Limber Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Limber Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	13% 6% 2 5% 4 4 4 4 5% 7% 46%	100975
	Night	14% 6% 2 4 3 3 3 3 5% 7% 51%	98171
Transparency	Day	37% 4 9% 22% 19% 10%	104832
	Night	34% 4 10% 20% 19% 12%	102441
Seeing	Day	15% 9% 25% 31% 18% 3	14767
	Night	17% 8% 26% 35% 14% 1	24685

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	14% 7% 2 4 2 2 3 3 4 6% 53%	2847
	11th to 20th	Day	16% 6% 2 3 2 2 2 2 4 5% 56%	2856
	21st to end	Day	18% 7% 2 4 3 2 3 3 5% 9% 44%	3487
February	1st to 10th	Day	17% 9% 2 4 3 3 4 3 4 5% 46%	1900
	11th to 20th	Day	19% 7% 2 5% 3 3 4 3 4 4 45%	1849
	21st to end	Day	18% 6% 2 4 3 2 3 3 4 6% 50%	1570
March	1st to 10th	Day	17% 8% 2 6% 3 3 4 3 4 5% 45%	3329
	11th to 20th	Day	22% 10% 3 8% 4 4 4 3 4 4 33%	3480
	21st to end	Day	17% 6% 2 5% 3 3 4 3 5% 7% 46%	3814
April	1st to 10th	Day	15% 8% 2 6% 4 3 3 3 4 6% 45%	2090
	11th to 20th	Day	19% 7% 2 6% 4 4 3 4 5% 5% 42%	2140
	21st to end	Day	16% 7% 2 6% 5% 3 3 3 5% 5% 44%	2356
May	1st to 10th	Day	22% 8% 3 6% 4 4 4 3 5% 6% 34%	4082
	11th to 20th	Day	15% 6% 3 5% 4 4 5% 3 5% 7% 43%	4082
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	4477
June	1st to 10th	Day	8% 4 1 5% 5% 4 5% 5% 7% 9% 46%	2470
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 4 6% 8% 45%	2470
	21st to end	Day	9% 6% 2 7% 5% 4 7% 6% 7% 9% 38%	2470
July	1st to 10th	Day	8% 5% 2 6% 4 6% 5% 4 6% 8% 46%	4120
	11th to 20th	Day	6% 4 2 5% 5% 5% 5% 4 6% 10% 47%	4120
	21st to end	Day	8% 6% 2 7% 5% 6% 6% 5% 8% 9% 39%	4465
August	1st to 10th	Day	1 2 1 2 3 3 4 3 5% 9% 66%	3894
	11th to 20th	Day	4 3 1 3 3 4 4 3 7% 12% 57%	3726
	21st to end	Day	4 4 1 6% 5% 5% 5% 4 7% 11% 46%	4070
September	1st to 10th	Day	12% 6% 3 7% 6% 5% 5% 4 6% 7% 40%	2090
	11th to 20th	Day	10% 7% 2 6% 5% 5% 6% 4 7% 7% 41%	2090
	21st to end	Day	8% 4 2 6% 5% 4 6% 4 7% 7% 48%	2090
October	1st to 10th	Day	7% 5% 2 5% 4 3 4 4 5% 7% 55%	2090
	11th to 20th	Day	14% 5% 1 5% 3 3 4 3 5% 6% 51%	2022
	21st to end	Day	13% 4 2 5% 3 3 3 3 4 4 58%	2090
November	1st to 10th	Day	17% 7% 3 6% 3 3 3 3 5% 5% 44%	1898
	11th to 20th	Day	15% 6% 2 6% 3 4 4 3 4 5% 48%	1725
	21st to end	Day	18% 7% 3 5% 4 3 3 3 3 4 46%	1710
December	1st to 10th	Day	17% 7% 2 5% 3 3 3 3 4 7% 47%	1710
	11th to 20th	Day	18% 7% 2 4 4 3 3 3 4 5% 45%	2161
	21st to end	Day	17% 5% 1 4 3 2 3 2 3 5% 55%	3135
January	1st to 10th	Night	17% 5% 2 3 3 2 3 2 4 6% 53%	4108
	11th to 20th	Night	13% 5% 1 3 2 2 2 1 3 4 66%	4120
	21st to end	Night	22% 6% 2 6% 3 3 3 2 4 6% 44%	4202
February	1st to 10th	Night	17% 7% 2 4 3 3 3 2 4 6% 50%	2280
	11th to 20th	Night	18% 7% 2 5% 3 3 2 3 3 4 51%	2218
	21st to end	Night	17% 6% 2 4 3 3 4 3 5% 6% 47%	1884
March	1st to 10th	Night	18% 9% 2 6% 4 3 3 3 4 5% 42%	3525
	11th to 20th	Night	21% 11% 3 7% 4 4 3 2 4 5% 36%	3480
	21st to end	Night	19% 7% 2 4 3 3 3 3 4 5% 46%	3817
April	1st to 10th	Night	13% 7% 2 5% 4 3 3 3 5% 6% 48%	2090
	11th to 20th	Night	19% 6% 2 6% 3 3 2 3 4 5% 47%	1985
	21st to end	Night	21% 6% 2 4 3 3 2 3 4 4 47%	1820
May	1st to 10th	Night	23% 10% 2 5% 4 2 3 2 4 6% 38%	2823
	11th to 20th	Night	13% 5% 2 4 4 4 4 3 4 7% 50%	2823
	21st to end	Night	14% 7% 2 5% 3 3 4 3 6% 8% 45%	3090
June	1st to 10th	Night	7% 3 1 2 3 3 4 3 6% 9% 59%	1710
	11th to 20th	Night	6% 3 1 4 3 3 3 4 5% 9% 58%	1710
	21st to end	Night	7% 5% 2 4 4 4 4 5% 6% 10% 49%	1710
July	1st to 10th	Night	6% 4 1 5% 4 3 4 4 6% 11% 51%	2850
	11th to 20th	Night	4 4 2 4 4 4 5% 4 7% 9% 52%	2850
	21st to end	Night	11% 7% 3 6% 4 5% 4 4 7% 9% 42%	3098
August	1st to 10th	Night	2 2 1 2 2 2 3 3 5% 8% 71%	3041
	11th to 20th	Night	3 2 1 3 2 3 4 4 6% 11% 60%	3113
	21st to end	Night	4 4 2 4 4 3 5% 4 7% 9% 55%	3580
September	1st to 10th	Night	9% 5% 3 6% 4 5% 5% 3 6% 8% 46%	2090
	11th to 20th	Night	10% 6% 2 6% 4 3 4 4 6% 7% 46%	2090
	21st to end	Night	8% 5% 2 6% 4 3 4 3 6% 8% 50%	2090
October	1st to 10th	Night	7% 4 1 4 3 3 3 3 5% 6% 61%	2090
	11th to 20th	Night	13% 5% 2 4 3 2 3 4 4 6% 54%	2137
	21st to end	Night	15% 4 1 3 3 2 2 2 2 5% 61%	2508
November	1st to 10th	Night	13% 7% 2 5% 3 3 3 2 4 6% 52%	2280
	11th to 20th	Night	12% 6% 1 4 3 3 3 3 4 6% 54%	2451
	21st to end	Night	19% 4 2 4 3 3 3 3 5% 6% 46%	2470
December	1st to 10th	Night	16% 7% 1 4 3 2 3 3 4 7% 52%	2470
	11th to 20th	Night	18% 8% 2 6% 3 3 3 2 4 5% 47%	3036
	21st to end	Night	19% 6% 1 3 2 2 3 2 3 5% 54%	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	34% 2 2 18% 27% 18%	2848
	11th to 20th	Day	34% 1 5% 14% 27% 19%	2856
	21st to end	Day	41% 2 4 14% 29% 10%	3487
February	1st to 10th	Day	43% 3 4 13% 20% 16%	1900
	11th to 20th	Day	43% 2 5% 17% 18% 14%	1859
	21st to end	Day	40% 2 6% 18% 19% 16%	1570
March	1st to 10th	Day	45% 2 5% 15% 21% 11%	3329
	11th to 20th	Day	56% 2 5% 11% 16% 10%	3480
	21st to end	Day	40% 2 8% 17% 19% 14%	3814
April	1st to 10th	Day	42% 3 8% 17% 18% 13%	2090
	11th to 20th	Day	45% 3 5% 18% 17% 12%	2140
	21st to end	Day	44% 3 6% 20% 17% 11%	2356
May	1st to 10th	Day	54% 2 9% 16% 14% 6%	4120
	11th to 20th	Day	42% 3 8% 21% 19% 7%	4086
	21st to end	Day	43% 3 9% 33% 11% 1	4489
June	1st to 10th	Day	33% 5% 13% 26% 19% 3	2470
	11th to 20th	Day	37% 4 11% 25% 18% 5%	2470
	21st to end	Day	41% 7% 10% 25% 14% 3	2470
July	1st to 10th	Day	34% 6% 15% 38% 7% 1	4056
	11th to 20th	Day	30% 6% 19% 29% 15% 1	4051
	21st to end	Day	37% 7% 18% 28% 9%	4325
August	1st to 10th	Day	15% 4 11% 45% 24%	3880
	11th to 20th	Day	20% 4 24% 37% 11% 2	3762
	21st to end	Day	31% 8% 18% 24% 18% 2	4069
September	1st to 10th	Day	42% 5% 10% 19% 16% 7%	2090
	11th to 20th	Day	40% 6% 10% 20% 18% 5%	2090
	21st to end	Day	34% 4 10% 22% 18% 12%	2090
October	1st to 10th	Day	19% 3 6% 12% 25% 36%	3480
	11th to 20th	Day	27% 4 7% 18% 22% 21%	3340
	21st to end	Day	28% 3 4 17% 33% 13%	3428
November	1st to 10th	Day	43% 3 6% 21% 17% 11%	1898
	11th to 20th	Day	39% 3 7% 16% 20% 15%	1725
	21st to end	Day	43% 3 5% 16% 19% 14%	1710
December	1st to 10th	Day	40% 2 7% 21% 20% 10%	1710
	11th to 20th	Day	44% 2 7% 10% 21% 16%	2159
	21st to end	Day	35% 2 4 16% 28% 15%	3135
January	1st to 10th	Night	34% 2 3 16% 23% 22%	4108
	11th to 20th	Night	27% 1 3 18% 27% 24%	4120
	21st to end	Night	44% 2 3 14% 25% 13%	4202
February	1st to 10th	Night	38% 2 6% 14% 21% 19%	2280
	11th to 20th	Night	40% 2 5% 16% 20% 17%	2218
	21st to end	Night	40% 3 6% 16% 19% 16%	1884
March	1st to 10th	Night	46% 3 5% 16% 20% 10%	3525
	11th to 20th	Night	54% 3 7% 12% 13% 11%	3480
	21st to end	Night	41% 3 9% 16% 19% 12%	3817
April	1st to 10th	Night	39% 3 9% 18% 16% 15%	2090
	11th to 20th	Night	43% 3 8% 14% 16% 16%	1985
	21st to end	Night	43% 4 8% 19% 16% 11%	1820
May	1st to 10th	Night	50% 2 9% 18% 12% 9%	2850
	11th to 20th	Night	36% 3 11% 23% 19% 8%	2824
	21st to end	Night	40% 3 12% 30% 11% 3	3099
June	1st to 10th	Night	24% 4 17% 32% 20% 3	1710
	11th to 20th	Night	25% 5% 15% 29% 21% 5%	1710
	21st to end	Night	31% 6% 18% 28% 15% 3	1710
July	1st to 10th	Night	27% 7% 24% 35% 6% 1	2805
	11th to 20th	Night	27% 8% 21% 30% 14% 1	2796
	21st to end	Night	37% 8% 23% 25% 7% 1	2999
August	1st to 10th	Night	13% 4 18% 45% 20%	3031
	11th to 20th	Night	20% 6% 31% 34% 8% 1	3143
	21st to end	Night	26% 10% 22% 25% 16% 2	3580
September	1st to 10th	Night	36% 6% 14% 20% 17% 7%	2090
	11th to 20th	Night	37% 7% 14% 22% 15% 5%	2090
	21st to end	Night	31% 5% 12% 22% 18% 12%	2090
October	1st to 10th	Night	17% 2 7% 16% 21% 37%	3480
	11th to 20th	Night	24% 3 9% 15% 30% 18%	3545
	21st to end	Night	27% 2 6% 17% 33% 15%	4120
November	1st to 10th	Night	37% 3 6% 19% 22% 13%	2280
	11th to 20th	Night	33% 3 8% 19% 20% 16%	2451
	21st to end	Night	40% 3 7% 16% 19% 15%	2470
December	1st to 10th	Night	36% 2 7% 19% 21% 13%	2470
	11th to 20th	Night	43% 2 4 14% 18% 20%	3037
	21st to end	Night	37% 2 4 14% 28% 15%	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	23% 16% 36% 21% 5%	270
	11th to 20th	Day	26% 15% 31% 21% 6%	270
	21st to end	Day	20% 18% 35% 21% 6%	297
February	1st to 10th	Day	29% 18% 26% 22% 5%	270
	11th to 20th	Day	29% 21% 32% 13% 4	270
	21st to end	Day	26% 21% 38% 13% 2	225
March	1st to 10th	Day	26% 19% 40% 13% 1	270
	11th to 20th	Day	20% 23% 42% 13% 3	270
	21st to end	Day	22% 22% 38% 16% 1	297
April	1st to 10th	Day	24% 20% 38% 16% 2	270
	11th to 20th	Day	20% 23% 35% 20% 3	338
	21st to end	Day	20% 17% 42% 18% 3	536
May	1st to 10th	Day	20% 15% 38% 24% 4	653
	11th to 20th	Day	17% 13% 32% 32% 5% 1	675
	21st to end	Day	19% 6% 32% 32% 11%	734
June	1st to 10th	Day	8% 3 23% 43% 20% 2	680
	11th to 20th	Day	9% 2 25% 45% 17% 2	680
	21st to end	Day	10% 4 17% 38% 26% 5%	680
July	1st to 10th	Day	12% 3 13% 37% 29% 7%	671
	11th to 20th	Day	7% 1 8% 41% 40% 3	668
	21st to end	Day	5% 1 10% 39% 38% 8%	739
August	1st to 10th	Day	3 1 5% 44% 38% 10%	557
	11th to 20th	Day	7% 1 7% 44% 35% 7%	477
	21st to end	Day	5% 2 7% 38% 39% 10%	481
September	1st to 10th	Day	11% 1 12% 30% 34% 11%	300
	11th to 20th	Day	6% 2 6% 36% 45% 6%	300
	21st to end	Day	8% 2 15% 33% 34% 8%	300
October	1st to 10th	Day	5% 3 18% 41% 27% 5%	300
	11th to 20th	Day	13% 4 23% 42% 16% 2	300
	21st to end	Day	19% 14% 26% 25% 13% 3	330
November	1st to 10th	Day	18% 11% 34% 23% 11% 2	282
	11th to 20th	Day	23% 11% 30% 26% 8% 2	270
	21st to end	Day	26% 18% 34% 14% 7% 1	270
December	1st to 10th	Day	17% 13% 33% 28% 8% 1	270
	11th to 20th	Day	24% 17% 33% 22% 4	270
	21st to end	Day	24% 12% 36% 23% 5% 1	297
January	1st to 10th	Night	20% 11% 26% 35% 8%	950
	11th to 20th	Night	21% 12% 31% 29% 7%	950
	21st to end	Night	23% 11% 27% 32% 7%	845
February	1st to 10th	Night	24% 14% 28% 27% 7% 1	760
	11th to 20th	Night	26% 13% 31% 25% 4	744
	21st to end	Night	25% 13% 38% 22% 1	628
March	1st to 10th	Night	23% 14% 34% 26% 3	642
	11th to 20th	Night	23% 12% 35% 27% 3	570
	21st to end	Night	21% 14% 38% 24% 4	627
April	1st to 10th	Night	15% 15% 41% 26% 2	570
	11th to 20th	Night	21% 14% 42% 21% 2	563
	21st to end	Night	23% 11% 39% 21% 5% 1	570
May	1st to 10th	Night	18% 12% 41% 26% 3	570
	11th to 20th	Night	17% 9% 35% 32% 7% 1	561
	21st to end	Night	18% 8% 36% 31% 8%	617
June	1st to 10th	Night	7% 2 29% 44% 17% 1	570
	11th to 20th	Night	7% 2 38% 43% 10%	570
	21st to end	Night	8% 3 25% 41% 22% 1	570
July	1st to 10th	Night	10% 2 17% 48% 23% 1	555
	11th to 20th	Night	3 1 13% 55% 25% 2	552
	21st to end	Night	6% 2 12% 52% 24% 3	624
August	1st to 10th	Night	2 1 12% 51% 34% 1	567
	11th to 20th	Night	5% 1 10% 53% 29% 2	564
	21st to end	Night	6% 2 8% 45% 35% 4	627
September	1st to 10th	Night	9% 1 11% 44% 30% 4	570
	11th to 20th	Night	12% 2 11% 40% 33% 2	570
	21st to end	Night	10% 2 14% 41% 30% 4	570
October	1st to 10th	Night	7% 2 13% 52% 24% 3	570
	11th to 20th	Night	15% 5% 23% 39% 18% 1	617
	21st to end	Night	17% 7% 24% 29% 19% 2	836
November	1st to 10th	Night	15% 7% 22% 36% 18% 2	760
	11th to 20th	Night	15% 8% 23% 38% 14% 1	931
	21st to end	Night	23% 10% 25% 30% 11% 1	950
December	1st to 10th	Night	21% 8% 25% 35% 11% 1	950
	11th to 20th	Night	26% 10% 25% 30% 8%	950
	21st to end	Night	22% 9% 26% 34% 8%	1045

Page generated at 2024-11-03 01:11:11. Version ac07

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