Space Hut Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Space Hut 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	9% 9% 3 9% 6% 5% 5% 4 6% 8% 35%	135636
	Night	8% 9% 4 10% 6% 6% 5% 4 6% 8% 34%	135490
Transparency	Day	45% 6% 17% 23% 9%	135335
	Night	47% 6% 16% 21% 9% 1	135372
Seeing	Day	13% 7% 25% 30% 19% 7%	17313
	Night	12% 6% 29% 35% 15% 2	26492

By Month

Percentage Cloud Cover NW (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	7% 13% 5% 12% 7% 5% 6% 6% 7% 9% 24%	4125
	11th to 20th	Day	2 6% 2 10% 8% 7% 7% 5% 8% 10% 34%	4119
	21st to end	Day	6% 10% 3 10% 7% 6% 6% 4 6% 8% 35%	4811
February	1st to 10th	Day	8% 12% 4 13% 9% 5% 6% 5% 6% 8% 25%	1680
	11th to 20th	Day	5% 12% 6% 13% 7% 6% 6% 5% 6% 7% 28%	1803
	21st to end	Day	4 13% 5% 12% 9% 6% 6% 5% 6% 8% 27%	1594
March	1st to 10th	Day	4 9% 4 12% 8% 5% 6% 5% 7% 10% 30%	4618
	11th to 20th	Day	5% 12% 4 10% 6% 5% 5% 4 5% 9% 34%	5101
	21st to end	Day	8% 13% 5% 15% 6% 5% 4 4 6% 8% 25%	5642
April	1st to 10th	Day	8% 11% 4 8% 6% 6% 6% 4 6% 8% 31%	2641
	11th to 20th	Day	10% 11% 4 8% 6% 5% 6% 4 7% 8% 31%	2700
	21st to end	Day	11% 10% 3 9% 5% 5% 5% 4 7% 7% 33%	2730
May	1st to 10th	Day	11% 8% 3 9% 5% 5% 5% 4 5% 6% 39%	6642
	11th to 20th	Day	14% 11% 3 8% 6% 6% 6% 4 6% 8% 27%	6734
	21st to end	Day	10% 8% 3 7% 5% 6% 5% 4 6% 8% 40%	7405
June	1st to 10th	Day	14% 9% 3 8% 6% 5% 5% 5% 6% 8% 32%	3000
	11th to 20th	Day	19% 9% 3 9% 7% 6% 6% 4 7% 8% 23%	3000
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 11% 36%	3000
July	1st to 10th	Day	8% 5% 2 5% 5% 4 5% 4 7% 10% 46%	6780
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 7% 9% 42%	6780
	21st to end	Day	11% 6% 2 7% 5% 4 5% 4 6% 8% 42%	7376
August	1st to 10th	Day	11% 6% 3 6% 4 4 5% 4 7% 9% 39%	4691
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 5% 7% 11% 42%	4256
	21st to end	Day	11% 4 2 6% 4 4 5% 4 7% 9% 45%	4664
September	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 5% 9% 43%	2548
	11th to 20th	Day	13% 8% 2 5% 4 4 4 4 6% 8% 42%	2200
	21st to end	Day	8% 7% 3 7% 4 5% 5% 4 6% 8% 44%	2200
October	1st to 10th	Day	10% 8% 3 9% 6% 6% 4 4 6% 6% 39%	3374
	11th to 20th	Day	10% 8% 4 8% 6% 4 4 4 6% 9% 36%	3006
	21st to end	Day	7% 12% 4 8% 5% 5% 5% 4 6% 8% 38%	3119
November	1st to 10th	Day	10% 12% 5% 10% 6% 6% 5% 4 6% 8% 27%	1648
	11th to 20th	Day	6% 12% 4 13% 8% 5% 5% 4 6% 6% 31%	1532
	21st to end	Day	5% 12% 6% 12% 7% 5% 6% 4 6% 8% 29%	1470
December	1st to 10th	Day	7% 15% 5% 11% 7% 7% 7% 5% 6% 8% 22%	2360
	11th to 20th	Day	8% 13% 5% 11% 8% 6% 7% 5% 7% 8% 21%	2712
	21st to end	Day	3 6% 3 9% 7% 6% 6% 5% 6% 8% 42%	3575
January	1st to 10th	Night	7% 11% 5% 13% 8% 8% 7% 5% 6% 7% 24%	8768
	11th to 20th	Night	2 7% 3 10% 7% 6% 5% 5% 6% 7% 41%	8779
	21st to end	Night	6% 11% 4 11% 7% 5% 5% 4 6% 8% 34%	9413
February	1st to 10th	Night	5% 10% 5% 13% 9% 7% 7% 5% 5% 7% 27%	2940
	11th to 20th	Night	5% 12% 4 10% 6% 7% 7% 5% 7% 7% 30%	2703
	21st to end	Night	4 11% 3 12% 8% 7% 6% 5% 6% 8% 30%	2211
March	1st to 10th	Night	4 10% 5% 12% 6% 5% 6% 5% 7% 10% 33%	5496
	11th to 20th	Night	4 9% 4 11% 8% 6% 6% 5% 7% 9% 31%	5118
	21st to end	Night	10% 13% 6% 14% 7% 6% 5% 4 6% 6% 24%	5571
April	1st to 10th	Night	7% 10% 3 8% 7% 6% 6% 5% 8% 8% 32%	1979
	11th to 20th	Night	9% 11% 4 10% 7% 6% 6% 5% 7% 7% 28%	1871
	21st to end	Night	11% 11% 3 7% 5% 5% 5% 4 5% 8% 35%	1890
May	1st to 10th	Night	16% 7% 3 6% 5% 4 4 4 5% 5% 41%	3341
	11th to 20th	Night	13% 10% 4 10% 7% 6% 6% 4 6% 7% 26%	3159
	21st to end	Night	12% 8% 3 7% 6% 5% 5% 4 6% 8% 35%	3470
June	1st to 10th	Night	14% 9% 4 8% 6% 5% 6% 4 6% 8% 30%	1400
	11th to 20th	Night	17% 9% 3 8% 8% 7% 6% 6% 6% 9% 22%	1400
	21st to end	Night	9% 7% 3 8% 5% 4 6% 4 7% 9% 38%	1343
July	1st to 10th	Night	7% 6% 2 7% 5% 5% 5% 5% 6% 8% 44%	3180
	11th to 20th	Night	12% 6% 2 7% 6% 5% 5% 4 6% 10% 37%	3180
	21st to end	Night	12% 6% 2 5% 4 4 5% 4 6% 10% 42%	3467
August	1st to 10th	Night	14% 5% 2 6% 5% 4 5% 4 5% 8% 42%	2444
	11th to 20th	Night	12% 7% 3 6% 4 5% 5% 5% 6% 9% 39%	2798
	21st to end	Night	11% 4 2 6% 5% 4 5% 4 7% 9% 44%	3245
September	1st to 10th	Night	11% 5% 3 7% 4 4 4 3 5% 8% 47%	1848
	11th to 20th	Night	11% 6% 2 6% 4 3 4 4 6% 8% 46%	2200
	21st to end	Night	9% 6% 3 7% 5% 4 5% 4 6% 7% 46%	2200
October	1st to 10th	Night	8% 7% 3 8% 5% 5% 5% 4 7% 8% 41%	3819
	11th to 20th	Night	9% 7% 2 6% 5% 4 5% 4 7% 10% 40%	4139
	21st to end	Night	6% 9% 4 9% 6% 6% 5% 4 6% 9% 37%	4648
November	1st to 10th	Night	12% 15% 5% 9% 6% 5% 5% 4 5% 6% 28%	2870
	11th to 20th	Night	6% 14% 6% 10% 7% 6% 5% 4 6% 7% 27%	3087
	21st to end	Night	5% 12% 5% 11% 8% 6% 6% 5% 6% 7% 29%	3150
December	1st to 10th	Night	8% 16% 5% 12% 8% 7% 6% 4 6% 7% 22%	5040
	11th to 20th	Night	7% 14% 6% 14% 8% 6% 6% 5% 7% 8% 21%	5700
	21st to end	Night	3 7% 3 9% 6% 6% 6% 5% 6% 8% 42%	7623

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	56% 5% 11% 17% 11%	4125
	11th to 20th	Day	44% 5% 15% 16% 19% 1	4140
	21st to end	Day	47% 6% 20% 22% 5%	4812
February	1st to 10th	Day	56% 5% 14% 15% 9% 1	1680
	11th to 20th	Day	53% 6% 15% 16% 10%	1812
	21st to end	Day	53% 6% 11% 21% 8%	1594
March	1st to 10th	Day	47% 6% 18% 20% 10%	4618
	11th to 20th	Day	47% 5% 14% 23% 10%	5102
	21st to end	Day	56% 6% 9% 23% 7%	5642
April	1st to 10th	Day	48% 7% 16% 20% 8%	2641
	11th to 20th	Day	48% 6% 15% 22% 9%	2700
	21st to end	Day	47% 6% 15% 24% 7% 1	2730
May	1st to 10th	Day	44% 5% 10% 24% 16% 1	6642
	11th to 20th	Day	52% 7% 11% 24% 6%	6738
	21st to end	Day	40% 6% 21% 22% 11% 1	7406
June	1st to 10th	Day	48% 6% 14% 22% 9% 1	3000
	11th to 20th	Day	56% 8% 16% 16% 4	3000
	21st to end	Day	40% 9% 23% 21% 7% 1	3000
July	1st to 10th	Day	33% 7% 21% 28% 11% 1	6706
	11th to 20th	Day	37% 7% 18% 29% 10%	6699
	21st to end	Day	38% 7% 22% 25% 8%	7169
August	1st to 10th	Day	38% 8% 20% 31% 2	4673
	11th to 20th	Day	34% 8% 24% 26% 8%	4297
	21st to end	Day	35% 6% 27% 26% 5%	4663
September	1st to 10th	Day	37% 7% 19% 27% 7% 2	2548
	11th to 20th	Day	39% 6% 19% 29% 8%	2200
	21st to end	Day	37% 8% 18% 27% 8% 2	2200
October	1st to 10th	Day	44% 6% 21% 24% 6%	3374
	11th to 20th	Day	44% 5% 15% 26% 10%	3006
	21st to end	Day	44% 6% 18% 28% 4	3119
November	1st to 10th	Day	54% 6% 16% 17% 7% 1	1648
	11th to 20th	Day	53% 5% 16% 19% 6%	1532
	21st to end	Day	52% 7% 16% 19% 6% 1	1470
December	1st to 10th	Day	59% 7% 17% 12% 4 1	2360
	11th to 20th	Day	58% 6% 17% 15% 4	2714
	21st to end	Day	40% 4 13% 28% 13% 1	3575
January	1st to 10th	Night	57% 5% 12% 14% 11% 1	8769
	11th to 20th	Night	42% 5% 17% 18% 17% 2	8820
	21st to end	Night	48% 5% 21% 19% 7%	9413
February	1st to 10th	Night	55% 5% 12% 17% 9% 1	2940
	11th to 20th	Night	49% 6% 14% 18% 13% 1	2704
	21st to end	Night	49% 6% 12% 22% 10% 1	2211
March	1st to 10th	Night	45% 5% 17% 22% 11%	5496
	11th to 20th	Night	47% 5% 16% 21% 10% 1	5118
	21st to end	Night	58% 6% 9% 18% 9%	5571
April	1st to 10th	Night	46% 7% 13% 20% 12% 1	1979
	11th to 20th	Night	52% 7% 11% 19% 10% 2	1871
	21st to end	Night	46% 6% 11% 25% 12% 1	1890
May	1st to 10th	Night	44% 4 8% 23% 17% 3	3340
	11th to 20th	Night	54% 7% 13% 19% 7%	3159
	21st to end	Night	44% 7% 16% 23% 9% 1	3470
June	1st to 10th	Night	50% 6% 13% 20% 10% 1	1400
	11th to 20th	Night	56% 8% 14% 16% 5%	1400
	21st to end	Night	40% 9% 22% 23% 6% 1	1343
July	1st to 10th	Night	36% 6% 22% 21% 14% 1	3145
	11th to 20th	Night	42% 6% 14% 30% 8% 1	3138
	21st to end	Night	36% 7% 23% 27% 7%	3369
August	1st to 10th	Night	40% 7% 20% 30% 2	2437
	11th to 20th	Night	40% 8% 21% 23% 8%	2823
	21st to end	Night	36% 6% 23% 28% 6%	3245
September	1st to 10th	Night	35% 6% 18% 28% 11% 2	1848
	11th to 20th	Night	35% 6% 17% 30% 10% 2	2200
	21st to end	Night	36% 7% 15% 26% 13% 2	2200
October	1st to 10th	Night	39% 6% 20% 27% 7%	3819
	11th to 20th	Night	38% 6% 14% 34% 7% 1	4139
	21st to end	Night	42% 6% 22% 25% 5%	4648
November	1st to 10th	Night	56% 6% 10% 20% 7%	2870
	11th to 20th	Night	54% 6% 13% 19% 7% 1	3087
	21st to end	Night	52% 7% 16% 18% 6% 1	3150
December	1st to 10th	Night	62% 6% 15% 12% 5% 1	5040
	11th to 20th	Night	59% 6% 18% 12% 5%	5697
	21st to end	Night	40% 4 15% 23% 15% 2	7623

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	12% 5% 31% 31% 18% 4	220
	11th to 20th	Day	9% 10% 36% 28% 14% 3	220
	21st to end	Day	11% 9% 36% 30% 10% 4	242
February	1st to 10th	Day	11% 8% 31% 34% 13% 3	220
	11th to 20th	Day	10% 6% 31% 32% 17% 4	308
	21st to end	Day	6% 8% 33% 28% 16% 8%	310
March	1st to 10th	Day	14% 6% 28% 32% 17% 4	540
	11th to 20th	Day	10% 5% 28% 35% 16% 6%	540
	21st to end	Day	12% 5% 27% 33% 19% 4	594
April	1st to 10th	Day	11% 8% 25% 33% 19% 5%	540
	11th to 20th	Day	14% 8% 20% 30% 20% 7%	532
	21st to end	Day	16% 8% 19% 30% 21% 7%	540
May	1st to 10th	Day	12% 9% 22% 33% 19% 6%	683
	11th to 20th	Day	12% 6% 22% 33% 20% 8%	725
	21st to end	Day	15% 5% 19% 31% 19% 10%	789
June	1st to 10th	Day	17% 9% 22% 32% 16% 5%	730
	11th to 20th	Day	20% 8% 22% 23% 19% 8%	730
	21st to end	Day	14% 5% 19% 28% 24% 11%	730
July	1st to 10th	Day	11% 4 15% 33% 27% 9%	721
	11th to 20th	Day	11% 5% 20% 30% 24% 10%	718
	21st to end	Day	10% 5% 18% 31% 27% 10%	794
August	1st to 10th	Day	11% 4 20% 29% 24% 12%	625
	11th to 20th	Day	11% 4 25% 31% 23% 6%	517
	21st to end	Day	11% 6% 21% 30% 22% 10%	583
September	1st to 10th	Day	13% 9% 24% 27% 19% 7%	530
	11th to 20th	Day	17% 7% 22% 31% 18% 5%	530
	21st to end	Day	11% 15% 31% 26% 13% 4	530
October	1st to 10th	Day	14% 7% 33% 27% 14% 5%	395
	11th to 20th	Day	12% 11% 32% 30% 12% 3	330
	21st to end	Day	15% 12% 36% 23% 11% 2	363
November	1st to 10th	Day	18% 7% 33% 30% 11% 2	330
	11th to 20th	Day	10% 6% 38% 33% 11% 2	252
	21st to end	Day	5% 8% 37% 30% 13% 6%	220
December	1st to 10th	Day	11% 7% 33% 32% 14% 3	220
	11th to 20th	Day	10% 10% 33% 34% 11% 3	220
	21st to end	Day	9% 6% 25% 37% 18% 5%	242
January	1st to 10th	Night	10% 7% 34% 35% 12% 2	1050
	11th to 20th	Night	9% 9% 36% 31% 13% 1	1050
	21st to end	Night	13% 10% 36% 29% 11% 2	1073
February	1st to 10th	Night	9% 9% 27% 36% 17% 3	840
	11th to 20th	Night	9% 5% 34% 36% 15% 1	824
	21st to end	Night	8% 6% 30% 33% 18% 5%	692
March	1st to 10th	Night	10% 5% 30% 38% 14% 3	840
	11th to 20th	Night	12% 5% 31% 35% 13% 3	840
	21st to end	Night	13% 6% 27% 36% 15% 2	924
April	1st to 10th	Night	10% 7% 27% 35% 17% 3	719
	11th to 20th	Night	12% 7% 28% 36% 16% 1	623
	21st to end	Night	16% 7% 24% 35% 16% 2	630
May	1st to 10th	Night	16% 6% 23% 37% 17% 2	453
	11th to 20th	Night	11% 6% 24% 38% 18% 3	394
	21st to end	Night	19% 7% 19% 34% 19% 2	433
June	1st to 10th	Night	19% 7% 23% 35% 14% 2	400
	11th to 20th	Night	20% 5% 21% 32% 20% 3	400
	21st to end	Night	11% 4 21% 36% 25% 4	400
July	1st to 10th	Night	14% 3 16% 43% 24% 1	390
	11th to 20th	Night	11% 4 20% 43% 22% 2	388
	21st to end	Night	12% 3 16% 41% 25% 3	438
August	1st to 10th	Night	13% 2 17% 33% 29% 5%	398
	11th to 20th	Night	13% 4 17% 40% 24% 3	527
	21st to end	Night	12% 3 19% 40% 25% 1	660
September	1st to 10th	Night	13% 3 21% 38% 24% 2	622
	11th to 20th	Night	14% 4 21% 42% 18% 1	800
	21st to end	Night	11% 6% 31% 38% 13% 2	800
October	1st to 10th	Night	14% 6% 28% 39% 13% 1	800
	11th to 20th	Night	13% 7% 32% 35% 12% 2	800
	21st to end	Night	12% 9% 35% 32% 11%	904
November	1st to 10th	Night	19% 8% 34% 30% 8% 2	1025
	11th to 20th	Night	13% 8% 37% 30% 10% 3	1050
	21st to end	Night	10% 6% 38% 33% 11% 2	1050
December	1st to 10th	Night	12% 9% 36% 27% 12% 3	1050
	11th to 20th	Night	12% 7% 34% 32% 13% 2	1050
	21st to end	Night	10% 5% 33% 34% 15% 3	1155

Page generated at 2026-04-29 00:21:43. Version ac07

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