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 2024-03-08.

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% 4 8% 7% 4 5% 5% 6% 7% 31%	78349
	Night	16% 10% 4 8% 7% 4 5% 5% 5% 7% 29%	81153
Transparency	Day	37% 36% 11% 11% 4 1	78065
	Night	39% 35% 10% 11% 4 1	81017
Seeing	Day	18% 10% 21% 26% 19% 5%	14199
	Night	21% 9% 19% 26% 21% 4	22767

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% 15% 6% 11% 9% 5% 6% 5% 5% 5% 12%	2219
	11th to 20th	Day	18% 10% 5% 8% 8% 4 6% 5% 7% 10% 20%	2427
	21st to end	Day	21% 16% 6% 11% 8% 5% 5% 5% 5% 5% 12%	2886
February	1st to 10th	Day	19% 13% 5% 8% 8% 3 7% 6% 7% 8% 17%	1710
	11th to 20th	Day	16% 12% 5% 9% 10% 4 5% 6% 7% 7% 19%	1665
	21st to end	Day	15% 13% 5% 10% 9% 3 6% 5% 5% 6% 23%	1460
March	1st to 10th	Day	16% 11% 5% 7% 7% 5% 7% 7% 5% 8% 22%	1926
	11th to 20th	Day	18% 11% 4 8% 8% 4 6% 6% 5% 6% 23%	1980
	21st to end	Day	15% 10% 5% 10% 9% 5% 7% 7% 7% 7% 18%	2240
April	1st to 10th	Day	17% 12% 4 9% 8% 5% 6% 6% 6% 8% 21%	2160
	11th to 20th	Day	17% 9% 5% 9% 7% 4 5% 5% 6% 7% 24%	2171
	21st to end	Day	14% 10% 4 8% 7% 5% 7% 6% 6% 8% 25%	2374
May	1st to 10th	Day	11% 9% 3 8% 7% 4 6% 4 6% 8% 33%	2520
	11th to 20th	Day	13% 9% 3 7% 6% 4 5% 6% 6% 8% 33%	2477
	21st to end	Day	18% 11% 4 7% 7% 5% 5% 5% 5% 6% 29%	2723
June	1st to 10th	Day	17% 7% 3 8% 7% 4 6% 6% 5% 7% 29%	2610
	11th to 20th	Day	17% 10% 4 8% 7% 5% 7% 7% 6% 8% 22%	2700
	21st to end	Day	10% 7% 2 6% 6% 3 5% 6% 7% 8% 40%	2700
July	1st to 10th	Day	8% 6% 2 5% 5% 3 4 4 5% 6% 49%	2700
	11th to 20th	Day	8% 5% 2 5% 4 3 4 5% 5% 7% 51%	2628
	21st to end	Day	7% 4 2 4 3 2 3 4 4 6% 60%	2741
August	1st to 10th	Day	9% 4 2 5% 4 3 4 4 5% 8% 53%	2459
	11th to 20th	Day	6% 5% 2 4 4 3 3 5% 6% 8% 55%	2298
	21st to end	Day	10% 5% 2 6% 4 3 5% 5% 5% 8% 46%	2482
September	1st to 10th	Day	9% 5% 3 5% 4 3 4 4 4 8% 52%	2160
	11th to 20th	Day	10% 7% 3 6% 6% 4 4 5% 6% 7% 41%	2160
	21st to end	Day	12% 8% 3 6% 6% 4 4 5% 6% 7% 40%	1900
October	1st to 10th	Day	14% 9% 4 7% 6% 3 5% 6% 5% 8% 34%	1800
	11th to 20th	Day	14% 10% 4 7% 7% 4 6% 5% 6% 8% 29%	1800
	21st to end	Day	17% 10% 5% 9% 8% 3 6% 4 7% 8% 23%	1879
November	1st to 10th	Day	19% 12% 5% 10% 7% 4 6% 6% 5% 6% 18%	1508
	11th to 20th	Day	19% 12% 5% 9% 8% 4 5% 5% 5% 8% 21%	1520
	21st to end	Day	22% 11% 4 9% 7% 4 5% 4 6% 8% 19%	1520
December	1st to 10th	Day	16% 12% 6% 8% 7% 5% 5% 5% 6% 7% 24%	1520
	11th to 20th	Day	17% 14% 7% 13% 11% 5% 6% 5% 5% 5% 12%	1884
	21st to end	Day	16% 15% 6% 12% 11% 5% 7% 5% 5% 5% 13%	2442
January	1st to 10th	Night	20% 16% 5% 10% 9% 5% 6% 6% 5% 5% 12%	4726
	11th to 20th	Night	19% 11% 5% 7% 6% 4 7% 5% 6% 9% 22%	4467
	21st to end	Night	24% 12% 5% 9% 8% 4 6% 6% 6% 7% 13%	4769
February	1st to 10th	Night	19% 15% 5% 8% 7% 4 5% 5% 5% 7% 20%	2470
	11th to 20th	Night	15% 13% 5% 9% 7% 5% 6% 5% 5% 6% 25%	2402
	21st to end	Night	15% 15% 5% 8% 7% 4 6% 5% 6% 7% 24%	1992
March	1st to 10th	Night	15% 10% 5% 7% 7% 4 6% 7% 6% 7% 25%	2192
	11th to 20th	Night	16% 12% 4 7% 7% 4 5% 5% 6% 8% 26%	1979
	21st to end	Night	15% 13% 4 8% 7% 4 6% 6% 6% 7% 22%	2116
April	1st to 10th	Night	16% 11% 4 9% 8% 4 7% 6% 7% 8% 21%	1800
	11th to 20th	Night	16% 9% 5% 7% 7% 5% 5% 5% 6% 7% 29%	1736
	21st to end	Night	18% 9% 3 8% 7% 3 5% 5% 6% 7% 28%	1584
May	1st to 10th	Night	14% 9% 3 5% 5% 4 4 5% 5% 7% 38%	1440
	11th to 20th	Night	14% 6% 3 6% 7% 4 5% 4 5% 7% 38%	1416
	21st to end	Night	18% 8% 5% 7% 7% 3 5% 4 4 7% 32%	1552
June	1st to 10th	Night	17% 8% 3 7% 7% 3 6% 5% 4 7% 33%	1346
	11th to 20th	Night	20% 9% 4 8% 6% 4 6% 5% 5% 7% 26%	1260
	21st to end	Night	9% 5% 2 5% 6% 3 5% 4 6% 10% 44%	1260
July	1st to 10th	Night	10% 5% 3 5% 3 3 4 5% 4 6% 53%	1260
	11th to 20th	Night	7% 3 3 4 3 2 4 3 5% 6% 59%	1327
	21st to end	Night	8% 3 2 3 3 2 2 3 3 4 66%	1576
August	1st to 10th	Night	7% 4 2 4 4 2 3 3 5% 5% 59%	1476
	11th to 20th	Night	6% 3 1 4 2 2 2 3 5% 8% 64%	1602
	21st to end	Night	9% 5% 3 5% 4 3 4 4 5% 7% 52%	1873
September	1st to 10th	Night	7% 5% 2 5% 4 3 4 4 5% 7% 56%	1800
	11th to 20th	Night	12% 6% 3 7% 5% 4 4 4 6% 6% 42%	1800
	21st to end	Night	12% 7% 3 7% 5% 3 4 4 6% 6% 42%	2059
October	1st to 10th	Night	11% 8% 4 7% 6% 4 5% 5% 6% 5% 40%	2160
	11th to 20th	Night	15% 8% 3 7% 6% 4 4 6% 5% 7% 35%	2160
	21st to end	Night	17% 9% 3 7% 6% 3 5% 4 5% 8% 32%	2476
November	1st to 10th	Night	23% 10% 3 7% 6% 3 6% 6% 5% 6% 26%	2567
	11th to 20th	Night	18% 10% 5% 8% 7% 4 6% 6% 6% 6% 25%	2660
	21st to end	Night	17% 11% 4 9% 8% 4 6% 6% 6% 7% 22%	2660
December	1st to 10th	Night	18% 12% 4 8% 7% 4 6% 5% 6% 5% 25%	2660
	11th to 20th	Night	17% 13% 5% 11% 9% 4 6% 6% 6% 6% 16%	3316
	21st to end	Night	18% 15% 7% 11% 9% 5% 6% 5% 5% 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	61% 26% 7% 5% 1	2219
	11th to 20th	Day	47% 27% 8% 15% 2 1	2451
	21st to end	Day	63% 24% 7% 5% 1	2886
February	1st to 10th	Day	43% 39% 9% 7% 1	1710
	11th to 20th	Day	42% 38% 8% 6% 5%	1674
	21st to end	Day	43% 38% 9% 8% 3	1460
March	1st to 10th	Day	44% 37% 10% 7% 2	1926
	11th to 20th	Day	43% 37% 10% 8% 2	1980
	21st to end	Day	44% 38% 10% 8% 1	2240
April	1st to 10th	Day	41% 38% 12% 8% 1	2160
	11th to 20th	Day	39% 36% 9% 10% 5% 1	2171
	21st to end	Day	38% 37% 11% 9% 4 1	2374
May	1st to 10th	Day	36% 37% 13% 11% 3	2520
	11th to 20th	Day	30% 38% 14% 14% 5%	2480
	21st to end	Day	41% 36% 12% 9% 2	2724
June	1st to 10th	Day	38% 37% 14% 7% 3 1	2610
	11th to 20th	Day	40% 37% 14% 8% 1	2700
	21st to end	Day	26% 38% 18% 11% 5% 2	2700
July	1st to 10th	Day	20% 38% 14% 18% 7% 2	2626
	11th to 20th	Day	20% 37% 13% 21% 8% 1	2547
	21st to end	Day	16% 37% 12% 22% 10% 2	2589
August	1st to 10th	Day	22% 36% 17% 17% 7% 1	2442
	11th to 20th	Day	18% 36% 16% 18% 9% 3	2298
	21st to end	Day	24% 36% 14% 19% 6% 1	2482
September	1st to 10th	Day	19% 36% 13% 19% 10% 4	2160
	11th to 20th	Day	26% 37% 12% 13% 10% 1	2160
	21st to end	Day	30% 38% 11% 12% 6% 2	1900
October	1st to 10th	Day	32% 38% 11% 15% 5%	1800
	11th to 20th	Day	36% 38% 13% 11% 2 1	1800
	21st to end	Day	40% 38% 8% 8% 5%	1879
November	1st to 10th	Day	42% 41% 7% 6% 3	1508
	11th to 20th	Day	41% 42% 8% 7% 3	1520
	21st to end	Day	41% 43% 6% 8% 2	1520
December	1st to 10th	Day	40% 41% 8% 7% 4	1520
	11th to 20th	Day	52% 34% 7% 6% 1	1887
	21st to end	Day	58% 25% 11% 5% 1	2442
January	1st to 10th	Night	59% 29% 6% 5% 1	4726
	11th to 20th	Night	43% 29% 9% 16% 2 1	4505
	21st to end	Night	61% 23% 9% 5% 2	4769
February	1st to 10th	Night	44% 37% 9% 9% 2	2470
	11th to 20th	Night	39% 37% 10% 8% 6%	2404
	21st to end	Night	42% 36% 9% 9% 4	1992
March	1st to 10th	Night	39% 37% 12% 10% 2	2192
	11th to 20th	Night	40% 38% 9% 9% 3	1980
	21st to end	Night	42% 38% 10% 8% 1	2116
April	1st to 10th	Night	40% 40% 9% 8% 2	1800
	11th to 20th	Night	35% 37% 11% 9% 6% 1	1736
	21st to end	Night	37% 38% 10% 10% 4 1	1584
May	1st to 10th	Night	35% 37% 10% 13% 5%	1440
	11th to 20th	Night	29% 38% 13% 12% 6% 1	1416
	21st to end	Night	41% 37% 11% 11% 1	1552
June	1st to 10th	Night	38% 37% 12% 8% 3 2	1346
	11th to 20th	Night	41% 37% 13% 8% 1	1260
	21st to end	Night	25% 36% 18% 13% 5% 3	1260
July	1st to 10th	Night	21% 37% 10% 21% 7% 3	1225
	11th to 20th	Night	15% 37% 13% 24% 9% 1	1285
	21st to end	Night	15% 38% 8% 20% 14% 5%	1488
August	1st to 10th	Night	20% 36% 13% 20% 9% 2	1468
	11th to 20th	Night	14% 36% 13% 19% 14% 3	1602
	21st to end	Night	23% 36% 13% 18% 8% 1	1873
September	1st to 10th	Night	16% 36% 12% 21% 10% 5%	1800
	11th to 20th	Night	27% 36% 9% 13% 12% 3	1800
	21st to end	Night	29% 37% 9% 16% 8% 1	2059
October	1st to 10th	Night	31% 37% 9% 16% 8%	2160
	11th to 20th	Night	31% 38% 13% 14% 4 1	2160
	21st to end	Night	33% 38% 10% 12% 6%	2476
November	1st to 10th	Night	38% 42% 7% 8% 3 1	2567
	11th to 20th	Night	39% 41% 11% 7% 2	2660
	21st to end	Night	40% 42% 8% 7% 2	2660
December	1st to 10th	Night	39% 40% 9% 8% 3	2660
	11th to 20th	Night	47% 36% 11% 5% 1	3312
	21st to end	Night	56% 26% 9% 7% 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	22% 17% 27% 22% 11% 2	449
	11th to 20th	Day	24% 17% 20% 21% 13% 5%	420
	21st to end	Day	22% 18% 27% 21% 11% 2	462
April	1st to 10th	Day	23% 15% 23% 25% 12% 4	420
	11th to 20th	Day	19% 15% 31% 19% 12% 5%	412
	21st to end	Day	20% 12% 26% 27% 12% 2	420
May	1st to 10th	Day	13% 7% 24% 35% 17% 3	423
	11th to 20th	Day	19% 6% 19% 30% 18% 9%	448
	21st to end	Day	19% 7% 17% 29% 19% 9%	485
June	1st to 10th	Day	18% 8% 24% 29% 18% 4	540
	11th to 20th	Day	18% 7% 22% 32% 17% 3	630
	21st to end	Day	11% 5% 20% 35% 23% 6%	630
July	1st to 10th	Day	11% 4 19% 32% 28% 7%	621
	11th to 20th	Day	7% 5% 17% 32% 31% 8%	546
	21st to end	Day	7% 3 11% 32% 36% 12%	487
August	1st to 10th	Day	8% 3 10% 30% 36% 14%	447
	11th to 20th	Day	5% 1 10% 37% 35% 12%	437
	21st to end	Day	11% 4 18% 34% 25% 8%	495
September	1st to 10th	Day	14% 6% 20% 34% 24% 4	450
	11th to 20th	Day	15% 6% 17% 29% 28% 4	450
	21st to end	Day	16% 8% 23% 29% 20% 3	450
October	1st to 10th	Day	20% 9% 22% 21% 20% 7%	450
	11th to 20th	Day	21% 11% 23% 21% 19% 4	450
	21st to end	Day	25% 19% 20% 22% 13% 3	394
November	1st to 10th	Day	35% 13% 24% 19% 9% 1	189
	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% 27% 15% 2	750
	11th to 20th	Night	24% 15% 19% 25% 14% 2	720
	21st to end	Night	24% 11% 24% 28% 12% 2	792
April	1st to 10th	Night	24% 8% 21% 29% 16% 2	720
	11th to 20th	Night	21% 8% 22% 27% 18% 3	668
	21st to end	Night	23% 7% 20% 34% 14% 3	504
May	1st to 10th	Night	17% 6% 19% 35% 19% 4	360
	11th to 20th	Night	19% 3 16% 28% 32% 3	354
	21st to end	Night	23% 5% 14% 30% 23% 5%	389
June	1st to 10th	Night	21% 5% 19% 32% 21% 3	360
	11th to 20th	Night	19% 11% 17% 32% 19% 2	360
	21st to end	Night	13% 3 15% 36% 29% 4	360
July	1st to 10th	Night	13% 3 10% 30% 39% 5%	350
	11th to 20th	Night	8% 3 12% 35% 38% 4	348
	21st to end	Night	9% 3 6% 31% 46% 6%	394
August	1st to 10th	Night	11% 2 6% 25% 47% 9%	402
	11th to 20th	Night	8% 1 6% 28% 46% 11%	534
	21st to end	Night	10% 3 13% 32% 37% 5%	685
September	1st to 10th	Night	11% 2 11% 38% 32% 6%	720
	11th to 20th	Night	16% 4 13% 22% 34% 11%	720
	21st to end	Night	15% 6% 20% 29% 26% 5%	720
October	1st to 10th	Night	15% 7% 18% 28% 26% 6%	720
	11th to 20th	Night	20% 9% 19% 25% 22% 5%	720
	21st to end	Night	22% 10% 21% 27% 17% 3	792
November	1st to 10th	Night	27% 13% 22% 25% 12%	740
	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 2024-03-05 04:23:57. Version ac07

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