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 2024-03-18.

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% 9% 4 7% 6% 3 5% 4 5% 6% 34%	78649
	Night	18% 9% 4 7% 6% 3 4 4 5% 6% 34%	81152
Transparency	Day	52% 3 12% 19% 11% 3	78355
	Night	53% 3 12% 19% 10% 3	80967
Seeing	Day	18% 7% 18% 26% 23% 9%	13829
	Night	20% 5% 17% 35% 22% 2	22962

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% 15% 7% 15% 8% 4 5% 4 3 3 7%	2539
	11th to 20th	Day	36% 11% 5% 10% 7% 4 4 3 3 3 14%	2554
	21st to end	Day	25% 14% 6% 11% 8% 4 5% 5% 5% 6% 12%	3146
February	1st to 10th	Day	25% 12% 5% 10% 9% 5% 5% 5% 4 6% 14%	1710
	11th to 20th	Day	23% 11% 6% 9% 8% 5% 6% 5% 4 6% 18%	1665
	21st to end	Day	23% 15% 6% 10% 8% 3 4 4 4 4 18%	1478
March	1st to 10th	Day	23% 11% 5% 10% 6% 5% 7% 5% 6% 6% 15%	2028
	11th to 20th	Day	23% 11% 4 8% 7% 4 4 5% 5% 7% 22%	2059
	21st to end	Day	23% 12% 6% 9% 8% 5% 7% 6% 4 6% 15%	2199
April	1st to 10th	Day	21% 11% 5% 10% 9% 4 6% 5% 5% 6% 17%	2160
	11th to 20th	Day	21% 10% 4 8% 6% 4 6% 5% 5% 6% 25%	2130
	21st to end	Day	17% 9% 4 7% 7% 4 6% 6% 5% 7% 28%	2340
May	1st to 10th	Day	13% 8% 3 7% 6% 4 5% 5% 5% 8% 36%	2425
	11th to 20th	Day	16% 8% 4 7% 7% 4 4 5% 5% 8% 31%	2477
	21st to end	Day	17% 8% 3 6% 6% 4 6% 5% 6% 8% 31%	2723
June	1st to 10th	Day	17% 8% 5% 7% 5% 2 4 4 6% 6% 35%	2520
	11th to 20th	Day	13% 8% 3 6% 7% 4 5% 6% 7% 8% 33%	2520
	21st to end	Day	7% 4 2 4 5% 3 4 4 5% 7% 56%	2520
July	1st to 10th	Day	4 3 1 3 3 3 3 3 5% 6% 65%	2520
	11th to 20th	Day	5% 3 2 3 3 1 3 3 4 5% 68%	2520
	21st to end	Day	4 2 1 2 2 1 2 2 3 4 77%	2693
August	1st to 10th	Day	2 2 1 3 4 2 3 3 4 8% 67%	2328
	11th to 20th	Day	3 2 1 3 3 2 3 3 5% 6% 68%	2298
	21st to end	Day	4 3 1 3 4 3 4 4 5% 7% 62%	2457
September	1st to 10th	Day	5% 3 1 2 3 2 2 2 4 7% 68%	2160
	11th to 20th	Day	9% 6% 3 5% 6% 3 5% 5% 5% 8% 46%	2132
	21st to end	Day	13% 5% 3 5% 6% 3 3 4 5% 6% 46%	1910
October	1st to 10th	Day	15% 7% 3 6% 5% 4 5% 4 5% 7% 40%	1800
	11th to 20th	Day	15% 8% 5% 9% 8% 4 5% 5% 5% 6% 31%	1800
	21st to end	Day	20% 12% 5% 8% 6% 4 5% 4 4 5% 28%	1980
November	1st to 10th	Day	23% 13% 5% 9% 8% 4 7% 5% 5% 5% 15%	1576
	11th to 20th	Day	26% 11% 5% 10% 8% 3 4 4 5% 6% 18%	1520
	21st to end	Day	23% 12% 5% 9% 9% 4 5% 4 5% 5% 19%	1520
December	1st to 10th	Day	23% 10% 7% 11% 8% 3 5% 3 5% 5% 22%	1520
	11th to 20th	Day	23% 11% 5% 11% 8% 5% 7% 7% 6% 5% 11%	1928
	21st to end	Day	27% 14% 8% 17% 10% 3 4 4 4 3 6%	2794
January	1st to 10th	Night	28% 17% 7% 10% 7% 4 5% 4 4 4 11%	4406
	11th to 20th	Night	33% 15% 6% 8% 6% 3 4 3 3 4 16%	4391
	21st to end	Night	32% 13% 5% 10% 7% 4 4 4 3 4 15%	4521
February	1st to 10th	Night	22% 13% 5% 9% 7% 4 5% 5% 6% 6% 18%	2470
	11th to 20th	Night	22% 11% 4 7% 5% 4 6% 5% 5% 6% 24%	2402
	21st to end	Night	22% 10% 5% 8% 7% 3 6% 5% 5% 6% 23%	1975
March	1st to 10th	Night	21% 11% 5% 8% 7% 4 6% 5% 6% 5% 22%	2147
	11th to 20th	Night	19% 9% 4 7% 6% 4 4 5% 6% 8% 27%	2067
	21st to end	Night	22% 11% 4 8% 8% 4 5% 5% 4 7% 21%	2156
April	1st to 10th	Night	23% 11% 4 8% 6% 4 5% 5% 5% 6% 24%	1800
	11th to 20th	Night	17% 8% 4 7% 6% 3 4 5% 6% 6% 34%	1775
	21st to end	Night	16% 7% 3 6% 7% 3 5% 4 5% 8% 35%	1620
May	1st to 10th	Night	10% 7% 3 8% 6% 2 4 5% 5% 6% 43%	1535
	11th to 20th	Night	12% 7% 3 8% 6% 5% 5% 4 6% 7% 37%	1416
	21st to end	Night	12% 7% 3 6% 5% 3 4 4 6% 10% 39%	1552
June	1st to 10th	Night	13% 7% 3 5% 4 3 5% 5% 5% 6% 44%	1440
	11th to 20th	Night	11% 5% 3 5% 5% 2 4 4 7% 8% 45%	1440
	21st to end	Night	5% 4 2 3 3 2 3 3 3 6% 65%	1440
July	1st to 10th	Night	3 3 1 3 3 2 2 3 2 5% 74%	1440
	11th to 20th	Night	4 3 1 2 2 1 3 3 4 5% 72%	1440
	21st to end	Night	2 1 1 1 1 1 1 2 2 3 84%	1620
August	1st to 10th	Night	2 1 1 1 2 1 2 4 4 7% 74%	1611
	11th to 20th	Night	3 2 1 2 3 2 2 3 3 6% 74%	1602
	21st to end	Night	4 3 1 3 3 2 2 3 4 6% 70%	1898
September	1st to 10th	Night	5% 3 1 2 3 2 3 3 4 5% 71%	1800
	11th to 20th	Night	7% 4 2 3 4 3 5% 4 5% 6% 56%	1826
	21st to end	Night	10% 4 2 4 4 3 4 4 5% 7% 53%	2049
October	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 5% 7% 47%	2160
	11th to 20th	Night	14% 7% 3 6% 5% 3 5% 5% 5% 6% 42%	2160
	21st to end	Night	18% 8% 3 6% 6% 3 4 4 4 5% 38%	2376
November	1st to 10th	Night	23% 8% 4 7% 7% 4 5% 5% 5% 6% 27%	2499
	11th to 20th	Night	25% 11% 3 8% 8% 4 5% 4 4 6% 22%	2660
	21st to end	Night	18% 9% 3 8% 8% 4 6% 5% 5% 7% 28%	2660
December	1st to 10th	Night	24% 10% 4 8% 6% 3 5% 4 5% 6% 25%	2660
	11th to 20th	Night	23% 12% 6% 10% 8% 4 6% 5% 5% 5% 15%	3276
	21st to end	Night	23% 13% 8% 14% 9% 5% 5% 5% 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	67% 4 11% 14% 4	2028
	11th to 20th	Day	63% 3 12% 16% 6% 1	2059
	21st to end	Day	70% 5% 12% 11% 2	2199
April	1st to 10th	Day	67% 3 12% 13% 4	2160
	11th to 20th	Day	59% 4 12% 16% 7% 3	2133
	21st to end	Day	54% 4 16% 16% 7% 1	2340
May	1st to 10th	Day	47% 3 15% 24% 10% 1	2425
	11th to 20th	Day	52% 4 14% 22% 8% 1	2480
	21st to end	Day	50% 4 19% 21% 4	2724
June	1st to 10th	Day	51% 2 17% 24% 6% 1	2520
	11th to 20th	Day	47% 3 21% 23% 6%	2520
	21st to end	Day	29% 3 19% 32% 14% 5%	2520
July	1st to 10th	Day	21% 2 14% 31% 25% 7%	2451
	11th to 20th	Day	20% 2 8% 28% 32% 10%	2445
	21st to end	Day	13% 1 6% 34% 38% 9%	2543
August	1st to 10th	Day	17% 2 15% 37% 23% 6%	2312
	11th to 20th	Day	17% 3 13% 35% 26% 7%	2298
	21st to end	Day	22% 2 12% 31% 28% 4	2457
September	1st to 10th	Day	19% 2 10% 34% 23% 12%	2160
	11th to 20th	Day	36% 4 12% 25% 16% 7%	2132
	21st to end	Day	40% 3 11% 24% 16% 6%	1910
October	1st to 10th	Day	44% 4 11% 21% 17% 4	1800
	11th to 20th	Day	53% 5% 12% 17% 12% 2	1800
	21st to end	Day	60% 3 10% 14% 12% 1	1980
November	1st to 10th	Day	70% 4 10% 12% 5%	1576
	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% 4 11% 16% 6%	2147
	11th to 20th	Night	54% 5% 16% 18% 7% 1	2067
	21st to end	Night	64% 4 15% 15% 3	2156
April	1st to 10th	Night	62% 3 14% 14% 7%	1800
	11th to 20th	Night	52% 4 16% 18% 6% 3	1775
	21st to end	Night	50% 4 16% 21% 6% 3	1620
May	1st to 10th	Night	42% 2 17% 28% 9% 2	1535
	11th to 20th	Night	47% 3 18% 23% 6% 3	1416
	21st to end	Night	42% 5% 22% 25% 5%	1552
June	1st to 10th	Night	42% 4 17% 31% 5% 1	1440
	11th to 20th	Night	37% 3 22% 30% 7%	1440
	21st to end	Night	23% 2 20% 37% 14% 4	1440
July	1st to 10th	Night	17% 2 13% 34% 26% 8%	1400
	11th to 20th	Night	17% 2 11% 26% 34% 11%	1392
	21st to end	Night	7% 1 6% 35% 38% 11%	1530
August	1st to 10th	Night	13% 1 16% 42% 21% 6%	1602
	11th to 20th	Night	15% 2 12% 41% 24% 7%	1602
	21st to end	Night	17% 3 10% 39% 26% 6%	1898
September	1st to 10th	Night	18% 2 10% 32% 26% 11%	1800
	11th to 20th	Night	29% 3 15% 29% 15% 9%	1826
	21st to end	Night	32% 2 16% 24% 18% 8%	2049
October	1st to 10th	Night	38% 3 10% 26% 18% 5%	2160
	11th to 20th	Night	42% 4 14% 22% 14% 3	2160
	21st to end	Night	49% 4 12% 17% 17% 2	2376
November	1st to 10th	Night	58% 4 12% 19% 7%	2499
	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% 4	449
	21st to end	Day	25% 13% 19% 25% 13% 3	462
April	1st to 10th	Day	27% 11% 19% 22% 14% 6%	420
	11th to 20th	Day	23% 15% 22% 23% 11% 7%	412
	21st to end	Day	20% 10% 21% 25% 19% 4	420
May	1st to 10th	Day	13% 9% 25% 24% 21% 8%	423
	11th to 20th	Day	23% 8% 16% 24% 17% 12%	448
	21st to end	Day	12% 7% 18% 23% 26% 14%	485
June	1st to 10th	Day	18% 8% 15% 24% 27% 8%	450
	11th to 20th	Day	15% 6% 22% 32% 21% 4	450
	21st to end	Day	5% 4 14% 31% 35% 11%	450
July	1st to 10th	Day	7% 2 13% 31% 34% 13%	446
	11th to 20th	Day	3 2 17% 33% 31% 14%	444
	21st to end	Day	3 1 10% 32% 39% 15%	487
August	1st to 10th	Day	1 1 10% 29% 39% 20%	447
	11th to 20th	Day	3 1 9% 27% 40% 20%	437
	21st to end	Day	5% 2 13% 36% 32% 12%	495
September	1st to 10th	Day	6% 3 16% 32% 31% 12%	450
	11th to 20th	Day	11% 4 12% 27% 31% 15%	450
	21st to end	Day	15% 5% 19% 27% 26% 8%	450
October	1st to 10th	Day	19% 4 20% 23% 21% 12%	450
	11th to 20th	Day	18% 7% 16% 22% 26% 10%	450
	21st to end	Day	24% 11% 21% 22% 15% 7%	495
November	1st to 10th	Day	27% 8% 24% 23% 13% 5%	226
	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	752
	21st to end	Night	27% 6% 21% 30% 16% 1	792
April	1st to 10th	Night	28% 6% 19% 28% 19% 1	720
	11th to 20th	Night	21% 6% 20% 36% 17% 1	707
	21st to end	Night	20% 4 18% 37% 21% 1	540
May	1st to 10th	Night	11% 5% 21% 42% 20% 2	455
	11th to 20th	Night	16% 1 15% 41% 26% 1	354
	21st to end	Night	15% 3 18% 39% 23% 2	389
June	1st to 10th	Night	15% 3 15% 41% 24% 1	360
	11th to 20th	Night	11% 4 18% 47% 18% 1	360
	21st to end	Night	8% 1 14% 53% 23% 1	360
July	1st to 10th	Night	5% 1 9% 52% 32% 1	350
	11th to 20th	Night	4 1 18% 51% 25% 1	348
	21st to end	Night	2 1 9% 50% 37% 1	438
August	1st to 10th	Night	2 1 7% 42% 42% 6%	537
	11th to 20th	Night	4 5% 39% 49% 3	534
	21st to end	Night	6% 1 13% 45% 33% 2	710
September	1st to 10th	Night	7% 1 13% 47% 32% 1	720
	11th to 20th	Night	9% 2 10% 37% 35% 7%	720
	21st to end	Night	11% 2 14% 41% 29% 3	720
October	1st to 10th	Night	13% 3 17% 37% 27% 3	720
	11th to 20th	Night	17% 4 12% 35% 28% 4	720
	21st to end	Night	23% 5% 19% 31% 18% 4	792
November	1st to 10th	Night	24% 6% 18% 34% 18% 1	740
	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 2024-03-15 11:01:42. Version ac07

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