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Camp Delany
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Camp Delany clear sky chart from 2005-11-06 to 2024-01-16.

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	8% 7% 3 6% 5% 3 4 5% 5% 7% 46%	74809
	Night	9% 9% 3 6% 6% 3 5% 5% 5% 7% 42%	75008
Transparency	Day	37% 6% 11% 22% 18% 6%	74512
	Night	41% 6% 11% 21% 15% 5%	74823
Seeing	Day	10% 8% 21% 29% 22% 9%	13197
	Night	13% 5% 19% 37% 22% 3	22347

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	18% 18% 7% 11% 8% 4 5% 4 3 4 18%	1519
	11th to 20th	Day	16% 15% 6% 12% 10% 5% 5% 5% 4 5% 18%	1480
	21st to end	Day	13% 18% 6% 11% 7% 4 5% 4 6% 5% 21%	1584
February	1st to 10th	Day	12% 13% 4 9% 8% 4 6% 5% 7% 6% 26%	1533
	11th to 20th	Day	9% 12% 4 8% 6% 3 4 5% 7% 8% 34%	1604
	21st to end	Day	7% 12% 5% 8% 7% 4 6% 6% 4 7% 35%	1480
March	1st to 10th	Day	10% 9% 3 7% 5% 3 5% 6% 7% 8% 37%	1800
	11th to 20th	Day	9% 10% 4 7% 5% 3 5% 6% 7% 7% 37%	1876
	21st to end	Day	8% 9% 4 7% 6% 4 6% 6% 7% 8% 35%	2353
April	1st to 10th	Day	9% 7% 3 6% 7% 4 5% 6% 6% 9% 37%	2160
	11th to 20th	Day	6% 7% 2 6% 5% 3 6% 6% 7% 9% 42%	2132
	21st to end	Day	5% 6% 3 6% 7% 3 5% 5% 6% 8% 46%	2371
May	1st to 10th	Day	4 4 2 4 5% 3 5% 6% 7% 8% 52%	2520
	11th to 20th	Day	7% 5% 3 6% 6% 4 5% 6% 8% 10% 40%	2477
	21st to end	Day	7% 6% 3 6% 6% 3 6% 6% 6% 8% 42%	2723
June	1st to 10th	Day	8% 5% 3 6% 6% 3 5% 6% 6% 8% 44%	2520
	11th to 20th	Day	7% 4 3 5% 4 3 5% 5% 7% 8% 48%	2520
	21st to end	Day	4 3 2 4 4 2 3 4 5% 7% 62%	2520
July	1st to 10th	Day	2 2 1 2 3 2 3 4 5% 6% 70%	2520
	11th to 20th	Day	2 2 1 3 4 2 3 3 4 5% 72%	2520
	21st to end	Day	1 1 1 2 2 1 2 2 2 5% 81%	2741
August	1st to 10th	Day	3 3 1 2 2 2 3 3 4 5% 72%	2507
	11th to 20th	Day	2 3 1 2 2 2 3 4 4 6% 72%	2390
	21st to end	Day	2 3 1 3 4 2 4 4 4 7% 67%	2376
September	1st to 10th	Day	3 3 1 3 3 2 3 4 4 7% 70%	2160
	11th to 20th	Day	4 3 2 5% 5% 3 5% 5% 6% 7% 56%	2129
	21st to end	Day	7% 5% 2 4 4 3 4 5% 5% 6% 55%	1980
October	1st to 10th	Day	7% 5% 3 5% 5% 4 4 4 4 7% 53%	1807
	11th to 20th	Day	8% 5% 2 5% 5% 4 4 6% 6% 8% 49%	1772
	21st to end	Day	14% 6% 2 5% 6% 3 4 4 6% 7% 43%	1782
November	1st to 10th	Day	16% 9% 3 7% 7% 3 5% 5% 6% 7% 32%	1674
	11th to 20th	Day	12% 14% 5% 8% 7% 3 4 5% 5% 5% 32%	1520
	21st to end	Day	13% 13% 6% 9% 8% 4 6% 5% 5% 7% 26%	1520
December	1st to 10th	Day	12% 14% 6% 9% 8% 3 5% 5% 5% 7% 24%	1520
	11th to 20th	Day	18% 16% 10% 13% 8% 4 4 4 4 5% 13%	1925
	21st to end	Day	12% 21% 7% 11% 8% 4 5% 5% 4 6% 16%	2794
January	1st to 10th	Night	19% 16% 5% 10% 8% 3 5% 5% 5% 5% 19%	2646
	11th to 20th	Night	15% 14% 5% 12% 8% 3 4 5% 5% 8% 21%	2590
	21st to end	Night	12% 15% 6% 11% 7% 4 5% 6% 5% 7% 22%	2772
February	1st to 10th	Night	10% 12% 4 7% 7% 4 5% 5% 6% 8% 32%	2426
	11th to 20th	Night	10% 9% 4 8% 5% 4 5% 6% 6% 7% 37%	2242
	21st to end	Night	8% 11% 5% 7% 6% 4 6% 5% 6% 9% 34%	1776
March	1st to 10th	Night	11% 10% 3 7% 6% 4 4 6% 7% 8% 35%	2160
	11th to 20th	Night	8% 7% 3 6% 6% 3 6% 6% 7% 8% 39%	2081
	21st to end	Night	8% 9% 3 8% 6% 5% 6% 7% 6% 9% 33%	2002
April	1st to 10th	Night	9% 8% 4 7% 6% 4 4 5% 5% 8% 40%	1800
	11th to 20th	Night	7% 8% 2 6% 5% 3 5% 5% 6% 7% 46%	1779
	21st to end	Night	6% 5% 2 5% 7% 4 5% 7% 6% 9% 43%	1586
May	1st to 10th	Night	5% 4 2 4 4 4 4 6% 7% 9% 51%	1440
	11th to 20th	Night	8% 5% 3 5% 6% 3 5% 5% 6% 7% 47%	1416
	21st to end	Night	7% 3 2 5% 6% 3 5% 6% 7% 8% 47%	1552
June	1st to 10th	Night	7% 5% 3 4 6% 4 5% 5% 6% 8% 47%	1440
	11th to 20th	Night	5% 3 2 4 5% 3 5% 5% 7% 8% 53%	1440
	21st to end	Night	4 3 1 4 4 3 5% 4 4 6% 62%	1440
July	1st to 10th	Night	2 2 1 3 2 2 3 4 4 8% 70%	1440
	11th to 20th	Night	2 2 1 2 2 1 3 3 4 6% 75%	1440
	21st to end	Night	1 1 1 1 2 3 4 4 83%	1576
August	1st to 10th	Night	1 3 1 2 3 1 2 3 3 6% 77%	1432
	11th to 20th	Night	1 2 1 2 3 1 3 3 4 6% 73%	1505
	21st to end	Night	2 2 1 2 3 2 3 4 6% 7% 68%	1980
September	1st to 10th	Night	2 2 2 2 3 2 3 3 5% 9% 68%	1800
	11th to 20th	Night	4 4 2 4 4 2 3 4 6% 7% 59%	1831
	21st to end	Night	6% 3 2 4 5% 3 4 4 5% 8% 57%	1980
October	1st to 10th	Night	9% 5% 2 5% 5% 3 4 4 4 7% 52%	2150
	11th to 20th	Night	8% 5% 2 4 5% 3 5% 5% 5% 7% 50%	2186
	21st to end	Night	12% 7% 2 5% 6% 3 4 5% 6% 7% 43%	2574
November	1st to 10th	Night	14% 9% 3 5% 6% 3 5% 4 6% 8% 36%	2405
	11th to 20th	Night	11% 11% 4 7% 7% 4 5% 6% 5% 6% 35%	2659
	21st to end	Night	13% 12% 5% 9% 6% 4 6% 5% 5% 6% 29%	2660
December	1st to 10th	Night	13% 12% 6% 9% 7% 4 5% 5% 6% 7% 27%	2660
	11th to 20th	Night	16% 14% 9% 14% 8% 4 5% 5% 4 5% 14%	3280
	21st to end	Night	15% 19% 5% 9% 7% 4 5% 5% 5% 6% 20%	4862

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	71% 6% 7% 10% 4 1	1519
	11th to 20th	Day	70% 5% 11% 11% 2 1	1480
	21st to end	Day	64% 6% 13% 12% 5% 1	1584
February	1st to 10th	Day	54% 9% 16% 14% 5% 1	1533
	11th to 20th	Day	46% 7% 18% 18% 10% 1	1613
	21st to end	Day	48% 8% 14% 19% 10% 1	1480
March	1st to 10th	Day	42% 7% 17% 22% 11% 1	1800
	11th to 20th	Day	43% 7% 12% 27% 11%	1876
	21st to end	Day	45% 7% 17% 21% 9% 1	2353
April	1st to 10th	Day	42% 6% 14% 23% 12% 3	2160
	11th to 20th	Day	36% 7% 14% 22% 16% 4	2132
	21st to end	Day	34% 6% 12% 26% 18% 4	2371
May	1st to 10th	Day	25% 6% 11% 33% 20% 4	2520
	11th to 20th	Day	36% 6% 13% 27% 16% 3	2480
	21st to end	Day	37% 7% 12% 25% 16% 2	2724
June	1st to 10th	Day	37% 6% 11% 23% 20% 5%	2520
	11th to 20th	Day	30% 7% 11% 28% 20% 5%	2520
	21st to end	Day	22% 4 7% 29% 28% 9%	2520
July	1st to 10th	Day	15% 4 7% 24% 33% 18%	2451
	11th to 20th	Day	16% 3 5% 19% 33% 24%	2445
	21st to end	Day	9% 2 3 18% 43% 26%	2589
August	1st to 10th	Day	16% 4 6% 22% 33% 19%	2490
	11th to 20th	Day	14% 3 7% 26% 36% 13%	2390
	21st to end	Day	18% 4 7% 30% 34% 7%	2376
September	1st to 10th	Day	15% 4 10% 27% 32% 12%	2160
	11th to 20th	Day	26% 6% 11% 23% 26% 8%	2129
	21st to end	Day	28% 6% 16% 28% 16% 6%	1980
October	1st to 10th	Day	32% 4 12% 32% 17% 2	1807
	11th to 20th	Day	32% 6% 18% 30% 13% 1	1772
	21st to end	Day	41% 6% 15% 25% 13% 1	1782
November	1st to 10th	Day	50% 8% 13% 18% 9% 2	1674
	11th to 20th	Day	53% 6% 15% 18% 7% 1	1520
	21st to end	Day	58% 8% 14% 12% 6% 2	1520
December	1st to 10th	Day	59% 6% 14% 14% 6%	1520
	11th to 20th	Day	74% 7% 7% 7% 4 1	1928
	21st to end	Day	69% 6% 11% 10% 4	2794
January	1st to 10th	Night	66% 6% 12% 11% 4 1	2646
	11th to 20th	Night	63% 7% 14% 14% 3	2590
	21st to end	Night	60% 7% 15% 13% 3 1	2772
February	1st to 10th	Night	49% 9% 18% 16% 7% 1	2426
	11th to 20th	Night	43% 8% 19% 19% 10% 1	2244
	21st to end	Night	46% 7% 14% 21% 11% 1	1776
March	1st to 10th	Night	43% 8% 14% 24% 11% 1	2160
	11th to 20th	Night	40% 7% 12% 29% 12% 1	2082
	21st to end	Night	45% 8% 13% 25% 8% 1	2002
April	1st to 10th	Night	42% 5% 12% 27% 11% 2	1800
	11th to 20th	Night	36% 6% 11% 25% 18% 5%	1779
	21st to end	Night	35% 6% 11% 25% 18% 5%	1586
May	1st to 10th	Night	28% 6% 8% 30% 24% 4	1440
	11th to 20th	Night	33% 6% 10% 28% 19% 4	1416
	21st to end	Night	31% 6% 10% 33% 15% 3	1552
June	1st to 10th	Night	34% 6% 10% 23% 22% 5%	1440
	11th to 20th	Night	27% 6% 10% 30% 22% 5%	1440
	21st to end	Night	23% 4 8% 27% 29% 9%	1440
July	1st to 10th	Night	14% 4 6% 22% 33% 21%	1400
	11th to 20th	Night	11% 3 6% 20% 34% 26%	1392
	21st to end	Night	6% 2 3 15% 41% 33%	1488
August	1st to 10th	Night	12% 3 5% 16% 37% 26%	1424
	11th to 20th	Night	13% 4 6% 23% 39% 16%	1505
	21st to end	Night	15% 4 8% 24% 36% 14%	1980
September	1st to 10th	Night	15% 3 8% 27% 32% 16%	1800
	11th to 20th	Night	24% 5% 9% 23% 29% 11%	1831
	21st to end	Night	25% 6% 11% 32% 19% 8%	1980
October	1st to 10th	Night	33% 4 9% 30% 23% 1	2150
	11th to 20th	Night	32% 6% 13% 29% 17% 3	2186
	21st to end	Night	39% 6% 11% 29% 14% 2	2574
November	1st to 10th	Night	44% 7% 17% 19% 10% 2	2405
	11th to 20th	Night	49% 9% 14% 17% 9% 2	2659
	21st to end	Night	55% 7% 13% 16% 8% 1	2660
December	1st to 10th	Night	56% 8% 14% 18% 5%	2660
	11th to 20th	Night	71% 7% 10% 8% 3	3276
	21st to end	Night	63% 8% 11% 10% 7% 1	4862

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	24% 9% 23% 26% 16% 2	180
	11th to 20th	Day	25% 7% 16% 29% 17% 6%	170
	21st to end	Day	24% 3 15% 40% 15% 3	176
February	1st to 10th	Day	15% 6% 28% 36% 15% 2	253
	11th to 20th	Day	17% 7% 23% 33% 16% 4	349
	21st to end	Day	10% 8% 25% 32% 21% 3	346
March	1st to 10th	Day	15% 7% 26% 30% 16% 6%	420
	11th to 20th	Day	15% 11% 19% 30% 18% 7%	420
	21st to end	Day	15% 11% 27% 27% 15% 4	462
April	1st to 10th	Day	16% 12% 21% 32% 14% 5%	420
	11th to 20th	Day	10% 20% 28% 23% 13% 6%	412
	21st to end	Day	7% 14% 27% 25% 21% 7%	420
May	1st to 10th	Day	7% 11% 24% 35% 17% 6%	423
	11th to 20th	Day	14% 8% 17% 24% 23% 13%	448
	21st to end	Day	9% 7% 18% 25% 27% 14%	485
June	1st to 10th	Day	7% 10% 24% 28% 20% 11%	450
	11th to 20th	Day	9% 9% 29% 29% 16% 7%	450
	21st to end	Day	3 6% 20% 28% 30% 13%	450
July	1st to 10th	Day	2 6% 16% 37% 29% 9%	446
	11th to 20th	Day	2 4 22% 31% 30% 12%	444
	21st to end	Day	1 4 15% 29% 35% 17%	487
August	1st to 10th	Day	3 5% 14% 29% 29% 20%	447
	11th to 20th	Day	3 3 15% 25% 32% 21%	437
	21st to end	Day	4 5% 17% 32% 27% 15%	495
September	1st to 10th	Day	5% 5% 17% 30% 30% 12%	450
	11th to 20th	Day	6% 7% 16% 28% 32% 11%	450
	21st to end	Day	10% 9% 18% 31% 25% 7%	450
October	1st to 10th	Day	10% 6% 26% 28% 22% 8%	450
	11th to 20th	Day	11% 8% 20% 26% 27% 8%	422
	21st to end	Day	18% 10% 25% 30% 15% 4	297
November	1st to 10th	Day	19% 10% 18% 35% 17% 1	270
	11th to 20th	Day	20% 12% 24% 22% 17% 5%	180
	21st to end	Day	17% 6% 21% 31% 24% 1	180
December	1st to 10th	Day	20% 7% 19% 28% 19% 6%	180
	11th to 20th	Day	19% 8% 26% 29% 16% 2	180
	21st to end	Day	20% 7% 18% 37% 16% 4	198
January	1st to 10th	Night	27% 5% 21% 31% 14% 2	760
	11th to 20th	Night	21% 5% 20% 32% 18% 4	740
	21st to end	Night	20% 5% 15% 41% 17% 3	792
February	1st to 10th	Night	18% 3 28% 34% 15% 2	720
	11th to 20th	Night	14% 5% 24% 35% 19% 3	704
	21st to end	Night	14% 7% 22% 38% 16% 4	592
March	1st to 10th	Night	16% 6% 19% 38% 18% 3	720
	11th to 20th	Night	11% 6% 23% 38% 22% 2	720
	21st to end	Night	11% 7% 24% 39% 16% 3	792
April	1st to 10th	Night	12% 8% 18% 36% 23% 3	720
	11th to 20th	Night	12% 8% 26% 33% 18% 4	711
	21st to end	Night	8% 10% 27% 33% 19% 4	506
May	1st to 10th	Night	7% 7% 26% 36% 21% 3	360
	11th to 20th	Night	10% 5% 17% 34% 28% 6%	354
	21st to end	Night	8% 3 17% 38% 29% 5%	389
June	1st to 10th	Night	7% 7% 22% 37% 24% 3	360
	11th to 20th	Night	7% 9% 23% 38% 21% 2	360
	21st to end	Night	6% 4 22% 36% 29% 4	360
July	1st to 10th	Night	3 3 15% 42% 34% 3	350
	11th to 20th	Night	2 4 20% 40% 32% 2	348
	21st to end	Night	1 3 14% 40% 40% 2	394
August	1st to 10th	Night	3 3 12% 34% 40% 8%	358
	11th to 20th	Night	3 1 11% 36% 38% 11%	437
	21st to end	Night	3 4 15% 38% 35% 5%	792
September	1st to 10th	Night	2 4 16% 40% 31% 6%	720
	11th to 20th	Night	6% 5% 12% 32% 38% 8%	720
	21st to end	Night	8% 4 16% 36% 31% 4	720
October	1st to 10th	Night	12% 4 15% 38% 27% 3	720
	11th to 20th	Night	11% 6% 17% 37% 25% 5%	720
	21st to end	Night	15% 6% 19% 39% 17% 4	792
November	1st to 10th	Night	19% 5% 16% 46% 12% 1	740
	11th to 20th	Night	18% 8% 24% 33% 14% 3	760
	21st to end	Night	19% 5% 16% 36% 21% 2	760
December	1st to 10th	Night	18% 5% 19% 37% 18% 3	760
	11th to 20th	Night	23% 5% 18% 39% 14% 1	760
	21st to end	Night	24% 6% 20% 39% 11% 1	836

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