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 2024-01-17.

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	10% 8% 4 8% 7% 4 5% 6% 6% 8% 34%	74662
	Night	8% 9% 4 8% 7% 4 6% 6% 6% 8% 33%	75123
Transparency	Day	46% 7% 17% 22% 7% 1	74343
	Night	48% 7% 15% 21% 9% 1	74960
Seeing	Day	13% 6% 24% 31% 19% 7%	14321
	Night	12% 6% 28% 35% 16% 2	23511

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	5% 10% 5% 11% 10% 6% 8% 7% 6% 7% 24%	1329
	11th to 20th	Day	6% 12% 5% 10% 9% 5% 5% 4 6% 9% 30%	1302
	21st to end	Day	5% 15% 6% 10% 10% 5% 7% 6% 5% 7% 24%	1472
February	1st to 10th	Day	8% 11% 6% 10% 11% 4 5% 6% 7% 8% 24%	1440
	11th to 20th	Day	6% 11% 7% 12% 7% 4 7% 7% 6% 6% 26%	1539
	21st to end	Day	4 10% 7% 11% 9% 4 7% 7% 6% 7% 27%	1363
March	1st to 10th	Day	7% 12% 6% 10% 10% 5% 7% 6% 6% 8% 23%	1800
	11th to 20th	Day	8% 12% 5% 8% 7% 2 4 5% 6% 9% 34%	1971
	21st to end	Day	9% 11% 6% 11% 9% 4 6% 6% 6% 8% 23%	2187
April	1st to 10th	Day	9% 10% 5% 8% 7% 4 7% 6% 6% 8% 30%	2263
	11th to 20th	Day	11% 11% 4 7% 7% 4 6% 5% 6% 9% 31%	2310
	21st to end	Day	12% 9% 3 7% 7% 4 5% 5% 7% 8% 33%	2340
May	1st to 10th	Day	10% 10% 4 8% 7% 5% 6% 6% 6% 8% 30%	2628
	11th to 20th	Day	8% 6% 3 6% 7% 3 7% 5% 6% 9% 40%	2654
	21st to end	Day	17% 8% 3 6% 5% 4 5% 5% 5% 7% 34%	2917
June	1st to 10th	Day	15% 9% 3 7% 7% 4 5% 5% 6% 7% 31%	2700
	11th to 20th	Day	20% 8% 3 8% 8% 4 6% 5% 7% 8% 23%	2700
	21st to end	Day	12% 5% 2 6% 6% 4 6% 6% 7% 11% 36%	2700
July	1st to 10th	Day	11% 6% 3 6% 7% 4 5% 5% 6% 9% 39%	2700
	11th to 20th	Day	11% 6% 3 6% 6% 4 5% 6% 7% 10% 37%	2700
	21st to end	Day	9% 5% 2 5% 5% 3 5% 6% 6% 9% 45%	2938
August	1st to 10th	Day	10% 5% 2 5% 5% 4 5% 6% 8% 11% 38%	2596
	11th to 20th	Day	9% 5% 2 6% 5% 3 5% 5% 7% 11% 43%	2358
	21st to end	Day	11% 5% 2 6% 5% 4 4 5% 7% 8% 44%	2574
September	1st to 10th	Day	12% 7% 2 6% 5% 3 5% 6% 6% 9% 40%	2295
	11th to 20th	Day	14% 8% 2 5% 5% 4 4 5% 6% 8% 40%	1980
	21st to end	Day	9% 7% 3 5% 6% 3 5% 5% 6% 8% 43%	1980
October	1st to 10th	Day	12% 8% 4 9% 7% 4 4 5% 5% 6% 36%	1859
	11th to 20th	Day	9% 8% 5% 7% 7% 3 4 5% 6% 9% 37%	1666
	21st to end	Day	9% 12% 4 8% 7% 4 6% 6% 6% 8% 31%	1742
November	1st to 10th	Day	10% 11% 6% 9% 8% 6% 5% 6% 6% 8% 26%	1488
	11th to 20th	Day	7% 12% 5% 11% 9% 4 5% 4 6% 6% 31%	1387
	21st to end	Day	5% 9% 7% 12% 8% 4 5% 5% 6% 8% 32%	1330
December	1st to 10th	Day	6% 11% 5% 9% 10% 6% 8% 7% 5% 9% 25%	1330
	11th to 20th	Day	6% 9% 5% 11% 9% 4 7% 7% 7% 8% 27%	1682
	21st to end	Day	4 7% 3 7% 7% 4 5% 5% 5% 8% 43%	2442
January	1st to 10th	Night	6% 10% 5% 11% 10% 6% 8% 7% 6% 7% 25%	2836
	11th to 20th	Night	6% 9% 5% 10% 8% 4 6% 5% 7% 9% 31%	2803
	21st to end	Night	7% 13% 6% 11% 8% 4 7% 5% 6% 7% 26%	2900
February	1st to 10th	Night	5% 9% 6% 12% 10% 6% 7% 6% 5% 7% 27%	2520
	11th to 20th	Night	6% 12% 5% 9% 7% 5% 6% 6% 7% 8% 29%	2308
	21st to end	Night	5% 9% 4 10% 8% 5% 6% 7% 7% 8% 31%	1892
March	1st to 10th	Night	6% 11% 5% 10% 8% 4 6% 6% 6% 8% 29%	2160
	11th to 20th	Night	8% 9% 4 9% 8% 4 5% 6% 7% 10% 29%	1988
	21st to end	Night	8% 11% 7% 9% 7% 4 6% 5% 7% 10% 27%	2165
April	1st to 10th	Night	7% 9% 4 7% 8% 4 7% 6% 7% 8% 33%	1697
	11th to 20th	Night	10% 10% 5% 9% 8% 5% 5% 6% 7% 6% 29%	1601
	21st to end	Night	13% 10% 3 6% 6% 3 5% 5% 5% 9% 35%	1620
May	1st to 10th	Night	12% 9% 5% 7% 8% 5% 6% 6% 6% 5% 31%	1328
	11th to 20th	Night	9% 7% 4 8% 9% 3 5% 5% 6% 7% 37%	1239
	21st to end	Night	19% 8% 3 6% 6% 4 6% 4 5% 7% 32%	1358
June	1st to 10th	Night	15% 9% 4 7% 7% 3 6% 5% 6% 8% 29%	1260
	11th to 20th	Night	18% 8% 3 7% 9% 5% 7% 7% 5% 9% 22%	1260
	21st to end	Night	10% 6% 3 6% 6% 3 6% 5% 7% 10% 39%	1209
July	1st to 10th	Night	11% 6% 2 6% 6% 3 6% 7% 6% 9% 39%	1260
	11th to 20th	Night	10% 7% 2 5% 7% 4 6% 6% 8% 11% 35%	1260
	21st to end	Night	9% 5% 2 4 5% 2 4 6% 6% 11% 45%	1379
August	1st to 10th	Night	10% 4 3 5% 5% 4 6% 5% 6% 9% 42%	1342
	11th to 20th	Night	12% 6% 2 5% 5% 3 4 5% 5% 8% 43%	1541
	21st to end	Night	12% 5% 2 6% 7% 3 5% 5% 6% 8% 41%	1782
September	1st to 10th	Night	12% 6% 3 6% 5% 3 4 4 5% 7% 45%	1661
	11th to 20th	Night	11% 6% 2 5% 4 2 4 4 6% 8% 46%	1980
	21st to end	Night	9% 6% 3 6% 6% 3 5% 5% 6% 7% 46%	1980
October	1st to 10th	Night	11% 8% 3 7% 5% 3 4 5% 6% 7% 39%	2101
	11th to 20th	Night	9% 9% 4 6% 6% 4 5% 5% 7% 8% 37%	2291
	21st to end	Night	8% 10% 5% 8% 7% 4 5% 7% 6% 8% 32%	2595
November	1st to 10th	Night	12% 14% 5% 8% 6% 4 6% 5% 5% 6% 27%	2590
	11th to 20th	Night	7% 13% 6% 9% 8% 5% 5% 6% 6% 7% 27%	2793
	21st to end	Night	6% 9% 5% 10% 9% 5% 7% 6% 6% 7% 29%	2850
December	1st to 10th	Night	8% 13% 5% 10% 9% 5% 6% 5% 6% 7% 28%	2850
	11th to 20th	Night	5% 11% 5% 12% 8% 4 6% 6% 7% 9% 25%	3510
	21st to end	Night	3 7% 3 7% 7% 4 6% 6% 6% 9% 42%	5214

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% 7% 13% 16% 7% 1	1329
	11th to 20th	Day	51% 6% 15% 16% 10% 2	1302
	21st to end	Day	58% 7% 11% 17% 7%	1472
February	1st to 10th	Day	55% 6% 15% 16% 8%	1440
	11th to 20th	Day	55% 7% 16% 16% 7%	1548
	21st to end	Day	52% 6% 12% 21% 8%	1363
March	1st to 10th	Day	57% 6% 16% 16% 5%	1800
	11th to 20th	Day	46% 5% 15% 22% 11%	1972
	21st to end	Day	57% 8% 13% 17% 4	2187
April	1st to 10th	Day	49% 7% 15% 20% 8% 1	2263
	11th to 20th	Day	49% 6% 15% 21% 8%	2310
	21st to end	Day	47% 6% 16% 22% 7% 2	2340
May	1st to 10th	Day	49% 7% 14% 20% 8% 1	2628
	11th to 20th	Day	40% 6% 13% 29% 11% 1	2658
	21st to end	Day	49% 6% 12% 22% 11%	2918
June	1st to 10th	Day	50% 6% 15% 21% 7%	2700
	11th to 20th	Day	56% 7% 17% 15% 4	2700
	21st to end	Day	40% 9% 24% 21% 5% 1	2700
July	1st to 10th	Day	41% 7% 20% 26% 4 1	2626
	11th to 20th	Day	40% 11% 26% 22% 2	2619
	21st to end	Day	34% 8% 29% 25% 3	2775
August	1st to 10th	Day	37% 10% 28% 22% 3	2578
	11th to 20th	Day	33% 9% 26% 26% 6%	2358
	21st to end	Day	37% 7% 22% 26% 7% 1	2574
September	1st to 10th	Day	40% 8% 20% 24% 7% 2	2295
	11th to 20th	Day	41% 5% 19% 27% 7%	1980
	21st to end	Day	38% 8% 18% 26% 8% 2	1980
October	1st to 10th	Day	48% 5% 17% 21% 9%	1859
	11th to 20th	Day	43% 6% 17% 24% 10%	1666
	21st to end	Day	49% 7% 13% 23% 6%	1742
November	1st to 10th	Day	55% 6% 16% 16% 6% 1	1488
	11th to 20th	Day	54% 5% 16% 19% 5%	1387
	21st to end	Day	51% 7% 17% 19% 5% 1	1330
December	1st to 10th	Day	54% 8% 12% 17% 8% 1	1330
	11th to 20th	Day	51% 6% 18% 17% 7%	1684
	21st to end	Day	39% 4 11% 27% 17% 2	2442
January	1st to 10th	Night	57% 6% 15% 14% 7% 1	2836
	11th to 20th	Night	49% 7% 17% 17% 8% 1	2803
	21st to end	Night	57% 5% 13% 16% 8% 1	2900
February	1st to 10th	Night	56% 6% 13% 17% 8% 1	2520
	11th to 20th	Night	50% 7% 15% 17% 10%	2309
	21st to end	Night	48% 6% 13% 21% 10% 1	1892
March	1st to 10th	Night	51% 7% 14% 20% 7%	2160
	11th to 20th	Night	49% 6% 13% 21% 11% 1	1988
	21st to end	Night	51% 7% 14% 19% 8% 1	2165
April	1st to 10th	Night	46% 8% 13% 21% 12% 1	1697
	11th to 20th	Night	53% 6% 10% 19% 9% 2	1601
	21st to end	Night	45% 6% 12% 24% 12% 1	1620
May	1st to 10th	Night	51% 6% 11% 22% 9% 1	1328
	11th to 20th	Night	44% 6% 10% 25% 13% 1	1239
	21st to end	Night	51% 5% 10% 20% 11% 2	1358
June	1st to 10th	Night	51% 6% 14% 21% 8% 1	1260
	11th to 20th	Night	57% 8% 14% 15% 5%	1260
	21st to end	Night	39% 9% 22% 24% 5% 1	1209
July	1st to 10th	Night	40% 8% 19% 24% 7% 2	1225
	11th to 20th	Night	42% 10% 22% 22% 4	1218
	21st to end	Night	32% 8% 25% 31% 5%	1302
August	1st to 10th	Night	37% 9% 26% 25% 3	1335
	11th to 20th	Night	37% 7% 23% 26% 6% 1	1541
	21st to end	Night	39% 7% 17% 27% 9% 1	1782
September	1st to 10th	Night	38% 6% 19% 25% 10% 2	1661
	11th to 20th	Night	35% 6% 18% 30% 9% 2	1980
	21st to end	Night	36% 7% 15% 27% 14% 2	1980
October	1st to 10th	Night	43% 6% 14% 26% 10% 1	2101
	11th to 20th	Night	42% 7% 16% 27% 8% 1	2291
	21st to end	Night	47% 7% 15% 23% 7% 1	2595
November	1st to 10th	Night	56% 7% 11% 20% 7%	2590
	11th to 20th	Night	55% 6% 12% 19% 6% 1	2793
	21st to end	Night	52% 7% 17% 18% 5% 1	2850
December	1st to 10th	Night	55% 5% 12% 18% 9% 1	2850
	11th to 20th	Night	54% 7% 17% 16% 6%	3507
	21st to end	Night	39% 5% 16% 20% 17% 3	5214

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	11% 3 29% 32% 21% 4	180
	11th to 20th	Day	8% 9% 33% 29% 17% 4	172
	21st to end	Day	11% 8% 34% 32% 10% 6%	176
February	1st to 10th	Day	12% 8% 31% 33% 14% 3	160
	11th to 20th	Day	12% 6% 32% 31% 16% 4	224
	21st to end	Day	7% 6% 28% 29% 19% 11%	229
March	1st to 10th	Day	14% 5% 27% 33% 19% 3	420
	11th to 20th	Day	10% 4 27% 35% 17% 7%	420
	21st to end	Day	13% 4 24% 34% 22% 4	462
April	1st to 10th	Day	11% 7% 25% 33% 18% 6%	420
	11th to 20th	Day	17% 5% 16% 31% 23% 9%	412
	21st to end	Day	15% 7% 19% 30% 22% 6%	420
May	1st to 10th	Day	11% 8% 22% 33% 19% 6%	580
	11th to 20th	Day	12% 5% 21% 34% 21% 8%	625
	21st to end	Day	17% 5% 19% 32% 18% 10%	679
June	1st to 10th	Day	17% 7% 22% 32% 17% 6%	630
	11th to 20th	Day	20% 7% 22% 23% 20% 8%	630
	21st to end	Day	14% 5% 17% 28% 25% 12%	630
July	1st to 10th	Day	12% 3 15% 32% 27% 10%	621
	11th to 20th	Day	11% 5% 20% 31% 24% 9%	618
	21st to end	Day	9% 4 18% 32% 26% 10%	684
August	1st to 10th	Day	12% 4 19% 29% 23% 13%	536
	11th to 20th	Day	9% 5% 23% 32% 24% 7%	437
	21st to end	Day	12% 5% 21% 31% 22% 10%	495
September	1st to 10th	Day	15% 10% 24% 28% 18% 5%	450
	11th to 20th	Day	18% 8% 23% 31% 16% 4	450
	21st to end	Day	12% 14% 28% 26% 15% 4	450
October	1st to 10th	Day	16% 7% 31% 27% 14% 6%	329
	11th to 20th	Day	11% 11% 30% 32% 13% 3	270
	21st to end	Day	15% 11% 34% 25% 12% 3	297
November	1st to 10th	Day	18% 6% 29% 33% 12% 3	270
	11th to 20th	Day	12% 7% 35% 34% 11% 2	207
	21st to end	Day	3 9% 41% 29% 12% 6%	180
December	1st to 10th	Day	9% 6% 32% 32% 17% 4	180
	11th to 20th	Day	7% 9% 32% 37% 12% 3	180
	21st to end	Day	8% 5% 24% 39% 20% 5%	198
January	1st to 10th	Night	10% 7% 33% 36% 13% 2	950
	11th to 20th	Night	10% 7% 35% 33% 14% 2	935
	21st to end	Night	12% 10% 35% 29% 11% 2	920
February	1st to 10th	Night	9% 9% 25% 36% 18% 3	720
	11th to 20th	Night	10% 5% 34% 35% 15% 1	704
	21st to end	Night	8% 4 28% 34% 20% 6%	592
March	1st to 10th	Night	10% 5% 28% 38% 16% 3	720
	11th to 20th	Night	13% 4 29% 36% 15% 3	720
	21st to end	Night	12% 5% 26% 37% 17% 3	792
April	1st to 10th	Night	11% 6% 26% 34% 19% 3	617
	11th to 20th	Night	13% 6% 26% 37% 17% 1	533
	21st to end	Night	17% 6% 24% 36% 16% 2	540
May	1st to 10th	Night	15% 6% 21% 37% 18% 2	406
	11th to 20th	Night	12% 5% 23% 38% 18% 3	354
	21st to end	Night	20% 6% 20% 32% 20% 2	389
June	1st to 10th	Night	19% 7% 20% 38% 14% 2	360
	11th to 20th	Night	21% 5% 19% 33% 20% 2	360
	21st to end	Night	11% 4 20% 36% 25% 5%	360
July	1st to 10th	Night	15% 3 14% 43% 26% 1	350
	11th to 20th	Night	11% 3 20% 43% 22% 2	348
	21st to end	Night	12% 2 17% 40% 25% 4	394
August	1st to 10th	Night	13% 2 18% 33% 29% 6%	358
	11th to 20th	Night	13% 4 16% 39% 25% 3	473
	21st to end	Night	13% 2 19% 40% 25% 2	594
September	1st to 10th	Night	14% 2 21% 38% 22% 2	559
	11th to 20th	Night	14% 4 22% 40% 18% 2	720
	21st to end	Night	11% 5% 28% 40% 14% 2	720
October	1st to 10th	Night	15% 5% 28% 38% 14% 1	720
	11th to 20th	Night	13% 6% 33% 34% 13% 2	720
	21st to end	Night	13% 8% 33% 33% 12%	813
November	1st to 10th	Night	19% 7% 33% 30% 9% 2	925
	11th to 20th	Night	13% 8% 36% 30% 10% 3	950
	21st to end	Night	9% 6% 39% 33% 11% 2	950
December	1st to 10th	Night	12% 9% 33% 29% 14% 4	950
	11th to 20th	Night	11% 7% 33% 34% 14% 2	950
	21st to end	Night	10% 5% 32% 34% 16% 3	1045

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