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 2024-11-11.

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 5% 4 6% 8% 42%	101193
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 43%	97931
Transparency	Day	38% 7% 12% 23% 16% 4	104837
	Night	38% 6% 11% 23% 18% 4	102427
Seeing	Day	18% 11% 26% 25% 14% 5%	15058
	Night	17% 9% 29% 30% 13% 1	24667

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	18% 5% 2 4 3 2 3 3 5% 6% 48%	2737
	11th to 20th	Day	14% 9% 2 7% 5% 5% 4 3 5% 5% 41%	2840
	21st to end	Day	18% 9% 3 6% 5% 4 4 3 4 5% 38%	3124
February	1st to 10th	Day	13% 9% 3 7% 5% 4 4 4 6% 7% 40%	1710
	11th to 20th	Day	18% 7% 2 6% 4 3 3 3 5% 7% 42%	1695
	21st to end	Day	18% 8% 3 7% 4 4 4 4 6% 6% 36%	1582
March	1st to 10th	Day	21% 8% 2 6% 5% 4 4 3 4 6% 36%	3435
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 7% 50%	3480
	21st to end	Day	20% 7% 2 6% 4 4 4 4 5% 6% 38%	3832
April	1st to 10th	Day	11% 7% 2 6% 4 4 4 4 5% 7% 47%	2280
	11th to 20th	Day	14% 6% 2 5% 3 4 4 3 5% 6% 48%	2254
	21st to end	Day	17% 6% 2 6% 4 4 5% 3 6% 6% 41%	2280
May	1st to 10th	Day	19% 8% 2 7% 4 5% 6% 4 6% 8% 31%	4046
	11th to 20th	Day	22% 7% 2 5% 4 4 4 4 6% 8% 33%	4135
	21st to end	Day	11% 4 2 4 4 5% 5% 4 7% 9% 44%	4823
June	1st to 10th	Day	11% 5% 2 5% 4 5% 6% 4 6% 9% 43%	2660
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 4 6% 9% 42%	2660
	21st to end	Day	8% 4 1 5% 5% 5% 5% 5% 6% 9% 45%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 5% 7% 5% 10% 11% 39%	4440
	11th to 20th	Day	9% 6% 2 5% 5% 5% 5% 5% 10% 13% 36%	4120
	21st to end	Day	11% 7% 2 8% 6% 6% 6% 5% 7% 9% 35%	4466
August	1st to 10th	Day	14% 6% 2 7% 4 5% 5% 5% 8% 11% 32%	4104
	11th to 20th	Day	9% 5% 2 7% 5% 6% 6% 5% 8% 9% 39%	3897
	21st to end	Day	10% 4 2 5% 4 4 4 3 6% 8% 49%	4180
September	1st to 10th	Day	14% 5% 1 5% 5% 5% 5% 4 5% 7% 45%	2280
	11th to 20th	Day	13% 5% 2 5% 3 4 4 4 6% 8% 46%	2270
	21st to end	Day	22% 5% 2 6% 3 4 5% 4 5% 6% 37%	1987
October	1st to 10th	Day	15% 6% 2 5% 4 4 4 3 4 6% 47%	1900
	11th to 20th	Day	16% 4 2 5% 3 3 4 3 4 5% 52%	1900
	21st to end	Day	13% 5% 2 5% 3 3 3 3 5% 6% 51%	2090
November	1st to 10th	Day	12% 5% 1 4 4 3 4 2 4 6% 53%	1927
	11th to 20th	Day	15% 5% 2 4 3 3 4 4 6% 5% 50%	1677
	21st to end	Day	16% 5% 2 4 3 4 3 3 4 5% 51%	1520
December	1st to 10th	Day	17% 7% 2 5% 4 4 4 4 6% 6% 42%	1520
	11th to 20th	Day	17% 7% 2 4 3 3 3 2 4 6% 49%	1910
	21st to end	Day	19% 7% 3 6% 4 4 4 3 5% 8% 38%	2772
January	1st to 10th	Night	15% 7% 2 5% 4 3 3 3 4 6% 49%	4205
	11th to 20th	Night	17% 8% 2 5% 3 3 3 3 5% 4 47%	4120
	21st to end	Night	19% 8% 3 6% 3 3 3 2 4 5% 43%	4532
February	1st to 10th	Night	14% 7% 3 5% 4 5% 5% 4 5% 6% 42%	2470
	11th to 20th	Night	19% 7% 2 6% 4 3 3 3 4 5% 43%	2370
	21st to end	Night	16% 8% 3 5% 4 3 3 4 4 6% 43%	1869
March	1st to 10th	Night	21% 6% 2 6% 4 3 4 4 5% 5% 39%	3418
	11th to 20th	Night	13% 4 2 5% 4 3 4 3 5% 7% 50%	3480
	21st to end	Night	14% 6% 2 6% 4 3 4 3 5% 5% 48%	3800
April	1st to 10th	Night	15% 7% 2 5% 3 3 4 3 6% 7% 45%	1900
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 5% 7% 49%	1875
	21st to end	Night	16% 6% 2 5% 4 3 4 3 6% 7% 44%	1900
May	1st to 10th	Night	20% 9% 4 7% 4 4 4 3 5% 8% 32%	2876
	11th to 20th	Night	24% 8% 3 6% 4 3 4 3 5% 7% 32%	2754
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 6% 9% 44%	2732
June	1st to 10th	Night	10% 6% 2 6% 5% 4 4 4 7% 9% 45%	1520
	11th to 20th	Night	11% 6% 1 6% 5% 4 5% 5% 6% 8% 42%	1520
	21st to end	Night	8% 5% 2 5% 4 5% 6% 5% 8% 11% 43%	1520
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 5% 5% 8% 10% 40%	2520
	11th to 20th	Night	8% 6% 2 7% 6% 6% 6% 5% 7% 10% 37%	2834
	21st to end	Night	9% 8% 3 8% 7% 6% 5% 5% 7% 9% 33%	3087
August	1st to 10th	Night	16% 5% 2 8% 5% 5% 6% 4 6% 10% 32%	2825
	11th to 20th	Night	11% 8% 3 8% 6% 6% 5% 4 6% 8% 35%	2899
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 8% 47%	3476
September	1st to 10th	Night	14% 6% 3 5% 4 4 4 4 5% 7% 45%	1900
	11th to 20th	Night	11% 6% 3 5% 4 4 4 3 5% 7% 49%	1907
	21st to end	Night	21% 8% 3 6% 4 3 3 2 5% 6% 39%	2192
October	1st to 10th	Night	18% 6% 2 5% 4 3 3 2 4 6% 46%	2280
	11th to 20th	Night	15% 6% 2 6% 3 3 4 3 4 5% 50%	2280
	21st to end	Night	14% 4 2 4 3 4 4 3 5% 6% 50%	2508
November	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 4 6% 53%	2368
	11th to 20th	Night	14% 6% 2 6% 4 3 3 2 5% 5% 49%	2505
	21st to end	Night	13% 4 1 4 4 3 4 4 5% 7% 50%	2660
December	1st to 10th	Night	17% 7% 2 6% 4 3 4 3 5% 6% 42%	2660
	11th to 20th	Night	17% 6% 2 5% 4 3 3 3 5% 5% 45%	3285
	21st to end	Night	17% 7% 2 6% 4 4 5% 4 5% 7% 40%	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	36% 5% 8% 30% 16% 5%	2738
	11th to 20th	Day	44% 5% 8% 19% 17% 6%	2840
	21st to end	Day	47% 6% 9% 21% 15% 2	3124
February	1st to 10th	Day	43% 6% 10% 25% 13% 2	1710
	11th to 20th	Day	42% 5% 8% 23% 18% 4	1704
	21st to end	Day	47% 6% 11% 14% 18% 4	1582
March	1st to 10th	Day	48% 6% 8% 20% 13% 5%	3435
	11th to 20th	Day	31% 6% 8% 24% 24% 6%	3480
	21st to end	Day	46% 7% 10% 19% 15% 4	3832
April	1st to 10th	Day	36% 6% 12% 21% 18% 8%	2280
	11th to 20th	Day	36% 6% 11% 20% 22% 6%	2254
	21st to end	Day	42% 7% 10% 23% 13% 5%	2280
May	1st to 10th	Day	47% 11% 11% 19% 11% 1	4083
	11th to 20th	Day	47% 8% 12% 23% 9% 1	4139
	21st to end	Day	31% 11% 15% 22% 19% 2	4837
June	1st to 10th	Day	35% 9% 14% 26% 15% 1	2660
	11th to 20th	Day	36% 8% 15% 23% 16% 2	2660
	21st to end	Day	33% 10% 14% 25% 17% 1	2660
July	1st to 10th	Day	34% 11% 20% 18% 11% 6%	4370
	11th to 20th	Day	35% 10% 18% 27% 9% 1	4051
	21st to end	Day	44% 8% 11% 21% 16% 1	4324
August	1st to 10th	Day	43% 8% 17% 25% 7%	4091
	11th to 20th	Day	38% 9% 13% 25% 15% 1	3936
	21st to end	Day	32% 7% 15% 27% 17% 2	4180
September	1st to 10th	Day	38% 9% 11% 18% 20% 5%	2280
	11th to 20th	Day	34% 6% 9% 27% 20% 3	2270
	21st to end	Day	46% 7% 10% 18% 17% 3	1987
October	1st to 10th	Day	36% 4 7% 18% 30% 5%	3160
	11th to 20th	Day	26% 3 6% 24% 29% 11%	3140
	21st to end	Day	21% 3 10% 28% 24% 12%	3428
November	1st to 10th	Day	32% 4 10% 25% 24% 5%	1927
	11th to 20th	Day	35% 5% 10% 22% 21% 7%	1677
	21st to end	Day	35% 6% 9% 24% 22% 4	1520
December	1st to 10th	Day	40% 7% 12% 25% 12% 4	1520
	11th to 20th	Day	38% 4 7% 31% 14% 6%	1906
	21st to end	Day	43% 8% 11% 26% 11% 1	2772
January	1st to 10th	Night	36% 5% 9% 25% 20% 5%	4205
	11th to 20th	Night	39% 4 8% 23% 20% 5%	4120
	21st to end	Night	45% 4 7% 25% 17% 2	4532
February	1st to 10th	Night	41% 6% 10% 24% 16% 2	2470
	11th to 20th	Night	43% 4 8% 21% 18% 7%	2372
	21st to end	Night	41% 5% 10% 20% 17% 6%	1869
March	1st to 10th	Night	45% 7% 8% 23% 15% 2	3418
	11th to 20th	Night	31% 6% 8% 23% 26% 5%	3480
	21st to end	Night	38% 6% 9% 22% 20% 5%	3800
April	1st to 10th	Night	38% 7% 10% 17% 22% 5%	1900
	11th to 20th	Night	34% 7% 12% 21% 21% 6%	1875
	21st to end	Night	38% 6% 11% 26% 13% 6%	1900
May	1st to 10th	Night	50% 9% 10% 19% 10% 2	2904
	11th to 20th	Night	49% 9% 12% 19% 9% 1	2755
	21st to end	Night	34% 10% 16% 25% 13% 2	2739
June	1st to 10th	Night	34% 9% 15% 27% 15% 2	1520
	11th to 20th	Night	37% 9% 16% 23% 14% 2	1520
	21st to end	Night	32% 11% 17% 19% 18% 3	1520
July	1st to 10th	Night	36% 9% 22% 17% 12% 3	2480
	11th to 20th	Night	40% 9% 20% 22% 8% 1	2781
	21st to end	Night	43% 10% 14% 19% 13%	2988
August	1st to 10th	Night	46% 9% 15% 22% 7% 1	2814
	11th to 20th	Night	44% 8% 12% 22% 14% 1	2926
	21st to end	Night	34% 7% 12% 29% 17% 1	3476
September	1st to 10th	Night	38% 8% 11% 20% 16% 6%	1900
	11th to 20th	Night	34% 7% 9% 24% 22% 3	1907
	21st to end	Night	45% 6% 10% 19% 16% 3	2192
October	1st to 10th	Night	42% 4 9% 19% 19% 7%	3800
	11th to 20th	Night	25% 4 9% 22% 31% 10%	3779
	21st to end	Night	22% 4 8% 31% 26% 10%	4120
November	1st to 10th	Night	33% 5% 9% 24% 23% 6%	2368
	11th to 20th	Night	37% 4 8% 21% 23% 7%	2505
	21st to end	Night	33% 5% 10% 25% 21% 5%	2660
December	1st to 10th	Night	42% 5% 10% 23% 15% 4	2660
	11th to 20th	Night	40% 5% 9% 21% 20% 5%	3288
	21st to end	Night	40% 8% 13% 23% 14% 1	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	25% 22% 28% 21% 4	241
	11th to 20th	Day	27% 28% 24% 18% 3	270
	21st to end	Day	23% 24% 36% 12% 4	297
February	1st to 10th	Day	22% 27% 31% 16% 4	270
	11th to 20th	Day	33% 25% 31% 11% 1	302
	21st to end	Day	29% 19% 30% 19% 3	382
March	1st to 10th	Day	22% 20% 34% 19% 5%	460
	11th to 20th	Day	22% 23% 32% 18% 6%	460
	21st to end	Day	24% 17% 34% 18% 6% 1	506
April	1st to 10th	Day	23% 21% 29% 20% 6% 1	460
	11th to 20th	Day	17% 18% 29% 21% 12% 3	452
	21st to end	Day	22% 14% 33% 22% 9% 1	460
May	1st to 10th	Day	20% 15% 32% 19% 11% 3	463
	11th to 20th	Day	22% 9% 30% 25% 13% 3	487
	21st to end	Day	18% 5% 25% 26% 21% 5%	529
June	1st to 10th	Day	12% 6% 27% 31% 18% 7%	490
	11th to 20th	Day	11% 6% 27% 30% 20% 7%	490
	21st to end	Day	9% 5% 25% 36% 19% 5%	490
July	1st to 10th	Day	10% 3 17% 33% 27% 11%	485
	11th to 20th	Day	7% 1 15% 38% 27% 12%	484
	21st to end	Day	12% 4 18% 32% 24% 9%	532
August	1st to 10th	Day	11% 4 20% 27% 28% 10%	486
	11th to 20th	Day	12% 2 18% 31% 27% 10%	479
	21st to end	Day	11% 3 18% 29% 24% 15%	539
September	1st to 10th	Day	16% 4 18% 28% 18% 16%	490
	11th to 20th	Day	15% 3 18% 30% 23% 11%	490
	21st to end	Day	28% 9% 23% 24% 12% 4	490
October	1st to 10th	Day	21% 5% 23% 26% 17% 7%	490
	11th to 20th	Day	17% 13% 23% 27% 17% 3	490
	21st to end	Day	15% 12% 34% 28% 8% 4	539
November	1st to 10th	Day	16% 10% 31% 26% 13% 3	480
	11th to 20th	Day	19% 10% 36% 21% 12% 2	337
	21st to end	Day	22% 12% 33% 21% 11% 1	180
December	1st to 10th	Day	19% 21% 36% 17% 6% 2	180
	11th to 20th	Day	21% 16% 34% 21% 9%	180
	21st to end	Day	26% 18% 28% 18% 9% 1	198
January	1st to 10th	Night	21% 17% 39% 20% 4	760
	11th to 20th	Night	21% 15% 33% 27% 4	760
	21st to end	Night	19% 16% 38% 25% 2	836
February	1st to 10th	Night	20% 13% 38% 26% 3	760
	11th to 20th	Night	25% 18% 38% 18% 1	743
	21st to end	Night	22% 16% 38% 21% 3	628
March	1st to 10th	Night	19% 16% 37% 25% 3	760
	11th to 20th	Night	21% 16% 37% 21% 5% 1	760
	21st to end	Night	17% 16% 38% 23% 5%	836
April	1st to 10th	Night	17% 17% 38% 22% 5%	760
	11th to 20th	Night	14% 13% 35% 28% 9%	751
	21st to end	Night	19% 9% 33% 31% 8%	760
May	1st to 10th	Night	20% 8% 32% 27% 12% 1	608
	11th to 20th	Night	20% 5% 28% 33% 15%	529
	21st to end	Night	14% 3 20% 39% 23% 1	411
June	1st to 10th	Night	10% 3 22% 45% 19% 1	380
	11th to 20th	Night	14% 3 19% 42% 21% 1	380
	21st to end	Night	9% 3 22% 46% 19% 1	380
July	1st to 10th	Night	11% 2 19% 35% 29% 3	370
	11th to 20th	Night	7% 1 13% 39% 34% 5%	547
	21st to end	Night	9% 2 17% 40% 29% 3	624
August	1st to 10th	Night	12% 2 12% 42% 30% 3	567
	11th to 20th	Night	12% 3 13% 42% 28% 3	626
	21st to end	Night	12% 3 13% 37% 29% 6%	836
September	1st to 10th	Night	16% 3 15% 34% 29% 5%	760
	11th to 20th	Night	13% 3 17% 34% 30% 3	760
	21st to end	Night	24% 4 19% 32% 19% 1	760
October	1st to 10th	Night	20% 4 20% 31% 21% 3	760
	11th to 20th	Night	17% 8% 29% 29% 16% 1	760
	21st to end	Night	17% 8% 33% 29% 13% 1	836
November	1st to 10th	Night	14% 8% 33% 30% 13% 1	780
	11th to 20th	Night	18% 11% 35% 27% 9%	763
	21st to end	Night	15% 11% 33% 30% 10% 1	760
December	1st to 10th	Night	20% 10% 38% 23% 9%	760
	11th to 20th	Night	19% 9% 39% 28% 5%	760
	21st to end	Night	21% 11% 33% 31% 4	836

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