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 2024-11-05.

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	11% 7% 2 6% 4 4 4 3 4 6% 50%	105367
	Night	13% 8% 2 6% 4 4 4 3 5% 6% 45%	102397
Transparency	Day	34% 6% 11% 21% 18% 9%	105118
	Night	39% 7% 13% 21% 15% 6%	102235
Seeing	Day	14% 9% 21% 27% 20% 9%	14940
	Night	17% 4 12% 35% 28% 4	23960

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	22% 13% 3 12% 8% 7% 5% 4 6% 5% 14%	2539
	11th to 20th	Day	32% 15% 4 8% 5% 4 4 3 4 4 18%	2704
	21st to end	Day	27% 11% 3 8% 5% 5% 4 3 5% 7% 21%	3146
February	1st to 10th	Day	16% 11% 4 8% 6% 6% 6% 5% 6% 6% 25%	1710
	11th to 20th	Day	16% 11% 3 9% 6% 5% 6% 4 5% 6% 30%	1665
	21st to end	Day	17% 14% 4 10% 6% 4 5% 4 5% 6% 24%	1516
March	1st to 10th	Day	19% 15% 5% 11% 5% 5% 4 3 5% 5% 24%	3379
	11th to 20th	Day	12% 9% 2 6% 5% 4 4 3 5% 7% 43%	3490
	21st to end	Day	16% 12% 4 10% 6% 5% 6% 5% 6% 8% 21%	3853
April	1st to 10th	Day	15% 10% 5% 10% 7% 5% 6% 4 5% 7% 27%	2280
	11th to 20th	Day	15% 11% 4 7% 5% 5% 4 3 6% 7% 32%	2249
	21st to end	Day	10% 9% 3 8% 5% 4 4 4 6% 8% 39%	2403
May	1st to 10th	Day	11% 7% 2 7% 5% 5% 5% 3 5% 5% 45%	4158
	11th to 20th	Day	6% 4 2 4 3 3 3 3 4 5% 64%	4377
	21st to end	Day	7% 5% 2 4 4 4 4 4 5% 8% 54%	4813
June	1st to 10th	Day	10% 6% 2 5% 4 4 4 3 6% 8% 46%	2660
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 5% 6% 56%	2660
	21st to end	Day	4 3 1 2 3 2 3 2 4 5% 71%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 2 88%	4420
	11th to 20th	Day	2 2 1 2 2 1 2 2 3 3 80%	4420
	21st to end	Day	1 1 1 1 2 1 1 2 3 86%	4549
August	1st to 10th	Day	2 2 1 2 1 2 2 2 3 4 77%	4091
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 77%	4026
	21st to end	Day	2 3 1 3 2 2 2 2 2 4 77%	4242
September	1st to 10th	Day	2 2 3 2 2 2 2 3 5% 77%	2280
	11th to 20th	Day	4 4 2 4 4 3 4 3 5% 6% 60%	2255
	21st to end	Day	7% 3 2 5% 3 3 3 2 4 7% 61%	2012
October	1st to 10th	Day	5% 3 1 3 3 3 3 2 4 5% 67%	3180
	11th to 20th	Day	7% 5% 3 5% 5% 5% 6% 4 6% 9% 46%	3161
	21st to end	Day	13% 7% 3 8% 5% 5% 5% 4 5% 8% 36%	3448
November	1st to 10th	Day	19% 10% 4 10% 6% 5% 6% 3 5% 7% 25%	1739
	11th to 20th	Day	19% 12% 5% 8% 5% 6% 5% 4 6% 8% 23%	1520
	21st to end	Day	18% 10% 3 10% 7% 5% 5% 3 5% 7% 27%	1520
December	1st to 10th	Day	15% 9% 4 9% 5% 5% 5% 4 5% 6% 31%	1520
	11th to 20th	Day	23% 12% 4 8% 6% 6% 5% 4 7% 8% 18%	1928
	21st to end	Day	25% 14% 5% 13% 7% 7% 5% 4 4 5% 12%	2794
January	1st to 10th	Night	24% 14% 4 10% 7% 6% 6% 4 6% 5% 15%	4406
	11th to 20th	Night	28% 14% 3 8% 5% 4 4 3 5% 5% 19%	4258
	21st to end	Night	32% 12% 4 8% 5% 4 3 3 4 5% 22%	4521
February	1st to 10th	Night	16% 13% 4 8% 5% 3 5% 4 6% 7% 31%	2470
	11th to 20th	Night	19% 11% 3 8% 5% 4 4 3 5% 6% 33%	2402
	21st to end	Night	14% 13% 3 7% 6% 5% 5% 3 6% 8% 30%	1937
March	1st to 10th	Night	20% 15% 4 10% 5% 4 4 3 6% 7% 22%	3493
	11th to 20th	Night	13% 8% 3 6% 4 4 3 3 4 7% 45%	3490
	21st to end	Night	15% 12% 4 10% 7% 7% 6% 4 5% 6% 22%	3798
April	1st to 10th	Night	17% 10% 3 7% 5% 6% 5% 4 5% 7% 31%	1900
	11th to 20th	Night	14% 9% 3 6% 6% 4 5% 4 5% 6% 39%	1879
	21st to end	Night	12% 8% 3 7% 4 5% 4 4 7% 8% 39%	1774
May	1st to 10th	Night	12% 6% 3 6% 4 4 4 3 4 5% 49%	2810
	11th to 20th	Night	5% 4 1 4 2 3 3 3 3 5% 68%	2516
	21st to end	Night	7% 4 2 5% 3 3 3 3 5% 7% 57%	2762
June	1st to 10th	Night	11% 5% 2 6% 3 4 4 3 5% 7% 49%	1520
	11th to 20th	Night	6% 4 2 4 3 3 3 3 4 6% 62%	1520
	21st to end	Night	3 2 1 2 2 2 3 2 3 4 76%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 3 87%	2540
	11th to 20th	Night	2 1 1 2 1 2 1 2 2 3 82%	2540
	21st to end	Night	1 1 1 1 1 1 1 2 4 86%	3007
August	1st to 10th	Night	1 1 1 2 2 2 2 2 3 4 80%	2848
	11th to 20th	Night	1 2 1 3 2 2 2 1 4 6% 78%	2812
	21st to end	Night	4 2 1 3 2 2 2 2 3 3 76%	3434
September	1st to 10th	Night	2 2 2 1 1 2 2 3 4 81%	1900
	11th to 20th	Night	4 3 1 3 2 3 3 3 4 7% 66%	1923
	21st to end	Night	7% 3 1 4 3 3 3 2 3 6% 64%	2167
October	1st to 10th	Night	4 3 1 4 3 3 2 2 3 4 73%	3800
	11th to 20th	Night	8% 5% 2 5% 3 3 4 3 6% 6% 53%	3777
	21st to end	Night	13% 8% 3 8% 5% 5% 6% 4 6% 6% 36%	4121
November	1st to 10th	Night	19% 8% 3 9% 6% 4 5% 3 6% 5% 32%	2434
	11th to 20th	Night	20% 8% 4 9% 6% 6% 5% 4 6% 8% 25%	2660
	21st to end	Night	18% 9% 2 8% 5% 5% 4 4 5% 7% 33%	2660
December	1st to 10th	Night	19% 10% 3 7% 5% 4 4 4 5% 6% 34%	2660
	11th to 20th	Night	24% 12% 4 9% 5% 4 4 4 6% 8% 20%	3276
	21st to end	Night	22% 14% 4 10% 8% 8% 5% 3 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% 8% 11% 18% 4	3379
	11th to 20th	Day	38% 8% 11% 21% 20% 2	3490
	21st to end	Day	55% 10% 17% 14% 4	3853
April	1st to 10th	Day	54% 8% 14% 15% 7% 2	2280
	11th to 20th	Day	50% 7% 16% 14% 9% 4	2252
	21st to end	Day	42% 8% 17% 21% 11% 1	2403
May	1st to 10th	Day	37% 7% 13% 24% 15% 3	4158
	11th to 20th	Day	24% 3 11% 33% 25% 5%	4380
	21st to end	Day	29% 5% 24% 33% 9%	4814
June	1st to 10th	Day	35% 6% 17% 29% 12% 1	2660
	11th to 20th	Day	28% 6% 14% 34% 16% 2	2660
	21st to end	Day	18% 3 12% 34% 26% 8%	2660
July	1st to 10th	Day	7% 1 6% 16% 24% 46%	4351
	11th to 20th	Day	11% 2 5% 15% 30% 37%	4345
	21st to end	Day	7% 1 4 19% 45% 22%	4405
August	1st to 10th	Day	13% 2 6% 20% 38% 21%	4076
	11th to 20th	Day	12% 3 7% 35% 31% 13%	4065
	21st to end	Day	14% 3 8% 29% 34% 13%	4241
September	1st to 10th	Day	11% 2 5% 26% 33% 22%	2280
	11th to 20th	Day	23% 5% 11% 28% 24% 9%	2255
	21st to end	Day	23% 5% 9% 27% 23% 12%	2012
October	1st to 10th	Day	20% 4 10% 19% 25% 22%	3180
	11th to 20th	Day	32% 7% 18% 26% 14% 4	3161
	21st to end	Day	43% 6% 10% 21% 16% 4	3448
November	1st to 10th	Day	55% 7% 11% 15% 10% 2	1739
	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	56% 8% 15% 17% 4	3493
	11th to 20th	Night	37% 9% 13% 25% 14% 2	3490
	21st to end	Night	56% 12% 16% 13% 3	3798
April	1st to 10th	Night	51% 7% 18% 17% 6% 1	1900
	11th to 20th	Night	44% 9% 20% 18% 7% 3	1879
	21st to end	Night	41% 9% 22% 21% 6% 1	1774
May	1st to 10th	Night	34% 8% 20% 24% 12% 2	2810
	11th to 20th	Night	22% 3 18% 40% 16% 1	2516
	21st to end	Night	29% 6% 33% 29% 3	2762
June	1st to 10th	Night	35% 7% 19% 33% 6%	1520
	11th to 20th	Night	25% 6% 19% 36% 14% 1	1520
	21st to end	Night	14% 3 15% 41% 22% 4	1520
July	1st to 10th	Night	7% 1 6% 18% 24% 43%	2500
	11th to 20th	Night	9% 2 3 19% 34% 33%	2492
	21st to end	Night	6% 2 5% 24% 48% 15%	2913
August	1st to 10th	Night	10% 2 6% 24% 48% 10%	2839
	11th to 20th	Night	10% 3 11% 40% 26% 10%	2839
	21st to end	Night	15% 3 8% 32% 35% 7%	3434
September	1st to 10th	Night	9% 2 7% 31% 35% 17%	1900
	11th to 20th	Night	19% 4 15% 31% 24% 8%	1923
	21st to end	Night	22% 4 13% 28% 21% 12%	2167
October	1st to 10th	Night	18% 4 10% 21% 28% 19%	3800
	11th to 20th	Night	31% 6% 16% 32% 12% 4	3777
	21st to end	Night	45% 8% 12% 20% 11% 4	4121
November	1st to 10th	Night	51% 7% 13% 14% 11% 2	2434
	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	31% 10% 19% 24% 13% 3	460
	11th to 20th	Day	22% 9% 20% 26% 18% 5%	460
	21st to end	Day	25% 15% 21% 23% 14% 3	506
April	1st to 10th	Day	21% 12% 22% 28% 12% 5%	460
	11th to 20th	Day	21% 14% 24% 23% 13% 4	452
	21st to end	Day	17% 18% 24% 22% 13% 6%	460
May	1st to 10th	Day	15% 15% 24% 26% 15% 6%	463
	11th to 20th	Day	16% 11% 24% 26% 16% 8%	488
	21st to end	Day	14% 11% 24% 24% 19% 8%	529
June	1st to 10th	Day	11% 11% 27% 23% 21% 6%	490
	11th to 20th	Day	11% 13% 29% 25% 16% 6%	490
	21st to end	Day	4 9% 26% 29% 22% 10%	490
July	1st to 10th	Day	3 7% 26% 32% 20% 12%	486
	11th to 20th	Day	2 6% 28% 30% 24% 11%	484
	21st to end	Day	1 5% 25% 31% 24% 14%	531
August	1st to 10th	Day	2 3 23% 33% 21% 17%	487
	11th to 20th	Day	2 6% 21% 31% 25% 16%	477
	21st to end	Day	5% 6% 22% 27% 26% 14%	539
September	1st to 10th	Day	3 7% 19% 31% 26% 15%	490
	11th to 20th	Day	6% 8% 20% 31% 24% 11%	490
	21st to end	Day	7% 8% 19% 29% 25% 12%	490
October	1st to 10th	Day	11% 8% 19% 26% 24% 13%	490
	11th to 20th	Day	13% 8% 15% 24% 26% 14%	490
	21st to end	Day	19% 10% 17% 24% 19% 11%	539
November	1st to 10th	Day	18% 9% 16% 29% 20% 8%	323
	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% 16% 32% 17% 1	760
	11th to 20th	Night	24% 5% 11% 37% 21% 2	760
	21st to end	Night	23% 8% 19% 33% 17% 1	836
April	1st to 10th	Night	22% 5% 17% 33% 20% 2	760
	11th to 20th	Night	18% 7% 20% 33% 20% 3	751
	21st to end	Night	17% 4 16% 36% 24% 3	634
May	1st to 10th	Night	14% 4 13% 39% 26% 4	546
	11th to 20th	Night	10% 5% 14% 35% 33% 3	374
	21st to end	Night	13% 3 15% 34% 32% 3	411
June	1st to 10th	Night	12% 3 11% 36% 38% 1	380
	11th to 20th	Night	7% 4 15% 39% 32% 2	380
	21st to end	Night	4 2 11% 38% 44% 1	380
July	1st to 10th	Night	2 1 7% 36% 52% 2	370
	11th to 20th	Night	2 1 3 46% 46% 1	368
	21st to end	Night	1 3 30% 56% 10%	561
August	1st to 10th	Night	2 1 1 31% 55% 10%	567
	11th to 20th	Night	2 1 3 30% 55% 9%	564
	21st to end	Night	2 2 12% 36% 43% 6%	798
September	1st to 10th	Night	3 2 11% 33% 45% 6%	760
	11th to 20th	Night	6% 3 11% 31% 41% 9%	760
	21st to end	Night	9% 3 10% 37% 34% 8%	760
October	1st to 10th	Night	9% 2 11% 39% 32% 7%	760
	11th to 20th	Night	13% 3 10% 36% 34% 5%	760
	21st to end	Night	17% 3 12% 35% 25% 7%	836
November	1st to 10th	Night	23% 4 10% 41% 19% 4	760
	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 2024-11-02 23:11:06. Version ac07

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