Stayton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stayton clear sky chart from 2005-11-06 to 2026-09-14.

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	18% 7% 2 5% 4 3 3 3 4 6% 44%	158485
	Night	22% 9% 2 6% 4 3 3 3 4 5% 39%	149957
Transparency	Day	41% 7% 12% 20% 14% 5%	153280
	Night	47% 7% 12% 19% 12% 4	146160
Seeing	Day	23% 7% 23% 27% 15% 4	17029
	Night	27% 5% 17% 31% 18% 2	25925

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	40% 16% 4 8% 5% 4 4 3 3 4 9%	4722
	11th to 20th	Day	23% 8% 2 5% 4 3 3 2 4 7% 40%	4740
	21st to end	Day	27% 8% 3 6% 4 4 4 3 5% 6% 30%	5765
February	1st to 10th	Day	31% 13% 4 7% 4 3 4 4 5% 7% 18%	1890
	11th to 20th	Day	31% 13% 3 8% 5% 4 4 3 5% 4 19%	1845
	21st to end	Day	32% 16% 3 7% 4 3 3 3 3 5% 21%	1648
March	1st to 10th	Day	22% 15% 4 8% 5% 4 5% 4 6% 6% 21%	4860
	11th to 20th	Day	31% 13% 3 7% 4 3 3 3 3 4 26%	5110
	21st to end	Day	28% 12% 4 9% 6% 5% 5% 4 5% 7% 14%	5713
April	1st to 10th	Day	29% 13% 4 9% 5% 5% 4 3 4 6% 17%	2520
	11th to 20th	Day	25% 12% 3 7% 5% 4 3 3 5% 5% 27%	2489
	21st to end	Day	24% 10% 3 8% 4 4 4 3 5% 6% 28%	2707
May	1st to 10th	Day	14% 7% 2 6% 5% 4 4 3 5% 7% 44%	8001
	11th to 20th	Day	16% 7% 2 7% 5% 4 4 3 5% 7% 38%	8160
	21st to end	Day	15% 6% 2 6% 4 4 4 3 5% 8% 41%	8992
June	1st to 10th	Day	23% 8% 2 6% 4 3 3 4 4 5% 36%	2940
	11th to 20th	Day	19% 7% 3 6% 5% 4 5% 4 6% 6% 35%	2940
	21st to end	Day	11% 5% 1 5% 3 3 4 2 4 6% 55%	2940
July	1st to 10th	Day	3 2 1 2 1 2 2 2 3 5% 78%	8219
	11th to 20th	Day	4 2 1 2 1 2 1 2 2 3 80%	8220
	21st to end	Day	4 2 1 2 2 2 2 1 2 4 78%	8891
August	1st to 10th	Day	4 3 1 3 2 2 3 2 3 5% 74%	7547
	11th to 20th	Day	6% 3 1 4 2 3 3 3 5% 7% 63%	7563
	21st to end	Day	7% 5% 1 3 3 3 3 3 5% 7% 60%	7940
September	1st to 10th	Day	8% 3 1 4 2 2 3 3 5% 6% 64%	2520
	11th to 20th	Day	13% 5% 2 5% 4 4 4 3 5% 6% 48%	2437
	21st to end	Day	16% 5% 2 5% 3 3 3 3 4 7% 49%	2101
October	1st to 10th	Day	17% 5% 1 4 3 2 3 3 5% 4 53%	3280
	11th to 20th	Day	20% 7% 2 7% 4 4 5% 4 5% 7% 36%	3261
	21st to end	Day	30% 9% 2 7% 4 4 4 3 5% 7% 24%	3505
November	1st to 10th	Day	35% 10% 3 7% 4 3 3 3 5% 5% 22%	1759
	11th to 20th	Day	35% 10% 2 8% 4 4 4 4 5% 5% 18%	1680
	21st to end	Day	31% 10% 3 7% 4 4 4 4 5% 5% 24%	1680
December	1st to 10th	Day	25% 8% 2 5% 3 3 3 3 6% 7% 34%	2700
	11th to 20th	Day	37% 12% 3 8% 6% 4 5% 5% 5% 6% 9%	3108
	21st to end	Day	39% 15% 4 8% 4 4 4 3 4 5% 10%	4092
January	1st to 10th	Night	40% 15% 3 8% 5% 4 4 3 3 4 11%	8172
	11th to 20th	Night	23% 10% 2 5% 3 2 2 2 3 5% 42%	8220
	21st to end	Night	25% 11% 3 7% 4 3 3 2 3 5% 32%	8428
February	1st to 10th	Night	30% 13% 3 8% 6% 4 3 3 4 5% 20%	2730
	11th to 20th	Night	33% 13% 3 6% 3 3 3 3 4 4 25%	2662
	21st to end	Night	32% 14% 3 7% 3 3 3 4 4 5% 22%	2157
March	1st to 10th	Night	21% 17% 4 8% 5% 4 5% 4 6% 6% 21%	5238
	11th to 20th	Night	30% 13% 3 7% 4 3 3 2 3 4 29%	5110
	21st to end	Night	31% 14% 4 9% 5% 5% 4 3 5% 6% 15%	5504
April	1st to 10th	Night	29% 12% 3 8% 5% 4 4 3 6% 4 23%	2100
	11th to 20th	Night	25% 12% 3 6% 3 4 4 3 5% 7% 28%	2079
	21st to end	Night	24% 11% 3 6% 4 4 3 3 5% 5% 32%	1910
May	1st to 10th	Night	17% 7% 2 6% 3 3 3 2 5% 6% 45%	4912
	11th to 20th	Night	17% 11% 3 8% 4 4 3 2 5% 6% 38%	4700
	21st to end	Night	16% 7% 2 6% 3 4 4 3 5% 8% 41%	5181
June	1st to 10th	Night	19% 8% 3 7% 4 3 4 3 4 5% 40%	1680
	11th to 20th	Night	17% 7% 2 7% 4 4 4 3 5% 5% 42%	1680
	21st to end	Night	11% 5% 2 6% 3 2 3 3 3 4 59%	1680
July	1st to 10th	Night	4 2 1 2 1 1 2 2 4 5% 76%	4740
	11th to 20th	Night	3 2 1 2 1 2 2 2 2 3 80%	4740
	21st to end	Night	4 2 1 2 2 2 2 2 2 4 79%	5170
August	1st to 10th	Night	4 2 1 3 2 2 2 2 4 5% 74%	5275
	11th to 20th	Night	8% 3 1 4 3 3 3 3 4 5% 62%	5292
	21st to end	Night	8% 4 2 4 2 2 2 2 4 5% 65%	6298
September	1st to 10th	Night	9% 4 1 3 2 2 3 2 4 5% 64%	2100
	11th to 20th	Night	12% 4 1 4 4 4 4 3 5% 5% 53%	2030
	21st to end	Night	13% 5% 1 5% 3 4 3 2 5% 6% 53%	2293
October	1st to 10th	Night	15% 5% 2 5% 3 3 3 2 4 5% 54%	3920
	11th to 20th	Night	17% 7% 2 5% 3 4 4 4 6% 8% 40%	3897
	21st to end	Night	30% 10% 3 7% 4 3 4 3 4 5% 28%	4302
November	1st to 10th	Night	32% 10% 2 7% 5% 4 4 3 5% 6% 23%	2755
	11th to 20th	Night	37% 9% 3 7% 4 4 4 3 4 4 21%	2940
	21st to end	Night	29% 9% 2 7% 4 4 4 4 4 5% 28%	2940
December	1st to 10th	Night	22% 7% 2 5% 3 3 3 3 4 6% 41%	4700
	11th to 20th	Night	40% 12% 3 8% 4 4 4 2 4 5% 14%	5316
	21st to end	Night	37% 13% 3 8% 6% 5% 4 3 4 5% 13%	7106

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	78% 7% 6% 5% 3 1	4723
	11th to 20th	Day	45% 6% 11% 17% 14% 8%	4740
	21st to end	Day	55% 6% 8% 14% 14% 4	5765
February	1st to 10th	Day	66% 8% 11% 10% 5%	1890
	11th to 20th	Day	67% 9% 9% 9% 5% 2	1854
	21st to end	Day	68% 6% 8% 9% 7% 2	1648
March	1st to 10th	Day	59% 8% 14% 15% 4	4860
	11th to 20th	Day	61% 6% 8% 17% 7%	5110
	21st to end	Day	67% 10% 13% 8% 3	5713
April	1st to 10th	Day	68% 7% 11% 11% 3	2520
	11th to 20th	Day	59% 7% 11% 13% 8% 2	2492
	21st to end	Day	56% 8% 13% 15% 7% 2	2707
May	1st to 10th	Day	37% 8% 12% 29% 14%	8001
	11th to 20th	Day	41% 9% 19% 24% 7%	8163
	21st to end	Day	39% 9% 25% 22% 5%	8994
June	1st to 10th	Day	49% 6% 15% 21% 7% 1	2940
	11th to 20th	Day	47% 8% 17% 18% 9% 1	2940
	21st to end	Day	31% 6% 16% 31% 12% 4	2940
July	1st to 10th	Day	11% 4 12% 33% 22% 18%	8151
	11th to 20th	Day	12% 3 6% 16% 40% 24%	8145
	21st to end	Day	12% 3 13% 36% 30% 6%	8692
August	1st to 10th	Day	12% 3 7% 25% 33% 19%	5976
	11th to 20th	Day	18% 6% 17% 38% 17% 3	5962
	21st to end	Day	22% 5% 13% 33% 21% 6%	6231
September	1st to 10th	Day	21% 4 13% 29% 21% 11%	2520
	11th to 20th	Day	36% 7% 12% 23% 15% 7%	2437
	21st to end	Day	37% 6% 12% 21% 17% 6%	2101
October	1st to 10th	Day	34% 6% 9% 22% 23% 6%	3280
	11th to 20th	Day	46% 9% 16% 17% 11% 2	3261
	21st to end	Day	56% 10% 10% 14% 9% 1	3505
November	1st to 10th	Day	65% 8% 10% 12% 4	1759
	11th to 20th	Day	68% 8% 9% 8% 6% 2	1680
	21st to end	Day	61% 9% 10% 7% 12% 1	1680
December	1st to 10th	Day	49% 8% 13% 13% 15% 1	2700
	11th to 20th	Day	75% 9% 7% 7% 2	3108
	21st to end	Day	75% 10% 7% 5% 2	4092
January	1st to 10th	Night	76% 8% 7% 5% 3 1	8172
	11th to 20th	Night	46% 6% 11% 18% 11% 7%	8220
	21st to end	Night	56% 4 5% 13% 15% 6%	8428
February	1st to 10th	Night	66% 7% 11% 10% 5% 1	2730
	11th to 20th	Night	62% 7% 11% 10% 6% 3	2664
	21st to end	Night	64% 6% 10% 12% 7% 2	2157
March	1st to 10th	Night	60% 8% 13% 13% 5%	5238
	11th to 20th	Night	58% 7% 11% 14% 9% 1	5110
	21st to end	Night	68% 9% 13% 9% 1	5504
April	1st to 10th	Night	63% 7% 13% 12% 4	2100
	11th to 20th	Night	55% 8% 15% 12% 7% 3	2079
	21st to end	Night	54% 7% 14% 16% 6% 3	1910
May	1st to 10th	Night	37% 7% 14% 30% 11% 1	4910
	11th to 20th	Night	44% 10% 15% 25% 5% 1	4700
	21st to end	Night	39% 10% 25% 22% 4	5182
June	1st to 10th	Night	45% 8% 15% 26% 6%	1680
	11th to 20th	Night	42% 7% 18% 23% 9% 1	1680
	21st to end	Night	30% 5% 17% 31% 13% 4	1680
July	1st to 10th	Night	12% 4 11% 34% 21% 18%	4700
	11th to 20th	Night	13% 2 8% 16% 39% 22%	4692
	21st to end	Night	12% 3 18% 35% 26% 5%	5057
August	1st to 10th	Night	9% 2 7% 31% 32% 19%	4169
	11th to 20th	Night	21% 6% 18% 38% 14% 3	4169
	21st to end	Night	20% 5% 13% 38% 18% 6%	4930
September	1st to 10th	Night	23% 5% 12% 28% 21% 11%	2100
	11th to 20th	Night	32% 6% 14% 25% 13% 9%	2030
	21st to end	Night	32% 6% 13% 25% 16% 9%	2293
October	1st to 10th	Night	32% 5% 8% 26% 25% 4	3920
	11th to 20th	Night	41% 8% 19% 19% 11% 2	3897
	21st to end	Night	57% 7% 10% 14% 10% 2	4302
November	1st to 10th	Night	62% 8% 10% 12% 8% 1	2755
	11th to 20th	Night	66% 8% 8% 8% 8% 2	2940
	21st to end	Night	57% 8% 10% 11% 10% 4	2940
December	1st to 10th	Night	44% 6% 17% 20% 12% 1	4700
	11th to 20th	Night	73% 8% 8% 7% 3	5316
	21st to end	Night	70% 12% 10% 5% 2	7106

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	49% 6% 18% 16% 9% 1	220
	11th to 20th	Day	35% 6% 20% 20% 12% 7%	220
	21st to end	Day	33% 8% 21% 20% 13% 5%	447
February	1st to 10th	Day	39% 6% 23% 19% 12% 2	430
	11th to 20th	Day	37% 9% 26% 19% 7% 2	425
	21st to end	Day	38% 11% 20% 20% 11%	404
March	1st to 10th	Day	38% 9% 26% 18% 9%	540
	11th to 20th	Day	34% 10% 24% 20% 10% 3	540
	21st to end	Day	36% 11% 27% 17% 9% 1	594
April	1st to 10th	Day	34% 10% 21% 21% 10% 4	540
	11th to 20th	Day	28% 12% 24% 20% 11% 3	532
	21st to end	Day	30% 8% 26% 20% 13% 3	540
May	1st to 10th	Day	17% 12% 29% 26% 13% 3	543
	11th to 20th	Day	26% 9% 21% 26% 13% 4	568
	21st to end	Day	19% 7% 22% 29% 18% 4	617
June	1st to 10th	Day	22% 8% 24% 31% 14% 2	570
	11th to 20th	Day	18% 7% 30% 31% 12% 1	570
	21st to end	Day	10% 6% 22% 41% 16% 5%	570
July	1st to 10th	Day	7% 4 23% 40% 20% 6%	566
	11th to 20th	Day	4 7% 28% 38% 19% 4	564
	21st to end	Day	4 3 20% 44% 23% 6%	619
August	1st to 10th	Day	5% 3 20% 40% 26% 7%	567
	11th to 20th	Day	4 3 15% 45% 24% 8%	557
	21st to end	Day	6% 5% 26% 37% 21% 6%	627
September	1st to 10th	Day	9% 5% 25% 33% 22% 6%	570
	11th to 20th	Day	14% 7% 22% 32% 21% 5%	543
	21st to end	Day	18% 8% 23% 31% 16% 4	530
October	1st to 10th	Day	19% 7% 24% 25% 19% 5%	530
	11th to 20th	Day	24% 7% 18% 26% 22% 4	530
	21st to end	Day	31% 9% 25% 20% 11% 5%	554
November	1st to 10th	Day	35% 11% 22% 17% 13% 3	280
	11th to 20th	Day	37% 7% 21% 17% 12% 5%	220
	21st to end	Day	36% 7% 20% 17% 16% 5%	220
December	1st to 10th	Day	40% 8% 16% 18% 11% 8%	220
	11th to 20th	Day	48% 9% 20% 13% 8% 2	220
	21st to end	Day	45% 8% 18% 16% 10% 2	242
January	1st to 10th	Night	43% 7% 15% 20% 13% 2	840
	11th to 20th	Night	37% 6% 13% 25% 17% 2	840
	21st to end	Night	33% 5% 14% 31% 15% 2	924
February	1st to 10th	Night	34% 7% 17% 26% 15% 2	840
	11th to 20th	Night	39% 6% 17% 24% 13% 1	824
	21st to end	Night	40% 8% 15% 27% 10%	692
March	1st to 10th	Night	35% 7% 18% 29% 11%	840
	11th to 20th	Night	33% 7% 21% 24% 14% 1	840
	21st to end	Night	35% 7% 21% 23% 12% 1	924
April	1st to 10th	Night	33% 5% 18% 26% 17%	840
	11th to 20th	Night	29% 6% 21% 27% 16% 1	831
	21st to end	Night	26% 5% 21% 31% 16% 1	650
May	1st to 10th	Night	20% 4 26% 33% 16% 2	492
	11th to 20th	Night	22% 5% 18% 34% 20% 2	414
	21st to end	Night	22% 3 19% 34% 20% 2	455
June	1st to 10th	Night	21% 4 22% 36% 15% 1	420
	11th to 20th	Night	20% 4 22% 42% 11%	420
	21st to end	Night	11% 2 25% 41% 20%	420
July	1st to 10th	Night	7% 2 17% 50% 24%	410
	11th to 20th	Night	5% 3 27% 45% 19% 1	408
	21st to end	Night	3 2 18% 50% 25% 2	465
August	1st to 10th	Night	5% 2 15% 39% 36% 4	627
	11th to 20th	Night	7% 3 9% 43% 36% 2	624
	21st to end	Night	8% 3 21% 42% 24% 2	849
September	1st to 10th	Night	10% 3 19% 41% 25% 1	840
	11th to 20th	Night	13% 3 14% 33% 31% 6%	812
	21st to end	Night	14% 4 16% 38% 25% 3	800
October	1st to 10th	Night	19% 4 18% 34% 23% 3	800
	11th to 20th	Night	21% 4 15% 33% 24% 3	800
	21st to end	Night	30% 5% 20% 26% 15% 4	880
November	1st to 10th	Night	36% 7% 14% 28% 14% 1	820
	11th to 20th	Night	41% 6% 17% 22% 13% 1	840
	21st to end	Night	29% 7% 16% 28% 18% 2	840
December	1st to 10th	Night	34% 5% 13% 30% 16% 3	840
	11th to 20th	Night	43% 5% 14% 23% 14% 1	840
	21st to end	Night	45% 8% 17% 19% 10% 1	924

Page generated at 2026-09-11 01:11:56. Version ac07

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