	11th to 20th	Day	9% 12% 30% 31% 14% 4	528
	21st to end	Day	8% 11% 29% 33% 13% 6%	573
June	1st to 10th	Day	4 5% 32% 35% 17% 7%	530
	11th to 20th	Day	2 8% 30% 37% 18% 4	530
	21st to end	Day	2 5% 23% 41% 23% 6%	530
July	1st to 10th	Day	2 2 22% 43% 24% 8%	526
	11th to 20th	Day	2 1 10% 48% 30% 10%	524
	21st to end	Day	1 3 12% 49% 25% 10%	575
August	1st to 10th	Day	4 2 23% 43% 18% 9%	527
	11th to 20th	Day	2 1 18% 45% 25% 10%	517
	21st to end	Day	2 2 14% 47% 26% 10%	583
September	1st to 10th	Day	2 5% 18% 39% 26% 10%	530
	11th to 20th	Day	4 7% 25% 36% 19% 8%	530
	21st to end	Day	3 8% 16% 38% 27% 8%	530
October	1st to 10th	Day	4 6% 22% 36% 24% 9%	530
	11th to 20th	Day	5% 6% 20% 33% 27% 9%	530
	21st to end	Day	6% 5% 22% 32% 27% 7%	583
November	1st to 10th	Day	4 10% 20% 30% 30% 6%	493
	11th to 20th	Day	6% 7% 22% 34% 25% 6%	330
	21st to end	Day	9% 3 25% 33% 26% 4	291
December	1st to 10th	Day	9% 9% 18% 35% 22% 7%	220
	11th to 20th	Day	11% 9% 22% 25% 27% 5%	220
	21st to end	Day	15% 15% 24% 26% 17% 3	242
January	1st to 10th	Night	14% 6% 18% 34% 22% 6%	804
	11th to 20th	Night	10% 5% 17% 35% 26% 7%	800
	21st to end	Night	14% 6% 14% 36% 26% 4	880
February	1st to 10th	Night	15% 8% 18% 32% 23% 6%	800
	11th to 20th	Night	15% 7% 17% 32% 23% 5%	784
	21st to end	Night	13% 7% 20% 38% 20% 3	660
March	1st to 10th	Night	16% 8% 20% 33% 19% 4	800
	11th to 20th	Night	13% 6% 19% 35% 22% 6%	800
	21st to end	Night	12% 7% 21% 34% 21% 3	880
April	1st to 10th	Night	11% 4 22% 34% 26% 4	800
	11th to 20th	Night	10% 8% 21% 32% 24% 5%	791
	21st to end	Night	9% 6% 21% 30% 26% 8%	800
May	1st to 10th	Night	7% 6% 18% 36% 26% 7%	800
	11th to 20th	Night	10% 4 15% 32% 32% 7%	556
	21st to end	Night	10% 6% 17% 34% 27% 7%	433
June	1st to 10th	Night	6% 4 17% 33% 33% 8%	400
	11th to 20th	Night	6% 2 15% 39% 35% 4	400
	21st to end	Night	4 1 8% 28% 50% 10%	400
July	1st to 10th	Night	3 7% 28% 51% 11%	390
	11th to 20th	Night	4 4 21% 49% 22%	582
	21st to end	Night	5% 2 5% 25% 47% 16%	657
August	1st to 10th	Night	8% 1 6% 27% 44% 14%	597
	11th to 20th	Night	4 3 5% 34% 44% 11%	782
	21st to end	Night	4 1 5% 28% 49% 14%	880
September	1st to 10th	Night	4 2 6% 24% 49% 15%	800
	11th to 20th	Night	5% 3 9% 31% 41% 11%	800
	21st to end	Night	4 2 9% 28% 42% 16%	800
October	1st to 10th	Night	7% 2 8% 34% 39% 11%	800
	11th to 20th	Night	7% 3 12% 29% 35% 13%	800
	21st to end	Night	6% 3 11% 32% 31% 16%	880
November	1st to 10th	Night	7% 5% 13% 33% 33% 10%	820
	11th to 20th	Night	10% 4 15% 33% 31% 7%	840
	21st to end	Night	9% 3 14% 41% 28% 6%	840
December	1st to 10th	Night	12% 5% 15% 38% 26% 5%	840
	11th to 20th	Night	17% 6% 15% 34% 24% 4	840
	21st to end	Night	17% 8% 23% 32% 17% 4	924

Page generated at 2025-12-29 22:14:06. Version ac07

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