Denison
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Denison clear sky chart from 2005-11-06 to 2026-07-31.

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% 8% 3 8% 5% 4 4 4 5% 7% 41%	138405
	Night	10% 8% 3 8% 4 4 4 3 5% 7% 44%	134923
Transparency	Day	41% 5% 12% 25% 14% 2	142011
	Night	39% 5% 12% 26% 16% 2	139384
Seeing	Day	16% 10% 32% 28% 12% 3	18272
	Night	15% 9% 35% 31% 9% 1	28095

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	8% 12% 4 17% 9% 6% 6% 3 5% 5% 25%	5051
	11th to 20th	Day	4 10% 4 12% 6% 7% 6% 5% 5% 6% 34%	5310
	21st to end	Day	6% 11% 6% 14% 7% 7% 5% 3 5% 5% 33%	5812
February	1st to 10th	Day	10% 13% 5% 10% 7% 6% 5% 4 5% 8% 27%	1890
	11th to 20th	Day	9% 12% 4 10% 5% 5% 5% 2 4 6% 38%	1844
	21st to end	Day	11% 11% 3 9% 6% 5% 4 4 5% 6% 37%	1691
March	1st to 10th	Day	14% 9% 3 7% 4 3 2 2 3 4 48%	5044
	11th to 20th	Day	12% 8% 2 6% 3 3 4 3 5% 8% 46%	5090
	21st to end	Day	21% 12% 5% 10% 5% 4 4 3 5% 6% 24%	5583
April	1st to 10th	Day	16% 10% 3 7% 4 4 4 3 5% 6% 37%	2420
	11th to 20th	Day	17% 10% 3 7% 4 4 3 3 5% 6% 37%	2574
	21st to end	Day	20% 9% 2 7% 5% 4 4 4 4 6% 35%	2730
May	1st to 10th	Day	12% 7% 2 6% 4 4 5% 4 5% 7% 43%	7617
	11th to 20th	Day	14% 8% 2 6% 3 3 4 3 4 5% 47%	7682
	21st to end	Day	17% 9% 3 7% 4 4 5% 4 6% 6% 35%	9047
June	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 6% 8% 44%	2940
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 7% 9% 46%	2940
	21st to end	Day	8% 5% 2 6% 4 5% 5% 5% 6% 7% 46%	2940
July	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 7% 9% 43%	6500
	11th to 20th	Day	8% 5% 2 6% 4 4 4 4 5% 7% 52%	6062
	21st to end	Day	5% 4 2 6% 5% 4 5% 4 7% 10% 47%	6553
August	1st to 10th	Day	9% 6% 2 5% 4 5% 5% 4 7% 9% 44%	4234
	11th to 20th	Day	14% 7% 3 7% 4 4 5% 3 5% 7% 41%	4171
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 48%	4550
September	1st to 10th	Day	12% 5% 2 5% 3 3 4 3 6% 7% 52%	2398
	11th to 20th	Day	9% 5% 2 5% 3 4 3 3 5% 9% 51%	2200
	21st to end	Day	11% 4 1 4 3 3 4 4 5% 8% 54%	2200
October	1st to 10th	Day	14% 5% 2 5% 4 3 3 3 4 6% 51%	2005
	11th to 20th	Day	13% 5% 3 5% 4 4 3 2 4 6% 52%	2000
	21st to end	Day	14% 8% 3 7% 3 4 4 3 5% 6% 44%	2200
November	1st to 10th	Day	10% 6% 2 7% 4 4 4 3 5% 7% 48%	1903
	11th to 20th	Day	11% 8% 3 9% 6% 3 4 3 5% 7% 40%	1696
	21st to end	Day	12% 10% 3 7% 4 2 3 4 6% 6% 42%	1680
December	1st to 10th	Day	6% 6% 4 8% 7% 4 3 3 4 7% 48%	2690
	11th to 20th	Day	11% 10% 4 9% 6% 5% 5% 5% 6% 6% 33%	3088
	21st to end	Day	17% 10% 5% 16% 5% 4 4 4 4 5% 25%	4070
January	1st to 10th	Night	9% 11% 3 17% 9% 6% 4 3 5% 5% 28%	7854
	11th to 20th	Night	4 9% 3 9% 6% 5% 6% 5% 8% 6% 38%	7680
	21st to end	Night	6% 10% 5% 14% 6% 6% 5% 3 5% 5% 36%	8402
February	1st to 10th	Night	10% 11% 4 10% 6% 5% 5% 3 5% 6% 35%	2730
	11th to 20th	Night	10% 10% 4 7% 5% 5% 5% 3 5% 6% 40%	2663
	21st to end	Night	9% 7% 4 9% 5% 4 5% 3 4 6% 45%	2134
March	1st to 10th	Night	14% 8% 3 5% 3 3 2 3 4 5% 52%	5030
	11th to 20th	Night	10% 7% 2 5% 3 3 3 3 5% 8% 52%	5090
	21st to end	Night	17% 11% 3 8% 5% 5% 4 3 5% 7% 32%	5588
April	1st to 10th	Night	13% 9% 2 6% 4 3 4 3 6% 7% 42%	2198
	11th to 20th	Night	12% 9% 3 6% 4 4 3 3 5% 7% 44%	1993
	21st to end	Night	17% 10% 2 6% 4 4 4 3 5% 7% 38%	1890
May	1st to 10th	Night	11% 6% 2 5% 4 3 4 3 5% 7% 51%	5266
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	5206
	21st to end	Night	16% 9% 3 7% 4 3 4 3 5% 6% 40%	5139
June	1st to 10th	Night	6% 4 2 6% 4 4 5% 4 6% 9% 51%	1680
	11th to 20th	Night	6% 4 1 5% 4 3 4 4 6% 10% 51%	1680
	21st to end	Night	6% 4 2 5% 3 3 5% 4 7% 8% 53%	1680
July	1st to 10th	Night	6% 5% 2 5% 4 3 4 3 6% 9% 52%	3698
	11th to 20th	Night	8% 4 2 4 3 3 3 3 5% 8% 59%	4117
	21st to end	Night	5% 4 2 6% 3 4 5% 4 7% 9% 51%	4539
August	1st to 10th	Night	5% 4 2 5% 3 4 4 4 6% 9% 53%	2926
	11th to 20th	Night	10% 6% 2 5% 3 3 3 2 5% 7% 53%	2888
	21st to end	Night	8% 5% 2 5% 3 4 3 3 5% 7% 55%	3353
September	1st to 10th	Night	9% 4 1 4 3 3 3 3 4 7% 58%	2000
	11th to 20th	Night	8% 4 1 4 4 3 4 4 6% 7% 55%	2199
	21st to end	Night	10% 5% 1 4 3 3 3 3 5% 5% 58%	2200
October	1st to 10th	Night	13% 7% 2 5% 3 3 3 2 5% 6% 52%	2375
	11th to 20th	Night	14% 7% 2 5% 2 3 3 2 4 6% 52%	2400
	21st to end	Night	15% 8% 2 6% 3 3 3 3 3 6% 49%	2640
November	1st to 10th	Night	9% 5% 2 5% 3 4 3 4 5% 7% 53%	2615
	11th to 20th	Night	9% 8% 2 7% 4 4 3 4 6% 6% 47%	2921
	21st to end	Night	12% 10% 4 6% 4 3 3 3 4 6% 46%	2940
December	1st to 10th	Night	5% 7% 3 9% 6% 4 4 3 5% 7% 45%	4720
	11th to 20th	Night	10% 9% 4 11% 6% 5% 4 4 5% 6% 35%	5339
	21st to end	Night	16% 13% 5% 13% 5% 4 4 3 4 5% 27%	7150

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	61% 4 11% 14% 9% 1	5052
	11th to 20th	Day	50% 3 10% 21% 13% 2	5310
	21st to end	Day	53% 4 14% 20% 8%	5812
February	1st to 10th	Day	55% 5% 12% 17% 10% 1	1890
	11th to 20th	Day	49% 4 10% 21% 14% 2	1853
	21st to end	Day	48% 5% 9% 23% 11% 3	1691
March	1st to 10th	Day	41% 3 7% 30% 16% 2	5044
	11th to 20th	Day	36% 4 8% 28% 20% 3	5090
	21st to end	Day	60% 6% 14% 15% 4 1	5585
April	1st to 10th	Day	48% 5% 12% 25% 10% 1	2420
	11th to 20th	Day	48% 5% 11% 22% 12% 2	2574
	21st to end	Day	51% 5% 9% 21% 13% 1	2730
May	1st to 10th	Day	39% 6% 9% 30% 15% 1	7655
	11th to 20th	Day	39% 5% 7% 26% 20% 3	7686
	21st to end	Day	47% 7% 10% 22% 13% 1	9061
June	1st to 10th	Day	36% 6% 15% 28% 12% 2	2940
	11th to 20th	Day	33% 6% 14% 28% 17% 2	2940
	21st to end	Day	34% 7% 15% 28% 13% 3	2940
July	1st to 10th	Day	36% 7% 14% 32% 10% 1	6431
	11th to 20th	Day	31% 6% 14% 31% 16% 2	5992
	21st to end	Day	29% 8% 19% 28% 15% 1	6371
August	1st to 10th	Day	36% 7% 14% 28% 15% 1	4220
	11th to 20th	Day	43% 5% 11% 30% 11% 1	4210
	21st to end	Day	32% 7% 14% 25% 18% 3	4549
September	1st to 10th	Day	32% 5% 12% 28% 20% 3	2398
	11th to 20th	Day	31% 4 15% 32% 17% 1	2200
	21st to end	Day	28% 4 12% 29% 24% 2	2200
October	1st to 10th	Day	22% 3 6% 26% 41% 2	3265
	11th to 20th	Day	25% 3 13% 30% 22% 6%	3240
	21st to end	Day	38% 4 8% 28% 18% 4	3538
November	1st to 10th	Day	36% 4 16% 24% 19% 2	1903
	11th to 20th	Day	44% 4 12% 24% 16% 1	1696
	21st to end	Day	42% 3 15% 25% 13% 1	1680
December	1st to 10th	Day	38% 4 16% 30% 11% 1	2690
	11th to 20th	Day	49% 5% 17% 21% 8%	3085
	21st to end	Day	61% 5% 11% 17% 7% 1	4070
January	1st to 10th	Night	58% 4 12% 16% 8% 1	7855
	11th to 20th	Night	42% 5% 12% 21% 17% 3	7680
	21st to end	Night	50% 4 12% 20% 13% 1	8402
February	1st to 10th	Night	51% 4 11% 22% 10% 2	2730
	11th to 20th	Night	45% 4 11% 23% 14% 3	2664
	21st to end	Night	41% 4 11% 22% 19% 3	2134
March	1st to 10th	Night	36% 3 7% 32% 20% 2	5030
	11th to 20th	Night	31% 4 7% 34% 19% 4	5090
	21st to end	Night	51% 8% 14% 20% 5% 2	5588
April	1st to 10th	Night	41% 4 12% 25% 16% 1	2198
	11th to 20th	Night	40% 4 12% 23% 18% 2	1993
	21st to end	Night	45% 5% 12% 22% 14% 1	1890
May	1st to 10th	Night	33% 5% 8% 27% 24% 2	5293
	11th to 20th	Night	34% 5% 9% 23% 22% 6%	5207
	21st to end	Night	44% 5% 11% 23% 14% 2	5149
June	1st to 10th	Night	30% 7% 14% 31% 15% 4	1680
	11th to 20th	Night	27% 7% 14% 25% 22% 4	1680
	21st to end	Night	27% 8% 14% 29% 18% 3	1680
July	1st to 10th	Night	29% 6% 16% 33% 15% 2	3660
	11th to 20th	Night	25% 5% 15% 34% 19% 2	4068
	21st to end	Night	27% 9% 18% 30% 16% 1	4410
August	1st to 10th	Night	27% 6% 16% 33% 16% 2	2916
	11th to 20th	Night	31% 5% 16% 29% 16% 2	2915
	21st to end	Night	28% 6% 15% 26% 19% 6%	3353
September	1st to 10th	Night	26% 4 12% 31% 23% 4	2000
	11th to 20th	Night	28% 5% 13% 33% 20% 2	2199
	21st to end	Night	29% 3 10% 30% 24% 4	2200
October	1st to 10th	Night	22% 2 6% 22% 45% 3	3882
	11th to 20th	Night	27% 3 10% 26% 27% 6%	3899
	21st to end	Night	37% 3 11% 30% 18% 1	4252
November	1st to 10th	Night	30% 5% 16% 25% 21% 3	2615
	11th to 20th	Night	37% 4 13% 27% 17% 2	2921
	21st to end	Night	41% 4 11% 29% 14% 2	2940
December	1st to 10th	Night	38% 4 11% 36% 10%	4720
	11th to 20th	Night	49% 5% 14% 25% 7%	5341
	21st to end	Night	59% 4 10% 19% 7%	7150

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	18% 15% 35% 25% 8%	330
	11th to 20th	Day	17% 15% 43% 22% 3 1	330
	21st to end	Day	16% 12% 44% 22% 5% 1	363
February	1st to 10th	Day	16% 16% 42% 22% 2 1	330
	11th to 20th	Day	16% 17% 39% 22% 5% 1	330
	21st to end	Day	19% 16% 41% 19% 4	273
March	1st to 10th	Day	19% 16% 44% 17% 4 1	330
	11th to 20th	Day	24% 15% 34% 20% 7%	330
	21st to end	Day	33% 16% 33% 15% 2	363
April	1st to 10th	Day	26% 17% 35% 18% 3	440
	11th to 20th	Day	27% 14% 33% 20% 6% 1	612
	21st to end	Day	27% 13% 31% 21% 6% 1	750
May	1st to 10th	Day	22% 12% 31% 25% 9% 2	753
	11th to 20th	Day	23% 11% 28% 22% 13% 3	775
	21st to end	Day	19% 7% 31% 28% 12% 2	844
June	1st to 10th	Day	9% 7% 26% 35% 21% 3	780
	11th to 20th	Day	10% 8% 33% 30% 15% 3	780
	21st to end	Day	9% 8% 36% 30% 14% 3	780
July	1st to 10th	Day	9% 4 19% 35% 25% 8%	771
	11th to 20th	Day	7% 4 27% 37% 17% 9%	768
	21st to end	Day	7% 3 23% 39% 24% 4	845
August	1st to 10th	Day	8% 3 23% 38% 23% 4	726
	11th to 20th	Day	12% 3 23% 36% 23% 4	715
	21st to end	Day	10% 4 21% 40% 20% 5%	730
September	1st to 10th	Day	13% 5% 25% 34% 17% 5%	528
	11th to 20th	Day	6% 8% 36% 31% 15% 4	330
	21st to end	Day	11% 7% 35% 30% 13% 3	330
October	1st to 10th	Day	17% 9% 30% 26% 14% 4	330
	11th to 20th	Day	16% 17% 41% 20% 5% 2	330
	21st to end	Day	21% 16% 36% 21% 5% 1	363
November	1st to 10th	Day	18% 15% 41% 19% 6% 2	330
	11th to 20th	Day	19% 18% 39% 19% 5%	330
	21st to end	Day	21% 18% 33% 22% 6%	330
December	1st to 10th	Day	11% 15% 42% 25% 6% 1	330
	11th to 20th	Day	17% 18% 37% 21% 6% 1	330
	21st to end	Day	24% 16% 39% 18% 2	363
January	1st to 10th	Night	13% 14% 38% 29% 4 1	1050
	11th to 20th	Night	14% 14% 41% 25% 5% 1	1050
	21st to end	Night	18% 9% 42% 26% 5%	1155
February	1st to 10th	Night	15% 10% 44% 25% 4	1050
	11th to 20th	Night	16% 11% 44% 24% 4	1029
	21st to end	Night	13% 12% 46% 23% 5% 1	750
March	1st to 10th	Night	18% 12% 38% 25% 6% 1	631
	11th to 20th	Night	19% 11% 38% 25% 7%	630
	21st to end	Night	24% 11% 36% 24% 5% 1	693
April	1st to 10th	Night	18% 15% 41% 23% 3	630
	11th to 20th	Night	19% 13% 38% 24% 7%	623
	21st to end	Night	23% 11% 33% 26% 8%	630
May	1st to 10th	Night	18% 7% 34% 32% 8%	630
	11th to 20th	Night	17% 10% 29% 34% 10%	621
	21st to end	Night	16% 6% 32% 33% 12%	683
June	1st to 10th	Night	8% 4 27% 45% 15%	630
	11th to 20th	Night	8% 5% 34% 40% 12% 1	630
	21st to end	Night	7% 7% 33% 39% 14%	630
July	1st to 10th	Night	7% 3 19% 46% 25% 1	615
	11th to 20th	Night	5% 1 21% 48% 21% 3	612
	21st to end	Night	5% 2 18% 51% 22% 1	687
August	1st to 10th	Night	9% 3 21% 44% 22% 2	597
	11th to 20th	Night	11% 3 20% 41% 23% 2	594
	21st to end	Night	8% 2 22% 46% 19% 3	660
September	1st to 10th	Night	11% 4 23% 41% 19% 3	600
	11th to 20th	Night	10% 3 32% 40% 13% 2	600
	21st to end	Night	13% 4 33% 34% 15% 1	600
October	1st to 10th	Night	17% 8% 30% 33% 11% 2	775
	11th to 20th	Night	19% 11% 37% 28% 5%	800
	21st to end	Night	21% 12% 30% 28% 8%	880
November	1st to 10th	Night	12% 12% 39% 29% 8%	975
	11th to 20th	Night	14% 14% 42% 24% 5%	1050
	21st to end	Night	18% 11% 36% 26% 8%	1050
December	1st to 10th	Night	14% 12% 39% 28% 5%	1050
	11th to 20th	Night	17% 11% 39% 27% 5%	1050
	21st to end	Night	20% 12% 38% 25% 4	1155

Page generated at 2026-07-28 02:25:20. Version ac07

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