Camp Crosley/WAS Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Camp Crosley/WAS Observatory clear sky chart from 2005-11-06 to 2026-07-01.

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% 10% 4 8% 5% 5% 5% 4 5% 7% 34%	137247
	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 34%	135287
Transparency	Day	49% 4 11% 22% 13% 1	140815
	Night	50% 4 11% 21% 13% 1	139795
Seeing	Day	19% 11% 28% 23% 14% 5%	17931
	Night	19% 10% 29% 28% 12% 1	27771

By Month

Percentage Cloud Cover SE (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	14% 15% 10% 20% 7% 4 4 3 4 4 14%	4691
	11th to 20th	Day	11% 15% 9% 14% 7% 8% 5% 5% 5% 5% 16%	4710
	21st to end	Day	18% 17% 7% 14% 6% 5% 6% 3 3 4 17%	5270
February	1st to 10th	Day	15% 17% 7% 11% 7% 5% 4 3 5% 5% 23%	2016
	11th to 20th	Day	15% 12% 6% 13% 8% 4 5% 4 4 6% 24%	2048
	21st to end	Day	15% 15% 6% 12% 5% 4 4 3 5% 7% 24%	1730
March	1st to 10th	Day	18% 13% 6% 11% 4 4 3 3 4 5% 29%	4580
	11th to 20th	Day	11% 10% 5% 6% 4 4 4 4 6% 7% 38%	4949
	21st to end	Day	18% 16% 5% 10% 5% 5% 5% 3 4 6% 22%	5770
April	1st to 10th	Day	18% 13% 4 7% 5% 4 4 3 5% 6% 30%	2520
	11th to 20th	Day	18% 9% 3 7% 4 5% 4 4 5% 6% 35%	2520
	21st to end	Day	18% 9% 2 7% 4 4 5% 4 5% 7% 35%	2730
May	1st to 10th	Day	19% 8% 3 7% 5% 4 5% 4 5% 7% 32%	7616
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	7626
	21st to end	Day	14% 6% 2 7% 5% 4 4 4 6% 8% 39%	8763
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 4 4 7% 8% 42%	2940
	11th to 20th	Day	10% 6% 2 6% 4 5% 4 4 7% 8% 44%	2940
	21st to end	Day	12% 5% 2 6% 6% 5% 6% 4 6% 9% 40%	2940
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 5% 7% 10% 41%	6361
	11th to 20th	Day	8% 5% 2 6% 4 5% 6% 4 8% 11% 42%	6360
	21st to end	Day	10% 7% 2 7% 5% 5% 5% 5% 6% 9% 40%	6817
August	1st to 10th	Day	9% 4 2 6% 4 5% 5% 3 6% 8% 47%	4234
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 45%	4142
	21st to end	Day	7% 4 2 6% 4 4 4 4 6% 9% 49%	4312
September	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 6% 7% 47%	2358
	11th to 20th	Day	9% 4 2 5% 3 4 5% 4 6% 8% 50%	2200
	21st to end	Day	13% 7% 2 6% 4 4 5% 4 5% 8% 44%	2200
October	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 6% 7% 45%	2200
	11th to 20th	Day	17% 7% 3 7% 4 4 4 4 6% 7% 37%	1997
	21st to end	Day	19% 11% 3 8% 5% 5% 4 3 5% 7% 29%	1980
November	1st to 10th	Day	12% 9% 3 6% 4 4 4 3 5% 6% 43%	1852
	11th to 20th	Day	17% 16% 4 8% 6% 3 3 3 4 6% 30%	1890
	21st to end	Day	21% 15% 5% 9% 5% 4 3 3 4 5% 26%	1890
December	1st to 10th	Day	11% 16% 4 12% 5% 5% 4 4 5% 7% 27%	2937
	11th to 20th	Day	16% 17% 9% 13% 6% 4 3 3 4 5% 21%	3088
	21st to end	Day	27% 20% 6% 13% 5% 4 4 3 3 3 11%	4070
January	1st to 10th	Night	14% 16% 7% 17% 6% 5% 4 4 5% 5% 19%	8232
	11th to 20th	Night	10% 17% 8% 17% 7% 6% 5% 4 5% 4 17%	8280
	21st to end	Night	17% 13% 6% 10% 6% 6% 5% 4 5% 5% 22%	8922
February	1st to 10th	Night	17% 15% 5% 10% 6% 4 3 4 5% 5% 25%	2599
	11th to 20th	Night	14% 13% 5% 10% 7% 4 4 3 5% 6% 29%	2458
	21st to end	Night	19% 13% 5% 10% 5% 4 4 3 4 5% 29%	2076
March	1st to 10th	Night	16% 12% 4 8% 5% 4 4 3 4 6% 34%	5493
	11th to 20th	Night	12% 8% 3 6% 5% 4 5% 4 5% 7% 41%	5231
	21st to end	Night	18% 11% 3 8% 4 4 4 3 6% 6% 34%	5430
April	1st to 10th	Night	17% 10% 2 5% 5% 4 4 4 5% 7% 37%	2100
	11th to 20th	Night	19% 8% 2 6% 5% 4 4 4 4 6% 37%	2047
	21st to end	Night	16% 9% 3 7% 5% 4 4 3 6% 6% 38%	1890
May	1st to 10th	Night	19% 9% 3 7% 5% 4 4 3 4 6% 34%	5237
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 5% 8% 42%	5234
	21st to end	Night	15% 7% 2 6% 4 4 4 4 6% 7% 41%	5391
June	1st to 10th	Night	11% 5% 2 6% 4 4 5% 3 6% 8% 47%	1680
	11th to 20th	Night	8% 6% 3 6% 5% 4 5% 4 6% 8% 46%	1680
	21st to end	Night	10% 5% 2 6% 4 4 4 4 7% 10% 43%	1680
July	1st to 10th	Night	8% 5% 2 6% 5% 5% 4 3 6% 9% 47%	3618
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 6% 10% 48%	3617
	21st to end	Night	11% 6% 2 7% 5% 4 4 4 7% 9% 43%	4046
August	1st to 10th	Night	12% 5% 2 6% 4 3 4 4 7% 9% 44%	2915
	11th to 20th	Night	9% 6% 2 5% 4 4 4 3 6% 8% 48%	2903
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 8% 51%	3586
September	1st to 10th	Night	11% 5% 2 5% 4 4 3 2 4 7% 53%	2021
	11th to 20th	Night	9% 4 1 5% 3 3 3 3 5% 8% 57%	2200
	21st to end	Night	13% 7% 3 6% 4 4 4 4 4 5% 47%	2200
October	1st to 10th	Night	12% 5% 2 5% 4 3 4 3 5% 6% 51%	2200
	11th to 20th	Night	18% 7% 2 6% 5% 4 4 3 4 6% 41%	2398
	21st to end	Night	20% 8% 2 6% 4 3 3 3 5% 7% 37%	2860
November	1st to 10th	Night	14% 9% 3 6% 4 4 4 3 5% 7% 43%	2666
	11th to 20th	Night	16% 12% 4 7% 4 4 4 3 6% 7% 33%	2730
	21st to end	Night	20% 15% 4 8% 5% 3 3 4 5% 6% 26%	2730
December	1st to 10th	Night	13% 12% 5% 10% 5% 6% 5% 4 6% 7% 28%	4448
	11th to 20th	Night	17% 18% 8% 14% 6% 4 4 3 4 4 19%	5339
	21st to end	Night	26% 19% 7% 12% 5% 4 4 3 4 4 12%	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	74% 2 10% 11% 3	4692
	11th to 20th	Day	71% 3 7% 9% 10% 1	4710
	21st to end	Day	74% 1 8% 12% 5%	5270
February	1st to 10th	Day	63% 4 10% 14% 7% 1	2016
	11th to 20th	Day	62% 4 8% 17% 8% 1	2058
	21st to end	Day	59% 4 13% 16% 7% 1	1730
March	1st to 10th	Day	59% 3 7% 21% 9%	4580
	11th to 20th	Day	45% 4 12% 31% 8% 1	4949
	21st to end	Day	65% 4 11% 15% 5% 1	5772
April	1st to 10th	Day	56% 5% 10% 18% 11%	2520
	11th to 20th	Day	49% 5% 10% 22% 11% 2	2520
	21st to end	Day	48% 5% 12% 21% 11% 2	2730
May	1st to 10th	Day	52% 4 10% 20% 14%	7651
	11th to 20th	Day	45% 4 14% 22% 14% 1	7630
	21st to end	Day	42% 4 9% 23% 17% 5%	8777
June	1st to 10th	Day	39% 5% 11% 25% 18% 2	2940
	11th to 20th	Day	37% 5% 12% 26% 18% 2	2940
	21st to end	Day	39% 7% 15% 21% 16% 2	2940
July	1st to 10th	Day	40% 3 10% 28% 17% 2	6292
	11th to 20th	Day	37% 3 15% 29% 16% 1	6285
	21st to end	Day	41% 4 13% 22% 18% 2	6622
August	1st to 10th	Day	36% 5% 14% 28% 16% 1	4221
	11th to 20th	Day	37% 5% 13% 28% 17% 1	4181
	21st to end	Day	33% 4 13% 29% 18% 3	4311
September	1st to 10th	Day	36% 7% 14% 22% 18% 3	2358
	11th to 20th	Day	31% 6% 11% 27% 23% 2	2200
	21st to end	Day	40% 6% 10% 24% 20% 1	2200
October	1st to 10th	Day	29% 3 10% 35% 22% 1	3590
	11th to 20th	Day	39% 3 11% 22% 25%	3226
	21st to end	Day	47% 3 10% 26% 13% 1	3180
November	1st to 10th	Day	42% 5% 11% 26% 15% 1	1852
	11th to 20th	Day	57% 3 10% 19% 11% 1	1890
	21st to end	Day	62% 3 11% 17% 6% 1	1890
December	1st to 10th	Day	58% 3 15% 20% 4	2937
	11th to 20th	Day	67% 3 10% 16% 4	3085
	21st to end	Day	80% 3 6% 8% 4	4070
January	1st to 10th	Night	69% 3 9% 14% 5%	8233
	11th to 20th	Night	71% 2 7% 10% 9%	8280
	21st to end	Night	65% 2 12% 14% 7%	8922
February	1st to 10th	Night	61% 4 11% 15% 8% 2	2599
	11th to 20th	Night	57% 4 9% 19% 9% 1	2459
	21st to end	Night	58% 3 12% 16% 8% 2	2076
March	1st to 10th	Night	52% 3 9% 26% 8% 1	5493
	11th to 20th	Night	42% 4 12% 28% 12% 2	5231
	21st to end	Night	51% 4 11% 22% 11% 1	5430
April	1st to 10th	Night	47% 6% 11% 20% 14% 1	2100
	11th to 20th	Night	48% 4 9% 20% 16% 2	2047
	21st to end	Night	46% 4 11% 23% 13% 2	1890
May	1st to 10th	Night	52% 4 8% 20% 14% 2	5264
	11th to 20th	Night	42% 5% 11% 25% 17% 1	5235
	21st to end	Night	42% 3 11% 19% 20% 5%	5401
June	1st to 10th	Night	34% 5% 11% 28% 19% 3	1680
	11th to 20th	Night	36% 7% 11% 24% 19% 2	1680
	21st to end	Night	35% 6% 18% 22% 16% 3	1680
July	1st to 10th	Night	36% 4 11% 27% 18% 5%	3580
	11th to 20th	Night	34% 3 18% 23% 20% 2	3572
	21st to end	Night	38% 3 16% 20% 20% 3	3929
August	1st to 10th	Night	35% 6% 14% 29% 15% 1	2904
	11th to 20th	Night	34% 5% 11% 30% 18% 1	2930
	21st to end	Night	33% 4 10% 29% 20% 3	3586
September	1st to 10th	Night	32% 5% 12% 25% 20% 5%	2021
	11th to 20th	Night	27% 4 8% 32% 26% 2	2200
	21st to end	Night	39% 4 8% 27% 19% 2	2200
October	1st to 10th	Night	24% 3 7% 34% 31% 1	3590
	11th to 20th	Night	38% 2 8% 24% 27% 1	3908
	21st to end	Night	38% 2 9% 30% 20% 1	4610
November	1st to 10th	Night	42% 4 10% 26% 16% 1	2666
	11th to 20th	Night	51% 4 12% 21% 11% 2	2730
	21st to end	Night	59% 4 11% 19% 6%	2730
December	1st to 10th	Night	57% 3 13% 22% 5%	4448
	11th to 20th	Night	69% 3 11% 10% 6% 1	5341
	21st to end	Night	77% 3 8% 8% 3	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	22% 21% 36% 15% 5%	330
	11th to 20th	Day	25% 21% 40% 11% 3	330
	21st to end	Day	31% 18% 32% 16% 3	363
February	1st to 10th	Day	25% 21% 35% 15% 4	330
	11th to 20th	Day	25% 23% 35% 15% 3	330
	21st to end	Day	26% 27% 36% 8% 3	273
March	1st to 10th	Day	24% 21% 40% 12% 2	330
	11th to 20th	Day	27% 15% 33% 19% 6%	477
	21st to end	Day	30% 18% 30% 16% 4 1	594
April	1st to 10th	Day	26% 16% 32% 19% 6% 1	540
	11th to 20th	Day	23% 19% 31% 16% 9% 2	532
	21st to end	Day	24% 13% 32% 21% 9% 2	540
May	1st to 10th	Day	25% 15% 31% 18% 8% 3	543
	11th to 20th	Day	21% 13% 27% 23% 12% 4	567
	21st to end	Day	14% 6% 31% 26% 16% 7%	742
June	1st to 10th	Day	14% 9% 29% 27% 16% 5%	780
	11th to 20th	Day	13% 8% 31% 27% 16% 5%	780
	21st to end	Day	13% 6% 28% 31% 17% 5%	780
July	1st to 10th	Day	11% 3 19% 31% 23% 12%	722
	11th to 20th	Day	9% 3 25% 29% 23% 10%	718
	21st to end	Day	10% 4 19% 31% 25% 11%	749
August	1st to 10th	Day	10% 3 13% 30% 29% 15%	526
	11th to 20th	Day	12% 3 21% 28% 27% 9%	519
	21st to end	Day	11% 4 15% 30% 29% 12%	583
September	1st to 10th	Day	14% 5% 20% 26% 26% 10%	530
	11th to 20th	Day	9% 4 14% 25% 34% 14%	530
	21st to end	Day	21% 8% 19% 24% 21% 7%	530
October	1st to 10th	Day	13% 6% 27% 29% 17% 7%	530
	11th to 20th	Day	18% 16% 30% 24% 11%	457
	21st to end	Day	29% 14% 36% 18% 2	363
November	1st to 10th	Day	17% 15% 35% 21% 9% 2	330
	11th to 20th	Day	28% 16% 33% 15% 7%	330
	21st to end	Day	33% 15% 36% 14% 3	330
December	1st to 10th	Day	24% 18% 38% 14% 6%	330
	11th to 20th	Day	22% 23% 36% 15% 4	330
	21st to end	Day	29% 21% 37% 11% 2	363
January	1st to 10th	Night	24% 16% 36% 21% 4	1050
	11th to 20th	Night	24% 17% 36% 18% 4 1	1050
	21st to end	Night	23% 15% 37% 23% 3	1110
February	1st to 10th	Night	26% 12% 34% 24% 4	840
	11th to 20th	Night	21% 15% 37% 24% 2	823
	21st to end	Night	27% 16% 37% 18% 3	692
March	1st to 10th	Night	21% 14% 35% 24% 6%	840
	11th to 20th	Night	19% 14% 37% 25% 5% 1	840
	21st to end	Night	26% 12% 31% 27% 5%	856
April	1st to 10th	Night	21% 14% 34% 24% 6% 1	630
	11th to 20th	Night	22% 13% 33% 25% 7% 1	623
	21st to end	Night	20% 9% 34% 27% 8% 1	630
May	1st to 10th	Night	21% 7% 34% 30% 7%	630
	11th to 20th	Night	20% 6% 30% 29% 14% 1	621
	21st to end	Night	14% 4 27% 38% 16% 1	683
June	1st to 10th	Night	12% 3 27% 41% 16%	630
	11th to 20th	Night	9% 4 30% 41% 15%	630
	21st to end	Night	10% 3 24% 37% 24% 1	630
July	1st to 10th	Night	9% 1 15% 42% 29% 3	585
	11th to 20th	Night	10% 3 16% 40% 29% 3	582
	21st to end	Night	8% 2 16% 40% 32% 2	657
August	1st to 10th	Night	10% 1 11% 44% 30% 4	597
	11th to 20th	Night	9% 2 15% 40% 30% 3	594
	21st to end	Night	10% 2 16% 35% 34% 4	660
September	1st to 10th	Night	12% 4 17% 36% 27% 4	621
	11th to 20th	Night	11% 3 16% 36% 32% 3	800
	21st to end	Night	17% 5% 24% 30% 20% 3	800
October	1st to 10th	Night	15% 6% 24% 35% 19% 2	800
	11th to 20th	Night	22% 11% 29% 29% 9% 1	800
	21st to end	Night	26% 11% 32% 26% 6%	880
November	1st to 10th	Night	17% 14% 32% 27% 10% 1	820
	11th to 20th	Night	23% 15% 34% 22% 5% 1	840
	21st to end	Night	29% 13% 31% 23% 5%	840
December	1st to 10th	Night	24% 17% 35% 19% 5%	882
	11th to 20th	Night	25% 15% 34% 22% 4	1050
	21st to end	Night	31% 15% 33% 18% 3	1155

Page generated at 2026-06-28 02:10:48. Version ac07

Copyright © 2026 Attilla Danko.