Woodburn
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Woodburn 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	16% 9% 3 8% 5% 5% 5% 4 5% 6% 35%	118031
	Night	19% 9% 3 8% 5% 5% 4 3 5% 6% 33%	119731
Transparency	Day	47% 8% 12% 17% 12% 4	117774
	Night	50% 8% 12% 16% 11% 3	119577
Seeing	Day	19% 8% 18% 25% 22% 8%	15231
	Night	23% 6% 17% 32% 21% 2	24318

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	33% 15% 5% 12% 6% 5% 4 3 4 4 8%	3639
	11th to 20th	Day	26% 11% 3 10% 7% 6% 5% 4 4 4 19%	3640
	21st to end	Day	20% 10% 4 8% 6% 6% 5% 4 5% 5% 27%	4436
February	1st to 10th	Day	25% 13% 4 9% 6% 5% 6% 5% 6% 6% 14%	1800
	11th to 20th	Day	26% 11% 5% 12% 7% 4 5% 4 4 4 18%	1755
	21st to end	Day	26% 14% 4 10% 6% 5% 5% 4 4 5% 18%	1564
March	1st to 10th	Day	15% 12% 3 11% 7% 7% 8% 5% 7% 7% 19%	4755
	11th to 20th	Day	23% 14% 4 9% 5% 5% 3 3 5% 5% 25%	5000
	21st to end	Day	19% 12% 5% 11% 8% 7% 7% 5% 6% 6% 14%	5590
April	1st to 10th	Day	23% 12% 4 10% 6% 6% 5% 4 5% 6% 18%	2400
	11th to 20th	Day	20% 11% 3 8% 5% 5% 5% 4 5% 6% 27%	2369
	21st to end	Day	17% 9% 4 10% 6% 5% 5% 4 6% 7% 26%	2591
May	1st to 10th	Day	18% 9% 3 8% 5% 5% 4 3 5% 5% 35%	4464
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 3 6% 7% 49%	4380
	21st to end	Day	17% 7% 3 8% 6% 6% 7% 5% 7% 7% 27%	4813
June	1st to 10th	Day	19% 9% 3 7% 6% 4 4 3 5% 7% 33%	2660
	11th to 20th	Day	16% 8% 3 9% 5% 6% 5% 5% 7% 8% 29%	2660
	21st to end	Day	7% 5% 2 5% 4 4 4 4 5% 6% 54%	2660
July	1st to 10th	Day	4 2 1 2 2 2 3 2 4 5% 74%	4420
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 5% 75%	4420
	21st to end	Day	5% 2 1 2 2 2 2 2 3 5% 74%	4790
August	1st to 10th	Day	2 3 1 3 2 3 3 3 5% 6% 68%	4096
	11th to 20th	Day	5% 4 1 5% 3 3 4 4 6% 8% 57%	4026
	21st to end	Day	7% 5% 2 4 3 3 4 3 5% 7% 56%	4304
September	1st to 10th	Day	6% 3 1 3 3 4 4 3 4 7% 62%	2280
	11th to 20th	Day	10% 7% 4 6% 4 4 5% 4 6% 6% 44%	2276
	21st to end	Day	13% 5% 3 7% 5% 4 3 3 5% 6% 45%	2000
October	1st to 10th	Day	14% 6% 2 6% 5% 4 4 3 5% 6% 45%	3180
	11th to 20th	Day	15% 7% 3 8% 6% 6% 6% 5% 7% 8% 30%	3161
	21st to end	Day	21% 11% 4 10% 6% 6% 5% 4 5% 8% 21%	3391
November	1st to 10th	Day	26% 13% 4 11% 6% 5% 5% 4 4 6% 15%	1659
	11th to 20th	Day	27% 11% 5% 10% 7% 6% 5% 4 4 4 17%	1600
	21st to end	Day	24% 12% 4 11% 7% 6% 5% 4 4 5% 19%	1600
December	1st to 10th	Day	19% 9% 3 9% 6% 7% 5% 4 5% 6% 26%	2620
	11th to 20th	Day	27% 14% 5% 12% 7% 6% 6% 4 6% 5% 8%	3028
	21st to end	Day	31% 17% 5% 14% 7% 6% 4 3 3 3 6%	4004
January	1st to 10th	Night	30% 16% 6% 12% 5% 5% 4 3 4 4 11%	6306
	11th to 20th	Night	27% 12% 4 8% 7% 5% 4 3 4 4 21%	6320
	21st to end	Night	24% 10% 4 8% 5% 4 4 3 4 5% 30%	6538
February	1st to 10th	Night	24% 14% 4 9% 6% 6% 5% 4 5% 5% 17%	2600
	11th to 20th	Night	27% 12% 3 9% 4 4 4 3 4 4 25%	2532
	21st to end	Night	24% 14% 4 8% 6% 4 4 4 6% 6% 21%	2065
March	1st to 10th	Night	16% 10% 4 11% 7% 7% 7% 5% 6% 6% 21%	5124
	11th to 20th	Night	19% 11% 4 9% 5% 5% 5% 3 5% 5% 29%	5000
	21st to end	Night	20% 14% 4 10% 7% 7% 6% 4 6% 7% 15%	5385
April	1st to 10th	Night	23% 13% 4 10% 6% 5% 4 2 6% 5% 22%	2000
	11th to 20th	Night	19% 10% 3 7% 5% 4 4 4 5% 7% 32%	1979
	21st to end	Night	20% 10% 4 8% 5% 3 4 4 5% 7% 29%	1805
May	1st to 10th	Night	19% 8% 3 8% 4 4 3 3 5% 5% 38%	2719
	11th to 20th	Night	9% 5% 2 6% 4 3 4 3 5% 8% 52%	2519
	21st to end	Night	14% 7% 4 8% 5% 6% 6% 5% 7% 9% 31%	2762
June	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 3 5% 6% 36%	1520
	11th to 20th	Night	14% 9% 4 7% 5% 5% 4 4 5% 7% 37%	1520
	21st to end	Night	6% 6% 2 6% 4 3 4 3 3 5% 58%	1520
July	1st to 10th	Night	4 2 1 3 2 2 2 2 3 3 78%	2540
	11th to 20th	Night	3 2 1 2 2 2 2 1 3 3 77%	2540
	21st to end	Night	3 3 1 2 1 1 2 2 3 4 77%	2761
August	1st to 10th	Night	2 2 1 3 2 2 2 2 4 6% 74%	2839
	11th to 20th	Night	5% 6% 2 5% 4 4 4 3 5% 6% 57%	2812
	21st to end	Night	9% 5% 2 5% 3 3 3 3 3 5% 61%	3370
September	1st to 10th	Night	6% 4 1 4 2 2 3 2 4 6% 66%	1900
	11th to 20th	Night	9% 5% 2 7% 4 4 5% 3 5% 6% 50%	1900
	21st to end	Night	11% 5% 2 5% 3 4 4 3 6% 7% 51%	2180
October	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 5% 7% 48%	3800
	11th to 20th	Night	15% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	3777
	21st to end	Night	20% 9% 3 10% 6% 5% 5% 4 6% 6% 25%	4174
November	1st to 10th	Night	26% 10% 3 8% 6% 4 5% 3 5% 5% 23%	2636
	11th to 20th	Night	29% 12% 4 9% 5% 4 4 4 4 4 21%	2800
	21st to end	Night	22% 10% 3 9% 7% 5% 5% 3 5% 5% 26%	2800
December	1st to 10th	Night	18% 8% 3 8% 6% 6% 5% 4 8% 7% 27%	4560
	11th to 20th	Night	31% 14% 5% 11% 6% 5% 5% 3 4 5% 11%	5176
	21st to end	Night	29% 13% 5% 12% 7% 6% 5% 3 4 5% 11%	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	79% 8% 5% 5% 3	3639
	11th to 20th	Day	67% 5% 6% 13% 7% 1	3640
	21st to end	Day	56% 8% 7% 12% 15% 3	4436
February	1st to 10th	Day	66% 9% 11% 9% 4	1800
	11th to 20th	Day	67% 10% 9% 8% 4 2	1764
	21st to end	Day	67% 7% 10% 8% 6% 2	1564
March	1st to 10th	Day	56% 10% 14% 15% 4	4755
	11th to 20th	Day	59% 7% 8% 17% 8%	5000
	21st to end	Day	65% 11% 12% 9% 3	5590
April	1st to 10th	Day	65% 9% 11% 12% 3	2400
	11th to 20th	Day	56% 9% 11% 13% 8% 2	2372
	21st to end	Day	55% 11% 12% 13% 7% 1	2591
May	1st to 10th	Day	48% 11% 11% 17% 12%	4464
	11th to 20th	Day	31% 11% 19% 26% 12% 1	4383
	21st to end	Day	50% 18% 17% 14% 2	4814
June	1st to 10th	Day	50% 9% 16% 19% 6%	2660
	11th to 20th	Day	50% 11% 18% 15% 6%	2660
	21st to end	Day	30% 8% 16% 30% 11% 4	2660
July	1st to 10th	Day	14% 5% 9% 18% 23% 30%	4351
	11th to 20th	Day	13% 3 7% 18% 38% 20%	4345
	21st to end	Day	14% 3 10% 28% 37% 7%	4639
August	1st to 10th	Day	17% 5% 11% 29% 27% 11%	4080
	11th to 20th	Day	23% 6% 20% 33% 15% 4	4065
	21st to end	Day	27% 6% 14% 25% 22% 7%	4303
September	1st to 10th	Day	20% 7% 13% 29% 20% 12%	2280
	11th to 20th	Day	38% 8% 14% 20% 14% 7%	2276
	21st to end	Day	38% 8% 14% 19% 15% 6%	2000
October	1st to 10th	Day	37% 7% 8% 23% 21% 4	3180
	11th to 20th	Day	48% 8% 18% 14% 11% 1	3161
	21st to end	Day	58% 7% 9% 15% 9% 1	3391
November	1st to 10th	Day	67% 9% 10% 10% 4	1659
	11th to 20th	Day	67% 8% 9% 8% 6% 2	1600
	21st to end	Day	63% 10% 7% 8% 11% 1	1600
December	1st to 10th	Day	58% 5% 11% 14% 11% 1	2620
	11th to 20th	Day	72% 9% 10% 7% 1	3028
	21st to end	Day	77% 10% 7% 5% 2	4004
January	1st to 10th	Night	75% 7% 7% 5% 4 1	6306
	11th to 20th	Night	64% 7% 6% 15% 6% 2	6320
	21st to end	Night	55% 7% 5% 13% 16% 3	6538
February	1st to 10th	Night	66% 10% 9% 9% 5% 1	2600
	11th to 20th	Night	62% 7% 13% 10% 6% 2	2534
	21st to end	Night	63% 9% 10% 11% 5% 2	2065
March	1st to 10th	Night	58% 9% 13% 14% 6%	5124
	11th to 20th	Night	54% 11% 10% 15% 10% 1	5000
	21st to end	Night	64% 12% 14% 9% 1	5385
April	1st to 10th	Night	62% 9% 13% 12% 4	2000
	11th to 20th	Night	52% 9% 15% 14% 7% 3	1979
	21st to end	Night	54% 8% 15% 14% 6% 2	1805
May	1st to 10th	Night	45% 12% 12% 20% 9% 1	2719
	11th to 20th	Night	29% 9% 20% 30% 9% 2	2519
	21st to end	Night	42% 20% 23% 11% 3	2762
June	1st to 10th	Night	48% 8% 17% 21% 5% 1	1520
	11th to 20th	Night	46% 9% 18% 20% 6%	1520
	21st to end	Night	30% 7% 17% 31% 12% 4	1520
July	1st to 10th	Night	14% 4 8% 19% 27% 28%	2500
	11th to 20th	Night	14% 3 7% 18% 34% 23%	2492
	21st to end	Night	11% 3 14% 27% 37% 8%	2674
August	1st to 10th	Night	12% 4 9% 38% 29% 8%	2831
	11th to 20th	Night	26% 7% 20% 31% 12% 4	2839
	21st to end	Night	26% 5% 13% 29% 21% 6%	3370
September	1st to 10th	Night	20% 6% 13% 30% 20% 11%	1900
	11th to 20th	Night	33% 8% 14% 23% 13% 9%	1900
	21st to end	Night	31% 8% 16% 21% 16% 8%	2180
October	1st to 10th	Night	34% 6% 8% 29% 20% 3	3800
	11th to 20th	Night	42% 7% 19% 18% 11% 2	3777
	21st to end	Night	56% 8% 11% 14% 10% 2	4174
November	1st to 10th	Night	60% 10% 10% 13% 7%	2636
	11th to 20th	Night	65% 9% 9% 8% 8% 2	2800
	21st to end	Night	58% 9% 9% 10% 12% 3	2800
December	1st to 10th	Night	52% 6% 10% 18% 12% 1	4560
	11th to 20th	Night	72% 8% 9% 7% 3	5176
	21st to end	Night	69% 11% 12% 6% 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	42% 10% 17% 17% 12% 3	200
	11th to 20th	Day	36% 7% 18% 20% 13% 8%	200
	21st to end	Day	29% 7% 17% 22% 15% 10%	405
February	1st to 10th	Day	31% 11% 20% 17% 18% 4	400
	11th to 20th	Day	33% 9% 25% 18% 11% 4	395
	21st to end	Day	34% 13% 17% 20% 14% 2	371
March	1st to 10th	Day	29% 12% 23% 22% 11% 3	500
	11th to 20th	Day	28% 13% 19% 20% 16% 4	500
	21st to end	Day	29% 13% 23% 20% 14% 2	550
April	1st to 10th	Day	27% 15% 19% 21% 12% 5%	500
	11th to 20th	Day	26% 11% 24% 22% 11% 6%	492
	21st to end	Day	20% 12% 23% 23% 18% 5%	500
May	1st to 10th	Day	17% 9% 21% 27% 20% 6%	503
	11th to 20th	Day	21% 8% 16% 25% 21% 9%	489
	21st to end	Day	16% 6% 17% 26% 25% 11%	529
June	1st to 10th	Day	19% 8% 16% 26% 23% 7%	490
	11th to 20th	Day	17% 9% 21% 28% 21% 5%	490
	21st to end	Day	6% 6% 13% 33% 33% 9%	490
July	1st to 10th	Day	6% 3 14% 33% 33% 12%	486
	11th to 20th	Day	4 3 14% 37% 30% 13%	484
	21st to end	Day	4 2 10% 31% 41% 13%	531
August	1st to 10th	Day	3 3 8% 30% 41% 15%	487
	11th to 20th	Day	3 2 9% 32% 33% 21%	477
	21st to end	Day	6% 3 15% 33% 30% 12%	539
September	1st to 10th	Day	7% 3 19% 27% 31% 12%	490
	11th to 20th	Day	11% 6% 15% 27% 30% 12%	490
	21st to end	Day	15% 6% 19% 29% 23% 7%	490
October	1st to 10th	Day	17% 8% 19% 25% 21% 10%	490
	11th to 20th	Day	20% 7% 17% 24% 22% 10%	490
	21st to end	Day	27% 11% 24% 20% 11% 8%	506
November	1st to 10th	Day	30% 11% 22% 18% 13% 6%	247
	11th to 20th	Day	31% 11% 21% 16% 15% 8%	200
	21st to end	Day	27% 12% 19% 18% 18% 8%	200
December	1st to 10th	Day	35% 5% 14% 19% 17% 11%	200
	11th to 20th	Day	38% 10% 22% 19% 9% 3	200
	21st to end	Day	38% 14% 18% 15% 11% 3	220
January	1st to 10th	Night	37% 11% 17% 20% 14% 2	800
	11th to 20th	Night	34% 8% 14% 24% 17% 2	800
	21st to end	Night	28% 6% 16% 30% 18% 3	880
February	1st to 10th	Night	29% 8% 18% 29% 15% 2	800
	11th to 20th	Night	32% 6% 20% 25% 16% 1	784
	21st to end	Night	32% 8% 17% 31% 11%	660
March	1st to 10th	Night	27% 9% 20% 29% 14% 1	800
	11th to 20th	Night	26% 7% 20% 31% 15% 1	800
	21st to end	Night	28% 7% 24% 26% 13% 1	880
April	1st to 10th	Night	28% 8% 18% 28% 18% 1	800
	11th to 20th	Night	23% 7% 23% 29% 17% 1	791
	21st to end	Night	23% 6% 20% 33% 18% 1	605
May	1st to 10th	Night	17% 5% 19% 40% 18% 1	460
	11th to 20th	Night	15% 4 18% 37% 25% 2	375
	21st to end	Night	19% 4 17% 35% 24% 2	411
June	1st to 10th	Night	18% 5% 16% 37% 23% 1	380
	11th to 20th	Night	18% 3 21% 41% 17% 1	380
	21st to end	Night	8% 2 19% 44% 26% 1	380
July	1st to 10th	Night	6% 2 8% 52% 31% 1	370
	11th to 20th	Night	6% 17% 48% 29% 1	368
	21st to end	Night	3 2 7% 49% 36% 2	416
August	1st to 10th	Night	3 2 7% 38% 43% 7%	558
	11th to 20th	Night	5% 2 5% 37% 49% 3	564
	21st to end	Night	7% 2 12% 44% 32% 3	760
September	1st to 10th	Night	8% 2 14% 39% 36% 2	760
	11th to 20th	Night	11% 4 10% 33% 37% 6%	760
	21st to end	Night	12% 4 14% 38% 30% 3	760
October	1st to 10th	Night	17% 2 19% 31% 27% 4	760
	11th to 20th	Night	19% 5% 13% 32% 26% 5%	760
	21st to end	Night	26% 6% 20% 28% 17% 4	836
November	1st to 10th	Night	30% 6% 18% 31% 15% 1	780
	11th to 20th	Night	35% 9% 19% 24% 13% 2	800
	21st to end	Night	27% 5% 19% 29% 18% 3	800
December	1st to 10th	Night	31% 6% 13% 29% 17% 4	800
	11th to 20th	Night	36% 8% 18% 23% 15% 1	800
	21st to end	Night	35% 9% 21% 23% 10% 1	880

Page generated at 2025-05-08 06:33:56. Version ac07

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