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Winter Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Winter Star Party clear sky chart from 2005-11-06 to 2024-01-15.

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	6% 4 2 5% 5% 4 6% 7% 8% 12% 41%	74810
	Night	6% 4 2 5% 5% 4 6% 6% 7% 11% 43%	74976
Transparency	Day	22% 40% 14% 15% 7% 1	74533
	Night	23% 39% 13% 15% 8% 1	74772
Seeing	Day	6% 2 8% 23% 37% 24%	14774
	Night	7% 2 9% 26% 37% 19%	24933

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% 3 2 5% 5% 4 5% 5% 6% 14% 43%	1706
	11th to 20th	Day	8% 5% 3 4 6% 4 6% 6% 7% 10% 40%	1662
	21st to end	Day	8% 5% 2 5% 5% 4 5% 7% 7% 10% 42%	1962
February	1st to 10th	Day	7% 4 2 3 4 3 6% 5% 7% 10% 50%	1800
	11th to 20th	Day	4 5% 2 4 3 2 4 4 5% 10% 57%	1802
	21st to end	Day	4 2 1 3 3 3 3 4 6% 12% 59%	1628
March	1st to 10th	Day	3 3 2 3 4 2 5% 5% 6% 11% 58%	1980
	11th to 20th	Day	4 3 1 3 3 2 4 6% 8% 11% 54%	1980
	21st to end	Day	4 3 2 4 4 2 4 4 6% 9% 59%	2178
April	1st to 10th	Day	2 2 1 2 3 3 5% 6% 7% 13% 57%	1980
	11th to 20th	Day	4 3 1 3 4 2 5% 4 7% 12% 56%	1956
	21st to end	Day	4 3 1 3 4 2 3 5% 7% 10% 58%	2139
May	1st to 10th	Day	3 2 1 3 3 2 3 4 6% 10% 63%	2160
	11th to 20th	Day	9% 5% 3 6% 5% 3 6% 5% 7% 11% 39%	2188
	21st to end	Day	8% 5% 3 6% 5% 3 6% 7% 8% 11% 38%	2531
June	1st to 10th	Day	10% 8% 4 7% 7% 4 7% 7% 8% 12% 25%	2340
	11th to 20th	Day	6% 4 2 7% 7% 4 8% 9% 12% 12% 29%	2340
	21st to end	Day	5% 4 2 6% 7% 5% 6% 8% 10% 18% 30%	2340
July	1st to 10th	Day	4 3 2 5% 6% 4 8% 8% 11% 15% 34%	2340
	11th to 20th	Day	3 3 3 4 5% 4 8% 9% 13% 17% 31%	2340
	21st to end	Day	3 4 2 5% 6% 4 7% 9% 12% 17% 33%	2547
August	1st to 10th	Day	3 4 2 5% 7% 5% 8% 9% 13% 16% 29%	2310
	11th to 20th	Day	3 3 2 5% 7% 4 7% 9% 12% 16% 32%	1949
	21st to end	Day	6% 5% 3 7% 8% 5% 8% 9% 10% 15% 26%	2178
September	1st to 10th	Day	5% 4 2 6% 8% 5% 8% 10% 11% 14% 26%	1980
	11th to 20th	Day	5% 5% 3 6% 6% 4 8% 10% 11% 13% 27%	1980
	21st to end	Day	9% 7% 3 7% 7% 5% 7% 8% 10% 12% 25%	1980
October	1st to 10th	Day	6% 5% 3 7% 7% 4 9% 7% 10% 14% 28%	1977
	11th to 20th	Day	8% 5% 2 6% 6% 5% 6% 8% 9% 12% 34%	1800
	21st to end	Day	9% 5% 2 5% 5% 4 6% 6% 8% 9% 40%	1980
November	1st to 10th	Day	8% 4 2 4 5% 4 5% 6% 7% 10% 47%	1857
	11th to 20th	Day	7% 5% 3 5% 6% 4 5% 7% 6% 8% 43%	1900
	21st to end	Day	6% 4 2 4 5% 3 4 5% 7% 11% 47%	1900
December	1st to 10th	Day	6% 4 2 5% 5% 4 4 5% 7% 10% 47%	1843
	11th to 20th	Day	8% 4 2 4 5% 3 4 7% 7% 11% 45%	2153
	21st to end	Day	10% 6% 3 6% 6% 4 6% 6% 8% 9% 37%	3124
January	1st to 10th	Night	7% 4 3 4 5% 3 5% 5% 8% 13% 44%	2459
	11th to 20th	Night	8% 6% 3 6% 6% 3 5% 6% 7% 9% 42%	2404
	21st to end	Night	7% 4 3 5% 6% 3 6% 6% 8% 11% 42%	2390
February	1st to 10th	Night	6% 4 2 4 5% 3 6% 6% 6% 9% 49%	2160
	11th to 20th	Night	5% 3 2 4 4 3 5% 5% 6% 8% 56%	2042
	21st to end	Night	5% 3 1 3 3 3 4 4 5% 10% 60%	1628
March	1st to 10th	Night	3 2 2 5% 5% 4 5% 5% 6% 9% 53%	1980
	11th to 20th	Night	4 3 1 4 4 3 4 5% 5% 9% 58%	1980
	21st to end	Night	3 3 1 4 4 3 4 4 5% 8% 59%	2178
April	1st to 10th	Night	4 2 1 3 4 3 4 5% 7% 12% 56%	1980
	11th to 20th	Night	5% 3 2 4 5% 3 4 5% 7% 11% 51%	1953
	21st to end	Night	5% 3 2 3 4 2 4 5% 6% 10% 55%	1818
May	1st to 10th	Night	3 2 1 2 2 2 3 4 6% 10% 64%	1800
	11th to 20th	Night	9% 5% 2 5% 6% 4 5% 6% 8% 11% 41%	1717
	21st to end	Night	8% 6% 3 5% 5% 3 7% 5% 8% 10% 40%	1744
June	1st to 10th	Night	12% 8% 5% 8% 8% 6% 6% 6% 6% 11% 24%	1620
	11th to 20th	Night	5% 4 2 5% 7% 5% 7% 8% 10% 14% 34%	1620
	21st to end	Night	4 3 2 5% 7% 5% 8% 9% 9% 13% 35%	1620
July	1st to 10th	Night	3 3 2 5% 5% 4 5% 6% 10% 16% 41%	1620
	11th to 20th	Night	2 3 2 6% 5% 5% 6% 8% 9% 16% 39%	1620
	21st to end	Night	2 3 1 5% 5% 4 5% 8% 9% 14% 43%	1771
August	1st to 10th	Night	3 4 2 5% 5% 5% 7% 7% 10% 17% 36%	1621
	11th to 20th	Night	3 3 1 6% 6% 4 8% 7% 9% 15% 38%	1930
	21st to end	Night	5% 6% 2 6% 7% 5% 7% 8% 9% 14% 30%	2178
September	1st to 10th	Night	5% 4 3 3 6% 4 7% 8% 11% 15% 34%	1980
	11th to 20th	Night	4 5% 3 7% 7% 5% 8% 9% 10% 13% 28%	1980
	21st to end	Night	8% 7% 3 8% 7% 4 8% 9% 9% 11% 26%	1980
October	1st to 10th	Night	6% 6% 3 7% 7% 5% 8% 7% 8% 13% 30%	1980
	11th to 20th	Night	8% 5% 2 6% 7% 5% 5% 7% 9% 12% 34%	2160
	21st to end	Night	10% 6% 3 6% 6% 4 6% 6% 7% 10% 35%	2376
November	1st to 10th	Night	8% 4 2 5% 5% 3 5% 5% 7% 11% 44%	2221
	11th to 20th	Night	8% 5% 2 6% 5% 3 6% 5% 7% 10% 43%	2280
	21st to end	Night	7% 4 2 4 4 4 5% 5% 7% 9% 47%	2280
December	1st to 10th	Night	6% 4 2 6% 5% 3 6% 5% 7% 10% 45%	2332
	11th to 20th	Night	7% 4 2 5% 6% 3 5% 6% 7% 10% 45%	3042
	21st to end	Night	10% 6% 3 7% 7% 4 6% 6% 6% 9% 35%	4532

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	18% 41% 12% 18% 9% 3	1707
	11th to 20th	Day	23% 43% 11% 13% 6% 3	1662
	21st to end	Day	22% 40% 9% 15% 11% 3	1962
February	1st to 10th	Day	22% 37% 7% 20% 13% 2	1800
	11th to 20th	Day	17% 38% 10% 21% 10% 3	1812
	21st to end	Day	12% 36% 4 24% 20% 4	1628
March	1st to 10th	Day	15% 37% 9% 23% 15% 1	1980
	11th to 20th	Day	14% 38% 9% 24% 13% 2	1980
	21st to end	Day	12% 37% 10% 24% 15% 2	2178
April	1st to 10th	Day	12% 37% 14% 27% 8% 1	1980
	11th to 20th	Day	15% 36% 13% 25% 11% 1	1956
	21st to end	Day	13% 38% 11% 22% 14% 2	2139
May	1st to 10th	Day	9% 37% 12% 26% 15% 1	2160
	11th to 20th	Day	24% 41% 13% 18% 5%	2192
	21st to end	Day	27% 40% 13% 15% 5%	2531
June	1st to 10th	Day	31% 41% 15% 10% 3	2340
	11th to 20th	Day	25% 44% 21% 10% 1	2340
	21st to end	Day	31% 42% 20% 7% 1	2340
July	1st to 10th	Day	26% 44% 22% 8%	2275
	11th to 20th	Day	22% 45% 24% 8%	2271
	21st to end	Day	18% 45% 25% 11% 1	2405
August	1st to 10th	Day	22% 45% 21% 11%	2297
	11th to 20th	Day	24% 43% 24% 8%	1949
	21st to end	Day	28% 45% 20% 7%	2178
September	1st to 10th	Day	25% 46% 21% 7% 1	1980
	11th to 20th	Day	29% 45% 19% 7% 1	1980
	21st to end	Day	31% 42% 14% 10% 2	1980
October	1st to 10th	Day	28% 41% 15% 10% 5% 2	1977
	11th to 20th	Day	25% 41% 14% 14% 5% 1	1800
	21st to end	Day	25% 41% 7% 16% 10% 1	1980
November	1st to 10th	Day	23% 42% 4 14% 14% 3	1857
	11th to 20th	Day	23% 40% 7% 16% 12% 2	1900
	21st to end	Day	20% 41% 9% 17% 12% 2	1900
December	1st to 10th	Day	18% 42% 10% 20% 10% 1	1843
	11th to 20th	Day	24% 35% 7% 18% 11% 5%	2150
	21st to end	Day	35% 27% 14% 10% 13% 2	3124
January	1st to 10th	Night	18% 41% 9% 21% 7% 3	2459
	11th to 20th	Night	24% 42% 10% 14% 8% 2	2404
	21st to end	Night	22% 39% 7% 19% 10% 3	2390
February	1st to 10th	Night	22% 38% 7% 17% 14% 2	2160
	11th to 20th	Night	19% 39% 10% 18% 12% 2	2043
	21st to end	Night	15% 36% 6% 18% 21% 5%	1628
March	1st to 10th	Night	19% 38% 8% 19% 14% 2	1980
	11th to 20th	Night	16% 37% 9% 18% 17% 2	1980
	21st to end	Night	15% 36% 10% 21% 14% 3	2178
April	1st to 10th	Night	15% 38% 13% 23% 10% 1	1980
	11th to 20th	Night	19% 37% 11% 21% 11% 1	1953
	21st to end	Night	16% 38% 9% 23% 13% 1	1818
May	1st to 10th	Night	9% 37% 10% 26% 16%	1800
	11th to 20th	Night	23% 39% 14% 16% 7%	1718
	21st to end	Night	28% 40% 10% 15% 7%	1745
June	1st to 10th	Night	36% 39% 14% 8% 3	1620
	11th to 20th	Night	24% 41% 23% 11% 2	1620
	21st to end	Night	29% 44% 20% 5% 1	1620
July	1st to 10th	Night	23% 44% 21% 12%	1575
	11th to 20th	Night	24% 43% 21% 11%	1566
	21st to end	Night	17% 43% 25% 12% 2	1672
August	1st to 10th	Night	21% 42% 22% 14% 1	1610
	11th to 20th	Night	25% 42% 23% 9%	1930
	21st to end	Night	29% 42% 20% 8% 1	2178
September	1st to 10th	Night	22% 46% 24% 8% 1	1980
	11th to 20th	Night	30% 44% 18% 7% 1	1980
	21st to end	Night	33% 43% 14% 8% 1	1980
October	1st to 10th	Night	28% 41% 13% 11% 6% 1	1980
	11th to 20th	Night	27% 40% 15% 13% 4 1	2160
	21st to end	Night	28% 40% 7% 15% 10% 1	2376
November	1st to 10th	Night	22% 44% 3 15% 13% 3	2221
	11th to 20th	Night	20% 40% 8% 19% 12% 1	2280
	21st to end	Night	20% 41% 9% 16% 13% 1	2280
December	1st to 10th	Night	19% 41% 11% 20% 9%	2332
	11th to 20th	Night	24% 34% 7% 20% 11% 5%	3044
	21st to end	Night	37% 28% 12% 10% 12% 1	4532

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	9% 3 18% 37% 31% 3	270
	11th to 20th	Day	13% 5% 17% 39% 23% 2	254
	21st to end	Day	11% 4 20% 41% 21% 2	264
February	1st to 10th	Day	4 4 13% 42% 33% 5%	240
	11th to 20th	Day	5% 1 11% 36% 40% 6%	294
	21st to end	Day	5% 2 12% 32% 43% 6%	346
March	1st to 10th	Day	3 2 18% 42% 30% 4	420
	11th to 20th	Day	7% 1 15% 36% 36% 5%	420
	21st to end	Day	5% 2 12% 39% 38% 5%	462
April	1st to 10th	Day	2 1 10% 43% 40% 4	420
	11th to 20th	Day	4 3 10% 47% 33% 4	412
	21st to end	Day	4 5% 45% 43% 2	420
May	1st to 10th	Day	3 5% 33% 50% 9%	423
	11th to 20th	Day	10% 1 7% 29% 42% 12%	447
	21st to end	Day	9% 2 5% 15% 48% 21%	485
June	1st to 10th	Day	13% 1 5% 18% 36% 27%	450
	11th to 20th	Day	7% 2 2 8% 37% 44%	450
	21st to end	Day	3 2 4 29% 61%	450
July	1st to 10th	Day	4 2 4 35% 56%	445
	11th to 20th	Day	4 2 4 34% 57%	444
	21st to end	Day	6% 1 1 4 33% 55%	488
August	1st to 10th	Day	4 1 1 2 41% 51%	446
	11th to 20th	Day	3 2 5% 39% 51%	439
	21st to end	Day	5% 2 4 9% 38% 42%	495
September	1st to 10th	Day	6% 1 2 4 36% 52%	450
	11th to 20th	Day	7% 1 6% 24% 61%	450
	21st to end	Day	10% 2 4 9% 30% 45%	450
October	1st to 10th	Day	6% 2 5% 22% 47% 18%	450
	11th to 20th	Day	9% 2 6% 21% 40% 22%	450
	21st to end	Day	9% 2 11% 26% 38% 15%	495
November	1st to 10th	Day	6% 3 12% 30% 39% 10%	455
	11th to 20th	Day	9% 4 10% 35% 34% 8%	460
	21st to end	Day	6% 3 13% 35% 35% 8%	460
December	1st to 10th	Day	9% 2 11% 32% 39% 7%	403
	11th to 20th	Day	7% 4 13% 27% 40% 9%	270
	21st to end	Day	9% 5% 13% 28% 37% 7%	297
January	1st to 10th	Night	7% 3 13% 35% 36% 5%	760
	11th to 20th	Night	10% 4 20% 35% 28% 3	740
	21st to end	Night	9% 5% 19% 36% 30% 1	792
February	1st to 10th	Night	7% 3 15% 39% 33% 2	720
	11th to 20th	Night	5% 3 18% 35% 35% 3	703
	21st to end	Night	4 3 9% 36% 42% 6%	592
March	1st to 10th	Night	3 2 18% 43% 31% 3	720
	11th to 20th	Night	4 1 13% 41% 38% 4	720
	21st to end	Night	5% 2 13% 42% 35% 4	792
April	1st to 10th	Night	4 1 7% 44% 41% 3	720
	11th to 20th	Night	5% 1 12% 44% 35% 4	711
	21st to end	Night	6% 2 7% 43% 39% 4	720
May	1st to 10th	Night	4 6% 34% 45% 11%	720
	11th to 20th	Night	11% 1 5% 31% 45% 8%	656
	21st to end	Night	9% 2 6% 23% 44% 16%	584
June	1st to 10th	Night	14% 2 6% 19% 39% 20%	540
	11th to 20th	Night	6% 1 3 9% 43% 38%	540
	21st to end	Night	4 1 1 7% 35% 53%	540
July	1st to 10th	Night	4 2 5% 31% 58%	525
	11th to 20th	Night	2 1 1 6% 38% 53%	522
	21st to end	Night	4 1 5% 32% 58%	591
August	1st to 10th	Night	4 1 5% 40% 49%	537
	11th to 20th	Night	3 1 1 6% 36% 53%	688
	21st to end	Night	8% 1 4 9% 35% 44%	792
September	1st to 10th	Night	6% 1 2 6% 34% 50%	720
	11th to 20th	Night	5% 1 2 8% 28% 56%	720
	21st to end	Night	11% 1 3 10% 32% 43%	720
October	1st to 10th	Night	8% 2 7% 20% 46% 18%	720
	11th to 20th	Night	11% 1 7% 19% 43% 20%	720
	21st to end	Night	12% 2 9% 26% 38% 12%	792
November	1st to 10th	Night	9% 3 14% 28% 38% 8%	740
	11th to 20th	Night	9% 2 10% 28% 42% 10%	760
	21st to end	Night	7% 3 14% 35% 36% 6%	760
December	1st to 10th	Night	8% 2 10% 33% 41% 6%	760
	11th to 20th	Night	8% 3 12% 33% 38% 6%	760
	21st to end	Night	9% 3 13% 31% 37% 6%	836

Page generated at 2024-01-12 16:17:46. Version ac07

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