Seabeck
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Seabeck clear sky chart from 2005-11-06 to 2024-02-10.

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	15% 9% 4 8% 7% 4 6% 5% 5% 7% 30%	78105
	Night	16% 10% 4 7% 7% 4 6% 5% 5% 6% 31%	80811
Transparency	Day	53% 8% 15% 16% 7% 1	77821
	Night	54% 8% 14% 16% 7% 1	80675
Seeing	Day	19% 14% 25% 25% 14% 3	14144
	Night	18% 10% 22% 28% 19% 3	22690

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% 14% 5% 9% 9% 5% 6% 6% 5% 5% 14%	2219
	11th to 20th	Day	21% 9% 4 9% 7% 3 5% 4 6% 7% 25%	2422
	21st to end	Day	31% 12% 4 8% 7% 4 6% 5% 4 5% 13%	2919
February	1st to 10th	Day	16% 12% 5% 8% 9% 6% 7% 6% 6% 7% 17%	1702
	11th to 20th	Day	15% 12% 5% 8% 7% 4 6% 6% 6% 7% 24%	1575
	21st to end	Day	12% 11% 5% 8% 8% 5% 6% 6% 7% 5% 27%	1372
March	1st to 10th	Day	16% 11% 4 8% 7% 6% 6% 7% 6% 7% 24%	1867
	11th to 20th	Day	16% 11% 5% 9% 8% 5% 7% 6% 5% 7% 22%	1980
	21st to end	Day	17% 9% 4 9% 10% 5% 7% 6% 7% 7% 18%	2232
April	1st to 10th	Day	18% 10% 4 9% 7% 4 7% 7% 7% 7% 21%	2160
	11th to 20th	Day	17% 11% 4 8% 9% 4 6% 6% 5% 6% 24%	2178
	21st to end	Day	14% 9% 5% 9% 7% 5% 7% 6% 6% 7% 25%	2358
May	1st to 10th	Day	12% 8% 4 8% 8% 5% 7% 5% 5% 7% 31%	2520
	11th to 20th	Day	15% 8% 4 7% 8% 4 6% 6% 6% 6% 30%	2477
	21st to end	Day	20% 11% 4 7% 7% 5% 6% 5% 4 5% 26%	2723
June	1st to 10th	Day	16% 9% 5% 9% 7% 4 6% 6% 6% 7% 25%	2611
	11th to 20th	Day	18% 12% 5% 9% 8% 6% 7% 6% 6% 6% 17%	2700
	21st to end	Day	12% 6% 3 7% 8% 4 5% 6% 6% 8% 36%	2700
July	1st to 10th	Day	10% 7% 3 6% 6% 4 5% 4 4 6% 45%	2700
	11th to 20th	Day	9% 5% 2 5% 5% 3 5% 6% 6% 8% 45%	2633
	21st to end	Day	7% 5% 3 6% 5% 3 3 3 4 5% 57%	2741
August	1st to 10th	Day	8% 7% 2 5% 5% 3 5% 4 5% 6% 49%	2438
	11th to 20th	Day	8% 5% 2 4 4 3 4 5% 5% 8% 53%	2298
	21st to end	Day	9% 7% 3 7% 6% 4 5% 4 6% 6% 43%	2488
September	1st to 10th	Day	8% 7% 2 5% 5% 3 3 4 5% 6% 50%	2160
	11th to 20th	Day	10% 7% 3 6% 6% 3 6% 6% 6% 6% 41%	2160
	21st to end	Day	11% 7% 3 7% 6% 4 5% 5% 5% 6% 42%	1895
October	1st to 10th	Day	14% 9% 4 6% 5% 3 4 5% 5% 7% 36%	1800
	11th to 20th	Day	14% 7% 3 8% 6% 4 5% 7% 6% 8% 31%	1800
	21st to end	Day	19% 8% 4 7% 6% 4 5% 5% 6% 8% 29%	1893
November	1st to 10th	Day	20% 11% 4 9% 6% 4 8% 5% 6% 6% 20%	1503
	11th to 20th	Day	20% 11% 4 8% 8% 4 6% 4 4 6% 26%	1520
	21st to end	Day	20% 9% 4 8% 8% 4 6% 5% 6% 7% 24%	1520
December	1st to 10th	Day	18% 10% 5% 7% 7% 4 5% 5% 5% 6% 27%	1520
	11th to 20th	Day	23% 10% 3 10% 10% 5% 8% 6% 5% 7% 14%	1879
	21st to end	Day	20% 12% 6% 11% 10% 5% 7% 5% 5% 6% 14%	2442
January	1st to 10th	Night	24% 13% 5% 9% 7% 5% 6% 6% 5% 5% 16%	4726
	11th to 20th	Night	20% 11% 4 7% 6% 3 5% 4 5% 7% 28%	4473
	21st to end	Night	28% 14% 4 9% 7% 4 6% 5% 5% 5% 13%	4738
February	1st to 10th	Night	16% 14% 4 9% 7% 4 6% 5% 6% 7% 22%	2462
	11th to 20th	Night	14% 13% 3 7% 7% 4 6% 6% 6% 6% 28%	2272
	21st to end	Night	12% 10% 5% 8% 10% 4 6% 5% 7% 7% 26%	1884
March	1st to 10th	Night	15% 10% 4 8% 6% 4 5% 6% 6% 8% 28%	2092
	11th to 20th	Night	14% 11% 4 7% 7% 4 7% 6% 7% 9% 25%	1979
	21st to end	Night	15% 12% 4 8% 8% 4 7% 6% 6% 7% 22%	2124
April	1st to 10th	Night	16% 10% 4 7% 8% 5% 6% 7% 6% 6% 25%	1800
	11th to 20th	Night	16% 9% 4 8% 6% 4 6% 6% 7% 7% 28%	1728
	21st to end	Night	14% 9% 3 8% 6% 3 7% 6% 5% 7% 31%	1602
May	1st to 10th	Night	13% 8% 3 7% 7% 4 5% 4 5% 7% 39%	1440
	11th to 20th	Night	11% 7% 3 6% 6% 4 6% 6% 6% 8% 37%	1416
	21st to end	Night	13% 9% 3 8% 8% 4 6% 5% 6% 6% 31%	1552
June	1st to 10th	Night	15% 6% 3 7% 6% 5% 7% 6% 6% 7% 32%	1345
	11th to 20th	Night	15% 10% 5% 8% 8% 4 6% 4 5% 9% 26%	1260
	21st to end	Night	8% 5% 2 6% 6% 4 5% 5% 5% 7% 47%	1260
July	1st to 10th	Night	8% 6% 2 5% 4 3 4 3 4 6% 54%	1260
	11th to 20th	Night	6% 4 2 4 4 2 4 4 5% 7% 59%	1324
	21st to end	Night	5% 3 2 3 3 3 3 3 5% 6% 65%	1576
August	1st to 10th	Night	5% 3 1 5% 4 3 3 4 4 6% 60%	1498
	11th to 20th	Night	4 4 2 3 4 2 2 3 4 8% 64%	1602
	21st to end	Night	8% 5% 2 4 6% 3 4 5% 4 6% 51%	1867
September	1st to 10th	Night	5% 4 2 4 5% 4 4 4 6% 6% 58%	1800
	11th to 20th	Night	10% 7% 3 6% 6% 4 5% 5% 6% 6% 43%	1800
	21st to end	Night	13% 6% 3 6% 5% 4 6% 5% 4 6% 42%	2063
October	1st to 10th	Night	11% 8% 3 6% 6% 3 5% 4 5% 6% 41%	2160
	11th to 20th	Night	15% 8% 4 6% 7% 4 6% 5% 5% 7% 35%	2160
	21st to end	Night	16% 8% 3 7% 7% 4 4 5% 5% 7% 33%	2462
November	1st to 10th	Night	21% 9% 4 7% 7% 4 6% 5% 6% 5% 26%	2572
	11th to 20th	Night	19% 9% 4 8% 7% 4 6% 5% 5% 6% 26%	2660
	21st to end	Night	15% 10% 4 7% 7% 5% 6% 6% 8% 6% 25%	2660
December	1st to 10th	Night	17% 12% 5% 7% 7% 4 6% 5% 5% 5% 28%	2660
	11th to 20th	Night	20% 12% 5% 9% 7% 4 8% 6% 5% 7% 17%	3320
	21st to end	Night	23% 15% 6% 10% 8% 5% 5% 5% 5% 4 15%	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	70% 8% 10% 9% 3	2219
	11th to 20th	Day	61% 7% 13% 15% 3 1	2446
	21st to end	Day	76% 7% 9% 6% 2	2919
February	1st to 10th	Day	68% 8% 13% 7% 4	1702
	11th to 20th	Day	61% 9% 13% 10% 6% 1	1584
	21st to end	Day	59% 9% 12% 14% 6% 1	1372
March	1st to 10th	Day	60% 8% 14% 14% 3 1	1867
	11th to 20th	Day	64% 7% 11% 13% 3 1	1980
	21st to end	Day	64% 10% 12% 12% 1	2232
April	1st to 10th	Day	60% 9% 17% 11% 3	2160
	11th to 20th	Day	57% 9% 12% 15% 6% 1	2178
	21st to end	Day	56% 10% 15% 12% 6% 1	2358
May	1st to 10th	Day	49% 9% 19% 16% 7%	2520
	11th to 20th	Day	51% 9% 18% 16% 5%	2480
	21st to end	Day	58% 9% 16% 14% 3	2724
June	1st to 10th	Day	54% 9% 19% 12% 5% 1	2611
	11th to 20th	Day	62% 9% 16% 10% 2	2700
	21st to end	Day	43% 10% 21% 17% 7% 2	2700
July	1st to 10th	Day	39% 8% 15% 26% 11% 2	2626
	11th to 20th	Day	32% 11% 16% 28% 12% 1	2552
	21st to end	Day	26% 7% 15% 36% 14% 3	2589
August	1st to 10th	Day	33% 7% 18% 26% 13% 2	2421
	11th to 20th	Day	29% 7% 21% 27% 13% 3	2298
	21st to end	Day	38% 8% 16% 27% 10% 1	2488
September	1st to 10th	Day	34% 7% 17% 24% 14% 5%	2160
	11th to 20th	Day	41% 10% 14% 17% 16% 2	2160
	21st to end	Day	44% 8% 16% 19% 11% 2	1895
October	1st to 10th	Day	48% 7% 17% 19% 9%	1800
	11th to 20th	Day	51% 9% 18% 16% 5% 1	1800
	21st to end	Day	58% 8% 13% 12% 9%	1893
November	1st to 10th	Day	63% 9% 13% 10% 5%	1503
	11th to 20th	Day	62% 9% 9% 12% 6% 2	1520
	21st to end	Day	63% 6% 11% 12% 7% 1	1520
December	1st to 10th	Day	61% 8% 11% 14% 7%	1520
	11th to 20th	Day	73% 10% 8% 7% 2 1	1882
	21st to end	Day	72% 9% 10% 7% 2	2442
January	1st to 10th	Night	73% 7% 9% 8% 3 1	4726
	11th to 20th	Night	57% 5% 14% 18% 5% 1	4511
	21st to end	Night	74% 7% 8% 8% 3	4738
February	1st to 10th	Night	62% 9% 12% 10% 6%	2462
	11th to 20th	Night	57% 10% 13% 12% 7% 1	2274
	21st to end	Night	58% 8% 12% 15% 6% 1	1884
March	1st to 10th	Night	56% 8% 14% 16% 5%	2092
	11th to 20th	Night	55% 8% 14% 16% 5% 1	1980
	21st to end	Night	61% 9% 16% 12% 2	2124
April	1st to 10th	Night	54% 12% 15% 15% 3	1800
	11th to 20th	Night	51% 9% 16% 14% 8% 1	1728
	21st to end	Night	52% 9% 15% 16% 7% 1	1602
May	1st to 10th	Night	46% 8% 18% 17% 10% 1	1440
	11th to 20th	Night	44% 10% 19% 18% 7% 1	1416
	21st to end	Night	49% 11% 19% 17% 4	1552
June	1st to 10th	Night	46% 8% 23% 17% 4 1	1345
	11th to 20th	Night	52% 9% 23% 14% 3	1260
	21st to end	Night	36% 7% 27% 19% 7% 4	1260
July	1st to 10th	Night	31% 7% 17% 29% 12% 5%	1225
	11th to 20th	Night	23% 9% 19% 32% 15% 2	1282
	21st to end	Night	17% 6% 17% 36% 19% 5%	1488
August	1st to 10th	Night	24% 7% 20% 29% 17% 4	1490
	11th to 20th	Night	19% 7% 22% 29% 18% 5%	1602
	21st to end	Night	32% 8% 17% 28% 14% 2	1867
September	1st to 10th	Night	26% 6% 19% 27% 16% 5%	1800
	11th to 20th	Night	40% 8% 14% 17% 16% 6%	1800
	21st to end	Night	43% 8% 12% 22% 13% 2	2063
October	1st to 10th	Night	44% 8% 14% 24% 10%	2160
	11th to 20th	Night	50% 8% 14% 19% 8%	2160
	21st to end	Night	52% 7% 13% 17% 10%	2462
November	1st to 10th	Night	60% 8% 13% 13% 4 1	2572
	11th to 20th	Night	60% 8% 13% 11% 7% 2	2660
	21st to end	Night	59% 8% 14% 10% 8% 2	2660
December	1st to 10th	Night	61% 8% 10% 13% 7% 1	2660
	11th to 20th	Night	68% 10% 12% 6% 3	3316
	21st to end	Night	70% 9% 8% 9% 3	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	32% 16% 22% 16% 9% 4	180
	11th to 20th	Day	36% 14% 19% 16% 15% 1	180
	21st to end	Day	27% 20% 24% 18% 8% 2	271
February	1st to 10th	Day	25% 21% 28% 17% 7% 1	368
	11th to 20th	Day	25% 24% 28% 17% 6%	335
	21st to end	Day	20% 24% 30% 19% 5% 1	298
March	1st to 10th	Day	21% 23% 31% 18% 6%	420
	11th to 20th	Day	23% 23% 24% 19% 9% 3	420
	21st to end	Day	25% 21% 27% 18% 8%	462
April	1st to 10th	Day	24% 23% 25% 18% 8% 3	420
	11th to 20th	Day	20% 23% 27% 18% 10% 3	412
	21st to end	Day	21% 19% 33% 21% 5% 1	420
May	1st to 10th	Day	14% 13% 30% 29% 12% 2	423
	11th to 20th	Day	23% 11% 27% 22% 14% 4	448
	21st to end	Day	22% 9% 24% 27% 15% 3	485
June	1st to 10th	Day	20% 14% 27% 25% 12% 2	541
	11th to 20th	Day	22% 17% 25% 26% 9% 1	630
	21st to end	Day	14% 8% 28% 31% 16% 3	630
July	1st to 10th	Day	14% 7% 20% 36% 19% 3	621
	11th to 20th	Day	8% 6% 22% 37% 23% 4	551
	21st to end	Day	10% 4 14% 34% 31% 7%	487
August	1st to 10th	Day	11% 7% 16% 32% 27% 7%	447
	11th to 20th	Day	8% 3 16% 37% 28% 8%	437
	21st to end	Day	12% 10% 25% 31% 17% 5%	495
September	1st to 10th	Day	12% 9% 29% 34% 14% 3	450
	11th to 20th	Day	12% 12% 22% 34% 17% 3	450
	21st to end	Day	16% 14% 25% 27% 16% 2	450
October	1st to 10th	Day	17% 14% 26% 23% 16% 4	450
	11th to 20th	Day	22% 14% 25% 22% 14% 3	450
	21st to end	Day	24% 21% 24% 18% 10% 3	408
November	1st to 10th	Day	26% 19% 28% 20% 7%	187
	11th to 20th	Day	28% 17% 20% 17% 12% 5%	180
	21st to end	Day	28% 13% 26% 14% 12% 7%	180
December	1st to 10th	Day	25% 18% 23% 14% 15% 4	180
	11th to 20th	Day	28% 19% 28% 17% 8%	180
	21st to end	Day	25% 17% 29% 19% 9% 2	198
January	1st to 10th	Night	29% 14% 25% 17% 12% 2	850
	11th to 20th	Night	25% 13% 20% 23% 17% 2	784
	21st to end	Night	23% 9% 23% 26% 15% 3	836
February	1st to 10th	Night	21% 12% 30% 24% 11% 2	758
	11th to 20th	Night	20% 11% 27% 28% 13% 2	704
	21st to end	Night	18% 10% 34% 25% 11% 2	592
March	1st to 10th	Night	17% 13% 29% 26% 13% 1	720
	11th to 20th	Night	19% 18% 23% 26% 13% 2	720
	21st to end	Night	18% 16% 26% 28% 11% 1	792
April	1st to 10th	Night	19% 12% 24% 29% 14% 3	720
	11th to 20th	Night	17% 11% 27% 28% 16% 2	660
	21st to end	Night	19% 9% 20% 34% 15% 2	522
May	1st to 10th	Night	14% 10% 19% 37% 18% 3	360
	11th to 20th	Night	15% 4 19% 31% 28% 3	354
	21st to end	Night	16% 5% 18% 33% 24% 4	389
June	1st to 10th	Night	16% 7% 21% 32% 22% 2	360
	11th to 20th	Night	19% 8% 21% 32% 18% 2	360
	21st to end	Night	11% 5% 17% 38% 27% 4	360
July	1st to 10th	Night	11% 3 14% 28% 40% 4	350
	11th to 20th	Night	7% 2 13% 38% 35% 5%	348
	21st to end	Night	6% 3 8% 33% 44% 6%	394
August	1st to 10th	Night	7% 3 8% 28% 42% 13%	424
	11th to 20th	Night	6% 2 7% 28% 45% 11%	534
	21st to end	Night	10% 4 14% 33% 35% 5%	679
September	1st to 10th	Night	8% 3 15% 39% 29% 5%	720
	11th to 20th	Night	12% 5% 17% 26% 34% 7%	720
	21st to end	Night	17% 7% 18% 32% 23% 4	720
October	1st to 10th	Night	14% 8% 20% 30% 24% 4	720
	11th to 20th	Night	18% 10% 18% 28% 21% 4	720
	21st to end	Night	21% 11% 22% 27% 17% 2	792
November	1st to 10th	Night	24% 14% 24% 29% 9% 1	740
	11th to 20th	Night	24% 13% 25% 22% 14% 1	760
	21st to end	Night	21% 13% 24% 25% 14% 3	760
December	1st to 10th	Night	22% 12% 20% 31% 14% 1	760
	11th to 20th	Night	24% 14% 27% 24% 9% 2	773
	21st to end	Night	26% 14% 29% 21% 8% 1	935

Page generated at 2024-02-07 03:11:53. Version ac07

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