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 2024-12-24.

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% 10% 5% 10% 6% 5% 4 3 5% 5% 43%	105449
	Night	2 7% 4 8% 5% 4 4 3 5% 7% 51%	103412
Transparency	Day	43% 3 7% 18% 20% 8%	105210
	Night	32% 3 9% 22% 24% 9%	103240
Seeing	Day	19% 20% 27% 21% 11% 3	15402
	Night	10% 11% 24% 32% 19% 3	25628

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	5% 3 12% 9% 5% 4 5% 6% 7% 44%	2798
	11th to 20th	Day	10% 4 14% 6% 5% 5% 2 5% 6% 43%	2860
	21st to end	Day	1 8% 8% 12% 6% 5% 3 3 5% 6% 44%	3146
February	1st to 10th	Day	8% 6% 16% 6% 4 3 3 5% 4 45%	1710
	11th to 20th	Day	1 9% 7% 12% 6% 5% 4 4 5% 5% 42%	1715
	21st to end	Day	1 8% 5% 18% 8% 5% 4 3 4 4 40%	1570
March	1st to 10th	Day	1 10% 9% 15% 6% 3 3 3 4 5% 41%	3439
	11th to 20th	Day	1 12% 10% 17% 5% 5% 5% 4 5% 6% 32%	3490
	21st to end	Day	1 17% 12% 16% 5% 3 4 3 4 4 31%	3843
April	1st to 10th	Day	2 15% 5% 9% 6% 4 3 3 4 6% 43%	2280
	11th to 20th	Day	2 15% 8% 11% 6% 5% 3 3 4 5% 39%	2251
	21st to end	Day	2 17% 6% 9% 5% 4 4 3 4 5% 40%	2280
May	1st to 10th	Day	2 17% 8% 8% 5% 5% 4 3 4 4 39%	4003
	11th to 20th	Day	3 13% 3 8% 6% 6% 5% 4 6% 7% 37%	4093
	21st to end	Day	4 15% 3 6% 4 5% 4 3 5% 6% 45%	4825
June	1st to 10th	Day	5% 6% 2 5% 5% 4 5% 4 6% 7% 52%	2660
	11th to 20th	Day	6% 6% 2 5% 5% 4 4 3 4 4 58%	2660
	21st to end	Day	7% 6% 2 8% 5% 5% 5% 4 5% 6% 48%	2660
July	1st to 10th	Day	9% 6% 2 6% 5% 4 4 2 4 4 54%	4371
	11th to 20th	Day	9% 8% 3 10% 8% 8% 8% 5% 7% 7% 28%	4110
	21st to end	Day	12% 8% 4 8% 7% 5% 5% 4 5% 5% 37%	4454
August	1st to 10th	Day	16% 9% 4 11% 8% 7% 6% 5% 6% 7% 20%	4092
	11th to 20th	Day	12% 9% 3 11% 7% 7% 6% 5% 5% 4 32%	3885
	21st to end	Day	15% 10% 4 10% 8% 6% 6% 4 5% 6% 26%	4180
September	1st to 10th	Day	15% 9% 3 10% 6% 5% 4 3 4 5% 37%	2280
	11th to 20th	Day	14% 10% 2 7% 5% 4 4 3 3 5% 43%	2275
	21st to end	Day	10% 9% 2 6% 4 3 3 2 3 4 52%	2000
October	1st to 10th	Day	8% 9% 2 5% 3 3 3 2 3 5% 58%	3170
	11th to 20th	Day	5% 15% 4 8% 4 4 3 3 4 6% 44%	3150
	21st to end	Day	3 7% 3 7% 2 2 2 2 3 5% 65%	3438
November	1st to 10th	Day	1 6% 3 7% 3 3 2 2 5% 5% 63%	1942
	11th to 20th	Day	1 7% 3 5% 2 3 2 3 4 5% 65%	1795
	21st to end	Day	1 9% 4 8% 5% 4 2 3 3 5% 57%	1600
December	1st to 10th	Day	1 8% 4 8% 5% 5% 4 3 4 6% 53%	1600
	11th to 20th	Day	10% 6% 11% 6% 5% 3 3 5% 5% 45%	2006
	21st to end	Day	6% 5% 10% 5% 3 5% 4 5% 6% 51%	2818
January	1st to 10th	Night	3 2 12% 12% 7% 6% 4 5% 6% 41%	4185
	11th to 20th	Night	6% 6% 14% 7% 3 5% 4 5% 7% 42%	4110
	21st to end	Night	6% 5% 13% 6% 4 4 3 5% 6% 48%	4521
February	1st to 10th	Night	7% 5% 12% 7% 4 3 2 4 7% 48%	2470
	11th to 20th	Night	1 7% 4 10% 6% 5% 4 4 5% 6% 49%	2350
	21st to end	Night	7% 4 12% 8% 7% 4 3 5% 6% 44%	1884
March	1st to 10th	Night	6% 7% 13% 4 4 4 4 5% 7% 44%	3430
	11th to 20th	Night	9% 8% 13% 6% 5% 6% 4 5% 7% 36%	3490
	21st to end	Night	17% 8% 13% 6% 4 4 3 5% 5% 34%	3807
April	1st to 10th	Night	1 11% 4 7% 5% 4 3 4 5% 7% 47%	1900
	11th to 20th	Night	2 11% 5% 9% 5% 4 5% 4 4 5% 46%	1877
	21st to end	Night	1 9% 4 8% 6% 4 4 3 5% 7% 49%	1900
May	1st to 10th	Night	1 9% 4 7% 4 4 5% 3 4 7% 52%	2963
	11th to 20th	Night	2 6% 2 6% 4 4 5% 4 6% 8% 54%	2809
	21st to end	Night	3 8% 2 4 3 3 3 3 4 5% 63%	2762
June	1st to 10th	Night	2 3 1 3 3 3 3 4 7% 7% 65%	1520
	11th to 20th	Night	4 3 1 3 3 3 3 3 4 5% 68%	1520
	21st to end	Night	2 4 1 4 4 4 5% 4 5% 8% 59%	1520
July	1st to 10th	Night	4 5% 1 4 3 3 4 3 5% 5% 63%	2594
	11th to 20th	Night	2 4 1 4 4 4 5% 5% 7% 12% 53%	2860
	21st to end	Night	4 4 1 5% 4 5% 4 4 7% 8% 51%	3109
August	1st to 10th	Night	6% 6% 2 6% 5% 6% 6% 6% 9% 13% 37%	2847
	11th to 20th	Night	6% 4 2 5% 4 4 6% 5% 7% 10% 47%	2952
	21st to end	Night	10% 7% 2 6% 4 4 5% 4 6% 9% 41%	3487
September	1st to 10th	Night	6% 4 2 7% 4 4 4 4 6% 8% 51%	1900
	11th to 20th	Night	5% 7% 2 5% 3 4 4 3 5% 6% 57%	1900
	21st to end	Night	5% 6% 2 5% 3 2 3 2 3 4 65%	2179
October	1st to 10th	Night	4 5% 1 3 2 2 2 2 3 4 72%	3800
	11th to 20th	Night	2 11% 2 5% 3 3 4 4 5% 6% 56%	3778
	21st to end	Night	3 7% 2 5% 2 2 2 2 3 5% 65%	4120
November	1st to 10th	Night	1 8% 2 4 4 3 4 4 5% 7% 59%	2340
	11th to 20th	Night	1 6% 3 4 3 3 3 3 4 7% 64%	2595
	21st to end	Night	1 8% 4 7% 4 3 3 3 5% 5% 56%	2800
December	1st to 10th	Night	1 5% 4 7% 5% 5% 4 3 5% 6% 56%	2800
	11th to 20th	Night	9% 4 8% 5% 5% 5% 4 6% 9% 46%	3411
	21st to end	Night	6% 5% 12% 6% 3 4 3 4 7% 51%	4922

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	36% 2 12% 17% 26% 8%	2799
	11th to 20th	Day	41% 1 12% 23% 18% 5%	2860
	21st to end	Day	41% 2 5% 23% 22% 7%	3146
February	1st to 10th	Day	42% 3 13% 17% 15% 10%	1710
	11th to 20th	Day	42% 4 5% 18% 21% 9%	1724
	21st to end	Day	47% 3 4 15% 21% 11%	1570
March	1st to 10th	Day	47% 1 4 21% 19% 8%	3439
	11th to 20th	Day	54% 2 5% 25% 11% 3	3490
	21st to end	Day	58% 2 6% 15% 16% 3	3843
April	1st to 10th	Day	43% 3 7% 18% 21% 7%	2280
	11th to 20th	Day	48% 3 6% 19% 18% 5%	2254
	21st to end	Day	46% 3 7% 26% 16% 2	2280
May	1st to 10th	Day	49% 2 6% 18% 18% 7%	4003
	11th to 20th	Day	47% 2 6% 23% 20% 2	4096
	21st to end	Day	40% 1 4 23% 27% 4	4825
June	1st to 10th	Day	31% 3 10% 29% 19% 7%	2660
	11th to 20th	Day	31% 2 5% 19% 29% 14%	2660
	21st to end	Day	37% 3 7% 17% 23% 13%	2660
July	1st to 10th	Day	34% 3 6% 9% 14% 34%	4303
	11th to 20th	Day	50% 7% 13% 15% 11% 4	4041
	21st to end	Day	46% 5% 11% 12% 14% 12%	4314
August	1st to 10th	Day	60% 8% 13% 7% 10% 3	4078
	11th to 20th	Day	54% 6% 8% 9% 17% 6%	3924
	21st to end	Day	57% 4 8% 13% 14% 4	4179
September	1st to 10th	Day	51% 3 6% 14% 20% 7%	2280
	11th to 20th	Day	45% 2 4 17% 23% 8%	2275
	21st to end	Day	38% 2 3 23% 27% 7%	2000
October	1st to 10th	Day	32% 1 4 17% 32% 14%	3170
	11th to 20th	Day	41% 2 7% 21% 22% 7%	3150
	21st to end	Day	25% 1 5% 22% 39% 7%	3438
November	1st to 10th	Day	24% 3 9% 27% 27% 10%	1942
	11th to 20th	Day	23% 2 7% 28% 29% 11%	1795
	21st to end	Day	31% 2 7% 22% 23% 15%	1600
December	1st to 10th	Day	32% 4 12% 23% 22% 8%	1600
	11th to 20th	Day	41% 3 8% 20% 23% 6%	2004
	21st to end	Day	34% 4 6% 16% 23% 18%	2818
January	1st to 10th	Night	38% 2 5% 21% 24% 10%	4185
	11th to 20th	Night	41% 2 10% 22% 19% 7%	4110
	21st to end	Night	37% 2 2 23% 28% 8%	4521
February	1st to 10th	Night	36% 3 10% 19% 22% 11%	2470
	11th to 20th	Night	34% 4 6% 22% 24% 10%	2351
	21st to end	Night	40% 3 4 19% 23% 11%	1884
March	1st to 10th	Night	42% 1 4 21% 27% 5%	3430
	11th to 20th	Night	49% 2 6% 25% 16% 3	3490
	21st to end	Night	51% 2 8% 20% 16% 3	3807
April	1st to 10th	Night	36% 3 10% 23% 20% 8%	1900
	11th to 20th	Night	38% 3 8% 23% 24% 4	1877
	21st to end	Night	33% 3 10% 32% 19% 3	1900
May	1st to 10th	Night	34% 2 7% 22% 31% 4	2963
	11th to 20th	Night	30% 2 7% 35% 25% 2	2810
	21st to end	Night	25% 1 6% 24% 35% 8%	2762
June	1st to 10th	Night	18% 3 10% 33% 28% 7%	1520
	11th to 20th	Night	21% 2 6% 20% 36% 15%	1520
	21st to end	Night	24% 4 7% 23% 28% 15%	1520
July	1st to 10th	Night	25% 3 8% 9% 18% 38%	2553
	11th to 20th	Night	22% 6% 17% 29% 18% 7%	2806
	21st to end	Night	27% 9% 17% 19% 16% 11%	3011
August	1st to 10th	Night	37% 11% 24% 11% 13% 4	2838
	11th to 20th	Night	31% 9% 19% 13% 21% 7%	2979
	21st to end	Night	40% 5% 13% 20% 18% 4	3487
September	1st to 10th	Night	31% 5% 12% 21% 25% 6%	1900
	11th to 20th	Night	30% 3 9% 23% 25% 9%	1900
	21st to end	Night	25% 3 4 30% 30% 8%	2179
October	1st to 10th	Night	19% 2 5% 21% 39% 14%	3800
	11th to 20th	Night	28% 3 6% 32% 24% 7%	3778
	21st to end	Night	23% 1 5% 22% 40% 9%	4120
November	1st to 10th	Night	25% 3 11% 24% 26% 12%	2340
	11th to 20th	Night	21% 3 7% 27% 29% 13%	2595
	21st to end	Night	30% 2 6% 22% 25% 15%	2800
December	1st to 10th	Night	29% 4 12% 20% 23% 12%	2800
	11th to 20th	Night	34% 4 7% 21% 25% 9%	3412
	21st to end	Night	34% 3 6% 16% 22% 19%	4922

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	20% 21% 31% 20% 8%	270
	11th to 20th	Day	23% 30% 21% 21% 5%	270
	21st to end	Day	12% 25% 35% 19% 8% 2	297
February	1st to 10th	Day	25% 30% 31% 10% 3 1	270
	11th to 20th	Day	24% 29% 28% 14% 5%	270
	21st to end	Day	34% 27% 22% 14% 2	225
March	1st to 10th	Day	29% 25% 28% 14% 3	455
	11th to 20th	Day	25% 25% 26% 17% 5% 1	460
	21st to end	Day	30% 30% 28% 11% 1	506
April	1st to 10th	Day	21% 28% 33% 14% 3 1	460
	11th to 20th	Day	29% 31% 28% 9% 3 1	452
	21st to end	Day	24% 30% 30% 12% 4	460
May	1st to 10th	Day	25% 27% 33% 11% 3	463
	11th to 20th	Day	23% 22% 29% 20% 5% 1	497
	21st to end	Day	21% 22% 25% 20% 10% 3	734
June	1st to 10th	Day	10% 9% 29% 27% 22% 3	680
	11th to 20th	Day	11% 18% 31% 22% 15% 3	680
	21st to end	Day	9% 13% 29% 26% 18% 5%	680
July	1st to 10th	Day	12% 11% 18% 29% 24% 5%	639
	11th to 20th	Day	16% 11% 18% 32% 18% 6%	484
	21st to end	Day	21% 8% 21% 27% 20% 5%	531
August	1st to 10th	Day	20% 11% 22% 30% 12% 6%	487
	11th to 20th	Day	16% 10% 27% 29% 12% 6%	477
	21st to end	Day	17% 12% 25% 27% 15% 5%	539
September	1st to 10th	Day	16% 11% 23% 25% 17% 8%	490
	11th to 20th	Day	16% 17% 34% 20% 10% 4	490
	21st to end	Day	19% 17% 27% 21% 10% 6%	400
October	1st to 10th	Day	24% 16% 19% 20% 13% 7%	300
	11th to 20th	Day	16% 21% 27% 20% 14% 3	300
	21st to end	Day	19% 22% 29% 18% 10% 2	330
November	1st to 10th	Day	19% 23% 29% 19% 8% 3	300
	11th to 20th	Day	17% 24% 28% 22% 7% 2	300
	21st to end	Day	19% 20% 28% 22% 10% 1	300
December	1st to 10th	Day	17% 26% 28% 19% 9% 2	300
	11th to 20th	Day	22% 21% 30% 18% 8%	300
	21st to end	Day	24% 27% 27% 14% 6% 2	306
January	1st to 10th	Night	9% 14% 28% 33% 14% 3	809
	11th to 20th	Night	11% 13% 31% 31% 13% 2	760
	21st to end	Night	9% 14% 29% 34% 11% 3	836
February	1st to 10th	Night	11% 18% 31% 31% 8% 1	760
	11th to 20th	Night	12% 13% 37% 28% 9% 1	744
	21st to end	Night	14% 15% 38% 26% 8%	628
March	1st to 10th	Night	14% 17% 30% 27% 10% 1	760
	11th to 20th	Night	9% 14% 27% 33% 16% 1	760
	21st to end	Night	13% 19% 31% 27% 8% 1	827
April	1st to 10th	Night	13% 20% 31% 27% 9%	570
	11th to 20th	Night	17% 16% 28% 29% 10%	563
	21st to end	Night	9% 17% 33% 28% 11% 2	570
May	1st to 10th	Night	11% 13% 27% 34% 13% 1	570
	11th to 20th	Night	8% 8% 26% 32% 22% 5%	561
	21st to end	Night	10% 13% 26% 30% 18% 4	617
June	1st to 10th	Night	4 6% 21% 36% 30% 4	570
	11th to 20th	Night	8% 7% 22% 37% 22% 3	570
	21st to end	Night	5% 5% 17% 35% 35% 4	570
July	1st to 10th	Night	7% 2 9% 35% 41% 5%	555
	11th to 20th	Night	5% 4 6% 30% 46% 9%	552
	21st to end	Night	9% 3 4 27% 46% 10%	624
August	1st to 10th	Night	9% 4 5% 28% 48% 6%	567
	11th to 20th	Night	8% 3 8% 34% 40% 8%	564
	21st to end	Night	8% 4 6% 35% 38% 8%	627
September	1st to 10th	Night	6% 4 10% 38% 36% 6%	570
	11th to 20th	Night	9% 6% 14% 35% 31% 5%	570
	21st to end	Night	11% 7% 16% 32% 28% 7%	760
October	1st to 10th	Night	16% 8% 21% 33% 20% 3	760
	11th to 20th	Night	7% 10% 24% 37% 19% 3	760
	21st to end	Night	10% 11% 23% 35% 18% 4	836
November	1st to 10th	Night	10% 8% 26% 35% 18% 3	780
	11th to 20th	Night	10% 10% 32% 33% 12% 3	995
	21st to end	Night	13% 13% 26% 32% 13% 3	1000
December	1st to 10th	Night	10% 13% 33% 34% 10% 2	1000
	11th to 20th	Night	12% 16% 34% 26% 11% 1	1000
	21st to end	Night	12% 14% 34% 30% 7% 1	1063

Page generated at 2024-12-21 02:13:53. Version ac07

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