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 2024-09-29.

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 6% 7% 35%	100772
	Night	16% 11% 4 8% 5% 4 4 3 5% 6% 35%	97488
Transparency	Day	48% 5% 12% 21% 13% 1	100566
	Night	50% 5% 11% 20% 12% 2	97365
Seeing	Day	18% 11% 28% 23% 15% 5%	15566
	Night	19% 10% 29% 29% 12% 1	25371

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	15% 15% 11% 13% 5% 4 4 3 5% 5% 19%	2527
	11th to 20th	Day	14% 17% 8% 12% 7% 6% 4 7% 7% 5% 11%	2530
	21st to end	Day	27% 24% 8% 12% 4 3 3 1 3 3 14%	2845
February	1st to 10th	Day	16% 17% 6% 10% 7% 5% 4 3 5% 5% 23%	1824
	11th to 20th	Day	15% 12% 6% 12% 8% 4 5% 4 4 6% 24%	1848
	21st to end	Day	16% 15% 6% 11% 5% 4 4 3 5% 7% 24%	1570
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	14% 7% 2 5% 3 4 5% 3 5% 8% 43%	2069
October	1st to 10th	Day	14% 6% 2 6% 4 4 4 3 6% 7% 42%	1980
	11th to 20th	Day	18% 8% 3 7% 5% 4 4 5% 6% 7% 35%	1799
	21st to end	Day	21% 11% 4 9% 5% 5% 4 3 5% 6% 28%	1782
November	1st to 10th	Day	12% 9% 3 6% 4 4 4 3 5% 6% 44%	1672
	11th to 20th	Day	17% 16% 4 8% 5% 3 3 3 4 7% 30%	1710
	21st to end	Day	21% 15% 5% 9% 5% 4 3 3 4 5% 27%	1710
December	1st to 10th	Day	15% 19% 5% 12% 5% 4 3 4 4 6% 22%	1668
	11th to 20th	Day	13% 17% 8% 12% 6% 4 3 4 4 5% 23%	1918
	21st to end	Day	23% 22% 7% 14% 5% 4 4 3 3 4 10%	2783
January	1st to 10th	Night	17% 17% 8% 11% 6% 4 4 3 5% 5% 20%	4428
	11th to 20th	Night	15% 20% 7% 15% 6% 5% 5% 5% 6% 4 13%	4440
	21st to end	Night	26% 18% 9% 11% 4 3 3 3 3 4 16%	4818
February	1st to 10th	Night	19% 14% 5% 10% 6% 4 3 4 5% 5% 25%	2352
	11th to 20th	Night	14% 14% 5% 10% 7% 4 5% 3 5% 6% 29%	2218
	21st to end	Night	21% 13% 5% 10% 5% 3 4 3 3 5% 29%	1884
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 6% 47%	2079
October	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 5% 7% 48%	1980
	11th to 20th	Night	19% 8% 2 6% 5% 4 4 3 4 7% 39%	2156
	21st to end	Night	22% 9% 2 6% 4 3 3 3 4 6% 36%	2574
November	1st to 10th	Night	13% 9% 3 7% 4 4 4 3 5% 7% 42%	2406
	11th to 20th	Night	16% 13% 4 7% 4 4 4 3 6% 7% 32%	2470
	21st to end	Night	20% 15% 4 8% 5% 3 4 4 5% 6% 27%	2470
December	1st to 10th	Night	17% 15% 6% 9% 5% 5% 5% 3 5% 6% 23%	2508
	11th to 20th	Night	17% 16% 7% 12% 6% 4 4 3 4 4 22%	3279
	21st to end	Night	26% 18% 8% 10% 5% 4 4 3 4 4 13%	4884

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	67% 4 11% 14% 5%	2528
	11th to 20th	Day	72% 5% 8% 10% 5%	2530
	21st to end	Day	79% 2 7% 9% 3	2845
February	1st to 10th	Day	63% 5% 10% 14% 7% 1	1824
	11th to 20th	Day	61% 5% 9% 17% 8% 1	1858
	21st to end	Day	60% 5% 12% 16% 6% 1	1570
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	2069
October	1st to 10th	Day	40% 6% 12% 24% 17% 2	1980
	11th to 20th	Day	47% 5% 11% 21% 16%	1799
	21st to end	Day	57% 4 12% 17% 9% 1	1782
November	1st to 10th	Day	41% 6% 12% 25% 16% 1	1672
	11th to 20th	Day	56% 4 11% 18% 10% 1	1710
	21st to end	Day	61% 4 12% 17% 6% 1	1710
December	1st to 10th	Day	63% 5% 11% 14% 6%	1668
	11th to 20th	Day	63% 5% 11% 17% 4	1915
	21st to end	Day	79% 4 6% 7% 4	2783
January	1st to 10th	Night	65% 6% 10% 13% 6%	4428
	11th to 20th	Night	74% 3 9% 11% 3	4440
	21st to end	Night	73% 3 9% 11% 3	4818
February	1st to 10th	Night	61% 5% 11% 14% 8% 2	2352
	11th to 20th	Night	56% 5% 10% 19% 9% 1	2219
	21st to end	Night	59% 4 11% 16% 9% 2	1884
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% 5% 9% 27% 19% 2	2079
October	1st to 10th	Night	36% 5% 9% 28% 20% 1	1980
	11th to 20th	Night	46% 4 9% 23% 16% 1	2156
	21st to end	Night	50% 4 11% 21% 13% 1	2574
November	1st to 10th	Night	41% 4 11% 25% 17% 2	2406
	11th to 20th	Night	51% 5% 13% 20% 11% 1	2470
	21st to end	Night	58% 4 12% 19% 6%	2470
December	1st to 10th	Night	61% 5% 12% 15% 7%	2508
	11th to 20th	Night	64% 5% 11% 13% 6% 1	3281
	21st to end	Night	74% 5% 10% 8% 3	4884

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% 35% 16% 5%	270
	11th to 20th	Day	26% 16% 42% 13% 4	270
	21st to end	Day	33% 15% 30% 18% 3	297
February	1st to 10th	Day	25% 21% 34% 16% 4	270
	11th to 20th	Day	25% 21% 36% 14% 3	270
	21st to end	Day	27% 28% 34% 8% 4	225
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	20% 10% 18% 25% 21% 6%	483
October	1st to 10th	Day	14% 6% 28% 28% 16% 8%	450
	11th to 20th	Day	20% 18% 30% 23% 10%	385
	21st to end	Day	32% 14% 35% 16% 2	297
November	1st to 10th	Day	15% 14% 35% 22% 11% 3	270
	11th to 20th	Day	26% 16% 33% 16% 8%	270
	21st to end	Day	31% 14% 37% 14% 3	270
December	1st to 10th	Day	24% 20% 35% 14% 7%	270
	11th to 20th	Day	20% 21% 37% 16% 4	270
	21st to end	Day	27% 22% 38% 12% 1	297
January	1st to 10th	Night	24% 16% 35% 21% 4	950
	11th to 20th	Night	25% 16% 35% 20% 4 1	950
	21st to end	Night	23% 14% 36% 24% 3	1005
February	1st to 10th	Night	27% 12% 34% 23% 4	760
	11th to 20th	Night	21% 14% 38% 24% 2	743
	21st to end	Night	28% 15% 36% 18% 3	628
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	756
October	1st to 10th	Night	16% 6% 24% 33% 18% 3	720
	11th to 20th	Night	22% 12% 29% 28% 8% 1	720
	21st to end	Night	28% 10% 31% 25% 6%	792
November	1st to 10th	Night	16% 14% 31% 27% 11% 1	740
	11th to 20th	Night	23% 15% 34% 22% 6% 1	760
	21st to end	Night	27% 11% 31% 25% 5%	760
December	1st to 10th	Night	24% 17% 34% 19% 5%	798
	11th to 20th	Night	24% 15% 34% 22% 5%	950
	21st to end	Night	31% 15% 33% 18% 3	1045

Page generated at 2024-09-26 09:52:19. Version ac07

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