Oregon Vortex
Clear Sky Chart
History

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

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	13% 7% 3 6% 5% 3 4 4 5% 6% 44%	78581
	Night	16% 8% 3 6% 5% 3 4 4 5% 6% 41%	80969
Transparency	Day	39% 6% 12% 21% 16% 6%	78292
	Night	42% 7% 13% 20% 13% 4	80779
Seeing	Day	15% 9% 21% 27% 20% 9%	13967
	Night	17% 3 12% 35% 28% 4	23179

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	23% 12% 4 10% 9% 5% 6% 5% 6% 5% 14%	2539
	11th to 20th	Day	32% 15% 4 7% 6% 3 4 3 4 4 19%	2704
	21st to end	Day	28% 11% 4 7% 6% 4 4 4 5% 7% 21%	3146
February	1st to 10th	Day	16% 10% 4 8% 7% 4 6% 6% 7% 7% 25%	1710
	11th to 20th	Day	16% 11% 3 8% 7% 3 6% 5% 5% 6% 30%	1665
	21st to end	Day	18% 13% 5% 8% 8% 3 5% 5% 5% 6% 24%	1516
March	1st to 10th	Day	20% 12% 5% 9% 6% 4 5% 5% 4 6% 24%	1994
	11th to 20th	Day	17% 11% 4 7% 7% 3 6% 5% 5% 7% 28%	1980
	21st to end	Day	17% 12% 5% 9% 6% 3 6% 6% 5% 8% 23%	2194
April	1st to 10th	Day	16% 9% 5% 9% 8% 3 7% 5% 4 8% 25%	2160
	11th to 20th	Day	16% 9% 5% 7% 6% 3 5% 4 6% 7% 32%	2129
	21st to end	Day	10% 9% 3 7% 6% 3 4 5% 6% 7% 40%	2276
May	1st to 10th	Day	10% 6% 2 6% 5% 3 5% 4 5% 7% 48%	2362
	11th to 20th	Day	10% 7% 3 6% 6% 3 5% 5% 5% 7% 43%	2477
	21st to end	Day	13% 6% 3 4 6% 3 4 5% 6% 9% 41%	2723
June	1st to 10th	Day	11% 5% 3 5% 5% 3 5% 4 6% 8% 45%	2520
	11th to 20th	Day	6% 4 2 4 5% 3 5% 4 5% 6% 56%	2520
	21st to end	Day	5% 3 1 2 3 1 3 2 4 6% 71%	2520
July	1st to 10th	Day	2 2 1 2 2 1 2 3 3 4 79%	2520
	11th to 20th	Day	3 2 1 2 2 1 2 2 3 4 79%	2520
	21st to end	Day	2 1 1 1 2 1 2 2 2 4 82%	2601
August	1st to 10th	Day	2 2 1 2 1 2 2 3 3 5% 78%	2328
	11th to 20th	Day	2 2 1 2 2 1 2 2 3 5% 79%	2298
	21st to end	Day	2 2 1 2 2 1 1 3 2 5% 79%	2412
September	1st to 10th	Day	2 2 1 2 2 1 2 2 3 5% 78%	2160
	11th to 20th	Day	5% 4 2 3 4 2 4 4 5% 6% 62%	2137
	21st to end	Day	7% 4 2 4 4 3 3 3 4 7% 60%	1907
October	1st to 10th	Day	9% 4 2 4 5% 3 4 4 5% 6% 54%	1800
	11th to 20th	Day	11% 5% 3 4 6% 3 4 5% 6% 8% 45%	1800
	21st to end	Day	15% 7% 3 7% 6% 3 5% 4 5% 6% 40%	1980
November	1st to 10th	Day	19% 9% 5% 8% 7% 4 5% 5% 6% 7% 26%	1701
	11th to 20th	Day	20% 11% 5% 7% 6% 4 5% 5% 6% 8% 24%	1520
	21st to end	Day	19% 9% 4 9% 8% 3 6% 4 4 7% 28%	1520
December	1st to 10th	Day	15% 8% 5% 8% 6% 4 6% 5% 5% 7% 31%	1520
	11th to 20th	Day	23% 12% 4 7% 7% 4 6% 5% 6% 8% 18%	1928
	21st to end	Day	25% 13% 5% 11% 9% 6% 6% 5% 4 5% 12%	2794
January	1st to 10th	Night	24% 13% 4 8% 8% 4 6% 6% 6% 5% 15%	4406
	11th to 20th	Night	28% 13% 4 7% 6% 3 4 4 5% 5% 20%	4258
	21st to end	Night	32% 11% 4 7% 6% 3 3 4 4 5% 22%	4521
February	1st to 10th	Night	16% 12% 4 7% 6% 2 5% 5% 6% 7% 31%	2470
	11th to 20th	Night	19% 10% 3 7% 6% 3 4 4 5% 6% 33%	2402
	21st to end	Night	15% 12% 3 7% 6% 3 5% 4 6% 8% 30%	1937
March	1st to 10th	Night	21% 13% 4 7% 5% 3 4 4 5% 7% 27%	2080
	11th to 20th	Night	18% 11% 4 8% 6% 4 5% 4 4 7% 30%	1980
	21st to end	Night	19% 11% 5% 7% 7% 4 6% 5% 5% 7% 25%	2160
April	1st to 10th	Night	18% 9% 4 7% 6% 4 6% 5% 5% 7% 30%	1800
	11th to 20th	Night	14% 8% 4 6% 6% 3 5% 5% 5% 6% 38%	1779
	21st to end	Night	12% 7% 4 6% 4 3 5% 5% 6% 9% 40%	1681
May	1st to 10th	Night	9% 6% 3 5% 4 4 4 4 4 6% 52%	1598
	11th to 20th	Night	9% 6% 2 6% 5% 3 6% 6% 6% 6% 46%	1416
	21st to end	Night	12% 5% 2 4 4 3 4 4 5% 9% 46%	1552
June	1st to 10th	Night	11% 4 2 6% 4 3 4 4 5% 7% 49%	1440
	11th to 20th	Night	7% 3 2 4 4 2 3 3 4 6% 62%	1440
	21st to end	Night	4 2 1 2 2 1 3 2 3 4 76%	1440
July	1st to 10th	Night	2 1 1 2 2 2 3 3 3 5% 77%	1440
	11th to 20th	Night	2 1 1 3 1 2 1 3 2 3 80%	1440
	21st to end	Night	1 1 1 1 1 1 1 2 2 4 86%	1713
August	1st to 10th	Night	1 1 1 2 2 2 2 3 3 5% 79%	1611
	11th to 20th	Night	1 1 1 2 2 1 2 2 3 5% 81%	1602
	21st to end	Night	1 1 2 2 1 2 2 3 4 82%	1944
September	1st to 10th	Night	2 2 1 1 1 2 2 3 4 81%	1800
	11th to 20th	Night	5% 2 1 3 3 2 3 4 4 7% 67%	1821
	21st to end	Night	7% 3 1 4 3 2 3 3 3 6% 63%	2052
October	1st to 10th	Night	7% 4 1 4 3 2 3 3 4 6% 62%	2160
	11th to 20th	Night	11% 4 1 4 4 2 4 5% 5% 6% 53%	2160
	21st to end	Night	15% 6% 2 5% 4 3 4 5% 6% 5% 46%	2376
November	1st to 10th	Night	20% 8% 4 8% 7% 3 5% 4 6% 5% 32%	2372
	11th to 20th	Night	20% 8% 4 8% 7% 4 6% 5% 5% 8% 25%	2660
	21st to end	Night	18% 8% 3 6% 6% 4 5% 4 4 7% 33%	2660
December	1st to 10th	Night	19% 9% 4 6% 5% 3 4 5% 5% 6% 34%	2660
	11th to 20th	Night	24% 11% 4 8% 6% 4 4 5% 6% 8% 20%	3276
	21st to end	Night	22% 13% 4 9% 9% 6% 6% 4 5% 5% 17%	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	63% 11% 13% 10% 3 1	2539
	11th to 20th	Day	66% 8% 5% 12% 5% 3	2704
	21st to end	Day	57% 12% 12% 13% 5% 2	3146
February	1st to 10th	Day	54% 7% 15% 16% 7% 1	1710
	11th to 20th	Day	51% 8% 13% 19% 7% 2	1674
	21st to end	Day	57% 8% 12% 15% 7% 2	1516
March	1st to 10th	Day	59% 6% 12% 16% 6%	1994
	11th to 20th	Day	53% 7% 13% 18% 8% 1	1980
	21st to end	Day	56% 8% 17% 13% 5%	2194
April	1st to 10th	Day	56% 7% 13% 14% 7% 2	2160
	11th to 20th	Day	51% 7% 16% 14% 8% 4	2132
	21st to end	Day	42% 7% 17% 21% 11% 1	2276
May	1st to 10th	Day	37% 5% 16% 27% 14% 1	2362
	11th to 20th	Day	40% 5% 16% 26% 10% 3	2480
	21st to end	Day	42% 5% 21% 24% 8%	2724
June	1st to 10th	Day	36% 6% 17% 29% 11% 1	2520
	11th to 20th	Day	29% 6% 14% 34% 15% 2	2520
	21st to end	Day	18% 3 12% 34% 25% 8%	2520
July	1st to 10th	Day	12% 2 10% 29% 31% 16%	2451
	11th to 20th	Day	12% 2 6% 23% 37% 21%	2445
	21st to end	Day	11% 2 3 21% 45% 19%	2456
August	1st to 10th	Day	11% 2 10% 32% 32% 13%	2312
	11th to 20th	Day	11% 3 8% 26% 38% 15%	2298
	21st to end	Day	12% 2 8% 27% 37% 14%	2412
September	1st to 10th	Day	11% 2 5% 26% 33% 22%	2160
	11th to 20th	Day	23% 4 10% 28% 25% 10%	2137
	21st to end	Day	24% 6% 9% 26% 22% 13%	1907
October	1st to 10th	Day	29% 6% 12% 21% 20% 12%	1800
	11th to 20th	Day	36% 6% 14% 20% 18% 7%	1800
	21st to end	Day	43% 5% 12% 16% 17% 6%	1980
November	1st to 10th	Day	54% 7% 12% 15% 10% 2	1701
	11th to 20th	Day	55% 9% 12% 13% 8% 3	1520
	21st to end	Day	54% 7% 11% 12% 12% 4	1520
December	1st to 10th	Day	50% 8% 11% 19% 11% 1	1520
	11th to 20th	Day	58% 11% 13% 13% 5%	1928
	21st to end	Day	62% 17% 7% 11% 3 1	2794
January	1st to 10th	Night	63% 12% 13% 8% 4 1	4406
	11th to 20th	Night	62% 8% 8% 13% 5% 4	4258
	21st to end	Night	63% 7% 9% 13% 8% 2	4521
February	1st to 10th	Night	51% 8% 14% 17% 8% 1	2470
	11th to 20th	Night	51% 7% 14% 20% 6% 2	2404
	21st to end	Night	49% 10% 15% 18% 6% 2	1937
March	1st to 10th	Night	55% 6% 14% 20% 5%	2080
	11th to 20th	Night	52% 6% 14% 19% 8%	1980
	21st to end	Night	57% 8% 17% 14% 4	2160
April	1st to 10th	Night	52% 6% 17% 18% 6% 1	1800
	11th to 20th	Night	45% 8% 20% 18% 7% 3	1779
	21st to end	Night	40% 9% 22% 21% 7% 1	1681
May	1st to 10th	Night	34% 8% 20% 27% 10% 2	1598
	11th to 20th	Night	39% 5% 21% 26% 6% 2	1416
	21st to end	Night	37% 7% 27% 24% 5%	1552
June	1st to 10th	Night	36% 7% 19% 33% 5%	1440
	11th to 20th	Night	26% 6% 20% 36% 13% 1	1440
	21st to end	Night	15% 3 15% 41% 22% 3	1440
July	1st to 10th	Night	13% 3 11% 32% 27% 14%	1400
	11th to 20th	Night	11% 2 5% 28% 38% 16%	1392
	21st to end	Night	8% 2 3 26% 49% 13%	1618
August	1st to 10th	Night	10% 3 10% 38% 32% 7%	1602
	11th to 20th	Night	9% 3 8% 33% 38% 9%	1602
	21st to end	Night	9% 2 9% 32% 37% 10%	1944
September	1st to 10th	Night	9% 2 7% 30% 34% 18%	1800
	11th to 20th	Night	18% 4 14% 31% 24% 8%	1821
	21st to end	Night	23% 4 13% 27% 20% 13%	2052
October	1st to 10th	Night	24% 6% 15% 23% 23% 9%	2160
	11th to 20th	Night	31% 5% 14% 22% 21% 7%	2160
	21st to end	Night	38% 7% 13% 19% 15% 8%	2376
November	1st to 10th	Night	51% 7% 13% 14% 12% 2	2372
	11th to 20th	Night	55% 7% 13% 13% 9% 2	2660
	21st to end	Night	50% 7% 13% 15% 12% 4	2660
December	1st to 10th	Night	47% 8% 12% 19% 12% 1	2660
	11th to 20th	Night	57% 10% 12% 16% 5%	3276
	21st to end	Night	60% 14% 10% 12% 3 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	33% 8% 19% 22% 14% 4	180
	11th to 20th	Day	32% 5% 11% 23% 17% 12%	279
	21st to end	Day	27% 7% 14% 23% 19% 10%	407
February	1st to 10th	Day	20% 7% 16% 29% 21% 6%	370
	11th to 20th	Day	28% 8% 23% 22% 15% 5%	365
	21st to end	Day	24% 13% 20% 24% 16% 3	357
March	1st to 10th	Day	30% 10% 20% 25% 13% 3	441
	11th to 20th	Day	23% 9% 20% 25% 18% 4	420
	21st to end	Day	24% 15% 21% 23% 15% 3	462
April	1st to 10th	Day	22% 13% 21% 28% 11% 4	420
	11th to 20th	Day	22% 15% 24% 22% 12% 4	412
	21st to end	Day	16% 19% 24% 21% 14% 6%	420
May	1st to 10th	Day	14% 14% 24% 26% 15% 6%	423
	11th to 20th	Day	17% 11% 23% 26% 15% 7%	448
	21st to end	Day	15% 11% 24% 24% 18% 8%	485
June	1st to 10th	Day	11% 11% 28% 23% 20% 7%	450
	11th to 20th	Day	12% 14% 29% 25% 16% 6%	450
	21st to end	Day	4 10% 26% 29% 22% 10%	450
July	1st to 10th	Day	4 7% 27% 32% 21% 10%	446
	11th to 20th	Day	2 6% 28% 30% 23% 11%	444
	21st to end	Day	1 5% 25% 31% 25% 14%	487
August	1st to 10th	Day	2 3 23% 33% 21% 17%	447
	11th to 20th	Day	2 5% 20% 31% 25% 16%	437
	21st to end	Day	5% 6% 22% 27% 26% 13%	495
September	1st to 10th	Day	3 7% 19% 31% 25% 15%	450
	11th to 20th	Day	7% 7% 19% 32% 25% 11%	450
	21st to end	Day	8% 8% 19% 30% 25% 11%	450
October	1st to 10th	Day	12% 8% 20% 25% 23% 12%	450
	11th to 20th	Day	13% 8% 14% 24% 26% 14%	450
	21st to end	Day	19% 8% 17% 23% 20% 12%	495
November	1st to 10th	Day	17% 8% 15% 30% 21% 8%	309
	11th to 20th	Day	21% 4 13% 27% 24% 11%	180
	21st to end	Day	20% 3 16% 26% 27% 8%	180
December	1st to 10th	Day	22% 6% 15% 25% 20% 13%	180
	11th to 20th	Day	32% 4 16% 22% 20% 7%	180
	21st to end	Day	27% 5% 17% 27% 21% 4	198
January	1st to 10th	Night	29% 2 15% 34% 16% 3	760
	11th to 20th	Night	28% 3 13% 31% 20% 4	760
	21st to end	Night	25% 3 11% 34% 23% 4	836
February	1st to 10th	Night	23% 3 13% 36% 23% 2	760
	11th to 20th	Night	24% 4 13% 36% 21% 2	744
	21st to end	Night	20% 6% 17% 39% 16% 1	628
March	1st to 10th	Night	28% 6% 15% 32% 17% 1	742
	11th to 20th	Night	25% 5% 12% 36% 21% 2	720
	21st to end	Night	23% 8% 18% 33% 17% 1	792
April	1st to 10th	Night	23% 5% 18% 32% 20% 2	720
	11th to 20th	Night	18% 7% 19% 32% 20% 4	711
	21st to end	Night	17% 4 15% 36% 25% 3	601
May	1st to 10th	Night	14% 4 12% 39% 27% 4	518
	11th to 20th	Night	11% 5% 14% 34% 33% 3	354
	21st to end	Night	13% 3 15% 34% 31% 3	389
June	1st to 10th	Night	12% 3 11% 35% 38% 1	360
	11th to 20th	Night	8% 4 15% 39% 33% 2	360
	21st to end	Night	5% 2 10% 36% 46% 1	360
July	1st to 10th	Night	3 1 5% 37% 52% 2	350
	11th to 20th	Night	3 1 3 46% 47% 1	348
	21st to end	Night	2 3 29% 56% 10%	531
August	1st to 10th	Night	2 1 1 29% 56% 10%	537
	11th to 20th	Night	2 2 29% 56% 10%	534
	21st to end	Night	2 1 12% 36% 44% 6%	756
September	1st to 10th	Night	3 2 11% 33% 45% 6%	720
	11th to 20th	Night	6% 2 11% 30% 43% 9%	720
	21st to end	Night	9% 3 9% 37% 34% 8%	720
October	1st to 10th	Night	10% 3 12% 38% 31% 7%	720
	11th to 20th	Night	13% 3 9% 36% 34% 5%	720
	21st to end	Night	17% 3 11% 34% 26% 8%	792
November	1st to 10th	Night	23% 3 9% 41% 20% 4	740
	11th to 20th	Night	23% 4 13% 37% 21% 3	760
	21st to end	Night	23% 3 13% 36% 22% 3	760
December	1st to 10th	Night	22% 4 11% 34% 24% 5%	760
	11th to 20th	Night	28% 5% 13% 33% 19% 3	760
	21st to end	Night	32% 4 16% 34% 12% 2	836

Page generated at 2024-03-03 03:29:00. Version ac07

Copyright © 2024 Attilla Danko.