OCA Silverado
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the OCA Silverado clear sky chart from 2005-11-06 to 2025-04-11.

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	4 3 1 3 3 3 3 3 4 6% 66%	118681
	Night	5% 5% 2 4 3 3 4 3 4 6% 62%	118614
Transparency	Day	18% 4 6% 17% 26% 28%	118446
	Night	22% 6% 7% 15% 22% 29%	118439
Seeing	Day	7% 7% 21% 35% 22% 8%	16359
	Night	7% 2 8% 34% 38% 11%	26313

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	5% 3 1 3 2 3 2 2 3 5% 70%	4098
	11th to 20th	Day	6% 3 1 3 2 2 3 3 5% 6% 67%	4399
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 8% 49%	5016
February	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 5% 4 57%	2000
	11th to 20th	Day	9% 4 2 4 3 3 4 3 5% 5% 58%	1950
	21st to end	Day	9% 7% 2 6% 4 3 3 3 5% 6% 53%	1650
March	1st to 10th	Day	10% 7% 2 5% 4 4 4 4 7% 7% 45%	4518
	11th to 20th	Day	9% 5% 2 5% 3 3 3 3 5% 7% 53%	4687
	21st to end	Day	7% 5% 1 4 4 4 4 3 6% 8% 54%	5920
April	1st to 10th	Day	6% 5% 1 3 4 3 4 4 5% 7% 58%	2400
	11th to 20th	Day	4 4 2 5% 3 3 3 2 5% 5% 64%	2251
	21st to end	Day	5% 4 1 4 2 3 3 3 5% 7% 65%	2280
May	1st to 10th	Day	4 3 1 3 2 2 2 2 4 5% 72%	3945
	11th to 20th	Day	2 5% 2 5% 2 3 3 3 4 7% 64%	4071
	21st to end	Day	3 5% 2 4 3 3 3 3 5% 7% 63%	4477
June	1st to 10th	Day	4 5% 1 4 3 3 3 3 5% 9% 61%	2470
	11th to 20th	Day	2 3 1 3 2 2 3 2 4 6% 72%	2526
	21st to end	Day	1 2 1 3 2 2 2 2 3 5% 77%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 1 2 3 85%	4420
	11th to 20th	Day	1 2 1 2 2 2 2 3 4 6% 77%	4151
	21st to end	Day	1 1 1 2 2 2 2 3 4 81%	4213
August	1st to 10th	Day	1 1 1 2 2 1 2 2 3 5% 81%	3783
	11th to 20th	Day	1 1 1 1 1 1 1 2 4 87%	3724
	21st to end	Day	1 1 1 1 1 2 2 2 4 86%	4180
September	1st to 10th	Day	2 2 1 2 1 2 2 2 4 6% 77%	2280
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 78%	2112
	21st to end	Day	1 1 1 2 2 2 2 3 4 4 78%	2090
October	1st to 10th	Day	2 2 1 2 2 2 2 2 3 4 80%	3490
	11th to 20th	Day	3 3 1 3 3 3 4 2 5% 8% 67%	3354
	21st to end	Day	3 2 1 2 2 3 4 4 5% 6% 67%	3333
November	1st to 10th	Day	4 3 1 3 3 2 3 2 5% 5% 70%	1764
	11th to 20th	Day	4 3 1 3 3 2 3 3 3 6% 68%	1800
	21st to end	Day	5% 4 2 5% 4 3 3 4 6% 7% 57%	1800
December	1st to 10th	Day	4 3 1 3 3 3 4 3 5% 8% 63%	2950
	11th to 20th	Day	8% 4 2 4 4 4 5% 5% 6% 8% 49%	3409
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 4 6% 9% 43%	4510
January	1st to 10th	Night	5% 4 1 4 2 3 3 2 4 6% 67%	5867
	11th to 20th	Night	5% 5% 2 5% 3 3 4 2 4 6% 63%	5589
	21st to end	Night	11% 7% 2 5% 3 3 4 4 5% 5% 51%	5984
February	1st to 10th	Night	9% 6% 2 5% 3 3 3 3 4 6% 58%	2400
	11th to 20th	Night	9% 5% 1 4 3 3 4 2 4 5% 58%	2338
	21st to end	Night	11% 6% 2 5% 4 4 4 3 4 4 53%	1980
March	1st to 10th	Night	10% 13% 2 6% 4 3 3 3 5% 7% 44%	5376
	11th to 20th	Night	6% 9% 3 6% 4 4 3 3 5% 7% 50%	5311
	21st to end	Night	7% 10% 3 8% 4 4 4 3 4 5% 49%	5050
April	1st to 10th	Night	7% 6% 2 5% 3 3 4 3 5% 8% 55%	2000
	11th to 20th	Night	4 7% 2 5% 4 4 4 3 4 5% 60%	1883
	21st to end	Night	4 6% 1 3 4 4 5% 3 4 6% 60%	1900
May	1st to 10th	Night	4 5% 2 4 2 2 3 2 3 4 67%	3026
	11th to 20th	Night	1 5% 4 10% 4 5% 9% 3 4 6% 48%	2834
	21st to end	Night	3 9% 2 5% 3 3 5% 3 3 5% 58%	3110
June	1st to 10th	Night	2 6% 2 6% 3 4 6% 5% 5% 7% 53%	1710
	11th to 20th	Night	2 2 1 4 3 4 4 3 5% 8% 64%	1644
	21st to end	Night	2 2 1 2 1 3 4 4 5% 7% 69%	1520
July	1st to 10th	Night	1 1 2 2 2 2 2 3 4 81%	2540
	11th to 20th	Night	1 1 1 2 2 2 4 3 4 6% 76%	2796
	21st to end	Night	2 1 2 2 2 2 2 3 5% 79%	3353
August	1st to 10th	Night	1 1 1 2 1 2 2 2 4 5% 80%	3166
	11th to 20th	Night	1 1 1 1 2 2 1 3 6% 82%	3126
	21st to end	Night	1 1 1 1 2 3 2 3 5% 82%	3498
September	1st to 10th	Night	2 2 1 3 3 3 3 3 4 5% 72%	1900
	11th to 20th	Night	2 2 1 2 2 3 2 2 3 5% 76%	2066
	21st to end	Night	2 3 1 2 2 2 2 2 3 4 78%	2090
October	1st to 10th	Night	2 2 1 2 2 2 2 1 2 4 81%	3490
	11th to 20th	Night	2 5% 2 8% 4 4 3 2 4 5% 61%	3581
	21st to end	Night	2 3 2 4 2 3 3 2 3 5% 72%	4232
November	1st to 10th	Night	4 4 2 3 2 2 3 2 4 6% 68%	2535
	11th to 20th	Night	3 3 2 4 3 3 3 2 3 6% 68%	2600
	21st to end	Night	6% 4 1 5% 4 3 4 3 6% 7% 56%	2600
December	1st to 10th	Night	4 3 1 4 3 3 3 2 4 7% 65%	4240
	11th to 20th	Night	8% 6% 2 5% 4 5% 5% 4 5% 6% 50%	4811
	21st to end	Night	7% 7% 2 6% 4 5% 5% 4 7% 11% 42%	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	18% 2 4 21% 29% 25%	4099
	11th to 20th	Day	18% 5% 9% 16% 18% 33%	4399
	21st to end	Day	31% 5% 4 13% 26% 21%	5016
February	1st to 10th	Day	29% 4 5% 13% 24% 25%	2000
	11th to 20th	Day	26% 4 6% 17% 26% 20%	1960
	21st to end	Day	31% 4 7% 15% 22% 19%	1650
March	1st to 10th	Day	31% 6% 10% 18% 19% 16%	4518
	11th to 20th	Day	28% 6% 10% 26% 19% 11%	4687
	21st to end	Day	25% 6% 13% 30% 17% 10%	5920
April	1st to 10th	Day	25% 4 10% 25% 23% 13%	2400
	11th to 20th	Day	21% 4 8% 20% 27% 19%	2254
	21st to end	Day	19% 4 9% 24% 31% 12%	2280
May	1st to 10th	Day	15% 4 8% 21% 39% 12%	3945
	11th to 20th	Day	18% 8% 8% 22% 36% 9%	4074
	21st to end	Day	19% 7% 9% 26% 34% 5%	4477
June	1st to 10th	Day	19% 6% 8% 24% 29% 14%	2470
	11th to 20th	Day	13% 4 4 15% 31% 32%	2526
	21st to end	Day	12% 3 4 11% 25% 45%	2660
July	1st to 10th	Day	6% 2 3 8% 14% 68%	4351
	11th to 20th	Day	10% 3 5% 11% 29% 43%	4080
	21st to end	Day	7% 3 5% 20% 28% 37%	4080
August	1st to 10th	Day	8% 2 2 13% 44% 30%	3770
	11th to 20th	Day	5% 2 3 14% 27% 50%	3760
	21st to end	Day	6% 2 2 8% 28% 54%	4179
September	1st to 10th	Day	10% 3 5% 9% 33% 39%	2280
	11th to 20th	Day	10% 3 3 12% 36% 36%	2112
	21st to end	Day	11% 2 5% 14% 33% 35%	2090
October	1st to 10th	Day	11% 2 3 11% 16% 57%	3490
	11th to 20th	Day	13% 3 3 13% 34% 34%	3354
	21st to end	Day	17% 4 3 10% 31% 35%	3333
November	1st to 10th	Day	17% 3 6% 17% 25% 32%	1764
	11th to 20th	Day	17% 4 6% 15% 20% 37%	1800
	21st to end	Day	24% 4 8% 12% 22% 30%	1800
December	1st to 10th	Day	19% 4 5% 13% 24% 35%	2950
	11th to 20th	Day	31% 5% 7% 15% 23% 19%	3408
	21st to end	Day	34% 6% 9% 21% 20% 9%	4510
January	1st to 10th	Night	19% 3 5% 13% 32% 28%	5867
	11th to 20th	Night	21% 5% 9% 17% 16% 33%	5589
	21st to end	Night	34% 6% 5% 10% 22% 23%	5984
February	1st to 10th	Night	28% 4 6% 14% 21% 27%	2400
	11th to 20th	Night	28% 4 6% 16% 21% 24%	2339
	21st to end	Night	33% 5% 5% 13% 19% 25%	1980
March	1st to 10th	Night	36% 7% 10% 16% 16% 15%	5376
	11th to 20th	Night	33% 6% 10% 22% 18% 11%	5311
	21st to end	Night	32% 7% 11% 20% 20% 10%	5050
April	1st to 10th	Night	27% 6% 10% 22% 20% 15%	2000
	11th to 20th	Night	23% 7% 10% 18% 22% 19%	1883
	21st to end	Night	23% 7% 11% 22% 23% 14%	1900
May	1st to 10th	Night	20% 7% 9% 17% 34% 13%	3026
	11th to 20th	Night	24% 17% 9% 19% 23% 7%	2835
	21st to end	Night	22% 14% 9% 23% 27% 6%	3110
June	1st to 10th	Night	24% 10% 14% 16% 21% 14%	1710
	11th to 20th	Night	13% 9% 9% 17% 25% 27%	1644
	21st to end	Night	10% 8% 6% 15% 23% 38%	1520
July	1st to 10th	Night	6% 3 4 10% 12% 65%	2500
	11th to 20th	Night	8% 5% 5% 11% 23% 49%	2744
	21st to end	Night	9% 3 6% 16% 27% 39%	3248
August	1st to 10th	Night	7% 3 3 12% 40% 33%	3156
	11th to 20th	Night	5% 3 4 14% 24% 49%	3156
	21st to end	Night	5% 3 2 9% 18% 63%	3498
September	1st to 10th	Night	14% 5% 5% 10% 27% 39%	1900
	11th to 20th	Night	11% 5% 6% 11% 28% 39%	2066
	21st to end	Night	12% 3 4 13% 32% 36%	2090
October	1st to 10th	Night	10% 2 4 11% 13% 59%	3490
	11th to 20th	Night	22% 4 3 11% 22% 39%	3581
	21st to end	Night	16% 3 3 7% 26% 45%	4232
November	1st to 10th	Night	18% 3 5% 16% 21% 37%	2535
	11th to 20th	Night	20% 3 5% 13% 19% 40%	2600
	21st to end	Night	26% 4 9% 14% 16% 31%	2600
December	1st to 10th	Night	20% 3 5% 12% 19% 41%	4240
	11th to 20th	Night	32% 6% 7% 12% 20% 22%	4811
	21st to end	Night	31% 8% 10% 21% 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% 7% 18% 36% 18% 4	300
	11th to 20th	Day	13% 9% 22% 38% 15% 3	430
	21st to end	Day	13% 12% 27% 28% 17% 3	550
February	1st to 10th	Day	17% 8% 27% 28% 16% 4	500
	11th to 20th	Day	12% 10% 32% 34% 11% 2	495
	21st to end	Day	12% 15% 29% 32% 11% 1	414
March	1st to 10th	Day	15% 15% 33% 23% 11% 2	500
	11th to 20th	Day	14% 10% 33% 27% 14% 2	500
	21st to end	Day	9% 16% 33% 29% 10% 3	550
April	1st to 10th	Day	8% 11% 30% 28% 16% 6%	500
	11th to 20th	Day	6% 13% 35% 30% 11% 5%	453
	21st to end	Day	5% 11% 30% 33% 15% 7%	460
May	1st to 10th	Day	10% 11% 26% 34% 13% 6%	463
	11th to 20th	Day	7% 6% 27% 37% 19% 4	488
	21st to end	Day	8% 9% 24% 35% 18% 7%	529
June	1st to 10th	Day	3 5% 18% 37% 29% 8%	490
	11th to 20th	Day	3 3 21% 38% 24% 10%	490
	21st to end	Day	3 1 14% 41% 29% 11%	490
July	1st to 10th	Day	2 1 5% 40% 37% 15%	486
	11th to 20th	Day	2 4 36% 39% 19%	484
	21st to end	Day	1 1 3 39% 36% 19%	531
August	1st to 10th	Day	1 1 9% 39% 34% 16%	487
	11th to 20th	Day	2 1 6% 42% 32% 18%	477
	21st to end	Day	1 1 7% 40% 35% 16%	539
September	1st to 10th	Day	3 2 11% 45% 27% 13%	490
	11th to 20th	Day	3 2 19% 44% 23% 8%	490
	21st to end	Day	2 3 21% 37% 24% 13%	490
October	1st to 10th	Day	4 4 22% 37% 25% 8%	490
	11th to 20th	Day	5% 4 22% 36% 24% 8%	490
	21st to end	Day	4 5% 21% 35% 27% 9%	473
November	1st to 10th	Day	6% 5% 18% 32% 31% 6%	300
	11th to 20th	Day	5% 4 20% 39% 24% 9%	300
	21st to end	Day	6% 8% 20% 36% 19% 9%	300
December	1st to 10th	Day	10% 5% 17% 34% 29% 5%	300
	11th to 20th	Day	8% 5% 22% 31% 27% 8%	300
	21st to end	Day	15% 9% 22% 32% 17% 4	330
January	1st to 10th	Night	11% 5% 12% 41% 23% 10%	800
	11th to 20th	Night	9% 3 12% 41% 27% 8%	800
	21st to end	Night	13% 5% 14% 37% 26% 5%	880
February	1st to 10th	Night	12% 5% 11% 38% 24% 9%	800
	11th to 20th	Night	11% 2 14% 41% 25% 7%	784
	21st to end	Night	15% 3 15% 39% 23% 6%	660
March	1st to 10th	Night	11% 4 13% 45% 23% 5%	800
	11th to 20th	Night	12% 3 12% 37% 27% 9%	800
	21st to end	Night	9% 3 13% 40% 30% 5%	880
April	1st to 10th	Night	10% 2 9% 42% 32% 5%	800
	11th to 20th	Night	6% 4 12% 41% 31% 7%	753
	21st to end	Night	7% 3 7% 38% 36% 9%	760
May	1st to 10th	Night	8% 2 11% 37% 37% 6%	671
	11th to 20th	Night	6% 2 10% 34% 40% 7%	561
	21st to end	Night	7% 2 11% 38% 37% 5%	617
June	1st to 10th	Night	4 3 8% 39% 39% 7%	570
	11th to 20th	Night	2 1 6% 35% 49% 8%	504
	21st to end	Night	3 1 2 24% 58% 12%	380
July	1st to 10th	Night	2 1 2 14% 62% 18%	370
	11th to 20th	Night	2 1 17% 60% 20%	516
	21st to end	Night	2 1 1 13% 62% 21%	767
August	1st to 10th	Night	2 1 1 17% 59% 20%	756
	11th to 20th	Night	1 1 1 14% 61% 23%	752
	21st to end	Night	2 17% 59% 22%	836
September	1st to 10th	Night	4 1 2 19% 55% 19%	760
	11th to 20th	Night	3 1 2 26% 53% 15%	760
	21st to end	Night	3 1 4 30% 47% 15%	760
October	1st to 10th	Night	3 2 4 41% 40% 10%	760
	11th to 20th	Night	6% 2 6% 33% 40% 14%	760
	21st to end	Night	5% 3 9% 33% 35% 16%	836
November	1st to 10th	Night	5% 2 9% 36% 35% 14%	780
	11th to 20th	Night	5% 2 8% 38% 34% 13%	800
	21st to end	Night	7% 3 12% 40% 29% 9%	800
December	1st to 10th	Night	9% 4 11% 41% 27% 8%	800
	11th to 20th	Night	13% 4 11% 39% 27% 6%	800
	21st to end	Night	11% 6% 15% 34% 26% 8%	880

Page generated at 2025-04-08 06:17:30. Version ac07

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