Coos Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Coos Bay clear sky chart from 2005-11-06 to 2026-10-29.

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% 10% 3 7% 4 4 4 3 5% 7% 38%	158775
	Night	21% 14% 3 7% 4 3 3 3 4 5% 32%	150765
Transparency	Day	44% 8% 14% 19% 11% 4	153547
	Night	54% 7% 11% 15% 10% 4	146995
Seeing	Day	21% 10% 26% 28% 13% 3	17456
	Night	27% 7% 16% 27% 20% 3	26351

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	37% 15% 5% 9% 5% 4 3 3 4 5% 11%	4722
	11th to 20th	Day	21% 6% 2 4 2 2 2 3 4 6% 48%	5142
	21st to end	Day	25% 9% 3 8% 5% 5% 5% 3 4 5% 30%	5843
February	1st to 10th	Day	28% 12% 4 8% 6% 4 4 4 5% 6% 20%	1890
	11th to 20th	Day	29% 12% 4 8% 4 4 4 3 5% 5% 22%	1845
	21st to end	Day	30% 14% 3 8% 5% 4 4 2 3 5% 22%	1611
March	1st to 10th	Day	21% 16% 3 8% 5% 5% 6% 4 5% 6% 20%	5062
	11th to 20th	Day	29% 13% 4 8% 4 3 3 3 4 4 24%	5110
	21st to end	Day	30% 13% 3 10% 6% 5% 6% 4 5% 6% 12%	5607
April	1st to 10th	Day	28% 13% 4 9% 6% 4 3 4 4 6% 19%	2489
	11th to 20th	Day	23% 13% 4 8% 5% 4 4 3 5% 5% 26%	2525
	21st to end	Day	23% 8% 3 9% 4 5% 5% 4 7% 7% 27%	2730
May	1st to 10th	Day	14% 10% 3 7% 4 3 3 3 4 8% 41%	7627
	11th to 20th	Day	13% 8% 3 7% 4 4 4 4 6% 9% 40%	8119
	21st to end	Day	12% 9% 2 6% 4 4 4 4 6% 10% 40%	8992
June	1st to 10th	Day	23% 9% 3 6% 4 4 4 4 6% 7% 32%	2940
	11th to 20th	Day	15% 9% 2 7% 5% 4 4 3 6% 7% 37%	2940
	21st to end	Day	11% 8% 3 5% 3 4 3 3 5% 6% 48%	2940
July	1st to 10th	Day	2 7% 2 4 2 2 3 3 5% 8% 62%	8219
	11th to 20th	Day	4 6% 2 5% 3 3 3 3 4 7% 60%	8220
	21st to end	Day	5% 10% 3 5% 3 3 4 3 5% 8% 51%	8360
August	1st to 10th	Day	4 9% 3 5% 3 3 4 3 5% 8% 54%	7547
	11th to 20th	Day	6% 9% 3 6% 3 3 4 4 6% 10% 46%	7563
	21st to end	Day	5% 8% 3 5% 4 4 4 3 5% 9% 51%	8071
September	1st to 10th	Day	6% 6% 2 4 3 2 3 3 5% 7% 59%	2520
	11th to 20th	Day	10% 7% 2 7% 3 4 3 3 4 9% 47%	2407
	21st to end	Day	12% 5% 2 5% 4 4 4 2 5% 8% 49%	2276
October	1st to 10th	Day	13% 6% 3 5% 4 3 3 2 4 5% 52%	3380
	11th to 20th	Day	19% 8% 2 7% 4 5% 4 4 6% 9% 31%	3361
	21st to end	Day	24% 9% 3 7% 4 4 4 4 6% 8% 26%	3639
November	1st to 10th	Day	32% 9% 3 8% 4 5% 4 4 5% 6% 22%	1818
	11th to 20th	Day	32% 10% 4 9% 4 4 4 3 5% 6% 19%	1680
	21st to end	Day	26% 10% 3 7% 5% 3 4 3 4 7% 28%	1680
December	1st to 10th	Day	21% 7% 2 6% 4 4 4 3 5% 7% 37%	2700
	11th to 20th	Day	35% 14% 4 8% 5% 4 4 3 4 4 15%	3108
	21st to end	Day	37% 16% 4 9% 4 4 4 3 3 4 11%	4092
January	1st to 10th	Night	41% 13% 3 8% 5% 4 4 3 3 4 13%	8172
	11th to 20th	Night	22% 8% 2 4 3 2 3 2 4 5% 44%	7821
	21st to end	Night	29% 10% 3 7% 3 4 4 2 3 4 31%	8371
February	1st to 10th	Night	27% 11% 4 7% 6% 4 4 4 5% 5% 21%	2730
	11th to 20th	Night	29% 13% 3 8% 4 4 4 3 4 5% 24%	2662
	21st to end	Night	30% 13% 3 8% 4 4 4 3 5% 4 22%	2192
March	1st to 10th	Night	22% 18% 4 10% 5% 5% 5% 4 5% 5% 17%	5052
	11th to 20th	Night	26% 15% 4 8% 4 3 4 2 3 4 26%	5110
	21st to end	Night	33% 15% 3 10% 5% 5% 4 3 4 5% 13%	5610
April	1st to 10th	Night	30% 13% 3 7% 4 4 3 3 4 5% 23%	2130
	11th to 20th	Night	22% 14% 4 8% 4 3 3 3 4 6% 29%	2038
	21st to end	Night	25% 12% 4 7% 4 3 4 3 5% 6% 28%	1890
May	1st to 10th	Night	16% 16% 3 6% 3 3 3 2 3 5% 39%	5321
	11th to 20th	Night	16% 12% 3 8% 4 5% 4 4 4 6% 33%	4741
	21st to end	Night	15% 13% 2 6% 3 3 4 3 5% 8% 40%	5181
June	1st to 10th	Night	20% 10% 3 6% 5% 4 4 3 5% 7% 34%	1680
	11th to 20th	Night	12% 9% 3 5% 4 3 3 3 5% 8% 44%	1680
	21st to end	Night	12% 12% 2 5% 3 3 3 3 5% 6% 46%	1680
July	1st to 10th	Night	3 19% 3 4 2 3 3 2 3 5% 53%	4740
	11th to 20th	Night	3 17% 4 6% 4 3 4 4 3 6% 47%	4740
	21st to end	Night	8% 29% 4 5% 3 3 3 2 3 5% 35%	5741
August	1st to 10th	Night	8% 26% 4 5% 3 2 3 2 3 5% 40%	5275
	11th to 20th	Night	12% 26% 3 6% 3 3 3 3 4 5% 32%	5292
	21st to end	Night	7% 17% 4 5% 3 3 3 3 4 5% 47%	6161
September	1st to 10th	Night	8% 9% 2 4 2 3 3 2 4 6% 56%	2100
	11th to 20th	Night	9% 8% 3 6% 4 3 3 3 4 5% 51%	2210
	21st to end	Night	13% 7% 2 5% 4 3 3 3 4 7% 48%	2342
October	1st to 10th	Night	10% 8% 3 6% 4 3 3 3 4 5% 52%	4040
	11th to 20th	Night	16% 13% 3 7% 5% 3 3 3 5% 7% 34%	4017
	21st to end	Night	27% 10% 3 8% 4 5% 4 3 4 6% 26%	4349
November	1st to 10th	Night	30% 9% 3 6% 4 4 4 3 5% 7% 24%	2695
	11th to 20th	Night	33% 10% 3 8% 5% 4 4 3 4 5% 23%	2940
	21st to end	Night	24% 9% 3 8% 4 4 4 3 5% 6% 30%	2940
December	1st to 10th	Night	20% 9% 3 6% 3 3 4 3 5% 5% 40%	4700
	11th to 20th	Night	38% 12% 4 8% 5% 4 3 3 4 6% 14%	5316
	21st to end	Night	37% 12% 4 8% 4 4 3 3 4 5% 18%	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	74% 7% 7% 7% 4 1	4723
	11th to 20th	Day	39% 5% 8% 17% 18% 14%	5142
	21st to end	Day	56% 6% 6% 10% 10% 12%	5843
February	1st to 10th	Day	64% 7% 10% 12% 4 2	1890
	11th to 20th	Day	63% 8% 11% 10% 5% 2	1854
	21st to end	Day	65% 8% 9% 11% 6% 2	1611
March	1st to 10th	Day	59% 10% 12% 15% 3	5062
	11th to 20th	Day	61% 8% 7% 14% 9% 1	5110
	21st to end	Day	69% 11% 10% 8% 2	5607
April	1st to 10th	Day	64% 10% 11% 12% 4	2489
	11th to 20th	Day	58% 10% 10% 14% 7% 2	2528
	21st to end	Day	53% 11% 13% 18% 5% 1	2730
May	1st to 10th	Day	41% 8% 12% 28% 10% 1	7627
	11th to 20th	Day	38% 8% 24% 22% 7% 1	8122
	21st to end	Day	37% 11% 27% 24% 2	8994
June	1st to 10th	Day	50% 8% 15% 22% 5%	2940
	11th to 20th	Day	42% 11% 18% 22% 7% 1	2940
	21st to end	Day	35% 8% 18% 27% 10% 2	2940
July	1st to 10th	Day	21% 7% 15% 25% 17% 15%	8151
	11th to 20th	Day	23% 6% 12% 14% 35% 10%	8145
	21st to end	Day	31% 6% 18% 28% 14% 2	8174
August	1st to 10th	Day	29% 7% 13% 17% 25% 10%	5976
	11th to 20th	Day	33% 8% 22% 27% 8% 1	5962
	21st to end	Day	26% 8% 19% 30% 15% 2	6326
September	1st to 10th	Day	24% 6% 15% 30% 16% 8%	2520
	11th to 20th	Day	35% 8% 18% 24% 11% 4	2407
	21st to end	Day	33% 8% 16% 23% 15% 5%	2276
October	1st to 10th	Day	35% 6% 9% 20% 19% 11%	3380
	11th to 20th	Day	48% 10% 13% 17% 11% 2	3361
	21st to end	Day	53% 7% 10% 18% 10% 3	3639
November	1st to 10th	Day	62% 9% 9% 13% 7% 1	1818
	11th to 20th	Day	64% 7% 10% 8% 6% 4	1680
	21st to end	Day	56% 6% 11% 10% 9% 7%	1680
December	1st to 10th	Day	46% 6% 10% 14% 17% 7%	2700
	11th to 20th	Day	72% 6% 9% 8% 4 1	3108
	21st to end	Day	76% 7% 6% 8% 2 1	4092
January	1st to 10th	Night	74% 7% 7% 8% 3 2	8172
	11th to 20th	Night	43% 5% 7% 15% 19% 12%	7821
	21st to end	Night	58% 4 5% 8% 14% 12%	8371
February	1st to 10th	Night	63% 9% 10% 12% 5% 1	2730
	11th to 20th	Night	63% 8% 10% 13% 6% 2	2664
	21st to end	Night	64% 8% 9% 10% 7% 2	2192
March	1st to 10th	Night	66% 8% 10% 12% 3	5052
	11th to 20th	Night	61% 8% 10% 11% 8% 2	5110
	21st to end	Night	72% 10% 10% 7% 1	5610
April	1st to 10th	Night	64% 6% 14% 13% 4	2130
	11th to 20th	Night	57% 8% 12% 15% 5% 3	2038
	21st to end	Night	57% 8% 12% 16% 6% 1	1890
May	1st to 10th	Night	46% 8% 11% 25% 9% 1	5319
	11th to 20th	Night	49% 8% 18% 19% 5% 2	4741
	21st to end	Night	42% 9% 28% 19% 2	5182
June	1st to 10th	Night	51% 6% 16% 23% 4	1680
	11th to 20th	Night	38% 8% 20% 26% 7% 1	1680
	21st to end	Night	38% 6% 17% 27% 8% 3	1680
July	1st to 10th	Night	37% 4 11% 19% 14% 15%	4700
	11th to 20th	Night	40% 6% 7% 12% 28% 7%	4692
	21st to end	Night	54% 4 11% 15% 14% 2	5616
August	1st to 10th	Night	46% 6% 8% 14% 19% 7%	4169
	11th to 20th	Night	55% 5% 12% 18% 7% 2	4169
	21st to end	Night	36% 5% 11% 30% 15% 2	4832
September	1st to 10th	Night	30% 5% 12% 25% 18% 10%	2100
	11th to 20th	Night	36% 7% 15% 25% 14% 4	2210
	21st to end	Night	37% 6% 14% 21% 16% 6%	2342
October	1st to 10th	Night	34% 6% 9% 20% 24% 7%	4040
	11th to 20th	Night	50% 8% 15% 15% 10% 2	4017
	21st to end	Night	58% 7% 9% 14% 8% 4	4349
November	1st to 10th	Night	59% 7% 12% 12% 9% 1	2695
	11th to 20th	Night	64% 6% 9% 12% 6% 4	2940
	21st to end	Night	54% 8% 9% 12% 10% 7%	2940
December	1st to 10th	Night	45% 5% 8% 17% 21% 4	4700
	11th to 20th	Night	72% 6% 9% 7% 5% 1	5316
	21st to end	Night	68% 7% 10% 11% 3 1	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	43% 15% 16% 15% 8% 3	220
	11th to 20th	Day	34% 10% 18% 17% 15% 6%	362
	21st to end	Day	28% 12% 22% 19% 14% 5%	473
February	1st to 10th	Day	28% 11% 24% 26% 10% 1	430
	11th to 20th	Day	34% 13% 22% 24% 6% 1	425
	21st to end	Day	34% 14% 24% 22% 5% 1	376
March	1st to 10th	Day	33% 15% 23% 21% 8%	540
	11th to 20th	Day	33% 9% 24% 22% 11% 2	540
	21st to end	Day	30% 16% 26% 21% 6% 1	594
April	1st to 10th	Day	31% 12% 24% 22% 9% 2	540
	11th to 20th	Day	27% 16% 26% 21% 8% 3	532
	21st to end	Day	24% 13% 29% 25% 8% 2	540
May	1st to 10th	Day	17% 13% 33% 26% 9% 2	543
	11th to 20th	Day	24% 11% 31% 21% 11% 2	568
	21st to end	Day	18% 12% 28% 30% 11% 1	617
June	1st to 10th	Day	20% 10% 29% 29% 10% 2	570
	11th to 20th	Day	16% 8% 42% 25% 8% 1	570
	21st to end	Day	11% 6% 29% 40% 13% 1	570
July	1st to 10th	Day	8% 3 33% 40% 14% 2	566
	11th to 20th	Day	6% 7% 33% 37% 16% 2	564
	21st to end	Day	7% 4 27% 43% 17% 2	619
August	1st to 10th	Day	7% 6% 26% 37% 20% 4	567
	11th to 20th	Day	5% 5% 22% 42% 22% 4	557
	21st to end	Day	8% 4 27% 41% 16% 5%	627
September	1st to 10th	Day	8% 5% 28% 35% 23% 2	570
	11th to 20th	Day	13% 6% 28% 31% 18% 3	570
	21st to end	Day	14% 7% 25% 37% 14% 3	570
October	1st to 10th	Day	17% 6% 26% 31% 17% 4	570
	11th to 20th	Day	18% 8% 22% 30% 17% 5%	570
	21st to end	Day	26% 12% 23% 27% 9% 3	616
November	1st to 10th	Day	31% 11% 25% 20% 11% 3	358
	11th to 20th	Day	34% 11% 23% 16% 12% 4	220
	21st to end	Day	28% 13% 20% 19% 19% 2	220
December	1st to 10th	Day	34% 10% 15% 20% 14% 8%	220
	11th to 20th	Day	40% 13% 19% 18% 9% 2	220
	21st to end	Day	38% 13% 19% 19% 8% 3	242
January	1st to 10th	Night	43% 10% 15% 18% 11% 2	840
	11th to 20th	Night	34% 7% 16% 22% 15% 5%	840
	21st to end	Night	30% 6% 16% 27% 17% 4	924
February	1st to 10th	Night	33% 7% 16% 25% 17% 2	840
	11th to 20th	Night	35% 8% 19% 24% 13% 2	824
	21st to end	Night	34% 12% 17% 25% 12%	692
March	1st to 10th	Night	33% 12% 17% 25% 12% 1	840
	11th to 20th	Night	30% 9% 18% 28% 13% 2	840
	21st to end	Night	36% 10% 18% 24% 11% 1	924
April	1st to 10th	Night	35% 6% 17% 22% 17% 3	840
	11th to 20th	Night	28% 8% 21% 26% 14% 3	790
	21st to end	Night	30% 7% 16% 26% 19% 2	630
May	1st to 10th	Night	24% 7% 19% 29% 19% 2	630
	11th to 20th	Night	24% 6% 17% 27% 22% 3	430
	21st to end	Night	25% 7% 15% 29% 23% 2	455
June	1st to 10th	Night	21% 5% 16% 35% 20% 3	420
	11th to 20th	Night	16% 4 22% 36% 18% 3	420
	21st to end	Night	19% 2 15% 32% 30% 1	420
July	1st to 10th	Night	14% 2 15% 32% 34% 3	410
	11th to 20th	Night	13% 3 16% 42% 23% 2	408
	21st to end	Night	16% 2 11% 35% 33% 4	664
August	1st to 10th	Night	22% 1 10% 29% 31% 6%	627
	11th to 20th	Night	15% 2 10% 23% 41% 9%	624
	21st to end	Night	13% 2 15% 31% 33% 6%	803
September	1st to 10th	Night	13% 2 14% 31% 36% 3	840
	11th to 20th	Night	13% 4 14% 29% 31% 10%	840
	21st to end	Night	17% 4 15% 33% 28% 4	840
October	1st to 10th	Night	17% 4 18% 29% 29% 4	840
	11th to 20th	Night	18% 5% 15% 33% 25% 5%	840
	21st to end	Night	27% 8% 20% 26% 16% 4	912
November	1st to 10th	Night	32% 8% 17% 26% 16% 1	820
	11th to 20th	Night	36% 10% 16% 22% 13% 2	840
	21st to end	Night	24% 8% 19% 28% 17% 3	840
December	1st to 10th	Night	29% 9% 15% 27% 16% 3	840
	11th to 20th	Night	39% 8% 17% 19% 15% 2	840
	21st to end	Night	42% 10% 17% 21% 9% 1	924

Page generated at 2026-10-26 01:37:51. Version ac07

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