Clay Center Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clay Center Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	17% 7% 2 6% 4 4 4 4 5% 7% 39%	101188
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 39%	97829
Transparency	Day	43% 7% 12% 22% 15% 2	104752
	Night	44% 6% 12% 22% 15% 2	102354
Seeing	Day	23% 17% 33% 18% 7% 2	15075
	Night	21% 14% 34% 23% 6% 1	23947

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	14% 8% 2 7% 3 3 3 4 4 6% 46%	2517
	11th to 20th	Day	17% 7% 3 7% 3 3 4 4 5% 5% 42%	2520
	21st to end	Day	21% 11% 3 7% 4 4 4 3 5% 6% 33%	2772
February	1st to 10th	Day	20% 7% 3 5% 4 5% 5% 4 5% 7% 37%	1781
	11th to 20th	Day	13% 7% 3 6% 4 5% 4 4 5% 7% 42%	1848
	21st to end	Day	17% 10% 2 5% 5% 3 5% 4 5% 7% 37%	1570
March	1st to 10th	Day	24% 14% 2 6% 4 3 4 3 5% 5% 30%	3116
	11th to 20th	Day	13% 7% 2 5% 4 4 5% 5% 6% 8% 41%	3347
	21st to end	Day	24% 8% 2 6% 4 4 4 3 6% 5% 34%	4001
April	1st to 10th	Day	18% 9% 3 6% 5% 4 4 4 3 7% 36%	2280
	11th to 20th	Day	18% 7% 2 5% 5% 4 4 4 5% 8% 38%	2276
	21st to end	Day	19% 6% 3 6% 4 4 4 4 6% 7% 37%	2470
May	1st to 10th	Day	23% 12% 3 8% 5% 4 4 3 5% 6% 27%	4106
	11th to 20th	Day	23% 9% 3 7% 5% 3 4 4 4 6% 32%	4112
	21st to end	Day	15% 5% 2 5% 4 4 3 3 5% 8% 44%	4837
June	1st to 10th	Day	20% 5% 2 6% 4 5% 5% 4 7% 9% 34%	2660
	11th to 20th	Day	16% 6% 2 6% 4 4 5% 4 6% 8% 38%	2660
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 4 6% 9% 34%	2660
July	1st to 10th	Day	13% 7% 2 6% 5% 6% 6% 5% 7% 9% 35%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 10% 40%	4440
	21st to end	Day	16% 7% 3 7% 5% 5% 5% 4 6% 7% 35%	4814
August	1st to 10th	Day	15% 6% 3 7% 5% 5% 6% 5% 7% 8% 32%	4119
	11th to 20th	Day	13% 8% 3 7% 4 4 5% 4 6% 8% 39%	4014
	21st to end	Day	7% 4 2 5% 4 4 5% 4 7% 10% 47%	4180
September	1st to 10th	Day	14% 5% 2 5% 4 4 4 3 5% 7% 47%	2266
	11th to 20th	Day	15% 6% 2 5% 3 3 2 3 4 6% 52%	2090
	21st to end	Day	18% 5% 3 6% 4 3 4 3 5% 7% 43%	2090
October	1st to 10th	Day	24% 5% 2 5% 3 4 3 3 4 6% 41%	2090
	11th to 20th	Day	14% 6% 2 5% 3 3 4 3 5% 6% 48%	1862
	21st to end	Day	19% 7% 3 5% 3 4 4 3 5% 6% 41%	1881
November	1st to 10th	Day	16% 7% 2 4 4 3 3 3 3 5% 49%	1698
	11th to 20th	Day	18% 8% 2 4 3 3 4 3 5% 5% 46%	1710
	21st to end	Day	17% 8% 2 4 4 4 4 3 5% 6% 43%	1710
December	1st to 10th	Day	18% 7% 3 6% 5% 4 5% 2 5% 6% 40%	1573
	11th to 20th	Day	21% 8% 3 4 3 3 3 2 4 6% 44%	1906
	21st to end	Day	21% 10% 3 7% 4 4 4 2 4 5% 35%	2772
January	1st to 10th	Night	17% 9% 3 4 3 3 3 3 4 5% 47%	4429
	11th to 20th	Night	14% 9% 3 9% 5% 4 3 2 4 5% 40%	4440
	21st to end	Night	21% 14% 4 8% 5% 4 4 3 4 5% 30%	4884
February	1st to 10th	Night	17% 9% 2 6% 5% 4 4 3 5% 7% 38%	2396
	11th to 20th	Night	15% 9% 3 7% 4 4 4 4 5% 6% 40%	2218
	21st to end	Night	18% 9% 2 5% 4 3 4 3 4 6% 42%	1884
March	1st to 10th	Night	29% 10% 2 4 3 4 3 3 4 5% 32%	3724
	11th to 20th	Night	11% 10% 3 7% 4 4 5% 4 6% 6% 40%	3612
	21st to end	Night	24% 9% 2 6% 5% 4 4 4 5% 4 33%	3626
April	1st to 10th	Night	18% 9% 2 6% 5% 4 4 4 5% 7% 36%	1900
	11th to 20th	Night	18% 9% 2 6% 4 4 4 3 5% 6% 39%	1851
	21st to end	Night	21% 6% 3 6% 4 4 4 3 5% 5% 39%	1710
May	1st to 10th	Night	24% 11% 4 7% 5% 4 4 3 6% 6% 28%	2834
	11th to 20th	Night	23% 9% 3 7% 5% 5% 5% 4 6% 7% 26%	2796
	21st to end	Night	16% 7% 2 6% 4 3 4 3 6% 9% 40%	2738
June	1st to 10th	Night	17% 9% 3 7% 3 5% 4 4 5% 7% 37%	1520
	11th to 20th	Night	17% 7% 3 6% 4 4 4 4 6% 8% 37%	1520
	21st to end	Night	16% 5% 2 5% 4 4 5% 5% 5% 10% 39%	1520
July	1st to 10th	Night	11% 6% 3 8% 6% 4 6% 5% 7% 10% 35%	2520
	11th to 20th	Night	11% 7% 2 7% 5% 4 5% 4 6% 10% 39%	2520
	21st to end	Night	16% 9% 3 7% 5% 5% 5% 4 5% 7% 35%	2739
August	1st to 10th	Night	19% 7% 3 7% 5% 6% 5% 5% 6% 8% 31%	2780
	11th to 20th	Night	9% 7% 3 8% 5% 6% 6% 5% 7% 7% 37%	2809
	21st to end	Night	9% 4 1 4 4 4 4 3 5% 8% 55%	3476
September	1st to 10th	Night	12% 5% 2 6% 4 5% 5% 3 6% 6% 46%	1913
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 4 7% 53%	2090
	21st to end	Night	18% 6% 2 6% 4 3 4 4 6% 5% 43%	2090
October	1st to 10th	Night	20% 6% 2 6% 3 5% 3 3 4 6% 42%	2090
	11th to 20th	Night	15% 5% 2 5% 3 4 4 3 5% 6% 47%	2315
	21st to end	Night	20% 7% 3 6% 3 4 3 3 5% 6% 40%	2717
November	1st to 10th	Night	14% 5% 2 6% 4 4 3 3 5% 5% 49%	2453
	11th to 20th	Night	16% 8% 2 5% 4 3 4 3 4 4 46%	2470
	21st to end	Night	17% 6% 2 5% 4 3 4 3 5% 6% 45%	2470
December	1st to 10th	Night	19% 8% 3 6% 4 3 4 3 5% 6% 39%	2603
	11th to 20th	Night	19% 7% 3 5% 3 3 4 3 5% 5% 41%	3288
	21st to end	Night	20% 10% 3 7% 4 4 3 3 5% 6% 35%	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	41% 5% 8% 31% 13% 2	2518
	11th to 20th	Day	45% 7% 9% 25% 12% 2	2520
	21st to end	Day	51% 6% 11% 21% 9% 1	2772
February	1st to 10th	Day	48% 6% 13% 18% 14% 3	1781
	11th to 20th	Day	43% 6% 12% 21% 15% 3	1857
	21st to end	Day	47% 6% 10% 19% 14% 3	1570
March	1st to 10th	Day	57% 5% 11% 15% 10% 2	3119
	11th to 20th	Day	37% 9% 15% 24% 14% 2	3347
	21st to end	Day	50% 6% 7% 16% 15% 6%	4001
April	1st to 10th	Day	48% 5% 10% 18% 16% 3	2280
	11th to 20th	Day	43% 7% 11% 21% 16% 3	2276
	21st to end	Day	46% 6% 10% 19% 16% 4	2470
May	1st to 10th	Day	55% 9% 10% 14% 10% 1	4120
	11th to 20th	Day	51% 9% 14% 14% 10% 2	4116
	21st to end	Day	36% 7% 12% 24% 19% 2	4837
June	1st to 10th	Day	45% 7% 13% 22% 11% 1	2660
	11th to 20th	Day	42% 8% 14% 19% 15% 2	2660
	21st to end	Day	44% 7% 14% 20% 13% 1	2660
July	1st to 10th	Day	44% 9% 11% 20% 14% 1	4370
	11th to 20th	Day	39% 8% 15% 23% 13% 2	4365
	21st to end	Day	47% 7% 12% 19% 13% 2	4661
August	1st to 10th	Day	47% 9% 16% 20% 8% 1	4105
	11th to 20th	Day	43% 7% 13% 27% 10%	4053
	21st to end	Day	31% 8% 12% 30% 18% 2	4180
September	1st to 10th	Day	37% 6% 12% 23% 21% 2	2266
	11th to 20th	Day	35% 4 10% 26% 22% 3	2090
	21st to end	Day	42% 6% 8% 20% 22% 2	2090
October	1st to 10th	Day	40% 5% 9% 24% 18% 4	3480
	11th to 20th	Day	31% 4 7% 28% 26% 4	3078
	21st to end	Day	32% 5% 11% 28% 21% 3	3081
November	1st to 10th	Day	39% 4 12% 25% 17% 2	1698
	11th to 20th	Day	40% 4 10% 23% 20% 2	1710
	21st to end	Day	42% 6% 13% 24% 12% 2	1710
December	1st to 10th	Day	46% 5% 14% 16% 17% 1	1573
	11th to 20th	Day	44% 4 14% 17% 16% 6%	1906
	21st to end	Day	52% 5% 11% 20% 11% 1	2772
January	1st to 10th	Night	39% 4 11% 30% 12% 3	4429
	11th to 20th	Night	46% 5% 11% 23% 11% 3	4440
	21st to end	Night	57% 6% 9% 15% 11% 2	4884
February	1st to 10th	Night	46% 5% 13% 21% 14% 2	2396
	11th to 20th	Night	46% 5% 10% 20% 16% 4	2220
	21st to end	Night	45% 4 9% 23% 15% 4	1884
March	1st to 10th	Night	54% 5% 9% 18% 11% 3	3734
	11th to 20th	Night	40% 8% 14% 18% 17% 2	3613
	21st to end	Night	53% 4 6% 13% 17% 7%	3626
April	1st to 10th	Night	47% 6% 10% 19% 15% 3	1900
	11th to 20th	Night	46% 5% 9% 20% 17% 3	1851
	21st to end	Night	45% 7% 10% 18% 16% 4	1710
May	1st to 10th	Night	55% 9% 12% 16% 8% 2	2840
	11th to 20th	Night	54% 11% 13% 13% 8% 2	2797
	21st to end	Night	40% 8% 15% 22% 14% 1	2739
June	1st to 10th	Night	46% 7% 13% 21% 11% 1	1520
	11th to 20th	Night	44% 7% 13% 22% 13% 1	1520
	21st to end	Night	41% 9% 14% 23% 13% 1	1520
July	1st to 10th	Night	43% 8% 13% 21% 15%	2480
	11th to 20th	Night	40% 7% 16% 23% 12% 1	2472
	21st to end	Night	48% 7% 10% 18% 14% 1	2651
August	1st to 10th	Night	51% 8% 14% 18% 9% 1	2770
	11th to 20th	Night	42% 10% 14% 24% 10%	2836
	21st to end	Night	27% 6% 16% 28% 23% 1	3476
September	1st to 10th	Night	38% 7% 11% 23% 19% 1	1913
	11th to 20th	Night	33% 6% 10% 23% 26% 2	2090
	21st to end	Night	42% 7% 9% 21% 19% 2	2090
October	1st to 10th	Night	40% 4 13% 24% 16% 2	3480
	11th to 20th	Night	27% 4 10% 27% 30% 3	3838
	21st to end	Night	34% 4 11% 29% 19% 2	4467
November	1st to 10th	Night	38% 6% 11% 23% 19% 3	2453
	11th to 20th	Night	41% 4 10% 22% 19% 3	2470
	21st to end	Night	40% 5% 13% 26% 14% 2	2470
December	1st to 10th	Night	46% 6% 12% 21% 14% 1	2603
	11th to 20th	Night	44% 4 16% 17% 18% 2	3288
	21st to end	Night	50% 5% 9% 25% 10% 1	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	31% 23% 26% 16% 4	180
	11th to 20th	Day	30% 24% 34% 11% 1 1	180
	21st to end	Day	25% 26% 34% 12% 3 1	198
February	1st to 10th	Day	31% 21% 35% 12% 2	383
	11th to 20th	Day	28% 28% 34% 9% 1	456
	21st to end	Day	30% 21% 33% 13% 3	382
March	1st to 10th	Day	31% 21% 33% 12% 3	460
	11th to 20th	Day	30% 24% 31% 11% 4 1	460
	21st to end	Day	29% 23% 32% 8% 7% 1	506
April	1st to 10th	Day	33% 22% 26% 13% 6% 1	460
	11th to 20th	Day	27% 26% 29% 13% 3	452
	21st to end	Day	28% 19% 35% 15% 2 1	460
May	1st to 10th	Day	33% 24% 28% 11% 3 1	463
	11th to 20th	Day	24% 19% 38% 13% 5% 1	487
	21st to end	Day	18% 15% 37% 22% 6% 1	529
June	1st to 10th	Day	22% 13% 38% 19% 6% 1	490
	11th to 20th	Day	16% 15% 42% 20% 6% 1	490
	21st to end	Day	16% 14% 41% 21% 7% 1	490
July	1st to 10th	Day	18% 10% 34% 26% 11% 1	485
	11th to 20th	Day	15% 8% 34% 31% 10% 2	484
	21st to end	Day	12% 9% 40% 31% 8% 1	532
August	1st to 10th	Day	12% 11% 35% 31% 10% 1	486
	11th to 20th	Day	15% 10% 33% 26% 14% 2	479
	21st to end	Day	14% 9% 33% 28% 12% 4	539
September	1st to 10th	Day	19% 12% 29% 24% 12% 4	490
	11th to 20th	Day	20% 13% 27% 19% 13% 8%	490
	21st to end	Day	23% 11% 33% 21% 8% 4	490
October	1st to 10th	Day	28% 12% 26% 21% 8% 5%	490
	11th to 20th	Day	19% 16% 35% 19% 9% 3	430
	21st to end	Day	26% 15% 33% 17% 8% 1	429
November	1st to 10th	Day	21% 17% 35% 15% 10% 2	374
	11th to 20th	Day	27% 20% 33% 15% 5% 1	370
	21st to end	Day	28% 19% 31% 15% 6% 1	370
December	1st to 10th	Day	27% 27% 30% 12% 4	233
	11th to 20th	Day	33% 23% 34% 7% 2	180
	21st to end	Day	26% 24% 33% 12% 4 2	198
January	1st to 10th	Night	22% 19% 39% 17% 3	760
	11th to 20th	Night	28% 19% 36% 16% 2	760
	21st to end	Night	22% 19% 36% 19% 3	836
February	1st to 10th	Night	25% 18% 37% 19% 1	760
	11th to 20th	Night	24% 20% 40% 15% 1	743
	21st to end	Night	26% 21% 34% 17% 3	628
March	1st to 10th	Night	26% 18% 36% 17% 4	760
	11th to 20th	Night	22% 22% 37% 16% 3	760
	21st to end	Night	25% 19% 33% 18% 4	836
April	1st to 10th	Night	25% 20% 32% 20% 4	760
	11th to 20th	Night	23% 20% 34% 18% 4	727
	21st to end	Night	24% 17% 37% 20% 2	570
May	1st to 10th	Night	29% 17% 31% 19% 4	570
	11th to 20th	Night	21% 18% 39% 20% 3	558
	21st to end	Night	19% 9% 39% 27% 5% 1	411
June	1st to 10th	Night	19% 8% 37% 28% 6% 1	380
	11th to 20th	Night	18% 8% 41% 28% 6%	380
	21st to end	Night	17% 6% 41% 31% 5%	380
July	1st to 10th	Night	14% 4 37% 37% 8%	370
	11th to 20th	Night	14% 5% 32% 40% 8% 1	368
	21st to end	Night	14% 4 34% 39% 9%	416
August	1st to 10th	Night	13% 6% 36% 36% 9%	535
	11th to 20th	Night	13% 5% 32% 40% 10% 1	576
	21st to end	Night	14% 5% 25% 39% 15% 2	836
September	1st to 10th	Night	15% 6% 35% 33% 11%	760
	11th to 20th	Night	17% 8% 29% 27% 17% 3	760
	21st to end	Night	22% 8% 27% 30% 11% 2	760
October	1st to 10th	Night	24% 10% 27% 26% 12% 1	760
	11th to 20th	Night	18% 13% 34% 23% 11% 1	760
	21st to end	Night	25% 14% 33% 21% 7%	836
November	1st to 10th	Night	18% 14% 35% 24% 8% 1	755
	11th to 20th	Night	22% 20% 32% 18% 7%	760
	21st to end	Night	23% 20% 34% 18% 5% 1	760
December	1st to 10th	Night	24% 18% 35% 17% 5%	760
	11th to 20th	Night	25% 18% 33% 21% 2 1	760
	21st to end	Night	26% 18% 35% 19% 2	836

Page generated at 2024-11-01 22:47:41. Version ac07

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