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 2026-05-02.

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	8% 5% 1 3 2 2 2 2 3 5% 66%	140396
	Night	10% 6% 1 3 2 2 3 2 4 5% 61%	139532
Transparency	Day	23% 3 7% 18% 26% 24%	135367
	Night	27% 4 7% 18% 23% 21%	135544
Seeing	Day	13% 12% 32% 28% 11% 4	17048
	Night	13% 4 18% 36% 23% 5%	26522

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	19% 10% 1 3 2 3 3 3 4 6% 47%	4722
	11th to 20th	Day	11% 5% 1 4 3 3 2 2 3 5% 61%	5100
	21st to end	Day	13% 7% 2 6% 4 4 4 3 5% 7% 45%	5843
February	1st to 10th	Day	19% 9% 2 5% 2 3 3 3 4 5% 47%	1890
	11th to 20th	Day	14% 12% 2 5% 3 3 3 3 4 6% 44%	2031
	21st to end	Day	19% 11% 2 4 3 2 3 3 5% 5% 43%	1730
March	1st to 10th	Day	14% 16% 4 7% 4 4 4 3 5% 6% 33%	4658
	11th to 20th	Day	15% 11% 2 4 3 2 3 2 3 5% 49%	5110
	21st to end	Day	17% 13% 2 7% 4 4 4 3 5% 6% 36%	5893
April	1st to 10th	Day	14% 9% 2 5% 3 3 3 3 4 6% 47%	2520
	11th to 20th	Day	12% 7% 2 4 4 3 4 3 4 6% 52%	2489
	21st to end	Day	12% 5% 1 4 3 3 3 3 5% 7% 56%	2520
May	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 4 71%	5572
	11th to 20th	Day	4 3 1 2 2 2 2 2 3 5% 74%	6222
	21st to end	Day	4 2 1 2 1 1 2 2 3 4 78%	6902
June	1st to 10th	Day	5% 4 1 3 3 2 3 3 4 6% 65%	2800
	11th to 20th	Day	2 1 1 2 2 2 2 2 4 4 79%	2800
	21st to end	Day	2 2 1 1 2 1 2 1 3 3 83%	2800
July	1st to 10th	Day	1 1 1 1 1 1 1 93%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 88%	6320
	21st to end	Day	2 1 1 1 1 2 1 3 3 85%	6516
August	1st to 10th	Day	1 1 2 1 1 1 1 2 3 85%	5744
	11th to 20th	Day	1 1 1 1 1 2 3 91%	5364
	21st to end	Day	2 2 1 2 2 2 2 1 3 4 81%	5984
September	1st to 10th	Day	2 1 1 1 1 2 1 2 2 87%	2400
	11th to 20th	Day	3 2 1 3 2 2 2 2 4 4 75%	2395
	21st to end	Day	4 3 1 2 2 2 2 2 2 3 78%	2190
October	1st to 10th	Day	4 2 1 3 2 2 3 2 4 5% 73%	3280
	11th to 20th	Day	5% 2 1 2 2 2 2 2 3 3 76%	3261
	21st to end	Day	6% 3 1 4 3 3 3 2 4 6% 65%	3558
November	1st to 10th	Day	11% 5% 1 4 4 3 3 3 4 7% 54%	1860
	11th to 20th	Day	12% 5% 1 4 4 3 4 3 5% 7% 51%	1890
	21st to end	Day	12% 7% 1 4 3 3 2 3 4 6% 55%	1813
December	1st to 10th	Day	9% 3 1 4 2 4 4 2 5% 7% 60%	2700
	11th to 20th	Day	24% 9% 3 5% 3 3 3 3 5% 6% 36%	3108
	21st to end	Day	22% 8% 2 6% 3 4 5% 4 6% 8% 32%	4092
January	1st to 10th	Night	17% 9% 2 4 3 3 3 3 5% 7% 43%	8172
	11th to 20th	Night	11% 5% 1 4 3 3 3 3 4 5% 59%	7861
	21st to end	Night	12% 8% 2 6% 4 4 4 3 4 6% 46%	8371
February	1st to 10th	Night	17% 8% 2 5% 3 3 3 2 4 5% 48%	2730
	11th to 20th	Night	14% 11% 2 4 4 3 4 3 5% 6% 43%	2475
	21st to end	Night	16% 10% 2 4 2 3 3 3 4 4 49%	2076
March	1st to 10th	Night	16% 16% 3 5% 3 3 4 3 4 5% 37%	5451
	11th to 20th	Night	18% 11% 2 4 2 2 2 2 3 4 49%	5110
	21st to end	Night	19% 12% 2 5% 3 3 4 3 4 7% 37%	5324
April	1st to 10th	Night	13% 7% 2 5% 4 3 3 4 4 6% 49%	2100
	11th to 20th	Night	11% 6% 2 5% 4 4 3 2 4 7% 52%	2079
	21st to end	Night	10% 5% 1 3 2 2 3 4 5% 6% 58%	2100
May	1st to 10th	Night	3 4 1 2 2 2 2 2 3 6% 73%	4442
	11th to 20th	Night	3 2 1 2 2 2 2 2 4 5% 76%	3670
	21st to end	Night	3 2 1 1 1 2 2 1 3 4 80%	3972
June	1st to 10th	Night	5% 4 1 3 2 2 3 3 4 6% 67%	1600
	11th to 20th	Night	1 1 2 1 2 2 2 3 3 83%	1600
	21st to end	Night	2 2 2 2 1 2 1 2 3 83%	1600
July	1st to 10th	Night	1 1 1 1 1 1 94%	3640
	11th to 20th	Night	2 2 1 2 1 1 2 1 2 3 84%	3640
	21st to end	Night	2 1 1 2 2 2 2 2 4 4 78%	4334
August	1st to 10th	Night	2 2 1 2 1 1 2 2 3 3 83%	4070
	11th to 20th	Night	1 1 1 1 1 1 2 2 90%	4506
	21st to end	Night	3 1 2 1 1 2 1 2 3 82%	5015
September	1st to 10th	Night	2 1 1 1 1 1 1 2 4 87%	2000
	11th to 20th	Night	3 2 2 1 1 2 2 2 4 79%	2005
	21st to end	Night	2 2 1 2 2 2 2 2 3 4 79%	2207
October	1st to 10th	Night	4 2 1 3 2 2 2 2 2 3 78%	3920
	11th to 20th	Night	3 2 1 2 1 1 2 2 3 4 79%	3897
	21st to end	Night	8% 2 1 2 3 3 3 3 3 5% 66%	4253
November	1st to 10th	Night	12% 5% 1 3 2 2 2 3 4 7% 58%	2656
	11th to 20th	Night	11% 5% 1 4 3 3 3 3 5% 7% 54%	2730
	21st to end	Night	12% 5% 1 4 3 3 3 3 4 6% 57%	2804
December	1st to 10th	Night	10% 4 1 3 2 2 3 3 4 5% 62%	4700
	11th to 20th	Night	23% 9% 2 5% 3 3 4 4 7% 8% 32%	5316
	21st to end	Night	21% 11% 3 7% 5% 4 4 3 5% 6% 32%	7106

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	40% 3 12% 21% 17% 7%	4723
	11th to 20th	Day	28% 4 5% 11% 26% 26%	5100
	21st to end	Day	37% 5% 7% 17% 21% 13%	5843
February	1st to 10th	Day	41% 3 8% 20% 16% 12%	1890
	11th to 20th	Day	41% 4 8% 20% 21% 7%	2041
	21st to end	Day	44% 3 8% 21% 16% 7%	1730
March	1st to 10th	Day	48% 7% 9% 14% 16% 5%	4658
	11th to 20th	Day	38% 4 12% 28% 11% 7%	5110
	21st to end	Day	45% 8% 12% 22% 11% 2	5893
April	1st to 10th	Day	38% 5% 13% 23% 17% 5%	2520
	11th to 20th	Day	32% 5% 13% 27% 17% 5%	2492
	21st to end	Day	28% 5% 13% 30% 22% 3	2520
May	1st to 10th	Day	17% 3 9% 29% 29% 13%	5572
	11th to 20th	Day	14% 3 8% 30% 38% 7%	6225
	21st to end	Day	12% 2 7% 27% 43% 9%	6904
June	1st to 10th	Day	20% 4 10% 25% 31% 10%	2800
	11th to 20th	Day	10% 3 6% 22% 36% 23%	2800
	21st to end	Day	9% 2 3 12% 34% 40%	2800
July	1st to 10th	Day	3 1 1 5% 20% 71%	6251
	11th to 20th	Day	5% 1 3 5% 13% 73%	6245
	21st to end	Day	7% 1 3 12% 32% 45%	6328
August	1st to 10th	Day	11% 2 3 7% 24% 55%	4184
	11th to 20th	Day	4 1 2 6% 36% 51%	3880
	21st to end	Day	7% 1 2 7% 41% 41%	4311
September	1st to 10th	Day	6% 1 3 10% 33% 47%	2400
	11th to 20th	Day	13% 3 6% 20% 38% 20%	2395
	21st to end	Day	13% 2 5% 19% 36% 26%	2190
October	1st to 10th	Day	14% 3 4 12% 27% 40%	3280
	11th to 20th	Day	15% 2 4 18% 41% 20%	3261
	21st to end	Day	21% 3 6% 19% 36% 15%	3558
November	1st to 10th	Day	30% 3 10% 19% 24% 14%	1860
	11th to 20th	Day	32% 5% 9% 18% 25% 11%	1890
	21st to end	Day	31% 3 7% 18% 26% 14%	1813
December	1st to 10th	Day	25% 3 6% 23% 27% 16%	2700
	11th to 20th	Day	50% 3 7% 14% 17% 9%	3108
	21st to end	Day	46% 7% 13% 18% 10% 5%	4092
January	1st to 10th	Night	39% 5% 14% 18% 17% 7%	8172
	11th to 20th	Night	28% 3 5% 11% 25% 28%	7861
	21st to end	Night	39% 4 5% 15% 18% 18%	8371
February	1st to 10th	Night	40% 3 7% 17% 19% 14%	2730
	11th to 20th	Night	39% 5% 8% 21% 19% 9%	2476
	21st to end	Night	38% 3 10% 23% 18% 8%	2076
March	1st to 10th	Night	47% 6% 7% 17% 15% 8%	5451
	11th to 20th	Night	39% 4 9% 24% 16% 8%	5110
	21st to end	Night	46% 6% 13% 21% 12% 3	5324
April	1st to 10th	Night	36% 6% 13% 20% 20% 6%	2100
	11th to 20th	Night	32% 5% 13% 26% 15% 9%	2079
	21st to end	Night	26% 6% 11% 34% 18% 5%	2100
May	1st to 10th	Night	14% 4 10% 30% 27% 14%	4439
	11th to 20th	Night	12% 3 9% 31% 35% 11%	3670
	21st to end	Night	11% 3 7% 33% 39% 8%	3972
June	1st to 10th	Night	17% 5% 12% 24% 29% 12%	1600
	11th to 20th	Night	7% 3 6% 24% 34% 26%	1600
	21st to end	Night	9% 2 3 13% 34% 40%	1600
July	1st to 10th	Night	2 1 1 4 22% 70%	3600
	11th to 20th	Night	9% 1 2 5% 16% 67%	3592
	21st to end	Night	9% 3 4 13% 24% 47%	4211
August	1st to 10th	Night	11% 2 2 8% 23% 53%	2952
	11th to 20th	Night	5% 1 3 7% 32% 52%	3256
	21st to end	Night	8% 1 1 11% 37% 42%	3608
September	1st to 10th	Night	5% 2 2 9% 34% 47%	2000
	11th to 20th	Night	12% 2 5% 19% 40% 22%	2005
	21st to end	Night	12% 2 3 20% 34% 29%	2207
October	1st to 10th	Night	14% 2 4 11% 25% 44%	3920
	11th to 20th	Night	12% 2 4 24% 37% 22%	3897
	21st to end	Night	21% 3 5% 18% 35% 19%	4253
November	1st to 10th	Night	27% 3 9% 22% 22% 17%	2656
	11th to 20th	Night	30% 4 9% 20% 25% 13%	2730
	21st to end	Night	30% 4 6% 19% 24% 16%	2804
December	1st to 10th	Night	24% 3 6% 21% 26% 19%	4700
	11th to 20th	Night	47% 5% 7% 13% 20% 7%	5316
	21st to end	Night	50% 7% 10% 16% 10% 6%	7106

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	33% 11% 25% 20% 9% 2	220
	11th to 20th	Day	20% 9% 25% 30% 13% 3	346
	21st to end	Day	20% 11% 27% 25% 15% 3	473
February	1st to 10th	Day	28% 13% 24% 22% 11% 2	430
	11th to 20th	Day	25% 16% 31% 19% 7% 1	526
	21st to end	Day	22% 17% 34% 19% 8%	446
March	1st to 10th	Day	29% 22% 26% 17% 5% 1	540
	11th to 20th	Day	27% 19% 25% 18% 9% 2	540
	21st to end	Day	24% 18% 32% 21% 5%	594
April	1st to 10th	Day	20% 19% 33% 19% 9%	540
	11th to 20th	Day	19% 24% 26% 24% 5% 2	532
	21st to end	Day	12% 19% 31% 24% 11% 3	540
May	1st to 10th	Day	12% 21% 33% 23% 8% 3	508
	11th to 20th	Day	14% 15% 30% 25% 12% 4	528
	21st to end	Day	11% 13% 29% 30% 12% 5%	573
June	1st to 10th	Day	7% 13% 33% 29% 9% 8%	530
	11th to 20th	Day	6% 15% 35% 30% 8% 5%	530
	21st to end	Day	3 9% 37% 32% 11% 8%	530
July	1st to 10th	Day	1 7% 42% 32% 12% 6%	526
	11th to 20th	Day	2 3 37% 38% 13% 7%	524
	21st to end	Day	2 2 39% 37% 12% 7%	575
August	1st to 10th	Day	4 6% 41% 32% 13% 4	527
	11th to 20th	Day	2 5% 39% 36% 12% 6%	517
	21st to end	Day	2 5% 36% 39% 14% 4	583
September	1st to 10th	Day	3 7% 42% 32% 13% 2	530
	11th to 20th	Day	6% 12% 34% 34% 13% 1	530
	21st to end	Day	5% 11% 34% 40% 8% 3	530
October	1st to 10th	Day	8% 12% 32% 33% 12% 3	530
	11th to 20th	Day	8% 12% 28% 33% 15% 4	530
	21st to end	Day	11% 11% 29% 32% 14% 4	583
November	1st to 10th	Day	15% 9% 22% 29% 18% 7%	336
	11th to 20th	Day	18% 9% 23% 29% 14% 8%	330
	21st to end	Day	17% 9% 24% 28% 19% 3	289
December	1st to 10th	Day	16% 8% 23% 28% 15% 9%	220
	11th to 20th	Day	20% 11% 24% 26% 13% 6%	220
	21st to end	Day	28% 14% 23% 18% 13% 4	242
January	1st to 10th	Night	24% 6% 25% 24% 15% 7%	840
	11th to 20th	Night	16% 6% 24% 38% 13% 4	840
	21st to end	Night	20% 6% 23% 29% 17% 5%	924
February	1st to 10th	Night	21% 6% 23% 31% 16% 3	840
	11th to 20th	Night	21% 7% 22% 28% 16% 5%	824
	21st to end	Night	21% 8% 25% 31% 13% 2	692
March	1st to 10th	Night	24% 8% 21% 30% 14% 3	840
	11th to 20th	Night	21% 8% 19% 28% 18% 5%	840
	21st to end	Night	22% 8% 20% 32% 16% 2	924
April	1st to 10th	Night	18% 4 20% 40% 17% 2	840
	11th to 20th	Night	14% 7% 22% 36% 18% 4	831
	21st to end	Night	11% 4 21% 38% 20% 5%	840
May	1st to 10th	Night	9% 5% 23% 38% 21% 4	754
	11th to 20th	Night	8% 3 17% 39% 30% 3	422
	21st to end	Night	7% 3 14% 39% 33% 4	433
June	1st to 10th	Night	6% 2 11% 41% 35% 5%	400
	11th to 20th	Night	1 1 15% 45% 34% 5%	400
	21st to end	Night	2 1 8% 45% 38% 6%	400
July	1st to 10th	Night	1 6% 44% 45% 5%	390
	11th to 20th	Night	2 1 7% 42% 43% 6%	388
	21st to end	Night	3 1 7% 34% 43% 13%	597
August	1st to 10th	Night	3 1 9% 42% 39% 7%	607
	11th to 20th	Night	1 1 10% 46% 34% 8%	792
	21st to end	Night	1 1 8% 46% 40% 5%	880
September	1st to 10th	Night	2 9% 46% 36% 6%	800
	11th to 20th	Night	4 2 13% 36% 36% 9%	800
	21st to end	Night	3 2 15% 42% 29% 9%	800
October	1st to 10th	Night	7% 3 17% 43% 23% 7%	800
	11th to 20th	Night	7% 4 16% 41% 27% 6%	800
	21st to end	Night	8% 5% 19% 34% 22% 12%	880
November	1st to 10th	Night	14% 4 15% 36% 24% 7%	820
	11th to 20th	Night	14% 6% 22% 35% 18% 5%	840
	21st to end	Night	15% 6% 26% 30% 16% 6%	840
December	1st to 10th	Night	19% 6% 21% 34% 16% 5%	840
	11th to 20th	Night	27% 4 24% 28% 15% 3	840
	21st to end	Night	27% 7% 24% 26% 12% 3	924

Page generated at 2026-04-28 23:21:42. Version ac07

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