Apple Orchard Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Apple Orchard Observatory clear sky chart from 2005-11-06 to 2025-09-19.

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	15% 10% 4 9% 5% 5% 5% 4 5% 6% 32%	126729
	Night	16% 11% 4 9% 6% 5% 4 3 5% 6% 31%	122317
Transparency	Day	50% 7% 12% 20% 10% 1	130220
	Night	52% 7% 12% 19% 10% 1	126913
Seeing	Day	22% 17% 31% 20% 8% 3	15537
	Night	21% 14% 30% 24% 9% 1	24609

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	13% 16% 6% 14% 8% 7% 4 3 4 5% 20%	3597
	11th to 20th	Day	12% 16% 6% 15% 8% 5% 5% 4 5% 4 21%	3570
	21st to end	Day	11% 18% 7% 17% 6% 5% 4 3 4 5% 20%	4216
February	1st to 10th	Day	13% 16% 5% 13% 9% 5% 5% 4 4 4 23%	1800
	11th to 20th	Day	11% 15% 6% 12% 7% 6% 4 4 5% 6% 27%	1753
	21st to end	Day	19% 13% 3 10% 7% 5% 5% 4 4 4 25%	1625
March	1st to 10th	Day	18% 13% 6% 12% 5% 4 4 3 4 5% 26%	4563
	11th to 20th	Day	10% 12% 5% 10% 6% 5% 5% 4 5% 6% 29%	4980
	21st to end	Day	15% 12% 4 7% 5% 4 3 3 4 5% 37%	5710
April	1st to 10th	Day	21% 13% 3 7% 5% 4 4 4 4 6% 31%	2400
	11th to 20th	Day	21% 11% 3 6% 4 4 4 3 4 4 36%	2374
	21st to end	Day	21% 10% 3 8% 5% 4 4 3 4 6% 32%	2545
May	1st to 10th	Day	22% 10% 3 8% 4 4 5% 4 5% 6% 29%	6346
	11th to 20th	Day	15% 9% 3 9% 5% 5% 5% 4 6% 8% 31%	6318
	21st to end	Day	20% 8% 2 7% 4 4 5% 4 5% 6% 35%	6949
June	1st to 10th	Day	19% 10% 3 7% 6% 5% 4 4 6% 6% 31%	2800
	11th to 20th	Day	14% 6% 3 6% 5% 5% 5% 5% 6% 7% 40%	2800
	21st to end	Day	17% 8% 3 6% 5% 5% 5% 4 7% 7% 33%	2800
July	1st to 10th	Day	13% 7% 3 7% 5% 5% 6% 4 7% 9% 34%	6360
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 8% 43%	6360
	21st to end	Day	9% 5% 2 6% 4 4 4 5% 6% 10% 46%	6926
August	1st to 10th	Day	14% 7% 3 8% 5% 4 5% 4 6% 7% 37%	4414
	11th to 20th	Day	16% 6% 2 7% 5% 4 5% 4 5% 7% 38%	4174
	21st to end	Day	11% 5% 2 6% 4 4 5% 5% 7% 9% 40%	4312
September	1st to 10th	Day	13% 6% 2 6% 5% 5% 4 4 5% 8% 42%	2400
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 5% 8% 46%	2376
	21st to end	Day	17% 7% 3 6% 4 4 4 4 6% 6% 40%	2015
October	1st to 10th	Day	19% 8% 3 7% 4 4 5% 4 4 6% 34%	1900
	11th to 20th	Day	20% 10% 3 7% 5% 6% 5% 4 5% 7% 28%	1900
	21st to end	Day	25% 11% 3 8% 5% 4 5% 3 4 5% 27%	1967
November	1st to 10th	Day	14% 11% 3 8% 5% 4 6% 4 5% 6% 35%	1733
	11th to 20th	Day	16% 12% 4 10% 6% 6% 4 4 5% 6% 28%	1600
	21st to end	Day	20% 14% 5% 11% 6% 7% 5% 3 4 6% 20%	1600
December	1st to 10th	Day	21% 20% 6% 13% 6% 5% 4 4 4 5% 12%	2600
	11th to 20th	Day	16% 16% 6% 12% 7% 5% 4 3 4 4 24%	2986
	21st to end	Day	22% 16% 5% 15% 6% 4 3 3 3 4 19%	3960
January	1st to 10th	Night	13% 18% 9% 15% 7% 5% 4 3 4 5% 18%	6349
	11th to 20th	Night	11% 13% 6% 15% 9% 6% 5% 4 5% 5% 21%	6315
	21st to end	Night	12% 18% 7% 12% 7% 6% 5% 3 4 4 21%	6738
February	1st to 10th	Night	12% 15% 6% 11% 8% 5% 4 4 6% 6% 23%	2600
	11th to 20th	Night	12% 14% 5% 11% 7% 5% 5% 3 4 5% 28%	2533
	21st to end	Night	14% 12% 5% 9% 7% 5% 5% 4 5% 6% 28%	2005
March	1st to 10th	Night	20% 14% 5% 10% 6% 4 3 3 3 3 29%	5272
	11th to 20th	Night	11% 12% 4 9% 5% 5% 5% 5% 7% 8% 30%	4979
	21st to end	Night	17% 10% 4 10% 6% 4 3 3 5% 6% 32%	5221
April	1st to 10th	Night	20% 11% 3 9% 4 3 4 3 5% 6% 32%	2000
	11th to 20th	Night	20% 9% 3 8% 4 4 4 3 4 5% 36%	1975
	21st to end	Night	20% 10% 3 8% 5% 4 4 3 4 5% 33%	1871
May	1st to 10th	Night	21% 10% 4 7% 5% 4 5% 4 6% 6% 27%	3594
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 8% 41%	3575
	21st to end	Night	17% 9% 3 7% 5% 4 5% 4 6% 8% 33%	3926
June	1st to 10th	Night	15% 7% 3 7% 5% 5% 4 5% 6% 9% 34%	1600
	11th to 20th	Night	13% 6% 3 6% 4 3 4 4 6% 7% 44%	1600
	21st to end	Night	16% 8% 2 6% 5% 5% 5% 4 6% 7% 37%	1600
July	1st to 10th	Night	12% 7% 3 7% 5% 5% 6% 4 6% 8% 34%	3600
	11th to 20th	Night	12% 5% 2 5% 4 4 5% 4 6% 8% 45%	3600
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 8% 47%	3926
August	1st to 10th	Night	11% 6% 2 7% 5% 5% 4 4 7% 8% 41%	2732
	11th to 20th	Night	13% 7% 3 6% 4 4 4 4 5% 7% 43%	2875
	21st to end	Night	12% 6% 3 6% 5% 4 5% 4 6% 8% 42%	3552
September	1st to 10th	Night	11% 6% 2 6% 5% 4 4 4 5% 6% 47%	2000
	11th to 20th	Night	14% 5% 2 4 4 4 3 3 5% 6% 50%	1981
	21st to end	Night	16% 6% 2 6% 5% 4 4 3 5% 6% 43%	2162
October	1st to 10th	Night	17% 8% 2 6% 5% 4 4 3 5% 6% 38%	2280
	11th to 20th	Night	19% 10% 3 8% 5% 4 4 3 5% 7% 31%	2280
	21st to end	Night	21% 11% 3 8% 4 4 5% 3 5% 6% 28%	2630
November	1st to 10th	Night	18% 11% 3 7% 6% 4 4 3 5% 6% 34%	2562
	11th to 20th	Night	17% 12% 4 9% 6% 4 5% 3 5% 6% 29%	2800
	21st to end	Night	20% 14% 5% 10% 6% 5% 4 3 5% 6% 22%	2800
December	1st to 10th	Night	19% 18% 5% 12% 7% 6% 5% 4 5% 6% 14%	4580
	11th to 20th	Night	20% 14% 5% 12% 6% 4 4 3 4 4 25%	5208
	21st to end	Night	25% 17% 5% 12% 5% 3 3 3 4 4 20%	6996

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	64% 8% 10% 12% 5%	3598
	11th to 20th	Day	64% 6% 10% 12% 8%	3600
	21st to end	Day	67% 5% 8% 11% 8% 1	4216
February	1st to 10th	Day	63% 5% 9% 16% 5% 1	1800
	11th to 20th	Day	58% 6% 12% 15% 9% 1	1762
	21st to end	Day	60% 7% 10% 13% 9% 2	1625
March	1st to 10th	Day	60% 5% 9% 12% 12% 2	4566
	11th to 20th	Day	51% 9% 14% 15% 9% 2	4980
	21st to end	Day	49% 5% 6% 19% 18% 3	5710
April	1st to 10th	Day	54% 5% 7% 18% 13% 3	2400
	11th to 20th	Day	50% 6% 7% 20% 15% 2	2374
	21st to end	Day	53% 5% 8% 15% 15% 4	2545
May	1st to 10th	Day	55% 6% 8% 19% 10% 3	6357
	11th to 20th	Day	48% 8% 12% 18% 12% 1	6322
	21st to end	Day	48% 7% 11% 20% 12% 1	6949
June	1st to 10th	Day	52% 8% 10% 19% 11% 1	2800
	11th to 20th	Day	41% 8% 11% 24% 13% 2	2800
	21st to end	Day	47% 9% 12% 20% 11% 1	2800
July	1st to 10th	Day	44% 7% 14% 26% 9%	6290
	11th to 20th	Day	35% 8% 14% 29% 14%	6285
	21st to end	Day	32% 7% 15% 35% 10%	6728
August	1st to 10th	Day	44% 7% 15% 23% 10%	4400
	11th to 20th	Day	43% 8% 14% 27% 8% 1	4213
	21st to end	Day	37% 7% 16% 28% 11% 1	4312
September	1st to 10th	Day	39% 8% 14% 29% 11%	2400
	11th to 20th	Day	35% 7% 14% 30% 13%	2376
	21st to end	Day	44% 8% 13% 26% 10%	2015
October	1st to 10th	Day	48% 6% 10% 29% 7%	3160
	11th to 20th	Day	46% 6% 15% 22% 11%	3140
	21st to end	Day	50% 6% 19% 20% 6%	3218
November	1st to 10th	Day	47% 8% 15% 23% 6% 1	1733
	11th to 20th	Day	56% 7% 13% 15% 9% 1	1600
	21st to end	Day	65% 8% 12% 9% 6% 1	1600
December	1st to 10th	Day	73% 7% 11% 7% 2	2600
	11th to 20th	Day	63% 6% 10% 14% 7%	2986
	21st to end	Day	70% 4 8% 14% 4	3960
January	1st to 10th	Night	67% 7% 11% 12% 4	6349
	11th to 20th	Night	63% 7% 11% 13% 6%	6360
	21st to end	Night	65% 5% 8% 10% 10% 1	6738
February	1st to 10th	Night	60% 6% 11% 16% 6% 1	2600
	11th to 20th	Night	57% 6% 11% 18% 7% 1	2535
	21st to end	Night	55% 6% 10% 18% 9%	2005
March	1st to 10th	Night	60% 5% 8% 15% 10% 3	5282
	11th to 20th	Night	49% 9% 17% 16% 8% 2	4980
	21st to end	Night	50% 6% 8% 21% 11% 3	5221
April	1st to 10th	Night	52% 6% 8% 18% 13% 2	2000
	11th to 20th	Night	50% 4 8% 22% 14% 1	1975
	21st to end	Night	52% 6% 6% 17% 15% 3	1871
May	1st to 10th	Night	54% 8% 9% 18% 8% 3	3600
	11th to 20th	Night	40% 8% 15% 20% 15% 2	3576
	21st to end	Night	46% 9% 14% 16% 13% 1	3927
June	1st to 10th	Night	45% 8% 12% 23% 10% 1	1600
	11th to 20th	Night	39% 7% 12% 23% 17% 2	1600
	21st to end	Night	44% 10% 13% 19% 13% 1	1600
July	1st to 10th	Night	44% 9% 15% 19% 13% 1	3560
	11th to 20th	Night	35% 7% 14% 30% 13%	3552
	21st to end	Night	33% 8% 12% 32% 14%	3809
August	1st to 10th	Night	38% 9% 14% 26% 12% 1	2722
	11th to 20th	Night	39% 8% 15% 29% 8%	2902
	21st to end	Night	37% 8% 15% 27% 11% 2	3552
September	1st to 10th	Night	36% 7% 13% 29% 14% 1	2000
	11th to 20th	Night	33% 7% 14% 35% 10% 1	1981
	21st to end	Night	41% 6% 13% 29% 10%	2162
October	1st to 10th	Night	39% 5% 12% 30% 13%	3800
	11th to 20th	Night	46% 6% 16% 23% 9%	3779
	21st to end	Night	48% 7% 18% 20% 7%	4329
November	1st to 10th	Night	50% 6% 14% 20% 9%	2562
	11th to 20th	Night	54% 8% 11% 18% 8% 1	2800
	21st to end	Night	61% 7% 12% 15% 4	2800
December	1st to 10th	Night	70% 6% 13% 9% 2	4580
	11th to 20th	Night	63% 5% 8% 13% 9% 1	5208
	21st to end	Night	69% 5% 6% 12% 9%	6996

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	22% 24% 35% 16% 5%	200
	11th to 20th	Day	29% 18% 37% 12% 5% 1	200
	21st to end	Day	20% 21% 39% 17% 3	277
February	1st to 10th	Day	31% 26% 30% 11% 2	300
	11th to 20th	Day	27% 29% 38% 5% 1	300
	21st to end	Day	29% 25% 34% 11% 1	389
March	1st to 10th	Day	27% 21% 34% 14% 3	500
	11th to 20th	Day	27% 20% 34% 16% 3 1	500
	21st to end	Day	31% 21% 29% 13% 5%	550
April	1st to 10th	Day	32% 22% 29% 12% 6%	500
	11th to 20th	Day	33% 22% 21% 15% 8% 1	492
	21st to end	Day	29% 20% 32% 12% 6% 1	500
May	1st to 10th	Day	25% 17% 32% 18% 6% 2	503
	11th to 20th	Day	19% 17% 33% 21% 7% 3	527
	21st to end	Day	20% 16% 32% 20% 9% 2	573
June	1st to 10th	Day	23% 13% 34% 20% 9% 1	530
	11th to 20th	Day	16% 13% 34% 22% 12% 2	530
	21st to end	Day	19% 16% 33% 21% 10% 2	530
July	1st to 10th	Day	11% 9% 32% 32% 13% 3	525
	11th to 20th	Day	10% 11% 32% 29% 14% 4	524
	21st to end	Day	12% 10% 34% 29% 11% 3	576
August	1st to 10th	Day	14% 7% 27% 33% 14% 4	526
	11th to 20th	Day	13% 8% 27% 31% 15% 6%	519
	21st to end	Day	13% 13% 30% 24% 14% 7%	583
September	1st to 10th	Day	15% 12% 30% 22% 14% 8%	530
	11th to 20th	Day	10% 11% 24% 24% 20% 11%	522
	21st to end	Day	18% 14% 29% 20% 13% 6%	490
October	1st to 10th	Day	24% 15% 25% 22% 10% 4	490
	11th to 20th	Day	24% 22% 29% 18% 6% 1	490
	21st to end	Day	29% 20% 26% 20% 4 1	474
November	1st to 10th	Day	27% 19% 30% 18% 6% 1	367
	11th to 20th	Day	25% 25% 32% 14% 4 1	200
	21st to end	Day	31% 25% 34% 8% 3 1	200
December	1st to 10th	Day	30% 20% 35% 14% 2	200
	11th to 20th	Day	33% 26% 30% 9% 3 1	200
	21st to end	Day	29% 21% 33% 12% 4 1	220
January	1st to 10th	Night	25% 19% 37% 16% 3	800
	11th to 20th	Night	25% 20% 29% 20% 6%	800
	21st to end	Night	19% 15% 38% 24% 4	880
February	1st to 10th	Night	21% 18% 38% 20% 3	800
	11th to 20th	Night	20% 19% 39% 18% 3	783
	21st to end	Night	22% 21% 29% 23% 4	660
March	1st to 10th	Night	25% 17% 34% 21% 4	800
	11th to 20th	Night	23% 21% 32% 18% 5%	800
	21st to end	Night	23% 17% 31% 21% 7%	880
April	1st to 10th	Night	27% 17% 30% 23% 4	800
	11th to 20th	Night	24% 20% 28% 19% 8%	791
	21st to end	Night	26% 14% 29% 22% 8% 1	671
May	1st to 10th	Night	23% 10% 30% 27% 10% 1	400
	11th to 20th	Night	21% 11% 33% 27% 7% 1	394
	21st to end	Night	13% 10% 37% 27% 12%	433
June	1st to 10th	Night	16% 10% 32% 33% 8%	400
	11th to 20th	Night	15% 9% 32% 33% 11% 1	400
	21st to end	Night	18% 9% 28% 33% 12%	400
July	1st to 10th	Night	7% 9% 29% 40% 14% 1	390
	11th to 20th	Night	10% 7% 28% 43% 12% 1	388
	21st to end	Night	9% 5% 29% 45% 11% 1	438
August	1st to 10th	Night	9% 5% 23% 42% 19%	479
	11th to 20th	Night	11% 4 24% 37% 22% 3	594
	21st to end	Night	13% 7% 27% 33% 18% 2	859
September	1st to 10th	Night	13% 7% 30% 30% 18% 2	800
	11th to 20th	Night	15% 7% 20% 31% 23% 4	793
	21st to end	Night	18% 10% 25% 25% 19% 2	760
October	1st to 10th	Night	23% 11% 28% 23% 15% 1	760
	11th to 20th	Night	24% 15% 32% 20% 8% 1	760
	21st to end	Night	26% 19% 27% 23% 5%	836
November	1st to 10th	Night	26% 15% 28% 24% 7%	780
	11th to 20th	Night	24% 18% 33% 16% 9% 1	800
	21st to end	Night	31% 19% 26% 20% 5%	800
December	1st to 10th	Night	29% 18% 32% 17% 4	800
	11th to 20th	Night	27% 19% 31% 18% 4 1	800
	21st to end	Night	32% 17% 30% 17% 3	880

Page generated at 2025-09-16 01:49:15. Version ac07

Copyright © 2025 Attilla Danko.