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 2024-01-14.

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	7% 6% 2 4 4 2 3 4 4 7% 55%	74695
	Night	8% 8% 3 5% 4 3 4 4 5% 7% 50%	75071
Transparency	Day	26% 5% 10% 19% 24% 16%	74417
	Night	31% 6% 10% 17% 21% 15%	74871
Seeing	Day	7% 8% 24% 35% 20% 6%	14347
	Night	10% 4 14% 32% 32% 9%	23878

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	16% 7% 3 6% 5% 3 3 4 4 7% 41%	1636
	11th to 20th	Day	10% 5% 1 4 4 2 5% 5% 5% 7% 52%	1648
	21st to end	Day	13% 7% 3 6% 5% 3 5% 4 4 6% 44%	1782
February	1st to 10th	Day	14% 8% 3 3 4 2 3 4 4 6% 49%	1620
	11th to 20th	Day	11% 7% 3 5% 4 2 4 5% 5% 6% 47%	1705
	21st to end	Day	12% 8% 3 5% 6% 3 4 4 4 6% 46%	1480
March	1st to 10th	Day	14% 8% 3 6% 5% 4 4 5% 6% 8% 38%	1916
	11th to 20th	Day	12% 8% 2 6% 6% 3 4 4 7% 9% 38%	1980
	21st to end	Day	11% 7% 3 5% 5% 3 4 4 4 7% 47%	2227
April	1st to 10th	Day	10% 8% 3 5% 5% 3 3 4 5% 6% 47%	2160
	11th to 20th	Day	9% 8% 2 5% 4 3 4 3 4 6% 52%	2129
	21st to end	Day	7% 7% 3 5% 3 2 2 4 5% 7% 54%	2160
May	1st to 10th	Day	6% 6% 2 4 4 3 3 4 4 9% 55%	2160
	11th to 20th	Day	6% 6% 2 5% 5% 2 3 4 5% 10% 54%	2325
	21st to end	Day	8% 10% 3 5% 5% 2 4 4 5% 8% 48%	2723
June	1st to 10th	Day	4 6% 3 5% 4 2 4 4 5% 8% 54%	2520
	11th to 20th	Day	4 4 2 3 3 2 3 3 4 7% 66%	2520
	21st to end	Day	2 5% 2 4 4 2 3 3 3 7% 66%	2520
July	1st to 10th	Day	1 5% 3 3 3 2 3 3 4 9% 63%	2516
	11th to 20th	Day	3 4 2 4 4 3 4 3 3 9% 62%	2340
	21st to end	Day	1 3 2 3 3 2 3 3 5% 11% 64%	2546
August	1st to 10th	Day	3 7% 2 4 4 2 3 3 4 10% 57%	2328
	11th to 20th	Day	1 4 1 3 3 2 3 4 4 7% 67%	2131
	21st to end	Day	1 4 2 4 4 2 3 4 4 8% 64%	2376
September	1st to 10th	Day	2 4 2 2 2 1 2 2 3 7% 74%	2160
	11th to 20th	Day	3 6% 2 3 3 2 3 3 4 8% 63%	2160
	21st to end	Day	3 3 1 2 2 1 2 3 4 6% 72%	1930
October	1st to 10th	Day	4 3 2 2 3 2 3 4 4 6% 68%	1800
	11th to 20th	Day	5% 4 1 4 4 2 3 3 3 6% 66%	1800
	21st to end	Day	5% 5% 2 4 3 2 3 3 4 7% 64%	1980
November	1st to 10th	Day	6% 5% 2 4 4 3 4 4 5% 7% 56%	1821
	11th to 20th	Day	7% 5% 3 5% 4 2 4 4 4 6% 55%	1710
	21st to end	Day	10% 4 2 3 3 2 3 4 5% 7% 57%	1644
December	1st to 10th	Day	10% 7% 2 5% 5% 3 4 4 5% 7% 47%	1520
	11th to 20th	Day	19% 10% 4 6% 5% 3 3 4 6% 6% 33%	1928
	21st to end	Day	14% 8% 3 5% 5% 3 4 5% 6% 8% 38%	2794
January	1st to 10th	Night	13% 7% 3 6% 5% 3 4 4 5% 8% 42%	2527
	11th to 20th	Night	10% 6% 2 6% 4 3 4 5% 5% 7% 48%	2384
	21st to end	Night	13% 7% 2 5% 5% 2 4 4 5% 6% 46%	2574
February	1st to 10th	Night	13% 7% 2 5% 4 2 4 3 4 6% 50%	2340
	11th to 20th	Night	11% 8% 3 5% 4 3 4 4 5% 7% 47%	2140
	21st to end	Night	11% 8% 3 4 5% 2 3 3 4 6% 51%	1776
March	1st to 10th	Night	14% 10% 3 5% 4 3 4 5% 4 6% 41%	2039
	11th to 20th	Night	13% 9% 2 6% 6% 3 5% 4 4 8% 41%	1980
	21st to end	Night	11% 8% 3 5% 4 2 4 4 5% 6% 47%	2127
April	1st to 10th	Night	11% 7% 3 5% 5% 3 4 4 7% 6% 47%	1800
	11th to 20th	Night	9% 9% 2 5% 3 2 4 3 4 7% 52%	1779
	21st to end	Night	6% 8% 3 4 4 2 4 3 5% 8% 54%	1800
May	1st to 10th	Night	6% 10% 3 6% 5% 3 3 3 5% 7% 50%	1800
	11th to 20th	Night	7% 10% 3 7% 6% 3 3 4 5% 5% 46%	1564
	21st to end	Night	8% 14% 3 7% 4 2 3 3 4 6% 46%	1552
June	1st to 10th	Night	6% 10% 3 5% 5% 2 3 3 5% 6% 50%	1440
	11th to 20th	Night	3 9% 3 5% 5% 3 3 3 5% 7% 56%	1440
	21st to end	Night	2 9% 4 5% 4 3 3 3 4 6% 58%	1440
July	1st to 10th	Night	1 11% 5% 6% 5% 2 3 4 4 8% 51%	1440
	11th to 20th	Night	1 9% 5% 6% 4 2 4 3 6% 7% 52%	1620
	21st to end	Night	1 13% 5% 7% 5% 4 5% 4 7% 9% 41%	1773
August	1st to 10th	Night	2 15% 5% 9% 7% 3 3 5% 4 7% 39%	1611
	11th to 20th	Night	2 8% 4 5% 6% 3 4 4 4 7% 55%	1770
	21st to end	Night	1 11% 4 6% 5% 2 3 4 4 7% 54%	1980
September	1st to 10th	Night	3 5% 2 4 3 2 3 3 5% 7% 63%	1800
	11th to 20th	Night	4 8% 3 4 4 2 2 4 4 7% 58%	1800
	21st to end	Night	3 4 2 3 3 2 3 2 3 6% 69%	2025
October	1st to 10th	Night	6% 5% 2 4 4 2 3 2 3 6% 63%	2160
	11th to 20th	Night	5% 5% 3 6% 4 3 4 3 4 5% 58%	2160
	21st to end	Night	5% 7% 2 3 3 3 3 3 4 5% 61%	2376
November	1st to 10th	Night	7% 7% 2 5% 3 2 3 2 4 6% 58%	2255
	11th to 20th	Night	8% 6% 3 5% 3 2 3 3 4 9% 54%	2470
	21st to end	Night	8% 4 2 4 3 3 4 3 4 7% 58%	2531
December	1st to 10th	Night	11% 6% 3 5% 4 2 3 5% 4 6% 51%	2660
	11th to 20th	Night	19% 9% 4 6% 5% 3 5% 4 5% 6% 34%	3276
	21st to end	Night	14% 8% 3 6% 7% 3 5% 6% 6% 7% 35%	4862

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	43% 6% 11% 22% 14% 5%	1636
	11th to 20th	Day	31% 7% 13% 18% 18% 14%	1648
	21st to end	Day	41% 8% 8% 12% 22% 9%	1782
February	1st to 10th	Day	37% 5% 8% 19% 20% 12%	1620
	11th to 20th	Day	36% 7% 9% 19% 21% 8%	1715
	21st to end	Day	39% 7% 8% 21% 19% 6%	1480
March	1st to 10th	Day	42% 9% 11% 17% 16% 4	1916
	11th to 20th	Day	40% 8% 12% 19% 16% 4	1980
	21st to end	Day	37% 7% 15% 21% 16% 4	2227
April	1st to 10th	Day	36% 7% 13% 23% 16% 4	2160
	11th to 20th	Day	33% 5% 12% 26% 18% 6%	2132
	21st to end	Day	28% 6% 12% 29% 20% 5%	2160
May	1st to 10th	Day	24% 5% 13% 24% 28% 5%	2160
	11th to 20th	Day	23% 4 12% 28% 25% 8%	2328
	21st to end	Day	31% 6% 14% 25% 20% 3	2724
June	1st to 10th	Day	23% 8% 12% 22% 27% 8%	2520
	11th to 20th	Day	14% 3 10% 22% 33% 17%	2520
	21st to end	Day	14% 2 7% 14% 33% 30%	2520
July	1st to 10th	Day	12% 2 5% 12% 28% 40%	2447
	11th to 20th	Day	15% 2 7% 12% 25% 38%	2271
	21st to end	Day	9% 3 6% 13% 34% 35%	2405
August	1st to 10th	Day	17% 2 6% 13% 29% 32%	2312
	11th to 20th	Day	11% 2 6% 15% 32% 35%	2131
	21st to end	Day	13% 3 5% 15% 33% 31%	2376
September	1st to 10th	Day	10% 3 3 11% 29% 44%	2160
	11th to 20th	Day	15% 3 9% 22% 32% 19%	2160
	21st to end	Day	12% 3 6% 22% 37% 19%	1930
October	1st to 10th	Day	17% 4 9% 19% 27% 24%	1800
	11th to 20th	Day	19% 4 10% 21% 23% 24%	1800
	21st to end	Day	20% 4 9% 20% 24% 22%	1980
November	1st to 10th	Day	26% 6% 10% 20% 25% 13%	1821
	11th to 20th	Day	28% 5% 12% 19% 23% 11%	1710
	21st to end	Day	28% 5% 9% 17% 26% 15%	1644
December	1st to 10th	Day	33% 8% 11% 16% 18% 13%	1520
	11th to 20th	Day	49% 8% 9% 14% 13% 6%	1928
	21st to end	Day	44% 7% 12% 21% 11% 4	2794
January	1st to 10th	Night	40% 7% 12% 20% 16% 5%	2527
	11th to 20th	Night	34% 8% 13% 15% 16% 14%	2384
	21st to end	Night	38% 7% 11% 14% 18% 12%	2574
February	1st to 10th	Night	36% 4 9% 16% 21% 13%	2340
	11th to 20th	Night	36% 6% 11% 17% 23% 7%	2141
	21st to end	Night	36% 6% 11% 25% 16% 6%	1776
March	1st to 10th	Night	43% 9% 13% 15% 15% 5%	2039
	11th to 20th	Night	41% 7% 11% 18% 17% 7%	1980
	21st to end	Night	35% 9% 15% 20% 15% 6%	2127
April	1st to 10th	Night	36% 9% 13% 22% 15% 5%	1800
	11th to 20th	Night	33% 5% 15% 24% 18% 6%	1779
	21st to end	Night	26% 7% 14% 26% 20% 5%	1800
May	1st to 10th	Night	31% 5% 10% 21% 24% 8%	1800
	11th to 20th	Night	32% 8% 10% 18% 24% 7%	1565
	21st to end	Night	37% 6% 14% 20% 19% 4	1552
June	1st to 10th	Night	29% 7% 10% 20% 23% 11%	1440
	11th to 20th	Night	21% 4 11% 15% 28% 20%	1440
	21st to end	Night	18% 4 5% 14% 29% 30%	1440
July	1st to 10th	Night	21% 5% 6% 8% 24% 36%	1400
	11th to 20th	Night	21% 5% 5% 11% 24% 34%	1566
	21st to end	Night	25% 4 7% 11% 26% 27%	1674
August	1st to 10th	Night	29% 4 6% 12% 21% 27%	1602
	11th to 20th	Night	19% 3 5% 11% 28% 35%	1770
	21st to end	Night	20% 4 4 14% 29% 29%	1980
September	1st to 10th	Night	16% 4 3 9% 25% 42%	1800
	11th to 20th	Night	19% 6% 6% 18% 30% 22%	1800
	21st to end	Night	14% 4 6% 17% 36% 22%	2025
October	1st to 10th	Night	20% 4 7% 19% 24% 26%	2160
	11th to 20th	Night	24% 6% 6% 19% 23% 23%	2160
	21st to end	Night	21% 5% 6% 21% 25% 22%	2376
November	1st to 10th	Night	27% 6% 9% 20% 22% 16%	2255
	11th to 20th	Night	29% 6% 11% 19% 25% 10%	2470
	21st to end	Night	27% 5% 10% 18% 25% 16%	2531
December	1st to 10th	Night	33% 6% 10% 17% 19% 14%	2660
	11th to 20th	Night	50% 7% 10% 14% 14% 5%	3276
	21st to end	Night	45% 12% 13% 16% 11% 5%	4862

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	21% 13% 24% 26% 14% 2	297
	11th to 20th	Day	11% 10% 25% 32% 20% 2	350
	21st to end	Day	14% 9% 23% 32% 18% 3	374
February	1st to 10th	Day	13% 13% 25% 22% 22% 5%	340
	11th to 20th	Day	12% 16% 26% 30% 14% 2	395
	21st to end	Day	10% 15% 30% 28% 15% 1	346
March	1st to 10th	Day	16% 14% 32% 27% 10% 1	420
	11th to 20th	Day	15% 14% 31% 24% 13% 3	420
	21st to end	Day	11% 17% 35% 25% 10% 2	462
April	1st to 10th	Day	11% 15% 35% 23% 15% 2	420
	11th to 20th	Day	11% 19% 30% 25% 12% 2	412
	21st to end	Day	6% 15% 31% 30% 12% 6%	420
May	1st to 10th	Day	8% 12% 33% 30% 13% 4	423
	11th to 20th	Day	9% 13% 31% 32% 11% 3	448
	21st to end	Day	9% 12% 29% 33% 12% 5%	485
June	1st to 10th	Day	4 5% 34% 33% 17% 7%	450
	11th to 20th	Day	2 8% 28% 39% 19% 4	450
	21st to end	Day	2 5% 24% 41% 24% 5%	450
July	1st to 10th	Day	2 2 22% 44% 25% 6%	446
	11th to 20th	Day	2 10% 49% 30% 9%	444
	21st to end	Day	1 11% 50% 27% 10%	487
August	1st to 10th	Day	5% 2 23% 44% 19% 7%	447
	11th to 20th	Day	1 16% 46% 27% 10%	437
	21st to end	Day	2 1 14% 48% 28% 8%	495
September	1st to 10th	Day	2 5% 15% 41% 27% 10%	450
	11th to 20th	Day	4 4 24% 38% 22% 7%	450
	21st to end	Day	2 7% 15% 39% 29% 7%	450
October	1st to 10th	Day	3 6% 22% 37% 24% 8%	450
	11th to 20th	Day	5% 5% 20% 32% 28% 10%	450
	21st to end	Day	7% 5% 20% 33% 28% 7%	495
November	1st to 10th	Day	4 10% 20% 31% 29% 6%	417
	11th to 20th	Day	4 6% 17% 36% 30% 7%	270
	21st to end	Day	9% 3 23% 33% 27% 5%	239
December	1st to 10th	Day	11% 11% 20% 32% 21% 5%	180
	11th to 20th	Day	13% 8% 23% 25% 24% 6%	180
	21st to end	Day	15% 13% 22% 27% 20% 4	198
January	1st to 10th	Night	14% 7% 17% 33% 22% 7%	760
	11th to 20th	Night	10% 5% 16% 34% 27% 7%	734
	21st to end	Night	15% 4 14% 35% 27% 4	792
February	1st to 10th	Night	14% 5% 16% 33% 25% 6%	720
	11th to 20th	Night	15% 7% 17% 31% 25% 5%	704
	21st to end	Night	14% 6% 20% 36% 20% 3	592
March	1st to 10th	Night	16% 6% 20% 33% 20% 4	720
	11th to 20th	Night	13% 5% 18% 34% 23% 6%	720
	21st to end	Night	12% 7% 21% 35% 22% 3	792
April	1st to 10th	Night	12% 4 21% 34% 26% 3	720
	11th to 20th	Night	10% 8% 22% 31% 23% 6%	711
	21st to end	Night	9% 4 22% 31% 25% 9%	720
May	1st to 10th	Night	8% 6% 18% 35% 27% 7%	720
	11th to 20th	Night	10% 4 15% 32% 32% 8%	502
	21st to end	Night	11% 5% 18% 32% 27% 7%	389
June	1st to 10th	Night	7% 3 16% 33% 34% 8%	360
	11th to 20th	Night	6% 1 14% 38% 36% 5%	360
	21st to end	Night	4 1 8% 28% 49% 9%	360
July	1st to 10th	Night	3 7% 29% 49% 12%	350
	11th to 20th	Night	4 3 21% 50% 21%	522
	21st to end	Night	4 4 26% 49% 17%	591
August	1st to 10th	Night	9% 6% 29% 44% 11%	537
	11th to 20th	Night	3 1 5% 33% 46% 12%	702
	21st to end	Night	4 5% 28% 49% 14%	792
September	1st to 10th	Night	4 1 6% 23% 50% 16%	720
	11th to 20th	Night	4 2 8% 32% 43% 11%	720
	21st to end	Night	4 2 8% 26% 43% 17%	720
October	1st to 10th	Night	7% 2 8% 34% 38% 11%	720
	11th to 20th	Night	8% 3 11% 28% 37% 14%	720
	21st to end	Night	6% 2 10% 32% 31% 18%	792
November	1st to 10th	Night	7% 5% 12% 33% 32% 10%	740
	11th to 20th	Night	9% 3 13% 33% 34% 8%	760
	21st to end	Night	9% 2 13% 40% 29% 6%	760
December	1st to 10th	Night	13% 5% 15% 36% 26% 6%	760
	11th to 20th	Night	17% 5% 16% 34% 23% 4	760
	21st to end	Night	17% 7% 22% 32% 19% 4	836

Page generated at 2024-01-11 01:22:41. Version ac07

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