OAS Port Gamble Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the OAS Port Gamble Site clear sky chart from 2005-11-06 to 2024-11-02.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	101754
	Night	16% 11% 4 8% 5% 5% 5% 4 5% 6% 31%	97273
Transparency	Day	48% 8% 15% 19% 9% 2	101509
	Night	53% 8% 13% 17% 7% 1	97164
Seeing	Day	18% 10% 21% 26% 19% 5%	15188
	Night	21% 9% 19% 26% 21% 4	23490

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	21% 16% 5% 13% 8% 6% 5% 4 5% 4 12%	2219
	11th to 20th	Day	18% 10% 4 9% 7% 6% 5% 4 7% 9% 20%	2427
	21st to end	Day	21% 16% 6% 13% 7% 6% 5% 5% 5% 5% 11%	2886
February	1st to 10th	Day	18% 14% 5% 9% 7% 5% 6% 5% 7% 7% 17%	1710
	11th to 20th	Day	16% 13% 5% 11% 8% 6% 5% 5% 7% 6% 19%	1665
	21st to end	Day	14% 14% 4 11% 8% 5% 6% 4 6% 5% 23%	1460
March	1st to 10th	Day	12% 10% 4 9% 8% 8% 8% 6% 8% 8% 19%	3231
	11th to 20th	Day	13% 9% 3 7% 5% 5% 5% 4 6% 6% 36%	3490
	21st to end	Day	16% 11% 4 12% 7% 6% 7% 5% 6% 7% 19%	3938
April	1st to 10th	Day	16% 14% 4 10% 7% 6% 5% 5% 6% 7% 20%	2280
	11th to 20th	Day	16% 11% 4 9% 7% 5% 5% 4 6% 7% 27%	2294
	21st to end	Day	15% 11% 3 9% 7% 6% 6% 5% 6% 7% 25%	2506
May	1st to 10th	Day	15% 8% 2 7% 5% 5% 5% 3 6% 6% 38%	4420
	11th to 20th	Day	13% 8% 3 7% 5% 4 4 5% 6% 8% 37%	4377
	21st to end	Day	23% 12% 3 8% 6% 6% 5% 4 5% 7% 21%	4813
June	1st to 10th	Day	17% 8% 2 9% 6% 6% 6% 5% 6% 7% 29%	2755
	11th to 20th	Day	16% 11% 3 9% 6% 7% 6% 5% 6% 7% 23%	2850
	21st to end	Day	10% 7% 2 7% 5% 4 5% 5% 7% 7% 39%	2850
July	1st to 10th	Day	6% 5% 2 4 3 3 3 2 4 5% 63%	4740
	11th to 20th	Day	5% 4 1 4 3 3 4 3 5% 5% 64%	4612
	21st to end	Day	11% 6% 2 5% 3 3 4 3 4 7% 53%	4790
August	1st to 10th	Day	5% 4 1 5% 3 3 4 4 5% 7% 60%	4314
	11th to 20th	Day	8% 9% 3 7% 4 4 5% 4 6% 8% 41%	4026
	21st to end	Day	14% 8% 3 8% 4 4 4 3 5% 5% 43%	4351
September	1st to 10th	Day	9% 6% 2 5% 3 4 4 3 5% 7% 52%	2280
	11th to 20th	Day	11% 8% 3 8% 5% 5% 4 4 6% 7% 39%	2280
	21st to end	Day	12% 8% 2 7% 6% 5% 4 4 6% 7% 39%	2004
October	1st to 10th	Day	13% 9% 3 8% 5% 5% 5% 5% 6% 8% 33%	1900
	11th to 20th	Day	15% 10% 4 9% 6% 6% 5% 4 6% 8% 28%	1900
	21st to end	Day	16% 11% 5% 12% 6% 5% 6% 4 7% 7% 22%	1983
November	1st to 10th	Day	20% 13% 5% 11% 6% 7% 5% 5% 5% 6% 18%	1517
	11th to 20th	Day	18% 13% 5% 10% 7% 5% 4 5% 6% 7% 21%	1520
	21st to end	Day	21% 12% 4 10% 6% 5% 5% 4 6% 8% 19%	1520
December	1st to 10th	Day	16% 13% 4 9% 6% 6% 5% 4 6% 7% 24%	1520
	11th to 20th	Day	16% 15% 7% 15% 8% 7% 6% 4 5% 5% 12%	1884
	21st to end	Day	16% 15% 6% 14% 9% 6% 6% 4 6% 5% 13%	2442
January	1st to 10th	Night	20% 17% 5% 12% 7% 6% 6% 4 5% 5% 12%	4726
	11th to 20th	Night	19% 11% 4 8% 5% 5% 6% 4 6% 9% 22%	4467
	21st to end	Night	24% 13% 5% 11% 6% 5% 6% 5% 6% 7% 13%	4769
February	1st to 10th	Night	18% 16% 4 10% 6% 5% 5% 4 5% 7% 20%	2470
	11th to 20th	Night	15% 13% 5% 10% 6% 6% 5% 5% 6% 5% 25%	2402
	21st to end	Night	15% 16% 4 8% 6% 5% 4 5% 6% 6% 24%	1992
March	1st to 10th	Night	12% 13% 5% 11% 7% 7% 6% 6% 7% 7% 18%	3629
	11th to 20th	Night	11% 9% 3 7% 5% 5% 4 3 7% 6% 40%	3489
	21st to end	Night	18% 15% 5% 11% 5% 6% 5% 4 5% 5% 20%	3715
April	1st to 10th	Night	16% 12% 4 10% 7% 5% 7% 4 6% 7% 21%	1900
	11th to 20th	Night	16% 10% 4 7% 6% 6% 5% 4 6% 7% 30%	1833
	21st to end	Night	18% 11% 3 9% 6% 5% 5% 4 6% 7% 27%	1672
May	1st to 10th	Night	14% 9% 3 5% 4 4 4 4 5% 5% 43%	2540
	11th to 20th	Night	14% 7% 2 6% 5% 5% 4 3 5% 6% 44%	2516
	21st to end	Night	26% 10% 4 8% 5% 5% 4 3 4 6% 25%	2762
June	1st to 10th	Night	17% 9% 2 9% 5% 5% 5% 4 5% 7% 32%	1420
	11th to 20th	Night	19% 11% 4 8% 5% 5% 5% 4 6% 6% 27%	1330
	21st to end	Night	10% 6% 2 7% 4 5% 4 4 6% 9% 42%	1330
July	1st to 10th	Night	9% 5% 2 4 3 3 3 2 3 4 63%	2220
	11th to 20th	Night	4 2 1 3 2 2 3 2 4 5% 72%	2343
	21st to end	Night	15% 5% 2 5% 3 3 3 3 4 5% 53%	2762
August	1st to 10th	Night	4 3 1 3 2 3 4 3 5% 6% 66%	2615
	11th to 20th	Night	11% 7% 3 7% 4 3 3 3 5% 7% 48%	2812
	21st to end	Night	15% 7% 3 6% 3 3 3 3 4 5% 48%	3321
September	1st to 10th	Night	7% 5% 2 6% 3 4 3 3 5% 7% 55%	1900
	11th to 20th	Night	12% 7% 3 8% 5% 5% 4 3 5% 6% 41%	1900
	21st to end	Night	12% 7% 3 8% 5% 4 4 3 6% 6% 41%	2174
October	1st to 10th	Night	11% 8% 3 8% 5% 5% 5% 4 6% 6% 40%	2280
	11th to 20th	Night	16% 9% 3 8% 5% 5% 4 4 5% 7% 35%	2280
	21st to end	Night	17% 9% 3 9% 5% 5% 5% 3 6% 8% 31%	2614
November	1st to 10th	Night	22% 10% 3 8% 5% 5% 6% 4 5% 6% 26%	2580
	11th to 20th	Night	18% 11% 4 9% 7% 5% 5% 5% 6% 6% 24%	2660
	21st to end	Night	16% 13% 3 10% 7% 6% 6% 4 6% 7% 22%	2660
December	1st to 10th	Night	18% 13% 3 9% 6% 5% 5% 5% 6% 5% 25%	2660
	11th to 20th	Night	17% 14% 5% 13% 7% 6% 5% 5% 6% 6% 16%	3316
	21st to end	Night	18% 16% 6% 12% 7% 6% 6% 4 6% 6% 13%	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	74% 9% 7% 8% 2	2219
	11th to 20th	Day	62% 6% 14% 14% 3 1	2451
	21st to end	Day	76% 7% 9% 6% 1	2886
February	1st to 10th	Day	68% 9% 10% 8% 4 1	1710
	11th to 20th	Day	67% 8% 9% 9% 6%	1674
	21st to end	Day	62% 8% 13% 11% 5%	1460
March	1st to 10th	Day	58% 9% 15% 13% 4	3231
	11th to 20th	Day	46% 11% 15% 25% 3 1	3490
	21st to end	Day	61% 10% 15% 13% 1	3938
April	1st to 10th	Day	60% 10% 17% 12% 1	2280
	11th to 20th	Day	55% 8% 13% 15% 7% 2	2294
	21st to end	Day	55% 8% 16% 15% 6% 1	2506
May	1st to 10th	Day	42% 9% 15% 24% 9% 1	4420
	11th to 20th	Day	39% 10% 24% 20% 6%	4380
	21st to end	Day	59% 10% 18% 10% 2	4814
June	1st to 10th	Day	48% 9% 20% 15% 6% 1	2755
	11th to 20th	Day	54% 8% 20% 14% 4	2850
	21st to end	Day	39% 9% 22% 21% 7% 1	2850
July	1st to 10th	Day	22% 5% 10% 24% 25% 14%	4666
	11th to 20th	Day	18% 5% 10% 31% 32% 4	4531
	21st to end	Day	27% 5% 18% 32% 15% 2	4639
August	1st to 10th	Day	20% 6% 15% 39% 18% 2	4297
	11th to 20th	Day	36% 9% 21% 24% 8% 2	4065
	21st to end	Day	42% 5% 13% 28% 11%	4350
September	1st to 10th	Day	32% 6% 18% 26% 13% 5%	2280
	11th to 20th	Day	44% 8% 15% 17% 15% 1	2280
	21st to end	Day	46% 7% 18% 18% 9% 2	2004
October	1st to 10th	Day	47% 9% 16% 22% 7%	1900
	11th to 20th	Day	57% 8% 15% 15% 5% 1	1900
	21st to end	Day	61% 8% 12% 13% 7%	1983
November	1st to 10th	Day	65% 9% 12% 10% 4	1517
	11th to 20th	Day	65% 7% 10% 11% 5% 2	1520
	21st to end	Day	66% 8% 9% 11% 6%	1520
December	1st to 10th	Day	62% 8% 9% 13% 6% 1	1520
	11th to 20th	Day	74% 9% 8% 7% 2 1	1887
	21st to end	Day	72% 9% 11% 6% 2	2442
January	1st to 10th	Night	74% 9% 7% 7% 2	4726
	11th to 20th	Night	59% 7% 13% 18% 3 1	4505
	21st to end	Night	73% 9% 9% 7% 2	4769
February	1st to 10th	Night	64% 8% 12% 11% 4 1	2470
	11th to 20th	Night	61% 8% 13% 11% 7% 1	2404
	21st to end	Night	61% 7% 14% 14% 4 1	1992
March	1st to 10th	Night	61% 10% 12% 13% 3	3629
	11th to 20th	Night	40% 11% 18% 27% 3 1	3490
	21st to end	Night	64% 11% 14% 10% 1	3715
April	1st to 10th	Night	58% 12% 15% 13% 2	1900
	11th to 20th	Night	54% 8% 14% 15% 8% 2	1833
	21st to end	Night	56% 10% 14% 13% 7% 1	1672
May	1st to 10th	Night	42% 7% 14% 26% 11% 1	2540
	11th to 20th	Night	39% 10% 24% 18% 7% 1	2516
	21st to end	Night	59% 15% 15% 10% 2	2762
June	1st to 10th	Night	50% 10% 19% 15% 5% 1	1420
	11th to 20th	Night	57% 9% 16% 15% 3	1330
	21st to end	Night	40% 6% 24% 20% 7% 3	1330
July	1st to 10th	Night	29% 4 9% 22% 21% 15%	2185
	11th to 20th	Night	16% 4 10% 30% 38% 2	2301
	21st to end	Night	31% 6% 13% 28% 19% 3	2674
August	1st to 10th	Night	19% 4 14% 39% 21% 2	2607
	11th to 20th	Night	34% 7% 24% 23% 10% 2	2839
	21st to end	Night	39% 6% 15% 28% 11% 1	3321
September	1st to 10th	Night	29% 7% 17% 27% 15% 5%	1900
	11th to 20th	Night	44% 7% 12% 18% 15% 4	1900
	21st to end	Night	45% 7% 13% 25% 10% 1	2174
October	1st to 10th	Night	46% 7% 14% 25% 8%	2280
	11th to 20th	Night	51% 7% 17% 18% 7% 1	2280
	21st to end	Night	54% 8% 13% 17% 8%	2614
November	1st to 10th	Night	62% 7% 15% 12% 4 1	2580
	11th to 20th	Night	63% 8% 12% 11% 5% 2	2660
	21st to end	Night	64% 7% 11% 11% 7%	2660
December	1st to 10th	Night	62% 7% 11% 14% 6%	2660
	11th to 20th	Night	69% 9% 12% 6% 3	3312
	21st to end	Night	71% 9% 9% 9% 2	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	28% 15% 24% 18% 11% 3	180
	11th to 20th	Day	27% 17% 28% 10% 17% 2	180
	21st to end	Day	32% 16% 24% 17% 8% 3	251
February	1st to 10th	Day	28% 19% 23% 18% 11% 1	370
	11th to 20th	Day	30% 16% 25% 21% 8% 2	365
	21st to end	Day	22% 20% 27% 19% 12% 1	330
March	1st to 10th	Day	23% 17% 26% 22% 11% 1	460
	11th to 20th	Day	23% 17% 19% 22% 14% 6%	460
	21st to end	Day	22% 17% 28% 21% 11% 2	506
April	1st to 10th	Day	23% 15% 22% 24% 12% 3	460
	11th to 20th	Day	18% 17% 31% 19% 11% 4	452
	21st to end	Day	21% 12% 26% 26% 13% 2	460
May	1st to 10th	Day	14% 7% 25% 34% 17% 3	463
	11th to 20th	Day	17% 6% 19% 30% 18% 9%	488
	21st to end	Day	20% 8% 17% 28% 19% 8%	529
June	1st to 10th	Day	18% 8% 24% 29% 17% 4	585
	11th to 20th	Day	18% 7% 23% 31% 18% 3	680
	21st to end	Day	12% 5% 19% 35% 22% 6%	680
July	1st to 10th	Day	10% 4 19% 32% 28% 7%	671
	11th to 20th	Day	6% 5% 16% 32% 33% 9%	592
	21st to end	Day	8% 3 11% 32% 35% 11%	531
August	1st to 10th	Day	7% 3 10% 31% 35% 14%	487
	11th to 20th	Day	5% 2 11% 35% 34% 13%	477
	21st to end	Day	12% 4 17% 33% 25% 8%	539
September	1st to 10th	Day	13% 6% 18% 33% 25% 5%	490
	11th to 20th	Day	15% 7% 18% 29% 28% 4	490
	21st to end	Day	16% 9% 23% 29% 21% 2	490
October	1st to 10th	Day	20% 9% 22% 23% 21% 6%	490
	11th to 20th	Day	23% 12% 22% 21% 18% 4	490
	21st to end	Day	24% 19% 19% 23% 13% 2	432
November	1st to 10th	Day	36% 13% 24% 18% 9% 1	192
	11th to 20th	Day	26% 18% 24% 13% 11% 7%	180
	21st to end	Day	27% 14% 26% 16% 9% 8%	180
December	1st to 10th	Day	26% 18% 20% 14% 15% 7%	180
	11th to 20th	Day	28% 22% 27% 15% 6% 2	180
	21st to end	Day	27% 18% 27% 20% 6% 2	198
January	1st to 10th	Night	30% 13% 24% 19% 12% 3	850
	11th to 20th	Night	28% 14% 18% 20% 19% 2	781
	21st to end	Night	26% 12% 20% 23% 16% 3	836
February	1st to 10th	Night	28% 13% 22% 23% 11% 3	760
	11th to 20th	Night	23% 12% 22% 25% 17% 1	744
	21st to end	Night	25% 13% 23% 25% 13% 3	628
March	1st to 10th	Night	21% 13% 23% 26% 14% 2	760
	11th to 20th	Night	23% 15% 19% 25% 15% 2	760
	21st to end	Night	23% 12% 25% 27% 12% 2	836
April	1st to 10th	Night	24% 9% 21% 28% 16% 2	760
	11th to 20th	Night	21% 8% 23% 27% 17% 3	705
	21st to end	Night	23% 7% 20% 33% 14% 3	532
May	1st to 10th	Night	16% 6% 20% 35% 19% 4	380
	11th to 20th	Night	18% 3 17% 28% 32% 3	374
	21st to end	Night	23% 6% 14% 29% 23% 5%	411
June	1st to 10th	Night	22% 5% 19% 32% 21% 2	380
	11th to 20th	Night	20% 11% 16% 32% 19% 2	380
	21st to end	Night	15% 3 14% 36% 28% 4	380
July	1st to 10th	Night	13% 3 10% 31% 38% 5%	370
	11th to 20th	Night	8% 3 12% 34% 40% 4	368
	21st to end	Night	10% 3 6% 31% 45% 6%	416
August	1st to 10th	Night	10% 2 6% 26% 47% 10%	425
	11th to 20th	Night	8% 2 6% 27% 45% 12%	564
	21st to end	Night	11% 3 13% 32% 36% 5%	724
September	1st to 10th	Night	11% 2 10% 37% 33% 7%	760
	11th to 20th	Night	17% 4 13% 23% 33% 11%	760
	21st to end	Night	15% 6% 19% 29% 26% 5%	760
October	1st to 10th	Night	15% 7% 18% 28% 26% 6%	760
	11th to 20th	Night	21% 8% 18% 26% 22% 5%	760
	21st to end	Night	23% 10% 22% 27% 16% 3	836
November	1st to 10th	Night	28% 13% 22% 25% 12%	744
	11th to 20th	Night	25% 12% 24% 22% 14% 3	760
	21st to end	Night	25% 13% 22% 21% 14% 4	760
December	1st to 10th	Night	24% 11% 20% 26% 16% 3	760
	11th to 20th	Night	26% 17% 22% 22% 11% 2	771
	21st to end	Night	32% 15% 24% 19% 9% 1	935

Page generated at 2024-10-29 22:22:56. Version ac07

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