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 2025-02-06.

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% 3 8% 5% 4 4 3 5% 6% 29%	108873
	Night	21% 12% 4 8% 5% 4 4 3 5% 6% 29%	109440
Transparency	Day	53% 7% 12% 18% 9% 1	112502
	Night	55% 7% 11% 18% 9% 1	113975
Seeing	Day	26% 11% 30% 24% 8% 1	17621
	Night	26% 13% 29% 23% 8% 1	25391

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% 4 4 3 3 4 20%	3616
	11th to 20th	Day	15% 16% 7% 16% 6% 5% 5% 4 5% 5% 16%	3744
	21st to end	Day	15% 11% 5% 9% 6% 6% 5% 3 5% 5% 29%	4466
February	1st to 10th	Day	22% 14% 5% 9% 7% 5% 5% 4 5% 5% 21%	1755
	11th to 20th	Day	17% 13% 5% 13% 5% 4 5% 3 5% 4 25%	1663
	21st to end	Day	14% 12% 4 7% 7% 4 5% 4 5% 7% 31%	1447
March	1st to 10th	Day	25% 14% 3 7% 5% 5% 4 2 3 5% 27%	3420
	11th to 20th	Day	18% 17% 4 8% 6% 4 4 3 4 5% 27%	3480
	21st to end	Day	32% 14% 3 9% 4 4 3 2 3 3 22%	3816
April	1st to 10th	Day	27% 12% 4 6% 5% 3 4 3 4 6% 26%	2274
	11th to 20th	Day	22% 10% 3 6% 4 4 4 3 5% 8% 33%	2305
	21st to end	Day	24% 10% 3 6% 4 4 4 3 5% 7% 32%	2470
May	1st to 10th	Day	25% 14% 3 8% 6% 5% 4 3 5% 6% 21%	4195
	11th to 20th	Day	24% 12% 3 8% 5% 4 3 3 4 5% 30%	4398
	21st to end	Day	21% 9% 3 6% 4 4 4 4 6% 9% 28%	4836
June	1st to 10th	Day	26% 11% 3 7% 5% 4 3 4 5% 6% 26%	2660
	11th to 20th	Day	23% 9% 3 6% 5% 4 3 3 4 7% 33%	2660
	21st to end	Day	30% 9% 3 7% 5% 4 4 4 5% 6% 24%	2814
July	1st to 10th	Day	25% 11% 3 7% 4 3 4 4 6% 8% 26%	4440
	11th to 20th	Day	25% 13% 3 6% 3 3 4 3 5% 8% 28%	4440
	21st to end	Day	24% 10% 3 6% 4 4 4 3 5% 7% 30%	4659
August	1st to 10th	Day	28% 11% 3 6% 4 3 4 3 5% 7% 26%	4105
	11th to 20th	Day	19% 8% 2 8% 4 4 5% 4 6% 9% 31%	4045
	21st to end	Day	11% 6% 2 5% 3 4 4 4 6% 8% 46%	4326
September	1st to 10th	Day	18% 7% 2 5% 4 4 4 3 5% 8% 41%	2280
	11th to 20th	Day	21% 6% 2 5% 3 3 4 3 4 6% 43%	2214
	21st to end	Day	20% 6% 2 6% 4 3 4 3 5% 6% 40%	2024
October	1st to 10th	Day	19% 7% 2 5% 3 4 4 4 5% 7% 40%	1900
	11th to 20th	Day	20% 8% 2 6% 4 4 5% 3 5% 7% 36%	1900
	21st to end	Day	21% 9% 4 6% 6% 4 4 3 5% 5% 33%	2090
November	1st to 10th	Day	22% 10% 3 8% 5% 4 4 3 4 7% 30%	1643
	11th to 20th	Day	23% 12% 4 8% 4 4 4 4 5% 6% 26%	1600
	21st to end	Day	21% 13% 4 9% 6% 4 4 3 4 6% 25%	1600
December	1st to 10th	Day	23% 13% 5% 9% 5% 4 4 3 5% 5% 23%	2610
	11th to 20th	Day	31% 10% 3 6% 5% 4 4 3 4 4 26%	2996
	21st to end	Day	22% 13% 5% 11% 4 3 3 2 4 6% 27%	3982
January	1st to 10th	Night	15% 16% 5% 13% 8% 4 4 4 5% 5% 21%	6349
	11th to 20th	Night	18% 14% 5% 16% 6% 5% 5% 3 5% 5% 17%	6149
	21st to end	Night	13% 13% 4 11% 7% 6% 5% 3 5% 6% 26%	6490
February	1st to 10th	Night	21% 14% 4 10% 5% 6% 5% 4 5% 6% 21%	2536
	11th to 20th	Night	19% 10% 5% 9% 7% 7% 4 4 6% 6% 23%	2403
	21st to end	Night	13% 13% 4 10% 6% 5% 5% 4 5% 5% 28%	2005
March	1st to 10th	Night	23% 11% 4 8% 7% 6% 4 4 5% 5% 24%	3418
	11th to 20th	Night	20% 17% 4 7% 5% 5% 4 3 5% 5% 23%	3479
	21st to end	Night	31% 12% 5% 10% 4 3 2 2 3 3 25%	3816
April	1st to 10th	Night	26% 11% 4 6% 4 3 4 4 4 5% 29%	1905
	11th to 20th	Night	23% 11% 3 6% 4 5% 4 3 4 6% 32%	1821
	21st to end	Night	24% 11% 3 6% 4 3 3 3 4 5% 32%	1710
May	1st to 10th	Night	23% 15% 3 7% 5% 4 4 3 5% 7% 24%	2746
	11th to 20th	Night	25% 11% 2 7% 4 4 4 4 5% 6% 29%	2506
	21st to end	Night	23% 12% 4 8% 5% 3 4 3 5% 6% 28%	2749
June	1st to 10th	Night	31% 10% 3 7% 5% 3 3 2 4 5% 28%	1520
	11th to 20th	Night	23% 11% 3 5% 4 4 4 3 4 6% 33%	1520
	21st to end	Night	31% 13% 3 6% 4 3 4 3 4 5% 24%	1362
July	1st to 10th	Night	26% 12% 4 10% 4 4 4 3 4 6% 23%	2484
	11th to 20th	Night	25% 16% 5% 8% 4 3 3 3 4 5% 23%	2530
	21st to end	Night	22% 10% 3 6% 4 4 3 3 4 7% 33%	2897
August	1st to 10th	Night	26% 13% 2 5% 3 3 3 3 4 6% 31%	2825
	11th to 20th	Night	19% 11% 4 7% 4 3 4 3 5% 7% 33%	2782
	21st to end	Night	13% 7% 1 5% 3 3 4 3 5% 6% 52%	3316
September	1st to 10th	Night	18% 9% 3 5% 4 2 4 3 5% 7% 42%	1900
	11th to 20th	Night	19% 7% 3 5% 3 3 3 3 5% 7% 43%	1963
	21st to end	Night	22% 9% 2 6% 3 3 3 3 4 6% 38%	2155
October	1st to 10th	Night	19% 7% 3 6% 4 4 3 3 4 7% 41%	2280
	11th to 20th	Night	20% 6% 2 6% 4 4 4 3 5% 6% 40%	2280
	21st to end	Night	26% 8% 2 6% 3 3 4 3 4 6% 35%	2508
November	1st to 10th	Night	20% 9% 3 6% 5% 4 4 3 6% 6% 34%	2647
	11th to 20th	Night	22% 11% 3 7% 5% 4 4 3 5% 7% 28%	2800
	21st to end	Night	22% 12% 3 8% 6% 5% 4 3 5% 6% 26%	2800
December	1st to 10th	Night	17% 11% 4 12% 6% 5% 4 3 5% 6% 26%	4580
	11th to 20th	Night	27% 12% 3 7% 4 3 4 3 4 5% 28%	5213
	21st to end	Night	25% 11% 4 9% 4 3 3 2 4 5% 30%	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	65% 7% 14% 10% 4	3617
	11th to 20th	Day	61% 8% 13% 14% 3	3774
	21st to end	Day	53% 6% 12% 13% 14% 2	4466
February	1st to 10th	Day	62% 7% 11% 12% 7% 1	1755
	11th to 20th	Day	61% 7% 12% 13% 6% 1	1671
	21st to end	Day	50% 8% 13% 17% 9% 3	1447
March	1st to 10th	Day	58% 6% 10% 16% 8% 2	3424
	11th to 20th	Day	48% 10% 14% 18% 9% 1	3480
	21st to end	Day	62% 5% 8% 15% 9% 1	3816
April	1st to 10th	Day	55% 6% 9% 15% 12% 2	2274
	11th to 20th	Day	47% 6% 12% 21% 12% 2	2305
	21st to end	Day	48% 5% 14% 18% 12% 2	2470
May	1st to 10th	Day	58% 9% 14% 13% 4 1	4209
	11th to 20th	Day	54% 7% 12% 19% 7%	4402
	21st to end	Day	48% 10% 17% 17% 8% 1	4836
June	1st to 10th	Day	56% 8% 11% 17% 7%	2660
	11th to 20th	Day	50% 6% 13% 18% 11% 1	2660
	21st to end	Day	62% 7% 8% 14% 8% 1	2814
July	1st to 10th	Day	60% 7% 10% 12% 11% 1	4370
	11th to 20th	Day	57% 8% 9% 18% 7% 1	4364
	21st to end	Day	53% 7% 11% 18% 9% 1	4510
August	1st to 10th	Day	58% 7% 11% 16% 7%	4092
	11th to 20th	Day	47% 8% 17% 22% 6%	4084
	21st to end	Day	33% 7% 12% 30% 18% 1	4326
September	1st to 10th	Day	40% 7% 14% 23% 15% 2	2280
	11th to 20th	Day	43% 6% 9% 25% 16% 2	2214
	21st to end	Day	43% 7% 10% 24% 16% 1	2024
October	1st to 10th	Day	42% 6% 11% 26% 13% 1	3160
	11th to 20th	Day	39% 6% 10% 26% 19% 1	3140
	21st to end	Day	45% 6% 13% 21% 12% 3	3428
November	1st to 10th	Day	54% 6% 10% 21% 8% 1	1643
	11th to 20th	Day	57% 8% 13% 15% 6% 1	1600
	21st to end	Day	60% 7% 12% 15% 6%	1600
December	1st to 10th	Day	61% 6% 12% 18% 2	2610
	11th to 20th	Day	60% 5% 11% 14% 9%	2995
	21st to end	Day	58% 6% 16% 13% 7%	3982
January	1st to 10th	Night	61% 10% 11% 15% 4	6349
	11th to 20th	Night	63% 9% 13% 12% 4	6194
	21st to end	Night	57% 8% 10% 15% 9% 1	6490
February	1st to 10th	Night	65% 8% 10% 9% 7% 1	2536
	11th to 20th	Night	61% 7% 12% 13% 6% 1	2406
	21st to end	Night	56% 6% 11% 18% 7% 1	2005
March	1st to 10th	Night	60% 6% 10% 15% 9% 1	3427
	11th to 20th	Night	56% 9% 11% 15% 8% 1	3480
	21st to end	Night	64% 4 8% 15% 8% 1	3816
April	1st to 10th	Night	56% 6% 9% 15% 12% 3	1905
	11th to 20th	Night	52% 5% 10% 18% 14% 2	1821
	21st to end	Night	53% 5% 10% 18% 11% 3	1710
May	1st to 10th	Night	58% 8% 14% 13% 6% 1	2752
	11th to 20th	Night	55% 8% 9% 20% 7%	2507
	21st to end	Night	56% 8% 12% 17% 6% 1	2750
June	1st to 10th	Night	57% 5% 10% 19% 8%	1520
	11th to 20th	Night	52% 8% 9% 19% 11% 1	1520
	21st to end	Night	64% 6% 8% 12% 8% 1	1362
July	1st to 10th	Night	64% 5% 9% 12% 9% 1	2445
	11th to 20th	Night	66% 5% 7% 13% 8% 1	2482
	21st to end	Night	52% 7% 10% 19% 12% 1	2806
August	1st to 10th	Night	55% 6% 11% 21% 7%	2813
	11th to 20th	Night	49% 8% 14% 22% 6%	2809
	21st to end	Night	32% 6% 14% 29% 20%	3315
September	1st to 10th	Night	41% 6% 10% 24% 16% 2	1900
	11th to 20th	Night	41% 5% 9% 28% 16% 1	1963
	21st to end	Night	48% 4 8% 25% 13% 1	2155
October	1st to 10th	Night	44% 5% 12% 26% 11% 1	3800
	11th to 20th	Night	36% 5% 13% 27% 19%	3779
	21st to end	Night	44% 4 11% 23% 17% 1	4120
November	1st to 10th	Night	51% 7% 13% 18% 11% 1	2647
	11th to 20th	Night	55% 9% 13% 15% 8%	2800
	21st to end	Night	58% 8% 15% 13% 5%	2800
December	1st to 10th	Night	58% 7% 12% 19% 4	4580
	11th to 20th	Night	59% 6% 10% 16% 9% 1	5215
	21st to end	Night	57% 6% 12% 16% 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	26% 24% 35% 14% 3	400
	11th to 20th	Day	29% 17% 33% 15% 6%	400
	21st to end	Day	22% 18% 38% 19% 3	440
February	1st to 10th	Day	29% 17% 34% 16% 3	385
	11th to 20th	Day	25% 25% 31% 17% 2	366
	21st to end	Day	19% 18% 40% 19% 4 1	307
March	1st to 10th	Day	24% 18% 39% 17% 2	456
	11th to 20th	Day	22% 18% 34% 21% 4 1	460
	21st to end	Day	27% 15% 35% 16% 6% 1	506
April	1st to 10th	Day	32% 15% 32% 18% 3	460
	11th to 20th	Day	23% 11% 42% 19% 4	452
	21st to end	Day	23% 11% 33% 24% 9%	460
May	1st to 10th	Day	28% 9% 34% 23% 5% 1	513
	11th to 20th	Day	24% 7% 31% 30% 8% 1	674
	21st to end	Day	28% 8% 29% 28% 6% 1	735
June	1st to 10th	Day	31% 6% 26% 26% 11%	680
	11th to 20th	Day	24% 6% 28% 30% 10% 1	680
	21st to end	Day	38% 4 21% 26% 10% 1	680
July	1st to 10th	Day	29% 4 22% 31% 13% 1	670
	11th to 20th	Day	29% 4 20% 30% 15% 2	668
	21st to end	Day	27% 5% 22% 32% 12% 1	646
August	1st to 10th	Day	21% 5% 23% 37% 11% 3	486
	11th to 20th	Day	21% 6% 24% 29% 16% 3	479
	21st to end	Day	18% 5% 25% 29% 19% 4	539
September	1st to 10th	Day	19% 6% 28% 33% 12% 2	490
	11th to 20th	Day	23% 8% 28% 25% 12% 4	490
	21st to end	Day	22% 5% 31% 25% 14% 3	455
October	1st to 10th	Day	20% 9% 30% 25% 14% 3	390
	11th to 20th	Day	19% 13% 33% 21% 11% 3	390
	21st to end	Day	26% 14% 32% 21% 6% 1	429
November	1st to 10th	Day	23% 15% 35% 19% 8% 1	395
	11th to 20th	Day	29% 21% 28% 16% 5% 1	400
	21st to end	Day	29% 18% 37% 13% 4	400
December	1st to 10th	Day	31% 18% 32% 15% 4	400
	11th to 20th	Day	31% 24% 29% 15% 1	400
	21st to end	Day	28% 19% 33% 17% 3 1	440
January	1st to 10th	Night	27% 21% 33% 16% 3	900
	11th to 20th	Night	27% 19% 32% 19% 4	863
	21st to end	Night	21% 23% 36% 16% 3	880
February	1st to 10th	Night	28% 19% 32% 19% 2	781
	11th to 20th	Night	24% 24% 34% 16% 2	743
	21st to end	Night	19% 17% 38% 21% 4 1	628
March	1st to 10th	Night	24% 17% 39% 17% 3	760
	11th to 20th	Night	23% 14% 32% 23% 7% 1	760
	21st to end	Night	25% 16% 31% 21% 6%	836
April	1st to 10th	Night	32% 12% 29% 23% 4	575
	11th to 20th	Night	27% 7% 38% 21% 7%	564
	21st to end	Night	29% 8% 29% 24% 9% 1	570
May	1st to 10th	Night	30% 6% 30% 25% 7% 1	570
	11th to 20th	Night	29% 7% 26% 26% 11% 2	562
	21st to end	Night	25% 5% 29% 31% 9% 1	616
June	1st to 10th	Night	34% 5% 21% 31% 9%	570
	11th to 20th	Night	26% 5% 24% 33% 10% 1	570
	21st to end	Night	34% 4 19% 30% 12% 1	412
July	1st to 10th	Night	26% 4 18% 36% 15% 1	523
	11th to 20th	Night	29% 4 18% 33% 15% 2	552
	21st to end	Night	26% 3 19% 34% 17% 1	623
August	1st to 10th	Night	21% 4 18% 34% 20% 3	568
	11th to 20th	Night	23% 3 21% 31% 20% 2	562
	21st to end	Night	19% 4 21% 34% 18% 4	627
September	1st to 10th	Night	20% 5% 25% 33% 15% 2	570
	11th to 20th	Night	23% 6% 24% 27% 17% 3	633
	21st to end	Night	26% 7% 25% 28% 11% 2	760
October	1st to 10th	Night	22% 8% 27% 31% 10% 1	760
	11th to 20th	Night	22% 12% 30% 24% 11% 1	760
	21st to end	Night	27% 16% 30% 22% 5%	836
November	1st to 10th	Night	25% 13% 33% 22% 6% 1	867
	11th to 20th	Night	27% 19% 27% 20% 6%	900
	21st to end	Night	29% 18% 30% 16% 6%	900
December	1st to 10th	Night	31% 16% 34% 15% 5%	900
	11th to 20th	Night	29% 24% 32% 13% 2	900
	21st to end	Night	29% 17% 33% 17% 3	990

Page generated at 2025-02-03 04:05:52. Version ac07

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