Casey Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Casey Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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	13% 9% 4 7% 6% 3 5% 5% 5% 7% 35%	78584
	Night	13% 10% 4 7% 6% 3 4 4 5% 6% 37%	81265
Transparency	Day	47% 6% 13% 22% 10% 1	78284
	Night	48% 6% 12% 22% 11% 1	81085
Seeing	Day	16% 9% 29% 27% 14% 4	15023
	Night	17% 8% 30% 32% 11% 1	25130

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	11% 17% 9% 14% 6% 3 4 4 5% 5% 23%	2527
	11th to 20th	Day	7% 11% 6% 14% 9% 6% 10% 10% 6% 4 18%	2530
	21st to end	Day	13% 18% 8% 12% 6% 3 3 4 4 6% 23%	3007
February	1st to 10th	Day	8% 12% 5% 9% 7% 3 6% 5% 5% 6% 33%	1710
	11th to 20th	Day	10% 10% 4 8% 6% 5% 5% 4 5% 8% 34%	1664
	21st to end	Day	12% 12% 5% 8% 6% 3 5% 5% 4 7% 31%	1553
March	1st to 10th	Day	14% 10% 5% 6% 6% 3 5% 4 5% 5% 36%	1943
	11th to 20th	Day	13% 10% 4 7% 6% 3 5% 4 5% 7% 35%	2057
	21st to end	Day	18% 11% 4 7% 5% 3 4 4 5% 7% 32%	2268
April	1st to 10th	Day	15% 11% 4 7% 6% 3 4 4 5% 6% 34%	2160
	11th to 20th	Day	22% 10% 4 7% 5% 3 4 4 4 6% 31%	2134
	21st to end	Day	20% 11% 4 6% 6% 3 4 5% 5% 7% 29%	2243
May	1st to 10th	Day	16% 8% 3 7% 6% 3 6% 5% 5% 8% 33%	2520
	11th to 20th	Day	17% 9% 2 6% 6% 4 5% 4 6% 6% 36%	2479
	21st to end	Day	14% 6% 3 6% 6% 3 5% 4 5% 8% 39%	2725
June	1st to 10th	Day	13% 5% 3 5% 5% 3 5% 4 6% 8% 44%	2520
	11th to 20th	Day	12% 6% 3 6% 7% 3 5% 5% 6% 9% 38%	2520
	21st to end	Day	10% 5% 3 5% 5% 3 5% 6% 7% 10% 40%	2520
July	1st to 10th	Day	7% 4 2 4 5% 4 5% 6% 8% 10% 46%	2520
	11th to 20th	Day	9% 4 2 5% 4 3 5% 5% 7% 11% 45%	2520
	21st to end	Day	6% 4 2 4 5% 3 5% 5% 7% 10% 48%	2743
August	1st to 10th	Day	9% 6% 3 5% 5% 4 6% 7% 7% 10% 40%	2406
	11th to 20th	Day	12% 5% 3 6% 5% 3 5% 5% 7% 8% 41%	2301
	21st to end	Day	11% 5% 2 4 4 3 4 4 6% 8% 48%	2386
September	1st to 10th	Day	13% 6% 3 5% 4 3 4 4 4 8% 46%	2160
	11th to 20th	Day	13% 5% 2 6% 5% 3 4 5% 5% 7% 45%	2160
	21st to end	Day	16% 7% 3 4 4 3 5% 5% 6% 7% 41%	1909
October	1st to 10th	Day	16% 7% 3 5% 5% 2 5% 4 6% 6% 41%	1800
	11th to 20th	Day	17% 11% 3 6% 6% 4 4 5% 5% 6% 34%	1800
	21st to end	Day	21% 11% 3 6% 6% 2 3 3 4 6% 36%	1877
November	1st to 10th	Day	13% 9% 4 7% 5% 4 5% 4 6% 6% 38%	1661
	11th to 20th	Day	16% 13% 7% 8% 7% 3 4 4 5% 5% 28%	1520
	21st to end	Day	14% 12% 4 6% 6% 3 4 3 5% 6% 37%	1520
December	1st to 10th	Day	11% 12% 6% 11% 10% 4 7% 5% 5% 6% 24%	1520
	11th to 20th	Day	11% 14% 7% 10% 9% 4 5% 5% 3 5% 27%	1918
	21st to end	Day	21% 17% 8% 13% 8% 2 3 3 3 3 18%	2783
January	1st to 10th	Night	10% 16% 9% 13% 6% 3 4 3 4 4 29%	4428
	11th to 20th	Night	9% 12% 6% 13% 9% 5% 8% 10% 6% 4 20%	4440
	21st to end	Night	13% 19% 8% 11% 7% 4 4 4 4 4 23%	4659
February	1st to 10th	Night	7% 11% 6% 10% 8% 5% 5% 4 5% 5% 34%	2470
	11th to 20th	Night	8% 9% 4 8% 6% 4 6% 4 5% 6% 38%	2403
	21st to end	Night	13% 10% 4 7% 7% 4 5% 4 5% 5% 35%	1900
March	1st to 10th	Night	11% 9% 4 6% 5% 3 5% 4 4 8% 40%	2253
	11th to 20th	Night	11% 9% 4 8% 6% 3 5% 4 4 6% 39%	2068
	21st to end	Night	18% 9% 5% 6% 5% 3 5% 3 4 6% 36%	2088
April	1st to 10th	Night	19% 9% 3 6% 5% 3 4 5% 6% 6% 35%	1800
	11th to 20th	Night	23% 8% 4 6% 5% 3 4 4 5% 5% 34%	1775
	21st to end	Night	20% 9% 3 6% 4 2 4 4 4 8% 36%	1714
May	1st to 10th	Night	21% 7% 3 6% 6% 3 4 5% 5% 6% 34%	1440
	11th to 20th	Night	18% 6% 3 4 5% 3 3 4 5% 8% 41%	1416
	21st to end	Night	13% 6% 3 7% 5% 3 5% 4 5% 7% 42%	1551
June	1st to 10th	Night	11% 5% 2 4 5% 3 5% 5% 6% 8% 45%	1440
	11th to 20th	Night	11% 5% 2 6% 4 3 4 4 7% 7% 45%	1440
	21st to end	Night	8% 4 3 5% 4 3 5% 5% 7% 9% 48%	1440
July	1st to 10th	Night	6% 4 2 4 3 2 4 5% 5% 11% 54%	1440
	11th to 20th	Night	8% 4 1 4 5% 3 4 4 6% 8% 52%	1440
	21st to end	Night	5% 4 1 2 3 2 4 5% 6% 11% 57%	1575
August	1st to 10th	Night	6% 4 2 5% 5% 4 5% 5% 7% 9% 49%	1529
	11th to 20th	Night	11% 5% 2 5% 5% 3 4 3 5% 7% 50%	1600
	21st to end	Night	11% 6% 2 4 4 2 4 4 4 6% 53%	1969
September	1st to 10th	Night	10% 6% 2 5% 5% 3 4 5% 5% 7% 51%	1800
	11th to 20th	Night	11% 5% 2 4 4 3 4 3 5% 8% 51%	1800
	21st to end	Night	14% 5% 2 5% 4 2 3 4 6% 7% 48%	2031
October	1st to 10th	Night	14% 7% 2 5% 4 3 3 4 4 7% 48%	2160
	11th to 20th	Night	16% 9% 3 6% 5% 3 3 4 5% 7% 39%	2160
	21st to end	Night	18% 11% 3 7% 5% 3 4 5% 5% 5% 36%	2478
November	1st to 10th	Night	13% 9% 4 5% 4 3 4 4 4 7% 41%	2415
	11th to 20th	Night	14% 11% 6% 8% 6% 3 4 5% 5% 6% 32%	2660
	21st to end	Night	15% 10% 5% 7% 5% 3 4 4 4 6% 36%	2660
December	1st to 10th	Night	12% 12% 6% 9% 8% 3 4 4 4 6% 30%	2660
	11th to 20th	Night	12% 15% 6% 11% 7% 4 5% 5% 4 6% 26%	3279
	21st to end	Night	25% 15% 6% 10% 6% 3 4 3 3 5% 21%	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	64% 4 12% 16% 4	2528
	11th to 20th	Day	65% 7% 8% 14% 6%	2530
	21st to end	Day	62% 6% 14% 15% 4	3007
February	1st to 10th	Day	50% 6% 13% 19% 10% 1	1710
	11th to 20th	Day	47% 5% 13% 24% 9% 1	1673
	21st to end	Day	52% 5% 10% 21% 10% 2	1553
March	1st to 10th	Day	50% 5% 14% 21% 9% 1	1943
	11th to 20th	Day	48% 5% 14% 22% 10% 1	2057
	21st to end	Day	51% 7% 11% 22% 8% 1	2268
April	1st to 10th	Day	51% 6% 11% 20% 12% 1	2160
	11th to 20th	Day	54% 5% 10% 19% 11% 2	2134
	21st to end	Day	56% 6% 12% 18% 8% 1	2243
May	1st to 10th	Day	48% 7% 13% 22% 9% 1	2520
	11th to 20th	Day	47% 6% 13% 21% 11% 1	2483
	21st to end	Day	44% 8% 11% 23% 12% 2	2725
June	1st to 10th	Day	36% 7% 14% 29% 12% 2	2520
	11th to 20th	Day	43% 7% 13% 25% 12% 1	2520
	21st to end	Day	37% 8% 17% 27% 10% 2	2520
July	1st to 10th	Day	31% 8% 17% 30% 13% 1	2451
	11th to 20th	Day	30% 8% 17% 26% 17% 3	2445
	21st to end	Day	29% 8% 19% 28% 15% 2	2591
August	1st to 10th	Day	36% 9% 16% 28% 9% 2	2391
	11th to 20th	Day	38% 8% 14% 27% 12%	2301
	21st to end	Day	33% 5% 14% 30% 16% 1	2386
September	1st to 10th	Day	36% 6% 13% 29% 14% 1	2160
	11th to 20th	Day	37% 7% 16% 32% 8% 1	2160
	21st to end	Day	41% 7% 14% 29% 9%	1909
October	1st to 10th	Day	41% 6% 12% 29% 11%	1800
	11th to 20th	Day	50% 6% 12% 21% 10% 1	1800
	21st to end	Day	51% 5% 14% 22% 9%	1877
November	1st to 10th	Day	45% 6% 14% 20% 14% 2	1661
	11th to 20th	Day	57% 6% 12% 17% 7% 1	1520
	21st to end	Day	48% 5% 16% 22% 7% 1	1520
December	1st to 10th	Day	60% 6% 13% 16% 5%	1520
	11th to 20th	Day	60% 6% 14% 14% 6% 1	1915
	21st to end	Day	72% 4 7% 13% 4	2783
January	1st to 10th	Night	59% 5% 11% 19% 6%	4428
	11th to 20th	Night	62% 6% 11% 14% 6%	4440
	21st to end	Night	64% 5% 9% 16% 5% 1	4659
February	1st to 10th	Night	52% 4 12% 21% 9% 2	2470
	11th to 20th	Night	45% 6% 13% 27% 8% 1	2404
	21st to end	Night	49% 5% 13% 22% 10% 2	1900
March	1st to 10th	Night	44% 6% 14% 25% 9% 1	2253
	11th to 20th	Night	46% 5% 11% 23% 14% 1	2068
	21st to end	Night	50% 5% 10% 22% 11% 1	2088
April	1st to 10th	Night	49% 6% 9% 18% 17% 2	1800
	11th to 20th	Night	51% 5% 8% 18% 15% 2	1775
	21st to end	Night	48% 6% 9% 21% 14% 2	1714
May	1st to 10th	Night	50% 7% 12% 17% 13% 1	1440
	11th to 20th	Night	42% 6% 10% 25% 15% 2	1417
	21st to end	Night	41% 6% 12% 21% 18% 1	1552
June	1st to 10th	Night	34% 8% 13% 27% 17% 2	1440
	11th to 20th	Night	35% 7% 14% 23% 19% 1	1440
	21st to end	Night	30% 8% 14% 33% 12% 3	1440
July	1st to 10th	Night	24% 7% 13% 35% 20% 2	1400
	11th to 20th	Night	28% 6% 15% 28% 21% 2	1392
	21st to end	Night	21% 8% 18% 31% 19% 5%	1487
August	1st to 10th	Night	30% 8% 14% 28% 16% 3	1520
	11th to 20th	Night	34% 7% 14% 27% 17% 2	1600
	21st to end	Night	31% 7% 14% 29% 17% 4	1969
September	1st to 10th	Night	33% 6% 11% 32% 17% 1	1800
	11th to 20th	Night	31% 6% 15% 32% 16%	1800
	21st to end	Night	35% 6% 13% 32% 13% 1	2031
October	1st to 10th	Night	37% 5% 9% 33% 15% 2	2160
	11th to 20th	Night	44% 6% 14% 23% 13% 1	2160
	21st to end	Night	49% 5% 12% 21% 12% 1	2478
November	1st to 10th	Night	43% 4 13% 25% 14% 1	2415
	11th to 20th	Night	52% 6% 14% 16% 11% 1	2660
	21st to end	Night	49% 5% 15% 23% 7% 1	2660
December	1st to 10th	Night	55% 5% 14% 20% 5%	2660
	11th to 20th	Night	59% 5% 12% 17% 5%	3281
	21st to end	Night	67% 4 10% 14% 4	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	16% 14% 29% 24% 13% 3	270
	11th to 20th	Day	16% 10% 37% 27% 7% 2	270
	21st to end	Day	18% 8% 36% 28% 9% 2	297
February	1st to 10th	Day	14% 13% 40% 23% 7% 2	270
	11th to 20th	Day	14% 16% 37% 24% 8%	270
	21st to end	Day	18% 10% 40% 27% 4	225
March	1st to 10th	Day	19% 14% 34% 20% 12% 1	270
	11th to 20th	Day	19% 11% 32% 25% 10% 2	261
	21st to end	Day	23% 11% 31% 22% 10% 4	354
April	1st to 10th	Day	25% 13% 32% 21% 7% 1	420
	11th to 20th	Day	29% 12% 24% 25% 9% 2	412
	21st to end	Day	26% 13% 27% 23% 9% 3	503
May	1st to 10th	Day	19% 13% 30% 27% 8% 1	603
	11th to 20th	Day	21% 12% 27% 24% 12% 4	625
	21st to end	Day	19% 9% 24% 29% 16% 4	679
June	1st to 10th	Day	11% 7% 25% 34% 18% 5%	630
	11th to 20th	Day	13% 8% 34% 29% 12% 3	630
	21st to end	Day	12% 7% 29% 28% 17% 7%	630
July	1st to 10th	Day	10% 3 19% 30% 27% 12%	621
	11th to 20th	Day	9% 6% 25% 31% 21% 9%	618
	21st to end	Day	7% 4 23% 36% 21% 9%	684
August	1st to 10th	Day	10% 4 22% 32% 24% 8%	626
	11th to 20th	Day	13% 4 20% 29% 27% 7%	615
	21st to end	Day	14% 5% 23% 29% 22% 7%	505
September	1st to 10th	Day	14% 8% 25% 28% 20% 5%	450
	11th to 20th	Day	12% 6% 28% 30% 20% 4	450
	21st to end	Day	18% 12% 28% 27% 12% 3	351
October	1st to 10th	Day	19% 9% 31% 24% 13% 5%	270
	11th to 20th	Day	21% 18% 31% 22% 7% 1	270
	21st to end	Day	27% 17% 33% 15% 6% 2	297
November	1st to 10th	Day	18% 11% 35% 24% 10% 1	270
	11th to 20th	Day	21% 16% 37% 21% 6%	270
	21st to end	Day	21% 15% 38% 18% 7%	270
December	1st to 10th	Day	16% 11% 38% 25% 8% 1	270
	11th to 20th	Day	19% 13% 40% 18% 9% 1	270
	21st to end	Day	26% 11% 38% 21% 3 1	297
January	1st to 10th	Night	13% 11% 35% 31% 9% 1	950
	11th to 20th	Night	18% 9% 34% 30% 7% 1	950
	21st to end	Night	20% 8% 31% 32% 8% 1	1045
February	1st to 10th	Night	13% 10% 38% 30% 8% 1	950
	11th to 20th	Night	13% 11% 39% 29% 8% 1	929
	21st to end	Night	19% 12% 32% 30% 7%	644
March	1st to 10th	Night	15% 10% 37% 30% 6% 1	733
	11th to 20th	Night	16% 10% 32% 34% 6% 1	564
	21st to end	Night	22% 8% 29% 27% 12% 2	594
April	1st to 10th	Night	22% 13% 34% 25% 5% 1	540
	11th to 20th	Night	26% 10% 27% 29% 7%	533
	21st to end	Night	24% 9% 31% 26% 9% 1	540
May	1st to 10th	Night	23% 10% 30% 30% 6%	540
	11th to 20th	Night	20% 8% 29% 32% 10% 2	531
	21st to end	Night	14% 6% 25% 40% 14% 1	584
June	1st to 10th	Night	12% 5% 27% 43% 13%	540
	11th to 20th	Night	14% 4 30% 40% 11%	540
	21st to end	Night	8% 6% 23% 44% 18% 1	540
July	1st to 10th	Night	8% 3 23% 35% 29% 3	525
	11th to 20th	Night	8% 5% 21% 41% 22% 2	522
	21st to end	Night	6% 2 19% 46% 24% 3	591
August	1st to 10th	Night	7% 2 14% 48% 27% 1	537
	11th to 20th	Night	12% 1 19% 39% 25% 3	534
	21st to end	Night	13% 3 22% 36% 23% 2	594
September	1st to 10th	Night	12% 4 23% 39% 18% 4	540
	11th to 20th	Night	12% 4 27% 36% 19% 3	540
	21st to end	Night	16% 8% 31% 29% 15% 1	674
October	1st to 10th	Night	18% 7% 27% 32% 15% 1	720
	11th to 20th	Night	20% 10% 32% 30% 8% 1	720
	21st to end	Night	22% 11% 28% 30% 8%	792
November	1st to 10th	Night	19% 9% 33% 32% 7%	749
	11th to 20th	Night	19% 12% 38% 24% 7%	950
	21st to end	Night	21% 13% 34% 25% 7%	950
December	1st to 10th	Night	19% 10% 35% 28% 8% 1	950
	11th to 20th	Night	22% 9% 36% 25% 8% 1	950
	21st to end	Night	28% 10% 31% 25% 6%	1045

Page generated at 2024-03-15 13:01:40. Version ac07

Copyright © 2024 Attilla Danko.