Duncan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Duncan clear sky chart from 2005-11-06 to 2024-11-25.

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% 10% 3 8% 5% 5% 5% 4 5% 6% 34%	105659
	Night	17% 10% 3 7% 5% 5% 5% 4 5% 6% 35%	102352
Transparency	Day	48% 9% 15% 19% 8% 1	105407
	Night	49% 8% 14% 19% 9% 1	102250
Seeing	Day	18% 12% 24% 26% 16% 4	15526
	Night	21% 8% 18% 28% 21% 4	23679

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	26% 20% 4 9% 6% 4 4 3 4 4 15%	2219
	11th to 20th	Day	22% 14% 4 7% 5% 4 4 4 6% 6% 24%	2199
	21st to end	Day	35% 19% 4 9% 5% 5% 3 2 3 4 10%	2838
February	1st to 10th	Day	21% 16% 5% 10% 7% 6% 5% 3 4 6% 17%	1710
	11th to 20th	Day	19% 17% 4 9% 5% 4 5% 3 5% 6% 22%	1665
	21st to end	Day	16% 16% 4 10% 8% 6% 6% 4 6% 6% 17%	1413
March	1st to 10th	Day	13% 16% 5% 12% 7% 6% 6% 5% 6% 6% 18%	3303
	11th to 20th	Day	14% 10% 3 8% 6% 5% 5% 3 5% 7% 33%	3490
	21st to end	Day	23% 14% 4 9% 6% 5% 5% 4 4 6% 20%	3877
April	1st to 10th	Day	20% 13% 4 10% 7% 5% 5% 5% 6% 6% 18%	2280
	11th to 20th	Day	17% 14% 3 8% 7% 6% 5% 4 6% 6% 23%	2372
	21st to end	Day	20% 12% 4 9% 6% 4 5% 4 6% 6% 24%	2482
May	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 5% 6% 36%	4420
	11th to 20th	Day	10% 7% 3 7% 5% 5% 5% 5% 7% 10% 36%	4377
	21st to end	Day	21% 12% 4 9% 6% 5% 5% 4 6% 6% 22%	4936
June	1st to 10th	Day	19% 9% 3 8% 6% 5% 6% 5% 6% 7% 27%	2850
	11th to 20th	Day	15% 9% 3 10% 7% 7% 6% 4 6% 7% 25%	2850
	21st to end	Day	11% 7% 3 7% 7% 5% 5% 4 6% 7% 37%	2850
July	1st to 10th	Day	6% 3 1 4 3 3 3 3 4 5% 64%	4740
	11th to 20th	Day	5% 2 1 3 3 2 3 2 4 5% 70%	4740
	21st to end	Day	7% 4 1 5% 4 3 4 3 6% 9% 54%	4902
August	1st to 10th	Day	5% 3 1 4 2 2 3 2 4 6% 68%	4265
	11th to 20th	Day	10% 7% 3 7% 5% 5% 5% 5% 6% 8% 38%	4026
	21st to end	Day	11% 5% 3 6% 5% 6% 6% 3 6% 7% 43%	4445
September	1st to 10th	Day	10% 4 2 6% 4 4 4 3 6% 8% 49%	2280
	11th to 20th	Day	14% 7% 3 6% 5% 4 5% 3 5% 6% 41%	2238
	21st to end	Day	17% 6% 3 7% 5% 4 5% 4 5% 7% 38%	2024
October	1st to 10th	Day	15% 8% 3 8% 6% 6% 6% 5% 7% 7% 31%	3180
	11th to 20th	Day	23% 11% 3 9% 6% 4 5% 3 4 6% 27%	3161
	21st to end	Day	18% 11% 4 10% 6% 6% 6% 4 4 7% 23%	3198
November	1st to 10th	Day	25% 12% 5% 11% 6% 7% 5% 4 4 5% 16%	1568
	11th to 20th	Day	22% 13% 4 10% 5% 6% 4 4 5% 5% 23%	1600
	21st to end	Day	24% 15% 4 9% 6% 5% 4 4 5% 5% 22%	1552
December	1st to 10th	Day	18% 16% 5% 10% 5% 6% 4 3 4 5% 24%	1482
	11th to 20th	Day	26% 15% 4 9% 5% 5% 6% 4 5% 5% 16%	1685
	21st to end	Day	26% 18% 5% 10% 6% 5% 4 3 5% 4 14%	2442
January	1st to 10th	Night	23% 16% 5% 10% 6% 6% 5% 4 5% 5% 15%	4726
	11th to 20th	Night	23% 13% 4 7% 5% 4 4 3 5% 6% 27%	4699
	21st to end	Night	32% 15% 4 9% 5% 5% 5% 3 4 5% 13%	4803
February	1st to 10th	Night	21% 14% 3 9% 6% 5% 6% 4 6% 5% 22%	2470
	11th to 20th	Night	18% 15% 4 6% 4 4 3 3 5% 6% 30%	2402
	21st to end	Night	17% 13% 4 8% 5% 5% 5% 2 5% 6% 28%	2041
March	1st to 10th	Night	15% 13% 4 9% 6% 6% 6% 5% 6% 7% 25%	3566
	11th to 20th	Night	10% 7% 2 6% 5% 5% 5% 6% 8% 9% 39%	3489
	21st to end	Night	19% 12% 4 9% 6% 5% 5% 3 5% 6% 26%	3775
April	1st to 10th	Night	16% 10% 3 8% 7% 6% 5% 4 6% 7% 28%	1900
	11th to 20th	Night	14% 9% 4 6% 5% 4 5% 3 6% 8% 35%	1755
	21st to end	Night	16% 8% 3 8% 5% 5% 5% 5% 6% 8% 33%	1697
May	1st to 10th	Night	11% 7% 2 5% 4 4 4 3 4 5% 50%	2540
	11th to 20th	Night	8% 4 1 5% 3 4 5% 4 6% 8% 53%	2516
	21st to end	Night	15% 8% 3 8% 6% 5% 5% 4 6% 6% 34%	2635
June	1st to 10th	Night	12% 8% 3 7% 5% 4 5% 4 5% 7% 40%	1330
	11th to 20th	Night	9% 5% 3 5% 4 5% 4 5% 7% 10% 43%	1330
	21st to end	Night	6% 3 2 5% 4 4 5% 5% 7% 9% 50%	1330
July	1st to 10th	Night	4 2 1 3 3 3 3 3 3 5% 71%	2220
	11th to 20th	Night	2 2 1 1 2 2 2 1 3 5% 79%	2220
	21st to end	Night	6% 3 1 4 3 3 3 3 6% 6% 65%	2635
August	1st to 10th	Night	3 2 1 2 2 2 2 2 3 5% 76%	2654
	11th to 20th	Night	9% 5% 2 7% 4 4 4 3 4 7% 49%	2812
	21st to end	Night	10% 3 2 4 3 3 4 3 5% 8% 55%	3210
September	1st to 10th	Night	5% 2 1 4 3 3 4 3 4 8% 62%	1900
	11th to 20th	Night	13% 5% 2 5% 5% 4 5% 4 5% 6% 46%	1938
	21st to end	Night	13% 5% 2 7% 4 5% 4 4 5% 7% 43%	2155
October	1st to 10th	Night	11% 7% 2 7% 5% 5% 5% 3 5% 6% 44%	3800
	11th to 20th	Night	19% 7% 4 7% 5% 6% 6% 4 5% 7% 31%	3777
	21st to end	Night	21% 10% 4 9% 5% 4 4 3 5% 4 31%	4348
November	1st to 10th	Night	25% 12% 2 8% 6% 5% 6% 4 5% 5% 22%	2730
	11th to 20th	Night	23% 12% 3 7% 5% 5% 5% 3 5% 5% 26%	2800
	21st to end	Night	22% 11% 4 9% 6% 5% 5% 4 4 6% 24%	2722
December	1st to 10th	Night	19% 16% 4 8% 6% 5% 5% 4 5% 5% 24%	2693
	11th to 20th	Night	25% 15% 5% 10% 5% 5% 5% 4 4 5% 17%	3520
	21st to end	Night	25% 15% 4 10% 6% 6% 5% 3 4 4 17%	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	72% 8% 5% 11% 4	2219
	11th to 20th	Day	60% 6% 17% 11% 5% 1	2220
	21st to end	Day	80% 6% 6% 7% 1	2838
February	1st to 10th	Day	68% 8% 9% 10% 4	1710
	11th to 20th	Day	64% 7% 10% 14% 5%	1674
	21st to end	Day	63% 10% 13% 8% 4 1	1413
March	1st to 10th	Day	60% 11% 12% 11% 6%	3303
	11th to 20th	Day	50% 7% 13% 26% 4 1	3490
	21st to end	Day	62% 9% 14% 12% 3	3877
April	1st to 10th	Day	62% 12% 12% 12% 3	2280
	11th to 20th	Day	58% 9% 12% 11% 8% 2	2372
	21st to end	Day	57% 10% 12% 14% 6% 1	2482
May	1st to 10th	Day	46% 7% 17% 21% 9% 1	4420
	11th to 20th	Day	39% 11% 26% 18% 6%	4380
	21st to end	Day	56% 12% 16% 13% 3	4937
June	1st to 10th	Day	51% 11% 16% 14% 5% 2	2850
	11th to 20th	Day	52% 12% 19% 14% 4	2850
	21st to end	Day	41% 11% 20% 19% 8% 2	2850
July	1st to 10th	Day	22% 6% 10% 30% 22% 11%	4666
	11th to 20th	Day	16% 6% 12% 40% 25% 1	4659
	21st to end	Day	24% 8% 24% 26% 15% 2	4747
August	1st to 10th	Day	18% 6% 13% 44% 18% 1	4248
	11th to 20th	Day	38% 10% 25% 17% 8% 1	4065
	21st to end	Day	38% 9% 20% 25% 8%	4444
September	1st to 10th	Day	30% 11% 18% 26% 12% 3	2280
	11th to 20th	Day	42% 8% 15% 20% 15% 1	2238
	21st to end	Day	45% 10% 15% 19% 10% 1	2024
October	1st to 10th	Day	49% 9% 16% 20% 6%	3180
	11th to 20th	Day	59% 7% 12% 16% 6%	3161
	21st to end	Day	59% 8% 13% 14% 6%	3198
November	1st to 10th	Day	70% 8% 9% 8% 4 1	1568
	11th to 20th	Day	64% 8% 9% 13% 6% 1	1600
	21st to end	Day	65% 8% 9% 13% 5%	1552
December	1st to 10th	Day	63% 9% 9% 12% 5% 1	1482
	11th to 20th	Day	68% 10% 12% 7% 2	1688
	21st to end	Day	72% 7% 10% 7% 4	2442
January	1st to 10th	Night	70% 9% 7% 9% 4	4726
	11th to 20th	Night	58% 7% 14% 15% 5% 1	4740
	21st to end	Night	73% 8% 6% 10% 3	4803
February	1st to 10th	Night	63% 8% 12% 11% 5% 1	2470
	11th to 20th	Night	55% 9% 12% 15% 8%	2404
	21st to end	Night	58% 7% 11% 16% 7% 2	2041
March	1st to 10th	Night	54% 10% 12% 18% 6%	3566
	11th to 20th	Night	39% 11% 16% 28% 6% 1	3490
	21st to end	Night	58% 10% 13% 17% 2	3775
April	1st to 10th	Night	53% 8% 17% 16% 5%	1900
	11th to 20th	Night	47% 9% 13% 20% 10% 2	1755
	21st to end	Night	48% 9% 16% 17% 9% 1	1697
May	1st to 10th	Night	35% 7% 14% 27% 17%	2540
	11th to 20th	Night	27% 8% 26% 30% 8%	2516
	21st to end	Night	47% 9% 21% 19% 4	2635
June	1st to 10th	Night	43% 7% 18% 22% 7% 3	1330
	11th to 20th	Night	34% 10% 26% 23% 7%	1330
	21st to end	Night	28% 10% 26% 22% 12% 3	1330
July	1st to 10th	Night	18% 5% 10% 33% 19% 14%	2185
	11th to 20th	Night	11% 3 13% 37% 34% 1	2178
	21st to end	Night	21% 4 17% 32% 24% 2	2551
August	1st to 10th	Night	14% 4 13% 41% 27% 2	2646
	11th to 20th	Night	35% 8% 26% 18% 9% 4	2839
	21st to end	Night	27% 7% 21% 32% 11% 1	3210
September	1st to 10th	Night	21% 9% 19% 29% 17% 5%	1900
	11th to 20th	Night	36% 8% 15% 19% 16% 5%	1938
	21st to end	Night	38% 8% 17% 22% 12% 3	2155
October	1st to 10th	Night	41% 7% 20% 23% 9% 1	3800
	11th to 20th	Night	53% 6% 14% 21% 6%	3777
	21st to end	Night	54% 7% 13% 16% 9%	4348
November	1st to 10th	Night	64% 8% 10% 14% 4 1	2730
	11th to 20th	Night	59% 8% 11% 13% 8% 1	2800
	21st to end	Night	61% 8% 11% 13% 8%	2722
December	1st to 10th	Night	62% 8% 12% 13% 5% 1	2693
	11th to 20th	Night	68% 10% 12% 7% 3	3516
	21st to end	Night	68% 7% 10% 10% 5%	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	36% 21% 16% 14% 8% 6%	180
	11th to 20th	Day	39% 15% 13% 15% 14% 3	180
	21st to end	Day	32% 16% 23% 18% 10% 2	269
February	1st to 10th	Day	28% 21% 24% 20% 6% 1	370
	11th to 20th	Day	28% 19% 30% 15% 6% 1	365
	21st to end	Day	30% 21% 25% 17% 7% 1	307
March	1st to 10th	Day	25% 18% 25% 22% 8% 2	458
	11th to 20th	Day	24% 18% 22% 23% 10% 2	460
	21st to end	Day	26% 16% 25% 23% 7% 1	506
April	1st to 10th	Day	26% 15% 29% 19% 9% 1	460
	11th to 20th	Day	21% 16% 31% 20% 10% 2	452
	21st to end	Day	22% 16% 30% 20% 11% 2	460
May	1st to 10th	Day	13% 11% 30% 30% 14% 2	463
	11th to 20th	Day	16% 9% 24% 27% 20% 4	488
	21st to end	Day	14% 12% 25% 31% 14% 4	600
June	1st to 10th	Day	17% 10% 29% 27% 14% 3	680
	11th to 20th	Day	13% 13% 32% 25% 15% 3	680
	21st to end	Day	9% 9% 25% 32% 21% 3	680
July	1st to 10th	Day	10% 6% 20% 36% 24% 4	671
	11th to 20th	Day	6% 4 23% 38% 24% 6%	668
	21st to end	Day	5% 3 21% 36% 28% 7%	604
August	1st to 10th	Day	8% 3 17% 31% 31% 9%	487
	11th to 20th	Day	5% 5% 19% 35% 28% 9%	477
	21st to end	Day	10% 7% 24% 35% 18% 7%	539
September	1st to 10th	Day	10% 6% 26% 35% 18% 5%	490
	11th to 20th	Day	20% 8% 21% 28% 19% 4	490
	21st to end	Day	18% 13% 25% 25% 16% 3	490
October	1st to 10th	Day	21% 8% 27% 23% 18% 3	490
	11th to 20th	Day	27% 12% 20% 23% 14% 4	490
	21st to end	Day	24% 19% 27% 17% 9% 4	426
November	1st to 10th	Day	31% 14% 25% 23% 7% 1	200
	11th to 20th	Day	28% 14% 20% 20% 12% 7%	200
	21st to end	Day	34% 15% 21% 13% 9% 9%	188
December	1st to 10th	Day	33% 12% 19% 13% 15% 8%	180
	11th to 20th	Day	32% 12% 19% 22% 13% 2	180
	21st to end	Day	33% 14% 25% 19% 8% 2	198
January	1st to 10th	Night	33% 15% 21% 18% 11% 3	850
	11th to 20th	Night	31% 12% 16% 24% 16% 2	850
	21st to end	Night	31% 9% 17% 27% 14% 3	854
February	1st to 10th	Night	29% 13% 20% 21% 13% 3	760
	11th to 20th	Night	25% 12% 20% 29% 14% 1	744
	21st to end	Night	25% 13% 20% 26% 12% 3	628
March	1st to 10th	Night	20% 13% 24% 25% 16% 2	760
	11th to 20th	Night	22% 12% 23% 26% 16% 1	760
	21st to end	Night	23% 10% 21% 28% 15% 3	836
April	1st to 10th	Night	19% 11% 22% 28% 16% 4	760
	11th to 20th	Night	17% 9% 25% 30% 18% 2	627
	21st to end	Night	18% 5% 22% 37% 15% 2	557
May	1st to 10th	Night	12% 7% 16% 39% 23% 3	380
	11th to 20th	Night	13% 5% 11% 36% 28% 6%	374
	21st to end	Night	12% 4 19% 36% 26% 3	411
June	1st to 10th	Night	16% 5% 19% 32% 25% 2	380
	11th to 20th	Night	9% 6% 22% 37% 22% 3	380
	21st to end	Night	6% 5% 18% 36% 29% 6%	380
July	1st to 10th	Night	6% 2 13% 30% 45% 5%	370
	11th to 20th	Night	3 2 13% 32% 42% 7%	368
	21st to end	Night	4 2 9% 28% 47% 10%	416
August	1st to 10th	Night	7% 1 6% 25% 45% 15%	451
	11th to 20th	Night	4 1 8% 25% 51% 11%	564
	21st to end	Night	8% 3 14% 32% 38% 6%	665
September	1st to 10th	Night	6% 2 12% 35% 36% 8%	760
	11th to 20th	Night	14% 4 13% 24% 31% 14%	760
	21st to end	Night	16% 4 18% 29% 28% 6%	760
October	1st to 10th	Night	17% 4 14% 33% 26% 6%	760
	11th to 20th	Night	21% 9% 15% 28% 20% 7%	760
	21st to end	Night	27% 9% 21% 25% 15% 4	836
November	1st to 10th	Night	32% 8% 22% 27% 10% 1	780
	11th to 20th	Night	29% 12% 21% 24% 11% 2	800
	21st to end	Night	26% 10% 24% 23% 14% 4	778
December	1st to 10th	Night	26% 10% 20% 26% 17% 2	775
	11th to 20th	Night	32% 10% 22% 25% 9% 1	850
	21st to end	Night	34% 13% 22% 23% 7% 1	935

Page generated at 2024-11-22 05:02:27. Version ac07

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