Silverton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Silverton clear sky chart from 2005-11-06 to 2026-04-17.

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	5% 9% 4 10% 5% 5% 4 3 5% 6% 44%	140388
	Night	2 6% 3 7% 4 4 4 3 5% 7% 54%	139322
Transparency	Day	41% 3 8% 19% 21% 9%	135300
	Night	30% 3 9% 23% 25% 10%	135416
Seeing	Day	20% 20% 27% 20% 10% 3	17146
	Night	10% 11% 26% 32% 18% 3	27414

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	6% 4 14% 6% 4 4 4 5% 6% 46%	5218
	11th to 20th	Day	5% 2 9% 6% 5% 4 2 4 6% 58%	5340
	21st to end	Day	6% 5% 10% 5% 5% 4 3 4 6% 51%	5844
February	1st to 10th	Day	8% 6% 14% 5% 4 3 3 5% 5% 47%	1890
	11th to 20th	Day	1 9% 8% 14% 6% 5% 4 4 5% 5% 40%	1901
	21st to end	Day	1 7% 5% 16% 7% 5% 3 2 4 4 44%	1730
March	1st to 10th	Day	8% 8% 19% 5% 3 3 3 4 5% 43%	5059
	11th to 20th	Day	1 9% 8% 19% 5% 5% 5% 4 5% 6% 33%	5110
	21st to end	Day	1 15% 10% 13% 5% 3 4 3 4 5% 36%	5638
April	1st to 10th	Day	2 14% 5% 9% 6% 4 3 3 4 6% 43%	2520
	11th to 20th	Day	1 14% 8% 11% 6% 5% 3 3 5% 5% 39%	2444
	21st to end	Day	2 16% 6% 9% 5% 4 4 3 5% 5% 41%	2400
May	1st to 10th	Day	3 19% 7% 9% 6% 6% 5% 4 4 5% 33%	5734
	11th to 20th	Day	3 14% 4 8% 6% 5% 5% 4 5% 6% 40%	5877
	21st to end	Day	3 11% 2 5% 5% 5% 5% 4 6% 6% 48%	6925
June	1st to 10th	Day	5% 6% 2 5% 5% 4 5% 4 6% 7% 51%	2800
	11th to 20th	Day	6% 5% 2 5% 5% 3 4 3 4 4 58%	2800
	21st to end	Day	6% 6% 2 8% 5% 4 5% 4 5% 6% 48%	2800
July	1st to 10th	Day	7% 5% 2 7% 6% 5% 5% 3 5% 5% 50%	6252
	11th to 20th	Day	8% 7% 3 10% 8% 8% 8% 5% 7% 7% 29%	5880
	21st to end	Day	10% 8% 4 9% 7% 6% 6% 4 5% 6% 36%	6401
August	1st to 10th	Day	11% 7% 3 9% 7% 6% 6% 5% 6% 8% 33%	5779
	11th to 20th	Day	12% 8% 3 10% 7% 6% 6% 4 5% 5% 34%	5590
	21st to end	Day	14% 10% 3 11% 8% 7% 7% 5% 6% 5% 24%	5984
September	1st to 10th	Day	14% 9% 3 10% 6% 5% 4 4 4 5% 37%	2400
	11th to 20th	Day	13% 10% 2 7% 5% 4 4 3 3 5% 43%	2395
	21st to end	Day	10% 9% 2 7% 4 3 3 2 3 4 51%	2105
October	1st to 10th	Day	8% 9% 2 5% 3 3 3 2 3 4 58%	3270
	11th to 20th	Day	5% 15% 4 8% 4 4 3 3 4 6% 45%	3250
	21st to end	Day	3 7% 3 6% 2 2 2 2 3 5% 66%	3548
November	1st to 10th	Day	1 6% 3 6% 3 2 2 2 5% 5% 63%	2041
	11th to 20th	Day	1 8% 3 5% 2 3 2 3 4 5% 64%	1885
	21st to end	Day	1 9% 4 8% 5% 4 2 2 3 5% 58%	1680
December	1st to 10th	Day	1 5% 3 8% 3 3 3 2 4 7% 62%	2700
	11th to 20th	Day	7% 4 10% 4 3 2 2 5% 6% 57%	3106
	21st to end	Day	6% 5% 10% 4 3 4 3 5% 7% 52%	4092
January	1st to 10th	Night	6% 3 11% 9% 6% 6% 5% 6% 7% 41%	7746
	11th to 20th	Night	3 4 9% 5% 3 4 3 4 5% 60%	7650
	21st to end	Night	4 4 10% 4 4 4 2 4 6% 58%	8370
February	1st to 10th	Night	7% 5% 11% 6% 4 3 2 5% 7% 51%	2730
	11th to 20th	Night	1 8% 4 11% 6% 6% 4 4 5% 6% 46%	2604
	21st to end	Night	7% 4 11% 7% 6% 3 3 4 7% 47%	2076
March	1st to 10th	Night	6% 7% 14% 4 4 3 3 5% 6% 47%	5050
	11th to 20th	Night	8% 8% 15% 7% 4 5% 4 5% 7% 38%	5110
	21st to end	Night	15% 8% 12% 5% 4 3 3 5% 5% 40%	5575
April	1st to 10th	Night	1 12% 4 7% 5% 4 3 3 5% 7% 48%	2100
	11th to 20th	Night	2 11% 5% 9% 5% 4 5% 4 5% 6% 46%	2037
	21st to end	Night	1 9% 4 8% 5% 3 4 3 5% 7% 51%	2000
May	1st to 10th	Night	1 10% 4 7% 4 5% 5% 4 6% 7% 48%	4242
	11th to 20th	Night	1 6% 3 5% 3 3 4 4 5% 9% 56%	4035
	21st to end	Night	2 5% 1 3 2 2 2 2 4 6% 70%	3972
June	1st to 10th	Night	2 4 1 3 3 3 3 4 7% 7% 64%	1600
	11th to 20th	Night	4 3 1 3 3 2 3 3 4 5% 69%	1600
	21st to end	Night	2 4 1 4 4 4 5% 4 5% 8% 59%	1600
July	1st to 10th	Night	3 4 1 3 3 4 4 4 6% 5% 63%	3722
	11th to 20th	Night	2 3 1 4 3 3 5% 5% 8% 14% 52%	4100
	21st to end	Night	3 4 1 5% 4 5% 5% 5% 7% 9% 51%	4472
August	1st to 10th	Night	4 4 2 5% 4 5% 5% 5% 7% 11% 48%	4033
	11th to 20th	Night	5% 4 2 4 3 4 5% 5% 7% 10% 52%	4257
	21st to end	Night	9% 7% 3 7% 5% 5% 6% 5% 8% 9% 37%	4993
September	1st to 10th	Night	5% 4 2 7% 4 4 4 4 6% 8% 51%	2000
	11th to 20th	Night	5% 7% 1 5% 3 3 4 3 5% 6% 57%	2000
	21st to end	Night	5% 6% 2 5% 3 2 3 2 3 5% 63%	2294
October	1st to 10th	Night	4 5% 1 3 2 2 2 2 3 4 72%	3920
	11th to 20th	Night	2 11% 2 5% 3 3 4 3 5% 6% 56%	3898
	21st to end	Night	3 7% 2 5% 2 2 2 2 3 5% 66%	4252
November	1st to 10th	Night	1 8% 2 4 4 3 4 3 5% 6% 61%	2460
	11th to 20th	Night	1 6% 3 4 3 3 3 3 5% 7% 63%	2725
	21st to end	Night	1 8% 4 8% 4 3 3 3 5% 5% 56%	2940
December	1st to 10th	Night	3 2 5% 3 3 3 2 4 6% 68%	4710
	11th to 20th	Night	6% 3 6% 3 4 4 3 5% 8% 58%	5321
	21st to end	Night	6% 6% 11% 5% 3 3 3 5% 7% 51%	7128

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	37% 1 9% 25% 21% 8%	5221
	11th to 20th	Day	29% 1 7% 20% 24% 20%	5340
	21st to end	Day	33% 1 6% 20% 26% 14%	5844
February	1st to 10th	Day	38% 2 12% 18% 19% 11%	1890
	11th to 20th	Day	44% 4 5% 17% 21% 9%	1910
	21st to end	Day	43% 3 4 16% 22% 12%	1730
March	1st to 10th	Day	45% 1 5% 15% 21% 13%	5059
	11th to 20th	Day	52% 2 6% 22% 15% 4	5110
	21st to end	Day	49% 3 9% 22% 14% 3	5638
April	1st to 10th	Day	43% 3 7% 19% 20% 8%	2520
	11th to 20th	Day	48% 3 7% 19% 19% 5%	2447
	21st to end	Day	45% 3 7% 27% 17% 2	2400
May	1st to 10th	Day	52% 3 7% 18% 15% 5%	5734
	11th to 20th	Day	44% 2 6% 23% 21% 4	5880
	21st to end	Day	35% 3 6% 24% 28% 4	6926
June	1st to 10th	Day	32% 3 10% 29% 18% 7%	2800
	11th to 20th	Day	30% 2 5% 18% 29% 15%	2800
	21st to end	Day	37% 3 7% 16% 23% 14%	2800
July	1st to 10th	Day	35% 3 7% 8% 14% 33%	6185
	11th to 20th	Day	48% 7% 14% 15% 11% 5%	5811
	21st to end	Day	46% 5% 12% 12% 16% 9%	6217
August	1st to 10th	Day	59% 7% 13% 8% 10% 3	4208
	11th to 20th	Day	53% 6% 8% 9% 17% 6%	4049
	21st to end	Day	57% 5% 9% 13% 14% 3	4311
September	1st to 10th	Day	51% 3 6% 14% 19% 7%	2400
	11th to 20th	Day	45% 3 4 17% 23% 8%	2395
	21st to end	Day	38% 2 3 22% 26% 7%	2105
October	1st to 10th	Day	32% 1 4 18% 32% 14%	3270
	11th to 20th	Day	40% 2 6% 21% 22% 8%	3250
	21st to end	Day	24% 1 5% 22% 40% 8%	3548
November	1st to 10th	Day	23% 3 9% 28% 28% 9%	2041
	11th to 20th	Day	23% 2 7% 29% 28% 11%	1885
	21st to end	Day	31% 2 7% 24% 22% 14%	1680
December	1st to 10th	Day	23% 2 9% 26% 30% 9%	2700
	11th to 20th	Day	30% 2 10% 25% 27% 7%	3104
	21st to end	Day	32% 3 7% 20% 24% 13%	4092
January	1st to 10th	Night	38% 1 6% 23% 24% 9%	7747
	11th to 20th	Night	27% 1 7% 21% 24% 20%	7650
	21st to end	Night	28% 1 5% 18% 30% 17%	8370
February	1st to 10th	Night	33% 2 10% 19% 24% 12%	2730
	11th to 20th	Night	37% 3 6% 20% 24% 10%	2605
	21st to end	Night	37% 2 5% 20% 24% 12%	2076
March	1st to 10th	Night	39% 1 4 15% 30% 10%	5050
	11th to 20th	Night	46% 1 7% 20% 21% 5%	5110
	21st to end	Night	46% 2 9% 27% 13% 3	5575
April	1st to 10th	Night	36% 3 10% 23% 20% 8%	2100
	11th to 20th	Night	38% 3 8% 23% 24% 4	2037
	21st to end	Night	32% 3 10% 33% 20% 3	2000
May	1st to 10th	Night	34% 4 9% 26% 23% 3	4239
	11th to 20th	Night	27% 2 7% 36% 27% 1	4036
	21st to end	Night	18% 1 9% 27% 39% 7%	3972
June	1st to 10th	Night	19% 3 11% 33% 27% 7%	1600
	11th to 20th	Night	20% 2 6% 19% 35% 17%	1600
	21st to end	Night	24% 3 7% 22% 28% 17%	1600
July	1st to 10th	Night	23% 4 8% 11% 15% 38%	3681
	11th to 20th	Night	20% 8% 19% 29% 15% 9%	4046
	21st to end	Night	26% 9% 18% 20% 19% 8%	4344
August	1st to 10th	Night	36% 11% 23% 12% 13% 5%	2928
	11th to 20th	Night	30% 9% 19% 13% 21% 7%	3074
	21st to end	Night	40% 6% 13% 20% 18% 4	3597
September	1st to 10th	Night	30% 5% 12% 21% 25% 6%	2000
	11th to 20th	Night	29% 4 9% 23% 26% 9%	2000
	21st to end	Night	26% 3 5% 29% 30% 8%	2294
October	1st to 10th	Night	19% 2 4 21% 39% 14%	3920
	11th to 20th	Night	29% 3 6% 31% 24% 7%	3898
	21st to end	Night	23% 1 5% 22% 40% 9%	4252
November	1st to 10th	Night	24% 3 10% 25% 27% 11%	2460
	11th to 20th	Night	21% 3 8% 28% 28% 12%	2725
	21st to end	Night	29% 2 6% 24% 24% 15%	2940
December	1st to 10th	Night	19% 2 9% 29% 30% 11%	4710
	11th to 20th	Night	25% 2 7% 26% 30% 10%	5322
	21st to end	Night	34% 3 7% 18% 24% 14%	7128

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	22% 22% 32% 18% 7%	330
	11th to 20th	Day	23% 29% 23% 20% 5%	330
	21st to end	Day	17% 23% 34% 17% 7% 1	363
February	1st to 10th	Day	28% 28% 28% 12% 3 1	330
	11th to 20th	Day	30% 27% 26% 12% 4	330
	21st to end	Day	33% 26% 24% 14% 3	273
March	1st to 10th	Day	28% 26% 27% 15% 4	535
	11th to 20th	Day	29% 25% 24% 16% 5% 1	540
	21st to end	Day	28% 30% 27% 12% 2	594
April	1st to 10th	Day	22% 26% 32% 15% 3 1	540
	11th to 20th	Day	30% 31% 27% 8% 3 1	517
	21st to end	Day	24% 29% 30% 12% 4	500
May	1st to 10th	Day	25% 28% 33% 11% 4	503
	11th to 20th	Day	24% 23% 29% 18% 5% 1	538
	21st to end	Day	20% 22% 24% 21% 10% 3	789
June	1st to 10th	Day	11% 10% 29% 26% 21% 3	730
	11th to 20th	Day	11% 18% 31% 22% 15% 3	730
	21st to end	Day	9% 14% 29% 25% 18% 5%	730
July	1st to 10th	Day	12% 13% 19% 29% 24% 5%	687
	11th to 20th	Day	15% 12% 18% 31% 18% 6%	524
	21st to end	Day	20% 8% 21% 27% 19% 4	575
August	1st to 10th	Day	20% 12% 23% 28% 12% 5%	527
	11th to 20th	Day	15% 10% 27% 28% 14% 6%	517
	21st to end	Day	17% 12% 25% 27% 15% 5%	583
September	1st to 10th	Day	16% 12% 24% 24% 17% 8%	530
	11th to 20th	Day	16% 18% 33% 20% 9% 4	530
	21st to end	Day	20% 18% 26% 21% 11% 5%	435
October	1st to 10th	Day	24% 17% 20% 20% 13% 6%	330
	11th to 20th	Day	20% 21% 25% 19% 13% 3	330
	21st to end	Day	19% 21% 29% 19% 9% 2	363
November	1st to 10th	Day	18% 23% 29% 19% 8% 3	330
	11th to 20th	Day	17% 24% 28% 22% 7% 2	330
	21st to end	Day	19% 21% 28% 21% 10% 1	330
December	1st to 10th	Day	19% 26% 28% 18% 8% 2	330
	11th to 20th	Day	21% 22% 29% 18% 8% 1	330
	21st to end	Day	26% 26% 28% 13% 5% 1	363
January	1st to 10th	Night	9% 14% 31% 31% 13% 3	893
	11th to 20th	Night	11% 12% 32% 31% 13% 2	840
	21st to end	Night	9% 13% 33% 32% 10% 3	924
February	1st to 10th	Night	12% 16% 32% 30% 8% 1	840
	11th to 20th	Night	14% 13% 38% 26% 8%	824
	21st to end	Night	12% 15% 41% 25% 7%	692
March	1st to 10th	Night	14% 16% 32% 28% 10% 1	840
	11th to 20th	Night	11% 14% 29% 30% 15% 1	840
	21st to end	Night	12% 17% 33% 29% 8% 1	914
April	1st to 10th	Night	13% 19% 31% 28% 9%	630
	11th to 20th	Night	16% 17% 29% 28% 9%	611
	21st to end	Night	9% 17% 32% 29% 11% 2	600
May	1st to 10th	Night	11% 13% 28% 34% 13% 1	600
	11th to 20th	Night	8% 9% 26% 30% 21% 5%	591
	21st to end	Night	9% 12% 26% 31% 18% 4	650
June	1st to 10th	Night	4 6% 21% 38% 29% 3	600
	11th to 20th	Night	8% 7% 22% 38% 22% 3	600
	21st to end	Night	5% 5% 18% 35% 33% 4	600
July	1st to 10th	Night	7% 2 9% 37% 40% 5%	585
	11th to 20th	Night	5% 3 7% 32% 45% 8%	582
	21st to end	Night	9% 3 5% 29% 45% 10%	657
August	1st to 10th	Night	8% 5% 6% 29% 46% 6%	597
	11th to 20th	Night	8% 3 8% 35% 39% 7%	594
	21st to end	Night	9% 4 7% 35% 37% 8%	660
September	1st to 10th	Night	7% 4 10% 39% 35% 6%	600
	11th to 20th	Night	8% 6% 15% 36% 30% 5%	600
	21st to end	Night	11% 7% 16% 33% 28% 7%	800
October	1st to 10th	Night	16% 8% 21% 33% 19% 3	800
	11th to 20th	Night	10% 10% 24% 36% 18% 3	800
	21st to end	Night	10% 10% 25% 35% 17% 4	880
November	1st to 10th	Night	10% 8% 27% 35% 17% 3	820
	11th to 20th	Night	9% 10% 32% 33% 12% 3	1045
	21st to end	Night	12% 13% 28% 31% 13% 3	1050
December	1st to 10th	Night	9% 13% 34% 33% 9% 2	1050
	11th to 20th	Night	12% 15% 34% 26% 11% 1	1050
	21st to end	Night	14% 15% 35% 29% 7% 1	1155

Page generated at 2026-04-14 00:44:27. Version ac07

Copyright © 2026 Attilla Danko.