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 2025-02-25.

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	14% 10% 4 8% 5% 4 4 4 5% 7% 34%	108482
	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 33%	110311
Transparency	Day	49% 5% 12% 21% 13% 1	112095
	Night	50% 4 11% 20% 13% 1	114838
Seeing	Day	18% 11% 28% 23% 14% 5%	16030
	Night	19% 10% 29% 28% 12% 1	26017

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	12% 14% 11% 21% 7% 4 4 3 4 4 17%	3617
	11th to 20th	Day	13% 16% 9% 13% 7% 7% 5% 6% 6% 5% 15%	3620
	21st to end	Day	21% 19% 8% 14% 4 3 3 2 3 4 18%	4070
February	1st to 10th	Day	15% 17% 7% 11% 7% 5% 4 3 5% 5% 22%	1920
	11th to 20th	Day	15% 12% 6% 13% 8% 4 5% 4 4 6% 23%	1948
	21st to end	Day	16% 15% 6% 11% 5% 4 4 3 5% 7% 25%	1610
March	1st to 10th	Day	19% 16% 6% 9% 4 5% 3 3 4 6% 25%	3120
	11th to 20th	Day	13% 8% 5% 7% 5% 4 5% 4 6% 8% 33%	3384
	21st to end	Day	19% 13% 5% 10% 5% 5% 4 3 4 6% 24%	3941
April	1st to 10th	Day	17% 14% 4 7% 5% 4 4 3 5% 6% 31%	2280
	11th to 20th	Day	18% 9% 3 6% 4 5% 4 4 5% 6% 36%	2278
	21st to end	Day	19% 9% 2 7% 4 4 5% 4 5% 7% 34%	2470
May	1st to 10th	Day	20% 8% 3 7% 4 4 4 4 6% 7% 32%	4082
	11th to 20th	Day	16% 7% 2 6% 5% 4 5% 4 6% 8% 38%	4081
	21st to end	Day	10% 5% 2 6% 5% 4 4 4 7% 9% 43%	4680
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 4 4 7% 7% 43%	2660
	11th to 20th	Day	9% 6% 2 5% 4 5% 4 5% 7% 8% 44%	2660
	21st to end	Day	12% 5% 2 6% 6% 5% 6% 5% 6% 9% 40%	2660
July	1st to 10th	Day	13% 6% 3 7% 5% 4 5% 4 6% 9% 38%	4440
	11th to 20th	Day	8% 4 1 5% 3 4 5% 4 8% 10% 47%	4440
	21st to end	Day	7% 7% 3 7% 6% 6% 5% 4 6% 9% 41%	4734
August	1st to 10th	Day	9% 5% 2 7% 4 5% 5% 4 6% 8% 46%	4104
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 6% 8% 46%	4013
	21st to end	Day	7% 4 2 6% 4 4 4 4 6% 9% 49%	4180
September	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 4 6% 7% 46%	2240
	11th to 20th	Day	10% 4 2 5% 3 4 5% 4 7% 8% 49%	2090
	21st to end	Day	13% 7% 2 6% 3 4 5% 3 5% 8% 43%	2090
October	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 6% 7% 44%	2090
	11th to 20th	Day	17% 7% 3 7% 4 4 4 4 6% 7% 36%	1898
	21st to end	Day	20% 11% 3 8% 5% 5% 4 3 5% 7% 28%	1881
November	1st to 10th	Day	12% 9% 3 6% 4 4 4 3 5% 6% 43%	1762
	11th to 20th	Day	17% 16% 4 8% 6% 3 3 3 4 7% 29%	1800
	21st to end	Day	21% 15% 5% 9% 5% 4 3 3 4 5% 26%	1800
December	1st to 10th	Day	11% 16% 4 12% 5% 5% 4 4 5% 7% 28%	2849
	11th to 20th	Day	16% 17% 9% 13% 5% 4 3 3 4 5% 21%	3008
	21st to end	Day	28% 20% 6% 13% 5% 4 4 3 3 3 11%	3982
January	1st to 10th	Night	15% 16% 7% 17% 6% 4 4 3 4 4 19%	6348
	11th to 20th	Night	13% 19% 8% 16% 7% 5% 5% 4 5% 4 15%	6360
	21st to end	Night	20% 14% 7% 11% 5% 4 4 3 4 4 24%	6888
February	1st to 10th	Night	18% 15% 5% 10% 6% 4 3 4 5% 5% 25%	2475
	11th to 20th	Night	14% 13% 5% 10% 7% 5% 4 3 5% 6% 28%	2338
	21st to end	Night	20% 13% 4 10% 5% 3 4 3 3 5% 29%	1939
March	1st to 10th	Night	17% 12% 4 7% 5% 4 4 2 4 7% 34%	3733
	11th to 20th	Night	10% 8% 3 6% 5% 5% 5% 3 5% 7% 43%	3576
	21st to end	Night	18% 10% 4 9% 4 4 4 3 5% 6% 33%	3704
April	1st to 10th	Night	16% 10% 2 5% 5% 4 4 4 5% 7% 37%	1900
	11th to 20th	Night	19% 8% 3 7% 5% 4 4 4 4 6% 37%	1850
	21st to end	Night	17% 9% 3 7% 5% 4 4 4 6% 5% 36%	1710
May	1st to 10th	Night	16% 9% 3 7% 5% 4 5% 4 6% 8% 32%	2813
	11th to 20th	Night	20% 6% 3 6% 4 4 3 3 5% 8% 38%	2812
	21st to end	Night	13% 6% 2 5% 4 4 3 4 6% 7% 45%	2878
June	1st to 10th	Night	10% 5% 2 6% 4 3 5% 3 7% 8% 48%	1520
	11th to 20th	Night	7% 6% 3 6% 5% 4 5% 4 5% 8% 47%	1520
	21st to end	Night	10% 6% 2 6% 5% 4 4 4 7% 10% 43%	1520
July	1st to 10th	Night	9% 5% 2 6% 5% 5% 4 4 6% 9% 46%	2530
	11th to 20th	Night	7% 4 1 4 3 4 4 4 5% 9% 55%	2530
	21st to end	Night	8% 6% 2 7% 4 4 4 5% 7% 9% 44%	2823
August	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 7% 9% 44%	2825
	11th to 20th	Night	9% 6% 2 5% 4 4 4 3 6% 8% 48%	2812
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 8% 50%	3476
September	1st to 10th	Night	11% 5% 2 5% 4 4 3 3 4 8% 52%	1920
	11th to 20th	Night	9% 4 1 5% 3 3 3 3 5% 8% 56%	2090
	21st to end	Night	13% 7% 3 6% 4 4 4 4 4 5% 47%	2090
October	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 5% 6% 50%	2090
	11th to 20th	Night	18% 8% 2 6% 5% 4 3 3 4 6% 40%	2277
	21st to end	Night	21% 8% 2 6% 4 3 3 3 5% 6% 37%	2717
November	1st to 10th	Night	14% 8% 3 6% 4 4 4 3 5% 7% 43%	2536
	11th to 20th	Night	16% 13% 4 7% 4 4 4 3 6% 7% 32%	2600
	21st to end	Night	20% 15% 4 8% 5% 3 3 4 5% 6% 26%	2600
December	1st to 10th	Night	13% 11% 5% 10% 5% 6% 5% 4 6% 7% 28%	4316
	11th to 20th	Night	17% 18% 8% 13% 5% 4 4 3 4 4 19%	5199
	21st to end	Night	26% 19% 7% 11% 5% 4 4 3 4 4 12%	6996

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% 3 8% 13% 4	3618
	11th to 20th	Day	71% 3 8% 8% 8% 1	3620
	21st to end	Day	73% 1 8% 12% 6%	4070
February	1st to 10th	Day	64% 5% 10% 13% 7% 1	1920
	11th to 20th	Day	63% 4 8% 16% 8% 1	1958
	21st to end	Day	59% 4 12% 16% 7% 1	1610
March	1st to 10th	Day	61% 5% 8% 19% 7%	3120
	11th to 20th	Day	47% 6% 13% 27% 8% 1	3384
	21st to end	Day	61% 5% 13% 17% 3	3941
April	1st to 10th	Day	54% 5% 10% 19% 11%	2280
	11th to 20th	Day	49% 5% 10% 22% 12% 2	2278
	21st to end	Day	49% 6% 12% 19% 12% 2	2470
May	1st to 10th	Day	49% 7% 12% 23% 9%	4120
	11th to 20th	Day	44% 6% 15% 25% 9% 1	4085
	21st to end	Day	35% 7% 12% 23% 21% 2	4693
June	1st to 10th	Day	38% 6% 11% 25% 17% 2	2660
	11th to 20th	Day	36% 6% 12% 26% 18% 3	2660
	21st to end	Day	40% 8% 15% 19% 16% 3	2660
July	1st to 10th	Day	44% 5% 12% 21% 16% 3	4371
	11th to 20th	Day	31% 4 15% 31% 18% 1	4365
	21st to end	Day	40% 5% 15% 17% 20% 3	4584
August	1st to 10th	Day	36% 5% 15% 27% 16% 1	4091
	11th to 20th	Day	36% 5% 13% 29% 17% 1	4052
	21st to end	Day	33% 4 13% 28% 18% 3	4179
September	1st to 10th	Day	37% 7% 14% 20% 18% 3	2240
	11th to 20th	Day	32% 6% 12% 26% 22% 2	2090
	21st to end	Day	39% 6% 10% 25% 19% 1	2090
October	1st to 10th	Day	29% 3 10% 35% 22% 1	3480
	11th to 20th	Day	39% 3 11% 21% 25%	3127
	21st to end	Day	47% 3 10% 26% 12% 1	3081
November	1st to 10th	Day	41% 5% 12% 25% 15% 1	1762
	11th to 20th	Day	57% 3 10% 18% 11% 1	1800
	21st to end	Day	61% 4 11% 17% 6% 1	1800
December	1st to 10th	Day	57% 3 15% 20% 4	2849
	11th to 20th	Day	67% 3 10% 16% 4	3005
	21st to end	Day	80% 3 6% 8% 4	3982
January	1st to 10th	Night	68% 4 8% 15% 5%	6348
	11th to 20th	Night	74% 2 7% 8% 8%	6360
	21st to end	Night	65% 2 12% 13% 7%	6888
February	1st to 10th	Night	61% 4 11% 14% 8% 2	2475
	11th to 20th	Night	58% 4 9% 19% 9% 1	2339
	21st to end	Night	58% 3 12% 16% 8% 2	1939
March	1st to 10th	Night	51% 5% 11% 24% 8% 1	3733
	11th to 20th	Night	40% 6% 11% 27% 14% 2	3576
	21st to end	Night	51% 6% 13% 22% 7% 1	3704
April	1st to 10th	Night	45% 7% 12% 20% 14% 1	1900
	11th to 20th	Night	48% 4 8% 20% 16% 2	1850
	21st to end	Night	48% 5% 11% 20% 14% 3	1710
May	1st to 10th	Night	49% 7% 10% 21% 11% 1	2840
	11th to 20th	Night	43% 7% 11% 28% 11% 1	2813
	21st to end	Night	37% 6% 13% 20% 21% 3	2886
June	1st to 10th	Night	32% 6% 12% 29% 19% 3	1520
	11th to 20th	Night	35% 7% 11% 24% 19% 3	1520
	21st to end	Night	36% 6% 18% 21% 16% 3	1520
July	1st to 10th	Night	37% 5% 13% 24% 16% 6%	2490
	11th to 20th	Night	28% 4 16% 27% 24% 2	2482
	21st to end	Night	36% 4 17% 17% 23% 4	2733
August	1st to 10th	Night	36% 6% 14% 29% 14% 1	2814
	11th to 20th	Night	34% 5% 11% 30% 18% 1	2839
	21st to end	Night	34% 4 10% 29% 20% 3	3476
September	1st to 10th	Night	33% 5% 13% 24% 20% 5%	1920
	11th to 20th	Night	27% 5% 9% 31% 25% 3	2090
	21st to end	Night	39% 4 9% 27% 19% 2	2090
October	1st to 10th	Night	24% 3 7% 34% 31% 1	3480
	11th to 20th	Night	38% 2 8% 24% 27% 1	3787
	21st to end	Night	38% 2 9% 30% 19% 1	4467
November	1st to 10th	Night	41% 4 10% 26% 16% 1	2536
	11th to 20th	Night	51% 4 12% 20% 11% 2	2600
	21st to end	Night	59% 4 12% 19% 6%	2600
December	1st to 10th	Night	56% 3 13% 22% 5%	4316
	11th to 20th	Night	69% 3 11% 9% 6% 1	5201
	21st to end	Night	77% 3 8% 8% 3	6996

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	21% 22% 36% 16% 5%	300
	11th to 20th	Day	25% 18% 41% 12% 3	300
	21st to end	Day	31% 17% 33% 16% 3	330
February	1st to 10th	Day	26% 22% 34% 14% 3	300
	11th to 20th	Day	26% 22% 35% 14% 3	300
	21st to end	Day	26% 27% 35% 8% 4	237
March	1st to 10th	Day	23% 22% 38% 14% 3	270
	11th to 20th	Day	26% 13% 33% 21% 6%	403
	21st to end	Day	32% 16% 28% 18% 5% 2	506
April	1st to 10th	Day	23% 15% 33% 20% 7% 1	460
	11th to 20th	Day	23% 18% 31% 17% 9% 3	452
	21st to end	Day	25% 14% 31% 19% 9% 2	460
May	1st to 10th	Day	25% 13% 31% 19% 8% 3	463
	11th to 20th	Day	21% 11% 26% 23% 14% 5%	487
	21st to end	Day	13% 6% 30% 26% 17% 8%	642
June	1st to 10th	Day	12% 9% 29% 28% 17% 5%	680
	11th to 20th	Day	12% 7% 30% 27% 18% 6%	680
	21st to end	Day	13% 7% 28% 30% 16% 6%	680
July	1st to 10th	Day	12% 3 19% 30% 22% 13%	671
	11th to 20th	Day	9% 4 25% 29% 23% 11%	668
	21st to end	Day	9% 4 20% 30% 25% 11%	696
August	1st to 10th	Day	11% 3 14% 28% 28% 15%	486
	11th to 20th	Day	11% 4 22% 28% 27% 9%	479
	21st to end	Day	10% 4 15% 29% 30% 12%	539
September	1st to 10th	Day	14% 5% 20% 27% 26% 9%	490
	11th to 20th	Day	9% 4 15% 24% 35% 13%	490
	21st to end	Day	21% 9% 19% 25% 21% 6%	490
October	1st to 10th	Day	13% 7% 28% 29% 17% 7%	490
	11th to 20th	Day	19% 17% 29% 23% 11%	421
	21st to end	Day	30% 15% 35% 18% 2	330
November	1st to 10th	Day	17% 15% 34% 22% 10% 3	300
	11th to 20th	Day	27% 16% 34% 16% 8%	300
	21st to end	Day	32% 15% 36% 14% 3	300
December	1st to 10th	Day	24% 19% 37% 14% 6%	300
	11th to 20th	Day	21% 22% 37% 15% 4	300
	21st to end	Day	29% 21% 36% 12% 2	330
January	1st to 10th	Night	24% 16% 35% 21% 4	1000
	11th to 20th	Night	25% 16% 35% 19% 4 1	1000
	21st to end	Night	22% 14% 37% 23% 3	1057
February	1st to 10th	Night	27% 12% 34% 23% 4	800
	11th to 20th	Night	22% 15% 37% 24% 2	783
	21st to end	Night	28% 15% 37% 18% 3	647
March	1st to 10th	Night	20% 14% 35% 25% 6% 1	760
	11th to 20th	Night	18% 14% 37% 26% 5% 1	760
	21st to end	Night	26% 11% 30% 28% 5%	774
April	1st to 10th	Night	19% 13% 35% 26% 6% 1	570
	11th to 20th	Night	22% 12% 33% 25% 7% 1	563
	21st to end	Night	21% 9% 35% 26% 8% 1	570
May	1st to 10th	Night	21% 7% 34% 31% 8%	570
	11th to 20th	Night	22% 5% 27% 30% 15% 1	561
	21st to end	Night	14% 4 26% 37% 18% 1	617
June	1st to 10th	Night	11% 4 26% 42% 16%	570
	11th to 20th	Night	8% 3 29% 42% 16% 1	570
	21st to end	Night	11% 3 24% 36% 24% 2	570
July	1st to 10th	Night	9% 1 16% 41% 29% 4	555
	11th to 20th	Night	10% 3 15% 39% 29% 3	552
	21st to end	Night	8% 2 16% 40% 32% 2	624
August	1st to 10th	Night	10% 1 12% 44% 29% 5%	567
	11th to 20th	Night	9% 2 15% 40% 29% 4	564
	21st to end	Night	11% 2 16% 33% 34% 4	627
September	1st to 10th	Night	12% 4 17% 37% 27% 4	590
	11th to 20th	Night	11% 3 16% 35% 32% 3	760
	21st to end	Night	17% 6% 25% 30% 19% 3	760
October	1st to 10th	Night	15% 6% 24% 34% 18% 3	760
	11th to 20th	Night	22% 11% 29% 28% 9% 1	760
	21st to end	Night	27% 11% 31% 25% 6%	836
November	1st to 10th	Night	17% 14% 31% 27% 11% 1	780
	11th to 20th	Night	23% 15% 34% 22% 5% 1	800
	21st to end	Night	27% 12% 32% 24% 5%	800
December	1st to 10th	Night	24% 17% 35% 19% 5%	840
	11th to 20th	Night	25% 15% 34% 22% 4	1000
	21st to end	Night	31% 14% 33% 19% 3	1100

Page generated at 2025-02-22 06:51:34. Version ac07

Copyright © 2025 Attilla Danko.