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 2024-12-24.

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% 54%	101510
	Night	8% 5% 2 4 3 3 3 3 5% 7% 58%	98723
Transparency	Day	29% 4 9% 23% 24% 10%	105318
	Night	26% 4 9% 23% 25% 13%	103042
Seeing	Day	10% 7% 23% 30% 22% 7%	15214
	Night	10% 7% 31% 36% 15% 1	25182

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	10% 6% 2 5% 3 2 2 2 3 4 60%	2847
	11th to 20th	Day	10% 6% 1 3 2 2 2 3 4 6% 61%	2850
	21st to end	Day	16% 8% 2 6% 2 3 3 3 3 5% 51%	3231
February	1st to 10th	Day	11% 5% 3 6% 4 3 3 3 5% 6% 51%	1900
	11th to 20th	Day	13% 8% 2 6% 4 3 4 2 3 5% 50%	1849
	21st to end	Day	17% 7% 2 4 3 2 2 2 3 4 55%	1570
March	1st to 10th	Day	12% 6% 1 4 3 4 3 3 5% 6% 52%	3359
	11th to 20th	Day	15% 7% 2 5% 3 4 4 4 5% 6% 45%	3480
	21st to end	Day	8% 5% 1 7% 4 5% 4 4 6% 8% 47%	3814
April	1st to 10th	Day	10% 5% 2 5% 4 4 4 3 5% 7% 51%	2090
	11th to 20th	Day	13% 6% 2 4 4 3 3 3 5% 6% 52%	2135
	21st to end	Day	9% 5% 2 5% 4 4 3 3 5% 6% 54%	2465
May	1st to 10th	Day	14% 7% 2 6% 4 4 4 3 5% 6% 43%	4082
	11th to 20th	Day	13% 7% 2 5% 4 4 3 3 4 6% 50%	4082
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 43%	4477
June	1st to 10th	Day	5% 4 1 4 5% 4 5% 4 6% 8% 55%	2470
	11th to 20th	Day	4 3 1 4 3 4 4 4 7% 8% 56%	2470
	21st to end	Day	5% 4 1 4 4 4 4 4 6% 8% 56%	2470
July	1st to 10th	Day	4 4 2 6% 5% 4 5% 4 5% 8% 54%	4120
	11th to 20th	Day	3 2 1 3 3 4 3 3 5% 9% 63%	4120
	21st to end	Day	4 4 2 5% 4 4 6% 5% 7% 10% 49%	4465
August	1st to 10th	Day	2 1 1 3 3 3 4 3 4 8% 70%	4104
	11th to 20th	Day	4 2 1 3 3 3 4 4 5% 9% 63%	3856
	21st to end	Day	3 3 1 4 4 4 5% 5% 6% 9% 58%	4066
September	1st to 10th	Day	10% 4 1 5% 4 4 3 3 5% 6% 54%	2090
	11th to 20th	Day	9% 5% 3 7% 4 4 4 4 5% 7% 49%	2090
	21st to end	Day	8% 4 1 4 3 4 3 3 4 7% 60%	2090
October	1st to 10th	Day	5% 3 1 4 4 3 3 3 5% 6% 64%	2090
	11th to 20th	Day	10% 4 1 2 2 2 3 3 4 5% 64%	1942
	21st to end	Day	11% 4 2 5% 2 1 2 1 3 4 64%	2090
November	1st to 10th	Day	11% 5% 2 4 3 3 3 3 4 6% 57%	1933
	11th to 20th	Day	5% 4 2 4 2 3 4 4 4 6% 62%	1800
	21st to end	Day	13% 5% 2 5% 3 3 3 3 3 5% 55%	1800
December	1st to 10th	Day	12% 8% 1 5% 3 3 3 4 4 6% 53%	1800
	11th to 20th	Day	10% 7% 2 6% 3 4 5% 4 4 5% 50%	2251
	21st to end	Day	13% 6% 2 4 3 3 3 2 3 4 55%	3162
January	1st to 10th	Night	13% 5% 2 4 2 2 2 1 3 6% 60%	4108
	11th to 20th	Night	10% 5% 1 3 2 2 2 2 3 4 66%	4120
	21st to end	Night	14% 8% 2 5% 3 3 3 2 4 5% 49%	4464
February	1st to 10th	Night	11% 6% 3 5% 4 2 3 2 5% 6% 54%	2280
	11th to 20th	Night	13% 6% 3 5% 3 3 2 3 4 6% 52%	2218
	21st to end	Night	14% 6% 2 4 2 3 3 2 4 5% 56%	1884
March	1st to 10th	Night	10% 8% 2 6% 4 4 4 3 4 5% 50%	3494
	11th to 20th	Night	13% 5% 2 5% 4 3 3 3 6% 7% 48%	3480
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 5% 6% 50%	3817
April	1st to 10th	Night	7% 4 2 4 3 4 3 3 5% 7% 57%	2090
	11th to 20th	Night	9% 5% 2 5% 3 4 4 3 5% 7% 53%	1990
	21st to end	Night	8% 5% 1 3 3 3 3 3 5% 6% 59%	1713
May	1st to 10th	Night	16% 10% 2 5% 4 2 3 2 4 6% 45%	2823
	11th to 20th	Night	8% 8% 3 6% 4 4 3 3 5% 7% 50%	2823
	21st to end	Night	10% 5% 2 4 3 3 4 4 6% 8% 52%	3090
June	1st to 10th	Night	3 2 1 3 4 3 3 4 5% 9% 62%	1710
	11th to 20th	Night	2 3 1 3 3 3 3 4 5% 9% 65%	1710
	21st to end	Night	2 3 1 3 4 3 2 4 6% 9% 62%	1710
July	1st to 10th	Night	3 4 2 3 3 3 4 3 5% 9% 62%	2850
	11th to 20th	Night	2 1 2 2 2 2 3 5% 10% 71%	2850
	21st to end	Night	3 3 2 4 3 4 4 3 6% 9% 58%	3098
August	1st to 10th	Night	1 1 2 1 2 2 2 4 8% 78%	2836
	11th to 20th	Night	3 2 1 3 2 2 3 3 5% 11% 66%	2978
	21st to end	Night	3 2 1 3 3 3 3 4 6% 11% 61%	3597
September	1st to 10th	Night	8% 4 2 4 4 3 3 3 7% 7% 55%	2090
	11th to 20th	Night	9% 5% 2 5% 4 4 3 3 6% 6% 53%	2090
	21st to end	Night	7% 3 2 3 2 2 2 3 5% 7% 63%	2090
October	1st to 10th	Night	4 3 1 3 2 3 3 2 5% 7% 67%	2090
	11th to 20th	Night	9% 4 1 3 3 2 3 2 4 5% 64%	2218
	21st to end	Night	12% 5% 2 3 2 2 2 2 3 4 62%	2508
November	1st to 10th	Night	9% 5% 2 4 3 3 3 2 4 4 62%	2360
	11th to 20th	Night	4 4 1 4 3 3 4 3 4 6% 64%	2600
	21st to end	Night	13% 5% 2 3 3 3 3 3 4 6% 55%	2600
December	1st to 10th	Night	10% 5% 2 4 2 3 3 3 4 6% 57%	2600
	11th to 20th	Night	9% 6% 3 5% 4 4 3 3 5% 6% 52%	3166
	21st to end	Night	13% 6% 2 4 2 3 3 2 3 5% 56%	4578

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 4 16% 34% 13%	2848
	11th to 20th	Day	26% 3 6% 20% 33% 12%	2850
	21st to end	Day	39% 2 4 15% 28% 12%	3231
February	1st to 10th	Day	34% 4 5% 19% 23% 16%	1900
	11th to 20th	Day	38% 2 6% 20% 21% 13%	1859
	21st to end	Day	35% 2 4 14% 26% 19%	1570
March	1st to 10th	Day	33% 4 5% 14% 28% 15%	3359
	11th to 20th	Day	41% 4 15% 16% 18% 7%	3480
	21st to end	Day	34% 4 12% 20% 20% 9%	3814
April	1st to 10th	Day	33% 6% 8% 20% 18% 14%	2090
	11th to 20th	Day	34% 4 8% 20% 21% 12%	2135
	21st to end	Day	32% 4 8% 20% 27% 8%	2465
May	1st to 10th	Day	41% 5% 9% 19% 18% 8%	4120
	11th to 20th	Day	38% 4 8% 20% 28% 3	4086
	21st to end	Day	39% 6% 12% 24% 12% 6%	4489
June	1st to 10th	Day	27% 5% 14% 30% 20% 4	2470
	11th to 20th	Day	23% 5% 14% 30% 21% 7%	2470
	21st to end	Day	25% 5% 12% 26% 25% 7%	2470
July	1st to 10th	Day	27% 6% 13% 38% 14% 1	4056
	11th to 20th	Day	18% 4 13% 37% 25% 3	4051
	21st to end	Day	25% 8% 14% 34% 18% 1	4325
August	1st to 10th	Day	13% 4 10% 30% 38% 5%	4090
	11th to 20th	Day	18% 4 14% 35% 26% 2	3895
	21st to end	Day	21% 8% 16% 33% 20% 3	4065
September	1st to 10th	Day	32% 5% 10% 20% 23% 11%	2090
	11th to 20th	Day	35% 5% 10% 21% 22% 8%	2090
	21st to end	Day	26% 4 9% 18% 29% 14%	2090
October	1st to 10th	Day	13% 2 6% 14% 33% 31%	3480
	11th to 20th	Day	16% 3 7% 19% 33% 22%	3208
	21st to end	Day	20% 2 4 24% 35% 15%	3428
November	1st to 10th	Day	29% 5% 6% 22% 24% 14%	1933
	11th to 20th	Day	23% 4 8% 22% 27% 16%	1800
	21st to end	Day	34% 3 4 21% 24% 14%	1800
December	1st to 10th	Day	34% 3 6% 22% 26% 9%	1800
	11th to 20th	Day	37% 3 6% 14% 26% 13%	2249
	21st to end	Day	34% 3 4 19% 25% 15%	3162
January	1st to 10th	Night	28% 2 4 17% 34% 15%	4108
	11th to 20th	Night	26% 2 4 19% 30% 20%	4120
	21st to end	Night	38% 3 5% 16% 25% 14%	4464
February	1st to 10th	Night	33% 4 7% 15% 24% 17%	2280
	11th to 20th	Night	35% 3 6% 15% 26% 15%	2218
	21st to end	Night	32% 4 6% 15% 22% 21%	1884
March	1st to 10th	Night	36% 4 5% 14% 24% 16%	3494
	11th to 20th	Night	34% 5% 13% 22% 16% 9%	3480
	21st to end	Night	33% 5% 9% 20% 26% 7%	3817
April	1st to 10th	Night	28% 4 8% 23% 20% 17%	2090
	11th to 20th	Night	31% 5% 10% 18% 21% 15%	1990
	21st to end	Night	26% 5% 12% 21% 28% 8%	1713
May	1st to 10th	Night	42% 6% 7% 21% 16% 9%	2850
	11th to 20th	Night	34% 5% 12% 21% 23% 5%	2824
	21st to end	Night	29% 6% 13% 30% 15% 6%	3099
June	1st to 10th	Night	20% 5% 15% 36% 19% 5%	1710
	11th to 20th	Night	16% 5% 14% 32% 25% 8%	1710
	21st to end	Night	19% 6% 10% 30% 27% 7%	1710
July	1st to 10th	Night	18% 6% 13% 45% 16% 2	2805
	11th to 20th	Night	10% 4 12% 40% 29% 4	2796
	21st to end	Night	21% 6% 14% 38% 20% 1	2999
August	1st to 10th	Night	7% 3 11% 33% 40% 7%	2826
	11th to 20th	Night	15% 3 16% 39% 24% 4	3005
	21st to end	Night	16% 7% 22% 33% 20% 3	3597
September	1st to 10th	Night	27% 6% 9% 23% 23% 11%	2090
	11th to 20th	Night	31% 5% 11% 20% 23% 9%	2090
	21st to end	Night	21% 4 8% 23% 26% 18%	2090
October	1st to 10th	Night	12% 2 6% 15% 28% 37%	3480
	11th to 20th	Night	15% 2 9% 17% 32% 24%	3678
	21st to end	Night	21% 2 4 21% 37% 15%	4120
November	1st to 10th	Night	28% 3 5% 21% 25% 17%	2360
	11th to 20th	Night	23% 4 6% 22% 26% 19%	2600
	21st to end	Night	32% 3 7% 17% 27% 15%	2600
December	1st to 10th	Night	28% 3 7% 23% 25% 13%	2600
	11th to 20th	Night	34% 3 5% 14% 28% 16%	3167
	21st to end	Night	32% 3 5% 17% 25% 19%	4578

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	14% 17% 38% 25% 6%	270
	11th to 20th	Day	15% 15% 35% 25% 8% 2	270
	21st to end	Day	15% 15% 36% 25% 7% 1	297
February	1st to 10th	Day	16% 17% 40% 23% 4	270
	11th to 20th	Day	21% 16% 39% 20% 3	270
	21st to end	Day	25% 16% 42% 15% 1	225
March	1st to 10th	Day	15% 17% 41% 23% 4	270
	11th to 20th	Day	19% 16% 34% 25% 5% 2	270
	21st to end	Day	10% 18% 42% 23% 6%	297
April	1st to 10th	Day	16% 19% 38% 21% 5%	270
	11th to 20th	Day	16% 16% 41% 23% 5%	333
	21st to end	Day	13% 14% 42% 22% 8% 1	645
May	1st to 10th	Day	12% 12% 38% 31% 7%	653
	11th to 20th	Day	15% 6% 30% 32% 14% 3	675
	21st to end	Day	10% 7% 31% 35% 14% 3	734
June	1st to 10th	Day	5% 2 19% 40% 26% 7%	680
	11th to 20th	Day	4 2 18% 48% 23% 5%	680
	21st to end	Day	4 1 12% 38% 33% 11%	680
July	1st to 10th	Day	5% 1 8% 36% 36% 13%	671
	11th to 20th	Day	2 1 6% 35% 43% 14%	668
	21st to end	Day	2 1 5% 30% 45% 16%	739
August	1st to 10th	Day	2 4 34% 43% 16%	676
	11th to 20th	Day	7% 1 6% 31% 42% 14%	558
	21st to end	Day	5% 1 5% 27% 35% 26%	477
September	1st to 10th	Day	11% 6% 19% 38% 25%	300
	11th to 20th	Day	4 1 5% 22% 48% 20%	300
	21st to end	Day	10% 2 5% 28% 37% 17%	300
October	1st to 10th	Day	3 2 13% 35% 34% 13%	300
	11th to 20th	Day	12% 4 29% 31% 21% 3	300
	21st to end	Day	17% 11% 25% 26% 17% 3	330
November	1st to 10th	Day	19% 5% 29% 29% 14% 4	300
	11th to 20th	Day	10% 12% 31% 30% 12% 4	300
	21st to end	Day	17% 14% 36% 20% 11% 2	300
December	1st to 10th	Day	15% 11% 35% 27% 10% 2	300
	11th to 20th	Day	12% 12% 41% 25% 9% 1	300
	21st to end	Day	18% 11% 33% 28% 8% 2	306
January	1st to 10th	Night	13% 9% 41% 30% 8%	950
	11th to 20th	Night	15% 11% 34% 33% 7%	950
	21st to end	Night	14% 14% 35% 31% 7%	1003
February	1st to 10th	Night	14% 11% 43% 27% 5%	760
	11th to 20th	Night	15% 13% 41% 28% 3	744
	21st to end	Night	18% 14% 46% 20% 2	628
March	1st to 10th	Night	16% 13% 39% 27% 5%	623
	11th to 20th	Night	15% 11% 41% 28% 6%	570
	21st to end	Night	8% 14% 47% 28% 3	627
April	1st to 10th	Night	11% 11% 46% 28% 3	570
	11th to 20th	Night	11% 12% 46% 26% 5%	563
	21st to end	Night	9% 10% 47% 26% 7%	570
May	1st to 10th	Night	10% 11% 44% 31% 4	570
	11th to 20th	Night	11% 6% 38% 32% 13% 1	561
	21st to end	Night	7% 6% 37% 37% 13% 1	617
June	1st to 10th	Night	3 2 23% 49% 21% 2	570
	11th to 20th	Night	2 2 29% 53% 14%	570
	21st to end	Night	3 1 18% 49% 25% 3	570
July	1st to 10th	Night	5% 1 10% 49% 31% 3	555
	11th to 20th	Night	3 1 10% 53% 33% 2	552
	21st to end	Night	2 1 5% 54% 36% 2	624
August	1st to 10th	Night	2 6% 50% 39% 3	567
	11th to 20th	Night	6% 1 7% 46% 36% 4	564
	21st to end	Night	5% 4 44% 41% 6%	627
September	1st to 10th	Night	8% 1 8% 43% 36% 4	570
	11th to 20th	Night	12% 1 10% 43% 33% 2	570
	21st to end	Night	9% 1 13% 41% 34% 2	570
October	1st to 10th	Night	6% 2 18% 45% 26% 2	570
	11th to 20th	Night	10% 5% 29% 40% 15% 1	698
	21st to end	Night	13% 9% 28% 34% 14% 1	836
November	1st to 10th	Night	11% 5% 31% 40% 13% 1	800
	11th to 20th	Night	6% 9% 35% 36% 13% 1	1000
	21st to end	Night	15% 9% 39% 27% 10% 1	1000
December	1st to 10th	Night	13% 8% 36% 36% 6%	1000
	11th to 20th	Night	16% 10% 34% 34% 6%	1000
	21st to end	Night	14% 11% 38% 29% 8%	1063

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