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 2025-10-04.

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 7% 4 4 4 4 5% 7% 49%	130569
	Night	8% 9% 3 7% 4 4 4 4 5% 7% 45%	127529
Transparency	Day	35% 4 10% 23% 20% 8%	130296
	Night	39% 5% 11% 23% 17% 6%	127379
Seeing	Day	10% 8% 20% 29% 23% 9%	15441
	Night	13% 5% 19% 37% 22% 3	24394

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	15% 19% 7% 17% 6% 5% 3 3 3 4 18%	3639
	11th to 20th	Day	12% 10% 3 8% 6% 5% 4 3 5% 5% 38%	3616
	21st to end	Day	17% 18% 7% 9% 3 3 3 2 4 4 30%	4004
February	1st to 10th	Day	12% 14% 4 11% 7% 5% 5% 4 7% 5% 26%	1704
	11th to 20th	Day	9% 13% 4 10% 5% 4 4 4 7% 8% 32%	1787
	21st to end	Day	7% 13% 4 10% 5% 5% 6% 5% 5% 7% 34%	1650
March	1st to 10th	Day	5% 7% 3 8% 5% 6% 7% 5% 6% 8% 41%	4518
	11th to 20th	Day	6% 7% 3 7% 4 4 4 4 5% 7% 48%	4753
	21st to end	Day	8% 8% 3 9% 6% 6% 6% 5% 7% 9% 33%	5920
April	1st to 10th	Day	9% 8% 3 7% 7% 5% 4 5% 6% 9% 37%	2400
	11th to 20th	Day	5% 7% 2 6% 4 5% 5% 5% 7% 8% 45%	2372
	21st to end	Day	5% 6% 3 7% 6% 5% 4 4 5% 9% 46%	2635
May	1st to 10th	Day	6% 5% 2 5% 3 3 3 4 5% 9% 56%	6320
	11th to 20th	Day	6% 5% 2 7% 4 5% 5% 4 7% 8% 47%	6277
	21st to end	Day	5% 6% 2 6% 5% 4 5% 4 6% 8% 49%	6903
June	1st to 10th	Day	7% 6% 2 7% 6% 5% 4 4 6% 8% 45%	2800
	11th to 20th	Day	6% 4 2 6% 4 5% 5% 4 7% 8% 50%	2800
	21st to end	Day	4 3 1 5% 3 3 3 3 5% 7% 62%	2800
July	1st to 10th	Day	1 2 1 2 2 2 3 3 4 5% 78%	6320
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 4 80%	6320
	21st to end	Day	2 2 1 2 2 2 3 2 4 6% 75%	6874
August	1st to 10th	Day	2 2 1 3 2 3 3 3 4 6% 72%	4541
	11th to 20th	Day	1 2 1 3 2 3 3 3 5% 7% 70%	4301
	21st to end	Day	3 4 2 5% 3 3 3 3 4 6% 64%	4312
September	1st to 10th	Day	2 3 1 3 2 3 3 3 4 7% 69%	2400
	11th to 20th	Day	4 3 2 6% 4 4 5% 4 5% 7% 57%	2365
	21st to end	Day	6% 5% 1 4 4 4 4 4 5% 6% 56%	2200
October	1st to 10th	Day	5% 4 1 4 3 4 3 3 5% 8% 61%	3218
	11th to 20th	Day	5% 5% 2 6% 5% 6% 6% 5% 6% 7% 47%	3106
	21st to end	Day	9% 6% 2 6% 4 5% 5% 4 6% 7% 46%	3101
November	1st to 10th	Day	15% 9% 3 8% 6% 5% 5% 4 6% 7% 32%	1764
	11th to 20th	Day	12% 15% 4 9% 6% 4 4 4 5% 5% 32%	1600
	21st to end	Day	13% 14% 6% 12% 7% 5% 5% 4 5% 7% 24%	1600
December	1st to 10th	Day	9% 11% 4 14% 7% 5% 5% 5% 6% 7% 26%	2620
	11th to 20th	Day	16% 22% 8% 15% 6% 4 4 3 3 5% 15%	3025
	21st to end	Day	13% 22% 8% 16% 6% 5% 4 3 4 5% 14%	4004
January	1st to 10th	Night	18% 21% 8% 11% 5% 4 4 3 4 5% 18%	6306
	11th to 20th	Night	12% 9% 3 9% 4 3 3 3 5% 8% 40%	6282
	21st to end	Night	15% 18% 7% 9% 3 3 3 3 4 4 31%	6952
February	1st to 10th	Night	10% 13% 4 9% 6% 5% 5% 4 6% 8% 30%	2695
	11th to 20th	Night	10% 11% 4 9% 5% 4 5% 5% 6% 7% 36%	2499
	21st to end	Night	8% 12% 4 8% 5% 6% 5% 4 6% 8% 33%	1980
March	1st to 10th	Night	5% 8% 2 6% 4 5% 5% 5% 8% 10% 41%	5376
	11th to 20th	Night	8% 9% 3 6% 4 4 4 3 5% 6% 48%	5231
	21st to end	Night	7% 8% 3 10% 7% 7% 6% 5% 7% 9% 30%	5054
April	1st to 10th	Night	8% 9% 3 8% 6% 5% 4 4 6% 8% 40%	2000
	11th to 20th	Night	6% 8% 2 6% 5% 4 4 4 6% 7% 48%	1979
	21st to end	Night	6% 6% 2 6% 6% 6% 5% 5% 6% 8% 45%	1762
May	1st to 10th	Night	3 4 2 5% 4 4 4 4 5% 7% 57%	3640
	11th to 20th	Night	5% 6% 3 6% 4 3 5% 3 5% 6% 53%	3616
	21st to end	Night	5% 5% 2 4 3 3 4 3 5% 8% 57%	3972
June	1st to 10th	Night	6% 5% 2 5% 5% 4 5% 4 6% 8% 48%	1600
	11th to 20th	Night	5% 4 1 5% 4 4 5% 4 7% 7% 53%	1600
	21st to end	Night	4 3 1 5% 4 4 4 4 5% 6% 61%	1600
July	1st to 10th	Night	2 2 1 2 1 1 2 2 3 4 81%	3640
	11th to 20th	Night	1 1 1 1 1 2 2 2 4 85%	3640
	21st to end	Night	1 2 1 2 2 2 2 2 4 5% 77%	3969
August	1st to 10th	Night	2 3 1 3 2 2 2 3 3 6% 73%	2609
	11th to 20th	Night	2 2 1 4 3 3 3 3 5% 6% 68%	2747
	21st to end	Night	2 4 2 5% 3 3 3 3 4 6% 66%	3608
September	1st to 10th	Night	2 2 2 2 3 3 3 3 5% 9% 67%	2000
	11th to 20th	Night	4 4 2 5% 4 3 4 3 6% 7% 60%	2035
	21st to end	Night	5% 3 1 4 4 4 4 3 5% 8% 58%	2200
October	1st to 10th	Night	5% 3 1 4 3 3 4 3 6% 8% 61%	3826
	11th to 20th	Night	6% 4 2 5% 4 5% 6% 5% 6% 8% 49%	3828
	21st to end	Night	11% 7% 2 6% 5% 4 4 4 5% 6% 44%	4457
November	1st to 10th	Night	14% 10% 3 6% 5% 4 4 3 6% 8% 36%	2535
	11th to 20th	Night	11% 12% 3 8% 6% 5% 5% 5% 6% 6% 34%	2799
	21st to end	Night	14% 13% 4 11% 6% 5% 5% 4 5% 6% 28%	2800
December	1st to 10th	Night	7% 9% 4 9% 6% 6% 5% 4 6% 8% 38%	4560
	11th to 20th	Night	17% 17% 8% 15% 6% 6% 5% 4 5% 5% 12%	5180
	21st to end	Night	17% 20% 5% 11% 6% 4 4 3 5% 6% 19%	6952

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% 4 5% 13% 6%	3639
	11th to 20th	Day	49% 4 16% 25% 6% 1	3640
	21st to end	Day	59% 3 12% 20% 6%	4004
February	1st to 10th	Day	55% 9% 15% 14% 6% 1	1704
	11th to 20th	Day	48% 7% 17% 17% 10% 1	1796
	21st to end	Day	48% 8% 15% 19% 9% 1	1650
March	1st to 10th	Day	38% 5% 12% 23% 20% 1	4518
	11th to 20th	Day	35% 5% 9% 34% 16% 1	4753
	21st to end	Day	45% 7% 16% 21% 9% 2	5920
April	1st to 10th	Day	42% 6% 14% 24% 12% 2	2400
	11th to 20th	Day	34% 6% 13% 23% 18% 5%	2372
	21st to end	Day	34% 6% 11% 26% 19% 4	2635
May	1st to 10th	Day	25% 3 5% 21% 37% 7%	6320
	11th to 20th	Day	33% 4 9% 29% 20% 5%	6280
	21st to end	Day	31% 6% 12% 30% 18% 3	6904
June	1st to 10th	Day	35% 6% 10% 22% 21% 6%	2800
	11th to 20th	Day	29% 6% 10% 27% 22% 6%	2800
	21st to end	Day	22% 4 7% 31% 27% 9%	2800
July	1st to 10th	Day	12% 2 3 19% 30% 34%	6251
	11th to 20th	Day	11% 1 2 15% 33% 37%	6245
	21st to end	Day	13% 1 3 24% 36% 23%	6681
August	1st to 10th	Day	15% 2 4 18% 36% 24%	4524
	11th to 20th	Day	16% 2 6% 37% 31% 8%	4343
	21st to end	Day	23% 2 8% 28% 30% 8%	4311
September	1st to 10th	Day	15% 4 10% 27% 32% 12%	2400
	11th to 20th	Day	25% 5% 11% 25% 26% 7%	2365
	21st to end	Day	27% 5% 15% 30% 17% 5%	2200
October	1st to 10th	Day	24% 3 12% 36% 24% 2	3218
	11th to 20th	Day	36% 4 17% 25% 17% 1	3106
	21st to end	Day	38% 4 14% 27% 13% 4	3101
November	1st to 10th	Day	50% 8% 14% 19% 9% 2	1764
	11th to 20th	Day	53% 6% 15% 18% 7% 1	1600
	21st to end	Day	59% 8% 14% 12% 6% 2	1600
December	1st to 10th	Day	58% 5% 14% 19% 4	2620
	11th to 20th	Day	75% 5% 7% 9% 4	3028
	21st to end	Day	74% 4 9% 10% 4	4004
January	1st to 10th	Night	70% 4 10% 12% 3	6306
	11th to 20th	Night	43% 5% 18% 24% 9%	6320
	21st to end	Night	57% 4 13% 19% 6%	6952
February	1st to 10th	Night	50% 9% 16% 16% 8% 1	2695
	11th to 20th	Night	45% 8% 18% 18% 10% 1	2501
	21st to end	Night	46% 7% 14% 21% 10% 2	1980
March	1st to 10th	Night	33% 6% 11% 28% 20% 2	5376
	11th to 20th	Night	37% 4 9% 32% 16% 2	5232
	21st to end	Night	46% 8% 15% 23% 7% 1	5054
April	1st to 10th	Night	41% 5% 13% 28% 11% 2	2000
	11th to 20th	Night	34% 6% 10% 26% 19% 5%	1979
	21st to end	Night	34% 6% 10% 26% 20% 4	1762
May	1st to 10th	Night	26% 3 5% 19% 42% 6%	3637
	11th to 20th	Night	31% 4 7% 30% 26% 3	3616
	21st to end	Night	24% 5% 13% 37% 19% 2	3972
June	1st to 10th	Night	32% 5% 9% 24% 23% 6%	1600
	11th to 20th	Night	26% 6% 9% 28% 25% 6%	1600
	21st to end	Night	24% 3 7% 28% 28% 9%	1600
July	1st to 10th	Night	9% 2 3 19% 31% 37%	3600
	11th to 20th	Night	6% 1 2 16% 33% 41%	3592
	21st to end	Night	12% 1 3 21% 35% 28%	3857
August	1st to 10th	Night	14% 2 3 15% 38% 28%	2601
	11th to 20th	Night	19% 2 4 34% 32% 9%	2771
	21st to end	Night	21% 2 5% 27% 31% 14%	3608
September	1st to 10th	Night	16% 3 7% 27% 31% 17%	2000
	11th to 20th	Night	24% 4 9% 25% 28% 10%	2035
	21st to end	Night	24% 5% 11% 32% 20% 8%	2200
October	1st to 10th	Night	23% 3 7% 41% 25% 1	3826
	11th to 20th	Night	32% 4 15% 27% 19% 3	3828
	21st to end	Night	40% 4 11% 28% 15% 3	4457
November	1st to 10th	Night	44% 7% 18% 19% 10% 2	2535
	11th to 20th	Night	49% 9% 13% 17% 9% 2	2799
	21st to end	Night	56% 7% 13% 15% 7% 1	2800
December	1st to 10th	Night	45% 8% 19% 24% 3	4560
	11th to 20th	Night	74% 5% 11% 7% 3	5176
	21st to end	Night	66% 6% 10% 12% 6% 1	6952

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% 8% 24% 28% 16% 2	200
	11th to 20th	Day	24% 6% 17% 29% 19% 5%	200
	21st to end	Day	25% 3 15% 39% 14% 4	220
February	1st to 10th	Day	16% 5% 26% 34% 16% 3	304
	11th to 20th	Day	18% 7% 23% 31% 17% 4	412
	21st to end	Day	12% 8% 25% 32% 20% 3	414
March	1st to 10th	Day	13% 7% 26% 30% 19% 5%	500
	11th to 20th	Day	15% 11% 19% 30% 18% 8%	500
	21st to end	Day	15% 12% 27% 27% 15% 4	550
April	1st to 10th	Day	15% 12% 21% 30% 16% 5%	500
	11th to 20th	Day	9% 19% 27% 24% 15% 6%	492
	21st to end	Day	6% 13% 25% 26% 23% 8%	500
May	1st to 10th	Day	7% 11% 23% 33% 19% 7%	503
	11th to 20th	Day	13% 10% 17% 25% 23% 13%	528
	21st to end	Day	9% 8% 18% 25% 26% 14%	573
June	1st to 10th	Day	8% 10% 23% 28% 20% 12%	530
	11th to 20th	Day	9% 9% 27% 30% 17% 7%	530
	21st to end	Day	3 6% 19% 29% 29% 13%	530
July	1st to 10th	Day	2 6% 17% 37% 29% 10%	526
	11th to 20th	Day	1 4 21% 29% 31% 14%	524
	21st to end	Day	2 3 14% 29% 35% 17%	575
August	1st to 10th	Day	3 4 14% 30% 29% 20%	527
	11th to 20th	Day	3 3 15% 28% 31% 21%	517
	21st to end	Day	5% 4 17% 31% 27% 16%	583
September	1st to 10th	Day	4 5% 15% 28% 29% 19%	530
	11th to 20th	Day	6% 6% 16% 28% 31% 12%	530
	21st to end	Day	10% 8% 18% 29% 27% 7%	530
October	1st to 10th	Day	10% 6% 25% 30% 22% 8%	503
	11th to 20th	Day	11% 8% 20% 26% 27% 8%	460
	21st to end	Day	16% 10% 24% 32% 15% 3	330
November	1st to 10th	Day	19% 10% 17% 36% 17% 1	300
	11th to 20th	Day	21% 12% 26% 22% 16% 5%	200
	21st to end	Day	19% 6% 20% 31% 25% 2	200
December	1st to 10th	Day	19% 6% 18% 28% 21% 9%	200
	11th to 20th	Day	22% 8% 25% 29% 15% 2	200
	21st to end	Day	22% 6% 18% 36% 14% 4	220
January	1st to 10th	Night	28% 5% 20% 32% 14% 2	800
	11th to 20th	Night	21% 5% 20% 33% 17% 4	800
	21st to end	Night	20% 5% 16% 40% 17% 3	880
February	1st to 10th	Night	17% 4 29% 34% 15% 2	800
	11th to 20th	Night	15% 5% 23% 36% 18% 2	784
	21st to end	Night	14% 7% 22% 37% 16% 3	660
March	1st to 10th	Night	15% 6% 19% 39% 19% 3	800
	11th to 20th	Night	12% 5% 22% 38% 22% 2	800
	21st to end	Night	11% 7% 25% 39% 15% 3	880
April	1st to 10th	Night	12% 8% 19% 36% 22% 2	800
	11th to 20th	Night	11% 8% 27% 33% 17% 3	791
	21st to end	Night	7% 10% 26% 34% 20% 3	562
May	1st to 10th	Night	7% 8% 24% 37% 21% 3	400
	11th to 20th	Night	10% 6% 18% 34% 27% 5%	394
	21st to end	Night	8% 3 17% 38% 28% 5%	433
June	1st to 10th	Night	7% 7% 22% 38% 24% 3	400
	11th to 20th	Night	7% 9% 24% 40% 20% 2	400
	21st to end	Night	6% 4 21% 37% 28% 4	400
July	1st to 10th	Night	3 3 16% 42% 33% 3	390
	11th to 20th	Night	2 4 19% 42% 32% 2	388
	21st to end	Night	1 3 14% 39% 40% 2	438
August	1st to 10th	Night	3 3 12% 37% 39% 7%	398
	11th to 20th	Night	4 1 11% 37% 37% 10%	488
	21st to end	Night	4 4 14% 38% 35% 5%	880
September	1st to 10th	Night	3 4 15% 39% 34% 6%	800
	11th to 20th	Night	5% 5% 12% 33% 38% 7%	800
	21st to end	Night	7% 4 17% 36% 31% 4	800
October	1st to 10th	Night	12% 4 16% 40% 26% 3	772
	11th to 20th	Night	11% 5% 17% 38% 25% 4	760
	21st to end	Night	16% 5% 19% 39% 17% 4	836
November	1st to 10th	Night	19% 5% 16% 46% 12% 1	780
	11th to 20th	Night	18% 7% 24% 34% 14% 3	800
	21st to end	Night	21% 5% 15% 36% 21% 3	800
December	1st to 10th	Night	17% 5% 19% 37% 19% 3	800
	11th to 20th	Night	24% 5% 17% 40% 13% 1	800
	21st to end	Night	25% 5% 20% 40% 10% 1	880

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