Stephenville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stephenville clear sky chart from 2005-11-06 to 2026-04-17.

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 5% 3 3 4 3 5% 7% 55%	131848
	Night	9% 5% 2 4 3 3 3 3 5% 7% 58%	130672
Transparency	Day	29% 4 9% 23% 24% 10%	135617
	Night	27% 4 8% 22% 25% 14%	134967
Seeing	Day	10% 7% 24% 30% 21% 7%	16902
	Night	10% 8% 31% 36% 15% 1	26944

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	8% 5% 2 5% 3 2 3 2 4 5% 60%	5289
	11th to 20th	Day	6% 5% 1 3 2 3 3 2 4 6% 64%	5310
	21st to end	Day	19% 7% 2 5% 3 3 3 2 3 5% 48%	6006
February	1st to 10th	Day	12% 5% 2 6% 3 3 3 3 5% 6% 52%	2100
	11th to 20th	Day	13% 7% 2 6% 4 3 4 2 4 5% 50%	2049
	21st to end	Day	16% 7% 2 4 2 2 2 2 3 4 58%	1730
March	1st to 10th	Day	11% 5% 2 4 3 4 3 2 5% 6% 54%	4927
	11th to 20th	Day	10% 5% 1 4 3 3 3 3 4 6% 58%	5090
	21st to end	Day	8% 5% 1 6% 3 4 4 4 6% 7% 53%	5583
April	1st to 10th	Day	9% 6% 2 6% 4 4 4 3 5% 7% 50%	2310
	11th to 20th	Day	13% 6% 2 4 4 4 3 3 5% 6% 51%	2316
	21st to end	Day	9% 5% 2 5% 4 4 4 3 5% 6% 53%	2595
May	1st to 10th	Day	13% 7% 2 6% 4 4 4 3 5% 6% 46%	5862
	11th to 20th	Day	12% 7% 2 6% 4 4 3 3 4 6% 49%	5862
	21st to end	Day	11% 6% 3 6% 5% 4 5% 4 6% 7% 43%	6434
June	1st to 10th	Day	5% 4 1 5% 5% 4 5% 4 6% 8% 55%	2600
	11th to 20th	Day	5% 3 1 4 3 4 4 4 7% 8% 57%	2600
	21st to end	Day	5% 4 1 4 4 4 4 4 6% 8% 57%	2600
July	1st to 10th	Day	10% 6% 3 7% 5% 5% 5% 4 5% 7% 43%	5900
	11th to 20th	Day	3 2 1 4 3 3 4 3 6% 9% 61%	5900
	21st to end	Day	3 3 1 4 3 3 5% 5% 7% 10% 56%	6422
August	1st to 10th	Day	2 1 1 3 3 3 3 3 4 8% 70%	4234
	11th to 20th	Day	4 2 1 3 3 3 4 4 5% 9% 63%	3980
	21st to end	Day	3 3 1 4 4 4 5% 5% 6% 9% 57%	4195
September	1st to 10th	Day	10% 4 1 5% 4 4 3 3 5% 6% 54%	2200
	11th to 20th	Day	9% 5% 3 7% 4 4 4 4 5% 7% 50%	2200
	21st to end	Day	8% 3 1 4 3 4 3 3 4 7% 60%	2200
October	1st to 10th	Day	5% 3 1 4 4 3 3 3 4 6% 65%	2200
	11th to 20th	Day	10% 3 1 2 2 2 3 3 4 5% 64%	2044
	21st to end	Day	11% 4 2 5% 2 1 2 2 3 4 65%	2200
November	1st to 10th	Day	11% 4 2 4 3 3 3 3 4 6% 59%	2032
	11th to 20th	Day	5% 4 1 4 2 3 4 4 4 6% 62%	1890
	21st to end	Day	12% 5% 2 5% 4 3 3 3 3 6% 54%	1890
December	1st to 10th	Day	14% 7% 2 5% 2 4 3 4 4 5% 50%	3030
	11th to 20th	Day	10% 7% 2 6% 3 4 5% 4 4 4 50%	3481
	21st to end	Day	12% 6% 2 5% 3 2 3 2 3 4 58%	4587
January	1st to 10th	Night	10% 6% 2 4 2 3 3 2 4 6% 59%	7634
	11th to 20th	Night	6% 3 1 3 2 2 3 3 4 4 71%	7680
	21st to end	Night	19% 8% 2 5% 3 3 4 3 4 6% 44%	8264
February	1st to 10th	Night	11% 6% 3 5% 3 2 3 2 5% 6% 56%	2520
	11th to 20th	Night	13% 5% 3 5% 3 3 3 3 4 6% 52%	2458
	21st to end	Night	13% 6% 2 4 2 3 3 2 4 5% 57%	2076
March	1st to 10th	Night	9% 7% 3 6% 3 3 4 3 4 6% 53%	5149
	11th to 20th	Night	10% 4 2 4 3 2 3 3 5% 7% 57%	5090
	21st to end	Night	9% 6% 2 5% 3 3 4 3 4 5% 55%	5588
April	1st to 10th	Night	8% 5% 2 4 4 4 3 3 5% 7% 56%	2310
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 5% 7% 52%	2162
	21st to end	Night	8% 5% 1 3 3 3 3 3 5% 6% 58%	1803
May	1st to 10th	Night	13% 8% 2 6% 4 3 4 2 4 6% 47%	4053
	11th to 20th	Night	6% 7% 3 7% 5% 5% 3 3 5% 6% 49%	4053
	21st to end	Night	9% 6% 2 5% 3 3 4 4 6% 9% 48%	4443
June	1st to 10th	Night	3 2 1 4 4 3 4 4 6% 9% 61%	1800
	11th to 20th	Night	2 3 1 3 3 3 3 4 5% 10% 64%	1800
	21st to end	Night	2 3 1 3 4 3 2 4 6% 9% 63%	1800
July	1st to 10th	Night	8% 6% 3 5% 3 4 5% 4 5% 9% 49%	4078
	11th to 20th	Night	2 1 1 2 2 2 3 3 6% 10% 69%	4077
	21st to end	Night	2 3 2 4 3 4 4 3 6% 9% 62%	4449
August	1st to 10th	Night	1 1 2 1 2 2 2 4 8% 78%	2926
	11th to 20th	Night	3 2 1 3 2 2 3 3 5% 11% 66%	3074
	21st to end	Night	3 2 1 3 3 3 3 4 6% 11% 61%	3710
September	1st to 10th	Night	8% 4 2 4 4 3 3 3 7% 7% 56%	2200
	11th to 20th	Night	8% 5% 2 5% 4 4 3 3 6% 6% 54%	2200
	21st to end	Night	7% 3 2 3 2 2 2 3 5% 7% 63%	2200
October	1st to 10th	Night	4 3 1 3 2 3 3 2 5% 7% 68%	2200
	11th to 20th	Night	8% 4 1 3 2 2 3 2 4 5% 65%	2335
	21st to end	Night	11% 5% 2 3 2 2 2 2 3 4 63%	2640
November	1st to 10th	Night	9% 5% 1 4 3 3 3 2 4 4 63%	2481
	11th to 20th	Night	4 4 1 4 3 3 4 2 4 6% 64%	2730
	21st to end	Night	14% 5% 2 3 3 3 3 3 4 6% 54%	2730
December	1st to 10th	Night	13% 5% 2 5% 3 3 3 3 4 5% 55%	4380
	11th to 20th	Night	10% 7% 3 5% 3 3 3 3 4 6% 52%	4946
	21st to end	Night	11% 6% 2 4 2 3 3 2 3 5% 59%	6633

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	29% 3 6% 23% 30% 10%	5290
	11th to 20th	Day	23% 2 5% 23% 35% 12%	5310
	21st to end	Day	42% 2 3 16% 23% 13%	6006
February	1st to 10th	Day	34% 3 5% 18% 24% 16%	2100
	11th to 20th	Day	38% 2 6% 21% 20% 12%	2059
	21st to end	Day	32% 2 4 15% 28% 19%	1730
March	1st to 10th	Day	32% 4 6% 14% 24% 22%	4927
	11th to 20th	Day	30% 3 10% 13% 18% 27%	5090
	21st to end	Day	30% 4 10% 22% 22% 11%	5585
April	1st to 10th	Day	34% 6% 8% 20% 19% 14%	2310
	11th to 20th	Day	34% 4 8% 20% 21% 13%	2316
	21st to end	Day	33% 4 8% 20% 27% 8%	2595
May	1st to 10th	Day	38% 5% 9% 20% 21% 6%	5900
	11th to 20th	Day	38% 4 7% 17% 27% 7%	5866
	21st to end	Day	39% 6% 11% 25% 14% 5%	6447
June	1st to 10th	Day	27% 5% 14% 30% 20% 4	2600
	11th to 20th	Day	23% 5% 14% 30% 21% 7%	2600
	21st to end	Day	24% 5% 13% 26% 24% 7%	2600
July	1st to 10th	Day	39% 6% 12% 30% 11% 1	5836
	11th to 20th	Day	18% 6% 17% 34% 22% 3	5831
	21st to end	Day	20% 8% 15% 33% 22% 1	6240
August	1st to 10th	Day	13% 4 10% 31% 37% 5%	4220
	11th to 20th	Day	18% 4 14% 35% 26% 2	4019
	21st to end	Day	21% 8% 16% 32% 19% 3	4194
September	1st to 10th	Day	32% 5% 9% 20% 24% 10%	2200
	11th to 20th	Day	34% 5% 10% 22% 22% 8%	2200
	21st to end	Day	25% 4 9% 19% 28% 14%	2200
October	1st to 10th	Day	13% 2 6% 14% 34% 30%	3590
	11th to 20th	Day	16% 3 7% 20% 33% 21%	3310
	21st to end	Day	20% 2 4 24% 35% 15%	3538
November	1st to 10th	Day	28% 4 6% 21% 27% 14%	2032
	11th to 20th	Day	23% 4 8% 22% 28% 16%	1890
	21st to end	Day	35% 3 4 21% 24% 13%	1890
December	1st to 10th	Day	37% 3 5% 20% 25% 9%	3030
	11th to 20th	Day	38% 4 5% 11% 28% 14%	3479
	21st to end	Day	32% 3 4 21% 26% 15%	4587
January	1st to 10th	Night	29% 3 5% 20% 33% 11%	7635
	11th to 20th	Night	19% 2 3 20% 35% 21%	7680
	21st to end	Night	43% 3 4 13% 23% 13%	8264
February	1st to 10th	Night	32% 4 6% 15% 25% 18%	2520
	11th to 20th	Night	35% 3 7% 16% 26% 14%	2458
	21st to end	Night	31% 4 5% 15% 24% 21%	2076
March	1st to 10th	Night	33% 4 5% 15% 22% 20%	5149
	11th to 20th	Night	27% 4 9% 17% 15% 27%	5090
	21st to end	Night	30% 4 7% 19% 28% 12%	5588
April	1st to 10th	Night	28% 4 9% 23% 19% 17%	2310
	11th to 20th	Night	32% 5% 9% 18% 21% 15%	2162
	21st to end	Night	27% 5% 12% 21% 27% 8%	1803
May	1st to 10th	Night	39% 5% 7% 24% 17% 8%	4080
	11th to 20th	Night	35% 5% 11% 17% 21% 11%	4054
	21st to end	Night	32% 6% 14% 28% 13% 8%	4452
June	1st to 10th	Night	20% 6% 15% 35% 19% 5%	1800
	11th to 20th	Night	16% 5% 15% 32% 24% 8%	1800
	21st to end	Night	18% 7% 11% 30% 27% 7%	1800
July	1st to 10th	Night	31% 6% 14% 35% 12% 2	4035
	11th to 20th	Night	12% 5% 16% 34% 29% 4	4026
	21st to end	Night	18% 7% 15% 33% 25% 2	4320
August	1st to 10th	Night	7% 3 11% 34% 40% 7%	2916
	11th to 20th	Night	15% 3 16% 39% 23% 3	3101
	21st to end	Night	16% 7% 22% 33% 20% 3	3710
September	1st to 10th	Night	27% 6% 9% 23% 24% 11%	2200
	11th to 20th	Night	30% 5% 11% 21% 23% 9%	2200
	21st to end	Night	21% 4 8% 24% 26% 17%	2200
October	1st to 10th	Night	11% 2 6% 16% 29% 36%	3590
	11th to 20th	Night	15% 2 8% 18% 33% 24%	3795
	21st to end	Night	21% 2 4 21% 37% 15%	4252
November	1st to 10th	Night	27% 3 5% 21% 26% 17%	2481
	11th to 20th	Night	22% 4 7% 23% 27% 18%	2730
	21st to end	Night	32% 3 7% 17% 27% 14%	2730
December	1st to 10th	Night	33% 3 5% 21% 25% 12%	4380
	11th to 20th	Night	35% 4 5% 12% 29% 16%	4947
	21st to end	Night	30% 3 5% 19% 25% 17%	6633

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	13% 17% 40% 25% 5%	330
	11th to 20th	Day	14% 14% 36% 27% 7% 2	330
	21st to end	Day	18% 15% 37% 23% 6% 1	363
February	1st to 10th	Day	17% 15% 38% 25% 5%	330
	11th to 20th	Day	19% 18% 40% 20% 3	330
	21st to end	Day	21% 15% 41% 19% 3 1	273
March	1st to 10th	Day	16% 18% 38% 24% 4	330
	11th to 20th	Day	18% 16% 35% 25% 4 2	330
	21st to end	Day	9% 16% 40% 28% 6%	363
April	1st to 10th	Day	16% 18% 37% 21% 8%	330
	11th to 20th	Day	15% 17% 41% 23% 4	386
	21st to end	Day	13% 14% 41% 23% 8% 1	695
May	1st to 10th	Day	12% 12% 39% 31% 6%	703
	11th to 20th	Day	15% 7% 30% 31% 14% 3	725
	21st to end	Day	11% 7% 30% 36% 13% 3	789
June	1st to 10th	Day	5% 2 20% 41% 25% 7%	730
	11th to 20th	Day	5% 2 18% 47% 23% 5%	730
	21st to end	Day	4 1 12% 38% 34% 11%	730
July	1st to 10th	Day	7% 2 8% 36% 35% 13%	721
	11th to 20th	Day	2 1 6% 35% 42% 14%	718
	21st to end	Day	2 1 6% 30% 45% 16%	794
August	1st to 10th	Day	2 4 34% 44% 16%	726
	11th to 20th	Day	7% 6% 31% 41% 14%	602
	21st to end	Day	6% 1 5% 28% 35% 25%	518
September	1st to 10th	Day	10% 2 6% 22% 38% 23%	330
	11th to 20th	Day	3 2 5% 23% 48% 19%	330
	21st to end	Day	10% 2 6% 29% 37% 16%	330
October	1st to 10th	Day	3 2 12% 34% 35% 15%	330
	11th to 20th	Day	11% 4 29% 29% 23% 4	330
	21st to end	Day	18% 10% 25% 27% 17% 3	363
November	1st to 10th	Day	17% 6% 28% 29% 16% 4	330
	11th to 20th	Day	10% 12% 30% 32% 13% 4	330
	21st to end	Day	17% 14% 36% 21% 11% 2	330
December	1st to 10th	Day	15% 11% 36% 27% 10% 2	330
	11th to 20th	Day	11% 13% 40% 25% 9% 1	330
	21st to end	Day	17% 11% 33% 30% 8% 1	363
January	1st to 10th	Night	12% 9% 40% 31% 7%	1050
	11th to 20th	Night	14% 12% 35% 33% 6%	1050
	21st to end	Night	15% 14% 35% 29% 6%	1108
February	1st to 10th	Night	13% 10% 43% 29% 5%	840
	11th to 20th	Night	16% 14% 40% 27% 3	824
	21st to end	Night	17% 14% 46% 22% 2	692
March	1st to 10th	Night	15% 15% 39% 27% 4	689
	11th to 20th	Night	14% 11% 42% 28% 5%	630
	21st to end	Night	8% 13% 45% 31% 3	693
April	1st to 10th	Night	11% 12% 45% 29% 3	630
	11th to 20th	Night	11% 13% 45% 26% 5%	611
	21st to end	Night	9% 11% 46% 27% 7%	600
May	1st to 10th	Night	10% 11% 43% 32% 4	600
	11th to 20th	Night	10% 6% 38% 32% 12% 1	591
	21st to end	Night	7% 6% 37% 37% 13% 1	650
June	1st to 10th	Night	4 2 24% 49% 20% 2	600
	11th to 20th	Night	3 2 28% 53% 14%	600
	21st to end	Night	3 1 18% 50% 25% 3	600
July	1st to 10th	Night	6% 2 10% 48% 31% 3	585
	11th to 20th	Night	3 1 10% 53% 32% 2	582
	21st to end	Night	2 1 6% 52% 36% 2	657
August	1st to 10th	Night	2 6% 50% 40% 3	597
	11th to 20th	Night	6% 1 7% 46% 36% 4	594
	21st to end	Night	5% 5% 43% 42% 5%	660
September	1st to 10th	Night	8% 1 8% 45% 35% 4	600
	11th to 20th	Night	11% 1 10% 44% 33% 2	600
	21st to end	Night	9% 2 14% 41% 33% 2	600
October	1st to 10th	Night	6% 2 18% 45% 27% 2	600
	11th to 20th	Night	10% 5% 29% 40% 16% 1	735
	21st to end	Night	13% 10% 28% 34% 14% 1	880
November	1st to 10th	Night	11% 5% 31% 40% 13% 1	841
	11th to 20th	Night	6% 9% 35% 37% 13% 1	1050
	21st to end	Night	15% 9% 38% 27% 10% 1	1050
December	1st to 10th	Night	13% 8% 37% 36% 6%	1050
	11th to 20th	Night	15% 10% 34% 34% 6%	1050
	21st to end	Night	14% 10% 38% 29% 8%	1155

Page generated at 2026-04-14 01:44:30. Version ac07

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