Smithville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Smithville clear sky chart from 2005-11-06 to 2025-04-11.

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	13% 8% 3 7% 5% 4 5% 4 6% 7% 38%	113995
	Night	13% 8% 3 7% 4 4 4 3 5% 7% 41%	114298
Transparency	Day	42% 6% 10% 22% 17% 3	117751
	Night	41% 5% 10% 22% 18% 4	118683
Seeing	Day	16% 9% 22% 22% 20% 11%	15334
	Night	17% 7% 23% 30% 20% 3	25225

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	15% 13% 6% 13% 5% 4 5% 3 5% 5% 27%	4056
	11th to 20th	Day	17% 8% 5% 13% 3 3 4 2 3 5% 36%	4060
	21st to end	Day	19% 10% 5% 6% 3 4 3 3 5% 7% 34%	4742
February	1st to 10th	Day	18% 13% 5% 7% 5% 4 3 3 4 4 34%	2000
	11th to 20th	Day	21% 11% 4 8% 5% 4 3 3 4 6% 30%	1948
	21st to end	Day	20% 9% 3 7% 4 4 4 3 5% 6% 36%	1650
March	1st to 10th	Day	16% 11% 4 7% 5% 5% 4 3 5% 6% 34%	4480
	11th to 20th	Day	12% 8% 3 7% 5% 4 4 3 4 6% 45%	4883
	21st to end	Day	12% 8% 2 7% 5% 4 4 4 6% 7% 42%	5567
April	1st to 10th	Day	12% 7% 2 7% 4 3 5% 4 6% 7% 43%	2400
	11th to 20th	Day	13% 8% 3 7% 4 4 4 3 5% 6% 43%	2254
	21st to end	Day	12% 8% 3 7% 6% 4 5% 4 6% 7% 39%	2375
May	1st to 10th	Day	17% 7% 3 6% 5% 4 5% 4 6% 8% 35%	4082
	11th to 20th	Day	15% 9% 4 8% 5% 4 4 3 5% 7% 34%	4081
	21st to end	Day	10% 7% 3 8% 5% 4 5% 4 6% 8% 40%	4476
June	1st to 10th	Day	9% 7% 3 6% 4 6% 6% 4 6% 10% 39%	2470
	11th to 20th	Day	4 5% 2 6% 5% 5% 6% 5% 7% 11% 44%	2470
	21st to end	Day	6% 5% 1 6% 6% 6% 6% 6% 8% 12% 38%	2606
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 7% 6% 9% 11% 36%	4280
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 5% 7% 10% 36%	4120
	21st to end	Day	15% 11% 4 11% 7% 6% 6% 5% 7% 8% 21%	4466
August	1st to 10th	Day	5% 4 2 5% 4 5% 6% 5% 8% 11% 46%	4047
	11th to 20th	Day	5% 5% 2 7% 5% 5% 6% 5% 9% 12% 38%	3729
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 6% 9% 49%	4180
September	1st to 10th	Day	12% 5% 3 7% 5% 5% 5% 5% 6% 8% 40%	2200
	11th to 20th	Day	14% 7% 3 6% 4 4 5% 3 5% 6% 42%	2090
	21st to end	Day	12% 5% 2 6% 4 3 4 4 5% 6% 47%	2090
October	1st to 10th	Day	11% 4 2 5% 4 4 4 3 5% 6% 53%	2090
	11th to 20th	Day	12% 5% 1 5% 4 4 3 2 4 7% 53%	2048
	21st to end	Day	15% 6% 2 5% 4 3 4 3 5% 6% 47%	1924
November	1st to 10th	Day	11% 6% 2 5% 4 2 3 3 4 7% 53%	1762
	11th to 20th	Day	14% 8% 2 5% 4 3 3 4 5% 6% 47%	1800
	21st to end	Day	14% 10% 3 6% 4 4 4 3 5% 5% 44%	1800
December	1st to 10th	Day	14% 8% 3 8% 5% 5% 4 3 4 5% 41%	2930
	11th to 20th	Day	18% 14% 5% 9% 6% 4 4 3 4 5% 28%	3373
	21st to end	Day	17% 13% 5% 9% 5% 4 4 4 5% 7% 27%	4466
January	1st to 10th	Night	15% 12% 5% 10% 5% 3 3 3 4 5% 35%	5889
	11th to 20th	Night	19% 9% 4 7% 5% 5% 3 2 3 5% 39%	5900
	21st to end	Night	16% 12% 3 8% 4 4 4 3 4 6% 37%	6196
February	1st to 10th	Night	20% 10% 4 9% 4 4 4 3 5% 6% 32%	2400
	11th to 20th	Night	23% 10% 4 8% 4 4 4 3 4 5% 32%	2338
	21st to end	Night	22% 11% 3 7% 4 3 3 3 5% 7% 32%	1980
March	1st to 10th	Night	18% 12% 4 7% 4 4 4 3 5% 6% 33%	5373
	11th to 20th	Night	12% 6% 2 5% 3 3 4 4 6% 7% 48%	5076
	21st to end	Night	14% 7% 3 8% 5% 5% 4 3 5% 6% 40%	5404
April	1st to 10th	Night	12% 5% 2 5% 5% 5% 5% 4 6% 8% 45%	2000
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 5% 7% 47%	1881
	21st to end	Night	13% 6% 3 6% 5% 4 4 3 6% 8% 43%	1802
May	1st to 10th	Night	12% 8% 3 7% 5% 4 4 4 6% 9% 38%	2813
	11th to 20th	Night	14% 9% 3 7% 5% 4 4 3 6% 7% 39%	2812
	21st to end	Night	7% 5% 2 7% 6% 4 6% 5% 7% 11% 41%	3079
June	1st to 10th	Night	7% 6% 3 7% 5% 4 5% 5% 6% 9% 45%	1710
	11th to 20th	Night	4 3 2 5% 4 4 4 4 7% 12% 52%	1710
	21st to end	Night	5% 4 2 4 6% 4 6% 5% 8% 12% 45%	1556
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 5% 6% 9% 10% 37%	2671
	11th to 20th	Night	8% 6% 2 5% 5% 5% 5% 4 8% 10% 45%	2840
	21st to end	Night	10% 10% 4 10% 7% 6% 7% 5% 7% 9% 24%	3087
August	1st to 10th	Night	3 5% 2 5% 5% 4 4 3 6% 9% 53%	2878
	11th to 20th	Night	5% 4 2 6% 4 4 5% 5% 8% 12% 45%	3100
	21st to end	Night	5% 2 1 5% 4 4 4 4 7% 9% 56%	3476
September	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 6% 7% 46%	1959
	11th to 20th	Night	10% 6% 2 8% 5% 3 5% 3 5% 7% 44%	2090
	21st to end	Night	11% 5% 2 5% 3 4 3 3 5% 8% 51%	2090
October	1st to 10th	Night	10% 4 1 4 3 3 3 3 4 6% 59%	2090
	11th to 20th	Night	15% 5% 2 6% 4 3 3 3 4 5% 51%	2130
	21st to end	Night	14% 8% 2 5% 3 3 3 3 5% 6% 49%	2670
November	1st to 10th	Night	12% 7% 2 5% 4 3 4 3 4 6% 52%	2536
	11th to 20th	Night	13% 8% 2 5% 4 3 3 2 5% 7% 48%	2600
	21st to end	Night	15% 9% 4 5% 3 3 4 3 5% 6% 43%	2600
December	1st to 10th	Night	16% 11% 3 9% 4 4 4 3 4 4 38%	4250
	11th to 20th	Night	22% 11% 3 7% 4 3 3 2 4 5% 36%	4822
	21st to end	Night	14% 12% 5% 9% 6% 5% 5% 4 5% 7% 28%	6490

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	58% 4 8% 17% 12% 1	4057
	11th to 20th	Day	51% 3 6% 17% 22% 1	4060
	21st to end	Day	49% 3 7% 23% 13% 4	4742
February	1st to 10th	Day	54% 4 7% 17% 16% 2	2000
	11th to 20th	Day	56% 4 6% 16% 14% 3	1958
	21st to end	Day	51% 3 7% 16% 18% 5%	1650
March	1st to 10th	Day	50% 5% 5% 14% 17% 8%	4480
	11th to 20th	Day	40% 4 7% 21% 19% 9%	4883
	21st to end	Day	42% 5% 10% 28% 15% 1	5569
April	1st to 10th	Day	40% 5% 11% 23% 18% 3	2400
	11th to 20th	Day	41% 4 6% 21% 24% 4	2254
	21st to end	Day	42% 5% 9% 27% 15% 2	2375
May	1st to 10th	Day	45% 8% 11% 23% 12% 1	4120
	11th to 20th	Day	49% 6% 10% 24% 11%	4085
	21st to end	Day	41% 7% 9% 21% 19% 1	4489
June	1st to 10th	Day	40% 7% 13% 24% 15% 2	2470
	11th to 20th	Day	33% 8% 17% 23% 18% 2	2470
	21st to end	Day	35% 9% 17% 20% 15% 4	2606
July	1st to 10th	Day	36% 10% 20% 23% 8% 2	4215
	11th to 20th	Day	39% 9% 17% 25% 8% 2	4051
	21st to end	Day	59% 8% 11% 15% 6% 1	4324
August	1st to 10th	Day	28% 9% 16% 31% 14% 1	4034
	11th to 20th	Day	34% 9% 16% 26% 15% 1	3765
	21st to end	Day	29% 9% 11% 31% 18% 2	4179
September	1st to 10th	Day	41% 8% 11% 19% 17% 5%	2200
	11th to 20th	Day	41% 6% 11% 21% 18% 2	2090
	21st to end	Day	37% 6% 9% 23% 20% 5%	2090
October	1st to 10th	Day	24% 5% 7% 17% 35% 11%	3480
	11th to 20th	Day	23% 2 7% 24% 30% 14%	3379
	21st to end	Day	30% 3 8% 24% 25% 10%	3148
November	1st to 10th	Day	33% 3 9% 22% 29% 5%	1762
	11th to 20th	Day	38% 4 6% 23% 24% 6%	1800
	21st to end	Day	43% 3 7% 23% 21% 4	1800
December	1st to 10th	Day	44% 5% 5% 22% 22% 2	2930
	11th to 20th	Day	58% 4 6% 18% 11% 2	3370
	21st to end	Day	54% 5% 10% 21% 9% 1	4466
January	1st to 10th	Night	51% 3 10% 19% 15% 1	5889
	11th to 20th	Night	49% 3 6% 17% 20% 5%	5900
	21st to end	Night	50% 3 5% 20% 17% 5%	6196
February	1st to 10th	Night	53% 4 8% 18% 16% 1	2400
	11th to 20th	Night	56% 3 6% 17% 14% 4	2339
	21st to end	Night	52% 4 7% 16% 17% 4	1980
March	1st to 10th	Night	51% 4 7% 15% 18% 4	5373
	11th to 20th	Night	34% 5% 7% 21% 20% 13%	5076
	21st to end	Night	45% 4 8% 26% 15% 2	5404
April	1st to 10th	Night	38% 4 10% 24% 21% 3	2000
	11th to 20th	Night	37% 4 7% 21% 23% 7%	1881
	21st to end	Night	39% 5% 10% 29% 17% 1	1802
May	1st to 10th	Night	41% 8% 13% 25% 13% 1	2840
	11th to 20th	Night	42% 8% 13% 21% 15% 1	2813
	21st to end	Night	34% 10% 13% 24% 18% 2	3087
June	1st to 10th	Night	36% 7% 13% 28% 15% 2	1710
	11th to 20th	Night	24% 7% 20% 30% 17% 3	1710
	21st to end	Night	29% 10% 16% 27% 14% 5%	1556
July	1st to 10th	Night	35% 11% 21% 23% 9% 2	2627
	11th to 20th	Night	32% 8% 18% 30% 8% 3	2786
	21st to end	Night	54% 10% 12% 15% 7% 1	2988
August	1st to 10th	Night	25% 7% 12% 37% 17% 1	2867
	11th to 20th	Night	28% 8% 23% 27% 13% 1	3130
	21st to end	Night	23% 8% 13% 36% 19% 2	3476
September	1st to 10th	Night	36% 7% 13% 22% 18% 5%	1959
	11th to 20th	Night	38% 7% 11% 19% 24% 2	2090
	21st to end	Night	33% 5% 10% 23% 25% 5%	2090
October	1st to 10th	Night	23% 6% 7% 21% 33% 12%	3480
	11th to 20th	Night	22% 3 5% 23% 30% 16%	3538
	21st to end	Night	25% 3 7% 25% 31% 10%	4396
November	1st to 10th	Night	35% 3 7% 23% 24% 7%	2536
	11th to 20th	Night	37% 2 7% 21% 26% 7%	2600
	21st to end	Night	42% 3 6% 25% 20% 4	2600
December	1st to 10th	Night	49% 4 6% 15% 23% 1	4250
	11th to 20th	Night	51% 3 5% 21% 18% 2	4824
	21st to end	Night	54% 5% 9% 21% 10% 1	6490

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	25% 17% 35% 17% 5% 1	300
	11th to 20th	Day	28% 20% 34% 10% 7% 1	300
	21st to end	Day	22% 16% 43% 15% 4	330
February	1st to 10th	Day	28% 17% 32% 15% 8%	300
	11th to 20th	Day	35% 15% 36% 9% 4 1	300
	21st to end	Day	29% 19% 36% 12% 2	249
March	1st to 10th	Day	25% 18% 33% 17% 6% 1	300
	11th to 20th	Day	24% 15% 34% 20% 7% 1	455
	21st to end	Day	23% 17% 31% 19% 10% 1	550
April	1st to 10th	Day	19% 18% 27% 24% 10% 3	500
	11th to 20th	Day	17% 13% 25% 28% 15% 2	452
	21st to end	Day	17% 9% 32% 25% 14% 3	460
May	1st to 10th	Day	17% 10% 27% 25% 16% 5%	463
	11th to 20th	Day	15% 7% 21% 24% 21% 11%	487
	21st to end	Day	12% 4 17% 27% 22% 18%	529
June	1st to 10th	Day	11% 6% 17% 23% 25% 18%	490
	11th to 20th	Day	6% 3 13% 27% 31% 22%	490
	21st to end	Day	8% 2 15% 29% 27% 19%	626
July	1st to 10th	Day	10% 3 8% 27% 28% 24%	580
	11th to 20th	Day	12% 3 7% 21% 30% 27%	484
	21st to end	Day	11% 3 10% 18% 30% 28%	532
August	1st to 10th	Day	10% 3 10% 21% 31% 25%	486
	11th to 20th	Day	11% 1 14% 24% 37% 14%	479
	21st to end	Day	11% 1 7% 21% 32% 28%	539
September	1st to 10th	Day	13% 1 10% 20% 34% 21%	490
	11th to 20th	Day	14% 3 11% 19% 32% 21%	490
	21st to end	Day	17% 4 13% 25% 28% 13%	490
October	1st to 10th	Day	13% 2 18% 28% 28% 12%	490
	11th to 20th	Day	12% 8% 28% 28% 19% 5%	490
	21st to end	Day	18% 10% 22% 28% 17% 4	373
November	1st to 10th	Day	17% 6% 27% 29% 15% 5%	300
	11th to 20th	Day	14% 13% 33% 31% 9%	300
	21st to end	Day	20% 11% 35% 19% 12% 3	300
December	1st to 10th	Day	25% 15% 33% 19% 6% 1	300
	11th to 20th	Day	23% 15% 29% 21% 12% 1	300
	21st to end	Day	25% 18% 29% 20% 7% 1	330
January	1st to 10th	Night	23% 13% 34% 26% 5%	800
	11th to 20th	Night	26% 16% 33% 21% 5%	800
	21st to end	Night	20% 12% 41% 24% 3	880
February	1st to 10th	Night	26% 12% 33% 26% 4	800
	11th to 20th	Night	29% 14% 34% 21% 2	783
	21st to end	Night	29% 13% 35% 22% 1	660
March	1st to 10th	Night	22% 12% 31% 31% 4	800
	11th to 20th	Night	23% 10% 35% 24% 7% 1	800
	21st to end	Night	20% 10% 32% 29% 9%	855
April	1st to 10th	Night	15% 10% 33% 32% 10%	600
	11th to 20th	Night	18% 7% 31% 32% 12% 1	565
	21st to end	Night	16% 6% 28% 35% 13% 1	570
May	1st to 10th	Night	13% 5% 29% 31% 20% 1	570
	11th to 20th	Night	14% 3 20% 36% 22% 5%	561
	21st to end	Night	8% 2 13% 37% 32% 7%	617
June	1st to 10th	Night	9% 2 15% 34% 35% 5%	570
	11th to 20th	Night	5% 1 12% 35% 39% 8%	570
	21st to end	Night	6% 2 9% 39% 38% 7%	570
July	1st to 10th	Night	11% 1 8% 28% 40% 13%	555
	11th to 20th	Night	7% 1 7% 28% 43% 12%	552
	21st to end	Night	9% 2 7% 30% 42% 10%	624
August	1st to 10th	Night	8% 2 4 28% 48% 10%	567
	11th to 20th	Night	8% 1 9% 32% 44% 7%	564
	21st to end	Night	9% 2 6% 26% 48% 10%	627
September	1st to 10th	Night	12% 3 8% 31% 39% 8%	629
	11th to 20th	Night	13% 2 12% 30% 37% 7%	760
	21st to end	Night	13% 2 16% 29% 34% 5%	760
October	1st to 10th	Night	12% 3 15% 32% 31% 6%	760
	11th to 20th	Night	17% 5% 22% 36% 18% 2	760
	21st to end	Night	18% 5% 24% 35% 17% 2	836
November	1st to 10th	Night	15% 7% 23% 34% 20% 2	780
	11th to 20th	Night	17% 9% 30% 32% 11% 1	800
	21st to end	Night	20% 10% 28% 31% 10% 1	800
December	1st to 10th	Night	27% 11% 28% 28% 7%	800
	11th to 20th	Night	24% 8% 31% 29% 8% 1	800
	21st to end	Night	25% 14% 28% 27% 7%	880

Page generated at 2025-04-08 08:17:25. Version ac07

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