Salem (OR)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salem (OR) clear sky chart from 2005-11-06 to 2024-10-25.

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	16% 8% 3 8% 5% 4 4 3 5% 6% 38%	101462
	Night	18% 9% 3 8% 5% 4 4 3 4 5% 36%	97516
Transparency	Day	47% 4 12% 19% 13% 5%	101206
	Night	51% 4 12% 18% 11% 4	97361
Seeing	Day	18% 10% 20% 26% 21% 7%	14665
	Night	20% 7% 19% 33% 20% 2	23583

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	33% 17% 6% 15% 7% 5% 4 2 3 2 7%	2539
	11th to 20th	Day	39% 12% 4 11% 5% 5% 4 3 2 3 12%	2540
	21st to end	Day	28% 12% 5% 13% 7% 5% 5% 3 5% 5% 12%	3118
February	1st to 10th	Day	26% 11% 5% 10% 7% 5% 5% 4 5% 6% 14%	1710
	11th to 20th	Day	25% 13% 4 12% 7% 5% 4 3 4 6% 16%	1665
	21st to end	Day	26% 15% 4 11% 6% 4 5% 3 5% 5% 17%	1482
March	1st to 10th	Day	17% 13% 5% 11% 7% 7% 6% 5% 6% 6% 16%	3321
	11th to 20th	Day	17% 9% 3 8% 6% 5% 5% 3 5% 5% 35%	3490
	21st to end	Day	21% 12% 5% 11% 7% 6% 6% 4 6% 5% 17%	3881
April	1st to 10th	Day	24% 12% 4 10% 7% 6% 5% 3 5% 6% 18%	2280
	11th to 20th	Day	20% 11% 4 9% 5% 5% 5% 4 5% 5% 26%	2249
	21st to end	Day	18% 10% 4 8% 6% 5% 6% 3 6% 8% 27%	2468
May	1st to 10th	Day	20% 8% 3 7% 5% 5% 4 4 5% 6% 34%	4309
	11th to 20th	Day	10% 5% 2 6% 3 3 4 3 4 7% 53%	4377
	21st to end	Day	16% 7% 3 8% 7% 6% 6% 5% 6% 7% 28%	4813
June	1st to 10th	Day	19% 8% 3 7% 5% 4 4 4 5% 6% 34%	2660
	11th to 20th	Day	15% 8% 3 8% 6% 6% 5% 4 6% 7% 32%	2660
	21st to end	Day	8% 4 2 5% 4 4 4 3 5% 6% 55%	2660
July	1st to 10th	Day	3 2 1 2 2 2 2 2 3 5% 75%	4420
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 76%	4420
	21st to end	Day	4 2 1 2 2 1 2 2 3 4 77%	4762
August	1st to 10th	Day	2 2 1 3 3 3 3 2 4 6% 70%	4091
	11th to 20th	Day	4 4 2 5% 4 4 3 3 6% 7% 58%	4026
	21st to end	Day	6% 5% 2 5% 3 3 4 4 5% 7% 57%	4309
September	1st to 10th	Day	6% 3 1 4 3 3 2 3 5% 7% 64%	2280
	11th to 20th	Day	9% 7% 3 7% 5% 3 5% 4 5% 6% 45%	2266
	21st to end	Day	14% 5% 3 7% 4 4 5% 3 4 6% 46%	2006
October	1st to 10th	Day	16% 7% 3 7% 5% 4 5% 4 5% 7% 39%	1900
	11th to 20th	Day	16% 10% 4 10% 6% 5% 5% 3 5% 7% 30%	1900
	21st to end	Day	20% 12% 4 11% 6% 4 4 3 5% 5% 27%	2007
November	1st to 10th	Day	27% 14% 5% 12% 6% 4 4 4 4 5% 15%	1571
	11th to 20th	Day	27% 12% 4 11% 8% 5% 4 4 4 5% 17%	1520
	21st to end	Day	24% 11% 4 12% 6% 5% 4 4 4 7% 19%	1520
December	1st to 10th	Day	25% 13% 5% 11% 6% 4 3 4 4 5% 21%	1520
	11th to 20th	Day	26% 11% 5% 13% 8% 6% 6% 5% 5% 6% 9%	1928
	21st to end	Day	30% 14% 6% 17% 8% 6% 5% 3 4 3 6%	2794
January	1st to 10th	Night	31% 18% 6% 11% 5% 5% 4 3 4 3 10%	4406
	11th to 20th	Night	37% 15% 4 8% 4 4 4 2 3 4 15%	4420
	21st to end	Night	32% 14% 5% 11% 6% 5% 4 3 4 4 14%	4548
February	1st to 10th	Night	24% 13% 5% 10% 6% 6% 5% 3 5% 6% 17%	2470
	11th to 20th	Night	25% 12% 4 9% 5% 4 5% 3 4 5% 24%	2402
	21st to end	Night	25% 13% 4 9% 6% 4 4 4 4 6% 21%	1971
March	1st to 10th	Night	16% 14% 4 12% 6% 7% 6% 5% 5% 6% 20%	3550
	11th to 20th	Night	15% 7% 3 7% 5% 4 5% 3 6% 6% 39%	3490
	21st to end	Night	19% 13% 5% 12% 7% 6% 6% 4 5% 5% 18%	3772
April	1st to 10th	Night	24% 11% 3 9% 6% 4 4 3 6% 5% 23%	1900
	11th to 20th	Night	18% 11% 3 7% 5% 5% 5% 3 5% 7% 32%	1879
	21st to end	Night	19% 9% 3 8% 5% 5% 5% 4 6% 7% 31%	1710
May	1st to 10th	Night	19% 8% 3 8% 4 4 4 3 4 5% 38%	2651
	11th to 20th	Night	8% 5% 2 4 4 3 3 3 4 6% 57%	2516
	21st to end	Night	13% 7% 2 6% 4 5% 5% 4 7% 9% 37%	2762
June	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 4 8% 38%	1520
	11th to 20th	Night	13% 8% 3 7% 5% 5% 4 3 6% 6% 43%	1520
	21st to end	Night	6% 5% 2 5% 4 3 3 3 4 6% 60%	1520
July	1st to 10th	Night	3 1 1 2 1 1 2 1 2 4 81%	2540
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 4 79%	2540
	21st to end	Night	3 2 2 1 2 1 1 3 4 81%	2786
August	1st to 10th	Night	1 2 1 2 2 1 2 2 3 6% 77%	2848
	11th to 20th	Night	5% 4 2 4 3 4 4 3 5% 7% 61%	2812
	21st to end	Night	8% 4 1 4 2 3 2 3 3 5% 65%	3365
September	1st to 10th	Night	5% 3 1 3 2 2 2 3 5% 6% 68%	1900
	11th to 20th	Night	8% 5% 2 6% 5% 5% 4 3 5% 6% 51%	1911
	21st to end	Night	9% 5% 2 6% 4 3 4 3 4 8% 53%	2173
October	1st to 10th	Night	14% 7% 2 6% 4 3 4 4 5% 6% 46%	2280
	11th to 20th	Night	16% 6% 2 6% 5% 5% 5% 4 6% 7% 40%	2280
	21st to end	Night	20% 9% 3 7% 5% 4 3 3 4 6% 36%	2452
November	1st to 10th	Night	26% 9% 3 8% 4 5% 5% 4 6% 6% 23%	2504
	11th to 20th	Night	29% 10% 4 9% 5% 4 5% 3 5% 5% 22%	2660
	21st to end	Night	22% 9% 4 10% 6% 5% 5% 3 5% 5% 27%	2660
December	1st to 10th	Night	26% 10% 3 9% 5% 5% 4 3 5% 5% 24%	2660
	11th to 20th	Night	27% 12% 4 11% 7% 6% 5% 4 5% 6% 15%	3276
	21st to end	Night	24% 13% 5% 15% 7% 6% 5% 4 5% 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	86% 2 6% 4 1 1	2539
	11th to 20th	Day	78% 2 6% 8% 3 1	2540
	21st to end	Day	74% 3 9% 8% 5%	3118
February	1st to 10th	Day	68% 5% 11% 10% 5%	1710
	11th to 20th	Day	69% 5% 10% 10% 5% 1	1674
	21st to end	Day	70% 4 10% 10% 5% 2	1482
March	1st to 10th	Day	66% 3 12% 15% 3	3321
	11th to 20th	Day	51% 4 10% 24% 11% 1	3490
	21st to end	Day	69% 4 14% 8% 4	3881
April	1st to 10th	Day	67% 5% 12% 13% 4	2280
	11th to 20th	Day	60% 6% 12% 13% 7% 3	2252
	21st to end	Day	56% 6% 16% 14% 7% 1	2468
May	1st to 10th	Day	52% 4 12% 20% 12%	4309
	11th to 20th	Day	32% 4 16% 34% 13% 1	4380
	21st to end	Day	52% 6% 23% 16% 3	4814
June	1st to 10th	Day	51% 4 16% 22% 6% 1	2660
	11th to 20th	Day	49% 5% 21% 18% 7%	2660
	21st to end	Day	30% 4 18% 32% 13% 4	2660
July	1st to 10th	Day	14% 2 9% 19% 23% 32%	4351
	11th to 20th	Day	14% 2 6% 19% 38% 22%	4345
	21st to end	Day	13% 3 10% 28% 39% 8%	4611
August	1st to 10th	Day	16% 3 10% 31% 28% 12%	4076
	11th to 20th	Day	24% 5% 18% 33% 17% 3	4065
	21st to end	Day	27% 5% 12% 26% 24% 6%	4308
September	1st to 10th	Day	20% 2 13% 31% 22% 12%	2280
	11th to 20th	Day	38% 4 14% 22% 15% 6%	2266
	21st to end	Day	38% 4 14% 22% 16% 5%	2006
October	1st to 10th	Day	42% 5% 11% 20% 17% 4	1900
	11th to 20th	Day	54% 4 14% 15% 12% 2	1900
	21st to end	Day	59% 4 10% 13% 13% 1	2007
November	1st to 10th	Day	69% 5% 11% 10% 5%	1571
	11th to 20th	Day	70% 4 9% 9% 6% 2	1520
	21st to end	Day	66% 4 8% 9% 12% 1	1520
December	1st to 10th	Day	65% 4 9% 11% 10% 1	1520
	11th to 20th	Day	76% 5% 8% 10% 2	1928
	21st to end	Day	83% 3 8% 4 2	2794
January	1st to 10th	Night	81% 3 7% 5% 3 1	4406
	11th to 20th	Night	76% 2 6% 10% 4 1	4420
	21st to end	Night	76% 2 7% 9% 5% 1	4548
February	1st to 10th	Night	68% 5% 10% 11% 5% 1	2470
	11th to 20th	Night	63% 4 13% 12% 7% 2	2404
	21st to end	Night	65% 4 11% 12% 6% 2	1971
March	1st to 10th	Night	65% 4 12% 15% 4	3550
	11th to 20th	Night	46% 4 15% 22% 12% 1	3490
	21st to end	Night	69% 5% 14% 12% 1	3772
April	1st to 10th	Night	63% 4 14% 13% 6%	1900
	11th to 20th	Night	53% 6% 16% 15% 7% 3	1879
	21st to end	Night	54% 5% 15% 18% 6% 2	1710
May	1st to 10th	Night	49% 5% 11% 23% 10% 2	2651
	11th to 20th	Night	28% 5% 15% 37% 12% 2	2516
	21st to end	Night	44% 6% 31% 16% 3	2762
June	1st to 10th	Night	46% 5% 16% 27% 5% 1	1520
	11th to 20th	Night	42% 6% 19% 25% 8%	1520
	21st to end	Night	27% 4 18% 35% 13% 4	1520
July	1st to 10th	Night	12% 2 8% 21% 26% 31%	2500
	11th to 20th	Night	14% 1 7% 19% 33% 26%	2492
	21st to end	Night	10% 2 12% 31% 37% 8%	2699
August	1st to 10th	Night	12% 3 9% 38% 30% 9%	2839
	11th to 20th	Night	24% 5% 20% 34% 12% 4	2839
	21st to end	Night	24% 4 14% 30% 22% 6%	3365
September	1st to 10th	Night	19% 4 13% 31% 22% 12%	1900
	11th to 20th	Night	33% 4 15% 25% 14% 9%	1911
	21st to end	Night	31% 4 16% 24% 17% 8%	2173
October	1st to 10th	Night	40% 5% 9% 25% 18% 4	2280
	11th to 20th	Night	43% 5% 14% 20% 15% 4	2280
	21st to end	Night	51% 4 10% 16% 16% 3	2452
November	1st to 10th	Night	61% 5% 11% 16% 7%	2504
	11th to 20th	Night	66% 4 10% 10% 8% 2	2660
	21st to end	Night	60% 5% 8% 12% 12% 3	2660
December	1st to 10th	Night	61% 4 11% 12% 10% 1	2660
	11th to 20th	Night	71% 5% 10% 10% 4	3276
	21st to end	Night	77% 4 9% 7% 2 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	40% 13% 19% 17% 9% 2	180
	11th to 20th	Day	32% 14% 14% 24% 11% 4	180
	21st to end	Day	27% 12% 18% 22% 16% 5%	392
February	1st to 10th	Day	33% 12% 17% 18% 16% 4	370
	11th to 20th	Day	30% 11% 27% 17% 10% 4	365
	21st to end	Day	28% 17% 23% 18% 11% 3	341
March	1st to 10th	Day	26% 14% 26% 22% 10% 2	460
	11th to 20th	Day	25% 13% 21% 20% 16% 4	460
	21st to end	Day	26% 17% 23% 22% 11% 2	506
April	1st to 10th	Day	26% 16% 23% 18% 13% 4	460
	11th to 20th	Day	25% 15% 24% 21% 9% 6%	452
	21st to end	Day	20% 15% 24% 23% 15% 3	460
May	1st to 10th	Day	17% 12% 21% 28% 17% 5%	463
	11th to 20th	Day	22% 9% 17% 24% 19% 8%	488
	21st to end	Day	13% 9% 19% 26% 24% 9%	529
June	1st to 10th	Day	19% 9% 18% 27% 23% 5%	490
	11th to 20th	Day	17% 10% 24% 30% 17% 3	490
	21st to end	Day	6% 6% 17% 35% 30% 7%	490
July	1st to 10th	Day	5% 4 16% 37% 29% 9%	486
	11th to 20th	Day	3 2 18% 38% 29% 10%	484
	21st to end	Day	3 2 14% 32% 38% 10%	531
August	1st to 10th	Day	3 2 12% 34% 35% 14%	487
	11th to 20th	Day	3 3 10% 32% 38% 15%	477
	21st to end	Day	4 4 18% 35% 29% 9%	539
September	1st to 10th	Day	6% 4 20% 28% 33% 9%	490
	11th to 20th	Day	12% 6% 18% 29% 27% 9%	490
	21st to end	Day	12% 7% 23% 29% 22% 6%	490
October	1st to 10th	Day	17% 7% 21% 25% 21% 9%	490
	11th to 20th	Day	18% 10% 17% 26% 20% 9%	490
	21st to end	Day	23% 13% 25% 21% 12% 6%	496
November	1st to 10th	Day	27% 11% 28% 19% 10% 5%	221
	11th to 20th	Day	23% 15% 22% 16% 18% 7%	180
	21st to end	Day	25% 14% 19% 19% 17% 6%	180
December	1st to 10th	Day	31% 10% 19% 19% 15% 6%	180
	11th to 20th	Day	32% 13% 25% 18% 9% 3	180
	21st to end	Day	32% 15% 19% 19% 13% 3	198
January	1st to 10th	Night	35% 11% 18% 20% 13% 3	760
	11th to 20th	Night	32% 11% 16% 21% 18% 2	760
	21st to end	Night	27% 7% 17% 29% 17% 3	836
February	1st to 10th	Night	25% 11% 20% 27% 16% 2	760
	11th to 20th	Night	27% 9% 22% 26% 16% 1	744
	21st to end	Night	28% 13% 20% 27% 12%	628
March	1st to 10th	Night	24% 10% 25% 27% 13% 1	760
	11th to 20th	Night	21% 11% 20% 29% 16% 1	760
	21st to end	Night	25% 11% 23% 27% 13% 1	836
April	1st to 10th	Night	26% 10% 21% 25% 18% 1	760
	11th to 20th	Night	20% 10% 23% 30% 16% 1	751
	21st to end	Night	19% 7% 23% 34% 16% 1	570
May	1st to 10th	Night	13% 6% 25% 39% 17% 1	452
	11th to 20th	Night	16% 4 17% 39% 23% 2	374
	21st to end	Night	14% 6% 19% 38% 21% 1	411
June	1st to 10th	Night	17% 6% 16% 41% 20%	380
	11th to 20th	Night	12% 5% 28% 42% 12% 1	380
	21st to end	Night	8% 1 23% 49% 19%	380
July	1st to 10th	Night	3 2 12% 59% 24%	370
	11th to 20th	Night	5% 2 18% 53% 21%	368
	21st to end	Night	2 2 12% 56% 27% 1	429
August	1st to 10th	Night	3 1 9% 47% 36% 4	567
	11th to 20th	Night	5% 2 7% 43% 41% 2	564
	21st to end	Night	6% 2 15% 45% 29% 2	755
September	1st to 10th	Night	5% 2 17% 45% 31% 1	760
	11th to 20th	Night	9% 3 14% 36% 31% 6%	760
	21st to end	Night	9% 4 16% 40% 27% 3	760
October	1st to 10th	Night	14% 3 21% 33% 26% 3	760
	11th to 20th	Night	18% 4 15% 34% 25% 4	760
	21st to end	Night	22% 8% 22% 27% 18% 4	812
November	1st to 10th	Night	26% 10% 18% 31% 15% 1	740
	11th to 20th	Night	31% 9% 21% 25% 13% 1	760
	21st to end	Night	23% 7% 20% 29% 18% 2	760
December	1st to 10th	Night	28% 8% 17% 28% 16% 3	760
	11th to 20th	Night	31% 11% 20% 23% 15% 1	760
	21st to end	Night	32% 12% 21% 23% 10% 1	836

Page generated at 2024-10-22 17:21:06. Version ac07

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