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 2026-09-14.

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	13% 11% 4 10% 6% 5% 5% 4 5% 7% 32%	148781
	Night	13% 12% 5% 11% 6% 5% 4 3 5% 6% 31%	142507
Transparency	Day	51% 5% 10% 20% 12% 1	152294
	Night	54% 4 11% 19% 10% 1	147071
Seeing	Day	20% 16% 31% 21% 9% 3	18415
	Night	19% 12% 31% 28% 9% 1	28262

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	12% 20% 10% 24% 10% 5% 3 2 2 3 8%	4691
	11th to 20th	Day	10% 16% 9% 22% 13% 11% 7% 2 2 3 6%	4710
	21st to end	Day	11% 15% 9% 15% 9% 9% 6% 4 4 4 14%	5156
February	1st to 10th	Day	10% 15% 8% 14% 13% 7% 6% 3 4 4 16%	1848
	11th to 20th	Day	11% 15% 6% 17% 11% 7% 4 3 5% 4 17%	2048
	21st to end	Day	10% 18% 8% 14% 8% 5% 5% 3 4 5% 20%	1730
March	1st to 10th	Day	11% 11% 4 11% 8% 5% 5% 3 6% 6% 31%	4580
	11th to 20th	Day	12% 9% 5% 13% 6% 5% 5% 3 6% 8% 29%	4948
	21st to end	Day	20% 12% 7% 13% 6% 4 4 3 4 4 24%	5788
April	1st to 10th	Day	18% 16% 4 8% 5% 4 3 3 6% 5% 27%	2520
	11th to 20th	Day	20% 13% 4 7% 4 4 4 3 5% 5% 33%	2582
	21st to end	Day	15% 12% 3 8% 5% 4 5% 4 5% 7% 32%	2730
May	1st to 10th	Day	14% 9% 3 7% 5% 4 4 3 6% 8% 38%	7616
	11th to 20th	Day	12% 10% 3 8% 5% 4 5% 4 5% 7% 38%	7796
	21st to end	Day	14% 7% 2 6% 4 4 4 4 5% 6% 43%	9047
June	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 7% 43%	2940
	11th to 20th	Day	12% 7% 3 7% 5% 5% 4 4 6% 8% 40%	2940
	21st to end	Day	13% 7% 2 6% 5% 4 6% 4 6% 7% 40%	2940
July	1st to 10th	Day	12% 6% 3 7% 4 4 5% 4 6% 9% 39%	8280
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 6% 10% 49%	8280
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 6% 10% 44%	8990
August	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 5% 6% 8% 40%	6159
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 4 6% 8% 44%	5951
	21st to end	Day	10% 6% 2 8% 5% 5% 6% 4 7% 8% 38%	6249
September	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 4 6% 7% 40%	2489
	11th to 20th	Day	11% 6% 2 5% 4 5% 4 4 5% 7% 47%	2233
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 3 6% 8% 38%	2200
October	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 41%	2200
	11th to 20th	Day	20% 15% 4 8% 5% 5% 4 3 5% 6% 23%	1916
	21st to end	Day	19% 13% 4 10% 7% 6% 5% 3 5% 7% 22%	1980
November	1st to 10th	Day	15% 14% 4 7% 5% 5% 5% 4 6% 7% 30%	1852
	11th to 20th	Day	14% 20% 7% 11% 5% 4 4 4 5% 6% 19%	1890
	21st to end	Day	17% 22% 8% 14% 4 3 3 3 3 5% 17%	1885
December	1st to 10th	Day	10% 22% 14% 21% 6% 4 4 3 3 3 10%	2527
	11th to 20th	Day	12% 22% 11% 17% 9% 5% 4 3 3 3 9%	3020
	21st to end	Day	21% 24% 8% 14% 6% 5% 4 2 3 4 10%	4070
January	1st to 10th	Night	13% 15% 9% 24% 10% 5% 3 3 3 3 11%	8232
	11th to 20th	Night	9% 18% 9% 21% 11% 12% 5% 2 3 3 6%	8280
	21st to end	Night	9% 15% 8% 20% 9% 7% 7% 3 4 5% 12%	9058
February	1st to 10th	Night	10% 15% 6% 14% 12% 6% 6% 5% 4 5% 17%	2765
	11th to 20th	Night	12% 12% 6% 14% 10% 5% 5% 4 6% 6% 21%	2458
	21st to end	Night	12% 14% 5% 14% 7% 6% 4 3 5% 6% 23%	2076
March	1st to 10th	Night	15% 9% 4 9% 5% 4 4 3 5% 6% 35%	5493
	11th to 20th	Night	12% 10% 4 8% 5% 4 4 4 5% 8% 36%	5231
	21st to end	Night	16% 13% 5% 10% 5% 5% 4 3 5% 6% 29%	5412
April	1st to 10th	Night	15% 12% 4 9% 5% 4 4 4 5% 7% 31%	2100
	11th to 20th	Night	20% 10% 3 7% 4 4 4 2 4 6% 35%	1985
	21st to end	Night	17% 9% 3 8% 5% 3 4 3 5% 6% 37%	1890
May	1st to 10th	Night	12% 7% 3 6% 5% 4 4 3 5% 8% 41%	5237
	11th to 20th	Night	12% 10% 2 6% 4 4 4 3 6% 8% 40%	5069
	21st to end	Night	16% 6% 2 5% 3 3 3 3 5% 6% 47%	5139
June	1st to 10th	Night	12% 8% 3 5% 4 4 4 3 7% 7% 43%	1680
	11th to 20th	Night	12% 6% 2 7% 5% 4 5% 3 6% 9% 42%	1680
	21st to end	Night	11% 6% 2 7% 5% 3 4 4 6% 7% 46%	1680
July	1st to 10th	Night	11% 7% 2 6% 4 4 5% 4 6% 8% 42%	4708
	11th to 20th	Night	6% 4 1 4 3 3 4 3 6% 8% 57%	4707
	21st to end	Night	8% 7% 2 5% 4 4 4 3 5% 7% 51%	5117
August	1st to 10th	Night	14% 6% 3 6% 4 4 4 4 6% 7% 43%	3995
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 8% 51%	4095
	21st to end	Night	9% 7% 2 6% 4 4 4 3 6% 8% 45%	4861
September	1st to 10th	Night	11% 4 2 5% 3 4 5% 3 4 6% 53%	2110
	11th to 20th	Night	10% 5% 2 4 3 3 4 4 6% 8% 52%	2234
	21st to end	Night	14% 9% 2 7% 3 4 4 4 5% 7% 41%	2200
October	1st to 10th	Night	15% 7% 2 6% 3 3 4 3 4 7% 45%	2200
	11th to 20th	Night	17% 13% 4 7% 5% 5% 4 4 5% 5% 32%	2480
	21st to end	Night	22% 13% 3 8% 5% 4 3 3 5% 6% 29%	2860
November	1st to 10th	Night	12% 15% 4 8% 5% 4 4 3 5% 6% 34%	2666
	11th to 20th	Night	14% 16% 5% 12% 6% 5% 4 4 6% 6% 22%	2730
	21st to end	Night	15% 20% 7% 11% 5% 4 5% 3 5% 5% 19%	2730
December	1st to 10th	Night	11% 17% 7% 19% 7% 5% 4 4 4 5% 16%	4844
	11th to 20th	Night	13% 23% 8% 17% 9% 6% 4 3 4 5% 11%	5355
	21st to end	Night	22% 24% 7% 12% 5% 4 3 2 3 4 14%	7150

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	84% 3 6% 6% 1	4692
	11th to 20th	Day	87% 3 3 5% 2	4710
	21st to end	Day	76% 3 8% 10% 3	5156
February	1st to 10th	Day	71% 5% 8% 13% 3	1848
	11th to 20th	Day	70% 4 9% 11% 5%	2058
	21st to end	Day	66% 5% 11% 13% 5%	1730
March	1st to 10th	Day	54% 3 14% 17% 10% 1	4580
	11th to 20th	Day	53% 4 15% 17% 9% 2	4948
	21st to end	Day	65% 3 10% 14% 7% 1	5790
April	1st to 10th	Day	58% 5% 9% 17% 11%	2520
	11th to 20th	Day	54% 4 9% 19% 13% 2	2582
	21st to end	Day	52% 4 12% 16% 14% 2	2730
May	1st to 10th	Day	43% 4 9% 25% 17% 2	7651
	11th to 20th	Day	46% 5% 9% 21% 18% 1	7800
	21st to end	Day	42% 4 8% 20% 23% 4	9061
June	1st to 10th	Day	40% 5% 10% 26% 18% 2	2940
	11th to 20th	Day	42% 6% 11% 23% 17% 1	2940
	21st to end	Day	41% 7% 13% 24% 14% 1	2940
July	1st to 10th	Day	40% 6% 12% 25% 16% 1	8211
	11th to 20th	Day	30% 5% 11% 32% 21% 1	8205
	21st to end	Day	35% 6% 13% 28% 17% 1	8794
August	1st to 10th	Day	39% 6% 12% 26% 16% 1	6144
	11th to 20th	Day	37% 6% 16% 26% 14% 1	5990
	21st to end	Day	42% 6% 14% 27% 10% 1	6248
September	1st to 10th	Day	42% 6% 12% 25% 14% 1	2489
	11th to 20th	Day	36% 5% 14% 30% 15% 1	2233
	21st to end	Day	44% 5% 12% 26% 12%	2200
October	1st to 10th	Day	31% 4 8% 35% 20% 3	3590
	11th to 20th	Day	51% 4 11% 22% 12%	3093
	21st to end	Day	58% 5% 13% 18% 6%	3180
November	1st to 10th	Day	52% 6% 12% 21% 9%	1852
	11th to 20th	Day	65% 5% 12% 13% 4	1890
	21st to end	Day	71% 4 11% 10% 3	1885
December	1st to 10th	Day	82% 5% 6% 6% 1	2527
	11th to 20th	Day	81% 4 7% 7% 1	3017
	21st to end	Day	80% 2 6% 8% 4	4070
January	1st to 10th	Night	79% 4 7% 7% 4	8233
	11th to 20th	Night	87% 3 5% 4 2	8280
	21st to end	Night	76% 4 7% 8% 4	9058
February	1st to 10th	Night	69% 5% 7% 13% 4 1	2765
	11th to 20th	Night	64% 6% 9% 15% 6%	2459
	21st to end	Night	63% 4 12% 16% 5% 1	2076
March	1st to 10th	Night	51% 3 16% 20% 9%	5493
	11th to 20th	Night	47% 4 19% 19% 9% 1	5231
	21st to end	Night	57% 5% 10% 19% 9% 1	5412
April	1st to 10th	Night	53% 6% 9% 19% 13% 1	2100
	11th to 20th	Night	51% 4 8% 21% 14% 2	1985
	21st to end	Night	48% 4 11% 20% 14% 3	1890
May	1st to 10th	Night	40% 5% 12% 24% 16% 2	5264
	11th to 20th	Night	41% 5% 10% 29% 14% 1	5070
	21st to end	Night	38% 3 9% 24% 20% 6%	5149
June	1st to 10th	Night	38% 6% 11% 25% 18% 2	1680
	11th to 20th	Night	39% 6% 13% 22% 18% 1	1680
	21st to end	Night	37% 6% 13% 27% 16% 2	1680
July	1st to 10th	Night	40% 5% 14% 22% 15% 4	4670
	11th to 20th	Night	24% 4 12% 37% 21% 1	4662
	21st to end	Night	32% 6% 14% 27% 21% 1	5002
August	1st to 10th	Night	40% 4 14% 25% 15% 1	3986
	11th to 20th	Night	32% 5% 19% 32% 12%	4122
	21st to end	Night	36% 5% 14% 29% 14% 1	4861
September	1st to 10th	Night	33% 5% 12% 30% 18% 2	2110
	11th to 20th	Night	30% 5% 15% 34% 15% 1	2234
	21st to end	Night	43% 5% 13% 27% 11% 1	2200
October	1st to 10th	Night	33% 3 10% 37% 15% 1	3590
	11th to 20th	Night	45% 4 10% 25% 15%	4042
	21st to end	Night	49% 4 12% 26% 9%	4610
November	1st to 10th	Night	52% 5% 11% 21% 10% 1	2666
	11th to 20th	Night	62% 6% 13% 12% 6% 1	2730
	21st to end	Night	68% 5% 13% 11% 2 1	2730
December	1st to 10th	Night	72% 6% 12% 9% 1	4844
	11th to 20th	Night	78% 4 8% 8% 2	5357
	21st to end	Night	76% 2 9% 7% 6%	7150

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% 21% 37% 15% 6%	330
	11th to 20th	Day	24% 23% 41% 11% 1	330
	21st to end	Day	24% 18% 39% 17% 3	363
February	1st to 10th	Day	19% 29% 33% 13% 4 1	330
	11th to 20th	Day	21% 33% 31% 14% 1	330
	21st to end	Day	29% 34% 28% 9% 1	273
March	1st to 10th	Day	26% 27% 35% 10% 2	330
	11th to 20th	Day	28% 17% 31% 16% 7% 1	476
	21st to end	Day	28% 21% 28% 17% 5% 1	594
April	1st to 10th	Day	28% 20% 34% 14% 4 1	540
	11th to 20th	Day	31% 20% 27% 13% 6% 3	532
	21st to end	Day	25% 15% 30% 22% 7% 1	540
May	1st to 10th	Day	23% 21% 32% 16% 5% 2	543
	11th to 20th	Day	19% 16% 31% 23% 8% 4	620
	21st to end	Day	17% 15% 31% 26% 10% 2	844
June	1st to 10th	Day	13% 15% 34% 25% 10% 2	780
	11th to 20th	Day	19% 14% 33% 23% 8% 2	780
	21st to end	Day	17% 12% 32% 26% 9% 3	780
July	1st to 10th	Day	9% 8% 32% 31% 15% 5%	771
	11th to 20th	Day	10% 9% 30% 32% 15% 5%	768
	21st to end	Day	10% 8% 35% 28% 14% 6%	849
August	1st to 10th	Day	12% 7% 25% 29% 20% 8%	634
	11th to 20th	Day	14% 5% 22% 32% 18% 10%	559
	21st to end	Day	15% 8% 25% 30% 17% 6%	627
September	1st to 10th	Day	16% 11% 23% 26% 17% 7%	570
	11th to 20th	Day	10% 7% 23% 30% 21% 10%	542
	21st to end	Day	18% 13% 23% 26% 15% 5%	530
October	1st to 10th	Day	19% 15% 30% 21% 13% 2	530
	11th to 20th	Day	29% 14% 35% 18% 4	418
	21st to end	Day	28% 23% 30% 14% 4 1	363
November	1st to 10th	Day	27% 19% 34% 15% 5%	330
	11th to 20th	Day	26% 23% 37% 10% 3 1	330
	21st to end	Day	27% 25% 36% 9% 3	330
December	1st to 10th	Day	27% 23% 28% 15% 5% 1	278
	11th to 20th	Day	26% 28% 32% 12% 2 1	308
	21st to end	Day	30% 25% 33% 8% 2 1	363
January	1st to 10th	Night	21% 18% 35% 21% 5% 1	1050
	11th to 20th	Night	22% 17% 35% 20% 5%	1050
	21st to end	Night	20% 11% 40% 25% 5% 1	1155
February	1st to 10th	Night	17% 17% 38% 24% 4	905
	11th to 20th	Night	18% 18% 37% 24% 4	823
	21st to end	Night	22% 19% 37% 19% 3	692
March	1st to 10th	Night	19% 13% 38% 22% 8%	840
	11th to 20th	Night	20% 16% 35% 22% 6%	840
	21st to end	Night	21% 13% 34% 25% 5% 1	851
April	1st to 10th	Night	21% 16% 36% 23% 3 1	630
	11th to 20th	Night	26% 13% 30% 24% 7%	623
	21st to end	Night	21% 12% 32% 27% 7%	630
May	1st to 10th	Night	16% 10% 37% 30% 7%	630
	11th to 20th	Night	18% 10% 36% 27% 9%	621
	21st to end	Night	15% 6% 34% 32% 13% 1	683
June	1st to 10th	Night	14% 6% 32% 37% 10% 1	630
	11th to 20th	Night	14% 6% 33% 35% 11% 1	630
	21st to end	Night	14% 4 28% 40% 14% 1	630
July	1st to 10th	Night	11% 2 21% 42% 22% 2	615
	11th to 20th	Night	9% 3 22% 42% 22% 2	612
	21st to end	Night	9% 4 23% 42% 21% 1	690
August	1st to 10th	Night	10% 3 21% 43% 21% 2	627
	11th to 20th	Night	10% 4 18% 41% 23% 4	624
	21st to end	Night	11% 4 22% 40% 21% 2	693
September	1st to 10th	Night	13% 4 23% 36% 21% 3	640
	11th to 20th	Night	12% 5% 21% 36% 23% 3	813
	21st to end	Night	17% 8% 27% 29% 15% 3	800
October	1st to 10th	Night	20% 8% 27% 31% 13% 2	800
	11th to 20th	Night	25% 12% 29% 26% 7% 1	800
	21st to end	Night	29% 11% 29% 23% 7%	880
November	1st to 10th	Night	21% 16% 30% 26% 7% 1	820
	11th to 20th	Night	23% 17% 36% 20% 4	840
	21st to end	Night	25% 17% 32% 23% 3	840
December	1st to 10th	Night	22% 18% 34% 21% 4	1050
	11th to 20th	Night	23% 18% 38% 16% 4 1	1050
	21st to end	Night	30% 15% 33% 21% 2	1155

Page generated at 2026-09-11 04:11:58. Version ac07

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