TAMUK Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TAMUK Observatory clear sky chart from 2005-11-06 to 2026-10-29.

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	11% 5% 2 6% 4 4 5% 4 6% 9% 45%	149102
	Night	13% 6% 2 5% 3 3 3 3 5% 7% 49%	143406
Transparency	Day	34% 7% 15% 24% 14% 7%	152894
	Night	34% 6% 16% 22% 14% 8%	147681
Seeing	Day	11% 5% 22% 33% 22% 7%	17099
	Night	14% 5% 23% 37% 20% 2	26990

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% 7% 3 6% 4 3 3 2 4 5% 45%	5289
	11th to 20th	Day	16% 6% 2 6% 4 3 4 3 4 7% 46%	5347
	21st to end	Day	24% 8% 3 7% 4 3 3 3 4 5% 37%	6468
February	1st to 10th	Day	19% 7% 2 6% 4 4 3 3 5% 5% 40%	2100
	11th to 20th	Day	19% 6% 3 6% 3 3 3 3 5% 6% 44%	2049
	21st to end	Day	16% 7% 2 6% 4 3 3 3 4 4 47%	1756
March	1st to 10th	Day	15% 6% 2 7% 4 3 4 3 6% 7% 43%	5046
	11th to 20th	Day	17% 6% 2 6% 3 3 3 2 3 5% 48%	5090
	21st to end	Day	13% 6% 2 5% 4 4 4 3 4 7% 49%	5583
April	1st to 10th	Day	11% 6% 3 6% 4 4 4 4 6% 7% 45%	2310
	11th to 20th	Day	13% 7% 3 7% 4 5% 4 3 6% 7% 40%	2286
	21st to end	Day	11% 6% 2 6% 6% 4 5% 4 7% 8% 41%	2484
May	1st to 10th	Day	16% 7% 3 8% 5% 5% 5% 4 6% 9% 31%	7617
	11th to 20th	Day	6% 5% 2 6% 4 4 5% 4 6% 9% 48%	7627
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 10% 40%	8392
June	1st to 10th	Day	4 3 1 5% 4 5% 6% 5% 7% 10% 50%	2730
	11th to 20th	Day	5% 3 1 6% 5% 5% 5% 5% 7% 11% 47%	2730
	21st to end	Day	6% 5% 1 6% 4 5% 7% 6% 8% 10% 42%	2730
July	1st to 10th	Day	5% 5% 2 6% 5% 5% 6% 5% 7% 11% 43%	7680
	11th to 20th	Day	5% 5% 2 7% 5% 6% 6% 5% 8% 12% 37%	7680
	21st to end	Day	5% 4 2 5% 4 4 5% 4 7% 9% 52%	8337
August	1st to 10th	Day	1 1 1 2 3 3 4 4 6% 11% 65%	5759
	11th to 20th	Day	2 2 1 3 3 4 5% 4 9% 14% 53%	5483
	21st to end	Day	3 3 1 5% 4 4 6% 4 8% 12% 51%	5661
September	1st to 10th	Day	8% 6% 2 8% 7% 6% 6% 5% 7% 9% 35%	2310
	11th to 20th	Day	10% 6% 3 8% 5% 6% 5% 5% 6% 10% 37%	2310
	21st to end	Day	7% 5% 2 6% 4 5% 5% 4 8% 10% 44%	2310
October	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 5% 6% 8% 49%	2310
	11th to 20th	Day	10% 4 2 5% 5% 4 4 4 5% 8% 49%	2189
	21st to end	Day	8% 4 2 5% 2 4 3 3 5% 6% 58%	2280
November	1st to 10th	Day	10% 4 2 6% 5% 4 5% 4 6% 7% 47%	2058
	11th to 20th	Day	13% 7% 2 6% 4 4 3 3 4 6% 47%	2100
	21st to end	Day	17% 7% 3 4 4 4 5% 3 4 6% 41%	1903
December	1st to 10th	Day	29% 9% 3 7% 4 3 3 2 4 6% 30%	3030
	11th to 20th	Day	13% 7% 3 7% 5% 4 5% 4 6% 6% 40%	3481
	21st to end	Day	12% 5% 2 6% 3 4 4 3 5% 6% 50%	4587
January	1st to 10th	Night	19% 6% 2 5% 3 2 3 3 3 4 49%	7634
	11th to 20th	Night	14% 6% 2 6% 3 3 3 3 4 7% 49%	7680
	21st to end	Night	27% 8% 3 7% 3 3 3 3 4 5% 34%	7764
February	1st to 10th	Night	17% 7% 2 4 3 4 4 4 5% 5% 45%	2520
	11th to 20th	Night	19% 7% 2 5% 3 4 3 3 4 5% 45%	2458
	21st to end	Night	17% 7% 2 5% 4 3 3 3 4 5% 48%	2049
March	1st to 10th	Night	20% 7% 2 5% 3 3 4 3 5% 6% 42%	5029
	11th to 20th	Night	17% 8% 2 6% 3 3 2 3 3 4 47%	5090
	21st to end	Night	18% 6% 2 4 3 2 2 2 4 6% 52%	5588
April	1st to 10th	Night	14% 7% 2 5% 5% 4 5% 4 6% 9% 40%	2310
	11th to 20th	Night	18% 7% 2 5% 4 3 4 4 5% 6% 42%	2283
	21st to end	Night	17% 8% 2 7% 5% 4 4 4 5% 7% 38%	2129
May	1st to 10th	Night	24% 9% 3 7% 4 3 4 3 5% 7% 31%	5266
	11th to 20th	Night	13% 7% 2 5% 3 3 4 3 6% 9% 45%	5265
	21st to end	Night	13% 9% 3 7% 4 4 4 4 6% 10% 36%	5793
June	1st to 10th	Night	4 4 1 4 4 4 4 3 7% 10% 55%	1890
	11th to 20th	Night	5% 3 2 5% 4 3 4 3 7% 10% 55%	1890
	21st to end	Night	4 4 1 4 3 4 3 4 8% 10% 53%	1890
July	1st to 10th	Night	4 4 2 5% 4 4 4 4 6% 11% 52%	5308
	11th to 20th	Night	5% 5% 2 6% 5% 5% 7% 5% 8% 11% 42%	5307
	21st to end	Night	6% 4 2 4 3 3 3 3 5% 9% 59%	5770
August	1st to 10th	Night	1 1 1 1 1 2 3 7% 82%	4404
	11th to 20th	Night	2 2 1 3 3 3 4 4 6% 11% 62%	4583
	21st to end	Night	2 1 1 3 2 2 3 3 5% 11% 67%	5467
September	1st to 10th	Night	6% 5% 1 6% 5% 4 4 4 7% 9% 48%	2310
	11th to 20th	Night	8% 5% 2 5% 4 4 5% 4 6% 9% 48%	2310
	21st to end	Night	5% 4 2 4 4 4 4 3 6% 9% 56%	2310
October	1st to 10th	Night	4 3 1 4 2 3 4 3 5% 7% 65%	2310
	11th to 20th	Night	9% 5% 2 3 3 2 3 3 5% 6% 59%	2410
	21st to end	Night	9% 4 1 5% 2 2 3 2 3 4 64%	2737
November	1st to 10th	Night	10% 4 2 4 3 3 3 3 4 5% 57%	2460
	11th to 20th	Night	13% 5% 2 6% 3 3 3 3 3 4 56%	2520
	21st to end	Night	16% 7% 3 5% 3 3 3 3 5% 5% 46%	2713
December	1st to 10th	Night	34% 11% 3 5% 3 2 2 2 3 4 31%	4380
	11th to 20th	Night	14% 7% 2 5% 3 4 4 3 4 5% 48%	4946
	21st to end	Night	11% 7% 2 5% 3 3 4 3 4 5% 53%	6633

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	39% 6% 11% 19% 17% 9%	5290
	11th to 20th	Day	40% 3 6% 19% 21% 11%	5347
	21st to end	Day	51% 4 6% 14% 17% 8%	6468
February	1st to 10th	Day	45% 5% 8% 11% 18% 14%	2100
	11th to 20th	Day	42% 3 10% 18% 16% 10%	2059
	21st to end	Day	40% 5% 6% 19% 20% 10%	1756
March	1st to 10th	Day	40% 6% 10% 18% 10% 17%	5046
	11th to 20th	Day	38% 5% 6% 11% 20% 20%	5090
	21st to end	Day	35% 4 9% 26% 16% 10%	5585
April	1st to 10th	Day	37% 6% 13% 18% 16% 10%	2310
	11th to 20th	Day	40% 8% 11% 18% 14% 10%	2286
	21st to end	Day	37% 8% 14% 20% 13% 9%	2484
May	1st to 10th	Day	46% 9% 13% 21% 9% 3	7655
	11th to 20th	Day	30% 8% 16% 23% 15% 7%	7631
	21st to end	Day	35% 8% 12% 35% 10%	8405
June	1st to 10th	Day	24% 9% 17% 32% 17% 2	2730
	11th to 20th	Day	26% 10% 12% 29% 19% 3	2730
	21st to end	Day	29% 12% 19% 28% 11% 1	2730
July	1st to 10th	Day	31% 9% 29% 27% 3	7616
	11th to 20th	Day	36% 9% 30% 20% 4	7611
	21st to end	Day	26% 7% 22% 38% 7%	8155
August	1st to 10th	Day	11% 7% 24% 45% 13%	5745
	11th to 20th	Day	17% 8% 36% 35% 3	5519
	21st to end	Day	22% 9% 24% 35% 9% 1	5660
September	1st to 10th	Day	41% 10% 17% 17% 12% 2	2310
	11th to 20th	Day	38% 11% 16% 22% 11% 2	2310
	21st to end	Day	30% 10% 14% 26% 13% 8%	2310
October	1st to 10th	Day	23% 6% 7% 13% 27% 24%	3700
	11th to 20th	Day	30% 6% 8% 18% 22% 17%	3481
	21st to end	Day	25% 7% 7% 20% 30% 12%	3618
November	1st to 10th	Day	33% 7% 10% 20% 20% 9%	2058
	11th to 20th	Day	39% 5% 11% 17% 16% 12%	2100
	21st to end	Day	43% 5% 10% 15% 18% 9%	1903
December	1st to 10th	Day	58% 4 7% 12% 14% 4	3030
	11th to 20th	Day	40% 8% 8% 19% 14% 12%	3479
	21st to end	Day	34% 6% 6% 21% 21% 12%	4587
January	1st to 10th	Night	39% 4 9% 18% 18% 12%	7635
	11th to 20th	Night	37% 3 7% 19% 19% 15%	7680
	21st to end	Night	53% 4 7% 13% 15% 8%	7764
February	1st to 10th	Night	41% 5% 10% 14% 15% 16%	2520
	11th to 20th	Night	42% 5% 10% 16% 17% 10%	2458
	21st to end	Night	40% 4 8% 21% 18% 9%	2049
March	1st to 10th	Night	43% 4 11% 18% 12% 12%	5029
	11th to 20th	Night	43% 4 7% 10% 16% 20%	5090
	21st to end	Night	35% 4 11% 23% 19% 8%	5588
April	1st to 10th	Night	41% 7% 14% 18% 12% 8%	2310
	11th to 20th	Night	42% 6% 11% 17% 13% 11%	2283
	21st to end	Night	45% 8% 12% 16% 13% 8%	2129
May	1st to 10th	Night	52% 6% 15% 17% 7% 3	5293
	11th to 20th	Night	36% 7% 12% 25% 15% 5%	5266
	21st to end	Night	42% 7% 20% 25% 5%	5805
June	1st to 10th	Night	22% 7% 20% 33% 16% 2	1890
	11th to 20th	Night	23% 7% 14% 35% 19% 2	1890
	21st to end	Night	24% 9% 26% 30% 10% 1	1890
July	1st to 10th	Night	27% 8% 34% 29% 2	5265
	11th to 20th	Night	32% 11% 34% 19% 4	5256
	21st to end	Night	23% 6% 26% 35% 10%	5641
August	1st to 10th	Night	5% 4 30% 48% 12%	4394
	11th to 20th	Night	16% 8% 41% 33% 3	4613
	21st to end	Night	13% 8% 31% 38% 9% 1	5467
September	1st to 10th	Night	31% 10% 25% 20% 11% 3	2310
	11th to 20th	Night	32% 8% 20% 27% 10% 2	2310
	21st to end	Night	25% 7% 17% 30% 15% 6%	2310
October	1st to 10th	Night	17% 5% 10% 19% 25% 25%	3700
	11th to 20th	Night	22% 6% 12% 19% 27% 15%	3844
	21st to end	Night	23% 4 8% 22% 31% 12%	4349
November	1st to 10th	Night	28% 7% 11% 21% 24% 9%	2460
	11th to 20th	Night	34% 5% 11% 20% 19% 11%	2520
	21st to end	Night	39% 5% 12% 21% 14% 10%	2713
December	1st to 10th	Night	60% 4 7% 11% 13% 6%	4380
	11th to 20th	Night	37% 6% 9% 24% 12% 13%	4947
	21st to end	Night	32% 5% 8% 21% 17% 16%	6633

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	20% 9% 32% 27% 10% 3	330
	11th to 20th	Day	17% 10% 33% 28% 9% 2	330
	21st to end	Day	24% 13% 31% 22% 9% 1	363
February	1st to 10th	Day	22% 9% 28% 25% 17%	330
	11th to 20th	Day	24% 9% 32% 26% 9% 1	330
	21st to end	Day	17% 10% 40% 25% 7% 1	273
March	1st to 10th	Day	18% 12% 37% 27% 6%	330
	11th to 20th	Day	18% 10% 43% 22% 7%	330
	21st to end	Day	13% 9% 39% 32% 6% 1	363
April	1st to 10th	Day	17% 11% 38% 28% 7% 1	330
	11th to 20th	Day	13% 14% 40% 25% 8% 1	324
	21st to end	Day	13% 11% 41% 28% 7%	504
May	1st to 10th	Day	13% 9% 44% 25% 8%	753
	11th to 20th	Day	12% 6% 40% 30% 11% 2	775
	21st to end	Day	8% 4 36% 36% 14% 1	844
June	1st to 10th	Day	5% 2 19% 42% 27% 5%	780
	11th to 20th	Day	6% 2 17% 46% 25% 4	780
	21st to end	Day	6% 2 14% 42% 28% 9%	780
July	1st to 10th	Day	6% 1 11% 41% 32% 9%	771
	11th to 20th	Day	4 2 7% 43% 35% 10%	768
	21st to end	Day	5% 1 8% 41% 35% 11%	849
August	1st to 10th	Day	1 1 6% 44% 33% 16%	664
	11th to 20th	Day	2 1 9% 44% 30% 14%	557
	21st to end	Day	4 2 4 32% 31% 27%	441
September	1st to 10th	Day	10% 1 7% 27% 38% 17%	360
	11th to 20th	Day	6% 1 6% 24% 43% 20%	360
	21st to end	Day	6% 2 9% 21% 42% 21%	360
October	1st to 10th	Day	9% 2 5% 33% 36% 15%	360
	11th to 20th	Day	10% 1 12% 35% 29% 13%	360
	21st to end	Day	11% 5% 22% 32% 23% 7%	387
November	1st to 10th	Day	13% 4 18% 32% 27% 7%	330
	11th to 20th	Day	18% 5% 20% 25% 25% 7%	330
	21st to end	Day	24% 8% 26% 25% 13% 4	330
December	1st to 10th	Day	25% 4 20% 31% 16% 5%	330
	11th to 20th	Day	19% 11% 23% 29% 15% 3	330
	21st to end	Day	16% 11% 25% 31% 14% 4	363
January	1st to 10th	Night	21% 7% 26% 35% 11%	1050
	11th to 20th	Night	18% 7% 30% 36% 7%	1050
	21st to end	Night	23% 8% 26% 34% 8%	929
February	1st to 10th	Night	21% 7% 32% 34% 6%	840
	11th to 20th	Night	22% 8% 32% 31% 6%	824
	21st to end	Night	21% 8% 38% 28% 5%	665
March	1st to 10th	Night	23% 10% 32% 28% 6% 1	630
	11th to 20th	Night	17% 10% 37% 30% 6%	630
	21st to end	Night	14% 8% 39% 34% 5%	693
April	1st to 10th	Night	13% 9% 41% 31% 6%	630
	11th to 20th	Night	20% 9% 35% 30% 6%	623
	21st to end	Night	19% 7% 40% 28% 6%	630
May	1st to 10th	Night	15% 7% 39% 33% 6%	630
	11th to 20th	Night	13% 5% 34% 39% 9%	621
	21st to end	Night	9% 4 29% 45% 13%	683
June	1st to 10th	Night	4 1 18% 52% 24% 1	630
	11th to 20th	Night	5% 1 17% 56% 20% 1	630
	21st to end	Night	5% 2 14% 45% 32% 2	630
July	1st to 10th	Night	6% 1 10% 47% 32% 4	615
	11th to 20th	Night	1 1 7% 48% 40% 2	612
	21st to end	Night	3 1 6% 49% 38% 3	690
August	1st to 10th	Night	4 44% 47% 4	627
	11th to 20th	Night	4 4 44% 44% 4	624
	21st to end	Night	4 5% 31% 52% 8%	693
September	1st to 10th	Night	6% 1 6% 30% 50% 7%	630
	11th to 20th	Night	10% 1 5% 27% 49% 9%	630
	21st to end	Night	7% 7% 31% 47% 6%	630
October	1st to 10th	Night	5% 1 5% 35% 49% 4	630
	11th to 20th	Night	11% 2 14% 42% 28% 3	730
	21st to end	Night	9% 3 23% 41% 22% 2	913
November	1st to 10th	Night	10% 3 19% 42% 24% 2	820
	11th to 20th	Night	16% 2 24% 37% 19% 2	840
	21st to end	Night	18% 6% 24% 35% 16% 1	1033
December	1st to 10th	Night	22% 5% 23% 34% 15% 1	1050
	11th to 20th	Night	23% 7% 25% 34% 11%	1050
	21st to end	Night	19% 5% 28% 36% 12% 1	1155

Page generated at 2026-10-26 03:37:47. Version ac07

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