Apple Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Apple Ridge Observatory clear sky chart from 2005-11-06 to 2025-05-11.

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	13% 11% 5% 10% 6% 5% 5% 4 5% 6% 30%	113392
	Night	13% 12% 5% 11% 6% 5% 4 3 5% 6% 29%	115634
Transparency	Day	53% 5% 11% 19% 11% 1	116952
	Night	56% 5% 11% 18% 10% 1	120217
Seeing	Day	20% 16% 31% 21% 10% 3	16452
	Night	19% 11% 32% 28% 9% 1	26522

By Month

Percentage Cloud Cover SE (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	9% 18% 11% 27% 8% 5% 3 2 2 3 10%	3617
	11th to 20th	Day	11% 15% 8% 20% 15% 10% 7% 3 3 3 5%	3620
	21st to end	Day	13% 17% 11% 16% 9% 4 5% 4 4 4 13%	3982
February	1st to 10th	Day	10% 15% 7% 13% 13% 7% 6% 3 4 4 16%	1760
	11th to 20th	Day	11% 15% 6% 17% 11% 7% 4 3 5% 4 17%	1948
	21st to end	Day	10% 18% 8% 14% 8% 5% 5% 3 4 5% 21%	1650
March	1st to 10th	Day	11% 11% 4 11% 8% 5% 5% 3 6% 6% 30%	4480
	11th to 20th	Day	12% 9% 5% 13% 5% 5% 5% 3 6% 8% 30%	4841
	21st to end	Day	20% 12% 7% 13% 6% 4 4 3 4 4 24%	5663
April	1st to 10th	Day	18% 16% 4 8% 5% 5% 3 4 6% 5% 28%	2400
	11th to 20th	Day	19% 13% 4 7% 4 4 4 3 4 5% 33%	2458
	21st to end	Day	15% 12% 3 8% 5% 4 5% 4 5% 7% 32%	2600
May	1st to 10th	Day	15% 9% 2 7% 4 4 4 3 5% 8% 39%	4212
	11th to 20th	Day	11% 8% 3 6% 4 4 4 4 5% 7% 42%	4167
	21st to end	Day	12% 7% 2 6% 4 4 4 4 6% 8% 42%	4824
June	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 7% 42%	2660
	11th to 20th	Day	12% 7% 2 7% 5% 5% 4 4 6% 8% 41%	2660
	21st to end	Day	13% 7% 2 6% 5% 4 5% 4 7% 7% 40%	2660
July	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 9% 35%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 6% 11% 47%	4440
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 4 6% 9% 43%	4813
August	1st to 10th	Day	11% 5% 2 7% 5% 5% 6% 5% 6% 8% 38%	4204
	11th to 20th	Day	14% 5% 2 6% 3 4 5% 3 5% 7% 45%	4044
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	4292
September	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 7% 41%	2252
	11th to 20th	Day	12% 7% 2 5% 4 5% 4 4 5% 7% 46%	2090
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 3 6% 8% 37%	2090
October	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 40%	2090
	11th to 20th	Day	20% 15% 4 8% 5% 5% 4 3 5% 6% 23%	1821
	21st to end	Day	20% 14% 4 10% 6% 6% 5% 3 5% 7% 20%	1881
November	1st to 10th	Day	15% 14% 4 7% 5% 5% 5% 3 6% 7% 30%	1762
	11th to 20th	Day	14% 20% 7% 11% 5% 4 4 4 5% 6% 19%	1800
	21st to end	Day	17% 22% 8% 14% 4 3 3 3 3 5% 17%	1795
December	1st to 10th	Day	10% 22% 14% 21% 6% 4 4 3 3 3 10%	2452
	11th to 20th	Day	12% 23% 12% 16% 9% 4 4 3 4 3 10%	2942
	21st to end	Day	21% 24% 8% 14% 6% 5% 4 2 3 4 10%	3982
January	1st to 10th	Night	11% 15% 9% 25% 8% 6% 3 3 3 3 13%	6348
	11th to 20th	Night	11% 15% 8% 22% 11% 13% 5% 2 3 3 7%	6360
	21st to end	Night	11% 18% 10% 20% 7% 5% 6% 3 4 4 11%	6996
February	1st to 10th	Night	10% 15% 6% 14% 12% 6% 6% 5% 4 5% 17%	2634
	11th to 20th	Night	12% 12% 6% 14% 10% 5% 5% 4 6% 6% 20%	2338
	21st to end	Night	12% 14% 5% 14% 7% 6% 4 3 5% 6% 23%	1980
March	1st to 10th	Night	15% 9% 4 9% 5% 4 4 3 5% 6% 35%	5373
	11th to 20th	Night	12% 10% 4 8% 5% 4 4 4 6% 8% 37%	5118
	21st to end	Night	16% 13% 5% 10% 5% 5% 4 3 5% 5% 29%	5294
April	1st to 10th	Night	15% 12% 4 9% 5% 4 4 4 5% 7% 32%	2000
	11th to 20th	Night	19% 10% 3 7% 4 4 4 2 4 7% 35%	1889
	21st to end	Night	17% 9% 3 9% 5% 3 4 3 5% 6% 37%	1800
May	1st to 10th	Night	14% 8% 3 6% 5% 5% 4 3 5% 7% 40%	2903
	11th to 20th	Night	15% 6% 2 6% 5% 4 4 3 7% 8% 40%	2731
	21st to end	Night	17% 7% 2 5% 4 3 3 3 5% 7% 44%	2743
June	1st to 10th	Night	12% 8% 3 5% 4 4 4 3 7% 7% 43%	1520
	11th to 20th	Night	11% 5% 2 7% 4 4 5% 3 6% 9% 44%	1520
	21st to end	Night	10% 6% 2 7% 5% 3 4 4 6% 7% 46%	1520
July	1st to 10th	Night	11% 8% 2 6% 4 4 5% 4 7% 9% 39%	2530
	11th to 20th	Night	6% 4 2 4 4 4 4 3 5% 7% 57%	2530
	21st to end	Night	7% 5% 2 5% 4 4 4 3 5% 7% 52%	2750
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 5% 6% 7% 45%	2727
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 51%	2785
	21st to end	Night	8% 7% 2 6% 5% 4 4 3 6% 7% 48%	3348
September	1st to 10th	Night	11% 4 2 5% 4 4 4 3 4 6% 53%	1909
	11th to 20th	Night	11% 5% 2 4 3 3 4 4 6% 8% 51%	2090
	21st to end	Night	14% 9% 2 7% 3 4 4 4 5% 7% 40%	2090
October	1st to 10th	Night	16% 8% 3 6% 3 3 4 3 4 6% 44%	2090
	11th to 20th	Night	17% 13% 4 7% 5% 5% 4 4 5% 5% 32%	2355
	21st to end	Night	22% 13% 3 8% 5% 4 3 3 5% 6% 28%	2717
November	1st to 10th	Night	12% 15% 4 8% 5% 4 4 3 5% 6% 34%	2536
	11th to 20th	Night	15% 17% 5% 12% 7% 5% 4 4 6% 6% 21%	2600
	21st to end	Night	15% 20% 7% 11% 5% 4 4 3 4 5% 20%	2600
December	1st to 10th	Night	11% 17% 6% 19% 7% 5% 4 4 4 5% 16%	4700
	11th to 20th	Night	13% 23% 9% 16% 9% 6% 4 3 4 5% 11%	5214
	21st to end	Night	22% 24% 7% 12% 5% 4 3 2 3 4 14%	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	82% 3 5% 8% 2	3618
	11th to 20th	Day	87% 3 3 4 2	3620
	21st to end	Day	77% 4 9% 9% 2	3982
February	1st to 10th	Day	71% 5% 7% 13% 3	1760
	11th to 20th	Day	71% 4 8% 11% 5%	1958
	21st to end	Day	66% 5% 11% 13% 5%	1650
March	1st to 10th	Day	54% 3 14% 17% 10% 1	4480
	11th to 20th	Day	53% 4 16% 17% 9% 2	4841
	21st to end	Day	65% 3 10% 15% 7% 1	5665
April	1st to 10th	Day	58% 5% 9% 17% 11%	2400
	11th to 20th	Day	54% 4 8% 19% 13% 2	2458
	21st to end	Day	52% 4 12% 16% 14% 2	2600
May	1st to 10th	Day	44% 5% 10% 23% 18% 2	4250
	11th to 20th	Day	39% 6% 11% 25% 17% 2	4171
	21st to end	Day	39% 5% 11% 22% 20% 3	4837
June	1st to 10th	Day	41% 5% 11% 25% 17% 2	2660
	11th to 20th	Day	41% 5% 11% 23% 18% 2	2660
	21st to end	Day	41% 7% 13% 24% 14% 1	2660
July	1st to 10th	Day	45% 6% 11% 22% 13% 2	4371
	11th to 20th	Day	29% 6% 14% 30% 18% 2	4365
	21st to end	Day	36% 8% 11% 24% 20% 2	4662
August	1st to 10th	Day	40% 6% 12% 26% 14% 1	4189
	11th to 20th	Day	38% 5% 13% 25% 18% 1	4083
	21st to end	Day	40% 7% 12% 27% 13% 1	4291
September	1st to 10th	Day	42% 6% 11% 25% 15% 2	2252
	11th to 20th	Day	36% 5% 13% 29% 15% 1	2090
	21st to end	Day	45% 5% 12% 26% 12%	2090
October	1st to 10th	Day	32% 4 8% 35% 19% 3	3480
	11th to 20th	Day	51% 4 11% 21% 12%	2998
	21st to end	Day	59% 5% 14% 17% 6%	3081
November	1st to 10th	Day	53% 6% 11% 20% 9%	1762
	11th to 20th	Day	66% 5% 12% 13% 4	1800
	21st to end	Day	71% 4 11% 10% 3	1795
December	1st to 10th	Day	82% 5% 6% 6% 1	2452
	11th to 20th	Day	81% 4 7% 7% 1	2939
	21st to end	Day	80% 2 6% 8% 4	3982
January	1st to 10th	Night	77% 4 6% 9% 4	6348
	11th to 20th	Night	85% 3 6% 4 2	6360
	21st to end	Night	77% 4 8% 8% 3	6996
February	1st to 10th	Night	69% 5% 7% 13% 5% 1	2634
	11th to 20th	Night	65% 6% 9% 14% 6%	2339
	21st to end	Night	63% 4 12% 16% 5% 1	1980
March	1st to 10th	Night	51% 3 16% 20% 9%	5373
	11th to 20th	Night	46% 4 20% 20% 10% 1	5118
	21st to end	Night	57% 5% 10% 19% 9% 1	5294
April	1st to 10th	Night	52% 6% 9% 19% 13% 1	2000
	11th to 20th	Night	51% 4 8% 21% 14% 2	1889
	21st to end	Night	49% 4 10% 20% 14% 3	1800
May	1st to 10th	Night	43% 6% 12% 19% 17% 3	2930
	11th to 20th	Night	41% 6% 9% 29% 14% 2	2732
	21st to end	Night	41% 4 12% 22% 16% 5%	2751
June	1st to 10th	Night	38% 6% 12% 26% 16% 2	1520
	11th to 20th	Night	37% 6% 13% 23% 20% 1	1520
	21st to end	Night	36% 7% 13% 27% 16% 2	1520
July	1st to 10th	Night	41% 6% 12% 24% 12% 6%	2490
	11th to 20th	Night	25% 5% 14% 35% 19% 1	2482
	21st to end	Night	31% 7% 15% 24% 22% 1	2662
August	1st to 10th	Night	36% 5% 16% 27% 15% 1	2718
	11th to 20th	Night	33% 5% 13% 33% 16%	2812
	21st to end	Night	35% 5% 13% 26% 19% 2	3348
September	1st to 10th	Night	32% 6% 12% 29% 19% 2	1909
	11th to 20th	Night	31% 5% 15% 34% 14% 1	2090
	21st to end	Night	43% 4 14% 28% 11% 1	2090
October	1st to 10th	Night	34% 4 10% 37% 15% 1	3480
	11th to 20th	Night	44% 4 11% 25% 15%	3917
	21st to end	Night	50% 4 13% 26% 8%	4467
November	1st to 10th	Night	52% 5% 12% 20% 10% 1	2536
	11th to 20th	Night	64% 6% 12% 11% 6% 1	2600
	21st to end	Night	68% 5% 13% 11% 2 1	2600
December	1st to 10th	Night	72% 6% 12% 9% 2	4700
	11th to 20th	Night	78% 4 8% 8% 2	5216
	21st to end	Night	76% 3 9% 7% 6%	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	19% 20% 39% 16% 6%	300
	11th to 20th	Day	25% 20% 41% 12% 1	300
	21st to end	Day	24% 18% 37% 18% 3	330
February	1st to 10th	Day	20% 28% 33% 14% 4 1	300
	11th to 20th	Day	21% 32% 31% 14% 1	300
	21st to end	Day	29% 33% 28% 9% 1	249
March	1st to 10th	Day	25% 27% 35% 11% 2	300
	11th to 20th	Day	27% 17% 31% 16% 8% 1	439
	21st to end	Day	29% 19% 28% 18% 5% 1	550
April	1st to 10th	Day	27% 20% 34% 14% 4 1	500
	11th to 20th	Day	30% 21% 28% 12% 6% 3	492
	21st to end	Day	26% 16% 29% 22% 7% 1	500
May	1st to 10th	Day	23% 21% 31% 17% 6% 2	503
	11th to 20th	Day	18% 14% 32% 24% 8% 4	534
	21st to end	Day	16% 13% 30% 27% 11% 2	734
June	1st to 10th	Day	13% 16% 35% 24% 11% 2	680
	11th to 20th	Day	18% 13% 32% 25% 9% 3	680
	21st to end	Day	17% 12% 31% 27% 9% 4	680
July	1st to 10th	Day	9% 9% 30% 31% 16% 6%	671
	11th to 20th	Day	9% 9% 30% 30% 16% 5%	668
	21st to end	Day	10% 7% 34% 27% 15% 6%	739
August	1st to 10th	Day	12% 7% 25% 28% 20% 8%	548
	11th to 20th	Day	13% 5% 21% 32% 18% 12%	479
	21st to end	Day	16% 8% 24% 30% 18% 6%	539
September	1st to 10th	Day	16% 10% 24% 26% 18% 7%	490
	11th to 20th	Day	11% 7% 24% 30% 21% 8%	490
	21st to end	Day	19% 13% 23% 26% 14% 5%	490
October	1st to 10th	Day	20% 15% 31% 20% 12% 2	490
	11th to 20th	Day	30% 15% 34% 18% 4 1	384
	21st to end	Day	30% 23% 29% 12% 4 1	330
November	1st to 10th	Day	26% 19% 34% 14% 6%	300
	11th to 20th	Day	24% 23% 40% 9% 3 1	300
	21st to end	Day	27% 24% 36% 10% 3	300
December	1st to 10th	Day	28% 23% 28% 16% 4 1	253
	11th to 20th	Day	23% 28% 34% 13% 2 1	280
	21st to end	Day	29% 25% 33% 9% 2 1	330
January	1st to 10th	Night	21% 18% 35% 21% 5% 1	1000
	11th to 20th	Night	21% 17% 35% 21% 6%	1000
	21st to end	Night	20% 10% 40% 25% 5% 1	1100
February	1st to 10th	Night	18% 17% 38% 23% 4	862
	11th to 20th	Night	18% 17% 37% 24% 4	783
	21st to end	Night	21% 19% 37% 19% 3	660
March	1st to 10th	Night	19% 13% 38% 22% 8%	800
	11th to 20th	Night	18% 16% 36% 23% 7%	800
	21st to end	Night	22% 13% 33% 26% 5% 1	810
April	1st to 10th	Night	20% 15% 37% 24% 3 1	600
	11th to 20th	Night	25% 13% 31% 24% 7%	593
	21st to end	Night	22% 12% 32% 27% 8% 1	600
May	1st to 10th	Night	17% 10% 38% 29% 7%	600
	11th to 20th	Night	18% 9% 35% 29% 10%	563
	21st to end	Night	15% 6% 31% 33% 14% 1	617
June	1st to 10th	Night	15% 6% 32% 36% 11% 1	570
	11th to 20th	Night	13% 6% 33% 35% 12% 1	570
	21st to end	Night	14% 4 27% 40% 15% 1	570
July	1st to 10th	Night	10% 2 21% 43% 23% 2	555
	11th to 20th	Night	9% 3 23% 42% 21% 2	552
	21st to end	Night	9% 4 23% 42% 22% 1	624
August	1st to 10th	Night	10% 3 23% 43% 21% 2	567
	11th to 20th	Night	9% 4 18% 40% 25% 5%	564
	21st to end	Night	11% 4 22% 41% 20% 2	627
September	1st to 10th	Night	13% 4 22% 37% 20% 3	579
	11th to 20th	Night	13% 5% 22% 36% 21% 3	760
	21st to end	Night	17% 8% 28% 30% 14% 3	760
October	1st to 10th	Night	21% 8% 27% 31% 12% 2	760
	11th to 20th	Night	25% 11% 28% 27% 7% 1	760
	21st to end	Night	30% 11% 30% 22% 7%	836
November	1st to 10th	Night	21% 15% 30% 26% 7% 1	780
	11th to 20th	Night	23% 17% 36% 20% 4	800
	21st to end	Night	24% 16% 33% 23% 3	800
December	1st to 10th	Night	22% 17% 35% 22% 4	1000
	11th to 20th	Night	23% 18% 39% 16% 4 1	1000
	21st to end	Night	29% 14% 33% 21% 2	1100

Page generated at 2025-05-08 09:33:58. Version ac07

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