Elk Horn Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elk Horn Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	127203
	Night	13% 7% 2 6% 4 4 4 4 6% 8% 42%	123842
Transparency	Day	26% 41% 7% 13% 10% 3	130848
	Night	24% 40% 7% 15% 11% 4	128266
Seeing	Day	23% 15% 25% 20% 12% 5%	16719
	Night	20% 14% 23% 25% 15% 2	26803

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% 7% 2 5% 4 4 4 2 4 6% 49%	4056
	11th to 20th	Day	10% 7% 2 6% 4 4 4 3 5% 5% 50%	4060
	21st to end	Day	15% 8% 3 8% 4 4 4 3 4 5% 43%	4466
February	1st to 10th	Day	12% 9% 3 7% 4 5% 4 3 6% 7% 39%	1800
	11th to 20th	Day	18% 10% 3 6% 4 3 5% 3 6% 6% 38%	1871
	21st to end	Day	18% 8% 2 6% 5% 4 4 3 5% 6% 39%	1689
March	1st to 10th	Day	17% 7% 3 6% 4 5% 5% 4 5% 6% 37%	4935
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 4 7% 50%	4980
	21st to end	Day	16% 8% 2 7% 4 4 4 3 6% 6% 41%	5465
April	1st to 10th	Day	11% 7% 3 6% 5% 4 4 4 6% 7% 45%	2221
	11th to 20th	Day	14% 7% 3 5% 4 4 4 3 6% 8% 42%	2374
	21st to end	Day	14% 7% 2 7% 5% 5% 5% 3 6% 7% 38%	2588
May	1st to 10th	Day	12% 7% 3 8% 7% 7% 6% 6% 8% 8% 29%	5862
	11th to 20th	Day	20% 8% 3 8% 5% 6% 6% 5% 7% 8% 25%	5861
	21st to end	Day	14% 6% 3 7% 5% 5% 6% 5% 7% 9% 35%	6433
June	1st to 10th	Day	11% 7% 2 6% 6% 6% 6% 5% 7% 9% 35%	2600
	11th to 20th	Day	9% 6% 2 7% 6% 6% 6% 6% 8% 10% 35%	2600
	21st to end	Day	10% 5% 2 7% 6% 4 6% 5% 9% 10% 36%	2600
July	1st to 10th	Day	7% 5% 3 8% 6% 7% 7% 6% 8% 10% 33%	5900
	11th to 20th	Day	7% 7% 3 9% 7% 7% 8% 7% 9% 11% 24%	5900
	21st to end	Day	11% 8% 3 10% 7% 8% 7% 6% 8% 10% 22%	6424
August	1st to 10th	Day	14% 8% 3 10% 6% 6% 7% 6% 8% 9% 23%	4234
	11th to 20th	Day	9% 6% 2 7% 6% 7% 7% 6% 8% 11% 31%	4174
	21st to end	Day	7% 4 2 5% 3 4 5% 5% 7% 10% 46%	4413
September	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 4 7% 7% 42%	2274
	11th to 20th	Day	17% 7% 3 7% 5% 5% 4 4 6% 8% 36%	2200
	21st to end	Day	22% 8% 3 6% 5% 5% 4 4 6% 5% 33%	2200
October	1st to 10th	Day	14% 6% 2 6% 4 4 3 3 5% 6% 47%	2060
	11th to 20th	Day	14% 5% 2 5% 3 4 4 3 4 6% 51%	2000
	21st to end	Day	15% 6% 2 6% 3 3 3 3 4 6% 50%	2200
November	1st to 10th	Day	12% 5% 3 5% 3 3 4 3 4 6% 52%	2057
	11th to 20th	Day	12% 5% 2 4 4 5% 4 4 5% 6% 50%	1894
	21st to end	Day	13% 6% 2 7% 4 4 4 3 5% 6% 46%	1890
December	1st to 10th	Day	11% 8% 3 6% 4 5% 4 3 5% 6% 45%	3020
	11th to 20th	Day	15% 7% 3 7% 4 4 4 3 6% 7% 41%	3436
	21st to end	Day	18% 8% 3 6% 4 4 4 3 7% 8% 34%	4466
January	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 5% 7% 47%	5889
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 4 6% 48%	5900
	21st to end	Night	16% 8% 2 5% 4 3 3 3 4 4 48%	6490
February	1st to 10th	Night	13% 8% 2 6% 4 5% 4 3 6% 8% 41%	2600
	11th to 20th	Night	19% 9% 2 5% 3 5% 4 3 5% 7% 39%	2410
	21st to end	Night	14% 8% 3 6% 5% 5% 4 4 7% 6% 39%	1940
March	1st to 10th	Night	17% 8% 3 6% 4 4 5% 3 4 5% 41%	4918
	11th to 20th	Night	10% 4 2 4 3 3 4 4 6% 8% 53%	4980
	21st to end	Night	14% 6% 2 7% 5% 4 5% 4 6% 6% 42%	5467
April	1st to 10th	Night	12% 7% 2 6% 4 5% 4 4 6% 8% 42%	2177
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 5% 8% 46%	1975
	21st to end	Night	14% 6% 2 5% 4 3 4 4 6% 7% 45%	1829
May	1st to 10th	Night	14% 9% 3 6% 4 4 4 4 6% 9% 36%	4033
	11th to 20th	Night	19% 8% 3 7% 4 4 4 4 5% 9% 33%	4032
	21st to end	Night	17% 6% 2 7% 5% 5% 5% 3 6% 9% 35%	4421
June	1st to 10th	Night	10% 6% 1 6% 4 4 6% 5% 8% 10% 42%	1800
	11th to 20th	Night	11% 7% 3 4 4 4 4 5% 7% 10% 42%	1800
	21st to end	Night	7% 5% 2 6% 4 5% 5% 5% 7% 11% 45%	1800
July	1st to 10th	Night	9% 6% 3 7% 5% 5% 5% 5% 7% 10% 38%	4058
	11th to 20th	Night	8% 6% 2 7% 6% 6% 7% 5% 8% 12% 33%	4057
	21st to end	Night	8% 9% 3 9% 7% 6% 6% 6% 8% 9% 29%	4427
August	1st to 10th	Night	16% 9% 3 8% 5% 4 5% 4 7% 10% 29%	2915
	11th to 20th	Night	10% 6% 3 6% 5% 5% 6% 4 8% 9% 39%	2875
	21st to end	Night	7% 4 1 6% 4 4 4 4 6% 8% 51%	3449
September	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 6% 8% 46%	2121
	11th to 20th	Night	15% 7% 2 7% 4 4 4 3 5% 8% 39%	2200
	21st to end	Night	19% 8% 2 7% 5% 4 5% 4 4 5% 38%	2200
October	1st to 10th	Night	14% 7% 2 5% 3 4 4 3 5% 6% 47%	2340
	11th to 20th	Night	13% 6% 2 4 4 3 4 3 4 6% 50%	2400
	21st to end	Night	14% 5% 2 5% 4 3 3 2 4 6% 54%	2640
November	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 4 5% 51%	2461
	11th to 20th	Night	13% 5% 1 4 3 4 4 4 5% 6% 50%	2724
	21st to end	Night	13% 5% 2 5% 3 4 4 3 5% 7% 47%	2730
December	1st to 10th	Night	11% 6% 2 6% 5% 3 4 3 6% 6% 48%	4380
	11th to 20th	Night	16% 11% 4 7% 4 4 4 3 5% 7% 36%	4914
	21st to end	Night	19% 8% 2 5% 4 4 5% 4 6% 8% 36%	6490

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	23% 30% 3 15% 24% 5%	4057
	11th to 20th	Day	22% 29% 3 13% 29% 5%	4060
	21st to end	Day	30% 31% 4 15% 17% 4	4466
February	1st to 10th	Day	18% 63% 3 8% 7% 2	1800
	11th to 20th	Day	20% 61% 2 7% 7% 2	1880
	21st to end	Day	18% 62% 3 7% 8% 2	1689
March	1st to 10th	Day	35% 31% 4 11% 9% 10%	4935
	11th to 20th	Day	20% 30% 3 18% 17% 12%	4980
	21st to end	Day	29% 30% 6% 17% 14% 4	5465
April	1st to 10th	Day	17% 64% 4 9% 6% 1	2221
	11th to 20th	Day	17% 63% 4 10% 5% 2	2374
	21st to end	Day	17% 63% 5% 10% 5% 1	2588
May	1st to 10th	Day	35% 34% 10% 14% 6% 1	5897
	11th to 20th	Day	40% 32% 7% 15% 5%	5865
	21st to end	Day	30% 32% 9% 13% 11% 3	6447
June	1st to 10th	Day	16% 63% 7% 9% 5%	2600
	11th to 20th	Day	15% 66% 7% 7% 5%	2600
	21st to end	Day	16% 63% 8% 9% 3	2600
July	1st to 10th	Day	31% 33% 13% 15% 6% 2	5835
	11th to 20th	Day	36% 36% 16% 12% 1	5831
	21st to end	Day	39% 33% 11% 13% 4	6240
August	1st to 10th	Day	35% 40% 11% 12% 1	4221
	11th to 20th	Day	22% 43% 15% 14% 4 2	4213
	21st to end	Day	15% 40% 12% 24% 8% 1	4413
September	1st to 10th	Day	15% 60% 8% 9% 7% 2	2274
	11th to 20th	Day	20% 59% 5% 9% 6% 1	2200
	21st to end	Day	26% 59% 6% 7% 3	2200
October	1st to 10th	Day	15% 39% 6% 12% 19% 8%	3359
	11th to 20th	Day	12% 36% 3 16% 16% 17%	3240
	21st to end	Day	14% 37% 6% 17% 12% 13%	3538
November	1st to 10th	Day	19% 54% 5% 10% 9% 3	2057
	11th to 20th	Day	16% 55% 4 8% 14% 3	1894
	21st to end	Day	17% 56% 5% 10% 12% 1	1890
December	1st to 10th	Day	23% 37% 4 13% 19% 4	3020
	11th to 20th	Day	28% 33% 7% 11% 16% 4	3433
	21st to end	Day	36% 30% 7% 16% 9% 2	4466
January	1st to 10th	Night	22% 29% 3 18% 20% 8%	5889
	11th to 20th	Night	23% 28% 4 14% 22% 8%	5900
	21st to end	Night	27% 29% 4 15% 22% 3	6490
February	1st to 10th	Night	16% 63% 5% 8% 7% 1	2600
	11th to 20th	Night	19% 61% 4 7% 7% 2	2412
	21st to end	Night	16% 62% 3 9% 6% 3	1940
March	1st to 10th	Night	34% 32% 3 15% 10% 7%	4918
	11th to 20th	Night	16% 30% 4 17% 19% 14%	4980
	21st to end	Night	28% 31% 6% 19% 13% 3	5467
April	1st to 10th	Night	16% 63% 5% 8% 6% 1	2177
	11th to 20th	Night	16% 63% 5% 9% 5% 2	1975
	21st to end	Night	14% 62% 6% 11% 6%	1829
May	1st to 10th	Night	31% 35% 11% 16% 7%	4060
	11th to 20th	Night	37% 31% 10% 17% 5%	4033
	21st to end	Night	30% 33% 11% 18% 6% 2	4429
June	1st to 10th	Night	14% 64% 7% 10% 5% 1	1800
	11th to 20th	Night	12% 65% 9% 10% 4 1	1800
	21st to end	Night	14% 62% 8% 11% 5%	1800
July	1st to 10th	Night	31% 33% 12% 18% 6%	4015
	11th to 20th	Night	31% 34% 20% 13% 1	4006
	21st to end	Night	37% 32% 12% 13% 5%	4297
August	1st to 10th	Night	35% 39% 14% 10% 1	2904
	11th to 20th	Night	20% 42% 15% 18% 5%	2902
	21st to end	Night	15% 39% 11% 29% 6% 1	3449
September	1st to 10th	Night	16% 58% 8% 10% 7% 1	2121
	11th to 20th	Night	19% 59% 6% 10% 7%	2200
	21st to end	Night	25% 59% 6% 8% 3	2200
October	1st to 10th	Night	21% 37% 6% 13% 16% 8%	3821
	11th to 20th	Night	11% 37% 5% 15% 16% 16%	3899
	21st to end	Night	13% 36% 4 19% 14% 13%	4252
November	1st to 10th	Night	19% 54% 5% 11% 9% 2	2461
	11th to 20th	Night	14% 55% 3 10% 13% 6%	2724
	21st to end	Night	15% 56% 5% 11% 12% 1	2730
December	1st to 10th	Night	21% 36% 6% 17% 17% 1	4380
	11th to 20th	Night	33% 34% 6% 12% 11% 4	4916
	21st to end	Night	31% 29% 10% 18% 10% 2	6490

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	43% 25% 23% 7% 1 1	300
	11th to 20th	Day	43% 24% 27% 5% 1	300
	21st to end	Day	37% 28% 27% 7% 2	330
February	1st to 10th	Day	35% 29% 27% 8% 2	300
	11th to 20th	Day	52% 22% 22% 4	300
	21st to end	Day	39% 27% 26% 7% 2	288
March	1st to 10th	Day	31% 25% 28% 12% 4 1	500
	11th to 20th	Day	31% 27% 27% 10% 4 1	500
	21st to end	Day	31% 23% 27% 14% 3 1	550
April	1st to 10th	Day	28% 26% 26% 12% 7% 1	500
	11th to 20th	Day	27% 19% 25% 18% 9% 1	492
	21st to end	Day	25% 16% 31% 17% 9% 3	500
May	1st to 10th	Day	24% 18% 32% 15% 10% 2	503
	11th to 20th	Day	23% 14% 27% 20% 10% 6%	527
	21st to end	Day	22% 9% 23% 23% 16% 7%	573
June	1st to 10th	Day	13% 11% 31% 26% 13% 6%	530
	11th to 20th	Day	9% 11% 24% 31% 17% 8%	530
	21st to end	Day	12% 7% 25% 35% 14% 6%	530
July	1st to 10th	Day	11% 3 18% 33% 23% 11%	525
	11th to 20th	Day	7% 6% 15% 35% 25% 11%	524
	21st to end	Day	12% 6% 19% 28% 22% 12%	576
August	1st to 10th	Day	17% 8% 20% 25% 17% 13%	526
	11th to 20th	Day	13% 6% 18% 27% 22% 14%	519
	21st to end	Day	10% 6% 17% 30% 21% 16%	583
September	1st to 10th	Day	13% 5% 19% 27% 25% 12%	530
	11th to 20th	Day	17% 8% 16% 24% 23% 12%	530
	21st to end	Day	21% 14% 21% 25% 15% 4	530
October	1st to 10th	Day	19% 11% 22% 24% 17% 7%	530
	11th to 20th	Day	20% 18% 23% 22% 15% 2	530
	21st to end	Day	24% 15% 29% 20% 9% 2	583
November	1st to 10th	Day	22% 15% 31% 21% 9% 2	535
	11th to 20th	Day	28% 26% 25% 14% 6% 1	334
	21st to end	Day	30% 23% 29% 13% 4 1	330
December	1st to 10th	Day	35% 25% 32% 6% 2	330
	11th to 20th	Day	33% 19% 35% 10% 3 1	321
	21st to end	Day	33% 18% 32% 12% 5%	330
January	1st to 10th	Night	30% 25% 28% 14% 3	800
	11th to 20th	Night	29% 19% 32% 18% 2	800
	21st to end	Night	25% 23% 35% 15% 2	880
February	1st to 10th	Night	24% 20% 32% 21% 3	800
	11th to 20th	Night	35% 27% 27% 11% 1	783
	21st to end	Night	27% 22% 35% 15% 2	660
March	1st to 10th	Night	25% 20% 33% 19% 3	800
	11th to 20th	Night	26% 19% 29% 19% 6% 1	800
	21st to end	Night	24% 19% 32% 21% 4	880
April	1st to 10th	Night	24% 21% 29% 21% 5%	800
	11th to 20th	Night	22% 18% 25% 25% 8% 1	791
	21st to end	Night	18% 14% 29% 30% 8%	629
May	1st to 10th	Night	17% 12% 28% 28% 14% 1	600
	11th to 20th	Night	18% 10% 21% 32% 18% 2	591
	21st to end	Night	18% 6% 15% 29% 27% 4	650
June	1st to 10th	Night	12% 3 20% 36% 26% 4	600
	11th to 20th	Night	11% 7% 15% 32% 30% 5%	600
	21st to end	Night	6% 5% 16% 35% 34% 4	600
July	1st to 10th	Night	11% 4 9% 29% 40% 7%	585
	11th to 20th	Night	6% 3 7% 33% 44% 7%	582
	21st to end	Night	8% 5% 10% 33% 36% 8%	657
August	1st to 10th	Night	15% 5% 11% 29% 35% 5%	597
	11th to 20th	Night	13% 5% 10% 30% 36% 6%	594
	21st to end	Night	12% 5% 10% 28% 36% 9%	795
September	1st to 10th	Night	12% 5% 11% 32% 34% 7%	800
	11th to 20th	Night	17% 5% 13% 28% 32% 6%	800
	21st to end	Night	22% 8% 17% 32% 20% 2	800
October	1st to 10th	Night	18% 10% 18% 24% 25% 5%	800
	11th to 20th	Night	19% 14% 25% 26% 15% 2	800
	21st to end	Night	21% 13% 23% 31% 10% 1	880
November	1st to 10th	Night	19% 12% 27% 26% 14% 1	820
	11th to 20th	Night	23% 16% 26% 26% 8% 1	840
	21st to end	Night	23% 18% 28% 23% 8% 1	840
December	1st to 10th	Night	25% 23% 30% 18% 4	840
	11th to 20th	Night	24% 20% 29% 21% 6%	829
	21st to end	Night	28% 19% 25% 23% 4	880

Page generated at 2025-12-15 01:13:50. Version ac07

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