Lake of the Woods Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake of the Woods Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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% 4 4 4 4 6% 8% 42%	126927
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	124129
Transparency	Day	38% 7% 12% 22% 17% 4	130527
	Night	38% 6% 11% 22% 18% 4	128599
Seeing	Day	18% 12% 27% 25% 14% 5%	16452
	Night	17% 10% 29% 30% 13% 1	26113

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% 5% 2 5% 3 3 4 3 5% 5% 50%	3915
	11th to 20th	Day	13% 8% 2 5% 4 4 3 3 4 4 49%	4060
	21st to end	Day	15% 8% 3 6% 5% 4 4 3 4 5% 44%	4466
February	1st to 10th	Day	13% 9% 3 7% 5% 4 4 4 5% 7% 40%	1800
	11th to 20th	Day	19% 7% 2 6% 4 3 3 3 5% 6% 41%	1787
	21st to end	Day	17% 8% 3 7% 4 4 4 4 6% 6% 38%	1663
March	1st to 10th	Day	18% 6% 2 6% 5% 4 4 4 5% 7% 40%	4935
	11th to 20th	Day	10% 6% 2 6% 4 4 4 3 5% 6% 51%	4980
	21st to end	Day	16% 7% 2 6% 4 4 4 4 5% 6% 40%	5482
April	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 5% 7% 46%	2400
	11th to 20th	Day	14% 6% 2 5% 4 4 4 3 5% 6% 48%	2374
	21st to end	Day	17% 6% 2 6% 4 4 5% 3 6% 6% 41%	2400
May	1st to 10th	Day	16% 7% 2 7% 4 5% 6% 5% 7% 9% 33%	5812
	11th to 20th	Day	21% 7% 2 6% 4 4 4 4 7% 9% 33%	5943
	21st to end	Day	16% 5% 2 5% 4 4 4 4 6% 9% 40%	6934
June	1st to 10th	Day	11% 5% 2 5% 4 5% 6% 4 6% 10% 43%	2800
	11th to 20th	Day	11% 5% 2 7% 5% 5% 5% 4 6% 9% 42%	2800
	21st to end	Day	8% 4 1 5% 5% 5% 5% 5% 6% 10% 46%	2800
July	1st to 10th	Day	7% 4 2 6% 4 5% 6% 5% 8% 11% 41%	6360
	11th to 20th	Day	8% 7% 2 7% 5% 5% 7% 6% 11% 13% 28%	5900
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 11% 39%	6424
August	1st to 10th	Day	14% 6% 2 7% 4 5% 5% 5% 8% 11% 33%	4234
	11th to 20th	Day	9% 5% 2 7% 5% 6% 6% 5% 8% 9% 38%	4022
	21st to end	Day	10% 4 2 5% 4 4 4 3 6% 8% 49%	4312
September	1st to 10th	Day	14% 5% 1 5% 4 5% 4 4 5% 7% 46%	2400
	11th to 20th	Day	13% 5% 2 5% 3 4 4 4 6% 8% 46%	2389
	21st to end	Day	23% 6% 2 6% 3 4 5% 4 5% 6% 36%	2091
October	1st to 10th	Day	14% 6% 2 5% 4 4 4 3 4 6% 48%	2000
	11th to 20th	Day	16% 4 2 5% 3 3 4 3 4 5% 52%	2000
	21st to end	Day	14% 5% 2 5% 3 3 3 3 5% 6% 51%	2200
November	1st to 10th	Day	12% 4 1 4 4 3 4 3 4 7% 53%	2025
	11th to 20th	Day	15% 5% 2 4 3 3 4 4 6% 5% 50%	1853
	21st to end	Day	16% 5% 2 5% 3 4 3 3 4 5% 50%	1680
December	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 5% 6% 50%	2680
	11th to 20th	Day	18% 8% 3 4 3 2 3 3 5% 6% 46%	3046
	21st to end	Day	17% 7% 3 6% 4 4 4 3 5% 7% 39%	3960
January	1st to 10th	Night	13% 6% 2 4 3 3 3 3 4 6% 53%	6027
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 4 4 54%	5900
	21st to end	Night	15% 7% 3 6% 3 3 3 2 4 5% 48%	6490
February	1st to 10th	Night	15% 7% 3 5% 4 5% 5% 4 5% 6% 41%	2600
	11th to 20th	Night	20% 7% 2 6% 3 3 3 3 4 5% 43%	2498
	21st to end	Night	15% 7% 3 5% 5% 3 3 4 5% 6% 43%	1964
March	1st to 10th	Night	16% 6% 2 6% 3 3 4 3 4 5% 48%	4918
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 51%	4980
	21st to end	Night	12% 6% 2 6% 4 4 4 4 6% 6% 46%	5450
April	1st to 10th	Night	15% 7% 2 6% 3 3 5% 3 6% 7% 44%	2000
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 5% 7% 48%	1975
	21st to end	Night	16% 6% 2 5% 4 4 4 3 6% 7% 45%	2000
May	1st to 10th	Night	18% 9% 4 7% 5% 4 5% 4 5% 8% 31%	4124
	11th to 20th	Night	24% 7% 3 6% 4 4 4 4 6% 8% 31%	3946
	21st to end	Night	16% 7% 2 7% 5% 5% 5% 4 6% 8% 36%	3920
June	1st to 10th	Night	10% 6% 2 6% 5% 4 4 4 7% 8% 45%	1600
	11th to 20th	Night	12% 6% 1 6% 5% 5% 5% 5% 6% 8% 42%	1600
	21st to end	Night	8% 5% 2 5% 4 4 6% 5% 7% 11% 43%	1600
July	1st to 10th	Night	9% 6% 2 7% 5% 5% 5% 5% 7% 10% 38%	3598
	11th to 20th	Night	10% 8% 3 9% 6% 7% 6% 6% 7% 10% 28%	4051
	21st to end	Night	7% 7% 2 7% 6% 6% 5% 5% 8% 10% 37%	4427
August	1st to 10th	Night	16% 6% 2 8% 5% 5% 6% 4 6% 10% 33%	2915
	11th to 20th	Night	11% 8% 3 8% 6% 6% 5% 4 6% 8% 35%	2992
	21st to end	Night	12% 6% 2 6% 4 4 4 4 5% 8% 47%	3586
September	1st to 10th	Night	13% 6% 3 5% 4 4 4 4 5% 7% 47%	2000
	11th to 20th	Night	11% 6% 3 5% 4 4 4 3 5% 7% 49%	2008
	21st to end	Night	21% 8% 3 6% 4 3 3 2 5% 6% 38%	2308
October	1st to 10th	Night	18% 6% 2 5% 4 3 3 2 4 6% 47%	2400
	11th to 20th	Night	16% 6% 2 6% 3 3 4 3 4 5% 50%	2400
	21st to end	Night	14% 4 2 4 4 4 4 3 5% 6% 50%	2640
November	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 4 6% 53%	2490
	11th to 20th	Night	15% 6% 2 6% 4 3 3 2 5% 6% 49%	2762
	21st to end	Night	12% 5% 1 5% 4 3 4 4 5% 7% 50%	2940
December	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 5% 6% 54%	4720
	11th to 20th	Night	20% 7% 3 6% 4 3 4 3 5% 5% 42%	5304
	21st to end	Night	16% 7% 2 5% 4 4 5% 4 5% 7% 42%	6996

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	36% 4 6% 24% 22% 9%	3916
	11th to 20th	Day	38% 4 6% 20% 20% 11%	4060
	21st to end	Day	42% 5% 7% 25% 18% 3	4466
February	1st to 10th	Day	43% 6% 10% 25% 13% 2	1800
	11th to 20th	Day	43% 5% 8% 22% 18% 4	1796
	21st to end	Day	46% 6% 11% 16% 18% 4	1663
March	1st to 10th	Day	43% 5% 7% 20% 16% 9%	4935
	11th to 20th	Day	33% 5% 8% 24% 23% 8%	4980
	21st to end	Day	43% 6% 11% 17% 17% 7%	5482
April	1st to 10th	Day	37% 6% 11% 20% 18% 7%	2400
	11th to 20th	Day	36% 6% 11% 20% 22% 6%	2374
	21st to end	Day	41% 7% 10% 24% 14% 4	2400
May	1st to 10th	Day	44% 10% 14% 18% 12% 1	5846
	11th to 20th	Day	47% 7% 11% 24% 10% 1	5947
	21st to end	Day	38% 9% 13% 21% 17% 2	6949
June	1st to 10th	Day	35% 9% 14% 25% 16% 1	2800
	11th to 20th	Day	37% 8% 15% 23% 16% 2	2800
	21st to end	Day	32% 10% 14% 25% 18% 1	2800
July	1st to 10th	Day	34% 10% 19% 19% 13% 5%	6290
	11th to 20th	Day	40% 12% 20% 20% 7% 1	5831
	21st to end	Day	37% 7% 12% 23% 20% 1	6240
August	1st to 10th	Day	42% 8% 16% 26% 7%	4221
	11th to 20th	Day	38% 9% 13% 25% 15% 1	4061
	21st to end	Day	31% 7% 15% 27% 18% 2	4312
September	1st to 10th	Day	37% 8% 11% 19% 20% 5%	2400
	11th to 20th	Day	34% 6% 9% 27% 20% 3	2389
	21st to end	Day	46% 7% 10% 18% 16% 3	2091
October	1st to 10th	Day	36% 4 7% 18% 30% 5%	3260
	11th to 20th	Day	27% 3 6% 24% 29% 11%	3240
	21st to end	Day	22% 3 10% 28% 25% 13%	3538
November	1st to 10th	Day	32% 4 10% 25% 24% 5%	2025
	11th to 20th	Day	35% 5% 10% 23% 22% 7%	1853
	21st to end	Day	36% 5% 10% 25% 21% 3	1680
December	1st to 10th	Day	34% 5% 10% 26% 18% 6%	2680
	11th to 20th	Day	40% 4 13% 26% 14% 4	3042
	21st to end	Day	42% 7% 12% 22% 15% 1	3960
January	1st to 10th	Night	33% 4 7% 23% 28% 6%	6027
	11th to 20th	Night	34% 3 6% 24% 24% 9%	5900
	21st to end	Night	40% 3 7% 27% 19% 4	6490
February	1st to 10th	Night	42% 6% 11% 24% 16% 2	2600
	11th to 20th	Night	43% 4 8% 20% 18% 7%	2500
	21st to end	Night	40% 5% 10% 20% 17% 7%	1964
March	1st to 10th	Night	37% 5% 7% 23% 20% 8%	4918
	11th to 20th	Night	32% 5% 9% 22% 25% 7%	4980
	21st to end	Night	38% 5% 8% 22% 20% 6%	5450
April	1st to 10th	Night	39% 7% 10% 17% 22% 5%	2000
	11th to 20th	Night	35% 6% 11% 21% 21% 5%	1975
	21st to end	Night	38% 6% 11% 26% 14% 5%	2000
May	1st to 10th	Night	50% 8% 13% 17% 8% 3	4152
	11th to 20th	Night	49% 7% 12% 20% 10% 1	3947
	21st to end	Night	44% 8% 13% 23% 10% 2	3927
June	1st to 10th	Night	34% 8% 14% 26% 15% 2	1600
	11th to 20th	Night	38% 9% 16% 23% 14% 1	1600
	21st to end	Night	32% 11% 16% 20% 19% 3	1600
July	1st to 10th	Night	40% 10% 18% 17% 14% 2	3560
	11th to 20th	Night	49% 10% 18% 16% 6% 1	4001
	21st to end	Night	38% 10% 14% 22% 16%	4297
August	1st to 10th	Night	46% 9% 15% 22% 7% 1	2904
	11th to 20th	Night	44% 8% 13% 22% 14%	3019
	21st to end	Night	34% 7% 12% 28% 17% 1	3586
September	1st to 10th	Night	37% 8% 11% 22% 17% 6%	2000
	11th to 20th	Night	35% 7% 9% 25% 22% 3	2008
	21st to end	Night	46% 7% 10% 18% 15% 3	2308
October	1st to 10th	Night	41% 4 9% 20% 20% 7%	3920
	11th to 20th	Night	25% 4 8% 22% 31% 10%	3899
	21st to end	Night	22% 4 8% 30% 26% 10%	4252
November	1st to 10th	Night	33% 5% 9% 24% 24% 6%	2490
	11th to 20th	Night	37% 4 8% 22% 23% 7%	2762
	21st to end	Night	34% 5% 10% 25% 22% 5%	2940
December	1st to 10th	Night	31% 4 11% 28% 22% 4	4720
	11th to 20th	Night	45% 4 10% 18% 17% 5%	5307
	21st to end	Night	40% 7% 13% 24% 16% 1	6996

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	27% 22% 28% 19% 3	268
	11th to 20th	Day	27% 29% 25% 17% 3	300
	21st to end	Day	22% 24% 36% 14% 4	330
February	1st to 10th	Day	23% 28% 31% 14% 4	300
	11th to 20th	Day	35% 24% 30% 10% 1	334
	21st to end	Day	28% 19% 30% 19% 3	414
March	1st to 10th	Day	23% 19% 34% 20% 4	500
	11th to 20th	Day	22% 22% 32% 18% 6% 1	500
	21st to end	Day	24% 18% 34% 17% 6% 1	550
April	1st to 10th	Day	25% 21% 28% 19% 6% 1	500
	11th to 20th	Day	19% 17% 29% 21% 11% 3	492
	21st to end	Day	21% 13% 33% 22% 10% 1	500
May	1st to 10th	Day	19% 16% 33% 19% 10% 3	503
	11th to 20th	Day	21% 9% 30% 24% 12% 3	527
	21st to end	Day	20% 6% 26% 25% 20% 4	573
June	1st to 10th	Day	12% 5% 28% 31% 17% 7%	530
	11th to 20th	Day	12% 6% 26% 29% 20% 6%	530
	21st to end	Day	9% 5% 24% 36% 21% 5%	530
July	1st to 10th	Day	10% 3 17% 33% 26% 10%	525
	11th to 20th	Day	6% 1 16% 37% 27% 13%	524
	21st to end	Day	12% 3 18% 32% 26% 9%	576
August	1st to 10th	Day	13% 4 20% 27% 27% 10%	526
	11th to 20th	Day	13% 3 16% 32% 26% 10%	519
	21st to end	Day	11% 3 19% 29% 23% 14%	583
September	1st to 10th	Day	15% 5% 19% 28% 17% 15%	530
	11th to 20th	Day	15% 3 18% 30% 23% 11%	530
	21st to end	Day	28% 9% 23% 24% 12% 4	530
October	1st to 10th	Day	20% 5% 23% 26% 17% 8%	530
	11th to 20th	Day	18% 14% 24% 26% 16% 2	530
	21st to end	Day	16% 13% 33% 26% 8% 3	583
November	1st to 10th	Day	15% 12% 33% 25% 12% 3	518
	11th to 20th	Day	20% 11% 36% 21% 10% 2	393
	21st to end	Day	24% 15% 32% 19% 10%	220
December	1st to 10th	Day	21% 21% 33% 19% 5% 1	220
	11th to 20th	Day	20% 16% 35% 21% 8%	214
	21st to end	Day	26% 20% 27% 18% 9%	220
January	1st to 10th	Night	20% 17% 39% 20% 4	800
	11th to 20th	Night	21% 15% 34% 27% 4	800
	21st to end	Night	18% 17% 39% 25% 2	880
February	1st to 10th	Night	20% 13% 39% 25% 3	800
	11th to 20th	Night	26% 18% 37% 18% 1	783
	21st to end	Night	21% 17% 39% 21% 2	660
March	1st to 10th	Night	19% 17% 37% 25% 3	800
	11th to 20th	Night	21% 16% 37% 21% 5% 1	800
	21st to end	Night	18% 17% 38% 22% 5%	880
April	1st to 10th	Night	18% 18% 38% 22% 5%	800
	11th to 20th	Night	15% 14% 35% 28% 9%	791
	21st to end	Night	19% 9% 33% 31% 8%	800
May	1st to 10th	Night	20% 9% 32% 28% 11% 1	640
	11th to 20th	Night	20% 5% 29% 32% 14%	557
	21st to end	Night	15% 3 21% 38% 22% 1	433
June	1st to 10th	Night	10% 3 22% 46% 19% 1	400
	11th to 20th	Night	15% 3 19% 42% 20% 1	400
	21st to end	Night	9% 3 23% 45% 19% 2	400
July	1st to 10th	Night	11% 3 19% 36% 29% 3	390
	11th to 20th	Night	8% 2 13% 38% 34% 5%	577
	21st to end	Night	8% 2 16% 40% 30% 3	657
August	1st to 10th	Night	12% 2 12% 41% 30% 3	597
	11th to 20th	Night	13% 3 12% 42% 28% 3	659
	21st to end	Night	12% 3 14% 37% 29% 5%	880
September	1st to 10th	Night	16% 3 16% 33% 29% 4	800
	11th to 20th	Night	13% 3 17% 34% 30% 3	800
	21st to end	Night	25% 4 19% 33% 18% 1	800
October	1st to 10th	Night	20% 4 20% 31% 22% 4	800
	11th to 20th	Night	18% 8% 29% 29% 16% 1	800
	21st to end	Night	17% 8% 33% 29% 12% 1	880
November	1st to 10th	Night	15% 9% 33% 30% 13% 1	820
	11th to 20th	Night	18% 11% 35% 27% 8%	840
	21st to end	Night	15% 11% 35% 30% 9% 1	840
December	1st to 10th	Night	20% 11% 38% 23% 8%	840
	11th to 20th	Night	20% 9% 38% 28% 5%	829
	21st to end	Night	21% 10% 33% 31% 4	880

Page generated at 2025-12-15 01:13:50. Version ac07

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