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 2026-10-29.

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 2 4 6% 68%	157641
	Night	7% 7% 2 4 2 2 2 2 4 6% 61%	152258
Transparency	Day	17% 3 7% 16% 28% 29%	152738
	Night	22% 5% 8% 14% 24% 28%	148138
Seeing	Day	8% 6% 24% 36% 19% 7%	18474
	Night	10% 2 8% 35% 35% 10%	28813

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	10% 5% 2 4 2 2 3 2 3 5% 61%	5318
	11th to 20th	Day	4 3 1 2 2 1 2 2 4 6% 72%	5657
	21st to end	Day	10% 6% 2 5% 3 4 4 4 6% 8% 48%	6500
February	1st to 10th	Day	10% 5% 1 4 4 3 4 3 4 5% 57%	2100
	11th to 20th	Day	11% 6% 2 4 3 3 3 4 4 7% 52%	2050
	21st to end	Day	12% 7% 2 5% 3 4 4 3 5% 6% 49%	1730
March	1st to 10th	Day	11% 8% 2 5% 3 4 4 4 8% 9% 42%	4618
	11th to 20th	Day	11% 5% 2 3 3 3 3 3 5% 7% 55%	4898
	21st to end	Day	10% 7% 2 4 3 3 3 3 5% 7% 54%	5870
April	1st to 10th	Day	7% 6% 2 5% 3 3 3 3 6% 7% 56%	2520
	11th to 20th	Day	4 4 2 4 3 3 3 3 4 6% 62%	2489
	21st to end	Day	7% 5% 2 3 2 2 3 3 5% 7% 63%	2520
May	1st to 10th	Day	6% 5% 2 4 2 2 2 2 3 6% 67%	7431
	11th to 20th	Day	2 4 2 4 3 2 3 2 4 8% 66%	7596
	21st to end	Day	3 5% 2 3 2 2 3 2 4 7% 67%	8370
June	1st to 10th	Day	4 5% 2 3 3 2 2 2 4 6% 66%	2730
	11th to 20th	Day	2 4 1 2 2 2 2 1 2 5% 77%	2730
	21st to end	Day	1 3 1 2 2 2 2 2 3 5% 77%	2730
July	1st to 10th	Day	1 1 1 2 1 1 1 1 2 4 85%	7649
	11th to 20th	Day	1 1 1 2 2 2 3 3 5% 7% 72%	7650
	21st to end	Day	1 1 1 1 1 2 2 4 6% 82%	7971
August	1st to 10th	Day	1 1 1 1 2 2 3 5% 84%	6986
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 5% 82%	7001
	21st to end	Day	2 1 1 2 2 2 2 2 3 5% 78%	7750
September	1st to 10th	Day	2 2 1 3 2 3 3 2 4 6% 73%	2493
	11th to 20th	Day	3 3 1 2 1 1 2 2 2 4 80%	2310
	21st to end	Day	3 3 1 2 2 1 2 2 3 4 77%	2310
October	1st to 10th	Day	3 2 1 3 2 2 2 1 3 4 79%	3710
	11th to 20th	Day	3 3 1 2 2 2 2 2 3 5% 74%	3689
	21st to end	Day	3 2 1 3 2 2 2 2 4 6% 72%	3483
November	1st to 10th	Day	5% 3 1 3 2 2 2 3 4 6% 69%	1854
	11th to 20th	Day	5% 3 2 3 2 3 3 3 5% 6% 66%	1890
	21st to end	Day	7% 5% 2 4 3 3 3 3 5% 7% 58%	1890
December	1st to 10th	Day	5% 2 1 2 2 2 2 2 4 8% 69%	3040
	11th to 20th	Day	8% 4 1 3 4 3 5% 5% 6% 8% 53%	3499
	21st to end	Day	9% 5% 2 5% 4 5% 5% 5% 8% 8% 44%	4609
January	1st to 10th	Night	13% 6% 2 4 3 3 3 2 4 5% 56%	7605
	11th to 20th	Night	5% 4 1 3 2 2 2 2 3 7% 68%	7334
	21st to end	Night	13% 8% 2 6% 3 4 4 3 5% 6% 47%	7747
February	1st to 10th	Night	10% 6% 2 4 3 3 3 3 4 6% 57%	2520
	11th to 20th	Night	12% 7% 2 5% 4 3 3 3 4 5% 52%	2458
	21st to end	Night	12% 7% 3 5% 3 2 4 2 4 6% 52%	2076
March	1st to 10th	Night	21% 13% 2 5% 2 2 3 2 4 6% 40%	5496
	11th to 20th	Night	13% 13% 2 4 3 3 3 3 4 6% 48%	5320
	21st to end	Night	12% 14% 3 6% 3 3 3 2 5% 6% 44%	5342
April	1st to 10th	Night	9% 9% 3 5% 3 3 2 2 5% 8% 51%	2100
	11th to 20th	Night	8% 11% 2 4 3 2 3 3 4 6% 54%	2079
	21st to end	Night	9% 10% 2 4 3 3 3 3 4 8% 52%	2100
May	1st to 10th	Night	10% 8% 3 5% 3 2 2 2 3 6% 55%	5525
	11th to 20th	Night	6% 15% 4 6% 3 2 2 2 4 8% 48%	5296
	21st to end	Night	7% 16% 4 6% 2 2 2 2 3 6% 51%	5837
June	1st to 10th	Night	5% 11% 3 5% 3 3 3 3 4 10% 52%	1890
	11th to 20th	Night	3 7% 2 4 2 2 3 2 3 8% 65%	1890
	21st to end	Night	3 4 1 3 2 2 2 2 4 8% 69%	1890
July	1st to 10th	Night	2 1 1 1 1 1 1 2 6% 82%	5340
	11th to 20th	Night	1 1 1 3 3 3 3 3 5% 10% 69%	5340
	21st to end	Night	1 3 1 2 1 2 2 2 3 6% 77%	6138
August	1st to 10th	Night	1 1 1 1 1 2 3 6% 84%	5866
	11th to 20th	Night	1 2 1 2 2 2 2 2 3 8% 74%	5886
	21st to end	Night	2 2 1 2 2 2 2 2 3 6% 77%	6499
September	1st to 10th	Night	3 4 1 3 2 3 3 2 4 7% 68%	2126
	11th to 20th	Night	5% 5% 1 3 2 2 2 2 3 5% 72%	2310
	21st to end	Night	4 5% 1 2 2 2 1 2 2 6% 73%	2310
October	1st to 10th	Night	3 3 1 2 2 2 2 2 2 5% 77%	3710
	11th to 20th	Night	6% 10% 2 4 2 2 1 1 2 5% 65%	3689
	21st to end	Night	4 4 1 3 2 2 3 2 4 5% 68%	4492
November	1st to 10th	Night	6% 4 1 3 2 2 2 3 3 5% 68%	2665
	11th to 20th	Night	5% 5% 2 4 3 2 3 2 4 6% 65%	2730
	21st to end	Night	8% 5% 2 4 3 3 4 4 5% 6% 56%	2730
December	1st to 10th	Night	5% 3 1 3 3 2 3 3 4 6% 67%	4370
	11th to 20th	Night	10% 6% 2 5% 3 3 4 4 7% 7% 50%	4941
	21st to end	Night	9% 8% 2 5% 3 3 3 4 6% 10% 46%	6611

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	27% 4 6% 14% 21% 28%	5321
	11th to 20th	Day	15% 3 6% 14% 19% 44%	5657
	21st to end	Day	32% 4 7% 8% 22% 27%	6500
February	1st to 10th	Day	29% 4 5% 13% 21% 29%	2100
	11th to 20th	Day	32% 4 6% 14% 23% 20%	2060
	21st to end	Day	35% 5% 6% 12% 21% 21%	1730
March	1st to 10th	Day	34% 6% 8% 18% 19% 15%	4618
	11th to 20th	Day	27% 5% 10% 23% 22% 13%	4898
	21st to end	Day	28% 6% 8% 30% 17% 11%	5870
April	1st to 10th	Day	28% 4 8% 22% 24% 14%	2520
	11th to 20th	Day	21% 5% 7% 18% 30% 19%	2492
	21st to end	Day	20% 4 8% 23% 33% 12%	2520
May	1st to 10th	Day	18% 4 6% 19% 37% 16%	7431
	11th to 20th	Day	11% 4 10% 18% 41% 16%	7599
	21st to end	Day	12% 5% 8% 18% 43% 12%	8371
June	1st to 10th	Day	15% 5% 7% 20% 32% 21%	2730
	11th to 20th	Day	11% 3 5% 9% 28% 45%	2730
	21st to end	Day	10% 2 5% 5% 24% 54%	2730
July	1st to 10th	Day	6% 1 4 5% 18% 67%	7586
	11th to 20th	Day	9% 3 9% 14% 40% 24%	7581
	21st to end	Day	6% 2 6% 22% 32% 32%	7794
August	1st to 10th	Day	7% 2 5% 22% 37% 26%	5530
	11th to 20th	Day	8% 2 7% 20% 29% 34%	5517
	21st to end	Day	8% 1 4 11% 31% 44%	6077
September	1st to 10th	Day	13% 3 7% 10% 31% 37%	2493
	11th to 20th	Day	8% 2 5% 7% 34% 44%	2310
	21st to end	Day	13% 2 4 11% 30% 40%	2310
October	1st to 10th	Day	11% 2 4 8% 16% 59%	3710
	11th to 20th	Day	12% 3 5% 11% 27% 42%	3689
	21st to end	Day	14% 2 4 8% 32% 40%	3483
November	1st to 10th	Day	18% 3 5% 14% 23% 38%	1854
	11th to 20th	Day	20% 3 6% 11% 22% 38%	1890
	21st to end	Day	25% 4 6% 12% 20% 33%	1890
December	1st to 10th	Day	17% 2 4 12% 26% 39%	3040
	11th to 20th	Day	28% 4 8% 14% 24% 22%	3498
	21st to end	Day	33% 6% 8% 22% 23% 9%	4609
January	1st to 10th	Night	31% 4 4 11% 24% 25%	7605
	11th to 20th	Night	17% 4 7% 13% 15% 44%	7334
	21st to end	Night	38% 4 6% 7% 20% 27%	7747
February	1st to 10th	Night	29% 4 6% 12% 21% 29%	2520
	11th to 20th	Night	35% 5% 6% 12% 20% 22%	2459
	21st to end	Night	33% 5% 5% 13% 22% 23%	2076
March	1st to 10th	Night	44% 7% 8% 11% 16% 14%	5496
	11th to 20th	Night	36% 7% 7% 22% 19% 10%	5320
	21st to end	Night	38% 9% 8% 16% 17% 12%	5342
April	1st to 10th	Night	31% 5% 8% 19% 21% 16%	2100
	11th to 20th	Night	27% 6% 9% 16% 23% 19%	2079
	21st to end	Night	29% 6% 9% 18% 22% 15%	2100
May	1st to 10th	Night	24% 7% 10% 19% 29% 11%	5523
	11th to 20th	Night	22% 7% 16% 16% 26% 12%	5297
	21st to end	Night	23% 9% 13% 15% 29% 11%	5838
June	1st to 10th	Night	21% 8% 12% 15% 25% 19%	1890
	11th to 20th	Night	14% 3 10% 11% 22% 40%	1890
	21st to end	Night	13% 2 9% 6% 21% 49%	1890
July	1st to 10th	Night	5% 1 6% 6% 19% 64%	5295
	11th to 20th	Night	6% 3 13% 19% 41% 19%	5286
	21st to end	Night	7% 3 7% 24% 32% 27%	6003
August	1st to 10th	Night	5% 3 8% 23% 37% 25%	4636
	11th to 20th	Night	9% 3 8% 23% 24% 33%	4636
	21st to end	Night	8% 2 7% 11% 31% 42%	5092
September	1st to 10th	Night	15% 3 8% 10% 25% 38%	2126
	11th to 20th	Night	14% 2 9% 7% 29% 40%	2310
	21st to end	Night	14% 3 4 11% 33% 35%	2310
October	1st to 10th	Night	13% 2 4 8% 17% 56%	3710
	11th to 20th	Night	18% 4 8% 8% 21% 41%	3689
	21st to end	Night	18% 3 4 8% 25% 41%	4492
November	1st to 10th	Night	19% 3 6% 12% 21% 39%	2665
	11th to 20th	Night	22% 4 4 12% 19% 39%	2730
	21st to end	Night	28% 4 7% 13% 17% 31%	2730
December	1st to 10th	Night	19% 3 5% 12% 23% 38%	4370
	11th to 20th	Night	31% 5% 7% 12% 20% 27%	4941
	21st to end	Night	30% 8% 10% 22% 21% 10%	6611

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% 8% 26% 28% 19% 1	330
	11th to 20th	Day	12% 7% 23% 41% 15% 3	439
	21st to end	Day	13% 9% 29% 34% 12% 3	594
February	1st to 10th	Day	13% 9% 31% 32% 11% 3	540
	11th to 20th	Day	16% 12% 30% 30% 10% 2	535
	21st to end	Day	15% 11% 35% 28% 9% 1	446
March	1st to 10th	Day	16% 13% 31% 29% 10% 2	540
	11th to 20th	Day	14% 9% 30% 32% 11% 4	540
	21st to end	Day	10% 13% 36% 26% 12% 2	594
April	1st to 10th	Day	10% 13% 31% 27% 15% 5%	540
	11th to 20th	Day	6% 12% 37% 30% 11% 4	532
	21st to end	Day	8% 13% 30% 28% 16% 5%	540
May	1st to 10th	Day	11% 11% 30% 29% 14% 6%	543
	11th to 20th	Day	8% 9% 28% 36% 15% 4	568
	21st to end	Day	7% 9% 29% 33% 18% 4	617
June	1st to 10th	Day	4 5% 24% 34% 26% 8%	570
	11th to 20th	Day	5% 2 24% 39% 23% 7%	570
	21st to end	Day	2 2 21% 42% 24% 9%	570
July	1st to 10th	Day	2 1 13% 41% 30% 13%	566
	11th to 20th	Day	1 1 8% 44% 31% 16%	564
	21st to end	Day	2 7% 46% 30% 15%	619
August	1st to 10th	Day	1 1 11% 45% 26% 15%	567
	11th to 20th	Day	3 9% 48% 24% 15%	557
	21st to end	Day	3 1 14% 45% 25% 13%	627
September	1st to 10th	Day	4 2 20% 46% 20% 9%	570
	11th to 20th	Day	5% 3 25% 43% 18% 6%	570
	21st to end	Day	5% 6% 27% 34% 19% 8%	570
October	1st to 10th	Day	4 6% 30% 34% 20% 6%	570
	11th to 20th	Day	8% 7% 30% 36% 16% 4	570
	21st to end	Day	5% 6% 26% 35% 22% 6%	503
November	1st to 10th	Day	8% 3 21% 38% 25% 6%	330
	11th to 20th	Day	8% 5% 24% 37% 22% 4	330
	21st to end	Day	11% 5% 26% 35% 17% 5%	330
December	1st to 10th	Day	8% 5% 24% 38% 21% 4	330
	11th to 20th	Day	5% 5% 21% 39% 24% 7%	330
	21st to end	Day	18% 5% 26% 33% 15% 3	363
January	1st to 10th	Night	14% 2 18% 36% 21% 9%	840
	11th to 20th	Night	9% 2 14% 44% 23% 7%	840
	21st to end	Night	14% 3 15% 44% 20% 4	924
February	1st to 10th	Night	14% 2 12% 40% 24% 7%	840
	11th to 20th	Night	16% 4 13% 39% 21% 6%	824
	21st to end	Night	13% 3 15% 42% 22% 4	692
March	1st to 10th	Night	17% 3 14% 43% 21% 3	840
	11th to 20th	Night	14% 3 10% 39% 27% 8%	840
	21st to end	Night	13% 2 11% 41% 27% 5%	924
April	1st to 10th	Night	13% 4 8% 46% 24% 5%	840
	11th to 20th	Night	13% 4 11% 40% 27% 6%	831
	21st to end	Night	12% 5% 9% 37% 30% 8%	840
May	1st to 10th	Night	12% 6% 9% 37% 31% 6%	704
	11th to 20th	Night	13% 4 9% 30% 38% 7%	621
	21st to end	Night	14% 5% 7% 34% 36% 3	683
June	1st to 10th	Night	9% 3 7% 37% 38% 7%	630
	11th to 20th	Night	6% 1 5% 39% 43% 6%	630
	21st to end	Night	4 2 4 34% 48% 7%	630
July	1st to 10th	Night	2 1 1 24% 60% 12%	615
	11th to 20th	Night	1 1 17% 67% 14%	612
	21st to end	Night	3 1 16% 60% 19%	805
August	1st to 10th	Night	2 2 1 18% 58% 20%	836
	11th to 20th	Night	2 1 1 14% 58% 24%	832
	21st to end	Night	3 1 15% 58% 22%	924
September	1st to 10th	Night	5% 2 1 22% 55% 15%	840
	11th to 20th	Night	7% 2 3 29% 48% 11%	840
	21st to end	Night	6% 2 4 35% 39% 14%	840
October	1st to 10th	Night	7% 1 4 41% 40% 7%	840
	11th to 20th	Night	10% 2 7% 39% 32% 10%	840
	21st to end	Night	7% 3 7% 36% 32% 14%	912
November	1st to 10th	Night	7% 1 7% 41% 34% 9%	820
	11th to 20th	Night	8% 1 11% 40% 29% 12%	840
	21st to end	Night	9% 2 12% 42% 25% 9%	840
December	1st to 10th	Night	10% 2 14% 42% 23% 8%	840
	11th to 20th	Night	14% 3 14% 40% 23% 6%	840
	21st to end	Night	14% 3 15% 40% 21% 7%	924

Page generated at 2026-10-26 01:37:45. Version ac07

Copyright © 2026 Attilla Danko.