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 2025-02-21.

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% 2 6% 4 4 4 3 5% 7% 46%	108264
	Night	14% 5% 2 5% 3 3 3 3 5% 6% 50%	110454
Transparency	Day	37% 5% 10% 24% 19% 5%	111910
	Night	34% 4 9% 24% 22% 6%	114947
Seeing	Day	16% 4 18% 25% 26% 12%	15716
	Night	16% 4 19% 37% 21% 2	25693

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	18% 8% 2 6% 3 3 3 2 3 4 49%	4077
	11th to 20th	Day	9% 7% 2 6% 4 4 4 4 5% 5% 51%	4080
	21st to end	Day	22% 7% 2 4 3 2 3 2 3 4 48%	4488
February	1st to 10th	Day	23% 9% 2 5% 4 2 3 2 3 4 43%	1800
	11th to 20th	Day	21% 7% 2 5% 3 3 3 3 4 4 44%	1829
	21st to end	Day	22% 9% 2 5% 5% 4 3 3 4 5% 38%	1665
March	1st to 10th	Day	22% 8% 3 6% 3 3 3 2 3 5% 42%	3436
	11th to 20th	Day	15% 5% 2 6% 3 4 4 3 4 5% 48%	3480
	21st to end	Day	17% 8% 2 6% 4 4 4 3 4 5% 43%	3814
April	1st to 10th	Day	16% 5% 3 6% 5% 3 4 4 5% 6% 43%	2244
	11th to 20th	Day	18% 6% 2 5% 4 3 4 3 5% 6% 44%	2254
	21st to end	Day	19% 6% 3 6% 4 4 4 4 4 6% 40%	2280
May	1st to 10th	Day	19% 7% 3 7% 5% 5% 4 4 5% 5% 36%	3859
	11th to 20th	Day	13% 6% 2 7% 5% 5% 4 4 6% 8% 42%	4082
	21st to end	Day	16% 6% 3 7% 5% 5% 5% 4 6% 7% 35%	4477
June	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 9% 43%	2470
	11th to 20th	Day	6% 4 2 5% 6% 5% 6% 5% 7% 10% 45%	2470
	21st to end	Day	5% 3 1 4 5% 4 6% 6% 7% 9% 50%	2470
July	1st to 10th	Day	9% 5% 2 5% 5% 5% 5% 4 6% 10% 43%	4120
	11th to 20th	Day	5% 4 2 4 3 4 4 3 5% 9% 56%	4120
	21st to end	Day	9% 7% 3 8% 5% 5% 5% 5% 7% 10% 36%	4465
August	1st to 10th	Day	4 3 1 3 3 4 3 3 5% 9% 60%	4104
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 6% 10% 44%	3834
	21st to end	Day	5% 3 2 4 3 5% 5% 3 6% 8% 56%	4180
September	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 5% 8% 49%	2280
	11th to 20th	Day	13% 5% 1 5% 4 4 4 3 5% 7% 48%	2220
	21st to end	Day	9% 4 2 6% 3 3 5% 4 5% 6% 54%	2009
October	1st to 10th	Day	8% 4 1 6% 3 4 3 2 5% 6% 58%	1900
	11th to 20th	Day	14% 5% 1 4 3 3 3 3 4 5% 56%	1900
	21st to end	Day	20% 4 2 5% 2 3 3 3 4 4 49%	2090
November	1st to 10th	Day	14% 5% 2 4 3 3 4 3 5% 5% 53%	1958
	11th to 20th	Day	14% 5% 1 5% 2 2 4 3 5% 6% 54%	2000
	21st to end	Day	19% 7% 2 5% 3 2 3 2 4 6% 47%	1675
December	1st to 10th	Day	17% 6% 2 6% 3 3 3 2 4 5% 50%	2610
	11th to 20th	Day	18% 9% 3 5% 4 4 4 3 4 5% 43%	3036
	21st to end	Day	24% 9% 3 7% 4 3 3 2 4 5% 37%	4488
January	1st to 10th	Night	17% 6% 2 5% 3 3 3 3 5% 6% 48%	5888
	11th to 20th	Night	10% 4 2 3 3 3 3 3 4 5% 59%	5900
	21st to end	Night	22% 7% 2 5% 3 2 2 2 3 5% 47%	6490
February	1st to 10th	Night	19% 8% 2 5% 4 3 3 3 5% 5% 43%	2600
	11th to 20th	Night	18% 7% 3 5% 4 3 3 3 4 5% 45%	2456
	21st to end	Night	20% 6% 2 4 3 2 3 3 5% 5% 47%	1804
March	1st to 10th	Night	23% 6% 2 5% 3 3 3 3 4 5% 42%	3419
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 3 6% 50%	3480
	21st to end	Night	16% 6% 2 6% 4 4 4 3 5% 7% 45%	3817
April	1st to 10th	Night	14% 5% 2 5% 3 3 4 3 5% 7% 49%	1934
	11th to 20th	Night	13% 5% 2 5% 4 4 3 3 4 6% 49%	1875
	21st to end	Night	18% 6% 2 4 4 4 4 3 6% 6% 45%	1900
May	1st to 10th	Night	20% 6% 2 6% 4 4 4 3 5% 7% 40%	3022
	11th to 20th	Night	15% 6% 2 5% 3 4 4 4 6% 7% 43%	2823
	21st to end	Night	17% 6% 3 6% 4 5% 4 3 5% 8% 40%	3090
June	1st to 10th	Night	6% 4 1 5% 4 4 4 4 6% 10% 53%	1710
	11th to 20th	Night	4 4 1 3 4 3 3 4 5% 10% 59%	1710
	21st to end	Night	4 3 1 3 2 3 3 4 6% 9% 62%	1710
July	1st to 10th	Night	7% 4 2 5% 4 5% 5% 5% 7% 9% 48%	2850
	11th to 20th	Night	5% 3 1 3 3 3 4 2 6% 9% 61%	2850
	21st to end	Night	6% 5% 3 7% 5% 5% 5% 5% 6% 9% 43%	3098
August	1st to 10th	Night	3 2 1 3 3 3 3 3 6% 8% 65%	2836
	11th to 20th	Night	5% 3 2 5% 4 4 4 4 6% 8% 55%	2983
	21st to end	Night	4 3 2 5% 3 4 4 3 6% 9% 57%	3476
September	1st to 10th	Night	8% 4 2 4 4 3 4 4 5% 6% 57%	1900
	11th to 20th	Night	10% 4 2 4 4 4 4 4 6% 7% 51%	1955
	21st to end	Night	9% 4 1 4 3 3 3 3 5% 7% 59%	2150
October	1st to 10th	Night	9% 3 1 3 2 3 3 3 5% 7% 61%	2280
	11th to 20th	Night	13% 3 1 4 3 2 2 2 4 4 61%	2280
	21st to end	Night	18% 5% 2 5% 3 3 2 2 3 4 54%	2508
November	1st to 10th	Night	13% 5% 2 4 3 3 3 2 4 6% 55%	2340
	11th to 20th	Night	14% 4 2 4 2 2 3 3 4 6% 57%	2400
	21st to end	Night	16% 6% 2 4 3 2 3 2 4 6% 51%	2715
December	1st to 10th	Night	15% 7% 2 5% 3 4 3 2 4 4 51%	4580
	11th to 20th	Night	21% 6% 2 5% 4 3 3 2 3 4 47%	5135
	21st to end	Night	23% 8% 3 5% 4 3 3 3 4 5% 40%	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	41% 2 10% 25% 20% 2	4078
	11th to 20th	Day	35% 3 9% 25% 24% 5%	4080
	21st to end	Day	42% 3 5% 18% 25% 8%	4488
February	1st to 10th	Day	46% 3 10% 21% 16% 4	1800
	11th to 20th	Day	44% 4 7% 23% 18% 4	1838
	21st to end	Day	49% 4 7% 16% 17% 8%	1665
March	1st to 10th	Day	45% 4 8% 15% 17% 11%	3436
	11th to 20th	Day	38% 5% 10% 23% 20% 4	3480
	21st to end	Day	44% 4 9% 25% 16% 1	3814
April	1st to 10th	Day	40% 5% 9% 20% 22% 4	2244
	11th to 20th	Day	41% 5% 9% 21% 18% 6%	2254
	21st to end	Day	44% 6% 9% 22% 18% 2	2280
May	1st to 10th	Day	47% 7% 9% 19% 16% 2	3894
	11th to 20th	Day	37% 9% 13% 27% 13% 1	4086
	21st to end	Day	44% 8% 14% 19% 14% 2	4489
June	1st to 10th	Day	36% 7% 14% 26% 15% 1	2470
	11th to 20th	Day	32% 7% 15% 25% 19% 2	2470
	21st to end	Day	26% 9% 13% 28% 19% 4	2470
July	1st to 10th	Day	36% 5% 17% 30% 11% 2	4056
	11th to 20th	Day	25% 5% 10% 35% 23% 2	4051
	21st to end	Day	43% 5% 18% 25% 8%	4325
August	1st to 10th	Day	21% 5% 15% 31% 21% 6%	4090
	11th to 20th	Day	36% 5% 16% 29% 13% 1	3872
	21st to end	Day	26% 6% 14% 34% 17% 3	4179
September	1st to 10th	Day	35% 6% 11% 23% 18% 8%	2280
	11th to 20th	Day	35% 5% 12% 21% 22% 5%	2220
	21st to end	Day	31% 5% 9% 21% 28% 6%	2009
October	1st to 10th	Day	16% 3 5% 14% 39% 24%	3160
	11th to 20th	Day	20% 2 3 20% 38% 17%	3140
	21st to end	Day	33% 3 5% 30% 24% 6%	3428
November	1st to 10th	Day	32% 5% 8% 25% 22% 8%	1958
	11th to 20th	Day	30% 4 7% 24% 26% 9%	2000
	21st to end	Day	41% 3 8% 20% 24% 5%	1675
December	1st to 10th	Day	39% 2 7% 30% 19% 3	2610
	11th to 20th	Day	44% 3 6% 21% 22% 3	3033
	21st to end	Day	49% 5% 7% 23% 12% 4	4488
January	1st to 10th	Night	37% 3 9% 28% 21% 3	5888
	11th to 20th	Night	28% 3 9% 22% 32% 6%	5900
	21st to end	Night	43% 2 8% 16% 26% 5%	6490
February	1st to 10th	Night	44% 4 8% 22% 17% 4	2600
	11th to 20th	Night	42% 4 7% 22% 20% 5%	2457
	21st to end	Night	40% 3 7% 19% 22% 9%	1804
March	1st to 10th	Night	43% 6% 9% 14% 17% 11%	3419
	11th to 20th	Night	37% 5% 7% 26% 19% 5%	3480
	21st to end	Night	39% 5% 10% 26% 18% 2	3817
April	1st to 10th	Night	35% 4 10% 22% 20% 9%	1934
	11th to 20th	Night	35% 5% 7% 24% 20% 9%	1875
	21st to end	Night	39% 6% 9% 23% 20% 3	1900
May	1st to 10th	Night	42% 8% 12% 21% 14% 3	3052
	11th to 20th	Night	37% 8% 15% 26% 13% 1	2824
	21st to end	Night	41% 7% 14% 23% 13% 2	3099
June	1st to 10th	Night	25% 7% 15% 31% 19% 3	1710
	11th to 20th	Night	20% 6% 13% 35% 24% 2	1710
	21st to end	Night	19% 6% 14% 30% 23% 7%	1710
July	1st to 10th	Night	30% 6% 18% 26% 18% 2	2805
	11th to 20th	Night	20% 5% 12% 36% 25% 3	2796
	21st to end	Night	37% 6% 17% 27% 13% 1	2999
August	1st to 10th	Night	17% 4 16% 35% 24% 4	2826
	11th to 20th	Night	26% 4 19% 33% 16% 2	3010
	21st to end	Night	24% 5% 12% 31% 26% 3	3476
September	1st to 10th	Night	26% 6% 10% 27% 22% 9%	1900
	11th to 20th	Night	31% 6% 11% 21% 25% 6%	1955
	21st to end	Night	26% 5% 9% 22% 30% 8%	2150
October	1st to 10th	Night	15% 3 7% 14% 32% 30%	3800
	11th to 20th	Night	18% 2 3 16% 39% 22%	3779
	21st to end	Night	30% 2 4 24% 28% 11%	4120
November	1st to 10th	Night	31% 4 8% 23% 25% 9%	2340
	11th to 20th	Night	29% 4 6% 24% 27% 10%	2400
	21st to end	Night	36% 3 7% 22% 26% 5%	2715
December	1st to 10th	Night	39% 2 6% 32% 19% 3	4580
	11th to 20th	Night	43% 2 5% 22% 21% 7%	5137
	21st to end	Night	46% 4 9% 25% 13% 4	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	26% 5% 30% 26% 11% 2	300
	11th to 20th	Day	22% 8% 38% 24% 7% 1	300
	21st to end	Day	21% 8% 36% 25% 9% 1	330
February	1st to 10th	Day	30% 7% 26% 27% 9% 1	300
	11th to 20th	Day	25% 9% 36% 24% 5%	300
	21st to end	Day	31% 8% 36% 18% 7%	225
March	1st to 10th	Day	26% 6% 29% 27% 11% 1	270
	11th to 20th	Day	25% 11% 33% 22% 9%	270
	21st to end	Day	22% 11% 35% 23% 7% 2	297
April	1st to 10th	Day	20% 9% 33% 25% 11% 3	424
	11th to 20th	Day	25% 6% 25% 31% 10% 2	452
	21st to end	Day	24% 4 27% 29% 13% 3	460
May	1st to 10th	Day	21% 5% 24% 32% 17% 2	518
	11th to 20th	Day	18% 3 16% 30% 25% 8%	675
	21st to end	Day	13% 2 15% 35% 24% 10%	734
June	1st to 10th	Day	12% 1 10% 25% 37% 16%	680
	11th to 20th	Day	8% 1 9% 28% 36% 19%	680
	21st to end	Day	5% 1 10% 31% 34% 18%	680
July	1st to 10th	Day	7% 2 7% 24% 36% 25%	671
	11th to 20th	Day	6% 1 6% 25% 36% 26%	668
	21st to end	Day	7% 1 4 23% 39% 25%	739
August	1st to 10th	Day	9% 6% 21% 46% 18%	676
	11th to 20th	Day	14% 1 5% 18% 44% 19%	548
	21st to end	Day	12% 1 14% 41% 32%	539
September	1st to 10th	Day	10% 1 3 20% 44% 22%	490
	11th to 20th	Day	12% 1 7% 21% 40% 19%	430
	21st to end	Day	13% 2 11% 26% 30% 19%	300
October	1st to 10th	Day	8% 17% 28% 30% 16%	300
	11th to 20th	Day	13% 3 23% 31% 24% 6%	300
	21st to end	Day	26% 8% 24% 23% 16% 4	330
November	1st to 10th	Day	18% 3 26% 23% 24% 6%	300
	11th to 20th	Day	16% 3 32% 29% 18% 2	300
	21st to end	Day	22% 13% 20% 24% 18% 3	300
December	1st to 10th	Day	21% 4 39% 18% 15% 4	300
	11th to 20th	Day	23% 8% 30% 27% 11%	300
	21st to end	Day	28% 9% 27% 27% 8% 1	330
January	1st to 10th	Night	22% 8% 27% 36% 6%	1000
	11th to 20th	Night	20% 8% 30% 35% 6%	1000
	21st to end	Night	21% 5% 33% 36% 5%	1100
February	1st to 10th	Night	24% 8% 26% 37% 5%	1000
	11th to 20th	Night	21% 9% 33% 35% 3	902
	21st to end	Night	23% 8% 33% 33% 2	548
March	1st to 10th	Night	20% 5% 29% 41% 5%	570
	11th to 20th	Night	22% 6% 26% 39% 7%	570
	21st to end	Night	22% 5% 29% 35% 8%	627
April	1st to 10th	Night	18% 5% 34% 34% 9%	570
	11th to 20th	Night	14% 6% 31% 37% 11%	563
	21st to end	Night	22% 4 26% 35% 13%	570
May	1st to 10th	Night	17% 2 19% 47% 15%	570
	11th to 20th	Night	18% 1 17% 37% 25% 2	561
	21st to end	Night	12% 1 13% 41% 29% 4	617
June	1st to 10th	Night	8% 1 8% 36% 42% 5%	570
	11th to 20th	Night	5% 1 6% 41% 43% 4	570
	21st to end	Night	5% 1 7% 34% 47% 6%	570
July	1st to 10th	Night	4 1 5% 32% 49% 9%	555
	11th to 20th	Night	5% 3 29% 50% 12%	552
	21st to end	Night	4 2 31% 51% 10%	624
August	1st to 10th	Night	5% 3 33% 51% 7%	567
	11th to 20th	Night	10% 4 36% 42% 8%	564
	21st to end	Night	6% 4 27% 54% 8%	627
September	1st to 10th	Night	10% 1 4 29% 50% 6%	570
	11th to 20th	Night	13% 1 5% 34% 44% 4	570
	21st to end	Night	11% 2 9% 36% 39% 4	630
October	1st to 10th	Night	11% 1 10% 39% 37% 3	760
	11th to 20th	Night	13% 3 20% 44% 19% 1	760
	21st to end	Night	21% 4 20% 36% 17% 1	836
November	1st to 10th	Night	15% 4 17% 43% 20% 1	780
	11th to 20th	Night	16% 6% 23% 43% 12%	800
	21st to end	Night	20% 6% 22% 38% 14% 1	920
December	1st to 10th	Night	23% 5% 25% 39% 8%	1000
	11th to 20th	Night	24% 7% 21% 41% 7%	1000
	21st to end	Night	24% 8% 24% 36% 7%	1100

Page generated at 2025-02-18 02:26:31. Version ac07

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