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 2025-04-26.

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% 5% 4 3 5% 6% 36%	117850
	Night	18% 9% 3 8% 5% 4 4 3 5% 6% 34%	119598
Transparency	Day	49% 4 12% 18% 13% 4	117594
	Night	52% 5% 12% 18% 11% 3	119443
Seeing	Day	18% 10% 20% 26% 20% 6%	15201
	Night	20% 7% 19% 33% 19% 2	24307

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	32% 16% 5% 14% 7% 5% 4 2 3 4 7%	3639
	11th to 20th	Day	27% 9% 3 10% 7% 6% 5% 4 4 6% 18%	3640
	21st to end	Day	20% 9% 4 10% 6% 5% 5% 3 5% 5% 27%	4482
February	1st to 10th	Day	26% 12% 5% 10% 7% 5% 6% 4 5% 7% 14%	1800
	11th to 20th	Day	25% 14% 4 12% 7% 5% 4 3 4 5% 16%	1755
	21st to end	Day	25% 14% 4 11% 6% 4 5% 3 4 5% 17%	1558
March	1st to 10th	Day	16% 12% 5% 11% 7% 7% 6% 5% 7% 7% 18%	4779
	11th to 20th	Day	21% 13% 4 9% 6% 5% 5% 3 5% 5% 25%	5000
	21st to end	Day	19% 11% 5% 12% 7% 7% 7% 5% 7% 7% 14%	5568
April	1st to 10th	Day	24% 11% 4 10% 7% 6% 5% 3 5% 6% 18%	2400
	11th to 20th	Day	20% 11% 4 9% 5% 5% 5% 3 5% 6% 28%	2369
	21st to end	Day	18% 10% 4 8% 6% 5% 6% 3 6% 8% 28%	2536
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	13% 5% 2 6% 4 4 4 4 5% 6% 45%	3180
	11th to 20th	Day	15% 8% 3 8% 6% 6% 6% 4 7% 8% 29%	3161
	21st to end	Day	19% 11% 4 11% 6% 5% 4 3 6% 8% 22%	3417
November	1st to 10th	Day	26% 14% 5% 12% 6% 4 4 4 4 6% 15%	1655
	11th to 20th	Day	26% 13% 4 11% 8% 5% 4 4 4 5% 16%	1600
	21st to end	Day	24% 11% 4 13% 6% 5% 4 4 4 6% 19%	1600
December	1st to 10th	Day	20% 9% 4 13% 7% 5% 4 3 4 7% 26%	2620
	11th to 20th	Day	25% 12% 6% 15% 8% 7% 6% 4 5% 5% 7%	3028
	21st to end	Day	30% 15% 6% 16% 7% 6% 4 3 4 3 6%	4004
January	1st to 10th	Night	30% 17% 6% 12% 6% 5% 4 3 4 4 11%	6306
	11th to 20th	Night	27% 11% 3 8% 7% 5% 4 3 4 5% 22%	6320
	21st to end	Night	23% 11% 4 9% 5% 4 4 3 4 4 30%	6495
February	1st to 10th	Night	23% 14% 5% 10% 6% 6% 5% 4 5% 6% 17%	2600
	11th to 20th	Night	26% 12% 4 9% 5% 4 5% 3 4 5% 24%	2532
	21st to end	Night	24% 13% 3 9% 6% 4 4 4 4 6% 21%	2071
March	1st to 10th	Night	15% 12% 4 11% 7% 7% 7% 6% 7% 6% 20%	5112
	11th to 20th	Night	18% 11% 4 10% 6% 5% 5% 3 5% 5% 28%	5000
	21st to end	Night	18% 12% 5% 13% 8% 6% 6% 4 6% 7% 16%	5407
April	1st to 10th	Night	23% 11% 4 10% 6% 5% 4 3 6% 5% 23%	2000
	11th to 20th	Night	17% 10% 3 7% 5% 4 4 3 5% 7% 34%	1979
	21st to end	Night	18% 9% 3 8% 5% 5% 5% 3 6% 7% 31%	1758
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	11% 5% 2 6% 4 4 4 3 5% 6% 50%	3800
	11th to 20th	Night	14% 6% 2 6% 4 5% 6% 4 6% 9% 38%	3777
	21st to end	Night	19% 9% 3 9% 6% 5% 5% 4 5% 7% 28%	4149
November	1st to 10th	Night	25% 9% 3 9% 4 6% 5% 4 6% 6% 23%	2640
	11th to 20th	Night	29% 11% 4 9% 5% 4 4 3 5% 4 21%	2800
	21st to end	Night	22% 9% 4 11% 6% 5% 5% 3 5% 5% 26%	2800
December	1st to 10th	Night	17% 8% 3 8% 7% 5% 5% 4 6% 7% 31%	4560
	11th to 20th	Night	30% 14% 6% 13% 7% 5% 4 3 4 4 10%	5176
	21st to end	Night	26% 13% 5% 14% 7% 6% 5% 4 5% 4 11%	6952

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 6% 5% 3	3639
	11th to 20th	Day	65% 5% 7% 15% 8% 1	3640
	21st to end	Day	58% 4 8% 13% 15% 3	4482
February	1st to 10th	Day	69% 5% 11% 10% 5%	1800
	11th to 20th	Day	69% 5% 10% 10% 5% 1	1764
	21st to end	Day	69% 4 10% 9% 5% 2	1558
March	1st to 10th	Day	62% 4 13% 17% 4	4779
	11th to 20th	Day	61% 4 9% 18% 8% 1	5000
	21st to end	Day	69% 5% 15% 9% 3	5568
April	1st to 10th	Day	67% 5% 11% 13% 3	2400
	11th to 20th	Day	58% 5% 12% 15% 8% 2	2372
	21st to end	Day	55% 5% 16% 14% 8% 1	2536
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	35% 6% 9% 23% 23% 3	3180
	11th to 20th	Day	50% 6% 16% 16% 11% 1	3161
	21st to end	Day	58% 5% 10% 16% 10% 1	3417
November	1st to 10th	Day	69% 5% 11% 11% 4	1655
	11th to 20th	Day	70% 4 9% 9% 5% 2	1600
	21st to end	Day	66% 4 8% 9% 11% 1	1600
December	1st to 10th	Day	58% 4 10% 15% 13% 1	2620
	11th to 20th	Day	79% 5% 7% 8% 1	3028
	21st to end	Day	83% 4 7% 5% 2	4004
January	1st to 10th	Night	79% 3 8% 6% 4 1	6306
	11th to 20th	Night	63% 5% 7% 16% 7% 1	6320
	21st to end	Night	59% 3 6% 14% 15% 4	6495
February	1st to 10th	Night	68% 5% 10% 11% 5% 1	2600
	11th to 20th	Night	63% 4 13% 12% 7% 2	2534
	21st to end	Night	65% 4 11% 12% 6% 2	2071
March	1st to 10th	Night	62% 5% 13% 15% 5%	5112
	11th to 20th	Night	58% 4 12% 17% 8% 1	5000
	21st to end	Night	67% 6% 15% 10% 1	5407
April	1st to 10th	Night	63% 4 14% 14% 6%	2000
	11th to 20th	Night	52% 5% 15% 17% 8% 3	1979
	21st to end	Night	53% 5% 15% 18% 7% 2	1758
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	33% 6% 8% 29% 22% 2	3800
	11th to 20th	Night	42% 6% 21% 19% 10% 2	3777
	21st to end	Night	56% 5% 11% 16% 10% 2	4149
November	1st to 10th	Night	61% 6% 11% 15% 7%	2640
	11th to 20th	Night	67% 4 10% 10% 8% 2	2800
	21st to end	Night	61% 5% 9% 11% 12% 3	2800
December	1st to 10th	Night	50% 6% 10% 21% 12% 1	4560
	11th to 20th	Night	78% 5% 8% 7% 3	5176
	21st to end	Night	76% 5% 10% 6% 2	6952

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	41% 12% 20% 18% 9% 2	200
	11th to 20th	Day	29% 14% 16% 25% 12% 6%	200
	21st to end	Day	25% 12% 19% 22% 17% 6%	425
February	1st to 10th	Day	33% 13% 18% 18% 15% 4	400
	11th to 20th	Day	31% 12% 27% 17% 10% 3	395
	21st to end	Day	28% 17% 21% 20% 11% 3	369
March	1st to 10th	Day	25% 14% 28% 21% 10% 1	500
	11th to 20th	Day	27% 14% 21% 19% 15% 3	500
	21st to end	Day	26% 17% 23% 22% 10% 1	550
April	1st to 10th	Day	26% 16% 23% 19% 12% 4	500
	11th to 20th	Day	23% 15% 24% 22% 10% 5%	492
	21st to end	Day	20% 15% 23% 23% 16% 3	481
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	24% 13% 25% 20% 12% 6%	520
November	1st to 10th	Day	28% 11% 27% 18% 11% 5%	245
	11th to 20th	Day	26% 16% 20% 17% 16% 6%	200
	21st to end	Day	25% 13% 18% 21% 18% 6%	200
December	1st to 10th	Day	29% 9% 18% 20% 18% 8%	200
	11th to 20th	Day	32% 15% 25% 18% 8% 3	200
	21st to end	Day	33% 16% 19% 19% 11% 2	220
January	1st to 10th	Night	36% 11% 18% 20% 12% 2	800
	11th to 20th	Night	31% 11% 17% 22% 18% 2	800
	21st to end	Night	26% 7% 17% 30% 17% 3	880
February	1st to 10th	Night	25% 11% 20% 27% 16% 2	800
	11th to 20th	Night	28% 9% 22% 25% 15% 1	784
	21st to end	Night	28% 13% 20% 27% 12%	660
March	1st to 10th	Night	24% 10% 25% 28% 13% 1	800
	11th to 20th	Night	22% 12% 21% 29% 16% 1	800
	21st to end	Night	26% 11% 23% 26% 13% 1	880
April	1st to 10th	Night	26% 10% 20% 26% 18% 1	800
	11th to 20th	Night	19% 10% 24% 31% 16% 1	791
	21st to end	Night	19% 6% 23% 34% 17% 1	586
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% 9% 22% 27% 17% 3	836
November	1st to 10th	Night	26% 9% 18% 31% 15% 1	780
	11th to 20th	Night	32% 10% 20% 24% 13% 1	800
	21st to end	Night	23% 8% 20% 29% 19% 2	800
December	1st to 10th	Night	27% 8% 17% 28% 17% 3	800
	11th to 20th	Night	32% 10% 20% 22% 14% 1	800
	21st to end	Night	32% 13% 21% 23% 10% 1	880

Page generated at 2025-04-23 06:25:01. Version ac07

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