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 2024-01-14.

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	7% 7% 3 6% 5% 3 5% 5% 6% 8% 44%	74632
	Night	5% 7% 3 6% 5% 3 4 5% 6% 9% 47%	75130
Transparency	Day	38% 4 16% 25% 13% 3	74322
	Night	35% 5% 18% 26% 13% 3	74959
Seeing	Day	19% 19% 28% 21% 10% 3	14180
	Night	15% 20% 29% 26% 9% 1	23554

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	2 7% 3 8% 6% 4 6% 6% 7% 11% 40%	1329
	11th to 20th	Day	6% 3 7% 8% 6% 5% 6% 6% 10% 42%	1380
	21st to end	Day	2 7% 4 9% 6% 4 5% 5% 10% 11% 37%	1584
February	1st to 10th	Day	2 7% 5% 10% 8% 4 7% 6% 6% 11% 35%	1521
	11th to 20th	Day	2 9% 6% 9% 6% 5% 4 5% 5% 11% 38%	1575
	21st to end	Day	2 7% 4 10% 8% 3 5% 6% 7% 9% 39%	1453
March	1st to 10th	Day	2 6% 4 9% 6% 3 5% 5% 7% 9% 43%	1807
	11th to 20th	Day	3 8% 4 7% 4 3 5% 6% 7% 11% 42%	1979
	21st to end	Day	4 11% 5% 8% 5% 3 6% 6% 7% 9% 36%	2178
April	1st to 10th	Day	5% 11% 5% 8% 6% 4 6% 6% 7% 9% 33%	2188
	11th to 20th	Day	7% 15% 5% 7% 6% 3 3 5% 6% 8% 36%	2310
	21st to end	Day	8% 16% 4 6% 5% 2 5% 5% 6% 8% 35%	2340
May	1st to 10th	Day	10% 12% 3 5% 5% 4 5% 5% 6% 7% 38%	2340
	11th to 20th	Day	15% 10% 3 5% 6% 3 5% 5% 6% 6% 36%	2598
	21st to end	Day	24% 9% 3 5% 5% 3 5% 4 5% 7% 30%	2917
June	1st to 10th	Day	15% 7% 2 6% 5% 3 5% 6% 7% 8% 36%	2700
	11th to 20th	Day	14% 7% 3 5% 6% 5% 6% 6% 6% 7% 35%	2700
	21st to end	Day	7% 4 1 4 4 4 5% 5% 6% 9% 51%	2700
July	1st to 10th	Day	6% 3 1 3 4 3 6% 6% 6% 7% 55%	2700
	11th to 20th	Day	4 3 1 3 3 3 5% 5% 5% 7% 61%	2700
	21st to end	Day	4 2 1 3 3 2 3 4 5% 6% 67%	2794
August	1st to 10th	Day	8% 2 1 3 4 3 3 4 6% 7% 58%	2442
	11th to 20th	Day	8% 3 1 3 3 3 3 5% 6% 8% 57%	2299
	21st to end	Day	8% 4 1 4 4 2 4 3 6% 7% 55%	2574
September	1st to 10th	Day	11% 6% 2 4 3 2 4 4 4 6% 54%	2192
	11th to 20th	Day	8% 6% 2 4 6% 3 5% 4 5% 8% 51%	1980
	21st to end	Day	11% 6% 2 4 4 2 3 4 5% 7% 51%	1980
October	1st to 10th	Day	10% 9% 3 4 6% 2 3 5% 5% 8% 45%	1898
	11th to 20th	Day	4 8% 3 7% 5% 3 5% 5% 5% 9% 46%	1728
	21st to end	Day	4 9% 3 7% 6% 3 6% 5% 6% 9% 42%	1782
November	1st to 10th	Day	6% 10% 3 6% 6% 3 4 5% 6% 9% 43%	1598
	11th to 20th	Day	1 8% 3 5% 5% 3 4 5% 7% 12% 47%	1520
	21st to end	Day	3 7% 3 7% 5% 4 4 5% 6% 9% 44%	1392
December	1st to 10th	Day	1 6% 4 7% 6% 4 6% 8% 9% 10% 39%	1330
	11th to 20th	Day	3 8% 4 10% 8% 3 6% 6% 6% 11% 36%	1682
	21st to end	Day	2 6% 5% 6% 6% 3 5% 5% 5% 8% 48%	2442
January	1st to 10th	Night	2 6% 3 7% 6% 4 6% 6% 8% 10% 42%	2836
	11th to 20th	Night	1 7% 4 7% 6% 4 6% 6% 6% 9% 43%	2672
	21st to end	Night	1 5% 3 7% 5% 3 4 6% 7% 11% 47%	2772
February	1st to 10th	Night	2 8% 4 8% 7% 3 5% 6% 6% 8% 41%	2439
	11th to 20th	Night	2 8% 5% 7% 7% 4 6% 6% 7% 8% 39%	2272
	21st to end	Night	2 7% 4 9% 8% 4 5% 6% 7% 10% 37%	1799
March	1st to 10th	Night	1 6% 4 8% 7% 4 5% 5% 7% 10% 43%	2152
	11th to 20th	Night	3 6% 4 6% 5% 3 4 5% 7% 11% 46%	1980
	21st to end	Night	4 8% 4 8% 5% 3 5% 6% 7% 9% 40%	2178
April	1st to 10th	Night	5% 8% 3 7% 6% 3 5% 4 6% 9% 43%	1768
	11th to 20th	Night	7% 11% 4 6% 5% 3 5% 5% 6% 6% 40%	1601
	21st to end	Night	6% 12% 3 7% 6% 3 5% 4 5% 6% 43%	1620
May	1st to 10th	Night	8% 9% 4 6% 5% 4 4 6% 7% 7% 42%	1620
	11th to 20th	Night	11% 8% 2 5% 3 2 5% 6% 6% 7% 46%	1293
	21st to end	Night	20% 7% 3 4 5% 3 4 4 5% 7% 39%	1358
June	1st to 10th	Night	13% 6% 2 5% 5% 3 4 6% 6% 7% 43%	1260
	11th to 20th	Night	15% 4 2 5% 4 2 5% 6% 5% 8% 43%	1260
	21st to end	Night	6% 3 1 3 4 3 5% 5% 6% 9% 56%	1260
July	1st to 10th	Night	5% 2 1 3 3 2 3 4 3 7% 67%	1260
	11th to 20th	Night	3 2 1 4 3 2 2 4 6% 5% 67%	1260
	21st to end	Night	5% 2 1 2 2 2 2 3 3 5% 73%	1521
August	1st to 10th	Night	6% 3 1 2 3 2 3 4 5% 6% 65%	1495
	11th to 20th	Night	5% 2 1 2 3 2 2 3 6% 12% 61%	1602
	21st to end	Night	7% 4 1 4 3 3 3 3 6% 6% 59%	1782
September	1st to 10th	Night	10% 4 2 3 4 3 4 4 5% 7% 55%	1764
	11th to 20th	Night	7% 8% 2 4 4 2 4 5% 5% 6% 53%	1980
	21st to end	Night	9% 6% 1 4 3 3 3 5% 6% 8% 52%	1980
October	1st to 10th	Night	10% 8% 2 4 4 2 3 4 4 8% 50%	2061
	11th to 20th	Night	5% 7% 2 5% 4 2 3 5% 6% 9% 50%	2228
	21st to end	Night	4 7% 4 7% 5% 3 4 5% 6% 8% 47%	2574
November	1st to 10th	Night	6% 9% 4 7% 5% 3 4 4 6% 8% 45%	2462
	11th to 20th	Night	1 6% 3 5% 5% 4 5% 4 6% 12% 50%	2660
	21st to end	Night	2 6% 5% 7% 6% 3 4 5% 6% 10% 46%	2787
December	1st to 10th	Night	1 7% 4 7% 6% 3 6% 6% 7% 9% 44%	2850
	11th to 20th	Night	2 7% 4 9% 7% 5% 5% 6% 7% 9% 39%	3510
	21st to end	Night	2 7% 3 6% 6% 3 5% 6% 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% 6% 19% 24% 8% 2	1329
	11th to 20th	Day	38% 5% 24% 20% 8% 4	1380
	21st to end	Day	38% 7% 18% 25% 10% 1	1584
February	1st to 10th	Day	45% 6% 22% 18% 7% 2	1521
	11th to 20th	Day	43% 4 21% 23% 9% 1	1584
	21st to end	Day	43% 4 18% 20% 13% 2	1453
March	1st to 10th	Day	39% 6% 20% 24% 10%	1807
	11th to 20th	Day	37% 6% 20% 26% 9% 3	1980
	21st to end	Day	43% 5% 21% 23% 6% 1	2178
April	1st to 10th	Day	46% 6% 16% 24% 8%	2188
	11th to 20th	Day	48% 5% 16% 21% 9% 1	2310
	21st to end	Day	47% 4 17% 22% 9% 1	2340
May	1st to 10th	Day	46% 4 16% 25% 9%	2340
	11th to 20th	Day	47% 4 16% 24% 8% 1	2602
	21st to end	Day	54% 4 15% 20% 7%	2918
June	1st to 10th	Day	44% 5% 18% 23% 10% 1	2700
	11th to 20th	Day	48% 4 13% 21% 13% 2	2700
	21st to end	Day	30% 4 18% 33% 13% 2	2700
July	1st to 10th	Day	26% 4 11% 32% 20% 6%	2626
	11th to 20th	Day	23% 3 12% 26% 27% 9%	2619
	21st to end	Day	19% 3 6% 28% 34% 9%	2639
August	1st to 10th	Day	27% 3 12% 27% 23% 8%	2425
	11th to 20th	Day	26% 4 12% 34% 20% 4	2299
	21st to end	Day	29% 3 10% 30% 23% 6%	2574
September	1st to 10th	Day	33% 2 10% 29% 19% 7%	2192
	11th to 20th	Day	33% 3 12% 30% 18% 4	1980
	21st to end	Day	35% 3 15% 31% 13% 4	1980
October	1st to 10th	Day	38% 4 17% 28% 11% 2	1898
	11th to 20th	Day	37% 3 19% 26% 13% 2	1728
	21st to end	Day	39% 7% 16% 26% 11% 1	1782
November	1st to 10th	Day	39% 6% 17% 23% 12% 2	1598
	11th to 20th	Day	32% 6% 23% 27% 10% 1	1520
	21st to end	Day	36% 6% 24% 21% 10% 3	1392
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	37% 7% 22% 20% 11% 3	2836
	11th to 20th	Night	38% 7% 19% 23% 10% 3	2672
	21st to end	Night	32% 5% 19% 27% 14% 1	2772
February	1st to 10th	Night	41% 6% 17% 22% 11% 3	2439
	11th to 20th	Night	42% 5% 20% 21% 11% 1	2273
	21st to end	Night	43% 5% 14% 23% 13% 2	1799
March	1st to 10th	Night	38% 7% 22% 24% 9% 1	2152
	11th to 20th	Night	33% 6% 23% 25% 13% 1	1980
	21st to end	Night	40% 6% 22% 23% 9% 1	2178
April	1st to 10th	Night	38% 5% 17% 30% 9% 1	1768
	11th to 20th	Night	44% 5% 14% 26% 10% 1	1601
	21st to end	Night	44% 4 15% 28% 8% 1	1620
May	1st to 10th	Night	41% 2 19% 28% 10%	1620
	11th to 20th	Night	36% 5% 18% 30% 11%	1293
	21st to end	Night	46% 4 20% 22% 8%	1358
June	1st to 10th	Night	39% 3 20% 27% 10% 1	1260
	11th to 20th	Night	39% 4 18% 24% 13% 1	1260
	21st to end	Night	26% 3 20% 33% 17% 2	1260
July	1st to 10th	Night	20% 3 11% 37% 23% 7%	1225
	11th to 20th	Night	19% 4 12% 29% 27% 8%	1218
	21st to end	Night	17% 2 8% 29% 31% 14%	1437
August	1st to 10th	Night	22% 2 13% 34% 20% 9%	1487
	11th to 20th	Night	20% 2 14% 40% 19% 5%	1602
	21st to end	Night	26% 2 10% 30% 26% 6%	1782
September	1st to 10th	Night	30% 3 13% 29% 18% 7%	1764
	11th to 20th	Night	32% 3 13% 30% 17% 5%	1980
	21st to end	Night	30% 4 18% 29% 17% 3	1980
October	1st to 10th	Night	34% 3 18% 29% 14% 2	2061
	11th to 20th	Night	32% 4 18% 29% 14% 3	2228
	21st to end	Night	37% 5% 19% 25% 12% 1	2574
November	1st to 10th	Night	40% 4 21% 21% 10% 3	2462
	11th to 20th	Night	30% 6% 23% 27% 13% 1	2660
	21st to end	Night	35% 5% 25% 22% 11% 3	2787
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	19% 19% 29% 19% 11% 2	166
	21st to end	Day	19% 28% 32% 14% 5% 3	176
February	1st to 10th	Day	27% 22% 32% 16% 4	196
	11th to 20th	Day	17% 29% 32% 15% 7%	240
	21st to end	Day	19% 31% 29% 17% 3 1	319
March	1st to 10th	Day	20% 27% 30% 15% 5% 2	420
	11th to 20th	Day	21% 21% 30% 17% 7% 4	420
	21st to end	Day	24% 24% 29% 16% 4 3	462
April	1st to 10th	Day	24% 25% 31% 16% 4	420
	11th to 20th	Day	21% 26% 28% 19% 5% 1	412
	21st to end	Day	26% 21% 25% 20% 6% 2	420
May	1st to 10th	Day	24% 17% 26% 21% 10% 2	423
	11th to 20th	Day	24% 12% 22% 23% 14% 4	606
	21st to end	Day	27% 11% 19% 21% 19% 3	679
June	1st to 10th	Day	21% 19% 23% 24% 10% 3	630
	11th to 20th	Day	25% 21% 24% 20% 8% 2	630
	21st to end	Day	11% 13% 32% 25% 16% 4	630
July	1st to 10th	Day	10% 12% 28% 28% 18% 5%	621
	11th to 20th	Day	10% 13% 33% 29% 14% 1	618
	21st to end	Day	8% 11% 34% 31% 12% 4	540
August	1st to 10th	Day	13% 15% 28% 29% 10% 4	447
	11th to 20th	Day	8% 13% 32% 27% 14% 5%	437
	21st to end	Day	13% 15% 31% 27% 11% 3	495
September	1st to 10th	Day	19% 19% 30% 20% 10% 2	450
	11th to 20th	Day	14% 18% 32% 22% 10% 4	450
	21st to end	Day	24% 20% 29% 18% 6% 3	450
October	1st to 10th	Day	21% 18% 27% 19% 9% 5%	368
	11th to 20th	Day	23% 18% 26% 20% 10% 4	270
	21st to end	Day	25% 23% 29% 17% 3 2	297
November	1st to 10th	Day	26% 26% 30% 15% 3	270
	11th to 20th	Day	26% 29% 31% 11% 1	270
	21st to end	Day	23% 33% 15% 19% 8% 2	210
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% 31% 21% 6% 1	834
	21st to end	Night	14% 29% 31% 19% 5% 2	792
February	1st to 10th	Night	16% 24% 29% 23% 5% 3	720
	11th to 20th	Night	14% 23% 31% 23% 8% 1	704
	21st to end	Night	12% 24% 31% 22% 10%	592
March	1st to 10th	Night	12% 22% 35% 22% 8% 2	720
	11th to 20th	Night	15% 22% 28% 26% 8% 2	720
	21st to end	Night	15% 21% 27% 26% 8% 2	792
April	1st to 10th	Night	14% 18% 30% 28% 9% 1	673
	11th to 20th	Night	16% 22% 32% 22% 8% 1	533
	21st to end	Night	16% 15% 31% 25% 12% 1	540
May	1st to 10th	Night	16% 14% 22% 31% 14% 2	540
	11th to 20th	Night	14% 9% 25% 33% 16% 2	390
	21st to end	Night	24% 8% 20% 28% 18% 3	389
June	1st to 10th	Night	17% 13% 24% 29% 15% 2	360
	11th to 20th	Night	20% 17% 29% 22% 11% 1	360
	21st to end	Night	9% 9% 27% 36% 19%	360
July	1st to 10th	Night	8% 7% 21% 43% 19% 1	350
	11th to 20th	Night	6% 5% 39% 37% 14% 1	348
	21st to end	Night	7% 6% 24% 45% 18% 1	394
August	1st to 10th	Night	8% 4 26% 40% 20% 1	421
	11th to 20th	Night	7% 4 28% 38% 21% 3	534
	21st to end	Night	11% 9% 29% 37% 13% 2	594
September	1st to 10th	Night	14% 8% 25% 34% 15% 3	630
	11th to 20th	Night	12% 9% 25% 35% 16% 4	720
	21st to end	Night	15% 14% 26% 30% 12% 2	720
October	1st to 10th	Night	17% 14% 24% 30% 12% 2	720
	11th to 20th	Night	16% 18% 25% 28% 11% 2	720
	21st to end	Night	17% 25% 27% 24% 6% 1	792
November	1st to 10th	Night	21% 27% 28% 21% 3 1	797
	11th to 20th	Night	20% 33% 28% 15% 3 1	950
	21st to end	Night	16% 30% 30% 18% 5% 1	950
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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