Rubicon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rubicon Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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	10% 4 2 4 4 2 3 3 4 6% 58%	74690
	Night	12% 5% 2 4 4 2 4 4 4 6% 53%	75084
Transparency	Day	28% 4 9% 20% 23% 16%	74409
	Night	32% 5% 9% 18% 21% 14%	74887
Seeing	Day	14% 10% 23% 27% 17% 8%	14181
	Night	14% 5% 13% 32% 28% 8%	23485

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	22% 8% 3 6% 6% 2 5% 5% 5% 7% 32%	1614
	11th to 20th	Day	21% 5% 4 5% 4 3 3 2 3 6% 45%	1648
	21st to end	Day	16% 8% 4 5% 5% 3 4 3 5% 7% 41%	1782
February	1st to 10th	Day	18% 7% 3 5% 5% 3 4 4 4 5% 43%	1620
	11th to 20th	Day	15% 7% 3 4 6% 3 4 3 4 7% 44%	1575
	21st to end	Day	19% 7% 3 5% 5% 2 3 3 4 7% 42%	1484
March	1st to 10th	Day	21% 11% 4 6% 5% 3 4 4 3 6% 33%	1980
	11th to 20th	Day	20% 8% 3 6% 5% 3 5% 4 4 7% 35%	1980
	21st to end	Day	17% 6% 4 6% 5% 4 4 5% 5% 7% 37%	2178
April	1st to 10th	Day	16% 7% 3 6% 6% 3 4 5% 5% 9% 36%	2150
	11th to 20th	Day	13% 6% 2 5% 4 3 4 4 4 6% 48%	2129
	21st to end	Day	8% 5% 2 4 3 3 4 4 5% 10% 52%	2184
May	1st to 10th	Day	7% 4 2 3 3 2 3 3 5% 8% 59%	2340
	11th to 20th	Day	7% 4 2 4 4 1 4 5% 5% 8% 57%	2343
	21st to end	Day	7% 4 2 4 4 3 4 4 5% 7% 57%	2723
June	1st to 10th	Day	7% 4 1 4 3 2 4 4 6% 7% 57%	2520
	11th to 20th	Day	3 2 1 2 2 1 2 3 4 6% 74%	2520
	21st to end	Day	3 1 1 2 2 2 2 2 3 5% 77%	2520
July	1st to 10th	Day	1 2 1 2 2 1 2 3 3 4 80%	2520
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 4 81%	2361
	21st to end	Day	1 1 1 1 2 1 2 3 3 5% 82%	2546
August	1st to 10th	Day	1 2 1 2 2 1 2 3 3 4 79%	2328
	11th to 20th	Day	1 1 1 1 2 1 2 2 3 3 84%	2277
	21st to end	Day	1 1 1 2 1 1 2 3 3 5% 81%	2376
September	1st to 10th	Day	1 1 1 1 1 2 2 3 4 83%	2160
	11th to 20th	Day	3 3 2 3 3 2 3 3 4 5% 69%	2116
	21st to end	Day	3 2 1 3 2 2 2 3 3 5% 75%	1918
October	1st to 10th	Day	7% 3 1 2 3 2 3 3 3 4 70%	1800
	11th to 20th	Day	8% 3 1 3 3 2 3 3 4 6% 64%	1800
	21st to end	Day	10% 3 2 4 3 2 3 3 4 7% 59%	1980
November	1st to 10th	Day	12% 5% 2 5% 5% 2 4 4 5% 8% 49%	1845
	11th to 20th	Day	15% 5% 2 5% 5% 3 5% 4 5% 7% 45%	1611
	21st to end	Day	13% 3 2 4 4 2 5% 5% 4 6% 51%	1520
December	1st to 10th	Day	16% 8% 3 5% 4 3 5% 4 4 5% 44%	1520
	11th to 20th	Day	28% 10% 3 5% 6% 3 4 3 4 5% 29%	1928
	21st to end	Day	24% 8% 3 7% 5% 3 4 4 5% 6% 31%	2794
January	1st to 10th	Night	20% 7% 3 5% 6% 3 5% 5% 5% 8% 31%	2547
	11th to 20th	Night	20% 8% 3 5% 4 3 3 4 4 6% 40%	2390
	21st to end	Night	17% 7% 3 5% 5% 3 4 4 4 7% 41%	2574
February	1st to 10th	Night	16% 7% 3 6% 4 2 4 4 5% 5% 44%	2340
	11th to 20th	Night	15% 8% 3 5% 5% 3 5% 5% 5% 6% 40%	2272
	21st to end	Night	17% 7% 2 4 4 2 4 4 5% 6% 46%	1767
March	1st to 10th	Night	20% 11% 4 5% 5% 3 4 5% 5% 5% 33%	1980
	11th to 20th	Night	20% 8% 2 5% 6% 3 4 4 5% 7% 37%	1980
	21st to end	Night	17% 9% 3 5% 4 2 3 4 4 6% 43%	2178
April	1st to 10th	Night	13% 8% 4 6% 6% 3 4 5% 4 8% 38%	1809
	11th to 20th	Night	10% 7% 3 6% 4 2 4 4 5% 8% 47%	1779
	21st to end	Night	6% 4 2 4 3 3 5% 4 5% 8% 57%	1773
May	1st to 10th	Night	6% 4 2 3 3 2 4 3 4 6% 63%	1620
	11th to 20th	Night	4 5% 2 5% 5% 3 4 4 5% 9% 55%	1550
	21st to end	Night	5% 5% 1 4 4 2 4 4 4 8% 59%	1552
June	1st to 10th	Night	5% 4 2 4 4 2 4 4 4 8% 57%	1440
	11th to 20th	Night	2 2 1 2 1 1 2 2 3 6% 77%	1440
	21st to end	Night	2 2 1 2 2 2 3 3 3 5% 76%	1440
July	1st to 10th	Night	1 2 1 1 2 2 2 2 2 4 84%	1440
	11th to 20th	Night	1 1 1 1 2 1 2 2 3 6% 80%	1593
	21st to end	Night	1 1 1 1 2 2 4 5% 81%	1773
August	1st to 10th	Night	1 1 1 2 3 2 2 3 3 5% 76%	1611
	11th to 20th	Night	1 1 1 2 2 2 3 3 6% 79%	1621
	21st to end	Night	1 2 1 2 2 1 2 2 2 5% 80%	1980
September	1st to 10th	Night	1 1 2 2 1 2 2 4 5% 81%	1800
	11th to 20th	Night	3 3 1 5% 4 2 3 4 3 7% 64%	1840
	21st to end	Night	3 3 1 3 3 1 3 2 3 6% 71%	2042
October	1st to 10th	Night	5% 3 2 3 3 2 3 3 3 5% 68%	2160
	11th to 20th	Night	6% 5% 2 4 4 2 4 4 4 4 62%	2160
	21st to end	Night	10% 3 1 4 4 2 4 5% 4 6% 56%	2376
November	1st to 10th	Night	12% 6% 3 5% 5% 3 4 4 6% 7% 45%	2233
	11th to 20th	Night	13% 6% 3 5% 6% 3 5% 5% 6% 7% 42%	2566
	21st to end	Night	11% 5% 3 5% 4 3 4 4 4 7% 50%	2660
December	1st to 10th	Night	21% 6% 2 4 4 2 4 4 5% 6% 42%	2660
	11th to 20th	Night	31% 8% 3 5% 4 3 3 4 5% 6% 28%	3276
	21st to end	Night	25% 9% 3 6% 5% 3 4 4 4 5% 31%	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	52% 7% 10% 17% 7% 7%	1614
	11th to 20th	Day	45% 2 9% 14% 15% 15%	1648
	21st to end	Day	45% 5% 7% 14% 20% 10%	1782
February	1st to 10th	Day	44% 4 8% 15% 19% 9%	1620
	11th to 20th	Day	41% 5% 8% 19% 21% 6%	1584
	21st to end	Day	44% 5% 12% 20% 13% 6%	1484
March	1st to 10th	Day	53% 8% 8% 14% 14% 3	1980
	11th to 20th	Day	48% 5% 10% 17% 15% 5%	1980
	21st to end	Day	46% 7% 13% 17% 14% 3	2178
April	1st to 10th	Day	44% 6% 13% 21% 13% 2	2150
	11th to 20th	Day	36% 6% 15% 23% 16% 4	2132
	21st to end	Day	28% 6% 16% 28% 19% 4	2184
May	1st to 10th	Day	23% 6% 12% 32% 21% 6%	2340
	11th to 20th	Day	25% 5% 13% 29% 21% 7%	2346
	21st to end	Day	26% 6% 13% 36% 16% 2	2724
June	1st to 10th	Day	26% 6% 12% 28% 24% 5%	2520
	11th to 20th	Day	12% 4 10% 24% 35% 14%	2520
	21st to end	Day	11% 2 5% 20% 38% 25%	2520
July	1st to 10th	Day	8% 2 5% 14% 33% 38%	2451
	11th to 20th	Day	8% 2 6% 14% 30% 40%	2290
	21st to end	Day	7% 2 4 12% 29% 46%	2405
August	1st to 10th	Day	9% 3 5% 20% 33% 30%	2312
	11th to 20th	Day	6% 2 3 15% 39% 34%	2277
	21st to end	Day	7% 2 6% 18% 35% 32%	2376
September	1st to 10th	Day	7% 2 4 12% 32% 44%	2160
	11th to 20th	Day	16% 4 7% 24% 34% 14%	2116
	21st to end	Day	13% 4 7% 20% 32% 25%	1918
October	1st to 10th	Day	21% 3 5% 20% 28% 24%	1800
	11th to 20th	Day	23% 4 8% 17% 26% 22%	1800
	21st to end	Day	26% 5% 9% 19% 25% 17%	1980
November	1st to 10th	Day	33% 5% 10% 24% 17% 11%	1845
	11th to 20th	Day	39% 5% 11% 19% 17% 9%	1611
	21st to end	Day	34% 5% 11% 17% 20% 13%	1520
December	1st to 10th	Day	42% 6% 7% 15% 17% 12%	1520
	11th to 20th	Day	60% 4 6% 12% 13% 5%	1928
	21st to end	Day	53% 6% 10% 18% 9% 4	2794
January	1st to 10th	Night	51% 6% 13% 15% 10% 6%	2547
	11th to 20th	Night	46% 5% 9% 13% 13% 14%	2390
	21st to end	Night	43% 5% 11% 12% 19% 10%	2574
February	1st to 10th	Night	42% 5% 9% 17% 18% 10%	2340
	11th to 20th	Night	43% 6% 7% 21% 17% 6%	2274
	21st to end	Night	38% 5% 14% 22% 16% 4	1767
March	1st to 10th	Night	51% 9% 9% 15% 14% 2	1980
	11th to 20th	Night	47% 4 11% 18% 15% 4	1980
	21st to end	Night	42% 7% 14% 20% 13% 3	2178
April	1st to 10th	Night	42% 8% 14% 19% 13% 3	1809
	11th to 20th	Night	35% 6% 15% 22% 18% 5%	1779
	21st to end	Night	26% 5% 15% 30% 20% 4	1773
May	1st to 10th	Night	23% 5% 9% 27% 29% 7%	1620
	11th to 20th	Night	26% 5% 12% 27% 23% 7%	1551
	21st to end	Night	23% 6% 15% 35% 18% 2	1552
June	1st to 10th	Night	25% 6% 12% 28% 25% 5%	1440
	11th to 20th	Night	11% 4 10% 25% 37% 14%	1440
	21st to end	Night	13% 2 5% 18% 34% 29%	1440
July	1st to 10th	Night	7% 2 3 15% 33% 41%	1400
	11th to 20th	Night	7% 2 5% 13% 31% 41%	1541
	21st to end	Night	5% 1 2 11% 30% 50%	1674
August	1st to 10th	Night	9% 3 4 18% 34% 32%	1602
	11th to 20th	Night	7% 2 4 16% 34% 37%	1621
	21st to end	Night	8% 2 5% 19% 31% 35%	1980
September	1st to 10th	Night	7% 2 3 13% 30% 45%	1800
	11th to 20th	Night	18% 3 8% 18% 36% 16%	1840
	21st to end	Night	15% 3 6% 21% 27% 29%	2042
October	1st to 10th	Night	19% 4 7% 21% 25% 25%	2160
	11th to 20th	Night	22% 6% 6% 18% 28% 20%	2160
	21st to end	Night	27% 5% 10% 19% 19% 20%	2376
November	1st to 10th	Night	36% 7% 11% 19% 17% 10%	2233
	11th to 20th	Night	38% 8% 14% 17% 16% 8%	2566
	21st to end	Night	35% 5% 10% 17% 21% 12%	2660
December	1st to 10th	Night	43% 6% 8% 15% 17% 10%	2660
	11th to 20th	Night	57% 5% 9% 11% 14% 4	3276
	21st to end	Night	55% 7% 11% 15% 10% 3	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	34% 13% 22% 15% 13% 3	275
	11th to 20th	Day	27% 11% 21% 19% 17% 5%	350
	21st to end	Day	23% 10% 18% 24% 18% 7%	374
February	1st to 10th	Day	25% 11% 20% 21% 17% 5%	340
	11th to 20th	Day	28% 15% 21% 21% 14% 2	335
	21st to end	Day	23% 14% 24% 24% 13% 2	344
March	1st to 10th	Day	34% 16% 23% 17% 9% 2	420
	11th to 20th	Day	29% 13% 25% 19% 11% 3	420
	21st to end	Day	23% 20% 27% 20% 7% 3	462
April	1st to 10th	Day	24% 17% 29% 18% 8% 4	420
	11th to 20th	Day	22% 17% 28% 21% 8% 4	412
	21st to end	Day	15% 19% 34% 18% 10% 5%	420
May	1st to 10th	Day	13% 19% 28% 23% 12% 5%	423
	11th to 20th	Day	15% 15% 29% 23% 11% 6%	448
	21st to end	Day	13% 13% 24% 27% 15% 7%	485
June	1st to 10th	Day	11% 11% 30% 27% 15% 6%	450
	11th to 20th	Day	8% 13% 33% 28% 14% 5%	450
	21st to end	Day	2 7% 26% 37% 18% 10%	450
July	1st to 10th	Day	2 4 25% 41% 20% 8%	446
	11th to 20th	Day	1 3 20% 41% 23% 12%	444
	21st to end	Day	1 2 14% 45% 25% 14%	487
August	1st to 10th	Day	2 3 26% 37% 22% 10%	447
	11th to 20th	Day	1 3 23% 37% 22% 14%	437
	21st to end	Day	2 3 21% 38% 26% 10%	495
September	1st to 10th	Day	3 4 24% 37% 23% 10%	450
	11th to 20th	Day	6% 7% 22% 35% 20% 10%	450
	21st to end	Day	7% 8% 21% 32% 22% 10%	450
October	1st to 10th	Day	8% 9% 22% 26% 24% 10%	450
	11th to 20th	Day	9% 7% 19% 26% 24% 15%	450
	21st to end	Day	13% 7% 21% 26% 24% 8%	495
November	1st to 10th	Day	16% 9% 19% 24% 22% 10%	441
	11th to 20th	Day	14% 6% 11% 24% 27% 17%	223
	21st to end	Day	17% 7% 19% 21% 22% 14%	180
December	1st to 10th	Day	26% 6% 17% 22% 17% 12%	180
	11th to 20th	Day	27% 11% 17% 17% 16% 12%	180
	21st to end	Day	26% 10% 17% 21% 19% 7%	198
January	1st to 10th	Night	25% 5% 15% 30% 20% 6%	760
	11th to 20th	Night	26% 5% 13% 31% 19% 6%	736
	21st to end	Night	22% 4 14% 31% 23% 5%	792
February	1st to 10th	Night	22% 5% 13% 34% 21% 5%	720
	11th to 20th	Night	21% 6% 17% 30% 20% 6%	704
	21st to end	Night	21% 8% 20% 31% 17% 3	592
March	1st to 10th	Night	26% 8% 16% 30% 16% 4	720
	11th to 20th	Night	25% 7% 12% 33% 20% 4	720
	21st to end	Night	23% 9% 17% 33% 16% 3	792
April	1st to 10th	Night	19% 7% 23% 28% 18% 4	720
	11th to 20th	Night	15% 10% 19% 32% 19% 6%	711
	21st to end	Night	10% 9% 22% 30% 24% 6%	693
May	1st to 10th	Night	8% 7% 20% 32% 27% 6%	540
	11th to 20th	Night	7% 2 19% 34% 31% 6%	488
	21st to end	Night	7% 6% 20% 30% 31% 6%	389
June	1st to 10th	Night	5% 7% 19% 37% 29% 4	360
	11th to 20th	Night	3 6% 20% 38% 29% 4	360
	21st to end	Night	3 2 11% 45% 34% 5%	360
July	1st to 10th	Night	1 1 13% 33% 44% 8%	350
	11th to 20th	Night	2 6% 30% 44% 19%	497
	21st to end	Night	1 4 26% 52% 17%	591
August	1st to 10th	Night	2 4 31% 46% 15%	537
	11th to 20th	Night	1 6% 29% 49% 15%	553
	21st to end	Night	2 1 5% 30% 50% 12%	792
September	1st to 10th	Night	2 2 8% 31% 46% 12%	720
	11th to 20th	Night	6% 3 9% 35% 35% 12%	720
	21st to end	Night	5% 4 10% 32% 35% 13%	720
October	1st to 10th	Night	7% 3 11% 37% 33% 9%	720
	11th to 20th	Night	10% 3 8% 33% 36% 11%	720
	21st to end	Night	11% 4 10% 30% 31% 13%	792
November	1st to 10th	Night	16% 3 14% 28% 30% 9%	740
	11th to 20th	Night	17% 4 11% 34% 28% 6%	760
	21st to end	Night	14% 6% 14% 34% 26% 6%	760
December	1st to 10th	Night	26% 4 12% 30% 20% 7%	760
	11th to 20th	Night	30% 5% 11% 31% 17% 5%	760
	21st to end	Night	28% 6% 16% 28% 18% 4	836

Page generated at 2024-01-11 10:32:00. Version ac07

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