Otter Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Otter Lake clear sky chart from 2005-11-06 to 2026-01-02.

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	16% 11% 4 9% 5% 5% 5% 4 5% 6% 31%	127680
	Night	16% 12% 4 10% 6% 5% 4 3 5% 6% 30%	123676
Transparency	Day	52% 6% 12% 20% 9% 1	131158
	Night	54% 5% 12% 19% 9% 1	128285
Seeing	Day	23% 17% 32% 19% 8% 2	15796
	Night	22% 14% 30% 24% 9% 1	24968

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	13% 17% 7% 18% 8% 5% 4 3 3 4 18%	3605
	11th to 20th	Day	10% 15% 7% 17% 9% 5% 5% 3 5% 4 19%	3570
	21st to end	Day	8% 17% 9% 16% 8% 5% 4 3 5% 5% 21%	4167
February	1st to 10th	Day	12% 17% 6% 14% 7% 5% 5% 3 5% 5% 22%	1800
	11th to 20th	Day	10% 18% 6% 13% 6% 5% 4 3 4 6% 25%	1753
	21st to end	Day	16% 15% 5% 10% 6% 5% 4 3 5% 4 25%	1620
March	1st to 10th	Day	17% 16% 5% 11% 6% 4 4 3 5% 6% 23%	4557
	11th to 20th	Day	11% 14% 6% 10% 6% 5% 5% 4 6% 6% 28%	4980
	21st to end	Day	16% 12% 3 8% 5% 4 4 2 3 5% 36%	5728
April	1st to 10th	Day	22% 13% 3 7% 5% 4 4 3 4 5% 30%	2400
	11th to 20th	Day	22% 10% 3 7% 4 4 3 3 4 5% 34%	2374
	21st to end	Day	22% 11% 4 8% 5% 4 4 2 4 5% 32%	2571
May	1st to 10th	Day	21% 11% 3 9% 5% 4 5% 4 5% 6% 28%	6346
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 4 6% 7% 33%	6318
	21st to end	Day	21% 9% 3 8% 4 5% 4 4 5% 6% 32%	6949
June	1st to 10th	Day	21% 8% 3 8% 6% 4 5% 4 5% 7% 30%	2800
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 4 6% 8% 38%	2800
	21st to end	Day	19% 7% 2 7% 5% 5% 4 4 6% 7% 33%	2800
July	1st to 10th	Day	14% 6% 2 7% 5% 6% 5% 5% 7% 9% 33%	6360
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 6% 8% 43%	6360
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 7% 10% 45%	6926
August	1st to 10th	Day	13% 6% 3 8% 5% 5% 6% 5% 6% 8% 35%	4465
	11th to 20th	Day	18% 7% 2 6% 4 4 6% 4 6% 7% 36%	4174
	21st to end	Day	13% 5% 2 6% 4 4 6% 5% 8% 9% 38%	4319
September	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 6% 8% 42%	2400
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 45%	2400
	21st to end	Day	20% 6% 2 6% 4 4 4 3 6% 7% 38%	2120
October	1st to 10th	Day	20% 8% 2 7% 4 4 4 4 5% 6% 36%	2000
	11th to 20th	Day	23% 11% 3 8% 6% 4 4 3 5% 5% 27%	2000
	21st to end	Day	26% 11% 3 9% 5% 4 4 3 5% 5% 27%	2056
November	1st to 10th	Day	15% 13% 3 8% 4 5% 5% 4 5% 6% 32%	1808
	11th to 20th	Day	18% 15% 5% 10% 7% 5% 5% 3 5% 5% 23%	1680
	21st to end	Day	20% 19% 6% 12% 6% 4 4 3 4 5% 17%	1680
December	1st to 10th	Day	19% 22% 6% 11% 6% 6% 5% 3 4 4 13%	2680
	11th to 20th	Day	16% 16% 6% 13% 6% 4 4 3 3 4 23%	3066
	21st to end	Day	20% 20% 5% 13% 5% 5% 4 3 3 4 19%	4048
January	1st to 10th	Night	13% 21% 9% 17% 6% 4 4 2 3 4 18%	6364
	11th to 20th	Night	10% 13% 6% 16% 9% 6% 5% 4 4 6% 21%	6315
	21st to end	Night	9% 17% 6% 15% 8% 8% 5% 3 4 4 21%	6786
February	1st to 10th	Night	12% 14% 6% 13% 8% 5% 4 3 5% 6% 23%	2600
	11th to 20th	Night	12% 16% 5% 11% 7% 5% 5% 3 4 5% 26%	2533
	21st to end	Night	12% 15% 6% 10% 7% 6% 5% 4 4 4 27%	2010
March	1st to 10th	Night	18% 17% 4 10% 5% 4 4 3 3 4 28%	5282
	11th to 20th	Night	11% 14% 4 10% 5% 5% 6% 4 7% 8% 27%	4979
	21st to end	Night	16% 11% 4 11% 5% 4 4 3 5% 6% 32%	5203
April	1st to 10th	Night	20% 12% 3 8% 5% 4 4 3 5% 6% 30%	2000
	11th to 20th	Night	19% 10% 3 7% 5% 5% 4 4 4 6% 35%	1975
	21st to end	Night	22% 10% 4 8% 5% 4 3 3 5% 6% 32%	1843
May	1st to 10th	Night	21% 10% 3 8% 5% 5% 5% 4 6% 7% 27%	3594
	11th to 20th	Night	15% 7% 3 6% 5% 5% 4 3 5% 7% 39%	3575
	21st to end	Night	18% 9% 4 8% 5% 5% 5% 4 5% 7% 32%	3926
June	1st to 10th	Night	18% 6% 2 6% 6% 3 5% 4 7% 9% 34%	1600
	11th to 20th	Night	15% 6% 2 5% 5% 4 4 3 6% 7% 42%	1600
	21st to end	Night	18% 8% 2 5% 5% 5% 5% 4 6% 7% 36%	1600
July	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 4 6% 8% 35%	3600
	11th to 20th	Night	12% 6% 2 7% 4 4 4 3 6% 7% 45%	3600
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 8% 48%	3926
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 5% 5% 6% 7% 39%	2681
	11th to 20th	Night	16% 8% 2 7% 4 3 4 4 5% 7% 40%	2875
	21st to end	Night	15% 5% 2 7% 4 4 4 3 6% 7% 42%	3544
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 5% 7% 46%	2000
	11th to 20th	Night	14% 5% 2 5% 3 2 2 3 4 8% 50%	2000
	21st to end	Night	18% 7% 3 7% 4 3 4 3 4 5% 43%	2276
October	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 4 6% 42%	2400
	11th to 20th	Night	20% 10% 2 7% 5% 5% 4 4 5% 6% 31%	2400
	21st to end	Night	22% 12% 3 8% 5% 5% 5% 3 4 5% 28%	2782
November	1st to 10th	Night	17% 13% 4 8% 5% 4 5% 4 5% 7% 30%	2709
	11th to 20th	Night	18% 13% 5% 9% 5% 6% 5% 3 4 5% 27%	2940
	21st to end	Night	20% 16% 5% 11% 6% 4 5% 4 4 5% 21%	2940
December	1st to 10th	Night	18% 19% 6% 13% 6% 6% 5% 3 5% 5% 14%	4720
	11th to 20th	Night	21% 15% 5% 11% 6% 4 3 3 4 4 25%	5348
	21st to end	Night	22% 20% 5% 11% 5% 4 3 2 3 4 21%	7150

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	70% 6% 7% 11% 5%	3606
	11th to 20th	Day	67% 5% 9% 11% 8%	3600
	21st to end	Day	65% 4 9% 12% 8% 1	4167
February	1st to 10th	Day	64% 5% 10% 15% 6% 1	1800
	11th to 20th	Day	61% 4 12% 13% 9% 1	1762
	21st to end	Day	61% 5% 10% 13% 10% 1	1620
March	1st to 10th	Day	62% 4 8% 12% 12% 2	4560
	11th to 20th	Day	54% 6% 16% 13% 9% 2	4980
	21st to end	Day	50% 5% 7% 20% 16% 2	5728
April	1st to 10th	Day	57% 4 7% 18% 13% 3	2400
	11th to 20th	Day	52% 4 7% 20% 15% 2	2374
	21st to end	Day	56% 5% 7% 16% 13% 3	2571
May	1st to 10th	Day	55% 6% 9% 19% 8% 3	6357
	11th to 20th	Day	47% 7% 13% 21% 11% 1	6322
	21st to end	Day	52% 6% 11% 17% 13% 1	6949
June	1st to 10th	Day	53% 6% 10% 19% 11% 1	2800
	11th to 20th	Day	42% 8% 11% 24% 12% 2	2800
	21st to end	Day	49% 8% 13% 20% 10% 1	2800
July	1st to 10th	Day	45% 6% 15% 26% 8%	6290
	11th to 20th	Day	36% 7% 15% 32% 10%	6285
	21st to end	Day	33% 6% 17% 34% 9%	6728
August	1st to 10th	Day	45% 7% 16% 24% 8%	4451
	11th to 20th	Day	45% 7% 15% 26% 6%	4213
	21st to end	Day	38% 8% 17% 25% 11% 1	4319
September	1st to 10th	Day	39% 7% 14% 29% 10%	2400
	11th to 20th	Day	37% 7% 12% 32% 12% 1	2400
	21st to end	Day	45% 7% 14% 24% 11%	2120
October	1st to 10th	Day	49% 6% 11% 27% 7%	3260
	11th to 20th	Day	51% 7% 12% 21% 8% 1	3240
	21st to end	Day	53% 5% 19% 17% 5%	3294
November	1st to 10th	Day	51% 7% 13% 22% 6% 1	1808
	11th to 20th	Day	61% 7% 12% 12% 7% 1	1680
	21st to end	Day	70% 6% 10% 8% 6%	1680
December	1st to 10th	Day	75% 5% 9% 9% 2	2680
	11th to 20th	Day	65% 6% 8% 14% 8%	3066
	21st to end	Day	71% 4 7% 14% 4	4048
January	1st to 10th	Night	71% 5% 11% 10% 3	6364
	11th to 20th	Night	64% 6% 12% 13% 5%	6360
	21st to end	Night	67% 5% 8% 9% 11%	6786
February	1st to 10th	Night	62% 5% 9% 16% 7% 1	2600
	11th to 20th	Night	61% 4 10% 18% 7% 1	2535
	21st to end	Night	58% 5% 9% 18% 9% 1	2010
March	1st to 10th	Night	61% 4 9% 13% 11% 3	5292
	11th to 20th	Night	52% 7% 15% 16% 8% 2	4980
	21st to end	Night	51% 5% 9% 20% 12% 3	5203
April	1st to 10th	Night	55% 4 9% 17% 12% 2	2000
	11th to 20th	Night	49% 5% 9% 21% 14% 2	1975
	21st to end	Night	54% 5% 8% 16% 15% 3	1843
May	1st to 10th	Night	53% 8% 9% 18% 9% 3	3600
	11th to 20th	Night	42% 8% 14% 21% 14% 2	3576
	21st to end	Night	51% 6% 11% 18% 13% 1	3927
June	1st to 10th	Night	45% 6% 15% 24% 8% 2	1600
	11th to 20th	Night	40% 6% 12% 26% 14% 2	1600
	21st to end	Night	46% 8% 12% 21% 12% 1	1600
July	1st to 10th	Night	45% 5% 17% 22% 10% 1	3560
	11th to 20th	Night	37% 6% 15% 32% 11%	3552
	21st to end	Night	32% 7% 14% 36% 12%	3809
August	1st to 10th	Night	41% 8% 15% 25% 11%	2671
	11th to 20th	Night	42% 6% 16% 28% 8%	2902
	21st to end	Night	40% 6% 17% 25% 11% 2	3544
September	1st to 10th	Night	37% 7% 12% 30% 14%	2000
	11th to 20th	Night	34% 5% 15% 35% 11% 1	2000
	21st to end	Night	43% 5% 13% 28% 11%	2276
October	1st to 10th	Night	40% 5% 13% 28% 13%	3920
	11th to 20th	Night	47% 6% 16% 22% 9% 1	3899
	21st to end	Night	51% 5% 19% 16% 8%	4494
November	1st to 10th	Night	52% 7% 14% 19% 8%	2709
	11th to 20th	Night	59% 6% 11% 15% 8% 1	2940
	21st to end	Night	65% 6% 12% 14% 3	2940
December	1st to 10th	Night	71% 5% 11% 10% 2	4720
	11th to 20th	Night	64% 4 7% 14% 11%	5348
	21st to end	Night	69% 3 5% 12% 10%	7150

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	20% 23% 37% 17% 1	202
	11th to 20th	Day	23% 19% 39% 15% 5% 1	200
	21st to end	Day	17% 27% 35% 16% 5%	265
February	1st to 10th	Day	30% 27% 31% 9% 3	300
	11th to 20th	Day	28% 31% 34% 7% 1	300
	21st to end	Day	30% 23% 33% 12% 1	384
March	1st to 10th	Day	27% 21% 34% 13% 4	500
	11th to 20th	Day	26% 24% 31% 15% 3 1	500
	21st to end	Day	30% 22% 29% 13% 4 1	550
April	1st to 10th	Day	33% 21% 25% 15% 4 1	500
	11th to 20th	Day	35% 20% 22% 14% 8% 1	492
	21st to end	Day	31% 22% 31% 11% 5% 1	500
May	1st to 10th	Day	27% 16% 34% 14% 6% 2	503
	11th to 20th	Day	20% 18% 33% 19% 7% 3	527
	21st to end	Day	23% 17% 32% 20% 7% 2	573
June	1st to 10th	Day	26% 14% 34% 19% 6% 2	530
	11th to 20th	Day	17% 15% 33% 24% 9% 2	530
	21st to end	Day	21% 15% 33% 22% 9% 2	530
July	1st to 10th	Day	12% 8% 34% 33% 10% 2	525
	11th to 20th	Day	13% 12% 36% 27% 10% 3	524
	21st to end	Day	13% 9% 36% 29% 11% 2	576
August	1st to 10th	Day	14% 8% 30% 30% 14% 4	526
	11th to 20th	Day	17% 8% 26% 31% 13% 6%	519
	21st to end	Day	16% 12% 31% 23% 13% 5%	583
September	1st to 10th	Day	17% 11% 32% 20% 13% 6%	530
	11th to 20th	Day	14% 10% 25% 23% 20% 9%	530
	21st to end	Day	21% 13% 29% 19% 12% 5%	530
October	1st to 10th	Day	24% 16% 26% 20% 11% 3	530
	11th to 20th	Day	28% 21% 31% 14% 6% 1	530
	21st to end	Day	30% 16% 32% 17% 4	503
November	1st to 10th	Day	27% 20% 31% 18% 3 1	382
	11th to 20th	Day	24% 26% 33% 10% 5% 1	220
	21st to end	Day	30% 25% 31% 10% 3 1	220
December	1st to 10th	Day	30% 17% 39% 13% 2	220
	11th to 20th	Day	30% 27% 35% 6% 1 1	220
	21st to end	Day	32% 19% 34% 12% 3	242
January	1st to 10th	Night	27% 16% 37% 16% 3	805
	11th to 20th	Night	26% 18% 29% 21% 5%	800
	21st to end	Night	17% 15% 39% 22% 6% 1	880
February	1st to 10th	Night	19% 22% 36% 20% 4	800
	11th to 20th	Night	23% 19% 39% 16% 3	783
	21st to end	Night	22% 21% 32% 21% 4	660
March	1st to 10th	Night	25% 18% 34% 20% 4	800
	11th to 20th	Night	24% 18% 35% 18% 5% 1	800
	21st to end	Night	23% 18% 34% 18% 7%	880
April	1st to 10th	Night	28% 15% 31% 21% 5%	800
	11th to 20th	Night	25% 19% 29% 19% 7% 1	791
	21st to end	Night	27% 16% 28% 23% 5%	643
May	1st to 10th	Night	25% 10% 31% 25% 8% 1	400
	11th to 20th	Night	23% 12% 28% 29% 8%	394
	21st to end	Night	18% 10% 36% 27% 10%	433
June	1st to 10th	Night	20% 9% 33% 32% 7% 1	400
	11th to 20th	Night	17% 9% 29% 31% 13% 1	400
	21st to end	Night	19% 6% 30% 32% 12% 1	400
July	1st to 10th	Night	10% 6% 29% 40% 14% 1	390
	11th to 20th	Night	14% 6% 24% 39% 17%	388
	21st to end	Night	9% 6% 28% 41% 15% 1	438
August	1st to 10th	Night	11% 6% 22% 40% 21%	454
	11th to 20th	Night	13% 3 21% 37% 23% 3	594
	21st to end	Night	14% 8% 27% 31% 18% 2	851
September	1st to 10th	Night	14% 7% 30% 30% 17% 1	800
	11th to 20th	Night	16% 6% 24% 31% 20% 4	800
	21st to end	Night	21% 10% 25% 26% 16% 2	800
October	1st to 10th	Night	22% 13% 27% 23% 14% 1	800
	11th to 20th	Night	25% 15% 31% 22% 6% 1	800
	21st to end	Night	28% 16% 28% 24% 4	880
November	1st to 10th	Night	26% 17% 28% 22% 6% 1	820
	11th to 20th	Night	26% 18% 31% 17% 9%	840
	21st to end	Night	31% 18% 27% 20% 5%	840
December	1st to 10th	Night	28% 20% 30% 18% 4	840
	11th to 20th	Night	27% 19% 31% 18% 4 1	840
	21st to end	Night	32% 18% 30% 17% 3 1	924

Page generated at 2025-12-30 01:14:08. Version ac07

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