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 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	14% 8% 3 7% 5% 4 4 4 5% 6% 41%	158539
	Night	17% 9% 3 8% 5% 4 4 3 5% 6% 36%	149931
Transparency	Day	42% 7% 13% 20% 13% 4	153321
	Night	47% 8% 12% 18% 11% 3	146148
Seeing	Day	19% 8% 18% 25% 22% 9%	16999
	Night	23% 6% 17% 32% 21% 2	25878

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	31% 15% 6% 13% 7% 6% 5% 3 4 3 7%	4722
	11th to 20th	Day	20% 9% 2 9% 7% 5% 5% 4 5% 5% 29%	4740
	21st to end	Day	20% 9% 4 9% 6% 6% 6% 4 5% 5% 26%	5741
February	1st to 10th	Day	25% 13% 4 9% 6% 5% 6% 5% 6% 7% 14%	1890
	11th to 20th	Day	26% 11% 5% 12% 7% 4 5% 4 4 4 18%	1845
	21st to end	Day	26% 14% 3 10% 6% 5% 5% 3 4 5% 18%	1640
March	1st to 10th	Day	15% 12% 3 11% 7% 7% 7% 5% 7% 7% 19%	4860
	11th to 20th	Day	23% 13% 4 9% 5% 5% 3 3 5% 5% 25%	5110
	21st to end	Day	19% 12% 5% 11% 8% 7% 7% 5% 6% 6% 14%	5713
April	1st to 10th	Day	23% 12% 4 10% 6% 6% 5% 4 6% 6% 19%	2520
	11th to 20th	Day	19% 11% 3 8% 6% 5% 5% 4 5% 7% 26%	2489
	21st to end	Day	17% 9% 3 10% 6% 5% 5% 4 6% 7% 27%	2721
May	1st to 10th	Day	11% 6% 3 6% 5% 4 4 4 5% 7% 45%	8024
	11th to 20th	Day	10% 7% 3 8% 5% 6% 6% 4 7% 8% 36%	8160
	21st to end	Day	13% 6% 2 6% 5% 5% 6% 4 7% 8% 38%	8992
June	1st to 10th	Day	18% 8% 3 6% 6% 4 4 3 5% 7% 35%	2940
	11th to 20th	Day	15% 7% 3 8% 5% 5% 5% 5% 7% 8% 32%	2940
	21st to end	Day	8% 6% 2 5% 4 4 4 4 5% 6% 52%	2940
July	1st to 10th	Day	3 2 1 2 2 2 3 2 4 5% 72%	8219
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 78%	8220
	21st to end	Day	3 2 1 2 2 2 2 2 4 5% 75%	8922
August	1st to 10th	Day	2 3 1 3 2 3 3 3 4 5% 71%	7552
	11th to 20th	Day	5% 4 1 5% 3 3 4 4 6% 8% 59%	7563
	21st to end	Day	6% 5% 2 4 3 3 4 4 6% 9% 55%	7974
September	1st to 10th	Day	6% 3 2 4 3 4 4 3 5% 7% 59%	2520
	11th to 20th	Day	9% 7% 4 6% 4 4 5% 4 6% 6% 45%	2433
	21st to end	Day	13% 5% 3 6% 5% 4 3 3 5% 6% 46%	2105
October	1st to 10th	Day	14% 6% 2 6% 5% 4 4 3 5% 6% 44%	3280
	11th to 20th	Day	15% 7% 3 8% 6% 6% 5% 5% 7% 8% 30%	3261
	21st to end	Day	21% 11% 4 10% 6% 6% 5% 4 5% 8% 20%	3499
November	1st to 10th	Day	26% 13% 4 11% 6% 5% 5% 4 4 6% 15%	1744
	11th to 20th	Day	27% 11% 5% 10% 7% 6% 5% 4 4 4 16%	1680
	21st to end	Day	24% 11% 4 11% 7% 6% 5% 4 4 5% 19%	1680
December	1st to 10th	Day	20% 9% 3 9% 6% 7% 5% 4 5% 6% 25%	2700
	11th to 20th	Day	26% 14% 5% 12% 7% 6% 6% 4 6% 5% 8%	3108
	21st to end	Day	31% 17% 5% 14% 7% 6% 4 3 3 3 7%	4092
January	1st to 10th	Night	29% 15% 6% 13% 6% 6% 5% 3 4 4 10%	8172
	11th to 20th	Night	21% 9% 3 8% 7% 5% 5% 3 4 6% 29%	8220
	21st to end	Night	22% 10% 4 9% 5% 4 4 3 5% 5% 28%	8454
February	1st to 10th	Night	24% 14% 4 9% 6% 6% 5% 4 6% 5% 18%	2730
	11th to 20th	Night	27% 12% 4 9% 5% 5% 4 3 4 4 24%	2662
	21st to end	Night	24% 14% 4 8% 6% 4 4 4 5% 6% 21%	2165
March	1st to 10th	Night	16% 11% 4 11% 7% 7% 7% 5% 6% 6% 20%	5239
	11th to 20th	Night	19% 11% 4 9% 5% 5% 5% 3 5% 5% 29%	5110
	21st to end	Night	20% 14% 4 10% 7% 7% 6% 4 6% 7% 15%	5504
April	1st to 10th	Night	22% 13% 4 10% 5% 5% 4 2 6% 6% 22%	2100
	11th to 20th	Night	19% 10% 3 8% 5% 4 5% 4 5% 7% 31%	2079
	21st to end	Night	20% 10% 4 8% 5% 3 4 4 5% 7% 30%	1895
May	1st to 10th	Night	14% 5% 2 6% 4 3 3 4 6% 7% 47%	4903
	11th to 20th	Night	12% 7% 3 9% 5% 5% 5% 4 5% 7% 39%	4700
	21st to end	Night	11% 7% 3 7% 4 5% 5% 4 7% 9% 39%	5181
June	1st to 10th	Night	17% 7% 3 7% 5% 5% 5% 3 5% 5% 38%	1680
	11th to 20th	Night	13% 9% 3 7% 5% 4 4 4 5% 6% 40%	1680
	21st to end	Night	7% 6% 2 6% 4 3 4 3 4 5% 57%	1680
July	1st to 10th	Night	4 3 1 3 2 2 3 2 4 4 72%	4740
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 3 79%	4740
	21st to end	Night	3 2 1 3 2 2 3 2 4 5% 73%	5153
August	1st to 10th	Night	3 3 1 3 2 2 3 3 4 6% 70%	5266
	11th to 20th	Night	8% 5% 2 5% 4 3 4 3 4 6% 56%	5292
	21st to end	Night	6% 4 2 5% 3 3 3 3 4 6% 59%	6263
September	1st to 10th	Night	7% 4 1 5% 2 2 3 2 4 6% 64%	2100
	11th to 20th	Night	9% 5% 2 7% 4 4 5% 3 5% 6% 49%	2030
	21st to end	Night	10% 5% 2 5% 3 3 3 3 6% 7% 52%	2295
October	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 5% 7% 48%	3920
	11th to 20th	Night	15% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	3897
	21st to end	Night	20% 9% 3 10% 7% 5% 5% 4 6% 6% 25%	4308
November	1st to 10th	Night	26% 10% 3 9% 6% 4 5% 3 5% 5% 22%	2771
	11th to 20th	Night	29% 12% 4 9% 5% 4 4 4 4 4 20%	2940
	21st to end	Night	23% 10% 3 10% 7% 5% 5% 3 5% 5% 25%	2940
December	1st to 10th	Night	18% 8% 3 8% 6% 6% 5% 4 8% 7% 27%	4700
	11th to 20th	Night	31% 14% 5% 11% 6% 5% 5% 3 4 5% 11%	5316
	21st to end	Night	28% 13% 5% 12% 7% 6% 5% 3 4 5% 11%	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	80% 7% 5% 4 2	4723
	11th to 20th	Day	56% 5% 7% 13% 13% 6%	4740
	21st to end	Day	57% 7% 6% 12% 15% 2	5741
February	1st to 10th	Day	66% 9% 11% 10% 4	1890
	11th to 20th	Day	67% 10% 9% 8% 5% 2	1854
	21st to end	Day	68% 7% 10% 8% 6% 2	1640
March	1st to 10th	Day	57% 10% 14% 15% 4	4860
	11th to 20th	Day	60% 7% 8% 17% 8%	5110
	21st to end	Day	65% 11% 12% 9% 3	5713
April	1st to 10th	Day	63% 9% 12% 13% 3	2520
	11th to 20th	Day	56% 9% 11% 13% 8% 2	2492
	21st to end	Day	54% 11% 12% 14% 8% 2	2721
May	1st to 10th	Day	37% 8% 12% 28% 15%	8024
	11th to 20th	Day	40% 9% 20% 22% 7%	8163
	21st to end	Day	39% 11% 22% 22% 6%	8994
June	1st to 10th	Day	48% 8% 16% 20% 7% 1	2940
	11th to 20th	Day	47% 10% 17% 17% 7% 1	2940
	21st to end	Day	31% 8% 16% 30% 11% 4	2940
July	1st to 10th	Day	14% 4 13% 34% 19% 17%	8151
	11th to 20th	Day	13% 2 6% 19% 40% 19%	8145
	21st to end	Day	13% 3 15% 37% 28% 4	8723
August	1st to 10th	Day	14% 4 9% 27% 30% 17%	5980
	11th to 20th	Day	21% 5% 19% 37% 15% 3	5962
	21st to end	Day	24% 5% 15% 33% 18% 5%	6253
September	1st to 10th	Day	23% 7% 13% 28% 19% 11%	2520
	11th to 20th	Day	38% 8% 14% 20% 14% 7%	2433
	21st to end	Day	37% 8% 14% 20% 16% 6%	2105
October	1st to 10th	Day	38% 7% 8% 23% 21% 3	3280
	11th to 20th	Day	48% 8% 18% 14% 11% 1	3261
	21st to end	Day	58% 7% 10% 15% 9% 1	3499
November	1st to 10th	Day	67% 9% 10% 10% 4	1744
	11th to 20th	Day	68% 8% 8% 8% 6% 2	1680
	21st to end	Day	63% 10% 8% 8% 10% 1	1680
December	1st to 10th	Day	59% 5% 11% 13% 11% 1	2700
	11th to 20th	Day	72% 9% 10% 7% 1	3108
	21st to end	Day	76% 10% 7% 5% 2	4092
January	1st to 10th	Night	75% 8% 8% 6% 3 1	8172
	11th to 20th	Night	56% 6% 6% 14% 12% 6%	8220
	21st to end	Night	56% 6% 6% 13% 15% 4	8454
February	1st to 10th	Night	65% 10% 9% 9% 5% 1	2730
	11th to 20th	Night	62% 7% 12% 10% 6% 2	2664
	21st to end	Night	62% 9% 10% 11% 6% 2	2165
March	1st to 10th	Night	59% 9% 13% 13% 6%	5239
	11th to 20th	Night	54% 10% 10% 15% 10% 1	5110
	21st to end	Night	64% 12% 14% 9% 1	5504
April	1st to 10th	Night	61% 9% 14% 12% 4	2100
	11th to 20th	Night	53% 9% 15% 13% 7% 3	2079
	21st to end	Night	53% 8% 14% 16% 7% 2	1895
May	1st to 10th	Night	34% 8% 12% 33% 11% 1	4901
	11th to 20th	Night	43% 8% 19% 24% 5% 1	4700
	21st to end	Night	38% 13% 24% 23% 3	5182
June	1st to 10th	Night	46% 8% 17% 23% 6% 1	1680
	11th to 20th	Night	44% 8% 17% 23% 8% 1	1680
	21st to end	Night	30% 6% 16% 31% 12% 4	1680
July	1st to 10th	Night	17% 3 10% 33% 22% 15%	4700
	11th to 20th	Night	13% 2 8% 17% 44% 16%	4692
	21st to end	Night	13% 3 20% 34% 26% 4	5040
August	1st to 10th	Night	11% 3 8% 32% 32% 15%	4161
	11th to 20th	Night	25% 6% 20% 35% 11% 3	4169
	21st to end	Night	23% 5% 16% 34% 16% 5%	4908
September	1st to 10th	Night	22% 6% 14% 28% 19% 10%	2100
	11th to 20th	Night	34% 8% 14% 22% 14% 9%	2030
	21st to end	Night	31% 8% 16% 21% 16% 8%	2295
October	1st to 10th	Night	34% 6% 9% 28% 20% 2	3920
	11th to 20th	Night	42% 7% 19% 18% 11% 2	3897
	21st to end	Night	55% 8% 11% 14% 10% 2	4308
November	1st to 10th	Night	61% 9% 10% 13% 7%	2771
	11th to 20th	Night	66% 9% 8% 8% 7% 2	2940
	21st to end	Night	59% 9% 9% 10% 11% 3	2940
December	1st to 10th	Night	53% 6% 11% 18% 11% 1	4700
	11th to 20th	Night	73% 8% 9% 7% 3	5316
	21st to end	Night	69% 11% 12% 6% 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	41% 10% 17% 17% 12% 2	220
	11th to 20th	Day	33% 6% 16% 21% 16% 8%	220
	21st to end	Day	28% 7% 18% 23% 15% 9%	436
February	1st to 10th	Day	31% 10% 19% 17% 19% 4	430
	11th to 20th	Day	33% 9% 25% 18% 11% 4	425
	21st to end	Day	34% 12% 17% 22% 13% 2	399
March	1st to 10th	Day	29% 12% 24% 21% 11% 3	540
	11th to 20th	Day	29% 13% 19% 20% 15% 4	540
	21st to end	Day	28% 12% 24% 21% 13% 2	594
April	1st to 10th	Day	26% 14% 19% 21% 14% 7%	540
	11th to 20th	Day	25% 11% 24% 22% 12% 7%	532
	21st to end	Day	19% 11% 22% 24% 18% 5%	540
May	1st to 10th	Day	17% 8% 21% 27% 21% 7%	543
	11th to 20th	Day	20% 10% 18% 24% 20% 8%	568
	21st to end	Day	14% 6% 16% 26% 26% 11%	617
June	1st to 10th	Day	18% 7% 17% 26% 23% 9%	570
	11th to 20th	Day	15% 8% 20% 31% 21% 5%	570
	21st to end	Day	7% 6% 13% 32% 33% 9%	570
July	1st to 10th	Day	5% 3 14% 31% 33% 14%	566
	11th to 20th	Day	4 3 15% 37% 29% 13%	564
	21st to end	Day	4 2 10% 30% 39% 16%	619
August	1st to 10th	Day	3 3 9% 29% 39% 17%	567
	11th to 20th	Day	4 2 8% 31% 33% 22%	557
	21st to end	Day	6% 3 15% 32% 30% 14%	627
September	1st to 10th	Day	7% 3 18% 27% 31% 14%	570
	11th to 20th	Day	10% 6% 16% 27% 29% 12%	543
	21st to end	Day	15% 6% 19% 29% 24% 8%	530
October	1st to 10th	Day	17% 8% 18% 26% 21% 10%	530
	11th to 20th	Day	19% 9% 17% 23% 22% 9%	530
	21st to end	Day	27% 11% 24% 20% 11% 7%	548
November	1st to 10th	Day	31% 11% 22% 17% 13% 6%	272
	11th to 20th	Day	30% 10% 20% 16% 15% 7%	220
	21st to end	Day	28% 10% 18% 18% 18% 7%	220
December	1st to 10th	Day	37% 5% 15% 18% 15% 10%	220
	11th to 20th	Day	39% 10% 21% 18% 9% 3	220
	21st to end	Day	36% 14% 19% 16% 11% 3	242
January	1st to 10th	Night	37% 11% 18% 20% 14% 2	840
	11th to 20th	Night	33% 8% 15% 24% 18% 3	840
	21st to end	Night	27% 6% 16% 31% 18% 3	924
February	1st to 10th	Night	28% 8% 17% 30% 16% 2	840
	11th to 20th	Night	32% 6% 20% 25% 16% 1	824
	21st to end	Night	32% 8% 17% 32% 11%	692
March	1st to 10th	Night	28% 9% 20% 29% 13% 1	840
	11th to 20th	Night	27% 7% 20% 31% 14% 1	840
	21st to end	Night	27% 7% 25% 27% 13% 1	924
April	1st to 10th	Night	27% 8% 17% 28% 19% 1	840
	11th to 20th	Night	23% 7% 22% 30% 17% 1	831
	21st to end	Night	23% 6% 19% 34% 17% 1	635
May	1st to 10th	Night	16% 5% 18% 40% 19% 1	483
	11th to 20th	Night	16% 4 18% 38% 23% 2	414
	21st to end	Night	18% 4 16% 36% 24% 2	455
June	1st to 10th	Night	16% 5% 17% 37% 23% 1	420
	11th to 20th	Night	17% 3 20% 43% 17% 1	420
	21st to end	Night	8% 3 18% 45% 26% 1	420
July	1st to 10th	Night	6% 3 7% 52% 31% 1	410
	11th to 20th	Night	5% 17% 48% 28% 1	408
	21st to end	Night	2 2 8% 49% 37% 2	460
August	1st to 10th	Night	4 2 7% 38% 42% 7%	618
	11th to 20th	Night	6% 2 5% 37% 48% 3	624
	21st to end	Night	7% 2 12% 46% 31% 3	840
September	1st to 10th	Night	8% 2 13% 39% 36% 2	840
	11th to 20th	Night	11% 4 10% 33% 36% 5%	812
	21st to end	Night	11% 4 14% 38% 30% 3	800
October	1st to 10th	Night	17% 3 19% 31% 27% 4	800
	11th to 20th	Night	19% 5% 14% 32% 25% 5%	800
	21st to end	Night	25% 6% 20% 28% 17% 4	880
November	1st to 10th	Night	31% 6% 18% 30% 15% 1	820
	11th to 20th	Night	35% 9% 19% 24% 13% 2	840
	21st to end	Night	27% 5% 18% 30% 17% 3	840
December	1st to 10th	Night	32% 6% 13% 28% 17% 3	840
	11th to 20th	Night	37% 8% 18% 23% 15% 1	840
	21st to end	Night	34% 9% 21% 23% 11% 1	924

Page generated at 2026-09-11 01:11:51. Version ac07

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