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 2025-03-27.

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	12% 8% 3 8% 5% 4 4 4 5% 7% 41%	109200
	Night	10% 8% 3 8% 5% 4 4 3 5% 6% 44%	110333
Transparency	Day	42% 5% 12% 25% 14% 2	112845
	Night	40% 5% 12% 25% 16% 2	114816
Seeing	Day	16% 10% 31% 28% 13% 3	16286
	Night	15% 9% 35% 31% 10% 1	26361

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% 13% 4 20% 9% 7% 5% 3 4 5% 23%	3893
	11th to 20th	Day	5% 11% 4 12% 6% 6% 7% 5% 5% 6% 33%	4080
	21st to end	Day	7% 11% 6% 14% 7% 6% 5% 3 4 5% 32%	4488
February	1st to 10th	Day	10% 13% 5% 10% 7% 6% 5% 4 5% 8% 28%	1800
	11th to 20th	Day	10% 12% 4 10% 5% 5% 5% 2 4 6% 37%	1754
	21st to end	Day	11% 11% 3 9% 6% 5% 3 4 5% 6% 37%	1613
March	1st to 10th	Day	13% 10% 3 7% 4 3 3 2 4 5% 46%	3544
	11th to 20th	Day	11% 8% 3 7% 4 3 4 3 5% 6% 46%	3590
	21st to end	Day	22% 13% 6% 11% 5% 5% 4 3 5% 5% 21%	3880
April	1st to 10th	Day	15% 10% 3 7% 4 4 4 3 5% 6% 38%	2190
	11th to 20th	Day	18% 10% 3 7% 4 5% 3 3 5% 6% 36%	2326
	21st to end	Day	21% 9% 2 7% 5% 3 4 4 4 6% 36%	2470
May	1st to 10th	Day	18% 9% 3 7% 5% 4 6% 5% 6% 7% 31%	4082
	11th to 20th	Day	13% 8% 3 6% 4 4 4 4 5% 6% 44%	4109
	21st to end	Day	15% 7% 3 6% 4 4 5% 4 7% 7% 39%	4824
June	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 6% 8% 45%	2660
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 7% 9% 45%	2660
	21st to end	Day	8% 5% 2 5% 4 5% 5% 5% 6% 8% 47%	2660
July	1st to 10th	Day	11% 5% 2 7% 4 5% 5% 5% 7% 9% 40%	4440
	11th to 20th	Day	6% 3 1 5% 4 4 4 4 5% 7% 57%	4137
	21st to end	Day	4 3 2 5% 4 5% 5% 4 7% 10% 51%	4465
August	1st to 10th	Day	9% 6% 2 5% 4 5% 5% 4 7% 9% 44%	4104
	11th to 20th	Day	15% 7% 3 7% 4 4 5% 3 5% 7% 40%	4041
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 48%	4411
September	1st to 10th	Day	12% 5% 2 5% 3 3 4 3 5% 7% 52%	2278
	11th to 20th	Day	10% 5% 2 5% 3 3 3 3 5% 9% 52%	2090
	21st to end	Day	11% 4 1 4 3 3 4 4 5% 8% 54%	2090
October	1st to 10th	Day	14% 5% 2 5% 4 3 3 3 4 6% 50%	1905
	11th to 20th	Day	13% 5% 3 5% 3 4 3 2 3 6% 53%	1900
	21st to end	Day	15% 8% 3 7% 3 3 3 3 4 5% 44%	2090
November	1st to 10th	Day	10% 6% 2 6% 4 4 4 3 5% 7% 48%	1811
	11th to 20th	Day	12% 8% 3 9% 7% 3 4 3 5% 7% 40%	1615
	21st to end	Day	12% 9% 4 7% 4 2 3 4 6% 7% 42%	1600
December	1st to 10th	Day	6% 6% 3 8% 7% 4 3 3 4 7% 48%	2610
	11th to 20th	Day	11% 10% 4 9% 6% 5% 5% 5% 6% 6% 33%	3008
	21st to end	Day	17% 10% 5% 17% 5% 4 4 4 4 5% 25%	3982
January	1st to 10th	Night	9% 11% 4 21% 10% 6% 4 3 5% 5% 23%	6054
	11th to 20th	Night	6% 10% 4 10% 7% 5% 6% 5% 8% 5% 34%	5900
	21st to end	Night	7% 11% 5% 14% 5% 5% 5% 3 5% 5% 36%	6490
February	1st to 10th	Night	10% 11% 4 10% 6% 5% 5% 3 5% 6% 35%	2600
	11th to 20th	Night	10% 10% 4 7% 5% 5% 5% 3 5% 6% 39%	2533
	21st to end	Night	9% 8% 4 9% 5% 4 5% 3 4 5% 45%	2035
March	1st to 10th	Night	12% 8% 3 6% 3 3 3 3 3 5% 51%	3530
	11th to 20th	Night	10% 7% 3 5% 3 3 3 3 4 7% 52%	3590
	21st to end	Night	20% 11% 4 10% 6% 5% 4 3 5% 7% 25%	3889
April	1st to 10th	Night	13% 9% 2 6% 4 3 4 3 6% 7% 43%	1989
	11th to 20th	Night	13% 9% 3 6% 4 4 3 3 5% 6% 43%	1801
	21st to end	Night	17% 10% 2 6% 4 4 4 3 5% 8% 38%	1710
May	1st to 10th	Night	18% 7% 2 6% 3 3 3 3 5% 7% 42%	2823
	11th to 20th	Night	11% 6% 2 6% 3 3 4 3 5% 7% 50%	2792
	21st to end	Night	14% 7% 2 7% 4 4 4 3 5% 7% 43%	2743
June	1st to 10th	Night	6% 4 2 6% 4 4 5% 4 6% 8% 52%	1520
	11th to 20th	Night	7% 4 1 6% 4 3 4 4 6% 10% 50%	1520
	21st to end	Night	5% 4 2 5% 3 3 4 4 7% 9% 54%	1520
July	1st to 10th	Night	8% 5% 2 5% 4 3 4 3 6% 9% 50%	2530
	11th to 20th	Night	5% 2 1 3 2 3 3 3 5% 8% 66%	2815
	21st to end	Night	3 3 1 5% 3 4 5% 4 7% 9% 57%	3098
August	1st to 10th	Night	5% 4 2 5% 3 4 4 3 6% 9% 54%	2836
	11th to 20th	Night	10% 6% 2 5% 3 3 3 3 5% 7% 53%	2798
	21st to end	Night	8% 5% 2 5% 3 4 3 3 5% 7% 55%	3250
September	1st to 10th	Night	9% 4 1 4 3 3 3 3 4 7% 59%	1900
	11th to 20th	Night	9% 4 1 4 4 3 4 4 5% 7% 56%	2089
	21st to end	Night	10% 5% 1 4 3 3 3 3 5% 5% 58%	2090
October	1st to 10th	Night	13% 7% 2 5% 2 2 3 2 5% 6% 52%	2256
	11th to 20th	Night	14% 7% 3 5% 2 3 3 2 4 5% 52%	2280
	21st to end	Night	15% 8% 2 6% 3 3 3 3 3 6% 49%	2508
November	1st to 10th	Night	9% 5% 2 5% 3 3 3 4 5% 6% 54%	2487
	11th to 20th	Night	9% 8% 2 7% 4 4 3 4 6% 6% 47%	2782
	21st to end	Night	12% 10% 3 6% 4 3 3 3 4 6% 46%	2800
December	1st to 10th	Night	5% 7% 3 9% 6% 4 4 4 5% 8% 46%	4580
	11th to 20th	Night	10% 9% 4 11% 7% 5% 4 4 5% 6% 35%	5199
	21st to end	Night	17% 13% 5% 13% 6% 4 4 3 4 5% 27%	6996

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	64% 4 10% 16% 6%	3894
	11th to 20th	Day	52% 3 11% 19% 13% 2	4080
	21st to end	Day	54% 4 13% 20% 8% 1	4488
February	1st to 10th	Day	55% 5% 11% 18% 10% 1	1800
	11th to 20th	Day	50% 4 10% 20% 14% 2	1763
	21st to end	Day	48% 6% 9% 22% 11% 4	1613
March	1st to 10th	Day	43% 3 8% 29% 15% 2	3544
	11th to 20th	Day	39% 5% 10% 28% 14% 3	3590
	21st to end	Day	64% 7% 11% 13% 4 1	3880
April	1st to 10th	Day	47% 5% 12% 25% 11% 1	2190
	11th to 20th	Day	49% 5% 11% 21% 12% 2	2326
	21st to end	Day	50% 5% 9% 22% 13%	2470
May	1st to 10th	Day	49% 7% 12% 19% 12% 1	4120
	11th to 20th	Day	41% 6% 9% 28% 15% 1	4113
	21st to end	Day	41% 7% 12% 23% 16% 1	4837
June	1st to 10th	Day	36% 6% 16% 28% 12% 2	2660
	11th to 20th	Day	34% 7% 15% 27% 16% 2	2660
	21st to end	Day	33% 7% 16% 28% 13% 3	2660
July	1st to 10th	Day	38% 8% 15% 29% 9% 2	4371
	11th to 20th	Day	26% 5% 15% 32% 20% 3	4067
	21st to end	Day	24% 9% 18% 27% 20% 2	4325
August	1st to 10th	Day	36% 7% 13% 28% 15% 1	4090
	11th to 20th	Day	44% 5% 10% 30% 11% 1	4080
	21st to end	Day	32% 8% 15% 25% 18% 3	4410
September	1st to 10th	Day	32% 5% 11% 28% 20% 3	2278
	11th to 20th	Day	30% 4 14% 33% 17% 2	2090
	21st to end	Day	28% 4 12% 30% 24% 1	2090
October	1st to 10th	Day	22% 3 6% 26% 41% 2	3165
	11th to 20th	Day	24% 3 13% 31% 22% 7%	3140
	21st to end	Day	38% 4 8% 28% 19% 4	3428
November	1st to 10th	Day	36% 4 16% 23% 19% 2	1811
	11th to 20th	Day	44% 3 12% 24% 16% 1	1615
	21st to end	Day	42% 3 15% 26% 13% 1	1600
December	1st to 10th	Day	37% 4 16% 30% 11% 1	2610
	11th to 20th	Day	49% 5% 17% 20% 8%	3005
	21st to end	Day	61% 5% 10% 17% 7% 1	3982
January	1st to 10th	Night	63% 4 10% 13% 9% 1	6054
	11th to 20th	Night	47% 5% 13% 17% 16% 2	5900
	21st to end	Night	52% 3 11% 19% 14% 1	6490
February	1st to 10th	Night	51% 4 11% 21% 11% 2	2600
	11th to 20th	Night	45% 4 11% 23% 14% 3	2534
	21st to end	Night	42% 4 11% 22% 19% 3	2035
March	1st to 10th	Night	37% 3 8% 29% 20% 2	3530
	11th to 20th	Night	33% 5% 9% 34% 16% 4	3590
	21st to end	Night	58% 8% 15% 13% 4 1	3889
April	1st to 10th	Night	41% 4 12% 25% 16% 2	1989
	11th to 20th	Night	42% 4 12% 22% 18% 2	1801
	21st to end	Night	45% 5% 12% 23% 14% 1	1710
May	1st to 10th	Night	41% 5% 12% 23% 17% 2	2850
	11th to 20th	Night	34% 7% 11% 25% 18% 5%	2793
	21st to end	Night	41% 6% 13% 22% 16% 3	2751
June	1st to 10th	Night	29% 7% 14% 31% 15% 4	1520
	11th to 20th	Night	28% 7% 14% 26% 21% 4	1520
	21st to end	Night	25% 8% 15% 31% 18% 3	1520
July	1st to 10th	Night	30% 6% 17% 32% 13% 2	2490
	11th to 20th	Night	18% 5% 18% 35% 22% 3	2763
	21st to end	Night	22% 9% 16% 32% 20% 2	2999
August	1st to 10th	Night	26% 6% 16% 34% 16% 2	2826
	11th to 20th	Night	31% 5% 16% 29% 16% 2	2825
	21st to end	Night	28% 6% 16% 26% 19% 6%	3250
September	1st to 10th	Night	26% 4 12% 31% 24% 4	1900
	11th to 20th	Night	27% 5% 12% 33% 21% 2	2089
	21st to end	Night	28% 3 10% 31% 24% 4	2090
October	1st to 10th	Night	21% 2 6% 22% 46% 3	3763
	11th to 20th	Night	26% 3 11% 27% 27% 6%	3779
	21st to end	Night	37% 3 10% 30% 18% 1	4120
November	1st to 10th	Night	30% 5% 17% 24% 21% 3	2487
	11th to 20th	Night	37% 4 13% 27% 17% 2	2782
	21st to end	Night	40% 4 11% 29% 14% 2	2800
December	1st to 10th	Night	37% 4 12% 36% 11%	4580
	11th to 20th	Night	49% 5% 14% 25% 7%	5201
	21st to end	Night	60% 4 10% 19% 7%	6996

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% 14% 35% 25% 8%	300
	11th to 20th	Day	18% 14% 42% 23% 3 1	300
	21st to end	Day	17% 11% 43% 23% 5% 1	330
February	1st to 10th	Day	18% 16% 41% 23% 2	300
	11th to 20th	Day	16% 18% 39% 22% 5% 1	300
	21st to end	Day	21% 16% 41% 20% 3	249
March	1st to 10th	Day	19% 15% 43% 18% 4 1	300
	11th to 20th	Day	24% 13% 36% 21% 6%	300
	21st to end	Day	35% 14% 34% 14% 3	315
April	1st to 10th	Day	25% 16% 37% 19% 3	370
	11th to 20th	Day	27% 13% 33% 20% 7% 1	524
	21st to end	Day	27% 13% 30% 21% 7% 2	650
May	1st to 10th	Day	24% 12% 31% 23% 8% 1	653
	11th to 20th	Day	21% 11% 29% 23% 12% 3	675
	21st to end	Day	19% 7% 31% 29% 13% 2	734
June	1st to 10th	Day	8% 6% 27% 35% 21% 3	680
	11th to 20th	Day	10% 8% 33% 30% 15% 3	680
	21st to end	Day	9% 8% 34% 31% 15% 3	680
July	1st to 10th	Day	9% 3 19% 35% 25% 8%	671
	11th to 20th	Day	7% 3 28% 39% 16% 7%	668
	21st to end	Day	6% 3 23% 38% 26% 4	739
August	1st to 10th	Day	9% 3 22% 38% 24% 4	676
	11th to 20th	Day	12% 3 23% 35% 22% 4	665
	21st to end	Day	10% 4 21% 40% 19% 5%	679
September	1st to 10th	Day	13% 4 26% 35% 17% 5%	488
	11th to 20th	Day	7% 7% 36% 30% 16% 4	300
	21st to end	Day	12% 7% 37% 29% 12% 2	300
October	1st to 10th	Day	18% 9% 29% 26% 14% 4	300
	11th to 20th	Day	16% 17% 39% 22% 5% 2	300
	21st to end	Day	21% 16% 35% 21% 6% 1	330
November	1st to 10th	Day	18% 14% 39% 19% 7% 2	300
	11th to 20th	Day	20% 19% 37% 19% 5%	300
	21st to end	Day	20% 17% 34% 22% 6%	300
December	1st to 10th	Day	11% 15% 41% 26% 7% 1	300
	11th to 20th	Day	16% 18% 38% 22% 6% 1	300
	21st to end	Day	25% 16% 38% 18% 2	330
January	1st to 10th	Night	13% 15% 38% 29% 5% 1	1000
	11th to 20th	Night	15% 14% 40% 25% 6% 1	1000
	21st to end	Night	19% 9% 42% 26% 5%	1100
February	1st to 10th	Night	16% 10% 44% 26% 4	1000
	11th to 20th	Night	16% 11% 44% 24% 5%	979
	21st to end	Night	14% 12% 46% 23% 5% 1	715
March	1st to 10th	Night	18% 12% 38% 25% 6% 1	601
	11th to 20th	Night	19% 10% 38% 26% 7%	600
	21st to end	Night	25% 10% 35% 24% 5% 1	647
April	1st to 10th	Night	18% 15% 41% 23% 4	570
	11th to 20th	Night	20% 12% 37% 24% 7%	563
	21st to end	Night	22% 11% 32% 26% 8%	570
May	1st to 10th	Night	20% 7% 35% 30% 8%	570
	11th to 20th	Night	17% 8% 30% 35% 10%	561
	21st to end	Night	16% 6% 33% 33% 12%	617
June	1st to 10th	Night	8% 4 27% 46% 16% 1	570
	11th to 20th	Night	9% 4 34% 39% 13% 1	570
	21st to end	Night	6% 6% 32% 41% 15%	570
July	1st to 10th	Night	6% 3 18% 46% 25% 1	555
	11th to 20th	Night	5% 1 22% 49% 21% 2	552
	21st to end	Night	4 2 17% 52% 24% 1	624
August	1st to 10th	Night	9% 2 20% 44% 23% 2	567
	11th to 20th	Night	12% 3 21% 41% 22% 2	564
	21st to end	Night	8% 2 23% 45% 19% 3	627
September	1st to 10th	Night	11% 4 24% 39% 20% 2	570
	11th to 20th	Night	10% 2 32% 40% 14% 2	570
	21st to end	Night	13% 5% 34% 34% 14% 1	570
October	1st to 10th	Night	16% 8% 30% 33% 11% 2	736
	11th to 20th	Night	19% 10% 37% 28% 5%	760
	21st to end	Night	21% 12% 30% 28% 8%	836
November	1st to 10th	Night	12% 12% 38% 29% 8%	927
	11th to 20th	Night	14% 14% 42% 24% 5%	1000
	21st to end	Night	18% 11% 37% 26% 8%	1000
December	1st to 10th	Night	14% 13% 39% 28% 5%	1000
	11th to 20th	Night	17% 10% 39% 27% 5%	1000
	21st to end	Night	20% 13% 37% 25% 4	1100

Page generated at 2025-03-24 08:04:32. Version ac07

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