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 2025-05-11.

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	21% 8% 2 6% 4 3 4 3 4 5% 39%	118003
	Night	24% 10% 3 6% 4 3 3 3 4 5% 36%	119742
Transparency	Day	46% 7% 12% 17% 13% 5%	117747
	Night	50% 7% 12% 16% 11% 4	119587
Seeing	Day	24% 7% 23% 27% 15% 4	15260
	Night	27% 5% 17% 30% 18% 2	24363

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	42% 15% 4 7% 5% 4 4 2 3 3 11%	3639
	11th to 20th	Day	30% 10% 3 6% 4 3 3 3 3 6% 29%	3640
	21st to end	Day	29% 9% 2 5% 3 3 4 3 5% 5% 32%	4446
February	1st to 10th	Day	32% 13% 4 7% 4 3 4 4 5% 6% 18%	1800
	11th to 20th	Day	31% 13% 3 8% 5% 4 4 3 5% 4 20%	1755
	21st to end	Day	32% 16% 3 7% 4 3 3 3 3 5% 21%	1572
March	1st to 10th	Day	21% 15% 4 8% 5% 4 5% 4 6% 6% 21%	4755
	11th to 20th	Day	31% 13% 3 7% 4 3 3 3 3 4 27%	5000
	21st to end	Day	28% 13% 4 9% 6% 5% 5% 4 5% 7% 13%	5590
April	1st to 10th	Day	30% 14% 4 9% 5% 5% 4 3 4 5% 17%	2400
	11th to 20th	Day	25% 12% 3 7% 5% 4 3 3 4 5% 27%	2369
	21st to end	Day	24% 10% 3 8% 4 4 4 3 5% 7% 27%	2578
May	1st to 10th	Day	22% 9% 3 7% 5% 3 5% 3 5% 5% 33%	4454
	11th to 20th	Day	13% 5% 2 5% 4 3 3 3 4 6% 52%	4380
	21st to end	Day	21% 9% 3 8% 6% 5% 5% 4 6% 7% 28%	4813
June	1st to 10th	Day	25% 8% 2 6% 4 4 3 4 4 5% 34%	2660
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 4 6% 6% 32%	2660
	21st to end	Day	10% 5% 1 4 3 3 4 2 4 6% 57%	2660
July	1st to 10th	Day	4 2 1 2 1 1 2 2 3 4 78%	4420
	11th to 20th	Day	4 2 1 2 1 2 2 2 3 4 77%	4420
	21st to end	Day	5% 2 1 2 1 1 2 1 2 3 78%	4772
August	1st to 10th	Day	3 2 1 3 2 2 3 2 4 5% 72%	4091
	11th to 20th	Day	6% 3 1 4 3 3 3 3 5% 7% 62%	4026
	21st to end	Day	7% 5% 1 4 3 3 3 3 4 6% 60%	4283
September	1st to 10th	Day	8% 3 1 3 1 2 2 2 4 6% 67%	2280
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 5% 6% 47%	2280
	21st to end	Day	16% 5% 2 5% 3 3 4 3 4 6% 48%	1996
October	1st to 10th	Day	17% 5% 1 4 3 2 3 3 5% 4 53%	3180
	11th to 20th	Day	20% 7% 2 7% 4 4 5% 4 5% 7% 36%	3161
	21st to end	Day	30% 9% 2 7% 4 4 4 3 5% 7% 24%	3397
November	1st to 10th	Day	35% 10% 3 7% 4 3 3 3 5% 5% 22%	1674
	11th to 20th	Day	36% 10% 2 7% 4 4 4 4 5% 6% 19%	1600
	21st to end	Day	30% 10% 3 7% 4 4 4 4 4 5% 24%	1600
December	1st to 10th	Day	24% 8% 2 5% 3 3 3 3 6% 7% 35%	2620
	11th to 20th	Day	37% 12% 3 8% 6% 4 5% 5% 5% 6% 9%	3028
	21st to end	Day	40% 15% 4 8% 4 4 4 3 4 4 9%	4004
January	1st to 10th	Night	41% 14% 3 9% 5% 4 4 2 3 3 12%	6306
	11th to 20th	Night	30% 12% 3 6% 3 2 2 2 3 4 32%	6320
	21st to end	Night	28% 12% 3 6% 3 3 2 2 3 4 34%	6512
February	1st to 10th	Night	30% 14% 4 8% 6% 4 3 3 4 5% 19%	2600
	11th to 20th	Night	33% 12% 2 6% 3 3 3 3 4 4 25%	2532
	21st to end	Night	32% 15% 3 7% 3 3 3 4 4 5% 22%	2057
March	1st to 10th	Night	20% 17% 4 8% 5% 4 5% 4 6% 6% 21%	5123
	11th to 20th	Night	30% 13% 3 7% 3 3 3 2 3 4 29%	5000
	21st to end	Night	31% 14% 4 9% 5% 5% 4 3 5% 6% 14%	5385
April	1st to 10th	Night	30% 13% 3 8% 5% 4 4 2 5% 4 22%	2000
	11th to 20th	Night	25% 12% 3 6% 3 4 4 3 5% 6% 29%	1979
	21st to end	Night	24% 11% 3 6% 4 4 4 3 5% 5% 31%	1819
May	1st to 10th	Night	24% 11% 3 8% 3 3 3 2 4 4 35%	2728
	11th to 20th	Night	12% 6% 2 5% 3 3 3 2 5% 6% 53%	2519
	21st to end	Night	21% 7% 3 7% 4 4 4 4 5% 8% 33%	2762
June	1st to 10th	Night	20% 8% 3 7% 4 3 4 3 4 5% 38%	1520
	11th to 20th	Night	18% 8% 2 7% 4 4 4 3 5% 5% 39%	1520
	21st to end	Night	9% 5% 2 6% 3 2 3 3 3 4 60%	1520
July	1st to 10th	Night	4 2 1 2 2 1 2 1 2 2 81%	2540
	11th to 20th	Night	4 2 1 3 1 2 2 2 2 3 79%	2540
	21st to end	Night	5% 2 1 1 1 1 1 1 2 3 81%	2778
August	1st to 10th	Night	2 2 1 3 1 2 2 2 3 5% 77%	2848
	11th to 20th	Night	7% 3 2 5% 3 3 3 3 4 6% 61%	2812
	21st to end	Night	10% 4 2 4 2 2 2 2 3 5% 66%	3391
September	1st to 10th	Night	8% 3 1 3 2 2 2 2 4 5% 68%	1900
	11th to 20th	Night	12% 4 1 4 4 4 4 3 5% 5% 52%	1900
	21st to end	Night	13% 5% 1 5% 3 4 3 2 5% 7% 52%	2178
October	1st to 10th	Night	15% 5% 2 5% 3 2 2 2 4 5% 55%	3800
	11th to 20th	Night	17% 7% 2 5% 4 4 4 4 6% 8% 40%	3777
	21st to end	Night	30% 10% 3 7% 4 3 4 3 4 5% 28%	4168
November	1st to 10th	Night	32% 10% 2 7% 5% 4 4 3 4 6% 24%	2620
	11th to 20th	Night	37% 8% 3 7% 4 4 4 3 4 4 21%	2800
	21st to end	Night	29% 9% 2 7% 4 4 4 4 4 5% 29%	2800
December	1st to 10th	Night	21% 7% 2 5% 3 3 3 3 4 6% 41%	4560
	11th to 20th	Night	40% 12% 3 8% 4 4 4 2 4 5% 13%	5176
	21st to end	Night	37% 13% 3 8% 6% 5% 4 3 4 5% 13%	6952

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% 5% 5% 3 1	3639
	11th to 20th	Day	57% 7% 11% 16% 8% 2	3640
	21st to end	Day	53% 7% 8% 13% 15% 4	4446
February	1st to 10th	Day	67% 8% 11% 10% 5%	1800
	11th to 20th	Day	67% 9% 9% 8% 5% 2	1764
	21st to end	Day	68% 6% 8% 9% 6% 2	1572
March	1st to 10th	Day	59% 8% 14% 15% 4	4755
	11th to 20th	Day	61% 6% 8% 17% 7%	5000
	21st to end	Day	67% 10% 13% 8% 3	5590
April	1st to 10th	Day	69% 7% 10% 10% 4	2400
	11th to 20th	Day	59% 7% 10% 13% 8% 2	2372
	21st to end	Day	57% 8% 14% 14% 7% 2	2578
May	1st to 10th	Day	50% 10% 12% 18% 11%	4454
	11th to 20th	Day	32% 6% 18% 31% 12% 1	4383
	21st to end	Day	50% 13% 20% 15% 2	4814
June	1st to 10th	Day	52% 6% 16% 20% 6%	2660
	11th to 20th	Day	50% 8% 18% 17% 6%	2660
	21st to end	Day	30% 5% 16% 32% 12% 4	2660
July	1st to 10th	Day	13% 4 9% 18% 24% 33%	4351
	11th to 20th	Day	13% 3 6% 17% 36% 25%	4345
	21st to end	Day	12% 3 9% 27% 39% 10%	4621
August	1st to 10th	Day	15% 4 9% 30% 30% 12%	4076
	11th to 20th	Day	21% 6% 17% 35% 17% 4	4065
	21st to end	Day	25% 6% 13% 25% 24% 9%	4282
September	1st to 10th	Day	19% 3 13% 30% 23% 13%	2280
	11th to 20th	Day	36% 8% 12% 22% 15% 7%	2280
	21st to end	Day	37% 6% 13% 21% 16% 6%	1996
October	1st to 10th	Day	34% 6% 9% 22% 23% 7%	3180
	11th to 20th	Day	46% 9% 16% 17% 11% 1	3161
	21st to end	Day	56% 10% 10% 14% 10% 1	3397
November	1st to 10th	Day	65% 8% 10% 12% 5%	1674
	11th to 20th	Day	67% 8% 9% 8% 6% 2	1600
	21st to end	Day	61% 9% 9% 7% 12% 1	1600
December	1st to 10th	Day	48% 8% 13% 13% 16% 2	2620
	11th to 20th	Day	75% 9% 7% 7% 1	3028
	21st to end	Day	76% 10% 7% 5% 2	4004
January	1st to 10th	Night	76% 7% 7% 5% 4 1	6306
	11th to 20th	Night	57% 7% 11% 16% 6% 3	6320
	21st to end	Night	56% 4 6% 14% 15% 5%	6512
February	1st to 10th	Night	68% 6% 10% 9% 5% 2	2600
	11th to 20th	Night	62% 7% 11% 10% 6% 3	2534
	21st to end	Night	64% 6% 10% 12% 6% 2	2057
March	1st to 10th	Night	60% 8% 14% 13% 5%	5123
	11th to 20th	Night	58% 7% 11% 15% 9% 1	5000
	21st to end	Night	68% 10% 13% 8% 1	5385
April	1st to 10th	Night	64% 8% 12% 12% 5%	2000
	11th to 20th	Night	55% 7% 15% 13% 8% 3	1979
	21st to end	Night	55% 7% 15% 15% 6% 3	1819
May	1st to 10th	Night	51% 8% 11% 18% 10% 1	2728
	11th to 20th	Night	31% 6% 17% 35% 9% 2	2519
	21st to end	Night	45% 13% 27% 13% 3	2762
June	1st to 10th	Night	47% 8% 16% 24% 5%	1520
	11th to 20th	Night	45% 8% 19% 21% 7%	1520
	21st to end	Night	29% 5% 17% 32% 13% 4	1520
July	1st to 10th	Night	12% 3 8% 19% 25% 33%	2500
	11th to 20th	Night	14% 3 6% 18% 32% 28%	2492
	21st to end	Night	10% 2 11% 29% 37% 10%	2691
August	1st to 10th	Night	12% 3 10% 37% 27% 12%	2839
	11th to 20th	Night	23% 7% 19% 33% 14% 4	2839
	21st to end	Night	23% 5% 13% 29% 22% 8%	3391
September	1st to 10th	Night	20% 4 11% 30% 22% 12%	1900
	11th to 20th	Night	32% 6% 14% 24% 13% 10%	1900
	21st to end	Night	33% 6% 13% 24% 16% 9%	2178
October	1st to 10th	Night	32% 5% 8% 26% 25% 4	3800
	11th to 20th	Night	41% 8% 19% 19% 11% 2	3777
	21st to end	Night	58% 7% 10% 14% 10% 2	4168
November	1st to 10th	Night	61% 8% 10% 12% 8% 1	2620
	11th to 20th	Night	66% 8% 9% 7% 8% 2	2800
	21st to end	Night	57% 8% 9% 11% 11% 4	2800
December	1st to 10th	Night	43% 6% 17% 21% 12% 1	4560
	11th to 20th	Night	74% 8% 8% 7% 3	5176
	21st to end	Night	71% 12% 10% 5% 2	6952

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	52% 5% 18% 16% 9% 1	200
	11th to 20th	Day	39% 7% 21% 19% 10% 6%	200
	21st to end	Day	34% 7% 21% 20% 13% 5%	415
February	1st to 10th	Day	40% 6% 23% 19% 11% 2	400
	11th to 20th	Day	37% 9% 26% 18% 7% 2	395
	21st to end	Day	39% 11% 19% 19% 11% 1	376
March	1st to 10th	Day	37% 8% 27% 18% 10%	500
	11th to 20th	Day	33% 10% 22% 20% 11% 3	500
	21st to end	Day	35% 11% 27% 17% 9% 1	550
April	1st to 10th	Day	36% 11% 22% 21% 9% 2	500
	11th to 20th	Day	29% 12% 24% 21% 11% 3	492
	21st to end	Day	31% 8% 26% 19% 13% 2	500
May	1st to 10th	Day	18% 13% 30% 25% 11% 3	503
	11th to 20th	Day	28% 6% 20% 26% 15% 5%	489
	21st to end	Day	21% 7% 23% 27% 18% 4	529
June	1st to 10th	Day	24% 6% 23% 32% 13% 1	490
	11th to 20th	Day	20% 8% 30% 29% 12% 1	490
	21st to end	Day	8% 6% 23% 41% 16% 5%	490
July	1st to 10th	Day	8% 5% 24% 37% 21% 5%	486
	11th to 20th	Day	4 7% 25% 39% 20% 5%	484
	21st to end	Day	4 3 19% 47% 22% 5%	531
August	1st to 10th	Day	4 2 20% 40% 28% 7%	487
	11th to 20th	Day	4 3 16% 45% 24% 8%	477
	21st to end	Day	6% 5% 27% 37% 20% 5%	539
September	1st to 10th	Day	8% 5% 25% 34% 22% 5%	490
	11th to 20th	Day	15% 7% 21% 32% 20% 5%	490
	21st to end	Day	18% 8% 24% 29% 16% 4	490
October	1st to 10th	Day	19% 7% 24% 25% 19% 6%	490
	11th to 20th	Day	24% 6% 18% 26% 22% 4	490
	21st to end	Day	31% 8% 25% 19% 11% 5%	512
November	1st to 10th	Day	35% 11% 22% 16% 13% 3	255
	11th to 20th	Day	39% 6% 21% 17% 13% 6%	200
	21st to end	Day	36% 7% 21% 15% 17% 5%	200
December	1st to 10th	Day	37% 8% 16% 18% 13% 9%	200
	11th to 20th	Day	50% 8% 21% 14% 7% 3	200
	21st to end	Day	46% 8% 18% 16% 11% 1	220
January	1st to 10th	Night	43% 7% 15% 19% 14% 2	800
	11th to 20th	Night	39% 6% 13% 24% 15% 2	800
	21st to end	Night	33% 5% 14% 30% 15% 2	880
February	1st to 10th	Night	35% 7% 17% 25% 15% 2	800
	11th to 20th	Night	40% 5% 17% 24% 14% 1	784
	21st to end	Night	40% 8% 15% 27% 10%	660
March	1st to 10th	Night	34% 7% 18% 29% 12% 1	800
	11th to 20th	Night	32% 8% 19% 25% 15% 1	800
	21st to end	Night	36% 6% 21% 23% 12% 1	880
April	1st to 10th	Night	34% 5% 19% 26% 16% 1	800
	11th to 20th	Night	29% 6% 21% 27% 16% 1	791
	21st to end	Night	27% 5% 22% 29% 16% 1	619
May	1st to 10th	Night	21% 4 27% 32% 14% 2	469
	11th to 20th	Night	21% 4 18% 34% 21% 2	375
	21st to end	Night	23% 3 19% 32% 20% 1	411
June	1st to 10th	Night	22% 4 22% 36% 16% 1	380
	11th to 20th	Night	22% 4 22% 40% 11% 1	380
	21st to end	Night	10% 2 26% 41% 21%	380
July	1st to 10th	Night	8% 2 17% 49% 24%	370
	11th to 20th	Night	5% 4 27% 45% 19% 1	368
	21st to end	Night	3 2 19% 50% 24% 1	421
August	1st to 10th	Night	4 2 14% 38% 37% 4	567
	11th to 20th	Night	5% 3 10% 44% 36% 2	564
	21st to end	Night	8% 3 21% 41% 24% 2	768
September	1st to 10th	Night	9% 3 19% 41% 26% 2	760
	11th to 20th	Night	13% 3 14% 33% 31% 6%	760
	21st to end	Night	15% 4 16% 37% 25% 3	760
October	1st to 10th	Night	19% 3 19% 34% 23% 3	760
	11th to 20th	Night	21% 4 14% 33% 24% 4	760
	21st to end	Night	31% 5% 19% 25% 15% 4	836
November	1st to 10th	Night	36% 7% 14% 29% 14% 1	780
	11th to 20th	Night	41% 6% 16% 23% 13% 1	800
	21st to end	Night	29% 7% 15% 28% 18% 2	800
December	1st to 10th	Night	33% 5% 13% 30% 16% 3	800
	11th to 20th	Night	43% 5% 14% 23% 14% 1	800
	21st to end	Night	46% 7% 17% 19% 10% 1	880

Page generated at 2025-05-08 06:33:58. Version ac07

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