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 2024-11-28.

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% 5% 2 4 3 3 3 3 4 6% 60%	105343
	Night	12% 6% 2 5% 3 3 3 3 4 5% 54%	102946
Transparency	Day	26% 4 8% 19% 23% 20%	105102
	Night	31% 5% 9% 17% 20% 17%	102777
Seeing	Day	14% 10% 23% 27% 17% 8%	15386
	Night	14% 5% 13% 32% 28% 8%	24590

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% 10% 2 7% 4 3 4 4 5% 6% 34%	2699
	11th to 20th	Day	29% 8% 4 8% 5% 4 3 2 3 5% 30%	2860
	21st to end	Day	26% 9% 4 6% 4 4 3 3 5% 6% 30%	3146
February	1st to 10th	Day	18% 7% 3 6% 4 4 4 3 4 5% 42%	1710
	11th to 20th	Day	16% 8% 3 5% 5% 5% 3 3 4 6% 42%	1665
	21st to end	Day	18% 8% 2 6% 4 3 3 3 5% 7% 41%	1574
March	1st to 10th	Day	28% 16% 3 6% 3 2 3 2 3 4 28%	3442
	11th to 20th	Day	13% 6% 2 5% 3 4 4 3 4 6% 51%	3490
	21st to end	Day	21% 9% 3 7% 5% 5% 4 4 5% 7% 30%	3825
April	1st to 10th	Day	15% 8% 3 7% 5% 3 4 4 6% 9% 37%	2270
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 5% 6% 47%	2249
	21st to end	Day	7% 5% 2 5% 3 4 4 4 6% 9% 51%	2306
May	1st to 10th	Day	6% 4 1 3 2 2 3 3 4 7% 66%	4110
	11th to 20th	Day	4 2 1 2 2 2 2 3 3 5% 73%	4152
	21st to end	Day	4 2 1 3 3 2 3 2 4 6% 69%	4813
June	1st to 10th	Day	7% 5% 1 5% 3 3 4 3 6% 7% 57%	2660
	11th to 20th	Day	2 2 1 2 2 2 2 3 4 6% 74%	2660
	21st to end	Day	3 1 1 2 2 2 2 2 3 5% 77%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 2 89%	4420
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 4 82%	4144
	21st to end	Day	1 1 1 2 2 2 4 86%	4455
August	1st to 10th	Day	1 1 1 2 1 2 2 3 5% 7% 75%	4091
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 4 82%	3979
	21st to end	Day	1 1 1 3 1 2 2 2 3 4 81%	4180
September	1st to 10th	Day	1 1 2 1 2 2 2 3 4 83%	2280
	11th to 20th	Day	3 3 2 4 3 2 3 2 4 6% 68%	2233
	21st to end	Day	3 2 1 3 2 2 2 2 3 5% 76%	2024
October	1st to 10th	Day	4 2 1 2 2 2 2 2 3 5% 74%	3180
	11th to 20th	Day	7% 3 1 3 2 2 3 2 5% 6% 64%	3161
	21st to end	Day	7% 3 2 5% 4 4 5% 4 6% 7% 53%	3448
November	1st to 10th	Day	11% 5% 1 6% 4 3 4 3 5% 8% 50%	1944
	11th to 20th	Day	16% 5% 2 5% 5% 4 4 3 5% 6% 43%	1695
	21st to end	Day	14% 4 3 5% 3 3 5% 4 4 6% 50%	1576
December	1st to 10th	Day	16% 8% 3 6% 3 4 4 3 4 6% 44%	1520
	11th to 20th	Day	28% 11% 3 7% 5% 4 4 2 4 5% 29%	1928
	21st to end	Day	24% 9% 3 8% 4 4 4 3 5% 6% 31%	2794
January	1st to 10th	Night	19% 10% 2 6% 4 4 5% 4 5% 7% 34%	4247
	11th to 20th	Night	25% 12% 4 8% 5% 4 4 3 3 4 28%	4110
	21st to end	Night	28% 12% 3 7% 4 4 4 3 4 5% 26%	4521
February	1st to 10th	Night	17% 8% 2 6% 4 3 4 3 5% 5% 42%	2470
	11th to 20th	Night	16% 9% 3 6% 5% 4 5% 3 5% 6% 38%	2402
	21st to end	Night	16% 8% 2 4 3 3 4 3 4 6% 47%	1875
March	1st to 10th	Night	24% 20% 3 6% 4 3 3 3 3 4 26%	3432
	11th to 20th	Night	15% 6% 1 5% 4 4 4 3 4 4 49%	3490
	21st to end	Night	18% 15% 3 8% 4 4 4 3 4 6% 31%	3828
April	1st to 10th	Night	12% 9% 3 7% 5% 4 4 4 4 7% 39%	1909
	11th to 20th	Night	9% 8% 2 6% 4 4 3 3 5% 8% 47%	1879
	21st to end	Night	6% 5% 1 5% 3 4 4 3 5% 7% 56%	1871
May	1st to 10th	Night	6% 5% 1 3 2 2 2 2 3 4 69%	2860
	11th to 20th	Night	2 3 1 4 3 3 3 2 3 5% 71%	2748
	21st to end	Night	3 3 1 3 2 2 2 2 3 5% 73%	2762
June	1st to 10th	Night	4 5% 2 4 4 3 4 4 5% 8% 57%	1520
	11th to 20th	Night	2 2 1 2 1 2 1 2 3 6% 78%	1520
	21st to end	Night	2 2 1 3 1 2 2 2 3 5% 76%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 1 2 90%	2540
	11th to 20th	Night	1 1 1 2 2 2 2 1 2 4 81%	2819
	21st to end	Night	1 1 2 1 1 2 1 4 4 83%	3109
August	1st to 10th	Night	1 2 1 2 2 3 3 2 4 6% 75%	2848
	11th to 20th	Night	1 1 3 2 2 2 1 3 5% 80%	2859
	21st to end	Night	2 2 1 3 1 2 2 1 2 4 80%	3498
September	1st to 10th	Night	1 1 2 2 2 2 1 3 5% 81%	1900
	11th to 20th	Night	3 3 2 6% 3 3 3 3 3 7% 64%	1943
	21st to end	Night	3 3 1 3 3 2 3 2 3 5% 72%	2156
October	1st to 10th	Night	3 2 1 3 2 3 3 2 3 4 75%	3800
	11th to 20th	Night	5% 6% 2 7% 4 3 4 2 4 5% 58%	3777
	21st to end	Night	9% 4 2 5% 4 4 4 4 5% 7% 54%	4121
November	1st to 10th	Night	12% 6% 2 5% 4 3 5% 3 6% 7% 46%	2354
	11th to 20th	Night	13% 7% 2 6% 5% 4 5% 4 6% 7% 41%	2702
	21st to end	Night	12% 6% 2 6% 4 3 3 3 4 7% 49%	2758
December	1st to 10th	Night	21% 7% 2 5% 3 3 4 3 5% 6% 42%	2660
	11th to 20th	Night	31% 9% 2 6% 4 3 3 3 5% 6% 28%	3276
	21st to end	Night	24% 10% 3 7% 4 4 4 3 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	49% 7% 14% 19% 6% 4	2699
	11th to 20th	Day	58% 5% 9% 10% 9% 9%	2860
	21st to end	Day	54% 5% 9% 14% 12% 5%	3146
February	1st to 10th	Day	45% 5% 9% 16% 18% 9%	1710
	11th to 20th	Day	43% 5% 8% 19% 20% 6%	1674
	21st to end	Day	43% 6% 12% 21% 13% 5%	1574
March	1st to 10th	Day	60% 7% 6% 13% 12% 2	3442
	11th to 20th	Day	33% 7% 10% 24% 15% 12%	3490
	21st to end	Day	50% 10% 12% 18% 8% 2	3825
April	1st to 10th	Day	43% 6% 14% 22% 13% 2	2270
	11th to 20th	Day	36% 6% 15% 23% 15% 4	2252
	21st to end	Day	27% 7% 16% 28% 18% 3	2306
May	1st to 10th	Day	18% 6% 16% 29% 18% 13%	4110
	11th to 20th	Day	14% 3 7% 22% 39% 13%	4155
	21st to end	Day	15% 4 11% 47% 21% 2	4814
June	1st to 10th	Day	25% 6% 12% 28% 24% 5%	2660
	11th to 20th	Day	11% 4 10% 24% 37% 14%	2660
	21st to end	Day	10% 2 4 19% 37% 27%	2660
July	1st to 10th	Day	4 1 3 8% 19% 65%	4351
	11th to 20th	Day	6% 2 4 9% 22% 57%	4073
	21st to end	Day	5% 2 2 9% 31% 51%	4315
August	1st to 10th	Day	8% 3 4 13% 29% 43%	4076
	11th to 20th	Day	5% 3 5% 17% 41% 29%	4018
	21st to end	Day	8% 2 5% 17% 34% 33%	4179
September	1st to 10th	Day	6% 2 4 12% 31% 46%	2280
	11th to 20th	Day	16% 4 7% 25% 34% 13%	2233
	21st to end	Day	12% 3 6% 19% 34% 25%	2024
October	1st to 10th	Day	14% 2 3 15% 22% 42%	3180
	11th to 20th	Day	20% 4 7% 23% 31% 16%	3161
	21st to end	Day	28% 7% 9% 20% 26% 12%	3448
November	1st to 10th	Day	32% 5% 10% 24% 18% 11%	1944
	11th to 20th	Day	40% 6% 11% 18% 16% 9%	1695
	21st to end	Day	35% 5% 11% 17% 19% 13%	1576
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	47% 9% 19% 14% 7% 3	4247
	11th to 20th	Night	59% 7% 8% 10% 8% 8%	4110
	21st to end	Night	59% 6% 8% 10% 11% 6%	4521
February	1st to 10th	Night	42% 6% 9% 17% 17% 9%	2470
	11th to 20th	Night	45% 7% 7% 21% 16% 5%	2404
	21st to end	Night	38% 5% 14% 23% 16% 4	1875
March	1st to 10th	Night	59% 9% 8% 13% 10% 1	3432
	11th to 20th	Night	32% 7% 11% 23% 17% 10%	3490
	21st to end	Night	51% 10% 14% 16% 7% 2	3828
April	1st to 10th	Night	41% 8% 14% 20% 13% 3	1909
	11th to 20th	Night	34% 6% 15% 23% 17% 5%	1879
	21st to end	Night	25% 6% 15% 31% 20% 4	1871
May	1st to 10th	Night	19% 4 10% 29% 25% 13%	2860
	11th to 20th	Night	15% 3 7% 17% 43% 15%	2749
	21st to end	Night	13% 4 11% 47% 24% 2	2762
June	1st to 10th	Night	25% 6% 12% 28% 25% 6%	1520
	11th to 20th	Night	10% 4 9% 24% 39% 14%	1520
	21st to end	Night	12% 2 5% 17% 35% 30%	1520
July	1st to 10th	Night	4 1 2 8% 19% 67%	2500
	11th to 20th	Night	7% 2 4 8% 22% 58%	2767
	21st to end	Night	5% 2 2 8% 31% 52%	3011
August	1st to 10th	Night	10% 3 3 11% 28% 45%	2839
	11th to 20th	Night	7% 2 5% 16% 40% 29%	2886
	21st to end	Night	10% 3 4 21% 30% 32%	3498
September	1st to 10th	Night	7% 2 3 13% 29% 47%	1900
	11th to 20th	Night	19% 3 8% 19% 35% 15%	1943
	21st to end	Night	14% 3 6% 21% 28% 29%	2156
October	1st to 10th	Night	14% 3 5% 14% 22% 43%	3800
	11th to 20th	Night	24% 7% 8% 19% 27% 15%	3777
	21st to end	Night	28% 5% 9% 22% 21% 16%	4121
November	1st to 10th	Night	35% 7% 11% 20% 17% 10%	2354
	11th to 20th	Night	38% 8% 15% 17% 15% 8%	2702
	21st to end	Night	36% 5% 10% 17% 20% 12%	2758
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% 20% 16% 5%	370
	21st to end	Day	25% 10% 19% 23% 17% 6%	407
February	1st to 10th	Day	26% 12% 19% 21% 16% 5%	370
	11th to 20th	Day	29% 15% 20% 21% 14% 2	365
	21st to end	Day	22% 14% 22% 26% 13% 2	379
March	1st to 10th	Day	35% 17% 22% 16% 8% 2	460
	11th to 20th	Day	28% 12% 25% 20% 12% 4	460
	21st to end	Day	25% 20% 26% 19% 7% 2	506
April	1st to 10th	Day	24% 16% 28% 18% 8% 5%	460
	11th to 20th	Day	21% 17% 27% 22% 9% 4	452
	21st to end	Day	15% 20% 33% 17% 11% 4	460
May	1st to 10th	Day	13% 19% 28% 24% 12% 4	463
	11th to 20th	Day	13% 15% 29% 24% 11% 8%	488
	21st to end	Day	12% 12% 25% 27% 16% 7%	529
June	1st to 10th	Day	11% 11% 30% 27% 15% 6%	490
	11th to 20th	Day	7% 14% 32% 27% 14% 5%	490
	21st to end	Day	2 7% 26% 37% 17% 11%	490
July	1st to 10th	Day	2 4 24% 41% 20% 9%	486
	11th to 20th	Day	1 3 20% 41% 23% 12%	484
	21st to end	Day	1 2 14% 45% 25% 14%	531
August	1st to 10th	Day	2 3 26% 37% 22% 10%	487
	11th to 20th	Day	2 4 24% 36% 22% 13%	477
	21st to end	Day	2 4 21% 37% 25% 11%	539
September	1st to 10th	Day	3 4 25% 36% 23% 10%	490
	11th to 20th	Day	7% 7% 22% 34% 20% 10%	490
	21st to end	Day	6% 8% 21% 33% 20% 12%	490
October	1st to 10th	Day	7% 9% 21% 27% 24% 11%	490
	11th to 20th	Day	10% 7% 19% 25% 24% 14%	490
	21st to end	Day	12% 8% 22% 26% 23% 8%	539
November	1st to 10th	Day	15% 9% 20% 25% 21% 10%	480
	11th to 20th	Day	17% 8% 12% 23% 25% 15%	247
	21st to end	Day	19% 7% 19% 20% 21% 14%	194
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	25% 5% 13% 31% 19% 6%	760
	21st to end	Night	24% 4 14% 30% 22% 5%	836
February	1st to 10th	Night	22% 6% 14% 33% 21% 4	760
	11th to 20th	Night	22% 7% 16% 30% 20% 6%	744
	21st to end	Night	20% 8% 19% 32% 17% 3	628
March	1st to 10th	Night	27% 8% 16% 30% 16% 4	760
	11th to 20th	Night	24% 6% 13% 32% 21% 4	760
	21st to end	Night	23% 10% 17% 32% 15% 3	836
April	1st to 10th	Night	19% 7% 23% 28% 19% 4	760
	11th to 20th	Night	15% 9% 19% 33% 19% 5%	751
	21st to end	Night	10% 9% 23% 30% 23% 5%	731
May	1st to 10th	Night	8% 7% 21% 32% 26% 6%	570
	11th to 20th	Night	7% 2 18% 34% 33% 6%	515
	21st to end	Night	7% 6% 20% 30% 31% 6%	411
June	1st to 10th	Night	5% 7% 20% 37% 28% 4	380
	11th to 20th	Night	2 6% 21% 39% 28% 4	380
	21st to end	Night	2 2 11% 45% 35% 5%	380
July	1st to 10th	Night	1 1 12% 33% 45% 7%	370
	11th to 20th	Night	2 1 6% 30% 44% 18%	526
	21st to end	Night	1 4 26% 53% 17%	624
August	1st to 10th	Night	3 4 32% 47% 15%	567
	11th to 20th	Night	1 1 6% 30% 48% 14%	585
	21st to end	Night	3 2 5% 30% 49% 12%	836
September	1st to 10th	Night	2 1 8% 32% 46% 11%	760
	11th to 20th	Night	6% 3 9% 36% 34% 11%	760
	21st to end	Night	5% 4 10% 32% 36% 13%	760
October	1st to 10th	Night	6% 3 11% 37% 35% 9%	760
	11th to 20th	Night	10% 3 9% 33% 36% 11%	760
	21st to end	Night	11% 4 11% 31% 31% 12%	836
November	1st to 10th	Night	15% 3 15% 29% 30% 8%	780
	11th to 20th	Night	17% 5% 12% 34% 26% 5%	800
	21st to end	Night	16% 6% 14% 33% 25% 6%	788
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 2024-11-24 21:22:21. Version ac07

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