D.A.R.C. Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the D.A.R.C. Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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	4 3 1 3 3 2 3 3 4 6% 69%	74721
	Night	4 3 1 3 3 2 3 3 4 6% 67%	75009
Transparency	Day	18% 4 7% 19% 27% 24%	74438
	Night	19% 4 9% 20% 26% 23%	74814
Seeing	Day	5% 7% 19% 32% 27% 9%	14257
	Night	5% 4 15% 35% 32% 8%	23823

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% 6% 3 4 5% 3 6% 6% 6% 9% 42%	1564
	11th to 20th	Day	6% 3 2 3 5% 3 4 6% 5% 8% 54%	1630
	21st to end	Day	9% 6% 2 5% 5% 3 5% 5% 5% 7% 46%	1782
February	1st to 10th	Day	11% 5% 2 4 3 2 4 5% 4 8% 53%	1627
	11th to 20th	Day	6% 4 2 4 5% 3 5% 5% 5% 7% 54%	1750
	21st to end	Day	8% 6% 2 5% 5% 3 3 4 6% 7% 51%	1480
March	1st to 10th	Day	8% 6% 3 5% 5% 4 4 6% 7% 9% 45%	1858
	11th to 20th	Day	8% 5% 3 4 4 3 5% 5% 6% 10% 47%	1980
	21st to end	Day	6% 4 2 5% 4 2 5% 6% 5% 7% 54%	2268
April	1st to 10th	Day	6% 5% 3 5% 4 3 5% 4 5% 7% 54%	2160
	11th to 20th	Day	5% 4 2 3 4 3 3 4 5% 6% 63%	2129
	21st to end	Day	4 3 1 3 3 2 3 3 4 6% 69%	2160
May	1st to 10th	Day	3 2 1 3 3 2 2 3 4 6% 71%	2160
	11th to 20th	Day	2 1 1 2 2 2 3 3 4 6% 74%	2333
	21st to end	Day	3 1 1 2 3 2 3 3 3 6% 74%	2723
June	1st to 10th	Day	2 2 1 2 2 2 2 3 4 6% 75%	2520
	11th to 20th	Day	1 1 1 1 2 4 89%	2520
	21st to end	Day	1 1 1 1 1 1 1 2 2 89%	2520
July	1st to 10th	Day	1 1 1 1 1 2 3 90%	2520
	11th to 20th	Day	1 1 1 1 1 1 2 3 3 86%	2427
	21st to end	Day	1 1 1 1 1 1 2 2 2 3 85%	2546
August	1st to 10th	Day	1 1 1 1 1 1 2 2 3 86%	2289
	11th to 20th	Day	1 1 1 1 2 3 91%	2122
	21st to end	Day	1 1 1 1 2 2 90%	2376
September	1st to 10th	Day	1 1 1 1 1 1 2 92%	2160
	11th to 20th	Day	1 1 1 1 1 1 2 3 4 86%	2160
	21st to end	Day	1 1 1 2 1 1 2 3 4 83%	1963
October	1st to 10th	Day	2 2 1 2 2 2 3 3 3 5% 77%	1800
	11th to 20th	Day	2 2 1 2 2 2 3 3 3 5% 76%	1800
	21st to end	Day	3 2 1 2 3 2 3 4 3 6% 73%	1980
November	1st to 10th	Day	4 3 2 3 3 3 5% 4 5% 8% 61%	1756
	11th to 20th	Day	5% 3 1 3 3 2 4 4 4 7% 63%	1710
	21st to end	Day	5% 4 3 4 3 3 3 4 5% 7% 61%	1706
December	1st to 10th	Day	6% 5% 2 5% 5% 3 6% 6% 5% 8% 50%	1520
	11th to 20th	Day	12% 9% 4 7% 6% 5% 6% 4 5% 6% 36%	1928
	21st to end	Day	9% 8% 2 6% 6% 4 5% 6% 6% 8% 40%	2794
January	1st to 10th	Night	8% 6% 3 5% 6% 2 5% 4 6% 8% 47%	2598
	11th to 20th	Night	5% 5% 2 5% 5% 2 5% 5% 5% 8% 53%	2358
	21st to end	Night	8% 5% 2 4 4 2 3 4 5% 9% 53%	2574
February	1st to 10th	Night	9% 4 2 4 3 2 3 3 5% 8% 57%	2331
	11th to 20th	Night	5% 2 1 2 3 2 4 5% 6% 10% 59%	2098
	21st to end	Night	5% 4 2 3 4 3 3 4 4 6% 59%	1776
March	1st to 10th	Night	7% 5% 2 4 6% 3 5% 4 6% 7% 52%	2100
	11th to 20th	Night	4 5% 1 4 4 3 5% 6% 6% 8% 53%	1980
	21st to end	Night	7% 3 2 3 3 2 4 4 5% 7% 61%	2088
April	1st to 10th	Night	5% 4 2 3 4 2 4 4 5% 7% 60%	1800
	11th to 20th	Night	3 3 1 3 3 2 3 4 4 6% 68%	1779
	21st to end	Night	2 1 1 1 2 1 3 3 4 8% 74%	1800
May	1st to 10th	Night	2 1 1 2 2 2 2 3 4 7% 75%	1800
	11th to 20th	Night	2 1 1 2 2 1 2 2 2 7% 80%	1554
	21st to end	Night	2 1 1 1 2 1 1 2 3 4 82%	1552
June	1st to 10th	Night	1 1 2 2 1 3 3 3 5% 77%	1440
	11th to 20th	Night	1 1 1 1 1 2 3 89%	1440
	21st to end	Night	1 1 2 3 91%	1440
July	1st to 10th	Night	1 1 1 2 2 2 91%	1440
	11th to 20th	Night	1 1 1 1 1 2 2 2 3 87%	1529
	21st to end	Night	1 1 1 1 2 1 2 2 3 4 83%	1773
August	1st to 10th	Night	1 1 1 2 1 1 2 2 1 3 87%	1649
	11th to 20th	Night	1 1 2 1 1 2 2 3 87%	1780
	21st to end	Night	1 1 1 1 1 2 2 90%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 2 91%	1800
	11th to 20th	Night	1 1 1 1 1 1 2 2 2 88%	1800
	21st to end	Night	1 1 1 1 1 2 2 4 86%	1994
October	1st to 10th	Night	3 2 1 1 2 1 2 3 4 5% 77%	2160
	11th to 20th	Night	2 1 2 2 2 3 3 4 6% 75%	2160
	21st to end	Night	3 1 1 2 1 1 1 2 3 6% 78%	2376
November	1st to 10th	Night	4 2 1 2 2 2 3 3 4 7% 70%	2320
	11th to 20th	Night	5% 3 2 3 3 2 3 3 5% 8% 63%	2470
	21st to end	Night	4 3 1 2 3 2 4 4 5% 7% 63%	2472
December	1st to 10th	Night	8% 5% 2 4 4 3 4 4 4 7% 55%	2660
	11th to 20th	Night	11% 6% 2 5% 6% 4 6% 6% 7% 8% 39%	3276
	21st to end	Night	11% 6% 3 5% 5% 3 5% 5% 6% 8% 44%	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	38% 5% 14% 26% 12% 5%	1564
	11th to 20th	Day	28% 5% 13% 23% 20% 11%	1630
	21st to end	Day	37% 6% 11% 18% 23% 5%	1782
February	1st to 10th	Day	32% 4 8% 24% 21% 12%	1627
	11th to 20th	Day	29% 5% 10% 22% 26% 9%	1760
	21st to end	Day	33% 6% 10% 23% 22% 7%	1480
March	1st to 10th	Day	34% 6% 12% 22% 20% 5%	1858
	11th to 20th	Day	32% 6% 10% 25% 21% 5%	1980
	21st to end	Day	29% 5% 15% 27% 17% 6%	2268
April	1st to 10th	Day	29% 5% 11% 25% 20% 9%	2160
	11th to 20th	Day	23% 5% 9% 28% 27% 8%	2132
	21st to end	Day	18% 3 8% 32% 31% 7%	2160
May	1st to 10th	Day	15% 5% 8% 23% 38% 11%	2160
	11th to 20th	Day	13% 4 5% 23% 39% 15%	2336
	21st to end	Day	14% 3 8% 32% 33% 10%	2724
June	1st to 10th	Day	13% 4 8% 21% 34% 22%	2520
	11th to 20th	Day	4 1 4 17% 39% 35%	2520
	21st to end	Day	6% 1 1 7% 30% 54%	2520
July	1st to 10th	Day	4 2 1 4 22% 67%	2451
	11th to 20th	Day	6% 2 3 8% 23% 58%	2353
	21st to end	Day	7% 1 2 8% 26% 56%	2405
August	1st to 10th	Day	6% 1 2 9% 26% 55%	2273
	11th to 20th	Day	3 1 1 9% 33% 52%	2122
	21st to end	Day	4 1 10% 37% 48%	2376
September	1st to 10th	Day	4 1 2 7% 31% 55%	2160
	11th to 20th	Day	5% 2 2 18% 44% 29%	2160
	21st to end	Day	8% 2 2 17% 43% 28%	1963
October	1st to 10th	Day	12% 3 6% 19% 28% 32%	1800
	11th to 20th	Day	13% 3 5% 24% 28% 27%	1800
	21st to end	Day	15% 3 5% 20% 32% 25%	1980
November	1st to 10th	Day	21% 5% 9% 21% 27% 16%	1756
	11th to 20th	Day	21% 5% 12% 25% 28% 10%	1710
	21st to end	Day	25% 4 9% 22% 26% 14%	1706
December	1st to 10th	Day	31% 6% 12% 19% 19% 13%	1520
	11th to 20th	Day	46% 7% 9% 17% 15% 5%	1928
	21st to end	Day	38% 8% 14% 26% 11% 3	2794
January	1st to 10th	Night	33% 5% 12% 28% 17% 5%	2598
	11th to 20th	Night	29% 5% 13% 22% 18% 12%	2358
	21st to end	Night	31% 4 14% 18% 25% 9%	2574
February	1st to 10th	Night	27% 4 8% 23% 25% 12%	2331
	11th to 20th	Night	21% 5% 12% 25% 28% 10%	2099
	21st to end	Night	26% 5% 11% 29% 22% 7%	1776
March	1st to 10th	Night	31% 5% 15% 21% 20% 6%	2100
	11th to 20th	Night	26% 7% 14% 23% 22% 8%	1980
	21st to end	Night	24% 5% 14% 29% 21% 8%	2088
April	1st to 10th	Night	24% 4 15% 26% 22% 9%	1800
	11th to 20th	Night	18% 4 13% 28% 26% 10%	1779
	21st to end	Night	12% 3 12% 33% 31% 9%	1800
May	1st to 10th	Night	10% 4 9% 23% 36% 17%	1800
	11th to 20th	Night	10% 1 6% 24% 43% 16%	1554
	21st to end	Night	9% 2 8% 32% 37% 12%	1552
June	1st to 10th	Night	12% 3 8% 18% 32% 27%	1440
	11th to 20th	Night	5% 2 4 16% 36% 37%	1440
	21st to end	Night	3 1 1 10% 28% 57%	1440
July	1st to 10th	Night	4 1 5% 22% 68%	1400
	11th to 20th	Night	6% 1 3 6% 21% 63%	1481
	21st to end	Night	8% 1 2 7% 23% 59%	1674
August	1st to 10th	Night	7% 1 8% 23% 60%	1640
	11th to 20th	Night	6% 1 1 7% 28% 58%	1780
	21st to end	Night	4 1 8% 31% 55%	1980
September	1st to 10th	Night	5% 2 2 6% 24% 62%	1800
	11th to 20th	Night	6% 1 1 16% 39% 36%	1800
	21st to end	Night	6% 2 1 15% 43% 33%	1994
October	1st to 10th	Night	12% 2 6% 19% 25% 36%	2160
	11th to 20th	Night	12% 4 6% 18% 30% 30%	2160
	21st to end	Night	10% 2 4 21% 34% 28%	2376
November	1st to 10th	Night	16% 4 9% 23% 28% 20%	2320
	11th to 20th	Night	20% 4 12% 22% 31% 12%	2470
	21st to end	Night	21% 5% 9% 21% 29% 14%	2472
December	1st to 10th	Night	29% 5% 10% 22% 20% 13%	2660
	11th to 20th	Night	42% 6% 13% 17% 17% 5%	3276
	21st to end	Night	38% 5% 18% 22% 13% 4	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	19% 9% 27% 25% 17% 3	225
	11th to 20th	Day	9% 6% 22% 37% 21% 5%	344
	21st to end	Day	10% 7% 22% 30% 24% 5%	374
February	1st to 10th	Day	14% 11% 22% 23% 22% 8%	344
	11th to 20th	Day	10% 13% 25% 31% 19% 2	415
	21st to end	Day	11% 14% 25% 34% 14% 2	346
March	1st to 10th	Day	13% 16% 25% 32% 12% 2	420
	11th to 20th	Day	14% 13% 27% 28% 15% 4	420
	21st to end	Day	12% 12% 31% 32% 13% 1	462
April	1st to 10th	Day	10% 11% 28% 30% 18% 2	420
	11th to 20th	Day	7% 13% 32% 30% 17% 2	412
	21st to end	Day	4 15% 25% 32% 17% 7%	420
May	1st to 10th	Day	6% 10% 30% 31% 19% 4	423
	11th to 20th	Day	3 9% 28% 35% 18% 7%	448
	21st to end	Day	5% 10% 20% 33% 24% 9%	485
June	1st to 10th	Day	3 7% 22% 33% 24% 11%	450
	11th to 20th	Day	2 5% 21% 35% 27% 9%	450
	21st to end	Day	2 3 16% 38% 28% 13%	450
July	1st to 10th	Day	1 12% 36% 35% 15%	446
	11th to 20th	Day	6% 36% 39% 18%	444
	21st to end	Day	1 7% 37% 37% 18%	487
August	1st to 10th	Day	2 1 13% 39% 33% 12%	447
	11th to 20th	Day	1 11% 31% 39% 18%	437
	21st to end	Day	1 6% 33% 42% 19%	495
September	1st to 10th	Day	1 3 8% 35% 36% 17%	450
	11th to 20th	Day	2 3 16% 36% 30% 13%	450
	21st to end	Day	1 5% 13% 27% 42% 12%	450
October	1st to 10th	Day	2 4 20% 34% 32% 8%	450
	11th to 20th	Day	2 6% 14% 32% 36% 10%	450
	21st to end	Day	4 5% 18% 29% 34% 11%	495
November	1st to 10th	Day	6% 6% 18% 26% 34% 9%	352
	11th to 20th	Day	4 6% 16% 31% 30% 13%	270
	21st to end	Day	5% 4 22% 34% 26% 8%	268
December	1st to 10th	Day	11% 7% 20% 30% 23% 9%	180
	11th to 20th	Day	8% 12% 18% 31% 22% 9%	180
	21st to end	Day	10% 15% 22% 28% 16% 8%	198
January	1st to 10th	Night	12% 5% 16% 32% 25% 10%	760
	11th to 20th	Night	7% 4 16% 35% 29% 9%	726
	21st to end	Night	10% 5% 14% 39% 24% 8%	792
February	1st to 10th	Night	11% 4 14% 35% 27% 8%	720
	11th to 20th	Night	8% 8% 18% 32% 25% 9%	704
	21st to end	Night	9% 7% 18% 41% 20% 4	592
March	1st to 10th	Night	8% 9% 20% 36% 23% 5%	720
	11th to 20th	Night	7% 7% 19% 32% 28% 7%	720
	21st to end	Night	8% 7% 21% 35% 24% 4	792
April	1st to 10th	Night	6% 7% 23% 38% 23% 4	720
	11th to 20th	Night	5% 11% 24% 32% 20% 7%	711
	21st to end	Night	3 7% 26% 31% 26% 7%	720
May	1st to 10th	Night	3 5% 25% 35% 24% 7%	720
	11th to 20th	Night	2 5% 22% 38% 29% 4	492
	21st to end	Night	2 7% 21% 36% 31% 3	389
June	1st to 10th	Night	2 4 19% 43% 29% 3	360
	11th to 20th	Night	1 3 18% 45% 29% 5%	360
	21st to end	Night	1 9% 46% 37% 7%	360
July	1st to 10th	Night	1 10% 37% 47% 6%	350
	11th to 20th	Night	1 3 35% 50% 11%	437
	21st to end	Night	1 1 3 29% 52% 14%	591
August	1st to 10th	Night	1 8% 38% 44% 9%	575
	11th to 20th	Night	1 9% 35% 46% 8%	712
	21st to end	Night	1 5% 28% 57% 10%	792
September	1st to 10th	Night	1 8% 32% 48% 11%	720
	11th to 20th	Night	2 1 12% 33% 42% 10%	720
	21st to end	Night	1 2 10% 30% 43% 14%	720
October	1st to 10th	Night	4 3 10% 36% 36% 12%	720
	11th to 20th	Night	3 2 13% 32% 38% 12%	720
	21st to end	Night	4 2 10% 32% 35% 17%	792
November	1st to 10th	Night	4 3 13% 34% 33% 12%	740
	11th to 20th	Night	6% 2 11% 37% 32% 11%	760
	21st to end	Night	5% 3 15% 35% 32% 9%	760
December	1st to 10th	Night	9% 3 15% 38% 27% 8%	760
	11th to 20th	Night	12% 5% 16% 36% 26% 6%	760
	21st to end	Night	11% 9% 19% 35% 21% 5%	836

Page generated at 2024-01-09 04:14:41. Version ac07

Copyright 2024 Attilla Danko