Lake Murray Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Murray Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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 6% 4 4 5% 4 6% 8% 42%	101147
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 43%	97822
Transparency	Day	38% 7% 11% 20% 18% 6%	104863
	Night	38% 6% 10% 19% 19% 8%	102245
Seeing	Day	15% 10% 24% 24% 19% 7%	15278
	Night	15% 9% 25% 31% 18% 2	25330

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	16% 4 2 5% 3 4 4 3 6% 8% 47%	2836
	11th to 20th	Day	12% 6% 2 5% 3 3 3 3 4 6% 53%	2840
	21st to end	Day	18% 9% 3 6% 3 3 3 2 3 5% 45%	3124
February	1st to 10th	Day	14% 7% 3 6% 5% 4 4 4 6% 7% 40%	1753
	11th to 20th	Day	19% 7% 2 5% 3 3 4 3 4 6% 44%	1848
	21st to end	Day	17% 7% 2 6% 4 4 4 4 5% 5% 42%	1604
March	1st to 10th	Day	22% 9% 3 6% 4 3 3 2 3 4 39%	3435
	11th to 20th	Day	9% 4 2 5% 4 4 4 3 5% 7% 53%	3480
	21st to end	Day	19% 7% 3 5% 3 4 4 3 5% 5% 42%	3815
April	1st to 10th	Day	10% 4 3 4 3 3 5% 4 6% 7% 50%	2090
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 7% 7% 48%	2205
	21st to end	Day	9% 4 2 4 4 5% 4 4 6% 8% 51%	2432
May	1st to 10th	Day	9% 6% 3 6% 4 4 5% 4 7% 10% 41%	4082
	11th to 20th	Day	15% 8% 3 7% 4 5% 5% 4 6% 6% 37%	4081
	21st to end	Day	6% 4 2 5% 4 4 6% 4 7% 9% 48%	4476
June	1st to 10th	Day	10% 6% 3 7% 5% 6% 5% 5% 8% 10% 36%	2470
	11th to 20th	Day	6% 5% 1 5% 4 5% 7% 4 8% 11% 42%	2470
	21st to end	Day	4 5% 2 6% 5% 5% 6% 6% 9% 12% 39%	2470
July	1st to 10th	Day	13% 6% 2 8% 5% 7% 7% 6% 8% 9% 28%	4120
	11th to 20th	Day	6% 5% 2 7% 7% 7% 7% 6% 10% 14% 30%	4120
	21st to end	Day	11% 6% 3 9% 7% 7% 8% 6% 9% 12% 24%	4466
August	1st to 10th	Day	22% 6% 2 6% 6% 6% 6% 5% 7% 10% 25%	4104
	11th to 20th	Day	12% 5% 2 7% 5% 6% 6% 5% 8% 10% 35%	4044
	21st to end	Day	8% 4 2 5% 4 5% 5% 5% 7% 10% 47%	4163
September	1st to 10th	Day	7% 5% 2 8% 6% 6% 5% 5% 8% 8% 41%	2090
	11th to 20th	Day	15% 6% 3 6% 4 4 4 4 5% 8% 40%	2090
	21st to end	Day	17% 7% 2 5% 3 4 4 4 5% 6% 43%	2090
October	1st to 10th	Day	13% 7% 2 5% 4 3 2 3 4 6% 52%	2008
	11th to 20th	Day	11% 4 1 5% 3 2 3 2 4 5% 60%	1900
	21st to end	Day	11% 6% 2 5% 3 3 3 2 3 5% 57%	2090
November	1st to 10th	Day	13% 5% 2 5% 3 3 3 3 4 5% 55%	1887
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 4 6% 53%	1767
	21st to end	Day	14% 6% 2 5% 4 3 4 3 4 5% 49%	1710
December	1st to 10th	Day	18% 8% 3 6% 5% 4 4 4 6% 6% 38%	1710
	11th to 20th	Day	17% 4 2 4 3 3 4 3 4 6% 51%	2153
	21st to end	Day	18% 7% 2 6% 4 3 3 3 5% 7% 43%	3124
January	1st to 10th	Night	16% 6% 2 5% 4 4 4 3 4 6% 47%	4109
	11th to 20th	Night	9% 7% 2 6% 5% 4 4 4 6% 7% 45%	4120
	21st to end	Night	17% 9% 3 6% 3 3 4 2 4 3 45%	4532
February	1st to 10th	Night	16% 7% 2 5% 4 4 4 3 5% 6% 45%	2423
	11th to 20th	Night	19% 7% 3 5% 4 3 3 3 4 5% 45%	2218
	21st to end	Night	15% 5% 2 6% 4 4 4 3 6% 6% 45%	1848
March	1st to 10th	Night	21% 9% 3 6% 4 4 3 3 5% 6% 35%	3418
	11th to 20th	Night	12% 4 2 4 4 4 3 3 6% 8% 51%	3480
	21st to end	Night	18% 6% 2 5% 3 4 4 4 5% 7% 42%	3817
April	1st to 10th	Night	10% 5% 2 4 4 4 4 4 5% 7% 51%	2090
	11th to 20th	Night	11% 4 2 5% 4 4 4 3 4 6% 53%	1923
	21st to end	Night	8% 4 2 5% 4 3 4 3 6% 7% 54%	1762
May	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 7% 10% 42%	2813
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 5% 6% 8% 40%	2812
	21st to end	Night	6% 4 2 5% 5% 4 5% 5% 7% 10% 48%	3079
June	1st to 10th	Night	10% 6% 4 7% 6% 6% 6% 5% 8% 10% 34%	1710
	11th to 20th	Night	8% 6% 2 6% 5% 5% 4 5% 6% 11% 41%	1710
	21st to end	Night	6% 6% 3 7% 5% 5% 5% 7% 9% 12% 35%	1710
July	1st to 10th	Night	13% 8% 3 8% 5% 6% 6% 4 7% 10% 30%	2840
	11th to 20th	Night	9% 5% 2 7% 5% 5% 6% 6% 9% 14% 31%	2840
	21st to end	Night	12% 8% 3 9% 7% 7% 6% 6% 8% 11% 24%	3087
August	1st to 10th	Night	22% 6% 3 8% 5% 5% 6% 5% 7% 10% 23%	2825
	11th to 20th	Night	12% 6% 2 7% 5% 5% 6% 4 7% 10% 36%	2785
	21st to end	Night	6% 4 1 5% 4 4 5% 4 7% 10% 49%	3454
September	1st to 10th	Night	9% 6% 2 5% 5% 5% 6% 4 7% 9% 41%	2090
	11th to 20th	Night	13% 7% 3 7% 5% 5% 5% 4 7% 8% 38%	2090
	21st to end	Night	16% 5% 2 6% 4 4 4 4 5% 6% 44%	2090
October	1st to 10th	Night	13% 7% 2 4 3 3 3 3 4 6% 52%	2171
	11th to 20th	Night	13% 4 2 5% 3 3 3 3 4 5% 56%	2280
	21st to end	Night	10% 5% 1 5% 3 4 3 3 4 5% 57%	2508
November	1st to 10th	Night	12% 6% 3 4 3 3 3 2 3 5% 55%	2264
	11th to 20th	Night	13% 6% 2 5% 4 2 3 3 4 6% 53%	2410
	21st to end	Night	13% 6% 2 5% 4 3 4 4 6% 6% 48%	2470
December	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 6% 43%	2470
	11th to 20th	Night	16% 5% 2 5% 3 2 3 2 4 5% 52%	3042
	21st to end	Night	18% 7% 3 6% 4 4 4 3 5% 6% 39%	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% 6% 6% 23% 23% 7%	2837
	11th to 20th	Day	34% 4 5% 18% 29% 11%	2840
	21st to end	Day	44% 3 4 16% 25% 8%	3124
February	1st to 10th	Day	42% 4 9% 20% 19% 6%	1753
	11th to 20th	Day	42% 4 5% 18% 24% 6%	1858
	21st to end	Day	43% 5% 8% 14% 21% 9%	1604
March	1st to 10th	Day	51% 4 6% 16% 13% 10%	3435
	11th to 20th	Day	30% 6% 8% 16% 29% 11%	3480
	21st to end	Day	45% 4 6% 19% 22% 5%	3815
April	1st to 10th	Day	32% 5% 10% 19% 27% 6%	2090
	11th to 20th	Day	34% 5% 10% 18% 21% 11%	2205
	21st to end	Day	31% 7% 9% 26% 22% 4	2432
May	1st to 10th	Day	37% 9% 14% 24% 15% 2	4120
	11th to 20th	Day	45% 8% 11% 21% 15% 1	4085
	21st to end	Day	28% 9% 17% 22% 22% 2	4489
June	1st to 10th	Day	40% 11% 16% 21% 10% 2	2470
	11th to 20th	Day	32% 10% 16% 27% 14% 1	2470
	21st to end	Day	34% 12% 16% 22% 14% 2	2470
July	1st to 10th	Day	46% 11% 17% 17% 7% 2	4055
	11th to 20th	Day	37% 15% 25% 18% 4 1	4051
	21st to end	Day	48% 15% 18% 15% 4 1	4324
August	1st to 10th	Day	52% 10% 17% 16% 4	4091
	11th to 20th	Day	41% 10% 15% 19% 14% 1	4083
	21st to end	Day	30% 8% 15% 29% 17% 2	4163
September	1st to 10th	Day	37% 9% 14% 17% 18% 5%	2090
	11th to 20th	Day	42% 8% 10% 18% 19% 4	2090
	21st to end	Day	41% 5% 9% 20% 17% 7%	2090
October	1st to 10th	Day	31% 4 6% 18% 30% 10%	3333
	11th to 20th	Day	18% 2 5% 17% 27% 31%	3140
	21st to end	Day	26% 3 4 20% 31% 15%	3428
November	1st to 10th	Day	33% 4 6% 18% 27% 12%	1887
	11th to 20th	Day	33% 4 7% 21% 25% 11%	1767
	21st to end	Day	38% 5% 7% 19% 23% 9%	1710
December	1st to 10th	Day	45% 5% 8% 18% 17% 7%	1710
	11th to 20th	Day	36% 3 7% 22% 22% 11%	2150
	21st to end	Day	42% 4 7% 21% 24% 3	3124
January	1st to 10th	Night	38% 5% 5% 19% 26% 7%	4109
	11th to 20th	Night	37% 4 7% 20% 24% 8%	4120
	21st to end	Night	43% 5% 4 15% 26% 8%	4532
February	1st to 10th	Night	41% 4 7% 18% 21% 9%	2423
	11th to 20th	Night	42% 4 6% 18% 21% 9%	2219
	21st to end	Night	40% 5% 9% 17% 19% 10%	1848
March	1st to 10th	Night	49% 5% 9% 14% 15% 7%	3418
	11th to 20th	Night	32% 5% 8% 14% 27% 15%	3480
	21st to end	Night	41% 5% 7% 20% 18% 9%	3817
April	1st to 10th	Night	33% 4 10% 20% 24% 9%	2090
	11th to 20th	Night	33% 4 8% 20% 23% 11%	1923
	21st to end	Night	28% 6% 10% 27% 24% 5%	1762
May	1st to 10th	Night	35% 9% 14% 25% 15% 3	2840
	11th to 20th	Night	40% 8% 14% 21% 16% 1	2813
	21st to end	Night	27% 10% 12% 26% 21% 3	3087
June	1st to 10th	Night	42% 10% 15% 20% 11% 2	1710
	11th to 20th	Night	35% 9% 17% 24% 13% 2	1710
	21st to end	Night	36% 13% 18% 20% 11% 2	1710
July	1st to 10th	Night	47% 10% 20% 14% 7% 2	2795
	11th to 20th	Night	39% 15% 26% 15% 4 1	2786
	21st to end	Night	53% 13% 19% 11% 4	2988
August	1st to 10th	Night	55% 11% 17% 14% 3	2814
	11th to 20th	Night	41% 10% 21% 20% 8% 1	2812
	21st to end	Night	28% 9% 15% 29% 17% 3	3454
September	1st to 10th	Night	36% 9% 15% 19% 15% 5%	2090
	11th to 20th	Night	42% 8% 11% 18% 17% 3	2090
	21st to end	Night	40% 7% 12% 18% 18% 5%	2090
October	1st to 10th	Night	33% 4 9% 18% 30% 7%	3626
	11th to 20th	Night	19% 2 5% 16% 26% 31%	3779
	21st to end	Night	25% 4 5% 19% 29% 19%	4120
November	1st to 10th	Night	32% 4 7% 16% 27% 14%	2264
	11th to 20th	Night	35% 3 6% 18% 25% 14%	2410
	21st to end	Night	36% 4 8% 18% 24% 10%	2470
December	1st to 10th	Night	42% 5% 9% 19% 19% 7%	2470
	11th to 20th	Night	36% 4 7% 18% 27% 9%	3044
	21st to end	Night	45% 4 6% 20% 20% 4	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	17% 28% 39% 14% 3	270
	11th to 20th	Day	22% 24% 33% 19% 1	270
	21st to end	Day	22% 27% 38% 12% 2	297
February	1st to 10th	Day	17% 27% 38% 14% 4	270
	11th to 20th	Day	32% 19% 35% 13% 1	270
	21st to end	Day	25% 23% 34% 13% 4	259
March	1st to 10th	Day	19% 20% 32% 21% 8%	460
	11th to 20th	Day	19% 17% 42% 16% 5%	460
	21st to end	Day	20% 19% 38% 15% 8%	506
April	1st to 10th	Day	19% 17% 34% 20% 10%	460
	11th to 20th	Day	14% 16% 33% 21% 14% 2	452
	21st to end	Day	11% 12% 33% 25% 16% 3	460
May	1st to 10th	Day	10% 13% 34% 27% 13% 4	463
	11th to 20th	Day	16% 5% 21% 32% 17% 9%	487
	21st to end	Day	12% 7% 17% 27% 26% 12%	529
June	1st to 10th	Day	11% 5% 16% 33% 25% 10%	490
	11th to 20th	Day	10% 4 20% 25% 28% 13%	490
	21st to end	Day	7% 3 15% 34% 28% 13%	490
July	1st to 10th	Day	9% 2 9% 25% 32% 23%	485
	11th to 20th	Day	7% 2 12% 25% 37% 17%	484
	21st to end	Day	6% 2 11% 33% 35% 12%	532
August	1st to 10th	Day	14% 3 12% 26% 31% 13%	486
	11th to 20th	Day	13% 5% 11% 25% 29% 17%	479
	21st to end	Day	12% 4 10% 29% 29% 17%	539
September	1st to 10th	Day	8% 4 12% 31% 33% 13%	490
	11th to 20th	Day	18% 4 14% 26% 28% 11%	490
	21st to end	Day	20% 3 16% 28% 27% 7%	490
October	1st to 10th	Day	16% 5% 22% 31% 18% 8%	490
	11th to 20th	Day	11% 8% 25% 30% 21% 6%	490
	21st to end	Day	12% 9% 27% 28% 19% 5%	539
November	1st to 10th	Day	16% 10% 27% 27% 15% 6%	467
	11th to 20th	Day	19% 13% 37% 24% 6% 2	327
	21st to end	Day	11% 14% 40% 23% 11% 1	270
December	1st to 10th	Day	25% 19% 33% 18% 4	270
	11th to 20th	Day	23% 14% 41% 15% 6% 1	270
	21st to end	Day	26% 20% 32% 15% 4 2	297
January	1st to 10th	Night	20% 17% 33% 25% 6%	760
	11th to 20th	Night	18% 15% 33% 28% 6%	760
	21st to end	Night	20% 18% 37% 22% 3	836
February	1st to 10th	Night	19% 14% 34% 28% 4	760
	11th to 20th	Night	22% 17% 35% 24% 2	743
	21st to end	Night	18% 17% 37% 24% 4	628
March	1st to 10th	Night	17% 13% 35% 29% 6%	760
	11th to 20th	Night	18% 13% 39% 23% 7%	760
	21st to end	Night	16% 15% 37% 24% 7%	836
April	1st to 10th	Night	15% 16% 32% 28% 9%	760
	11th to 20th	Night	14% 13% 30% 32% 12%	751
	21st to end	Night	10% 9% 33% 36% 11%	622
May	1st to 10th	Night	11% 8% 32% 36% 12%	570
	11th to 20th	Night	11% 4 30% 34% 18% 3	561
	21st to end	Night	9% 3 17% 39% 28% 4	617
June	1st to 10th	Night	11% 2 22% 38% 22% 5%	570
	11th to 20th	Night	10% 3 16% 33% 30% 9%	570
	21st to end	Night	8% 2 15% 38% 31% 6%	570
July	1st to 10th	Night	10% 1 10% 36% 36% 7%	555
	11th to 20th	Night	9% 1 8% 36% 38% 8%	552
	21st to end	Night	7% 3 10% 37% 38% 5%	624
August	1st to 10th	Night	12% 2 9% 32% 39% 6%	567
	11th to 20th	Night	15% 2 8% 34% 37% 4	564
	21st to end	Night	12% 2 11% 31% 40% 5%	767
September	1st to 10th	Night	10% 4 10% 35% 36% 5%	760
	11th to 20th	Night	15% 3 14% 28% 35% 5%	760
	21st to end	Night	18% 3 15% 33% 27% 4	760
October	1st to 10th	Night	15% 5% 18% 31% 26% 4	760
	11th to 20th	Night	15% 6% 23% 31% 22% 3	760
	21st to end	Night	11% 9% 24% 32% 22% 2	836
November	1st to 10th	Night	14% 8% 24% 32% 19% 3	755
	11th to 20th	Night	15% 11% 31% 30% 12% 1	760
	21st to end	Night	15% 9% 30% 30% 14% 1	760
December	1st to 10th	Night	18% 14% 27% 32% 9% 1	760
	11th to 20th	Night	20% 9% 27% 33% 10% 1	760
	21st to end	Night	26% 14% 26% 27% 7% 1	836

Page generated at 2024-11-01 22:47:47. Version ac07

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