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 2024-11-06.

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	3 6% 2 5% 3 3 3 3 5% 6% 61%	105215
	Night	4 6% 2 5% 4 3 4 3 5% 6% 58%	102549
Transparency	Day	25% 4 6% 18% 26% 22%	104970
	Night	27% 3 7% 19% 25% 18%	102383
Seeing	Day	10% 16% 30% 27% 13% 3	14952
	Night	7% 10% 25% 33% 20% 4	24630

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	4 8% 8% 12% 5% 3 4 3 5% 7% 41%	2539
	11th to 20th	Day	4 13% 3 7% 5% 4 4 4 5% 8% 44%	2676
	21st to end	Day	4 15% 4 5% 3 3 3 3 4 7% 47%	3146
February	1st to 10th	Day	4 11% 4 6% 5% 4 3 3 5% 7% 48%	1838
	11th to 20th	Day	5% 9% 3 5% 5% 4 3 3 6% 7% 50%	1850
	21st to end	Day	3 9% 4 7% 4 4 3 3 5% 5% 54%	1570
March	1st to 10th	Day	3 13% 3 6% 4 4 4 3 5% 7% 48%	3138
	11th to 20th	Day	2 8% 2 6% 3 4 4 3 6% 8% 53%	3478
	21st to end	Day	4 14% 4 7% 4 4 5% 4 7% 9% 37%	3825
April	1st to 10th	Day	3 8% 2 7% 3 4 4 4 5% 7% 52%	2263
	11th to 20th	Day	4 8% 2 5% 4 3 4 3 5% 7% 54%	2268
	21st to end	Day	6% 6% 2 4 3 3 4 3 5% 6% 58%	2470
May	1st to 10th	Day	3 6% 2 4 3 4 4 3 5% 7% 59%	4110
	11th to 20th	Day	5% 4 2 4 3 3 4 4 5% 6% 60%	4071
	21st to end	Day	5% 5% 2 5% 4 4 4 3 5% 6% 59%	4477
June	1st to 10th	Day	4 3 2 4 4 4 4 3 5% 6% 61%	2508
	11th to 20th	Day	3 3 1 4 3 3 3 3 3 5% 69%	2660
	21st to end	Day	3 2 2 3 2 2 3 3 3 5% 72%	2660
July	1st to 10th	Day	2 2 1 3 2 2 2 2 3 3 78%	4420
	11th to 20th	Day	3 3 1 3 3 4 4 4 5% 7% 62%	4332
	21st to end	Day	3 3 1 5% 5% 4 5% 4 6% 6% 58%	4454
August	1st to 10th	Day	2 2 1 3 3 2 2 3 4 5% 73%	4092
	11th to 20th	Day	1 1 1 3 2 2 3 2 4 4 77%	3952
	21st to end	Day	2 2 1 3 2 2 3 2 4 4 76%	4180
September	1st to 10th	Day	2 2 1 4 2 3 3 3 5% 4 70%	2204
	11th to 20th	Day	2 2 1 3 2 3 3 3 4 4 72%	2090
	21st to end	Day	2 2 1 3 3 3 3 2 3 4 75%	2090
October	1st to 10th	Day	3 3 1 3 2 2 2 3 4 6% 73%	3490
	11th to 20th	Day	2 2 1 3 2 2 2 3 3 5% 74%	3283
	21st to end	Day	2 3 2 4 2 2 2 2 3 6% 73%	3145
November	1st to 10th	Day	3 5% 2 5% 3 3 4 3 6% 8% 58%	1719
	11th to 20th	Day	3 5% 1 4 3 2 2 2 5% 7% 66%	1710
	21st to end	Day	3 7% 2 5% 4 4 4 3 4 6% 58%	1710
December	1st to 10th	Day	4 8% 2 5% 3 4 3 3 5% 6% 58%	1710
	11th to 20th	Day	6% 10% 4 8% 6% 5% 4 4 5% 8% 41%	2169
	21st to end	Day	3 9% 3 8% 5% 5% 5% 5% 7% 7% 44%	2918
January	1st to 10th	Night	3 9% 4 11% 6% 3 4 3 5% 6% 47%	4406
	11th to 20th	Night	4 11% 4 8% 5% 4 4 3 4 5% 48%	4269
	21st to end	Night	5% 13% 5% 7% 3 3 3 2 5% 8% 46%	4521
February	1st to 10th	Night	4 9% 3 6% 4 4 4 3 5% 6% 53%	2337
	11th to 20th	Night	4 9% 2 6% 3 3 3 4 5% 8% 54%	2218
	21st to end	Night	3 8% 3 7% 4 4 5% 4 6% 6% 51%	1884
March	1st to 10th	Night	3 13% 3 8% 5% 4 5% 4 4 5% 48%	3736
	11th to 20th	Night	2 6% 2 6% 3 4 5% 4 7% 8% 54%	3501
	21st to end	Night	4 10% 3 7% 4 4 4 3 5% 7% 49%	3828
April	1st to 10th	Night	6% 7% 2 5% 3 3 3 4 6% 6% 55%	1914
	11th to 20th	Night	4 6% 2 5% 4 3 3 4 5% 7% 58%	1860
	21st to end	Night	6% 7% 1 4 3 3 3 3 5% 5% 59%	1710
May	1st to 10th	Night	5% 8% 2 5% 4 4 3 3 5% 6% 55%	2860
	11th to 20th	Night	5% 4 2 5% 3 3 4 3 5% 7% 59%	2834
	21st to end	Night	6% 6% 2 5% 4 4 4 3 4 6% 57%	3110
June	1st to 10th	Night	3 3 1 5% 3 2 4 4 5% 7% 62%	1667
	11th to 20th	Night	3 4 1 3 3 3 3 2 4 6% 68%	1520
	21st to end	Night	3 2 1 3 2 3 3 3 4 6% 70%	1520
July	1st to 10th	Night	2 2 1 3 2 2 3 2 3 4 76%	2540
	11th to 20th	Night	5% 4 2 5% 5% 5% 5% 5% 7% 8% 49%	2628
	21st to end	Night	3 4 3 7% 6% 6% 6% 4 6% 6% 49%	3109
August	1st to 10th	Night	3 3 1 5% 4 4 3 3 5% 7% 59%	2847
	11th to 20th	Night	1 1 1 2 2 2 2 2 3 4 79%	2872
	21st to end	Night	2 2 1 2 2 2 3 2 3 4 78%	3498
September	1st to 10th	Night	3 2 1 3 3 3 3 4 4 6% 68%	1976
	11th to 20th	Night	2 2 1 4 3 3 3 3 4 5% 70%	2090
	21st to end	Night	3 2 1 3 2 2 2 2 2 3 78%	2090
October	1st to 10th	Night	3 3 1 3 2 2 3 2 5% 4 73%	3490
	11th to 20th	Night	3 5% 2 3 2 3 2 2 3 5% 69%	3649
	21st to end	Night	2 4 1 3 3 2 3 3 4 5% 70%	4411
November	1st to 10th	Night	3 5% 2 4 2 3 3 3 5% 8% 62%	2482
	11th to 20th	Night	2 4 2 4 3 2 3 4 5% 6% 66%	2470
	21st to end	Night	3 6% 2 6% 3 3 3 3 5% 6% 58%	2470
December	1st to 10th	Night	4 7% 2 5% 4 4 4 3 5% 7% 55%	2470
	11th to 20th	Night	5% 9% 2 7% 5% 4 4 4 6% 9% 45%	3041
	21st to end	Night	3 8% 3 9% 6% 5% 5% 4 6% 8% 42%	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	44% 4 13% 25% 13% 1	2539
	11th to 20th	Day	41% 2 18% 21% 12% 6%	2676
	21st to end	Day	39% 3 14% 24% 17% 3	3146
February	1st to 10th	Day	37% 4 11% 23% 18% 7%	1838
	11th to 20th	Day	33% 4 11% 21% 24% 6%	1860
	21st to end	Day	33% 4 9% 25% 23% 4	1570
March	1st to 10th	Day	36% 2 6% 33% 15% 8%	3138
	11th to 20th	Day	29% 3 8% 33% 21% 5%	3478
	21st to end	Day	43% 3 12% 26% 14% 2	3825
April	1st to 10th	Day	32% 4 9% 25% 19% 10%	2263
	11th to 20th	Day	30% 5% 8% 24% 26% 8%	2271
	21st to end	Day	27% 4 6% 28% 29% 6%	2470
May	1st to 10th	Day	25% 4 3 26% 31% 11%	4110
	11th to 20th	Day	23% 6% 3 15% 42% 12%	4074
	21st to end	Day	25% 6% 2 17% 38% 12%	4477
June	1st to 10th	Day	23% 4 4 15% 35% 19%	2508
	11th to 20th	Day	19% 3 2 11% 32% 33%	2660
	21st to end	Day	15% 4 1 7% 26% 48%	2660
July	1st to 10th	Day	13% 2 2 4 10% 69%	4351
	11th to 20th	Day	19% 4 4 8% 21% 43%	4257
	21st to end	Day	22% 6% 5% 13% 18% 36%	4314
August	1st to 10th	Day	16% 2 3 12% 31% 36%	4078
	11th to 20th	Day	13% 3 2 8% 24% 51%	3991
	21st to end	Day	13% 3 2 7% 24% 50%	4179
September	1st to 10th	Day	17% 4 3 9% 28% 38%	2204
	11th to 20th	Day	15% 3 3 16% 31% 32%	2090
	21st to end	Day	16% 3 1 13% 37% 30%	2090
October	1st to 10th	Day	14% 2 3 9% 36% 36%	3490
	11th to 20th	Day	15% 3 2 18% 36% 26%	3283
	21st to end	Day	14% 4 3 25% 43% 12%	3145
November	1st to 10th	Day	25% 4 10% 25% 24% 13%	1719
	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	38% 3 13% 25% 18% 2	4406
	11th to 20th	Night	40% 2 18% 21% 12% 7%	4269
	21st to end	Night	39% 2 13% 24% 18% 5%	4521
February	1st to 10th	Night	33% 4 10% 28% 20% 5%	2337
	11th to 20th	Night	28% 5% 10% 21% 27% 9%	2219
	21st to end	Night	33% 6% 10% 22% 22% 6%	1884
March	1st to 10th	Night	39% 3 8% 21% 20% 8%	3736
	11th to 20th	Night	28% 4 8% 34% 22% 4	3501
	21st to end	Night	36% 2 10% 25% 23% 3	3828
April	1st to 10th	Night	30% 4 9% 27% 20% 10%	1914
	11th to 20th	Night	27% 4 8% 27% 27% 8%	1860
	21st to end	Night	28% 3 6% 27% 30% 6%	1710
May	1st to 10th	Night	30% 4 3 21% 31% 10%	2860
	11th to 20th	Night	25% 4 4 19% 36% 11%	2835
	21st to end	Night	28% 5% 4 18% 33% 12%	3110
June	1st to 10th	Night	22% 3 5% 18% 34% 18%	1667
	11th to 20th	Night	19% 2 3 13% 30% 33%	1520
	21st to end	Night	16% 2 2 11% 26% 44%	1520
July	1st to 10th	Night	14% 3 2 4 11% 67%	2500
	11th to 20th	Night	29% 4 4 11% 19% 33%	2580
	21st to end	Night	34% 5% 5% 12% 12% 32%	3011
August	1st to 10th	Night	23% 3 5% 11% 27% 31%	2838
	11th to 20th	Night	12% 2 3 6% 25% 52%	2899
	21st to end	Night	12% 3 2 10% 23% 50%	3498
September	1st to 10th	Night	17% 4 4 11% 25% 39%	1976
	11th to 20th	Night	17% 3 5% 14% 28% 32%	2090
	21st to end	Night	14% 2 2 13% 36% 33%	2090
October	1st to 10th	Night	16% 3 4 9% 35% 34%	3490
	11th to 20th	Night	19% 3 2 13% 38% 24%	3649
	21st to end	Night	17% 3 3 23% 40% 13%	4411
November	1st to 10th	Night	22% 3 11% 26% 26% 12%	2482
	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	14% 17% 30% 22% 12% 5%	220
	21st to end	Day	13% 12% 22% 32% 15% 5%	297
February	1st to 10th	Day	13% 24% 29% 17% 14% 3	398
	11th to 20th	Day	16% 18% 32% 22% 10% 3	455
	21st to end	Day	13% 20% 37% 22% 7% 1	382
March	1st to 10th	Day	18% 18% 34% 22% 7% 1	460
	11th to 20th	Day	11% 22% 37% 18% 10% 2	460
	21st to end	Day	17% 28% 29% 19% 6% 1	506
April	1st to 10th	Day	13% 25% 31% 19% 10% 2	460
	11th to 20th	Day	15% 28% 33% 19% 5%	452
	21st to end	Day	14% 22% 33% 20% 10% 1	460
May	1st to 10th	Day	14% 24% 36% 18% 7% 1	463
	11th to 20th	Day	14% 18% 31% 24% 10% 2	488
	21st to end	Day	13% 16% 30% 27% 12% 3	529
June	1st to 10th	Day	9% 14% 31% 29% 13% 4	490
	11th to 20th	Day	8% 20% 32% 26% 11% 3	490
	21st to end	Day	4 13% 32% 33% 16% 2	490
July	1st to 10th	Day	3 9% 36% 34% 14% 4	486
	11th to 20th	Day	5% 5% 31% 41% 15% 4	484
	21st to end	Day	5% 6% 26% 39% 19% 6%	531
August	1st to 10th	Day	5% 8% 33% 35% 17% 2	487
	11th to 20th	Day	4 9% 30% 36% 16% 5%	477
	21st to end	Day	4 7% 30% 36% 17% 6%	539
September	1st to 10th	Day	4 8% 28% 33% 18% 9%	490
	11th to 20th	Day	5% 18% 29% 25% 17% 6%	490
	21st to end	Day	6% 15% 25% 31% 18% 4	490
October	1st to 10th	Day	7% 17% 28% 25% 19% 4	490
	11th to 20th	Day	9% 16% 26% 25% 19% 5%	381
	21st to end	Day	11% 12% 32% 26% 17% 2	330
November	1st to 10th	Day	12% 17% 25% 26% 17% 3	285
	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% 11% 25% 28% 19% 7%	760
	11th to 20th	Night	8% 9% 26% 35% 16% 6%	760
	21st to end	Night	10% 11% 24% 31% 19% 5%	836
February	1st to 10th	Night	8% 14% 27% 30% 17% 4	760
	11th to 20th	Night	9% 12% 24% 38% 14% 3	744
	21st to end	Night	11% 12% 32% 30% 12% 3	628
March	1st to 10th	Night	9% 13% 29% 32% 13% 3	760
	11th to 20th	Night	8% 11% 28% 30% 19% 4	760
	21st to end	Night	10% 16% 31% 29% 12% 2	836
April	1st to 10th	Night	11% 16% 26% 33% 13% 2	760
	11th to 20th	Night	8% 17% 34% 25% 13% 2	732
	21st to end	Night	11% 15% 31% 27% 14% 3	570
May	1st to 10th	Night	10% 16% 34% 28% 10% 2	570
	11th to 20th	Night	8% 12% 24% 34% 19% 4	561
	21st to end	Night	10% 15% 25% 29% 19% 3	617
June	1st to 10th	Night	5% 13% 25% 32% 21% 4	527
	11th to 20th	Night	7% 12% 23% 38% 20%	380
	21st to end	Night	4 5% 28% 36% 25% 2	380
July	1st to 10th	Night	4 4 25% 35% 29% 4	370
	11th to 20th	Night	5% 3 21% 44% 23% 4	417
	21st to end	Night	6% 4 17% 37% 33% 3	624
August	1st to 10th	Night	6% 4 25% 42% 21% 3	567
	11th to 20th	Night	2 4 23% 42% 26% 4	599
	21st to end	Night	4 5% 18% 39% 30% 4	836
September	1st to 10th	Night	3 6% 17% 34% 34% 6%	760
	11th to 20th	Night	3 9% 20% 29% 30% 8%	760
	21st to end	Night	4 7% 21% 31% 28% 10%	760
October	1st to 10th	Night	5% 9% 23% 36% 22% 5%	760
	11th to 20th	Night	6% 7% 20% 37% 23% 7%	760
	21st to end	Night	4 12% 24% 29% 24% 7%	836
November	1st to 10th	Night	7% 10% 24% 28% 25% 6%	764
	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 2024-11-03 10:19:01. Version ac07

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