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 2024-05-13.

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	14% 6% 2 5% 4 4 4 3 5% 7% 46%	84071
	Night	14% 6% 2 4 3 3 3 3 5% 6% 51%	85505
Transparency	Day	39% 3 9% 20% 19% 10%	83796
	Night	36% 3 9% 20% 19% 12%	85300
Seeing	Day	15% 9% 25% 30% 18% 3	14051
	Night	17% 8% 26% 35% 13% 1	24138

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	18% 6% 3 6% 5% 4 5% 4 5% 6% 39%	2470
	11th to 20th	Day	15% 7% 3 6% 5% 5% 5% 3 5% 7% 38%	2330
	21st to end	Day	16% 7% 2 6% 5% 5% 5% 5% 6% 7% 36%	2531
June	1st to 10th	Day	8% 4 1 5% 5% 4 5% 5% 7% 9% 46%	2340
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 6% 8% 45%	2340
	21st to end	Day	10% 6% 2 7% 5% 4 7% 6% 7% 8% 38%	2340
July	1st to 10th	Day	13% 7% 2 7% 5% 6% 5% 4 6% 8% 36%	2340
	11th to 20th	Day	5% 3 2 5% 5% 5% 4 4 6% 10% 51%	2340
	21st to end	Day	6% 4 1 4 4 5% 5% 4 8% 9% 51%	2546
August	1st to 10th	Day	2 3 1 2 4 4 4 4 5% 10% 60%	2216
	11th to 20th	Day	6% 4 2 4 4 5% 5% 4 8% 10% 48%	2123
	21st to end	Day	7% 5% 2 7% 6% 5% 5% 5% 7% 11% 42%	2322
September	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 6% 7% 40%	1980
	11th to 20th	Day	10% 7% 2 6% 5% 5% 6% 4 7% 7% 40%	1980
	21st to end	Day	8% 4 2 6% 5% 4 6% 4 7% 7% 46%	1980
October	1st to 10th	Day	7% 5% 2 6% 4 4 4 4 5% 7% 53%	1980
	11th to 20th	Day	15% 5% 2 5% 3 3 4 3 5% 7% 50%	1916
	21st to end	Day	13% 4 2 5% 3 3 3 3 4 4 58%	1980
November	1st to 10th	Day	16% 7% 3 6% 3 3 3 3 5% 6% 45%	1858
	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	14% 8% 2 5% 4 3 4 2 4 8% 45%	1710
	11th to 20th	Night	14% 5% 2 5% 5% 4 4 3 4 8% 45%	1620
	21st to end	Night	15% 7% 2 5% 3 3 3 4 7% 9% 43%	1745
June	1st to 10th	Night	6% 3 1 2 3 3 4 3 6% 8% 60%	1620
	11th to 20th	Night	6% 3 1 4 3 3 3 4 5% 9% 58%	1620
	21st to end	Night	7% 5% 2 4 4 4 4 5% 6% 10% 48%	1620
July	1st to 10th	Night	9% 6% 2 5% 6% 3 4 4 7% 10% 44%	1620
	11th to 20th	Night	3 3 1 3 3 3 5% 4 6% 8% 61%	1620
	21st to end	Night	5% 3 1 3 2 3 3 4 7% 10% 58%	1772
August	1st to 10th	Night	3 2 1 2 3 2 2 3 5% 8% 68%	1718
	11th to 20th	Night	5% 3 2 4 3 4 5% 4 6% 11% 54%	1778
	21st to end	Night	7% 4 2 5% 4 4 5% 4 7% 10% 49%	2034
September	1st to 10th	Night	8% 5% 3 6% 4 5% 5% 3 6% 8% 47%	1980
	11th to 20th	Night	10% 6% 2 6% 4 3 5% 4 6% 8% 45%	1980
	21st to end	Night	8% 5% 2 6% 4 3 4 3 6% 8% 50%	1980
October	1st to 10th	Night	7% 4 1 4 3 3 3 3 5% 6% 59%	1980
	11th to 20th	Night	13% 6% 2 4 3 2 3 4 4 6% 53%	2024
	21st to end	Night	15% 5% 1 3 3 2 2 2 2 5% 61%	2376
November	1st to 10th	Night	12% 7% 2 5% 3 3 3 2 4 6% 54%	2220
	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	47% 4 8% 17% 18% 7%	2470
	11th to 20th	Day	46% 4 9% 20% 18% 4	2334
	21st to end	Day	48% 5% 10% 22% 15% 1	2531
June	1st to 10th	Day	33% 5% 13% 26% 19% 3	2340
	11th to 20th	Day	36% 4 12% 26% 17% 4	2340
	21st to end	Day	42% 7% 10% 24% 14% 3	2340
July	1st to 10th	Day	44% 5% 15% 25% 10% 1	2276
	11th to 20th	Day	29% 5% 17% 29% 18% 2	2271
	21st to end	Day	26% 5% 21% 34% 13% 1	2405
August	1st to 10th	Day	20% 4 16% 40% 19% 1	2202
	11th to 20th	Day	30% 5% 20% 31% 12% 3	2123
	21st to end	Day	36% 6% 17% 25% 13% 3	2322
September	1st to 10th	Day	42% 5% 11% 20% 16% 6%	1980
	11th to 20th	Day	41% 6% 10% 20% 17% 5%	1980
	21st to end	Day	35% 4 10% 22% 18% 10%	1980
October	1st to 10th	Day	32% 4 9% 20% 26% 9%	1980
	11th to 20th	Day	36% 4 8% 17% 19% 16%	1916
	21st to end	Day	32% 2 4 17% 24% 20%	1980
November	1st to 10th	Day	42% 3 6% 21% 17% 11%	1858
	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	41% 3 11% 20% 15% 10%	1710
	11th to 20th	Night	39% 4 11% 24% 16% 5%	1621
	21st to end	Night	40% 6% 14% 26% 13% 2	1746
June	1st to 10th	Night	24% 4 17% 32% 21% 3	1620
	11th to 20th	Night	25% 5% 15% 30% 20% 5%	1620
	21st to end	Night	32% 6% 18% 27% 14% 3	1620
July	1st to 10th	Night	34% 7% 20% 28% 9% 2	1575
	11th to 20th	Night	20% 7% 20% 32% 19% 2	1566
	21st to end	Night	20% 6% 28% 34% 10% 1	1673
August	1st to 10th	Night	16% 4 23% 40% 16% 1	1708
	11th to 20th	Night	25% 8% 23% 30% 12% 2	1778
	21st to end	Night	31% 6% 24% 24% 12% 3	2034
September	1st to 10th	Night	35% 6% 15% 21% 17% 6%	1980
	11th to 20th	Night	38% 7% 15% 21% 15% 4	1980
	21st to end	Night	32% 5% 12% 22% 18% 11%	1980
October	1st to 10th	Night	27% 3 11% 26% 21% 11%	1980
	11th to 20th	Night	33% 4 9% 17% 20% 17%	2024
	21st to end	Night	30% 2 5% 16% 25% 22%	2376
November	1st to 10th	Night	36% 3 6% 20% 22% 14%	2220
	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% 14% 38% 24% 4	653
	11th to 20th	Day	18% 12% 31% 32% 5% 1	637
	21st to end	Day	19% 5% 30% 33% 12%	679
June	1st to 10th	Day	8% 3 22% 44% 20% 3	630
	11th to 20th	Day	9% 2 24% 46% 17% 2	630
	21st to end	Day	11% 3 17% 39% 26% 5%	630
July	1st to 10th	Day	12% 3 13% 36% 29% 7%	621
	11th to 20th	Day	6% 8% 41% 41% 3	618
	21st to end	Day	4 1 8% 39% 40% 8%	684
August	1st to 10th	Day	3 5% 44% 39% 9%	514
	11th to 20th	Day	8% 1 7% 42% 35% 8%	437
	21st to end	Day	5% 2 6% 38% 39% 10%	441
September	1st to 10th	Day	12% 1 9% 29% 37% 12%	270
	11th to 20th	Day	7% 1 6% 35% 46% 6%	270
	21st to end	Day	9% 2 15% 31% 35% 8%	270
October	1st to 10th	Day	6% 4 19% 40% 27% 4	270
	11th to 20th	Day	14% 4 23% 40% 17% 2	270
	21st to end	Day	20% 15% 27% 24% 12% 2	297
November	1st to 10th	Day	17% 10% 34% 24% 11% 2	270
	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	19% 12% 41% 26% 3	570
	11th to 20th	Night	17% 9% 35% 31% 7% 1	540
	21st to end	Night	18% 6% 35% 32% 9%	584
June	1st to 10th	Night	6% 2 28% 46% 18% 1	540
	11th to 20th	Night	6% 1 38% 44% 11%	540
	21st to end	Night	8% 3 25% 40% 22% 1	540
July	1st to 10th	Night	10% 2 16% 48% 23% 2	525
	11th to 20th	Night	3 1 12% 56% 25% 2	522
	21st to end	Night	5% 1 12% 54% 25% 3	591
August	1st to 10th	Night	2 1 11% 52% 33% 1	537
	11th to 20th	Night	6% 1 9% 52% 29% 2	534
	21st to end	Night	6% 2 8% 45% 35% 4	594
September	1st to 10th	Night	9% 1 11% 44% 31% 4	540
	11th to 20th	Night	12% 2 11% 40% 33% 3	540
	21st to end	Night	11% 2 13% 40% 30% 4	540
October	1st to 10th	Night	8% 2 14% 50% 24% 3	540
	11th to 20th	Night	15% 5% 23% 38% 18% 1	584
	21st to end	Night	18% 7% 25% 29% 19% 3	792
November	1st to 10th	Night	14% 7% 21% 37% 19% 2	740
	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 2024-05-10 11:39:00. Version ac07

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