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 2026-05-17.

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	15% 10% 4 9% 5% 5% 5% 4 5% 7% 31%	132968
	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 32%	129878
Transparency	Day	51% 6% 11% 20% 11% 1	136597
	Night	50% 6% 11% 20% 12% 2	134306
Seeing	Day	19% 11% 27% 23% 14% 6%	17341
	Night	19% 9% 28% 29% 13% 1	26915

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	17% 18% 8% 18% 8% 6% 4 3 4 4 11%	5258
	11th to 20th	Day	13% 19% 6% 15% 9% 7% 6% 3 3 4 16%	5280
	21st to end	Day	20% 16% 8% 13% 8% 7% 5% 4 4 4 13%	5780
February	1st to 10th	Day	18% 15% 5% 13% 7% 5% 4 4 4 5% 21%	1890
	11th to 20th	Day	15% 14% 6% 14% 6% 5% 4 4 4 6% 22%	2011
	21st to end	Day	16% 13% 5% 11% 5% 4 4 4 5% 6% 26%	1730
March	1st to 10th	Day	18% 12% 7% 13% 5% 4 4 3 4 5% 25%	4768
	11th to 20th	Day	11% 11% 4 9% 4 4 4 3 4 6% 37%	5090
	21st to end	Day	20% 13% 4 10% 4 5% 4 3 4 5% 26%	5586
April	1st to 10th	Day	15% 14% 3 8% 5% 4 4 3 6% 6% 29%	2377
	11th to 20th	Day	17% 10% 2 7% 6% 4 4 4 5% 6% 35%	2659
	21st to end	Day	18% 9% 3 8% 4 5% 5% 3 5% 7% 33%	2730
May	1st to 10th	Day	23% 10% 3 7% 5% 4 5% 4 6% 6% 28%	5992
	11th to 20th	Day	18% 9% 3 8% 5% 4 4 4 5% 7% 34%	5939
	21st to end	Day	17% 6% 2 7% 4 5% 5% 4 6% 8% 35%	6433
June	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 4 6% 8% 39%	2600
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 5% 5% 10% 37%	2730
	21st to end	Day	11% 5% 2 6% 5% 4 6% 5% 8% 10% 38%	2800
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 5% 4 6% 9% 42%	6360
	11th to 20th	Day	10% 5% 3 6% 5% 4 5% 5% 8% 11% 37%	5956
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 9% 39%	6424
August	1st to 10th	Day	9% 6% 2 6% 6% 6% 5% 5% 7% 10% 38%	4234
	11th to 20th	Day	10% 5% 2 6% 4 5% 6% 5% 8% 10% 40%	4174
	21st to end	Day	7% 5% 2 6% 4 5% 6% 4 7% 10% 43%	4614
September	1st to 10th	Day	12% 6% 2 5% 4 4 4 3 4 7% 49%	2218
	11th to 20th	Day	9% 6% 2 6% 4 4 5% 3 6% 8% 47%	2200
	21st to end	Day	20% 6% 2 6% 4 5% 3 3 5% 5% 42%	2200
October	1st to 10th	Day	15% 6% 3 6% 4 4 3 3 5% 7% 44%	2140
	11th to 20th	Day	15% 9% 2 6% 4 4 4 4 6% 7% 40%	2000
	21st to end	Day	21% 10% 3 7% 4 4 4 4 5% 7% 30%	2115
November	1st to 10th	Day	11% 10% 2 6% 5% 4 3 4 5% 7% 43%	1852
	11th to 20th	Day	17% 14% 4 7% 5% 4 4 4 4 6% 32%	1890
	21st to end	Day	18% 17% 6% 10% 4 4 3 3 3 6% 26%	1890
December	1st to 10th	Day	17% 15% 7% 15% 6% 5% 4 3 3 4 20%	3020
	11th to 20th	Day	21% 17% 8% 11% 4 4 4 3 4 5% 19%	3463
	21st to end	Day	24% 22% 8% 12% 5% 4 3 2 3 3 12%	4565
January	1st to 10th	Night	15% 19% 8% 17% 6% 5% 4 3 4 4 14%	7635
	11th to 20th	Night	10% 18% 9% 18% 8% 7% 6% 3 3 4 14%	7680
	21st to end	Night	19% 15% 5% 11% 5% 5% 5% 3 5% 5% 22%	8401
February	1st to 10th	Night	20% 13% 5% 11% 6% 5% 5% 3 4 5% 24%	2730
	11th to 20th	Night	16% 14% 5% 10% 6% 5% 5% 4 5% 6% 25%	2491
	21st to end	Night	19% 15% 4 12% 5% 4 4 3 4 4 26%	2076
March	1st to 10th	Night	20% 13% 5% 8% 4 4 4 3 4 5% 32%	5305
	11th to 20th	Night	13% 8% 3 6% 4 4 4 4 5% 9% 41%	5090
	21st to end	Night	18% 10% 4 7% 5% 4 4 3 5% 5% 36%	5588
April	1st to 10th	Night	17% 12% 3 7% 5% 4 5% 3 5% 6% 34%	2261
	11th to 20th	Night	17% 8% 3 7% 5% 5% 4 3 6% 7% 36%	1909
	21st to end	Night	16% 8% 3 7% 4 4 5% 4 6% 7% 36%	1890
May	1st to 10th	Night	23% 10% 3 8% 5% 5% 4 4 5% 6% 27%	4123
	11th to 20th	Night	16% 7% 3 7% 4 4 4 3 6% 9% 37%	4086
	21st to end	Night	15% 6% 2 6% 4 4 5% 4 6% 8% 40%	4421
June	1st to 10th	Night	10% 7% 2 7% 5% 4 4 4 5% 7% 46%	1800
	11th to 20th	Night	9% 5% 2 5% 5% 6% 5% 4 7% 11% 43%	1662
	21st to end	Night	10% 4 2 6% 4 4 5% 4 8% 9% 44%	1600
July	1st to 10th	Night	10% 5% 3 5% 5% 4 4 5% 7% 9% 44%	3618
	11th to 20th	Night	10% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	3986
	21st to end	Night	9% 6% 3 7% 5% 4 4 4 6% 8% 44%	4427
August	1st to 10th	Night	9% 6% 3 8% 5% 4 5% 4 7% 10% 38%	2915
	11th to 20th	Night	9% 8% 3 8% 5% 4 4 3 6% 7% 43%	2875
	21st to end	Night	5% 4 2 5% 5% 4 6% 4 7% 8% 50%	3279
September	1st to 10th	Night	10% 5% 2 6% 3 4 4 3 4 7% 52%	2160
	11th to 20th	Night	10% 4 2 5% 3 3 3 3 4 7% 56%	2200
	21st to end	Night	16% 6% 2 6% 3 3 4 3 5% 6% 45%	2200
October	1st to 10th	Night	11% 5% 3 5% 4 4 4 5% 5% 6% 51%	2259
	11th to 20th	Night	17% 8% 2 7% 4 4 4 3 4 6% 41%	2400
	21st to end	Night	22% 9% 2 6% 4 3 4 3 4 6% 36%	2720
November	1st to 10th	Night	14% 8% 3 6% 4 3 4 3 5% 6% 44%	2666
	11th to 20th	Night	17% 13% 4 7% 5% 3 3 3 5% 7% 34%	2730
	21st to end	Night	20% 15% 5% 7% 5% 4 4 3 5% 6% 26%	2730
December	1st to 10th	Night	16% 13% 6% 12% 6% 5% 5% 4 5% 5% 22%	4380
	11th to 20th	Night	20% 19% 7% 12% 5% 3 3 3 4 4 20%	4952
	21st to end	Night	24% 21% 7% 10% 4 3 3 3 4 5% 14%	6633

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	76% 5% 9% 8% 2	5259
	11th to 20th	Day	74% 4 7% 7% 9%	5280
	21st to end	Day	76% 4 6% 10% 5%	5780
February	1st to 10th	Day	65% 6% 10% 14% 6%	1890
	11th to 20th	Day	64% 5% 8% 15% 7% 1	2021
	21st to end	Day	58% 6% 13% 15% 7% 2	1730
March	1st to 10th	Day	62% 5% 8% 19% 6%	4768
	11th to 20th	Day	47% 6% 10% 27% 9% 1	5090
	21st to end	Day	58% 6% 10% 18% 7% 1	5586
April	1st to 10th	Day	53% 6% 13% 17% 11% 1	2377
	11th to 20th	Day	49% 7% 12% 18% 13% 2	2659
	21st to end	Day	50% 6% 11% 21% 10% 2	2730
May	1st to 10th	Day	54% 8% 10% 16% 10% 1	6027
	11th to 20th	Day	48% 8% 13% 21% 10% 1	5943
	21st to end	Day	43% 9% 12% 22% 12% 3	6447
June	1st to 10th	Day	41% 8% 12% 22% 15% 1	2600
	11th to 20th	Day	42% 8% 14% 21% 13% 1	2730
	21st to end	Day	38% 10% 15% 20% 15% 3	2800
July	1st to 10th	Day	38% 6% 10% 28% 15% 2	6291
	11th to 20th	Day	37% 8% 15% 23% 15% 1	5885
	21st to end	Day	38% 8% 13% 20% 18% 3	6240
August	1st to 10th	Day	38% 9% 15% 24% 13% 1	4221
	11th to 20th	Day	36% 8% 12% 29% 14% 1	4213
	21st to end	Day	35% 8% 13% 30% 12% 3	4613
September	1st to 10th	Day	35% 7% 12% 23% 19% 4	2218
	11th to 20th	Day	34% 7% 12% 25% 20% 3	2200
	21st to end	Day	43% 6% 10% 20% 20% 1	2200
October	1st to 10th	Day	28% 5% 11% 32% 22% 1	3491
	11th to 20th	Day	36% 6% 10% 25% 21% 2	3240
	21st to end	Day	43% 5% 11% 22% 19% 1	3391
November	1st to 10th	Day	41% 5% 12% 24% 15% 2	1852
	11th to 20th	Day	54% 4 10% 19% 10% 2	1890
	21st to end	Day	61% 4 10% 17% 8% 1	1890
December	1st to 10th	Day	69% 4 13% 12% 3	3020
	11th to 20th	Day	67% 5% 10% 13% 4	3460
	21st to end	Day	78% 4 7% 8% 4	4565
January	1st to 10th	Night	74% 5% 6% 12% 3	7636
	11th to 20th	Night	75% 4 7% 8% 6% 1	7680
	21st to end	Night	65% 3 11% 13% 7% 1	8401
February	1st to 10th	Night	63% 4 11% 15% 7% 1	2730
	11th to 20th	Night	60% 6% 10% 15% 8% 1	2492
	21st to end	Night	62% 5% 9% 15% 9% 1	2076
March	1st to 10th	Night	54% 5% 10% 21% 9% 1	5305
	11th to 20th	Night	39% 6% 13% 30% 10% 1	5090
	21st to end	Night	50% 5% 9% 21% 14% 1	5588
April	1st to 10th	Night	50% 6% 13% 16% 13% 2	2261
	11th to 20th	Night	46% 6% 12% 17% 17% 2	1909
	21st to end	Night	46% 7% 11% 19% 15% 2	1890
May	1st to 10th	Night	56% 8% 10% 14% 10% 3	4150
	11th to 20th	Night	43% 8% 11% 23% 15% 1	4087
	21st to end	Night	39% 9% 13% 26% 12% 2	4429
June	1st to 10th	Night	37% 7% 13% 23% 18% 2	1800
	11th to 20th	Night	34% 10% 14% 24% 16% 3	1662
	21st to end	Night	34% 9% 14% 24% 16% 4	1600
July	1st to 10th	Night	35% 7% 11% 26% 17% 4	3580
	11th to 20th	Night	35% 8% 14% 27% 14% 1	3937
	21st to end	Night	35% 7% 13% 21% 21% 3	4297
August	1st to 10th	Night	38% 9% 14% 23% 14% 1	2904
	11th to 20th	Night	39% 7% 10% 26% 18% 1	2902
	21st to end	Night	29% 8% 14% 30% 16% 3	3279
September	1st to 10th	Night	32% 6% 12% 26% 18% 6%	2160
	11th to 20th	Night	28% 5% 11% 28% 25% 3	2200
	21st to end	Night	39% 7% 10% 20% 22% 2	2200
October	1st to 10th	Night	24% 5% 8% 29% 33% 1	3688
	11th to 20th	Night	35% 4 10% 26% 22% 3	3899
	21st to end	Night	37% 4 9% 28% 19% 3	4381
November	1st to 10th	Night	41% 5% 12% 23% 17% 2	2666
	11th to 20th	Night	50% 4 11% 20% 12% 3	2730
	21st to end	Night	58% 6% 11% 17% 7% 1	2730
December	1st to 10th	Night	63% 5% 10% 15% 6%	4380
	11th to 20th	Night	67% 5% 12% 12% 4	4954
	21st to end	Night	72% 5% 8% 10% 4	6633

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	26% 18% 33% 17% 4 1	330
	11th to 20th	Day	25% 22% 39% 9% 4	330
	21st to end	Day	26% 19% 31% 19% 4	363
February	1st to 10th	Day	25% 17% 37% 16% 3 1	330
	11th to 20th	Day	26% 20% 32% 18% 3	330
	21st to end	Day	22% 23% 41% 13% 1	273
March	1st to 10th	Day	24% 17% 38% 17% 4	414
	11th to 20th	Day	24% 18% 35% 18% 4 1	540
	21st to end	Day	28% 16% 31% 21% 4	594
April	1st to 10th	Day	23% 16% 33% 19% 7% 1	540
	11th to 20th	Day	20% 19% 29% 19% 9% 4	532
	21st to end	Day	22% 15% 30% 21% 9% 2	540
May	1st to 10th	Day	27% 12% 29% 21% 8% 3	543
	11th to 20th	Day	22% 7% 29% 24% 13% 5%	551
	21st to end	Day	13% 7% 27% 23% 20% 9%	573
June	1st to 10th	Day	14% 7% 23% 33% 19% 5%	530
	11th to 20th	Day	14% 6% 24% 29% 22% 5%	660
	21st to end	Day	13% 7% 27% 27% 19% 7%	730
July	1st to 10th	Day	11% 4 18% 30% 23% 15%	721
	11th to 20th	Day	11% 4 19% 27% 26% 12%	552
	21st to end	Day	12% 3 17% 26% 27% 15%	576
August	1st to 10th	Day	10% 3 13% 27% 29% 17%	526
	11th to 20th	Day	14% 2 18% 29% 26% 11%	519
	21st to end	Day	10% 4 16% 26% 31% 13%	583
September	1st to 10th	Day	12% 3 18% 26% 27% 13%	530
	11th to 20th	Day	11% 2 13% 24% 32% 18%	530
	21st to end	Day	18% 11% 18% 26% 18% 10%	530
October	1st to 10th	Day	12% 8% 23% 28% 19% 10%	530
	11th to 20th	Day	15% 13% 33% 24% 12% 3	530
	21st to end	Day	26% 14% 33% 22% 5% 1	498
November	1st to 10th	Day	15% 16% 34% 22% 10% 3	330
	11th to 20th	Day	24% 19% 32% 16% 8% 1	330
	21st to end	Day	28% 16% 36% 17% 3	330
December	1st to 10th	Day	24% 17% 37% 15% 5% 2	330
	11th to 20th	Day	25% 18% 38% 16% 3	330
	21st to end	Day	32% 18% 29% 18% 2	363
January	1st to 10th	Night	23% 16% 38% 19% 4	840
	11th to 20th	Night	27% 16% 38% 16% 3 1	840
	21st to end	Night	23% 15% 36% 22% 3	924
February	1st to 10th	Night	24% 12% 38% 24% 2	840
	11th to 20th	Night	24% 13% 36% 23% 3	823
	21st to end	Night	27% 13% 40% 17% 2	692
March	1st to 10th	Night	24% 13% 34% 24% 6%	840
	11th to 20th	Night	20% 14% 36% 24% 5% 1	840
	21st to end	Night	24% 12% 34% 25% 6%	924
April	1st to 10th	Night	22% 13% 36% 24% 5%	791
	11th to 20th	Night	19% 12% 36% 24% 8% 1	623
	21st to end	Night	20% 9% 37% 25% 7% 1	630
May	1st to 10th	Night	23% 8% 30% 30% 8% 1	630
	11th to 20th	Night	20% 7% 28% 31% 13% 1	609
	21st to end	Night	12% 3 22% 40% 21% 2	650
June	1st to 10th	Night	10% 3 25% 42% 19% 1	600
	11th to 20th	Night	12% 3 18% 46% 20% 1	600
	21st to end	Night	11% 3 20% 42% 23% 2	600
July	1st to 10th	Night	10% 3 14% 41% 29% 4	585
	11th to 20th	Night	8% 5% 14% 41% 29% 4	582
	21st to end	Night	8% 2 13% 43% 31% 2	657
August	1st to 10th	Night	7% 3 10% 46% 31% 4	597
	11th to 20th	Night	10% 3 12% 39% 31% 4	594
	21st to end	Night	7% 2 13% 40% 34% 5%	660
September	1st to 10th	Night	12% 3 16% 36% 28% 5%	760
	11th to 20th	Night	11% 3 13% 37% 31% 5%	800
	21st to end	Night	18% 6% 20% 33% 21% 3	800
October	1st to 10th	Night	13% 5% 24% 35% 20% 4	800
	11th to 20th	Night	20% 10% 30% 29% 11% 1	800
	21st to end	Night	26% 10% 31% 25% 8%	880
November	1st to 10th	Night	19% 8% 33% 29% 11% 1	820
	11th to 20th	Night	22% 14% 32% 25% 6% 1	840
	21st to end	Night	27% 12% 31% 24% 5%	840
December	1st to 10th	Night	26% 13% 35% 21% 4	840
	11th to 20th	Night	26% 11% 36% 22% 4	840
	21st to end	Night	30% 13% 33% 21% 3	924

Page generated at 2026-05-14 01:58:55. Version ac07

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