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 2025-01-07.

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% 1 3 2 2 3 2 4 5% 64%	108793
	Night	11% 6% 1 4 2 3 3 3 4 5% 59%	108971
Transparency	Day	24% 3 7% 18% 24% 23%	108543
	Night	27% 4 7% 18% 22% 21%	108811
Seeing	Day	13% 12% 31% 29% 11% 4	15322
	Night	13% 4 17% 35% 24% 6%	24769

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	18% 13% 2 4 3 3 2 2 3 6% 43%	2587
	11th to 20th	Day	21% 9% 2 6% 4 5% 3 3 5% 5% 36%	2732
	21st to end	Day	20% 11% 2 6% 4 4 4 3 5% 6% 35%	3146
February	1st to 10th	Day	18% 9% 2 5% 3 3 3 3 4 5% 47%	1710
	11th to 20th	Day	13% 11% 2 5% 3 3 3 3 4 7% 46%	1832
	21st to end	Day	19% 11% 2 4 3 2 3 3 4 4 43%	1570
March	1st to 10th	Day	15% 17% 4 8% 4 4 4 4 6% 6% 28%	3164
	11th to 20th	Day	14% 8% 2 4 3 2 3 2 3 5% 55%	3490
	21st to end	Day	15% 14% 3 8% 4 4 4 4 5% 6% 33%	4027
April	1st to 10th	Day	14% 9% 2 5% 3 3 3 3 5% 7% 46%	2280
	11th to 20th	Day	12% 7% 2 4 4 2 3 3 4 6% 52%	2249
	21st to end	Day	11% 4 1 3 3 3 3 2 4 7% 57%	2280
May	1st to 10th	Day	8% 3 1 3 2 2 2 2 4 4 69%	3880
	11th to 20th	Day	4 3 1 2 2 2 2 2 3 5% 76%	4335
	21st to end	Day	5% 3 1 3 2 2 2 2 4 5% 72%	4813
June	1st to 10th	Day	6% 4 1 4 3 2 3 3 4 6% 64%	2660
	11th to 20th	Day	2 1 1 2 2 2 2 2 4 4 79%	2660
	21st to end	Day	2 2 1 1 2 2 2 1 3 3 82%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 92%	4420
	11th to 20th	Day	2 1 1 1 1 2 1 3 3 83%	4420
	21st to end	Day	1 1 1 1 2 1 2 3 87%	4530
August	1st to 10th	Day	2 2 1 3 2 2 2 2 3 4 80%	4070
	11th to 20th	Day	1 1 1 1 1 1 2 3 88%	3724
	21st to end	Day	1 1 2 1 1 1 1 2 2 88%	4180
September	1st to 10th	Day	2 1 1 1 1 2 1 2 2 88%	2280
	11th to 20th	Day	3 2 1 3 2 2 2 2 4 5% 75%	2275
	21st to end	Day	4 3 1 2 1 2 2 2 2 3 78%	2081
October	1st to 10th	Day	3 2 1 3 2 2 3 2 4 5% 73%	3180
	11th to 20th	Day	5% 2 1 2 1 2 2 2 3 3 76%	3161
	21st to end	Day	5% 3 1 4 3 3 3 2 5% 6% 65%	3448
November	1st to 10th	Day	11% 6% 1 4 4 3 3 3 4 7% 53%	1770
	11th to 20th	Day	11% 5% 1 4 4 3 4 3 5% 7% 54%	1800
	21st to end	Day	12% 7% 1 4 3 3 2 3 5% 6% 53%	1727
December	1st to 10th	Day	9% 3 1 4 2 4 4 2 5% 7% 59%	2620
	11th to 20th	Day	25% 10% 3 5% 3 3 3 3 5% 6% 35%	3028
	21st to end	Day	21% 8% 2 6% 3 4 5% 4 6% 8% 32%	4004
January	1st to 10th	Night	14% 10% 2 5% 3 3 3 3 5% 6% 45%	4490
	11th to 20th	Night	21% 9% 2 6% 4 4 5% 4 5% 6% 35%	4230
	21st to end	Night	19% 11% 3 7% 5% 5% 4 3 4 6% 33%	4521
February	1st to 10th	Night	16% 8% 2 6% 3 3 3 2 4 5% 48%	2470
	11th to 20th	Night	14% 10% 2 4 3 2 4 4 5% 7% 45%	2234
	21st to end	Night	17% 10% 2 4 2 3 3 3 4 4 49%	1884
March	1st to 10th	Night	19% 17% 3 5% 4 3 4 3 4 4 33%	3705
	11th to 20th	Night	16% 6% 1 4 2 2 2 2 4 4 57%	3490
	21st to end	Night	20% 13% 2 5% 3 4 4 4 5% 6% 35%	3626
April	1st to 10th	Night	13% 8% 2 5% 4 3 3 4 4 6% 48%	1900
	11th to 20th	Night	11% 7% 2 5% 4 3 3 2 4 7% 53%	1879
	21st to end	Night	9% 5% 1 3 2 2 3 4 5% 6% 59%	1900
May	1st to 10th	Night	4 6% 1 2 1 1 2 2 4 6% 69%	3094
	11th to 20th	Night	4 2 1 1 2 1 2 2 4 5% 77%	2556
	21st to end	Night	4 3 1 2 2 2 2 2 3 5% 76%	2762
June	1st to 10th	Night	5% 4 1 4 2 2 3 3 4 6% 67%	1520
	11th to 20th	Night	1 1 2 1 2 2 2 3 3 83%	1520
	21st to end	Night	2 2 2 2 1 2 2 2 3 83%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 93%	2540
	11th to 20th	Night	3 2 1 3 1 2 2 2 3 3 77%	2540
	21st to end	Night	1 1 1 2 1 1 2 1 2 3 84%	3013
August	1st to 10th	Night	3 3 1 2 1 1 2 2 4 4 77%	2870
	11th to 20th	Night	1 1 1 1 1 1 2 2 3 87%	3126
	21st to end	Night	4 1 1 1 1 1 1 2 88%	3498
September	1st to 10th	Night	2 1 1 1 1 1 1 2 3 87%	1900
	11th to 20th	Night	3 2 2 1 1 2 2 2 4 79%	1905
	21st to end	Night	2 1 1 2 2 2 2 2 3 4 80%	2096
October	1st to 10th	Night	4 2 1 3 2 2 2 2 2 3 78%	3800
	11th to 20th	Night	3 1 1 2 1 1 2 2 3 5% 79%	3777
	21st to end	Night	8% 2 1 2 3 3 3 3 3 5% 66%	4121
November	1st to 10th	Night	12% 5% 1 3 2 2 2 3 4 7% 57%	2526
	11th to 20th	Night	10% 5% 1 4 3 3 3 3 5% 7% 57%	2600
	21st to end	Night	13% 6% 1 4 3 3 3 3 4 5% 56%	2670
December	1st to 10th	Night	10% 4 1 3 2 2 3 3 4 5% 61%	4560
	11th to 20th	Night	23% 9% 2 5% 3 3 4 4 7% 8% 31%	5176
	21st to end	Night	20% 10% 3 7% 5% 4 5% 3 5% 6% 32%	6952

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	45% 4 8% 23% 17% 4	2587
	11th to 20th	Day	49% 6% 9% 14% 13% 8%	2732
	21st to end	Day	49% 6% 10% 18% 12% 5%	3146
February	1st to 10th	Day	41% 3 8% 20% 17% 11%	1710
	11th to 20th	Day	39% 4 8% 20% 22% 7%	1842
	21st to end	Day	45% 3 8% 21% 18% 6%	1570
March	1st to 10th	Day	52% 9% 12% 12% 11% 4	3164
	11th to 20th	Day	32% 4 11% 31% 13% 10%	3490
	21st to end	Day	47% 9% 13% 20% 9% 2	4027
April	1st to 10th	Day	38% 5% 13% 23% 16% 4	2280
	11th to 20th	Day	32% 5% 14% 26% 17% 5%	2252
	21st to end	Day	27% 4 13% 31% 22% 3	2280
May	1st to 10th	Day	19% 4 11% 31% 21% 14%	3880
	11th to 20th	Day	14% 2 6% 27% 41% 9%	4338
	21st to end	Day	16% 3 10% 34% 32% 4	4814
June	1st to 10th	Day	21% 4 10% 24% 30% 10%	2660
	11th to 20th	Day	10% 3 6% 23% 36% 21%	2660
	21st to end	Day	10% 2 3 13% 32% 40%	2660
July	1st to 10th	Day	3 1 1 6% 15% 74%	4351
	11th to 20th	Day	7% 1 4 8% 16% 63%	4345
	21st to end	Day	6% 1 3 5% 27% 58%	4387
August	1st to 10th	Day	11% 2 3 7% 23% 55%	4055
	11th to 20th	Day	4 1 2 6% 36% 51%	3760
	21st to end	Day	7% 1 2 7% 40% 42%	4179
September	1st to 10th	Day	6% 1 3 8% 33% 49%	2280
	11th to 20th	Day	13% 3 6% 20% 38% 20%	2275
	21st to end	Day	13% 1 5% 19% 36% 26%	2081
October	1st to 10th	Day	14% 3 4 11% 27% 41%	3180
	11th to 20th	Day	14% 2 4 18% 41% 20%	3161
	21st to end	Day	21% 3 6% 19% 35% 16%	3448
November	1st to 10th	Day	30% 4 10% 19% 23% 14%	1770
	11th to 20th	Day	30% 5% 9% 19% 26% 12%	1800
	21st to end	Day	32% 4 7% 18% 25% 14%	1727
December	1st to 10th	Day	26% 3 7% 22% 27% 16%	2620
	11th to 20th	Day	50% 3 7% 14% 17% 9%	3028
	21st to end	Day	46% 7% 13% 19% 10% 5%	4004
January	1st to 10th	Night	39% 5% 13% 23% 16% 4	4490
	11th to 20th	Night	49% 6% 8% 15% 12% 10%	4230
	21st to end	Night	50% 6% 8% 15% 12% 7%	4521
February	1st to 10th	Night	40% 3 7% 18% 20% 13%	2470
	11th to 20th	Night	37% 5% 8% 22% 20% 10%	2235
	21st to end	Night	39% 3 10% 23% 19% 6%	1884
March	1st to 10th	Night	51% 7% 9% 16% 11% 5%	3705
	11th to 20th	Night	32% 4 8% 25% 20% 11%	3490
	21st to end	Night	48% 7% 11% 21% 9% 3	3626
April	1st to 10th	Night	36% 6% 13% 20% 19% 5%	1900
	11th to 20th	Night	32% 5% 12% 27% 16% 8%	1879
	21st to end	Night	25% 6% 12% 34% 18% 6%	1900
May	1st to 10th	Night	17% 4 12% 29% 23% 14%	3094
	11th to 20th	Night	11% 3 9% 26% 36% 15%	2556
	21st to end	Night	13% 3 9% 42% 28% 5%	2762
June	1st to 10th	Night	18% 6% 13% 23% 29% 12%	1520
	11th to 20th	Night	8% 3 6% 25% 34% 24%	1520
	21st to end	Night	9% 2 3 13% 33% 40%	1520
July	1st to 10th	Night	3 1 1 6% 16% 74%	2500
	11th to 20th	Night	12% 2 3 8% 14% 61%	2492
	21st to end	Night	8% 2 2 5% 22% 61%	2919
August	1st to 10th	Night	12% 2 2 8% 22% 54%	2861
	11th to 20th	Night	5% 1 3 7% 32% 52%	3156
	21st to end	Night	8% 1 1 11% 36% 43%	3498
September	1st to 10th	Night	5% 2 2 8% 33% 50%	1900
	11th to 20th	Night	12% 2 5% 18% 41% 23%	1905
	21st to end	Night	11% 2 3 21% 34% 29%	2096
October	1st to 10th	Night	14% 2 4 10% 25% 45%	3800
	11th to 20th	Night	11% 2 4 24% 37% 22%	3777
	21st to end	Night	21% 3 4 17% 35% 19%	4121
November	1st to 10th	Night	28% 3 9% 21% 22% 18%	2526
	11th to 20th	Night	27% 4 9% 21% 26% 13%	2600
	21st to end	Night	31% 4 6% 19% 24% 16%	2670
December	1st to 10th	Night	25% 3 7% 21% 26% 19%	4560
	11th to 20th	Night	48% 5% 8% 13% 21% 7%	5176
	21st to end	Night	49% 8% 11% 16% 10% 6%	6952

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	34% 10% 26% 19% 10% 2	192
	11th to 20th	Day	23% 9% 25% 28% 11% 3	294
	21st to end	Day	23% 10% 25% 23% 15% 3	407
February	1st to 10th	Day	28% 13% 23% 23% 12% 2	370
	11th to 20th	Day	23% 15% 32% 21% 8% 1	447
	21st to end	Day	23% 17% 31% 20% 8% 1	382
March	1st to 10th	Day	31% 23% 24% 16% 5% 2	460
	11th to 20th	Day	28% 20% 23% 17% 10% 2	460
	21st to end	Day	25% 19% 31% 20% 5%	506
April	1st to 10th	Day	20% 20% 34% 18% 8%	460
	11th to 20th	Day	20% 24% 25% 24% 5% 2	452
	21st to end	Day	10% 19% 31% 26% 11% 3	460
May	1st to 10th	Day	13% 21% 33% 22% 8% 3	463
	11th to 20th	Day	13% 15% 30% 26% 12% 4	488
	21st to end	Day	12% 13% 27% 30% 12% 5%	529
June	1st to 10th	Day	8% 14% 32% 29% 9% 8%	490
	11th to 20th	Day	6% 15% 35% 31% 8% 5%	490
	21st to end	Day	3 10% 37% 33% 11% 7%	490
July	1st to 10th	Day	1 5% 43% 33% 12% 7%	486
	11th to 20th	Day	2 4 36% 39% 12% 8%	484
	21st to end	Day	2 3 38% 38% 12% 7%	531
August	1st to 10th	Day	4 5% 41% 33% 13% 5%	487
	11th to 20th	Day	2 6% 40% 36% 11% 5%	477
	21st to end	Day	2 5% 37% 39% 13% 4	539
September	1st to 10th	Day	3 6% 43% 33% 13% 2	490
	11th to 20th	Day	6% 12% 35% 34% 12% 1	490
	21st to end	Day	4 11% 34% 41% 8% 3	490
October	1st to 10th	Day	6% 12% 32% 34% 12% 3	490
	11th to 20th	Day	7% 12% 29% 34% 15% 4	490
	21st to end	Day	10% 11% 30% 31% 15% 4	539
November	1st to 10th	Day	16% 10% 23% 26% 19% 6%	306
	11th to 20th	Day	15% 9% 23% 30% 15% 8%	300
	21st to end	Day	19% 9% 23% 27% 19% 3	263
December	1st to 10th	Day	18% 9% 22% 27% 16% 9%	200
	11th to 20th	Day	21% 12% 23% 28% 11% 6%	200
	21st to end	Day	25% 15% 23% 20% 14% 5%	220
January	1st to 10th	Night	23% 5% 25% 25% 16% 7%	784
	11th to 20th	Night	18% 6% 21% 37% 14% 5%	760
	21st to end	Night	21% 5% 22% 28% 18% 5%	836
February	1st to 10th	Night	21% 6% 20% 32% 18% 3	760
	11th to 20th	Night	20% 7% 22% 29% 18% 5%	744
	21st to end	Night	22% 8% 21% 33% 14% 2	628
March	1st to 10th	Night	26% 7% 19% 30% 15% 3	760
	11th to 20th	Night	22% 8% 18% 27% 20% 5%	760
	21st to end	Night	23% 8% 19% 30% 17% 2	836
April	1st to 10th	Night	18% 4 18% 40% 18% 3	760
	11th to 20th	Night	15% 7% 21% 35% 18% 4	751
	21st to end	Night	11% 4 19% 38% 22% 5%	760
May	1st to 10th	Night	10% 5% 22% 37% 22% 4	713
	11th to 20th	Night	8% 2 15% 39% 31% 3	401
	21st to end	Night	7% 3 13% 37% 34% 5%	411
June	1st to 10th	Night	6% 2 11% 40% 35% 5%	380
	11th to 20th	Night	1 1 14% 44% 35% 5%	380
	21st to end	Night	2 1 8% 44% 39% 6%	380
July	1st to 10th	Night	1 5% 41% 48% 5%	370
	11th to 20th	Night	2 1 7% 40% 44% 6%	368
	21st to end	Night	3 1 7% 32% 44% 13%	567
August	1st to 10th	Night	3 1 8% 41% 40% 8%	576
	11th to 20th	Night	1 1 10% 46% 34% 8%	752
	21st to end	Night	1 8% 44% 42% 5%	836
September	1st to 10th	Night	2 8% 45% 38% 6%	760
	11th to 20th	Night	4 2 13% 35% 36% 10%	760
	21st to end	Night	3 2 15% 41% 29% 9%	760
October	1st to 10th	Night	7% 3 16% 43% 24% 8%	760
	11th to 20th	Night	7% 3 15% 41% 28% 6%	760
	21st to end	Night	8% 5% 18% 34% 23% 13%	836
November	1st to 10th	Night	14% 4 16% 35% 24% 8%	780
	11th to 20th	Night	13% 5% 21% 36% 19% 6%	800
	21st to end	Night	16% 6% 24% 31% 17% 7%	800
December	1st to 10th	Night	20% 6% 20% 33% 16% 5%	800
	11th to 20th	Night	27% 4 23% 27% 15% 4	800
	21st to end	Night	26% 7% 24% 26% 13% 3	880

Page generated at 2025-01-04 00:24:03. Version ac07

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