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 2024-11-28.

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% 8% 3 6% 4 4 5% 4 6% 8% 46%	105627
	Night	4 7% 3 7% 4 4 4 4 6% 8% 48%	102478
Transparency	Day	35% 4 15% 26% 15% 4	105379
	Night	34% 4 17% 26% 14% 4	102373
Seeing	Day	20% 19% 28% 21% 9% 3	15407
	Night	15% 19% 29% 26% 9% 1	24612

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 7% 3 10% 7% 5% 5% 5% 7% 10% 40%	2219
	11th to 20th	Day	2 11% 4 9% 7% 8% 7% 7% 7% 7% 34%	2366
	21st to end	Day	1 7% 4 8% 4 5% 5% 5% 9% 12% 40%	2794
February	1st to 10th	Day	2 8% 4 12% 7% 6% 6% 4 6% 10% 33%	1605
	11th to 20th	Day	2 10% 5% 10% 5% 5% 4 4 6% 10% 38%	1665
	21st to end	Day	2 8% 4 11% 7% 5% 5% 5% 7% 8% 39%	1541
March	1st to 10th	Day	1 5% 3 8% 4 3 4 5% 8% 11% 47%	3158
	11th to 20th	Day	2 9% 3 6% 3 4 4 4 6% 10% 50%	3489
	21st to end	Day	4 15% 7% 13% 5% 4 5% 4 6% 7% 31%	3825
April	1st to 10th	Day	5% 13% 4 9% 5% 5% 5% 5% 7% 9% 34%	2310
	11th to 20th	Day	6% 15% 4 9% 4 4 3 4 6% 7% 36%	2440
	21st to end	Day	7% 16% 4 7% 5% 4 4 5% 6% 7% 35%	2470
May	1st to 10th	Day	13% 17% 4 7% 5% 5% 4 3 5% 6% 31%	4110
	11th to 20th	Day	10% 10% 2 5% 5% 5% 6% 4 7% 8% 37%	4598
	21st to end	Day	16% 9% 2 5% 4 4 5% 4 6% 8% 37%	5161
June	1st to 10th	Day	14% 7% 2 6% 5% 4 5% 5% 7% 7% 37%	2850
	11th to 20th	Day	14% 8% 2 6% 5% 6% 6% 5% 6% 7% 36%	2850
	21st to end	Day	7% 5% 1 4 4 5% 5% 5% 7% 9% 50%	2850
July	1st to 10th	Day	4 2 1 3 3 4 5% 4 7% 7% 59%	4740
	11th to 20th	Day	2 2 1 2 2 3 4 3 5% 6% 71%	4740
	21st to end	Day	2 2 1 2 2 2 3 2 5% 6% 73%	4871
August	1st to 10th	Day	9% 5% 2 6% 4 5% 6% 4 7% 7% 47%	4284
	11th to 20th	Day	6% 3 1 4 4 5% 5% 4 7% 8% 54%	4028
	21st to end	Day	6% 3 1 4 3 2 3 2 5% 7% 63%	4521
September	1st to 10th	Day	11% 6% 1 4 3 3 4 3 4 6% 55%	2313
	11th to 20th	Day	8% 6% 2 5% 5% 4 4 3 5% 8% 49%	2090
	21st to end	Day	11% 6% 2 4 3 3 3 3 5% 7% 53%	2090
October	1st to 10th	Day	6% 7% 2 5% 4 3 3 3 5% 11% 51%	3338
	11th to 20th	Day	3 8% 2 7% 4 4 6% 5% 6% 9% 47%	3028
	21st to end	Day	3 7% 2 7% 6% 4 5% 5% 6% 9% 46%	3101
November	1st to 10th	Day	5% 10% 3 7% 5% 4 3 5% 6% 8% 43%	1684
	11th to 20th	Day	1 9% 3 6% 4 4 4 4 8% 11% 46%	1600
	21st to end	Day	3 9% 2 8% 5% 6% 4 4 7% 9% 44%	1444
December	1st to 10th	Day	1 6% 3 9% 6% 5% 6% 6% 10% 10% 38%	1330
	11th to 20th	Day	3 8% 4 11% 6% 4 5% 5% 6% 11% 36%	1682
	21st to end	Day	2 7% 4 7% 5% 4 5% 4 5% 8% 48%	2442
January	1st to 10th	Night	1 7% 3 8% 5% 5% 6% 5% 8% 10% 41%	4726
	11th to 20th	Night	2 8% 4 8% 6% 7% 8% 6% 6% 8% 38%	4559
	21st to end	Night	2 9% 4 8% 4 4 4 4 7% 9% 46%	4862
February	1st to 10th	Night	2 10% 3 10% 6% 4 5% 4 7% 8% 40%	2575
	11th to 20th	Night	1 9% 4 9% 6% 6% 5% 5% 7% 8% 39%	2402
	21st to end	Night	2 7% 4 10% 7% 6% 5% 5% 7% 10% 38%	1909
March	1st to 10th	Night	1 5% 3 9% 6% 4 5% 4 7% 9% 46%	3715
	11th to 20th	Night	2 6% 3 6% 4 3 4 4 6% 9% 54%	3490
	21st to end	Night	5% 14% 6% 14% 5% 4 4 4 5% 7% 32%	3828
April	1st to 10th	Night	5% 10% 3 7% 5% 5% 5% 4 6% 8% 43%	1865
	11th to 20th	Night	7% 12% 4 7% 4 4 4 5% 6% 7% 40%	1691
	21st to end	Night	6% 12% 3 8% 5% 4 5% 3 5% 6% 43%	1710
May	1st to 10th	Night	11% 16% 4 8% 4 4 4 4 6% 5% 35%	2860
	11th to 20th	Night	7% 6% 2 5% 3 3 5% 4 6% 7% 51%	2281
	21st to end	Night	15% 9% 3 7% 4 5% 5% 4 6% 7% 36%	2414
June	1st to 10th	Night	12% 7% 2 5% 5% 4 4 5% 6% 7% 44%	1330
	11th to 20th	Night	14% 4 2 5% 4 4 5% 5% 5% 8% 43%	1330
	21st to end	Night	6% 3 1 4 3 4 5% 4 6% 8% 56%	1330
July	1st to 10th	Night	3 2 1 2 3 3 3 4 6% 8% 64%	2220
	11th to 20th	Night	2 2 1 3 2 2 2 2 5% 5% 75%	2220
	21st to end	Night	3 3 1 4 2 3 2 2 3 4 74%	2665
August	1st to 10th	Night	10% 5% 2 4 3 3 4 3 5% 6% 56%	2648
	11th to 20th	Night	4 3 2 4 5% 5% 5% 4 8% 11% 51%	2811
	21st to end	Night	5% 3 1 4 2 3 3 3 6% 7% 64%	3146
September	1st to 10th	Night	10% 4 2 3 3 3 4 3 5% 7% 56%	1863
	11th to 20th	Night	7% 8% 2 5% 3 3 4 4 6% 6% 52%	2090
	21st to end	Night	8% 6% 1 4 3 3 4 4 6% 8% 54%	2090
October	1st to 10th	Night	6% 5% 1 4 3 3 3 4 6% 8% 58%	3636
	11th to 20th	Night	3 5% 2 5% 4 4 4 4 7% 9% 53%	3896
	21st to end	Night	2 5% 3 8% 4 4 4 3 6% 9% 54%	4457
November	1st to 10th	Night	6% 10% 4 8% 4 4 4 3 6% 7% 44%	2595
	11th to 20th	Night	1 6% 3 6% 4 5% 4 4 7% 11% 49%	2800
	21st to end	Night	2 8% 4 8% 5% 4 4 4 6% 10% 45%	2890
December	1st to 10th	Night	1 7% 4 7% 5% 4 6% 5% 7% 9% 44%	2850
	11th to 20th	Night	2 7% 4 10% 6% 6% 5% 4 7% 9% 39%	3510
	21st to end	Night	2 7% 3 7% 5% 4 5% 5% 6% 8% 48%	5214

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	40% 4 19% 25% 10% 1	2219
	11th to 20th	Day	48% 5% 17% 13% 9% 7%	2389
	21st to end	Day	35% 4 24% 29% 6% 1	2794
February	1st to 10th	Day	46% 5% 21% 18% 7% 2	1605
	11th to 20th	Day	43% 4 20% 22% 9% 2	1674
	21st to end	Day	42% 4 18% 21% 13% 2	1541
March	1st to 10th	Day	30% 5% 17% 27% 21% 1	3158
	11th to 20th	Day	31% 4 29% 28% 7% 2	3490
	21st to end	Day	53% 3 15% 23% 5%	3825
April	1st to 10th	Day	46% 6% 17% 24% 8%	2310
	11th to 20th	Day	47% 5% 16% 21% 9% 1	2440
	21st to end	Day	47% 4 17% 21% 9% 1	2470
May	1st to 10th	Day	55% 3 12% 25% 6%	4110
	11th to 20th	Day	41% 6% 14% 29% 9% 1	4602
	21st to end	Day	46% 3 17% 23% 12%	5162
June	1st to 10th	Day	43% 5% 18% 23% 11% 1	2850
	11th to 20th	Day	47% 4 13% 21% 14% 2	2850
	21st to end	Day	30% 4 18% 33% 13% 2	2850
July	1st to 10th	Day	22% 4 10% 33% 23% 8%	4666
	11th to 20th	Day	15% 3 8% 23% 34% 18%	4659
	21st to end	Day	13% 3 5% 25% 34% 19%	4717
August	1st to 10th	Day	32% 5% 12% 21% 23% 6%	4267
	11th to 20th	Day	25% 6% 12% 34% 21% 3	4067
	21st to end	Day	23% 3 9% 42% 20% 4	4520
September	1st to 10th	Day	32% 2 10% 28% 19% 8%	2313
	11th to 20th	Day	35% 3 12% 29% 17% 4	2090
	21st to end	Day	33% 3 15% 32% 13% 4	2090
October	1st to 10th	Day	28% 4 16% 33% 17% 1	3338
	11th to 20th	Day	32% 5% 16% 26% 19% 1	3028
	21st to end	Day	34% 6% 15% 31% 14% 1	3101
November	1st to 10th	Day	39% 7% 17% 24% 12% 2	1684
	11th to 20th	Day	33% 6% 22% 27% 11% 1	1600
	21st to end	Day	37% 6% 23% 21% 10% 3	1444
December	1st to 10th	Day	39% 7% 23% 20% 8% 4	1330
	11th to 20th	Day	43% 6% 23% 21% 7% 1	1684
	21st to end	Day	35% 4 14% 25% 16% 5%	2442
January	1st to 10th	Night	38% 5% 21% 23% 11% 2	4726
	11th to 20th	Night	45% 5% 16% 17% 11% 6%	4598
	21st to end	Night	36% 3 23% 28% 10% 1	4862
February	1st to 10th	Night	42% 6% 16% 21% 11% 3	2575
	11th to 20th	Night	42% 5% 19% 21% 11% 1	2403
	21st to end	Night	42% 5% 16% 23% 12% 2	1909
March	1st to 10th	Night	34% 6% 17% 24% 19%	3715
	11th to 20th	Night	27% 5% 28% 27% 12% 1	3490
	21st to end	Night	53% 4 15% 21% 7%	3828
April	1st to 10th	Night	39% 4 18% 29% 9% 1	1865
	11th to 20th	Night	43% 4 15% 27% 10% 1	1691
	21st to end	Night	43% 4 15% 28% 9% 1	1710
May	1st to 10th	Night	52% 2 15% 23% 8%	2860
	11th to 20th	Night	30% 5% 15% 34% 15%	2281
	21st to end	Night	48% 3 18% 22% 9%	2414
June	1st to 10th	Night	38% 3 19% 29% 10% 1	1330
	11th to 20th	Night	38% 4 17% 24% 14% 2	1330
	21st to end	Night	26% 3 19% 32% 18% 2	1330
July	1st to 10th	Night	17% 3 12% 33% 25% 10%	2185
	11th to 20th	Night	13% 3 8% 28% 30% 19%	2178
	21st to end	Night	17% 2 6% 26% 28% 21%	2581
August	1st to 10th	Night	28% 4 14% 23% 22% 10%	2640
	11th to 20th	Night	26% 5% 15% 35% 15% 4	2838
	21st to end	Night	20% 2 11% 37% 24% 5%	3146
September	1st to 10th	Night	29% 3 13% 29% 18% 8%	1863
	11th to 20th	Night	33% 3 13% 29% 17% 5%	2090
	21st to end	Night	28% 4 18% 30% 17% 3	2090
October	1st to 10th	Night	25% 3 15% 35% 20% 2	3636
	11th to 20th	Night	27% 5% 18% 29% 18% 3	3896
	21st to end	Night	29% 4 16% 33% 16% 2	4457
November	1st to 10th	Night	41% 4 21% 21% 11% 3	2595
	11th to 20th	Night	30% 6% 23% 28% 13% 1	2800
	21st to end	Night	35% 5% 24% 22% 11% 3	2890
December	1st to 10th	Night	36% 6% 20% 23% 10% 4	2850
	11th to 20th	Night	41% 4 26% 22% 7% 1	3507
	21st to end	Night	34% 4 18% 24% 14% 7%	5214

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	18% 20% 30% 16% 10% 6%	180
	11th to 20th	Day	20% 19% 30% 18% 11% 2	180
	21st to end	Day	21% 27% 32% 14% 5% 3	198
February	1st to 10th	Day	25% 20% 30% 19% 5% 1	220
	11th to 20th	Day	17% 27% 32% 16% 7%	270
	21st to end	Day	22% 31% 28% 15% 3 1	353
March	1st to 10th	Day	19% 27% 31% 15% 5% 2	460
	11th to 20th	Day	20% 21% 31% 18% 7% 4	460
	21st to end	Day	24% 23% 29% 18% 4 2	506
April	1st to 10th	Day	25% 25% 31% 15% 4	460
	11th to 20th	Day	21% 26% 28% 19% 5% 1	452
	21st to end	Day	26% 21% 26% 20% 6% 2	460
May	1st to 10th	Day	25% 17% 26% 21% 10% 2	463
	11th to 20th	Day	24% 13% 23% 22% 13% 4	655
	21st to end	Day	27% 11% 20% 21% 18% 3	734
June	1st to 10th	Day	22% 19% 24% 23% 10% 3	680
	11th to 20th	Day	27% 21% 23% 19% 8% 2	680
	21st to end	Day	12% 13% 33% 24% 15% 4	680
July	1st to 10th	Day	10% 12% 28% 28% 17% 5%	671
	11th to 20th	Day	10% 13% 32% 30% 14% 1	668
	21st to end	Day	8% 12% 33% 31% 11% 4	586
August	1st to 10th	Day	14% 15% 28% 29% 10% 4	487
	11th to 20th	Day	8% 12% 32% 27% 15% 5%	477
	21st to end	Day	14% 16% 31% 27% 10% 3	539
September	1st to 10th	Day	17% 17% 29% 21% 11% 4	490
	11th to 20th	Day	15% 19% 31% 22% 10% 3	490
	21st to end	Day	24% 21% 28% 18% 6% 3	490
October	1st to 10th	Day	22% 19% 28% 19% 8% 4	403
	11th to 20th	Day	22% 20% 24% 19% 10% 4	300
	21st to end	Day	26% 22% 29% 18% 3 2	330
November	1st to 10th	Day	25% 27% 30% 16% 3	300
	11th to 20th	Day	28% 29% 31% 11% 2	300
	21st to end	Day	22% 32% 18% 18% 7% 2	227
December	1st to 10th	Day	22% 29% 27% 15% 4 2	180
	11th to 20th	Day	31% 19% 29% 16% 4 1	180
	21st to end	Day	19% 20% 32% 15% 10% 5%	198
January	1st to 10th	Night	21% 29% 29% 16% 5%	950
	11th to 20th	Night	15% 26% 32% 21% 6% 1	860
	21st to end	Night	14% 29% 32% 19% 4 2	836
February	1st to 10th	Night	16% 23% 29% 23% 6% 3	760
	11th to 20th	Night	13% 23% 32% 24% 8% 1	744
	21st to end	Night	13% 24% 31% 22% 10%	628
March	1st to 10th	Night	12% 21% 35% 23% 7% 2	760
	11th to 20th	Night	14% 21% 29% 26% 8% 2	760
	21st to end	Night	15% 20% 28% 27% 8% 2	836
April	1st to 10th	Night	15% 18% 31% 27% 9% 1	710
	11th to 20th	Night	15% 22% 33% 22% 7% 1	563
	21st to end	Night	16% 15% 30% 26% 11% 1	570
May	1st to 10th	Night	17% 14% 22% 31% 14% 2	570
	11th to 20th	Night	14% 10% 25% 33% 16% 2	411
	21st to end	Night	24% 9% 20% 28% 17% 2	411
June	1st to 10th	Night	18% 13% 25% 28% 14% 2	380
	11th to 20th	Night	20% 16% 30% 22% 11% 1	380
	21st to end	Night	9% 9% 28% 36% 18%	380
July	1st to 10th	Night	8% 8% 22% 43% 18% 1	370
	11th to 20th	Night	6% 5% 38% 37% 14% 1	368
	21st to end	Night	6% 7% 24% 45% 17%	416
August	1st to 10th	Night	9% 4 24% 42% 20% 1	445
	11th to 20th	Night	6% 4 26% 40% 21% 3	564
	21st to end	Night	11% 10% 29% 37% 12% 1	627
September	1st to 10th	Night	13% 8% 25% 35% 16% 3	666
	11th to 20th	Night	12% 9% 25% 34% 16% 3	760
	21st to end	Night	15% 15% 27% 29% 11% 2	760
October	1st to 10th	Night	18% 14% 25% 30% 11% 2	760
	11th to 20th	Night	16% 18% 25% 29% 11% 1	760
	21st to end	Night	17% 25% 29% 24% 5% 1	836
November	1st to 10th	Night	21% 27% 29% 20% 3	840
	11th to 20th	Night	21% 32% 28% 15% 3 1	1000
	21st to end	Night	16% 29% 30% 19% 5% 1	986
December	1st to 10th	Night	15% 24% 32% 23% 6% 1	950
	11th to 20th	Night	15% 27% 35% 19% 5%	950
	21st to end	Night	18% 25% 33% 17% 6% 1	1045

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