Rio Vista
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rio Vista clear sky chart from 2005-11-06 to 2026-08-30.

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	6% 3 1 3 2 2 3 2 4 5% 68%	152456
	Night	7% 4 1 4 3 3 3 2 4 6% 64%	147234
Transparency	Day	20% 4 7% 19% 26% 24%	147383
	Night	23% 5% 9% 19% 23% 21%	143294
Seeing	Day	7% 7% 24% 33% 21% 7%	17666
	Night	8% 5% 25% 39% 20% 2	26948

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	16% 8% 3 6% 5% 4 4 3 6% 7% 39%	4824
	11th to 20th	Day	10% 7% 2 6% 5% 5% 4 3 3 6% 49%	5340
	21st to end	Day	14% 8% 3 9% 6% 5% 5% 3 5% 6% 38%	5843
February	1st to 10th	Day	16% 6% 2 6% 5% 3 4 3 4 5% 45%	1890
	11th to 20th	Day	14% 5% 2 6% 4 5% 4 4 6% 6% 43%	1960
	21st to end	Day	13% 5% 2 5% 4 4 4 3 5% 7% 49%	1730
March	1st to 10th	Day	10% 7% 3 7% 5% 5% 5% 4 6% 7% 40%	4883
	11th to 20th	Day	12% 4 1 4 3 3 4 3 5% 7% 54%	5110
	21st to end	Day	9% 5% 2 6% 4 5% 6% 5% 6% 8% 43%	5754
April	1st to 10th	Day	11% 6% 2 4 4 3 3 4 6% 7% 50%	2520
	11th to 20th	Day	8% 4 1 4 3 3 4 3 5% 6% 59%	2489
	21st to end	Day	5% 3 1 3 4 2 3 3 4 8% 63%	2520
May	1st to 10th	Day	4 3 1 3 2 2 2 2 3 4 75%	7224
	11th to 20th	Day	1 1 1 1 1 1 1 2 4 85%	7967
	21st to end	Day	1 1 1 2 1 1 2 2 3 5% 82%	8992
June	1st to 10th	Day	3 3 1 2 2 2 2 2 4 7% 71%	2940
	11th to 20th	Day	1 1 1 2 2 4 5% 83%	2940
	21st to end	Day	1 1 1 1 1 1 1 2 2 4 85%	2940
July	1st to 10th	Day	1 1 1 2 3 92%	8219
	11th to 20th	Day	2 1 1 2 1 2 2 1 2 3 82%	7944
	21st to end	Day	1 1 1 2 2 2 4 87%	8304
August	1st to 10th	Day	1 1 1 1 1 1 2 3 4 85%	5907
	11th to 20th	Day	1 1 1 1 1 2 3 90%	5600
	21st to end	Day	1 1 1 1 1 1 1 2 4 86%	6093
September	1st to 10th	Day	1 1 1 1 1 1 1 2 4 87%	2400
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 77%	2400
	21st to end	Day	3 2 1 2 2 2 2 1 3 4 79%	2140
October	1st to 10th	Day	1 2 1 3 2 2 2 2 4 5% 77%	3280
	11th to 20th	Day	3 2 1 2 2 2 3 2 4 5% 75%	3261
	21st to end	Day	3 2 1 3 3 3 3 3 4 7% 66%	3558
November	1st to 10th	Day	7% 4 2 3 3 4 4 3 5% 8% 58%	1959
	11th to 20th	Day	10% 7% 2 6% 5% 5% 4 3 4 7% 47%	1890
	21st to end	Day	11% 5% 2 5% 5% 3 3 3 5% 6% 51%	1735
December	1st to 10th	Day	7% 5% 2 6% 3 4 4 4 6% 10% 47%	2700
	11th to 20th	Day	22% 11% 5% 13% 6% 4 4 3 4 6% 23%	3108
	21st to end	Day	20% 10% 4 8% 5% 5% 4 4 6% 7% 27%	4092
January	1st to 10th	Night	14% 6% 2 7% 4 4 4 3 6% 7% 43%	8058
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 6% 5% 51%	7650
	21st to end	Night	12% 7% 3 8% 4 4 4 3 5% 6% 44%	8371
February	1st to 10th	Night	15% 6% 3 5% 4 3 3 3 4 4 50%	2730
	11th to 20th	Night	12% 5% 2 6% 4 4 3 4 5% 8% 49%	2547
	21st to end	Night	12% 4 1 4 3 3 4 3 5% 6% 55%	2076
March	1st to 10th	Night	11% 6% 2 6% 4 4 5% 3 6% 7% 46%	5228
	11th to 20th	Night	13% 4 1 4 3 3 3 3 4 6% 56%	5110
	21st to end	Night	11% 5% 2 5% 3 4 4 4 5% 7% 49%	5461
April	1st to 10th	Night	8% 4 1 4 3 4 3 3 5% 8% 56%	2100
	11th to 20th	Night	7% 4 1 3 4 3 3 3 5% 7% 60%	2079
	21st to end	Night	4 3 1 2 2 1 3 3 5% 8% 67%	2100
May	1st to 10th	Night	3 3 1 3 2 2 2 2 3 5% 75%	5741
	11th to 20th	Night	1 1 1 1 1 2 2 3 5% 83%	4885
	21st to end	Night	1 1 1 1 1 2 2 2 4 84%	5181
June	1st to 10th	Night	3 2 3 2 2 2 2 4 7% 72%	1680
	11th to 20th	Night	1 1 1 1 2 1 2 3 86%	1680
	21st to end	Night	1 1 1 1 1 1 1 1 3 3 86%	1680
July	1st to 10th	Night	1 1 1 1 1 2 93%	4740
	11th to 20th	Night	2 2 1 2 1 1 1 1 2 3 83%	5013
	21st to end	Night	1 1 1 1 1 1 3 5% 84%	5806
August	1st to 10th	Night	2 1 1 1 1 1 2 2 5% 84%	4125
	11th to 20th	Night	1 1 1 2 4 90%	4470
	21st to end	Night	1 1 1 1 1 1 2 1 2 4 85%	5105
September	1st to 10th	Night	1 1 1 1 1 1 3 6% 86%	2000
	11th to 20th	Night	2 2 1 2 1 2 2 2 4 6% 77%	2000
	21st to end	Night	2 1 2 2 2 2 1 3 5% 81%	2256
October	1st to 10th	Night	2 2 2 2 1 2 2 4 4 79%	3920
	11th to 20th	Night	2 2 2 2 2 2 2 4 6% 76%	3897
	21st to end	Night	4 2 1 3 3 3 3 3 5% 5% 68%	4253
November	1st to 10th	Night	7% 4 1 3 3 2 4 2 5% 9% 61%	2558
	11th to 20th	Night	9% 5% 2 4 3 3 3 4 5% 7% 55%	2730
	21st to end	Night	10% 5% 2 4 3 3 4 3 5% 6% 56%	2882
December	1st to 10th	Night	8% 4 2 5% 3 4 4 4 5% 7% 55%	4700
	11th to 20th	Night	19% 7% 3 9% 6% 6% 5% 3 7% 8% 26%	5316
	21st to end	Night	21% 8% 3 8% 5% 5% 5% 3 5% 5% 32%	7106

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	42% 9% 14% 21% 11% 3	4825
	11th to 20th	Day	34% 7% 7% 18% 22% 12%	5340
	21st to end	Day	45% 7% 9% 15% 15% 9%	5843
February	1st to 10th	Day	40% 5% 9% 21% 18% 7%	1890
	11th to 20th	Day	38% 7% 13% 18% 19% 6%	1969
	21st to end	Day	34% 6% 11% 24% 18% 7%	1730
March	1st to 10th	Day	38% 8% 10% 22% 19% 3	4883
	11th to 20th	Day	29% 6% 13% 28% 15% 8%	5110
	21st to end	Day	34% 9% 16% 28% 12% 2	5754
April	1st to 10th	Day	33% 5% 12% 23% 21% 6%	2520
	11th to 20th	Day	25% 5% 13% 26% 23% 8%	2492
	21st to end	Day	19% 5% 13% 30% 28% 6%	2520
May	1st to 10th	Day	15% 2 5% 26% 32% 20%	7224
	11th to 20th	Day	6% 2 3 25% 45% 18%	7970
	21st to end	Day	7% 3 6% 31% 42% 11%	8994
June	1st to 10th	Day	14% 4 10% 26% 33% 13%	2940
	11th to 20th	Day	5% 2 7% 20% 39% 27%	2940
	21st to end	Day	7% 1 3 11% 35% 42%	2940
July	1st to 10th	Day	2 1 2 6% 23% 66%	8151
	11th to 20th	Day	10% 1 2 5% 11% 70%	7869
	21st to end	Day	4 2 4 11% 28% 51%	8119
August	1st to 10th	Day	7% 2 3 8% 28% 52%	4336
	11th to 20th	Day	3 1 2 10% 40% 44%	4081
	21st to end	Day	6% 1 3 11% 38% 41%	4420
September	1st to 10th	Day	5% 1 4 9% 31% 50%	2400
	11th to 20th	Day	11% 3 7% 21% 40% 19%	2400
	21st to end	Day	11% 2 5% 17% 36% 28%	2140
October	1st to 10th	Day	11% 2 4 12% 29% 42%	3280
	11th to 20th	Day	13% 3 7% 26% 31% 20%	3261
	21st to end	Day	18% 3 8% 23% 33% 14%	3558
November	1st to 10th	Day	25% 5% 11% 26% 24% 10%	1959
	11th to 20th	Day	36% 6% 11% 24% 18% 5%	1890
	21st to end	Day	32% 6% 11% 22% 22% 7%	1735
December	1st to 10th	Day	28% 7% 12% 29% 19% 5%	2700
	11th to 20th	Day	62% 6% 8% 13% 10% 1	3108
	21st to end	Day	53% 9% 12% 16% 9% 1	4092
January	1st to 10th	Night	37% 9% 17% 22% 11% 3	8058
	11th to 20th	Night	31% 6% 10% 17% 25% 11%	7650
	21st to end	Night	39% 7% 9% 17% 18% 9%	8371
February	1st to 10th	Night	37% 4 8% 21% 21% 9%	2730
	11th to 20th	Night	33% 5% 12% 22% 21% 7%	2549
	21st to end	Night	30% 5% 11% 27% 21% 7%	2076
March	1st to 10th	Night	35% 9% 12% 19% 21% 4	5228
	11th to 20th	Night	30% 5% 14% 25% 16% 10%	5110
	21st to end	Night	31% 8% 16% 26% 15% 3	5461
April	1st to 10th	Night	27% 5% 15% 23% 23% 8%	2100
	11th to 20th	Night	23% 6% 13% 27% 20% 11%	2079
	21st to end	Night	16% 5% 13% 31% 29% 6%	2100
May	1st to 10th	Night	15% 3 9% 23% 32% 18%	5739
	11th to 20th	Night	7% 2 4 22% 44% 20%	4885
	21st to end	Night	7% 2 7% 30% 42% 12%	5182
June	1st to 10th	Night	12% 5% 10% 25% 33% 15%	1680
	11th to 20th	Night	5% 2 7% 18% 37% 30%	1680
	21st to end	Night	6% 2 3 11% 34% 44%	1680
July	1st to 10th	Night	3 1 1 5% 24% 67%	4700
	11th to 20th	Night	10% 1 2 4 9% 73%	4965
	21st to end	Night	5% 2 3 12% 25% 54%	5679
August	1st to 10th	Night	8% 1 2 8% 27% 53%	3019
	11th to 20th	Night	3 1 2 9% 36% 49%	3257
	21st to end	Night	6% 1 3 9% 35% 46%	3698
September	1st to 10th	Night	4 2 4 9% 30% 52%	2000
	11th to 20th	Night	9% 2 7% 21% 35% 25%	2000
	21st to end	Night	9% 2 5% 18% 34% 32%	2256
October	1st to 10th	Night	10% 3 5% 11% 20% 51%	3920
	11th to 20th	Night	11% 3 6% 29% 27% 23%	3897
	21st to end	Night	18% 4 6% 21% 31% 20%	4253
November	1st to 10th	Night	22% 5% 11% 27% 21% 15%	2558
	11th to 20th	Night	28% 5% 12% 25% 23% 7%	2730
	21st to end	Night	29% 4 9% 22% 26% 10%	2882
December	1st to 10th	Night	27% 5% 10% 27% 22% 9%	4700
	11th to 20th	Night	54% 7% 11% 16% 11% 2	5316
	21st to end	Night	51% 9% 12% 16% 9% 3	7106

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	27% 8% 20% 24% 15% 6%	257
	11th to 20th	Day	16% 7% 18% 20% 27% 12%	430
	21st to end	Day	14% 6% 18% 25% 23% 13%	473
February	1st to 10th	Day	19% 9% 20% 19% 23% 11%	430
	11th to 20th	Day	15% 14% 27% 21% 16% 7%	486
	21st to end	Day	11% 11% 20% 35% 18% 5%	446
March	1st to 10th	Day	15% 13% 26% 27% 13% 7%	540
	11th to 20th	Day	17% 11% 22% 23% 18% 8%	540
	21st to end	Day	12% 12% 29% 28% 14% 4	594
April	1st to 10th	Day	12% 13% 27% 25% 15% 8%	540
	11th to 20th	Day	10% 12% 32% 25% 14% 7%	532
	21st to end	Day	4 15% 26% 30% 18% 6%	540
May	1st to 10th	Day	6% 11% 30% 32% 17% 4	543
	11th to 20th	Day	5% 9% 31% 31% 21% 3	568
	21st to end	Day	3 7% 27% 36% 22% 4	617
June	1st to 10th	Day	4 9% 28% 38% 17% 4	570
	11th to 20th	Day	1 9% 31% 44% 14% 1	570
	21st to end	Day	1 4 28% 44% 21% 3	570
July	1st to 10th	Day	1 2 26% 50% 20% 1	566
	11th to 20th	Day	1 1 20% 50% 27% 2	564
	21st to end	Day	1 22% 51% 22% 2	619
August	1st to 10th	Day	2 3 22% 48% 22% 4	567
	11th to 20th	Day	1 3 25% 45% 24% 4	557
	21st to end	Day	2 2 20% 47% 25% 5%	620
September	1st to 10th	Day	1 3 20% 42% 29% 5%	530
	11th to 20th	Day	3 7% 21% 40% 21% 9%	530
	21st to end	Day	2 5% 20% 36% 24% 12%	530
October	1st to 10th	Day	3 5% 23% 27% 27% 15%	530
	11th to 20th	Day	6% 6% 18% 26% 24% 19%	530
	21st to end	Day	7% 6% 20% 28% 24% 15%	583
November	1st to 10th	Day	8% 7% 20% 18% 26% 20%	435
	11th to 20th	Day	11% 7% 19% 26% 24% 13%	330
	21st to end	Day	11% 4 16% 29% 30% 10%	247
December	1st to 10th	Day	16% 7% 15% 22% 27% 13%	220
	11th to 20th	Day	19% 7% 17% 20% 26% 11%	220
	21st to end	Day	21% 10% 21% 26% 19% 3	242
January	1st to 10th	Night	18% 5% 16% 34% 23% 3	840
	11th to 20th	Night	13% 5% 15% 35% 26% 5%	840
	21st to end	Night	15% 4 15% 35% 28% 3	924
February	1st to 10th	Night	18% 5% 16% 38% 20% 3	840
	11th to 20th	Night	13% 9% 22% 32% 21% 3	824
	21st to end	Night	13% 7% 23% 38% 17% 2	692
March	1st to 10th	Night	13% 9% 25% 33% 18% 2	840
	11th to 20th	Night	15% 8% 24% 34% 18% 1	840
	21st to end	Night	12% 8% 32% 33% 15%	924
April	1st to 10th	Night	9% 7% 33% 35% 15% 1	840
	11th to 20th	Night	7% 10% 38% 29% 13% 2	831
	21st to end	Night	5% 8% 38% 33% 14% 1	840
May	1st to 10th	Night	4 6% 37% 38% 13% 1	777
	11th to 20th	Night	2 4 36% 46% 11%	484
	21st to end	Night	2 7% 36% 48% 7%	455
June	1st to 10th	Night	4 4 40% 46% 6%	420
	11th to 20th	Night	1 5% 42% 44% 8%	420
	21st to end	Night	1 3 40% 46% 10%	420
July	1st to 10th	Night	1 1 35% 53% 9%	410
	11th to 20th	Night	1 1 29% 56% 13% 1	499
	21st to end	Night	2 26% 56% 16% 1	690
August	1st to 10th	Night	2 1 26% 52% 18% 1	627
	11th to 20th	Night	1 33% 52% 14%	771
	21st to end	Night	1 2 27% 52% 17%	916
September	1st to 10th	Night	1 2 28% 46% 22% 1	800
	11th to 20th	Night	2 3 28% 46% 18% 2	800
	21st to end	Night	2 4 23% 41% 26% 4	800
October	1st to 10th	Night	3 4 24% 39% 26% 5%	800
	11th to 20th	Night	4 5% 22% 36% 29% 5%	800
	21st to end	Night	5% 3 20% 35% 29% 7%	880
November	1st to 10th	Night	6% 4 19% 33% 31% 6%	820
	11th to 20th	Night	11% 3 18% 37% 27% 4	840
	21st to end	Night	10% 4 15% 38% 28% 5%	840
December	1st to 10th	Night	14% 4 15% 38% 23% 6%	840
	11th to 20th	Night	22% 4 13% 33% 23% 4	840
	21st to end	Night	20% 7% 19% 33% 19% 1	924

Page generated at 2026-08-27 01:07:11. Version ac07

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