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 2024-01-13.

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% 6% 3 6% 6% 4 5% 5% 6% 8% 38%	74935
	Night	14% 6% 2 5% 5% 3 5% 5% 6% 8% 43%	74822
Transparency	Day	43% 7% 11% 21% 15% 3	74657
	Night	39% 6% 11% 23% 17% 4	74619
Seeing	Day	23% 15% 24% 21% 12% 6%	14092
	Night	20% 14% 23% 25% 16% 3	24236

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	14% 9% 3 4 4 3 5% 3 4 7% 44%	1706
	11th to 20th	Day	16% 9% 2 7% 5% 3 4 5% 5% 5% 39%	1644
	21st to end	Day	14% 7% 3 5% 5% 3 4 4 4 6% 44%	1782
February	1st to 10th	Day	13% 8% 3 6% 5% 4 5% 4 6% 7% 38%	1620
	11th to 20th	Day	17% 10% 3 5% 4 3 4 4 4 6% 39%	1679
	21st to end	Day	18% 8% 3 6% 5% 3 4 4 5% 6% 38%	1515
March	1st to 10th	Day	13% 6% 2 4 4 3 5% 4 6% 7% 47%	1980
	11th to 20th	Day	18% 8% 2 6% 5% 3 4 4 5% 8% 35%	1980
	21st to end	Day	17% 8% 3 7% 5% 3 4 3 6% 7% 37%	2178
April	1st to 10th	Day	10% 5% 3 4 5% 3 4 5% 6% 7% 46%	1998
	11th to 20th	Day	15% 6% 3 5% 5% 2 4 4 5% 8% 42%	2134
	21st to end	Day	15% 6% 2 6% 6% 4 5% 5% 5% 7% 38%	2328
May	1st to 10th	Day	15% 6% 3 6% 6% 4 5% 6% 6% 7% 36%	2340
	11th to 20th	Day	18% 6% 3 6% 6% 5% 6% 6% 6% 7% 31%	2301
	21st to end	Day	15% 5% 3 6% 6% 4 6% 6% 7% 9% 34%	2531
June	1st to 10th	Day	12% 7% 3 5% 6% 4 6% 6% 7% 10% 35%	2340
	11th to 20th	Day	10% 6% 2 6% 6% 5% 6% 7% 7% 9% 35%	2340
	21st to end	Day	10% 5% 3 7% 6% 3 6% 6% 9% 9% 35%	2340
July	1st to 10th	Day	10% 5% 3 6% 8% 5% 7% 8% 8% 11% 30%	2340
	11th to 20th	Day	9% 5% 3 7% 7% 5% 7% 8% 9% 10% 29%	2340
	21st to end	Day	12% 7% 3 7% 8% 5% 8% 7% 8% 9% 27%	2547
August	1st to 10th	Day	13% 7% 3 8% 8% 5% 6% 7% 8% 9% 27%	2327
	11th to 20th	Day	12% 7% 3 7% 8% 5% 7% 7% 7% 9% 27%	2303
	21st to end	Day	12% 5% 3 6% 6% 4 6% 6% 9% 9% 34%	2432
September	1st to 10th	Day	14% 5% 2 6% 5% 3 5% 5% 7% 7% 40%	2048
	11th to 20th	Day	17% 7% 3 5% 6% 4 5% 5% 6% 8% 36%	1980
	21st to end	Day	22% 7% 3 5% 5% 3 4 4 5% 5% 36%	1980
October	1st to 10th	Day	16% 6% 2 5% 5% 3 3 4 5% 6% 46%	1854
	11th to 20th	Day	16% 5% 2 4 4 3 4 4 4 6% 49%	1800
	21st to end	Day	15% 5% 2 6% 4 2 2 3 4 6% 50%	1980
November	1st to 10th	Day	12% 4 3 4 4 2 4 4 4 6% 53%	1857
	11th to 20th	Day	13% 5% 2 4 4 3 4 5% 4 6% 50%	1714
	21st to end	Day	14% 5% 2 5% 5% 3 4 4 5% 7% 47%	1710
December	1st to 10th	Day	16% 10% 3 6% 6% 3 4 3 5% 7% 36%	1710
	11th to 20th	Day	15% 5% 2 4 3 3 4 4 5% 8% 48%	2153
	21st to end	Day	20% 7% 3 5% 5% 3 5% 4 6% 8% 35%	3124
January	1st to 10th	Night	15% 7% 2 4 4 3 4 4 5% 7% 45%	2459
	11th to 20th	Night	15% 8% 3 5% 6% 3 4 5% 4 7% 41%	2378
	21st to end	Night	13% 8% 3 5% 4 3 4 5% 6% 6% 45%	2574
February	1st to 10th	Night	14% 7% 2 5% 4 4 5% 4 6% 7% 41%	2340
	11th to 20th	Night	18% 9% 3 5% 3 4 4 4 5% 7% 40%	2163
	21st to end	Night	15% 8% 3 5% 5% 3 4 5% 6% 6% 38%	1740
March	1st to 10th	Night	13% 5% 2 4 3 2 5% 5% 5% 5% 48%	1980
	11th to 20th	Night	17% 6% 3 5% 4 3 6% 6% 6% 8% 36%	1980
	21st to end	Night	15% 7% 3 5% 5% 3 6% 4 5% 6% 40%	2178
April	1st to 10th	Night	12% 6% 3 5% 4 3 5% 5% 6% 8% 44%	1960
	11th to 20th	Night	15% 5% 2 5% 4 3 4 4 5% 8% 46%	1775
	21st to end	Night	15% 6% 2 5% 4 2 4 4 5% 7% 46%	1647
May	1st to 10th	Night	12% 7% 3 5% 5% 3 4 5% 6% 7% 42%	1620
	11th to 20th	Night	15% 7% 2 6% 5% 3 4 4 6% 9% 38%	1592
	21st to end	Night	16% 6% 2 6% 5% 3 4 4 6% 10% 38%	1744
June	1st to 10th	Night	10% 5% 1 5% 4 3 6% 6% 8% 10% 42%	1620
	11th to 20th	Night	11% 6% 4 3 4 3 4 5% 6% 10% 43%	1620
	21st to end	Night	7% 4 3 5% 5% 3 6% 6% 6% 11% 44%	1620
July	1st to 10th	Night	10% 5% 3 5% 5% 4 6% 6% 6% 9% 41%	1620
	11th to 20th	Night	6% 4 2 4 5% 3 6% 6% 8% 13% 43%	1620
	21st to end	Night	6% 5% 3 5% 6% 4 6% 8% 9% 12% 38%	1771
August	1st to 10th	Night	13% 6% 2 6% 6% 3 5% 6% 7% 10% 35%	1611
	11th to 20th	Night	13% 6% 4 6% 5% 3 5% 5% 7% 8% 37%	1598
	21st to end	Night	10% 5% 2 6% 6% 4 5% 6% 6% 9% 41%	1903
September	1st to 10th	Night	10% 6% 2 6% 5% 3 4 6% 6% 8% 46%	1908
	11th to 20th	Night	15% 7% 3 6% 5% 3 4 4 5% 8% 40%	1980
	21st to end	Night	18% 6% 2 6% 6% 3 5% 4 5% 5% 40%	1980
October	1st to 10th	Night	14% 7% 2 4 4 3 4 3 5% 6% 47%	2106
	11th to 20th	Night	14% 6% 2 3 5% 3 4 4 4 7% 49%	2160
	21st to end	Night	13% 5% 2 4 5% 2 3 3 4 7% 53%	2376
November	1st to 10th	Night	14% 6% 2 4 4 2 3 3 4 5% 52%	2221
	11th to 20th	Night	14% 4 1 3 3 2 4 4 5% 6% 51%	2464
	21st to end	Night	14% 4 2 4 4 3 4 5% 5% 7% 47%	2470
December	1st to 10th	Night	17% 7% 3 5% 5% 3 4 3 6% 7% 40%	2470
	11th to 20th	Night	15% 7% 2 5% 4 3 5% 4 5% 7% 42%	3042
	21st to end	Night	20% 8% 3 5% 4 3 5% 5% 6% 8% 33%	4532

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	40% 5% 9% 23% 18% 5%	1707
	11th to 20th	Day	46% 5% 6% 23% 16% 4	1644
	21st to end	Day	41% 5% 7% 23% 20% 4	1782
February	1st to 10th	Day	45% 5% 10% 21% 16% 4	1620
	11th to 20th	Day	46% 5% 7% 21% 17% 4	1688
	21st to end	Day	47% 4 11% 15% 16% 6%	1515
March	1st to 10th	Day	36% 5% 9% 24% 20% 6%	1980
	11th to 20th	Day	46% 6% 9% 18% 16% 5%	1980
	21st to end	Day	47% 6% 8% 24% 12% 3	2178
April	1st to 10th	Day	35% 7% 11% 24% 18% 6%	1998
	11th to 20th	Day	39% 5% 11% 21% 18% 5%	2134
	21st to end	Day	44% 6% 11% 23% 13% 3	2328
May	1st to 10th	Day	45% 6% 15% 19% 12% 2	2340
	11th to 20th	Day	49% 8% 14% 19% 8% 2	2305
	21st to end	Day	44% 8% 16% 24% 7%	2531
June	1st to 10th	Day	43% 8% 16% 23% 10% 1	2340
	11th to 20th	Day	41% 10% 16% 19% 13% 2	2340
	21st to end	Day	41% 9% 16% 22% 12% 1	2340
July	1st to 10th	Day	44% 10% 16% 18% 8% 2	2275
	11th to 20th	Day	43% 11% 19% 16% 10% 1	2271
	21st to end	Day	48% 11% 15% 18% 7% 1	2405
August	1st to 10th	Day	50% 9% 15% 20% 6% 1	2314
	11th to 20th	Day	47% 10% 16% 19% 8%	2303
	21st to end	Day	42% 9% 16% 20% 10% 3	2432
September	1st to 10th	Day	41% 8% 12% 21% 15% 3	2048
	11th to 20th	Day	44% 6% 9% 24% 15% 2	1980
	21st to end	Day	49% 5% 9% 19% 16% 2	1980
October	1st to 10th	Day	39% 5% 8% 25% 19% 5%	1854
	11th to 20th	Day	36% 5% 8% 25% 20% 6%	1800
	21st to end	Day	36% 4 6% 27% 20% 6%	1980
November	1st to 10th	Day	33% 4 8% 23% 26% 7%	1857
	11th to 20th	Day	36% 4 7% 21% 26% 6%	1714
	21st to end	Day	37% 5% 7% 22% 25% 4	1710
December	1st to 10th	Day	48% 5% 8% 18% 17% 4	1710
	11th to 20th	Day	34% 7% 8% 21% 24% 7%	2150
	21st to end	Day	47% 5% 6% 23% 17% 2	3124
January	1st to 10th	Night	38% 6% 10% 21% 19% 6%	2459
	11th to 20th	Night	43% 7% 8% 19% 19% 4	2378
	21st to end	Night	39% 5% 8% 23% 22% 3	2574
February	1st to 10th	Night	41% 5% 10% 23% 18% 2	2340
	11th to 20th	Night	46% 4 7% 21% 17% 6%	2165
	21st to end	Night	44% 5% 11% 21% 14% 5%	1740
March	1st to 10th	Night	36% 6% 8% 24% 21% 5%	1980
	11th to 20th	Night	45% 8% 8% 23% 15% 2	1980
	21st to end	Night	44% 7% 10% 21% 15% 4	2178
April	1st to 10th	Night	37% 6% 12% 23% 18% 4	1960
	11th to 20th	Night	37% 4 11% 22% 19% 6%	1775
	21st to end	Night	38% 5% 12% 28% 14% 2	1647
May	1st to 10th	Night	39% 6% 15% 25% 13% 1	1620
	11th to 20th	Night	44% 7% 16% 23% 9% 1	1593
	21st to end	Night	41% 7% 19% 25% 7% 1	1745
June	1st to 10th	Night	35% 10% 18% 26% 11% 1	1620
	11th to 20th	Night	36% 8% 19% 23% 13% 1	1620
	21st to end	Night	33% 9% 18% 24% 13% 3	1620
July	1st to 10th	Night	39% 10% 15% 23% 10% 3	1575
	11th to 20th	Night	31% 11% 25% 21% 10% 3	1566
	21st to end	Night	35% 10% 22% 25% 8%	1672
August	1st to 10th	Night	42% 10% 18% 20% 10%	1600
	11th to 20th	Night	43% 8% 17% 21% 10% 1	1598
	21st to end	Night	38% 7% 18% 25% 9% 2	1903
September	1st to 10th	Night	35% 7% 16% 21% 16% 4	1908
	11th to 20th	Night	42% 5% 12% 23% 18% 1	1980
	21st to end	Night	46% 5% 8% 22% 16% 2	1980
October	1st to 10th	Night	38% 5% 8% 24% 21% 3	2106
	11th to 20th	Night	36% 5% 8% 27% 21% 5%	2160
	21st to end	Night	33% 4 6% 25% 25% 8%	2376
November	1st to 10th	Night	36% 3 8% 21% 24% 7%	2221
	11th to 20th	Night	33% 5% 7% 21% 25% 9%	2464
	21st to end	Night	35% 5% 7% 25% 23% 5%	2470
December	1st to 10th	Night	43% 6% 7% 23% 17% 4	2470
	11th to 20th	Night	38% 8% 7% 18% 23% 6%	3044
	21st to end	Night	46% 6% 8% 21% 17% 2	4532

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	39% 26% 25% 8% 1 1	270
	11th to 20th	Day	38% 26% 30% 5% 1	248
	21st to end	Day	38% 27% 27% 7% 2	264
February	1st to 10th	Day	36% 32% 24% 7% 1	240
	11th to 20th	Day	50% 22% 25% 3	240
	21st to end	Day	39% 26% 24% 8% 2	233
March	1st to 10th	Day	29% 26% 28% 13% 3	420
	11th to 20th	Day	32% 27% 25% 11% 4 1	420
	21st to end	Day	31% 21% 27% 15% 4 1	462
April	1st to 10th	Day	26% 26% 26% 14% 8% 1	420
	11th to 20th	Day	27% 17% 25% 20% 10% 2	412
	21st to end	Day	28% 17% 27% 17% 8% 4	420
May	1st to 10th	Day	23% 19% 32% 13% 10% 2	423
	11th to 20th	Day	21% 12% 28% 22% 10% 6%	447
	21st to end	Day	20% 7% 22% 25% 17% 8%	485
June	1st to 10th	Day	14% 9% 28% 27% 15% 7%	450
	11th to 20th	Day	11% 11% 22% 30% 18% 9%	450
	21st to end	Day	14% 8% 27% 34% 11% 6%	450
July	1st to 10th	Day	12% 3 17% 33% 23% 12%	445
	11th to 20th	Day	7% 6% 16% 36% 23% 12%	444
	21st to end	Day	13% 6% 18% 28% 23% 13%	488
August	1st to 10th	Day	15% 7% 20% 25% 18% 15%	446
	11th to 20th	Day	15% 5% 15% 27% 23% 16%	439
	21st to end	Day	12% 4 16% 29% 21% 17%	495
September	1st to 10th	Day	14% 4 17% 26% 25% 14%	450
	11th to 20th	Day	18% 7% 14% 25% 24% 12%	450
	21st to end	Day	21% 12% 19% 25% 17% 5%	450
October	1st to 10th	Day	22% 11% 20% 23% 17% 7%	450
	11th to 20th	Day	19% 18% 24% 22% 15% 2	450
	21st to end	Day	23% 15% 29% 21% 9% 2	495
November	1st to 10th	Day	23% 13% 30% 22% 9% 3	455
	11th to 20th	Day	28% 23% 24% 16% 8% 1	274
	21st to end	Day	25% 24% 31% 16% 4 1	270
December	1st to 10th	Day	35% 21% 33% 7% 3	270
	11th to 20th	Day	34% 19% 33% 10% 3 1	270
	21st to end	Day	33% 19% 31% 11% 6%	297
January	1st to 10th	Night	28% 26% 29% 14% 3	760
	11th to 20th	Night	27% 20% 32% 19% 3	732
	21st to end	Night	23% 24% 35% 16% 2	792
February	1st to 10th	Night	24% 21% 33% 20% 3	720
	11th to 20th	Night	34% 25% 29% 11%	703
	21st to end	Night	27% 22% 35% 15% 2	592
March	1st to 10th	Night	23% 21% 33% 20% 2	720
	11th to 20th	Night	26% 20% 28% 19% 6% 1	720
	21st to end	Night	23% 18% 32% 22% 5%	792
April	1st to 10th	Night	23% 20% 28% 22% 6%	720
	11th to 20th	Night	22% 18% 24% 25% 9% 1	711
	21st to end	Night	19% 13% 29% 30% 8%	567
May	1st to 10th	Night	17% 12% 28% 27% 14% 1	540
	11th to 20th	Night	18% 10% 21% 32% 18% 2	531
	21st to end	Night	16% 5% 14% 31% 29% 5%	584
June	1st to 10th	Night	11% 3 19% 36% 27% 4	540
	11th to 20th	Night	11% 8% 14% 31% 30% 6%	540
	21st to end	Night	6% 5% 17% 37% 31% 4	540
July	1st to 10th	Night	11% 4 8% 30% 40% 8%	525
	11th to 20th	Night	6% 2 7% 34% 43% 7%	522
	21st to end	Night	7% 4 10% 33% 37% 9%	591
August	1st to 10th	Night	15% 5% 9% 31% 35% 5%	537
	11th to 20th	Night	14% 4 9% 30% 37% 6%	534
	21st to end	Night	12% 4 9% 29% 36% 10%	715
September	1st to 10th	Night	12% 5% 10% 30% 36% 8%	720
	11th to 20th	Night	17% 5% 12% 28% 32% 6%	720
	21st to end	Night	21% 7% 16% 33% 21% 2	720
October	1st to 10th	Night	19% 10% 18% 23% 24% 6%	720
	11th to 20th	Night	19% 13% 25% 26% 15% 2	720
	21st to end	Night	20% 14% 24% 30% 10% 2	792
November	1st to 10th	Night	19% 11% 27% 25% 15% 2	740
	11th to 20th	Night	23% 15% 25% 27% 8% 1	760
	21st to end	Night	21% 18% 28% 24% 9% 1	760
December	1st to 10th	Night	26% 23% 28% 18% 5%	760
	11th to 20th	Night	24% 21% 28% 21% 6%	760
	21st to end	Night	28% 19% 26% 22% 4	836

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