Winnerwood Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Winnerwood Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	17% 11% 4 9% 5% 5% 4 4 5% 7% 31%	126706
	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 31%	123948
Transparency	Day	52% 5% 11% 20% 10% 1	130311
	Night	53% 5% 10% 19% 11% 1	128412
Seeing	Day	23% 13% 27% 21% 12% 4	16022
	Night	23% 10% 26% 28% 12% 1	25736

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	17% 20% 8% 21% 5% 4 3 2 3 4 15%	4056
	11th to 20th	Day	13% 24% 8% 17% 9% 5% 3 2 3 3 14%	4060
	21st to end	Day	23% 21% 7% 13% 7% 4 3 3 4 4 14%	4466
February	1st to 10th	Day	20% 18% 6% 12% 7% 4 3 2 3 3 22%	1800
	11th to 20th	Day	18% 15% 6% 14% 6% 4 4 3 4 6% 20%	1753
	21st to end	Day	20% 15% 5% 11% 5% 4 3 4 4 5% 24%	1644
March	1st to 10th	Day	18% 13% 6% 10% 5% 3 3 3 4 6% 30%	4935
	11th to 20th	Day	13% 10% 5% 8% 5% 5% 4 3 4 6% 36%	4980
	21st to end	Day	21% 11% 4 9% 5% 4 4 3 5% 5% 30%	5465
April	1st to 10th	Day	17% 13% 3 7% 5% 4 4 3 6% 7% 30%	2291
	11th to 20th	Day	19% 11% 3 7% 5% 4 4 4 5% 7% 32%	2446
	21st to end	Day	20% 10% 3 7% 4 4 4 3 5% 5% 35%	2600
May	1st to 10th	Day	22% 9% 3 8% 5% 5% 5% 4 6% 6% 28%	5862
	11th to 20th	Day	19% 8% 3 7% 5% 4 5% 4 6% 8% 31%	5861
	21st to end	Day	19% 7% 2 6% 4 4 6% 4 6% 7% 33%	6789
June	1st to 10th	Day	16% 7% 2 8% 5% 5% 5% 4 6% 9% 34%	2800
	11th to 20th	Day	16% 8% 2 6% 5% 5% 6% 5% 5% 9% 34%	2800
	21st to end	Day	14% 5% 2 5% 6% 5% 5% 5% 7% 9% 38%	2800
July	1st to 10th	Day	9% 6% 3 7% 4 5% 5% 5% 7% 9% 40%	6144
	11th to 20th	Day	12% 6% 2 7% 6% 5% 6% 4 8% 9% 35%	5900
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	6424
August	1st to 10th	Day	15% 7% 3 7% 6% 5% 6% 4 6% 9% 31%	4234
	11th to 20th	Day	14% 5% 3 7% 5% 5% 6% 5% 6% 9% 35%	4174
	21st to end	Day	9% 5% 2 7% 5% 6% 6% 5% 6% 9% 40%	4490
September	1st to 10th	Day	15% 6% 2 5% 4 4 4 4 5% 6% 45%	2381
	11th to 20th	Day	11% 5% 2 5% 4 5% 5% 4 5% 8% 46%	2200
	21st to end	Day	19% 9% 3 7% 4 5% 4 3 5% 7% 35%	2200
October	1st to 10th	Day	16% 6% 2 6% 4 4 4 5% 5% 8% 40%	2013
	11th to 20th	Day	20% 9% 3 7% 5% 5% 4 3 5% 6% 34%	2000
	21st to end	Day	24% 11% 3 7% 4 4 5% 3 4 6% 30%	2200
November	1st to 10th	Day	12% 8% 3 7% 5% 5% 4 3 5% 6% 42%	1932
	11th to 20th	Day	18% 17% 4 7% 5% 4 3 4 4 6% 28%	1760
	21st to end	Day	18% 18% 6% 8% 4 4 4 3 5% 5% 23%	1680
December	1st to 10th	Day	21% 17% 9% 13% 4 3 4 3 4 4 18%	2616
	11th to 20th	Day	24% 19% 7% 9% 4 3 3 3 4 4 21%	2990
	21st to end	Day	25% 22% 6% 12% 5% 4 4 3 4 5% 11%	3960
January	1st to 10th	Night	15% 19% 8% 22% 5% 4 3 3 3 4 14%	5889
	11th to 20th	Night	14% 20% 9% 16% 8% 5% 4 3 3 4 14%	5900
	21st to end	Night	24% 17% 7% 12% 6% 4 4 2 3 4 17%	6490
February	1st to 10th	Night	21% 16% 5% 11% 6% 4 4 3 4 5% 21%	2600
	11th to 20th	Night	18% 15% 5% 13% 5% 6% 4 3 5% 5% 22%	2533
	21st to end	Night	20% 13% 5% 11% 5% 5% 4 3 3 5% 24%	1981
March	1st to 10th	Night	22% 12% 4 10% 5% 3 3 2 3 5% 30%	4918
	11th to 20th	Night	15% 10% 4 6% 4 3 4 3 5% 6% 39%	4980
	21st to end	Night	19% 11% 3 8% 4 5% 4 3 4 4 35%	5467
April	1st to 10th	Night	19% 12% 4 7% 5% 4 4 3 5% 6% 32%	2107
	11th to 20th	Night	17% 10% 3 7% 4 4 4 4 5% 7% 34%	1919
	21st to end	Night	16% 10% 3 6% 5% 4 5% 4 5% 7% 36%	1800
May	1st to 10th	Night	27% 10% 3 8% 4 4 4 3 4 7% 26%	4033
	11th to 20th	Night	17% 9% 3 6% 4 4 4 3 5% 7% 38%	4032
	21st to end	Night	19% 6% 2 6% 4 3 4 4 6% 9% 37%	4061
June	1st to 10th	Night	11% 4 3 7% 4 5% 5% 3 7% 8% 43%	1600
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 4 6% 8% 43%	1600
	21st to end	Night	10% 5% 2 6% 5% 5% 6% 4 7% 8% 42%	1600
July	1st to 10th	Night	11% 7% 2 7% 5% 5% 5% 3 5% 8% 42%	3782
	11th to 20th	Night	11% 5% 2 6% 5% 5% 6% 4 6% 10% 39%	4057
	21st to end	Night	9% 5% 3 6% 4 5% 4 3 6% 8% 46%	4427
August	1st to 10th	Night	12% 8% 3 8% 5% 4 6% 3 5% 7% 39%	2915
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 6% 45%	2875
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 4 6% 9% 44%	3373
September	1st to 10th	Night	14% 5% 2 5% 3 4 3 3 5% 6% 50%	2015
	11th to 20th	Night	10% 5% 1 4 3 3 4 3 6% 9% 52%	2200
	21st to end	Night	17% 8% 2 6% 4 4 5% 3 5% 6% 39%	2200
October	1st to 10th	Night	15% 6% 2 5% 4 4 4 3 4 7% 47%	2385
	11th to 20th	Night	17% 7% 2 7% 5% 4 5% 3 5% 7% 38%	2400
	21st to end	Night	24% 8% 2 6% 4 4 4 3 4 6% 36%	2640
November	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 4 7% 42%	2581
	11th to 20th	Night	18% 14% 3 8% 5% 5% 4 3 5% 5% 29%	2856
	21st to end	Night	21% 16% 4 7% 5% 4 4 3 4 5% 27%	2940
December	1st to 10th	Night	18% 18% 10% 12% 5% 4 4 3 4 5% 17%	4609
	11th to 20th	Night	21% 20% 7% 10% 4 4 3 3 4 5% 19%	5205
	21st to end	Night	24% 19% 6% 10% 5% 4 5% 3 4 5% 15%	6978

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	76% 4 7% 8% 5%	4057
	11th to 20th	Day	78% 3 6% 9% 3 1	4060
	21st to end	Day	75% 3 8% 9% 4	4466
February	1st to 10th	Day	69% 3 8% 13% 7%	1800
	11th to 20th	Day	67% 5% 8% 14% 7%	1762
	21st to end	Day	62% 5% 11% 14% 7% 1	1644
March	1st to 10th	Day	56% 4 12% 21% 7%	4935
	11th to 20th	Day	49% 5% 14% 23% 8% 2	4980
	21st to end	Day	55% 4 9% 19% 12% 1	5465
April	1st to 10th	Day	53% 5% 11% 18% 12% 1	2291
	11th to 20th	Day	51% 5% 10% 19% 12% 2	2446
	21st to end	Day	50% 5% 10% 21% 11% 2	2600
May	1st to 10th	Day	55% 6% 10% 17% 9% 4	5897
	11th to 20th	Day	51% 6% 11% 22% 10% 1	5865
	21st to end	Day	47% 7% 12% 21% 11% 3	6804
June	1st to 10th	Day	46% 6% 12% 23% 11% 1	2800
	11th to 20th	Day	45% 7% 14% 21% 12% 1	2800
	21st to end	Day	41% 7% 12% 25% 13% 1	2800
July	1st to 10th	Day	39% 6% 12% 27% 14% 2	6078
	11th to 20th	Day	43% 7% 12% 25% 12%	5831
	21st to end	Day	40% 6% 11% 24% 19% 1	6240
August	1st to 10th	Day	48% 7% 13% 22% 9%	4221
	11th to 20th	Day	43% 7% 12% 28% 9% 1	4213
	21st to end	Day	39% 7% 13% 27% 13% 2	4490
September	1st to 10th	Day	39% 6% 11% 23% 18% 3	2381
	11th to 20th	Day	36% 6% 14% 26% 17% 1	2200
	21st to end	Day	50% 5% 11% 22% 12% 1	2200
October	1st to 10th	Day	33% 4 11% 31% 20% 1	3273
	11th to 20th	Day	46% 5% 9% 22% 14% 4	3240
	21st to end	Day	41% 5% 12% 27% 15% 1	3538
November	1st to 10th	Day	43% 5% 12% 23% 17% 2	1932
	11th to 20th	Day	57% 4 10% 19% 8% 2	1760
	21st to end	Day	63% 4 11% 16% 6% 1	1680
December	1st to 10th	Day	71% 5% 11% 11% 3	2616
	11th to 20th	Day	68% 3 10% 13% 5%	2986
	21st to end	Day	77% 4 8% 9% 3	3960
January	1st to 10th	Night	76% 3 7% 10% 4	5889
	11th to 20th	Night	76% 3 9% 9% 3	5900
	21st to end	Night	74% 3 7% 11% 4 1	6490
February	1st to 10th	Night	66% 4 9% 17% 5%	2600
	11th to 20th	Night	65% 4 9% 16% 6%	2535
	21st to end	Night	63% 3 9% 15% 9% 1	1981
March	1st to 10th	Night	59% 4 11% 19% 8%	4918
	11th to 20th	Night	46% 4 14% 25% 8% 3	4980
	21st to end	Night	53% 4 10% 18% 14% 1	5467
April	1st to 10th	Night	53% 6% 8% 18% 13% 2	2107
	11th to 20th	Night	49% 5% 11% 18% 14% 3	1919
	21st to end	Night	46% 7% 11% 21% 13% 3	1800
May	1st to 10th	Night	58% 5% 9% 15% 9% 4	4060
	11th to 20th	Night	47% 5% 10% 24% 12% 1	4033
	21st to end	Night	44% 6% 12% 24% 12% 2	4068
June	1st to 10th	Night	38% 6% 13% 25% 16% 2	1600
	11th to 20th	Night	38% 6% 15% 23% 16% 2	1600
	21st to end	Night	37% 8% 13% 24% 17% 1	1600
July	1st to 10th	Night	41% 5% 9% 24% 19% 1	3740
	11th to 20th	Night	39% 7% 16% 25% 12% 1	4006
	21st to end	Night	36% 6% 12% 19% 26% 2	4297
August	1st to 10th	Night	45% 7% 11% 24% 12% 1	2904
	11th to 20th	Night	40% 5% 10% 30% 14% 1	2902
	21st to end	Night	36% 6% 12% 31% 13% 2	3373
September	1st to 10th	Night	34% 5% 12% 25% 19% 4	2015
	11th to 20th	Night	28% 6% 15% 27% 22% 1	2200
	21st to end	Night	45% 5% 12% 20% 17% 1	2200
October	1st to 10th	Night	35% 4 9% 27% 24% 1	3905
	11th to 20th	Night	39% 5% 12% 23% 14% 6%	3899
	21st to end	Night	37% 4 11% 29% 18% 2	4252
November	1st to 10th	Night	42% 4 12% 23% 15% 3	2581
	11th to 20th	Night	56% 4 9% 19% 9% 3	2856
	21st to end	Night	60% 4 11% 19% 5% 1	2940
December	1st to 10th	Night	71% 4 10% 12% 3	4609
	11th to 20th	Night	68% 4 10% 14% 3	5208
	21st to end	Night	72% 5% 10% 12% 2	6978

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	34% 24% 28% 10% 3 1	300
	11th to 20th	Day	34% 27% 28% 8% 3	300
	21st to end	Day	32% 24% 32% 9% 2	330
February	1st to 10th	Day	33% 20% 39% 7% 1	300
	11th to 20th	Day	37% 24% 30% 8% 1	300
	21st to end	Day	36% 22% 34% 8%	256
March	1st to 10th	Day	30% 19% 31% 17% 3	500
	11th to 20th	Day	33% 15% 32% 14% 5% 1	500
	21st to end	Day	34% 18% 28% 16% 4 1	550
April	1st to 10th	Day	31% 18% 28% 15% 7% 1	500
	11th to 20th	Day	28% 15% 26% 19% 9% 3	492
	21st to end	Day	30% 12% 30% 19% 7% 1	500
May	1st to 10th	Day	30% 15% 26% 18% 8% 3	503
	11th to 20th	Day	23% 12% 30% 20% 11% 3	527
	21st to end	Day	18% 10% 24% 26% 16% 6%	573
June	1st to 10th	Day	16% 10% 31% 26% 11% 5%	530
	11th to 20th	Day	20% 8% 26% 28% 14% 4	530
	21st to end	Day	14% 10% 30% 27% 16% 4	530
July	1st to 10th	Day	11% 5% 19% 31% 22% 11%	525
	11th to 20th	Day	15% 4 26% 24% 23% 8%	524
	21st to end	Day	13% 5% 23% 29% 20% 10%	576
August	1st to 10th	Day	13% 6% 20% 30% 23% 9%	526
	11th to 20th	Day	15% 6% 20% 29% 19% 11%	519
	21st to end	Day	12% 5% 22% 29% 20% 12%	583
September	1st to 10th	Day	16% 8% 17% 27% 22% 9%	530
	11th to 20th	Day	11% 4 18% 31% 24% 12%	530
	21st to end	Day	24% 9% 23% 25% 14% 6%	530
October	1st to 10th	Day	15% 8% 26% 26% 21% 5%	530
	11th to 20th	Day	22% 14% 33% 21% 8% 2	530
	21st to end	Day	28% 14% 31% 20% 7%	583
November	1st to 10th	Day	18% 20% 34% 16% 10% 1	410
	11th to 20th	Day	34% 15% 31% 12% 6% 1	261
	21st to end	Day	30% 23% 34% 12% 1	220
December	1st to 10th	Day	36% 24% 27% 9% 3 1	204
	11th to 20th	Day	34% 20% 32% 13% 2	200
	21st to end	Day	37% 24% 25% 12% 2	220
January	1st to 10th	Night	30% 17% 35% 16% 3	800
	11th to 20th	Night	33% 16% 31% 17% 3	800
	21st to end	Night	29% 18% 30% 20% 4	880
February	1st to 10th	Night	30% 15% 29% 24% 2	800
	11th to 20th	Night	29% 17% 36% 17% 1	783
	21st to end	Night	30% 14% 33% 20% 3	660
March	1st to 10th	Night	26% 15% 32% 24% 3	800
	11th to 20th	Night	28% 14% 28% 25% 5%	800
	21st to end	Night	26% 13% 33% 23% 6%	880
April	1st to 10th	Night	27% 14% 28% 25% 5%	800
	11th to 20th	Night	24% 11% 33% 23% 9% 1	735
	21st to end	Night	22% 7% 33% 32% 6%	600
May	1st to 10th	Night	24% 7% 24% 36% 10% 1	600
	11th to 20th	Night	20% 7% 27% 34% 12% 1	591
	21st to end	Night	11% 4 23% 38% 20% 3	497
June	1st to 10th	Night	11% 4 24% 44% 17% 1	400
	11th to 20th	Night	14% 4 23% 43% 17%	400
	21st to end	Night	10% 4 25% 36% 25% 1	400
July	1st to 10th	Night	9% 3 13% 44% 24% 6%	466
	11th to 20th	Night	9% 2 14% 42% 29% 4	582
	21st to end	Night	12% 2 12% 42% 30% 2	657
August	1st to 10th	Night	11% 2 13% 42% 29% 3	597
	11th to 20th	Night	14% 3 8% 41% 28% 5%	594
	21st to end	Night	13% 3 16% 35% 29% 5%	745
September	1st to 10th	Night	15% 4 16% 34% 27% 3	800
	11th to 20th	Night	12% 4 13% 35% 32% 5%	800
	21st to end	Night	21% 6% 21% 29% 20% 4	800
October	1st to 10th	Night	17% 6% 20% 33% 22% 2	800
	11th to 20th	Night	20% 9% 32% 28% 10% 2	800
	21st to end	Night	28% 10% 27% 28% 7%	880
November	1st to 10th	Night	20% 9% 27% 31% 12%	820
	11th to 20th	Night	28% 14% 28% 22% 7% 1	840
	21st to end	Night	29% 14% 29% 21% 6%	840
December	1st to 10th	Night	34% 14% 27% 21% 4	809
	11th to 20th	Night	31% 14% 30% 21% 4	800
	21st to end	Night	32% 14% 29% 22% 3	880

Page generated at 2025-11-30 01:00:56. Version ac07

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