Oregon Star Party
Clear Sky Chart
History

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

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	6% 8% 3 7% 5% 4 4 4 5% 6% 48%	105334
	Night	7% 8% 3 7% 5% 4 5% 4 5% 7% 46%	102397
Transparency	Day	34% 8% 10% 19% 17% 11%	105077
	Night	36% 9% 12% 20% 16% 7%	102243
Seeing	Day	12% 15% 27% 26% 16% 5%	14598
	Night	10% 10% 21% 35% 21% 3	23678

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	8% 15% 5% 12% 8% 7% 7% 6% 8% 7% 16%	2539
	11th to 20th	Day	13% 18% 6% 9% 7% 6% 5% 4 5% 5% 21%	2540
	21st to end	Day	16% 18% 4 11% 7% 4 5% 4 6% 6% 19%	2891
February	1st to 10th	Day	6% 12% 5% 11% 7% 6% 6% 5% 8% 8% 26%	1710
	11th to 20th	Day	7% 13% 4 9% 7% 6% 5% 4 7% 7% 30%	1724
	21st to end	Day	5% 13% 4 10% 8% 8% 8% 6% 7% 8% 25%	1570
March	1st to 10th	Day	8% 13% 6% 11% 7% 6% 6% 4 6% 7% 28%	3138
	11th to 20th	Day	5% 10% 3 7% 5% 5% 4 3 4 5% 49%	3414
	21st to end	Day	7% 16% 5% 11% 7% 6% 7% 4 5% 6% 25%	4070
April	1st to 10th	Day	9% 13% 5% 10% 6% 6% 6% 4 6% 6% 30%	2280
	11th to 20th	Day	8% 11% 4 9% 6% 4 4 4 6% 6% 36%	2249
	21st to end	Day	7% 10% 3 8% 6% 5% 5% 4 6% 7% 39%	2339
May	1st to 10th	Day	10% 11% 2 7% 4 5% 5% 4 5% 6% 43%	4407
	11th to 20th	Day	5% 5% 2 5% 3 3 3 4 4 6% 60%	4377
	21st to end	Day	6% 10% 3 7% 5% 4 5% 4 6% 8% 43%	4813
June	1st to 10th	Day	12% 8% 3 7% 5% 5% 5% 4 5% 8% 39%	2660
	11th to 20th	Day	6% 6% 2 6% 4 4 4 3 6% 7% 50%	2660
	21st to end	Day	3 3 1 4 3 4 4 3 5% 6% 64%	2660
July	1st to 10th	Day	1 1 2 1 2 2 2 3 4 82%	4420
	11th to 20th	Day	2 1 1 2 3 2 2 2 3 4 79%	4420
	21st to end	Day	1 1 1 2 2 2 2 2 3 4 79%	4790
August	1st to 10th	Day	4 3 1 4 3 3 3 2 5% 7% 66%	4326
	11th to 20th	Day	2 2 1 3 2 2 2 2 4 5% 74%	3912
	21st to end	Day	3 2 1 3 3 2 3 2 4 4 73%	4180
September	1st to 10th	Day	2 2 1 3 2 2 2 3 3 5% 74%	2280
	11th to 20th	Day	5% 4 1 5% 4 3 4 3 5% 7% 57%	2271
	21st to end	Day	5% 5% 2 6% 3 4 3 3 5% 7% 57%	2071
October	1st to 10th	Day	4 5% 2 4 3 3 3 3 4 6% 64%	3180
	11th to 20th	Day	5% 5% 2 6% 5% 5% 6% 4 6% 8% 47%	3161
	21st to end	Day	9% 10% 4 9% 5% 5% 6% 4 6% 7% 37%	3200
November	1st to 10th	Day	11% 10% 4 8% 6% 5% 5% 4 6% 9% 32%	1719
	11th to 20th	Day	10% 12% 3 9% 7% 6% 6% 5% 6% 8% 28%	1601
	21st to end	Day	7% 11% 3 8% 7% 6% 5% 5% 5% 9% 33%	1520
December	1st to 10th	Day	9% 13% 4 11% 7% 5% 6% 5% 6% 6% 29%	1520
	11th to 20th	Day	12% 14% 5% 9% 7% 6% 6% 5% 8% 8% 21%	1928
	21st to end	Day	8% 16% 6% 15% 10% 8% 6% 4 5% 6% 17%	2794
January	1st to 10th	Night	10% 14% 4 10% 7% 6% 7% 5% 7% 8% 21%	4406
	11th to 20th	Night	13% 18% 5% 9% 6% 6% 5% 4 6% 6% 22%	4420
	21st to end	Night	16% 14% 3 8% 6% 6% 6% 4 6% 8% 23%	4765
February	1st to 10th	Night	7% 12% 4 10% 7% 5% 5% 5% 7% 8% 30%	2470
	11th to 20th	Night	8% 11% 4 8% 6% 5% 5% 5% 6% 9% 33%	2341
	21st to end	Night	6% 11% 4 9% 6% 6% 7% 5% 9% 9% 29%	1884
March	1st to 10th	Night	6% 12% 5% 8% 5% 5% 6% 6% 6% 8% 32%	3736
	11th to 20th	Night	5% 9% 2 5% 4 4 5% 4 5% 6% 50%	3563
	21st to end	Night	6% 11% 4 10% 7% 6% 7% 6% 8% 8% 26%	3581
April	1st to 10th	Night	9% 11% 3 7% 6% 4 5% 4 6% 7% 37%	1900
	11th to 20th	Night	7% 11% 4 7% 6% 5% 4 4 6% 6% 42%	1879
	21st to end	Night	6% 8% 3 7% 5% 5% 5% 5% 6% 8% 42%	1839
May	1st to 10th	Night	6% 12% 2 7% 4 3 4 3 6% 7% 45%	2550
	11th to 20th	Night	4 3 1 4 4 3 3 3 4 7% 65%	2516
	21st to end	Night	5% 6% 2 6% 4 3 4 4 5% 7% 54%	2762
June	1st to 10th	Night	10% 6% 2 6% 4 3 4 5% 6% 7% 48%	1520
	11th to 20th	Night	5% 4 2 5% 4 4 3 3 5% 7% 59%	1520
	21st to end	Night	4 3 1 3 3 3 3 3 4 7% 66%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 2 3 4 84%	2540
	11th to 20th	Night	2 1 1 2 2 2 2 3 3 4 78%	2540
	21st to end	Night	2 2 1 2 2 2 2 2 3 4 80%	2761
August	1st to 10th	Night	2 2 2 5% 2 3 4 3 5% 6% 65%	2590
	11th to 20th	Night	2 2 1 2 2 3 3 2 4 5% 73%	2930
	21st to end	Night	2 1 1 2 2 2 2 2 3 4 78%	3498
September	1st to 10th	Night	2 1 1 3 2 2 3 2 4 6% 74%	1900
	11th to 20th	Night	2 3 1 4 3 3 4 4 5% 7% 63%	1909
	21st to end	Night	5% 4 2 4 3 4 4 3 5% 5% 62%	2105
October	1st to 10th	Night	4 3 2 4 2 2 2 2 4 5% 69%	3800
	11th to 20th	Night	6% 6% 2 5% 4 3 4 3 5% 7% 55%	3777
	21st to end	Night	6% 7% 3 7% 4 5% 5% 5% 6% 8% 45%	4361
November	1st to 10th	Night	11% 11% 3 8% 5% 6% 5% 4 5% 7% 35%	2482
	11th to 20th	Night	11% 9% 4 8% 6% 6% 4 5% 7% 7% 33%	2574
	21st to end	Night	6% 11% 3 7% 6% 5% 6% 5% 7% 8% 37%	2660
December	1st to 10th	Night	10% 10% 4 10% 6% 5% 6% 4 5% 9% 31%	2660
	11th to 20th	Night	13% 13% 5% 10% 6% 5% 6% 4 6% 8% 24%	3276
	21st to end	Night	8% 13% 5% 13% 8% 6% 6% 4 5% 7% 25%	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	61% 14% 12% 10% 2	2539
	11th to 20th	Day	62% 9% 11% 11% 4 2	2540
	21st to end	Day	59% 13% 11% 12% 4 1	2891
February	1st to 10th	Day	52% 12% 15% 16% 5%	1710
	11th to 20th	Day	50% 11% 13% 15% 8% 2	1733
	21st to end	Day	52% 15% 13% 12% 6% 1	1570
March	1st to 10th	Day	47% 15% 11% 19% 7% 1	3138
	11th to 20th	Day	34% 9% 11% 34% 12%	3414
	21st to end	Day	53% 15% 14% 14% 4	4070
April	1st to 10th	Day	52% 10% 14% 15% 8% 1	2280
	11th to 20th	Day	45% 10% 12% 18% 12% 2	2252
	21st to end	Day	41% 10% 13% 23% 12% 2	2339
May	1st to 10th	Day	38% 10% 12% 25% 13% 1	4407
	11th to 20th	Day	25% 5% 9% 27% 29% 5%	4380
	21st to end	Day	35% 11% 19% 24% 10% 1	4814
June	1st to 10th	Day	42% 8% 11% 28% 11% 1	2660
	11th to 20th	Day	30% 8% 12% 27% 19% 4	2660
	21st to end	Day	20% 6% 10% 23% 30% 11%	2660
July	1st to 10th	Day	8% 3 5% 11% 20% 53%	4351
	11th to 20th	Day	10% 3 4 8% 21% 54%	4345
	21st to end	Day	10% 3 4 16% 36% 32%	4639
August	1st to 10th	Day	18% 4 5% 13% 30% 29%	4310
	11th to 20th	Day	13% 3 5% 23% 37% 19%	3951
	21st to end	Day	16% 4 7% 25% 27% 22%	4179
September	1st to 10th	Day	13% 4 6% 24% 29% 24%	2280
	11th to 20th	Day	25% 7% 10% 21% 24% 13%	2271
	21st to end	Day	27% 6% 11% 22% 23% 10%	2071
October	1st to 10th	Day	23% 6% 10% 21% 28% 13%	3180
	11th to 20th	Day	33% 6% 16% 24% 18% 3	3161
	21st to end	Day	45% 7% 10% 22% 15% 2	3200
November	1st to 10th	Day	46% 11% 14% 18% 10% 1	1719
	11th to 20th	Day	51% 12% 13% 16% 7% 1	1601
	21st to end	Day	47% 12% 11% 14% 13% 3	1520
December	1st to 10th	Day	54% 10% 12% 15% 8% 1	1520
	11th to 20th	Day	56% 11% 13% 14% 5% 1	1928
	21st to end	Day	60% 13% 11% 12% 4	2794
January	1st to 10th	Night	56% 15% 14% 10% 4	4406
	11th to 20th	Night	61% 10% 11% 11% 5% 2	4420
	21st to end	Night	55% 13% 14% 11% 6% 1	4765
February	1st to 10th	Night	51% 10% 15% 15% 8%	2470
	11th to 20th	Night	48% 10% 13% 17% 9% 2	2343
	21st to end	Night	48% 15% 13% 15% 8% 2	1884
March	1st to 10th	Night	41% 12% 13% 25% 8% 1	3736
	11th to 20th	Night	32% 10% 11% 35% 12% 1	3563
	21st to end	Night	49% 17% 14% 15% 4 1	3581
April	1st to 10th	Night	45% 10% 17% 19% 8% 1	1900
	11th to 20th	Night	41% 9% 15% 23% 10% 1	1879
	21st to end	Night	37% 12% 16% 23% 11% 1	1839
May	1st to 10th	Night	35% 10% 15% 27% 13%	2550
	11th to 20th	Night	20% 6% 11% 34% 27% 1	2516
	21st to end	Night	28% 9% 27% 29% 6%	2762
June	1st to 10th	Night	35% 9% 13% 30% 13% 1	1520
	11th to 20th	Night	26% 8% 14% 32% 18% 3	1520
	21st to end	Night	18% 5% 12% 29% 27% 9%	1520
July	1st to 10th	Night	7% 3 6% 13% 21% 50%	2500
	11th to 20th	Night	10% 3 5% 11% 23% 48%	2492
	21st to end	Night	10% 2 3 16% 37% 32%	2674
August	1st to 10th	Night	19% 4 6% 17% 30% 24%	2582
	11th to 20th	Night	13% 4 6% 30% 34% 13%	2957
	21st to end	Night	12% 3 10% 28% 27% 21%	3498
September	1st to 10th	Night	11% 4 6% 27% 33% 19%	1900
	11th to 20th	Night	19% 8% 9% 24% 26% 14%	1909
	21st to end	Night	23% 5% 10% 25% 23% 14%	2105
October	1st to 10th	Night	20% 4 8% 22% 34% 12%	3800
	11th to 20th	Night	30% 5% 19% 21% 23% 3	3777
	21st to end	Night	36% 7% 11% 27% 16% 2	4361
November	1st to 10th	Night	46% 11% 11% 15% 14% 2	2482
	11th to 20th	Night	47% 11% 15% 17% 9% 1	2574
	21st to end	Night	43% 11% 12% 15% 17% 3	2660
December	1st to 10th	Night	49% 11% 14% 15% 9% 2	2660
	11th to 20th	Night	55% 10% 12% 16% 7%	3276
	21st to end	Night	52% 13% 13% 13% 7% 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	32% 13% 29% 13% 12% 1	180
	11th to 20th	Day	22% 16% 27% 23% 9% 3	180
	21st to end	Day	13% 20% 29% 25% 11% 2	256
February	1st to 10th	Day	15% 25% 31% 22% 8% 1	370
	11th to 20th	Day	16% 25% 31% 21% 7% 1	394
	21st to end	Day	14% 23% 32% 23% 7%	382
March	1st to 10th	Day	16% 22% 33% 22% 6%	460
	11th to 20th	Day	16% 20% 30% 22% 11% 1	460
	21st to end	Day	20% 23% 29% 21% 6% 1	506
April	1st to 10th	Day	22% 20% 28% 19% 8% 3	460
	11th to 20th	Day	16% 24% 30% 16% 10% 4	452
	21st to end	Day	11% 23% 31% 23% 10% 2	460
May	1st to 10th	Day	14% 21% 29% 20% 12% 3	463
	11th to 20th	Day	16% 19% 24% 23% 15% 4	488
	21st to end	Day	14% 13% 23% 25% 18% 7%	529
June	1st to 10th	Day	15% 13% 26% 23% 17% 7%	490
	11th to 20th	Day	10% 21% 28% 24% 14% 3	490
	21st to end	Day	3 10% 28% 30% 21% 7%	490
July	1st to 10th	Day	3 7% 28% 35% 23% 4	486
	11th to 20th	Day	2 8% 28% 33% 22% 7%	484
	21st to end	Day	2 6% 27% 36% 21% 8%	531
August	1st to 10th	Day	2 6% 25% 35% 22% 9%	487
	11th to 20th	Day	3 5% 19% 33% 26% 14%	477
	21st to end	Day	4 9% 23% 30% 25% 9%	539
September	1st to 10th	Day	4 6% 23% 30% 27% 9%	490
	11th to 20th	Day	7% 10% 21% 33% 21% 7%	490
	21st to end	Day	10% 11% 23% 30% 22% 4	490
October	1st to 10th	Day	11% 14% 22% 28% 17% 7%	490
	11th to 20th	Day	12% 15% 19% 28% 19% 6%	490
	21st to end	Day	14% 18% 23% 22% 17% 5%	392
November	1st to 10th	Day	17% 17% 27% 27% 12%	285
	11th to 20th	Day	18% 14% 27% 24% 15% 2	219
	21st to end	Day	14% 15% 24% 34% 10% 2	180
December	1st to 10th	Day	18% 18% 29% 19% 9% 6%	180
	11th to 20th	Day	18% 20% 36% 20% 6%	180
	21st to end	Day	19% 16% 30% 26% 8% 2	198
January	1st to 10th	Night	16% 14% 26% 25% 16% 2	760
	11th to 20th	Night	16% 14% 20% 27% 19% 4	760
	21st to end	Night	16% 10% 19% 34% 18% 3	836
February	1st to 10th	Night	12% 16% 24% 31% 15% 1	760
	11th to 20th	Night	14% 12% 24% 32% 16% 2	744
	21st to end	Night	13% 14% 23% 37% 11% 1	628
March	1st to 10th	Night	12% 15% 26% 31% 14% 2	760
	11th to 20th	Night	12% 12% 25% 33% 17% 1	760
	21st to end	Night	12% 16% 25% 33% 13% 1	836
April	1st to 10th	Night	15% 13% 23% 30% 16% 2	760
	11th to 20th	Night	11% 16% 27% 27% 16% 3	751
	21st to end	Night	9% 12% 27% 33% 16% 2	699
May	1st to 10th	Night	8% 10% 29% 32% 20% 2	390
	11th to 20th	Night	8% 10% 18% 32% 30% 2	374
	21st to end	Night	9% 8% 21% 34% 24% 3	411
June	1st to 10th	Night	12% 6% 21% 38% 22% 1	380
	11th to 20th	Night	6% 8% 25% 44% 16% 1	380
	21st to end	Night	5% 4 19% 44% 25% 2	380
July	1st to 10th	Night	1 3 16% 48% 29% 2	370
	11th to 20th	Night	1 1 22% 49% 24% 2	368
	21st to end	Night	2 2 19% 46% 29% 3	416
August	1st to 10th	Night	3 13% 49% 32% 3	413
	11th to 20th	Night	3 2 11% 40% 38% 6%	630
	21st to end	Night	3 3 18% 42% 32% 3	836
September	1st to 10th	Night	2 3 17% 42% 34% 3	760
	11th to 20th	Night	4 4 16% 37% 32% 8%	760
	21st to end	Night	6% 6% 15% 36% 32% 5%	760
October	1st to 10th	Night	8% 5% 19% 38% 26% 4	760
	11th to 20th	Night	9% 9% 18% 35% 23% 5%	760
	21st to end	Night	11% 10% 20% 35% 18% 5%	836
November	1st to 10th	Night	15% 13% 21% 35% 17% 1	764
	11th to 20th	Night	14% 14% 21% 34% 15% 2	760
	21st to end	Night	12% 14% 20% 33% 17% 4	760
December	1st to 10th	Night	15% 11% 20% 32% 18% 3	760
	11th to 20th	Night	16% 13% 23% 30% 16% 1	760
	21st to end	Night	18% 16% 27% 28% 10% 1	836

Page generated at 2024-11-03 10:19:00. Version ac07

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