Keeton Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Keeton Observing Site clear sky chart from 2005-11-06 to 2024-01-17.

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	9% 5% 2 3 3 2 3 3 4 5% 62%	74791
	Night	11% 5% 2 3 3 2 3 3 4 6% 59%	75050
Transparency	Day	25% 4 8% 19% 25% 20%	74504
	Night	28% 4 8% 18% 23% 19%	74859
Seeing	Day	13% 12% 31% 29% 11% 4	14033
	Night	13% 4 16% 35% 25% 6%	23516

By Month

Percentage Cloud Cover SW (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 4 4 3 3 4 4 7% 42%	1519
	11th to 20th	Day	17% 5% 2 3 3 2 3 3 5% 6% 51%	1599
	21st to end	Day	16% 11% 2 4 3 3 3 4 5% 7% 42%	1782
February	1st to 10th	Day	18% 7% 2 4 3 2 3 3 4 5% 49%	1620
	11th to 20th	Day	13% 10% 2 4 3 2 3 3 4 7% 48%	1733
	21st to end	Day	20% 11% 3 4 4 2 3 3 4 4 43%	1480
March	1st to 10th	Day	18% 13% 3 6% 5% 3 4 4 5% 6% 35%	1813
	11th to 20th	Day	19% 10% 3 4 4 2 3 4 5% 7% 39%	1980
	21st to end	Day	17% 9% 2 5% 4 3 4 4 4 7% 40%	2290
April	1st to 10th	Day	15% 8% 2 4 4 2 3 4 4 7% 45%	2160
	11th to 20th	Day	13% 6% 2 4 4 2 3 4 4 6% 53%	2129
	21st to end	Day	12% 4 1 3 3 2 3 3 4 7% 58%	2160
May	1st to 10th	Day	8% 5% 2 4 2 1 3 3 5% 7% 60%	2201
	11th to 20th	Day	7% 5% 2 3 3 2 3 4 4 7% 61%	2448
	21st to end	Day	10% 4 2 4 4 2 3 4 5% 5% 57%	2723
June	1st to 10th	Day	6% 4 2 3 3 2 3 3 4 6% 64%	2520
	11th to 20th	Day	2 1 1 2 2 1 2 2 3 4 79%	2520
	21st to end	Day	2 2 1 1 2 1 2 2 3 3 82%	2520
July	1st to 10th	Day	1 1 1 1 1 1 2 2 3 87%	2520
	11th to 20th	Day	2 1 1 1 2 1 2 1 3 3 84%	2520
	21st to end	Day	1 2 1 2 2 1 2 2 3 4 80%	2595
August	1st to 10th	Day	2 1 2 2 1 2 2 3 4 80%	2320
	11th to 20th	Day	1 1 1 1 2 3 3 5% 83%	2122
	21st to end	Day	1 1 1 2 1 2 2 2 3 87%	2376
September	1st to 10th	Day	2 1 1 1 1 1 2 2 2 87%	2160
	11th to 20th	Day	3 2 1 3 2 1 2 2 4 5% 76%	2156
	21st to end	Day	4 3 1 2 2 2 2 2 2 3 77%	1972
October	1st to 10th	Day	6% 3 1 3 3 1 3 2 5% 5% 68%	1800
	11th to 20th	Day	5% 3 1 2 3 2 3 4 4 5% 69%	1800
	21st to end	Day	8% 2 1 3 3 2 3 3 4 5% 66%	1980
November	1st to 10th	Day	12% 5% 2 4 4 2 3 4 4 7% 52%	1680
	11th to 20th	Day	11% 4 1 3 4 2 4 4 5% 7% 55%	1710
	21st to end	Day	11% 7% 2 4 3 2 2 4 4 6% 54%	1641
December	1st to 10th	Day	15% 5% 2 4 3 3 3 3 4 6% 50%	1520
	11th to 20th	Day	25% 9% 4 6% 4 2 4 4 3 6% 33%	1928
	21st to end	Day	13% 8% 3 5% 5% 3 5% 6% 6% 8% 38%	2794
January	1st to 10th	Night	19% 8% 2 3 4 3 3 4 5% 7% 43%	2646
	11th to 20th	Night	14% 6% 2 4 4 3 5% 5% 5% 7% 45%	2501
	21st to end	Night	15% 8% 2 5% 4 3 3 4 4 6% 46%	2574
February	1st to 10th	Night	16% 7% 2 5% 4 2 3 3 4 6% 50%	2340
	11th to 20th	Night	13% 9% 3 3 4 2 3 4 5% 7% 47%	2113
	21st to end	Night	17% 10% 2 3 3 2 3 3 4 4 49%	1776
March	1st to 10th	Night	20% 11% 3 4 4 2 4 4 3 4 41%	2142
	11th to 20th	Night	19% 8% 2 5% 3 2 3 4 6% 7% 42%	1980
	21st to end	Night	18% 8% 2 4 4 2 4 5% 3 6% 44%	2066
April	1st to 10th	Night	14% 7% 2 4 5% 3 4 4 4 6% 47%	1800
	11th to 20th	Night	12% 6% 3 4 4 3 3 3 4 7% 53%	1779
	21st to end	Night	10% 4 2 3 2 2 3 4 5% 7% 59%	1800
May	1st to 10th	Night	8% 4 1 3 3 2 3 4 4 6% 62%	1756
	11th to 20th	Night	7% 3 1 2 3 1 3 4 5% 7% 64%	1442
	21st to end	Night	7% 4 2 3 3 2 2 3 4 7% 63%	1552
June	1st to 10th	Night	5% 4 1 3 2 2 3 4 3 6% 67%	1440
	11th to 20th	Night	1 1 1 1 2 2 2 3 4 82%	1440
	21st to end	Night	2 2 2 2 1 2 2 2 3 82%	1440
July	1st to 10th	Night	1 1 1 1 1 1 2 2 88%	1440
	11th to 20th	Night	1 1 1 2 1 1 2 2 2 3 83%	1440
	21st to end	Night	2 2 2 2 3 1 3 2 3 4 77%	1719
August	1st to 10th	Night	2 3 1 2 2 1 2 3 3 3 78%	1619
	11th to 20th	Night	1 1 1 1 2 1 2 4 4 4 79%	1780
	21st to end	Night	2 1 2 1 1 2 1 2 3 86%	1980
September	1st to 10th	Night	2 1 1 1 1 1 1 2 4 87%	1800
	11th to 20th	Night	3 2 1 1 1 2 2 2 5% 80%	1804
	21st to end	Night	3 2 1 1 2 1 2 2 3 4 79%	1985
October	1st to 10th	Night	6% 2 1 2 3 2 3 3 2 4 72%	2160
	11th to 20th	Night	6% 2 1 2 2 1 2 3 4 5% 72%	2160
	21st to end	Night	7% 2 1 2 2 2 2 3 3 5% 71%	2376
November	1st to 10th	Night	12% 5% 2 3 2 2 3 3 4 7% 57%	2396
	11th to 20th	Night	10% 4 1 3 3 2 3 4 4 7% 57%	2470
	21st to end	Night	12% 5% 2 3 4 2 4 3 4 5% 57%	2536
December	1st to 10th	Night	17% 6% 2 4 3 2 3 3 4 6% 50%	2660
	11th to 20th	Night	26% 8% 2 5% 3 2 4 4 4 6% 34%	3276
	21st to end	Night	16% 9% 3 6% 6% 3 5% 5% 5% 7% 36%	4862

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% 5% 9% 22% 15% 6%	1519
	11th to 20th	Day	36% 4 10% 17% 19% 14%	1599
	21st to end	Day	42% 4 9% 14% 20% 9%	1782
February	1st to 10th	Day	39% 3 9% 21% 17% 11%	1620
	11th to 20th	Day	37% 4 9% 20% 23% 8%	1743
	21st to end	Day	46% 3 7% 21% 18% 6%	1480
March	1st to 10th	Day	50% 5% 10% 16% 15% 4	1813
	11th to 20th	Day	45% 5% 9% 21% 16% 5%	1980
	21st to end	Day	43% 7% 13% 20% 12% 4	2290
April	1st to 10th	Day	39% 5% 13% 22% 17% 5%	2160
	11th to 20th	Day	33% 5% 13% 26% 18% 5%	2132
	21st to end	Day	27% 4 13% 30% 22% 3	2160
May	1st to 10th	Day	24% 4 13% 28% 24% 6%	2201
	11th to 20th	Day	24% 3 11% 28% 27% 7%	2451
	21st to end	Day	27% 5% 14% 29% 20% 5%	2724
June	1st to 10th	Day	22% 4 10% 24% 30% 11%	2520
	11th to 20th	Day	10% 3 7% 23% 35% 22%	2520
	21st to end	Day	10% 2 3 13% 34% 38%	2520
July	1st to 10th	Day	6% 1 2 10% 27% 54%	2451
	11th to 20th	Day	8% 2 5% 12% 26% 48%	2445
	21st to end	Day	9% 2 4 8% 28% 48%	2451
August	1st to 10th	Day	11% 2 3 12% 27% 45%	2304
	11th to 20th	Day	6% 2 3 11% 36% 43%	2122
	21st to end	Day	7% 1 2 11% 37% 42%	2376
September	1st to 10th	Day	6% 1 3 8% 33% 48%	2160
	11th to 20th	Day	12% 3 6% 20% 37% 21%	2156
	21st to end	Day	14% 2 5% 20% 36% 24%	1972
October	1st to 10th	Day	18% 3 7% 19% 28% 25%	1800
	11th to 20th	Day	18% 3 7% 19% 27% 26%	1800
	21st to end	Day	21% 3 7% 20% 27% 22%	1980
November	1st to 10th	Day	31% 4 10% 19% 22% 15%	1680
	11th to 20th	Day	29% 5% 9% 18% 27% 12%	1710
	21st to end	Day	32% 4 7% 18% 26% 13%	1641
December	1st to 10th	Day	36% 4 8% 19% 21% 12%	1520
	11th to 20th	Day	54% 4 6% 14% 14% 9%	1928
	21st to end	Day	39% 9% 13% 21% 12% 6%	2794
January	1st to 10th	Night	40% 4 11% 21% 17% 7%	2646
	11th to 20th	Night	37% 6% 9% 17% 16% 16%	2501
	21st to end	Night	40% 4 8% 14% 21% 13%	2574
February	1st to 10th	Night	38% 3 7% 18% 21% 14%	2340
	11th to 20th	Night	35% 5% 8% 21% 21% 10%	2114
	21st to end	Night	39% 3 9% 23% 19% 7%	1776
March	1st to 10th	Night	47% 5% 9% 17% 17% 5%	2142
	11th to 20th	Night	41% 6% 9% 19% 19% 7%	1980
	21st to end	Night	40% 7% 12% 20% 15% 6%	2066
April	1st to 10th	Night	37% 6% 13% 19% 19% 6%	1800
	11th to 20th	Night	32% 5% 12% 25% 17% 9%	1779
	21st to end	Night	25% 5% 12% 34% 18% 5%	1800
May	1st to 10th	Night	22% 5% 13% 26% 26% 8%	1756
	11th to 20th	Night	19% 4 13% 29% 26% 9%	1442
	21st to end	Night	21% 5% 15% 31% 23% 6%	1552
June	1st to 10th	Night	18% 5% 13% 23% 28% 12%	1440
	11th to 20th	Night	8% 3 7% 25% 33% 24%	1440
	21st to end	Night	9% 2 3 14% 34% 38%	1440
July	1st to 10th	Night	5% 1 2 10% 28% 54%	1400
	11th to 20th	Night	9% 1 4 11% 23% 51%	1392
	21st to end	Night	12% 3 3 9% 23% 50%	1624
August	1st to 10th	Night	11% 2 3 13% 26% 44%	1610
	11th to 20th	Night	8% 3 5% 12% 29% 45%	1780
	21st to end	Night	7% 1 1 11% 31% 48%	1980
September	1st to 10th	Night	6% 2 2 8% 33% 49%	1800
	11th to 20th	Night	11% 2 5% 18% 40% 24%	1804
	21st to end	Night	12% 2 3 21% 35% 27%	1985
October	1st to 10th	Night	19% 3 6% 17% 29% 26%	2160
	11th to 20th	Night	16% 4 6% 17% 31% 27%	2160
	21st to end	Night	17% 3 5% 20% 30% 24%	2376
November	1st to 10th	Night	28% 3 8% 20% 21% 18%	2396
	11th to 20th	Night	27% 4 9% 21% 26% 14%	2470
	21st to end	Night	31% 4 6% 19% 24% 16%	2536
December	1st to 10th	Night	36% 4 8% 18% 19% 15%	2660
	11th to 20th	Night	51% 5% 7% 13% 18% 7%	3276
	21st to end	Night	45% 8% 11% 16% 13% 6%	4862

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	35% 11% 24% 19% 9% 2	180
	11th to 20th	Day	24% 8% 24% 29% 11% 4	283
	21st to end	Day	23% 11% 24% 22% 16% 3	374
February	1st to 10th	Day	26% 12% 23% 24% 13% 2	340
	11th to 20th	Day	22% 14% 33% 22% 8% 1	408
	21st to end	Day	25% 18% 31% 19% 8% 1	346
March	1st to 10th	Day	30% 22% 25% 16% 5% 2	420
	11th to 20th	Day	29% 20% 23% 17% 10% 2	420
	21st to end	Day	25% 19% 31% 20% 5%	462
April	1st to 10th	Day	21% 19% 35% 17% 7%	420
	11th to 20th	Day	20% 25% 26% 23% 4 1	412
	21st to end	Day	11% 20% 31% 25% 11% 3	420
May	1st to 10th	Day	13% 21% 32% 23% 9% 3	423
	11th to 20th	Day	15% 16% 30% 25% 10% 4	448
	21st to end	Day	13% 15% 26% 30% 12% 5%	485
June	1st to 10th	Day	9% 14% 32% 28% 9% 8%	450
	11th to 20th	Day	6% 15% 35% 31% 8% 5%	450
	21st to end	Day	3 9% 36% 34% 10% 8%	450
July	1st to 10th	Day	1 4 44% 32% 11% 7%	446
	11th to 20th	Day	2 3 36% 39% 12% 9%	444
	21st to end	Day	2 2 38% 39% 13% 7%	487
August	1st to 10th	Day	4 6% 40% 33% 13% 5%	447
	11th to 20th	Day	2 4 39% 38% 12% 6%	437
	21st to end	Day	1 4 37% 41% 13% 4	495
September	1st to 10th	Day	3 5% 42% 34% 14% 2	450
	11th to 20th	Day	4 12% 35% 36% 12% 1	450
	21st to end	Day	4 12% 32% 42% 8% 2	450
October	1st to 10th	Day	6% 13% 32% 34% 12% 3	450
	11th to 20th	Day	7% 12% 28% 34% 15% 4	450
	21st to end	Day	10% 11% 28% 31% 16% 4	495
November	1st to 10th	Day	17% 9% 22% 26% 20% 6%	276
	11th to 20th	Day	13% 8% 22% 31% 17% 9%	270
	21st to end	Day	14% 10% 24% 28% 20% 4	237
December	1st to 10th	Day	20% 9% 22% 26% 15% 8%	180
	11th to 20th	Day	19% 13% 24% 26% 11% 6%	180
	21st to end	Day	24% 14% 22% 21% 15% 5%	198
January	1st to 10th	Night	23% 5% 23% 24% 16% 7%	760
	11th to 20th	Night	18% 6% 21% 37% 14% 5%	748
	21st to end	Night	21% 5% 21% 28% 19% 5%	792
February	1st to 10th	Night	20% 5% 20% 33% 18% 3	720
	11th to 20th	Night	19% 7% 21% 29% 19% 6%	704
	21st to end	Night	22% 8% 19% 34% 14% 2	592
March	1st to 10th	Night	25% 7% 19% 30% 15% 3	720
	11th to 20th	Night	22% 8% 17% 28% 20% 6%	720
	21st to end	Night	23% 8% 19% 30% 18% 2	792
April	1st to 10th	Night	18% 3 18% 40% 18% 3	720
	11th to 20th	Night	15% 7% 21% 35% 18% 4	711
	21st to end	Night	11% 4 19% 38% 23% 6%	720
May	1st to 10th	Night	10% 5% 21% 37% 23% 4	676
	11th to 20th	Night	9% 3 15% 38% 32% 4	380
	21st to end	Night	8% 4 13% 36% 35% 5%	389
June	1st to 10th	Night	6% 3 11% 38% 37% 6%	360
	11th to 20th	Night	1 1 14% 43% 36% 6%	360
	21st to end	Night	2 1 8% 41% 41% 7%	360
July	1st to 10th	Night	1 5% 39% 50% 5%	350
	11th to 20th	Night	2 6% 40% 46% 7%	348
	21st to end	Night	3 1 7% 31% 45% 14%	537
August	1st to 10th	Night	3 1 8% 39% 42% 8%	545
	11th to 20th	Night	1 1 8% 45% 36% 9%	712
	21st to end	Night	1 7% 44% 43% 5%	792
September	1st to 10th	Night	2 8% 43% 40% 7%	720
	11th to 20th	Night	4 1 12% 34% 38% 10%	720
	21st to end	Night	4 3 14% 40% 30% 10%	720
October	1st to 10th	Night	7% 3 16% 41% 25% 8%	720
	11th to 20th	Night	8% 3 14% 40% 29% 6%	720
	21st to end	Night	7% 5% 17% 33% 24% 13%	792
November	1st to 10th	Night	15% 3 14% 35% 25% 8%	740
	11th to 20th	Night	12% 4 20% 37% 20% 6%	760
	21st to end	Night	15% 6% 23% 32% 17% 7%	760
December	1st to 10th	Night	21% 6% 19% 33% 16% 5%	760
	11th to 20th	Night	27% 4 22% 28% 16% 4	760
	21st to end	Night	26% 7% 23% 27% 14% 3	836

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