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 2025-01-07.

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%	108907
	Night	8% 10% 4 10% 6% 6% 5% 4 6% 8% 33%	108619
Transparency	Day	45% 6% 17% 23% 8%	108650
	Night	47% 6% 16% 21% 9% 1	108522
Seeing	Day	13% 7% 24% 31% 19% 7%	15621
	Night	12% 6% 28% 35% 16% 2	24751

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	4 12% 4 14% 9% 6% 7% 6% 7% 8% 24%	2261
	11th to 20th	Day	4 10% 3 9% 7% 6% 6% 5% 9% 10% 31%	2199
	21st to end	Day	6% 13% 4 10% 6% 5% 5% 3 5% 7% 36%	2584
February	1st to 10th	Day	8% 13% 5% 13% 8% 5% 5% 5% 6% 7% 24%	1520
	11th to 20th	Day	5% 12% 7% 13% 6% 6% 6% 5% 6% 6% 27%	1627
	21st to end	Day	4 12% 5% 12% 9% 5% 7% 5% 6% 7% 27%	1446
March	1st to 10th	Day	4 11% 5% 14% 8% 5% 6% 4 6% 9% 27%	3138
	11th to 20th	Day	4 12% 3 9% 5% 4 4 4 5% 11% 39%	3481
	21st to end	Day	7% 12% 6% 17% 7% 6% 5% 4 6% 7% 24%	3846
April	1st to 10th	Day	8% 11% 4 8% 6% 6% 6% 4 6% 8% 30%	2389
	11th to 20th	Day	11% 12% 4 8% 6% 5% 6% 4 6% 8% 31%	2440
	21st to end	Day	12% 9% 3 8% 6% 5% 5% 4 7% 8% 32%	2470
May	1st to 10th	Day	14% 10% 4 10% 6% 5% 4 4 5% 7% 31%	4628
	11th to 20th	Day	11% 11% 3 8% 6% 6% 6% 5% 6% 8% 30%	4694
	21st to end	Day	12% 9% 3 9% 6% 6% 6% 4 7% 9% 29%	5161
June	1st to 10th	Day	15% 9% 3 8% 6% 5% 5% 5% 6% 7% 31%	2850
	11th to 20th	Day	19% 9% 3 9% 7% 6% 6% 4 7% 8% 23%	2850
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 4 7% 10% 36%	2850
July	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 4 6% 8% 47%	4740
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 4 6% 9% 47%	4740
	21st to end	Day	11% 6% 3 6% 4 4 4 4 6% 8% 45%	5138
August	1st to 10th	Day	11% 6% 3 6% 4 4 5% 4 7% 9% 40%	4546
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 7% 11% 43%	4123
	21st to end	Day	11% 4 2 6% 4 4 5% 3 7% 9% 44%	4521
September	1st to 10th	Day	11% 6% 2 7% 4 4 4 4 5% 9% 42%	2421
	11th to 20th	Day	13% 8% 2 6% 4 4 4 4 6% 8% 40%	2090
	21st to end	Day	9% 7% 2 7% 4 5% 5% 4 6% 8% 43%	2090
October	1st to 10th	Day	10% 8% 3 9% 6% 6% 4 4 6% 6% 39%	3271
	11th to 20th	Day	11% 8% 4 8% 6% 4 4 4 6% 9% 36%	2914
	21st to end	Day	7% 12% 4 8% 5% 5% 5% 4 6% 8% 37%	3022
November	1st to 10th	Day	10% 12% 5% 10% 7% 6% 5% 4 6% 8% 27%	1568
	11th to 20th	Day	6% 12% 5% 13% 8% 5% 5% 3 6% 6% 30%	1459
	21st to end	Day	5% 12% 6% 13% 7% 5% 6% 4 6% 8% 30%	1400
December	1st to 10th	Day	7% 15% 4 11% 7% 7% 7% 5% 6% 8% 22%	2290
	11th to 20th	Day	8% 13% 5% 11% 8% 6% 7% 5% 7% 7% 22%	2642
	21st to end	Day	3 6% 3 9% 7% 6% 6% 5% 6% 8% 43%	3498
January	1st to 10th	Night	3 9% 5% 15% 9% 8% 8% 5% 7% 7% 24%	4817
	11th to 20th	Night	3 8% 3 10% 9% 7% 6% 6% 7% 7% 34%	4699
	21st to end	Night	6% 13% 4 11% 6% 5% 5% 4 5% 7% 33%	5088
February	1st to 10th	Night	5% 11% 5% 14% 9% 7% 7% 5% 5% 7% 26%	2660
	11th to 20th	Night	5% 12% 5% 10% 6% 6% 6% 5% 7% 8% 30%	2440
	21st to end	Night	4 10% 4 12% 8% 6% 6% 5% 6% 8% 31%	2007
March	1st to 10th	Night	3 11% 6% 13% 6% 5% 6% 5% 7% 9% 29%	3736
	11th to 20th	Night	5% 8% 4 9% 6% 5% 5% 4 7% 10% 37%	3498
	21st to end	Night	6% 12% 6% 16% 8% 6% 6% 5% 7% 7% 22%	3803
April	1st to 10th	Night	7% 10% 3 8% 7% 6% 6% 5% 8% 7% 32%	1791
	11th to 20th	Night	10% 11% 4 10% 7% 7% 5% 5% 7% 6% 28%	1691
	21st to end	Night	12% 11% 3 7% 5% 5% 5% 4 5% 9% 34%	1710
May	1st to 10th	Night	23% 9% 4 8% 6% 5% 4 3 5% 4 30%	2330
	11th to 20th	Night	11% 10% 4 10% 7% 5% 5% 4 7% 7% 28%	2199
	21st to end	Night	13% 9% 3 8% 7% 6% 6% 4 6% 9% 28%	2414
June	1st to 10th	Night	15% 10% 4 8% 6% 5% 6% 4 7% 8% 29%	1330
	11th to 20th	Night	17% 8% 3 8% 8% 7% 6% 6% 5% 8% 23%	1330
	21st to end	Night	10% 6% 3 7% 5% 4 6% 4 7% 10% 38%	1276
July	1st to 10th	Night	9% 6% 2 7% 5% 5% 5% 5% 5% 7% 44%	2220
	11th to 20th	Night	9% 6% 2 6% 6% 5% 5% 4 7% 11% 40%	2220
	21st to end	Night	13% 7% 2 4 4 3 4 4 6% 11% 43%	2414
August	1st to 10th	Night	14% 5% 2 6% 4 4 5% 3 5% 8% 43%	2369
	11th to 20th	Night	12% 7% 3 6% 4 5% 5% 5% 6% 9% 40%	2711
	21st to end	Night	12% 4 2 6% 5% 4 5% 4 6% 9% 43%	3146
September	1st to 10th	Night	11% 6% 3 7% 4 4 4 3 5% 7% 46%	1755
	11th to 20th	Night	12% 7% 2 6% 4 3 4 3 6% 8% 45%	2090
	21st to end	Night	9% 6% 2 7% 5% 4 5% 4 6% 7% 45%	2090
October	1st to 10th	Night	8% 7% 3 8% 5% 5% 5% 4 7% 8% 40%	3702
	11th to 20th	Night	10% 7% 2 6% 5% 4 5% 4 8% 10% 39%	4011
	21st to end	Night	6% 9% 4 9% 6% 5% 5% 5% 6% 9% 37%	4504
November	1st to 10th	Night	12% 16% 5% 9% 6% 5% 5% 4 5% 6% 27%	2730
	11th to 20th	Night	6% 15% 6% 10% 7% 6% 5% 4 6% 7% 27%	2940
	21st to end	Night	5% 12% 5% 11% 8% 7% 7% 5% 6% 7% 28%	3000
December	1st to 10th	Night	9% 16% 5% 12% 7% 7% 6% 4 6% 7% 22%	4890
	11th to 20th	Night	7% 14% 6% 14% 8% 6% 6% 5% 7% 8% 21%	5550
	21st to end	Night	2 7% 3 9% 6% 6% 6% 5% 6% 8% 42%	7458

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	55% 6% 15% 19% 5%	2261
	11th to 20th	Day	46% 4 12% 17% 19% 1	2220
	21st to end	Day	48% 5% 18% 24% 5%	2584
February	1st to 10th	Day	57% 5% 14% 15% 8%	1520
	11th to 20th	Day	53% 6% 15% 16% 8%	1636
	21st to end	Day	52% 6% 12% 21% 9%	1446
March	1st to 10th	Day	53% 6% 14% 20% 8%	3138
	11th to 20th	Day	41% 6% 19% 22% 12%	3482
	21st to end	Day	57% 7% 10% 21% 4	3846
April	1st to 10th	Day	49% 7% 15% 20% 8% 1	2389
	11th to 20th	Day	49% 6% 14% 22% 9%	2440
	21st to end	Day	47% 6% 16% 22% 7% 2	2470
May	1st to 10th	Day	51% 6% 10% 25% 7%	4628
	11th to 20th	Day	48% 8% 11% 25% 8%	4698
	21st to end	Day	49% 6% 18% 18% 8%	5162
June	1st to 10th	Day	50% 6% 14% 21% 9%	2850
	11th to 20th	Day	55% 8% 17% 16% 4	2850
	21st to end	Day	40% 9% 23% 21% 7% 1	2850
July	1st to 10th	Day	35% 7% 16% 28% 13% 1	4666
	11th to 20th	Day	33% 7% 18% 28% 13%	4659
	21st to end	Day	37% 6% 22% 24% 10%	4976
August	1st to 10th	Day	38% 8% 19% 32% 2	4528
	11th to 20th	Day	33% 8% 24% 27% 8%	4164
	21st to end	Day	36% 6% 28% 26% 4	4520
September	1st to 10th	Day	38% 7% 19% 26% 7% 2	2421
	11th to 20th	Day	41% 5% 19% 28% 7%	2090
	21st to end	Day	38% 8% 18% 26% 8% 2	2090
October	1st to 10th	Day	44% 6% 21% 24% 5%	3271
	11th to 20th	Day	45% 5% 15% 26% 10%	2914
	21st to end	Day	44% 6% 19% 27% 4	3022
November	1st to 10th	Day	54% 6% 16% 16% 6% 1	1568
	11th to 20th	Day	54% 5% 15% 19% 5%	1459
	21st to end	Day	52% 7% 17% 18% 5% 1	1400
December	1st to 10th	Day	58% 7% 18% 12% 4 1	2290
	11th to 20th	Day	58% 6% 18% 14% 4	2644
	21st to end	Day	39% 4 13% 28% 14% 1	3498
January	1st to 10th	Night	56% 6% 14% 16% 6% 1	4817
	11th to 20th	Night	47% 6% 13% 18% 15% 1	4740
	21st to end	Night	50% 4 18% 20% 7% 1	5088
February	1st to 10th	Night	56% 5% 12% 17% 7% 1	2660
	11th to 20th	Night	49% 6% 15% 18% 11% 1	2441
	21st to end	Night	49% 6% 13% 22% 10% 1	2007
March	1st to 10th	Night	50% 6% 14% 21% 9%	3736
	11th to 20th	Night	41% 5% 21% 20% 12% 1	3498
	21st to end	Night	57% 7% 12% 18% 6%	3803
April	1st to 10th	Night	46% 8% 13% 21% 12% 1	1791
	11th to 20th	Night	53% 7% 10% 19% 10% 2	1691
	21st to end	Night	46% 6% 12% 23% 12% 1	1710
May	1st to 10th	Night	57% 4 7% 21% 9% 1	2330
	11th to 20th	Night	50% 7% 11% 22% 10% 1	2199
	21st to end	Night	50% 8% 14% 17% 9% 1	2414
June	1st to 10th	Night	50% 6% 13% 20% 9% 1	1330
	11th to 20th	Night	56% 8% 14% 17% 5%	1330
	21st to end	Night	39% 9% 22% 23% 6% 1	1276
July	1st to 10th	Night	38% 7% 17% 21% 17% 1	2185
	11th to 20th	Night	37% 7% 16% 29% 10% 1	2178
	21st to end	Night	35% 6% 22% 28% 9%	2337
August	1st to 10th	Night	39% 7% 20% 31% 2	2362
	11th to 20th	Night	39% 8% 21% 24% 8%	2736
	21st to end	Night	36% 7% 24% 28% 5%	3146
September	1st to 10th	Night	37% 6% 18% 26% 11% 2	1755
	11th to 20th	Night	36% 6% 17% 30% 9% 2	2090
	21st to end	Night	36% 7% 15% 26% 13% 2	2090
October	1st to 10th	Night	39% 6% 20% 27% 7%	3702
	11th to 20th	Night	38% 6% 14% 35% 7%	4011
	21st to end	Night	42% 6% 22% 25% 5%	4504
November	1st to 10th	Night	56% 7% 11% 20% 7%	2730
	11th to 20th	Night	55% 6% 12% 19% 7% 1	2940
	21st to end	Night	53% 7% 16% 18% 5% 1	3000
December	1st to 10th	Night	61% 6% 15% 12% 5% 1	4890
	11th to 20th	Night	59% 6% 18% 11% 5%	5547
	21st to end	Night	39% 5% 15% 23% 16% 2	7458

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	10% 4 29% 31% 21% 4	192
	11th to 20th	Day	9% 9% 33% 29% 17% 4	180
	21st to end	Day	11% 8% 33% 32% 11% 5%	198
February	1st to 10th	Day	13% 8% 30% 33% 13% 2	180
	11th to 20th	Day	10% 6% 31% 31% 17% 5%	252
	21st to end	Day	6% 6% 30% 31% 17% 10%	258
March	1st to 10th	Day	12% 6% 28% 32% 18% 4	460
	11th to 20th	Day	10% 5% 27% 35% 17% 7%	460
	21st to end	Day	12% 4 25% 33% 21% 4	506
April	1st to 10th	Day	12% 8% 25% 34% 17% 5%	460
	11th to 20th	Day	15% 6% 18% 31% 22% 9%	452
	21st to end	Day	16% 8% 19% 30% 21% 7%	460
May	1st to 10th	Day	13% 8% 21% 33% 19% 6%	629
	11th to 20th	Day	12% 6% 22% 34% 20% 7%	675
	21st to end	Day	16% 5% 19% 30% 19% 10%	734
June	1st to 10th	Day	17% 8% 22% 31% 16% 5%	680
	11th to 20th	Day	20% 8% 23% 23% 19% 8%	680
	21st to end	Day	14% 5% 18% 28% 24% 11%	680
July	1st to 10th	Day	12% 3 15% 33% 27% 10%	671
	11th to 20th	Day	11% 4 19% 31% 25% 10%	668
	21st to end	Day	10% 4 18% 31% 27% 10%	739
August	1st to 10th	Day	11% 5% 20% 29% 24% 12%	580
	11th to 20th	Day	10% 4 23% 32% 25% 6%	477
	21st to end	Day	12% 6% 21% 31% 21% 9%	539
September	1st to 10th	Day	14% 10% 24% 27% 18% 7%	490
	11th to 20th	Day	18% 8% 24% 30% 16% 4	490
	21st to end	Day	12% 15% 30% 26% 14% 4	490
October	1st to 10th	Day	15% 8% 32% 26% 13% 6%	362
	11th to 20th	Day	12% 12% 30% 31% 12% 3	300
	21st to end	Day	15% 11% 35% 25% 12% 3	330
November	1st to 10th	Day	17% 6% 31% 32% 12% 2	300
	11th to 20th	Day	11% 7% 37% 34% 10% 2	229
	21st to end	Day	5% 9% 38% 32% 13% 5%	200
December	1st to 10th	Day	10% 7% 33% 32% 15% 4	200
	11th to 20th	Day	10% 9% 31% 36% 12% 3	200
	21st to end	Day	8% 5% 24% 39% 20% 5%	220
January	1st to 10th	Night	9% 7% 33% 36% 13% 2	981
	11th to 20th	Night	10% 7% 35% 33% 14% 2	950
	21st to end	Night	12% 10% 34% 30% 12% 2	971
February	1st to 10th	Night	10% 9% 25% 36% 18% 3	760
	11th to 20th	Night	10% 5% 33% 35% 16% 1	744
	21st to end	Night	7% 5% 28% 34% 19% 6%	628
March	1st to 10th	Night	9% 5% 28% 39% 15% 3	760
	11th to 20th	Night	12% 4 31% 35% 14% 3	760
	21st to end	Night	12% 6% 27% 36% 16% 3	836
April	1st to 10th	Night	11% 7% 27% 34% 18% 3	651
	11th to 20th	Night	13% 6% 25% 37% 17% 1	563
	21st to end	Night	16% 6% 24% 35% 16% 2	570
May	1st to 10th	Night	17% 6% 21% 36% 18% 2	428
	11th to 20th	Night	12% 5% 24% 38% 18% 3	374
	21st to end	Night	19% 7% 20% 33% 19% 2	411
June	1st to 10th	Night	19% 7% 22% 36% 14% 2	380
	11th to 20th	Night	20% 6% 21% 32% 19% 2	380
	21st to end	Night	11% 4 21% 35% 25% 4	380
July	1st to 10th	Night	14% 3 14% 44% 25% 1	370
	11th to 20th	Night	11% 3 20% 42% 23% 2	368
	21st to end	Night	12% 2 17% 40% 25% 4	416
August	1st to 10th	Night	12% 2 18% 33% 29% 6%	378
	11th to 20th	Night	13% 4 16% 39% 25% 3	500
	21st to end	Night	12% 2 20% 40% 24% 1	627
September	1st to 10th	Night	14% 3 21% 38% 23% 2	591
	11th to 20th	Night	15% 4 22% 41% 18% 1	760
	21st to end	Night	11% 6% 29% 38% 13% 2	760
October	1st to 10th	Night	14% 6% 28% 38% 13% 1	760
	11th to 20th	Night	13% 6% 32% 35% 12% 2	760
	21st to end	Night	13% 9% 34% 33% 12%	859
November	1st to 10th	Night	18% 7% 33% 30% 9% 2	975
	11th to 20th	Night	13% 8% 36% 30% 10% 3	1000
	21st to end	Night	10% 7% 38% 33% 11% 2	1000
December	1st to 10th	Night	13% 9% 34% 28% 13% 3	1000
	11th to 20th	Night	11% 7% 33% 33% 14% 2	1000
	21st to end	Night	10% 4 32% 35% 16% 3	1100

Page generated at 2025-01-04 01:24:01. Version ac07

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