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 2024-11-11.

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% 7% 2 7% 5% 5% 5% 4 6% 8% 37%	101281
	Night	14% 7% 2 6% 4 4 4 4 6% 8% 42%	97846
Transparency	Day	22% 48% 6% 12% 8% 3	104970
	Night	21% 48% 6% 13% 9% 3	102296
Seeing	Day	22% 15% 25% 21% 12% 5%	15256
	Night	20% 14% 23% 25% 16% 2	25322

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% 7% 2 5% 4 3 4 3 5% 7% 45%	2836
	11th to 20th	Day	13% 8% 3 8% 4 4 4 4 5% 6% 42%	2840
	21st to end	Day	19% 9% 3 7% 4 4 4 3 5% 5% 37%	3124
February	1st to 10th	Day	13% 9% 3 7% 4 5% 4 3 6% 7% 39%	1710
	11th to 20th	Day	17% 10% 3 6% 4 3 4 3 6% 6% 39%	1775
	21st to end	Day	18% 8% 2 7% 5% 4 4 2 5% 6% 37%	1607
March	1st to 10th	Day	21% 8% 2 5% 4 4 4 4 5% 7% 36%	3435
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 5% 7% 49%	3480
	21st to end	Day	18% 9% 3 6% 4 3 4 3 6% 7% 39%	3815
April	1st to 10th	Day	10% 6% 3 5% 5% 4 4 4 6% 7% 46%	2110
	11th to 20th	Day	15% 7% 3 5% 4 3 4 3 5% 8% 42%	2254
	21st to end	Day	15% 7% 2 7% 6% 5% 5% 4 5% 7% 38%	2458
May	1st to 10th	Day	15% 8% 3 8% 6% 6% 6% 5% 7% 7% 30%	4082
	11th to 20th	Day	19% 8% 2 7% 5% 6% 6% 5% 7% 7% 28%	4081
	21st to end	Day	10% 4 2 6% 5% 5% 6% 5% 8% 9% 38%	4476
June	1st to 10th	Day	11% 7% 2 6% 6% 6% 6% 4 7% 9% 34%	2470
	11th to 20th	Day	9% 6% 2 7% 6% 6% 6% 6% 8% 10% 35%	2470
	21st to end	Day	10% 6% 2 7% 6% 4 6% 5% 9% 9% 35%	2470
July	1st to 10th	Day	7% 4 2 8% 7% 7% 7% 7% 9% 10% 33%	4120
	11th to 20th	Day	9% 7% 3 8% 6% 6% 8% 6% 8% 10% 29%	4120
	21st to end	Day	15% 10% 4 11% 8% 7% 7% 5% 7% 8% 20%	4466
August	1st to 10th	Day	14% 8% 3 9% 6% 6% 7% 6% 8% 9% 24%	4104
	11th to 20th	Day	9% 6% 2 7% 6% 7% 7% 6% 9% 11% 31%	4044
	21st to end	Day	7% 4 2 5% 4 4 5% 5% 7% 10% 47%	4278
September	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 4 7% 7% 41%	2161
	11th to 20th	Day	17% 7% 2 7% 5% 4 4 4 6% 8% 36%	2090
	21st to end	Day	22% 7% 3 6% 5% 4 4 3 5% 5% 34%	2090
October	1st to 10th	Day	15% 6% 2 6% 4 4 3 3 5% 6% 46%	1957
	11th to 20th	Day	15% 5% 2 5% 3 4 4 3 4 6% 50%	1900
	21st to end	Day	14% 6% 2 6% 3 3 2 3 4 6% 50%	2090
November	1st to 10th	Day	13% 5% 3 5% 4 3 4 3 4 6% 51%	1957
	11th to 20th	Day	13% 5% 2 4 4 5% 3 4 5% 6% 50%	1714
	21st to end	Day	14% 6% 2 6% 4 4 4 3 5% 6% 47%	1710
December	1st to 10th	Day	16% 10% 3 7% 5% 5% 4 3 5% 7% 36%	1710
	11th to 20th	Day	15% 6% 1 4 3 4 3 3 6% 8% 47%	2153
	21st to end	Day	19% 8% 3 6% 4 4 5% 3 6% 7% 34%	3124
January	1st to 10th	Night	14% 8% 2 5% 4 4 4 4 6% 8% 42%	4109
	11th to 20th	Night	14% 8% 2 7% 4 3 3 3 4 6% 44%	4120
	21st to end	Night	21% 10% 2 5% 4 3 3 3 5% 4 39%	4532
February	1st to 10th	Night	13% 8% 2 6% 4 5% 4 3 6% 7% 42%	2470
	11th to 20th	Night	18% 9% 2 5% 3 5% 4 3 5% 7% 40%	2287
	21st to end	Night	14% 9% 3 6% 5% 5% 4 4 7% 6% 38%	1846
March	1st to 10th	Night	21% 11% 3 6% 4 4 5% 3 5% 5% 33%	3418
	11th to 20th	Night	10% 4 2 4 3 4 5% 4 6% 8% 50%	3480
	21st to end	Night	15% 6% 2 5% 4 4 4 3 5% 7% 44%	3817
April	1st to 10th	Night	11% 7% 2 6% 4 5% 4 4 6% 8% 43%	2068
	11th to 20th	Night	15% 6% 2 5% 4 3 4 3 5% 8% 46%	1875
	21st to end	Night	15% 6% 2 5% 4 3 4 4 5% 7% 46%	1738
May	1st to 10th	Night	14% 10% 3 6% 4 4 4 4 6% 8% 37%	2813
	11th to 20th	Night	18% 8% 2 7% 4 4 4 3 5% 8% 37%	2812
	21st to end	Night	11% 5% 1 6% 4 4 5% 3 7% 11% 43%	3079
June	1st to 10th	Night	10% 6% 1 6% 4 4 6% 5% 8% 10% 41%	1710
	11th to 20th	Night	11% 7% 3 4 4 4 4 5% 7% 10% 43%	1710
	21st to end	Night	7% 5% 2 6% 4 5% 5% 5% 7% 11% 44%	1710
July	1st to 10th	Night	8% 5% 3 6% 5% 5% 6% 5% 8% 10% 38%	2840
	11th to 20th	Night	8% 5% 2 6% 5% 5% 6% 5% 8% 12% 41%	2840
	21st to end	Night	11% 10% 4 9% 7% 6% 6% 6% 7% 8% 27%	3087
August	1st to 10th	Night	16% 9% 3 8% 4 4 5% 4 7% 11% 29%	2825
	11th to 20th	Night	10% 5% 3 6% 5% 5% 6% 4 8% 9% 40%	2785
	21st to end	Night	6% 4 1 6% 4 4 4 4 6% 8% 52%	3343
September	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 6% 7% 45%	2015
	11th to 20th	Night	16% 7% 2 7% 4 4 4 3 5% 8% 39%	2090
	21st to end	Night	19% 7% 2 7% 5% 4 4 3 4 5% 38%	2090
October	1st to 10th	Night	14% 7% 2 5% 3 4 4 3 5% 5% 47%	2223
	11th to 20th	Night	14% 6% 2 4 4 3 3 3 4 6% 50%	2280
	21st to end	Night	13% 5% 2 5% 4 2 3 2 4 6% 54%	2508
November	1st to 10th	Night	14% 7% 2 5% 3 4 3 3 4 5% 51%	2341
	11th to 20th	Night	14% 5% 1 4 3 3 4 4 5% 6% 50%	2471
	21st to end	Night	14% 5% 2 5% 4 4 4 3 6% 7% 47%	2470
December	1st to 10th	Night	17% 8% 3 5% 5% 4 3 3 6% 7% 40%	2470
	11th to 20th	Night	15% 7% 2 6% 4 4 4 4 5% 7% 42%	3042
	21st to end	Night	20% 9% 2 6% 4 4 5% 4 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	22% 40% 2 15% 17% 4	2837
	11th to 20th	Day	24% 39% 2 12% 20% 2	2840
	21st to end	Day	30% 42% 2 10% 12% 3	3124
February	1st to 10th	Day	16% 66% 3 7% 7% 2	1710
	11th to 20th	Day	18% 64% 2 7% 7% 2	1784
	21st to end	Day	18% 65% 3 6% 7% 2	1607
March	1st to 10th	Day	33% 43% 4 10% 4 6%	3435
	11th to 20th	Day	16% 42% 3 19% 13% 8%	3480
	21st to end	Day	26% 41% 4 15% 11% 3	3815
April	1st to 10th	Day	14% 67% 3 8% 6% 1	2110
	11th to 20th	Day	16% 66% 4 8% 4 2	2254
	21st to end	Day	15% 66% 4 9% 5% 1	2458
May	1st to 10th	Day	31% 43% 8% 13% 4 1	4120
	11th to 20th	Day	32% 42% 5% 17% 4	4085
	21st to end	Day	20% 44% 10% 13% 11% 3	4489
June	1st to 10th	Day	16% 66% 6% 7% 4	2470
	11th to 20th	Day	14% 68% 6% 7% 5%	2470
	21st to end	Day	16% 66% 7% 8% 3	2470
July	1st to 10th	Day	25% 43% 13% 12% 4 2	4055
	11th to 20th	Day	28% 42% 14% 15% 1	4051
	21st to end	Day	41% 39% 6% 11% 2	4324
August	1st to 10th	Day	34% 41% 11% 12% 1	4091
	11th to 20th	Day	21% 44% 15% 13% 5% 2	4083
	21st to end	Day	14% 41% 13% 24% 8% 1	4278
September	1st to 10th	Day	15% 62% 7% 8% 6% 2	2161
	11th to 20th	Day	19% 62% 5% 8% 7% 1	2090
	21st to end	Day	23% 61% 6% 7% 3	2090
October	1st to 10th	Day	15% 40% 6% 12% 19% 8%	3256
	11th to 20th	Day	11% 37% 3 16% 15% 18%	3140
	21st to end	Day	13% 38% 6% 18% 11% 14%	3428
November	1st to 10th	Day	19% 56% 4 10% 8% 3	1957
	11th to 20th	Day	15% 60% 3 7% 12% 3	1714
	21st to end	Day	15% 61% 4 8% 12% 1	1710
December	1st to 10th	Day	23% 60% 3 7% 5% 2	1710
	11th to 20th	Day	15% 50% 3 10% 16% 6%	2150
	21st to end	Day	32% 39% 2 15% 11% 1	3124
January	1st to 10th	Night	24% 40% 3 15% 15% 4	4109
	11th to 20th	Night	24% 38% 4 11% 17% 5%	4120
	21st to end	Night	31% 40% 3 10% 14% 2	4532
February	1st to 10th	Night	14% 66% 4 7% 7% 1	2470
	11th to 20th	Night	17% 64% 3 7% 7% 2	2289
	21st to end	Night	16% 65% 3 9% 5% 3	1846
March	1st to 10th	Night	38% 44% 2 9% 5% 2	3418
	11th to 20th	Night	13% 42% 3 17% 13% 12%	3480
	21st to end	Night	22% 41% 5% 16% 12% 4	3817
April	1st to 10th	Night	15% 66% 4 8% 6% 1	2068
	11th to 20th	Night	15% 66% 4 8% 5% 1	1875
	21st to end	Night	12% 65% 5% 11% 6% 1	1738
May	1st to 10th	Night	28% 43% 10% 15% 4	2840
	11th to 20th	Night	29% 41% 7% 19% 4	2813
	21st to end	Night	17% 43% 11% 20% 7% 2	3087
June	1st to 10th	Night	13% 67% 6% 9% 4 1	1710
	11th to 20th	Night	10% 67% 8% 10% 4 1	1710
	21st to end	Night	13% 65% 8% 10% 4	1710
July	1st to 10th	Night	26% 43% 12% 13% 5%	2795
	11th to 20th	Night	20% 42% 19% 17% 2	2786
	21st to end	Night	38% 40% 8% 11% 3	2988
August	1st to 10th	Night	34% 40% 14% 10% 1	2814
	11th to 20th	Night	19% 42% 15% 18% 5%	2812
	21st to end	Night	14% 40% 11% 29% 6% 1	3343
September	1st to 10th	Night	16% 61% 7% 9% 6% 1	2015
	11th to 20th	Night	19% 62% 5% 8% 6%	2090
	21st to end	Night	23% 61% 5% 8% 3	2090
October	1st to 10th	Night	20% 38% 6% 12% 15% 8%	3704
	11th to 20th	Night	11% 38% 5% 15% 16% 16%	3779
	21st to end	Night	12% 37% 4 19% 14% 14%	4120
November	1st to 10th	Night	19% 57% 5% 9% 9% 2	2341
	11th to 20th	Night	13% 60% 3 8% 12% 6%	2471
	21st to end	Night	14% 61% 4 10% 11% 1	2470
December	1st to 10th	Night	20% 60% 3 9% 5% 2	2470
	11th to 20th	Night	18% 53% 2 8% 15% 4	3044
	21st to end	Night	30% 40% 4 14% 11% 1	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	41% 25% 29% 4 1	270
	21st to end	Day	37% 28% 27% 7% 2	297
February	1st to 10th	Day	34% 29% 26% 8% 2	270
	11th to 20th	Day	49% 23% 24% 4	270
	21st to end	Day	39% 27% 24% 7% 2	262
March	1st to 10th	Day	30% 25% 28% 13% 4 1	460
	11th to 20th	Day	31% 27% 26% 10% 4 1	460
	21st to end	Day	31% 22% 28% 15% 4 1	506
April	1st to 10th	Day	28% 26% 26% 13% 7% 1	460
	11th to 20th	Day	27% 18% 26% 19% 10% 2	452
	21st to end	Day	26% 16% 29% 17% 9% 3	460
May	1st to 10th	Day	24% 18% 32% 14% 10% 2	463
	11th to 20th	Day	22% 12% 28% 22% 11% 6%	487
	21st to end	Day	20% 8% 24% 25% 17% 7%	529
June	1st to 10th	Day	13% 10% 30% 27% 14% 6%	490
	11th to 20th	Day	10% 10% 24% 30% 18% 8%	490
	21st to end	Day	13% 8% 27% 34% 11% 6%	490
July	1st to 10th	Day	11% 3 18% 33% 23% 11%	485
	11th to 20th	Day	7% 7% 16% 36% 23% 11%	484
	21st to end	Day	13% 6% 19% 29% 21% 12%	532
August	1st to 10th	Day	15% 7% 21% 25% 17% 14%	486
	11th to 20th	Day	14% 5% 18% 26% 21% 15%	479
	21st to end	Day	11% 4 15% 30% 22% 17%	539
September	1st to 10th	Day	13% 5% 18% 27% 25% 13%	490
	11th to 20th	Day	18% 8% 15% 24% 23% 11%	490
	21st to end	Day	21% 14% 20% 25% 16% 4	490
October	1st to 10th	Day	21% 11% 22% 23% 17% 7%	490
	11th to 20th	Day	19% 17% 23% 22% 16% 2	490
	21st to end	Day	21% 15% 30% 22% 10% 2	539
November	1st to 10th	Day	22% 14% 30% 21% 9% 3	495
	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	28% 19% 32% 19% 3	760
	21st to end	Night	25% 23% 34% 16% 2	836
February	1st to 10th	Night	23% 20% 33% 21% 3	760
	11th to 20th	Night	34% 26% 28% 11% 1	743
	21st to end	Night	27% 22% 35% 15% 2	628
March	1st to 10th	Night	24% 20% 33% 20% 3	760
	11th to 20th	Night	26% 19% 29% 19% 6% 1	760
	21st to end	Night	23% 19% 32% 22% 4	836
April	1st to 10th	Night	23% 21% 29% 22% 5%	760
	11th to 20th	Night	23% 17% 25% 26% 9% 1	751
	21st to end	Night	19% 13% 29% 30% 8%	598
May	1st to 10th	Night	17% 12% 27% 28% 14% 1	570
	11th to 20th	Night	18% 9% 20% 32% 18% 2	561
	21st to end	Night	16% 6% 15% 30% 29% 4	617
June	1st to 10th	Night	12% 3 19% 36% 26% 4	570
	11th to 20th	Night	11% 7% 14% 32% 30% 6%	570
	21st to end	Night	6% 5% 17% 36% 32% 4	570
July	1st to 10th	Night	11% 4 9% 30% 39% 7%	555
	11th to 20th	Night	6% 3 7% 34% 44% 7%	552
	21st to end	Night	8% 5% 10% 33% 36% 8%	624
August	1st to 10th	Night	15% 5% 10% 30% 35% 5%	567
	11th to 20th	Night	13% 4 11% 30% 36% 6%	564
	21st to end	Night	11% 4 9% 29% 37% 10%	755
September	1st to 10th	Night	12% 5% 11% 31% 34% 7%	760
	11th to 20th	Night	18% 5% 13% 28% 31% 6%	760
	21st to end	Night	21% 8% 16% 32% 20% 2	760
October	1st to 10th	Night	19% 10% 18% 24% 24% 5%	760
	11th to 20th	Night	18% 14% 24% 26% 15% 2	760
	21st to end	Night	19% 14% 23% 31% 11% 1	836
November	1st to 10th	Night	19% 12% 27% 25% 15% 2	780
	11th to 20th	Night	23% 15% 25% 27% 8% 1	763
	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

Page generated at 2024-11-08 06:44:47. Version ac07

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