Abbey Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Abbey Ridge Observatory clear sky chart from 2005-11-06 to 2026-06-01.

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	22% 11% 4 8% 5% 4 4 3 5% 6% 28%	132736
	Night	22% 12% 4 9% 5% 4 4 3 4 5% 28%	130519
Transparency	Day	54% 7% 12% 18% 9% 1	136319
	Night	56% 6% 10% 18% 9% 1	135023
Seeing	Day	26% 12% 30% 23% 8% 1	19466
	Night	26% 13% 29% 23% 8% 1	27146

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	14% 15% 6% 16% 9% 5% 4 3 3 4 19%	4690
	11th to 20th	Day	19% 16% 8% 15% 6% 5% 4 3 4 5% 14%	4886
	21st to end	Day	14% 10% 4 10% 8% 7% 6% 4 5% 6% 27%	5781
February	1st to 10th	Day	21% 13% 5% 10% 7% 5% 5% 4 5% 5% 20%	1890
	11th to 20th	Day	17% 12% 5% 14% 5% 4 5% 3 5% 5% 26%	1843
	21st to end	Day	14% 12% 4 8% 7% 4 5% 4 5% 7% 31%	1595
March	1st to 10th	Day	23% 13% 4 11% 5% 5% 4 3 3 4 25%	5029
	11th to 20th	Day	19% 16% 4 7% 4 3 3 3 4 5% 31%	5090
	21st to end	Day	29% 14% 4 9% 5% 4 3 2 4 4 22%	5587
April	1st to 10th	Day	27% 12% 4 6% 5% 3 4 3 4 5% 27%	2514
	11th to 20th	Day	23% 10% 3 7% 4 3 4 3 5% 7% 32%	2551
	21st to end	Day	23% 10% 3 6% 3 4 4 3 4 7% 32%	2730
May	1st to 10th	Day	28% 15% 4 9% 5% 5% 4 3 4 4 18%	6150
	11th to 20th	Day	24% 13% 4 8% 5% 3 4 3 4 5% 28%	6458
	21st to end	Day	22% 12% 3 6% 4 4 4 4 5% 8% 28%	7102
June	1st to 10th	Day	25% 11% 3 7% 5% 4 3 4 5% 6% 27%	2800
	11th to 20th	Day	22% 9% 3 6% 4 4 3 3 4 7% 34%	2800
	21st to end	Day	29% 9% 3 7% 5% 4 4 4 5% 6% 25%	2963
July	1st to 10th	Day	25% 11% 3 7% 4 4 5% 4 7% 8% 22%	6360
	11th to 20th	Day	22% 14% 3 6% 4 3 4 3 5% 8% 28%	6360
	21st to end	Day	18% 8% 3 6% 4 4 4 3 5% 9% 36%	6701
August	1st to 10th	Day	28% 11% 3 6% 4 3 4 3 5% 7% 27%	4235
	11th to 20th	Day	19% 8% 2 8% 4 4 4 4 6% 9% 32%	4175
	21st to end	Day	11% 6% 2 5% 3 4 4 4 6% 8% 46%	4463
September	1st to 10th	Day	18% 7% 3 5% 4 4 4 2 5% 8% 40%	2400
	11th to 20th	Day	20% 6% 2 5% 3 3 4 3 4 6% 44%	2330
	21st to end	Day	19% 6% 2 6% 4 3 4 3 5% 6% 41%	2130
October	1st to 10th	Day	19% 6% 2 5% 3 4 4 4 5% 7% 41%	2000
	11th to 20th	Day	19% 9% 3 6% 4 5% 5% 3 5% 7% 35%	2000
	21st to end	Day	21% 9% 4 6% 6% 4 4 3 5% 5% 33%	2200
November	1st to 10th	Day	22% 10% 3 8% 5% 4 4 3 4 7% 30%	1727
	11th to 20th	Day	23% 12% 5% 8% 4 4 4 4 5% 6% 25%	1680
	21st to end	Day	21% 13% 4 9% 6% 4 4 3 4 6% 25%	1680
December	1st to 10th	Day	23% 13% 5% 10% 5% 4 4 3 5% 5% 23%	2690
	11th to 20th	Day	31% 10% 3 7% 4 4 4 3 4 4 26%	3076
	21st to end	Day	21% 13% 5% 11% 4 3 3 2 4 6% 27%	4070
January	1st to 10th	Night	15% 15% 5% 14% 8% 6% 4 3 5% 5% 19%	8234
	11th to 20th	Night	23% 15% 6% 16% 6% 5% 4 3 4 4 15%	8013
	21st to end	Night	12% 13% 4 12% 9% 7% 6% 4 5% 6% 23%	8400
February	1st to 10th	Night	20% 13% 5% 11% 5% 6% 5% 3 5% 6% 21%	2730
	11th to 20th	Night	18% 10% 4 10% 7% 6% 4 4 6% 6% 25%	2663
	21st to end	Night	14% 13% 4 10% 6% 5% 5% 4 6% 5% 28%	2209
March	1st to 10th	Night	25% 12% 4 9% 6% 5% 4 3 4 5% 22%	5028
	11th to 20th	Night	22% 15% 5% 7% 4 4 3 3 5% 5% 27%	5089
	21st to end	Night	30% 13% 5% 10% 3 3 2 2 3 4 24%	5587
April	1st to 10th	Night	27% 12% 4 6% 4 3 4 4 4 5% 28%	2105
	11th to 20th	Night	24% 11% 3 6% 4 5% 4 3 4 6% 31%	2015
	21st to end	Night	23% 10% 3 6% 4 3 4 3 5% 6% 32%	1890
May	1st to 10th	Night	29% 15% 3 7% 4 4 3 3 4 5% 22%	4014
	11th to 20th	Night	25% 14% 3 6% 4 4 4 3 4 5% 29%	3676
	21st to end	Night	20% 16% 4 7% 4 3 3 3 4 5% 30%	4036
June	1st to 10th	Night	30% 10% 3 6% 4 3 2 2 4 5% 29%	1601
	11th to 20th	Night	23% 10% 3 5% 4 4 4 3 4 6% 33%	1600
	21st to end	Night	31% 13% 3 6% 4 3 4 3 4 5% 24%	1433
July	1st to 10th	Night	26% 12% 4 10% 5% 4 5% 3 5% 6% 22%	3546
	11th to 20th	Night	25% 15% 4 8% 4 4 3 3 4 4 26%	3620
	21st to end	Night	19% 9% 4 7% 4 3 4 3 5% 7% 35%	4160
August	1st to 10th	Night	26% 13% 2 5% 3 3 3 3 4 6% 32%	2915
	11th to 20th	Night	19% 11% 4 7% 4 3 3 3 5% 7% 34%	2872
	21st to end	Night	13% 7% 1 5% 3 3 4 3 5% 6% 51%	3421
September	1st to 10th	Night	18% 9% 2 5% 4 2 4 3 5% 7% 43%	2000
	11th to 20th	Night	19% 7% 3 5% 3 3 3 3 5% 7% 44%	2067
	21st to end	Night	22% 9% 2 6% 3 3 3 3 4 6% 39%	2269
October	1st to 10th	Night	18% 7% 3 5% 3 4 3 3 4 7% 43%	2400
	11th to 20th	Night	20% 7% 3 6% 4 4 4 3 5% 6% 38%	2400
	21st to end	Night	26% 8% 2 6% 3 3 4 3 4 6% 34%	2640
November	1st to 10th	Night	21% 9% 3 6% 5% 4 4 3 6% 6% 34%	2783
	11th to 20th	Night	22% 12% 3 7% 5% 4 4 3 5% 7% 28%	2940
	21st to end	Night	22% 12% 3 8% 6% 5% 4 3 5% 6% 27%	2940
December	1st to 10th	Night	17% 11% 4 12% 6% 5% 4 3 5% 6% 26%	4720
	11th to 20th	Night	27% 12% 3 7% 4 3 4 3 4 5% 27%	5353
	21st to end	Night	24% 11% 4 9% 4 3 3 2 4 5% 30%	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	65% 7% 13% 11% 4	4691
	11th to 20th	Day	66% 7% 11% 13% 4	4916
	21st to end	Day	55% 6% 11% 13% 12% 2	5781
February	1st to 10th	Day	62% 7% 11% 12% 7% 1	1890
	11th to 20th	Day	60% 7% 12% 15% 6% 1	1851
	21st to end	Day	49% 8% 12% 18% 10% 3	1595
March	1st to 10th	Day	60% 6% 10% 13% 8% 3	5033
	11th to 20th	Day	49% 8% 15% 20% 8% 1	5090
	21st to end	Day	60% 5% 7% 17% 10% 1	5587
April	1st to 10th	Day	55% 6% 9% 16% 13% 2	2514
	11th to 20th	Day	49% 6% 11% 20% 13% 2	2551
	21st to end	Day	48% 5% 13% 19% 12% 2	2730
May	1st to 10th	Day	65% 6% 11% 12% 5% 1	6161
	11th to 20th	Day	55% 8% 10% 21% 6% 1	6462
	21st to end	Day	51% 8% 14% 17% 9% 1	7102
June	1st to 10th	Day	56% 8% 11% 18% 8%	2800
	11th to 20th	Day	49% 6% 13% 18% 12% 1	2800
	21st to end	Day	60% 7% 8% 15% 9% 1	2963
July	1st to 10th	Day	61% 6% 11% 12% 8% 1	6290
	11th to 20th	Day	56% 8% 9% 19% 7%	6284
	21st to end	Day	46% 7% 14% 22% 10% 1	6509
August	1st to 10th	Day	57% 7% 11% 17% 8%	4222
	11th to 20th	Day	47% 7% 17% 23% 6%	4214
	21st to end	Day	33% 7% 12% 30% 17% 1	4463
September	1st to 10th	Day	40% 7% 13% 24% 15% 2	2400
	11th to 20th	Day	42% 5% 10% 25% 16% 1	2330
	21st to end	Day	42% 7% 9% 24% 17% 1	2130
October	1st to 10th	Day	42% 6% 11% 27% 13% 1	3260
	11th to 20th	Day	40% 6% 10% 25% 18% 1	3240
	21st to end	Day	45% 6% 13% 22% 12% 3	3538
November	1st to 10th	Day	54% 6% 11% 21% 8% 1	1727
	11th to 20th	Day	57% 8% 13% 15% 6% 1	1680
	21st to end	Day	60% 6% 13% 15% 6%	1680
December	1st to 10th	Day	61% 6% 12% 18% 3	2690
	11th to 20th	Day	60% 5% 11% 14% 9%	3075
	21st to end	Day	58% 6% 16% 13% 7%	4070
January	1st to 10th	Night	64% 9% 10% 13% 4	8234
	11th to 20th	Night	67% 8% 11% 11% 4	8058
	21st to end	Night	61% 7% 9% 13% 8% 1	8400
February	1st to 10th	Night	65% 8% 10% 10% 7% 1	2730
	11th to 20th	Night	60% 7% 11% 15% 6% 1	2666
	21st to end	Night	55% 6% 11% 19% 7% 1	2209
March	1st to 10th	Night	62% 5% 8% 12% 11% 1	5037
	11th to 20th	Night	55% 7% 11% 19% 7% 1	5090
	21st to end	Night	63% 4 7% 17% 9% 1	5587
April	1st to 10th	Night	56% 5% 9% 15% 12% 3	2105
	11th to 20th	Night	53% 5% 9% 18% 13% 2	2015
	21st to end	Night	52% 5% 11% 19% 11% 3	1890
May	1st to 10th	Night	64% 6% 10% 12% 8% 1	4020
	11th to 20th	Night	57% 7% 7% 21% 7% 2	3677
	21st to end	Night	56% 6% 11% 20% 8% 1	4037
June	1st to 10th	Night	56% 5% 10% 20% 8%	1601
	11th to 20th	Night	51% 8% 9% 20% 12% 1	1600
	21st to end	Night	63% 6% 8% 12% 9% 1	1433
July	1st to 10th	Night	64% 5% 9% 14% 8% 1	3507
	11th to 20th	Night	63% 5% 6% 14% 10% 1	3572
	21st to end	Night	50% 6% 10% 21% 13% 1	4038
August	1st to 10th	Night	54% 6% 11% 21% 8%	2903
	11th to 20th	Night	48% 8% 14% 22% 7%	2899
	21st to end	Night	32% 6% 14% 29% 19%	3420
September	1st to 10th	Night	41% 6% 11% 25% 16% 2	2000
	11th to 20th	Night	40% 5% 9% 29% 16% 1	2067
	21st to end	Night	47% 4 8% 26% 14% 1	2269
October	1st to 10th	Night	43% 5% 13% 26% 12% 1	3920
	11th to 20th	Night	37% 5% 13% 27% 18%	3899
	21st to end	Night	44% 4 12% 23% 16% 1	4252
November	1st to 10th	Night	51% 7% 12% 17% 12% 1	2783
	11th to 20th	Night	55% 8% 13% 15% 8%	2940
	21st to end	Night	58% 7% 15% 14% 5%	2940
December	1st to 10th	Night	58% 7% 12% 19% 4	4720
	11th to 20th	Night	59% 6% 10% 15% 9% 1	5355
	21st to end	Night	57% 6% 12% 16% 9%	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	25% 24% 35% 13% 2	430
	11th to 20th	Day	30% 17% 32% 14% 6%	430
	21st to end	Day	22% 18% 38% 18% 3	473
February	1st to 10th	Day	28% 16% 36% 16% 4	430
	11th to 20th	Day	26% 23% 31% 17% 2	426
	21st to end	Day	18% 19% 39% 20% 3 1	355
March	1st to 10th	Day	24% 18% 40% 16% 2	535
	11th to 20th	Day	24% 18% 35% 19% 4 1	540
	21st to end	Day	29% 16% 35% 14% 5% 1	594
April	1st to 10th	Day	31% 16% 34% 16% 3	540
	11th to 20th	Day	25% 13% 40% 18% 4	532
	21st to end	Day	23% 11% 34% 23% 9% 1	540
May	1st to 10th	Day	29% 9% 34% 22% 5% 1	599
	11th to 20th	Day	24% 8% 32% 27% 8% 1	774
	21st to end	Day	27% 8% 30% 27% 6% 1	845
June	1st to 10th	Day	31% 6% 25% 27% 10%	730
	11th to 20th	Day	24% 7% 29% 29% 10% 1	730
	21st to end	Day	37% 4 21% 27% 10% 1	730
July	1st to 10th	Day	28% 5% 23% 31% 13% 1	720
	11th to 20th	Day	29% 5% 21% 29% 15% 2	718
	21st to end	Day	26% 5% 24% 32% 12% 1	696
August	1st to 10th	Day	20% 5% 23% 38% 11% 3	526
	11th to 20th	Day	20% 7% 24% 30% 16% 3	519
	21st to end	Day	18% 5% 27% 28% 17% 4	583
September	1st to 10th	Day	20% 5% 27% 33% 12% 2	530
	11th to 20th	Day	21% 8% 28% 26% 13% 4	530
	21st to end	Day	21% 5% 31% 26% 14% 3	491
October	1st to 10th	Day	19% 10% 30% 25% 14% 2	420
	11th to 20th	Day	20% 13% 34% 21% 10% 2	420
	21st to end	Day	25% 15% 32% 21% 6% 1	462
November	1st to 10th	Day	24% 16% 34% 18% 8% 1	425
	11th to 20th	Day	30% 20% 28% 16% 5%	430
	21st to end	Day	29% 18% 37% 12% 4	430
December	1st to 10th	Day	30% 19% 33% 15% 3	430
	11th to 20th	Day	32% 24% 30% 14% 1	430
	21st to end	Day	27% 20% 33% 16% 3 1	473
January	1st to 10th	Night	27% 21% 33% 16% 3	950
	11th to 20th	Night	29% 18% 31% 18% 4	909
	21st to end	Night	21% 24% 36% 16% 3	924
February	1st to 10th	Night	28% 18% 33% 18% 2	840
	11th to 20th	Night	24% 23% 34% 16% 3	823
	21st to end	Night	19% 17% 38% 21% 4 1	692
March	1st to 10th	Night	24% 18% 38% 17% 3	840
	11th to 20th	Night	24% 14% 33% 22% 7% 1	840
	21st to end	Night	26% 16% 32% 20% 6%	924
April	1st to 10th	Night	33% 13% 28% 22% 4	635
	11th to 20th	Night	27% 8% 36% 21% 6%	624
	21st to end	Night	28% 8% 29% 24% 10% 1	630
May	1st to 10th	Night	32% 7% 29% 25% 6% 1	630
	11th to 20th	Night	29% 7% 26% 26% 10% 2	622
	21st to end	Night	24% 6% 29% 31% 9% 1	682
June	1st to 10th	Night	34% 5% 21% 30% 9%	601
	11th to 20th	Night	27% 5% 25% 33% 10% 1	600
	21st to end	Night	34% 4 19% 30% 12% 1	433
July	1st to 10th	Night	26% 4 19% 35% 15% 1	551
	11th to 20th	Night	29% 3 18% 32% 16% 2	582
	21st to end	Night	26% 3 19% 34% 17% 1	656
August	1st to 10th	Night	21% 4 17% 34% 21% 3	598
	11th to 20th	Night	22% 3 21% 31% 21% 2	592
	21st to end	Night	19% 4 22% 35% 17% 3	660
September	1st to 10th	Night	20% 5% 25% 33% 16% 2	600
	11th to 20th	Night	22% 6% 24% 28% 17% 3	667
	21st to end	Night	26% 7% 25% 29% 11% 2	800
October	1st to 10th	Night	21% 9% 27% 31% 10% 1	800
	11th to 20th	Night	23% 12% 29% 24% 11% 1	800
	21st to end	Night	27% 16% 30% 22% 5%	880
November	1st to 10th	Night	26% 14% 32% 21% 5% 1	916
	11th to 20th	Night	28% 19% 28% 20% 6%	950
	21st to end	Night	29% 19% 30% 16% 6%	950
December	1st to 10th	Night	31% 17% 33% 15% 4	950
	11th to 20th	Night	29% 24% 32% 13% 2	950
	21st to end	Night	28% 18% 33% 17% 3	1045

Page generated at 2026-05-29 02:53:28. Version ac07

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