Primland Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Primland Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	14% 6% 2 6% 5% 5% 5% 4 6% 8% 39%	101229
	Night	14% 6% 2 5% 4 4 4 4 6% 7% 44%	97818
Transparency	Day	40% 7% 12% 21% 15% 5%	104892
	Night	37% 7% 11% 22% 18% 5%	102294
Seeing	Day	20% 16% 25% 21% 12% 5%	15298
	Night	18% 14% 25% 25% 15% 2	25369

By Month

Percentage Cloud Cover SE (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	17% 5% 2 5% 3 3 3 3 5% 6% 49%	2836
	11th to 20th	Day	15% 6% 3 6% 4 3 4 3 5% 5% 47%	2840
	21st to end	Day	23% 7% 2 6% 4 4 3 3 3 5% 40%	3124
February	1st to 10th	Day	12% 7% 3 6% 4 5% 5% 4 6% 7% 42%	1710
	11th to 20th	Day	19% 6% 2 6% 4 3 4 4 6% 6% 41%	1745
	21st to end	Day	19% 8% 2 6% 5% 4 4 3 4 6% 38%	1631
March	1st to 10th	Day	23% 7% 2 5% 4 4 4 4 5% 7% 37%	3435
	11th to 20th	Day	11% 4 2 4 4 4 4 3 5% 7% 52%	3480
	21st to end	Day	20% 8% 2 6% 4 3 3 3 5% 6% 40%	3815
April	1st to 10th	Day	11% 4 2 5% 4 4 5% 4 7% 7% 48%	2133
	11th to 20th	Day	15% 6% 2 6% 3 4 4 4 5% 7% 44%	2254
	21st to end	Day	15% 7% 2 6% 5% 5% 5% 4 5% 6% 41%	2422
May	1st to 10th	Day	15% 6% 3 8% 6% 6% 6% 5% 7% 7% 31%	4082
	11th to 20th	Day	20% 6% 3 7% 5% 5% 6% 4 6% 7% 31%	4081
	21st to end	Day	10% 5% 2 5% 5% 4 5% 5% 7% 9% 43%	4476
June	1st to 10th	Day	11% 6% 2 7% 6% 6% 5% 5% 8% 9% 35%	2470
	11th to 20th	Day	8% 5% 2 7% 6% 5% 6% 6% 8% 11% 36%	2470
	21st to end	Day	8% 5% 3 6% 6% 6% 7% 6% 7% 10% 36%	2470
July	1st to 10th	Day	7% 5% 2 7% 7% 6% 7% 6% 9% 10% 33%	4120
	11th to 20th	Day	8% 5% 3 8% 6% 6% 7% 6% 9% 11% 31%	4120
	21st to end	Day	13% 9% 3 10% 7% 7% 8% 6% 8% 8% 22%	4466
August	1st to 10th	Day	14% 8% 3 8% 6% 5% 6% 6% 8% 10% 26%	4104
	11th to 20th	Day	8% 5% 2 7% 5% 6% 7% 6% 9% 12% 33%	4044
	21st to end	Day	6% 4 2 5% 4 4 5% 5% 7% 11% 46%	4229
September	1st to 10th	Day	11% 6% 2 7% 4 5% 4 4 6% 8% 43%	2201
	11th to 20th	Day	15% 6% 2 7% 6% 4 5% 4 7% 8% 36%	2090
	21st to end	Day	21% 7% 3 7% 5% 4 4 3 5% 6% 35%	2090
October	1st to 10th	Day	14% 5% 2 5% 4 3 4 2 4 6% 50%	1933
	11th to 20th	Day	14% 5% 2 4 4 3 3 3 4 6% 53%	1900
	21st to end	Day	15% 5% 2 5% 3 3 2 2 3 6% 53%	2090
November	1st to 10th	Day	13% 5% 2 4 3 3 4 3 4 5% 54%	1927
	11th to 20th	Day	14% 4 2 4 3 4 4 4 4 7% 51%	1744
	21st to end	Day	15% 5% 1 5% 4 3 3 3 6% 6% 49%	1710
December	1st to 10th	Day	16% 8% 3 6% 4 5% 4 4 6% 6% 38%	1710
	11th to 20th	Day	15% 4 2 4 3 3 4 3 4 7% 53%	2153
	21st to end	Day	20% 7% 2 5% 4 4 4 4 5% 8% 36%	3124
January	1st to 10th	Night	15% 6% 2 4 3 3 4 3 5% 5% 49%	4109
	11th to 20th	Night	15% 8% 2 6% 4 3 4 3 4 5% 47%	4120
	21st to end	Night	23% 7% 2 5% 3 3 3 3 4 5% 42%	4532
February	1st to 10th	Night	14% 7% 2 4 4 4 5% 4 6% 6% 44%	2470
	11th to 20th	Night	19% 7% 2 5% 5% 3 3 3 5% 5% 42%	2318
	21st to end	Night	16% 7% 3 5% 5% 4 4 4 5% 7% 41%	1822
March	1st to 10th	Night	22% 9% 3 5% 4 4 4 3 5% 6% 35%	3418
	11th to 20th	Night	10% 4 2 4 3 3 4 3 6% 7% 54%	3480
	21st to end	Night	18% 6% 2 4 3 3 4 3 6% 6% 45%	3817
April	1st to 10th	Night	13% 7% 2 5% 4 3 4 3 5% 7% 46%	2046
	11th to 20th	Night	15% 5% 2 4 5% 3 4 4 4 7% 47%	1875
	21st to end	Night	15% 5% 2 3 4 4 5% 4 5% 6% 47%	1773
May	1st to 10th	Night	15% 9% 2 6% 5% 4 5% 4 4 8% 39%	2813
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 5% 7% 38%	2812
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 11% 45%	3079
June	1st to 10th	Night	10% 5% 2 6% 5% 5% 7% 4 6% 10% 40%	1710
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 6% 9% 45%	1710
	21st to end	Night	8% 5% 2 4 6% 4 6% 5% 8% 10% 44%	1710
July	1st to 10th	Night	8% 6% 3 7% 6% 5% 5% 5% 8% 9% 39%	2840
	11th to 20th	Night	8% 4 2 5% 5% 5% 6% 5% 8% 12% 41%	2840
	21st to end	Night	11% 9% 3 8% 5% 6% 6% 6% 8% 11% 27%	3087
August	1st to 10th	Night	16% 9% 4 7% 5% 4 5% 5% 8% 9% 29%	2825
	11th to 20th	Night	9% 6% 2 7% 5% 5% 6% 4 8% 10% 39%	2785
	21st to end	Night	6% 4 2 6% 4 4 4 4 6% 9% 52%	3380
September	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 5% 7% 46%	1975
	11th to 20th	Night	15% 6% 3 6% 5% 5% 5% 3 6% 7% 39%	2090
	21st to end	Night	20% 7% 3 8% 5% 5% 4 3 4 5% 37%	2090
October	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 4 6% 47%	2245
	11th to 20th	Night	13% 5% 2 4 3 4 4 3 4 5% 53%	2280
	21st to end	Night	14% 4 2 4 3 3 3 2 4 5% 56%	2508
November	1st to 10th	Night	14% 7% 2 5% 3 3 3 2 4 5% 52%	2312
	11th to 20th	Night	14% 4 2 4 3 3 3 3 5% 6% 54%	2433
	21st to end	Night	14% 5% 2 4 3 3 4 4 5% 6% 50%	2470
December	1st to 10th	Night	18% 6% 3 6% 4 4 3 3 4 5% 43%	2470
	11th to 20th	Night	15% 7% 2 4 3 3 4 3 5% 6% 48%	3042
	21st to end	Night	21% 6% 2 4 4 3 4 4 6% 7% 37%	4532

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% 3 9% 25% 20% 7%	2837
	11th to 20th	Day	38% 5% 7% 18% 27% 5%	2840
	21st to end	Day	47% 3 7% 20% 19% 4	3124
February	1st to 10th	Day	40% 6% 11% 20% 19% 4	1710
	11th to 20th	Day	42% 5% 9% 21% 18% 5%	1754
	21st to end	Day	46% 4 12% 15% 17% 6%	1631
March	1st to 10th	Day	46% 4 9% 20% 13% 8%	3435
	11th to 20th	Day	32% 6% 7% 26% 19% 10%	3480
	21st to end	Day	45% 4 9% 22% 16% 4	3815
April	1st to 10th	Day	32% 6% 12% 23% 20% 7%	2133
	11th to 20th	Day	38% 6% 11% 21% 19% 6%	2254
	21st to end	Day	43% 6% 12% 23% 13% 3	2422
May	1st to 10th	Day	47% 10% 14% 17% 11% 2	4120
	11th to 20th	Day	48% 10% 9% 22% 9% 1	4085
	21st to end	Day	34% 9% 16% 22% 16% 3	4489
June	1st to 10th	Day	41% 10% 14% 23% 10% 1	2470
	11th to 20th	Day	38% 12% 15% 20% 14% 2	2470
	21st to end	Day	39% 10% 16% 21% 12% 2	2470
July	1st to 10th	Day	40% 14% 17% 17% 8% 4	4055
	11th to 20th	Day	42% 12% 20% 20% 6% 1	4051
	21st to end	Day	55% 12% 12% 16% 5% 1	4324
August	1st to 10th	Day	49% 10% 16% 21% 4	4091
	11th to 20th	Day	38% 12% 20% 20% 8% 2	4083
	21st to end	Day	30% 9% 18% 29% 11% 2	4229
September	1st to 10th	Day	38% 8% 12% 20% 18% 4	2201
	11th to 20th	Day	43% 7% 11% 21% 16% 2	2090
	21st to end	Day	50% 5% 9% 18% 16% 2	2090
October	1st to 10th	Day	31% 5% 6% 19% 28% 10%	3206
	11th to 20th	Day	23% 2 6% 24% 27% 18%	3140
	21st to end	Day	27% 3 9% 25% 20% 15%	3428
November	1st to 10th	Day	33% 4 8% 22% 27% 6%	1927
	11th to 20th	Day	34% 4 8% 21% 25% 7%	1744
	21st to end	Day	36% 3 9% 22% 27% 4	1710
December	1st to 10th	Day	46% 6% 9% 17% 18% 4	1710
	11th to 20th	Day	33% 3 9% 22% 24% 8%	2150
	21st to end	Day	45% 5% 10% 21% 16% 3	3124
January	1st to 10th	Night	35% 4 10% 21% 24% 6%	4109
	11th to 20th	Night	38% 6% 8% 15% 26% 6%	4120
	21st to end	Night	45% 5% 6% 19% 20% 5%	4532
February	1st to 10th	Night	39% 5% 10% 23% 19% 4	2470
	11th to 20th	Night	44% 4 9% 19% 18% 7%	2320
	21st to end	Night	41% 5% 12% 21% 16% 5%	1822
March	1st to 10th	Night	48% 7% 8% 17% 16% 4	3418
	11th to 20th	Night	29% 6% 8% 22% 21% 14%	3480
	21st to end	Night	39% 4 10% 24% 17% 6%	3817
April	1st to 10th	Night	37% 5% 11% 20% 21% 5%	2046
	11th to 20th	Night	37% 5% 10% 21% 21% 6%	1875
	21st to end	Night	35% 8% 11% 27% 17% 3	1773
May	1st to 10th	Night	43% 9% 14% 23% 10% 1	2840
	11th to 20th	Night	46% 8% 10% 24% 11% 1	2813
	21st to end	Night	30% 10% 19% 26% 11% 4	3087
June	1st to 10th	Night	36% 10% 15% 25% 13% 1	1710
	11th to 20th	Night	34% 9% 18% 24% 13% 1	1710
	21st to end	Night	33% 11% 17% 22% 14% 3	1710
July	1st to 10th	Night	38% 13% 17% 19% 11% 2	2795
	11th to 20th	Night	33% 11% 24% 24% 6% 2	2786
	21st to end	Night	46% 12% 16% 20% 6%	2988
August	1st to 10th	Night	47% 10% 18% 18% 6%	2814
	11th to 20th	Night	33% 11% 19% 26% 10% 1	2812
	21st to end	Night	28% 8% 15% 37% 10% 2	3380
September	1st to 10th	Night	36% 9% 13% 20% 16% 6%	1975
	11th to 20th	Night	43% 6% 11% 19% 20% 1	2090
	21st to end	Night	49% 6% 8% 18% 16% 3	2090
October	1st to 10th	Night	36% 5% 8% 18% 24% 9%	3752
	11th to 20th	Night	23% 3 7% 23% 27% 17%	3779
	21st to end	Night	23% 4 7% 26% 23% 17%	4120
November	1st to 10th	Night	36% 3 9% 21% 23% 8%	2312
	11th to 20th	Night	31% 5% 8% 21% 26% 9%	2433
	21st to end	Night	33% 4 9% 24% 24% 6%	2470
December	1st to 10th	Night	43% 4 8% 22% 19% 4	2470
	11th to 20th	Night	36% 4 8% 19% 24% 9%	3044
	21st to end	Night	43% 5% 12% 20% 19% 2	4532

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	32% 31% 25% 10% 2	270
	11th to 20th	Day	37% 29% 27% 6% 1	270
	21st to end	Day	31% 34% 29% 4 2	297
February	1st to 10th	Day	28% 34% 25% 11% 1	270
	11th to 20th	Day	44% 26% 25% 3 1	270
	21st to end	Day	36% 29% 24% 9% 1	286
March	1st to 10th	Day	27% 27% 28% 13% 4	460
	11th to 20th	Day	27% 28% 30% 11% 3 1	460
	21st to end	Day	28% 23% 33% 12% 4	506
April	1st to 10th	Day	24% 28% 24% 17% 7%	460
	11th to 20th	Day	24% 19% 26% 21% 8% 2	452
	21st to end	Day	22% 18% 31% 18% 8% 2	460
May	1st to 10th	Day	21% 19% 33% 16% 7% 4	463
	11th to 20th	Day	18% 14% 28% 22% 13% 5%	487
	21st to end	Day	19% 9% 22% 27% 17% 6%	529
June	1st to 10th	Day	14% 10% 27% 28% 14% 6%	490
	11th to 20th	Day	10% 10% 22% 31% 19% 8%	490
	21st to end	Day	11% 8% 27% 31% 17% 6%	490
July	1st to 10th	Day	11% 4 18% 31% 24% 12%	485
	11th to 20th	Day	7% 4 18% 33% 27% 11%	484
	21st to end	Day	12% 4 20% 29% 21% 13%	532
August	1st to 10th	Day	16% 6% 23% 22% 20% 13%	486
	11th to 20th	Day	11% 5% 20% 27% 23% 14%	479
	21st to end	Day	12% 4 15% 30% 24% 15%	539
September	1st to 10th	Day	12% 5% 21% 27% 21% 13%	490
	11th to 20th	Day	17% 6% 18% 27% 24% 9%	490
	21st to end	Day	24% 13% 21% 25% 13% 4	490
October	1st to 10th	Day	19% 11% 23% 26% 16% 4	490
	11th to 20th	Day	16% 17% 26% 24% 15% 2	490
	21st to end	Day	20% 16% 30% 23% 8% 3	539
November	1st to 10th	Day	22% 15% 28% 21% 11% 2	483
	11th to 20th	Day	24% 23% 28% 18% 7% 1	304
	21st to end	Day	24% 23% 31% 17% 4 1	270
December	1st to 10th	Day	24% 31% 33% 10% 1	270
	11th to 20th	Day	25% 23% 34% 15% 3	270
	21st to end	Day	30% 25% 29% 12% 4	297
January	1st to 10th	Night	22% 27% 31% 16% 4	760
	11th to 20th	Night	23% 22% 33% 19% 3	760
	21st to end	Night	20% 23% 36% 19% 2	836
February	1st to 10th	Night	19% 22% 34% 23% 2	760
	11th to 20th	Night	28% 27% 30% 14% 1	743
	21st to end	Night	23% 22% 34% 19% 1	628
March	1st to 10th	Night	20% 22% 33% 22% 3	760
	11th to 20th	Night	24% 20% 31% 18% 6% 1	760
	21st to end	Night	23% 19% 31% 22% 6%	836
April	1st to 10th	Night	21% 20% 31% 22% 6%	760
	11th to 20th	Night	19% 18% 29% 22% 11% 1	751
	21st to end	Night	18% 12% 32% 29% 8%	633
May	1st to 10th	Night	15% 13% 33% 24% 14% 1	570
	11th to 20th	Night	17% 10% 24% 30% 17% 2	561
	21st to end	Night	18% 5% 17% 29% 26% 6%	617
June	1st to 10th	Night	12% 4 19% 34% 28% 3	570
	11th to 20th	Night	13% 4 19% 27% 32% 5%	570
	21st to end	Night	9% 2 18% 37% 29% 4	570
July	1st to 10th	Night	11% 3 11% 35% 35% 6%	555
	11th to 20th	Night	6% 1 14% 32% 41% 6%	552
	21st to end	Night	9% 2 15% 37% 32% 5%	624
August	1st to 10th	Night	16% 2 13% 32% 32% 4	567
	11th to 20th	Night	13% 2 15% 32% 33% 6%	564
	21st to end	Night	10% 1 13% 28% 38% 9%	779
September	1st to 10th	Night	13% 4 14% 29% 31% 9%	760
	11th to 20th	Night	20% 4 16% 26% 28% 6%	760
	21st to end	Night	24% 9% 19% 26% 20% 2	760
October	1st to 10th	Night	17% 11% 22% 21% 24% 5%	760
	11th to 20th	Night	17% 11% 28% 26% 15% 2	760
	21st to end	Night	17% 12% 26% 31% 12% 2	836
November	1st to 10th	Night	20% 11% 28% 26% 13% 2	771
	11th to 20th	Night	18% 16% 28% 28% 8% 1	760
	21st to end	Night	18% 19% 29% 24% 10% 1	760
December	1st to 10th	Night	22% 23% 26% 23% 7%	760
	11th to 20th	Night	18% 22% 31% 23% 6%	760
	21st to end	Night	27% 18% 27% 22% 5%	836

Page generated at 2024-11-05 08:15:50. Version ac07

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