Arkansas Sky Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arkansas Sky 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	13% 5% 2 5% 5% 3 4 5% 5% 7% 45%	74776
	Night	13% 5% 2 4 4 2 4 4 4 7% 50%	75354
Transparency	Day	38% 6% 11% 23% 18% 4	74499
	Night	34% 5% 10% 23% 22% 6%	75151
Seeing	Day	15% 7% 21% 26% 23% 9%	14283
	Night	15% 6% 24% 34% 19% 2	24244

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 2 4 4 48%	1707
	11th to 20th	Day	18% 7% 3 5% 5% 2 3 4 3 5% 44%	1710
	21st to end	Day	17% 6% 2 4 3 2 3 3 4 5% 50%	1872
February	1st to 10th	Day	22% 8% 2 5% 4 2 4 3 3 4 45%	1620
	11th to 20th	Day	18% 7% 3 6% 4 3 4 3 4 5% 42%	1684
	21st to end	Day	24% 8% 4 5% 4 3 3 3 4 6% 38%	1520
March	1st to 10th	Day	20% 5% 2 5% 4 3 4 4 4 5% 45%	1980
	11th to 20th	Day	21% 7% 3 6% 5% 2 4 4 4 4 41%	1980
	21st to end	Day	19% 7% 3 6% 5% 3 5% 3 5% 5% 40%	2178
April	1st to 10th	Day	14% 6% 2 6% 5% 3 4 4 6% 8% 42%	2160
	11th to 20th	Day	17% 6% 2 4 5% 3 4 4 4 6% 44%	2134
	21st to end	Day	16% 6% 2 5% 6% 3 5% 5% 5% 7% 40%	2160
May	1st to 10th	Day	16% 6% 3 5% 6% 3 5% 4 5% 7% 40%	2160
	11th to 20th	Day	13% 5% 2 5% 4 3 5% 5% 6% 9% 41%	2290
	21st to end	Day	10% 4 3 6% 7% 4 6% 7% 7% 9% 37%	2535
June	1st to 10th	Day	8% 5% 3 4 6% 4 6% 6% 8% 9% 42%	2520
	11th to 20th	Day	5% 3 1 5% 5% 3 5% 6% 8% 11% 47%	2520
	21st to end	Day	5% 3 2 4 5% 3 5% 6% 7% 10% 50%	2419
July	1st to 10th	Day	6% 5% 3 6% 8% 4 7% 7% 7% 11% 36%	2340
	11th to 20th	Day	5% 4 2 4 5% 4 6% 8% 8% 10% 44%	2340
	21st to end	Day	6% 4 2 5% 6% 3 6% 6% 8% 10% 45%	2546
August	1st to 10th	Day	7% 5% 2 6% 5% 4 5% 6% 7% 10% 41%	2328
	11th to 20th	Day	11% 5% 2 4 5% 3 5% 5% 7% 8% 44%	2148
	21st to end	Day	7% 4 2 5% 5% 4 6% 6% 6% 9% 48%	2376
September	1st to 10th	Day	12% 6% 2 4 5% 3 4 5% 5% 8% 47%	2160
	11th to 20th	Day	12% 5% 2 4 4 3 4 5% 5% 9% 46%	2160
	21st to end	Day	10% 4 2 4 4 3 4 4 5% 6% 54%	1882
October	1st to 10th	Day	8% 4 2 4 4 2 3 4 5% 6% 57%	1800
	11th to 20th	Day	15% 4 1 4 3 2 3 3 4 6% 55%	1800
	21st to end	Day	19% 4 2 5% 3 2 3 4 4 5% 49%	1980
November	1st to 10th	Day	13% 5% 2 4 2 2 3 3 3 6% 58%	1858
	11th to 20th	Day	13% 5% 2 4 3 2 4 3 4 6% 54%	1812
	21st to end	Day	21% 7% 2 4 4 2 4 3 4 6% 44%	1650
December	1st to 10th	Day	20% 6% 2 4 4 2 2 3 3 5% 48%	1520
	11th to 20th	Day	16% 7% 3 6% 6% 3 4 4 3 4 44%	1918
	21st to end	Day	16% 8% 4 7% 6% 3 4 4 5% 6% 38%	3009
January	1st to 10th	Night	20% 6% 2 4 3 2 3 3 4 5% 50%	2458
	11th to 20th	Night	17% 6% 2 5% 4 2 4 3 3 5% 48%	2470
	21st to end	Night	18% 5% 2 3 3 2 3 3 4 4 52%	2711
February	1st to 10th	Night	21% 7% 3 5% 5% 2 3 3 4 5% 42%	2340
	11th to 20th	Night	18% 7% 2 5% 4 3 3 3 4 5% 45%	2161
	21st to end	Night	20% 6% 2 4 4 2 4 3 3 6% 45%	1750
March	1st to 10th	Night	18% 7% 2 4 4 2 3 3 4 6% 47%	1980
	11th to 20th	Night	18% 7% 3 5% 5% 3 3 3 4 6% 43%	1980
	21st to end	Night	18% 6% 2 6% 5% 2 4 5% 4 6% 43%	2178
April	1st to 10th	Night	12% 5% 2 4 5% 3 4 4 5% 8% 50%	1800
	11th to 20th	Night	13% 5% 2 4 4 3 4 5% 5% 6% 50%	1775
	21st to end	Night	15% 5% 2 4 4 3 4 4 5% 8% 47%	1800
May	1st to 10th	Night	15% 5% 1 5% 4 3 4 5% 5% 8% 47%	1800
	11th to 20th	Night	15% 6% 2 4 3 2 3 3 5% 9% 48%	1601
	21st to end	Night	8% 5% 3 5% 6% 3 6% 5% 7% 10% 44%	1732
June	1st to 10th	Night	5% 4 2 3 4 3 4 5% 6% 12% 52%	1440
	11th to 20th	Night	3 3 2 3 3 2 4 4 5% 10% 61%	1440
	21st to end	Night	4 2 2 3 4 2 4 4 6% 9% 60%	1532
July	1st to 10th	Night	4 3 2 4 5% 2 5% 6% 7% 11% 48%	1620
	11th to 20th	Night	4 2 1 3 4 2 4 6% 6% 11% 56%	1620
	21st to end	Night	4 2 1 4 4 3 5% 5% 7% 11% 53%	1772
August	1st to 10th	Night	4 3 1 6% 5% 3 5% 4 8% 11% 50%	1611
	11th to 20th	Night	7% 4 2 5% 4 2 4 6% 6% 9% 51%	1750
	21st to end	Night	5% 4 2 4 6% 3 5% 5% 6% 11% 49%	1980
September	1st to 10th	Night	7% 4 2 5% 4 3 4 4 4 8% 56%	1800
	11th to 20th	Night	8% 5% 2 5% 4 3 4 4 5% 7% 53%	1800
	21st to end	Night	8% 4 2 3 3 2 3 4 5% 6% 61%	2056
October	1st to 10th	Night	8% 4 1 3 3 2 3 4 4 6% 60%	2160
	11th to 20th	Night	12% 3 2 3 3 2 3 3 3 4 61%	2160
	21st to end	Night	19% 5% 2 3 3 2 3 3 2 3 54%	2376
November	1st to 10th	Night	11% 5% 2 4 4 2 3 3 3 5% 57%	2220
	11th to 20th	Night	13% 4 2 3 3 2 3 3 4 6% 57%	2364
	21st to end	Night	16% 5% 2 5% 3 2 3 3 4 5% 50%	2527
December	1st to 10th	Night	19% 5% 2 5% 4 2 3 3 4 4 47%	2660
	11th to 20th	Night	17% 5% 3 4 6% 3 3 3 4 4 49%	3279
	21st to end	Night	17% 7% 3 6% 5% 3 4 4 4 5% 42%	4651

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% 3 7% 23% 18% 6%	1708
	11th to 20th	Day	44% 3 9% 23% 19% 2	1710
	21st to end	Day	38% 3 8% 26% 21% 5%	1872
February	1st to 10th	Day	46% 3 10% 22% 16% 3	1620
	11th to 20th	Day	46% 5% 6% 21% 18% 4	1693
	21st to end	Day	49% 4 7% 16% 16% 8%	1520
March	1st to 10th	Day	43% 4 9% 16% 19% 9%	1980
	11th to 20th	Day	47% 4 8% 20% 16% 4	1980
	21st to end	Day	46% 6% 10% 24% 13% 2	2178
April	1st to 10th	Day	40% 5% 9% 22% 21% 3	2160
	11th to 20th	Day	41% 5% 9% 23% 16% 6%	2134
	21st to end	Day	43% 6% 9% 21% 19% 2	2160
May	1st to 10th	Day	43% 7% 11% 18% 18% 2	2160
	11th to 20th	Day	38% 8% 14% 24% 14% 1	2294
	21st to end	Day	40% 9% 13% 24% 12% 1	2535
June	1st to 10th	Day	34% 8% 14% 25% 16% 1	2520
	11th to 20th	Day	28% 9% 17% 27% 17% 2	2520
	21st to end	Day	27% 9% 12% 27% 21% 4	2419
July	1st to 10th	Day	36% 10% 16% 23% 13% 2	2276
	11th to 20th	Day	30% 9% 15% 25% 18% 3	2271
	21st to end	Day	31% 10% 17% 29% 12% 1	2405
August	1st to 10th	Day	34% 10% 16% 28% 11% 1	2314
	11th to 20th	Day	35% 8% 13% 25% 17% 1	2148
	21st to end	Day	32% 9% 14% 25% 15% 5%	2376
September	1st to 10th	Day	35% 7% 11% 21% 19% 7%	2160
	11th to 20th	Day	35% 7% 11% 19% 23% 5%	2160
	21st to end	Day	31% 6% 9% 19% 28% 7%	1882
October	1st to 10th	Day	28% 5% 9% 23% 27% 7%	1800
	11th to 20th	Day	32% 3 6% 21% 28% 9%	1800
	21st to end	Day	38% 3 6% 24% 20% 9%	1980
November	1st to 10th	Day	30% 3 9% 26% 24% 8%	1858
	11th to 20th	Day	31% 4 7% 22% 27% 8%	1812
	21st to end	Day	43% 3 6% 19% 23% 5%	1650
December	1st to 10th	Day	41% 2 10% 25% 18% 5%	1520
	11th to 20th	Day	44% 4 5% 22% 20% 5%	1915
	21st to end	Day	45% 5% 9% 19% 16% 6%	3009
January	1st to 10th	Night	38% 3 7% 21% 26% 5%	2458
	11th to 20th	Night	39% 4 9% 23% 20% 4	2470
	21st to end	Night	37% 3 7% 24% 25% 5%	2711
February	1st to 10th	Night	45% 4 8% 20% 18% 5%	2340
	11th to 20th	Night	43% 3 7% 22% 19% 6%	2162
	21st to end	Night	43% 3 7% 19% 20% 8%	1750
March	1st to 10th	Night	39% 3 9% 16% 21% 11%	1980
	11th to 20th	Night	45% 4 9% 19% 17% 6%	1980
	21st to end	Night	43% 5% 9% 22% 18% 3	2178
April	1st to 10th	Night	33% 5% 10% 24% 20% 8%	1800
	11th to 20th	Night	33% 6% 8% 23% 21% 9%	1775
	21st to end	Night	36% 5% 11% 23% 22% 2	1800
May	1st to 10th	Night	37% 6% 11% 23% 19% 4	1800
	11th to 20th	Night	35% 6% 12% 26% 18% 2	1602
	21st to end	Night	35% 8% 15% 26% 14% 2	1733
June	1st to 10th	Night	24% 7% 15% 30% 22% 2	1440
	11th to 20th	Night	21% 5% 13% 33% 25% 3	1440
	21st to end	Night	21% 6% 14% 27% 23% 8%	1532
July	1st to 10th	Night	26% 9% 19% 26% 18% 2	1575
	11th to 20th	Night	20% 9% 19% 28% 18% 6%	1566
	21st to end	Night	22% 10% 15% 33% 19% 1	1673
August	1st to 10th	Night	25% 8% 20% 33% 13% 1	1601
	11th to 20th	Night	28% 7% 16% 27% 20% 2	1750
	21st to end	Night	28% 7% 16% 26% 18% 5%	1980
September	1st to 10th	Night	27% 6% 12% 25% 22% 8%	1800
	11th to 20th	Night	31% 6% 10% 21% 26% 7%	1800
	21st to end	Night	25% 5% 9% 22% 30% 9%	2056
October	1st to 10th	Night	25% 5% 10% 24% 25% 11%	2160
	11th to 20th	Night	29% 4 6% 19% 33% 10%	2160
	21st to end	Night	38% 3 5% 20% 25% 10%	2376
November	1st to 10th	Night	30% 4 8% 23% 26% 9%	2220
	11th to 20th	Night	30% 3 6% 25% 27% 9%	2364
	21st to end	Night	37% 3 7% 21% 26% 5%	2527
December	1st to 10th	Night	41% 4 9% 20% 21% 6%	2660
	11th to 20th	Night	40% 3 6% 21% 24% 5%	3281
	21st to end	Night	43% 4 9% 23% 18% 3	4651

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% 10% 31% 24% 8% 1	270
	11th to 20th	Day	24% 16% 39% 18% 3	270
	21st to end	Day	19% 17% 38% 19% 6%	294
February	1st to 10th	Day	26% 13% 37% 16% 7% 1	240
	11th to 20th	Day	24% 22% 36% 15% 3	240
	21st to end	Day	39% 11% 30% 16% 4	198
March	1st to 10th	Day	24% 14% 33% 22% 6%	240
	11th to 20th	Day	28% 17% 33% 21% 2	240
	21st to end	Day	25% 16% 40% 13% 5% 1	264
April	1st to 10th	Day	19% 12% 33% 25% 10% 1	420
	11th to 20th	Day	23% 10% 30% 25% 11%	412
	21st to end	Day	20% 9% 31% 26% 11% 2	420
May	1st to 10th	Day	18% 9% 29% 29% 13% 1	423
	11th to 20th	Day	16% 5% 22% 32% 19% 6%	613
	21st to end	Day	10% 4 20% 35% 24% 7%	679
June	1st to 10th	Day	10% 3 15% 26% 33% 13%	630
	11th to 20th	Day	6% 1 11% 36% 35% 11%	630
	21st to end	Day	4 2 15% 35% 30% 13%	630
July	1st to 10th	Day	6% 2 9% 27% 39% 16%	621
	11th to 20th	Day	5% 2 10% 30% 32% 22%	618
	21st to end	Day	6% 1 7% 25% 40% 19%	684
August	1st to 10th	Day	8% 1 9% 30% 38% 14%	626
	11th to 20th	Day	15% 3 6% 24% 39% 13%	462
	21st to end	Day	10% 2 4 19% 42% 23%	495
September	1st to 10th	Day	10% 3 9% 19% 42% 18%	450
	11th to 20th	Day	10% 2 10% 24% 38% 16%	450
	21st to end	Day	11% 4 13% 35% 27% 10%	280
October	1st to 10th	Day	8% 3 24% 31% 27% 7%	270
	11th to 20th	Day	16% 8% 30% 29% 14% 3	270
	21st to end	Day	26% 10% 27% 22% 12% 2	297
November	1st to 10th	Day	15% 9% 30% 26% 19% 2	270
	11th to 20th	Day	13% 11% 33% 32% 10% 1	270
	21st to end	Day	24% 12% 29% 21% 12% 1	270
December	1st to 10th	Day	21% 16% 32% 18% 11% 2	270
	11th to 20th	Day	26% 14% 29% 20% 10%	270
	21st to end	Day	24% 14% 37% 21% 4	297
January	1st to 10th	Night	22% 8% 34% 31% 5%	950
	11th to 20th	Night	21% 10% 35% 29% 4	950
	21st to end	Night	20% 8% 38% 30% 4	1043
February	1st to 10th	Night	23% 11% 32% 30% 4	900
	11th to 20th	Night	21% 9% 40% 28% 2	766
	21st to end	Night	23% 12% 38% 24% 2	566
March	1st to 10th	Night	20% 9% 33% 34% 4	540
	11th to 20th	Night	20% 10% 32% 32% 5% 1	540
	21st to end	Night	19% 8% 35% 30% 8%	594
April	1st to 10th	Night	15% 10% 35% 32% 8%	540
	11th to 20th	Night	15% 8% 34% 32% 10% 1	533
	21st to end	Night	16% 6% 35% 32% 11%	540
May	1st to 10th	Night	16% 3 24% 46% 12%	540
	11th to 20th	Night	15% 5% 26% 30% 22% 2	531
	21st to end	Night	9% 2 15% 42% 27% 5%	584
June	1st to 10th	Night	6% 3 10% 38% 38% 4	540
	11th to 20th	Night	4 1 6% 46% 40% 3	540
	21st to end	Night	4 1 8% 38% 43% 6%	540
July	1st to 10th	Night	5% 1 7% 32% 47% 8%	525
	11th to 20th	Night	4 1 6% 31% 48% 9%	522
	21st to end	Night	4 1 6% 33% 47% 10%	591
August	1st to 10th	Night	3 1 6% 37% 46% 7%	537
	11th to 20th	Night	9% 1 5% 37% 41% 7%	534
	21st to end	Night	7% 1 6% 28% 51% 7%	594
September	1st to 10th	Night	8% 1 6% 37% 44% 4	540
	11th to 20th	Night	9% 1 9% 37% 41% 4	540
	21st to end	Night	9% 2 13% 36% 37% 3	630
October	1st to 10th	Night	9% 2 16% 36% 33% 3	720
	11th to 20th	Night	12% 4 26% 38% 19%	720
	21st to end	Night	20% 6% 25% 32% 16% 1	792
November	1st to 10th	Night	13% 5% 24% 41% 17% 1	740
	11th to 20th	Night	14% 8% 28% 38% 12%	760
	21st to end	Night	17% 10% 28% 32% 13%	817
December	1st to 10th	Night	22% 6% 30% 35% 7%	950
	11th to 20th	Night	22% 9% 26% 36% 6%	950
	21st to end	Night	21% 11% 31% 30% 5%	1045

Page generated at 2024-01-28 04:26:36. Version ac07

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