Camp Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Camp Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	14% 11% 4 9% 6% 5% 5% 4 5% 7% 30%	131789
	Night	14% 11% 4 10% 6% 5% 4 3 5% 6% 30%	130706
Transparency	Day	53% 6% 10% 19% 11% 1	135278
	Night	54% 6% 11% 18% 10% 1	135304
Seeing	Day	25% 20% 28% 17% 7% 2	16636
	Night	23% 20% 26% 21% 8% 1	25870

By Month

Percentage Cloud Cover NE (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	9% 14% 9% 22% 9% 5% 4 2 4 4 18%	4661
	11th to 20th	Day	11% 15% 6% 15% 7% 6% 6% 4 5% 5% 20%	4650
	21st to end	Day	13% 13% 7% 10% 7% 6% 4 3 5% 6% 25%	5459
February	1st to 10th	Day	12% 14% 5% 12% 9% 5% 5% 5% 5% 5% 23%	1890
	11th to 20th	Day	10% 11% 6% 15% 8% 5% 5% 4 6% 6% 25%	1986
	21st to end	Day	15% 14% 4 11% 7% 5% 4 3 4 5% 27%	1730
March	1st to 10th	Day	18% 15% 6% 10% 5% 4 4 3 4 5% 28%	4576
	11th to 20th	Day	12% 14% 6% 9% 5% 4 4 3 4 5% 35%	4936
	21st to end	Day	16% 10% 4 10% 5% 5% 5% 3 5% 5% 32%	6023
April	1st to 10th	Day	15% 14% 4 9% 6% 4 4 3 5% 5% 30%	2520
	11th to 20th	Day	15% 12% 3 6% 5% 4 5% 4 5% 6% 34%	2494
	21st to end	Day	19% 11% 4 8% 5% 4 3 3 4 6% 32%	2568
May	1st to 10th	Day	28% 12% 3 7% 5% 5% 4 3 5% 6% 23%	6101
	11th to 20th	Day	16% 11% 3 8% 6% 5% 5% 4 5% 7% 30%	6318
	21st to end	Day	18% 9% 3 8% 5% 5% 5% 4 6% 8% 28%	6949
June	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 5% 7% 8% 30%	2800
	11th to 20th	Day	16% 8% 3 7% 5% 5% 6% 4 7% 10% 31%	2800
	21st to end	Day	15% 8% 3 7% 5% 6% 5% 4 6% 8% 32%	2800
July	1st to 10th	Day	9% 7% 3 9% 6% 6% 6% 5% 7% 9% 34%	6360
	11th to 20th	Day	8% 6% 2 7% 6% 6% 7% 6% 9% 12% 32%	6360
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 6% 7% 39%	6926
August	1st to 10th	Day	17% 7% 3 8% 5% 5% 5% 4 6% 7% 31%	4446
	11th to 20th	Day	12% 8% 3 8% 5% 6% 6% 5% 8% 10% 29%	3888
	21st to end	Day	13% 8% 3 6% 5% 5% 5% 4 7% 9% 35%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 5% 5% 4 6% 7% 41%	2400
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 5% 7% 46%	2336
	21st to end	Day	15% 7% 3 6% 4 5% 4 4 6% 9% 37%	2200
October	1st to 10th	Day	16% 10% 3 8% 4 4 4 3 5% 6% 35%	2044
	11th to 20th	Day	13% 11% 3 8% 4 4 4 4 6% 7% 36%	2000
	21st to end	Day	20% 14% 3 7% 4 5% 4 4 5% 6% 29%	2030
November	1st to 10th	Day	12% 13% 3 7% 4 4 4 3 6% 6% 39%	1851
	11th to 20th	Day	13% 16% 4 9% 5% 6% 5% 4 4 5% 31%	1890
	21st to end	Day	14% 15% 5% 8% 5% 5% 4 4 5% 6% 27%	1691
December	1st to 10th	Day	9% 17% 8% 17% 6% 4 5% 3 5% 6% 18%	2680
	11th to 20th	Day	16% 14% 6% 11% 5% 5% 4 4 4 5% 26%	3066
	21st to end	Day	14% 14% 7% 13% 6% 4 4 4 5% 6% 22%	4048
January	1st to 10th	Night	11% 14% 7% 22% 8% 5% 4 3 4 5% 18%	8234
	11th to 20th	Night	9% 16% 7% 20% 9% 6% 4 3 5% 5% 16%	8235
	21st to end	Night	11% 11% 4 12% 9% 9% 6% 3 5% 6% 24%	8718
February	1st to 10th	Night	11% 13% 4 11% 8% 5% 6% 4 7% 6% 24%	2730
	11th to 20th	Night	10% 10% 7% 12% 9% 6% 6% 5% 6% 6% 22%	2518
	21st to end	Night	14% 12% 6% 12% 7% 5% 5% 4 5% 6% 25%	2076
March	1st to 10th	Night	16% 10% 4 12% 7% 4 5% 3 6% 5% 27%	5484
	11th to 20th	Night	12% 13% 6% 9% 5% 4 4 3 4 7% 33%	5241
	21st to end	Night	17% 13% 5% 11% 5% 4 3 3 5% 5% 29%	5149
April	1st to 10th	Night	16% 13% 4 8% 6% 5% 5% 4 6% 6% 27%	2100
	11th to 20th	Night	17% 13% 3 6% 4 4 4 3 5% 7% 35%	2075
	21st to end	Night	19% 11% 3 7% 4 4 4 3 5% 6% 35%	2049
May	1st to 10th	Night	30% 13% 3 6% 4 3 3 3 4 5% 25%	3892
	11th to 20th	Night	17% 13% 3 8% 5% 4 5% 3 5% 6% 31%	3575
	21st to end	Night	19% 11% 4 7% 5% 5% 5% 3 6% 7% 29%	3926
June	1st to 10th	Night	15% 8% 2 6% 5% 4 4 4 6% 6% 40%	1600
	11th to 20th	Night	15% 7% 2 6% 3 3 4 4 6% 9% 39%	1600
	21st to end	Night	11% 5% 2 6% 5% 4 5% 4 7% 10% 41%	1600
July	1st to 10th	Night	9% 7% 3 7% 5% 5% 6% 4 7% 8% 41%	3600
	11th to 20th	Night	10% 7% 3 7% 6% 5% 5% 5% 6% 8% 38%	3600
	21st to end	Night	11% 6% 2 6% 4 4 4 3 5% 6% 47%	3926
August	1st to 10th	Night	18% 9% 2 6% 5% 4 4 3 5% 6% 36%	2700
	11th to 20th	Night	14% 7% 3 7% 5% 4 4 4 5% 7% 41%	3127
	21st to end	Night	11% 8% 2 6% 4 4 4 3 6% 6% 46%	3586
September	1st to 10th	Night	13% 7% 2 5% 3 4 4 4 5% 8% 45%	2000
	11th to 20th	Night	13% 6% 2 5% 2 3 3 3 4 7% 53%	2063
	21st to end	Night	14% 7% 2 7% 5% 4 4 4 5% 6% 42%	2200
October	1st to 10th	Night	17% 9% 2 7% 4 3 3 4 5% 6% 39%	2353
	11th to 20th	Night	16% 9% 2 6% 4 4 5% 4 5% 6% 39%	2400
	21st to end	Night	19% 13% 3 6% 3 5% 4 3 5% 8% 31%	2810
November	1st to 10th	Night	12% 12% 3 7% 4 4 4 3 5% 7% 38%	2667
	11th to 20th	Night	14% 14% 4 8% 5% 5% 5% 4 5% 6% 30%	2730
	21st to end	Night	12% 12% 7% 9% 5% 5% 5% 4 6% 6% 30%	2924
December	1st to 10th	Night	12% 15% 6% 15% 5% 5% 5% 4 6% 7% 20%	4720
	11th to 20th	Night	18% 13% 6% 11% 5% 5% 4 3 4 4 27%	5348
	21st to end	Night	17% 15% 6% 13% 5% 4 4 3 4 5% 23%	7150

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	69% 5% 8% 13% 4 1	4662
	11th to 20th	Day	66% 5% 6% 11% 10% 2	4680
	21st to end	Day	60% 4 6% 19% 9% 1	5459
February	1st to 10th	Day	61% 7% 9% 14% 8% 1	1890
	11th to 20th	Day	58% 7% 7% 17% 9% 1	1995
	21st to end	Day	58% 6% 10% 16% 9%	1730
March	1st to 10th	Day	61% 4 8% 13% 11% 3	4579
	11th to 20th	Day	52% 5% 13% 19% 7% 4	4936
	21st to end	Day	54% 6% 6% 14% 18% 3	6023
April	1st to 10th	Day	56% 5% 8% 19% 10% 2	2520
	11th to 20th	Day	51% 5% 11% 19% 13% 1	2494
	21st to end	Day	54% 5% 9% 17% 12% 2	2568
May	1st to 10th	Day	63% 5% 8% 15% 8% 1	6112
	11th to 20th	Day	54% 6% 11% 20% 9% 1	6322
	21st to end	Day	52% 7% 11% 21% 8% 1	6949
June	1st to 10th	Day	50% 7% 13% 19% 11%	2800
	11th to 20th	Day	48% 8% 14% 19% 10% 1	2800
	21st to end	Day	50% 7% 14% 19% 10% 1	2800
July	1st to 10th	Day	47% 5% 13% 23% 11%	6290
	11th to 20th	Day	43% 6% 15% 24% 11% 1	6285
	21st to end	Day	45% 4 11% 28% 13%	6728
August	1st to 10th	Day	52% 6% 13% 18% 10%	4432
	11th to 20th	Day	48% 6% 15% 25% 5%	3925
	21st to end	Day	44% 5% 12% 30% 9% 1	4312
September	1st to 10th	Day	41% 7% 12% 25% 15% 1	2400
	11th to 20th	Day	37% 7% 10% 26% 19% 1	2336
	21st to end	Day	43% 7% 12% 23% 14% 2	2200
October	1st to 10th	Day	50% 4 6% 22% 18% 1	3330
	11th to 20th	Day	42% 5% 9% 22% 18% 4	3240
	21st to end	Day	42% 5% 13% 26% 12% 3	3255
November	1st to 10th	Day	45% 7% 11% 22% 14% 2	1851
	11th to 20th	Day	55% 6% 9% 16% 12% 2	1890
	21st to end	Day	57% 7% 13% 16% 7% 1	1691
December	1st to 10th	Day	67% 4 9% 15% 4	2680
	11th to 20th	Day	61% 4 11% 15% 8%	3066
	21st to end	Day	62% 5% 8% 12% 11% 2	4048
January	1st to 10th	Night	68% 6% 8% 12% 6%	8234
	11th to 20th	Night	71% 4 8% 8% 7% 2	8280
	21st to end	Night	62% 3 8% 12% 12% 2	8718
February	1st to 10th	Night	58% 8% 10% 15% 8% 1	2730
	11th to 20th	Night	59% 9% 9% 14% 8% 1	2520
	21st to end	Night	58% 6% 10% 16% 8% 2	2076
March	1st to 10th	Night	58% 5% 10% 16% 10% 1	5494
	11th to 20th	Night	51% 7% 17% 17% 7% 2	5242
	21st to end	Night	57% 5% 5% 15% 16% 1	5149
April	1st to 10th	Night	56% 7% 11% 16% 8% 1	2100
	11th to 20th	Night	50% 6% 11% 19% 14%	2075
	21st to end	Night	49% 6% 11% 17% 14% 2	2049
May	1st to 10th	Night	62% 5% 9% 13% 9% 2	3898
	11th to 20th	Night	54% 7% 10% 20% 8% 1	3576
	21st to end	Night	53% 8% 11% 18% 9% 1	3927
June	1st to 10th	Night	44% 6% 12% 25% 13% 1	1600
	11th to 20th	Night	42% 7% 16% 27% 9%	1600
	21st to end	Night	37% 9% 17% 25% 11% 1	1600
July	1st to 10th	Night	42% 5% 17% 22% 14% 1	3560
	11th to 20th	Night	44% 5% 15% 23% 12% 1	3552
	21st to end	Night	39% 4 12% 32% 12% 1	3809
August	1st to 10th	Night	49% 6% 14% 22% 8% 1	2690
	11th to 20th	Night	43% 5% 17% 26% 8%	3156
	21st to end	Night	39% 5% 11% 34% 10% 1	3586
September	1st to 10th	Night	38% 7% 14% 28% 13% 1	2000
	11th to 20th	Night	33% 6% 11% 28% 21% 1	2063
	21st to end	Night	43% 7% 11% 22% 15% 1	2200
October	1st to 10th	Night	50% 5% 11% 23% 11% 1	3847
	11th to 20th	Night	41% 5% 12% 21% 17% 4	3899
	21st to end	Night	43% 5% 15% 27% 10% 1	4535
November	1st to 10th	Night	46% 6% 11% 19% 15% 2	2667
	11th to 20th	Night	52% 8% 10% 18% 11% 2	2730
	21st to end	Night	54% 6% 13% 19% 6% 1	2924
December	1st to 10th	Night	63% 6% 8% 19% 3	4720
	11th to 20th	Night	62% 4 10% 13% 12%	5348
	21st to end	Night	64% 5% 6% 11% 11% 2	7150

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	34% 29% 24% 10% 3	220
	11th to 20th	Day	40% 29% 23% 8% 1	220
	21st to end	Day	32% 31% 27% 7% 2	303
February	1st to 10th	Day	35% 32% 26% 7%	330
	11th to 20th	Day	35% 35% 22% 6% 2	474
	21st to end	Day	33% 29% 28% 9% 1	446
March	1st to 10th	Day	31% 28% 29% 10% 2	540
	11th to 20th	Day	37% 23% 26% 10% 3	540
	21st to end	Day	36% 29% 22% 9% 4 1	594
April	1st to 10th	Day	35% 26% 22% 11% 5%	540
	11th to 20th	Day	32% 27% 23% 11% 5% 2	532
	21st to end	Day	33% 21% 29% 11% 5% 2	540
May	1st to 10th	Day	34% 22% 26% 10% 5% 3	507
	11th to 20th	Day	22% 20% 31% 17% 7% 2	527
	21st to end	Day	22% 13% 32% 21% 9% 3	573
June	1st to 10th	Day	21% 16% 33% 22% 7% 1	530
	11th to 20th	Day	18% 17% 32% 20% 11% 2	530
	21st to end	Day	20% 19% 31% 22% 7% 1	530
July	1st to 10th	Day	13% 11% 36% 26% 12% 3	525
	11th to 20th	Day	11% 10% 36% 30% 11% 2	524
	21st to end	Day	14% 11% 39% 25% 8% 3	576
August	1st to 10th	Day	11% 11% 32% 26% 16% 5%	526
	11th to 20th	Day	16% 9% 28% 29% 12% 7%	519
	21st to end	Day	15% 14% 30% 23% 12% 5%	583
September	1st to 10th	Day	20% 11% 26% 23% 14% 7%	530
	11th to 20th	Day	13% 11% 26% 22% 18% 11%	530
	21st to end	Day	21% 13% 26% 23% 12% 5%	530
October	1st to 10th	Day	21% 17% 26% 18% 12% 5%	530
	11th to 20th	Day	26% 22% 25% 19% 7% 2	530
	21st to end	Day	28% 22% 30% 16% 4	489
November	1st to 10th	Day	29% 22% 24% 15% 9%	425
	11th to 20th	Day	30% 27% 22% 14% 5% 1	430
	21st to end	Day	35% 26% 28% 10% 1	231
December	1st to 10th	Day	35% 30% 24% 8% 4	220
	11th to 20th	Day	38% 27% 25% 10% 1	220
	21st to end	Day	31% 29% 30% 9% 2	242
January	1st to 10th	Night	25% 34% 29% 11% 1	840
	11th to 20th	Night	29% 27% 29% 13% 2	840
	21st to end	Night	20% 34% 28% 15% 2	924
February	1st to 10th	Night	26% 27% 33% 13% 1	840
	11th to 20th	Night	27% 30% 29% 13% 1	823
	21st to end	Night	31% 26% 28% 13% 2	692
March	1st to 10th	Night	28% 27% 29% 13% 3	840
	11th to 20th	Night	29% 27% 27% 15% 2	840
	21st to end	Night	29% 22% 29% 15% 5%	924
April	1st to 10th	Night	28% 24% 28% 17% 3	840
	11th to 20th	Night	26% 24% 27% 16% 6%	831
	21st to end	Night	28% 19% 26% 20% 6% 1	789
May	1st to 10th	Night	30% 15% 27% 20% 7% 1	536
	11th to 20th	Night	23% 14% 26% 30% 6% 1	394
	21st to end	Night	17% 9% 31% 30% 13% 1	433
June	1st to 10th	Night	18% 11% 28% 32% 11% 1	400
	11th to 20th	Night	17% 11% 23% 37% 13%	400
	21st to end	Night	14% 8% 31% 35% 12% 1	400
July	1st to 10th	Night	12% 8% 22% 44% 14% 2	390
	11th to 20th	Night	12% 6% 26% 37% 18% 1	388
	21st to end	Night	12% 5% 26% 42% 14% 1	438
August	1st to 10th	Night	12% 6% 25% 35% 22% 1	460
	11th to 20th	Night	16% 5% 21% 35% 20% 3	744
	21st to end	Night	16% 9% 21% 33% 19% 2	880
September	1st to 10th	Night	17% 9% 25% 32% 16% 2	800
	11th to 20th	Night	16% 10% 21% 27% 21% 6%	800
	21st to end	Night	17% 12% 25% 28% 15% 3	800
October	1st to 10th	Night	24% 16% 21% 23% 15% 2	800
	11th to 20th	Night	22% 18% 28% 25% 8% 1	800
	21st to end	Night	28% 20% 27% 21% 4	880
November	1st to 10th	Night	23% 22% 27% 21% 6%	820
	11th to 20th	Night	27% 24% 25% 16% 6% 1	840
	21st to end	Night	26% 26% 26% 18% 4	840
December	1st to 10th	Night	26% 30% 26% 13% 4	840
	11th to 20th	Night	28% 28% 28% 14% 2	840
	21st to end	Night	30% 30% 25% 12% 2	924

Page generated at 2026-04-29 02:21:45. Version ac07

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