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 2025-04-26.

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	7% 4 1 4 3 3 3 2 4 6% 65%	117680
	Night	8% 4 1 4 3 3 3 3 4 6% 62%	119808
Transparency	Day	22% 4 8% 19% 24% 22%	117433
	Night	24% 5% 9% 19% 23% 20%	119643
Seeing	Day	7% 7% 24% 33% 21% 7%	15850
	Night	8% 5% 25% 39% 20% 3	25309

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% 4 4 4 3 5% 8% 40%	3713
	11th to 20th	Day	13% 9% 2 6% 4 4 3 2 3 4 51%	4100
	21st to end	Day	17% 7% 3 7% 4 4 4 3 4 5% 41%	4510
February	1st to 10th	Day	17% 6% 2 6% 5% 3 4 3 4 5% 45%	1800
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 6% 6% 45%	1864
	21st to end	Day	13% 4 2 5% 4 4 4 3 5% 6% 50%	1650
March	1st to 10th	Day	10% 7% 3 8% 5% 5% 5% 4 7% 7% 39%	4777
	11th to 20th	Day	12% 4 1 4 3 3 4 3 5% 7% 53%	5000
	21st to end	Day	9% 5% 2 6% 4 5% 6% 5% 6% 8% 43%	5630
April	1st to 10th	Day	12% 6% 2 4 4 4 3 4 6% 7% 50%	2400
	11th to 20th	Day	8% 4 1 4 3 3 4 3 5% 6% 60%	2369
	21st to end	Day	4 3 1 3 3 2 3 3 4 8% 64%	2342
May	1st to 10th	Day	5% 2 1 2 1 1 1 2 3 4 77%	3889
	11th to 20th	Day	2 1 1 2 1 1 2 1 3 4 83%	4274
	21st to end	Day	2 1 1 2 1 2 2 2 3 5% 80%	4813
June	1st to 10th	Day	3 3 1 3 2 3 3 2 4 8% 69%	2660
	11th to 20th	Day	1 1 1 2 2 4 6% 82%	2660
	21st to end	Day	1 1 1 2 1 1 1 2 2 4 84%	2660
July	1st to 10th	Day	1 1 1 3 92%	4420
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 86%	4274
	21st to end	Day	1 1 1 2 4 89%	4455
August	1st to 10th	Day	1 1 2 1 1 2 3 4 5% 80%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 4 89%	3798
	21st to end	Day	1 1 1 1 1 1 1 2 3 89%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 2 4 87%	2280
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 77%	2280
	21st to end	Day	2 2 1 2 2 2 2 1 3 5% 80%	2033
October	1st to 10th	Day	1 1 1 3 2 2 2 2 4 5% 77%	3180
	11th to 20th	Day	3 2 1 2 2 2 3 2 4 5% 75%	3161
	21st to end	Day	3 2 1 3 2 3 3 3 4 7% 66%	3448
November	1st to 10th	Day	6% 5% 2 3 3 4 4 3 5% 8% 58%	1864
	11th to 20th	Day	9% 7% 2 6% 5% 4 4 3 4 7% 49%	1800
	21st to end	Day	11% 5% 2 4 4 3 3 3 6% 6% 52%	1653
December	1st to 10th	Day	8% 5% 2 5% 3 4 4 4 6% 10% 48%	2620
	11th to 20th	Day	23% 11% 5% 12% 6% 4 4 3 4 6% 23%	3028
	21st to end	Day	20% 10% 4 8% 5% 5% 4 4 6% 7% 27%	4004
January	1st to 10th	Night	9% 6% 2 6% 4 4 4 3 6% 8% 47%	6218
	11th to 20th	Night	15% 6% 2 6% 3 3 3 2 4 5% 51%	5880
	21st to end	Night	14% 6% 2 7% 4 4 4 3 5% 6% 47%	6468
February	1st to 10th	Night	16% 6% 3 5% 4 3 3 3 4 4 50%	2600
	11th to 20th	Night	12% 4 2 5% 3 4 3 3 5% 8% 50%	2423
	21st to end	Night	12% 4 1 4 3 3 3 3 5% 6% 56%	1980
March	1st to 10th	Night	12% 6% 2 6% 4 4 5% 3 6% 7% 46%	5114
	11th to 20th	Night	14% 4 1 4 3 3 3 3 4 6% 56%	5000
	21st to end	Night	11% 5% 2 5% 4 4 4 4 5% 7% 49%	5343
April	1st to 10th	Night	9% 4 1 4 3 4 3 3 5% 8% 56%	2000
	11th to 20th	Night	6% 4 1 3 3 3 3 3 4 7% 62%	1979
	21st to end	Night	4 3 1 2 2 2 3 3 5% 8% 68%	1954
May	1st to 10th	Night	2 1 2 1 2 2 2 3 5% 80%	3084
	11th to 20th	Night	2 1 1 1 1 1 1 3 4 84%	2619
	21st to end	Night	1 1 1 1 1 2 2 2 5% 84%	2762
June	1st to 10th	Night	3 2 3 2 3 2 2 4 7% 72%	1520
	11th to 20th	Night	1 1 1 1 2 1 3 4 86%	1520
	21st to end	Night	1 1 1 1 1 1 2 1 3 3 85%	1520
July	1st to 10th	Night	1 1 1 1 2 93%	2540
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 3 86%	2687
	21st to end	Night	1 1 1 1 1 1 1 3 5% 84%	3109
August	1st to 10th	Night	2 1 1 2 1 2 2 2 3 7% 77%	2848
	11th to 20th	Night	1 1 1 1 3 5% 88%	3035
	21st to end	Night	1 1 1 1 1 1 1 1 2 4 87%	3498
September	1st to 10th	Night	1 1 1 1 1 1 3 6% 86%	1900
	11th to 20th	Night	2 2 1 2 1 2 2 2 4 6% 77%	1900
	21st to end	Night	1 1 2 2 2 2 1 3 5% 82%	2143
October	1st to 10th	Night	2 2 1 2 2 1 2 2 4 4 79%	3800
	11th to 20th	Night	2 2 2 2 2 2 2 4 6% 76%	3777
	21st to end	Night	4 2 1 3 3 3 3 3 5% 5% 68%	4121
November	1st to 10th	Night	7% 4 1 3 3 2 4 3 5% 9% 60%	2433
	11th to 20th	Night	8% 5% 2 4 3 3 3 4 5% 7% 57%	2600
	21st to end	Night	10% 4 1 4 3 3 3 3 5% 6% 57%	2745
December	1st to 10th	Night	8% 4 2 4 3 4 4 4 5% 7% 56%	4560
	11th to 20th	Night	19% 7% 3 9% 6% 6% 5% 3 7% 8% 27%	5176
	21st to end	Night	20% 7% 3 8% 5% 5% 5% 3 5% 6% 33%	6952

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	41% 9% 15% 19% 13% 3	3713
	11th to 20th	Day	38% 6% 8% 17% 19% 12%	4100
	21st to end	Day	43% 7% 8% 14% 18% 10%	4510
February	1st to 10th	Day	41% 5% 9% 20% 18% 7%	1800
	11th to 20th	Day	37% 7% 13% 19% 19% 6%	1873
	21st to end	Day	33% 6% 10% 24% 19% 8%	1650
March	1st to 10th	Day	39% 8% 10% 22% 18% 3	4777
	11th to 20th	Day	30% 6% 14% 29% 14% 8%	5000
	21st to end	Day	34% 9% 16% 28% 11% 2	5630
April	1st to 10th	Day	33% 6% 12% 23% 20% 6%	2400
	11th to 20th	Day	24% 5% 13% 26% 23% 8%	2372
	21st to end	Day	18% 5% 13% 29% 29% 6%	2342
May	1st to 10th	Day	12% 3 8% 31% 25% 22%	3889
	11th to 20th	Day	8% 2 5% 27% 42% 16%	4277
	21st to end	Day	8% 3 9% 36% 34% 9%	4814
June	1st to 10th	Day	15% 5% 11% 26% 31% 13%	2660
	11th to 20th	Day	6% 2 8% 21% 38% 25%	2660
	21st to end	Day	7% 1 3 11% 35% 42%	2660
July	1st to 10th	Day	2 1 2 5% 15% 75%	4351
	11th to 20th	Day	6% 1 3 8% 15% 67%	4199
	21st to end	Day	3 1 2 6% 28% 61%	4315
August	1st to 10th	Day	8% 2 3 8% 27% 52%	4076
	11th to 20th	Day	3 1 2 9% 41% 45%	3835
	21st to end	Day	5% 1 3 10% 38% 43%	4179
September	1st to 10th	Day	5% 1 3 8% 31% 52%	2280
	11th to 20th	Day	10% 3 7% 21% 40% 19%	2280
	21st to end	Day	10% 2 5% 18% 36% 29%	2033
October	1st to 10th	Day	11% 2 4 12% 29% 43%	3180
	11th to 20th	Day	13% 3 7% 26% 30% 21%	3161
	21st to end	Day	18% 3 8% 23% 33% 15%	3448
November	1st to 10th	Day	25% 5% 10% 27% 23% 10%	1864
	11th to 20th	Day	35% 5% 11% 25% 19% 5%	1800
	21st to end	Day	31% 6% 11% 22% 23% 8%	1653
December	1st to 10th	Day	28% 7% 13% 29% 19% 5%	2620
	11th to 20th	Day	62% 6% 8% 13% 10% 1	3028
	21st to end	Day	53% 9% 12% 16% 9% 1	4004
January	1st to 10th	Night	31% 10% 19% 23% 12% 4	6218
	11th to 20th	Night	35% 6% 11% 16% 22% 11%	5880
	21st to end	Night	38% 7% 9% 13% 22% 11%	6468
February	1st to 10th	Night	38% 4 8% 21% 21% 9%	2600
	11th to 20th	Night	32% 5% 12% 22% 22% 8%	2425
	21st to end	Night	29% 5% 10% 28% 21% 7%	1980
March	1st to 10th	Night	35% 9% 13% 19% 21% 4	5114
	11th to 20th	Night	30% 5% 14% 25% 16% 9%	5000
	21st to end	Night	32% 9% 16% 26% 14% 3	5343
April	1st to 10th	Night	28% 5% 15% 23% 23% 7%	2000
	11th to 20th	Night	22% 6% 13% 27% 21% 11%	1979
	21st to end	Night	15% 5% 13% 30% 30% 7%	1954
May	1st to 10th	Night	10% 3 11% 28% 31% 18%	3084
	11th to 20th	Night	6% 2 6% 22% 41% 21%	2619
	21st to end	Night	6% 3 9% 39% 33% 10%	2762
June	1st to 10th	Night	13% 6% 11% 24% 32% 14%	1520
	11th to 20th	Night	6% 2 8% 19% 37% 28%	1520
	21st to end	Night	6% 2 3 11% 34% 44%	1520
July	1st to 10th	Night	2 1 1 5% 14% 76%	2500
	11th to 20th	Night	6% 2 3 6% 14% 69%	2639
	21st to end	Night	4 1 2 5% 24% 63%	3011
August	1st to 10th	Night	9% 1 2 9% 26% 53%	2839
	11th to 20th	Night	3 1 2 7% 37% 50%	3063
	21st to end	Night	6% 1 3 9% 34% 48%	3498
September	1st to 10th	Night	3 2 4 7% 30% 53%	1900
	11th to 20th	Night	9% 3 7% 20% 36% 25%	1900
	21st to end	Night	8% 2 5% 18% 34% 33%	2143
October	1st to 10th	Night	10% 2 5% 10% 20% 52%	3800
	11th to 20th	Night	11% 3 6% 29% 27% 24%	3777
	21st to end	Night	17% 4 6% 21% 31% 21%	4121
November	1st to 10th	Night	22% 5% 10% 26% 22% 15%	2433
	11th to 20th	Night	26% 5% 13% 25% 24% 8%	2600
	21st to end	Night	28% 4 10% 22% 27% 10%	2745
December	1st to 10th	Night	26% 5% 9% 27% 22% 10%	4560
	11th to 20th	Night	53% 7% 11% 16% 11% 2	5176
	21st to end	Night	50% 9% 12% 16% 9% 3	6952

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	28% 8% 18% 25% 16% 6%	235
	11th to 20th	Day	18% 7% 19% 21% 25% 10%	400
	21st to end	Day	14% 6% 19% 25% 23% 14%	440
February	1st to 10th	Day	20% 9% 20% 18% 23% 11%	400
	11th to 20th	Day	14% 14% 26% 22% 18% 7%	450
	21st to end	Day	11% 12% 19% 34% 18% 6%	414
March	1st to 10th	Day	16% 12% 26% 27% 13% 6%	500
	11th to 20th	Day	18% 12% 23% 23% 15% 8%	500
	21st to end	Day	13% 13% 29% 27% 14% 4	550
April	1st to 10th	Day	12% 13% 29% 24% 15% 7%	500
	11th to 20th	Day	10% 12% 32% 24% 14% 7%	492
	21st to end	Day	3 16% 28% 29% 18% 6%	481
May	1st to 10th	Day	6% 11% 30% 33% 15% 3	463
	11th to 20th	Day	5% 8% 32% 31% 22% 3	488
	21st to end	Day	4 8% 26% 36% 22% 5%	529
June	1st to 10th	Day	4 10% 28% 35% 18% 4	490
	11th to 20th	Day	1 9% 30% 44% 15% 1	490
	21st to end	Day	1 3 28% 44% 21% 2	490
July	1st to 10th	Day	1 2 23% 52% 21% 1	486
	11th to 20th	Day	1 20% 49% 29% 2	484
	21st to end	Day	1 1 21% 52% 22% 3	531
August	1st to 10th	Day	2 3 23% 49% 20% 3	487
	11th to 20th	Day	1 3 27% 45% 21% 4	477
	21st to end	Day	1 2 21% 47% 25% 5%	539
September	1st to 10th	Day	1 3 20% 41% 30% 6%	490
	11th to 20th	Day	3 8% 21% 40% 20% 8%	490
	21st to end	Day	1 5% 20% 36% 25% 13%	490
October	1st to 10th	Day	3 5% 23% 28% 26% 16%	490
	11th to 20th	Day	5% 6% 18% 26% 25% 19%	490
	21st to end	Day	7% 6% 20% 28% 24% 16%	539
November	1st to 10th	Day	8% 7% 22% 18% 26% 20%	400
	11th to 20th	Day	10% 6% 18% 26% 26% 14%	300
	21st to end	Day	12% 4 17% 29% 27% 10%	225
December	1st to 10th	Day	18% 8% 16% 22% 24% 14%	200
	11th to 20th	Day	20% 7% 18% 20% 28% 9%	200
	21st to end	Day	20% 10% 20% 25% 21% 3	220
January	1st to 10th	Night	17% 5% 16% 35% 24% 3	800
	11th to 20th	Night	13% 6% 16% 36% 24% 5%	800
	21st to end	Night	15% 4 16% 34% 28% 3	880
February	1st to 10th	Night	18% 6% 16% 37% 21% 3	800
	11th to 20th	Night	13% 9% 21% 33% 22% 3	784
	21st to end	Night	12% 8% 23% 37% 18% 2	660
March	1st to 10th	Night	14% 8% 24% 33% 18% 2	800
	11th to 20th	Night	16% 8% 24% 33% 17% 1	800
	21st to end	Night	12% 8% 32% 33% 15%	880
April	1st to 10th	Night	9% 7% 33% 35% 15% 1	800
	11th to 20th	Night	7% 10% 38% 29% 14% 2	791
	21st to end	Night	5% 8% 38% 33% 15% 1	782
May	1st to 10th	Night	4 6% 36% 38% 14% 1	703
	11th to 20th	Night	3 4 33% 49% 12%	438
	21st to end	Night	2 7% 34% 48% 8%	411
June	1st to 10th	Night	4 4 39% 47% 6% 1	380
	11th to 20th	Night	1 5% 39% 46% 9%	380
	21st to end	Night	1 3 38% 47% 12%	380
July	1st to 10th	Night	1 34% 55% 10%	370
	11th to 20th	Night	1 1 26% 57% 14% 1	450
	21st to end	Night	2 24% 56% 16% 1	624
August	1st to 10th	Night	2 1 26% 51% 18% 1	567
	11th to 20th	Night	1 33% 50% 15%	697
	21st to end	Night	1 1 25% 53% 19%	836
September	1st to 10th	Night	1 2 27% 47% 23% 1	760
	11th to 20th	Night	2 3 28% 46% 18% 2	760
	21st to end	Night	2 3 23% 42% 27% 4	760
October	1st to 10th	Night	3 4 23% 39% 26% 5%	760
	11th to 20th	Night	3 5% 22% 36% 29% 4	760
	21st to end	Night	5% 3 19% 36% 29% 8%	836
November	1st to 10th	Night	6% 4 20% 33% 32% 5%	780
	11th to 20th	Night	9% 3 18% 38% 29% 5%	800
	21st to end	Night	11% 3 16% 39% 26% 5%	800
December	1st to 10th	Night	14% 5% 16% 37% 23% 6%	800
	11th to 20th	Night	22% 5% 13% 34% 23% 3	800
	21st to end	Night	19% 8% 20% 34% 19% 1	880

Page generated at 2025-04-23 06:25:02. Version ac07

Copyright © 2025 Attilla Danko.