Eugene
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eugene clear sky chart from 2005-11-06 to 2024-11-03.

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	17% 8% 3 6% 4 4 4 3 5% 6% 40%	101505
	Night	20% 9% 3 7% 4 4 4 3 4 5% 37%	97663
Transparency	Day	45% 5% 12% 19% 14% 6%	101252
	Night	50% 5% 12% 18% 11% 4	97505
Seeing	Day	21% 9% 22% 27% 16% 5%	14783
	Night	24% 6% 13% 31% 23% 3	23732

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% 15% 4 7% 6% 6% 6% 3 5% 5% 9%	2539
	11th to 20th	Day	41% 14% 4 9% 5% 4 4 2 3 4 11%	2579
	21st to end	Day	31% 12% 4 9% 6% 5% 5% 4 5% 6% 13%	3146
February	1st to 10th	Day	28% 12% 4 8% 6% 5% 6% 5% 6% 6% 16%	1710
	11th to 20th	Day	28% 13% 4 8% 6% 5% 5% 3 6% 4 19%	1665
	21st to end	Day	29% 15% 4 8% 6% 4 4 3 4 5% 18%	1494
March	1st to 10th	Day	19% 13% 5% 10% 7% 5% 5% 4 6% 6% 21%	3346
	11th to 20th	Day	19% 10% 3 7% 5% 4 4 2 4 5% 38%	3490
	21st to end	Day	25% 11% 4 10% 7% 5% 5% 4 5% 6% 17%	3874
April	1st to 10th	Day	25% 15% 4 10% 6% 5% 5% 3 4 4 20%	2280
	11th to 20th	Day	24% 12% 4 8% 6% 4 5% 3 4 5% 26%	2249
	21st to end	Day	22% 9% 3 8% 5% 4 4 4 6% 7% 28%	2446
May	1st to 10th	Day	19% 9% 3 7% 5% 5% 4 4 5% 6% 34%	4251
	11th to 20th	Day	11% 5% 1 5% 3 3 3 3 5% 7% 53%	4377
	21st to end	Day	16% 7% 2 8% 6% 6% 6% 5% 6% 7% 32%	4813
June	1st to 10th	Day	21% 9% 3 7% 5% 4 3 3 6% 6% 34%	2660
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 4 5% 8% 36%	2660
	21st to end	Day	9% 4 2 4 3 3 3 3 4 6% 59%	2660
July	1st to 10th	Day	3 2 1 2 2 1 2 2 2 3 80%	4420
	11th to 20th	Day	4 3 1 2 2 2 2 2 2 4 77%	4420
	21st to end	Day	3 2 1 2 2 2 2 2 3 4 78%	4680
August	1st to 10th	Day	2 3 1 3 2 3 3 2 4 5% 72%	4091
	11th to 20th	Day	4 4 1 4 3 3 3 3 4 6% 64%	4026
	21st to end	Day	7% 5% 1 4 3 3 3 2 4 6% 63%	4283
September	1st to 10th	Day	6% 3 1 3 2 3 2 2 4 5% 70%	2280
	11th to 20th	Day	10% 7% 2 6% 4 3 4 3 5% 5% 49%	2259
	21st to end	Day	13% 6% 2 6% 4 4 4 3 4 6% 49%	2009
October	1st to 10th	Day	15% 7% 2 6% 3 4 4 3 4 7% 43%	1900
	11th to 20th	Day	19% 7% 2 8% 5% 5% 5% 4 5% 7% 33%	1900
	21st to end	Day	23% 8% 3 8% 5% 5% 5% 4 6% 7% 28%	2090
November	1st to 10th	Day	31% 9% 3 9% 5% 5% 4 3 6% 6% 19%	1626
	11th to 20th	Day	28% 10% 4 9% 5% 5% 4 4 6% 7% 18%	1520
	21st to end	Day	27% 10% 4 8% 5% 4 5% 4 7% 7% 20%	1520
December	1st to 10th	Day	26% 9% 3 8% 6% 6% 4 4 5% 7% 23%	1520
	11th to 20th	Day	26% 13% 4 11% 7% 6% 5% 4 6% 6% 11%	1928
	21st to end	Day	31% 15% 4 11% 6% 6% 6% 4 5% 5% 7%	2794
January	1st to 10th	Night	33% 18% 5% 11% 6% 5% 4 3 3 3 10%	4406
	11th to 20th	Night	39% 17% 4 8% 5% 3 3 3 3 3 12%	4380
	21st to end	Night	37% 14% 4 8% 4 4 3 3 3 4 15%	4521
February	1st to 10th	Night	28% 14% 4 9% 5% 5% 4 3 4 6% 18%	2470
	11th to 20th	Night	27% 12% 3 6% 5% 5% 4 3 5% 6% 24%	2402
	21st to end	Night	27% 13% 4 7% 5% 4 5% 3 5% 6% 22%	1960
March	1st to 10th	Night	19% 17% 4 10% 5% 5% 5% 3 5% 6% 20%	3525
	11th to 20th	Night	16% 10% 3 7% 4 4 3 4 4 5% 40%	3490
	21st to end	Night	23% 15% 5% 10% 6% 6% 5% 3 4 5% 17%	3777
April	1st to 10th	Night	26% 14% 4 8% 4 4 5% 3 4 4 24%	1900
	11th to 20th	Night	21% 12% 3 8% 4 4 4 3 5% 6% 30%	1879
	21st to end	Night	22% 9% 3 6% 5% 5% 5% 4 4 7% 31%	1729
May	1st to 10th	Night	22% 10% 3 6% 4 3 3 3 4 5% 37%	2712
	11th to 20th	Night	9% 6% 2 5% 3 3 3 3 4 5% 56%	2516
	21st to end	Night	17% 6% 3 6% 4 3 4 4 6% 7% 40%	2762
June	1st to 10th	Night	18% 8% 3 4 5% 4 4 5% 5% 6% 39%	1520
	11th to 20th	Night	13% 8% 2 5% 3 4 3 4 5% 8% 46%	1520
	21st to end	Night	8% 4 2 3 2 2 3 2 5% 5% 65%	1520
July	1st to 10th	Night	3 2 1 2 1 1 1 1 2 2 84%	2540
	11th to 20th	Night	2 2 1 2 2 1 2 2 2 3 80%	2540
	21st to end	Night	3 2 1 2 1 1 1 1 2 3 82%	2872
August	1st to 10th	Night	2 2 1 2 2 2 3 2 3 5% 76%	2848
	11th to 20th	Night	3 3 1 4 2 3 3 3 4 6% 67%	2812
	21st to end	Night	6% 4 2 3 3 2 3 2 3 4 69%	3392
September	1st to 10th	Night	6% 2 1 2 2 2 3 2 4 4 72%	1900
	11th to 20th	Night	10% 4 2 4 4 4 4 2 5% 6% 56%	1918
	21st to end	Night	11% 5% 2 5% 3 3 4 3 5% 7% 52%	2171
October	1st to 10th	Night	14% 6% 2 6% 3 3 3 3 5% 5% 49%	2280
	11th to 20th	Night	17% 6% 2 6% 3 4 4 5% 5% 6% 42%	2280
	21st to end	Night	23% 10% 2 6% 4 4 3 3 5% 6% 34%	2508
November	1st to 10th	Night	28% 9% 3 8% 4 6% 5% 4 5% 5% 23%	2495
	11th to 20th	Night	30% 10% 4 8% 4 4 4 4 4 5% 21%	2660
	21st to end	Night	22% 11% 3 7% 5% 5% 5% 4 5% 6% 28%	2660
December	1st to 10th	Night	27% 9% 3 7% 5% 4 4 4 5% 6% 26%	2660
	11th to 20th	Night	28% 11% 5% 10% 6% 6% 6% 3 5% 5% 16%	3276
	21st to end	Night	28% 13% 5% 13% 7% 5% 5% 3 5% 5% 11%	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	75% 4 13% 5% 2 1	2539
	11th to 20th	Day	77% 4 6% 6% 4 2	2579
	21st to end	Day	69% 5% 11% 9% 5% 1	3146
February	1st to 10th	Day	66% 6% 12% 10% 6%	1710
	11th to 20th	Day	66% 6% 12% 10% 4 2	1674
	21st to end	Day	69% 4 10% 10% 6% 2	1494
March	1st to 10th	Day	62% 5% 13% 17% 4	3346
	11th to 20th	Day	48% 6% 11% 23% 11% 1	3490
	21st to end	Day	67% 6% 14% 10% 3	3874
April	1st to 10th	Day	68% 5% 11% 11% 4	2280
	11th to 20th	Day	62% 6% 11% 13% 6% 3	2252
	21st to end	Day	55% 7% 14% 15% 7% 1	2446
May	1st to 10th	Day	51% 6% 13% 20% 9%	4251
	11th to 20th	Day	30% 5% 15% 34% 15% 1	4380
	21st to end	Day	48% 8% 24% 18% 2	4814
June	1st to 10th	Day	51% 6% 15% 22% 6%	2660
	11th to 20th	Day	46% 5% 20% 21% 7%	2660
	21st to end	Day	28% 4 16% 33% 16% 3	2660
July	1st to 10th	Day	12% 2 7% 17% 26% 36%	4351
	11th to 20th	Day	14% 2 5% 17% 33% 29%	4345
	21st to end	Day	12% 3 6% 27% 40% 12%	4532
August	1st to 10th	Day	16% 3 9% 27% 33% 12%	4076
	11th to 20th	Day	22% 4 12% 39% 20% 4	4065
	21st to end	Day	23% 4 13% 25% 26% 8%	4282
September	1st to 10th	Day	19% 3 9% 32% 24% 13%	2280
	11th to 20th	Day	35% 5% 12% 25% 16% 7%	2259
	21st to end	Day	36% 6% 12% 23% 17% 6%	2009
October	1st to 10th	Day	41% 6% 10% 18% 18% 6%	1900
	11th to 20th	Day	48% 6% 13% 18% 13% 3	1900
	21st to end	Day	53% 7% 11% 14% 13% 2	2090
November	1st to 10th	Day	65% 4 12% 13% 5%	1626
	11th to 20th	Day	63% 5% 12% 11% 6% 2	1520
	21st to end	Day	62% 5% 11% 7% 13% 2	1520
December	1st to 10th	Day	60% 4 11% 12% 11% 1	1520
	11th to 20th	Day	70% 5% 11% 10% 2	1928
	21st to end	Day	76% 4 13% 5% 2 1	2794
January	1st to 10th	Night	79% 4 8% 4 3 1	4406
	11th to 20th	Night	76% 6% 5% 7% 4 2	4380
	21st to end	Night	73% 4 7% 10% 5% 1	4521
February	1st to 10th	Night	68% 5% 9% 12% 4 1	2470
	11th to 20th	Night	62% 5% 13% 12% 5% 2	2404
	21st to end	Night	62% 5% 12% 12% 6% 2	1960
March	1st to 10th	Night	63% 6% 15% 12% 3	3525
	11th to 20th	Night	46% 5% 16% 23% 9% 1	3490
	21st to end	Night	69% 6% 14% 10% 1	3777
April	1st to 10th	Night	65% 5% 12% 13% 5%	1900
	11th to 20th	Night	55% 6% 16% 14% 5% 3	1879
	21st to end	Night	54% 8% 15% 16% 5% 3	1729
May	1st to 10th	Night	50% 7% 14% 20% 9% 1	2712
	11th to 20th	Night	31% 7% 11% 39% 11% 1	2516
	21st to end	Night	42% 9% 29% 17% 2	2762
June	1st to 10th	Night	45% 8% 14% 28% 4	1520
	11th to 20th	Night	37% 6% 22% 27% 8% 1	1520
	21st to end	Night	23% 5% 18% 36% 15% 3	1520
July	1st to 10th	Night	10% 2 7% 20% 26% 35%	2500
	11th to 20th	Night	13% 2 5% 19% 33% 28%	2492
	21st to end	Night	11% 2 9% 28% 42% 8%	2782
August	1st to 10th	Night	12% 3 9% 35% 31% 10%	2839
	11th to 20th	Night	19% 4 18% 36% 19% 4	2839
	21st to end	Night	21% 3 11% 29% 29% 6%	3392
September	1st to 10th	Night	17% 4 9% 32% 26% 13%	1900
	11th to 20th	Night	30% 4 14% 29% 15% 8%	1918
	21st to end	Night	32% 5% 13% 24% 17% 8%	2171
October	1st to 10th	Night	37% 5% 11% 22% 20% 6%	2280
	11th to 20th	Night	42% 6% 15% 20% 14% 3	2280
	21st to end	Night	51% 6% 10% 14% 15% 4	2508
November	1st to 10th	Night	61% 5% 11% 14% 8%	2495
	11th to 20th	Night	65% 6% 10% 11% 7% 2	2660
	21st to end	Night	57% 5% 10% 12% 11% 5%	2660
December	1st to 10th	Night	58% 4 12% 14% 10% 1	2660
	11th to 20th	Night	70% 5% 10% 10% 4	3276
	21st to end	Night	73% 5% 12% 8% 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	48% 11% 14% 13% 12% 2	180
	11th to 20th	Day	36% 11% 14% 21% 15% 3	206
	21st to end	Day	30% 10% 20% 20% 16% 4	407
February	1st to 10th	Day	33% 9% 19% 24% 12% 3	370
	11th to 20th	Day	35% 9% 26% 18% 10% 2	365
	21st to end	Day	35% 15% 17% 23% 9% 2	346
March	1st to 10th	Day	34% 13% 24% 19% 9% 1	460
	11th to 20th	Day	28% 10% 24% 24% 11% 3	460
	21st to end	Day	31% 15% 25% 18% 9% 1	506
April	1st to 10th	Day	30% 16% 19% 21% 12% 3	460
	11th to 20th	Day	31% 14% 24% 17% 10% 5%	452
	21st to end	Day	29% 13% 22% 23% 11% 3	460
May	1st to 10th	Day	21% 14% 24% 26% 13% 4	463
	11th to 20th	Day	26% 9% 16% 30% 15% 4	488
	21st to end	Day	19% 12% 21% 27% 17% 5%	529
June	1st to 10th	Day	21% 10% 20% 28% 17% 4	490
	11th to 20th	Day	17% 14% 28% 27% 12% 2	490
	21st to end	Day	8% 4 24% 40% 18% 5%	490
July	1st to 10th	Day	7% 5% 23% 40% 21% 4	486
	11th to 20th	Day	4 5% 29% 40% 17% 6%	484
	21st to end	Day	2 3 25% 40% 24% 5%	531
August	1st to 10th	Day	4 2 21% 42% 25% 7%	487
	11th to 20th	Day	3 3 18% 40% 28% 9%	477
	21st to end	Day	6% 6% 26% 33% 23% 6%	539
September	1st to 10th	Day	7% 4 25% 34% 23% 8%	490
	11th to 20th	Day	15% 7% 22% 31% 22% 5%	490
	21st to end	Day	16% 8% 24% 28% 17% 6%	490
October	1st to 10th	Day	17% 8% 24% 24% 20% 8%	490
	11th to 20th	Day	20% 9% 16% 28% 19% 8%	490
	21st to end	Day	25% 14% 21% 21% 15% 4	539
November	1st to 10th	Day	28% 12% 20% 23% 13% 4	250
	11th to 20th	Day	28% 11% 19% 19% 14% 8%	180
	21st to end	Day	33% 9% 14% 20% 19% 4	180
December	1st to 10th	Day	32% 11% 17% 19% 13% 8%	180
	11th to 20th	Day	37% 11% 16% 20% 13% 3	180
	21st to end	Day	37% 11% 17% 19% 16% 1	198
January	1st to 10th	Night	39% 7% 16% 22% 13% 3	760
	11th to 20th	Night	35% 7% 13% 23% 17% 4	760
	21st to end	Night	32% 5% 13% 29% 19% 3	836
February	1st to 10th	Night	34% 6% 11% 29% 18% 1	760
	11th to 20th	Night	32% 6% 13% 30% 18% 1	744
	21st to end	Night	31% 12% 14% 28% 15%	628
March	1st to 10th	Night	32% 9% 13% 31% 15% 1	760
	11th to 20th	Night	24% 7% 16% 32% 19% 1	760
	21st to end	Night	31% 9% 15% 28% 16% 1	836
April	1st to 10th	Night	32% 8% 15% 25% 19% 1	760
	11th to 20th	Night	26% 8% 17% 28% 20% 1	751
	21st to end	Night	26% 5% 15% 30% 22% 2	589
May	1st to 10th	Night	19% 6% 19% 31% 22% 2	487
	11th to 20th	Night	20% 2 11% 35% 29% 3	374
	21st to end	Night	20% 3 13% 34% 28% 2	411
June	1st to 10th	Night	21% 4 12% 38% 24% 2	380
	11th to 20th	Night	17% 3 22% 34% 22% 2	380
	21st to end	Night	11% 2 12% 45% 30% 1	380
July	1st to 10th	Night	6% 2 13% 45% 34% 1	370
	11th to 20th	Night	5% 3 21% 46% 25% 1	368
	21st to end	Night	3 2 17% 38% 38% 2	478
August	1st to 10th	Night	4 1 10% 36% 43% 7%	567
	11th to 20th	Night	4 1 7% 39% 44% 6%	564
	21st to end	Night	6% 4 14% 40% 33% 4	769
September	1st to 10th	Night	7% 2 14% 37% 37% 4	760
	11th to 20th	Night	11% 3 10% 31% 38% 7%	760
	21st to end	Night	13% 4 12% 34% 33% 4	760
October	1st to 10th	Night	15% 3 13% 34% 30% 5%	760
	11th to 20th	Night	19% 4 8% 33% 30% 6%	760
	21st to end	Night	29% 7% 11% 28% 20% 5%	836
November	1st to 10th	Night	30% 7% 14% 30% 18% 2	748
	11th to 20th	Night	34% 7% 13% 26% 17% 2	760
	21st to end	Night	28% 6% 12% 31% 19% 4	760
December	1st to 10th	Night	28% 7% 13% 27% 21% 3	760
	11th to 20th	Night	39% 7% 10% 26% 17% 1	760
	21st to end	Night	42% 8% 13% 27% 10% 1	836

Page generated at 2024-10-31 00:39:25. Version ac07

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