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 2026-05-02.

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	23% 14% 5% 12% 6% 4 4 3 4 5% 21%	131524
	Night	22% 16% 6% 15% 7% 4 3 2 3 4 16%	131238
Transparency	Day	43% 37% 8% 10% 3	134945
	Night	47% 36% 7% 9% 2	135921
Seeing	Day	32% 16% 26% 18% 7% 2	19920
	Night	31% 15% 24% 23% 7% 1	27129

By Month

Percentage Cloud Cover NE (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% 20% 8% 27% 9% 4 3 2 2 2 5%	4690
	11th to 20th	Day	24% 19% 10% 22% 6% 4 2 2 3 3 5%	4681
	21st to end	Day	6% 18% 9% 27% 17% 9% 3 2 2 2 5%	5157
February	1st to 10th	Day	18% 16% 6% 24% 15% 6% 3 3 3 2 5%	1733
	11th to 20th	Day	17% 19% 7% 18% 13% 5% 3 3 3 3 10%	1890
	21st to end	Day	14% 16% 7% 18% 12% 8% 4 2 3 3 12%	1730
March	1st to 10th	Day	20% 14% 5% 17% 11% 6% 3 2 3 4 14%	4574
	11th to 20th	Day	24% 19% 7% 15% 7% 5% 4 3 3 3 12%	4776
	21st to end	Day	25% 17% 7% 16% 5% 4 2 2 3 4 14%	6103
April	1st to 10th	Day	23% 18% 7% 13% 5% 4 4 2 3 5% 17%	2520
	11th to 20th	Day	21% 13% 3 10% 3 4 4 3 5% 6% 28%	2525
	21st to end	Day	25% 12% 5% 7% 4 4 4 3 4 4 30%	2793
May	1st to 10th	Day	27% 13% 4 8% 4 3 3 3 4 4 27%	6359
	11th to 20th	Day	18% 11% 3 7% 4 4 4 3 5% 7% 33%	6318
	21st to end	Day	25% 9% 3 7% 4 4 4 3 5% 7% 31%	6948
June	1st to 10th	Day	28% 10% 3 7% 4 4 4 4 5% 7% 24%	2958
	11th to 20th	Day	23% 7% 3 7% 4 3 4 4 6% 8% 32%	3000
	21st to end	Day	30% 11% 2 6% 4 4 3 3 4 6% 27%	2982
July	1st to 10th	Day	27% 13% 3 7% 4 4 4 3 5% 7% 23%	6360
	11th to 20th	Day	26% 10% 3 6% 4 4 4 4 5% 6% 28%	6360
	21st to end	Day	26% 8% 2 6% 4 3 3 3 5% 7% 34%	6927
August	1st to 10th	Day	27% 8% 2 6% 4 4 4 4 5% 7% 29%	4564
	11th to 20th	Day	24% 7% 3 6% 3 4 4 3 5% 5% 36%	4406
	21st to end	Day	21% 7% 2 7% 5% 4 5% 4 5% 8% 33%	4322
September	1st to 10th	Day	24% 7% 2 6% 5% 4 4 3 6% 7% 31%	2400
	11th to 20th	Day	26% 9% 3 7% 5% 4 4 4 6% 7% 26%	2321
	21st to end	Day	28% 11% 3 7% 4 4 4 4 6% 5% 25%	2200
October	1st to 10th	Day	25% 11% 3 7% 3 4 4 4 5% 7% 27%	2047
	11th to 20th	Day	28% 13% 5% 8% 4 5% 3 3 5% 7% 21%	1904
	21st to end	Day	27% 18% 4 10% 4 4 4 3 4 5% 17%	1980
November	1st to 10th	Day	30% 22% 6% 10% 6% 4 4 2 4 3 10%	1850
	11th to 20th	Day	28% 23% 7% 9% 5% 4 3 3 3 4 12%	1685
	21st to end	Day	23% 26% 10% 14% 5% 4 3 3 3 3 6%	1586
December	1st to 10th	Day	15% 25% 9% 20% 5% 5% 4 4 3 3 8%	2360
	11th to 20th	Day	28% 22% 10% 18% 5% 3 3 2 2 3 4	2698
	21st to end	Day	20% 20% 9% 23% 7% 3 2 2 3 4 8%	3817
January	1st to 10th	Night	15% 21% 11% 28% 10% 4 3 1 2 2 4	8234
	11th to 20th	Night	21% 19% 11% 24% 6% 4 3 2 3 2 5%	8234
	21st to end	Night	7% 17% 10% 27% 16% 9% 3 2 2 2 6%	9056
February	1st to 10th	Night	16% 18% 6% 24% 16% 7% 2 1 2 2 5%	2883
	11th to 20th	Night	16% 19% 8% 20% 12% 6% 4 2 3 3 8%	2616
	21st to end	Night	13% 17% 7% 19% 11% 6% 3 3 4 3 14%	2076
March	1st to 10th	Night	18% 16% 6% 17% 12% 5% 4 2 3 3 14%	5486
	11th to 20th	Night	21% 19% 7% 18% 7% 4 3 2 3 3 13%	5400
	21st to end	Night	23% 20% 7% 14% 5% 4 3 3 3 5% 14%	5071
April	1st to 10th	Night	23% 18% 7% 13% 4 3 4 2 4 5% 17%	2100
	11th to 20th	Night	21% 15% 5% 9% 4 4 4 3 4 6% 26%	2043
	21st to end	Night	21% 13% 6% 8% 4 5% 4 3 5% 6% 26%	1824
May	1st to 10th	Night	29% 13% 3 7% 4 4 3 3 4 6% 23%	3624
	11th to 20th	Night	21% 11% 3 7% 4 4 4 4 5% 7% 31%	3596
	21st to end	Night	27% 9% 3 5% 3 3 3 2 5% 7% 32%	3948
June	1st to 10th	Night	31% 11% 4 7% 4 3 4 3 5% 6% 23%	1440
	11th to 20th	Night	22% 9% 2 5% 3 4 5% 3 7% 7% 32%	1400
	21st to end	Night	28% 10% 3 8% 5% 4 5% 4 5% 6% 22%	1412
July	1st to 10th	Night	31% 16% 4 8% 4 3 4 3 3 5% 17%	3619
	11th to 20th	Night	23% 12% 4 6% 4 4 4 4 6% 7% 26%	3620
	21st to end	Night	30% 8% 2 5% 3 3 3 3 4 6% 32%	3948
August	1st to 10th	Night	21% 9% 3 7% 5% 4 5% 4 6% 8% 31%	2596
	11th to 20th	Night	24% 10% 3 6% 5% 4 4 3 4 5% 34%	2651
	21st to end	Night	22% 7% 3 6% 4 4 4 4 4 6% 35%	3572
September	1st to 10th	Night	25% 7% 3 6% 4 5% 4 3 6% 7% 31%	2000
	11th to 20th	Night	29% 9% 2 5% 3 4 4 3 6% 6% 28%	2079
	21st to end	Night	26% 10% 3 7% 4 3 4 2 4 6% 30%	2200
October	1st to 10th	Night	24% 10% 3 7% 4 4 4 3 6% 7% 29%	2350
	11th to 20th	Night	28% 13% 4 9% 4 4 4 3 5% 5% 22%	2495
	21st to end	Night	28% 16% 5% 9% 4 4 3 3 4 6% 19%	2860
November	1st to 10th	Night	27% 21% 5% 11% 5% 4 4 4 4 4 11%	2668
	11th to 20th	Night	30% 22% 6% 11% 5% 4 3 2 4 3 10%	2930
	21st to end	Night	24% 25% 8% 14% 6% 4 4 2 3 3 7%	3029
December	1st to 10th	Night	17% 24% 9% 20% 7% 5% 4 3 3 3 6%	5050
	11th to 20th	Night	30% 19% 10% 18% 5% 3 2 1 2 3 8%	5731
	21st to end	Night	18% 20% 10% 21% 6% 4 3 2 3 3 11%	7397

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	69% 22% 5% 3 1	4691
	11th to 20th	Day	70% 21% 5% 3 1	4710
	21st to end	Day	65% 26% 3 3 2 1	5157
February	1st to 10th	Day	35% 58% 3 3 1	1733
	11th to 20th	Day	33% 58% 3 4 1	1898
	21st to end	Day	33% 59% 1 5% 1	1730
March	1st to 10th	Day	54% 28% 5% 6% 6%	4578
	11th to 20th	Day	58% 29% 5% 6% 2	4776
	21st to end	Day	58% 29% 2 9% 2	6103
April	1st to 10th	Day	30% 58% 2 5% 3 1	2520
	11th to 20th	Day	25% 59% 3 8% 4	2525
	21st to end	Day	27% 60% 4 5% 3 1	2793
May	1st to 10th	Day	49% 28% 6% 14% 2	6371
	11th to 20th	Day	35% 29% 13% 17% 6%	6322
	21st to end	Day	38% 29% 14% 17% 2	6948
June	1st to 10th	Day	22% 62% 6% 8% 3	2958
	11th to 20th	Day	21% 62% 5% 9% 3	3000
	21st to end	Day	24% 60% 4 8% 4	2982
July	1st to 10th	Day	49% 27% 8% 12% 4	6290
	11th to 20th	Day	43% 27% 14% 13% 1	6284
	21st to end	Day	37% 27% 18% 15% 3	6730
August	1st to 10th	Day	37% 36% 11% 13% 3	4550
	11th to 20th	Day	30% 37% 12% 15% 6% 1	4448
	21st to end	Day	30% 38% 13% 16% 3	4322
September	1st to 10th	Day	21% 57% 6% 11% 5%	2400
	11th to 20th	Day	27% 58% 7% 7% 1	2321
	21st to end	Day	22% 57% 7% 11% 3	2200
October	1st to 10th	Day	35% 37% 9% 16% 4	3333
	11th to 20th	Day	39% 40% 11% 7% 3	3086
	21st to end	Day	40% 38% 9% 10% 2	3191
November	1st to 10th	Day	38% 54% 3 4 1	1850
	11th to 20th	Day	38% 54% 3 4 1	1685
	21st to end	Day	40% 54% 3 2 1	1586
December	1st to 10th	Day	50% 37% 8% 4 1	2360
	11th to 20th	Day	62% 31% 5% 2	2697
	21st to end	Day	61% 26% 6% 7%	3817
January	1st to 10th	Night	69% 22% 4 5% 1	8234
	11th to 20th	Night	68% 22% 6% 4 1	8280
	21st to end	Night	61% 24% 4 5% 4 1	9056
February	1st to 10th	Night	36% 58% 2 2 1	2883
	11th to 20th	Night	34% 58% 4 4	2619
	21st to end	Night	33% 58% 3 4 2	2076
March	1st to 10th	Night	53% 29% 5% 9% 4	5495
	11th to 20th	Night	59% 28% 5% 5% 3	5401
	21st to end	Night	57% 28% 4 9% 3	5071
April	1st to 10th	Night	30% 58% 3 6% 2	2100
	11th to 20th	Night	25% 59% 5% 7% 3	2043
	21st to end	Night	29% 59% 5% 5% 2	1824
May	1st to 10th	Night	48% 28% 9% 13% 1	3629
	11th to 20th	Night	37% 29% 11% 19% 3	3597
	21st to end	Night	38% 28% 12% 20% 1	3949
June	1st to 10th	Night	23% 62% 3 9% 3	1440
	11th to 20th	Night	22% 61% 3 10% 3	1400
	21st to end	Night	25% 61% 3 7% 3	1412
July	1st to 10th	Night	58% 26% 7% 7% 2	3581
	11th to 20th	Night	46% 27% 11% 13% 3	3572
	21st to end	Night	41% 26% 14% 17% 2	3831
August	1st to 10th	Night	35% 37% 12% 15% 2	2585
	11th to 20th	Night	34% 38% 12% 10% 4 2	2675
	21st to end	Night	32% 38% 14% 14% 3	3571
September	1st to 10th	Night	21% 57% 7% 11% 4	2000
	11th to 20th	Night	26% 57% 8% 7% 2	2079
	21st to end	Night	22% 57% 8% 11% 3	2200
October	1st to 10th	Night	29% 36% 11% 19% 5%	3844
	11th to 20th	Night	38% 37% 11% 11% 3	4057
	21st to end	Night	40% 37% 11% 11% 1	4610
November	1st to 10th	Night	37% 53% 3 5% 1	2668
	11th to 20th	Night	40% 54% 3 3 1	2930
	21st to end	Night	40% 53% 3 3	3029
December	1st to 10th	Night	52% 36% 6% 5% 1	5050
	11th to 20th	Night	56% 31% 7% 5% 1	5733
	21st to end	Night	60% 25% 6% 9% 1	7397

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	29% 26% 29% 13% 3 1	430
	11th to 20th	Day	34% 20% 25% 14% 5% 3	430
	21st to end	Day	26% 22% 31% 17% 4	473
February	1st to 10th	Day	30% 24% 27% 11% 7% 2	430
	11th to 20th	Day	30% 23% 29% 10% 6% 2	426
	21st to end	Day	27% 22% 31% 13% 5% 3	355
March	1st to 10th	Day	27% 24% 29% 16% 3 2	430
	11th to 20th	Day	35% 18% 24% 13% 7% 3	463
	21st to end	Day	35% 21% 24% 13% 6% 2	594
April	1st to 10th	Day	37% 23% 26% 11% 3	540
	11th to 20th	Day	29% 17% 30% 16% 7% 1	563
	21st to end	Day	31% 14% 25% 21% 6% 2	750
May	1st to 10th	Day	35% 13% 24% 19% 6% 3	708
	11th to 20th	Day	28% 12% 25% 22% 11% 2	724
	21st to end	Day	33% 12% 30% 18% 5% 2	790
June	1st to 10th	Day	34% 9% 26% 21% 9% 2	730
	11th to 20th	Day	28% 10% 25% 24% 10% 2	730
	21st to end	Day	34% 13% 23% 18% 9% 3	730
July	1st to 10th	Day	31% 8% 27% 21% 10% 2	720
	11th to 20th	Day	31% 10% 24% 22% 12%	718
	21st to end	Day	33% 9% 25% 21% 11% 1	795
August	1st to 10th	Day	26% 9% 24% 26% 13% 2	725
	11th to 20th	Day	27% 9% 25% 27% 10% 2	717
	21st to end	Day	26% 11% 31% 20% 10% 2	593
September	1st to 10th	Day	25% 15% 30% 22% 6% 2	530
	11th to 20th	Day	32% 15% 32% 15% 5% 1	486
	21st to end	Day	34% 14% 26% 18% 5% 2	420
October	1st to 10th	Day	29% 18% 29% 16% 7% 1	420
	11th to 20th	Day	34% 15% 23% 16% 11% 2	420
	21st to end	Day	37% 18% 19% 19% 6% 1	462
November	1st to 10th	Day	42% 22% 22% 11% 4	425
	11th to 20th	Day	43% 16% 20% 14% 6% 2	430
	21st to end	Day	41% 21% 24% 11% 3	430
December	1st to 10th	Day	35% 22% 24% 12% 6%	430
	11th to 20th	Day	39% 21% 27% 11% 1 1	430
	21st to end	Day	30% 22% 23% 16% 7% 1	473
January	1st to 10th	Night	31% 24% 26% 16% 4	950
	11th to 20th	Night	31% 23% 25% 14% 5% 1	950
	21st to end	Night	24% 20% 31% 20% 5%	1045
February	1st to 10th	Night	28% 22% 28% 16% 6% 1	920
	11th to 20th	Night	27% 22% 30% 15% 5%	823
	21st to end	Night	22% 17% 29% 20% 9% 2	692
March	1st to 10th	Night	26% 23% 29% 18% 4 1	840
	11th to 20th	Night	26% 17% 24% 24% 8% 1	835
	21st to end	Night	29% 14% 27% 22% 7% 1	693
April	1st to 10th	Night	36% 13% 27% 18% 6%	630
	11th to 20th	Night	28% 14% 24% 27% 7% 1	624
	21st to end	Night	28% 13% 24% 27% 8% 1	630
May	1st to 10th	Night	31% 8% 20% 30% 10% 2	604
	11th to 20th	Night	30% 6% 21% 29% 12% 2	592
	21st to end	Night	33% 8% 21% 30% 8% 1	649
June	1st to 10th	Night	36% 6% 21% 28% 9% 1	600
	11th to 20th	Night	25% 7% 21% 34% 12% 1	600
	21st to end	Night	29% 7% 23% 29% 12% 1	600
July	1st to 10th	Night	33% 8% 18% 28% 13% 1	586
	11th to 20th	Night	27% 6% 19% 35% 12%	582
	21st to end	Night	34% 5% 15% 33% 12%	656
August	1st to 10th	Night	24% 7% 16% 36% 16% 1	598
	11th to 20th	Night	28% 7% 21% 29% 14% 1	592
	21st to end	Night	27% 7% 21% 30% 15% 1	660
September	1st to 10th	Night	27% 11% 22% 29% 10% 1	600
	11th to 20th	Night	33% 8% 24% 29% 7%	600
	21st to end	Night	29% 12% 30% 22% 7% 1	600
October	1st to 10th	Night	29% 11% 25% 28% 6%	750
	11th to 20th	Night	35% 12% 18% 26% 8% 1	852
	21st to end	Night	36% 15% 22% 21% 6%	1001
November	1st to 10th	Night	39% 18% 22% 16% 3	930
	11th to 20th	Night	43% 13% 22% 15% 6% 1	950
	21st to end	Night	40% 19% 22% 16% 3	950
December	1st to 10th	Night	34% 22% 21% 17% 6%	950
	11th to 20th	Night	36% 24% 25% 13% 2	950
	21st to end	Night	27% 21% 27% 18% 6% 1	1045

Page generated at 2026-04-29 03:21:45. Version ac07

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