Artis Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Artis Observatory clear sky chart from 2005-11-06 to 2024-03-01.

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	7% 3 1 3 3 2 3 3 4 6% 64%	78607
	Night	9% 4 2 3 3 2 3 3 4 6% 62%	80812
Transparency	Day	22% 4 9% 18% 24% 22%	78320
	Night	24% 4 10% 20% 22% 19%	80621
Seeing	Day	7% 5% 20% 34% 25% 8%	14290
	Night	9% 2 12% 39% 32% 7%	23908

By Month

Percentage Cloud Cover SW (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% 9% 3 6% 6% 3 5% 6% 7% 7% 35%	2539
	11th to 20th	Day	14% 6% 3 7% 7% 5% 6% 5% 6% 6% 35%	2746
	21st to end	Day	19% 7% 2 5% 5% 3 5% 5% 7% 8% 33%	3146
February	1st to 10th	Day	15% 6% 1 4 3 2 4 5% 4 7% 49%	1783
	11th to 20th	Day	12% 5% 2 4 4 2 4 5% 5% 7% 50%	1850
	21st to end	Day	16% 5% 2 4 4 3 4 4 4 5% 49%	1570
March	1st to 10th	Day	14% 7% 2 6% 4 3 5% 6% 6% 8% 40%	1801
	11th to 20th	Day	14% 6% 3 4 4 3 5% 5% 5% 9% 44%	1950
	21st to end	Day	13% 4 2 3 3 2 4 5% 5% 7% 53%	2320
April	1st to 10th	Day	10% 4 2 4 3 2 3 3 4 7% 57%	2160
	11th to 20th	Day	9% 4 2 3 4 2 3 3 5% 6% 60%	2129
	21st to end	Day	7% 3 1 3 3 2 3 4 4 6% 64%	2160
May	1st to 10th	Day	4 3 2 3 2 2 2 2 3 6% 70%	2203
	11th to 20th	Day	4 2 1 3 2 2 2 3 3 7% 70%	2326
	21st to end	Day	5% 2 1 2 3 2 3 4 5% 6% 67%	2723
June	1st to 10th	Day	3 2 1 2 2 1 2 3 4 7% 73%	2520
	11th to 20th	Day	1 1 1 1 1 2 2 2 4 86%	2520
	21st to end	Day	1 1 1 1 1 1 2 1 2 3 86%	2520
July	1st to 10th	Day	1 1 1 1 1 2 2 2 3 87%	2520
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 3 84%	2520
	21st to end	Day	1 1 1 2 2 1 2 3 3 5% 79%	2584
August	1st to 10th	Day	2 1 1 1 1 1 2 2 2 3 84%	2231
	11th to 20th	Day	1 1 1 1 1 1 1 1 2 4 87%	2122
	21st to end	Day	1 1 1 1 1 1 2 2 3 87%	2376
September	1st to 10th	Day	1 1 1 1 1 1 2 2 2 88%	2160
	11th to 20th	Day	2 1 2 1 1 1 2 3 3 83%	2120
	21st to end	Day	2 1 1 2 1 1 1 2 3 4 82%	1980
October	1st to 10th	Day	3 2 1 2 3 1 3 3 4 5% 73%	1859
	11th to 20th	Day	3 1 1 2 2 2 3 3 4 4 76%	1800
	21st to end	Day	6% 2 1 2 2 1 2 2 4 6% 72%	1976
November	1st to 10th	Day	8% 3 1 2 3 2 4 4 5% 7% 61%	1674
	11th to 20th	Day	8% 2 1 3 4 2 3 5% 4 7% 61%	1710
	21st to end	Day	10% 4 2 3 3 3 4 3 3 7% 58%	1710
December	1st to 10th	Day	14% 4 2 3 4 3 4 4 5% 7% 51%	1577
	11th to 20th	Day	23% 7% 3 5% 5% 4 4 3 3 7% 37%	1928
	21st to end	Day	13% 6% 3 7% 7% 4 6% 6% 6% 8% 34%	2794
January	1st to 10th	Night	15% 8% 3 5% 5% 2 3 4 4 7% 44%	4406
	11th to 20th	Night	18% 7% 3 6% 4 2 4 5% 5% 7% 38%	4203
	21st to end	Night	21% 6% 2 5% 4 3 4 4 5% 8% 40%	4521
February	1st to 10th	Night	16% 5% 2 4 2 2 3 3 4 6% 52%	2394
	11th to 20th	Night	13% 3 2 3 3 2 3 4 5% 6% 56%	2218
	21st to end	Night	16% 5% 2 4 3 2 3 3 4 6% 52%	1884
March	1st to 10th	Night	16% 6% 2 5% 4 2 4 3 4 5% 49%	2165
	11th to 20th	Night	14% 4 2 4 3 2 3 3 5% 8% 51%	2007
	21st to end	Night	13% 3 2 3 3 2 3 4 3 6% 57%	2034
April	1st to 10th	Night	11% 3 2 4 2 1 2 3 5% 7% 60%	1800
	11th to 20th	Night	7% 4 2 3 2 2 4 3 4 6% 64%	1779
	21st to end	Night	6% 2 2 2 2 2 3 3 3 6% 70%	1800
May	1st to 10th	Night	4 2 1 3 2 2 3 3 5% 6% 70%	1756
	11th to 20th	Night	4 1 2 2 2 2 2 2 4 5% 74%	1563
	21st to end	Night	4 2 1 3 2 1 2 2 3 5% 75%	1552
June	1st to 10th	Night	3 2 1 2 2 2 2 3 3 5% 75%	1440
	11th to 20th	Night	1 1 1 1 1 2 2 3 87%	1440
	21st to end	Night	1 1 1 1 2 2 2 3 87%	1440
July	1st to 10th	Night	1 1 1 1 2 2 3 89%	1440
	11th to 20th	Night	2 2 1 1 2 1 1 2 3 4 81%	1440
	21st to end	Night	2 2 1 2 2 1 2 3 3 5% 77%	1729
August	1st to 10th	Night	1 2 1 1 1 1 1 1 2 3 85%	1706
	11th to 20th	Night	1 1 1 2 2 2 2 3 3 85%	1780
	21st to end	Night	1 1 1 1 2 1 2 4 88%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 3 89%	1800
	11th to 20th	Night	1 2 2 1 1 1 2 3 3 84%	1839
	21st to end	Night	2 1 1 1 1 1 1 2 2 4 83%	1980
October	1st to 10th	Night	3 2 1 2 2 2 3 2 3 4 75%	2097
	11th to 20th	Night	4 1 1 2 1 1 2 3 4 5% 76%	2160
	21st to end	Night	5% 1 1 2 2 1 2 1 3 5% 79%	2378
November	1st to 10th	Night	8% 3 2 2 3 2 2 2 3 6% 66%	2405
	11th to 20th	Night	6% 2 1 3 3 1 2 3 4 7% 66%	2470
	21st to end	Night	9% 3 2 3 3 2 3 4 5% 7% 61%	2470
December	1st to 10th	Night	13% 5% 2 4 4 2 3 4 4 6% 53%	2598
	11th to 20th	Night	21% 7% 3 4 5% 2 3 4 5% 7% 39%	3276
	21st to end	Night	15% 6% 3 6% 5% 3 6% 5% 6% 8% 37%	4862

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% 9% 22% 18% 8% 1	2539
	11th to 20th	Day	45% 11% 13% 16% 10% 6%	2746
	21st to end	Day	46% 9% 15% 17% 11% 2	3146
February	1st to 10th	Day	35% 6% 11% 24% 18% 6%	1783
	11th to 20th	Day	33% 5% 11% 25% 21% 6%	1860
	21st to end	Day	36% 6% 14% 25% 17% 2	1570
March	1st to 10th	Day	39% 6% 14% 21% 16% 4	1801
	11th to 20th	Day	35% 6% 13% 22% 19% 5%	1950
	21st to end	Day	30% 6% 16% 27% 16% 4	2320
April	1st to 10th	Day	29% 3 14% 27% 20% 8%	2160
	11th to 20th	Day	26% 5% 10% 26% 24% 10%	2132
	21st to end	Day	20% 5% 12% 28% 28% 7%	2160
May	1st to 10th	Day	16% 3 11% 22% 34% 12%	2203
	11th to 20th	Day	15% 3 8% 25% 32% 16%	2329
	21st to end	Day	17% 4 9% 31% 30% 10%	2724
June	1st to 10th	Day	13% 3 11% 20% 30% 23%	2520
	11th to 20th	Day	6% 1 6% 16% 37% 35%	2520
	21st to end	Day	7% 2 2 8% 31% 51%	2520
July	1st to 10th	Day	5% 1 2 6% 22% 63%	2451
	11th to 20th	Day	7% 2 3 8% 24% 56%	2445
	21st to end	Day	10% 2 4 9% 23% 52%	2440
August	1st to 10th	Day	8% 2 3 8% 25% 54%	2215
	11th to 20th	Day	6% 1 2 8% 30% 53%	2122
	21st to end	Day	6% 1 2 7% 33% 52%	2376
September	1st to 10th	Day	6% 1 3 6% 27% 56%	2160
	11th to 20th	Day	8% 2 3 19% 38% 31%	2120
	21st to end	Day	8% 2 3 18% 38% 32%	1980
October	1st to 10th	Day	13% 4 6% 19% 27% 31%	1859
	11th to 20th	Day	13% 2 7% 23% 28% 28%	1800
	21st to end	Day	15% 2 8% 21% 31% 23%	1976
November	1st to 10th	Day	24% 4 12% 22% 25% 12%	1674
	11th to 20th	Day	24% 5% 14% 25% 25% 7%	1710
	21st to end	Day	28% 5% 12% 20% 27% 9%	1710
December	1st to 10th	Day	34% 7% 12% 20% 18% 10%	1577
	11th to 20th	Day	49% 6% 11% 17% 13% 5%	1928
	21st to end	Day	45% 10% 18% 17% 8% 3	2794
January	1st to 10th	Night	39% 8% 20% 20% 10% 2	4406
	11th to 20th	Night	44% 7% 19% 15% 9% 7%	4203
	21st to end	Night	43% 7% 13% 21% 12% 3	4521
February	1st to 10th	Night	33% 5% 11% 24% 20% 8%	2394
	11th to 20th	Night	27% 4 12% 27% 23% 6%	2219
	21st to end	Night	34% 4 12% 28% 18% 4	1884
March	1st to 10th	Night	36% 5% 15% 20% 21% 4	2165
	11th to 20th	Night	32% 4 14% 23% 21% 6%	2007
	21st to end	Night	29% 4 15% 28% 19% 5%	2034
April	1st to 10th	Night	25% 4 15% 27% 21% 9%	1800
	11th to 20th	Night	22% 4 11% 28% 26% 9%	1779
	21st to end	Night	18% 3 12% 30% 30% 6%	1800
May	1st to 10th	Night	15% 3 11% 25% 34% 12%	1756
	11th to 20th	Night	14% 2 7% 27% 34% 15%	1564
	21st to end	Night	14% 3 9% 29% 32% 12%	1552
June	1st to 10th	Night	13% 3 8% 24% 31% 21%	1440
	11th to 20th	Night	5% 2 4 18% 37% 35%	1440
	21st to end	Night	5% 2 3 8% 27% 55%	1440
July	1st to 10th	Night	4 1 2 4 24% 65%	1400
	11th to 20th	Night	9% 1 2 6% 23% 59%	1392
	21st to end	Night	11% 1 4 8% 23% 53%	1633
August	1st to 10th	Night	8% 1 2 10% 25% 54%	1697
	11th to 20th	Night	6% 1 3 7% 28% 54%	1780
	21st to end	Night	6% 2 7% 32% 54%	1980
September	1st to 10th	Night	5% 1 2 7% 25% 60%	1800
	11th to 20th	Night	8% 2 4 14% 40% 33%	1839
	21st to end	Night	8% 2 3 14% 38% 36%	1980
October	1st to 10th	Night	14% 3 5% 17% 26% 34%	2097
	11th to 20th	Night	12% 3 7% 21% 27% 30%	2160
	21st to end	Night	12% 1 5% 23% 33% 26%	2378
November	1st to 10th	Night	22% 3 10% 23% 25% 17%	2405
	11th to 20th	Night	19% 4 12% 27% 25% 13%	2470
	21st to end	Night	24% 4 11% 22% 29% 10%	2470
December	1st to 10th	Night	33% 4 12% 20% 19% 12%	2598
	11th to 20th	Night	44% 6% 13% 17% 16% 5%	3276
	21st to end	Night	43% 8% 16% 21% 9% 3	4862

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	26% 5% 23% 27% 14% 4	180
	11th to 20th	Day	16% 5% 16% 34% 21% 8%	308
	21st to end	Day	17% 4 18% 35% 18% 8%	407
February	1st to 10th	Day	18% 7% 21% 26% 20% 9%	405
	11th to 20th	Day	15% 7% 26% 30% 17% 5%	455
	21st to end	Day	13% 9% 26% 33% 16% 2	382
March	1st to 10th	Day	15% 8% 27% 32% 14% 3	421
	11th to 20th	Day	15% 11% 28% 24% 18% 5%	420
	21st to end	Day	17% 10% 27% 29% 15% 2	462
April	1st to 10th	Day	13% 13% 26% 28% 16% 4	420
	11th to 20th	Day	12% 13% 26% 32% 14% 3	412
	21st to end	Day	5% 10% 28% 32% 19% 7%	420
May	1st to 10th	Day	4 11% 32% 33% 15% 5%	423
	11th to 20th	Day	6% 7% 28% 33% 18% 6%	448
	21st to end	Day	7% 9% 20% 35% 22% 7%	485
June	1st to 10th	Day	2 6% 25% 32% 26% 8%	450
	11th to 20th	Day	2 4 24% 37% 24% 8%	450
	21st to end	Day	1 3 19% 39% 28% 10%	450
July	1st to 10th	Day	1 10% 43% 35% 11%	446
	11th to 20th	Day	2 6% 36% 41% 15%	444
	21st to end	Day	1 9% 40% 37% 13%	487
August	1st to 10th	Day	3 1 15% 42% 28% 11%	447
	11th to 20th	Day	1 1 14% 41% 31% 13%	437
	21st to end	Day	2 1 9% 40% 36% 12%	495
September	1st to 10th	Day	1 2 13% 41% 32% 11%	450
	11th to 20th	Day	3 3 21% 38% 29% 7%	450
	21st to end	Day	2 3 18% 35% 35% 8%	450
October	1st to 10th	Day	2 4 22% 33% 31% 7%	450
	11th to 20th	Day	3 4 20% 32% 31% 9%	450
	21st to end	Day	5% 5% 15% 32% 34% 9%	491
November	1st to 10th	Day	9% 5% 16% 30% 31% 10%	270
	11th to 20th	Day	6% 3 16% 36% 28% 12%	270
	21st to end	Day	10% 3 18% 32% 30% 8%	270
December	1st to 10th	Day	15% 2 15% 36% 25% 7%	207
	11th to 20th	Day	16% 4 21% 30% 20% 9%	180
	21st to end	Day	21% 4 23% 29% 20% 5%	198
January	1st to 10th	Night	18% 2 13% 34% 24% 9%	760
	11th to 20th	Night	12% 3 13% 38% 27% 8%	760
	21st to end	Night	18% 2 10% 38% 25% 6%	836
February	1st to 10th	Night	17% 3 12% 37% 22% 9%	760
	11th to 20th	Night	14% 4 15% 34% 27% 7%	744
	21st to end	Night	17% 3 13% 44% 19% 4	628
March	1st to 10th	Night	17% 4 14% 39% 22% 4	722
	11th to 20th	Night	13% 4 16% 33% 28% 7%	720
	21st to end	Night	14% 2 18% 38% 25% 3	792
April	1st to 10th	Night	11% 4 20% 37% 25% 3	720
	11th to 20th	Night	7% 5% 23% 38% 22% 5%	711
	21st to end	Night	6% 3 22% 38% 25% 6%	720
May	1st to 10th	Night	4 4 20% 43% 24% 4	676
	11th to 20th	Night	5% 2 20% 46% 27% 1	501
	21st to end	Night	4 3 21% 40% 30% 2	389
June	1st to 10th	Night	4 3 17% 46% 27% 3	360
	11th to 20th	Night	1 1 17% 50% 31% 1	360
	21st to end	Night	1 12% 52% 34% 2	360
July	1st to 10th	Night	5% 49% 44% 2	350
	11th to 20th	Night	3 3 45% 45% 3	348
	21st to end	Night	1 6% 28% 56% 9%	547
August	1st to 10th	Night	2 8% 41% 41% 7%	632
	11th to 20th	Night	1 1 5% 41% 46% 7%	712
	21st to end	Night	2 3 31% 55% 8%	792
September	1st to 10th	Night	1 5% 34% 51% 9%	720
	11th to 20th	Night	1 2 9% 40% 38% 10%	720
	21st to end	Night	2 1 8% 34% 44% 11%	720
October	1st to 10th	Night	4 1 8% 42% 37% 8%	720
	11th to 20th	Night	5% 1 8% 38% 38% 11%	720
	21st to end	Night	5% 10% 35% 32% 17%	792
November	1st to 10th	Night	9% 3 9% 33% 34% 13%	740
	11th to 20th	Night	6% 1 10% 42% 31% 9%	760
	21st to end	Night	10% 12% 38% 30% 9%	760
December	1st to 10th	Night	15% 2 12% 39% 26% 7%	760
	11th to 20th	Night	19% 1 11% 40% 23% 6%	760
	21st to end	Night	19% 2 14% 41% 20% 4	836

Page generated at 2024-02-27 03:30:12. Version ac07

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