Sights Above Private Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sights Above Private Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	17% 7% 2 6% 4 4 4 4 5% 7% 39%	131341
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 41%	131145
Transparency	Day	43% 6% 12% 21% 15% 3	134872
	Night	44% 5% 11% 22% 16% 3	135700
Seeing	Day	24% 18% 31% 18% 7% 2	16886
	Night	22% 15% 32% 23% 7% 1	26015

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	12% 9% 2 8% 5% 5% 5% 3 5% 5% 42%	4661
	11th to 20th	Day	15% 9% 3 6% 3 3 4 3 4 4 44%	4650
	21st to end	Day	16% 9% 2 4 4 4 3 3 5% 6% 44%	5222
February	1st to 10th	Day	17% 8% 2 6% 4 4 5% 4 5% 6% 38%	1979
	11th to 20th	Day	15% 8% 2 7% 4 5% 4 3 6% 7% 40%	2048
	21st to end	Day	20% 10% 3 5% 4 4 4 3 4 6% 38%	1730
March	1st to 10th	Day	22% 10% 3 6% 4 3 3 3 4 5% 39%	4576
	11th to 20th	Day	14% 8% 2 6% 5% 5% 5% 4 5% 7% 40%	4748
	21st to end	Day	20% 8% 3 7% 4 4 4 4 6% 6% 35%	6102
April	1st to 10th	Day	19% 9% 2 5% 4 3 4 3 5% 7% 38%	2520
	11th to 20th	Day	20% 6% 2 5% 4 3 4 3 5% 6% 40%	2494
	21st to end	Day	22% 5% 1 5% 4 4 5% 3 5% 6% 40%	2651
May	1st to 10th	Day	30% 8% 3 6% 3 3 4 3 4 8% 26%	5899
	11th to 20th	Day	20% 9% 3 7% 4 4 5% 3 5% 7% 34%	6085
	21st to end	Day	21% 7% 2 5% 4 4 4 4 6% 8% 34%	6949
June	1st to 10th	Day	18% 6% 2 6% 5% 5% 5% 4 7% 9% 35%	2800
	11th to 20th	Day	17% 7% 2 5% 4 4 5% 5% 6% 9% 36%	2800
	21st to end	Day	15% 6% 3 6% 5% 5% 5% 4 6% 8% 39%	2800
July	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 9% 33%	6360
	11th to 20th	Day	12% 6% 3 7% 5% 4 6% 5% 7% 11% 35%	6360
	21st to end	Day	16% 6% 3 6% 4 4 4 3 5% 7% 41%	6926
August	1st to 10th	Day	20% 6% 2 7% 5% 5% 5% 4 6% 9% 30%	4371
	11th to 20th	Day	12% 5% 2 7% 5% 5% 4 4 6% 8% 42%	3898
	21st to end	Day	9% 5% 2 6% 4 5% 5% 5% 7% 9% 42%	4312
September	1st to 10th	Day	15% 6% 2 5% 4 4 4 4 4 6% 46%	2400
	11th to 20th	Day	13% 5% 3 5% 3 3 4 3 5% 6% 51%	2250
	21st to end	Day	19% 5% 2 7% 4 5% 4 4 5% 6% 40%	2200
October	1st to 10th	Day	20% 7% 2 5% 3 3 3 4 4 5% 43%	2188
	11th to 20th	Day	15% 5% 2 5% 4 3 4 3 5% 7% 46%	1969
	21st to end	Day	19% 6% 3 4 4 4 3 3 5% 5% 42%	1980
November	1st to 10th	Day	13% 7% 2 5% 4 4 4 3 3 5% 48%	1851
	11th to 20th	Day	18% 6% 2 5% 3 3 3 3 5% 6% 48%	1890
	21st to end	Day	16% 8% 2 6% 4 4 4 3 4 5% 44%	1878
December	1st to 10th	Day	15% 8% 2 6% 3 4 3 3 4 6% 45%	2680
	11th to 20th	Day	20% 8% 1 5% 3 2 3 2 4 5% 46%	3066
	21st to end	Day	20% 10% 3 7% 4 4 3 3 3 5% 38%	4048
January	1st to 10th	Night	14% 8% 3 6% 4 4 4 3 5% 6% 44%	8234
	11th to 20th	Night	15% 9% 3 7% 4 4 4 3 4 4 43%	8235
	21st to end	Night	16% 8% 3 7% 5% 4 4 3 4 6% 41%	8955
February	1st to 10th	Night	16% 10% 3 6% 4 3 3 3 5% 6% 40%	2639
	11th to 20th	Night	17% 8% 3 6% 4 3 3 3 5% 7% 40%	2458
	21st to end	Night	20% 9% 3 6% 4 4 4 4 4 5% 39%	2076
March	1st to 10th	Night	21% 10% 2 5% 3 3 3 3 4 5% 40%	5484
	11th to 20th	Night	16% 9% 3 7% 4 4 4 3 5% 6% 40%	5413
	21st to end	Night	21% 9% 3 7% 3 4 4 3 5% 5% 37%	5072
April	1st to 10th	Night	20% 7% 3 6% 5% 4 4 4 5% 6% 36%	2100
	11th to 20th	Night	19% 7% 3 6% 4 4 4 3 5% 6% 40%	2075
	21st to end	Night	21% 6% 3 6% 4 3 3 3 4 6% 41%	1967
May	1st to 10th	Night	28% 11% 3 7% 5% 3 4 3 5% 6% 26%	4064
	11th to 20th	Night	21% 11% 3 8% 4 4 4 3 5% 7% 31%	3851
	21st to end	Night	23% 8% 3 6% 4 3 4 3 5% 7% 34%	3926
June	1st to 10th	Night	18% 6% 2 7% 5% 4 4 4 5% 7% 39%	1600
	11th to 20th	Night	17% 6% 2 6% 5% 4 4 3 5% 9% 38%	1600
	21st to end	Night	13% 7% 3 6% 4 4 5% 3 7% 8% 41%	1600
July	1st to 10th	Night	16% 7% 3 7% 5% 5% 4 4 6% 9% 35%	3600
	11th to 20th	Night	16% 9% 3 7% 5% 5% 4 4 7% 8% 33%	3600
	21st to end	Night	14% 7% 2 6% 4 4 4 4 4 6% 44%	3926
August	1st to 10th	Night	22% 6% 3 7% 5% 4 5% 4 6% 8% 29%	2746
	11th to 20th	Night	12% 7% 3 7% 5% 5% 5% 4 5% 7% 40%	3133
	21st to end	Night	9% 4 2 4 3 4 4 3 5% 7% 54%	3586
September	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 5% 6% 44%	2000
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 5% 6% 52%	2150
	21st to end	Night	18% 8% 2 6% 4 3 5% 4 4 6% 41%	2200
October	1st to 10th	Night	19% 6% 2 7% 4 4 3 3 4 6% 43%	2210
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 5% 6% 48%	2430
	21st to end	Night	21% 8% 2 5% 3 3 3 3 5% 6% 41%	2860
November	1st to 10th	Night	13% 5% 2 6% 4 3 4 3 5% 7% 49%	2667
	11th to 20th	Night	18% 7% 2 4 3 3 3 3 4 5% 46%	2730
	21st to end	Night	16% 6% 2 6% 4 4 3 3 5% 7% 44%	2740
December	1st to 10th	Night	17% 8% 2 5% 3 4 3 3 4 4 47%	4720
	11th to 20th	Night	24% 8% 2 5% 3 3 3 3 3 4 41%	5348
	21st to end	Night	18% 10% 3 6% 4 4 3 2 4 5% 40%	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	43% 4 10% 26% 15% 2	4662
	11th to 20th	Day	42% 4 9% 22% 15% 8%	4680
	21st to end	Day	41% 4 10% 26% 17% 1	5222
February	1st to 10th	Day	46% 6% 12% 20% 15% 2	1979
	11th to 20th	Day	44% 5% 11% 23% 15% 3	2057
	21st to end	Day	47% 5% 12% 20% 13% 3	1730
March	1st to 10th	Day	49% 3 11% 16% 12% 9%	4579
	11th to 20th	Day	41% 5% 15% 27% 10% 2	4748
	21st to end	Day	48% 4 8% 15% 18% 6%	6102
April	1st to 10th	Day	46% 5% 11% 19% 15% 3	2520
	11th to 20th	Day	43% 5% 12% 20% 18% 2	2494
	21st to end	Day	45% 5% 10% 21% 15% 4	2651
May	1st to 10th	Day	56% 7% 14% 13% 8% 1	5910
	11th to 20th	Day	49% 6% 13% 18% 12% 1	6089
	21st to end	Day	46% 7% 11% 22% 13% 1	6949
June	1st to 10th	Day	45% 7% 13% 23% 12% 1	2800
	11th to 20th	Day	43% 8% 14% 21% 13% 2	2800
	21st to end	Day	42% 8% 14% 21% 14% 1	2800
July	1st to 10th	Day	48% 8% 10% 19% 14% 1	6290
	11th to 20th	Day	41% 8% 17% 22% 11% 1	6285
	21st to end	Day	41% 6% 10% 22% 19% 1	6728
August	1st to 10th	Day	49% 8% 13% 20% 8% 1	4357
	11th to 20th	Day	39% 6% 14% 29% 11% 1	3935
	21st to end	Day	35% 7% 13% 26% 17% 2	4312
September	1st to 10th	Day	39% 7% 12% 22% 19% 2	2400
	11th to 20th	Day	34% 4 11% 24% 24% 3	2250
	21st to end	Day	44% 6% 8% 20% 19% 2	2200
October	1st to 10th	Day	38% 5% 9% 19% 24% 5%	3565
	11th to 20th	Day	29% 3 9% 24% 30% 4	3185
	21st to end	Day	32% 5% 13% 25% 22% 3	3180
November	1st to 10th	Day	39% 4 12% 21% 21% 2	1851
	11th to 20th	Day	38% 4 10% 23% 20% 4	1890
	21st to end	Day	43% 4 12% 26% 12% 3	1878
December	1st to 10th	Day	41% 4 14% 28% 13% 1	2680
	11th to 20th	Day	42% 3 14% 19% 19% 3	3066
	21st to end	Day	49% 4 8% 19% 15% 5%	4048
January	1st to 10th	Night	40% 4 12% 26% 16% 2	8234
	11th to 20th	Night	45% 3 11% 20% 15% 6%	8280
	21st to end	Night	46% 3 9% 20% 19% 3	8955
February	1st to 10th	Night	46% 4 12% 24% 12% 2	2639
	11th to 20th	Night	44% 5% 10% 21% 17% 4	2460
	21st to end	Night	47% 4 9% 22% 14% 4	2076
March	1st to 10th	Night	47% 4 11% 18% 15% 6%	5494
	11th to 20th	Night	45% 5% 15% 21% 11% 4	5414
	21st to end	Night	50% 4 6% 12% 24% 5%	5072
April	1st to 10th	Night	48% 5% 11% 18% 15% 4	2100
	11th to 20th	Night	45% 5% 10% 19% 19% 2	2075
	21st to end	Night	45% 5% 9% 21% 15% 4	1967
May	1st to 10th	Night	58% 6% 14% 12% 9% 1	4070
	11th to 20th	Night	53% 7% 12% 15% 10% 3	3852
	21st to end	Night	49% 7% 13% 22% 9% 1	3927
June	1st to 10th	Night	44% 7% 12% 20% 16% 1	1600
	11th to 20th	Night	43% 7% 14% 25% 11% 1	1600
	21st to end	Night	39% 8% 13% 24% 14% 1	1600
July	1st to 10th	Night	46% 7% 14% 21% 11% 1	3560
	11th to 20th	Night	47% 7% 16% 20% 9% 1	3552
	21st to end	Night	40% 6% 12% 23% 18% 1	3809
August	1st to 10th	Night	52% 8% 13% 16% 10% 1	2736
	11th to 20th	Night	43% 6% 13% 29% 8%	3161
	21st to end	Night	28% 6% 15% 32% 18% 1	3586
September	1st to 10th	Night	40% 6% 9% 26% 18% 1	2000
	11th to 20th	Night	33% 4 12% 23% 25% 2	2150
	21st to end	Night	45% 5% 9% 20% 19% 2	2200
October	1st to 10th	Night	38% 5% 12% 24% 19% 3	3613
	11th to 20th	Night	27% 4 9% 26% 31% 3	3953
	21st to end	Night	32% 3 13% 28% 21% 2	4610
November	1st to 10th	Night	36% 5% 12% 23% 21% 4	2667
	11th to 20th	Night	41% 3 10% 22% 20% 4	2730
	21st to end	Night	41% 4 13% 29% 13% 1	2740
December	1st to 10th	Night	42% 3 12% 29% 13% 1	4720
	11th to 20th	Night	48% 4 12% 17% 18% 2	5348
	21st to end	Night	47% 3 9% 20% 17% 4	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	31% 24% 29% 15% 2	220
	11th to 20th	Day	31% 31% 26% 9% 2	220
	21st to end	Day	29% 29% 29% 8% 4	260
February	1st to 10th	Day	32% 24% 30% 14% 1	419
	11th to 20th	Day	30% 29% 32% 9% 1	536
	21st to end	Day	30% 27% 29% 10% 4	446
March	1st to 10th	Day	28% 24% 33% 12% 2	540
	11th to 20th	Day	28% 28% 30% 12% 2 1	540
	21st to end	Day	35% 23% 29% 8% 4 1	594
April	1st to 10th	Day	32% 27% 26% 11% 4	540
	11th to 20th	Day	31% 23% 29% 12% 5%	532
	21st to end	Day	29% 21% 32% 12% 4 1	540
May	1st to 10th	Day	33% 20% 29% 12% 6% 1	507
	11th to 20th	Day	25% 20% 35% 14% 6% 1	527
	21st to end	Day	21% 16% 31% 23% 8% 2	573
June	1st to 10th	Day	20% 14% 33% 22% 9% 2	530
	11th to 20th	Day	19% 15% 36% 22% 7% 1	530
	21st to end	Day	16% 17% 30% 27% 9% 1	530
July	1st to 10th	Day	18% 9% 31% 30% 10% 2	525
	11th to 20th	Day	13% 9% 34% 29% 13% 2	524
	21st to end	Day	16% 10% 39% 28% 7% 2	576
August	1st to 10th	Day	14% 9% 32% 32% 9% 4	526
	11th to 20th	Day	14% 8% 31% 28% 15% 4	519
	21st to end	Day	12% 12% 33% 25% 13% 6%	583
September	1st to 10th	Day	20% 11% 26% 24% 16% 3	530
	11th to 20th	Day	13% 12% 29% 26% 12% 8%	530
	21st to end	Day	21% 12% 36% 18% 10% 3	530
October	1st to 10th	Day	25% 13% 26% 19% 12% 5%	530
	11th to 20th	Day	20% 19% 31% 21% 8% 2	512
	21st to end	Day	25% 17% 31% 18% 7% 2	462
November	1st to 10th	Day	22% 18% 30% 21% 8% 2	425
	11th to 20th	Day	25% 24% 27% 19% 5%	430
	21st to end	Day	27% 22% 30% 15% 6% 1	418
December	1st to 10th	Day	24% 26% 30% 15% 5%	220
	11th to 20th	Day	36% 25% 28% 10% 2	220
	21st to end	Day	30% 23% 27% 15% 4 1	242
January	1st to 10th	Night	23% 22% 37% 15% 3	840
	11th to 20th	Night	29% 20% 32% 17% 2	840
	21st to end	Night	23% 23% 32% 19% 2	924
February	1st to 10th	Night	23% 20% 35% 20% 2	840
	11th to 20th	Night	26% 22% 36% 14% 1	823
	21st to end	Night	26% 23% 34% 15% 2	692
March	1st to 10th	Night	27% 20% 34% 17% 3	840
	11th to 20th	Night	25% 20% 33% 18% 3	840
	21st to end	Night	25% 23% 34% 15% 3	924
April	1st to 10th	Night	25% 22% 33% 18% 3	840
	11th to 20th	Night	23% 21% 33% 19% 3	831
	21st to end	Night	22% 19% 36% 18% 5%	707
May	1st to 10th	Night	26% 18% 30% 20% 5%	604
	11th to 20th	Night	20% 18% 38% 20% 4	514
	21st to end	Night	21% 7% 31% 33% 7%	433
June	1st to 10th	Night	21% 6% 33% 31% 9%	400
	11th to 20th	Night	20% 6% 33% 33% 8%	400
	21st to end	Night	14% 7% 34% 38% 7%	400
July	1st to 10th	Night	14% 4 32% 37% 13%	390
	11th to 20th	Night	14% 3 27% 41% 14% 1	388
	21st to end	Night	15% 7% 29% 39% 9%	438
August	1st to 10th	Night	12% 4 31% 40% 12% 1	493
	11th to 20th	Night	13% 5% 25% 39% 16% 1	750
	21st to end	Night	14% 5% 28% 35% 16% 2	880
September	1st to 10th	Night	16% 6% 32% 33% 12% 2	800
	11th to 20th	Night	17% 6% 26% 31% 17% 3	800
	21st to end	Night	21% 8% 28% 28% 15% 1	800
October	1st to 10th	Night	23% 9% 27% 26% 13% 2	800
	11th to 20th	Night	20% 15% 31% 25% 9% 1	800
	21st to end	Night	28% 12% 32% 22% 6%	880
November	1st to 10th	Night	17% 15% 34% 24% 9% 1	820
	11th to 20th	Night	24% 19% 32% 19% 6% 1	840
	21st to end	Night	22% 19% 31% 22% 5%	840
December	1st to 10th	Night	27% 18% 30% 20% 5% 1	840
	11th to 20th	Night	26% 21% 31% 20% 2	840
	21st to end	Night	28% 18% 35% 16% 2	924

Page generated at 2026-04-29 02:21:46. Version ac07

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