Justin's Space Pictures Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Justin's Space Pictures Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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	15% 7% 2 6% 4 4 4 4 6% 7% 40%	126480
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 43%	122889
Transparency	Day	42% 4 11% 23% 17% 3	130009
	Night	41% 3 10% 24% 18% 4	127435
Seeing	Day	23% 16% 29% 20% 9% 3	16227
	Night	20% 15% 30% 25% 9% 1	25431

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	13% 7% 2 4 3 3 3 3 5% 6% 50%	3597
	11th to 20th	Day	14% 8% 3 8% 5% 4 3 2 4 5% 43%	3634
	21st to end	Day	19% 9% 3 5% 4 3 3 3 4 5% 42%	4466
February	1st to 10th	Day	15% 8% 3 7% 4 4 4 3 5% 7% 39%	1800
	11th to 20th	Day	17% 8% 2 6% 3 4 4 4 5% 6% 41%	1933
	21st to end	Day	17% 10% 4 6% 4 3 5% 2 4 6% 40%	1650
March	1st to 10th	Day	21% 6% 2 4 3 3 4 3 4 5% 46%	4476
	11th to 20th	Day	11% 7% 2 6% 5% 5% 4 4 5% 6% 46%	4925
	21st to end	Day	17% 6% 2 6% 4 3 4 3 5% 6% 44%	5831
April	1st to 10th	Day	17% 8% 2 6% 4 4 4 3 5% 6% 40%	2400
	11th to 20th	Day	15% 6% 2 5% 5% 4 4 4 6% 7% 42%	2374
	21st to end	Day	15% 6% 3 6% 4 4 4 3 7% 7% 40%	2400
May	1st to 10th	Day	25% 8% 2 7% 4 4 4 4 5% 8% 29%	5763
	11th to 20th	Day	25% 7% 3 6% 4 4 3 3 5% 7% 33%	6315
	21st to end	Day	19% 7% 2 5% 4 4 4 4 6% 8% 37%	6949
June	1st to 10th	Day	13% 6% 2 7% 4 5% 4 4 7% 8% 40%	2800
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 9% 39%	2800
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 8% 42%	2800
July	1st to 10th	Day	9% 5% 2 7% 6% 6% 6% 5% 8% 10% 36%	6360
	11th to 20th	Day	11% 8% 3 7% 6% 6% 6% 5% 8% 11% 30%	6360
	21st to end	Day	10% 6% 3 7% 5% 5% 5% 5% 7% 10% 37%	6866
August	1st to 10th	Day	18% 7% 3 7% 5% 6% 5% 4 7% 8% 32%	4183
	11th to 20th	Day	13% 6% 2 6% 4 4 6% 4 7% 10% 38%	3850
	21st to end	Day	10% 5% 2 5% 4 5% 4 5% 6% 9% 45%	4312
September	1st to 10th	Day	13% 5% 2 7% 5% 4 4 4 6% 6% 45%	2400
	11th to 20th	Day	13% 6% 2 4 3 3 4 3 5% 8% 49%	2349
	21st to end	Day	18% 7% 3 7% 5% 4 5% 3 4 7% 38%	2200
October	1st to 10th	Day	18% 6% 2 5% 3 4 3 4 4 7% 45%	1965
	11th to 20th	Day	16% 5% 1 4 4 3 3 3 3 7% 51%	1900
	21st to end	Day	17% 5% 2 6% 3 3 4 2 4 6% 47%	2005
November	1st to 10th	Day	12% 5% 1 4 4 4 3 3 4 6% 53%	1761
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 5% 6% 47%	1800
	21st to end	Day	15% 5% 2 5% 4 4 3 3 5% 7% 47%	1710
December	1st to 10th	Day	13% 7% 1 5% 3 3 4 4 6% 8% 45%	2600
	11th to 20th	Day	20% 10% 2 4 3 3 3 2 3 4 46%	2986
	21st to end	Day	16% 6% 2 5% 4 5% 5% 4 6% 8% 41%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 3 4 3 5% 6% 50%	6349
	11th to 20th	Night	15% 7% 2 6% 4 3 3 2 4 5% 50%	6246
	21st to end	Night	17% 8% 2 6% 4 4 4 3 4 6% 42%	6490
February	1st to 10th	Night	17% 9% 3 5% 4 3 4 3 5% 6% 41%	2600
	11th to 20th	Night	18% 8% 2 6% 4 3 3 3 6% 5% 42%	2353
	21st to end	Night	18% 8% 2 6% 3 4 3 3 4 5% 43%	1980
March	1st to 10th	Night	19% 9% 2 5% 3 3 2 3 4 5% 45%	5364
	11th to 20th	Night	12% 9% 3 6% 4 3 3 2 4 5% 49%	5030
	21st to end	Night	16% 7% 2 6% 5% 3 4 3 4 5% 43%	5100
April	1st to 10th	Night	17% 7% 3 7% 5% 3 4 3 5% 5% 40%	2000
	11th to 20th	Night	15% 8% 2 7% 4 4 4 3 5% 6% 43%	1975
	21st to end	Night	17% 6% 2 4 4 4 4 3 5% 6% 44%	2000
May	1st to 10th	Night	21% 8% 3 8% 5% 4 5% 4 6% 8% 28%	4174
	11th to 20th	Night	22% 9% 3 7% 5% 4 3 3 5% 7% 33%	3607
	21st to end	Night	21% 7% 2 7% 3 4 4 3 5% 8% 37%	3926
June	1st to 10th	Night	14% 5% 2 6% 5% 4 4 4 5% 9% 43%	1600
	11th to 20th	Night	12% 7% 2 6% 5% 5% 5% 4 6% 7% 41%	1600
	21st to end	Night	9% 5% 1 6% 4 5% 5% 4 8% 10% 42%	1600
July	1st to 10th	Night	8% 6% 3 8% 5% 6% 6% 5% 7% 9% 36%	3600
	11th to 20th	Night	11% 8% 3 8% 5% 5% 6% 5% 8% 10% 32%	3600
	21st to end	Night	11% 6% 2 7% 5% 4 5% 4 6% 9% 41%	3970
August	1st to 10th	Night	20% 7% 2 6% 4 5% 5% 4 6% 9% 32%	2933
	11th to 20th	Night	12% 7% 2 6% 5% 4 4 4 5% 7% 43%	3197
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 7% 51%	3586
September	1st to 10th	Night	15% 5% 2 6% 5% 4 3 4 4 6% 46%	2000
	11th to 20th	Night	11% 6% 2 5% 3 3 4 3 5% 7% 53%	2050
	21st to end	Night	20% 7% 2 6% 4 3 4 4 6% 7% 39%	2200
October	1st to 10th	Night	18% 6% 2 6% 3 3 3 3 5% 7% 44%	2277
	11th to 20th	Night	15% 5% 2 4 3 3 4 3 4 6% 52%	2280
	21st to end	Night	17% 6% 2 5% 3 4 3 3 4 6% 48%	2593
November	1st to 10th	Night	11% 5% 2 5% 3 4 3 3 5% 6% 53%	2537
	11th to 20th	Night	16% 6% 3 5% 4 3 3 3 4 4 48%	2600
	21st to end	Night	13% 6% 2 5% 5% 4 4 4 6% 6% 46%	2688
December	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 48%	4580
	11th to 20th	Night	22% 7% 2 5% 3 3 3 2 5% 7% 41%	5208
	21st to end	Night	18% 7% 3 6% 4 3 4 3 5% 6% 41%	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	36% 2 8% 27% 24% 3	3598
	11th to 20th	Day	45% 2 7% 23% 18% 5%	3664
	21st to end	Day	47% 2 11% 25% 14% 2	4466
February	1st to 10th	Day	45% 3 12% 26% 12% 2	1800
	11th to 20th	Day	45% 3 8% 24% 16% 3	1942
	21st to end	Day	47% 2 8% 23% 15% 5%	1650
March	1st to 10th	Day	43% 2 7% 25% 16% 8%	4479
	11th to 20th	Day	39% 2 7% 30% 17% 5%	4925
	21st to end	Day	42% 3 8% 18% 23% 6%	5831
April	1st to 10th	Day	45% 3 9% 22% 16% 5%	2400
	11th to 20th	Day	41% 4 11% 23% 17% 4	2374
	21st to end	Day	43% 3 9% 22% 20% 4	2400
May	1st to 10th	Day	54% 4 13% 19% 10% 1	5774
	11th to 20th	Day	53% 2 9% 23% 12% 1	6319
	21st to end	Day	46% 4 10% 24% 16% 1	6949
June	1st to 10th	Day	41% 5% 11% 25% 17% 2	2800
	11th to 20th	Day	42% 4 12% 26% 13% 3	2800
	21st to end	Day	39% 5% 13% 24% 18% 2	2800
July	1st to 10th	Day	40% 10% 14% 19% 15% 2	6290
	11th to 20th	Day	45% 8% 17% 19% 10% 1	6285
	21st to end	Day	41% 6% 10% 21% 21% 1	6669
August	1st to 10th	Day	49% 5% 12% 22% 10% 1	4170
	11th to 20th	Day	40% 6% 13% 26% 14% 1	3886
	21st to end	Day	33% 5% 12% 28% 19% 2	4312
September	1st to 10th	Day	40% 3 11% 21% 22% 4	2400
	11th to 20th	Day	34% 4 8% 26% 25% 3	2349
	21st to end	Day	49% 3 8% 19% 20% 2	2200
October	1st to 10th	Day	36% 2 9% 18% 29% 5%	3238
	11th to 20th	Day	26% 2 9% 24% 31% 8%	3140
	21st to end	Day	26% 2 11% 27% 28% 5%	3282
November	1st to 10th	Day	34% 2 12% 27% 22% 3	1761
	11th to 20th	Day	39% 3 8% 25% 23% 3	1800
	21st to end	Day	39% 3 12% 31% 14% 2	1710
December	1st to 10th	Day	37% 4 16% 26% 15% 2	2600
	11th to 20th	Day	45% 2 10% 30% 11% 3	2986
	21st to end	Day	43% 3 11% 23% 18% 2	3960
January	1st to 10th	Night	37% 1 7% 26% 22% 6%	6349
	11th to 20th	Night	40% 2 9% 25% 18% 7%	6291
	21st to end	Night	45% 1 8% 24% 19% 2	6490
February	1st to 10th	Night	45% 2 13% 24% 14% 2	2600
	11th to 20th	Night	45% 3 7% 21% 18% 5%	2355
	21st to end	Night	45% 2 8% 23% 17% 6%	1980
March	1st to 10th	Night	44% 2 7% 25% 14% 10%	5374
	11th to 20th	Night	40% 2 12% 26% 15% 5%	5031
	21st to end	Night	44% 3 6% 17% 24% 5%	5100
April	1st to 10th	Night	46% 2 9% 20% 19% 5%	2000
	11th to 20th	Night	43% 3 9% 21% 20% 4	1975
	21st to end	Night	41% 4 8% 21% 21% 5%	2000
May	1st to 10th	Night	53% 4 12% 18% 11% 2	4180
	11th to 20th	Night	53% 3 10% 19% 13% 1	3608
	21st to end	Night	47% 3 12% 22% 15% 2	3927
June	1st to 10th	Night	40% 5% 11% 22% 21% 2	1600
	11th to 20th	Night	41% 5% 12% 27% 13% 1	1600
	21st to end	Night	36% 5% 15% 27% 15% 2	1600
July	1st to 10th	Night	43% 8% 15% 21% 12% 1	3560
	11th to 20th	Night	45% 8% 19% 20% 8% 1	3552
	21st to end	Night	39% 6% 12% 23% 19% 1	3853
August	1st to 10th	Night	48% 6% 17% 18% 10% 1	2922
	11th to 20th	Night	41% 4 12% 29% 13% 1	3227
	21st to end	Night	32% 4 10% 29% 22% 2	3586
September	1st to 10th	Night	39% 3 12% 21% 21% 3	2000
	11th to 20th	Night	32% 3 10% 26% 25% 4	2050
	21st to end	Night	44% 4 8% 23% 20% 2	2200
October	1st to 10th	Night	38% 4 10% 24% 22% 3	3771
	11th to 20th	Night	25% 2 9% 28% 31% 6%	3779
	21st to end	Night	27% 2 10% 31% 25% 5%	4266
November	1st to 10th	Night	34% 3 11% 25% 22% 6%	2537
	11th to 20th	Night	40% 3 8% 23% 21% 6%	2600
	21st to end	Night	39% 3 11% 27% 18% 2	2688
December	1st to 10th	Night	37% 2 12% 30% 15% 3	4580
	11th to 20th	Night	45% 2 10% 24% 15% 4	5208
	21st to end	Night	46% 2 10% 21% 19% 3	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	31% 24% 30% 12% 4 1	200
	11th to 20th	Day	39% 24% 26% 10% 1	213
	21st to end	Day	31% 29% 25% 12% 2 1	330
February	1st to 10th	Day	30% 31% 27% 10% 2	300
	11th to 20th	Day	36% 25% 29% 9% 1	481
	21st to end	Day	32% 26% 30% 11% 2	414
March	1st to 10th	Day	32% 23% 28% 15% 3	500
	11th to 20th	Day	28% 26% 30% 12% 3 2	500
	21st to end	Day	28% 25% 31% 12% 4 1	550
April	1st to 10th	Day	30% 29% 27% 10% 4 1	500
	11th to 20th	Day	25% 24% 32% 14% 5% 1	492
	21st to end	Day	28% 19% 33% 14% 5% 1	500
May	1st to 10th	Day	33% 18% 27% 15% 6% 1	503
	11th to 20th	Day	26% 15% 34% 18% 6% 2	527
	21st to end	Day	21% 12% 25% 27% 13% 3	573
June	1st to 10th	Day	17% 14% 29% 27% 11% 3	530
	11th to 20th	Day	19% 13% 31% 25% 11% 2	530
	21st to end	Day	13% 10% 32% 29% 12% 3	530
July	1st to 10th	Day	13% 6% 26% 33% 18% 5%	525
	11th to 20th	Day	8% 5% 30% 33% 20% 4	524
	21st to end	Day	13% 6% 29% 32% 16% 5%	576
August	1st to 10th	Day	13% 5% 32% 30% 14% 6%	526
	11th to 20th	Day	14% 5% 22% 36% 18% 5%	519
	21st to end	Day	13% 8% 30% 25% 16% 8%	583
September	1st to 10th	Day	16% 10% 28% 24% 15% 7%	530
	11th to 20th	Day	16% 7% 27% 30% 13% 8%	530
	21st to end	Day	27% 12% 26% 21% 10% 5%	530
October	1st to 10th	Day	24% 10% 26% 20% 14% 5%	502
	11th to 20th	Day	20% 18% 27% 20% 11% 3	490
	21st to end	Day	19% 18% 34% 17% 11% 1	494
November	1st to 10th	Day	18% 16% 34% 18% 12% 2	395
	11th to 20th	Day	24% 22% 30% 18% 7%	400
	21st to end	Day	25% 20% 30% 18% 6% 1	310
December	1st to 10th	Day	27% 31% 29% 8% 5%	200
	11th to 20th	Day	35% 20% 31% 12% 2 1	200
	21st to end	Day	30% 16% 30% 16% 6%	220
January	1st to 10th	Night	23% 25% 32% 16% 3	800
	11th to 20th	Night	26% 21% 28% 21% 3	800
	21st to end	Night	19% 24% 35% 20% 2	880
February	1st to 10th	Night	22% 22% 34% 21% 1	800
	11th to 20th	Night	28% 28% 30% 13% 1	783
	21st to end	Night	26% 23% 30% 18% 2	660
March	1st to 10th	Night	23% 23% 32% 17% 4	800
	11th to 20th	Night	24% 23% 30% 17% 6%	800
	21st to end	Night	22% 19% 39% 15% 4	880
April	1st to 10th	Night	24% 24% 33% 16% 4	800
	11th to 20th	Night	22% 17% 36% 21% 4	791
	21st to end	Night	22% 17% 35% 22% 5%	800
May	1st to 10th	Night	22% 15% 35% 22% 6%	655
	11th to 20th	Night	19% 14% 37% 25% 5%	413
	21st to end	Night	19% 8% 26% 36% 9% 1	433
June	1st to 10th	Night	18% 6% 32% 35% 9% 1	400
	11th to 20th	Night	13% 6% 33% 38% 11% 1	400
	21st to end	Night	11% 5% 31% 42% 11%	400
July	1st to 10th	Night	9% 3 31% 41% 15% 2	390
	11th to 20th	Night	9% 3 24% 46% 17% 1	388
	21st to end	Night	11% 4 29% 38% 17%	457
August	1st to 10th	Night	12% 3 19% 42% 21% 2	602
	11th to 20th	Night	14% 5% 20% 39% 19% 3	790
	21st to end	Night	14% 3 23% 38% 20% 2	880
September	1st to 10th	Night	17% 5% 28% 33% 15% 3	800
	11th to 20th	Night	13% 6% 23% 34% 21% 3	800
	21st to end	Night	24% 7% 25% 28% 15% 1	800
October	1st to 10th	Night	22% 8% 27% 25% 15% 3	773
	11th to 20th	Night	17% 14% 28% 28% 12% 1	760
	21st to end	Night	20% 13% 36% 22% 9%	836
November	1st to 10th	Night	15% 13% 35% 26% 10% 1	780
	11th to 20th	Night	20% 17% 30% 24% 8%	800
	21st to end	Night	19% 19% 34% 21% 7% 1	800
December	1st to 10th	Night	26% 18% 30% 19% 6% 1	800
	11th to 20th	Night	22% 20% 32% 22% 5%	800
	21st to end	Night	22% 19% 32% 25% 2	880

Page generated at 2025-10-01 01:39:04. Version ac07

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