Stillwater
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stillwater clear sky chart from 2005-11-06 to 2026-02-16.

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% 6% 2 5% 4 3 4 3 5% 7% 52%	131297
	Night	10% 5% 2 4 3 3 3 3 5% 7% 56%	129852
Transparency	Day	32% 4 10% 26% 23% 6%	134988
	Night	29% 3 9% 26% 25% 8%	134225
Seeing	Day	12% 8% 27% 30% 18% 4	17116
	Night	12% 8% 32% 35% 13% 1	27126

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	9% 6% 3 7% 4 3 4 3 5% 6% 50%	5289
	11th to 20th	Day	6% 6% 2 5% 3 2 3 2 4 5% 63%	5310
	21st to end	Day	14% 9% 4 5% 2 2 2 2 3 5% 51%	5812
February	1st to 10th	Day	12% 10% 3 7% 4 3 3 2 4 6% 46%	1923
	11th to 20th	Day	12% 6% 2 6% 4 4 3 3 4 5% 50%	1999
	21st to end	Day	10% 9% 3 5% 3 3 3 3 4 6% 50%	1650
March	1st to 10th	Day	11% 6% 2 4 3 3 3 2 3 5% 58%	4886
	11th to 20th	Day	7% 5% 2 6% 3 4 4 3 5% 6% 55%	4980
	21st to end	Day	12% 9% 3 7% 5% 4 4 3 5% 7% 42%	5462
April	1st to 10th	Day	11% 5% 2 5% 4 3 4 4 6% 6% 51%	2200
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 4 5% 7% 46%	2381
	21st to end	Day	16% 7% 2 5% 3 4 4 4 5% 6% 44%	2600
May	1st to 10th	Day	18% 8% 2 6% 4 3 4 3 5% 5% 42%	5862
	11th to 20th	Day	10% 5% 2 5% 4 3 4 4 5% 7% 51%	5862
	21st to end	Day	15% 7% 3 7% 5% 5% 4 4 5% 6% 39%	6434
June	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 6% 11% 50%	2600
	11th to 20th	Day	7% 4 1 5% 4 5% 4 4 7% 9% 50%	2600
	21st to end	Day	5% 3 1 3 3 3 5% 4 6% 7% 59%	2600
July	1st to 10th	Day	7% 5% 2 7% 5% 5% 5% 5% 6% 9% 44%	5900
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 6% 9% 53%	5900
	21st to end	Day	4 3 1 4 3 4 5% 4 7% 10% 56%	6422
August	1st to 10th	Day	5% 3 1 5% 4 4 4 4 7% 8% 55%	4234
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 7% 8% 52%	4171
	21st to end	Day	5% 3 1 4 3 4 4 3 5% 7% 60%	4431
September	1st to 10th	Day	10% 4 2 5% 3 4 3 3 5% 7% 55%	2200
	11th to 20th	Day	11% 5% 2 6% 4 5% 4 3 6% 7% 48%	2200
	21st to end	Day	8% 4 2 4 3 4 4 3 4 6% 58%	2200
October	1st to 10th	Day	7% 4 2 5% 3 3 3 3 4 7% 60%	2130
	11th to 20th	Day	10% 3 1 3 2 2 3 2 3 4 67%	2000
	21st to end	Day	13% 5% 1 4 3 3 3 2 4 4 57%	2200
November	1st to 10th	Day	9% 4 1 3 3 2 3 4 3 6% 62%	1981
	11th to 20th	Day	8% 4 1 4 2 2 3 2 4 5% 64%	1890
	21st to end	Day	12% 6% 2 4 3 2 3 2 5% 5% 58%	1890
December	1st to 10th	Day	7% 6% 2 5% 3 3 2 3 3 6% 60%	3030
	11th to 20th	Day	9% 5% 2 5% 3 2 3 3 4 5% 59%	3481
	21st to end	Day	17% 10% 3 7% 4 4 4 3 4 5% 41%	4587
January	1st to 10th	Night	13% 6% 2 6% 3 3 3 3 5% 6% 50%	7634
	11th to 20th	Night	4 3 1 4 3 3 4 3 4 6% 66%	7680
	21st to end	Night	16% 7% 2 5% 3 3 3 2 4 5% 50%	8402
February	1st to 10th	Night	13% 8% 3 5% 3 4 3 3 4 6% 49%	2714
	11th to 20th	Night	13% 7% 3 5% 3 3 3 3 5% 6% 50%	2398
	21st to end	Night	10% 7% 2 6% 3 3 3 3 4 5% 54%	1980
March	1st to 10th	Night	10% 7% 2 5% 3 3 3 2 4 5% 56%	4969
	11th to 20th	Night	7% 4 1 4 2 2 3 2 4 6% 66%	4980
	21st to end	Night	11% 6% 2 5% 4 3 4 4 5% 7% 50%	5467
April	1st to 10th	Night	11% 5% 1 4 3 4 4 3 5% 6% 55%	2200
	11th to 20th	Night	14% 5% 2 4 3 2 3 2 5% 6% 53%	1963
	21st to end	Night	13% 6% 2 5% 3 2 3 3 6% 7% 49%	1800
May	1st to 10th	Night	17% 7% 2 5% 4 3 3 2 4 6% 46%	4053
	11th to 20th	Night	10% 5% 2 5% 4 3 3 4 6% 7% 52%	4053
	21st to end	Night	13% 5% 1 4 3 3 3 3 5% 8% 51%	4443
June	1st to 10th	Night	6% 4 2 4 3 4 4 4 5% 9% 55%	1800
	11th to 20th	Night	6% 3 1 4 4 3 3 5% 7% 8% 57%	1800
	21st to end	Night	3 2 1 3 3 3 3 3 5% 10% 63%	1800
July	1st to 10th	Night	5% 4 1 5% 4 4 5% 4 7% 11% 49%	4078
	11th to 20th	Night	4 3 1 4 3 3 4 3 6% 10% 58%	4077
	21st to end	Night	5% 2 1 2 2 3 3 3 5% 10% 64%	4449
August	1st to 10th	Night	2 2 1 4 3 3 4 4 6% 9% 61%	2926
	11th to 20th	Night	5% 3 2 5% 5% 5% 5% 4 6% 9% 53%	2888
	21st to end	Night	3 3 1 3 3 3 4 3 5% 8% 64%	3456
September	1st to 10th	Night	8% 4 1 5% 3 3 3 3 4 7% 60%	2200
	11th to 20th	Night	10% 5% 3 4 3 4 4 4 5% 6% 53%	2200
	21st to end	Night	7% 4 1 4 3 3 3 3 5% 6% 61%	2200
October	1st to 10th	Night	7% 3 1 4 3 4 4 2 4 6% 64%	2249
	11th to 20th	Night	9% 4 1 4 2 2 2 2 4 5% 65%	2400
	21st to end	Night	14% 4 1 3 2 2 2 2 3 4 62%	2640
November	1st to 10th	Night	8% 4 1 3 2 2 3 2 4 5% 66%	2534
	11th to 20th	Night	9% 4 2 4 3 3 2 2 3 4 63%	2730
	21st to end	Night	13% 6% 2 4 3 2 2 2 4 6% 56%	2730
December	1st to 10th	Night	6% 5% 1 4 3 3 3 2 4 6% 64%	4380
	11th to 20th	Night	11% 5% 2 4 3 3 3 2 3 5% 58%	4946
	21st to end	Night	16% 8% 2 5% 3 3 3 3 3 5% 50%	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	37% 2 8% 29% 20% 4	5290
	11th to 20th	Day	26% 2 8% 25% 31% 8%	5310
	21st to end	Day	39% 2 5% 22% 28% 4	5812
February	1st to 10th	Day	41% 3 9% 24% 18% 5%	1923
	11th to 20th	Day	37% 3 8% 28% 19% 4	2009
	21st to end	Day	36% 3 6% 22% 23% 10%	1650
March	1st to 10th	Day	31% 2 5% 19% 22% 21%	4886
	11th to 20th	Day	30% 4 8% 18% 23% 17%	4980
	21st to end	Day	42% 4 9% 29% 13% 2	5464
April	1st to 10th	Day	33% 6% 10% 25% 20% 6%	2200
	11th to 20th	Day	37% 5% 11% 21% 19% 7%	2381
	21st to end	Day	41% 6% 10% 24% 18% 2	2600
May	1st to 10th	Day	45% 4 11% 20% 18% 3	5900
	11th to 20th	Day	32% 6% 10% 22% 22% 8%	5866
	21st to end	Day	46% 5% 10% 16% 18% 5%	6447
June	1st to 10th	Day	29% 8% 16% 27% 17% 4	2600
	11th to 20th	Day	29% 6% 15% 26% 20% 5%	2600
	21st to end	Day	23% 6% 14% 27% 24% 6%	2600
July	1st to 10th	Day	37% 3 15% 23% 18% 4	5836
	11th to 20th	Day	29% 3 11% 30% 24% 2	5831
	21st to end	Day	23% 3 17% 36% 19% 1	6240
August	1st to 10th	Day	26% 4 12% 28% 25% 6%	4220
	11th to 20th	Day	29% 4 17% 29% 18% 2	4210
	21st to end	Day	24% 4 12% 40% 16% 4	4430
September	1st to 10th	Day	29% 5% 9% 25% 23% 10%	2200
	11th to 20th	Day	34% 6% 9% 24% 22% 5%	2200
	21st to end	Day	27% 4 8% 23% 30% 7%	2200
October	1st to 10th	Day	18% 2 6% 15% 44% 14%	3468
	11th to 20th	Day	16% 1 5% 25% 38% 15%	3240
	21st to end	Day	25% 2 6% 29% 30% 7%	3538
November	1st to 10th	Day	25% 3 8% 25% 30% 9%	1981
	11th to 20th	Day	24% 3 8% 28% 27% 10%	1890
	21st to end	Day	30% 2 8% 28% 25% 7%	1890
December	1st to 10th	Day	28% 2 5% 39% 23% 2	3030
	11th to 20th	Day	29% 2 5% 28% 29% 6%	3479
	21st to end	Day	46% 3 8% 25% 15% 4	4587
January	1st to 10th	Night	36% 2 8% 29% 22% 3	7635
	11th to 20th	Night	21% 3 8% 23% 34% 10%	7680
	21st to end	Night	39% 1 6% 20% 28% 5%	8402
February	1st to 10th	Night	37% 4 9% 24% 20% 6%	2714
	11th to 20th	Night	35% 4 9% 26% 20% 6%	2398
	21st to end	Night	34% 3 6% 19% 27% 11%	1980
March	1st to 10th	Night	33% 3 5% 18% 25% 17%	4969
	11th to 20th	Night	22% 3 5% 23% 24% 24%	4980
	21st to end	Night	34% 4 10% 32% 17% 2	5467
April	1st to 10th	Night	30% 5% 10% 21% 23% 11%	2200
	11th to 20th	Night	32% 4 9% 25% 21% 9%	1963
	21st to end	Night	34% 4 12% 24% 23% 4	1800
May	1st to 10th	Night	40% 4 12% 18% 21% 4	4080
	11th to 20th	Night	31% 5% 11% 21% 23% 9%	4054
	21st to end	Night	32% 5% 14% 23% 19% 6%	4452
June	1st to 10th	Night	25% 7% 17% 30% 17% 4	1800
	11th to 20th	Night	23% 5% 15% 32% 19% 5%	1800
	21st to end	Night	19% 4 15% 30% 24% 8%	1800
July	1st to 10th	Night	29% 3 19% 29% 16% 3	4035
	11th to 20th	Night	22% 3 10% 35% 28% 3	4026
	21st to end	Night	19% 2 15% 38% 24% 2	4320
August	1st to 10th	Night	19% 4 14% 29% 25% 8%	2916
	11th to 20th	Night	28% 4 12% 32% 20% 3	2915
	21st to end	Night	20% 4 12% 39% 20% 5%	3456
September	1st to 10th	Night	27% 3 9% 26% 24% 12%	2200
	11th to 20th	Night	31% 5% 8% 23% 25% 8%	2200
	21st to end	Night	25% 4 7% 25% 31% 8%	2200
October	1st to 10th	Night	16% 3 6% 13% 41% 22%	3678
	11th to 20th	Night	17% 1 4 22% 37% 18%	3899
	21st to end	Night	23% 2 5% 28% 32% 10%	4252
November	1st to 10th	Night	23% 3 9% 23% 32% 11%	2534
	11th to 20th	Night	27% 3 7% 26% 28% 10%	2730
	21st to end	Night	31% 3 8% 23% 27% 8%	2730
December	1st to 10th	Night	24% 3 8% 39% 23% 3	4380
	11th to 20th	Night	31% 2 5% 26% 28% 8%	4947
	21st to end	Night	39% 3 7% 27% 20% 5%	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	15% 13% 37% 28% 7% 1	330
	11th to 20th	Day	18% 17% 37% 23% 5%	330
	21st to end	Day	14% 14% 40% 26% 6% 1	363
February	1st to 10th	Day	17% 16% 38% 22% 5%	330
	11th to 20th	Day	16% 17% 43% 20% 3	315
	21st to end	Day	19% 16% 42% 20% 3	249
March	1st to 10th	Day	17% 16% 40% 20% 6% 1	300
	11th to 20th	Day	20% 17% 41% 18% 4	300
	21st to end	Day	18% 19% 40% 16% 7%	330
April	1st to 10th	Day	18% 18% 36% 19% 9%	300
	11th to 20th	Day	17% 15% 43% 21% 4	499
	21st to end	Day	22% 13% 34% 21% 8% 2	700
May	1st to 10th	Day	15% 12% 36% 28% 9% 1	703
	11th to 20th	Day	15% 9% 31% 30% 12% 3	725
	21st to end	Day	18% 6% 31% 25% 16% 4	789
June	1st to 10th	Day	7% 3 20% 41% 23% 6%	730
	11th to 20th	Day	8% 3 25% 40% 22% 3	730
	21st to end	Day	4 2 23% 44% 21% 5%	730
July	1st to 10th	Day	8% 2 13% 33% 32% 11%	721
	11th to 20th	Day	4 1 12% 38% 38% 7%	718
	21st to end	Day	6% 1 8% 37% 36% 12%	794
August	1st to 10th	Day	6% 2 13% 43% 31% 5%	726
	11th to 20th	Day	8% 2 13% 35% 33% 9%	715
	21st to end	Day	8% 1 10% 31% 41% 10%	663
September	1st to 10th	Day	8% 2 10% 33% 36% 10%	330
	11th to 20th	Day	5% 2 16% 39% 29% 8%	330
	21st to end	Day	11% 4 19% 37% 22% 7%	330
October	1st to 10th	Day	7% 5% 28% 35% 18% 8%	330
	11th to 20th	Day	9% 10% 37% 30% 13% 1	330
	21st to end	Day	20% 9% 34% 24% 11% 2	363
November	1st to 10th	Day	13% 8% 38% 27% 12% 2	330
	11th to 20th	Day	14% 11% 39% 22% 12% 2	330
	21st to end	Day	19% 11% 40% 22% 7% 2	330
December	1st to 10th	Day	13% 12% 42% 23% 10% 1	330
	11th to 20th	Day	16% 11% 39% 25% 8% 2	330
	21st to end	Day	17% 16% 37% 27% 4	363
January	1st to 10th	Night	13% 11% 40% 29% 7%	1050
	11th to 20th	Night	12% 14% 38% 30% 6%	1050
	21st to end	Night	14% 11% 38% 32% 6%	1155
February	1st to 10th	Night	17% 12% 39% 27% 4	1034
	11th to 20th	Night	17% 14% 39% 26% 4	804
	21st to end	Night	14% 12% 40% 30% 3	660
March	1st to 10th	Night	12% 11% 40% 34% 3	626
	11th to 20th	Night	19% 11% 36% 30% 4	600
	21st to end	Night	17% 13% 41% 24% 5%	660
April	1st to 10th	Night	15% 13% 42% 26% 4 1	600
	11th to 20th	Night	15% 13% 42% 25% 5%	593
	21st to end	Night	15% 12% 40% 26% 7% 1	600
May	1st to 10th	Night	14% 8% 40% 31% 7%	600
	11th to 20th	Night	13% 7% 31% 32% 15% 1	591
	21st to end	Night	11% 5% 30% 35% 16% 2	650
June	1st to 10th	Night	8% 4 22% 43% 22% 1	600
	11th to 20th	Night	7% 2 30% 46% 15%	600
	21st to end	Night	4 2 28% 50% 16% 2	600
July	1st to 10th	Night	6% 1 15% 43% 32% 3	585
	11th to 20th	Night	3 1 13% 50% 31% 3	582
	21st to end	Night	5% 1 11% 47% 34% 1	657
August	1st to 10th	Night	3 1 13% 52% 29% 2	597
	11th to 20th	Night	5% 1 12% 48% 31% 2	594
	21st to end	Night	3 1 11% 41% 40% 3	660
September	1st to 10th	Night	10% 1 14% 45% 28% 3	600
	11th to 20th	Night	13% 1 20% 38% 24% 4	600
	21st to end	Night	8% 3 22% 43% 22% 3	600
October	1st to 10th	Night	8% 3 28% 37% 22% 2	649
	11th to 20th	Night	10% 6% 39% 35% 10%	800
	21st to end	Night	17% 10% 31% 30% 12% 1	880
November	1st to 10th	Night	11% 5% 38% 34% 11% 1	894
	11th to 20th	Night	11% 11% 36% 32% 9%	1050
	21st to end	Night	16% 12% 32% 31% 9%	1050
December	1st to 10th	Night	12% 10% 37% 33% 7%	1050
	11th to 20th	Night	17% 10% 38% 30% 5%	1050
	21st to end	Night	15% 12% 35% 32% 6%	1155

Page generated at 2026-02-13 00:42:11. Version ac07

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