Duck Lake
Clear Sky Chart
History

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

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	6% 7% 3 6% 4 4 5% 4 6% 8% 47%	131449
	Night	4 7% 3 7% 4 4 4 4 6% 8% 48%	129284
Transparency	Day	35% 4 15% 27% 15% 3	131159
	Night	34% 4 17% 27% 14% 3	129152
Seeing	Day	20% 19% 28% 21% 9% 3	16857
	Night	15% 20% 29% 26% 9% 1	26212

By Month

Percentage Cloud Cover NW (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	1 8% 6% 11% 6% 5% 4 5% 7% 9% 38%	3249
	11th to 20th	Day	1 8% 3 10% 9% 8% 6% 6% 6% 6% 36%	3486
	21st to end	Day	1 6% 3 7% 5% 5% 4 4 7% 10% 48%	4092
February	1st to 10th	Day	2 8% 4 12% 7% 7% 6% 4 6% 10% 33%	1690
	11th to 20th	Day	2 9% 5% 10% 5% 6% 4 4 6% 10% 39%	1755
	21st to end	Day	2 7% 4 11% 6% 5% 5% 5% 7% 9% 40%	1620
March	1st to 10th	Day	2 7% 4 8% 4 3 4 4 7% 10% 48%	4551
	11th to 20th	Day	1 6% 2 6% 4 5% 6% 5% 7% 10% 46%	4999
	21st to end	Day	4 14% 7% 14% 6% 5% 5% 4 6% 8% 28%	5486
April	1st to 10th	Day	5% 13% 4 9% 5% 5% 5% 4 7% 9% 34%	2432
	11th to 20th	Day	6% 15% 4 9% 4 4 4 4 6% 8% 36%	2570
	21st to end	Day	7% 15% 4 7% 5% 4 4 5% 6% 8% 35%	2600
May	1st to 10th	Day	11% 13% 3 6% 4 4 3 3 5% 7% 42%	5880
	11th to 20th	Day	10% 9% 2 6% 5% 5% 6% 5% 7% 8% 36%	6598
	21st to end	Day	11% 7% 2 5% 4 4 4 3 5% 8% 47%	7405
June	1st to 10th	Day	14% 7% 2 6% 5% 4 5% 5% 7% 7% 37%	3000
	11th to 20th	Day	14% 8% 2 6% 5% 6% 5% 5% 6% 8% 36%	3000
	21st to end	Day	7% 5% 1 4 4 5% 5% 5% 7% 9% 50%	3000
July	1st to 10th	Day	6% 3 1 3 4 4 4 4 6% 7% 57%	6780
	11th to 20th	Day	5% 3 1 3 2 3 4 3 5% 7% 65%	6780
	21st to end	Day	6% 3 1 3 2 3 3 3 5% 6% 65%	6997
August	1st to 10th	Day	9% 5% 2 6% 4 5% 6% 4 7% 7% 46%	4420
	11th to 20th	Day	6% 3 1 4 4 5% 5% 4 7% 8% 54%	4158
	21st to end	Day	6% 4 1 4 3 3 3 2 5% 7% 62%	4664
September	1st to 10th	Day	10% 6% 1 4 3 3 4 3 4 6% 55%	2435
	11th to 20th	Day	8% 6% 2 5% 5% 4 5% 4 5% 8% 49%	2200
	21st to end	Day	10% 6% 2 4 3 3 3 3 6% 7% 53%	2200
October	1st to 10th	Day	6% 7% 2 5% 4 3 3 3 5% 11% 51%	3443
	11th to 20th	Day	3 8% 2 7% 4 4 6% 5% 6% 9% 47%	3124
	21st to end	Day	3 7% 2 7% 6% 4 5% 5% 6% 8% 47%	3200
November	1st to 10th	Day	5% 10% 3 7% 5% 4 3 5% 6% 8% 43%	1770
	11th to 20th	Day	1 9% 3 6% 4 4 4 4 8% 11% 46%	1680
	21st to end	Day	3 9% 3 8% 4 5% 5% 4 7% 9% 43%	1538
December	1st to 10th	Day	4 2 6% 4 4 4 5% 8% 11% 53%	2360
	11th to 20th	Day	2 7% 3 9% 6% 5% 6% 5% 6% 11% 40%	2712
	21st to end	Day	2 8% 4 8% 5% 5% 5% 4 5% 8% 45%	3575
January	1st to 10th	Night	2 9% 4 9% 6% 6% 5% 4 7% 9% 40%	6916
	11th to 20th	Night	1 6% 3 8% 7% 7% 7% 6% 7% 9% 39%	6674
	21st to end	Night	1 7% 3 8% 4 4 4 4 7% 10% 49%	7106
February	1st to 10th	Night	2 9% 4 10% 7% 5% 6% 4 6% 8% 40%	2710
	11th to 20th	Night	1 9% 4 10% 6% 6% 5% 5% 7% 8% 39%	2532
	21st to end	Night	2 7% 3 10% 7% 6% 5% 5% 8% 10% 38%	2006
March	1st to 10th	Night	1 6% 3 8% 5% 4 4 4 7% 10% 49%	5342
	11th to 20th	Night	1 5% 2 5% 3 4 5% 5% 8% 10% 52%	5000
	21st to end	Night	4 14% 7% 13% 5% 5% 5% 4 6% 8% 29%	5489
April	1st to 10th	Night	5% 10% 3 7% 5% 4 4 4 6% 8% 44%	1963
	11th to 20th	Night	6% 11% 4 7% 4 4 4 5% 6% 7% 41%	1781
	21st to end	Night	6% 12% 3 8% 5% 4 5% 3 5% 6% 43%	1800
May	1st to 10th	Night	10% 12% 3 7% 4 3 4 4 5% 6% 42%	4100
	11th to 20th	Night	7% 7% 3 8% 4 5% 6% 4 5% 7% 43%	3283
	21st to end	Night	11% 7% 2 5% 3 4 4 3 5% 6% 52%	3470
June	1st to 10th	Night	12% 7% 2 5% 5% 4 4 5% 6% 7% 45%	1400
	11th to 20th	Night	14% 4 2 5% 5% 4 5% 5% 6% 8% 43%	1400
	21st to end	Night	6% 3 1 4 3 4 5% 4 6% 8% 55%	1400
July	1st to 10th	Night	5% 2 1 2 2 2 3 3 6% 8% 66%	3180
	11th to 20th	Night	5% 2 1 3 2 2 2 3 5% 6% 68%	3180
	21st to end	Night	6% 4 2 6% 3 3 2 2 3 5% 64%	3830
August	1st to 10th	Night	10% 5% 2 4 3 3 4 3 5% 7% 55%	2732
	11th to 20th	Night	4 3 2 4 5% 5% 5% 4 8% 11% 51%	2901
	21st to end	Night	4 3 1 4 2 3 3 3 6% 7% 64%	3245
September	1st to 10th	Night	9% 4 1 3 3 3 4 3 5% 7% 57%	1961
	11th to 20th	Night	7% 8% 2 5% 3 3 4 4 6% 6% 52%	2200
	21st to end	Night	8% 6% 1 4 3 3 4 4 6% 8% 55%	2200
October	1st to 10th	Night	6% 6% 1 4 3 3 3 4 6% 7% 58%	3751
	11th to 20th	Night	3 5% 2 5% 4 4 4 4 7% 9% 52%	4020
	21st to end	Night	2 5% 3 8% 4 4 4 3 5% 9% 54%	4600
November	1st to 10th	Night	6% 10% 4 7% 4 5% 3 4 6% 7% 44%	2728
	11th to 20th	Night	1 6% 3 6% 4 5% 4 4 7% 11% 49%	2940
	21st to end	Night	2 8% 4 8% 5% 4 4 4 6% 11% 44%	3081
December	1st to 10th	Night	1 5% 3 6% 4 3 4 4 6% 11% 52%	5040
	11th to 20th	Night	2 8% 4 10% 7% 6% 6% 5% 8% 9% 36%	5700
	21st to end	Night	2 10% 4 9% 5% 4 5% 4 6% 8% 42%	7623

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	44% 4 16% 24% 11% 1	3249
	11th to 20th	Day	47% 5% 17% 16% 9% 6%	3509
	21st to end	Day	32% 4 19% 31% 14% 1	4092
February	1st to 10th	Day	46% 5% 20% 17% 8% 3	1690
	11th to 20th	Day	43% 4 20% 23% 9% 2	1764
	21st to end	Day	41% 4 19% 22% 13% 2	1620
March	1st to 10th	Day	30% 5% 15% 25% 22% 3	4551
	11th to 20th	Day	32% 4 22% 28% 13% 1	5000
	21st to end	Day	53% 5% 16% 21% 5%	5486
April	1st to 10th	Day	46% 5% 16% 24% 9%	2432
	11th to 20th	Day	47% 5% 16% 22% 9% 1	2570
	21st to end	Day	46% 4 17% 22% 10% 1	2600
May	1st to 10th	Day	44% 3 11% 26% 16% 1	5880
	11th to 20th	Day	43% 5% 13% 30% 9% 1	6602
	21st to end	Day	37% 3 16% 31% 14%	7406
June	1st to 10th	Day	43% 5% 18% 23% 11% 1	3000
	11th to 20th	Day	46% 4 13% 20% 15% 2	3000
	21st to end	Day	31% 4 17% 33% 13% 2	3000
July	1st to 10th	Day	25% 4 12% 27% 24% 8%	6706
	11th to 20th	Day	20% 4 11% 27% 26% 12%	6699
	21st to end	Day	20% 4 9% 29% 25% 13%	6801
August	1st to 10th	Day	33% 5% 12% 21% 22% 6%	4403
	11th to 20th	Day	25% 6% 12% 33% 21% 3	4197
	21st to end	Day	23% 3 9% 42% 20% 4	4663
September	1st to 10th	Day	31% 2 11% 29% 19% 8%	2435
	11th to 20th	Day	35% 3 12% 29% 18% 4	2200
	21st to end	Day	32% 3 15% 32% 15% 4	2200
October	1st to 10th	Day	28% 4 16% 33% 17% 1	3443
	11th to 20th	Day	32% 4 16% 26% 19% 2	3124
	21st to end	Day	33% 6% 16% 30% 14% 1	3200
November	1st to 10th	Day	38% 7% 18% 23% 12% 2	1770
	11th to 20th	Day	33% 5% 23% 27% 11% 1	1680
	21st to end	Day	37% 6% 24% 21% 10% 3	1538
December	1st to 10th	Day	26% 6% 28% 27% 10% 3	2360
	11th to 20th	Day	39% 6% 23% 25% 7% 1	2714
	21st to end	Day	38% 4 12% 27% 15% 4	3575
January	1st to 10th	Night	42% 4 18% 25% 9% 2	6916
	11th to 20th	Night	42% 4 17% 21% 12% 4	6713
	21st to end	Night	33% 3 20% 30% 12% 2	7106
February	1st to 10th	Night	42% 6% 16% 21% 12% 3	2710
	11th to 20th	Night	43% 5% 18% 21% 11% 2	2533
	21st to end	Night	42% 5% 16% 23% 13% 2	2006
March	1st to 10th	Night	31% 5% 17% 25% 18% 4	5342
	11th to 20th	Night	27% 5% 22% 28% 18%	5000
	21st to end	Night	52% 5% 16% 21% 7%	5489
April	1st to 10th	Night	39% 4 17% 30% 10% 1	1963
	11th to 20th	Night	42% 4 15% 27% 10% 1	1781
	21st to end	Night	43% 4 15% 28% 10% 1	1800
May	1st to 10th	Night	44% 2 13% 26% 13% 2	4097
	11th to 20th	Night	38% 6% 13% 32% 11%	3283
	21st to end	Night	35% 3 17% 33% 13%	3470
June	1st to 10th	Night	37% 3 19% 29% 11% 1	1400
	11th to 20th	Night	38% 4 17% 23% 15% 2	1400
	21st to end	Night	27% 3 19% 33% 17% 2	1400
July	1st to 10th	Night	17% 3 14% 29% 24% 13%	3145
	11th to 20th	Night	18% 3 10% 32% 23% 13%	3138
	21st to end	Night	25% 3 10% 27% 20% 15%	3722
August	1st to 10th	Night	28% 4 14% 23% 21% 10%	2724
	11th to 20th	Night	26% 5% 15% 35% 15% 3	2928
	21st to end	Night	21% 2 11% 37% 25% 5%	3245
September	1st to 10th	Night	28% 3 13% 31% 17% 8%	1961
	11th to 20th	Night	33% 3 14% 30% 16% 5%	2200
	21st to end	Night	28% 4 17% 30% 18% 3	2200
October	1st to 10th	Night	25% 3 15% 35% 20% 2	3751
	11th to 20th	Night	28% 5% 17% 29% 18% 3	4020
	21st to end	Night	29% 4 16% 33% 16% 2	4600
November	1st to 10th	Night	40% 4 21% 22% 10% 2	2728
	11th to 20th	Night	30% 6% 23% 27% 12% 1	2940
	21st to end	Night	35% 5% 25% 22% 10% 3	3081
December	1st to 10th	Night	28% 6% 26% 26% 12% 2	5040
	11th to 20th	Night	43% 5% 26% 19% 7% 1	5697
	21st to end	Night	39% 4 16% 23% 14% 5%	7623

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	22% 21% 28% 15% 9% 5%	220
	11th to 20th	Day	21% 22% 31% 16% 9% 1	220
	21st to end	Day	22% 28% 33% 12% 4 2	242
February	1st to 10th	Day	24% 21% 31% 18% 5% 1	245
	11th to 20th	Day	15% 25% 35% 17% 7%	300
	21st to end	Day	24% 32% 26% 14% 3 1	384
March	1st to 10th	Day	20% 27% 30% 15% 5% 2	500
	11th to 20th	Day	19% 22% 31% 17% 7% 3	500
	21st to end	Day	25% 23% 28% 17% 4 2	550
April	1st to 10th	Day	26% 24% 32% 15% 4	500
	11th to 20th	Day	22% 27% 27% 18% 5% 1	492
	21st to end	Day	24% 21% 26% 20% 6% 3	500
May	1st to 10th	Day	24% 17% 27% 20% 9% 2	503
	11th to 20th	Day	24% 13% 24% 22% 13% 4	704
	21st to end	Day	25% 12% 21% 21% 18% 3	789
June	1st to 10th	Day	21% 19% 24% 23% 10% 2	730
	11th to 20th	Day	26% 21% 25% 19% 8% 2	730
	21st to end	Day	12% 14% 33% 24% 14% 3	730
July	1st to 10th	Day	10% 13% 28% 28% 17% 5%	721
	11th to 20th	Day	10% 13% 32% 30% 14% 1	718
	21st to end	Day	9% 12% 33% 31% 11% 4	633
August	1st to 10th	Day	14% 15% 27% 30% 11% 4	527
	11th to 20th	Day	8% 13% 33% 27% 14% 5%	517
	21st to end	Day	13% 15% 31% 28% 10% 3	583
September	1st to 10th	Day	16% 16% 29% 23% 11% 4	530
	11th to 20th	Day	14% 18% 30% 23% 11% 4	530
	21st to end	Day	24% 21% 28% 19% 6% 2	530
October	1st to 10th	Day	21% 19% 28% 19% 8% 4	438
	11th to 20th	Day	23% 19% 25% 19% 9% 3	330
	21st to end	Day	27% 24% 28% 17% 3 2	363
November	1st to 10th	Day	27% 26% 29% 15% 2	330
	11th to 20th	Day	29% 27% 30% 11% 2	330
	21st to end	Day	25% 33% 17% 17% 7% 2	256
December	1st to 10th	Day	24% 30% 27% 13% 4 2	220
	11th to 20th	Day	35% 19% 28% 14% 3	220
	21st to end	Day	21% 22% 31% 14% 8% 4	242
January	1st to 10th	Night	21% 29% 28% 16% 5%	1050
	11th to 20th	Night	15% 27% 32% 20% 6% 1	950
	21st to end	Night	14% 29% 34% 17% 4 2	924
February	1st to 10th	Night	16% 23% 30% 24% 6% 2	800
	11th to 20th	Night	13% 22% 32% 25% 8% 1	784
	21st to end	Night	13% 25% 31% 21% 9%	660
March	1st to 10th	Night	12% 21% 34% 24% 7% 2	800
	11th to 20th	Night	14% 21% 31% 26% 8% 2	800
	21st to end	Night	15% 20% 29% 26% 8% 2	880
April	1st to 10th	Night	15% 17% 32% 27% 8% 1	747
	11th to 20th	Night	15% 21% 35% 22% 7% 1	593
	21st to end	Night	16% 15% 30% 27% 12% 1	600
May	1st to 10th	Night	17% 13% 24% 32% 13% 2	600
	11th to 20th	Night	14% 10% 26% 33% 15% 2	433
	21st to end	Night	23% 9% 20% 29% 17% 2	433
June	1st to 10th	Night	18% 13% 26% 29% 14% 2	400
	11th to 20th	Night	19% 16% 30% 23% 11% 1	400
	21st to end	Night	10% 9% 29% 36% 18%	400
July	1st to 10th	Night	8% 8% 22% 44% 17% 1	390
	11th to 20th	Night	6% 5% 38% 38% 13% 1	388
	21st to end	Night	7% 6% 24% 45% 17%	438
August	1st to 10th	Night	8% 5% 25% 41% 20% 1	469
	11th to 20th	Night	6% 4 27% 40% 20% 3	594
	21st to end	Night	10% 9% 30% 37% 12% 1	660
September	1st to 10th	Night	13% 8% 24% 36% 17% 3	701
	11th to 20th	Night	12% 9% 25% 35% 17% 3	800
	21st to end	Night	15% 15% 28% 30% 11% 2	800
October	1st to 10th	Night	18% 14% 25% 30% 11% 2	800
	11th to 20th	Night	16% 18% 26% 28% 10% 1	800
	21st to end	Night	18% 25% 29% 23% 5% 1	880
November	1st to 10th	Night	22% 27% 29% 19% 2	883
	11th to 20th	Night	21% 32% 28% 16% 3 1	1050
	21st to end	Night	16% 30% 31% 19% 5% 1	1050
December	1st to 10th	Night	17% 25% 32% 21% 5% 1	1050
	11th to 20th	Night	16% 27% 34% 18% 4	1050
	21st to end	Night	18% 26% 33% 16% 6% 1	1155

Page generated at 2026-01-28 23:21:39. Version ac07

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