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 2024-01-31.

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% 5% 2 5% 5% 3 5% 4 5% 7% 45%	74549
	Night	14% 5% 2 4 4 2 4 4 5% 7% 51%	75579
Transparency	Day	38% 6% 11% 23% 18% 4	74272
	Night	34% 5% 10% 24% 22% 6%	75376
Seeing	Day	16% 3 17% 25% 27% 12%	14289
	Night	16% 4 19% 37% 22% 2	24261

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	20% 7% 2 5% 3 2 3 3 3 4 49%	1707
	11th to 20th	Day	17% 6% 3 6% 5% 3 3 3 4 6% 44%	1710
	21st to end	Day	17% 6% 2 4 4 2 3 4 4 5% 49%	1872
February	1st to 10th	Day	22% 8% 3 4 3 2 3 3 3 4 45%	1620
	11th to 20th	Day	20% 6% 2 5% 4 2 4 4 4 5% 43%	1642
	21st to end	Day	23% 8% 3 4 5% 3 3 3 3 5% 38%	1570
March	1st to 10th	Day	19% 6% 2 4 4 3 4 3 4 6% 47%	1980
	11th to 20th	Day	21% 6% 2 5% 4 2 4 4 3 4 42%	1980
	21st to end	Day	19% 7% 3 6% 4 3 5% 4 5% 5% 40%	2178
April	1st to 10th	Day	16% 5% 3 5% 5% 3 4 5% 5% 6% 43%	2125
	11th to 20th	Day	18% 6% 2 4 4 3 4 4 5% 6% 44%	2134
	21st to end	Day	18% 6% 3 5% 5% 3 5% 5% 4 7% 41%	2160
May	1st to 10th	Day	18% 7% 3 5% 5% 3 4 4 5% 5% 40%	2212
	11th to 20th	Day	13% 6% 2 6% 6% 3 5% 4 6% 8% 41%	2302
	21st to end	Day	11% 4 3 6% 6% 4 6% 6% 6% 8% 39%	2531
June	1st to 10th	Day	9% 5% 2 5% 6% 4 5% 5% 6% 9% 43%	2340
	11th to 20th	Day	6% 3 2 4 6% 4 6% 6% 7% 9% 46%	2340
	21st to end	Day	5% 3 1 3 5% 3 6% 7% 7% 9% 50%	2340
July	1st to 10th	Day	7% 5% 3 6% 7% 5% 7% 6% 7% 11% 38%	2340
	11th to 20th	Day	4 4 2 4 5% 4 7% 6% 6% 9% 48%	2340
	21st to end	Day	6% 3 2 5% 5% 3 6% 6% 8% 12% 44%	2546
August	1st to 10th	Day	7% 5% 2 5% 6% 5% 6% 6% 7% 10% 41%	2328
	11th to 20th	Day	11% 4 2 5% 4 3 5% 5% 6% 9% 45%	2191
	21st to end	Day	7% 4 2 4 4 4 6% 5% 6% 8% 49%	2376
September	1st to 10th	Day	11% 5% 2 4 4 3 5% 5% 4 8% 49%	2160
	11th to 20th	Day	13% 4 1 4 5% 2 4 4 6% 7% 50%	2104
	21st to end	Day	9% 3 2 5% 4 2 4 5% 4 6% 55%	1904
October	1st to 10th	Day	9% 4 1 5% 4 3 3 3 5% 7% 56%	1800
	11th to 20th	Day	15% 5% 1 4 3 2 3 3 4 5% 54%	1800
	21st to end	Day	21% 4 2 4 3 2 4 3 4 4 49%	1980
November	1st to 10th	Day	13% 4 2 3 3 2 4 3 4 5% 55%	1858
	11th to 20th	Day	14% 5% 2 4 2 2 4 3 5% 6% 54%	1900
	21st to end	Day	20% 6% 2 5% 3 3 2 3 3 6% 46%	1592
December	1st to 10th	Day	19% 4 2 5% 3 2 3 2 5% 7% 48%	1520
	11th to 20th	Day	16% 8% 2 5% 4 3 5% 4 4 5% 44%	1932
	21st to end	Day	19% 9% 3 6% 6% 3 4 4 4 6% 36%	3135
January	1st to 10th	Night	19% 5% 2 3 3 2 2 3 3 6% 51%	2458
	11th to 20th	Night	17% 5% 2 4 4 2 3 3 3 5% 50%	2470
	21st to end	Night	17% 5% 2 3 3 2 3 3 4 5% 53%	2711
February	1st to 10th	Night	19% 8% 2 4 5% 3 3 3 4 5% 43%	2340
	11th to 20th	Night	18% 6% 3 5% 4 3 3 3 4 6% 45%	2204
	21st to end	Night	22% 6% 2 3 3 2 4 3 4 5% 46%	1700
March	1st to 10th	Night	18% 5% 2 4 4 2 4 3 5% 5% 48%	1980
	11th to 20th	Night	19% 6% 3 5% 5% 3 3 4 3 7% 44%	1980
	21st to end	Night	20% 6% 2 5% 4 3 4 4 4 6% 43%	2178
April	1st to 10th	Night	14% 4 3 4 4 2 4 4 5% 8% 50%	1833
	11th to 20th	Night	13% 5% 2 5% 5% 3 4 4 4 7% 49%	1775
	21st to end	Night	18% 5% 2 4 4 3 4 4 6% 6% 45%	1800
May	1st to 10th	Night	15% 4 2 4 4 3 4 4 5% 8% 47%	1744
	11th to 20th	Night	16% 5% 2 4 3 2 4 4 5% 8% 48%	1593
	21st to end	Night	9% 5% 3 4 4 4 5% 4 6% 11% 45%	1745
June	1st to 10th	Night	6% 4 1 4 4 2 4 5% 6% 10% 54%	1620
	11th to 20th	Night	4 3 2 3 3 2 3 4 5% 11% 59%	1620
	21st to end	Night	4 2 2 3 2 2 3 5% 5% 9% 62%	1620
July	1st to 10th	Night	3 3 2 5% 4 3 6% 6% 8% 10% 48%	1620
	11th to 20th	Night	4 2 2 3 4 3 5% 4 7% 11% 56%	1620
	21st to end	Night	4 2 2 4 4 3 5% 6% 6% 12% 53%	1772
August	1st to 10th	Night	5% 3 1 4 6% 4 5% 5% 8% 11% 49%	1611
	11th to 20th	Night	7% 4 2 4 4 3 4 5% 5% 8% 52%	1707
	21st to end	Night	5% 3 2 5% 5% 3 5% 4 6% 10% 52%	1980
September	1st to 10th	Night	8% 4 2 3 4 2 4 5% 5% 6% 58%	1800
	11th to 20th	Night	10% 4 2 4 4 3 4 5% 6% 7% 51%	1852
	21st to end	Night	9% 4 1 3 3 2 3 4 5% 7% 60%	2036
October	1st to 10th	Night	9% 3 1 3 3 2 3 4 5% 7% 60%	2160
	11th to 20th	Night	14% 3 2 3 4 2 3 3 3 4 59%	2160
	21st to end	Night	19% 5% 2 4 3 2 3 2 3 4 54%	2376
November	1st to 10th	Night	11% 4 2 4 3 2 3 3 4 6% 58%	2220
	11th to 20th	Night	14% 3 2 4 3 1 3 4 4 5% 57%	2280
	21st to end	Night	17% 6% 2 4 3 2 3 3 4 7% 50%	2579
December	1st to 10th	Night	19% 5% 2 5% 4 2 4 3 4 5% 48%	2660
	11th to 20th	Night	19% 5% 2 5% 5% 2 3 4 3 5% 47%	3243
	21st to end	Night	19% 7% 3 5% 5% 3 4 4 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	42% 3 7% 23% 20% 5%	1708
	11th to 20th	Day	42% 3 9% 24% 19% 3	1710
	21st to end	Day	38% 4 7% 27% 20% 4	1872
February	1st to 10th	Day	45% 3 10% 21% 16% 4	1620
	11th to 20th	Day	44% 4 7% 23% 18% 4	1651
	21st to end	Day	50% 3 6% 16% 17% 8%	1570
March	1st to 10th	Day	41% 3 8% 19% 19% 10%	1980
	11th to 20th	Day	47% 4 8% 21% 16% 4	1980
	21st to end	Day	47% 4 10% 24% 13% 2	2178
April	1st to 10th	Day	40% 6% 9% 21% 21% 3	2125
	11th to 20th	Day	41% 5% 9% 22% 17% 6%	2134
	21st to end	Day	44% 6% 9% 22% 18% 2	2160
May	1st to 10th	Day	45% 6% 10% 19% 18% 2	2212
	11th to 20th	Day	39% 8% 14% 25% 13% 2	2306
	21st to end	Day	41% 8% 14% 22% 14% 1	2531
June	1st to 10th	Day	36% 7% 14% 27% 15% 1	2340
	11th to 20th	Day	32% 8% 16% 25% 18% 2	2340
	21st to end	Day	26% 9% 13% 27% 20% 4	2340
July	1st to 10th	Day	37% 9% 15% 26% 12% 1	2276
	11th to 20th	Day	29% 8% 15% 25% 19% 3	2271
	21st to end	Day	30% 9% 19% 30% 11% 1	2405
August	1st to 10th	Day	34% 9% 16% 29% 11% 1	2314
	11th to 20th	Day	35% 8% 14% 25% 18% 2	2191
	21st to end	Day	31% 9% 17% 24% 15% 5%	2376
September	1st to 10th	Day	34% 6% 10% 24% 19% 7%	2160
	11th to 20th	Day	33% 6% 12% 21% 23% 5%	2104
	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	37% 3 7% 23% 26% 5%	2458
	11th to 20th	Night	38% 3 10% 23% 21% 4	2470
	21st to end	Night	36% 2 7% 24% 25% 5%	2711
February	1st to 10th	Night	44% 4 8% 22% 18% 4	2340
	11th to 20th	Night	41% 4 7% 23% 20% 5%	2205
	21st to end	Night	42% 3 7% 18% 21% 8%	1700
March	1st to 10th	Night	39% 4 9% 16% 22% 11%	1980
	11th to 20th	Night	44% 4 8% 20% 17% 6%	1980
	21st to end	Night	44% 5% 8% 22% 18% 3	2178
April	1st to 10th	Night	34% 4 10% 23% 20% 8%	1833
	11th to 20th	Night	35% 5% 7% 24% 20% 8%	1775
	21st to end	Night	38% 6% 9% 23% 21% 2	1800
May	1st to 10th	Night	36% 6% 12% 23% 19% 4	1744
	11th to 20th	Night	35% 6% 14% 25% 17% 2	1594
	21st to end	Night	34% 8% 16% 27% 15% 1	1746
June	1st to 10th	Night	25% 7% 14% 31% 19% 3	1620
	11th to 20th	Night	20% 6% 13% 35% 23% 2	1620
	21st to end	Night	19% 6% 15% 29% 24% 8%	1620
July	1st to 10th	Night	25% 9% 21% 25% 19% 2	1575
	11th to 20th	Night	21% 8% 19% 28% 21% 4	1566
	21st to end	Night	22% 9% 17% 33% 17% 1	1673
August	1st to 10th	Night	27% 7% 18% 34% 14% 1	1601
	11th to 20th	Night	28% 6% 17% 26% 21% 3	1707
	21st to end	Night	28% 7% 16% 26% 19% 5%	1980
September	1st to 10th	Night	26% 7% 10% 28% 22% 8%	1800
	11th to 20th	Night	30% 7% 11% 20% 25% 6%	1852
	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% 9% 1	294
February	1st to 10th	Day	28% 5% 28% 27% 9% 2	240
	11th to 20th	Day	25% 7% 38% 25% 5%	240
	21st to end	Day	34% 7% 32% 19% 8% 1	198
March	1st to 10th	Day	26% 7% 30% 26% 10% 2	240
	11th to 20th	Day	28% 10% 31% 21% 9%	240
	21st to end	Day	21% 11% 36% 23% 8% 2	264
April	1st to 10th	Day	19% 6% 33% 27% 12% 3	385
	11th to 20th	Day	25% 7% 24% 31% 11% 2	412
	21st to end	Day	24% 4 26% 30% 13% 3	420
May	1st to 10th	Day	21% 5% 23% 32% 18% 2	475
	11th to 20th	Day	18% 3 16% 29% 26% 8%	625
	21st to end	Day	13% 1 13% 36% 26% 11%	679
June	1st to 10th	Day	12% 1 9% 23% 38% 17%	630
	11th to 20th	Day	8% 1 9% 27% 37% 19%	630
	21st to end	Day	5% 1 10% 32% 33% 19%	630
July	1st to 10th	Day	7% 1 6% 23% 37% 27%	621
	11th to 20th	Day	6% 6% 25% 36% 27%	618
	21st to end	Day	6% 1 3 21% 41% 27%	684
August	1st to 10th	Day	10% 6% 20% 46% 18%	626
	11th to 20th	Day	14% 3 18% 45% 20%	505
	21st to end	Day	12% 1 13% 42% 33%	495
September	1st to 10th	Day	11% 3 17% 46% 24%	450
	11th to 20th	Day	11% 6% 21% 41% 21%	394
	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%	1043
February	1st to 10th	Night	24% 7% 27% 37% 5%	900
	11th to 20th	Night	20% 8% 32% 37% 3	810
	21st to end	Night	24% 8% 32% 34% 2	516
March	1st to 10th	Night	19% 5% 29% 41% 6%	540
	11th to 20th	Night	22% 6% 25% 39% 7%	540
	21st to end	Night	22% 5% 28% 36% 8%	594
April	1st to 10th	Night	17% 4 34% 35% 10%	540
	11th to 20th	Night	14% 7% 30% 37% 12%	533
	21st to end	Night	21% 4 26% 35% 13%	540
May	1st to 10th	Night	16% 2 19% 46% 16%	540
	11th to 20th	Night	18% 1 17% 37% 25% 2	531
	21st to end	Night	11% 2 11% 41% 31% 4	584
June	1st to 10th	Night	8% 1 8% 34% 43% 5%	540
	11th to 20th	Night	5% 1 6% 41% 43% 4	540
	21st to end	Night	5% 1 7% 34% 47% 7%	540
July	1st to 10th	Night	3 5% 31% 50% 10%	525
	11th to 20th	Night	5% 3 28% 51% 12%	522
	21st to end	Night	4 2 30% 52% 11%	591
August	1st to 10th	Night	6% 3 32% 52% 7%	537
	11th to 20th	Night	10% 4 35% 42% 9%	534
	21st to end	Night	7% 4 27% 54% 8%	594
September	1st to 10th	Night	10% 4 29% 51% 6%	540
	11th to 20th	Night	12% 5% 33% 46% 4	540
	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 2024-01-28 04:26:33. Version ac07

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