Danville Conservation Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Danville Conservation Area clear sky chart from 2005-11-06 to 2024-03-06.

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	13% 7% 3 6% 5% 3 4 4 5% 7% 42%	78622
	Night	13% 8% 4 6% 5% 3 4 4 5% 6% 43%	80947
Transparency	Day	41% 6% 12% 23% 15% 2	78334
	Night	42% 5% 11% 23% 16% 3	80755
Seeing	Day	16% 13% 29% 26% 13% 3	14644
	Night	17% 13% 31% 27% 11% 1	24683

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	11% 14% 5% 10% 6% 3 5% 4 5% 7% 31%	2527
	11th to 20th	Day	12% 11% 4 7% 7% 5% 6% 4 4 6% 34%	2850
	21st to end	Day	19% 15% 7% 7% 5% 3 3 4 4 4 29%	3135
February	1st to 10th	Day	16% 11% 5% 8% 6% 3 4 3 3 6% 36%	1710
	11th to 20th	Day	15% 9% 4 6% 5% 3 4 4 5% 6% 40%	1760
	21st to end	Day	15% 12% 3 7% 5% 2 4 4 3 6% 39%	1570
March	1st to 10th	Day	14% 10% 4 5% 5% 3 5% 4 4 6% 40%	1949
	11th to 20th	Day	19% 9% 4 7% 5% 3 4 3 4 5% 36%	1980
	21st to end	Day	21% 11% 4 7% 5% 3 4 5% 4 6% 28%	2242
April	1st to 10th	Day	12% 7% 3 5% 6% 3 5% 4 5% 6% 44%	2160
	11th to 20th	Day	19% 8% 3 6% 5% 3 4 3 4 6% 41%	2134
	21st to end	Day	21% 6% 3 6% 5% 3 4 5% 6% 6% 35%	2160
May	1st to 10th	Day	16% 6% 3 6% 6% 4 4 4 6% 9% 36%	2223
	11th to 20th	Day	17% 7% 3 5% 5% 3 5% 4 5% 7% 40%	2461
	21st to end	Day	12% 6% 3 6% 6% 4 6% 5% 7% 7% 38%	2725
June	1st to 10th	Day	8% 4 2 4 5% 3 4 5% 7% 11% 47%	2520
	11th to 20th	Day	9% 3 2 4 5% 3 4 5% 6% 11% 48%	2520
	21st to end	Day	6% 3 2 4 5% 4 6% 6% 6% 11% 48%	2520
July	1st to 10th	Day	11% 3 2 4 5% 3 5% 6% 7% 11% 43%	2520
	11th to 20th	Day	5% 4 2 4 4 3 5% 5% 7% 10% 52%	2502
	21st to end	Day	9% 4 2 5% 5% 2 5% 6% 7% 10% 44%	2546
August	1st to 10th	Day	8% 5% 2 5% 5% 4 5% 6% 6% 9% 43%	2328
	11th to 20th	Day	9% 4 2 5% 5% 3 6% 6% 7% 10% 43%	2185
	21st to end	Day	8% 4 2 5% 5% 3 4 4 5% 9% 51%	2376
September	1st to 10th	Day	12% 5% 2 4 3 3 4 4 6% 7% 49%	2160
	11th to 20th	Day	10% 4 2 5% 4 2 4 3 6% 8% 52%	2160
	21st to end	Day	7% 5% 2 5% 4 3 4 4 4 8% 55%	1916
October	1st to 10th	Day	10% 5% 2 5% 5% 2 4 4 4 5% 54%	1800
	11th to 20th	Day	18% 6% 2 4 3 2 3 3 4 5% 51%	1800
	21st to end	Day	19% 8% 2 4 4 2 2 3 3 5% 46%	1980
November	1st to 10th	Day	12% 5% 2 4 3 2 4 3 4 6% 55%	1718
	11th to 20th	Day	15% 7% 4 4 4 2 3 3 6% 6% 47%	1710
	21st to end	Day	17% 9% 4 5% 4 2 3 3 4 5% 43%	1554
December	1st to 10th	Day	13% 11% 4 5% 4 2 4 3 5% 7% 41%	1520
	11th to 20th	Day	15% 9% 4 6% 5% 3 3 3 4 7% 41%	1918
	21st to end	Day	19% 14% 6% 10% 5% 3 5% 5% 5% 4 24%	2783
January	1st to 10th	Night	13% 12% 8% 9% 5% 4 4 4 4 4 34%	4424
	11th to 20th	Night	13% 12% 5% 10% 6% 4 7% 6% 5% 4 30%	4120
	21st to end	Night	21% 17% 6% 7% 5% 2 3 3 3 4 28%	4532
February	1st to 10th	Night	15% 11% 5% 7% 6% 3 5% 4 4 6% 34%	2470
	11th to 20th	Night	15% 7% 4 7% 5% 3 4 4 5% 6% 40%	2305
	21st to end	Night	16% 11% 4 6% 4 3 3 3 3 5% 42%	1884
March	1st to 10th	Night	17% 9% 3 5% 4 3 3 3 4 4 45%	2143
	11th to 20th	Night	19% 8% 4 5% 6% 4 5% 4 5% 6% 36%	1980
	21st to end	Night	21% 11% 4 7% 6% 3 5% 5% 5% 6% 28%	2112
April	1st to 10th	Night	11% 7% 3 7% 4 3 5% 4 4 6% 47%	1800
	11th to 20th	Night	14% 7% 3 6% 4 3 3 3 5% 6% 46%	1775
	21st to end	Night	20% 6% 3 4 4 3 4 4 4 7% 42%	1800
May	1st to 10th	Night	14% 6% 3 5% 4 3 4 4 6% 8% 43%	1733
	11th to 20th	Night	16% 7% 2 5% 5% 3 4 4 4 7% 43%	1434
	21st to end	Night	12% 5% 3 4 6% 4 4 5% 6% 9% 42%	1551
June	1st to 10th	Night	7% 3 2 4 4 3 5% 5% 6% 8% 52%	1440
	11th to 20th	Night	7% 4 2 5% 5% 3 5% 4 5% 10% 51%	1440
	21st to end	Night	4 3 2 3 4 3 5% 6% 5% 11% 55%	1440
July	1st to 10th	Night	9% 3 2 5% 3 3 4 5% 5% 10% 50%	1440
	11th to 20th	Night	5% 3 1 3 4 2 3 5% 6% 9% 59%	1454
	21st to end	Night	7% 4 2 4 5% 3 5% 5% 7% 8% 50%	1772
August	1st to 10th	Night	7% 3 1 5% 4 2 5% 5% 6% 10% 51%	1611
	11th to 20th	Night	6% 5% 3 4 4 3 4 5% 5% 9% 53%	1715
	21st to end	Night	5% 3 2 4 4 2 4 4 6% 9% 57%	1980
September	1st to 10th	Night	13% 4 2 3 4 2 3 4 4 7% 55%	1800
	11th to 20th	Night	9% 4 2 4 4 2 4 5% 6% 7% 53%	1800
	21st to end	Night	7% 4 2 5% 4 3 3 4 5% 7% 57%	2019
October	1st to 10th	Night	9% 3 2 4 4 2 3 4 4 6% 58%	2160
	11th to 20th	Night	15% 5% 2 3 3 2 4 4 4 6% 51%	2160
	21st to end	Night	18% 7% 2 4 4 3 3 3 3 5% 47%	2376
November	1st to 10th	Night	10% 6% 2 4 3 2 3 3 4 5% 56%	2360
	11th to 20th	Night	12% 7% 3 5% 4 2 3 4 4 6% 50%	2470
	21st to end	Night	17% 9% 3 4 4 2 3 4 4 5% 44%	2624
December	1st to 10th	Night	14% 11% 4 6% 5% 3 5% 4 4 6% 37%	2660
	11th to 20th	Night	15% 10% 4 7% 5% 2 3 4 5% 5% 39%	3279
	21st to end	Night	19% 19% 6% 8% 6% 3 4 3 3 4 23%	4884

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	52% 6% 10% 22% 9% 1	2528
	11th to 20th	Day	51% 5% 12% 20% 12%	2850
	21st to end	Day	57% 5% 10% 14% 13% 1	3135
February	1st to 10th	Day	52% 4 11% 22% 10% 1	1710
	11th to 20th	Day	46% 5% 11% 20% 15% 4	1769
	21st to end	Day	47% 5% 9% 22% 13% 4	1570
March	1st to 10th	Day	46% 4 9% 24% 15% 2	1949
	11th to 20th	Day	52% 5% 10% 18% 13% 2	1980
	21st to end	Day	57% 5% 10% 17% 9% 1	2242
April	1st to 10th	Day	41% 6% 10% 25% 17% 1	2160
	11th to 20th	Day	45% 5% 9% 23% 14% 3	2134
	21st to end	Day	49% 5% 12% 20% 13% 1	2160
May	1st to 10th	Day	47% 7% 14% 22% 10% 1	2223
	11th to 20th	Day	44% 7% 11% 22% 14% 2	2465
	21st to end	Day	42% 9% 13% 20% 13% 2	2725
June	1st to 10th	Day	31% 9% 15% 29% 15% 2	2520
	11th to 20th	Day	31% 8% 13% 25% 19% 4	2520
	21st to end	Day	30% 8% 17% 25% 15% 4	2520
July	1st to 10th	Day	33% 9% 16% 27% 12% 4	2451
	11th to 20th	Day	25% 9% 16% 29% 19% 3	2427
	21st to end	Day	33% 8% 13% 30% 14% 2	2405
August	1st to 10th	Day	34% 9% 15% 27% 13% 1	2314
	11th to 20th	Day	35% 8% 14% 27% 14% 1	2185
	21st to end	Day	30% 7% 13% 24% 21% 6%	2376
September	1st to 10th	Day	34% 6% 11% 25% 19% 4	2160
	11th to 20th	Day	31% 5% 9% 27% 23% 4	2160
	21st to end	Day	29% 6% 10% 28% 24% 3	1916
October	1st to 10th	Day	33% 5% 9% 26% 23% 4	1800
	11th to 20th	Day	36% 5% 7% 25% 22% 5%	1800
	21st to end	Day	43% 3 9% 24% 18% 4	1980
November	1st to 10th	Day	31% 5% 12% 25% 22% 5%	1718
	11th to 20th	Day	38% 3 9% 24% 21% 4	1710
	21st to end	Day	44% 5% 9% 27% 15%	1554
December	1st to 10th	Day	44% 4 12% 27% 12% 1	1520
	11th to 20th	Day	45% 4 11% 24% 13% 2	1915
	21st to end	Day	62% 6% 8% 15% 8% 1	2783
January	1st to 10th	Night	53% 4 10% 23% 10% 1	4424
	11th to 20th	Night	58% 4 9% 19% 9% 1	4120
	21st to end	Night	60% 5% 9% 19% 7% 1	4532
February	1st to 10th	Night	52% 5% 10% 19% 12% 2	2470
	11th to 20th	Night	45% 4 11% 21% 16% 3	2306
	21st to end	Night	47% 4 10% 21% 15% 3	1884
March	1st to 10th	Night	44% 4 10% 23% 17% 3	2143
	11th to 20th	Night	49% 5% 9% 21% 12% 3	1980
	21st to end	Night	56% 6% 11% 19% 8% 1	2112
April	1st to 10th	Night	37% 6% 11% 25% 18% 3	1800
	11th to 20th	Night	40% 5% 10% 24% 16% 5%	1775
	21st to end	Night	44% 4 10% 23% 18% 1	1800
May	1st to 10th	Night	39% 9% 15% 21% 16% 1	1733
	11th to 20th	Night	42% 6% 11% 23% 15% 2	1435
	21st to end	Night	38% 8% 16% 19% 17% 3	1552
June	1st to 10th	Night	28% 7% 16% 29% 18% 3	1440
	11th to 20th	Night	29% 7% 11% 26% 24% 3	1440
	21st to end	Night	23% 8% 16% 28% 19% 6%	1440
July	1st to 10th	Night	29% 8% 14% 31% 14% 4	1400
	11th to 20th	Night	21% 8% 14% 30% 23% 3	1406
	21st to end	Night	29% 6% 13% 32% 18% 1	1673
August	1st to 10th	Night	27% 8% 14% 34% 15% 2	1601
	11th to 20th	Night	28% 7% 12% 31% 21% 1	1715
	21st to end	Night	24% 7% 14% 27% 22% 6%	1980
September	1st to 10th	Night	30% 5% 11% 26% 22% 6%	1800
	11th to 20th	Night	29% 7% 10% 24% 26% 4	1800
	21st to end	Night	28% 5% 9% 26% 28% 4	2019
October	1st to 10th	Night	27% 5% 11% 26% 26% 5%	2160
	11th to 20th	Night	35% 4 7% 28% 20% 6%	2160
	21st to end	Night	42% 4 9% 20% 21% 4	2376
November	1st to 10th	Night	31% 5% 12% 26% 20% 6%	2360
	11th to 20th	Night	37% 4 8% 26% 22% 4	2470
	21st to end	Night	43% 4 11% 25% 16% 2	2624
December	1st to 10th	Night	48% 5% 11% 23% 13% 1	2660
	11th to 20th	Night	47% 4 9% 24% 15% 1	3281
	21st to end	Night	66% 5% 9% 13% 7% 1	4884

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	27% 21% 34% 16% 2	270
	11th to 20th	Day	29% 26% 35% 10% 1	270
	21st to end	Day	21% 24% 40% 13% 2	297
February	1st to 10th	Day	30% 23% 33% 13% 2	270
	11th to 20th	Day	25% 29% 31% 12% 3	270
	21st to end	Day	32% 24% 34% 9% 2	225
March	1st to 10th	Day	21% 27% 42% 10% 1	255
	11th to 20th	Day	30% 22% 34% 12% 2	240
	21st to end	Day	34% 24% 28% 11% 2	328
April	1st to 10th	Day	18% 17% 40% 19% 5%	420
	11th to 20th	Day	26% 18% 30% 20% 5%	412
	21st to end	Day	27% 16% 33% 19% 5%	420
May	1st to 10th	Day	18% 18% 37% 19% 6% 1	486
	11th to 20th	Day	18% 17% 28% 27% 10% 1	625
	21st to end	Day	14% 11% 31% 27% 11% 5%	679
June	1st to 10th	Day	9% 6% 27% 34% 19% 5%	630
	11th to 20th	Day	10% 4 29% 41% 15% 3	630
	21st to end	Day	7% 10% 31% 36% 13% 3	630
July	1st to 10th	Day	12% 2 17% 32% 29% 8%	621
	11th to 20th	Day	7% 6% 23% 36% 25% 3	618
	21st to end	Day	10% 4 21% 32% 29% 4	684
August	1st to 10th	Day	8% 4 19% 41% 23% 5%	626
	11th to 20th	Day	9% 4 21% 37% 22% 6%	499
	21st to end	Day	8% 3 20% 30% 30% 8%	495
September	1st to 10th	Day	14% 4 18% 34% 24% 6%	450
	11th to 20th	Day	10% 3 21% 32% 24% 11%	450
	21st to end	Day	7% 12% 25% 29% 23% 5%	360
October	1st to 10th	Day	11% 13% 33% 28% 12% 2	270
	11th to 20th	Day	21% 28% 27% 19% 5%	270
	21st to end	Day	32% 23% 28% 14% 3	297
November	1st to 10th	Day	14% 15% 40% 20% 10% 2	270
	11th to 20th	Day	22% 20% 29% 22% 4 2	270
	21st to end	Day	27% 17% 30% 22% 3	270
December	1st to 10th	Day	17% 21% 39% 14% 8% 1	270
	11th to 20th	Day	23% 18% 38% 18% 3	270
	21st to end	Day	25% 28% 35% 11% 1	297
January	1st to 10th	Night	19% 20% 39% 17% 5%	950
	11th to 20th	Night	24% 19% 36% 17% 3	950
	21st to end	Night	19% 21% 38% 21% 1	1045
February	1st to 10th	Night	22% 20% 35% 20% 3	950
	11th to 20th	Night	22% 20% 35% 20% 2	831
	21st to end	Night	26% 21% 34% 18% 2	628
March	1st to 10th	Night	23% 17% 40% 18% 2	659
	11th to 20th	Night	24% 15% 35% 22% 4	540
	21st to end	Night	27% 16% 37% 17% 4	594
April	1st to 10th	Night	17% 18% 36% 24% 4	540
	11th to 20th	Night	20% 14% 35% 24% 6%	533
	21st to end	Night	21% 11% 40% 22% 5%	540
May	1st to 10th	Night	16% 11% 33% 33% 8%	540
	11th to 20th	Night	19% 8% 29% 33% 11% 1	531
	21st to end	Night	13% 7% 30% 32% 17% 2	584
June	1st to 10th	Night	8% 4 23% 39% 24% 1	540
	11th to 20th	Night	9% 4 26% 41% 20% 1	540
	21st to end	Night	4 4 29% 44% 17% 1	540
July	1st to 10th	Night	10% 2 13% 38% 33% 5%	525
	11th to 20th	Night	5% 2 18% 42% 30% 2	522
	21st to end	Night	9% 2 18% 40% 31% 2	591
August	1st to 10th	Night	7% 3 12% 46% 31% 1	537
	11th to 20th	Night	8% 2 13% 41% 33% 3	534
	21st to end	Night	6% 2 18% 38% 34% 3	594
September	1st to 10th	Night	14% 4 18% 36% 24% 6%	540
	11th to 20th	Night	11% 3 19% 35% 27% 5%	540
	21st to end	Night	8% 7% 24% 34% 22% 5%	674
October	1st to 10th	Night	10% 8% 29% 28% 21% 3	720
	11th to 20th	Night	18% 12% 34% 27% 8% 1	720
	21st to end	Night	23% 13% 34% 23% 7%	792
November	1st to 10th	Night	13% 13% 37% 27% 9%	740
	11th to 20th	Night	17% 17% 34% 24% 7%	760
	21st to end	Night	22% 16% 34% 22% 5%	914
December	1st to 10th	Night	21% 19% 34% 20% 5% 1	950
	11th to 20th	Night	25% 14% 32% 25% 4	950
	21st to end	Night	24% 22% 34% 18% 2	1045

Page generated at 2024-03-03 05:28:58. Version ac07

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