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 2024-09-14.

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%	99943
	Night	14% 5% 2 5% 3 3 3 3 5% 6% 50%	97984
Transparency	Day	38% 5% 11% 24% 18% 4	99751
	Night	34% 5% 11% 24% 21% 5%	97846
Seeing	Day	16% 3 17% 26% 26% 12%	15234
	Night	16% 4 19% 37% 21% 2	24984

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	19% 8% 2 6% 3 3 3 2 3 4 47%	2847
	11th to 20th	Day	12% 8% 2 7% 4 4 3 3 3 5% 49%	2850
	21st to end	Day	25% 7% 1 4 3 2 3 2 3 4 45%	3135
February	1st to 10th	Day	22% 9% 2 5% 4 3 3 2 3 4 44%	1710
	11th to 20th	Day	20% 7% 2 6% 3 2 4 3 4 4 44%	1735
	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 6% 7% 49%	2141
	21st to end	Day	9% 4 2 5% 3 3 5% 4 4 6% 55%	1904
October	1st to 10th	Day	8% 5% 1 6% 3 4 3 3 5% 7% 56%	1800
	11th to 20th	Day	15% 5% 1 4 3 3 3 3 4 5% 54%	1800
	21st to end	Day	20% 4 2 5% 3 3 3 3 4 4 49%	1980
November	1st to 10th	Day	13% 5% 2 4 3 3 4 3 5% 5% 55%	1858
	11th to 20th	Day	13% 5% 1 5% 2 2 4 3 5% 6% 54%	1900
	21st to end	Day	20% 7% 2 5% 3 3 3 2 4 6% 46%	1592
December	1st to 10th	Day	19% 4 2 6% 3 3 2 2 5% 7% 48%	1520
	11th to 20th	Day	16% 9% 2 6% 4 4 5% 3 4 4 44%	1932
	21st to end	Day	19% 10% 3 7% 4 4 4 3 4 6% 36%	3135
January	1st to 10th	Night	17% 6% 3 6% 4 4 3 3 4 5% 45%	4108
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 3 5% 55%	4120
	21st to end	Night	23% 8% 2 4 2 2 2 2 3 5% 46%	4532
February	1st to 10th	Night	19% 8% 2 5% 4 3 3 3 5% 5% 42%	2470
	11th to 20th	Night	17% 7% 2 5% 4 3 3 3 4 5% 46%	2330
	21st to end	Night	20% 6% 2 4 3 2 3 3 5% 4 47%	1803
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%	1892
	21st to end	Night	9% 4 1 4 3 3 3 3 5% 7% 60%	2036
October	1st to 10th	Night	9% 3 1 3 2 3 3 4 5% 7% 60%	2160
	11th to 20th	Night	14% 4 2 4 3 2 3 2 4 4 59%	2160
	21st to end	Night	19% 5% 2 5% 3 2 2 2 3 4 54%	2376
November	1st to 10th	Night	11% 4 2 4 3 3 3 2 4 6% 57%	2220
	11th to 20th	Night	14% 4 2 4 2 2 4 3 4 5% 56%	2280
	21st to end	Night	17% 6% 2 4 3 2 3 2 4 6% 50%	2579
December	1st to 10th	Night	19% 5% 2 5% 3 3 3 2 4 5% 48%	2660
	11th to 20th	Night	19% 5% 2 6% 4 3 3 3 4 4 47%	3243
	21st to end	Night	19% 7% 3 6% 4 4 4 3 5% 6% 40%	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	43% 2 7% 24% 20% 3	2848
	11th to 20th	Day	38% 4 12% 23% 20% 3	2850
	21st to end	Day	44% 4 7% 18% 21% 6%	3135
February	1st to 10th	Day	45% 3 11% 21% 16% 4	1710
	11th to 20th	Day	44% 4 7% 22% 19% 5%	1744
	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	34% 5% 12% 21% 23% 5%	2141
	21st to end	Day	30% 5% 9% 21% 28% 7%	1904
October	1st to 10th	Day	29% 4 9% 24% 27% 8%	1800
	11th to 20th	Day	33% 4 5% 22% 26% 10%	1800
	21st to end	Day	38% 4 6% 23% 19% 8%	1980
November	1st to 10th	Day	31% 5% 8% 26% 23% 8%	1858
	11th to 20th	Day	30% 4 7% 24% 26% 8%	1900
	21st to end	Day	42% 3 8% 19% 23% 5%	1592
December	1st to 10th	Day	38% 3 10% 26% 19% 5%	1520
	11th to 20th	Day	43% 5% 5% 21% 22% 4	1929
	21st to end	Day	47% 7% 9% 18% 14% 5%	3135
January	1st to 10th	Night	41% 4 6% 21% 25% 3	4108
	11th to 20th	Night	33% 3 12% 23% 25% 3	4120
	21st to end	Night	43% 3 10% 17% 23% 4	4532
February	1st to 10th	Night	44% 4 8% 21% 18% 4	2470
	11th to 20th	Night	41% 4 7% 22% 20% 6%	2331
	21st to end	Night	40% 3 7% 19% 22% 9%	1803
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% 7% 11% 20% 25% 6%	1892
	21st to end	Night	24% 6% 8% 23% 31% 8%	2036
October	1st to 10th	Night	24% 6% 12% 23% 25% 11%	2160
	11th to 20th	Night	30% 4 5% 19% 31% 10%	2160
	21st to end	Night	36% 3 6% 20% 24% 10%	2376
November	1st to 10th	Night	29% 5% 8% 24% 25% 9%	2220
	11th to 20th	Night	29% 4 7% 25% 27% 9%	2280
	21st to end	Night	37% 3 7% 22% 27% 5%	2579
December	1st to 10th	Night	40% 3 8% 22% 21% 5%	2660
	11th to 20th	Night	41% 3 6% 22% 23% 5%	3245
	21st to end	Night	43% 6% 9% 24% 15% 3	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	27% 4 29% 26% 12% 2	270
	11th to 20th	Day	24% 8% 37% 23% 7% 1	270
	21st to end	Day	22% 7% 36% 25% 10% 1	297
February	1st to 10th	Day	29% 6% 27% 27% 10% 1	270
	11th to 20th	Day	24% 7% 36% 27% 6%	270
	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% 6% 22% 40% 20%	407
	21st to end	Day	13% 1 8% 26% 31% 21%	270
October	1st to 10th	Day	9% 18% 29% 29% 16%	270
	11th to 20th	Day	14% 4 24% 31% 22% 5%	270
	21st to end	Day	28% 7% 23% 22% 17% 4	297
November	1st to 10th	Day	15% 2 26% 24% 26% 7%	270
	11th to 20th	Day	15% 3 31% 30% 19% 2	270
	21st to end	Day	23% 11% 19% 24% 19% 4	270
December	1st to 10th	Day	21% 4 39% 17% 16% 4	270
	11th to 20th	Day	23% 6% 29% 29% 12%	270
	21st to end	Day	27% 8% 28% 28% 8% 1	297
January	1st to 10th	Night	22% 8% 27% 35% 6%	950
	11th to 20th	Night	21% 8% 30% 34% 6%	950
	21st to end	Night	21% 5% 33% 36% 5%	1045
February	1st to 10th	Night	24% 7% 26% 38% 5%	950
	11th to 20th	Night	20% 8% 33% 36% 3	856
	21st to end	Night	23% 8% 33% 33% 2	547
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% 5% 34% 45% 4	552
	21st to end	Night	10% 1 8% 36% 40% 5%	596
October	1st to 10th	Night	11% 1 10% 39% 36% 3	720
	11th to 20th	Night	14% 3 21% 43% 19% 1	720
	21st to end	Night	22% 4 19% 35% 18% 2	792
November	1st to 10th	Night	13% 4 17% 44% 21% 1	740
	11th to 20th	Night	16% 6% 23% 43% 13%	760
	21st to end	Night	20% 6% 22% 37% 14% 1	874
December	1st to 10th	Night	23% 4 25% 39% 8%	950
	11th to 20th	Night	24% 7% 20% 42% 7%	950
	21st to end	Night	23% 8% 24% 37% 7%	1045

Page generated at 2024-09-11 09:00:01. Version ac07

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