Rio Riley Solar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rio Riley Solar Observatory clear sky chart from 2005-11-06 to 2025-01-22.

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	16% 11% 4 8% 5% 5% 4 4 5% 7% 32%	106061
	Night	16% 11% 4 8% 5% 4 4 3 5% 6% 33%	103274
Transparency	Day	49% 7% 11% 20% 11% 1	109734
	Night	49% 6% 11% 20% 12% 2	107727
Seeing	Day	19% 11% 27% 23% 15% 6%	15567
	Night	19% 9% 28% 29% 13% 2	25182

By Month

Percentage Cloud Cover SE (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	19% 19% 8% 17% 6% 5% 3 3 4 4 12%	2926
	11th to 20th	Day	16% 22% 6% 13% 5% 6% 8% 3 4 4 13%	2930
	21st to end	Day	28% 19% 11% 11% 6% 6% 3 2 3 2 9%	3133
February	1st to 10th	Day	19% 15% 5% 12% 8% 5% 4 4 4 4 21%	1710
	11th to 20th	Day	15% 14% 6% 14% 6% 5% 4 4 4 6% 23%	1814
	21st to end	Day	17% 14% 5% 10% 6% 4 4 4 5% 6% 26%	1570
March	1st to 10th	Day	22% 16% 6% 10% 5% 4 4 3 4 5% 21%	3248
	11th to 20th	Day	12% 13% 5% 9% 5% 5% 4 3 4 6% 34%	3480
	21st to end	Day	21% 12% 5% 10% 4 4 4 3 4 5% 27%	3815
April	1st to 10th	Day	14% 14% 3 8% 5% 4 4 4 6% 6% 30%	2151
	11th to 20th	Day	18% 10% 2 7% 5% 4 4 3 5% 6% 35%	2403
	21st to end	Day	19% 9% 3 8% 4 5% 5% 3 5% 7% 32%	2470
May	1st to 10th	Day	20% 10% 3 6% 5% 5% 5% 5% 6% 6% 29%	4082
	11th to 20th	Day	20% 9% 3 7% 4 4 4 3 5% 7% 34%	4081
	21st to end	Day	12% 5% 2 7% 5% 5% 5% 5% 7% 9% 37%	4476
June	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 4 6% 9% 38%	2470
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 5% 5% 10% 38%	2593
	21st to end	Day	12% 5% 2 6% 5% 4 5% 5% 8% 10% 38%	2660
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 4 7% 9% 38%	4440
	11th to 20th	Day	9% 4 2 5% 5% 4 5% 5% 7% 11% 44%	4162
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 5% 7% 8% 40%	4466
August	1st to 10th	Day	10% 6% 2 6% 5% 6% 5% 5% 7% 10% 37%	4104
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 5% 8% 10% 40%	4044
	21st to end	Day	7% 5% 2 6% 4 5% 6% 4 7% 10% 43%	4473
September	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 47%	2107
	11th to 20th	Day	10% 7% 2 6% 4 4 5% 3 6% 8% 46%	2090
	21st to end	Day	20% 6% 2 6% 3 5% 3 3 4 5% 42%	2090
October	1st to 10th	Day	15% 7% 3 6% 4 4 3 3 6% 7% 43%	2033
	11th to 20th	Day	15% 9% 2 6% 5% 4 4 4 6% 6% 39%	1900
	21st to end	Day	21% 11% 3 7% 4 5% 4 4 5% 7% 30%	2009
November	1st to 10th	Day	11% 10% 2 6% 5% 4 3 4 5% 7% 43%	1762
	11th to 20th	Day	17% 14% 4 7% 5% 4 4 4 4 6% 32%	1800
	21st to end	Day	18% 17% 5% 10% 4 4 3 3 4 6% 27%	1800
December	1st to 10th	Day	18% 15% 6% 15% 6% 5% 4 3 3 4 21%	2930
	11th to 20th	Day	22% 17% 8% 11% 4 4 4 3 4 5% 19%	3373
	21st to end	Day	24% 22% 8% 12% 5% 4 3 2 3 3 12%	4466
January	1st to 10th	Night	16% 20% 9% 14% 5% 4 4 3 3 4 17%	4239
	11th to 20th	Night	15% 19% 8% 16% 7% 5% 5% 4 3 4 13%	4250
	21st to end	Night	28% 20% 7% 12% 5% 3 3 2 3 4 13%	4546
February	1st to 10th	Night	21% 14% 5% 10% 6% 5% 4 3 4 4 23%	2470
	11th to 20th	Night	16% 15% 5% 9% 6% 5% 5% 3 5% 5% 26%	2249
	21st to end	Night	20% 15% 4 11% 6% 4 4 3 5% 4 26%	1884
March	1st to 10th	Night	20% 15% 5% 7% 4 3 3 3 4 5% 31%	3605
	11th to 20th	Night	14% 9% 3 6% 4 3 4 3 5% 7% 41%	3480
	21st to end	Night	18% 10% 4 7% 5% 4 3 3 5% 5% 37%	3817
April	1st to 10th	Night	16% 11% 3 7% 6% 4 5% 3 5% 6% 35%	2046
	11th to 20th	Night	18% 9% 2 6% 4 4 4 3 6% 7% 36%	1725
	21st to end	Night	16% 8% 2 7% 4 4 5% 4 6% 7% 35%	1710
May	1st to 10th	Night	23% 10% 3 8% 4 5% 4 4 5% 6% 28%	2813
	11th to 20th	Night	18% 7% 2 7% 4 3 4 3 5% 8% 39%	2812
	21st to end	Night	10% 5% 2 5% 3 4 5% 4 7% 10% 45%	3079
June	1st to 10th	Night	10% 7% 2 7% 5% 4 4 4 5% 7% 45%	1710
	11th to 20th	Night	9% 5% 2 5% 4 5% 5% 4 7% 11% 44%	1579
	21st to end	Night	10% 4 2 6% 4 4 6% 3 8% 9% 44%	1520
July	1st to 10th	Night	11% 5% 3 4 5% 4 4 5% 6% 8% 45%	2530
	11th to 20th	Night	9% 3 2 5% 4 4 4 4 7% 9% 50%	2795
	21st to end	Night	8% 5% 2 7% 5% 5% 5% 4 6% 9% 43%	3087
August	1st to 10th	Night	10% 6% 3 8% 5% 5% 5% 4 7% 10% 37%	2825
	11th to 20th	Night	10% 8% 3 8% 5% 4 4 3 6% 7% 43%	2785
	21st to end	Night	5% 4 1 5% 5% 4 6% 4 7% 8% 51%	3178
September	1st to 10th	Night	11% 5% 2 6% 3 4 4 3 5% 7% 51%	2052
	11th to 20th	Night	10% 4 2 5% 3 3 3 3 4 7% 55%	2090
	21st to end	Night	16% 6% 2 6% 3 3 4 3 5% 6% 45%	2090
October	1st to 10th	Night	11% 5% 3 5% 4 4 4 5% 5% 6% 50%	2146
	11th to 20th	Night	18% 8% 2 7% 4 4 4 3 5% 6% 40%	2280
	21st to end	Night	22% 9% 2 6% 4 4 4 3 4 6% 36%	2584
November	1st to 10th	Night	15% 7% 3 7% 4 3 4 3 5% 6% 44%	2536
	11th to 20th	Night	17% 13% 4 7% 5% 3 3 3 5% 7% 34%	2600
	21st to end	Night	19% 15% 4 7% 5% 4 4 4 5% 6% 27%	2600
December	1st to 10th	Night	16% 13% 6% 12% 6% 5% 5% 3 5% 5% 22%	4250
	11th to 20th	Night	20% 19% 7% 12% 5% 3 3 3 4 4 20%	4822
	21st to end	Night	24% 21% 7% 10% 4 3 3 3 4 5% 14%	6490

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	73% 6% 7% 11% 3	2927
	11th to 20th	Day	75% 5% 9% 8% 3	2930
	21st to end	Day	83% 4 5% 6% 2	3133
February	1st to 10th	Day	65% 6% 10% 12% 7%	1710
	11th to 20th	Day	63% 6% 8% 15% 8% 1	1824
	21st to end	Day	59% 6% 12% 15% 7% 2	1570
March	1st to 10th	Day	64% 7% 9% 16% 4	3248
	11th to 20th	Day	49% 7% 10% 24% 8% 1	3480
	21st to end	Day	56% 7% 12% 19% 6%	3815
April	1st to 10th	Day	52% 6% 13% 17% 11% 1	2151
	11th to 20th	Day	49% 7% 12% 17% 13% 2	2403
	21st to end	Day	51% 6% 11% 19% 10% 2	2470
May	1st to 10th	Day	52% 9% 12% 20% 6% 1	4120
	11th to 20th	Day	47% 8% 14% 22% 8% 1	4085
	21st to end	Day	38% 12% 14% 20% 13% 4	4489
June	1st to 10th	Day	41% 8% 12% 23% 15% 1	2470
	11th to 20th	Day	42% 8% 14% 21% 14% 1	2593
	21st to end	Day	38% 10% 15% 20% 14% 3	2660
July	1st to 10th	Day	42% 7% 11% 22% 16% 2	4371
	11th to 20th	Day	32% 8% 15% 24% 19% 2	4091
	21st to end	Day	38% 9% 14% 18% 18% 4	4324
August	1st to 10th	Day	39% 9% 15% 24% 13% 1	4091
	11th to 20th	Day	36% 8% 12% 28% 14% 1	4083
	21st to end	Day	35% 8% 13% 30% 12% 3	4472
September	1st to 10th	Day	36% 7% 12% 22% 18% 4	2107
	11th to 20th	Day	35% 7% 12% 24% 19% 3	2090
	21st to end	Day	43% 6% 10% 21% 19% 1	2090
October	1st to 10th	Day	28% 5% 12% 32% 22% 1	3384
	11th to 20th	Day	37% 6% 10% 25% 21% 2	3140
	21st to end	Day	43% 5% 11% 22% 18% 1	3285
November	1st to 10th	Day	41% 5% 12% 24% 16% 2	1762
	11th to 20th	Day	54% 5% 10% 19% 10% 2	1800
	21st to end	Day	61% 4 10% 17% 8% 1	1800
December	1st to 10th	Day	68% 4 13% 12% 2	2930
	11th to 20th	Day	67% 5% 11% 13% 4	3370
	21st to end	Day	78% 4 6% 8% 4	4466
January	1st to 10th	Night	71% 6% 7% 12% 4	4239
	11th to 20th	Night	75% 5% 8% 8% 3	4250
	21st to end	Night	76% 4 7% 9% 3 1	4546
February	1st to 10th	Night	63% 5% 11% 14% 7% 1	2470
	11th to 20th	Night	59% 6% 11% 15% 8% 1	2250
	21st to end	Night	62% 5% 9% 14% 9% 1	1884
March	1st to 10th	Night	55% 6% 12% 19% 9%	3605
	11th to 20th	Night	40% 7% 13% 27% 11% 2	3480
	21st to end	Night	48% 5% 11% 25% 10% 1	3817
April	1st to 10th	Night	48% 6% 14% 16% 14% 2	2046
	11th to 20th	Night	46% 6% 12% 17% 17% 2	1725
	21st to end	Night	46% 7% 12% 19% 15% 2	1710
May	1st to 10th	Night	54% 8% 10% 18% 8% 2	2840
	11th to 20th	Night	42% 8% 12% 24% 11% 1	2813
	21st to end	Night	30% 11% 14% 27% 16% 2	3087
June	1st to 10th	Night	37% 7% 13% 23% 18% 2	1710
	11th to 20th	Night	32% 10% 15% 24% 16% 3	1579
	21st to end	Night	34% 9% 14% 24% 15% 4	1520
July	1st to 10th	Night	36% 6% 12% 24% 16% 6%	2490
	11th to 20th	Night	29% 7% 14% 31% 18% 1	2743
	21st to end	Night	35% 8% 15% 20% 19% 4	2988
August	1st to 10th	Night	39% 9% 14% 22% 14% 1	2814
	11th to 20th	Night	40% 7% 10% 25% 18% 1	2812
	21st to end	Night	29% 8% 14% 29% 16% 3	3178
September	1st to 10th	Night	33% 6% 13% 25% 17% 6%	2052
	11th to 20th	Night	29% 4 11% 27% 25% 3	2090
	21st to end	Night	39% 8% 10% 20% 21% 2	2090
October	1st to 10th	Night	24% 5% 8% 29% 32% 1	3575
	11th to 20th	Night	35% 4 10% 26% 21% 3	3779
	21st to end	Night	37% 4 9% 27% 19% 4	4245
November	1st to 10th	Night	41% 5% 12% 23% 17% 3	2536
	11th to 20th	Night	51% 4 11% 20% 12% 3	2600
	21st to end	Night	58% 6% 12% 17% 7% 1	2600
December	1st to 10th	Night	63% 5% 11% 15% 6%	4250
	11th to 20th	Night	67% 5% 12% 12% 4	4824
	21st to end	Night	72% 5% 9% 10% 4	6490

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% 19% 33% 17% 4 1	300
	11th to 20th	Day	25% 21% 40% 10% 5%	300
	21st to end	Day	29% 19% 30% 17% 5%	300
February	1st to 10th	Day	28% 18% 36% 16% 2 1	270
	11th to 20th	Day	24% 21% 34% 17% 3	270
	21st to end	Day	25% 24% 37% 13% 1	225
March	1st to 10th	Day	24% 18% 36% 18% 4	346
	11th to 20th	Day	23% 18% 35% 18% 4 1	460
	21st to end	Day	29% 14% 31% 21% 5%	506
April	1st to 10th	Day	22% 15% 33% 20% 8% 2	460
	11th to 20th	Day	20% 19% 28% 19% 9% 4	452
	21st to end	Day	23% 15% 32% 20% 8% 2	460
May	1st to 10th	Day	26% 12% 29% 22% 8% 3	463
	11th to 20th	Day	23% 6% 28% 23% 14% 6%	487
	21st to end	Day	11% 6% 26% 24% 22% 10%	529
June	1st to 10th	Day	13% 7% 23% 32% 19% 6%	490
	11th to 20th	Day	14% 6% 24% 28% 22% 6%	613
	21st to end	Day	13% 8% 29% 27% 18% 6%	680
July	1st to 10th	Day	11% 4 18% 30% 21% 15%	671
	11th to 20th	Day	11% 3 20% 27% 26% 13%	511
	21st to end	Day	11% 3 17% 27% 27% 15%	532
August	1st to 10th	Day	11% 4 14% 27% 28% 16%	486
	11th to 20th	Day	15% 2 19% 28% 25% 10%	479
	21st to end	Day	10% 4 16% 26% 30% 14%	539
September	1st to 10th	Day	13% 3 18% 28% 27% 12%	490
	11th to 20th	Day	11% 2 14% 25% 31% 17%	490
	21st to end	Day	19% 11% 19% 26% 17% 9%	490
October	1st to 10th	Day	12% 8% 24% 27% 19% 10%	490
	11th to 20th	Day	16% 14% 33% 22% 12% 4	490
	21st to end	Day	26% 14% 33% 22% 5% 1	458
November	1st to 10th	Day	13% 17% 34% 22% 10% 4	300
	11th to 20th	Day	24% 17% 31% 18% 9% 1	300
	21st to end	Day	27% 16% 36% 17% 3	300
December	1st to 10th	Day	24% 18% 36% 15% 5% 2	300
	11th to 20th	Day	26% 18% 38% 16% 3	300
	21st to end	Day	31% 18% 30% 18% 3	330
January	1st to 10th	Night	23% 16% 38% 19% 4	800
	11th to 20th	Night	28% 16% 37% 16% 3 1	800
	21st to end	Night	24% 15% 35% 22% 3	841
February	1st to 10th	Night	26% 12% 38% 23% 2	760
	11th to 20th	Night	25% 13% 36% 23% 3	743
	21st to end	Night	28% 13% 40% 17% 3	628
March	1st to 10th	Night	23% 12% 35% 24% 6%	760
	11th to 20th	Night	20% 13% 36% 25% 6% 1	760
	21st to end	Night	24% 11% 32% 26% 6%	836
April	1st to 10th	Night	21% 11% 37% 25% 5%	716
	11th to 20th	Night	20% 11% 35% 23% 9% 1	563
	21st to end	Night	20% 8% 38% 25% 8% 1	570
May	1st to 10th	Night	23% 8% 29% 30% 9% 1	570
	11th to 20th	Night	21% 6% 27% 31% 13% 2	561
	21st to end	Night	11% 3 21% 40% 22% 2	617
June	1st to 10th	Night	9% 3 25% 42% 19% 1	570
	11th to 20th	Night	12% 3 18% 46% 20% 1	570
	21st to end	Night	11% 3 21% 42% 22% 2	570
July	1st to 10th	Night	10% 2 14% 40% 29% 4	555
	11th to 20th	Night	8% 5% 14% 41% 29% 4	552
	21st to end	Night	8% 2 13% 44% 31% 2	624
August	1st to 10th	Night	8% 3 10% 46% 30% 4	567
	11th to 20th	Night	10% 3 12% 40% 30% 5%	564
	21st to end	Night	7% 2 12% 39% 34% 5%	627
September	1st to 10th	Night	12% 3 16% 36% 28% 5%	722
	11th to 20th	Night	12% 3 13% 36% 31% 5%	760
	21st to end	Night	18% 6% 21% 32% 20% 3	760
October	1st to 10th	Night	13% 5% 24% 36% 19% 4	760
	11th to 20th	Night	20% 10% 30% 28% 11% 1	760
	21st to end	Night	26% 10% 31% 25% 8%	836
November	1st to 10th	Night	19% 8% 32% 29% 12% 1	780
	11th to 20th	Night	22% 14% 31% 25% 7% 1	800
	21st to end	Night	26% 12% 32% 25% 5% 1	800
December	1st to 10th	Night	27% 13% 35% 21% 5%	800
	11th to 20th	Night	26% 11% 36% 22% 4 1	800
	21st to end	Night	30% 13% 33% 21% 3	880

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