Corvallis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Corvallis 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	14% 8% 3 8% 5% 4 4 3 5% 6% 39%	101521
	Night	16% 9% 3 8% 5% 4 4 3 5% 5% 38%	97629
Transparency	Day	47% 3 12% 20% 13% 5%	101267
	Night	49% 3 13% 20% 11% 4	97472
Seeing	Day	17% 7% 18% 26% 22% 9%	14746
	Night	20% 5% 17% 35% 22% 2	23667

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	28% 16% 7% 16% 7% 5% 5% 3 3 3 7%	2539
	11th to 20th	Day	36% 12% 5% 11% 6% 5% 4 3 3 3 14%	2554
	21st to end	Day	25% 15% 6% 13% 6% 5% 5% 4 5% 6% 12%	3146
February	1st to 10th	Day	24% 14% 5% 12% 8% 5% 5% 3 5% 5% 14%	1710
	11th to 20th	Day	23% 12% 5% 10% 6% 6% 5% 4 5% 5% 17%	1665
	21st to end	Day	22% 17% 5% 12% 7% 4 5% 3 4 4 18%	1478
March	1st to 10th	Day	17% 12% 5% 11% 7% 7% 7% 5% 7% 6% 16%	3349
	11th to 20th	Day	16% 9% 3 8% 6% 5% 4 4 5% 6% 34%	3490
	21st to end	Day	19% 13% 5% 11% 7% 7% 6% 5% 5% 5% 17%	3871
April	1st to 10th	Day	20% 13% 4 11% 7% 6% 5% 4 5% 6% 18%	2280
	11th to 20th	Day	20% 11% 4 9% 6% 5% 5% 4 5% 6% 25%	2251
	21st to end	Day	17% 10% 3 8% 6% 5% 6% 5% 6% 7% 27%	2470
May	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 6% 6% 33%	4260
	11th to 20th	Day	9% 5% 2 5% 4 4 3 3 5% 7% 54%	4377
	21st to end	Day	13% 7% 3 6% 5% 6% 6% 6% 8% 9% 31%	4813
June	1st to 10th	Day	17% 10% 4 8% 4 3 4 3 6% 6% 35%	2660
	11th to 20th	Day	12% 9% 2 7% 7% 5% 5% 5% 7% 8% 34%	2660
	21st to end	Day	7% 4 2 5% 4 3 4 3 5% 7% 56%	2660
July	1st to 10th	Day	3 2 1 2 2 2 2 2 4 4 77%	4420
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 3 77%	4420
	21st to end	Day	3 2 1 2 2 2 2 1 3 4 78%	4706
August	1st to 10th	Day	1 2 1 3 3 3 3 3 4 6% 71%	4091
	11th to 20th	Day	4 3 2 5% 3 3 4 3 6% 8% 58%	4026
	21st to end	Day	6% 5% 2 4 3 4 4 3 5% 6% 58%	4313
September	1st to 10th	Day	5% 3 1 3 3 2 2 2 4 7% 66%	2280
	11th to 20th	Day	9% 6% 2 6% 5% 4 5% 4 5% 8% 45%	2250
	21st to end	Day	13% 5% 3 6% 5% 4 4 3 5% 6% 47%	2016
October	1st to 10th	Day	14% 7% 3 7% 4 5% 5% 3 6% 6% 41%	1900
	11th to 20th	Day	14% 8% 4 10% 7% 6% 5% 4 5% 6% 31%	1900
	21st to end	Day	20% 12% 4 9% 5% 6% 5% 3 4 5% 27%	2090
November	1st to 10th	Day	23% 14% 5% 11% 6% 6% 7% 4 5% 4 15%	1594
	11th to 20th	Day	26% 12% 4 11% 7% 4 4 4 5% 6% 18%	1520
	21st to end	Day	22% 14% 5% 10% 8% 5% 4 3 5% 5% 19%	1520
December	1st to 10th	Day	23% 11% 6% 11% 7% 5% 4 2 5% 4 22%	1520
	11th to 20th	Day	23% 12% 5% 13% 7% 7% 6% 5% 6% 5% 11%	1928
	21st to end	Day	27% 15% 8% 19% 8% 4 4 3 4 3 6%	2794
January	1st to 10th	Night	28% 18% 6% 12% 6% 5% 5% 3 4 4 11%	4406
	11th to 20th	Night	33% 16% 5% 9% 5% 4 3 2 3 4 16%	4391
	21st to end	Night	32% 14% 4 11% 5% 5% 4 3 3 4 15%	4521
February	1st to 10th	Night	22% 14% 4 10% 6% 5% 5% 4 6% 6% 18%	2470
	11th to 20th	Night	22% 12% 4 8% 5% 5% 6% 4 5% 6% 24%	2402
	21st to end	Night	22% 12% 3 9% 6% 5% 5% 3 5% 6% 23%	1975
March	1st to 10th	Night	15% 12% 5% 12% 7% 7% 6% 5% 6% 6% 20%	3520
	11th to 20th	Night	13% 8% 3 7% 4 4 4 4 5% 6% 41%	3490
	21st to end	Night	19% 12% 5% 12% 8% 6% 5% 4 5% 6% 18%	3781
April	1st to 10th	Night	23% 11% 3 9% 5% 5% 5% 4 5% 6% 25%	1900
	11th to 20th	Night	16% 9% 4 7% 5% 4 4 4 6% 6% 34%	1874
	21st to end	Night	16% 8% 3 7% 6% 5% 4 4 5% 7% 34%	1710
May	1st to 10th	Night	18% 8% 3 8% 5% 3 3 3 4 4 40%	2705
	11th to 20th	Night	7% 5% 2 6% 4 4 3 2 4 5% 59%	2516
	21st to end	Night	9% 7% 2 6% 4 4 4 4 6% 11% 42%	2762
June	1st to 10th	Night	13% 8% 2 6% 4 3 4 5% 6% 5% 43%	1520
	11th to 20th	Night	10% 6% 2 6% 5% 4 4 3 8% 7% 46%	1520
	21st to end	Night	5% 5% 1 4 3 3 2 3 4 6% 64%	1520
July	1st to 10th	Night	1 1 1 2 1 1 1 2 2 3 84%	2540
	11th to 20th	Night	3 3 1 2 2 2 2 2 2 3 80%	2540
	21st to end	Night	2 2 1 2 1 1 2 2 2 3 82%	2844
August	1st to 10th	Night	1 2 1 1 2 2 2 2 3 5% 78%	2848
	11th to 20th	Night	3 3 1 4 2 3 4 3 4 7% 65%	2812
	21st to end	Night	6% 4 1 4 2 2 2 2 4 5% 66%	3360
September	1st to 10th	Night	4 3 1 3 2 2 3 3 5% 5% 70%	1900
	11th to 20th	Night	7% 5% 2 4 4 4 5% 3 6% 6% 55%	1928
	21st to end	Night	9% 4 2 5% 3 4 4 3 5% 7% 54%	2163
October	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 5% 6% 49%	2280
	11th to 20th	Night	14% 7% 3 7% 4 5% 5% 4 5% 6% 41%	2280
	21st to end	Night	18% 9% 3 8% 5% 4 4 3 5% 5% 37%	2508
November	1st to 10th	Night	23% 9% 3 8% 6% 5% 5% 3 5% 6% 26%	2525
	11th to 20th	Night	25% 11% 3 9% 7% 5% 4 3 5% 5% 22%	2660
	21st to end	Night	18% 10% 3 10% 6% 5% 5% 4 5% 6% 27%	2660
December	1st to 10th	Night	23% 11% 3 9% 5% 4 4 3 5% 6% 25%	2660
	11th to 20th	Night	23% 13% 5% 11% 7% 6% 5% 5% 5% 5% 15%	3276
	21st to end	Night	23% 13% 8% 15% 7% 6% 5% 4 4 4 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	83% 2 8% 6% 1 1	2539
	11th to 20th	Day	78% 2 8% 8% 2 1	2554
	21st to end	Day	75% 3 9% 9% 4	3146
February	1st to 10th	Day	72% 4 9% 10% 5%	1710
	11th to 20th	Day	69% 4 11% 11% 4 1	1674
	21st to end	Day	71% 3 9% 11% 5% 2	1478
March	1st to 10th	Day	66% 3 11% 17% 3	3349
	11th to 20th	Day	51% 3 10% 24% 11% 1	3490
	21st to end	Day	68% 3 14% 10% 4	3871
April	1st to 10th	Day	66% 3 12% 14% 4	2280
	11th to 20th	Day	58% 4 12% 15% 8% 3	2254
	21st to end	Day	55% 4 16% 17% 7% 1	2470
May	1st to 10th	Day	51% 1 13% 22% 12% 1	4260
	11th to 20th	Day	32% 2 15% 36% 14% 2	4380
	21st to end	Day	48% 4 25% 20% 3	4814
June	1st to 10th	Day	51% 2 17% 24% 7% 1	2660
	11th to 20th	Day	46% 3 20% 23% 7%	2660
	21st to end	Day	28% 3 18% 32% 14% 4	2660
July	1st to 10th	Day	13% 2 9% 19% 25% 33%	4351
	11th to 20th	Day	14% 2 5% 19% 36% 24%	4345
	21st to end	Day	12% 2 9% 29% 38% 9%	4557
August	1st to 10th	Day	15% 3 9% 32% 31% 11%	4076
	11th to 20th	Day	22% 5% 18% 34% 17% 4	4065
	21st to end	Day	25% 5% 12% 25% 26% 6%	4312
September	1st to 10th	Day	19% 2 10% 35% 22% 12%	2280
	11th to 20th	Day	36% 4 14% 24% 15% 6%	2250
	21st to end	Day	39% 3 13% 25% 16% 6%	2016
October	1st to 10th	Day	43% 4 11% 21% 18% 4	1900
	11th to 20th	Day	53% 4 12% 17% 11% 2	1900
	21st to end	Day	59% 3 9% 14% 12% 1	2090
November	1st to 10th	Day	70% 4 10% 12% 4	1594
	11th to 20th	Day	68% 4 10% 10% 6% 2	1520
	21st to end	Day	68% 3 8% 9% 12% 1	1520
December	1st to 10th	Day	66% 4 9% 11% 9% 1	1520
	11th to 20th	Day	74% 3 11% 9% 2	1928
	21st to end	Day	84% 2 6% 5% 3	2794
January	1st to 10th	Night	79% 3 8% 6% 3 1	4406
	11th to 20th	Night	75% 2 7% 11% 4 1	4391
	21st to end	Night	74% 1 8% 10% 5% 1	4521
February	1st to 10th	Night	67% 5% 11% 13% 4 1	2470
	11th to 20th	Night	61% 3 15% 13% 6% 2	2404
	21st to end	Night	62% 3 12% 14% 6% 2	1975
March	1st to 10th	Night	63% 2 12% 18% 4	3520
	11th to 20th	Night	42% 3 17% 27% 10% 1	3490
	21st to end	Night	67% 2 15% 15% 2	3781
April	1st to 10th	Night	61% 3 15% 14% 6%	1900
	11th to 20th	Night	52% 4 17% 19% 6% 3	1874
	21st to end	Night	50% 4 16% 22% 6% 2	1710
May	1st to 10th	Night	49% 1 12% 26% 11% 1	2705
	11th to 20th	Night	29% 2 14% 38% 15% 3	2516
	21st to end	Night	38% 4 35% 21% 3	2762
June	1st to 10th	Night	43% 4 17% 31% 5% 1	1520
	11th to 20th	Night	36% 3 22% 31% 8%	1520
	21st to end	Night	22% 2 20% 37% 14% 4	1520
July	1st to 10th	Night	10% 1 8% 23% 25% 34%	2500
	11th to 20th	Night	13% 1 7% 20% 31% 29%	2492
	21st to end	Night	9% 3 10% 31% 38% 9%	2755
August	1st to 10th	Night	10% 2 10% 38% 30% 10%	2839
	11th to 20th	Night	19% 4 21% 38% 14% 4	2839
	21st to end	Night	21% 4 12% 31% 26% 7%	3360
September	1st to 10th	Night	18% 2 11% 33% 25% 11%	1900
	11th to 20th	Night	30% 3 16% 28% 15% 8%	1928
	21st to end	Night	31% 2 17% 25% 18% 7%	2163
October	1st to 10th	Night	36% 4 10% 27% 19% 4	2280
	11th to 20th	Night	43% 4 15% 21% 14% 3	2280
	21st to end	Night	49% 4 12% 17% 16% 2	2508
November	1st to 10th	Night	58% 4 11% 19% 7%	2525
	11th to 20th	Night	64% 4 11% 12% 7% 2	2660
	21st to end	Night	57% 3 12% 13% 13% 2	2660
December	1st to 10th	Night	59% 3 12% 14% 10% 1	2660
	11th to 20th	Night	71% 4 10% 11% 4	3276
	21st to end	Night	78% 2 8% 9% 3	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	38% 14% 19% 15% 11% 3	180
	11th to 20th	Day	35% 10% 13% 27% 12% 4	194
	21st to end	Day	31% 11% 16% 19% 15% 7%	407
February	1st to 10th	Day	31% 7% 20% 19% 17% 5%	370
	11th to 20th	Day	28% 9% 25% 23% 11% 4	365
	21st to end	Day	24% 16% 23% 20% 13% 4	339
March	1st to 10th	Day	27% 11% 23% 25% 11% 3	460
	11th to 20th	Day	25% 10% 22% 21% 18% 5%	460
	21st to end	Day	24% 14% 21% 25% 13% 3	506
April	1st to 10th	Day	26% 11% 19% 23% 15% 6%	460
	11th to 20th	Day	22% 14% 23% 23% 12% 7%	452
	21st to end	Day	20% 11% 22% 25% 18% 4	460
May	1st to 10th	Day	14% 10% 24% 24% 20% 8%	463
	11th to 20th	Day	21% 7% 15% 26% 18% 13%	488
	21st to end	Day	11% 8% 17% 24% 25% 14%	529
June	1st to 10th	Day	18% 8% 15% 24% 27% 7%	490
	11th to 20th	Day	14% 7% 23% 32% 19% 4	490
	21st to end	Day	4 5% 14% 33% 34% 10%	490
July	1st to 10th	Day	6% 2 15% 32% 32% 12%	486
	11th to 20th	Day	2 2 18% 35% 30% 13%	484
	21st to end	Day	3 1 11% 33% 37% 15%	531
August	1st to 10th	Day	1 1 11% 30% 39% 19%	487
	11th to 20th	Day	3 2 10% 28% 38% 20%	477
	21st to end	Day	5% 3 14% 35% 31% 12%	539
September	1st to 10th	Day	6% 3 16% 32% 31% 13%	490
	11th to 20th	Day	11% 4 14% 28% 29% 14%	490
	21st to end	Day	15% 5% 19% 28% 26% 7%	490
October	1st to 10th	Day	18% 5% 20% 24% 22% 12%	490
	11th to 20th	Day	17% 7% 17% 23% 26% 10%	490
	21st to end	Day	24% 12% 21% 22% 15% 6%	539
November	1st to 10th	Day	27% 7% 25% 23% 13% 5%	232
	11th to 20th	Day	22% 9% 23% 24% 16% 7%	180
	21st to end	Day	28% 7% 23% 17% 17% 7%	180
December	1st to 10th	Day	28% 11% 17% 24% 13% 7%	180
	11th to 20th	Day	35% 7% 16% 27% 13% 3	180
	21st to end	Day	31% 11% 20% 23% 14% 2	198
January	1st to 10th	Night	34% 9% 19% 22% 13% 2	760
	11th to 20th	Night	33% 8% 17% 24% 16% 3	760
	21st to end	Night	28% 4 15% 32% 18% 3	836
February	1st to 10th	Night	27% 6% 20% 27% 18% 2	760
	11th to 20th	Night	26% 6% 20% 29% 18% 1	744
	21st to end	Night	25% 10% 20% 31% 15%	628
March	1st to 10th	Night	26% 6% 19% 33% 15% 1	760
	11th to 20th	Night	24% 5% 18% 35% 16% 2	760
	21st to end	Night	26% 6% 22% 30% 15% 1	836
April	1st to 10th	Night	27% 6% 19% 29% 18% 1	760
	11th to 20th	Night	20% 6% 22% 36% 16% 1	746
	21st to end	Night	19% 5% 19% 37% 20% 1	570
May	1st to 10th	Night	12% 5% 21% 41% 19% 2	480
	11th to 20th	Night	15% 1 16% 41% 26% 1	374
	21st to end	Night	15% 4 18% 38% 23% 2	411
June	1st to 10th	Night	16% 3 15% 42% 23% 1	380
	11th to 20th	Night	11% 4 19% 48% 17% 1	380
	21st to end	Night	7% 1 15% 52% 23% 1	380
July	1st to 10th	Night	5% 1 11% 52% 31% 1	370
	11th to 20th	Night	4 1 18% 51% 26% 1	368
	21st to end	Night	2 1 11% 49% 36% 1	463
August	1st to 10th	Night	2 1 7% 43% 42% 6%	567
	11th to 20th	Night	4 5% 38% 49% 3	564
	21st to end	Night	6% 1 13% 45% 33% 2	750
September	1st to 10th	Night	6% 1 13% 47% 32% 1	760
	11th to 20th	Night	9% 3 11% 37% 34% 7%	760
	21st to end	Night	11% 2 15% 42% 28% 3	760
October	1st to 10th	Night	13% 3 17% 36% 27% 3	760
	11th to 20th	Night	17% 4 12% 35% 28% 4	760
	21st to end	Night	23% 6% 19% 32% 18% 4	836
November	1st to 10th	Night	24% 6% 18% 34% 18% 1	748
	11th to 20th	Night	30% 7% 20% 27% 16% 1	760
	21st to end	Night	21% 5% 22% 31% 19% 3	760
December	1st to 10th	Night	25% 6% 18% 30% 18% 3	760
	11th to 20th	Night	29% 7% 22% 24% 16% 1	760
	21st to end	Night	35% 6% 20% 26% 11% 1	836

Page generated at 2024-10-31 00:39:26. Version ac07

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