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 2025-07-06.

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	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	120214
	Night	14% 6% 2 5% 3 3 3 3 5% 7% 48%	118852
Transparency	Day	35% 7% 13% 22% 15% 8%	124048
	Night	35% 6% 14% 21% 15% 9%	123148
Seeing	Day	11% 5% 23% 33% 22% 7%	15363
	Night	14% 5% 23% 37% 20% 2	25341

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	19% 7% 3 7% 4 3 4 3 4 6% 40%	4077
	11th to 20th	Day	17% 5% 2 5% 3 3 4 3 4 8% 44%	4103
	21st to end	Day	26% 8% 3 7% 4 3 3 3 5% 5% 33%	4994
February	1st to 10th	Day	19% 7% 2 6% 4 4 3 3 5% 5% 39%	2000
	11th to 20th	Day	20% 6% 3 6% 3 3 3 3 5% 6% 43%	1949
	21st to end	Day	16% 8% 2 6% 4 3 3 3 5% 4 46%	1675
March	1st to 10th	Day	15% 6% 2 6% 4 3 4 3 6% 7% 43%	4936
	11th to 20th	Day	18% 6% 2 6% 3 3 3 2 3 5% 48%	4980
	21st to end	Day	13% 6% 2 5% 4 4 4 3 4 7% 48%	5462
April	1st to 10th	Day	11% 6% 3 6% 4 4 4 4 6% 7% 46%	2200
	11th to 20th	Day	13% 7% 3 6% 4 5% 4 3 6% 7% 42%	2176
	21st to end	Day	11% 6% 2 6% 5% 4 5% 4 7% 7% 42%	2366
May	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 5% 7% 10% 33%	5862
	11th to 20th	Day	6% 4 2 6% 4 4 5% 4 6% 9% 52%	5862
	21st to end	Day	7% 4 2 5% 4 4 5% 5% 8% 10% 44%	6434
June	1st to 10th	Day	4 3 1 4 4 5% 5% 5% 7% 11% 52%	2600
	11th to 20th	Day	4 3 1 6% 5% 5% 5% 5% 7% 11% 48%	2600
	21st to end	Day	6% 5% 1 6% 5% 5% 7% 6% 8% 11% 41%	2600
July	1st to 10th	Day	6% 5% 2 7% 5% 5% 6% 4 7% 10% 43%	4186
	11th to 20th	Day	5% 5% 3 9% 6% 7% 7% 6% 9% 10% 34%	4120
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 39%	4465
August	1st to 10th	Day	1 1 1 2 2 3 3 3 5% 9% 70%	3925
	11th to 20th	Day	3 2 1 3 4 4 5% 5% 9% 13% 50%	3726
	21st to end	Day	4 3 2 7% 5% 6% 7% 5% 9% 12% 40%	3895
September	1st to 10th	Day	9% 6% 3 9% 7% 6% 6% 5% 7% 9% 34%	2090
	11th to 20th	Day	10% 6% 3 9% 5% 6% 6% 5% 6% 10% 35%	2090
	21st to end	Day	7% 5% 3 6% 4 5% 5% 4 8% 9% 44%	2090
October	1st to 10th	Day	6% 4 2 5% 5% 5% 6% 5% 6% 8% 49%	2090
	11th to 20th	Day	10% 5% 1 5% 5% 4 4 4 5% 7% 48%	1981
	21st to end	Day	8% 4 2 5% 2 4 3 3 4 6% 57%	2090
November	1st to 10th	Day	10% 4 3 6% 5% 4 5% 5% 6% 7% 45%	1958
	11th to 20th	Day	14% 8% 2 6% 4 4 3 3 4 6% 46%	2000
	21st to end	Day	17% 7% 3 4 4 4 5% 3 4 6% 42%	1813
December	1st to 10th	Day	30% 9% 3 7% 4 3 3 3 4 5% 29%	2940
	11th to 20th	Day	13% 7% 3 7% 5% 4 5% 4 6% 6% 40%	3391
	21st to end	Day	12% 5% 2 6% 3 4 4 3 5% 6% 50%	4488
January	1st to 10th	Night	24% 7% 2 5% 3 2 3 3 4 5% 43%	5888
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 5% 8% 47%	5900
	21st to end	Night	29% 8% 2 7% 3 3 3 3 5% 5% 31%	6002
February	1st to 10th	Night	18% 8% 2 5% 4 4 4 4 5% 5% 44%	2400
	11th to 20th	Night	19% 7% 2 5% 3 4 3 3 4 5% 44%	2338
	21st to end	Night	18% 7% 2 5% 4 3 3 3 4 5% 47%	1954
March	1st to 10th	Night	20% 7% 2 5% 3 3 4 3 5% 6% 42%	4919
	11th to 20th	Night	17% 8% 3 7% 4 3 2 3 3 4 46%	4980
	21st to end	Night	18% 6% 2 4 3 2 2 2 4 6% 52%	5467
April	1st to 10th	Night	13% 6% 2 5% 5% 4 5% 4 7% 9% 41%	2200
	11th to 20th	Night	17% 7% 2 5% 4 3 4 3 5% 6% 44%	2173
	21st to end	Night	17% 8% 2 6% 5% 4 4 4 5% 7% 39%	2028
May	1st to 10th	Night	23% 8% 4 7% 4 4 4 3 5% 7% 31%	4053
	11th to 20th	Night	11% 6% 2 5% 3 4 3 3 5% 8% 49%	4053
	21st to end	Night	11% 8% 3 7% 4 4 4 4 7% 10% 38%	4443
June	1st to 10th	Night	3 3 1 4 4 4 4 3 7% 10% 57%	1800
	11th to 20th	Night	4 3 2 4 4 3 4 3 7% 10% 56%	1800
	21st to end	Night	4 4 1 4 3 4 4 4 8% 11% 53%	1800
July	1st to 10th	Night	4 4 1 3 4 3 4 4 7% 12% 54%	2895
	11th to 20th	Night	4 4 2 6% 5% 5% 7% 5% 8% 11% 43%	2850
	21st to end	Night	7% 4 2 5% 4 3 4 3 6% 11% 51%	3098
August	1st to 10th	Night	1 1 1 1 2 3 6% 83%	3009
	11th to 20th	Night	2 2 1 3 3 3 4 4 7% 12% 60%	3113
	21st to end	Night	2 2 1 3 2 3 3 3 5% 12% 63%	3761
September	1st to 10th	Night	6% 5% 2 7% 5% 4 4 4 7% 9% 47%	2090
	11th to 20th	Night	8% 6% 3 6% 4 4 5% 4 5% 9% 46%	2090
	21st to end	Night	6% 4 2 5% 3 4 3 3 5% 8% 57%	2090
October	1st to 10th	Night	4 3 1 4 2 3 3 3 5% 7% 65%	2090
	11th to 20th	Night	10% 5% 2 3 3 2 3 3 5% 6% 58%	2180
	21st to end	Night	9% 4 1 5% 3 2 2 2 3 4 64%	2508
November	1st to 10th	Night	11% 5% 2 4 3 3 3 3 5% 5% 55%	2340
	11th to 20th	Night	14% 5% 2 6% 3 3 3 3 3 4 55%	2400
	21st to end	Night	16% 7% 2 5% 3 3 3 3 5% 5% 47%	2584
December	1st to 10th	Night	33% 11% 3 5% 4 2 2 2 3 4 31%	4250
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 4 5% 48%	4816
	21st to end	Night	11% 7% 2 5% 3 3 4 3 4 5% 53%	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	44% 6% 8% 16% 17% 10%	4078
	11th to 20th	Day	39% 4 7% 22% 18% 10%	4103
	21st to end	Day	53% 4 6% 12% 14% 10%	4994
February	1st to 10th	Day	46% 5% 8% 10% 18% 14%	2000
	11th to 20th	Day	43% 3 10% 17% 16% 10%	1959
	21st to end	Day	41% 5% 7% 19% 19% 10%	1675
March	1st to 10th	Day	39% 6% 10% 18% 9% 17%	4936
	11th to 20th	Day	39% 5% 6% 10% 19% 20%	4980
	21st to end	Day	36% 4 9% 25% 15% 10%	5464
April	1st to 10th	Day	36% 6% 13% 18% 17% 11%	2200
	11th to 20th	Day	38% 8% 10% 18% 15% 10%	2176
	21st to end	Day	36% 8% 12% 20% 13% 9%	2366
May	1st to 10th	Day	43% 9% 14% 20% 11% 4	5900
	11th to 20th	Day	28% 8% 15% 22% 18% 9%	5866
	21st to end	Day	29% 8% 12% 39% 11%	6447
June	1st to 10th	Day	22% 8% 16% 34% 17% 2	2600
	11th to 20th	Day	25% 10% 12% 30% 20% 3	2600
	21st to end	Day	30% 12% 20% 28% 9% 1	2600
July	1st to 10th	Day	32% 11% 22% 31% 5%	4122
	11th to 20th	Day	41% 10% 24% 18% 7%	4051
	21st to end	Day	37% 10% 24% 25% 4	4325
August	1st to 10th	Day	10% 6% 20% 45% 18%	3911
	11th to 20th	Day	20% 10% 34% 32% 4	3762
	21st to end	Day	30% 12% 22% 27% 9% 1	3894
September	1st to 10th	Day	43% 11% 15% 16% 13% 2	2090
	11th to 20th	Day	41% 11% 13% 20% 12% 3	2090
	21st to end	Day	31% 10% 14% 23% 14% 9%	2090
October	1st to 10th	Day	23% 6% 7% 12% 27% 25%	3480
	11th to 20th	Day	31% 6% 8% 16% 21% 17%	3273
	21st to end	Day	25% 7% 6% 20% 30% 12%	3428
November	1st to 10th	Day	34% 7% 11% 21% 18% 8%	1958
	11th to 20th	Day	40% 5% 11% 16% 16% 12%	2000
	21st to end	Day	42% 5% 10% 15% 18% 10%	1813
December	1st to 10th	Day	58% 4 7% 13% 14% 4	2940
	11th to 20th	Day	39% 8% 8% 19% 13% 12%	3389
	21st to end	Day	34% 6% 6% 21% 21% 12%	4488
January	1st to 10th	Night	44% 4 7% 13% 17% 14%	5888
	11th to 20th	Night	36% 4 9% 20% 19% 12%	5900
	21st to end	Night	54% 4 7% 12% 15% 8%	6002
February	1st to 10th	Night	42% 5% 10% 13% 14% 16%	2400
	11th to 20th	Night	43% 5% 10% 14% 17% 10%	2338
	21st to end	Night	41% 5% 8% 20% 17% 9%	1954
March	1st to 10th	Night	42% 4 11% 18% 12% 13%	4919
	11th to 20th	Night	43% 5% 7% 9% 16% 20%	4980
	21st to end	Night	35% 4 11% 23% 19% 8%	5467
April	1st to 10th	Night	39% 7% 14% 18% 13% 9%	2200
	11th to 20th	Night	41% 6% 12% 17% 14% 11%	2173
	21st to end	Night	44% 8% 11% 16% 13% 8%	2028
May	1st to 10th	Night	51% 7% 13% 16% 9% 4	4080
	11th to 20th	Night	33% 7% 12% 25% 18% 6%	4054
	21st to end	Night	39% 8% 20% 27% 6%	4452
June	1st to 10th	Night	21% 6% 20% 35% 17% 2	1800
	11th to 20th	Night	22% 7% 14% 36% 19% 2	1800
	21st to end	Night	24% 9% 27% 31% 9% 1	1800
July	1st to 10th	Night	23% 9% 30% 33% 4	2850
	11th to 20th	Night	31% 12% 30% 20% 6%	2796
	21st to end	Night	28% 9% 33% 26% 4	2999
August	1st to 10th	Night	5% 5% 24% 49% 17%	2999
	11th to 20th	Night	18% 8% 40% 31% 4	3143
	21st to end	Night	16% 10% 32% 32% 9% 1	3761
September	1st to 10th	Night	32% 10% 25% 18% 11% 3	2090
	11th to 20th	Night	34% 9% 18% 27% 11% 2	2090
	21st to end	Night	26% 7% 16% 28% 17% 7%	2090
October	1st to 10th	Night	16% 5% 10% 18% 25% 26%	3480
	11th to 20th	Night	23% 6% 12% 18% 26% 15%	3614
	21st to end	Night	23% 4 8% 21% 31% 12%	4120
November	1st to 10th	Night	28% 7% 12% 22% 23% 8%	2340
	11th to 20th	Night	35% 5% 11% 18% 20% 11%	2400
	21st to end	Night	39% 5% 11% 21% 14% 10%	2584
December	1st to 10th	Night	60% 4 7% 12% 12% 6%	4250
	11th to 20th	Night	37% 6% 9% 24% 12% 13%	4817
	21st to end	Night	32% 5% 8% 21% 17% 16%	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	21% 9% 31% 26% 9% 3	300
	11th to 20th	Day	18% 9% 35% 28% 9% 2	300
	21st to end	Day	23% 13% 32% 22% 10% 1	330
February	1st to 10th	Day	24% 9% 27% 25% 16%	300
	11th to 20th	Day	26% 9% 32% 25% 8%	300
	21st to end	Day	18% 10% 43% 22% 6%	249
March	1st to 10th	Day	19% 12% 36% 27% 6%	300
	11th to 20th	Day	20% 10% 44% 20% 6%	300
	21st to end	Day	14% 10% 41% 30% 5%	330
April	1st to 10th	Day	16% 12% 37% 28% 7% 1	300
	11th to 20th	Day	12% 15% 39% 26% 8% 1	294
	21st to end	Day	13% 11% 40% 29% 6%	466
May	1st to 10th	Day	12% 9% 45% 25% 8%	703
	11th to 20th	Day	12% 5% 39% 31% 11% 2	725
	21st to end	Day	8% 4 37% 36% 14% 1	789
June	1st to 10th	Day	4 1 19% 42% 28% 5%	730
	11th to 20th	Day	5% 2 18% 47% 25% 4	730
	21st to end	Day	6% 2 14% 40% 29% 9%	730
July	1st to 10th	Day	7% 1 10% 40% 33% 9%	697
	11th to 20th	Day	4 1 6% 40% 38% 11%	668
	21st to end	Day	4 1 7% 41% 36% 11%	739
August	1st to 10th	Day	1 1 6% 44% 33% 15%	575
	11th to 20th	Day	3 1 7% 44% 32% 14%	477
	21st to end	Day	4 2 4 31% 31% 27%	371
September	1st to 10th	Day	11% 1 8% 26% 38% 16%	300
	11th to 20th	Day	7% 1 6% 21% 43% 22%	300
	21st to end	Day	7% 1 8% 20% 42% 22%	300
October	1st to 10th	Day	8% 2 5% 31% 39% 16%	300
	11th to 20th	Day	11% 1 13% 32% 28% 15%	300
	21st to end	Day	11% 5% 23% 32% 22% 7%	330
November	1st to 10th	Day	13% 4 19% 33% 26% 5%	300
	11th to 20th	Day	20% 5% 18% 25% 25% 7%	300
	21st to end	Day	25% 6% 25% 26% 13% 5%	300
December	1st to 10th	Day	24% 4 20% 30% 17% 6%	300
	11th to 20th	Day	18% 12% 24% 28% 15% 3	300
	21st to end	Day	18% 12% 25% 30% 13% 4	330
January	1st to 10th	Night	22% 6% 26% 34% 11%	1000
	11th to 20th	Night	19% 7% 31% 36% 7% 1	1000
	21st to end	Night	24% 8% 26% 35% 8%	885
February	1st to 10th	Night	22% 7% 32% 32% 6%	800
	11th to 20th	Night	23% 8% 32% 31% 6%	784
	21st to end	Night	22% 9% 38% 26% 5%	634
March	1st to 10th	Night	21% 10% 33% 29% 6% 1	600
	11th to 20th	Night	17% 10% 38% 30% 5%	600
	21st to end	Night	14% 8% 40% 33% 4	660
April	1st to 10th	Night	13% 9% 41% 32% 6%	600
	11th to 20th	Night	19% 8% 35% 31% 7%	593
	21st to end	Night	19% 8% 39% 28% 6%	600
May	1st to 10th	Night	15% 7% 40% 32% 6%	600
	11th to 20th	Night	13% 5% 34% 39% 9%	591
	21st to end	Night	8% 4 29% 45% 13%	650
June	1st to 10th	Night	4 1 18% 52% 24% 1	600
	11th to 20th	Night	5% 1 18% 57% 19% 1	600
	21st to end	Night	5% 2 14% 44% 34% 2	600
July	1st to 10th	Night	6% 1 9% 48% 32% 4	570
	11th to 20th	Night	1 1 5% 47% 43% 3	552
	21st to end	Night	3 1 6% 47% 39% 4	624
August	1st to 10th	Night	4 44% 47% 4	567
	11th to 20th	Night	4 4 43% 45% 4	564
	21st to end	Night	5% 5% 29% 53% 8%	627
September	1st to 10th	Night	6% 1 5% 30% 50% 7%	570
	11th to 20th	Night	11% 1 5% 24% 49% 10%	570
	21st to end	Night	8% 1 8% 29% 48% 7%	570
October	1st to 10th	Night	4 1 5% 36% 49% 5%	570
	11th to 20th	Night	12% 2 14% 43% 26% 3	660
	21st to end	Night	9% 3 23% 41% 22% 2	836
November	1st to 10th	Night	11% 3 19% 42% 24% 2	780
	11th to 20th	Night	17% 2 24% 37% 19% 2	800
	21st to end	Night	19% 6% 23% 35% 16% 1	984
December	1st to 10th	Night	21% 5% 23% 35% 15% 1	1000
	11th to 20th	Night	23% 7% 25% 34% 10%	1000
	21st to end	Night	19% 5% 28% 36% 11% 1	1100

Page generated at 2025-07-03 00:30:12. Version ac07

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