Marble Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marble Lake Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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	17% 10% 4 7% 6% 3 5% 5% 5% 7% 32%	74727
	Night	16% 11% 4 7% 6% 3 4 4 5% 6% 33%	75041
Transparency	Day	53% 3 10% 21% 12% 2	74432
	Night	52% 3 11% 22% 11% 1	74870
Seeing	Day	24% 14% 31% 20% 8% 3	13334
	Night	23% 12% 31% 24% 9% 1	22653

By Month

Percentage Cloud Cover NE (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% 17% 7% 11% 7% 3 5% 4 5% 6% 20%	1517
	11th to 20th	Day	18% 16% 8% 9% 6% 4 4 4 4 4 23%	1472
	21st to end	Day	14% 13% 6% 13% 9% 4 5% 4 4 6% 22%	1741
February	1st to 10th	Day	14% 15% 7% 12% 8% 4 5% 5% 5% 5% 20%	1620
	11th to 20th	Day	12% 16% 6% 10% 7% 3 4 4 4 5% 29%	1573
	21st to end	Day	19% 15% 4 8% 7% 3 5% 4 4 5% 25%	1434
March	1st to 10th	Day	14% 12% 5% 8% 8% 4 6% 4 4 4 28%	1872
	11th to 20th	Day	12% 16% 5% 7% 7% 4 6% 4 5% 5% 30%	1980
	21st to end	Day	19% 12% 3 5% 5% 2 4 3 4 5% 38%	2240
April	1st to 10th	Day	20% 12% 3 7% 6% 3 5% 4 4 6% 31%	2160
	11th to 20th	Day	20% 9% 3 5% 5% 2 4 4 4 6% 38%	2134
	21st to end	Day	21% 9% 4 7% 6% 3 5% 4 4 5% 32%	2299
May	1st to 10th	Day	18% 9% 4 6% 5% 3 4 6% 6% 6% 34%	2488
	11th to 20th	Day	16% 7% 3 7% 6% 3 4 4 4 7% 38%	2478
	21st to end	Day	13% 5% 3 6% 6% 4 5% 6% 6% 8% 38%	2725
June	1st to 10th	Day	20% 9% 3 6% 6% 3 6% 5% 6% 7% 30%	2520
	11th to 20th	Day	15% 6% 2 5% 5% 4 5% 6% 6% 9% 37%	2520
	21st to end	Day	17% 7% 3 7% 5% 4 6% 6% 6% 8% 33%	2520
July	1st to 10th	Day	12% 6% 3 5% 6% 4 5% 6% 7% 8% 39%	2520
	11th to 20th	Day	11% 7% 3 7% 5% 4 6% 6% 7% 9% 37%	2520
	21st to end	Day	11% 6% 3 5% 6% 4 7% 6% 7% 9% 36%	2744
August	1st to 10th	Day	11% 6% 3 6% 6% 4 6% 5% 6% 8% 37%	2366
	11th to 20th	Day	13% 7% 2 7% 6% 4 5% 6% 6% 8% 36%	2303
	21st to end	Day	15% 6% 2 6% 6% 3 6% 6% 6% 7% 36%	2399
September	1st to 10th	Day	15% 6% 3 6% 6% 3 4 5% 5% 8% 40%	2160
	11th to 20th	Day	12% 6% 3 5% 5% 3 4 4 5% 8% 45%	2160
	21st to end	Day	18% 6% 2 6% 5% 4 5% 4 5% 6% 38%	1893
October	1st to 10th	Day	21% 8% 3 6% 6% 3 5% 4 4 6% 34%	1800
	11th to 20th	Day	22% 9% 4 8% 7% 4 5% 5% 4 8% 25%	1800
	21st to end	Day	27% 11% 3 7% 7% 3 4 4 4 5% 24%	1908
November	1st to 10th	Day	15% 8% 4 7% 6% 4 5% 5% 6% 8% 33%	1623
	11th to 20th	Day	16% 14% 5% 8% 7% 3 5% 4 4 5% 28%	1520
	21st to end	Day	22% 14% 6% 8% 7% 4 5% 4 5% 6% 19%	1520
December	1st to 10th	Day	21% 17% 7% 10% 7% 3 5% 5% 4 5% 16%	1520
	11th to 20th	Day	19% 14% 7% 8% 6% 3 4 4 5% 5% 26%	1906
	21st to end	Day	26% 19% 5% 11% 6% 3 2 3 2 4 19%	2772
January	1st to 10th	Night	18% 14% 7% 12% 8% 4 4 5% 4 5% 20%	2649
	11th to 20th	Night	17% 16% 6% 10% 7% 4 4 4 4 6% 22%	2577
	21st to end	Night	12% 14% 6% 10% 9% 4 4 5% 4 6% 27%	2614
February	1st to 10th	Night	13% 15% 6% 9% 7% 4 6% 5% 6% 6% 22%	2340
	11th to 20th	Night	13% 12% 6% 8% 7% 4 5% 5% 5% 6% 30%	2273
	21st to end	Night	13% 14% 5% 8% 6% 3 4 5% 6% 7% 29%	1821
March	1st to 10th	Night	15% 11% 4 7% 7% 4 5% 4 4 6% 32%	2074
	11th to 20th	Night	14% 13% 6% 6% 6% 3 4 4 5% 6% 34%	1979
	21st to end	Night	15% 9% 4 7% 5% 3 4 3 4 6% 39%	2116
April	1st to 10th	Night	19% 10% 4 6% 5% 2 4 4 5% 6% 34%	1800
	11th to 20th	Night	17% 9% 4 6% 5% 2 4 4 4 7% 37%	1775
	21st to end	Night	18% 9% 3 7% 5% 3 4 5% 6% 7% 33%	1674
May	1st to 10th	Night	19% 8% 3 4 4 3 4 4 4 7% 38%	1470
	11th to 20th	Night	15% 7% 3 5% 5% 3 4 4 5% 8% 42%	1415
	21st to end	Night	11% 5% 2 4 4 3 5% 4 6% 7% 47%	1550
June	1st to 10th	Night	15% 7% 3 6% 5% 4 5% 6% 6% 8% 35%	1440
	11th to 20th	Night	13% 4 3 5% 4 3 4 5% 5% 9% 44%	1440
	21st to end	Night	15% 7% 3 6% 5% 3 5% 4 5% 8% 38%	1440
July	1st to 10th	Night	8% 5% 2 6% 4 4 5% 5% 5% 8% 48%	1440
	11th to 20th	Night	11% 5% 3 5% 5% 3 5% 5% 6% 9% 44%	1440
	21st to end	Night	10% 4 3 4 4 3 5% 5% 7% 8% 47%	1574
August	1st to 10th	Night	10% 6% 3 5% 5% 3 3 4 6% 8% 47%	1568
	11th to 20th	Night	9% 6% 3 5% 5% 4 4 6% 7% 7% 44%	1598
	21st to end	Night	11% 5% 3 6% 5% 3 4 4 5% 8% 46%	1939
September	1st to 10th	Night	10% 5% 3 5% 5% 3 5% 4 7% 9% 45%	1800
	11th to 20th	Night	12% 4 2 4 4 2 4 6% 5% 7% 49%	1800
	21st to end	Night	17% 6% 2 5% 5% 2 4 4 5% 5% 44%	2061
October	1st to 10th	Night	18% 8% 3 6% 6% 3 3 5% 4 6% 38%	2160
	11th to 20th	Night	21% 10% 3 7% 6% 3 4 4 6% 6% 30%	2160
	21st to end	Night	22% 11% 3 8% 6% 3 4 4 5% 7% 27%	2448
November	1st to 10th	Night	16% 11% 4 6% 4 2 5% 5% 5% 7% 36%	2454
	11th to 20th	Night	18% 10% 5% 7% 6% 3 5% 5% 5% 7% 30%	2660
	21st to end	Night	20% 13% 4 8% 6% 4 5% 5% 5% 6% 24%	2660
December	1st to 10th	Night	20% 17% 5% 10% 7% 4 5% 5% 5% 6% 18%	2660
	11th to 20th	Night	20% 16% 6% 8% 6% 3 4 4 4 5% 26%	3288
	21st to end	Night	27% 19% 4 10% 6% 3 4 3 3 4 16%	4884

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	66% 2 10% 15% 6%	1518
	11th to 20th	Day	66% 2 7% 12% 11% 2	1472
	21st to end	Day	65% 2 7% 14% 11% 3	1741
February	1st to 10th	Day	67% 3 7% 16% 6% 1	1620
	11th to 20th	Day	60% 2 9% 17% 11% 2	1582
	21st to end	Day	64% 2 9% 13% 12% 1	1434
March	1st to 10th	Day	60% 2 11% 16% 10% 2	1875
	11th to 20th	Day	58% 3 9% 16% 12% 2	1980
	21st to end	Day	51% 2 7% 20% 14% 6%	2240
April	1st to 10th	Day	56% 2 6% 18% 14% 3	2160
	11th to 20th	Day	49% 2 7% 23% 17% 2	2134
	21st to end	Day	56% 1 7% 17% 15% 4	2299
May	1st to 10th	Day	50% 3 9% 18% 15% 4	2488
	11th to 20th	Day	48% 3 7% 23% 16% 3	2482
	21st to end	Day	44% 4 14% 21% 15% 3	2725
June	1st to 10th	Day	54% 3 9% 20% 13% 1	2520
	11th to 20th	Day	44% 4 11% 25% 14% 2	2520
	21st to end	Day	50% 3 13% 21% 13% 1	2520
July	1st to 10th	Day	42% 3 9% 29% 15% 1	2450
	11th to 20th	Day	43% 4 13% 28% 11%	2445
	21st to end	Day	44% 4 13% 27% 11% 1	2591
August	1st to 10th	Day	44% 4 14% 26% 12% 1	2352
	11th to 20th	Day	46% 3 15% 26% 10% 1	2303
	21st to end	Day	45% 3 11% 28% 12% 1	2399
September	1st to 10th	Day	43% 2 12% 29% 13% 1	2160
	11th to 20th	Day	39% 2 12% 31% 15% 1	2160
	21st to end	Day	47% 2 12% 28% 10%	1893
October	1st to 10th	Day	52% 2 11% 22% 12% 1	1800
	11th to 20th	Day	59% 2 13% 18% 6% 1	1800
	21st to end	Day	63% 3 9% 17% 8%	1908
November	1st to 10th	Day	50% 3 15% 24% 8% 1	1623
	11th to 20th	Day	59% 3 12% 16% 9% 2	1520
	21st to end	Day	67% 3 10% 11% 8% 1	1520
December	1st to 10th	Day	72% 2 9% 13% 5%	1520
	11th to 20th	Day	63% 2 14% 12% 8%	1906
	21st to end	Day	73% 1 6% 15% 6%	2772
January	1st to 10th	Night	67% 2 8% 16% 6%	2649
	11th to 20th	Night	66% 2 9% 14% 8% 1	2577
	21st to end	Night	60% 3 7% 17% 13% 1	2614
February	1st to 10th	Night	61% 3 10% 19% 7% 1	2340
	11th to 20th	Night	56% 2 10% 21% 10% 1	2275
	21st to end	Night	56% 3 9% 20% 11% 1	1821
March	1st to 10th	Night	53% 2 10% 19% 14% 2	2084
	11th to 20th	Night	53% 2 10% 21% 13% 2	1980
	21st to end	Night	48% 2 7% 23% 17% 3	2116
April	1st to 10th	Night	52% 2 7% 22% 15% 3	1800
	11th to 20th	Night	49% 2 7% 23% 18% 2	1775
	21st to end	Night	51% 3 8% 18% 17% 3	1674
May	1st to 10th	Night	46% 2 8% 21% 18% 4	1470
	11th to 20th	Night	42% 2 9% 27% 18% 3	1416
	21st to end	Night	37% 3 15% 22% 20% 3	1551
June	1st to 10th	Night	47% 3 12% 24% 13% 1	1440
	11th to 20th	Night	39% 3 13% 25% 18% 2	1440
	21st to end	Night	45% 3 15% 24% 13% 1	1440
July	1st to 10th	Night	34% 4 13% 27% 20% 3	1400
	11th to 20th	Night	37% 3 13% 34% 14%	1392
	21st to end	Night	35% 3 17% 32% 13% 1	1486
August	1st to 10th	Night	36% 4 18% 29% 12% 1	1558
	11th to 20th	Night	38% 4 16% 30% 12% 1	1598
	21st to end	Night	38% 3 14% 31% 13% 1	1939
September	1st to 10th	Night	36% 4 15% 29% 15% 1	1800
	11th to 20th	Night	35% 3 14% 36% 12% 1	1800
	21st to end	Night	42% 3 11% 32% 10% 1	2061
October	1st to 10th	Night	48% 3 10% 23% 15%	2160
	11th to 20th	Night	56% 2 13% 20% 8%	2160
	21st to end	Night	58% 3 12% 16% 10%	2448
November	1st to 10th	Night	49% 3 13% 24% 11% 1	2454
	11th to 20th	Night	55% 3 11% 20% 10% 2	2660
	21st to end	Night	61% 3 13% 18% 5%	2660
December	1st to 10th	Night	67% 3 10% 15% 4	2660
	11th to 20th	Night	62% 2 10% 17% 8% 1	3288
	21st to end	Night	74% 1 7% 13% 4	4884

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	26% 16% 33% 21% 4	180
	11th to 20th	Day	33% 14% 33% 14% 5%	168
	21st to end	Day	27% 18% 38% 12% 4 1	246
February	1st to 10th	Day	32% 28% 30% 9% 2	240
	11th to 20th	Day	33% 23% 39% 5% 1	240
	21st to end	Day	38% 17% 33% 11% 1	300
March	1st to 10th	Day	26% 21% 32% 16% 3	420
	11th to 20th	Day	28% 19% 33% 16% 4 1	420
	21st to end	Day	34% 18% 29% 13% 6%	462
April	1st to 10th	Day	28% 22% 29% 15% 6%	420
	11th to 20th	Day	32% 19% 24% 16% 8% 2	412
	21st to end	Day	28% 17% 34% 11% 8% 1	420
May	1st to 10th	Day	27% 14% 32% 18% 6% 3	423
	11th to 20th	Day	20% 14% 36% 20% 7% 3	447
	21st to end	Day	18% 14% 34% 21% 9% 4	485
June	1st to 10th	Day	24% 11% 36% 21% 7% 1	450
	11th to 20th	Day	18% 16% 29% 24% 11% 2	450
	21st to end	Day	20% 11% 34% 22% 11% 3	450
July	1st to 10th	Day	13% 8% 28% 33% 16% 3	445
	11th to 20th	Day	15% 8% 32% 28% 14% 3	444
	21st to end	Day	14% 9% 35% 28% 10% 3	488
August	1st to 10th	Day	14% 6% 29% 32% 14% 4	446
	11th to 20th	Day	14% 5% 27% 31% 18% 6%	439
	21st to end	Day	16% 8% 32% 25% 12% 6%	495
September	1st to 10th	Day	17% 10% 30% 23% 14% 6%	450
	11th to 20th	Day	14% 8% 27% 25% 15% 11%	450
	21st to end	Day	21% 11% 29% 20% 13% 6%	450
October	1st to 10th	Day	28% 13% 26% 16% 13% 4	450
	11th to 20th	Day	29% 17% 30% 18% 4 2	450
	21st to end	Day	33% 14% 30% 19% 4	459
November	1st to 10th	Day	28% 16% 30% 19% 6%	317
	11th to 20th	Day	31% 14% 37% 12% 4 1	180
	21st to end	Day	27% 24% 31% 13% 4 1	180
December	1st to 10th	Day	31% 15% 39% 12% 3 1	180
	11th to 20th	Day	36% 19% 32% 11% 1 1	180
	21st to end	Day	35% 21% 29% 12% 3 1	198
January	1st to 10th	Night	28% 16% 33% 19% 5%	760
	11th to 20th	Night	30% 15% 31% 19% 5% 1	737
	21st to end	Night	21% 15% 34% 22% 6% 1	792
February	1st to 10th	Night	24% 18% 37% 18% 2	720
	11th to 20th	Night	21% 17% 42% 16% 3	703
	21st to end	Night	24% 18% 37% 19% 2	592
March	1st to 10th	Night	22% 17% 37% 21% 3	720
	11th to 20th	Night	26% 16% 32% 21% 4 1	720
	21st to end	Night	23% 12% 35% 20% 9% 1	792
April	1st to 10th	Night	26% 14% 33% 23% 4	720
	11th to 20th	Night	24% 19% 29% 20% 7% 1	711
	21st to end	Night	24% 11% 29% 26% 9% 1	594
May	1st to 10th	Night	25% 8% 25% 32% 8% 2	390
	11th to 20th	Night	18% 10% 33% 31% 8%	354
	21st to end	Night	14% 8% 35% 28% 14% 1	389
June	1st to 10th	Night	19% 6% 31% 34% 9% 1	360
	11th to 20th	Night	14% 10% 30% 31% 13% 1	360
	21st to end	Night	17% 8% 25% 38% 12%	360
July	1st to 10th	Night	8% 5% 31% 39% 17% 1	350
	11th to 20th	Night	13% 3 29% 37% 17% 1	348
	21st to end	Night	10% 4 29% 42% 13% 1	394
August	1st to 10th	Night	12% 3 24% 36% 22% 2	494
	11th to 20th	Night	12% 3 21% 37% 24% 3	534
	21st to end	Night	14% 6% 28% 31% 19% 3	751
September	1st to 10th	Night	13% 6% 33% 27% 19% 2	720
	11th to 20th	Night	16% 5% 24% 29% 22% 4	720
	21st to end	Night	21% 9% 23% 26% 18% 3	720
October	1st to 10th	Night	24% 10% 27% 23% 14% 2	720
	11th to 20th	Night	29% 12% 30% 21% 8% 1	720
	21st to end	Night	30% 13% 30% 23% 5%	792
November	1st to 10th	Night	25% 13% 30% 24% 7% 1	740
	11th to 20th	Night	26% 15% 32% 17% 9% 1	760
	21st to end	Night	32% 16% 26% 21% 5% 1	760
December	1st to 10th	Night	32% 14% 31% 18% 4	760
	11th to 20th	Night	28% 17% 34% 19% 2 1	760
	21st to end	Night	35% 14% 32% 16% 3	836

Page generated at 2024-01-11 22:33:52. Version ac07

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