Tarleton Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tarleton Observatory clear sky chart from 2005-11-06 to 2025-02-06.

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	10% 5% 2 5% 3 3 4 3 5% 6% 55%	109023
	Night	9% 5% 2 4 3 3 3 3 5% 6% 58%	109483
Transparency	Day	30% 4 9% 23% 24% 10%	112818
	Night	27% 3 8% 23% 25% 13%	113815
Seeing	Day	10% 7% 23% 30% 22% 7%	15349
	Night	11% 7% 30% 36% 15% 1	25394

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	11% 8% 3 5% 3 3 2 2 3 4 56%	4077
	11th to 20th	Day	8% 4 1 3 2 2 2 2 4 5% 66%	4080
	21st to end	Day	20% 7% 2 5% 2 2 2 2 3 5% 50%	4603
February	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 5% 6% 52%	1950
	11th to 20th	Day	13% 7% 2 6% 4 4 3 2 3 5% 51%	1849
	21st to end	Day	18% 6% 2 4 2 2 2 1 3 5% 56%	1570
March	1st to 10th	Day	12% 6% 2 4 3 3 3 3 5% 7% 52%	3367
	11th to 20th	Day	17% 6% 2 5% 3 4 4 4 5% 6% 45%	3480
	21st to end	Day	9% 5% 2 6% 5% 4 4 4 6% 8% 48%	3814
April	1st to 10th	Day	10% 5% 2 5% 4 4 4 4 5% 7% 50%	2090
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 5% 5% 52%	2128
	21st to end	Day	11% 4 1 6% 4 4 3 4 5% 6% 54%	2470
May	1st to 10th	Day	15% 6% 3 6% 4 4 4 3 5% 6% 44%	4082
	11th to 20th	Day	13% 6% 2 6% 4 3 3 3 4 6% 50%	4082
	21st to end	Day	12% 6% 2 6% 4 4 5% 5% 6% 8% 42%	4477
June	1st to 10th	Day	5% 4 1 5% 4 4 4 4 6% 7% 56%	2470
	11th to 20th	Day	5% 3 1 4 4 4 5% 4 6% 9% 57%	2470
	21st to end	Day	6% 4 1 3 4 4 4 3 6% 8% 57%	2470
July	1st to 10th	Day	5% 4 2 5% 5% 5% 5% 4 6% 7% 54%	4120
	11th to 20th	Day	3 2 1 4 3 4 3 3 6% 9% 63%	4120
	21st to end	Day	4 4 2 5% 4 5% 5% 5% 8% 10% 49%	4465
August	1st to 10th	Day	1 1 1 3 3 3 3 3 5% 7% 71%	4104
	11th to 20th	Day	4 2 1 3 2 3 4 3 5% 9% 64%	3883
	21st to end	Day	3 2 1 4 4 4 5% 4 6% 9% 58%	4057
September	1st to 10th	Day	10% 4 2 4 3 4 5% 3 4 6% 54%	2090
	11th to 20th	Day	9% 6% 3 6% 4 4 4 4 5% 6% 50%	2090
	21st to end	Day	7% 3 1 4 4 4 4 3 4 6% 60%	2090
October	1st to 10th	Day	5% 3 1 4 2 3 3 3 5% 6% 64%	2090
	11th to 20th	Day	9% 4 1 3 2 2 3 3 4 5% 64%	1933
	21st to end	Day	11% 4 1 5% 2 2 2 2 3 4 64%	2090
November	1st to 10th	Day	12% 5% 2 4 2 2 3 3 4 6% 58%	1943
	11th to 20th	Day	6% 4 1 4 2 3 4 3 6% 5% 62%	1800
	21st to end	Day	13% 6% 2 5% 3 3 3 3 4 5% 55%	1800
December	1st to 10th	Day	15% 7% 2 4 3 3 3 3 4 6% 49%	2940
	11th to 20th	Day	10% 7% 3 7% 4 4 5% 4 5% 4 49%	3391
	21st to end	Day	14% 6% 2 4 3 3 3 2 3 4 57%	4488
January	1st to 10th	Night	13% 5% 2 4 2 2 2 2 3 5% 58%	5888
	11th to 20th	Night	8% 3 1 3 2 2 2 2 3 4 71%	5900
	21st to end	Night	20% 8% 2 4 3 3 3 2 4 5% 47%	6416
February	1st to 10th	Night	11% 6% 2 5% 3 3 2 3 4 5% 55%	2340
	11th to 20th	Night	13% 7% 2 5% 4 3 2 2 4 6% 52%	2218
	21st to end	Night	14% 6% 2 3 2 3 2 3 4 5% 55%	1884
March	1st to 10th	Night	10% 8% 2 6% 4 4 4 3 4 5% 50%	3488
	11th to 20th	Night	13% 5% 2 5% 3 4 3 3 6% 7% 47%	3480
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 7% 50%	3817
April	1st to 10th	Night	8% 5% 2 4 3 3 3 3 5% 6% 57%	2090
	11th to 20th	Night	11% 5% 2 5% 3 4 4 3 5% 7% 53%	1998
	21st to end	Night	9% 5% 1 4 3 2 3 3 6% 6% 58%	1710
May	1st to 10th	Night	18% 9% 2 5% 4 2 3 3 4 6% 44%	2823
	11th to 20th	Night	10% 7% 2 6% 3 3 4 3 6% 7% 49%	2823
	21st to end	Night	11% 5% 2 4 3 2 4 3 6% 9% 53%	3090
June	1st to 10th	Night	3 2 1 4 3 3 4 4 5% 9% 62%	1710
	11th to 20th	Night	2 2 1 3 2 3 3 4 5% 9% 65%	1710
	21st to end	Night	3 3 1 3 4 3 3 4 6% 9% 62%	1710
July	1st to 10th	Night	4 3 1 4 3 2 3 3 5% 9% 62%	2850
	11th to 20th	Night	2 1 1 2 2 3 2 3 5% 10% 70%	2850
	21st to end	Night	2 4 2 4 3 3 4 3 6% 10% 57%	3098
August	1st to 10th	Night	1 1 2 1 2 2 2 4 8% 79%	2836
	11th to 20th	Night	3 2 1 2 2 2 3 3 5% 10% 66%	2950
	21st to end	Night	2 2 1 3 3 3 4 4 6% 11% 62%	3603
September	1st to 10th	Night	7% 4 2 5% 3 3 3 4 6% 8% 55%	2090
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 7% 53%	2090
	21st to end	Night	7% 3 1 3 2 3 3 3 5% 7% 63%	2090
October	1st to 10th	Night	5% 3 1 3 2 2 3 3 4 6% 68%	2090
	11th to 20th	Night	9% 4 1 3 2 2 3 3 4 5% 64%	2227
	21st to end	Night	13% 4 1 3 3 2 2 2 3 4 63%	2508
November	1st to 10th	Night	9% 5% 1 4 3 3 3 2 4 5% 62%	2350
	11th to 20th	Night	5% 4 1 4 3 3 4 3 4 6% 64%	2600
	21st to end	Night	13% 5% 2 4 3 3 3 3 4 6% 55%	2600
December	1st to 10th	Night	14% 6% 2 5% 3 3 3 2 4 5% 54%	4250
	11th to 20th	Night	11% 7% 2 6% 3 3 3 3 5% 5% 51%	4816
	21st to end	Night	11% 7% 2 4 2 2 3 2 3 4 59%	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	34% 2 5% 23% 26% 9%	4078
	11th to 20th	Day	23% 2 4 21% 37% 12%	4080
	21st to end	Day	39% 2 4 14% 24% 17%	4603
February	1st to 10th	Day	33% 4 5% 18% 23% 16%	1950
	11th to 20th	Day	39% 2 6% 19% 21% 13%	1859
	21st to end	Day	35% 2 4 14% 26% 19%	1570
March	1st to 10th	Day	33% 3 6% 15% 28% 15%	3367
	11th to 20th	Day	41% 4 15% 16% 17% 7%	3480
	21st to end	Day	34% 4 12% 20% 19% 9%	3814
April	1st to 10th	Day	33% 5% 9% 20% 18% 14%	2090
	11th to 20th	Day	34% 4 9% 20% 21% 12%	2128
	21st to end	Day	33% 4 8% 20% 27% 8%	2470
May	1st to 10th	Day	42% 4 10% 19% 17% 8%	4120
	11th to 20th	Day	37% 4 9% 19% 27% 3	4086
	21st to end	Day	39% 6% 13% 24% 12% 6%	4489
June	1st to 10th	Day	27% 6% 14% 30% 19% 4	2470
	11th to 20th	Day	23% 5% 14% 30% 20% 7%	2470
	21st to end	Day	25% 5% 13% 25% 25% 7%	2470
July	1st to 10th	Day	28% 6% 13% 39% 13% 1	4056
	11th to 20th	Day	18% 4 12% 38% 24% 3	4051
	21st to end	Day	26% 7% 13% 34% 18% 1	4325
August	1st to 10th	Day	13% 4 10% 31% 38% 4	4090
	11th to 20th	Day	18% 4 13% 35% 26% 2	3922
	21st to end	Day	22% 7% 17% 33% 19% 3	4056
September	1st to 10th	Day	32% 5% 9% 20% 23% 11%	2090
	11th to 20th	Day	34% 5% 10% 21% 21% 8%	2090
	21st to end	Day	25% 5% 9% 19% 29% 14%	2090
October	1st to 10th	Day	14% 2 6% 14% 33% 31%	3480
	11th to 20th	Day	16% 3 7% 19% 34% 21%	3186
	21st to end	Day	21% 2 4 24% 34% 15%	3428
November	1st to 10th	Day	29% 4 6% 22% 24% 14%	1943
	11th to 20th	Day	24% 3 8% 22% 27% 16%	1800
	21st to end	Day	35% 3 4 21% 24% 14%	1800
December	1st to 10th	Day	38% 3 5% 21% 25% 8%	2940
	11th to 20th	Day	39% 3 6% 12% 27% 13%	3389
	21st to end	Day	33% 2 4 20% 26% 14%	4488
January	1st to 10th	Night	32% 2 5% 21% 30% 10%	5888
	11th to 20th	Night	20% 2 3 18% 36% 21%	5900
	21st to end	Night	42% 3 4 13% 22% 17%	6416
February	1st to 10th	Night	33% 3 7% 15% 23% 19%	2340
	11th to 20th	Night	35% 3 6% 15% 27% 15%	2218
	21st to end	Night	33% 4 5% 15% 22% 21%	1884
March	1st to 10th	Night	37% 4 5% 15% 23% 16%	3488
	11th to 20th	Night	36% 4 13% 22% 17% 9%	3480
	21st to end	Night	33% 5% 9% 20% 26% 7%	3817
April	1st to 10th	Night	28% 4 8% 24% 20% 17%	2090
	11th to 20th	Night	31% 4 11% 18% 21% 15%	1998
	21st to end	Night	27% 4 12% 20% 29% 8%	1710
May	1st to 10th	Night	43% 5% 7% 21% 15% 9%	2850
	11th to 20th	Night	34% 5% 12% 21% 23% 5%	2824
	21st to end	Night	30% 5% 13% 31% 15% 6%	3099
June	1st to 10th	Night	20% 5% 15% 36% 19% 5%	1710
	11th to 20th	Night	16% 5% 15% 32% 24% 8%	1710
	21st to end	Night	20% 6% 10% 29% 27% 7%	1710
July	1st to 10th	Night	19% 5% 13% 46% 16% 2	2805
	11th to 20th	Night	11% 3 12% 41% 29% 4	2796
	21st to end	Night	22% 5% 14% 38% 20% 1	2999
August	1st to 10th	Night	7% 2 10% 34% 40% 7%	2826
	11th to 20th	Night	15% 3 15% 40% 24% 4	2977
	21st to end	Night	17% 6% 21% 34% 19% 3	3603
September	1st to 10th	Night	27% 5% 9% 24% 23% 11%	2090
	11th to 20th	Night	31% 5% 12% 20% 23% 9%	2090
	21st to end	Night	22% 4 7% 24% 26% 18%	2090
October	1st to 10th	Night	12% 2 6% 16% 27% 38%	3480
	11th to 20th	Night	15% 2 8% 18% 32% 25%	3700
	21st to end	Night	21% 2 3 22% 37% 15%	4120
November	1st to 10th	Night	28% 3 6% 21% 26% 17%	2350
	11th to 20th	Night	24% 3 6% 23% 26% 18%	2600
	21st to end	Night	32% 3 6% 18% 26% 15%	2600
December	1st to 10th	Night	34% 3 5% 21% 25% 12%	4250
	11th to 20th	Night	36% 3 5% 12% 29% 15%	4817
	21st to end	Night	31% 3 5% 19% 25% 17%	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	15% 16% 38% 26% 5%	300
	11th to 20th	Day	15% 15% 36% 25% 7% 2	300
	21st to end	Day	17% 15% 38% 22% 8% 1	330
February	1st to 10th	Day	16% 16% 40% 24% 4	285
	11th to 20th	Day	22% 15% 41% 19% 4	270
	21st to end	Day	26% 14% 41% 16% 2	225
March	1st to 10th	Day	16% 14% 41% 25% 4	270
	11th to 20th	Day	18% 15% 36% 25% 5% 2	270
	21st to end	Day	11% 17% 42% 23% 6%	297
April	1st to 10th	Day	16% 17% 39% 23% 6%	270
	11th to 20th	Day	17% 15% 40% 23% 5%	326
	21st to end	Day	14% 14% 40% 25% 7% 1	650
May	1st to 10th	Day	12% 12% 37% 31% 7%	653
	11th to 20th	Day	15% 7% 28% 32% 15% 3	675
	21st to end	Day	11% 6% 31% 34% 16% 3	734
June	1st to 10th	Day	4 2 18% 41% 27% 7%	680
	11th to 20th	Day	4 1 19% 47% 23% 5%	680
	21st to end	Day	4 1 12% 38% 33% 12%	680
July	1st to 10th	Day	6% 1 7% 35% 37% 13%	671
	11th to 20th	Day	2 6% 34% 43% 15%	668
	21st to end	Day	2 1 6% 30% 45% 16%	739
August	1st to 10th	Day	2 4 33% 44% 17%	676
	11th to 20th	Day	7% 1 6% 31% 41% 14%	572
	21st to end	Day	5% 6% 27% 36% 26%	468
September	1st to 10th	Day	10% 1 7% 19% 39% 24%	300
	11th to 20th	Day	5% 1 5% 22% 47% 21%	300
	21st to end	Day	11% 1 6% 28% 36% 18%	300
October	1st to 10th	Day	4 2 12% 36% 35% 12%	300
	11th to 20th	Day	11% 4 28% 33% 21% 3	300
	21st to end	Day	18% 11% 27% 25% 17% 3	330
November	1st to 10th	Day	20% 6% 29% 27% 13% 4	300
	11th to 20th	Day	10% 11% 31% 31% 13% 3	300
	21st to end	Day	19% 14% 36% 21% 8% 2	300
December	1st to 10th	Day	16% 10% 36% 26% 10% 2	300
	11th to 20th	Day	16% 10% 40% 25% 8% 1	300
	21st to end	Day	18% 12% 34% 26% 8% 2	330
January	1st to 10th	Night	13% 9% 40% 31% 7%	1000
	11th to 20th	Night	15% 11% 34% 33% 6%	1000
	21st to end	Night	15% 13% 36% 30% 6%	1065
February	1st to 10th	Night	14% 10% 43% 28% 4	780
	11th to 20th	Night	15% 13% 42% 28% 3	744
	21st to end	Night	18% 14% 46% 20% 2	628
March	1st to 10th	Night	17% 13% 39% 27% 5%	617
	11th to 20th	Night	15% 10% 41% 29% 5%	570
	21st to end	Night	8% 14% 45% 30% 3	627
April	1st to 10th	Night	11% 11% 45% 29% 4	570
	11th to 20th	Night	12% 10% 45% 27% 5%	563
	21st to end	Night	8% 10% 47% 27% 7%	570
May	1st to 10th	Night	10% 12% 42% 32% 4	570
	11th to 20th	Night	11% 6% 37% 32% 13% 1	561
	21st to end	Night	7% 4 36% 37% 14% 1	617
June	1st to 10th	Night	3 2 22% 50% 21% 2	570
	11th to 20th	Night	3 2 28% 52% 15%	570
	21st to end	Night	3 1 16% 48% 27% 3	570
July	1st to 10th	Night	5% 1 10% 49% 31% 4	555
	11th to 20th	Night	3 11% 51% 33% 2	552
	21st to end	Night	2 1 6% 53% 37% 2	624
August	1st to 10th	Night	1 5% 50% 40% 4	567
	11th to 20th	Night	6% 1 8% 46% 37% 3	564
	21st to end	Night	4 4 43% 42% 6%	627
September	1st to 10th	Night	8% 1 8% 42% 37% 4	570
	11th to 20th	Night	12% 1 9% 41% 34% 3	570
	21st to end	Night	9% 1 14% 40% 35% 2	570
October	1st to 10th	Night	6% 2 18% 45% 27% 2	570
	11th to 20th	Night	11% 4 28% 41% 15% 1	707
	21st to end	Night	14% 9% 28% 34% 14% 2	836
November	1st to 10th	Night	12% 4 28% 40% 15% 1	790
	11th to 20th	Night	6% 9% 35% 35% 14% 1	1000
	21st to end	Night	15% 9% 38% 27% 10% 1	1000
December	1st to 10th	Night	13% 9% 35% 37% 7%	1000
	11th to 20th	Night	17% 9% 34% 33% 7%	1000
	21st to end	Night	16% 10% 37% 29% 8%	1100

Page generated at 2025-02-03 02:05:50. Version ac07

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