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 2024-05-30.

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	18% 12% 4 8% 5% 4 4 4 5% 7% 30%	83877
	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 31%	85986
Transparency	Day	54% 6% 11% 19% 9% 1	83597
	Night	54% 5% 11% 19% 10% 1	85785
Seeing	Day	23% 12% 27% 21% 12% 5%	14023
	Night	23% 10% 26% 28% 12% 1	23830

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	20% 10% 2 7% 5% 5% 5% 3 7% 8% 28%	2470
	11th to 20th	Day	21% 8% 2 6% 5% 5% 5% 3 5% 7% 31%	2431
	21st to end	Day	12% 6% 2 6% 5% 5% 6% 5% 7% 8% 38%	2787
June	1st to 10th	Day	16% 7% 3 8% 5% 5% 4 4 6% 9% 33%	2520
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 4 5% 9% 35%	2520
	21st to end	Day	14% 5% 2 5% 5% 5% 5% 5% 7% 9% 38%	2520
July	1st to 10th	Day	11% 6% 3 6% 5% 4 5% 4 6% 9% 40%	2444
	11th to 20th	Day	12% 7% 2 7% 5% 5% 5% 4 7% 8% 38%	2340
	21st to end	Day	12% 7% 2 6% 6% 5% 6% 5% 7% 9% 35%	2547
August	1st to 10th	Day	10% 6% 2 6% 6% 6% 7% 5% 7% 10% 35%	2327
	11th to 20th	Day	15% 5% 3 7% 5% 5% 5% 5% 6% 10% 33%	2303
	21st to end	Day	12% 6% 2 7% 6% 6% 5% 5% 6% 9% 37%	2479
September	1st to 10th	Day	17% 7% 2 5% 4 4 4 4 5% 7% 42%	2143
	11th to 20th	Day	12% 6% 3 5% 4 5% 5% 4 6% 8% 43%	1980
	21st to end	Day	18% 8% 3 7% 4 4 4 3 5% 7% 37%	1980
October	1st to 10th	Day	17% 6% 2 7% 5% 4 5% 5% 6% 7% 37%	1813
	11th to 20th	Day	21% 9% 3 7% 5% 5% 4 3 5% 5% 32%	1800
	21st to end	Day	25% 11% 3 7% 4 4 4 3 4 6% 28%	1980
November	1st to 10th	Day	12% 9% 3 7% 5% 5% 4 4 5% 6% 42%	1744
	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	19% 10% 3 7% 5% 4 5% 5% 4 8% 31%	1710
	11th to 20th	Night	17% 8% 3 6% 5% 4 4 3 6% 8% 37%	1682
	21st to end	Night	10% 5% 2 6% 5% 4 5% 4 7% 10% 42%	1682
June	1st to 10th	Night	11% 4 3 7% 4 5% 6% 3 7% 7% 43%	1440
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 5% 6% 8% 43%	1440
	21st to end	Night	10% 4 2 6% 5% 5% 6% 4 7% 8% 43%	1440
July	1st to 10th	Night	8% 6% 2 6% 6% 5% 5% 3 5% 8% 45%	1512
	11th to 20th	Night	8% 5% 2 5% 4 5% 4 4 6% 10% 46%	1620
	21st to end	Night	11% 5% 3 6% 5% 5% 5% 4 7% 9% 41%	1771
August	1st to 10th	Night	9% 5% 2 6% 4 3 5% 3 6% 9% 47%	1611
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 6% 7% 46%	1598
	21st to end	Night	11% 6% 2 5% 4 4 4 4 6% 8% 47%	1858
September	1st to 10th	Night	15% 5% 2 5% 3 4 3 3 6% 6% 48%	1813
	11th to 20th	Night	11% 5% 1 4 2 3 4 3 7% 8% 51%	1980
	21st to end	Night	16% 8% 2 6% 4 4 5% 3 5% 6% 42%	1980
October	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	2146
	11th to 20th	Night	18% 8% 2 7% 5% 4 5% 3 5% 7% 35%	2160
	21st to end	Night	25% 9% 2 6% 4 4 4 3 4 6% 33%	2376
November	1st to 10th	Night	15% 8% 2 6% 4 4 4 3 4 7% 42%	2329
	11th to 20th	Night	18% 14% 3 8% 5% 5% 4 4 5% 5% 30%	2584
	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	53% 6% 12% 19% 9% 1	2470
	11th to 20th	Day	52% 6% 12% 17% 12% 2	2435
	21st to end	Day	41% 8% 15% 24% 10% 2	2787
June	1st to 10th	Day	46% 6% 12% 23% 11% 1	2520
	11th to 20th	Day	45% 7% 14% 21% 12% 1	2520
	21st to end	Day	41% 7% 12% 26% 12% 1	2520
July	1st to 10th	Day	41% 7% 12% 24% 13% 3	2378
	11th to 20th	Day	41% 7% 12% 25% 14% 1	2271
	21st to end	Day	42% 8% 13% 21% 14% 1	2405
August	1st to 10th	Day	41% 7% 15% 27% 9%	2314
	11th to 20th	Day	44% 8% 14% 23% 10% 1	2303
	21st to end	Day	42% 7% 13% 21% 14% 3	2479
September	1st to 10th	Day	41% 7% 12% 21% 16% 4	2143
	11th to 20th	Day	37% 7% 14% 26% 16% 1	1980
	21st to end	Day	47% 5% 12% 23% 12% 1	1980
October	1st to 10th	Day	44% 6% 13% 21% 15% 1	1813
	11th to 20th	Day	53% 5% 10% 22% 10%	1800
	21st to end	Day	57% 5% 12% 16% 9% 1	1980
November	1st to 10th	Day	43% 5% 12% 22% 17% 2	1744
	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	50% 7% 10% 19% 12% 3	1710
	11th to 20th	Night	46% 6% 12% 19% 15% 3	1683
	21st to end	Night	36% 7% 15% 26% 14% 2	1683
June	1st to 10th	Night	38% 7% 13% 25% 15% 2	1440
	11th to 20th	Night	38% 6% 15% 23% 17% 2	1440
	21st to end	Night	37% 8% 12% 25% 17% 1	1440
July	1st to 10th	Night	38% 7% 10% 23% 19% 3	1468
	11th to 20th	Night	32% 6% 16% 25% 19% 2	1566
	21st to end	Night	36% 7% 18% 21% 14% 3	1672
August	1st to 10th	Night	33% 7% 14% 29% 17% 1	1600
	11th to 20th	Night	35% 6% 16% 27% 14% 2	1598
	21st to end	Night	35% 6% 12% 27% 16% 4	1858
September	1st to 10th	Night	35% 6% 12% 24% 18% 5%	1813
	11th to 20th	Night	29% 7% 15% 26% 22% 2	1980
	21st to end	Night	42% 5% 12% 21% 18% 1	1980
October	1st to 10th	Night	40% 5% 13% 24% 16% 2	2146
	11th to 20th	Night	47% 6% 12% 22% 12% 1	2160
	21st to end	Night	53% 5% 10% 20% 11% 2	2376
November	1st to 10th	Night	42% 4 12% 23% 15% 3	2329
	11th to 20th	Night	56% 4 9% 19% 9% 3	2584
	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% 17% 7%	521
June	1st to 10th	Day	16% 8% 31% 27% 12% 5%	450
	11th to 20th	Day	20% 8% 25% 28% 15% 5%	450
	21st to end	Day	14% 9% 30% 28% 14% 4	450
July	1st to 10th	Day	12% 4 18% 31% 23% 13%	445
	11th to 20th	Day	15% 3 26% 25% 23% 9%	444
	21st to end	Day	13% 5% 25% 28% 19% 10%	488
August	1st to 10th	Day	14% 4 18% 30% 24% 10%	446
	11th to 20th	Day	15% 5% 20% 28% 20% 12%	439
	21st to end	Day	14% 4 22% 29% 19% 13%	495
September	1st to 10th	Day	17% 6% 18% 28% 22% 9%	450
	11th to 20th	Day	12% 4 18% 31% 22% 12%	450
	21st to end	Day	21% 9% 24% 26% 14% 6%	450
October	1st to 10th	Day	16% 7% 27% 25% 19% 5%	450
	11th to 20th	Day	23% 14% 33% 20% 8% 1	450
	21st to end	Day	30% 14% 30% 20% 6%	495
November	1st to 10th	Day	18% 19% 33% 16% 12% 2	342
	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% 3 23% 39% 21% 3	468
June	1st to 10th	Night	10% 3 24% 45% 18% 1	360
	11th to 20th	Night	14% 4 22% 43% 18%	360
	21st to end	Night	10% 3 25% 38% 23% 1	360
July	1st to 10th	Night	8% 3 13% 44% 26% 7%	418
	11th to 20th	Night	9% 2 14% 42% 29% 4	522
	21st to end	Night	13% 2 12% 42% 30% 2	591
August	1st to 10th	Night	11% 2 12% 42% 31% 3	537
	11th to 20th	Night	14% 3 8% 42% 29% 5%	534
	21st to end	Night	13% 2 17% 34% 29% 5%	670
September	1st to 10th	Night	16% 3 16% 33% 28% 3	720
	11th to 20th	Night	13% 4 14% 34% 30% 5%	720
	21st to end	Night	19% 5% 22% 29% 21% 4	720
October	1st to 10th	Night	18% 7% 20% 33% 20% 3	720
	11th to 20th	Night	21% 9% 32% 27% 9% 1	720
	21st to end	Night	30% 10% 27% 27% 6%	792
November	1st to 10th	Night	21% 9% 26% 31% 13%	740
	11th to 20th	Night	28% 13% 28% 22% 8% 1	760
	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 2024-05-27 00:31:40. Version ac07

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