OneDarkSky.com Observation Site #1
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the OneDarkSky.com Observation Site #1 clear sky chart from 2005-11-06 to 2024-01-13.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 36%	74810
	Night	14% 9% 4 6% 5% 3 4 4 5% 7% 39%	74959
Transparency	Day	46% 6% 11% 22% 13% 2	74511
	Night	45% 6% 11% 22% 14% 2	74779
Seeing	Day	17% 14% 30% 23% 11% 4	14651
	Night	18% 12% 31% 27% 11% 1	24631

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	14% 13% 5% 7% 6% 4 5% 5% 4 6% 31%	1517
	11th to 20th	Day	13% 15% 7% 12% 7% 2 4 4 5% 7% 24%	1461
	21st to end	Day	14% 16% 9% 10% 7% 3 4 4 4 6% 23%	1632
February	1st to 10th	Day	15% 14% 6% 8% 8% 4 5% 4 5% 6% 26%	1643
	11th to 20th	Day	14% 12% 5% 8% 6% 4 5% 3 5% 5% 34%	1748
	21st to end	Day	15% 14% 6% 9% 6% 4 3 3 4 6% 30%	1480
March	1st to 10th	Day	15% 14% 5% 9% 6% 3 4 4 4 7% 29%	1800
	11th to 20th	Day	13% 9% 4 7% 6% 3 5% 5% 4 8% 36%	1857
	21st to end	Day	20% 11% 5% 9% 6% 4 5% 5% 5% 6% 25%	2376
April	1st to 10th	Day	17% 12% 5% 7% 6% 3 5% 4 5% 6% 31%	2160
	11th to 20th	Day	17% 10% 3 5% 6% 4 5% 5% 5% 7% 34%	2134
	21st to end	Day	20% 9% 3 7% 6% 4 4 5% 5% 7% 32%	2254
May	1st to 10th	Day	17% 8% 3 6% 6% 4 5% 6% 5% 8% 31%	2340
	11th to 20th	Day	18% 9% 3 6% 5% 3 5% 5% 6% 7% 33%	2438
	21st to end	Day	13% 6% 3 6% 7% 4 6% 5% 6% 8% 35%	2725
June	1st to 10th	Day	9% 5% 3 6% 4 3 5% 5% 6% 7% 45%	2520
	11th to 20th	Day	10% 6% 2 5% 5% 3 5% 6% 6% 8% 45%	2520
	21st to end	Day	11% 6% 3 7% 6% 3 5% 5% 7% 9% 38%	2520
July	1st to 10th	Day	8% 4 2 5% 6% 3 6% 6% 6% 9% 45%	2520
	11th to 20th	Day	9% 5% 3 5% 4 3 6% 5% 6% 9% 44%	2520
	21st to end	Day	6% 5% 2 5% 5% 4 5% 6% 8% 10% 43%	2743
August	1st to 10th	Day	8% 5% 2 6% 6% 4 5% 5% 7% 10% 41%	2472
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 6% 6% 9% 40%	2134
	21st to end	Day	9% 5% 2 4 5% 4 5% 6% 6% 8% 47%	2376
September	1st to 10th	Day	12% 5% 3 4 5% 3 5% 5% 4 8% 45%	2160
	11th to 20th	Day	12% 4 2 4 4 2 4 4 6% 7% 51%	2052
	21st to end	Day	11% 6% 2 6% 5% 3 5% 5% 6% 8% 43%	1980
October	1st to 10th	Day	12% 7% 3 6% 5% 2 3 4 5% 6% 46%	1922
	11th to 20th	Day	20% 9% 3 6% 5% 4 3 4 6% 7% 34%	1792
	21st to end	Day	21% 10% 3 5% 4 3 4 5% 4 6% 36%	1782
November	1st to 10th	Day	12% 8% 3 5% 4 3 4 5% 5% 6% 44%	1672
	11th to 20th	Day	16% 11% 4 7% 5% 3 4 5% 5% 7% 33%	1710
	21st to end	Day	18% 11% 3 8% 5% 2 4 4 3 5% 36%	1629
December	1st to 10th	Day	14% 13% 6% 7% 7% 4 4 4 4 5% 31%	1520
	11th to 20th	Day	12% 13% 5% 10% 6% 4 4 5% 5% 7% 29%	1918
	21st to end	Day	20% 24% 10% 10% 6% 3 4 3 3 3 15%	2783
January	1st to 10th	Night	14% 12% 6% 8% 7% 3 4 4 4 5% 35%	2648
	11th to 20th	Night	16% 15% 6% 9% 6% 3 4 4 4 5% 29%	2561
	21st to end	Night	15% 13% 6% 10% 6% 3 5% 4 5% 6% 26%	2722
February	1st to 10th	Night	15% 14% 6% 8% 7% 4 4 3 4 6% 30%	2315
	11th to 20th	Night	14% 11% 4 7% 6% 3 4 5% 5% 6% 36%	2098
	21st to end	Night	18% 12% 4 8% 6% 2 3 3 4 5% 36%	1776
March	1st to 10th	Night	16% 10% 5% 7% 6% 3 4 4 5% 5% 34%	2160
	11th to 20th	Night	12% 8% 4 5% 5% 3 5% 5% 5% 7% 41%	2116
	21st to end	Night	21% 9% 3 6% 6% 3 4 5% 5% 6% 32%	1980
April	1st to 10th	Night	16% 7% 4 6% 6% 3 5% 5% 5% 6% 38%	1800
	11th to 20th	Night	19% 10% 3 5% 5% 3 4 5% 4 5% 38%	1775
	21st to end	Night	19% 8% 3 6% 5% 2 4 4 5% 6% 38%	1706
May	1st to 10th	Night	15% 7% 3 6% 5% 4 6% 6% 6% 7% 35%	1620
	11th to 20th	Night	16% 6% 2 5% 5% 3 3 5% 5% 8% 40%	1453
	21st to end	Night	12% 5% 3 7% 6% 3 4 4 5% 8% 42%	1551
June	1st to 10th	Night	9% 4 2 4 5% 3 5% 5% 7% 8% 48%	1440
	11th to 20th	Night	9% 5% 3 4 6% 3 4 6% 5% 8% 47%	1440
	21st to end	Night	9% 5% 2 6% 6% 3 5% 6% 7% 9% 42%	1440
July	1st to 10th	Night	6% 4 1 4 4 3 6% 5% 7% 10% 50%	1440
	11th to 20th	Night	7% 4 2 4 5% 2 5% 5% 8% 9% 51%	1440
	21st to end	Night	6% 3 2 3 4 3 6% 5% 7% 10% 51%	1575
August	1st to 10th	Night	5% 3 1 4 5% 4 5% 6% 8% 9% 49%	1463
	11th to 20th	Night	8% 3 2 4 5% 2 4 4 6% 9% 53%	1765
	21st to end	Night	8% 4 2 5% 4 2 3 4 4 8% 56%	1980
September	1st to 10th	Night	11% 6% 2 5% 5% 2 3 3 4 7% 52%	1800
	11th to 20th	Night	10% 5% 2 4 4 3 3 3 5% 6% 55%	1890
	21st to end	Night	11% 6% 2 6% 4 3 4 4 5% 8% 48%	1980
October	1st to 10th	Night	11% 6% 3 5% 4 3 4 4 4 6% 50%	2036
	11th to 20th	Night	18% 8% 2 4 4 2 4 3 4 6% 44%	2166
	21st to end	Night	21% 9% 2 5% 4 2 4 3 5% 6% 37%	2574
November	1st to 10th	Night	11% 8% 3 5% 4 3 3 4 4 6% 49%	2406
	11th to 20th	Night	14% 10% 4 7% 5% 4 4 4 5% 6% 37%	2470
	21st to end	Night	16% 10% 5% 7% 5% 3 4 4 4 5% 37%	2550
December	1st to 10th	Night	16% 10% 5% 8% 6% 3 5% 4 4 7% 32%	2660
	11th to 20th	Night	15% 13% 5% 8% 6% 3 4 4 4 6% 32%	3279
	21st to end	Night	22% 18% 7% 9% 5% 3 4 5% 5% 5% 17%	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	54% 5% 12% 17% 11%	1518
	11th to 20th	Day	60% 6% 13% 15% 5% 1	1461
	21st to end	Day	62% 4 10% 14% 9%	1632
February	1st to 10th	Day	59% 5% 12% 14% 9% 1	1643
	11th to 20th	Day	52% 4 10% 21% 10% 2	1758
	21st to end	Day	56% 6% 9% 18% 10% 1	1480
March	1st to 10th	Day	55% 7% 11% 19% 8% 1	1800
	11th to 20th	Day	47% 6% 12% 22% 11% 2	1857
	21st to end	Day	60% 6% 11% 17% 6% 1	2376
April	1st to 10th	Day	54% 6% 10% 19% 11%	2160
	11th to 20th	Day	49% 6% 8% 21% 12% 3	2134
	21st to end	Day	51% 7% 12% 17% 12% 2	2254
May	1st to 10th	Day	50% 8% 12% 22% 7%	2340
	11th to 20th	Day	49% 7% 10% 22% 11%	2442
	21st to end	Day	45% 7% 12% 18% 16% 2	2725
June	1st to 10th	Day	36% 7% 11% 27% 18% 2	2520
	11th to 20th	Day	36% 8% 11% 23% 19% 3	2520
	21st to end	Day	40% 8% 13% 22% 14% 2	2520
July	1st to 10th	Day	33% 8% 13% 29% 14% 4	2451
	11th to 20th	Day	34% 8% 13% 25% 17% 2	2445
	21st to end	Day	32% 9% 15% 24% 16% 3	2591
August	1st to 10th	Day	37% 8% 14% 28% 12% 2	2457
	11th to 20th	Day	37% 7% 15% 25% 15% 1	2134
	21st to end	Day	32% 8% 12% 25% 20% 4	2376
September	1st to 10th	Day	37% 7% 11% 24% 17% 4	2160
	11th to 20th	Day	30% 7% 11% 30% 19% 3	2052
	21st to end	Day	38% 6% 10% 26% 19% 1	1980
October	1st to 10th	Day	39% 6% 11% 25% 17% 1	1922
	11th to 20th	Day	50% 5% 11% 21% 12% 1	1792
	21st to end	Day	50% 5% 10% 23% 10% 2	1782
November	1st to 10th	Day	40% 6% 14% 22% 17% 2	1672
	11th to 20th	Day	51% 5% 11% 22% 10% 1	1710
	21st to end	Day	52% 5% 11% 23% 9%	1629
December	1st to 10th	Day	55% 5% 12% 19% 8% 1	1520
	11th to 20th	Day	55% 5% 14% 17% 7% 2	1915
	21st to end	Day	76% 3 7% 10% 4	2783
January	1st to 10th	Night	53% 4 10% 20% 12% 1	2648
	11th to 20th	Night	58% 5% 13% 14% 10%	2561
	21st to end	Night	59% 5% 10% 15% 10% 1	2722
February	1st to 10th	Night	57% 4 10% 16% 12% 1	2315
	11th to 20th	Night	49% 5% 11% 20% 13% 1	2099
	21st to end	Night	52% 4 10% 20% 10% 4	1776
March	1st to 10th	Night	51% 7% 12% 20% 9% 1	2160
	11th to 20th	Night	42% 6% 12% 21% 16% 3	2116
	21st to end	Night	54% 6% 10% 19% 11% 1	1980
April	1st to 10th	Night	46% 6% 11% 23% 13% 2	1800
	11th to 20th	Night	48% 5% 6% 20% 16% 4	1775
	21st to end	Night	45% 6% 10% 22% 12% 3	1706
May	1st to 10th	Night	46% 7% 12% 23% 12%	1620
	11th to 20th	Night	41% 7% 11% 25% 14% 2	1454
	21st to end	Night	41% 6% 13% 21% 17% 2	1552
June	1st to 10th	Night	32% 7% 13% 25% 20% 3	1440
	11th to 20th	Night	34% 7% 10% 25% 23% 2	1440
	21st to end	Night	36% 8% 15% 22% 17% 2	1440
July	1st to 10th	Night	27% 8% 15% 29% 16% 5%	1400
	11th to 20th	Night	28% 9% 13% 29% 19% 3	1392
	21st to end	Night	27% 7% 15% 27% 19% 5%	1487
August	1st to 10th	Night	27% 9% 17% 30% 15% 2	1454
	11th to 20th	Night	27% 7% 15% 30% 19% 1	1765
	21st to end	Night	28% 5% 12% 30% 20% 5%	1980
September	1st to 10th	Night	33% 7% 10% 25% 23% 3	1800
	11th to 20th	Night	30% 5% 7% 33% 23% 2	1890
	21st to end	Night	35% 6% 11% 30% 16% 2	1980
October	1st to 10th	Night	35% 6% 9% 27% 21% 2	2036
	11th to 20th	Night	42% 4 10% 23% 19% 2	2166
	21st to end	Night	49% 5% 10% 23% 12% 1	2574
November	1st to 10th	Night	38% 5% 9% 26% 19% 3	2406
	11th to 20th	Night	48% 4 11% 23% 12% 2	2470
	21st to end	Night	49% 5% 11% 23% 12%	2550
December	1st to 10th	Night	53% 5% 11% 21% 9% 1	2660
	11th to 20th	Night	53% 5% 12% 19% 9% 1	3281
	21st to end	Night	69% 5% 9% 12% 5%	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	20% 19% 39% 19% 3	270
	11th to 20th	Day	24% 19% 39% 14% 4	248
	21st to end	Day	21% 24% 34% 15% 5% 1	264
February	1st to 10th	Day	23% 26% 38% 11% 2	240
	11th to 20th	Day	29% 23% 30% 15% 3	240
	21st to end	Day	29% 25% 36% 7% 3 1	198
March	1st to 10th	Day	23% 30% 35% 10% 1	240
	11th to 20th	Day	26% 23% 32% 16% 4	257
	21st to end	Day	30% 16% 29% 18% 5% 2	462
April	1st to 10th	Day	26% 17% 31% 21% 5%	420
	11th to 20th	Day	23% 25% 22% 20% 9% 2	412
	21st to end	Day	22% 19% 30% 20% 8% 1	420
May	1st to 10th	Day	22% 16% 32% 21% 7% 2	423
	11th to 20th	Day	21% 14% 32% 23% 8% 2	584
	21st to end	Day	16% 13% 30% 22% 14% 4	679
June	1st to 10th	Day	8% 11% 35% 28% 13% 4	630
	11th to 20th	Day	11% 11% 33% 28% 13% 4	630
	21st to end	Day	12% 12% 33% 29% 10% 4	630
July	1st to 10th	Day	7% 5% 26% 30% 19% 12%	621
	11th to 20th	Day	11% 7% 29% 31% 15% 7%	618
	21st to end	Day	6% 6% 32% 34% 16% 6%	684
August	1st to 10th	Day	9% 3 25% 32% 21% 9%	591
	11th to 20th	Day	10% 6% 21% 31% 21% 11%	439
	21st to end	Day	9% 6% 23% 33% 22% 8%	495
September	1st to 10th	Day	15% 8% 24% 27% 21% 5%	450
	11th to 20th	Day	10% 6% 21% 31% 23% 9%	450
	21st to end	Day	12% 16% 24% 25% 17% 6%	450
October	1st to 10th	Day	17% 13% 29% 25% 14% 4	392
	11th to 20th	Day	25% 25% 31% 14% 4	270
	21st to end	Day	33% 21% 29% 11% 5%	297
November	1st to 10th	Day	17% 18% 38% 19% 6% 2	270
	11th to 20th	Day	25% 24% 31% 13% 7%	270
	21st to end	Day	25% 16% 39% 17% 1 1	270
December	1st to 10th	Day	17% 26% 39% 13% 5%	270
	11th to 20th	Day	18% 27% 33% 16% 5% 1	270
	21st to end	Day	26% 25% 35% 11% 2	297
January	1st to 10th	Night	20% 17% 38% 22% 3	950
	11th to 20th	Night	22% 17% 36% 20% 4 1	915
	21st to end	Night	21% 14% 37% 24% 4	990
February	1st to 10th	Night	24% 15% 36% 21% 4	875
	11th to 20th	Night	20% 20% 34% 22% 4	703
	21st to end	Night	24% 18% 36% 19% 3	592
March	1st to 10th	Night	20% 16% 35% 22% 6%	720
	11th to 20th	Night	17% 12% 38% 25% 7% 1	694
	21st to end	Night	24% 12% 31% 25% 7% 1	594
April	1st to 10th	Night	21% 14% 35% 24% 7%	540
	11th to 20th	Night	24% 14% 30% 25% 7% 1	533
	21st to end	Night	23% 11% 31% 27% 8% 1	540
May	1st to 10th	Night	17% 11% 36% 28% 7% 1	540
	11th to 20th	Night	19% 9% 30% 29% 13%	531
	21st to end	Night	14% 5% 29% 33% 17% 1	584
June	1st to 10th	Night	9% 6% 28% 39% 17%	540
	11th to 20th	Night	11% 6% 33% 38% 13% 1	540
	21st to end	Night	10% 6% 31% 35% 17% 1	540
July	1st to 10th	Night	6% 2 21% 40% 27% 4	525
	11th to 20th	Night	6% 5% 26% 37% 23% 2	522
	21st to end	Night	6% 2 22% 44% 24% 1	591
August	1st to 10th	Night	5% 2 17% 45% 27% 4	537
	11th to 20th	Night	7% 3 18% 38% 31% 4	534
	21st to end	Night	9% 3 21% 38% 28% 2	594
September	1st to 10th	Night	13% 5% 21% 34% 23% 3	540
	11th to 20th	Night	10% 5% 22% 31% 28% 4	630
	21st to end	Night	12% 10% 24% 30% 22% 3	720
October	1st to 10th	Night	14% 8% 26% 31% 18% 2	720
	11th to 20th	Night	22% 14% 32% 23% 9% 1	720
	21st to end	Night	28% 13% 30% 21% 8%	792
November	1st to 10th	Night	16% 14% 37% 23% 9% 1	740
	11th to 20th	Night	20% 19% 32% 23% 5%	760
	21st to end	Night	21% 15% 37% 22% 6%	840
December	1st to 10th	Night	22% 16% 36% 21% 4	950
	11th to 20th	Night	23% 15% 34% 24% 4	950
	21st to end	Night	29% 16% 34% 18% 2	1045

Page generated at 2024-01-10 18:35:21. Version ac07

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