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 2024-12-02.

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	18% 11% 4 9% 6% 5% 5% 4 5% 6% 27%	105753
	Night	20% 12% 4 9% 6% 5% 5% 4 5% 6% 26%	102483
Transparency	Day	27% 49% 8% 10% 4 1	105500
	Night	32% 49% 7% 8% 4 1	102382
Seeing	Day	20% 10% 23% 26% 17% 3	15620
	Night	26% 11% 17% 23% 17% 5%	23778

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	35% 16% 4 10% 6% 4 4 2 4 4 11%	2219
	11th to 20th	Day	24% 16% 4 9% 6% 6% 4 4 4 6% 17%	2199
	21st to end	Day	36% 17% 5% 11% 6% 4 4 3 3 3 7%	2903
February	1st to 10th	Day	26% 16% 6% 10% 5% 5% 5% 4 5% 5% 13%	1710
	11th to 20th	Day	26% 14% 5% 10% 5% 6% 3 3 4 4 20%	1665
	21st to end	Day	21% 17% 5% 11% 8% 5% 5% 3 4 4 16%	1413
March	1st to 10th	Day	15% 15% 5% 12% 8% 7% 6% 5% 5% 5% 15%	3333
	11th to 20th	Day	17% 13% 3 8% 6% 5% 4 3 4 5% 31%	3490
	21st to end	Day	25% 15% 5% 11% 6% 5% 4 3 4 5% 17%	3842
April	1st to 10th	Day	24% 14% 4 11% 7% 6% 6% 5% 5% 4 14%	2280
	11th to 20th	Day	20% 14% 5% 11% 7% 5% 4 3 5% 5% 21%	2391
	21st to end	Day	23% 12% 5% 11% 6% 5% 5% 4 5% 5% 19%	2470
May	1st to 10th	Day	17% 10% 4 9% 5% 4 5% 3 4 4 34%	4379
	11th to 20th	Day	12% 10% 4 9% 6% 6% 5% 4 7% 8% 31%	4377
	21st to end	Day	23% 10% 4 10% 6% 6% 5% 4 5% 7% 19%	4938
June	1st to 10th	Day	22% 11% 4 9% 5% 5% 5% 4 6% 7% 22%	2850
	11th to 20th	Day	18% 13% 5% 11% 7% 6% 5% 4 5% 6% 19%	2850
	21st to end	Day	13% 11% 4 11% 7% 5% 5% 4 5% 5% 30%	2850
July	1st to 10th	Day	8% 5% 2 6% 4 3 3 3 4 6% 56%	4740
	11th to 20th	Day	6% 4 2 5% 3 3 4 4 5% 9% 55%	4740
	21st to end	Day	10% 7% 3 10% 5% 4 4 4 8% 9% 36%	4921
August	1st to 10th	Day	5% 5% 2 6% 4 4 4 4 7% 13% 47%	4186
	11th to 20th	Day	9% 8% 3 11% 6% 6% 6% 5% 8% 8% 31%	4026
	21st to end	Day	14% 9% 3 9% 4 5% 4 4 5% 6% 38%	4471
September	1st to 10th	Day	10% 8% 4 8% 5% 5% 4 3 6% 7% 40%	2280
	11th to 20th	Day	15% 9% 4 8% 7% 4 5% 4 5% 7% 33%	2206
	21st to end	Day	17% 7% 3 8% 5% 5% 4 4 6% 6% 34%	2047
October	1st to 10th	Day	13% 8% 4 10% 7% 7% 7% 5% 7% 7% 24%	3180
	11th to 20th	Day	25% 10% 4 10% 6% 6% 5% 3 5% 5% 22%	3161
	21st to end	Day	18% 9% 4 10% 7% 7% 6% 4 6% 8% 20%	3250
November	1st to 10th	Day	28% 13% 4 11% 6% 5% 5% 4 5% 4 15%	1568
	11th to 20th	Day	27% 14% 4 10% 6% 5% 4 3 4 4 18%	1600
	21st to end	Day	26% 13% 4 10% 7% 6% 6% 5% 4 5% 15%	1600
December	1st to 10th	Day	23% 13% 4 10% 6% 5% 4 2 4 5% 23%	1491
	11th to 20th	Day	30% 14% 4 9% 5% 5% 5% 3 5% 4 14%	1685
	21st to end	Day	30% 15% 5% 11% 6% 5% 5% 4 4 4 11%	2442
January	1st to 10th	Night	30% 18% 5% 12% 6% 4 4 3 3 3 11%	4726
	11th to 20th	Night	27% 12% 4 8% 4 4 4 4 4 7% 21%	4699
	21st to end	Night	35% 16% 5% 10% 6% 5% 4 3 3 3 10%	4754
February	1st to 10th	Night	27% 16% 4 8% 5% 5% 4 3 5% 5% 18%	2470
	11th to 20th	Night	24% 14% 4 9% 6% 4 3 2 3 5% 24%	2402
	21st to end	Night	24% 15% 4 10% 6% 4 4 2 5% 5% 21%	2041
March	1st to 10th	Night	16% 15% 4 11% 8% 6% 5% 4 5% 6% 20%	3536
	11th to 20th	Night	15% 9% 3 9% 6% 5% 4 4 6% 7% 33%	3489
	21st to end	Night	22% 18% 6% 12% 7% 5% 4 3 3 3 17%	3810
April	1st to 10th	Night	21% 13% 5% 10% 7% 6% 5% 3 5% 5% 19%	1900
	11th to 20th	Night	17% 13% 5% 11% 7% 5% 4 4 4 6% 25%	1737
	21st to end	Night	19% 12% 5% 10% 6% 5% 5% 4 4 8% 23%	1710
May	1st to 10th	Night	14% 10% 3 7% 4 4 3 3 5% 6% 40%	2582
	11th to 20th	Night	11% 12% 4 9% 5% 5% 5% 3 5% 8% 32%	2516
	21st to end	Night	16% 14% 4 12% 6% 5% 4 4 5% 6% 25%	2620
June	1st to 10th	Night	17% 12% 3 8% 5% 5% 5% 3 6% 7% 29%	1330
	11th to 20th	Night	15% 12% 4 10% 7% 7% 6% 4 6% 7% 23%	1330
	21st to end	Night	11% 8% 4 9% 7% 4 4 3 5% 9% 35%	1330
July	1st to 10th	Night	7% 8% 3 7% 3 4 4 2 4 5% 53%	2220
	11th to 20th	Night	4 5% 2 6% 3 4 5% 4 6% 9% 52%	2220
	21st to end	Night	7% 10% 4 8% 4 5% 5% 5% 7% 8% 37%	2630
August	1st to 10th	Night	4 6% 3 6% 4 3 5% 5% 7% 11% 47%	2747
	11th to 20th	Night	8% 6% 2 7% 6% 6% 7% 6% 8% 9% 35%	2812
	21st to end	Night	12% 8% 3 9% 5% 4 4 4 5% 8% 37%	3197
September	1st to 10th	Night	7% 6% 2 6% 5% 5% 5% 4 6% 8% 46%	1900
	11th to 20th	Night	15% 7% 2 9% 5% 5% 5% 4 6% 7% 35%	1971
	21st to end	Night	15% 8% 4 7% 5% 4 4 3 6% 6% 38%	2133
October	1st to 10th	Night	12% 7% 3 10% 5% 7% 6% 5% 7% 8% 30%	3800
	11th to 20th	Night	22% 10% 4 10% 5% 4 5% 3 5% 7% 25%	3777
	21st to end	Night	21% 9% 3 8% 6% 5% 5% 4 6% 6% 27%	4311
November	1st to 10th	Night	30% 11% 4 10% 5% 5% 5% 3 4 4 19%	2730
	11th to 20th	Night	28% 14% 4 9% 6% 4 4 4 4 4 19%	2800
	21st to end	Night	27% 12% 4 10% 6% 6% 5% 3 4 5% 18%	2800
December	1st to 10th	Night	24% 12% 4 8% 5% 5% 4 4 5% 6% 22%	2719
	11th to 20th	Night	29% 14% 5% 11% 7% 5% 4 4 4 4 13%	3520
	21st to end	Night	28% 15% 5% 12% 7% 5% 4 4 3 4 12%	5214

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	47% 40% 5% 6% 2	2219
	11th to 20th	Day	42% 44% 7% 6% 1	2220
	21st to end	Day	53% 42% 2 2	2903
February	1st to 10th	Day	27% 65% 3 3 2	1710
	11th to 20th	Day	26% 65% 2 4 2	1674
	21st to end	Day	21% 66% 5% 4 3 1	1413
March	1st to 10th	Day	36% 44% 9% 7% 3	3333
	11th to 20th	Day	26% 42% 8% 22% 2	3490
	21st to end	Day	39% 44% 10% 6% 1	3842
April	1st to 10th	Day	24% 69% 4 3 1	2280
	11th to 20th	Day	22% 68% 3 4 2 1	2391
	21st to end	Day	22% 67% 4 5% 1 1	2470
May	1st to 10th	Day	25% 42% 12% 14% 6% 1	4379
	11th to 20th	Day	21% 48% 18% 11% 2	4380
	21st to end	Day	36% 47% 9% 5% 3	4939
June	1st to 10th	Day	19% 68% 6% 5% 2	2850
	11th to 20th	Day	17% 68% 5% 7% 3	2850
	21st to end	Day	17% 67% 7% 6% 2	2850
July	1st to 10th	Day	12% 37% 5% 17% 19% 9%	4666
	11th to 20th	Day	10% 39% 11% 25% 14%	4659
	21st to end	Day	25% 42% 15% 14% 5%	4765
August	1st to 10th	Day	14% 41% 11% 22% 10% 1	4169
	11th to 20th	Day	28% 43% 18% 8% 4	4065
	21st to end	Day	29% 39% 9% 15% 6%	4470
September	1st to 10th	Day	19% 62% 8% 7% 4 1	2280
	11th to 20th	Day	20% 62% 5% 6% 6%	2206
	21st to end	Day	19% 62% 7% 8% 4	2047
October	1st to 10th	Day	34% 41% 12% 10% 3	3180
	11th to 20th	Day	41% 39% 5% 12% 3	3161
	21st to end	Day	35% 41% 8% 10% 5% 1	3250
November	1st to 10th	Day	30% 59% 5% 5% 1	1568
	11th to 20th	Day	28% 59% 3 6% 3 1	1600
	21st to end	Day	25% 60% 3 7% 4	1600
December	1st to 10th	Day	25% 60% 5% 7% 2 1	1491
	11th to 20th	Day	37% 53% 4 4 1	1688
	21st to end	Day	49% 41% 5% 4 1	2442
January	1st to 10th	Night	50% 39% 4 4 2	4726
	11th to 20th	Night	38% 42% 9% 9% 1	4740
	21st to end	Night	55% 41% 2 3	4754
February	1st to 10th	Night	25% 65% 4 3 3 1	2470
	11th to 20th	Night	27% 65% 3 3 2	2404
	21st to end	Night	21% 66% 5% 5% 3 1	2041
March	1st to 10th	Night	36% 43% 8% 9% 3	3536
	11th to 20th	Night	22% 45% 10% 20% 2 1	3490
	21st to end	Night	44% 43% 7% 5% 1	3810
April	1st to 10th	Night	23% 67% 4 4 1	1900
	11th to 20th	Night	24% 67% 2 6% 2 1	1737
	21st to end	Night	21% 66% 5% 4 4	1710
May	1st to 10th	Night	24% 42% 10% 17% 6%	2582
	11th to 20th	Night	26% 49% 10% 11% 5%	2516
	21st to end	Night	35% 45% 10% 7% 2	2620
June	1st to 10th	Night	20% 66% 6% 4 2 1	1330
	11th to 20th	Night	20% 66% 5% 7% 3	1330
	21st to end	Night	19% 66% 9% 5% 2	1330
July	1st to 10th	Night	18% 39% 6% 12% 18% 7%	2185
	11th to 20th	Night	15% 42% 11% 22% 10% 1	2178
	21st to end	Night	30% 44% 11% 12% 3	2547
August	1st to 10th	Night	20% 43% 12% 16% 9% 1	2739
	11th to 20th	Night	30% 46% 13% 6% 3 1	2839
	21st to end	Night	29% 40% 9% 16% 7%	3197
September	1st to 10th	Night	17% 64% 7% 8% 4 1	1900
	11th to 20th	Night	22% 62% 5% 4 6% 1	1971
	21st to end	Night	18% 61% 6% 9% 6%	2133
October	1st to 10th	Night	32% 42% 12% 12% 2	3800
	11th to 20th	Night	40% 39% 7% 11% 3	3777
	21st to end	Night	34% 42% 9% 8% 5% 1	4311
November	1st to 10th	Night	31% 57% 6% 4 2	2730
	11th to 20th	Night	28% 59% 4 4 4 2	2800
	21st to end	Night	28% 59% 3 4 6%	2800
December	1st to 10th	Night	28% 60% 3 5% 3	2719
	11th to 20th	Night	37% 54% 3 3 2	3516
	21st to end	Night	47% 40% 7% 4 1	5214

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	35% 19% 26% 12% 7% 1	180
	11th to 20th	Day	32% 18% 24% 16% 9%	180
	21st to end	Day	33% 16% 21% 23% 5% 1	316
February	1st to 10th	Day	34% 16% 25% 20% 5%	370
	11th to 20th	Day	31% 17% 25% 22% 4	365
	21st to end	Day	30% 16% 27% 21% 5% 1	307
March	1st to 10th	Day	23% 16% 30% 20% 11% 1	450
	11th to 20th	Day	25% 15% 24% 20% 12% 3	460
	21st to end	Day	29% 15% 25% 21% 8% 1	506
April	1st to 10th	Day	28% 14% 27% 22% 8% 2	460
	11th to 20th	Day	22% 13% 30% 19% 13% 3	452
	21st to end	Day	25% 12% 30% 22% 9% 2	460
May	1st to 10th	Day	15% 10% 26% 32% 15% 2	463
	11th to 20th	Day	19% 7% 21% 32% 18% 3	488
	21st to end	Day	13% 10% 28% 29% 17% 5%	602
June	1st to 10th	Day	22% 9% 22% 28% 17% 2	680
	11th to 20th	Day	15% 8% 32% 29% 15% 1	680
	21st to end	Day	13% 6% 21% 34% 23% 4	680
July	1st to 10th	Day	14% 3 17% 32% 30% 4	671
	11th to 20th	Day	10% 4 18% 36% 26% 6%	668
	21st to end	Day	6% 3 18% 31% 35% 8%	610
August	1st to 10th	Day	8% 5% 15% 29% 30% 13%	487
	11th to 20th	Day	7% 3 13% 29% 38% 10%	477
	21st to end	Day	10% 7% 23% 30% 23% 7%	539
September	1st to 10th	Day	15% 6% 19% 34% 23% 3	490
	11th to 20th	Day	18% 6% 18% 26% 25% 6%	490
	21st to end	Day	16% 11% 20% 30% 22% 2	490
October	1st to 10th	Day	20% 8% 25% 23% 21% 4	490
	11th to 20th	Day	30% 10% 17% 27% 13% 3	490
	21st to end	Day	26% 12% 28% 21% 10% 2	459
November	1st to 10th	Day	30% 16% 26% 23% 6%	200
	11th to 20th	Day	29% 16% 26% 18% 11% 2	200
	21st to end	Day	29% 17% 25% 14% 13% 3	200
December	1st to 10th	Day	29% 20% 24% 15% 11% 1	182
	11th to 20th	Day	32% 23% 21% 16% 7% 1	180
	21st to end	Day	33% 18% 25% 16% 8%	198
January	1st to 10th	Night	39% 18% 17% 17% 8%	850
	11th to 20th	Night	36% 15% 14% 25% 10% 1	850
	21st to end	Night	34% 14% 20% 19% 11% 2	858
February	1st to 10th	Night	32% 17% 21% 22% 7% 1	760
	11th to 20th	Night	29% 15% 22% 23% 10%	744
	21st to end	Night	30% 16% 23% 19% 9% 3	628
March	1st to 10th	Night	26% 16% 19% 22% 14% 2	760
	11th to 20th	Night	29% 15% 18% 24% 11% 3	760
	21st to end	Night	29% 15% 20% 22% 12% 2	836
April	1st to 10th	Night	28% 12% 17% 24% 14% 4	760
	11th to 20th	Night	22% 11% 20% 28% 15% 3	609
	21st to end	Night	23% 11% 17% 27% 18% 3	570
May	1st to 10th	Night	16% 9% 16% 29% 24% 6%	409
	11th to 20th	Night	18% 7% 14% 26% 28% 6%	374
	21st to end	Night	19% 9% 18% 22% 26% 5%	411
June	1st to 10th	Night	20% 7% 20% 25% 25% 3	380
	11th to 20th	Night	21% 8% 16% 33% 18% 4	380
	21st to end	Night	14% 5% 14% 28% 31% 8%	380
July	1st to 10th	Night	15% 5% 12% 24% 36% 8%	370
	11th to 20th	Night	8% 5% 15% 28% 31% 12%	368
	21st to end	Night	8% 3 11% 29% 34% 14%	416
August	1st to 10th	Night	12% 6% 13% 19% 31% 20%	505
	11th to 20th	Night	10% 2 8% 21% 38% 21%	564
	21st to end	Night	16% 7% 14% 23% 30% 10%	652
September	1st to 10th	Night	11% 4 12% 30% 31% 12%	760
	11th to 20th	Night	18% 6% 14% 23% 27% 13%	760
	21st to end	Night	21% 8% 17% 25% 23% 7%	760
October	1st to 10th	Night	22% 6% 11% 29% 27% 6%	760
	11th to 20th	Night	27% 7% 15% 25% 19% 6%	760
	21st to end	Night	29% 11% 19% 25% 14% 2	836
November	1st to 10th	Night	36% 13% 20% 22% 8%	780
	11th to 20th	Night	35% 16% 20% 21% 8% 1	800
	21st to end	Night	33% 12% 20% 22% 11% 1	800
December	1st to 10th	Night	29% 15% 20% 24% 12% 1	783
	11th to 20th	Night	34% 17% 24% 18% 7%	850
	21st to end	Night	38% 19% 21% 18% 4	935

Page generated at 2024-11-29 07:43:10. Version ac07

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