Sam Houston State University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sam Houston State University Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	101135
	Night	12% 6% 2 5% 4 4 4 3 5% 8% 48%	98085
Transparency	Day	38% 6% 11% 20% 18% 7%	104823
	Night	34% 6% 11% 20% 20% 9%	102524
Seeing	Day	13% 7% 20% 26% 25% 9%	14963
	Night	14% 7% 25% 34% 19% 2	24798

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	16% 9% 2 5% 3 3 3 3 4 7% 44%	2847
	11th to 20th	Day	18% 6% 2 3 3 2 3 2 3 5% 51%	2850
	21st to end	Day	22% 9% 3 7% 3 3 2 2 4 8% 37%	3135
February	1st to 10th	Day	20% 9% 3 6% 4 3 3 3 5% 5% 39%	1771
	11th to 20th	Day	20% 8% 2 6% 5% 3 4 3 4 4 40%	1849
	21st to end	Day	18% 7% 3 6% 4 3 3 3 5% 5% 41%	1726
March	1st to 10th	Day	16% 12% 4 8% 5% 6% 4 3 6% 6% 31%	3436
	11th to 20th	Day	18% 7% 3 7% 5% 5% 5% 5% 6% 8% 30%	3480
	21st to end	Day	14% 9% 3 8% 5% 4 4 3 5% 6% 39%	3814
April	1st to 10th	Day	14% 8% 2 7% 5% 5% 4 4 4 7% 39%	2090
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 5% 5% 6% 40%	2222
	21st to end	Day	9% 8% 2 6% 5% 5% 4 5% 7% 6% 45%	2280
May	1st to 10th	Day	17% 8% 3 9% 6% 6% 5% 5% 6% 7% 29%	3919
	11th to 20th	Day	13% 6% 2 7% 4 4 5% 4 6% 7% 42%	4082
	21st to end	Day	9% 6% 2 7% 5% 6% 6% 5% 8% 10% 34%	4477
June	1st to 10th	Day	5% 4 2 6% 6% 6% 6% 6% 8% 11% 40%	2470
	11th to 20th	Day	5% 4 1 5% 5% 5% 5% 5% 8% 11% 46%	2470
	21st to end	Day	5% 5% 2 7% 7% 6% 7% 5% 8% 11% 36%	2470
July	1st to 10th	Day	9% 5% 2 5% 5% 5% 6% 5% 8% 12% 39%	4120
	11th to 20th	Day	7% 5% 2 7% 6% 6% 6% 5% 8% 11% 37%	4120
	21st to end	Day	14% 8% 2 7% 6% 5% 5% 4 7% 9% 31%	4465
August	1st to 10th	Day	3 1 3 2 3 4 3 6% 8% 67%	4104
	11th to 20th	Day	3 2 1 4 3 4 5% 4 8% 13% 52%	3920
	21st to end	Day	6% 4 2 6% 5% 6% 6% 5% 8% 11% 42%	4134
September	1st to 10th	Day	6% 6% 2 7% 6% 5% 6% 5% 7% 9% 42%	2090
	11th to 20th	Day	12% 6% 2 6% 6% 5% 4 4 6% 8% 42%	2090
	21st to end	Day	7% 4 2 5% 4 4 4 4 6% 7% 53%	2090
October	1st to 10th	Day	6% 4 1 4 3 3 4 4 5% 7% 59%	1971
	11th to 20th	Day	12% 4 2 4 3 3 4 3 4 6% 56%	1900
	21st to end	Day	14% 4 2 4 3 2 3 3 4 5% 56%	2090
November	1st to 10th	Day	11% 6% 2 5% 4 4 5% 4 5% 6% 48%	1948
	11th to 20th	Day	11% 6% 2 6% 4 3 4 3 5% 7% 50%	1900
	21st to end	Day	16% 7% 2 6% 5% 3 5% 4 3 6% 44%	1799
December	1st to 10th	Day	15% 8% 2 5% 5% 4 4 4 5% 6% 45%	1710
	11th to 20th	Day	16% 8% 3 6% 4 4 4 3 4 5% 42%	2161
	21st to end	Day	16% 8% 3 7% 4 4 4 3 4 5% 43%	3135
January	1st to 10th	Night	17% 7% 2 4 3 3 3 3 4 5% 49%	4108
	11th to 20th	Night	17% 7% 2 5% 2 2 2 2 3 4 54%	4120
	21st to end	Night	21% 11% 3 5% 3 3 2 2 4 6% 40%	4532
February	1st to 10th	Night	16% 8% 3 6% 4 3 3 3 4 5% 42%	2423
	11th to 20th	Night	19% 8% 2 5% 3 3 3 2 3 6% 45%	2218
	21st to end	Night	18% 8% 3 5% 4 4 4 2 3 6% 43%	1727
March	1st to 10th	Night	20% 10% 3 7% 4 4 4 3 5% 6% 33%	3419
	11th to 20th	Night	19% 9% 3 8% 5% 4 4 4 5% 7% 33%	3480
	21st to end	Night	11% 8% 3 8% 5% 5% 4 3 5% 5% 43%	3817
April	1st to 10th	Night	10% 7% 2 6% 5% 4 4 4 6% 7% 46%	2090
	11th to 20th	Night	12% 5% 2 7% 5% 4 4 3 5% 7% 46%	1904
	21st to end	Night	12% 5% 2 6% 3 3 4 3 6% 7% 49%	1900
May	1st to 10th	Night	15% 8% 3 6% 5% 4 4 4 6% 8% 36%	2976
	11th to 20th	Night	12% 7% 3 7% 4 4 4 3 5% 7% 46%	2823
	21st to end	Night	9% 6% 2 6% 4 4 6% 4 8% 11% 40%	3090
June	1st to 10th	Night	4 4 1 5% 4 3 4 4 7% 10% 55%	1710
	11th to 20th	Night	2 3 1 4 2 4 4 4 6% 12% 59%	1710
	21st to end	Night	5% 4 1 5% 5% 4 5% 4 9% 12% 47%	1710
July	1st to 10th	Night	6% 5% 1 5% 5% 4 5% 5% 7% 14% 44%	2850
	11th to 20th	Night	3 5% 2 5% 4 5% 5% 4 7% 11% 50%	2850
	21st to end	Night	12% 7% 3 7% 5% 4 5% 4 6% 10% 37%	3098
August	1st to 10th	Night	1 1 1 1 1 2 3 4 10% 74%	2836
	11th to 20th	Night	3 2 1 3 2 3 4 3 7% 13% 60%	2912
	21st to end	Night	4 4 1 5% 4 5% 5% 4 8% 11% 48%	3503
September	1st to 10th	Night	6% 5% 2 6% 4 5% 5% 5% 6% 9% 49%	2090
	11th to 20th	Night	10% 7% 3 6% 4 4 4 4 6% 7% 45%	2090
	21st to end	Night	8% 4 1 4 3 3 4 4 6% 8% 56%	2090
October	1st to 10th	Night	4 3 1 4 3 3 3 3 6% 7% 63%	2190
	11th to 20th	Night	10% 4 1 3 3 3 3 2 4 5% 62%	2280
	21st to end	Night	12% 4 2 4 2 3 3 2 3 4 61%	2508
November	1st to 10th	Night	12% 5% 1 4 3 3 4 3 5% 6% 54%	2335
	11th to 20th	Night	10% 6% 2 5% 4 5% 4 3 4 7% 51%	2280
	21st to end	Night	14% 6% 2 6% 3 4 4 3 5% 6% 46%	2378
December	1st to 10th	Night	16% 6% 2 6% 4 4 3 3 5% 6% 45%	2470
	11th to 20th	Night	15% 9% 3 6% 4 3 3 3 4 6% 44%	3036
	21st to end	Night	14% 7% 2 6% 3 3 3 2 4 5% 49%	4532

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	41% 4 4 18% 26% 7%	2848
	11th to 20th	Day	38% 3 3 20% 31% 6%	2850
	21st to end	Day	48% 2 4 17% 18% 11%	3135
February	1st to 10th	Day	49% 3 5% 15% 18% 10%	1771
	11th to 20th	Day	49% 3 5% 14% 18% 10%	1859
	21st to end	Day	44% 5% 7% 15% 17% 11%	1726
March	1st to 10th	Day	54% 5% 7% 11% 18% 4	3436
	11th to 20th	Day	50% 6% 9% 15% 15% 5%	3480
	21st to end	Day	45% 6% 8% 17% 20% 4	3814
April	1st to 10th	Day	47% 5% 6% 18% 16% 8%	2090
	11th to 20th	Day	45% 5% 9% 15% 17% 9%	2222
	21st to end	Day	38% 5% 8% 21% 22% 5%	2280
May	1st to 10th	Day	52% 7% 11% 16% 10% 4	3954
	11th to 20th	Day	40% 7% 10% 17% 25% 2	4086
	21st to end	Day	41% 9% 12% 25% 11% 1	4489
June	1st to 10th	Day	35% 9% 15% 25% 15% 1	2470
	11th to 20th	Day	31% 8% 15% 27% 16% 3	2470
	21st to end	Day	39% 10% 15% 22% 13% 1	2470
July	1st to 10th	Day	34% 10% 25% 26% 4	4056
	11th to 20th	Day	38% 9% 17% 23% 12% 1	4051
	21st to end	Day	47% 8% 17% 22% 6% 1	4325
August	1st to 10th	Day	15% 6% 14% 37% 27% 1	4090
	11th to 20th	Day	21% 7% 28% 33% 9% 1	3959
	21st to end	Day	33% 13% 18% 22% 13% 2	4133
September	1st to 10th	Day	37% 8% 12% 20% 16% 7%	2090
	11th to 20th	Day	41% 7% 13% 17% 16% 6%	2090
	21st to end	Day	30% 7% 9% 22% 19% 13%	2090
October	1st to 10th	Day	16% 3 6% 14% 22% 38%	3270
	11th to 20th	Day	20% 3 4 18% 35% 20%	3140
	21st to end	Day	24% 4 5% 17% 37% 14%	3428
November	1st to 10th	Day	36% 5% 8% 19% 22% 9%	1948
	11th to 20th	Day	35% 3 8% 18% 23% 12%	1900
	21st to end	Day	44% 4 6% 18% 19% 10%	1799
December	1st to 10th	Day	42% 4 9% 19% 18% 8%	1710
	11th to 20th	Day	45% 4 6% 15% 21% 10%	2159
	21st to end	Day	45% 3 5% 13% 25% 9%	3135
January	1st to 10th	Night	37% 4 5% 20% 23% 11%	4108
	11th to 20th	Night	37% 3 4 17% 28% 11%	4120
	21st to end	Night	48% 3 4 16% 19% 10%	4532
February	1st to 10th	Night	46% 3 5% 14% 18% 14%	2423
	11th to 20th	Night	43% 4 6% 16% 19% 12%	2218
	21st to end	Night	45% 4 6% 14% 16% 15%	1727
March	1st to 10th	Night	51% 6% 7% 13% 16% 6%	3419
	11th to 20th	Night	51% 6% 8% 15% 15% 5%	3480
	21st to end	Night	43% 6% 9% 13% 22% 7%	3817
April	1st to 10th	Night	39% 5% 10% 18% 17% 12%	2090
	11th to 20th	Night	38% 5% 9% 18% 17% 11%	1904
	21st to end	Night	35% 6% 10% 19% 24% 6%	1900
May	1st to 10th	Night	46% 7% 9% 21% 12% 4	3006
	11th to 20th	Night	39% 5% 9% 19% 23% 4	2824
	21st to end	Night	36% 10% 15% 28% 11% 1	3099
June	1st to 10th	Night	24% 8% 18% 31% 18% 1	1710
	11th to 20th	Night	19% 7% 18% 32% 19% 5%	1710
	21st to end	Night	27% 9% 17% 31% 15% 2	1710
July	1st to 10th	Night	29% 10% 31% 26% 5%	2805
	11th to 20th	Night	27% 9% 22% 30% 12%	2796
	21st to end	Night	42% 9% 21% 22% 6%	2999
August	1st to 10th	Night	8% 4 17% 39% 31% 2	2826
	11th to 20th	Night	16% 7% 28% 39% 10% 1	2939
	21st to end	Night	29% 11% 20% 25% 13% 2	3503
September	1st to 10th	Night	30% 9% 18% 21% 14% 8%	2090
	11th to 20th	Night	37% 8% 15% 18% 16% 7%	2090
	21st to end	Night	26% 7% 12% 21% 22% 12%	2090
October	1st to 10th	Night	14% 4 6% 17% 18% 41%	3658
	11th to 20th	Night	16% 2 4 23% 30% 25%	3779
	21st to end	Night	22% 3 4 15% 39% 17%	4120
November	1st to 10th	Night	32% 5% 10% 19% 22% 11%	2335
	11th to 20th	Night	35% 4 8% 18% 23% 12%	2280
	21st to end	Night	40% 4 8% 15% 21% 11%	2378
December	1st to 10th	Night	42% 4 7% 20% 17% 10%	2470
	11th to 20th	Night	44% 4 5% 11% 22% 14%	3037
	21st to end	Night	38% 4 5% 15% 29% 9%	4532

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	23% 13% 38% 19% 5% 1	270
	11th to 20th	Day	25% 10% 37% 20% 7% 1	270
	21st to end	Day	24% 14% 36% 20% 5%	297
February	1st to 10th	Day	25% 16% 36% 18% 5%	270
	11th to 20th	Day	27% 18% 31% 20% 3	270
	21st to end	Day	25% 24% 37% 12% 2	225
March	1st to 10th	Day	24% 18% 33% 20% 6%	270
	11th to 20th	Day	17% 16% 43% 17% 5%	270
	21st to end	Day	17% 18% 39% 20% 6%	297
April	1st to 10th	Day	19% 17% 37% 22% 4	270
	11th to 20th	Day	21% 14% 28% 25% 10% 1	420
	21st to end	Day	13% 13% 33% 31% 9% 2	460
May	1st to 10th	Day	14% 11% 35% 29% 10% 1	552
	11th to 20th	Day	14% 5% 26% 34% 18% 2	675
	21st to end	Day	10% 7% 26% 34% 19% 4	734
June	1st to 10th	Day	6% 3 12% 33% 35% 11%	680
	11th to 20th	Day	6% 2 13% 37% 33% 9%	680
	21st to end	Day	8% 2 12% 27% 37% 15%	680
July	1st to 10th	Day	7% 2 8% 24% 39% 19%	671
	11th to 20th	Day	4 1 4 29% 44% 18%	668
	21st to end	Day	6% 2 5% 23% 48% 17%	739
August	1st to 10th	Day	4 3 21% 50% 21%	676
	11th to 20th	Day	6% 4 19% 46% 25%	596
	21st to end	Day	9% 1 6% 19% 38% 28%	519
September	1st to 10th	Day	3 2 8% 29% 38% 20%	300
	11th to 20th	Day	9% 2 8% 24% 40% 18%	300
	21st to end	Day	10% 1 8% 27% 37% 17%	300
October	1st to 10th	Day	6% 2 15% 36% 34% 8%	300
	11th to 20th	Day	10% 6% 20% 38% 19% 8%	300
	21st to end	Day	21% 10% 25% 22% 18% 5%	330
November	1st to 10th	Day	15% 6% 27% 30% 18% 4	297
	11th to 20th	Day	16% 9% 27% 36% 11% 1	270
	21st to end	Day	19% 19% 27% 21% 11% 2	270
December	1st to 10th	Day	20% 7% 33% 25% 10% 5%	270
	11th to 20th	Day	26% 15% 32% 19% 8%	270
	21st to end	Day	23% 11% 35% 22% 8% 1	297
January	1st to 10th	Night	21% 11% 31% 31% 7%	950
	11th to 20th	Night	21% 12% 31% 28% 8%	950
	21st to end	Night	21% 10% 33% 31% 5%	1045
February	1st to 10th	Night	21% 12% 35% 26% 5%	903
	11th to 20th	Night	25% 10% 35% 25% 4	744
	21st to end	Night	24% 11% 41% 22% 2	471
March	1st to 10th	Night	21% 11% 36% 28% 5%	570
	11th to 20th	Night	18% 11% 35% 30% 6%	570
	21st to end	Night	14% 11% 37% 32% 6%	627
April	1st to 10th	Night	14% 11% 39% 30% 6%	570
	11th to 20th	Night	15% 10% 35% 29% 9%	563
	21st to end	Night	15% 8% 38% 28% 11%	570
May	1st to 10th	Night	11% 10% 40% 30% 8% 1	570
	11th to 20th	Night	12% 6% 30% 37% 14% 1	561
	21st to end	Night	7% 5% 28% 39% 20% 2	617
June	1st to 10th	Night	5% 3 12% 43% 34% 4	570
	11th to 20th	Night	3 2 16% 51% 26% 2	570
	21st to end	Night	6% 1 10% 43% 34% 6%	570
July	1st to 10th	Night	5% 1 8% 41% 39% 7%	555
	11th to 20th	Night	2 1 7% 49% 36% 5%	552
	21st to end	Night	5% 1 7% 41% 41% 5%	624
August	1st to 10th	Night	3 3 47% 41% 6%	567
	11th to 20th	Night	6% 4 40% 44% 6%	564
	21st to end	Night	5% 1 6% 35% 46% 7%	627
September	1st to 10th	Night	7% 2 7% 35% 42% 8%	570
	11th to 20th	Night	12% 2 6% 31% 43% 7%	570
	21st to end	Night	10% 1 11% 33% 39% 6%	570
October	1st to 10th	Night	6% 2 11% 41% 34% 5%	670
	11th to 20th	Night	12% 4 21% 41% 20% 2	760
	21st to end	Night	13% 6% 26% 33% 20% 2	836
November	1st to 10th	Night	14% 3 23% 36% 22% 1	779
	11th to 20th	Night	12% 10% 25% 39% 13% 1	760
	21st to end	Night	19% 10% 31% 27% 13% 1	858
December	1st to 10th	Night	19% 8% 29% 33% 11% 1	950
	11th to 20th	Night	24% 10% 32% 29% 5%	950
	21st to end	Night	19% 11% 32% 30% 8%	1045

Page generated at 2024-11-07 05:55:47. Version ac07

Copyright © 2024 Attilla Danko.