Lund Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lund Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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	4 5% 2 4 4 3 4 4 5% 7% 58%	75084
	Night	4 5% 2 4 4 2 4 4 5% 7% 58%	74651
Transparency	Day	27% 4 7% 19% 25% 19%	74799
	Night	27% 4 8% 21% 25% 16%	74457
Seeing	Day	10% 16% 30% 27% 14% 3	13809
	Night	7% 10% 24% 33% 21% 5%	23595

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	6% 7% 4 5% 5% 3 5% 5% 6% 8% 47%	1519
	11th to 20th	Day	4 7% 3 4 5% 2 5% 4 5% 7% 55%	1536
	21st to end	Day	4 10% 3 5% 4 3 4 4 5% 6% 53%	1782
February	1st to 10th	Day	4 9% 4 5% 5% 4 4 4 4 8% 50%	1742
	11th to 20th	Day	5% 7% 4 4 5% 3 4 4 6% 7% 51%	1750
	21st to end	Day	4 9% 4 7% 4 3 4 3 5% 5% 53%	1480
March	1st to 10th	Day	5% 11% 4 6% 4 3 4 4 5% 7% 48%	1800
	11th to 20th	Day	2 7% 3 6% 4 2 5% 4 6% 9% 51%	1968
	21st to end	Day	5% 10% 4 4 4 2 4 4 6% 7% 49%	2178
April	1st to 10th	Day	3 7% 3 7% 4 3 4 5% 5% 7% 51%	2143
	11th to 20th	Day	5% 7% 2 5% 4 3 4 4 5% 7% 54%	2147
	21st to end	Day	6% 6% 2 4 4 2 4 4 4 7% 58%	2340
May	1st to 10th	Day	4 4 2 5% 5% 4 4 5% 6% 8% 54%	2340
	11th to 20th	Day	6% 5% 2 3 5% 3 4 5% 6% 8% 53%	2301
	21st to end	Day	6% 5% 2 5% 6% 4 5% 5% 6% 7% 50%	2530
June	1st to 10th	Day	4 3 2 4 4 3 4 4 5% 7% 61%	2376
	11th to 20th	Day	3 2 2 3 4 2 4 3 3 5% 68%	2520
	21st to end	Day	3 2 1 2 3 2 3 4 3 5% 71%	2520
July	1st to 10th	Day	3 3 2 4 4 3 4 4 5% 6% 63%	2520
	11th to 20th	Day	4 3 2 3 5% 2 5% 4 4 6% 61%	2471
	21st to end	Day	5% 4 2 5% 5% 4 5% 6% 6% 8% 50%	2545
August	1st to 10th	Day	3 3 1 3 4 2 3 4 4 5% 66%	2328
	11th to 20th	Day	2 2 1 4 4 2 4 4 6% 5% 66%	2262
	21st to end	Day	2 2 1 3 5% 2 4 4 5% 6% 66%	2376
September	1st to 10th	Day	2 2 1 3 3 2 4 4 4 4 70%	2088
	11th to 20th	Day	2 2 1 3 2 2 3 4 4 4 73%	1980
	21st to end	Day	2 3 1 3 3 2 3 3 3 4 74%	1980
October	1st to 10th	Day	5% 4 1 3 3 2 3 4 4 6% 64%	1980
	11th to 20th	Day	4 3 1 3 2 1 2 4 4 5% 71%	1877
	21st to end	Day	3 3 1 3 3 2 2 4 4 7% 70%	1814
November	1st to 10th	Day	4 5% 2 4 4 2 3 4 6% 9% 58%	1674
	11th to 20th	Day	3 4 2 3 3 2 2 3 4 8% 66%	1710
	21st to end	Day	3 6% 3 5% 4 2 5% 4 4 6% 58%	1710
December	1st to 10th	Day	4 7% 2 5% 4 3 4 4 4 6% 58%	1710
	11th to 20th	Day	6% 10% 4 7% 6% 3 4 5% 5% 8% 42%	2169
	21st to end	Day	4 9% 3 7% 6% 4 5% 6% 6% 8% 44%	2918
January	1st to 10th	Night	5% 8% 2 5% 5% 2 3 4 5% 7% 53%	2646
	11th to 20th	Night	3 7% 3 4 3 2 4 4 5% 6% 59%	2462
	21st to end	Night	5% 9% 3 6% 4 2 4 4 5% 7% 51%	2574
February	1st to 10th	Night	3 7% 3 5% 5% 3 4 3 4 7% 55%	2214
	11th to 20th	Night	5% 8% 2 5% 3 2 3 5% 5% 8% 54%	2098
	21st to end	Night	3 7% 3 6% 5% 3 5% 5% 6% 7% 50%	1776
March	1st to 10th	Night	4 9% 3 6% 5% 3 5% 6% 5% 7% 49%	2160
	11th to 20th	Night	3 8% 3 5% 4 3 5% 5% 6% 7% 51%	1991
	21st to end	Night	5% 8% 3 4 4 2 3 4 6% 8% 54%	2178
April	1st to 10th	Night	7% 6% 3 4 4 2 3 4 6% 6% 55%	1814
	11th to 20th	Night	4 6% 2 5% 4 3 3 4 5% 7% 58%	1761
	21st to end	Night	6% 6% 1 4 3 2 4 4 5% 5% 60%	1620
May	1st to 10th	Night	5% 4 2 5% 5% 4 3 5% 5% 7% 56%	1620
	11th to 20th	Night	5% 5% 2 4 4 2 4 3 5% 8% 59%	1594
	21st to end	Night	6% 6% 3 5% 5% 3 5% 5% 5% 7% 50%	1746
June	1st to 10th	Night	3 3 1 4 3 2 3 4 5% 7% 64%	1580
	11th to 20th	Night	4 3 1 3 3 2 3 2 4 6% 68%	1440
	21st to end	Night	3 2 1 3 3 3 3 4 4 6% 69%	1440
July	1st to 10th	Night	3 3 1 4 3 2 5% 5% 5% 6% 62%	1440
	11th to 20th	Night	6% 4 2 4 6% 3 5% 6% 5% 7% 53%	1486
	21st to end	Night	4 4 3 6% 6% 4 6% 6% 6% 7% 48%	1773
August	1st to 10th	Night	4 3 2 5% 5% 3 3 4 5% 6% 59%	1611
	11th to 20th	Night	2 3 1 3 3 2 3 4 5% 5% 68%	1635
	21st to end	Night	2 2 1 3 4 2 4 4 5% 6% 67%	1980
September	1st to 10th	Night	3 2 1 3 3 2 3 5% 4 6% 68%	1872
	11th to 20th	Night	2 2 1 3 3 2 3 3 4 5% 70%	1980
	21st to end	Night	3 2 1 3 2 1 2 2 2 3 78%	1980
October	1st to 10th	Night	5% 3 1 3 3 2 3 3 5% 4 67%	1980
	11th to 20th	Night	3 3 1 3 3 2 2 3 3 6% 70%	2083
	21st to end	Night	3 3 1 2 3 2 3 3 5% 6% 70%	2540
November	1st to 10th	Night	3 5% 2 3 3 2 3 4 5% 7% 63%	2405
	11th to 20th	Night	2 3 2 3 3 2 3 4 5% 6% 66%	2470
	21st to end	Night	4 5% 3 6% 3 2 4 3 5% 6% 59%	2470
December	1st to 10th	Night	4 7% 2 4 4 3 4 4 5% 7% 56%	2470
	11th to 20th	Night	5% 8% 2 6% 5% 3 4 5% 6% 9% 46%	3041
	21st to end	Night	4 7% 3 8% 7% 4 5% 5% 6% 8% 43%	4721

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	35% 5% 16% 28% 14% 2	1519
	11th to 20th	Day	31% 3 17% 24% 15% 11%	1536
	21st to end	Day	34% 4 10% 27% 18% 6%	1782
February	1st to 10th	Day	35% 4 11% 24% 19% 7%	1742
	11th to 20th	Day	33% 4 10% 22% 24% 7%	1760
	21st to end	Day	35% 4 10% 25% 22% 5%	1480
March	1st to 10th	Day	37% 3 9% 30% 17% 4	1800
	11th to 20th	Day	31% 4 9% 32% 16% 8%	1968
	21st to end	Day	35% 4 12% 29% 17% 3	2178
April	1st to 10th	Day	33% 4 10% 24% 19% 10%	2143
	11th to 20th	Day	30% 5% 8% 23% 26% 9%	2150
	21st to end	Day	27% 4 6% 29% 29% 6%	2340
May	1st to 10th	Day	27% 5% 5% 21% 32% 9%	2340
	11th to 20th	Day	30% 5% 5% 20% 32% 8%	2304
	21st to end	Day	33% 6% 4 21% 28% 8%	2530
June	1st to 10th	Day	23% 4 4 15% 34% 19%	2376
	11th to 20th	Day	19% 3 2 12% 30% 33%	2520
	21st to end	Day	15% 4 1 8% 26% 46%	2520
July	1st to 10th	Day	22% 4 3 6% 18% 46%	2451
	11th to 20th	Day	24% 5% 4 11% 21% 36%	2396
	21st to end	Day	30% 6% 7% 12% 18% 26%	2404
August	1st to 10th	Day	21% 3 4 10% 21% 42%	2313
	11th to 20th	Day	20% 4 3 9% 20% 43%	2262
	21st to end	Day	18% 5% 3 11% 28% 34%	2376
September	1st to 10th	Day	18% 4 3 9% 27% 39%	2088
	11th to 20th	Day	15% 3 3 16% 30% 33%	1980
	21st to end	Day	16% 3 2 14% 37% 29%	1980
October	1st to 10th	Day	23% 3 5% 16% 35% 19%	1980
	11th to 20th	Day	18% 3 3 20% 33% 22%	1877
	21st to end	Day	16% 3 5% 27% 35% 13%	1814
November	1st to 10th	Day	25% 4 10% 25% 24% 13%	1674
	11th to 20th	Day	20% 3 9% 28% 32% 8%	1710
	21st to end	Day	29% 4 7% 23% 26% 11%	1710
December	1st to 10th	Day	29% 4 11% 24% 24% 7%	1710
	11th to 20th	Day	43% 4 11% 20% 16% 6%	2168
	21st to end	Day	39% 3 13% 18% 20% 6%	2918
January	1st to 10th	Night	31% 5% 14% 28% 19% 3	2646
	11th to 20th	Night	27% 3 16% 24% 17% 12%	2462
	21st to end	Night	34% 4 10% 24% 21% 7%	2574
February	1st to 10th	Night	31% 4 10% 29% 20% 6%	2214
	11th to 20th	Night	28% 5% 10% 21% 27% 9%	2099
	21st to end	Night	34% 6% 11% 22% 21% 6%	1776
March	1st to 10th	Night	35% 4 9% 25% 21% 4	2160
	11th to 20th	Night	32% 4 8% 30% 19% 7%	1991
	21st to end	Night	29% 3 14% 31% 18% 4	2178
April	1st to 10th	Night	31% 4 9% 26% 20% 10%	1814
	11th to 20th	Night	27% 4 8% 26% 27% 8%	1761
	21st to end	Night	27% 3 6% 28% 29% 6%	1620
May	1st to 10th	Night	29% 4 6% 22% 31% 8%	1620
	11th to 20th	Night	24% 3 6% 22% 31% 13%	1595
	21st to end	Night	33% 5% 7% 24% 25% 6%	1746
June	1st to 10th	Night	22% 3 5% 18% 34% 19%	1580
	11th to 20th	Night	19% 2 3 14% 30% 33%	1440
	21st to end	Night	16% 2 2 11% 27% 43%	1440
July	1st to 10th	Night	22% 5% 3 6% 19% 45%	1400
	11th to 20th	Night	30% 5% 4 11% 15% 35%	1438
	21st to end	Night	34% 4 7% 15% 14% 26%	1674
August	1st to 10th	Night	25% 3 5% 11% 18% 37%	1602
	11th to 20th	Night	18% 3 5% 10% 22% 42%	1635
	21st to end	Night	18% 4 3 13% 24% 38%	1980
September	1st to 10th	Night	17% 4 4 10% 25% 39%	1872
	11th to 20th	Night	17% 3 4 14% 28% 33%	1980
	21st to end	Night	15% 2 2 13% 36% 32%	1980
October	1st to 10th	Night	22% 3 5% 15% 36% 20%	1980
	11th to 20th	Night	18% 3 3 18% 38% 20%	2083
	21st to end	Night	16% 3 5% 28% 34% 13%	2540
November	1st to 10th	Night	22% 3 11% 26% 26% 13%	2405
	11th to 20th	Night	20% 3 10% 24% 33% 10%	2470
	21st to end	Night	27% 3 6% 24% 30% 10%	2470
December	1st to 10th	Night	29% 5% 12% 25% 22% 8%	2470
	11th to 20th	Night	37% 4 12% 22% 18% 7%	3041
	21st to end	Night	40% 4 9% 20% 19% 7%	4721

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	20% 18% 27% 22% 11% 2	180
	11th to 20th	Day	13% 18% 30% 22% 13% 5%	200
	21st to end	Day	13% 13% 22% 30% 16% 6%	264
February	1st to 10th	Day	11% 25% 30% 17% 14% 3	362
	11th to 20th	Day	15% 18% 32% 21% 10% 3	415
	21st to end	Day	13% 20% 38% 21% 7% 1	346
March	1st to 10th	Day	17% 18% 35% 21% 8% 1	420
	11th to 20th	Day	10% 22% 37% 19% 10% 2	420
	21st to end	Day	16% 29% 29% 19% 6% 1	462
April	1st to 10th	Day	12% 25% 31% 20% 10% 1	420
	11th to 20th	Day	16% 29% 33% 18% 4	412
	21st to end	Day	14% 24% 32% 19% 10% 1	420
May	1st to 10th	Day	13% 23% 37% 18% 7% 1	423
	11th to 20th	Day	15% 19% 31% 24% 10% 2	448
	21st to end	Day	14% 15% 30% 26% 12% 3	485
June	1st to 10th	Day	9% 14% 30% 29% 13% 5%	450
	11th to 20th	Day	8% 18% 32% 27% 12% 3	450
	21st to end	Day	5% 13% 30% 34% 16% 2	450
July	1st to 10th	Day	4 8% 36% 35% 14% 4	446
	11th to 20th	Day	5% 5% 31% 42% 15% 3	444
	21st to end	Day	5% 5% 27% 40% 18% 5%	487
August	1st to 10th	Day	5% 9% 33% 34% 17% 1	447
	11th to 20th	Day	5% 7% 27% 38% 18% 6%	437
	21st to end	Day	4 6% 31% 36% 17% 6%	495
September	1st to 10th	Day	4 9% 28% 32% 18% 9%	450
	11th to 20th	Day	4 17% 29% 25% 18% 6%	450
	21st to end	Day	6% 16% 24% 31% 19% 4	450
October	1st to 10th	Day	8% 18% 28% 24% 18% 4	450
	11th to 20th	Day	9% 15% 25% 26% 20% 5%	347
	21st to end	Day	10% 12% 31% 27% 18% 2	297
November	1st to 10th	Day	11% 17% 24% 27% 18% 3	270
	11th to 20th	Day	6% 18% 29% 25% 17% 6%	270
	21st to end	Day	12% 17% 21% 26% 19% 5%	270
December	1st to 10th	Day	10% 17% 29% 26% 13% 4	270
	11th to 20th	Day	9% 13% 30% 33% 12% 3	270
	21st to end	Day	16% 21% 28% 23% 8% 4	232
January	1st to 10th	Night	9% 12% 25% 28% 19% 7%	760
	11th to 20th	Night	8% 9% 25% 35% 17% 6%	728
	21st to end	Night	9% 11% 25% 31% 19% 5%	792
February	1st to 10th	Night	7% 14% 27% 30% 18% 4	720
	11th to 20th	Night	9% 11% 23% 38% 15% 4	704
	21st to end	Night	10% 12% 32% 30% 13% 3	592
March	1st to 10th	Night	8% 13% 29% 33% 14% 3	720
	11th to 20th	Night	8% 11% 27% 31% 19% 4	720
	21st to end	Night	9% 15% 31% 30% 13% 2	792
April	1st to 10th	Night	11% 16% 25% 34% 13% 2	720
	11th to 20th	Night	8% 18% 34% 24% 14% 2	693
	21st to end	Night	10% 15% 31% 27% 14% 3	540
May	1st to 10th	Night	9% 16% 33% 30% 11% 2	540
	11th to 20th	Night	8% 11% 24% 34% 20% 4	531
	21st to end	Night	10% 14% 25% 29% 20% 3	584
June	1st to 10th	Night	5% 13% 25% 31% 21% 4	500
	11th to 20th	Night	7% 13% 21% 38% 21%	360
	21st to end	Night	4 5% 27% 36% 26% 2	360
July	1st to 10th	Night	4 3 23% 35% 30% 4	350
	11th to 20th	Night	5% 3 22% 43% 23% 4	394
	21st to end	Night	6% 4 16% 37% 34% 3	591
August	1st to 10th	Night	6% 4 26% 41% 21% 3	537
	11th to 20th	Night	2 3 20% 44% 27% 5%	567
	21st to end	Night	3 4 18% 39% 31% 5%	792
September	1st to 10th	Night	3 6% 17% 32% 35% 7%	720
	11th to 20th	Night	3 8% 20% 29% 32% 8%	720
	21st to end	Night	4 7% 20% 30% 29% 10%	720
October	1st to 10th	Night	5% 9% 23% 34% 23% 5%	720
	11th to 20th	Night	5% 7% 19% 37% 25% 7%	720
	21st to end	Night	4 11% 23% 29% 25% 7%	792
November	1st to 10th	Night	7% 10% 23% 29% 26% 6%	740
	11th to 20th	Night	4 9% 27% 36% 18% 7%	760
	21st to end	Night	7% 12% 23% 30% 22% 6%	760
December	1st to 10th	Night	8% 11% 24% 37% 16% 5%	760
	11th to 20th	Night	10% 9% 26% 34% 18% 3	760
	21st to end	Night	11% 15% 24% 33% 14% 2	836

Page generated at 2024-01-09 22:24:59. Version ac07

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