Clallam Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clallam Bay clear sky chart from 2005-11-06 to 2026-03-03.

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	17% 11% 4 10% 6% 5% 5% 4 5% 6% 27%	134836
	Night	19% 12% 4 10% 6% 5% 5% 4 5% 6% 25%	135056
Transparency	Day	32% 41% 10% 11% 5% 1	134542
	Night	38% 40% 8% 10% 4	134928
Seeing	Day	20% 10% 23% 26% 18% 4	17146
	Night	26% 11% 17% 24% 17% 5%	25455

By Month

Percentage Cloud Cover NW (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% 17% 5% 13% 6% 5% 4 2 3 3 9%	4125
	11th to 20th	Day	15% 11% 3 8% 5% 5% 4 4 6% 7% 32%	4119
	21st to end	Day	26% 14% 5% 10% 6% 5% 4 3 3 3 21%	5418
February	1st to 10th	Day	24% 15% 6% 11% 6% 6% 5% 4 5% 4 14%	1890
	11th to 20th	Day	26% 13% 5% 10% 6% 5% 3 3 4 4 21%	1845
	21st to end	Day	21% 16% 5% 11% 8% 5% 5% 3 5% 4 16%	1557
March	1st to 10th	Day	17% 15% 5% 14% 9% 7% 6% 4 4 5% 14%	4810
	11th to 20th	Day	18% 15% 5% 10% 7% 6% 5% 3 4 4 23%	5000
	21st to end	Day	22% 17% 6% 13% 7% 5% 5% 3 5% 5% 13%	5516
April	1st to 10th	Day	24% 13% 4 11% 7% 6% 6% 5% 5% 4 14%	2400
	11th to 20th	Day	19% 13% 5% 11% 7% 5% 5% 3 5% 5% 22%	2519
	21st to end	Day	22% 12% 4 11% 6% 5% 5% 4 5% 6% 21%	2600
May	1st to 10th	Day	14% 9% 4 9% 6% 5% 5% 3 5% 6% 35%	6266
	11th to 20th	Day	14% 11% 4 10% 6% 6% 6% 5% 7% 8% 23%	6277
	21st to end	Day	18% 9% 4 10% 6% 6% 5% 4 6% 8% 23%	7084
June	1st to 10th	Day	21% 11% 3 8% 5% 5% 5% 4 6% 7% 24%	3000
	11th to 20th	Day	18% 13% 5% 12% 8% 6% 5% 4 5% 6% 19%	3000
	21st to end	Day	14% 11% 5% 11% 7% 5% 5% 4 5% 5% 30%	3000
July	1st to 10th	Day	7% 5% 2 7% 4 4 4 4 5% 8% 50%	6780
	11th to 20th	Day	5% 4 2 5% 3 3 4 3 5% 9% 56%	6780
	21st to end	Day	7% 7% 3 9% 5% 4 5% 4 8% 10% 40%	7061
August	1st to 10th	Day	5% 5% 2 7% 4 4 4 4 7% 13% 46%	4319
	11th to 20th	Day	10% 8% 3 11% 6% 6% 6% 5% 8% 7% 31%	4156
	21st to end	Day	13% 9% 3 9% 4 5% 4 4 5% 6% 38%	4612
September	1st to 10th	Day	10% 8% 3 8% 5% 5% 4 4 6% 8% 39%	2400
	11th to 20th	Day	14% 9% 4 8% 7% 4 5% 4 5% 7% 33%	2322
	21st to end	Day	17% 7% 3 8% 5% 5% 4 4 7% 7% 33%	2154
October	1st to 10th	Day	13% 8% 4 10% 7% 7% 7% 5% 7% 7% 24%	3280
	11th to 20th	Day	24% 10% 4 10% 6% 6% 5% 3 4 5% 23%	3261
	21st to end	Day	19% 9% 4 10% 7% 7% 6% 4 6% 8% 20%	3354
November	1st to 10th	Day	27% 13% 4 11% 6% 5% 5% 4 5% 4 14%	1648
	11th to 20th	Day	28% 14% 4 10% 6% 5% 4 3 4 4 17%	1680
	21st to end	Day	25% 13% 4 9% 7% 6% 6% 5% 4 5% 15%	1680
December	1st to 10th	Day	19% 12% 5% 12% 7% 5% 5% 3 5% 8% 20%	2633
	11th to 20th	Day	32% 14% 4 11% 6% 5% 5% 3 4 4 10%	2715
	21st to end	Day	29% 15% 5% 11% 7% 6% 6% 4 4 4 9%	3575
January	1st to 10th	Night	29% 19% 6% 14% 7% 5% 4 3 3 3 8%	8770
	11th to 20th	Night	17% 10% 4 9% 4 4 4 3 5% 6% 33%	8779
	21st to end	Night	25% 13% 5% 10% 5% 5% 4 3 3 5% 23%	8764
February	1st to 10th	Night	25% 16% 4 9% 5% 5% 4 3 5% 5% 18%	2730
	11th to 20th	Night	24% 14% 4 10% 6% 4 4 3 4 5% 24%	2662
	21st to end	Night	23% 15% 4 10% 6% 4 4 3 5% 4 20%	2249
March	1st to 10th	Night	14% 14% 4 11% 8% 7% 5% 5% 6% 6% 19%	5123
	11th to 20th	Night	16% 11% 4 10% 6% 6% 5% 5% 6% 6% 25%	4999
	21st to end	Night	23% 18% 6% 13% 7% 5% 4 3 4 3 13%	5458
April	1st to 10th	Night	21% 13% 4 10% 7% 6% 5% 4 5% 5% 19%	2000
	11th to 20th	Night	17% 12% 5% 11% 7% 5% 4 3 5% 6% 25%	1829
	21st to end	Night	18% 12% 5% 10% 5% 5% 5% 4 5% 8% 23%	1800
May	1st to 10th	Night	12% 10% 3 7% 4 4 3 3 5% 6% 43%	3696
	11th to 20th	Night	14% 15% 4 9% 7% 6% 6% 4 5% 7% 24%	3616
	21st to end	Night	13% 12% 4 11% 6% 6% 6% 5% 6% 7% 23%	3774
June	1st to 10th	Night	16% 12% 3 8% 5% 5% 5% 3 6% 7% 30%	1400
	11th to 20th	Night	14% 12% 4 10% 7% 7% 6% 4 6% 7% 24%	1400
	21st to end	Night	11% 8% 4 9% 7% 5% 4 4 5% 8% 35%	1400
July	1st to 10th	Night	6% 9% 4 7% 3 4 4 3 5% 7% 49%	3180
	11th to 20th	Night	3 6% 3 6% 4 4 5% 3 5% 8% 54%	3180
	21st to end	Night	5% 8% 4 8% 4 5% 5% 5% 8% 10% 37%	3781
August	1st to 10th	Night	4 6% 3 6% 4 3 5% 5% 8% 11% 46%	2834
	11th to 20th	Night	8% 6% 2 7% 6% 6% 7% 6% 8% 9% 35%	2902
	21st to end	Night	12% 8% 3 9% 5% 4 5% 4 5% 8% 37%	3298
September	1st to 10th	Night	7% 6% 2 7% 5% 5% 6% 4 7% 8% 45%	2000
	11th to 20th	Night	14% 7% 2 8% 5% 5% 5% 4 6% 7% 36%	2075
	21st to end	Night	16% 8% 4 7% 5% 4 4 3 6% 6% 38%	2245
October	1st to 10th	Night	11% 7% 3 10% 5% 7% 6% 5% 7% 8% 31%	3920
	11th to 20th	Night	21% 10% 4 10% 5% 4 5% 3 5% 7% 26%	3897
	21st to end	Night	21% 9% 3 8% 6% 5% 5% 4 6% 6% 26%	4449
November	1st to 10th	Night	29% 11% 4 10% 5% 5% 5% 3 4 5% 19%	2870
	11th to 20th	Night	28% 14% 4 9% 6% 4 4 4 4 4 18%	2940
	21st to end	Night	27% 12% 4 10% 6% 6% 5% 3 4 4 18%	2940
December	1st to 10th	Night	20% 12% 5% 11% 7% 6% 5% 4 5% 6% 20%	4763
	11th to 20th	Night	33% 16% 5% 11% 6% 5% 5% 3 4 4 9%	5710
	21st to end	Night	28% 14% 5% 12% 7% 6% 5% 4 5% 4 10%	7623

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	62% 25% 5% 7% 1	4125
	11th to 20th	Day	35% 26% 12% 20% 7%	4140
	21st to end	Day	52% 25% 5% 13% 4	5419
February	1st to 10th	Day	30% 59% 4 4 3	1890
	11th to 20th	Day	30% 59% 3 5% 3	1854
	21st to end	Day	25% 61% 5% 4 3 1	1557
March	1st to 10th	Day	47% 32% 9% 9% 3	4810
	11th to 20th	Day	42% 31% 7% 18% 2	5000
	21st to end	Day	51% 33% 9% 6% 1	5516
April	1st to 10th	Day	25% 66% 4 4 1	2400
	11th to 20th	Day	22% 65% 4 6% 2 1	2519
	21st to end	Day	21% 64% 6% 6% 1 1	2600
May	1st to 10th	Day	28% 31% 15% 17% 9%	6266
	11th to 20th	Day	32% 37% 19% 12% 1	6280
	21st to end	Day	36% 35% 15% 9% 4	7085
June	1st to 10th	Day	18% 65% 7% 7% 2	3000
	11th to 20th	Day	19% 65% 6% 7% 3	3000
	21st to end	Day	19% 65% 8% 6% 2	3000
July	1st to 10th	Day	20% 31% 13% 17% 14% 6%	6706
	11th to 20th	Day	13% 30% 16% 24% 17%	6699
	21st to end	Day	24% 34% 22% 15% 4	6863
August	1st to 10th	Day	15% 41% 12% 22% 10% 1	4302
	11th to 20th	Day	28% 42% 18% 8% 4	4195
	21st to end	Day	29% 38% 10% 15% 7%	4611
September	1st to 10th	Day	21% 61% 8% 7% 3 1	2400
	11th to 20th	Day	21% 60% 6% 8% 6%	2322
	21st to end	Day	20% 59% 8% 8% 4	2154
October	1st to 10th	Day	35% 40% 12% 11% 3	3280
	11th to 20th	Day	41% 38% 5% 13% 3	3261
	21st to end	Day	36% 40% 8% 10% 5% 1	3354
November	1st to 10th	Day	32% 56% 6% 5% 1	1648
	11th to 20th	Day	30% 56% 3 6% 3 1	1680
	21st to end	Day	27% 58% 4 7% 4	1680
December	1st to 10th	Day	36% 37% 11% 13% 3	2633
	11th to 20th	Day	52% 38% 6% 4 1	2718
	21st to end	Day	57% 33% 7% 3 1	3575
January	1st to 10th	Night	64% 24% 4 6% 2	8770
	11th to 20th	Night	36% 26% 11% 16% 11%	8820
	21st to end	Night	49% 24% 7% 14% 5%	8764
February	1st to 10th	Night	28% 59% 4 4 4	2730
	11th to 20th	Night	30% 59% 3 4 3 1	2664
	21st to end	Night	25% 61% 5% 6% 3 1	2249
March	1st to 10th	Night	43% 33% 9% 11% 4	5123
	11th to 20th	Night	36% 34% 9% 18% 3	5000
	21st to end	Night	55% 32% 7% 5% 1	5458
April	1st to 10th	Night	25% 64% 5% 5% 1	2000
	11th to 20th	Night	24% 64% 3 7% 2 1	1829
	21st to end	Night	22% 64% 6% 5% 3	1800
May	1st to 10th	Night	28% 30% 14% 20% 8%	3693
	11th to 20th	Night	41% 39% 9% 9% 3	3616
	21st to end	Night	40% 35% 13% 11% 1	3774
June	1st to 10th	Night	20% 63% 8% 5% 3 1	1400
	11th to 20th	Night	21% 63% 5% 8% 3	1400
	21st to end	Night	20% 64% 10% 5% 2	1400
July	1st to 10th	Night	25% 36% 11% 10% 13% 5%	3145
	11th to 20th	Night	21% 33% 11% 21% 13%	3138
	21st to end	Night	32% 42% 13% 11% 2	3674
August	1st to 10th	Night	21% 43% 12% 15% 9% 1	2826
	11th to 20th	Night	31% 45% 13% 6% 3 1	2929
	21st to end	Night	28% 39% 9% 16% 7%	3298
September	1st to 10th	Night	18% 62% 7% 8% 4 1	2000
	11th to 20th	Night	22% 60% 5% 6% 6% 1	2075
	21st to end	Night	19% 59% 7% 9% 6%	2245
October	1st to 10th	Night	32% 41% 12% 13% 2	3920
	11th to 20th	Night	40% 38% 7% 12% 3	3897
	21st to end	Night	35% 41% 10% 9% 5% 1	4449
November	1st to 10th	Night	32% 55% 7% 5% 2	2870
	11th to 20th	Night	30% 57% 4 5% 3 2	2940
	21st to end	Night	30% 56% 3 5% 6%	2940
December	1st to 10th	Night	40% 39% 8% 11% 3	4763
	11th to 20th	Night	55% 36% 4 4 1	5706
	21st to end	Night	55% 32% 8% 5% 1	7623

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	37% 19% 26% 11% 6% 1	220
	11th to 20th	Day	28% 15% 23% 20% 13%	220
	21st to end	Day	31% 15% 22% 23% 7% 2	373
February	1st to 10th	Day	31% 16% 25% 23% 5% 1	430
	11th to 20th	Day	30% 16% 25% 24% 5%	425
	21st to end	Day	30% 16% 28% 20% 5% 1	355
March	1st to 10th	Day	23% 15% 29% 20% 13% 1	497
	11th to 20th	Day	26% 15% 24% 20% 12% 3	500
	21st to end	Day	29% 14% 26% 21% 8% 1	550
April	1st to 10th	Day	27% 13% 26% 23% 9% 2	500
	11th to 20th	Day	20% 13% 29% 21% 15% 3	492
	21st to end	Day	24% 12% 29% 22% 10% 4	500
May	1st to 10th	Day	15% 9% 27% 32% 16% 2	503
	11th to 20th	Day	20% 7% 21% 32% 18% 3	528
	21st to end	Day	12% 9% 27% 29% 17% 5%	650
June	1st to 10th	Day	21% 8% 21% 28% 19% 3	730
	11th to 20th	Day	15% 8% 30% 29% 16% 2	730
	21st to end	Day	13% 6% 20% 34% 23% 4	730
July	1st to 10th	Day	14% 3 17% 32% 30% 4	721
	11th to 20th	Day	9% 4 17% 36% 27% 7%	718
	21st to end	Day	6% 3 17% 31% 36% 8%	658
August	1st to 10th	Day	8% 4 15% 29% 31% 13%	527
	11th to 20th	Day	8% 3 13% 29% 38% 9%	517
	21st to end	Day	9% 7% 22% 29% 25% 8%	583
September	1st to 10th	Day	14% 6% 17% 34% 25% 4	530
	11th to 20th	Day	18% 6% 17% 27% 26% 6%	530
	21st to end	Day	16% 10% 21% 29% 22% 2	530
October	1st to 10th	Day	19% 8% 25% 24% 21% 4	530
	11th to 20th	Day	29% 10% 19% 26% 13% 3	530
	21st to end	Day	26% 12% 29% 21% 10% 2	497
November	1st to 10th	Day	30% 16% 26% 23% 5%	220
	11th to 20th	Day	30% 15% 26% 17% 11% 1	220
	21st to end	Day	27% 16% 28% 14% 12% 3	220
December	1st to 10th	Day	30% 18% 23% 17% 10% 1	220
	11th to 20th	Day	34% 23% 22% 15% 6%	220
	21st to end	Day	33% 19% 24% 18% 7%	242
January	1st to 10th	Night	38% 18% 19% 17% 8%	950
	11th to 20th	Night	33% 15% 13% 27% 11% 1	950
	21st to end	Night	33% 13% 20% 19% 12% 2	950
February	1st to 10th	Night	31% 17% 22% 23% 7% 1	840
	11th to 20th	Night	29% 15% 22% 24% 10%	824
	21st to end	Night	30% 16% 23% 21% 8% 2	692
March	1st to 10th	Night	25% 15% 19% 24% 15% 2	808
	11th to 20th	Night	30% 15% 19% 23% 11% 3	800
	21st to end	Night	30% 14% 20% 22% 12% 2	880
April	1st to 10th	Night	27% 12% 18% 25% 15% 4	800
	11th to 20th	Night	22% 11% 20% 28% 16% 3	641
	21st to end	Night	23% 11% 17% 27% 19% 4	600
May	1st to 10th	Night	16% 8% 16% 30% 24% 7%	430
	11th to 20th	Night	19% 7% 14% 26% 27% 6%	394
	21st to end	Night	19% 8% 18% 23% 27% 5%	433
June	1st to 10th	Night	20% 7% 19% 25% 26% 4	400
	11th to 20th	Night	20% 8% 16% 33% 20% 4	400
	21st to end	Night	14% 6% 14% 28% 31% 8%	400
July	1st to 10th	Night	15% 5% 11% 25% 36% 8%	390
	11th to 20th	Night	8% 5% 15% 28% 32% 11%	388
	21st to end	Night	8% 3 11% 29% 34% 15%	438
August	1st to 10th	Night	12% 5% 13% 20% 32% 19%	532
	11th to 20th	Night	10% 2 8% 22% 37% 21%	594
	21st to end	Night	16% 7% 13% 23% 31% 11%	687
September	1st to 10th	Night	10% 4 11% 31% 32% 13%	800
	11th to 20th	Night	18% 6% 13% 23% 28% 13%	800
	21st to end	Night	21% 8% 16% 25% 23% 7%	800
October	1st to 10th	Night	21% 6% 11% 30% 28% 6%	800
	11th to 20th	Night	27% 7% 16% 26% 19% 6%	800
	21st to end	Night	28% 11% 19% 25% 13% 2	880
November	1st to 10th	Night	36% 13% 21% 22% 8%	820
	11th to 20th	Night	35% 15% 20% 22% 7% 1	840
	21st to end	Night	33% 12% 20% 23% 10% 1	840
December	1st to 10th	Night	30% 14% 19% 24% 13%	859
	11th to 20th	Night	36% 17% 24% 17% 6%	950
	21st to end	Night	37% 18% 21% 19% 4	1045

Page generated at 2026-02-27 22:40:20. Version ac07

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