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 2025-07-06.

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	19% 10% 3 7% 4 4 4 3 5% 7% 36%	124176
	Night	23% 12% 3 7% 4 3 3 3 4 5% 32%	123469
Transparency	Day	47% 8% 14% 17% 10% 4	123931
	Night	54% 7% 11% 15% 10% 4	123302
Seeing	Day	21% 9% 26% 29% 13% 2	15720
	Night	27% 7% 16% 27% 20% 3	24700

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	38% 15% 4 8% 5% 3 3 3 3 5% 12%	3639
	11th to 20th	Day	27% 8% 3 5% 3 3 3 2 3 5% 38%	3944
	21st to end	Day	28% 9% 3 6% 4 4 3 3 4 5% 33%	4510
February	1st to 10th	Day	29% 13% 4 8% 6% 4 4 4 5% 5% 19%	1800
	11th to 20th	Day	29% 12% 4 8% 4 4 4 3 5% 5% 22%	1755
	21st to end	Day	30% 14% 3 8% 5% 4 4 2 3 5% 22%	1536
March	1st to 10th	Day	21% 16% 3 7% 5% 5% 6% 4 5% 6% 20%	4952
	11th to 20th	Day	29% 13% 4 9% 4 3 3 3 4 4 24%	5000
	21st to end	Day	30% 14% 3 10% 6% 5% 6% 4 5% 6% 12%	5486
April	1st to 10th	Day	29% 13% 4 9% 6% 4 3 4 4 5% 18%	2370
	11th to 20th	Day	23% 13% 4 8% 5% 4 4 3 5% 5% 26%	2403
	21st to end	Day	24% 8% 3 9% 4 5% 5% 4 6% 7% 26%	2600
May	1st to 10th	Day	17% 8% 2 7% 4 3 3 3 4 6% 42%	5880
	11th to 20th	Day	16% 9% 3 8% 4 4 4 4 5% 7% 37%	6248
	21st to end	Day	13% 8% 2 6% 4 4 4 4 6% 10% 39%	6902
June	1st to 10th	Day	23% 9% 3 6% 4 4 3 4 5% 7% 32%	2800
	11th to 20th	Day	15% 10% 2 7% 5% 4 4 3 7% 8% 35%	2800
	21st to end	Day	11% 8% 3 5% 3 4 3 3 5% 7% 49%	2800
July	1st to 10th	Day	4 5% 2 4 2 2 2 2 4 6% 68%	4491
	11th to 20th	Day	6% 7% 2 4 3 3 3 3 4 7% 58%	4420
	21st to end	Day	6% 9% 3 4 3 3 3 3 5% 7% 55%	4485
August	1st to 10th	Day	4 12% 3 7% 4 4 4 3 5% 9% 44%	4091
	11th to 20th	Day	6% 8% 2 5% 3 3 4 3 7% 9% 50%	4026
	21st to end	Day	6% 6% 2 5% 3 3 3 2 4 8% 57%	4349
September	1st to 10th	Day	5% 5% 1 4 3 2 3 2 5% 7% 62%	2280
	11th to 20th	Day	11% 7% 2 7% 3 4 3 3 4 10% 46%	2178
	21st to end	Day	12% 5% 2 5% 4 4 4 2 5% 8% 48%	2060
October	1st to 10th	Day	13% 6% 3 5% 3 3 3 2 4 5% 52%	3180
	11th to 20th	Day	20% 8% 3 8% 4 5% 4 4 7% 9% 29%	3161
	21st to end	Day	24% 9% 3 7% 4 4 4 4 6% 8% 27%	3448
November	1st to 10th	Day	31% 9% 3 8% 4 5% 4 4 5% 5% 22%	1730
	11th to 20th	Day	32% 9% 4 8% 4 4 4 3 5% 6% 20%	1600
	21st to end	Day	26% 10% 3 7% 4 3 3 3 4 7% 29%	1600
December	1st to 10th	Day	20% 7% 2 6% 4 4 4 3 5% 7% 38%	2620
	11th to 20th	Day	35% 14% 4 8% 5% 4 4 3 4 4 15%	3028
	21st to end	Day	38% 17% 4 9% 4 4 4 3 3 4 10%	4004
January	1st to 10th	Night	42% 13% 3 7% 5% 4 4 3 3 4 13%	6306
	11th to 20th	Night	28% 11% 3 5% 3 3 3 2 3 4 36%	6012
	21st to end	Night	34% 9% 3 5% 3 3 2 2 3 4 33%	6468
February	1st to 10th	Night	28% 12% 4 8% 6% 4 5% 4 5% 6% 21%	2600
	11th to 20th	Night	29% 13% 3 8% 4 4 3 2 4 5% 25%	2532
	21st to end	Night	30% 13% 3 8% 4 4 4 3 5% 4 22%	2091
March	1st to 10th	Night	22% 18% 4 10% 5% 5% 5% 4 5% 5% 17%	4942
	11th to 20th	Night	26% 16% 4 8% 4 3 4 2 3 4 26%	5000
	21st to end	Night	33% 16% 3 10% 5% 5% 4 3 4 5% 13%	5489
April	1st to 10th	Night	30% 13% 3 7% 4 4 4 3 4 5% 23%	2029
	11th to 20th	Night	22% 14% 4 8% 4 3 3 3 4 6% 30%	1940
	21st to end	Night	25% 11% 4 7% 5% 3 4 3 5% 6% 27%	1800
May	1st to 10th	Night	18% 9% 2 6% 4 3 3 2 3 5% 44%	4100
	11th to 20th	Night	17% 12% 4 8% 4 4 4 4 4 6% 33%	3644
	21st to end	Night	16% 11% 2 5% 3 3 3 3 4 8% 41%	3972
June	1st to 10th	Night	20% 10% 3 5% 5% 4 4 3 5% 7% 34%	1600
	11th to 20th	Night	13% 10% 3 5% 4 3 4 3 6% 8% 43%	1600
	21st to end	Night	12% 11% 2 5% 3 3 3 3 5% 6% 48%	1600
July	1st to 10th	Night	4 9% 1 3 2 2 3 2 3 5% 66%	2580
	11th to 20th	Night	5% 15% 3 5% 4 3 3 3 3 6% 51%	2540
	21st to end	Night	9% 20% 3 4 3 3 3 2 4 6% 44%	3072
August	1st to 10th	Night	5% 32% 4 6% 3 3 3 3 4 6% 31%	2848
	11th to 20th	Night	10% 18% 3 6% 3 3 3 3 5% 6% 41%	2812
	21st to end	Night	7% 8% 2 4 3 3 2 3 4 5% 58%	3324
September	1st to 10th	Night	8% 7% 2 4 2 2 3 2 4 6% 59%	1900
	11th to 20th	Night	10% 8% 2 7% 4 4 3 3 5% 6% 50%	2000
	21st to end	Night	14% 6% 2 5% 4 3 3 3 4 7% 48%	2118
October	1st to 10th	Night	10% 7% 3 6% 4 3 3 3 4 5% 52%	3800
	11th to 20th	Night	16% 14% 4 7% 5% 3 4 3 5% 7% 33%	3777
	21st to end	Night	28% 11% 3 8% 4 4 4 3 4 6% 26%	4121
November	1st to 10th	Night	30% 9% 3 6% 4 4 4 3 5% 7% 25%	2564
	11th to 20th	Night	33% 10% 2 8% 5% 4 4 3 4 5% 23%	2800
	21st to end	Night	24% 9% 3 8% 5% 4 4 3 5% 6% 31%	2800
December	1st to 10th	Night	19% 9% 3 6% 3 3 4 3 5% 5% 41%	4560
	11th to 20th	Night	37% 12% 4 8% 5% 4 3 3 4 6% 14%	5176
	21st to end	Night	37% 12% 4 8% 4 4 3 3 4 5% 18%	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	73% 7% 8% 7% 5% 1	3639
	11th to 20th	Day	49% 5% 7% 18% 16% 4	3944
	21st to end	Day	53% 7% 6% 10% 12% 13%	4510
February	1st to 10th	Day	66% 7% 10% 12% 4 1	1800
	11th to 20th	Day	63% 8% 11% 10% 5% 2	1764
	21st to end	Day	65% 8% 9% 11% 5% 2	1536
March	1st to 10th	Day	58% 10% 13% 15% 4	4952
	11th to 20th	Day	61% 8% 7% 14% 9% 1	5000
	21st to end	Day	69% 11% 9% 8% 2	5486
April	1st to 10th	Day	65% 10% 10% 11% 4	2370
	11th to 20th	Day	57% 10% 10% 14% 7% 2	2406
	21st to end	Day	54% 11% 13% 17% 5% 1	2600
May	1st to 10th	Day	41% 9% 12% 26% 11% 1	5880
	11th to 20th	Day	42% 8% 21% 20% 9% 1	6251
	21st to end	Day	38% 12% 31% 18% 2	6904
June	1st to 10th	Day	50% 8% 15% 21% 5%	2800
	11th to 20th	Day	44% 11% 19% 21% 6%	2800
	21st to end	Day	35% 8% 19% 27% 10% 2	2800
July	1st to 10th	Day	18% 5% 13% 15% 22% 27%	4422
	11th to 20th	Day	25% 5% 13% 18% 26% 13%	4345
	21st to end	Day	28% 4 16% 26% 20% 5%	4344
August	1st to 10th	Day	38% 8% 16% 19% 13% 6%	4076
	11th to 20th	Day	29% 8% 24% 28% 10% 2	4065
	21st to end	Day	25% 7% 20% 24% 21% 2	4348
September	1st to 10th	Day	22% 6% 15% 31% 17% 9%	2280
	11th to 20th	Day	36% 8% 18% 21% 12% 5%	2178
	21st to end	Day	33% 8% 16% 23% 14% 5%	2060
October	1st to 10th	Day	35% 6% 9% 20% 19% 11%	3180
	11th to 20th	Day	50% 10% 13% 16% 10% 1	3161
	21st to end	Day	52% 7% 10% 17% 10% 3	3448
November	1st to 10th	Day	62% 9% 9% 12% 7% 1	1730
	11th to 20th	Day	63% 7% 10% 8% 7% 4	1600
	21st to end	Day	56% 6% 11% 10% 10% 7%	1600
December	1st to 10th	Day	45% 6% 10% 14% 17% 7%	2620
	11th to 20th	Day	73% 7% 9% 8% 4	3028
	21st to end	Day	76% 7% 6% 7% 2 1	4004
January	1st to 10th	Night	75% 7% 5% 8% 3 2	6306
	11th to 20th	Night	52% 6% 7% 15% 16% 4	6012
	21st to end	Night	57% 4 5% 8% 13% 13%	6468
February	1st to 10th	Night	63% 9% 10% 12% 5% 1	2600
	11th to 20th	Night	63% 8% 10% 13% 6% 2	2534
	21st to end	Night	64% 8% 9% 10% 7% 2	2091
March	1st to 10th	Night	66% 8% 10% 12% 3	4942
	11th to 20th	Night	61% 9% 10% 11% 8% 2	5000
	21st to end	Night	72% 10% 10% 7% 1	5489
April	1st to 10th	Night	64% 6% 13% 12% 4	2029
	11th to 20th	Night	56% 8% 12% 16% 5% 3	1940
	21st to end	Night	57% 8% 12% 16% 5% 1	1800
May	1st to 10th	Night	41% 9% 11% 27% 11% 1	4097
	11th to 20th	Night	49% 7% 18% 17% 7% 2	3644
	21st to end	Night	41% 9% 31% 16% 2	3972
June	1st to 10th	Night	51% 6% 16% 23% 3	1600
	11th to 20th	Night	39% 9% 21% 25% 6%	1600
	21st to end	Night	37% 6% 18% 28% 8% 3	1600
July	1st to 10th	Night	25% 3 9% 14% 20% 29%	2540
	11th to 20th	Night	38% 4 7% 15% 25% 12%	2492
	21st to end	Night	43% 4 9% 20% 22% 4	2976
August	1st to 10th	Night	56% 6% 9% 17% 9% 2	2839
	11th to 20th	Night	44% 6% 15% 21% 10% 3	2839
	21st to end	Night	28% 6% 11% 30% 21% 3	3324
September	1st to 10th	Night	27% 5% 12% 26% 20% 10%	1900
	11th to 20th	Night	36% 7% 15% 24% 15% 4	2000
	21st to end	Night	37% 7% 13% 21% 16% 7%	2118
October	1st to 10th	Night	34% 5% 9% 20% 24% 8%	3800
	11th to 20th	Night	51% 8% 15% 15% 9% 2	3777
	21st to end	Night	59% 7% 9% 13% 8% 4	4121
November	1st to 10th	Night	58% 8% 12% 12% 9% 1	2564
	11th to 20th	Night	64% 6% 9% 11% 6% 4	2800
	21st to end	Night	54% 8% 9% 12% 10% 8%	2800
December	1st to 10th	Night	45% 6% 8% 17% 21% 4	4560
	11th to 20th	Night	72% 6% 9% 7% 5% 1	5176
	21st to end	Night	68% 7% 10% 11% 3 1	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	45% 14% 15% 17% 8% 3	200
	11th to 20th	Day	37% 10% 17% 18% 13% 4	335
	21st to end	Day	29% 12% 21% 19% 13% 5%	440
February	1st to 10th	Day	29% 11% 25% 26% 9% 1	400
	11th to 20th	Day	34% 13% 21% 25% 6% 1	395
	21st to end	Day	33% 15% 23% 24% 5% 1	350
March	1st to 10th	Day	33% 15% 23% 21% 8%	500
	11th to 20th	Day	33% 8% 24% 22% 11% 2	500
	21st to end	Day	31% 15% 25% 22% 7% 1	550
April	1st to 10th	Day	32% 13% 24% 21% 8% 1	500
	11th to 20th	Day	27% 17% 25% 21% 8% 3	492
	21st to end	Day	24% 13% 28% 26% 8% 2	500
May	1st to 10th	Day	18% 13% 33% 26% 9% 2	503
	11th to 20th	Day	26% 9% 30% 22% 11% 2	528
	21st to end	Day	18% 12% 28% 30% 11% 1	573
June	1st to 10th	Day	20% 9% 28% 31% 10% 2	530
	11th to 20th	Day	17% 8% 42% 25% 8% 1	530
	21st to end	Day	10% 5% 29% 42% 13% 1	530
July	1st to 10th	Day	8% 3 34% 40% 14% 2	507
	11th to 20th	Day	6% 5% 31% 40% 16% 2	484
	21st to end	Day	6% 4 27% 44% 17% 2	531
August	1st to 10th	Day	8% 5% 24% 38% 21% 4	487
	11th to 20th	Day	5% 4 19% 44% 24% 4	477
	21st to end	Day	8% 4 26% 41% 16% 5%	539
September	1st to 10th	Day	6% 4 27% 37% 24% 3	490
	11th to 20th	Day	15% 5% 27% 31% 19% 3	490
	21st to end	Day	14% 7% 24% 37% 14% 3	490
October	1st to 10th	Day	18% 6% 25% 30% 17% 4	490
	11th to 20th	Day	19% 8% 20% 30% 18% 5%	490
	21st to end	Day	26% 12% 23% 27% 9% 4	539
November	1st to 10th	Day	29% 12% 25% 21% 10% 3	330
	11th to 20th	Day	34% 11% 23% 17% 13% 4	200
	21st to end	Day	28% 14% 20% 18% 19% 2	200
December	1st to 10th	Day	33% 9% 14% 20% 16% 9%	200
	11th to 20th	Day	41% 13% 18% 19% 9% 1	200
	21st to end	Day	40% 13% 16% 20% 9% 2	220
January	1st to 10th	Night	43% 10% 15% 18% 12% 2	800
	11th to 20th	Night	36% 8% 17% 22% 14% 5%	800
	21st to end	Night	31% 6% 15% 26% 18% 4	880
February	1st to 10th	Night	34% 7% 17% 23% 17% 2	800
	11th to 20th	Night	35% 8% 18% 24% 13% 2	784
	21st to end	Night	34% 12% 16% 25% 13%	660
March	1st to 10th	Night	34% 12% 17% 24% 12% 1	800
	11th to 20th	Night	30% 9% 18% 27% 14% 2	800
	21st to end	Night	37% 9% 18% 24% 11% 1	880
April	1st to 10th	Night	35% 7% 18% 22% 16% 3	800
	11th to 20th	Night	28% 8% 21% 26% 14% 3	752
	21st to end	Night	30% 7% 16% 26% 19% 2	600
May	1st to 10th	Night	23% 7% 19% 29% 20% 2	600
	11th to 20th	Night	23% 6% 17% 27% 23% 4	409
	21st to end	Night	25% 6% 15% 27% 24% 2	433
June	1st to 10th	Night	22% 4 16% 35% 21% 3	400
	11th to 20th	Night	17% 4 22% 36% 18% 3	400
	21st to end	Night	19% 2 15% 32% 30% 2	400
July	1st to 10th	Night	13% 2 15% 32% 34% 3	380
	11th to 20th	Night	14% 3 15% 41% 25% 2	368
	21st to end	Night	15% 2 12% 35% 33% 4	600
August	1st to 10th	Night	21% 1 10% 29% 32% 7%	567
	11th to 20th	Night	13% 1 10% 24% 43% 10%	564
	21st to end	Night	12% 2 16% 31% 33% 6%	727
September	1st to 10th	Night	11% 1 14% 32% 38% 4	760
	11th to 20th	Night	12% 3 14% 28% 32% 10%	760
	21st to end	Night	17% 4 15% 32% 28% 5%	760
October	1st to 10th	Night	18% 4 18% 28% 28% 5%	760
	11th to 20th	Night	20% 5% 13% 32% 26% 5%	760
	21st to end	Night	27% 7% 20% 25% 16% 4	836
November	1st to 10th	Night	33% 7% 17% 26% 16% 1	780
	11th to 20th	Night	36% 11% 16% 22% 14% 2	800
	21st to end	Night	24% 9% 19% 27% 18% 3	800
December	1st to 10th	Night	28% 9% 16% 27% 17% 4	800
	11th to 20th	Night	39% 8% 17% 20% 15% 2	800
	21st to end	Night	43% 10% 16% 22% 9% 1	880

Page generated at 2025-07-02 22:30:11. Version ac07

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