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 2024-11-12.

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 5% 3 3 3 3 4 7% 55%	104985
	Night	8% 10% 3 7% 4 3 3 3 4 6% 49%	102957
Transparency	Day	24% 5% 9% 19% 24% 18%	104744
	Night	30% 8% 10% 16% 21% 15%	102788
Seeing	Day	7% 9% 24% 34% 20% 6%	15524
	Night	9% 4 14% 32% 32% 9%	24942

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	13% 8% 3 7% 4 4 3 3 4 6% 43%	2734
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 4 5% 6% 37%	2860
	21st to end	Day	18% 10% 3 8% 5% 4 5% 4 5% 7% 31%	3146
February	1st to 10th	Day	14% 8% 3 4 4 3 4 3 5% 6% 47%	1710
	11th to 20th	Day	11% 9% 2 5% 4 3 5% 4 6% 6% 46%	1802
	21st to end	Day	12% 8% 3 5% 5% 4 3 3 4 6% 46%	1570
March	1st to 10th	Day	11% 10% 3 8% 5% 6% 6% 6% 7% 8% 28%	3344
	11th to 20th	Day	9% 5% 2 5% 3 4 3 3 5% 7% 55%	3490
	21st to end	Day	12% 10% 3 7% 5% 5% 5% 4 5% 7% 36%	3912
April	1st to 10th	Day	10% 8% 2 6% 4 4 3 4 5% 6% 48%	2280
	11th to 20th	Day	8% 8% 2 6% 4 4 4 3 5% 6% 51%	2249
	21st to end	Day	7% 8% 3 5% 3 3 2 4 5% 7% 53%	2280
May	1st to 10th	Day	7% 4 1 3 2 2 2 2 3 7% 67%	3800
	11th to 20th	Day	3 5% 2 4 3 2 2 3 4 8% 63%	4134
	21st to end	Day	4 13% 3 5% 3 3 3 2 5% 7% 53%	4813
June	1st to 10th	Day	4 7% 2 5% 4 4 3 4 5% 8% 54%	2660
	11th to 20th	Day	3 4 2 3 3 3 3 2 4 7% 66%	2660
	21st to end	Day	2 5% 2 5% 3 2 3 2 4 7% 66%	2660
July	1st to 10th	Day	1 3 1 4 2 2 2 2 3 6% 73%	4403
	11th to 20th	Day	2 4 3 7% 3 3 3 2 3 8% 62%	4110
	21st to end	Day	1 10% 5% 5% 3 3 3 2 4 9% 56%	4455
August	1st to 10th	Day	2 4 2 7% 3 3 4 3 6% 10% 56%	4091
	11th to 20th	Day	3 2 7% 3 3 3 3 4 8% 64%	3733
	21st to end	Day	1 5% 1 6% 3 3 3 2 4 7% 66%	4180
September	1st to 10th	Day	1 4 1 3 2 1 2 2 3 6% 74%	2280
	11th to 20th	Day	3 7% 2 4 3 3 2 2 4 8% 62%	2280
	21st to end	Day	3 3 1 3 2 1 2 2 4 6% 72%	2036
October	1st to 10th	Day	2 3 1 3 2 2 2 3 3 5% 73%	3180
	11th to 20th	Day	3 7% 3 5% 3 2 3 2 3 6% 62%	3161
	21st to end	Day	4 4 1 4 3 3 3 3 5% 8% 62%	3448
November	1st to 10th	Day	6% 6% 1 4 4 4 3 3 4 7% 57%	1919
	11th to 20th	Day	7% 6% 2 6% 3 3 4 3 5% 6% 55%	1719
	21st to end	Day	10% 5% 1 4 3 3 3 3 5% 6% 57%	1644
December	1st to 10th	Day	9% 7% 3 6% 5% 4 4 3 5% 7% 47%	1520
	11th to 20th	Day	18% 11% 4 6% 4 4 4 3 6% 6% 33%	1928
	21st to end	Day	14% 9% 3 6% 5% 4 4 4 6% 8% 38%	2794
January	1st to 10th	Night	12% 8% 2 6% 4 3 3 3 5% 7% 47%	4215
	11th to 20th	Night	15% 8% 3 8% 5% 5% 5% 4 6% 7% 34%	4110
	21st to end	Night	20% 11% 3 7% 4 4 4 3 5% 6% 33%	4521
February	1st to 10th	Night	13% 9% 2 5% 4 3 4 2 4 6% 49%	2470
	11th to 20th	Night	11% 9% 3 5% 3 3 4 4 5% 7% 46%	2263
	21st to end	Night	11% 8% 2 5% 4 4 2 3 4 6% 51%	1884
March	1st to 10th	Night	17% 14% 3 8% 4 4 4 3 4 6% 32%	3525
	11th to 20th	Night	9% 7% 2 6% 4 4 3 2 3 6% 54%	3490
	21st to end	Night	15% 15% 3 7% 4 3 4 4 6% 6% 34%	3739
April	1st to 10th	Night	10% 8% 2 6% 4 3 4 3 7% 6% 47%	1900
	11th to 20th	Night	9% 10% 2 6% 3 3 3 3 4 7% 51%	1879
	21st to end	Night	6% 8% 3 4 3 3 4 3 5% 7% 54%	1900
May	1st to 10th	Night	4 11% 2 4 3 3 2 3 4 5% 59%	3180
	11th to 20th	Night	4 14% 5% 12% 5% 3 2 2 4 4 45%	2762
	21st to end	Night	4 18% 3 5% 2 2 2 2 3 4 54%	2762
June	1st to 10th	Night	6% 13% 2 6% 4 2 3 3 5% 6% 50%	1520
	11th to 20th	Night	3 10% 2 6% 4 4 3 2 5% 7% 56%	1520
	21st to end	Night	2 9% 3 6% 4 3 2 2 4 7% 57%	1520
July	1st to 10th	Night	6% 3 9% 5% 2 2 2 3 6% 60%	2540
	11th to 20th	Night	1 9% 6% 13% 4 3 3 2 4 6% 50%	2860
	21st to end	Night	1 28% 6% 8% 4 4 3 2 5% 6% 35%	3109
August	1st to 10th	Night	2 9% 3 23% 9% 5% 3 4 4 8% 31%	2848
	11th to 20th	Night	2 10% 4 8% 5% 3 2 2 3 5% 57%	3116
	21st to end	Night	2 13% 2 8% 3 3 2 2 3 5% 57%	3498
September	1st to 10th	Night	3 5% 2 4 2 3 3 2 5% 7% 64%	1900
	11th to 20th	Night	4 10% 4 5% 3 3 3 3 4 7% 55%	1900
	21st to end	Night	3 5% 2 4 2 3 2 2 3 6% 68%	2139
October	1st to 10th	Night	3 3 1 4 3 3 2 2 3 5% 72%	3800
	11th to 20th	Night	3 16% 4 7% 3 3 3 2 3 4 52%	3777
	21st to end	Night	5% 8% 2 3 2 3 2 2 5% 6% 62%	4121
November	1st to 10th	Night	7% 7% 2 5% 2 3 3 2 4 6% 58%	2377
	11th to 20th	Night	8% 7% 2 5% 3 3 3 3 5% 9% 53%	2483
	21st to end	Night	8% 5% 2 4 3 4 3 3 4 6% 58%	2531
December	1st to 10th	Night	11% 6% 2 6% 3 4 3 3 4 6% 51%	2660
	11th to 20th	Night	19% 11% 3 7% 4 4 5% 3 6% 6% 34%	3276
	21st to end	Night	14% 9% 3 7% 6% 5% 5% 5% 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	41% 7% 11% 28% 10% 3	2734
	11th to 20th	Day	46% 8% 12% 15% 11% 8%	2860
	21st to end	Day	50% 8% 8% 16% 13% 5%	3146
February	1st to 10th	Day	38% 5% 8% 18% 19% 11%	1710
	11th to 20th	Day	36% 8% 9% 19% 20% 8%	1812
	21st to end	Day	38% 7% 8% 22% 19% 5%	1570
March	1st to 10th	Day	45% 15% 12% 11% 14% 3	3344
	11th to 20th	Day	28% 6% 11% 27% 16% 11%	3490
	21st to end	Day	44% 10% 14% 21% 10% 2	3912
April	1st to 10th	Day	35% 7% 13% 25% 16% 4	2280
	11th to 20th	Day	33% 6% 12% 27% 17% 6%	2252
	21st to end	Day	28% 6% 13% 29% 21% 5%	2280
May	1st to 10th	Day	18% 4 11% 29% 30% 9%	3800
	11th to 20th	Day	14% 4 8% 29% 32% 13%	4137
	21st to end	Day	23% 5% 12% 25% 30% 5%	4814
June	1st to 10th	Day	22% 8% 12% 23% 27% 8%	2660
	11th to 20th	Day	14% 3 10% 23% 34% 16%	2660
	21st to end	Day	14% 2 7% 14% 32% 31%	2660
July	1st to 10th	Day	7% 1 6% 7% 18% 61%	4334
	11th to 20th	Day	14% 2 9% 8% 18% 49%	4041
	21st to end	Day	15% 4 8% 13% 32% 27%	4315
August	1st to 10th	Day	13% 4 8% 13% 33% 29%	4076
	11th to 20th	Day	7% 5% 6% 13% 41% 28%	3769
	21st to end	Day	12% 4 7% 12% 33% 33%	4179
September	1st to 10th	Day	10% 3 3 10% 29% 44%	2280
	11th to 20th	Day	16% 3 9% 21% 32% 18%	2280
	21st to end	Day	12% 3 6% 21% 38% 20%	2036
October	1st to 10th	Day	13% 3 6% 12% 29% 36%	3180
	11th to 20th	Day	19% 6% 9% 20% 28% 17%	3161
	21st to end	Day	18% 5% 7% 21% 33% 16%	3448
November	1st to 10th	Day	25% 6% 10% 21% 25% 13%	1919
	11th to 20th	Day	29% 5% 12% 19% 23% 11%	1719
	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	37% 10% 14% 22% 13% 3	4215
	11th to 20th	Night	45% 12% 14% 12% 10% 8%	4110
	21st to end	Night	50% 8% 9% 15% 11% 7%	4521
February	1st to 10th	Night	37% 5% 10% 15% 20% 13%	2470
	11th to 20th	Night	37% 6% 12% 17% 22% 7%	2264
	21st to end	Night	36% 6% 11% 25% 16% 6%	1884
March	1st to 10th	Night	52% 10% 11% 11% 13% 3	3525
	11th to 20th	Night	29% 8% 10% 23% 19% 10%	3490
	21st to end	Night	46% 11% 13% 17% 9% 3	3739
April	1st to 10th	Night	35% 9% 13% 23% 15% 5%	1900
	11th to 20th	Night	32% 6% 14% 25% 17% 6%	1879
	21st to end	Night	26% 8% 14% 26% 20% 5%	1900
May	1st to 10th	Night	25% 7% 12% 20% 24% 13%	3180
	11th to 20th	Night	20% 17% 7% 20% 22% 13%	2763
	21st to end	Night	29% 5% 12% 20% 27% 6%	2762
June	1st to 10th	Night	29% 7% 10% 20% 24% 10%	1520
	11th to 20th	Night	21% 5% 11% 15% 29% 19%	1520
	21st to end	Night	17% 4 5% 14% 28% 31%	1520
July	1st to 10th	Night	12% 3 9% 6% 18% 52%	2500
	11th to 20th	Night	22% 4 11% 8% 16% 40%	2806
	21st to end	Night	30% 8% 11% 12% 18% 21%	3011
August	1st to 10th	Night	19% 10% 23% 11% 18% 18%	2839
	11th to 20th	Night	15% 6% 7% 9% 36% 27%	3146
	21st to end	Night	19% 6% 8% 9% 34% 24%	3498
September	1st to 10th	Night	16% 4 3 9% 26% 42%	1900
	11th to 20th	Night	20% 7% 6% 17% 29% 20%	1900
	21st to end	Night	15% 4 6% 16% 36% 23%	2139
October	1st to 10th	Night	13% 3 5% 14% 25% 39%	3800
	11th to 20th	Night	25% 12% 6% 17% 25% 16%	3777
	21st to end	Night	20% 5% 6% 23% 30% 16%	4121
November	1st to 10th	Night	26% 6% 9% 20% 23% 16%	2377
	11th to 20th	Night	29% 6% 11% 19% 25% 10%	2483
	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	370
	21st to end	Day	14% 10% 25% 31% 17% 3	407
February	1st to 10th	Day	14% 13% 26% 21% 21% 5%	370
	11th to 20th	Day	12% 17% 27% 29% 14% 2	432
	21st to end	Day	10% 15% 30% 30% 15% 1	382
March	1st to 10th	Day	15% 15% 32% 27% 9% 1	460
	11th to 20th	Day	13% 15% 30% 25% 14% 3	460
	21st to end	Day	11% 18% 35% 25% 10% 1	506
April	1st to 10th	Day	11% 15% 35% 23% 15% 2	460
	11th to 20th	Day	11% 18% 28% 26% 13% 3	452
	21st to end	Day	6% 15% 31% 30% 12% 6%	460
May	1st to 10th	Day	8% 12% 33% 31% 13% 4	463
	11th to 20th	Day	9% 12% 30% 32% 13% 4	488
	21st to end	Day	9% 11% 29% 33% 13% 5%	529
June	1st to 10th	Day	4 5% 34% 34% 16% 7%	490
	11th to 20th	Day	2 7% 29% 38% 18% 4	490
	21st to end	Day	2 4 23% 42% 23% 5%	490
July	1st to 10th	Day	2 1 21% 44% 24% 8%	486
	11th to 20th	Day	2 1 10% 48% 30% 9%	484
	21st to end	Day	1 2 12% 49% 26% 11%	531
August	1st to 10th	Day	5% 2 22% 44% 19% 8%	487
	11th to 20th	Day	1 1 19% 44% 25% 9%	477
	21st to end	Day	2 2 14% 47% 27% 9%	539
September	1st to 10th	Day	2 4 16% 40% 27% 11%	490
	11th to 20th	Day	4 6% 25% 37% 20% 7%	490
	21st to end	Day	2 7% 16% 38% 29% 8%	490
October	1st to 10th	Day	3 6% 21% 37% 25% 9%	490
	11th to 20th	Day	6% 6% 19% 33% 28% 9%	490
	21st to end	Day	7% 5% 22% 33% 27% 6%	539
November	1st to 10th	Day	4 11% 20% 32% 28% 6%	455
	11th to 20th	Day	4 7% 17% 35% 30% 7%	273
	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	11% 6% 16% 34% 27% 7%	760
	21st to end	Night	15% 6% 14% 35% 26% 4	836
February	1st to 10th	Night	15% 6% 17% 32% 24% 6%	760
	11th to 20th	Night	15% 7% 17% 31% 25% 5%	744
	21st to end	Night	13% 7% 20% 37% 20% 3	628
March	1st to 10th	Night	16% 7% 20% 33% 19% 4	760
	11th to 20th	Night	13% 5% 19% 34% 23% 6%	760
	21st to end	Night	12% 7% 22% 34% 21% 3	836
April	1st to 10th	Night	12% 4 22% 34% 26% 3	760
	11th to 20th	Night	10% 8% 21% 31% 24% 5%	751
	21st to end	Night	9% 5% 22% 30% 25% 9%	760
May	1st to 10th	Night	7% 6% 19% 36% 26% 7%	760
	11th to 20th	Night	10% 3 15% 32% 33% 7%	529
	21st to end	Night	10% 5% 17% 34% 27% 7%	411
June	1st to 10th	Night	6% 3 16% 33% 33% 7%	380
	11th to 20th	Night	6% 1 15% 38% 36% 4	380
	21st to end	Night	4 1 7% 28% 49% 9%	380
July	1st to 10th	Night	3 7% 28% 51% 11%	370
	11th to 20th	Night	4 4 21% 51% 20%	552
	21st to end	Night	4 1 4 25% 48% 17%	624
August	1st to 10th	Night	9% 5% 28% 45% 13%	567
	11th to 20th	Night	3 2 5% 34% 44% 12%	742
	21st to end	Night	5% 1 5% 28% 48% 14%	836
September	1st to 10th	Night	4 1 5% 24% 50% 15%	760
	11th to 20th	Night	4 3 9% 31% 41% 11%	760
	21st to end	Night	4 1 8% 26% 43% 17%	760
October	1st to 10th	Night	7% 2 7% 34% 39% 11%	760
	11th to 20th	Night	8% 3 12% 29% 35% 13%	760
	21st to end	Night	6% 3 11% 33% 30% 17%	836
November	1st to 10th	Night	7% 5% 13% 34% 31% 10%	780
	11th to 20th	Night	10% 3 13% 32% 34% 8%	764
	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 2024-11-08 19:45:36. Version ac07

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