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 2026-08-30.

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	14% 7% 3 8% 5% 4 4 3 5% 6% 41%	153387
	Night	16% 8% 3 8% 5% 4 4 3 5% 6% 37%	146192
Transparency	Day	44% 4 13% 21% 14% 4	148170
	Night	49% 4 12% 19% 12% 3	142408
Seeing	Day	17% 10% 20% 26% 20% 6%	16970
	Night	20% 7% 19% 33% 19% 2	25849

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	30% 16% 5% 14% 7% 6% 5% 3 4 4 6%	4722
	11th to 20th	Day	21% 7% 3 9% 7% 6% 4 3 4 7% 29%	4740
	21st to end	Day	18% 9% 4 11% 7% 6% 5% 3 5% 5% 26%	5801
February	1st to 10th	Day	25% 12% 5% 10% 7% 5% 6% 4 5% 7% 14%	1890
	11th to 20th	Day	25% 14% 4 12% 7% 5% 4 3 4 5% 16%	1845
	21st to end	Day	26% 14% 4 11% 6% 4 5% 3 4 5% 17%	1634
March	1st to 10th	Day	16% 12% 5% 11% 7% 7% 6% 5% 7% 7% 18%	4885
	11th to 20th	Day	21% 13% 4 9% 6% 5% 5% 3 5% 5% 24%	5110
	21st to end	Day	19% 11% 5% 11% 7% 7% 7% 5% 7% 7% 14%	5691
April	1st to 10th	Day	23% 11% 4 9% 7% 6% 5% 3 6% 7% 18%	2520
	11th to 20th	Day	19% 11% 4 9% 5% 5% 5% 3 5% 6% 28%	2489
	21st to end	Day	18% 9% 4 8% 6% 5% 6% 4 6% 8% 28%	2728
May	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 5% 8% 46%	7980
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	8160
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	8992
June	1st to 10th	Day	18% 8% 3 7% 4 4 4 4 5% 7% 36%	2940
	11th to 20th	Day	14% 7% 3 7% 5% 6% 5% 4 6% 7% 35%	2940
	21st to end	Day	8% 5% 2 5% 4 4 4 3 5% 7% 53%	2940
July	1st to 10th	Day	3 2 1 2 2 2 2 2 3 5% 76%	8219
	11th to 20th	Day	3 2 1 2 1 2 2 2 3 4 79%	8220
	21st to end	Day	3 2 1 2 2 2 2 2 3 4 77%	8868
August	1st to 10th	Day	2 3 1 4 3 3 3 3 4 6% 68%	5907
	11th to 20th	Day	5% 4 2 5% 3 3 3 3 6% 8% 59%	5926
	21st to end	Day	6% 5% 2 5% 3 3 4 4 5% 8% 55%	6278
September	1st to 10th	Day	6% 3 1 4 3 3 3 3 5% 7% 63%	2400
	11th to 20th	Day	9% 7% 3 7% 5% 3 6% 4 5% 6% 46%	2385
	21st to end	Day	14% 5% 2 6% 4 4 5% 3 4 6% 47%	2111
October	1st to 10th	Day	13% 6% 2 7% 4 4 4 4 5% 6% 45%	3280
	11th to 20th	Day	15% 8% 3 8% 6% 6% 6% 4 7% 8% 30%	3261
	21st to end	Day	19% 11% 4 11% 7% 5% 4 3 6% 8% 22%	3526
November	1st to 10th	Day	26% 13% 5% 12% 6% 4 5% 4 4 6% 15%	1739
	11th to 20th	Day	26% 13% 4 12% 9% 5% 4 4 4 5% 16%	1680
	21st to end	Day	24% 11% 4 13% 6% 5% 4 4 4 7% 18%	1680
December	1st to 10th	Day	20% 9% 4 13% 7% 5% 4 3 4 7% 25%	2700
	11th to 20th	Day	24% 13% 5% 15% 8% 7% 6% 4 5% 5% 7%	3108
	21st to end	Day	30% 15% 6% 15% 7% 6% 4 3 4 3 6%	4092
January	1st to 10th	Night	27% 16% 6% 12% 7% 6% 5% 4 4 4 10%	8172
	11th to 20th	Night	21% 9% 3 9% 7% 5% 4 3 4 5% 32%	8220
	21st to end	Night	20% 11% 4 10% 5% 5% 4 3 4 5% 29%	8398
February	1st to 10th	Night	23% 13% 5% 10% 6% 6% 5% 4 5% 6% 17%	2730
	11th to 20th	Night	25% 11% 4 9% 5% 4 5% 3 4 5% 24%	2662
	21st to end	Night	25% 13% 4 9% 6% 4 4 4 4 6% 21%	2171
March	1st to 10th	Night	15% 12% 4 11% 7% 7% 7% 6% 6% 6% 20%	5226
	11th to 20th	Night	18% 11% 4 10% 6% 5% 5% 3 5% 5% 28%	5110
	21st to end	Night	18% 12% 5% 13% 8% 6% 6% 4 6% 7% 16%	5526
April	1st to 10th	Night	22% 11% 4 9% 6% 5% 4 3 6% 5% 24%	2100
	11th to 20th	Night	18% 11% 3 7% 5% 5% 4 3 5% 7% 33%	2079
	21st to end	Night	18% 9% 3 8% 5% 5% 4 3 6% 7% 33%	1890
May	1st to 10th	Night	13% 5% 2 6% 3 3 4 3 5% 8% 49%	4946
	11th to 20th	Night	11% 7% 3 6% 5% 4 4 3 5% 7% 45%	4700
	21st to end	Night	10% 6% 2 6% 4 5% 5% 4 7% 9% 43%	5181
June	1st to 10th	Night	15% 8% 3 7% 5% 4 4 3 4 7% 40%	1680
	11th to 20th	Night	12% 7% 2 7% 5% 5% 4 3 6% 6% 45%	1680
	21st to end	Night	7% 5% 2 5% 4 3 3 3 4 6% 58%	1680
July	1st to 10th	Night	3 2 1 2 1 2 2 2 4 5% 77%	4740
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 3 80%	4740
	21st to end	Night	2 2 1 2 2 2 2 2 3 4 78%	5206
August	1st to 10th	Night	2 4 2 4 3 3 3 3 4 6% 68%	4125
	11th to 20th	Night	9% 5% 2 4 3 3 3 2 4 6% 58%	4142
	21st to end	Night	7% 5% 1 5% 3 3 3 3 4 6% 62%	4912
September	1st to 10th	Night	5% 4 1 4 2 2 2 3 5% 6% 67%	2000
	11th to 20th	Night	8% 5% 2 6% 4 4 4 3 5% 6% 52%	2012
	21st to end	Night	9% 5% 2 6% 3 3 3 3 4 8% 54%	2288
October	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 5% 6% 49%	3920
	11th to 20th	Night	14% 6% 2 6% 4 5% 5% 4 6% 8% 38%	3897
	21st to end	Night	19% 9% 3 9% 6% 5% 5% 4 5% 7% 28%	4282
November	1st to 10th	Night	25% 9% 3 9% 5% 6% 5% 4 6% 6% 22%	2775
	11th to 20th	Night	29% 11% 4 9% 5% 4 4 3 5% 4 20%	2940
	21st to end	Night	22% 9% 4 11% 6% 5% 5% 3 5% 5% 25%	2940
December	1st to 10th	Night	18% 8% 3 8% 7% 5% 5% 4 6% 7% 30%	4700
	11th to 20th	Night	29% 14% 6% 13% 7% 5% 4 3 4 4 10%	5316
	21st to end	Night	26% 13% 5% 13% 7% 6% 5% 4 5% 5% 11%	7106

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% 3 6% 5% 2	4723
	11th to 20th	Day	53% 5% 8% 14% 14% 6%	4740
	21st to end	Day	59% 3 7% 14% 15% 2	5801
February	1st to 10th	Day	68% 5% 11% 10% 5%	1890
	11th to 20th	Day	69% 5% 9% 10% 5% 1	1854
	21st to end	Day	69% 4 10% 9% 6% 2	1634
March	1st to 10th	Day	62% 4 13% 17% 4	4885
	11th to 20th	Day	61% 4 9% 18% 8% 1	5110
	21st to end	Day	69% 5% 15% 9% 3	5691
April	1st to 10th	Day	66% 5% 12% 14% 3	2520
	11th to 20th	Day	58% 5% 12% 15% 8% 2	2492
	21st to end	Day	54% 5% 16% 15% 8% 1	2728
May	1st to 10th	Day	37% 4 12% 31% 15%	7980
	11th to 20th	Day	39% 7% 19% 27% 8% 1	8163
	21st to end	Day	39% 6% 25% 23% 6%	8994
June	1st to 10th	Day	49% 4 16% 22% 8% 1	2940
	11th to 20th	Day	46% 5% 20% 20% 9% 1	2940
	21st to end	Day	31% 4 17% 31% 13% 4	2940
July	1st to 10th	Day	13% 3 13% 36% 19% 18%	8151
	11th to 20th	Day	13% 2 5% 19% 41% 20%	8145
	21st to end	Day	13% 2 14% 37% 29% 5%	8669
August	1st to 10th	Day	16% 3 10% 30% 28% 12%	4336
	11th to 20th	Day	24% 5% 18% 33% 17% 4	4325
	21st to end	Day	27% 5% 12% 27% 23% 7%	4557
September	1st to 10th	Day	21% 3 14% 31% 21% 11%	2400
	11th to 20th	Day	37% 4 14% 22% 16% 6%	2385
	21st to end	Day	38% 4 13% 22% 17% 5%	2111
October	1st to 10th	Day	36% 5% 9% 23% 23% 3	3280
	11th to 20th	Day	49% 6% 16% 16% 11% 1	3261
	21st to end	Day	58% 5% 10% 16% 10% 1	3526
November	1st to 10th	Day	69% 5% 11% 11% 4	1739
	11th to 20th	Day	71% 4 9% 9% 5% 2	1680
	21st to end	Day	66% 5% 9% 9% 10% 1	1680
December	1st to 10th	Day	59% 4 10% 14% 12% 1	2700
	11th to 20th	Day	79% 5% 7% 8% 1	3108
	21st to end	Day	82% 4 7% 5% 2	4092
January	1st to 10th	Night	79% 4 8% 6% 3 1	8172
	11th to 20th	Night	54% 5% 7% 15% 14% 6%	8220
	21st to end	Night	58% 3 5% 14% 16% 4	8398
February	1st to 10th	Night	68% 5% 10% 11% 5% 1	2730
	11th to 20th	Night	63% 4 12% 12% 7% 2	2664
	21st to end	Night	64% 4 11% 12% 7% 2	2171
March	1st to 10th	Night	62% 5% 13% 15% 5%	5226
	11th to 20th	Night	58% 4 12% 17% 8% 1	5110
	21st to end	Night	67% 6% 15% 10% 1	5526
April	1st to 10th	Night	62% 4 15% 14% 5%	2100
	11th to 20th	Night	53% 6% 15% 16% 8% 3	2079
	21st to end	Night	52% 5% 15% 19% 7% 2	1890
May	1st to 10th	Night	35% 4 12% 36% 12% 1	4944
	11th to 20th	Night	38% 7% 18% 29% 7% 1	4700
	21st to end	Night	38% 5% 28% 25% 4	5182
June	1st to 10th	Night	44% 5% 16% 28% 6% 1	1680
	11th to 20th	Night	39% 5% 18% 27% 10% 1	1680
	21st to end	Night	28% 4 17% 34% 13% 4	1680
July	1st to 10th	Night	12% 3 12% 36% 21% 17%	4700
	11th to 20th	Night	12% 1 8% 17% 42% 19%	4692
	21st to end	Night	12% 2 19% 37% 25% 4	5093
August	1st to 10th	Night	12% 3 9% 37% 30% 9%	3019
	11th to 20th	Night	25% 5% 20% 34% 12% 4	3019
	21st to end	Night	23% 4 14% 31% 22% 7%	3557
September	1st to 10th	Night	20% 4 13% 30% 21% 11%	2000
	11th to 20th	Night	32% 4 15% 25% 15% 8%	2012
	21st to end	Night	31% 4 16% 25% 17% 8%	2288
October	1st to 10th	Night	33% 6% 8% 29% 21% 2	3920
	11th to 20th	Night	42% 6% 21% 18% 11% 2	3897
	21st to end	Night	56% 5% 11% 17% 10% 1	4282
November	1st to 10th	Night	62% 6% 11% 15% 6%	2775
	11th to 20th	Night	67% 4 9% 10% 7% 2	2940
	21st to end	Night	62% 5% 8% 11% 11% 3	2940
December	1st to 10th	Night	51% 6% 10% 20% 12% 1	4700
	11th to 20th	Night	78% 5% 8% 7% 3	5316
	21st to end	Night	76% 5% 10% 7% 2	7106

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% 20% 16% 9% 2	220
	11th to 20th	Day	26% 12% 15% 29% 11% 6%	220
	21st to end	Day	24% 13% 20% 22% 16% 5%	457
February	1st to 10th	Day	33% 12% 18% 18% 16% 3	430
	11th to 20th	Day	30% 12% 27% 18% 9% 3	425
	21st to end	Day	29% 16% 22% 20% 11% 3	397
March	1st to 10th	Day	25% 15% 28% 21% 10% 1	540
	11th to 20th	Day	28% 14% 23% 18% 14% 3	540
	21st to end	Day	26% 17% 24% 22% 10% 1	594
April	1st to 10th	Day	25% 15% 22% 19% 13% 5%	540
	11th to 20th	Day	24% 14% 24% 21% 10% 6%	532
	21st to end	Day	19% 14% 24% 24% 15% 4	540
May	1st to 10th	Day	15% 11% 21% 30% 18% 5%	543
	11th to 20th	Day	22% 11% 17% 25% 17% 7%	568
	21st to end	Day	12% 9% 20% 27% 23% 9%	617
June	1st to 10th	Day	18% 9% 18% 27% 22% 6%	570
	11th to 20th	Day	14% 9% 26% 32% 16% 3	570
	21st to end	Day	6% 5% 18% 36% 29% 6%	570
July	1st to 10th	Day	4 3 16% 38% 30% 9%	566
	11th to 20th	Day	4 2 21% 37% 27% 9%	564
	21st to end	Day	3 2 15% 32% 37% 11%	619
August	1st to 10th	Day	3 3 13% 34% 34% 13%	567
	11th to 20th	Day	3 3 10% 33% 37% 14%	557
	21st to end	Day	5% 4 18% 36% 29% 9%	620
September	1st to 10th	Day	5% 4 21% 29% 32% 9%	530
	11th to 20th	Day	11% 6% 18% 29% 28% 8%	530
	21st to end	Day	12% 7% 23% 29% 22% 6%	530
October	1st to 10th	Day	17% 8% 22% 25% 21% 8%	530
	11th to 20th	Day	18% 11% 17% 25% 21% 8%	530
	21st to end	Day	23% 13% 25% 21% 12% 6%	563
November	1st to 10th	Day	28% 11% 28% 18% 11% 4	269
	11th to 20th	Day	25% 14% 23% 18% 15% 5%	220
	21st to end	Day	26% 12% 18% 21% 17% 5%	220
December	1st to 10th	Day	31% 10% 17% 18% 16% 7%	220
	11th to 20th	Day	33% 15% 25% 16% 9% 3	220
	21st to end	Day	32% 17% 19% 19% 11% 2	242
January	1st to 10th	Night	35% 12% 19% 20% 12% 2	840
	11th to 20th	Night	29% 10% 17% 23% 18% 2	840
	21st to end	Night	26% 8% 17% 30% 17% 2	924
February	1st to 10th	Night	24% 10% 20% 27% 16% 2	840
	11th to 20th	Night	27% 10% 22% 26% 15%	824
	21st to end	Night	29% 12% 19% 28% 12%	692
March	1st to 10th	Night	24% 10% 25% 29% 12% 1	840
	11th to 20th	Night	23% 12% 21% 28% 15% 1	840
	21st to end	Night	26% 11% 24% 26% 12% 1	924
April	1st to 10th	Night	25% 10% 19% 27% 18% 1	840
	11th to 20th	Night	19% 10% 24% 30% 16% 1	831
	21st to end	Night	18% 7% 22% 36% 16%	630
May	1st to 10th	Night	12% 6% 24% 39% 18% 1	500
	11th to 20th	Night	16% 4 20% 38% 21% 1	414
	21st to end	Night	14% 6% 20% 39% 21% 1	455
June	1st to 10th	Night	16% 6% 17% 42% 19%	420
	11th to 20th	Night	11% 5% 28% 43% 12% 1	420
	21st to end	Night	8% 1 22% 50% 19%	420
July	1st to 10th	Night	2 2 13% 59% 23%	410
	11th to 20th	Night	5% 2 20% 53% 20%	408
	21st to end	Night	2 2 12% 56% 27% 1	475
August	1st to 10th	Night	3 2 10% 47% 34% 4	627
	11th to 20th	Night	5% 2 7% 44% 40% 2	624
	21st to end	Night	6% 2 15% 46% 28% 2	827
September	1st to 10th	Night	5% 2 17% 45% 30% 1	800
	11th to 20th	Night	9% 3 15% 37% 31% 6%	800
	21st to end	Night	9% 4 16% 41% 27% 3	800
October	1st to 10th	Night	14% 3 22% 33% 25% 3	800
	11th to 20th	Night	18% 5% 16% 34% 24% 4	800
	21st to end	Night	22% 9% 22% 27% 17% 3	880
November	1st to 10th	Night	26% 10% 18% 30% 15% 1	820
	11th to 20th	Night	32% 10% 20% 24% 13% 1	840
	21st to end	Night	23% 7% 20% 28% 19% 2	840
December	1st to 10th	Night	28% 9% 16% 28% 16% 3	840
	11th to 20th	Night	32% 11% 21% 22% 14%	840
	21st to end	Night	32% 13% 21% 24% 10% 1	924

Page generated at 2026-08-27 01:07:14. Version ac07

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