Arkansas Tech University Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arkansas Tech University Astronomical Observatory clear sky chart from 2005-11-06 to 2026-06-16.

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% 6% 2 6% 4 4 4 3 5% 7% 45%	136574
	Night	14% 5% 2 5% 3 3 4 3 5% 6% 49%	135689
Transparency	Day	38% 4 10% 24% 19% 5%	140181
	Night	35% 4 9% 24% 21% 7%	140161
Seeing	Day	16% 4 19% 26% 25% 11%	17537
	Night	16% 4 20% 37% 21% 2	27370

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	17% 7% 2 6% 4 4 4 3 4 5% 46%	5289
	11th to 20th	Day	8% 6% 2 6% 4 4 4 3 4 4 55%	5310
	21st to end	Day	19% 7% 2 5% 3 3 3 3 4 4 48%	5812
February	1st to 10th	Day	23% 8% 2 5% 3 2 3 2 3 4 44%	1890
	11th to 20th	Day	20% 7% 2 5% 3 3 4 3 4 4 44%	1923
	21st to end	Day	20% 8% 2 5% 5% 4 4 3 4 6% 41%	1835
March	1st to 10th	Day	20% 7% 2 6% 4 4 4 3 4 5% 40%	5046
	11th to 20th	Day	12% 4 2 5% 3 4 4 3 5% 6% 53%	5090
	21st to end	Day	15% 7% 2 6% 4 4 4 3 5% 6% 44%	5583
April	1st to 10th	Day	17% 5% 3 5% 5% 3 4 4 5% 6% 43%	2480
	11th to 20th	Day	18% 6% 2 5% 3 3 4 3 5% 6% 44%	2494
	21st to end	Day	18% 7% 3 6% 4 4 4 4 5% 7% 38%	2520
May	1st to 10th	Day	17% 8% 3 7% 4 4 4 3 5% 5% 40%	7198
	11th to 20th	Day	13% 7% 2 8% 5% 5% 5% 4 6% 7% 38%	7627
	21st to end	Day	19% 8% 3 8% 5% 5% 5% 4 6% 8% 29%	8392
June	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 4 6% 9% 42%	2730
	11th to 20th	Day	7% 5% 2 6% 6% 6% 6% 5% 7% 9% 43%	2666
	21st to end	Day	5% 3 1 4 5% 4 6% 6% 7% 9% 51%	2600
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 12% 39%	5900
	11th to 20th	Day	4 4 2 5% 3 4 5% 3 6% 9% 55%	5900
	21st to end	Day	7% 5% 2 7% 5% 5% 5% 5% 7% 10% 42%	6422
August	1st to 10th	Day	4 3 1 3 3 4 3 3 5% 8% 61%	4234
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 6% 10% 44%	3958
	21st to end	Day	5% 3 2 5% 3 5% 5% 3 6% 8% 55%	4312
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 5% 8% 49%	2400
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 5% 8% 47%	2337
	21st to end	Day	9% 4 2 6% 3 3 4 4 5% 6% 53%	2115
October	1st to 10th	Day	8% 4 1 6% 3 4 2 2 4 6% 59%	2000
	11th to 20th	Day	14% 5% 1 4 3 3 3 3 4 5% 57%	2000
	21st to end	Day	21% 4 2 5% 3 3 3 3 4 4 49%	2200
November	1st to 10th	Day	14% 5% 2 4 3 3 3 3 5% 5% 55%	2058
	11th to 20th	Day	14% 5% 1 5% 2 2 4 3 5% 6% 55%	2100
	21st to end	Day	19% 6% 2 5% 3 3 3 2 4 6% 47%	1759
December	1st to 10th	Day	17% 6% 3 6% 3 3 3 2 4 5% 49%	2690
	11th to 20th	Day	18% 8% 3 5% 4 4 4 3 4 5% 44%	3117
	21st to end	Day	23% 9% 3 6% 4 3 3 2 4 5% 37%	4587
January	1st to 10th	Night	16% 6% 2 5% 3 3 3 3 5% 7% 47%	7634
	11th to 20th	Night	9% 4 1 3 2 3 3 3 4 5% 64%	7680
	21st to end	Night	22% 8% 2 5% 3 3 3 2 4 5% 43%	8402
February	1st to 10th	Night	18% 8% 2 5% 4 3 3 3 5% 5% 43%	2730
	11th to 20th	Night	18% 7% 3 5% 4 3 3 3 4 5% 45%	2582
	21st to end	Night	19% 6% 2 3 3 3 3 3 4 5% 50%	1987
March	1st to 10th	Night	21% 6% 2 6% 3 3 3 3 4 4 44%	5029
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 4 7% 52%	5090
	21st to end	Night	15% 6% 2 6% 4 4 3 3 5% 8% 45%	5588
April	1st to 10th	Night	15% 5% 2 4 3 3 3 3 5% 7% 49%	2138
	11th to 20th	Night	14% 5% 2 5% 4 4 3 4 5% 6% 49%	2075
	21st to end	Night	18% 6% 2 4 4 4 4 3 5% 6% 44%	2100
May	1st to 10th	Night	17% 7% 3 6% 4 4 5% 3 6% 7% 39%	5647
	11th to 20th	Night	15% 8% 3 7% 4 4 4 4 6% 7% 38%	5265
	21st to end	Night	21% 8% 3 7% 4 5% 4 3 5% 7% 32%	5793
June	1st to 10th	Night	6% 4 2 6% 4 4 4 4 6% 9% 51%	1890
	11th to 20th	Night	6% 4 2 4 4 3 3 4 5% 10% 56%	1845
	21st to end	Night	4 3 1 3 3 3 4 4 6% 9% 62%	1800
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 6% 5% 8% 10% 41%	4078
	11th to 20th	Night	4 3 1 4 3 4 4 3 6% 9% 58%	4077
	21st to end	Night	5% 4 2 6% 4 4 5% 5% 7% 10% 48%	4449
August	1st to 10th	Night	3 2 1 3 3 3 3 3 6% 8% 64%	2926
	11th to 20th	Night	5% 3 2 5% 4 4 4 4 6% 8% 55%	3079
	21st to end	Night	4 3 2 5% 3 4 4 3 6% 9% 57%	3586
September	1st to 10th	Night	8% 4 2 4 4 3 4 4 5% 6% 57%	2000
	11th to 20th	Night	10% 4 2 4 4 4 4 4 6% 7% 51%	2058
	21st to end	Night	9% 4 1 4 3 3 4 3 5% 7% 58%	2263
October	1st to 10th	Night	8% 3 1 3 2 3 3 3 5% 6% 62%	2400
	11th to 20th	Night	12% 3 1 4 3 2 2 2 3 5% 61%	2400
	21st to end	Night	18% 5% 2 5% 3 3 2 2 3 4 54%	2640
November	1st to 10th	Night	13% 4 2 4 3 3 3 2 4 6% 56%	2460
	11th to 20th	Night	14% 4 2 4 2 2 3 3 4 6% 57%	2520
	21st to end	Night	16% 6% 2 4 3 2 3 2 4 6% 50%	2851
December	1st to 10th	Night	15% 7% 2 5% 3 4 3 2 4 4 51%	4720
	11th to 20th	Night	21% 6% 2 5% 4 3 3 2 3 4 47%	5274
	21st to end	Night	23% 7% 3 5% 4 3 3 3 4 5% 40%	6633

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	43% 2 9% 27% 17% 2	5290
	11th to 20th	Day	33% 2 7% 23% 29% 6%	5310
	21st to end	Day	41% 2 4 21% 24% 7%	5812
February	1st to 10th	Day	45% 3 10% 22% 16% 4	1890
	11th to 20th	Day	44% 4 8% 22% 18% 4	1932
	21st to end	Day	46% 3 6% 16% 19% 9%	1835
March	1st to 10th	Day	46% 3 6% 17% 15% 13%	5046
	11th to 20th	Day	33% 4 7% 19% 24% 13%	5090
	21st to end	Day	42% 3 9% 29% 16% 1	5585
April	1st to 10th	Day	41% 5% 9% 20% 21% 4	2480
	11th to 20th	Day	41% 5% 9% 21% 18% 6%	2494
	21st to end	Day	45% 5% 9% 21% 17% 2	2520
May	1st to 10th	Day	46% 4 8% 20% 19% 2	7233
	11th to 20th	Day	44% 6% 11% 22% 15% 2	7631
	21st to end	Day	53% 5% 13% 15% 13% 1	8405
June	1st to 10th	Day	37% 7% 13% 26% 15% 1	2730
	11th to 20th	Day	35% 7% 15% 24% 18% 2	2666
	21st to end	Day	26% 9% 14% 29% 19% 4	2600
July	1st to 10th	Day	36% 5% 17% 31% 10% 1	5836
	11th to 20th	Day	26% 4 13% 38% 17% 2	5831
	21st to end	Day	37% 4 16% 30% 12%	6240
August	1st to 10th	Day	21% 5% 15% 32% 21% 6%	4220
	11th to 20th	Day	36% 5% 16% 30% 13% 1	3996
	21st to end	Day	26% 6% 14% 34% 17% 3	4311
September	1st to 10th	Day	35% 6% 10% 23% 18% 8%	2400
	11th to 20th	Day	35% 5% 12% 22% 21% 5%	2337
	21st to end	Day	31% 5% 9% 20% 28% 6%	2115
October	1st to 10th	Day	16% 2 5% 14% 39% 23%	3260
	11th to 20th	Day	20% 2 3 20% 37% 17%	3240
	21st to end	Day	34% 3 5% 30% 23% 6%	3538
November	1st to 10th	Day	32% 4 8% 26% 23% 8%	2058
	11th to 20th	Day	30% 4 7% 25% 25% 9%	2100
	21st to end	Day	41% 3 8% 21% 23% 5%	1759
December	1st to 10th	Day	39% 2 7% 29% 19% 3	2690
	11th to 20th	Day	44% 3 6% 22% 22% 3	3114
	21st to end	Day	48% 5% 7% 24% 13% 3	4587
January	1st to 10th	Night	38% 2 8% 31% 18% 2	7635
	11th to 20th	Night	24% 2 7% 20% 37% 8%	7680
	21st to end	Night	45% 2 6% 16% 24% 7%	8402
February	1st to 10th	Night	43% 4 8% 23% 18% 4	2730
	11th to 20th	Night	41% 4 7% 22% 20% 5%	2583
	21st to end	Night	38% 3 7% 19% 23% 10%	1987
March	1st to 10th	Night	44% 4 7% 15% 18% 13%	5029
	11th to 20th	Night	34% 4 5% 24% 20% 13%	5090
	21st to end	Night	38% 4 10% 26% 19% 3	5588
April	1st to 10th	Night	35% 4 10% 23% 19% 8%	2138
	11th to 20th	Night	36% 5% 7% 23% 20% 9%	2075
	21st to end	Night	40% 5% 9% 23% 20% 3	2100
May	1st to 10th	Night	45% 5% 13% 19% 15% 3	5677
	11th to 20th	Night	45% 5% 12% 21% 14% 3	5266
	21st to end	Night	52% 5% 13% 17% 10% 3	5805
June	1st to 10th	Night	28% 7% 14% 29% 19% 3	1890
	11th to 20th	Night	24% 5% 12% 33% 23% 2	1845
	21st to end	Night	19% 6% 14% 31% 24% 7%	1800
July	1st to 10th	Night	36% 6% 16% 27% 14% 1	4035
	11th to 20th	Night	22% 4 14% 39% 19% 2	4026
	21st to end	Night	32% 5% 16% 30% 17% 1	4320
August	1st to 10th	Night	18% 4 15% 35% 24% 4	2916
	11th to 20th	Night	26% 4 19% 33% 15% 2	3106
	21st to end	Night	24% 5% 12% 31% 25% 3	3586
September	1st to 10th	Night	27% 6% 9% 27% 21% 9%	2000
	11th to 20th	Night	31% 6% 11% 22% 24% 6%	2058
	21st to end	Night	26% 5% 8% 22% 29% 8%	2263
October	1st to 10th	Night	15% 3 7% 14% 32% 29%	3920
	11th to 20th	Night	18% 2 4 16% 39% 21%	3899
	21st to end	Night	31% 2 4 24% 28% 11%	4252
November	1st to 10th	Night	31% 4 8% 23% 26% 9%	2460
	11th to 20th	Night	29% 3 6% 26% 26% 10%	2520
	21st to end	Night	36% 3 7% 23% 26% 5%	2851
December	1st to 10th	Night	39% 2 7% 31% 19% 3	4720
	11th to 20th	Night	43% 2 5% 22% 21% 7%	5276
	21st to end	Night	46% 4 9% 25% 13% 4	6633

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	25% 5% 30% 27% 11% 2	330
	11th to 20th	Day	21% 8% 39% 25% 7% 1	330
	21st to end	Day	20% 9% 37% 24% 8% 1	363
February	1st to 10th	Day	28% 7% 28% 26% 10% 1	330
	11th to 20th	Day	25% 9% 38% 23% 5%	330
	21st to end	Day	26% 10% 37% 19% 8% 1	273
March	1st to 10th	Day	25% 9% 31% 25% 9% 1	330
	11th to 20th	Day	25% 13% 33% 22% 7%	330
	21st to end	Day	20% 11% 38% 23% 6% 2	363
April	1st to 10th	Day	22% 8% 32% 25% 11% 2	500
	11th to 20th	Day	24% 8% 27% 30% 9% 1	532
	21st to end	Day	23% 6% 27% 28% 13% 2	540
May	1st to 10th	Day	20% 5% 25% 32% 16% 1	604
	11th to 20th	Day	18% 5% 19% 29% 23% 7%	775
	21st to end	Day	14% 2 16% 35% 22% 9%	844
June	1st to 10th	Day	13% 2 11% 25% 35% 14%	780
	11th to 20th	Day	9% 2 11% 28% 33% 17%	756
	21st to end	Day	5% 1 10% 30% 35% 18%	730
July	1st to 10th	Day	7% 2 7% 24% 37% 24%	721
	11th to 20th	Day	6% 1 6% 25% 36% 26%	718
	21st to end	Day	7% 1 4 23% 39% 26%	794
August	1st to 10th	Day	9% 6% 23% 46% 17%	726
	11th to 20th	Day	13% 1 5% 18% 43% 21%	592
	21st to end	Day	12% 1 2 15% 39% 30%	583
September	1st to 10th	Day	11% 1 3 21% 43% 22%	530
	11th to 20th	Day	11% 1 7% 20% 40% 20%	467
	21st to end	Day	12% 3 11% 27% 28% 19%	330
October	1st to 10th	Day	7% 1 18% 29% 30% 15%	330
	11th to 20th	Day	12% 4 23% 31% 24% 6%	330
	21st to end	Day	26% 9% 23% 23% 15% 3	363
November	1st to 10th	Day	16% 4 27% 25% 23% 5%	330
	11th to 20th	Day	15% 3 34% 28% 18% 2	330
	21st to end	Day	22% 13% 22% 24% 17% 3	330
December	1st to 10th	Day	21% 5% 38% 19% 14% 3	330
	11th to 20th	Day	22% 9% 29% 28% 11%	330
	21st to end	Day	26% 10% 28% 27% 8% 1	363
January	1st to 10th	Night	22% 8% 27% 36% 6%	1050
	11th to 20th	Night	19% 8% 31% 35% 6%	1050
	21st to end	Night	21% 5% 33% 36% 5%	1155
February	1st to 10th	Night	23% 7% 27% 38% 5%	1050
	11th to 20th	Night	21% 9% 33% 34% 3	948
	21st to end	Night	22% 8% 33% 36% 2	603
March	1st to 10th	Night	20% 6% 30% 39% 5%	630
	11th to 20th	Night	21% 7% 27% 39% 7%	630
	21st to end	Night	21% 6% 29% 36% 8%	693
April	1st to 10th	Night	19% 5% 33% 34% 9%	630
	11th to 20th	Night	15% 7% 31% 36% 10%	623
	21st to end	Night	21% 5% 26% 34% 13%	630
May	1st to 10th	Night	16% 3 19% 47% 14%	630
	11th to 20th	Night	18% 3 18% 36% 24% 2	621
	21st to end	Night	13% 2 13% 41% 27% 3	683
June	1st to 10th	Night	8% 1 8% 38% 40% 4	630
	11th to 20th	Night	7% 1 7% 41% 41% 4	615
	21st to end	Night	5% 1 7% 33% 48% 7%	600
July	1st to 10th	Night	5% 1 6% 31% 49% 9%	585
	11th to 20th	Night	5% 1 3 28% 51% 11%	582
	21st to end	Night	4 1 2 31% 51% 11%	657
August	1st to 10th	Night	6% 1 3 35% 50% 7%	597
	11th to 20th	Night	10% 4 35% 44% 8%	594
	21st to end	Night	7% 5% 28% 52% 7%	660
September	1st to 10th	Night	10% 1 4 30% 49% 6%	600
	11th to 20th	Night	13% 1 5% 33% 45% 4	600
	21st to end	Night	11% 2 9% 36% 39% 4	663
October	1st to 10th	Night	10% 1 9% 40% 37% 3	800
	11th to 20th	Night	13% 3 20% 45% 20% 1	800
	21st to end	Night	22% 5% 20% 36% 17% 1	880
November	1st to 10th	Night	15% 4 18% 43% 19% 1	820
	11th to 20th	Night	16% 6% 22% 44% 12%	840
	21st to end	Night	20% 7% 23% 37% 13% 1	966
December	1st to 10th	Night	22% 4 26% 40% 7%	1050
	11th to 20th	Night	24% 6% 21% 42% 7%	1050
	21st to end	Night	24% 8% 24% 37% 7%	1155

Page generated at 2026-06-13 01:31:42. Version ac07

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