Ramona Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ramona Observatory clear sky chart from 2005-11-06 to 2025-07-06.

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% 4 1 3 2 2 3 3 4 6% 66%	124262
	Night	7% 7% 2 4 3 2 3 2 4 7% 60%	123612
Transparency	Day	18% 4 7% 15% 27% 29%	124033
	Night	23% 5% 8% 14% 23% 28%	123429
Seeing	Day	8% 6% 24% 36% 19% 6%	16639
	Night	10% 2 8% 35% 35% 10%	26996

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% 3 1 3 2 2 3 2 3 5% 69%	4098
	11th to 20th	Day	6% 4 2 2 2 2 2 3 4 5% 68%	4347
	21st to end	Day	12% 5% 2 4 3 3 4 4 6% 9% 48%	5016
February	1st to 10th	Day	11% 5% 1 4 4 3 4 3 4 5% 57%	2000
	11th to 20th	Day	10% 5% 2 4 3 3 3 4 4 7% 53%	1950
	21st to end	Day	12% 8% 2 5% 4 4 4 3 5% 5% 48%	1650
March	1st to 10th	Day	11% 8% 3 5% 3 4 4 4 8% 9% 41%	4518
	11th to 20th	Day	12% 5% 2 4 3 3 3 3 5% 7% 54%	4793
	21st to end	Day	10% 7% 2 4 3 3 3 3 5% 6% 54%	5743
April	1st to 10th	Day	7% 6% 2 5% 3 3 3 2 6% 7% 56%	2400
	11th to 20th	Day	4 5% 1 4 3 3 3 3 4 6% 62%	2369
	21st to end	Day	7% 5% 2 3 2 2 2 3 4 7% 63%	2400
May	1st to 10th	Day	7% 5% 2 4 2 2 2 2 3 5% 67%	5737
	11th to 20th	Day	3 4 2 4 3 2 3 2 4 9% 63%	5841
	21st to end	Day	3 5% 2 4 2 2 2 2 4 7% 66%	6423
June	1st to 10th	Day	4 5% 2 3 3 2 2 2 4 6% 66%	2600
	11th to 20th	Day	2 4 1 2 2 2 2 1 2 5% 76%	2600
	21st to end	Day	1 3 1 2 2 2 2 2 3 5% 78%	2600
July	1st to 10th	Day	1 2 1 2 1 1 1 1 3 4 84%	4176
	11th to 20th	Day	1 2 1 2 2 2 3 3 5% 7% 73%	4110
	21st to end	Day	1 1 1 2 2 2 2 4 6% 79%	4277
August	1st to 10th	Day	1 1 2 1 2 2 2 4 6% 78%	3783
	11th to 20th	Day	1 1 1 2 2 1 1 2 3 4 84%	3724
	21st to end	Day	1 1 1 1 1 2 2 2 3 5% 82%	4180
September	1st to 10th	Day	2 2 1 3 2 3 3 2 4 6% 74%	2256
	11th to 20th	Day	3 3 1 2 1 1 2 2 2 4 80%	2090
	21st to end	Day	2 3 1 2 2 1 2 2 3 4 78%	2090
October	1st to 10th	Day	3 2 1 3 2 2 2 1 3 5% 78%	3490
	11th to 20th	Day	3 3 1 2 2 2 2 2 3 5% 74%	3469
	21st to end	Day	3 2 1 3 2 2 2 2 5% 6% 72%	3299
November	1st to 10th	Day	5% 3 1 3 2 2 2 3 4 6% 68%	1764
	11th to 20th	Day	4 3 2 3 2 3 3 3 4 5% 68%	1800
	21st to end	Day	7% 5% 2 4 3 3 3 4 5% 7% 58%	1800
December	1st to 10th	Day	5% 3 1 2 2 2 2 2 4 9% 68%	2950
	11th to 20th	Day	8% 4 1 3 4 4 5% 5% 6% 8% 52%	3409
	21st to end	Day	8% 5% 2 5% 4 5% 5% 5% 8% 8% 45%	4510
January	1st to 10th	Night	6% 4 1 3 2 3 3 2 4 6% 66%	5867
	11th to 20th	Night	7% 5% 1 4 3 3 3 2 4 6% 62%	5642
	21st to end	Night	15% 8% 2 4 3 3 4 3 5% 6% 48%	5984
February	1st to 10th	Night	10% 6% 2 4 3 3 3 3 4 6% 56%	2400
	11th to 20th	Night	11% 7% 2 5% 4 3 3 3 4 5% 54%	2338
	21st to end	Night	12% 8% 3 5% 3 2 4 2 4 6% 51%	1980
March	1st to 10th	Night	22% 13% 2 5% 2 2 3 2 4 6% 39%	5376
	11th to 20th	Night	13% 13% 2 4 3 3 3 3 4 6% 47%	5205
	21st to end	Night	13% 15% 3 6% 3 3 3 2 5% 5% 44%	5227
April	1st to 10th	Night	9% 9% 3 4 3 3 2 2 5% 8% 51%	2000
	11th to 20th	Night	8% 11% 2 4 2 3 3 3 4 6% 55%	1979
	21st to end	Night	9% 10% 3 4 3 3 3 3 4 8% 52%	2000
May	1st to 10th	Night	11% 9% 2 5% 2 2 2 2 3 7% 56%	4248
	11th to 20th	Night	7% 15% 3 6% 3 2 2 2 4 10% 46%	4074
	21st to end	Night	6% 15% 4 6% 3 2 3 2 3 7% 50%	4474
June	1st to 10th	Night	5% 11% 3 5% 4 2 3 3 4 10% 51%	1800
	11th to 20th	Night	3 7% 2 4 2 2 3 2 3 8% 65%	1800
	21st to end	Night	3 4 1 3 2 2 2 2 4 8% 71%	1800
July	1st to 10th	Night	3 1 2 1 1 1 1 2 5% 82%	2905
	11th to 20th	Night	1 1 1 3 3 2 3 3 5% 8% 72%	2860
	21st to end	Night	1 1 1 2 2 2 2 2 3 6% 77%	3288
August	1st to 10th	Night	1 2 1 2 1 1 1 2 4 7% 78%	3166
	11th to 20th	Night	1 1 1 1 1 1 2 1 3 8% 79%	3126
	21st to end	Night	1 2 1 3 2 2 2 1 3 6% 78%	3498
September	1st to 10th	Night	3 5% 1 3 2 3 3 2 4 7% 68%	1924
	11th to 20th	Night	4 5% 1 2 2 2 2 1 2 4 74%	2090
	21st to end	Night	4 4 1 1 2 2 1 2 2 6% 75%	2090
October	1st to 10th	Night	3 3 1 2 2 2 2 2 2 5% 77%	3490
	11th to 20th	Night	5% 10% 2 4 2 2 1 1 2 5% 64%	3469
	21st to end	Night	4 4 1 3 2 2 3 2 4 5% 68%	4258
November	1st to 10th	Night	6% 4 1 3 3 2 3 3 3 5% 67%	2535
	11th to 20th	Night	4 4 2 3 2 2 3 2 4 6% 67%	2600
	21st to end	Night	8% 5% 2 4 3 3 4 4 5% 6% 56%	2600
December	1st to 10th	Night	5% 3 1 3 3 2 3 3 4 6% 67%	4240
	11th to 20th	Night	10% 6% 2 5% 3 3 4 4 7% 8% 49%	4811
	21st to end	Night	9% 8% 2 5% 3 3 3 4 6% 10% 47%	6468

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	19% 4 4 16% 25% 32%	4099
	11th to 20th	Day	19% 4 7% 18% 21% 31%	4347
	21st to end	Day	30% 5% 8% 9% 26% 23%	5016
February	1st to 10th	Day	30% 4 5% 13% 21% 28%	2000
	11th to 20th	Day	31% 4 7% 14% 24% 21%	1960
	21st to end	Day	37% 5% 6% 12% 19% 21%	1650
March	1st to 10th	Day	34% 6% 8% 18% 18% 14%	4518
	11th to 20th	Day	28% 6% 10% 24% 21% 12%	4793
	21st to end	Day	28% 6% 8% 31% 17% 10%	5743
April	1st to 10th	Day	28% 4 9% 22% 24% 14%	2400
	11th to 20th	Day	20% 5% 7% 18% 29% 20%	2372
	21st to end	Day	20% 4 8% 22% 34% 13%	2400
May	1st to 10th	Day	19% 5% 5% 20% 37% 14%	5737
	11th to 20th	Day	13% 5% 10% 19% 39% 14%	5844
	21st to end	Day	12% 6% 9% 15% 44% 14%	6424
June	1st to 10th	Day	16% 5% 7% 20% 31% 21%	2600
	11th to 20th	Day	11% 3 5% 10% 27% 44%	2600
	21st to end	Day	10% 2 5% 5% 23% 55%	2600
July	1st to 10th	Day	7% 1 4 5% 13% 71%	4112
	11th to 20th	Day	8% 3 10% 12% 33% 34%	4041
	21st to end	Day	8% 4 8% 23% 23% 34%	4142
August	1st to 10th	Day	8% 3 6% 17% 38% 28%	3770
	11th to 20th	Day	7% 2 6% 11% 25% 48%	3760
	21st to end	Day	7% 2 4 7% 24% 56%	4179
September	1st to 10th	Day	13% 3 7% 10% 31% 37%	2256
	11th to 20th	Day	8% 2 4 7% 34% 45%	2090
	21st to end	Day	12% 2 4 11% 29% 42%	2090
October	1st to 10th	Day	12% 2 4 9% 15% 59%	3490
	11th to 20th	Day	11% 3 5% 12% 28% 41%	3469
	21st to end	Day	14% 2 4 8% 32% 40%	3299
November	1st to 10th	Day	19% 3 5% 14% 23% 37%	1764
	11th to 20th	Day	18% 3 6% 11% 23% 39%	1800
	21st to end	Day	25% 4 7% 11% 20% 33%	1800
December	1st to 10th	Day	17% 2 5% 12% 26% 39%	2950
	11th to 20th	Day	28% 4 8% 15% 23% 22%	3408
	21st to end	Day	33% 6% 8% 22% 23% 9%	4510
January	1st to 10th	Night	20% 4 4 13% 30% 29%	5867
	11th to 20th	Night	22% 5% 9% 17% 16% 31%	5642
	21st to end	Night	36% 4 7% 8% 22% 23%	5984
February	1st to 10th	Night	30% 4 6% 12% 21% 28%	2400
	11th to 20th	Night	33% 5% 6% 12% 21% 24%	2339
	21st to end	Night	34% 5% 5% 13% 20% 23%	1980
March	1st to 10th	Night	44% 7% 8% 11% 16% 13%	5376
	11th to 20th	Night	36% 7% 8% 22% 19% 9%	5205
	21st to end	Night	38% 9% 8% 16% 17% 12%	5227
April	1st to 10th	Night	31% 5% 8% 20% 21% 15%	2000
	11th to 20th	Night	27% 6% 9% 15% 23% 20%	1979
	21st to end	Night	29% 6% 9% 18% 22% 16%	2000
May	1st to 10th	Night	25% 8% 8% 18% 30% 11%	4245
	11th to 20th	Night	23% 9% 16% 17% 26% 9%	4075
	21st to end	Night	19% 10% 15% 15% 28% 13%	4474
June	1st to 10th	Night	22% 8% 12% 16% 24% 19%	1800
	11th to 20th	Night	15% 3 9% 11% 21% 41%	1800
	21st to end	Night	12% 3 8% 6% 20% 51%	1800
July	1st to 10th	Night	7% 1 5% 4 13% 69%	2860
	11th to 20th	Night	7% 3 11% 13% 38% 29%	2806
	21st to end	Night	9% 4 6% 21% 27% 31%	3185
August	1st to 10th	Night	6% 3 7% 18% 41% 25%	3156
	11th to 20th	Night	6% 3 7% 15% 22% 47%	3156
	21st to end	Night	6% 2 8% 7% 21% 56%	3498
September	1st to 10th	Night	14% 4 9% 10% 25% 38%	1924
	11th to 20th	Night	13% 2 8% 6% 29% 42%	2090
	21st to end	Night	12% 3 4 10% 33% 37%	2090
October	1st to 10th	Night	13% 2 4 9% 16% 56%	3490
	11th to 20th	Night	18% 4 8% 8% 21% 41%	3469
	21st to end	Night	18% 3 4 8% 25% 42%	4258
November	1st to 10th	Night	20% 3 6% 13% 20% 38%	2535
	11th to 20th	Night	20% 4 4 12% 20% 40%	2600
	21st to end	Night	28% 4 7% 13% 17% 31%	2600
December	1st to 10th	Night	19% 3 5% 12% 22% 38%	4240
	11th to 20th	Night	31% 5% 7% 12% 19% 27%	4811
	21st to end	Night	29% 8% 10% 22% 21% 10%	6468

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	16% 6% 25% 31% 20% 1	300
	11th to 20th	Day	13% 7% 25% 38% 15% 2	404
	21st to end	Day	13% 9% 30% 33% 11% 3	550
February	1st to 10th	Day	14% 8% 31% 32% 11% 3	500
	11th to 20th	Day	14% 11% 30% 32% 11% 2	495
	21st to end	Day	16% 12% 36% 27% 7% 1	414
March	1st to 10th	Day	16% 12% 31% 29% 10% 2	500
	11th to 20th	Day	15% 10% 31% 32% 10% 3	500
	21st to end	Day	11% 14% 38% 26% 10% 2	550
April	1st to 10th	Day	10% 13% 30% 27% 15% 5%	500
	11th to 20th	Day	6% 13% 37% 31% 10% 3	492
	21st to end	Day	8% 12% 29% 29% 17% 6%	500
May	1st to 10th	Day	12% 10% 30% 29% 14% 5%	503
	11th to 20th	Day	9% 8% 29% 36% 15% 4	528
	21st to end	Day	8% 9% 28% 33% 18% 4	573
June	1st to 10th	Day	4 5% 23% 34% 27% 8%	530
	11th to 20th	Day	5% 3 23% 39% 24% 7%	530
	21st to end	Day	3 2 20% 41% 25% 9%	530
July	1st to 10th	Day	3 1 11% 42% 31% 12%	507
	11th to 20th	Day	1 1 7% 43% 32% 15%	484
	21st to end	Day	2 5% 47% 31% 15%	531
August	1st to 10th	Day	1 1 12% 44% 27% 14%	487
	11th to 20th	Day	2 9% 49% 26% 14%	477
	21st to end	Day	3 1 11% 47% 26% 13%	539
September	1st to 10th	Day	4 1 19% 47% 19% 9%	490
	11th to 20th	Day	5% 3 25% 43% 18% 6%	490
	21st to end	Day	4 5% 26% 35% 20% 9%	490
October	1st to 10th	Day	4 6% 29% 35% 20% 5%	490
	11th to 20th	Day	7% 6% 29% 38% 17% 3	490
	21st to end	Day	6% 4 27% 36% 22% 6%	435
November	1st to 10th	Day	9% 3 22% 39% 23% 5%	300
	11th to 20th	Day	6% 4 24% 38% 24% 4	300
	21st to end	Day	11% 5% 27% 35% 16% 5%	300
December	1st to 10th	Day	9% 5% 25% 37% 20% 4	300
	11th to 20th	Day	6% 5% 22% 39% 22% 6%	300
	21st to end	Day	17% 4 25% 35% 15% 3	330
January	1st to 10th	Night	12% 2 17% 38% 22% 9%	800
	11th to 20th	Night	10% 2 14% 43% 23% 8%	800
	21st to end	Night	14% 3 15% 44% 21% 4	880
February	1st to 10th	Night	15% 2 12% 39% 24% 8%	800
	11th to 20th	Night	14% 3 13% 40% 22% 7%	784
	21st to end	Night	14% 4 16% 41% 21% 4	660
March	1st to 10th	Night	17% 3 13% 43% 22% 3	800
	11th to 20th	Night	15% 3 10% 39% 26% 8%	800
	21st to end	Night	14% 2 12% 41% 26% 5%	880
April	1st to 10th	Night	13% 4 9% 45% 25% 5%	800
	11th to 20th	Night	13% 4 10% 40% 27% 6%	791
	21st to end	Night	12% 5% 8% 36% 31% 8%	800
May	1st to 10th	Night	12% 5% 9% 37% 31% 6%	670
	11th to 20th	Night	13% 4 8% 29% 38% 7%	591
	21st to end	Night	13% 5% 7% 35% 36% 3	650
June	1st to 10th	Night	9% 3 8% 36% 38% 7%	600
	11th to 20th	Night	6% 1 5% 39% 43% 7%	600
	21st to end	Night	4 1 4 35% 49% 7%	600
July	1st to 10th	Night	2 1 1 23% 61% 12%	570
	11th to 20th	Night	1 1 16% 68% 14%	552
	21st to end	Night	2 1 14% 62% 20%	728
August	1st to 10th	Night	2 2 1 19% 57% 19%	756
	11th to 20th	Night	2 1 1 13% 59% 24%	752
	21st to end	Night	3 1 14% 58% 24%	836
September	1st to 10th	Night	5% 2 1 20% 56% 16%	760
	11th to 20th	Night	7% 2 2 28% 49% 11%	760
	21st to end	Night	5% 1 4 35% 41% 15%	760
October	1st to 10th	Night	7% 1 4 41% 39% 7%	760
	11th to 20th	Night	10% 2 6% 38% 34% 11%	760
	21st to end	Night	8% 3 8% 36% 31% 15%	836
November	1st to 10th	Night	8% 1 7% 41% 33% 10%	780
	11th to 20th	Night	7% 1 10% 41% 29% 12%	800
	21st to end	Night	9% 2 13% 42% 25% 9%	800
December	1st to 10th	Night	11% 2 14% 41% 23% 9%	800
	11th to 20th	Night	15% 3 14% 40% 22% 6%	800
	21st to end	Night	14% 3 15% 40% 21% 8%	880

Page generated at 2025-07-02 22:30:18. Version ac07

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