Dayville School
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dayville School 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	8% 9% 4 6% 6% 3 5% 4 5% 6% 44%	78448
	Night	9% 10% 4 6% 5% 3 5% 5% 5% 6% 41%	81089
Transparency	Day	42% 3 10% 21% 17% 7%	78151
	Night	44% 3 13% 21% 15% 5%	80907
Seeing	Day	13% 18% 29% 24% 12% 3	13586
	Night	13% 9% 21% 35% 20% 2	22885

By Month

Percentage Cloud Cover SW (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% 18% 7% 10% 7% 4 6% 5% 5% 6% 20%	2539
	11th to 20th	Day	13% 21% 6% 8% 6% 3 7% 4 6% 5% 21%	2540
	21st to end	Day	13% 15% 5% 9% 8% 4 4 5% 5% 7% 24%	2826
February	1st to 10th	Day	9% 15% 6% 8% 5% 4 5% 5% 6% 8% 29%	1710
	11th to 20th	Day	8% 13% 6% 8% 7% 4 5% 5% 5% 7% 32%	1750
	21st to end	Day	8% 15% 7% 11% 8% 3 5% 6% 5% 7% 25%	1570
March	1st to 10th	Day	9% 11% 7% 12% 8% 4 6% 5% 5% 6% 25%	1851
	11th to 20th	Day	8% 14% 5% 9% 7% 4 6% 5% 5% 7% 31%	1895
	21st to end	Day	10% 16% 7% 10% 9% 4 6% 6% 5% 6% 22%	2344
April	1st to 10th	Day	10% 14% 4 8% 8% 4 5% 5% 6% 6% 28%	2160
	11th to 20th	Day	9% 13% 6% 9% 7% 4 5% 4 5% 6% 34%	2129
	21st to end	Day	11% 11% 4 6% 5% 3 5% 4 5% 7% 39%	2248
May	1st to 10th	Day	7% 8% 3 6% 6% 3 5% 4 5% 8% 44%	2478
	11th to 20th	Day	12% 8% 3 7% 7% 4 5% 5% 5% 7% 38%	2477
	21st to end	Day	15% 9% 4 6% 6% 3 5% 5% 5% 7% 36%	2723
June	1st to 10th	Day	14% 7% 3 6% 5% 3 5% 4 5% 7% 39%	2520
	11th to 20th	Day	10% 6% 3 6% 4 3 4 4 6% 7% 48%	2520
	21st to end	Day	5% 3 1 3 4 2 3 3 4 6% 66%	2520
July	1st to 10th	Day	1 2 1 2 3 2 4 4 4 5% 71%	2520
	11th to 20th	Day	2 2 1 2 3 2 3 3 4 5% 74%	2520
	21st to end	Day	1 1 1 2 2 2 2 3 3 4 79%	2741
August	1st to 10th	Day	2 2 1 3 4 2 4 3 5% 6% 68%	2507
	11th to 20th	Day	3 2 1 2 3 2 2 2 3 5% 74%	2222
	21st to end	Day	3 2 1 3 3 2 2 3 3 6% 73%	2376
September	1st to 10th	Day	2 2 1 3 3 2 2 3 3 5% 74%	2160
	11th to 20th	Day	6% 4 2 4 4 2 4 4 5% 6% 60%	2128
	21st to end	Day	8% 6% 3 5% 4 3 3 4 5% 6% 54%	1980
October	1st to 10th	Day	12% 8% 3 6% 5% 3 3 3 4 6% 48%	1818
	11th to 20th	Day	10% 7% 2 5% 4 3 4 4 6% 7% 48%	1800
	21st to end	Day	11% 9% 3 6% 6% 4 4 5% 5% 6% 42%	1810
November	1st to 10th	Day	14% 11% 4 6% 6% 3 5% 4 5% 8% 33%	1674
	11th to 20th	Day	12% 12% 4 8% 7% 4 6% 6% 6% 7% 29%	1630
	21st to end	Day	8% 13% 5% 6% 7% 4 5% 5% 6% 7% 35%	1520
December	1st to 10th	Day	9% 13% 3 7% 7% 3 6% 5% 5% 6% 34%	1520
	11th to 20th	Day	10% 15% 4 8% 7% 3 6% 5% 7% 8% 27%	1928
	21st to end	Day	9% 13% 6% 9% 8% 5% 7% 6% 6% 7% 23%	2794
January	1st to 10th	Night	10% 18% 7% 9% 9% 4 5% 6% 6% 6% 20%	4406
	11th to 20th	Night	17% 22% 5% 8% 7% 4 4 4 3 5% 22%	4420
	21st to end	Night	13% 14% 4 8% 7% 4 6% 6% 6% 7% 26%	4827
February	1st to 10th	Night	11% 14% 6% 9% 7% 3 6% 5% 5% 6% 30%	2470
	11th to 20th	Night	9% 13% 5% 9% 6% 4 5% 5% 5% 6% 32%	2316
	21st to end	Night	8% 14% 6% 10% 8% 4 6% 6% 5% 6% 26%	1884
March	1st to 10th	Night	9% 12% 5% 7% 7% 3 6% 5% 7% 9% 30%	2225
	11th to 20th	Night	8% 12% 5% 8% 6% 4 6% 5% 7% 8% 30%	2062
	21st to end	Night	8% 13% 6% 9% 5% 5% 6% 6% 6% 8% 28%	2012
April	1st to 10th	Night	11% 12% 5% 7% 6% 3 4 5% 5% 6% 36%	1800
	11th to 20th	Night	9% 12% 5% 7% 6% 2 6% 5% 5% 5% 38%	1779
	21st to end	Night	10% 11% 3 6% 5% 3 4 5% 6% 7% 41%	1710
May	1st to 10th	Night	7% 8% 3 4 5% 3 4 5% 5% 7% 49%	1479
	11th to 20th	Night	11% 6% 2 5% 6% 2 4 4 6% 8% 46%	1416
	21st to end	Night	12% 10% 4 5% 4 3 4 4 5% 7% 41%	1552
June	1st to 10th	Night	11% 6% 3 4 4 3 3 4 5% 9% 47%	1440
	11th to 20th	Night	10% 7% 2 5% 4 2 3 4 3 6% 54%	1440
	21st to end	Night	4 3 1 2 4 2 4 4 4 5% 67%	1440
July	1st to 10th	Night	1 2 1 2 2 2 3 5% 5% 7% 70%	1440
	11th to 20th	Night	1 1 1 2 1 2 3 3 4 83%	1440
	21st to end	Night	1 1 1 2 2 2 2 3 3 4 79%	1576
August	1st to 10th	Night	3 2 1 2 3 2 3 4 5% 7% 67%	1432
	11th to 20th	Night	2 1 1 2 2 2 2 2 4 5% 76%	1678
	21st to end	Night	2 2 1 2 2 2 2 3 3 5% 74%	1980
September	1st to 10th	Night	3 2 1 2 2 2 2 3 4 6% 75%	1800
	11th to 20th	Night	4 3 2 3 3 2 4 5% 4 7% 64%	1831
	21st to end	Night	6% 5% 2 4 4 2 3 4 4 6% 58%	1980
October	1st to 10th	Night	9% 8% 2 5% 4 2 3 3 4 7% 53%	2140
	11th to 20th	Night	9% 6% 2 5% 4 2 4 5% 5% 7% 52%	2160
	21st to end	Night	8% 9% 3 8% 6% 3 4 4 5% 6% 44%	2544
November	1st to 10th	Night	14% 11% 3 6% 6% 3 4 5% 6% 7% 35%	2405
	11th to 20th	Night	14% 10% 3 7% 6% 3 6% 5% 7% 7% 32%	2547
	21st to end	Night	10% 12% 5% 6% 5% 3 5% 5% 6% 7% 36%	2660
December	1st to 10th	Night	10% 12% 4 7% 6% 3 6% 5% 5% 7% 35%	2660
	11th to 20th	Night	10% 12% 6% 9% 6% 4 6% 6% 7% 8% 26%	3276
	21st to end	Night	9% 13% 5% 9% 7% 4 7% 7% 6% 7% 27%	4862

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	65% 3 12% 17% 3	2539
	11th to 20th	Day	64% 2 13% 14% 5% 2	2540
	21st to end	Day	60% 3 14% 17% 5% 1	2826
February	1st to 10th	Day	54% 4 15% 21% 6%	1710
	11th to 20th	Day	53% 4 13% 19% 9% 2	1759
	21st to end	Day	59% 6% 11% 15% 8% 1	1570
March	1st to 10th	Day	60% 3 12% 16% 8% 1	1851
	11th to 20th	Day	53% 3 13% 24% 8%	1895
	21st to end	Day	63% 5% 12% 16% 5%	2344
April	1st to 10th	Day	58% 3 11% 16% 11% 2	2160
	11th to 20th	Day	53% 2 9% 20% 13% 2	2132
	21st to end	Day	46% 4 10% 24% 14% 1	2248
May	1st to 10th	Day	40% 3 10% 29% 17% 1	2478
	11th to 20th	Day	46% 3 11% 25% 14% 2	2480
	21st to end	Day	50% 3 12% 23% 11% 1	2724
June	1st to 10th	Day	44% 4 9% 31% 12% 1	2520
	11th to 20th	Day	36% 2 9% 29% 20% 4	2520
	21st to end	Day	21% 1 9% 29% 29% 11%	2520
July	1st to 10th	Day	17% 2 6% 21% 29% 26%	2451
	11th to 20th	Day	13% 2 6% 14% 31% 34%	2445
	21st to end	Day	12% 1 1 11% 41% 33%	2589
August	1st to 10th	Day	18% 2 4 21% 35% 19%	2490
	11th to 20th	Day	15% 1 4 23% 35% 22%	2222
	21st to end	Day	15% 1 3 24% 39% 18%	2376
September	1st to 10th	Day	16% 1 4 25% 32% 22%	2160
	11th to 20th	Day	26% 2 6% 25% 27% 14%	2128
	21st to end	Day	32% 2 8% 25% 24% 9%	1980
October	1st to 10th	Day	40% 3 8% 21% 20% 8%	1818
	11th to 20th	Day	36% 3 11% 25% 20% 5%	1800
	21st to end	Day	45% 3 11% 23% 17% 1	1810
November	1st to 10th	Day	50% 4 12% 22% 11% 1	1674
	11th to 20th	Day	55% 5% 13% 21% 6%	1630
	21st to end	Day	48% 4 14% 18% 14% 1	1520
December	1st to 10th	Day	51% 5% 16% 18% 9% 1	1520
	11th to 20th	Day	55% 3 20% 17% 5%	1928
	21st to end	Day	60% 2 16% 18% 4	2794
January	1st to 10th	Night	64% 3 14% 14% 3	4406
	11th to 20th	Night	66% 3 11% 12% 6% 2	4420
	21st to end	Night	57% 2 19% 15% 6% 1	4827
February	1st to 10th	Night	56% 4 15% 17% 8%	2470
	11th to 20th	Night	51% 4 14% 19% 8% 2	2318
	21st to end	Night	58% 4 10% 18% 8% 1	1884
March	1st to 10th	Night	51% 4 12% 21% 9% 2	2225
	11th to 20th	Night	50% 4 16% 24% 5% 1	2062
	21st to end	Night	53% 5% 15% 21% 5%	2012
April	1st to 10th	Night	50% 3 13% 24% 8% 1	1800
	11th to 20th	Night	47% 4 12% 25% 11% 2	1779
	21st to end	Night	42% 6% 14% 23% 14% 1	1710
May	1st to 10th	Night	35% 3 15% 32% 16%	1479
	11th to 20th	Night	38% 3 17% 29% 11% 1	1416
	21st to end	Night	44% 3 17% 24% 11% 1	1552
June	1st to 10th	Night	36% 5% 14% 30% 15% 1	1440
	11th to 20th	Night	33% 3 12% 34% 15% 3	1440
	21st to end	Night	20% 2 11% 33% 26% 8%	1440
July	1st to 10th	Night	14% 3 10% 25% 27% 21%	1400
	11th to 20th	Night	8% 2 8% 19% 35% 28%	1392
	21st to end	Night	11% 2 1 17% 43% 26%	1488
August	1st to 10th	Night	17% 3 6% 27% 33% 15%	1424
	11th to 20th	Night	13% 2 6% 26% 34% 20%	1678
	21st to end	Night	14% 2 4 26% 39% 15%	1980
September	1st to 10th	Night	13% 2 5% 28% 34% 18%	1800
	11th to 20th	Night	21% 2 8% 26% 29% 14%	1831
	21st to end	Night	28% 2 8% 26% 23% 12%	1980
October	1st to 10th	Night	34% 2 9% 26% 23% 7%	2140
	11th to 20th	Night	33% 3 12% 25% 22% 5%	2160
	21st to end	Night	42% 3 13% 21% 17% 3	2544
November	1st to 10th	Night	48% 4 10% 21% 15% 2	2405
	11th to 20th	Night	50% 5% 15% 23% 8%	2547
	21st to end	Night	47% 4 12% 18% 18% 1	2660
December	1st to 10th	Night	50% 5% 17% 17% 9% 1	2660
	11th to 20th	Night	55% 4 16% 17% 7%	3276
	21st to end	Night	56% 3 13% 19% 8% 1	4862

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	23% 21% 30% 15% 11% 1	180
	11th to 20th	Day	18% 23% 31% 18% 8% 1	180
	21st to end	Day	15% 19% 40% 18% 8%	217
February	1st to 10th	Day	20% 23% 31% 19% 5% 1	370
	11th to 20th	Day	18% 28% 31% 17% 6% 1	405
	21st to end	Day	18% 26% 31% 21% 4	382
March	1st to 10th	Day	20% 28% 29% 19% 4 1	441
	11th to 20th	Day	18% 25% 30% 22% 5% 1	420
	21st to end	Day	23% 24% 31% 18% 5%	462
April	1st to 10th	Day	21% 24% 25% 21% 7% 2	420
	11th to 20th	Day	19% 28% 27% 16% 7% 3	412
	21st to end	Day	19% 19% 32% 18% 10% 2	420
May	1st to 10th	Day	12% 22% 29% 23% 13% 2	423
	11th to 20th	Day	23% 17% 26% 21% 11% 4	448
	21st to end	Day	18% 13% 24% 27% 14% 5%	485
June	1st to 10th	Day	14% 17% 27% 22% 15% 6%	450
	11th to 20th	Day	13% 23% 29% 23% 11% 2	450
	21st to end	Day	4 12% 36% 25% 17% 6%	450
July	1st to 10th	Day	2 12% 35% 33% 14% 4	446
	11th to 20th	Day	2 15% 36% 25% 18% 5%	444
	21st to end	Day	2 11% 34% 32% 16% 5%	487
August	1st to 10th	Day	4 8% 32% 32% 21% 4	447
	11th to 20th	Day	3 6% 26% 33% 21% 10%	437
	21st to end	Day	4 10% 28% 34% 18% 5%	495
September	1st to 10th	Day	4 8% 29% 32% 22% 5%	450
	11th to 20th	Day	7% 10% 26% 35% 18% 5%	450
	21st to end	Day	10% 15% 25% 28% 18% 3	450
October	1st to 10th	Day	14% 16% 22% 27% 16% 5%	450
	11th to 20th	Day	13% 16% 25% 26% 14% 6%	450
	21st to end	Day	17% 17% 27% 23% 12% 4	325
November	1st to 10th	Day	17% 21% 27% 24% 11%	270
	11th to 20th	Day	15% 19% 30% 23% 11% 2	232
	21st to end	Day	15% 18% 31% 27% 9% 1	180
December	1st to 10th	Day	15% 24% 32% 15% 11% 3	180
	11th to 20th	Day	21% 21% 42% 15% 2	180
	21st to end	Day	17% 19% 38% 20% 5% 1	198
January	1st to 10th	Night	19% 14% 30% 24% 13%	760
	11th to 20th	Night	20% 14% 25% 26% 13% 2	760
	21st to end	Night	18% 8% 26% 35% 11% 1	836
February	1st to 10th	Night	19% 12% 28% 31% 10% 1	760
	11th to 20th	Night	16% 12% 24% 34% 13% 1	744
	21st to end	Night	16% 16% 28% 32% 7% 1	628
March	1st to 10th	Night	16% 12% 28% 32% 11% 1	742
	11th to 20th	Night	14% 12% 23% 34% 16% 1	720
	21st to end	Night	16% 16% 24% 31% 12% 1	792
April	1st to 10th	Night	18% 13% 21% 29% 18% 1	720
	11th to 20th	Night	13% 13% 26% 28% 17% 3	711
	21st to end	Night	15% 10% 22% 36% 16% 1	630
May	1st to 10th	Night	10% 9% 19% 39% 22% 1	399
	11th to 20th	Night	13% 5% 13% 34% 32% 3	354
	21st to end	Night	15% 9% 13% 33% 26% 4	389
June	1st to 10th	Night	13% 5% 14% 41% 26% 2	360
	11th to 20th	Night	13% 9% 16% 38% 23% 1	360
	21st to end	Night	4 3 16% 46% 28% 2	360
July	1st to 10th	Night	1 3 13% 49% 32% 2	350
	11th to 20th	Night	1 2 16% 53% 26% 2	348
	21st to end	Night	1 2 13% 45% 37% 2	394
August	1st to 10th	Night	3 9% 49% 36% 2	358
	11th to 20th	Night	2 2 9% 36% 44% 7%	610
	21st to end	Night	3 3 14% 43% 34% 4	792
September	1st to 10th	Night	4 2 12% 41% 37% 3	720
	11th to 20th	Night	5% 3 15% 36% 35% 7%	720
	21st to end	Night	9% 5% 14% 36% 29% 6%	720
October	1st to 10th	Night	12% 4 17% 38% 27% 1	720
	11th to 20th	Night	13% 8% 17% 38% 20% 4	720
	21st to end	Night	15% 8% 18% 37% 17% 5%	792
November	1st to 10th	Night	19% 9% 21% 38% 13% 1	740
	11th to 20th	Night	20% 12% 22% 32% 12% 2	760
	21st to end	Night	15% 13% 25% 31% 13% 3	760
December	1st to 10th	Night	17% 12% 25% 32% 14% 1	760
	11th to 20th	Night	17% 13% 28% 30% 11% 1	760
	21st to end	Night	24% 16% 28% 25% 7%	836

Page generated at 2024-03-03 03:28:57. Version ac07

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