Ruby Crest Observatory
Clear Sky Chart
History

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

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	5% 9% 3 6% 4 4 4 3 5% 6% 53%	101075
	Night	6% 9% 3 7% 4 4 4 3 5% 6% 49%	98062
Transparency	Day	29% 7% 9% 17% 21% 18%	100825
	Night	31% 7% 10% 18% 19% 14%	97902
Seeing	Day	10% 17% 28% 27% 15% 3	14733
	Night	9% 9% 22% 33% 23% 4	24250

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	6% 18% 8% 15% 4 3 3 3 4 6% 29%	2539
	11th to 20th	Day	7% 21% 5% 12% 5% 4 4 3 4 6% 30%	2540
	21st to end	Day	5% 18% 5% 9% 5% 3 4 3 4 8% 36%	2955
February	1st to 10th	Day	7% 12% 5% 10% 7% 4 4 4 4 6% 38%	1828
	11th to 20th	Day	5% 15% 5% 9% 5% 4 4 3 5% 7% 38%	1850
	21st to end	Day	4 14% 4 11% 5% 4 4 3 5% 6% 41%	1570
March	1st to 10th	Day	3 18% 6% 13% 5% 4 4 4 5% 7% 29%	3138
	11th to 20th	Day	3 10% 4 8% 4 3 3 2 4 6% 52%	3418
	21st to end	Day	6% 22% 9% 12% 5% 4 4 4 5% 5% 26%	3903
April	1st to 10th	Day	6% 14% 3 8% 5% 5% 4 4 4 7% 40%	2280
	11th to 20th	Day	6% 12% 3 9% 4 4 4 3 5% 7% 44%	2264
	21st to end	Day	8% 11% 3 6% 3 3 3 3 5% 7% 48%	2470
May	1st to 10th	Day	4 11% 5% 7% 4 4 5% 4 6% 6% 45%	4110
	11th to 20th	Day	4 5% 1 4 3 3 3 3 4 5% 63%	4071
	21st to end	Day	6% 7% 2 5% 4 4 4 3 5% 5% 56%	4559
June	1st to 10th	Day	5% 5% 2 5% 4 5% 5% 5% 5% 7% 52%	2660
	11th to 20th	Day	5% 4 1 4 3 3 4 3 5% 6% 62%	2660
	21st to end	Day	2 3 1 3 3 3 3 2 4 5% 71%	2660
July	1st to 10th	Day	2 2 1 3 2 2 3 2 3 4 76%	4420
	11th to 20th	Day	3 3 2 4 4 4 5% 4 6% 7% 60%	4420
	21st to end	Day	3 3 1 4 4 5% 4 4 6% 7% 59%	4622
August	1st to 10th	Day	3 3 1 4 3 3 4 3 5% 6% 65%	4092
	11th to 20th	Day	2 2 1 3 3 3 2 2 4 5% 74%	3966
	21st to end	Day	3 4 1 3 2 2 2 1 3 4 77%	4180
September	1st to 10th	Day	2 2 1 3 2 3 3 3 4 4 71%	2245
	11th to 20th	Day	5% 4 1 4 4 3 4 2 5% 5% 65%	2090
	21st to end	Day	5% 4 1 4 2 2 2 3 3 4 69%	2090
October	1st to 10th	Day	7% 7% 2 4 3 3 2 3 4 6% 59%	2090
	11th to 20th	Day	5% 6% 1 3 2 3 3 3 4 6% 63%	1946
	21st to end	Day	5% 5% 2 4 3 2 3 3 5% 7% 61%	1881
November	1st to 10th	Day	6% 10% 3 5% 5% 4 3 4 6% 7% 48%	1674
	11th to 20th	Day	9% 9% 3 5% 3 3 3 4 5% 7% 49%	1710
	21st to end	Day	6% 12% 5% 6% 4 4 3 2 5% 5% 47%	1710
December	1st to 10th	Day	7% 11% 4 8% 4 3 4 3 5% 7% 44%	1710
	11th to 20th	Day	9% 14% 4 9% 5% 4 6% 4 7% 8% 31%	1960
	21st to end	Day	7% 12% 4 11% 6% 5% 5% 4 6% 7% 34%	2794
January	1st to 10th	Night	5% 14% 8% 15% 6% 4 4 4 5% 7% 30%	4406
	11th to 20th	Night	10% 18% 5% 11% 7% 5% 4 3 4 5% 28%	4420
	21st to end	Night	8% 14% 6% 11% 5% 4 4 3 5% 7% 34%	4703
February	1st to 10th	Night	6% 12% 5% 9% 5% 4 4 3 5% 6% 41%	2351
	11th to 20th	Night	6% 11% 5% 9% 5% 3 4 3 5% 6% 44%	2218
	21st to end	Night	4 13% 4 10% 5% 4 5% 5% 7% 6% 38%	1884
March	1st to 10th	Night	3 15% 6% 12% 5% 4 5% 4 5% 6% 36%	3736
	11th to 20th	Night	4 9% 3 7% 4 3 5% 4 6% 7% 50%	3562
	21st to end	Night	6% 14% 7% 10% 5% 4 5% 4 6% 7% 34%	3746
April	1st to 10th	Night	8% 11% 3 7% 4 4 5% 3 6% 6% 44%	1900
	11th to 20th	Night	7% 10% 4 6% 3 3 4 3 6% 5% 49%	1862
	21st to end	Night	9% 11% 3 5% 2 3 3 3 5% 6% 51%	1710
May	1st to 10th	Night	8% 12% 4 7% 3 3 3 2 4 5% 48%	2860
	11th to 20th	Night	4 5% 1 4 3 3 3 2 4 5% 65%	2834
	21st to end	Night	7% 6% 3 6% 4 4 4 3 5% 7% 52%	3021
June	1st to 10th	Night	4 4 1 4 4 3 4 4 6% 9% 56%	1520
	11th to 20th	Night	6% 4 2 4 3 2 3 3 4 5% 64%	1520
	21st to end	Night	2 3 1 4 3 3 3 3 3 6% 69%	1520
July	1st to 10th	Night	2 3 2 3 3 3 3 3 4 3 72%	2540
	11th to 20th	Night	4 5% 2 6% 5% 5% 6% 5% 6% 7% 49%	2540
	21st to end	Night	4 4 2 6% 5% 5% 6% 4 6% 6% 52%	2918
August	1st to 10th	Night	5% 4 2 5% 4 3 4 3 5% 6% 59%	2847
	11th to 20th	Night	2 3 1 4 3 3 3 3 3 5% 69%	2871
	21st to end	Night	3 3 1 3 2 2 3 2 3 4 75%	3498
September	1st to 10th	Night	4 2 1 3 3 3 4 2 4 6% 68%	1933
	11th to 20th	Night	4 3 1 4 3 4 3 3 5% 5% 65%	2090
	21st to end	Night	5% 3 1 3 2 1 2 1 2 4 74%	2090
October	1st to 10th	Night	6% 4 1 4 3 3 4 2 4 4 63%	2090
	11th to 20th	Night	6% 5% 2 5% 3 2 2 2 5% 6% 62%	2231
	21st to end	Night	4 6% 2 4 3 2 3 3 4 6% 63%	2717
November	1st to 10th	Night	7% 8% 2 5% 4 4 4 3 7% 6% 50%	2411
	11th to 20th	Night	7% 8% 2 6% 4 3 4 3 5% 6% 53%	2470
	21st to end	Night	5% 9% 3 7% 5% 4 4 3 5% 8% 46%	2470
December	1st to 10th	Night	7% 10% 4 8% 5% 3 4 4 5% 7% 45%	2470
	11th to 20th	Night	9% 12% 3 10% 5% 4 5% 4 5% 9% 34%	3241
	21st to end	Night	7% 12% 4 11% 6% 6% 5% 4 6% 7% 32%	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	46% 11% 17% 16% 10%	2539
	11th to 20th	Day	48% 14% 14% 13% 7% 3	2540
	21st to end	Day	43% 15% 13% 19% 7% 3	2955
February	1st to 10th	Day	45% 8% 13% 20% 11% 3	1828
	11th to 20th	Day	41% 7% 12% 20% 14% 4	1860
	21st to end	Day	39% 8% 14% 23% 14% 2	1570
March	1st to 10th	Day	41% 14% 13% 17% 13% 2	3138
	11th to 20th	Day	28% 9% 15% 30% 16% 2	3418
	21st to end	Day	48% 14% 14% 15% 7% 2	3903
April	1st to 10th	Day	41% 8% 12% 21% 14% 5%	2280
	11th to 20th	Day	37% 5% 12% 22% 20% 4	2267
	21st to end	Day	34% 4 11% 29% 19% 3	2470
May	1st to 10th	Day	29% 9% 11% 26% 18% 7%	4110
	11th to 20th	Day	21% 4 9% 18% 39% 9%	4074
	21st to end	Day	26% 6% 8% 21% 33% 5%	4559
June	1st to 10th	Day	26% 7% 10% 17% 31% 8%	2660
	11th to 20th	Day	22% 4 6% 16% 32% 20%	2660
	21st to end	Day	14% 4 5% 12% 30% 35%	2660
July	1st to 10th	Day	14% 3 3 6% 12% 64%	4351
	11th to 20th	Day	22% 5% 3 7% 18% 44%	4345
	21st to end	Day	24% 4 4 11% 22% 35%	4476
August	1st to 10th	Day	19% 4 3 9% 26% 39%	4078
	11th to 20th	Day	15% 3 3 6% 24% 49%	4005
	21st to end	Day	15% 2 2 7% 31% 43%	4179
September	1st to 10th	Day	17% 4 4 10% 29% 37%	2245
	11th to 20th	Day	21% 4 5% 15% 29% 26%	2090
	21st to end	Day	19% 3 5% 14% 33% 26%	2090
October	1st to 10th	Day	26% 5% 8% 16% 30% 15%	2090
	11th to 20th	Day	22% 4 6% 22% 33% 13%	1946
	21st to end	Day	21% 4 11% 30% 27% 8%	1881
November	1st to 10th	Day	31% 9% 9% 21% 21% 8%	1674
	11th to 20th	Day	32% 6% 11% 28% 21% 4	1710
	21st to end	Day	37% 5% 11% 24% 18% 5%	1710
December	1st to 10th	Day	38% 7% 16% 23% 12% 4	1710
	11th to 20th	Day	43% 12% 14% 15% 13% 4	1960
	21st to end	Day	43% 11% 13% 15% 16% 3	2794
January	1st to 10th	Night	41% 12% 15% 20% 11% 1	4406
	11th to 20th	Night	46% 15% 15% 13% 8% 3	4420
	21st to end	Night	44% 14% 12% 18% 9% 3	4703
February	1st to 10th	Night	38% 7% 15% 25% 11% 4	2351
	11th to 20th	Night	37% 8% 12% 20% 17% 5%	2219
	21st to end	Night	39% 8% 12% 22% 15% 4	1884
March	1st to 10th	Night	38% 11% 12% 22% 12% 4	3736
	11th to 20th	Night	28% 9% 14% 29% 17% 2	3562
	21st to end	Night	39% 11% 15% 23% 11% 2	3746
April	1st to 10th	Night	38% 7% 13% 22% 15% 5%	1900
	11th to 20th	Night	33% 6% 11% 27% 19% 6%	1862
	21st to end	Night	32% 6% 9% 26% 24% 3	1710
May	1st to 10th	Night	30% 8% 8% 25% 23% 5%	2860
	11th to 20th	Night	19% 5% 7% 20% 40% 10%	2835
	21st to end	Night	26% 8% 9% 23% 27% 7%	3021
June	1st to 10th	Night	21% 7% 12% 23% 29% 9%	1520
	11th to 20th	Night	21% 4 7% 14% 33% 21%	1520
	21st to end	Night	16% 3 5% 13% 29% 34%	1520
July	1st to 10th	Night	17% 4 4 5% 11% 59%	2500
	11th to 20th	Night	31% 5% 3 8% 18% 34%	2492
	21st to end	Night	32% 4 4 10% 17% 34%	2826
August	1st to 10th	Night	25% 4 3 13% 18% 37%	2838
	11th to 20th	Night	19% 4 4 6% 16% 52%	2898
	21st to end	Night	16% 2 3 7% 25% 48%	3498
September	1st to 10th	Night	17% 3 5% 11% 26% 37%	1933
	11th to 20th	Night	21% 4 5% 14% 26% 29%	2090
	21st to end	Night	16% 3 4 14% 32% 31%	2090
October	1st to 10th	Night	24% 5% 7% 14% 33% 17%	2090
	11th to 20th	Night	22% 5% 6% 20% 33% 15%	2231
	21st to end	Night	21% 5% 7% 29% 30% 8%	2717
November	1st to 10th	Night	29% 6% 11% 23% 21% 9%	2411
	11th to 20th	Night	29% 4 12% 25% 25% 5%	2470
	21st to end	Night	33% 6% 11% 25% 19% 6%	2470
December	1st to 10th	Night	37% 7% 13% 25% 13% 5%	2470
	11th to 20th	Night	42% 8% 13% 19% 13% 5%	3241
	21st to end	Night	44% 10% 12% 18% 15% 2	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	18% 24% 28% 16% 12% 2	180
	11th to 20th	Day	13% 22% 24% 20% 16% 4	180
	21st to end	Day	11% 14% 31% 24% 16% 4	244
February	1st to 10th	Day	13% 28% 27% 19% 12% 1	388
	11th to 20th	Day	13% 23% 35% 20% 8% 1	455
	21st to end	Day	9% 28% 35% 23% 4 1	382
March	1st to 10th	Day	14% 21% 34% 24% 7% 1	460
	11th to 20th	Day	7% 26% 30% 24% 11% 1	460
	21st to end	Day	16% 24% 37% 18% 5% 1	506
April	1st to 10th	Day	16% 22% 28% 22% 10% 2	460
	11th to 20th	Day	13% 26% 35% 18% 7% 2	452
	21st to end	Day	14% 20% 32% 23% 9% 3	460
May	1st to 10th	Day	7% 29% 32% 20% 10% 3	463
	11th to 20th	Day	14% 17% 28% 26% 12% 2	488
	21st to end	Day	14% 16% 22% 28% 16% 3	529
June	1st to 10th	Day	6% 16% 28% 29% 19% 2	490
	11th to 20th	Day	11% 19% 33% 22% 13% 2	490
	21st to end	Day	3 14% 31% 31% 18% 3	490
July	1st to 10th	Day	6% 9% 34% 33% 14% 4	486
	11th to 20th	Day	5% 7% 27% 42% 16% 3	484
	21st to end	Day	5% 7% 24% 36% 22% 6%	531
August	1st to 10th	Day	7% 9% 28% 32% 21% 5%	487
	11th to 20th	Day	6% 10% 24% 31% 22% 7%	477
	21st to end	Day	6% 10% 24% 33% 20% 7%	539
September	1st to 10th	Day	5% 9% 25% 31% 21% 9%	490
	11th to 20th	Day	10% 12% 27% 24% 21% 6%	490
	21st to end	Day	7% 12% 25% 31% 20% 6%	490
October	1st to 10th	Day	9% 14% 24% 26% 21% 6%	490
	11th to 20th	Day	8% 16% 24% 25% 23% 4	390
	21st to end	Day	10% 17% 26% 28% 19%	330
November	1st to 10th	Day	12% 19% 20% 27% 18% 4	270
	11th to 20th	Day	8% 18% 24% 31% 13% 5%	270
	21st to end	Day	12% 14% 24% 29% 18% 2	270
December	1st to 10th	Day	12% 20% 24% 22% 16% 6%	270
	11th to 20th	Day	11% 19% 32% 25% 10% 3	194
	21st to end	Day	18% 18% 31% 24% 9%	198
January	1st to 10th	Night	13% 13% 19% 28% 22% 5%	760
	11th to 20th	Night	12% 12% 23% 28% 20% 5%	760
	21st to end	Night	12% 9% 22% 33% 17% 7%	836
February	1st to 10th	Night	11% 12% 28% 29% 16% 4	760
	11th to 20th	Night	9% 13% 27% 34% 15% 2	744
	21st to end	Night	10% 14% 29% 32% 12% 3	628
March	1st to 10th	Night	11% 11% 27% 36% 12% 4	760
	11th to 20th	Night	8% 10% 24% 34% 20% 3	760
	21st to end	Night	13% 14% 28% 31% 13% 1	836
April	1st to 10th	Night	11% 12% 28% 29% 18% 1	760
	11th to 20th	Night	10% 13% 29% 27% 17% 3	734
	21st to end	Night	12% 13% 24% 28% 21% 2	570
May	1st to 10th	Night	8% 12% 28% 31% 19% 2	570
	11th to 20th	Night	11% 11% 22% 30% 23% 3	561
	21st to end	Night	12% 9% 21% 30% 26% 2	567
June	1st to 10th	Night	5% 7% 22% 37% 24% 5%	380
	11th to 20th	Night	7% 10% 23% 32% 27% 1	380
	21st to end	Night	3 7% 16% 42% 28% 3	380
July	1st to 10th	Night	5% 2 18% 38% 32% 5%	370
	11th to 20th	Night	5% 1 16% 41% 34% 2	368
	21st to end	Night	4 3 15% 41% 34% 3	511
August	1st to 10th	Night	7% 4 19% 39% 29% 2	567
	11th to 20th	Night	4 3 16% 41% 31% 5%	598
	21st to end	Night	4 4 15% 39% 33% 5%	836
September	1st to 10th	Night	5% 4 13% 36% 34% 7%	760
	11th to 20th	Night	5% 6% 13% 35% 31% 9%	760
	21st to end	Night	7% 5% 18% 29% 32% 10%	760
October	1st to 10th	Night	7% 6% 21% 34% 26% 7%	760
	11th to 20th	Night	7% 8% 18% 32% 28% 7%	760
	21st to end	Night	8% 9% 22% 28% 26% 7%	836
November	1st to 10th	Night	9% 9% 19% 31% 25% 6%	742
	11th to 20th	Night	8% 9% 23% 36% 19% 5%	760
	21st to end	Night	7% 9% 25% 29% 22% 8%	760
December	1st to 10th	Night	9% 10% 26% 33% 17% 5%	760
	11th to 20th	Night	14% 8% 26% 32% 17% 3	760
	21st to end	Night	15% 14% 29% 29% 12% 2	836

Page generated at 2024-10-29 08:20:51. Version ac07

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