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 2024-11-11.

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 8% 5% 4 5% 4 5% 7% 31%	101176
	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 32%	97919
Transparency	Day	51% 6% 11% 21% 11% 1	104825
	Night	51% 5% 11% 20% 11% 1	102409
Seeing	Day	23% 12% 27% 21% 12% 5%	14677
	Night	23% 10% 26% 28% 12% 1	24366

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	21% 21% 9% 11% 4 4 3 2 3 4 17%	2836
	11th to 20th	Day	14% 26% 8% 13% 8% 4 2 2 3 4 17%	2840
	21st to end	Day	28% 21% 8% 14% 5% 3 2 3 3 3 10%	3124
February	1st to 10th	Day	20% 18% 6% 12% 7% 4 3 2 3 4 22%	1710
	11th to 20th	Day	18% 14% 6% 14% 6% 4 5% 3 4 6% 20%	1663
	21st to end	Day	21% 15% 5% 11% 5% 3 3 4 4 5% 24%	1563
March	1st to 10th	Day	22% 13% 5% 8% 5% 3 4 3 4 6% 27%	3435
	11th to 20th	Day	14% 13% 5% 9% 5% 5% 4 3 3 6% 33%	3480
	21st to end	Day	22% 10% 3 8% 5% 4 4 4 5% 6% 30%	3815
April	1st to 10th	Day	17% 14% 2 7% 5% 4 4 3 6% 7% 30%	2176
	11th to 20th	Day	19% 11% 3 7% 5% 4 4 4 5% 7% 32%	2322
	21st to end	Day	21% 10% 3 7% 4 4 4 3 4 6% 34%	2470
May	1st to 10th	Day	23% 9% 2 7% 5% 4 5% 3 6% 7% 28%	4082
	11th to 20th	Day	21% 8% 3 7% 5% 4 5% 3 5% 8% 32%	4081
	21st to end	Day	13% 6% 2 6% 4 5% 5% 4 6% 8% 39%	4720
June	1st to 10th	Day	15% 7% 2 8% 5% 5% 5% 5% 6% 9% 33%	2660
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 5% 5% 9% 35%	2660
	21st to end	Day	14% 5% 2 5% 5% 5% 5% 5% 7% 9% 38%	2660
July	1st to 10th	Day	10% 6% 3 7% 5% 5% 6% 4 7% 9% 39%	4294
	11th to 20th	Day	11% 6% 2 6% 5% 4 6% 4 7% 9% 40%	4120
	21st to end	Day	12% 6% 2 7% 6% 6% 6% 5% 7% 8% 36%	4466
August	1st to 10th	Day	16% 7% 3 7% 6% 5% 6% 4 6% 9% 30%	4104
	11th to 20th	Day	15% 5% 3 7% 5% 5% 6% 5% 6% 9% 34%	4044
	21st to end	Day	10% 5% 2 7% 5% 6% 6% 5% 6% 9% 40%	4353
September	1st to 10th	Day	16% 6% 2 5% 4 4 4 4 5% 6% 44%	2262
	11th to 20th	Day	12% 6% 2 5% 4 5% 4 4 5% 8% 44%	2090
	21st to end	Day	19% 8% 3 7% 4 4 4 3 5% 7% 35%	2090
October	1st to 10th	Day	16% 6% 2 6% 5% 4 4 5% 6% 8% 38%	1913
	11th to 20th	Day	21% 9% 3 7% 5% 5% 4 3 5% 5% 33%	1900
	21st to end	Day	24% 11% 3 7% 4 4 4 3 4 6% 30%	2090
November	1st to 10th	Day	12% 9% 3 7% 5% 4 4 3 5% 6% 42%	1838
	11th to 20th	Day	18% 16% 4 7% 5% 4 3 3 4 6% 30%	1593
	21st to end	Day	18% 18% 6% 8% 5% 4 4 3 5% 5% 24%	1520
December	1st to 10th	Day	22% 21% 7% 10% 5% 4 4 3 4 3 17%	1520
	11th to 20th	Day	19% 18% 9% 11% 4 4 4 4 4 5% 18%	1910
	21st to end	Day	28% 23% 7% 10% 4 4 3 2 3 4 12%	2772
January	1st to 10th	Night	17% 23% 8% 12% 5% 4 3 3 4 5% 16%	4109
	11th to 20th	Night	17% 21% 9% 15% 5% 5% 5% 3 3 4 14%	4120
	21st to end	Night	30% 17% 8% 12% 5% 3 3 2 3 3 14%	4532
February	1st to 10th	Night	21% 16% 4 11% 6% 4 4 3 4 5% 22%	2470
	11th to 20th	Night	18% 15% 5% 12% 5% 5% 4 3 5% 5% 23%	2403
	21st to end	Night	21% 14% 5% 11% 5% 5% 4 3 4 5% 24%	1886
March	1st to 10th	Night	24% 12% 3 8% 4 3 3 2 3 5% 32%	3418
	11th to 20th	Night	20% 13% 5% 7% 4 4 3 2 4 5% 34%	3480
	21st to end	Night	20% 10% 3 7% 4 4 4 3 4 4 38%	3817
April	1st to 10th	Night	18% 12% 3 7% 5% 4 4 3 5% 6% 33%	2002
	11th to 20th	Night	18% 9% 3 6% 4 4 4 4 5% 7% 35%	1822
	21st to end	Night	16% 10% 3 6% 5% 4 5% 4 5% 7% 35%	1710
May	1st to 10th	Night	27% 9% 2 7% 4 4 4 4 4 7% 28%	2813
	11th to 20th	Night	18% 9% 3 6% 5% 4 4 3 5% 7% 38%	2812
	21st to end	Night	11% 5% 2 5% 4 4 4 4 7% 10% 43%	2831
June	1st to 10th	Night	11% 4 3 7% 4 5% 6% 3 7% 7% 43%	1520
	11th to 20th	Night	11% 6% 2 5% 5% 4 4 4 6% 8% 43%	1520
	21st to end	Night	10% 5% 2 6% 5% 5% 6% 4 7% 8% 42%	1520
July	1st to 10th	Night	11% 8% 2 7% 5% 5% 5% 3 5% 8% 42%	2648
	11th to 20th	Night	10% 4 2 5% 4 5% 4 4 6% 10% 46%	2840
	21st to end	Night	10% 6% 3 7% 5% 5% 5% 4 6% 8% 44%	3087
August	1st to 10th	Night	13% 8% 3 8% 5% 4 6% 3 5% 7% 38%	2825
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 6% 44%	2785
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	3270
September	1st to 10th	Night	15% 5% 2 5% 3 4 3 3 5% 6% 49%	1914
	11th to 20th	Night	11% 5% 1 4 3 3 4 3 7% 8% 51%	2090
	21st to end	Night	18% 8% 2 6% 4 4 5% 3 5% 6% 40%	2090
October	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 4 7% 45%	2266
	11th to 20th	Night	17% 8% 2 7% 5% 4 5% 3 5% 7% 37%	2280
	21st to end	Night	24% 8% 2 6% 4 4 4 3 4 6% 35%	2508
November	1st to 10th	Night	15% 8% 2 6% 4 4 4 3 4 7% 42%	2455
	11th to 20th	Night	18% 14% 3 8% 5% 5% 4 4 5% 5% 30%	2591
	21st to end	Night	20% 16% 4 6% 5% 4 4 3 4 6% 28%	2660
December	1st to 10th	Night	23% 17% 6% 10% 5% 3 3 3 5% 5% 19%	2660
	11th to 20th	Night	19% 20% 6% 10% 5% 4 3 3 5% 5% 21%	3285
	21st to end	Night	27% 21% 6% 9% 5% 4 4 3 4 4 12%	4880

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	72% 4 9% 11% 4	2837
	11th to 20th	Day	72% 4 8% 12% 3	2840
	21st to end	Day	79% 4 7% 7% 2	3124
February	1st to 10th	Day	69% 3 8% 13% 7%	1710
	11th to 20th	Day	66% 5% 9% 14% 7%	1672
	21st to end	Day	62% 5% 10% 14% 7% 1	1563
March	1st to 10th	Day	58% 5% 11% 21% 5%	3435
	11th to 20th	Day	52% 6% 14% 20% 6% 1	3480
	21st to end	Day	53% 5% 10% 19% 12% 1	3815
April	1st to 10th	Day	52% 6% 11% 18% 12% 1	2176
	11th to 20th	Day	51% 5% 10% 18% 13% 2	2322
	21st to end	Day	51% 5% 10% 21% 10% 2	2470
May	1st to 10th	Day	55% 6% 10% 20% 8% 1	4120
	11th to 20th	Day	51% 6% 13% 21% 9% 1	4085
	21st to end	Day	40% 8% 14% 23% 12% 3	4734
June	1st to 10th	Day	46% 7% 12% 23% 11% 1	2660
	11th to 20th	Day	44% 7% 14% 22% 12% 1	2660
	21st to end	Day	41% 7% 12% 26% 13% 1	2660
July	1st to 10th	Day	41% 6% 12% 24% 14% 3	4228
	11th to 20th	Day	38% 6% 12% 27% 16% 1	4051
	21st to end	Day	42% 7% 13% 20% 17% 1	4324
August	1st to 10th	Day	49% 7% 13% 22% 9%	4091
	11th to 20th	Day	43% 7% 12% 28% 9% 1	4083
	21st to end	Day	39% 7% 13% 27% 13% 2	4353
September	1st to 10th	Day	39% 7% 11% 22% 18% 3	2262
	11th to 20th	Day	37% 6% 13% 26% 17% 1	2090
	21st to end	Day	49% 5% 11% 23% 12% 1	2090
October	1st to 10th	Day	34% 5% 12% 30% 19% 1	3173
	11th to 20th	Day	47% 5% 9% 22% 14% 4	3140
	21st to end	Day	40% 5% 12% 27% 15%	3428
November	1st to 10th	Day	42% 5% 12% 22% 17% 2	1838
	11th to 20th	Day	56% 4 10% 19% 8% 2	1593
	21st to end	Day	61% 4 11% 16% 6% 1	1520
December	1st to 10th	Day	71% 4 10% 12% 3	1520
	11th to 20th	Day	68% 5% 9% 14% 3	1906
	21st to end	Day	78% 4 8% 8% 2	2772
January	1st to 10th	Night	71% 4 9% 12% 3	4109
	11th to 20th	Night	74% 4 8% 11% 2	4120
	21st to end	Night	78% 3 6% 11% 3	4532
February	1st to 10th	Night	65% 4 9% 17% 5%	2470
	11th to 20th	Night	63% 4 9% 17% 6%	2405
	21st to end	Night	63% 3 9% 15% 9% 1	1886
March	1st to 10th	Night	56% 4 10% 22% 8%	3418
	11th to 20th	Night	52% 5% 14% 21% 7% 1	3480
	21st to end	Night	48% 5% 10% 23% 13% 1	3817
April	1st to 10th	Night	52% 6% 9% 19% 13% 2	2002
	11th to 20th	Night	48% 5% 12% 17% 15% 3	1822
	21st to end	Night	46% 7% 11% 21% 13% 3	1710
May	1st to 10th	Night	55% 5% 8% 20% 9% 2	2840
	11th to 20th	Night	46% 6% 12% 24% 10% 2	2813
	21st to end	Night	33% 8% 15% 26% 15% 4	2838
June	1st to 10th	Night	38% 6% 13% 25% 16% 2	1520
	11th to 20th	Night	37% 6% 16% 23% 16% 2	1520
	21st to end	Night	38% 8% 12% 25% 16% 1	1520
July	1st to 10th	Night	42% 5% 10% 22% 18% 2	2604
	11th to 20th	Night	35% 5% 14% 29% 16% 1	2786
	21st to end	Night	39% 7% 13% 17% 23% 2	2988
August	1st to 10th	Night	46% 7% 11% 23% 12% 1	2814
	11th to 20th	Night	40% 5% 11% 30% 14% 1	2812
	21st to end	Night	35% 6% 12% 31% 13% 2	3270
September	1st to 10th	Night	35% 5% 12% 24% 19% 4	1914
	11th to 20th	Night	29% 6% 15% 26% 23% 2	2090
	21st to end	Night	45% 5% 12% 21% 17% 1	2090
October	1st to 10th	Night	35% 4 9% 28% 23% 1	3786
	11th to 20th	Night	40% 5% 11% 24% 13% 7%	3779
	21st to end	Night	37% 4 11% 29% 18% 1	4120
November	1st to 10th	Night	42% 5% 11% 23% 15% 3	2455
	11th to 20th	Night	56% 4 9% 19% 9% 3	2591
	21st to end	Night	58% 4 12% 20% 6% 1	2660
December	1st to 10th	Night	68% 4 11% 12% 4	2660
	11th to 20th	Night	66% 5% 10% 15% 3	3288
	21st to end	Night	75% 5% 10% 9% 2	4880

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	33% 22% 30% 10% 3 1	270
	11th to 20th	Day	36% 23% 29% 9% 3	270
	21st to end	Day	32% 23% 32% 10% 2	297
February	1st to 10th	Day	32% 18% 41% 7% 1	270
	11th to 20th	Day	36% 24% 31% 8% 1	270
	21st to end	Day	37% 22% 32% 9%	231
March	1st to 10th	Day	31% 18% 30% 17% 3	460
	11th to 20th	Day	33% 14% 33% 14% 5% 1	460
	21st to end	Day	33% 17% 28% 17% 4 1	506
April	1st to 10th	Day	29% 18% 29% 15% 8% 1	460
	11th to 20th	Day	27% 15% 26% 19% 9% 4	452
	21st to end	Day	30% 13% 30% 19% 7% 2	460
May	1st to 10th	Day	31% 14% 25% 18% 8% 3	463
	11th to 20th	Day	23% 12% 30% 21% 11% 3	487
	21st to end	Day	16% 8% 24% 28% 18% 7%	529
June	1st to 10th	Day	16% 10% 31% 27% 12% 5%	490
	11th to 20th	Day	19% 8% 25% 29% 15% 4	490
	21st to end	Day	15% 10% 32% 26% 14% 4	490
July	1st to 10th	Day	12% 5% 20% 31% 22% 12%	485
	11th to 20th	Day	14% 4 26% 25% 22% 9%	484
	21st to end	Day	13% 5% 25% 29% 19% 10%	532
August	1st to 10th	Day	14% 6% 19% 29% 22% 9%	486
	11th to 20th	Day	16% 6% 20% 28% 19% 11%	479
	21st to end	Day	13% 4 22% 29% 20% 13%	539
September	1st to 10th	Day	16% 7% 18% 28% 22% 8%	490
	11th to 20th	Day	12% 4 19% 32% 22% 12%	490
	21st to end	Day	24% 9% 23% 25% 13% 6%	490
October	1st to 10th	Day	15% 8% 27% 25% 20% 5%	490
	11th to 20th	Day	23% 14% 32% 20% 9% 3	490
	21st to end	Day	28% 14% 31% 20% 7%	539
November	1st to 10th	Day	18% 20% 34% 16% 11% 2	376
	11th to 20th	Day	35% 15% 30% 12% 7% 1	214
	21st to end	Day	27% 22% 37% 13% 1	180
December	1st to 10th	Day	37% 23% 27% 9% 3 2	180
	11th to 20th	Day	32% 20% 34% 12% 2	180
	21st to end	Day	37% 25% 25% 11% 2	198
January	1st to 10th	Night	30% 16% 35% 15% 3	760
	11th to 20th	Night	33% 15% 31% 17% 3	760
	21st to end	Night	28% 18% 30% 21% 4	836
February	1st to 10th	Night	30% 15% 29% 25% 2	760
	11th to 20th	Night	28% 17% 37% 17% 1	743
	21st to end	Night	31% 14% 32% 20% 3	628
March	1st to 10th	Night	26% 15% 32% 25% 3	760
	11th to 20th	Night	28% 13% 28% 25% 5%	760
	21st to end	Night	25% 12% 32% 23% 6%	836
April	1st to 10th	Night	26% 14% 29% 26% 6%	760
	11th to 20th	Night	23% 10% 33% 24% 9% 1	698
	21st to end	Night	22% 6% 34% 31% 6%	570
May	1st to 10th	Night	22% 7% 24% 36% 10% 1	570
	11th to 20th	Night	20% 6% 26% 34% 13% 1	561
	21st to end	Night	10% 4 23% 39% 21% 3	472
June	1st to 10th	Night	10% 3 25% 44% 18% 1	380
	11th to 20th	Night	13% 4 21% 44% 18%	380
	21st to end	Night	10% 4 25% 37% 23% 1	380
July	1st to 10th	Night	9% 3 13% 44% 24% 7%	442
	11th to 20th	Night	9% 2 13% 43% 28% 4	552
	21st to end	Night	12% 2 11% 43% 30% 2	624
August	1st to 10th	Night	12% 2 13% 41% 29% 3	567
	11th to 20th	Night	15% 3 8% 41% 28% 4	564
	21st to end	Night	13% 2 16% 35% 29% 5%	708
September	1st to 10th	Night	16% 4 16% 33% 28% 3	760
	11th to 20th	Night	12% 4 14% 34% 31% 5%	760
	21st to end	Night	21% 6% 22% 29% 19% 4	760
October	1st to 10th	Night	17% 7% 21% 33% 20% 2	760
	11th to 20th	Night	21% 9% 32% 27% 10% 2	760
	21st to end	Night	28% 10% 27% 28% 7%	836
November	1st to 10th	Night	20% 9% 27% 31% 13%	780
	11th to 20th	Night	28% 13% 28% 22% 8% 1	763
	21st to end	Night	28% 14% 29% 22% 6%	760
December	1st to 10th	Night	35% 14% 27% 21% 4	760
	11th to 20th	Night	30% 14% 30% 21% 4	760
	21st to end	Night	33% 14% 29% 22% 2	836

Page generated at 2024-11-08 06:44:51. Version ac07

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