Au Sable Forks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Au Sable Forks Observatory clear sky chart from 2005-11-06 to 2024-09-14.

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	14% 10% 3 9% 6% 5% 5% 4 6% 7% 30%	100943
	Night	13% 10% 4 9% 6% 5% 5% 4 6% 7% 31%	96971
Transparency	Day	50% 8% 13% 19% 9% 1	100703
	Night	50% 8% 13% 19% 9% 1	96831
Seeing	Day	23% 18% 31% 18% 7% 2	14483
	Night	20% 17% 29% 24% 8% 1	23444

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	10% 13% 5% 12% 8% 7% 6% 4 6% 6% 22%	2517
	11th to 20th	Day	9% 16% 6% 19% 10% 5% 4 3 4 5% 18%	2520
	21st to end	Day	11% 16% 6% 13% 7% 7% 6% 4 5% 6% 19%	2772
February	1st to 10th	Day	10% 14% 4 13% 8% 7% 6% 4 6% 5% 21%	1700
	11th to 20th	Day	8% 11% 4 13% 9% 8% 6% 4 5% 6% 26%	1787
	21st to end	Day	12% 13% 5% 10% 8% 6% 5% 4 5% 6% 26%	1570
March	1st to 10th	Day	19% 15% 4 10% 6% 6% 4 3 5% 5% 23%	3116
	11th to 20th	Day	8% 15% 5% 13% 8% 7% 7% 4 5% 5% 24%	3278
	21st to end	Day	12% 11% 4 8% 6% 4 4 4 5% 5% 36%	4166
April	1st to 10th	Day	17% 13% 3 8% 6% 5% 4 4 4 6% 30%	2280
	11th to 20th	Day	16% 11% 3 8% 6% 5% 4 3 4 5% 34%	2254
	21st to end	Day	20% 11% 3 8% 5% 4 4 3 5% 6% 31%	2412
May	1st to 10th	Day	18% 13% 4 9% 5% 5% 4 4 5% 6% 28%	4290
	11th to 20th	Day	15% 10% 4 8% 5% 5% 5% 4 6% 7% 29%	4398
	21st to end	Day	13% 6% 2 7% 5% 5% 6% 5% 7% 9% 36%	4837
June	1st to 10th	Day	21% 9% 2 6% 5% 5% 5% 4 6% 8% 28%	2660
	11th to 20th	Day	14% 8% 3 7% 5% 5% 6% 5% 6% 8% 34%	2660
	21st to end	Day	19% 7% 3 8% 6% 5% 5% 5% 6% 7% 28%	2660
July	1st to 10th	Day	10% 6% 2 7% 5% 6% 7% 5% 8% 10% 34%	4440
	11th to 20th	Day	10% 6% 2 7% 5% 6% 7% 6% 9% 9% 34%	4440
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 5% 7% 9% 36%	4814
August	1st to 10th	Day	13% 8% 3 8% 6% 6% 6% 5% 8% 9% 30%	4423
	11th to 20th	Day	10% 6% 3 9% 5% 5% 7% 6% 8% 11% 29%	3891
	21st to end	Day	13% 7% 2 6% 5% 5% 5% 5% 7% 9% 38%	4180
September	1st to 10th	Day	13% 6% 1 6% 4 5% 4 4 6% 9% 42%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 5% 8% 45%	2118
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 5% 7% 8% 38%	1980
October	1st to 10th	Day	19% 9% 4 8% 4 4 4 4 6% 6% 31%	1872
	11th to 20th	Day	13% 12% 3 9% 5% 4 5% 5% 6% 6% 32%	1775
	21st to end	Day	20% 12% 3 9% 5% 4 4 5% 5% 6% 27%	1782
November	1st to 10th	Day	10% 12% 4 8% 7% 5% 5% 5% 6% 6% 31%	1671
	11th to 20th	Day	13% 11% 3 10% 7% 5% 5% 4 5% 7% 29%	1682
	21st to end	Day	12% 13% 5% 10% 7% 5% 5% 5% 5% 6% 27%	1520
December	1st to 10th	Day	13% 19% 7% 13% 7% 5% 5% 3 5% 5% 17%	1520
	11th to 20th	Day	15% 13% 5% 11% 7% 6% 4 4 6% 6% 23%	1906
	21st to end	Day	19% 17% 5% 11% 6% 5% 4 3 4 5% 22%	2772
January	1st to 10th	Night	13% 15% 5% 14% 6% 5% 5% 4 5% 6% 22%	4429
	11th to 20th	Night	8% 13% 8% 16% 9% 7% 6% 5% 5% 6% 18%	4440
	21st to end	Night	14% 15% 7% 13% 6% 5% 5% 3 5% 6% 21%	4884
February	1st to 10th	Night	8% 13% 5% 12% 8% 7% 6% 4 8% 7% 22%	2475
	11th to 20th	Night	8% 11% 5% 12% 8% 7% 6% 4 6% 6% 27%	2279
	21st to end	Night	10% 11% 5% 10% 8% 5% 6% 5% 6% 6% 29%	1884
March	1st to 10th	Night	18% 12% 4 9% 7% 5% 5% 4 5% 6% 27%	3724
	11th to 20th	Night	11% 14% 6% 12% 6% 5% 4 4 5% 6% 27%	3678
	21st to end	Night	11% 11% 5% 10% 6% 5% 4 3 4 4 37%	3466
April	1st to 10th	Night	14% 10% 4 9% 6% 6% 5% 3 5% 7% 31%	1900
	11th to 20th	Night	16% 11% 2 7% 6% 6% 4 4 5% 7% 31%	1875
	21st to end	Night	16% 10% 3 7% 5% 4 4 4 5% 6% 35%	1767
May	1st to 10th	Night	20% 14% 3 8% 5% 5% 4 4 6% 6% 24%	2679
	11th to 20th	Night	16% 10% 4 8% 4 4 4 3 5% 7% 34%	2495
	21st to end	Night	11% 7% 2 7% 4 5% 5% 4 6% 9% 39%	2738
June	1st to 10th	Night	18% 6% 3 6% 5% 4 5% 4 6% 9% 34%	1520
	11th to 20th	Night	15% 6% 3 7% 4 4 4 4 6% 8% 39%	1520
	21st to end	Night	14% 7% 2 7% 5% 4 5% 4 6% 8% 38%	1520
July	1st to 10th	Night	10% 7% 3 8% 6% 6% 5% 5% 6% 7% 37%	2520
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 4 6% 8% 47%	2520
	21st to end	Night	8% 5% 2 7% 6% 5% 5% 4 7% 7% 43%	2739
August	1st to 10th	Night	12% 8% 2 7% 5% 4 5% 4 6% 8% 40%	2506
	11th to 20th	Night	10% 7% 3 8% 6% 4 5% 4 7% 7% 40%	2901
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 6% 9% 46%	3476
September	1st to 10th	Night	10% 5% 2 6% 5% 5% 4 3 6% 8% 47%	1900
	11th to 20th	Night	12% 6% 2 5% 3 4 3 3 4 8% 49%	1920
	21st to end	Night	14% 5% 2 5% 5% 4 4 4 6% 7% 43%	1980
October	1st to 10th	Night	18% 8% 3 7% 4 4 5% 4 5% 7% 34%	2087
	11th to 20th	Night	15% 8% 3 7% 6% 6% 5% 4 5% 7% 34%	2183
	21st to end	Night	20% 10% 3 8% 5% 4 5% 4 6% 7% 27%	2574
November	1st to 10th	Night	12% 10% 4 9% 6% 5% 5% 5% 5% 7% 32%	2407
	11th to 20th	Night	12% 11% 4 10% 6% 5% 5% 4 6% 6% 31%	2493
	21st to end	Night	14% 12% 4 10% 6% 6% 5% 4 7% 7% 26%	2660
December	1st to 10th	Night	15% 15% 6% 12% 8% 6% 6% 4 5% 6% 18%	2660
	11th to 20th	Night	15% 14% 5% 11% 7% 6% 5% 4 6% 5% 24%	3288
	21st to end	Night	20% 14% 5% 13% 6% 5% 4 3 5% 5% 20%	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	56% 11% 12% 17% 4 1	2518
	11th to 20th	Day	66% 7% 11% 9% 6% 1	2520
	21st to end	Day	62% 8% 14% 10% 5% 1	2772
February	1st to 10th	Day	61% 8% 8% 16% 5% 2	1700
	11th to 20th	Day	56% 8% 10% 16% 9% 1	1796
	21st to end	Day	57% 6% 11% 14% 9% 2	1570
March	1st to 10th	Day	61% 7% 12% 12% 7% 2	3119
	11th to 20th	Day	56% 10% 12% 12% 8% 2	3278
	21st to end	Day	48% 6% 10% 15% 19% 3	4166
April	1st to 10th	Day	55% 6% 9% 18% 10% 3	2280
	11th to 20th	Day	51% 6% 9% 18% 15% 2	2254
	21st to end	Day	54% 5% 10% 16% 11% 3	2412
May	1st to 10th	Day	54% 8% 11% 17% 9% 1	4304
	11th to 20th	Day	48% 9% 17% 15% 9% 1	4402
	21st to end	Day	40% 9% 14% 24% 11% 2	4837
June	1st to 10th	Day	51% 8% 13% 16% 11% 1	2660
	11th to 20th	Day	45% 7% 13% 22% 12% 2	2660
	21st to end	Day	52% 8% 11% 19% 9% 1	2660
July	1st to 10th	Day	42% 7% 14% 25% 11%	4370
	11th to 20th	Day	40% 8% 16% 29% 7%	4365
	21st to end	Day	42% 8% 13% 28% 9%	4661
August	1st to 10th	Day	47% 7% 16% 21% 9% 1	4409
	11th to 20th	Day	43% 9% 19% 23% 6%	3932
	21st to end	Day	41% 7% 16% 24% 12% 1	4180
September	1st to 10th	Day	38% 7% 13% 29% 13% 1	2280
	11th to 20th	Day	36% 5% 13% 30% 14% 1	2118
	21st to end	Day	41% 9% 16% 23% 10% 2	1980
October	1st to 10th	Day	51% 6% 12% 19% 11%	1872
	11th to 20th	Day	50% 8% 16% 19% 7%	1775
	21st to end	Day	57% 7% 12% 16% 7% 1	1782
November	1st to 10th	Day	50% 8% 13% 18% 10% 1	1671
	11th to 20th	Day	53% 7% 12% 14% 11% 3	1682
	21st to end	Day	56% 7% 14% 17% 6% 1	1520
December	1st to 10th	Day	68% 6% 10% 12% 3	1520
	11th to 20th	Day	60% 7% 12% 14% 6%	1906
	21st to end	Day	62% 7% 10% 15% 5%	2772
January	1st to 10th	Night	60% 9% 13% 12% 5%	4429
	11th to 20th	Night	63% 9% 14% 10% 4	4440
	21st to end	Night	62% 7% 12% 12% 7% 1	4884
February	1st to 10th	Night	57% 9% 14% 12% 8% 1	2475
	11th to 20th	Night	53% 8% 12% 17% 9% 1	2281
	21st to end	Night	54% 7% 12% 17% 9% 2	1884
March	1st to 10th	Night	56% 8% 11% 15% 9% 2	3734
	11th to 20th	Night	54% 8% 11% 16% 9% 1	3679
	21st to end	Night	48% 6% 9% 19% 15% 3	3466
April	1st to 10th	Night	52% 6% 9% 18% 13% 1	1900
	11th to 20th	Night	52% 7% 10% 18% 12% 1	1875
	21st to end	Night	49% 6% 11% 18% 13% 3	1767
May	1st to 10th	Night	54% 8% 10% 16% 9% 2	2685
	11th to 20th	Night	48% 8% 13% 20% 10% 1	2496
	21st to end	Night	38% 10% 14% 20% 16% 2	2739
June	1st to 10th	Night	46% 9% 12% 21% 10% 2	1520
	11th to 20th	Night	40% 9% 14% 22% 13% 1	1520
	21st to end	Night	43% 9% 14% 23% 10% 1	1520
July	1st to 10th	Night	43% 7% 13% 23% 13% 1	2480
	11th to 20th	Night	34% 8% 16% 32% 10%	2472
	21st to end	Night	37% 9% 17% 25% 11%	2651
August	1st to 10th	Night	42% 8% 16% 25% 9%	2496
	11th to 20th	Night	40% 9% 18% 23% 9%	2926
	21st to end	Night	34% 8% 17% 28% 13% 1	3476
September	1st to 10th	Night	34% 8% 16% 28% 13% 1	1900
	11th to 20th	Night	35% 5% 15% 32% 13% 1	1920
	21st to end	Night	37% 8% 15% 26% 13% 1	1980
October	1st to 10th	Night	48% 7% 13% 20% 12% 1	2087
	11th to 20th	Night	48% 7% 15% 21% 8%	2183
	21st to end	Night	55% 7% 14% 15% 9% 1	2574
November	1st to 10th	Night	50% 7% 14% 17% 10% 2	2407
	11th to 20th	Night	50% 8% 13% 18% 8% 3	2493
	21st to end	Night	54% 9% 14% 16% 6%	2660
December	1st to 10th	Night	65% 7% 12% 14% 3	2660
	11th to 20th	Night	60% 8% 10% 13% 8%	3288
	21st to end	Night	65% 7% 10% 15% 3	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	21% 24% 32% 17% 7%	180
	11th to 20th	Day	25% 27% 34% 11% 2 1	180
	21st to end	Day	21% 23% 38% 14% 3 1	198
February	1st to 10th	Day	36% 32% 27% 4 2	265
	11th to 20th	Day	30% 27% 35% 6% 1	395
	21st to end	Day	31% 22% 32% 13% 2	382
March	1st to 10th	Day	28% 23% 30% 15% 4	460
	11th to 20th	Day	29% 26% 28% 13% 2 1	460
	21st to end	Day	28% 28% 25% 12% 6% 1	506
April	1st to 10th	Day	34% 20% 28% 15% 4 1	460
	11th to 20th	Day	33% 23% 24% 13% 5% 3	452
	21st to end	Day	34% 22% 26% 11% 6% 2	460
May	1st to 10th	Day	28% 20% 33% 11% 6% 2	463
	11th to 20th	Day	20% 19% 34% 20% 5% 2	487
	21st to end	Day	19% 19% 31% 22% 8% 1	529
June	1st to 10th	Day	26% 15% 33% 19% 5% 1	490
	11th to 20th	Day	18% 18% 35% 18% 10% 1	490
	21st to end	Day	21% 19% 33% 19% 6% 2	490
July	1st to 10th	Day	14% 13% 35% 25% 12% 1	485
	11th to 20th	Day	12% 11% 39% 27% 10% 1	484
	21st to end	Day	15% 11% 35% 30% 8% 2	532
August	1st to 10th	Day	13% 10% 33% 27% 14% 3	486
	11th to 20th	Day	13% 10% 33% 27% 13% 5%	479
	21st to end	Day	14% 14% 29% 28% 10% 5%	539
September	1st to 10th	Day	17% 13% 29% 23% 13% 6%	490
	11th to 20th	Day	14% 14% 26% 23% 15% 8%	463
	21st to end	Day	15% 13% 34% 23% 11% 5%	450
October	1st to 10th	Day	26% 16% 23% 19% 14% 2	450
	11th to 20th	Day	21% 22% 28% 20% 8% 1	437
	21st to end	Day	33% 14% 31% 18% 4 1	396
November	1st to 10th	Day	28% 16% 26% 21% 8% 1	365
	11th to 20th	Day	30% 22% 28% 13% 5% 1	342
	21st to end	Day	29% 24% 29% 16% 2	180
December	1st to 10th	Day	27% 25% 29% 13% 5% 1	180
	11th to 20th	Day	34% 21% 34% 9% 2	180
	21st to end	Day	30% 23% 31% 12% 3 1	198
January	1st to 10th	Night	23% 20% 35% 19% 3	760
	11th to 20th	Night	25% 20% 34% 18% 3	760
	21st to end	Night	15% 22% 37% 21% 5%	836
February	1st to 10th	Night	18% 23% 38% 18% 3	760
	11th to 20th	Night	21% 22% 36% 18% 2	743
	21st to end	Night	20% 23% 34% 19% 3	628
March	1st to 10th	Night	26% 18% 31% 22% 3	760
	11th to 20th	Night	26% 24% 28% 17% 4 1	760
	21st to end	Night	24% 20% 29% 21% 5% 1	836
April	1st to 10th	Night	25% 20% 30% 21% 5%	760
	11th to 20th	Night	23% 25% 26% 18% 7% 1	751
	21st to end	Night	25% 19% 27% 22% 6%	627
May	1st to 10th	Night	28% 14% 29% 23% 6%	480
	11th to 20th	Night	17% 18% 32% 26% 6% 1	374
	21st to end	Night	13% 15% 30% 29% 12%	411
June	1st to 10th	Night	20% 11% 28% 30% 11%	380
	11th to 20th	Night	16% 9% 27% 35% 12% 1	380
	21st to end	Night	17% 10% 30% 31% 11% 1	380
July	1st to 10th	Night	12% 8% 28% 37% 15% 1	370
	11th to 20th	Night	11% 5% 26% 41% 14% 2	368
	21st to end	Night	11% 5% 25% 44% 14%	416
August	1st to 10th	Night	12% 5% 24% 39% 19% 1	378
	11th to 20th	Night	11% 6% 21% 39% 20% 3	626
	21st to end	Night	12% 7% 24% 37% 18% 1	836
September	1st to 10th	Night	12% 9% 25% 37% 15% 2	760
	11th to 20th	Night	14% 8% 25% 29% 21% 4	736
	21st to end	Night	17% 10% 29% 25% 17% 2	720
October	1st to 10th	Night	24% 13% 24% 25% 14% 1	720
	11th to 20th	Night	22% 15% 25% 27% 10% 1	720
	21st to end	Night	28% 15% 28% 23% 6%	792
November	1st to 10th	Night	21% 19% 30% 22% 8% 1	740
	11th to 20th	Night	23% 19% 32% 18% 7% 2	760
	21st to end	Night	24% 21% 29% 19% 6% 1	760
December	1st to 10th	Night	26% 22% 30% 17% 4	760
	11th to 20th	Night	25% 21% 31% 19% 4 1	760
	21st to end	Night	26% 23% 32% 16% 3	836

Page generated at 2024-09-11 10:00:02. Version ac07

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