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 2024-11-02.

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% 8% 3 8% 5% 5% 4 3 5% 6% 38%	101553
	Night	18% 9% 3 8% 5% 4 4 3 5% 5% 35%	97583
Transparency	Day	45% 9% 12% 17% 12% 5%	101296
	Night	49% 9% 12% 16% 11% 4	97429
Seeing	Day	19% 8% 18% 25% 22% 8%	14663
	Night	23% 6% 16% 32% 21% 2	23584

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	34% 14% 6% 13% 7% 5% 4 3 3 3 7%	2539
	11th to 20th	Day	36% 15% 4 11% 5% 4 4 2 3 3 13%	2540
	21st to end	Day	27% 13% 5% 11% 7% 6% 5% 4 4 5% 13%	3086
February	1st to 10th	Day	26% 13% 4 9% 5% 5% 5% 5% 6% 6% 15%	1710
	11th to 20th	Day	26% 11% 5% 12% 7% 4 5% 4 4 4 18%	1665
	21st to end	Day	26% 14% 3 10% 6% 5% 5% 3 4 5% 18%	1488
March	1st to 10th	Day	16% 12% 3 11% 7% 7% 7% 5% 6% 7% 17%	3310
	11th to 20th	Day	17% 9% 3 8% 5% 6% 4 3 5% 5% 35%	3490
	21st to end	Day	20% 12% 5% 11% 7% 7% 6% 4 5% 5% 17%	3903
April	1st to 10th	Day	24% 12% 4 10% 6% 6% 5% 4 5% 5% 19%	2280
	11th to 20th	Day	21% 12% 3 8% 6% 5% 5% 4 5% 6% 25%	2249
	21st to end	Day	18% 10% 4 10% 6% 5% 4 4 6% 7% 25%	2461
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 4 3 5% 5% 34%	4327
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 3 6% 7% 49%	4377
	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	17% 7% 2 6% 6% 4 4 4 5% 7% 38%	1900
	11th to 20th	Day	16% 9% 4 9% 6% 6% 4 4 5% 7% 31%	1900
	21st to end	Day	22% 11% 4 10% 5% 5% 4 3 4 6% 25%	2057
November	1st to 10th	Day	27% 12% 4 11% 6% 5% 5% 4 4 6% 15%	1584
	11th to 20th	Day	27% 11% 5% 10% 7% 6% 5% 3 4 4 18%	1520
	21st to end	Day	25% 12% 4 10% 7% 6% 4 4 4 5% 20%	1520
December	1st to 10th	Day	24% 13% 5% 10% 6% 5% 4 2 4 5% 22%	1520
	11th to 20th	Day	25% 12% 4 11% 7% 7% 6% 4 7% 6% 11%	1928
	21st to end	Day	29% 16% 5% 16% 8% 6% 4 3 3 3 7%	2794
January	1st to 10th	Night	29% 18% 6% 13% 6% 5% 4 3 4 3 10%	4406
	11th to 20th	Night	36% 14% 4 9% 4 3 3 3 3 4 16%	4420
	21st to end	Night	32% 13% 5% 10% 6% 5% 4 3 4 5% 14%	4578
February	1st to 10th	Night	25% 13% 4 9% 6% 6% 5% 4 5% 5% 18%	2470
	11th to 20th	Night	27% 12% 3 9% 5% 4 4 3 4 4 25%	2402
	21st to end	Night	24% 14% 4 8% 6% 4 4 4 5% 6% 21%	1965
March	1st to 10th	Night	15% 12% 4 12% 6% 7% 6% 5% 5% 6% 21%	3562
	11th to 20th	Night	14% 7% 2 6% 5% 5% 4 3 6% 6% 40%	3490
	21st to end	Night	19% 14% 4 10% 7% 7% 6% 4 5% 6% 18%	3750
April	1st to 10th	Night	24% 13% 4 10% 5% 4 4 2 6% 5% 22%	1900
	11th to 20th	Night	19% 11% 3 7% 5% 4 4 4 6% 7% 30%	1879
	21st to end	Night	21% 10% 4 8% 4 3 4 4 5% 7% 29%	1715
May	1st to 10th	Night	19% 8% 3 8% 4 4 3 3 5% 5% 37%	2636
	11th to 20th	Night	9% 5% 2 6% 4 3 4 3 5% 8% 52%	2516
	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	15% 6% 2 6% 4 4 4 3 4 6% 45%	2280
	11th to 20th	Night	16% 6% 2 7% 5% 5% 4 4 5% 6% 41%	2280
	21st to end	Night	21% 9% 3 8% 5% 4 4 3 5% 6% 35%	2539
November	1st to 10th	Night	27% 10% 3 8% 6% 4 5% 3 5% 5% 23%	2513
	11th to 20th	Night	28% 11% 4 9% 5% 4 4 4 4 4 22%	2660
	21st to end	Night	23% 10% 3 9% 7% 5% 5% 3 5% 5% 26%	2660
December	1st to 10th	Night	26% 11% 4 8% 5% 4 4 3 5% 6% 24%	2660
	11th to 20th	Night	26% 12% 4 9% 6% 6% 5% 4 5% 7% 15%	3276
	21st to end	Night	25% 13% 6% 13% 7% 6% 6% 3 4 5% 12%	4862

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% 10% 5% 3 2 1	2539
	11th to 20th	Day	76% 5% 5% 9% 3 2	2540
	21st to end	Day	70% 11% 7% 7% 5%	3086
February	1st to 10th	Day	66% 9% 11% 9% 4	1710
	11th to 20th	Day	67% 10% 9% 8% 4 2	1674
	21st to end	Day	68% 7% 10% 8% 5% 2	1488
March	1st to 10th	Day	58% 13% 14% 12% 3	3310
	11th to 20th	Day	48% 9% 10% 22% 11% 1	3490
	21st to end	Day	65% 13% 11% 7% 4	3903
April	1st to 10th	Day	65% 9% 12% 11% 3	2280
	11th to 20th	Day	58% 10% 11% 11% 7% 3	2252
	21st to end	Day	57% 11% 12% 12% 7% 2	2461
May	1st to 10th	Day	49% 11% 12% 16% 12%	4327
	11th to 20th	Day	31% 11% 19% 27% 12% 1	4380
	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	42% 10% 11% 19% 15% 4	1900
	11th to 20th	Day	50% 9% 15% 13% 12% 2	1900
	21st to end	Day	57% 8% 10% 11% 12% 1	2057
November	1st to 10th	Day	67% 9% 10% 10% 4 1	1584
	11th to 20th	Day	67% 8% 9% 8% 6% 2	1520
	21st to end	Day	63% 10% 7% 8% 11% 1	1520
December	1st to 10th	Day	63% 6% 10% 10% 9% 2	1520
	11th to 20th	Day	65% 12% 12% 9% 2	1928
	21st to end	Day	74% 12% 8% 3 2	2794
January	1st to 10th	Night	76% 9% 7% 4 3 1	4406
	11th to 20th	Night	71% 8% 5% 10% 4 2	4420
	21st to end	Night	70% 9% 7% 7% 5% 1	4578
February	1st to 10th	Night	66% 10% 9% 9% 5% 1	2470
	11th to 20th	Night	61% 8% 13% 10% 6% 2	2404
	21st to end	Night	63% 9% 10% 10% 6% 2	1965
March	1st to 10th	Night	59% 11% 13% 13% 4	3562
	11th to 20th	Night	41% 13% 13% 19% 14% 1	3490
	21st to end	Night	64% 14% 11% 10% 1	3750
April	1st to 10th	Night	62% 9% 13% 11% 5%	1900
	11th to 20th	Night	53% 10% 16% 12% 6% 3	1879
	21st to end	Night	55% 8% 15% 14% 6% 2	1715
May	1st to 10th	Night	46% 13% 12% 19% 9% 1	2636
	11th to 20th	Night	29% 9% 20% 30% 9% 2	2516
	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	40% 7% 10% 22% 17% 4	2280
	11th to 20th	Night	42% 9% 13% 17% 15% 4	2280
	21st to end	Night	50% 9% 9% 13% 16% 3	2539
November	1st to 10th	Night	60% 10% 10% 13% 7%	2513
	11th to 20th	Night	64% 9% 9% 8% 8% 2	2660
	21st to end	Night	57% 9% 9% 10% 12% 3	2660
December	1st to 10th	Night	59% 8% 10% 10% 10% 2	2660
	11th to 20th	Night	64% 11% 12% 9% 4	3276
	21st to end	Night	67% 13% 11% 6% 2 1	4862

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% 11% 16% 17% 12% 3	180
	11th to 20th	Day	40% 7% 17% 17% 12% 7%	180
	21st to end	Day	31% 7% 17% 23% 14% 8%	373
February	1st to 10th	Day	32% 10% 19% 16% 18% 4	370
	11th to 20th	Day	33% 9% 24% 18% 12% 4	365
	21st to end	Day	34% 13% 18% 21% 12% 2	343
March	1st to 10th	Day	29% 12% 23% 22% 12% 2	460
	11th to 20th	Day	26% 13% 18% 22% 17% 5%	460
	21st to end	Day	28% 13% 24% 19% 14% 2	506
April	1st to 10th	Day	27% 15% 20% 20% 12% 5%	460
	11th to 20th	Day	27% 12% 25% 21% 9% 6%	452
	21st to end	Day	21% 13% 23% 23% 17% 3	460
May	1st to 10th	Day	19% 9% 21% 26% 19% 6%	463
	11th to 20th	Day	21% 8% 16% 25% 21% 9%	488
	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% 23% 19% 13% 5%	226
	11th to 20th	Day	28% 9% 22% 15% 17% 9%	180
	21st to end	Day	28% 11% 19% 18% 16% 8%	180
December	1st to 10th	Day	38% 5% 15% 19% 16% 7%	180
	11th to 20th	Day	37% 9% 22% 19% 10% 3	180
	21st to end	Day	37% 13% 18% 16% 13% 3	198
January	1st to 10th	Night	36% 11% 17% 19% 15% 2	760
	11th to 20th	Night	36% 8% 14% 23% 17% 2	760
	21st to end	Night	29% 6% 16% 30% 17% 3	836
February	1st to 10th	Night	30% 8% 17% 28% 16% 2	760
	11th to 20th	Night	32% 6% 19% 26% 17% 1	744
	21st to end	Night	32% 9% 18% 31% 11%	628
March	1st to 10th	Night	28% 9% 20% 28% 14% 1	760
	11th to 20th	Night	25% 7% 19% 32% 15% 1	760
	21st to end	Night	28% 7% 24% 26% 14% 1	836
April	1st to 10th	Night	29% 8% 18% 27% 18% 1	760
	11th to 20th	Night	24% 7% 23% 28% 18% 1	751
	21st to end	Night	24% 6% 21% 32% 17% 1	575
May	1st to 10th	Night	17% 5% 20% 39% 18% 1	437
	11th to 20th	Night	15% 4 17% 37% 25% 2	374
	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% 19% 28% 17% 4	836
November	1st to 10th	Night	31% 6% 17% 31% 14% 1	744
	11th to 20th	Night	34% 9% 19% 24% 13% 2	760
	21st to end	Night	27% 6% 18% 30% 17% 3	760
December	1st to 10th	Night	33% 6% 14% 29% 16% 3	760
	11th to 20th	Night	36% 7% 18% 23% 15% 1	760
	21st to end	Night	35% 8% 21% 24% 11% 1	836

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