Sequim
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sequim clear sky chart from 2005-11-06 to 2024-03-18.

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	11% 10% 4 8% 7% 4 6% 6% 6% 8% 31%	78329
	Night	10% 10% 4 8% 7% 4 6% 6% 6% 7% 33%	81400
Transparency	Day	50% 5% 18% 19% 7% 1	78042
	Night	50% 6% 16% 19% 8% 1	81268
Seeing	Day	18% 7% 22% 28% 19% 5%	14370
	Night	18% 6% 12% 31% 26% 7%	22871

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	12% 14% 5% 9% 9% 6% 7% 7% 8% 7% 16%	2219
	11th to 20th	Day	11% 11% 4 8% 7% 4 8% 6% 8% 10% 22%	2299
	21st to end	Day	11% 13% 5% 12% 9% 7% 8% 7% 6% 8% 14%	2904
February	1st to 10th	Day	12% 14% 4 8% 8% 5% 7% 6% 7% 9% 19%	1710
	11th to 20th	Day	11% 15% 5% 10% 8% 4 6% 6% 7% 8% 20%	1665
	21st to end	Day	9% 13% 6% 10% 9% 4 6% 6% 8% 8% 21%	1437
March	1st to 10th	Day	7% 12% 6% 9% 8% 5% 8% 6% 8% 8% 23%	1981
	11th to 20th	Day	9% 12% 5% 10% 9% 4 7% 6% 6% 6% 25%	2059
	21st to end	Day	10% 14% 7% 11% 9% 5% 6% 6% 7% 7% 18%	2222
April	1st to 10th	Day	13% 12% 5% 9% 9% 4 7% 6% 6% 8% 21%	2160
	11th to 20th	Day	12% 12% 6% 10% 8% 4 7% 7% 6% 6% 23%	2201
	21st to end	Day	13% 11% 4 9% 7% 4 7% 6% 6% 7% 26%	2358
May	1st to 10th	Day	10% 9% 4 6% 6% 4 6% 5% 7% 8% 33%	2520
	11th to 20th	Day	14% 10% 3 6% 6% 3 7% 6% 5% 9% 31%	2477
	21st to end	Day	17% 13% 5% 8% 6% 4 6% 5% 4 7% 26%	2723
June	1st to 10th	Day	17% 11% 5% 8% 7% 3 6% 5% 5% 7% 25%	2672
	11th to 20th	Day	16% 10% 6% 9% 8% 5% 7% 6% 6% 7% 21%	2700
	21st to end	Day	11% 8% 3 7% 6% 3 7% 6% 6% 8% 35%	2700
July	1st to 10th	Day	10% 7% 3 6% 5% 3 5% 4 6% 6% 46%	2700
	11th to 20th	Day	9% 7% 4 4 4 3 5% 5% 4 7% 47%	2687
	21st to end	Day	6% 5% 3 5% 4 2 4 4 4 5% 59%	2741
August	1st to 10th	Day	6% 7% 2 5% 5% 3 5% 4 5% 8% 50%	2441
	11th to 20th	Day	6% 6% 2 4 4 3 5% 4 5% 8% 52%	2298
	21st to end	Day	6% 7% 3 6% 5% 3 5% 5% 6% 8% 46%	2505
September	1st to 10th	Day	8% 7% 2 5% 5% 3 3 4 4 8% 51%	2160
	11th to 20th	Day	9% 9% 3 7% 6% 3 6% 4 5% 7% 40%	2152
	21st to end	Day	10% 6% 2 5% 6% 3 5% 6% 6% 9% 40%	1900
October	1st to 10th	Day	11% 8% 4 8% 7% 4 6% 6% 6% 7% 34%	1800
	11th to 20th	Day	11% 7% 3 7% 7% 4 6% 6% 6% 9% 31%	1800
	21st to end	Day	9% 11% 4 8% 7% 5% 7% 5% 8% 8% 28%	1887
November	1st to 10th	Day	14% 13% 5% 10% 8% 5% 7% 7% 7% 6% 19%	1488
	11th to 20th	Day	11% 11% 4 8% 9% 5% 6% 7% 6% 9% 24%	1520
	21st to end	Day	11% 12% 5% 10% 7% 4 6% 6% 7% 8% 23%	1520
December	1st to 10th	Day	9% 12% 4 8% 7% 5% 5% 5% 8% 9% 28%	1520
	11th to 20th	Day	8% 12% 5% 9% 8% 6% 8% 9% 9% 8% 18%	1761
	21st to end	Day	10% 16% 5% 10% 8% 5% 7% 6% 7% 8% 17%	2442
January	1st to 10th	Night	11% 13% 5% 9% 9% 6% 9% 7% 6% 7% 18%	4726
	11th to 20th	Night	12% 10% 4 9% 7% 5% 7% 6% 7% 9% 25%	4597
	21st to end	Night	12% 13% 5% 10% 9% 5% 7% 7% 7% 8% 17%	4742
February	1st to 10th	Night	10% 13% 4 10% 9% 4 6% 7% 7% 7% 23%	2470
	11th to 20th	Night	9% 12% 4 9% 8% 4 6% 6% 7% 7% 28%	2402
	21st to end	Night	9% 15% 5% 10% 6% 5% 6% 6% 7% 7% 24%	2015
March	1st to 10th	Night	8% 10% 4 7% 8% 4 7% 7% 8% 9% 29%	2199
	11th to 20th	Night	8% 11% 4 7% 7% 4 6% 7% 8% 9% 30%	2066
	21st to end	Night	9% 14% 5% 10% 8% 5% 6% 6% 7% 8% 22%	2133
April	1st to 10th	Night	10% 11% 4 8% 7% 5% 6% 6% 7% 7% 28%	1800
	11th to 20th	Night	11% 10% 4 8% 6% 4 6% 6% 6% 7% 32%	1705
	21st to end	Night	11% 9% 4 8% 7% 4 6% 6% 6% 8% 31%	1602
May	1st to 10th	Night	9% 6% 3 6% 5% 3 6% 5% 7% 8% 43%	1440
	11th to 20th	Night	12% 6% 2 7% 6% 3 5% 6% 8% 9% 37%	1416
	21st to end	Night	13% 9% 4 8% 7% 4 5% 5% 5% 9% 32%	1552
June	1st to 10th	Night	15% 7% 3 6% 6% 3 5% 6% 6% 7% 36%	1284
	11th to 20th	Night	12% 8% 4 8% 5% 3 5% 6% 6% 9% 34%	1260
	21st to end	Night	7% 5% 3 5% 4 3 5% 6% 7% 9% 45%	1260
July	1st to 10th	Night	7% 7% 2 4 5% 2 4 4 4 6% 55%	1260
	11th to 20th	Night	7% 5% 2 3 3 2 3 3 4 7% 60%	1270
	21st to end	Night	5% 3 1 2 2 1 3 3 4 5% 70%	1576
August	1st to 10th	Night	6% 4 2 4 5% 2 3 3 4 6% 61%	1496
	11th to 20th	Night	5% 3 1 3 3 1 3 3 4 8% 67%	1602
	21st to end	Night	7% 4 2 4 3 3 4 4 5% 7% 57%	1850
September	1st to 10th	Night	6% 4 2 4 4 3 4 5% 5% 7% 57%	1800
	11th to 20th	Night	11% 6% 2 5% 5% 3 4 5% 5% 7% 46%	1807
	21st to end	Night	8% 6% 3 5% 5% 3 5% 5% 6% 7% 46%	2060
October	1st to 10th	Night	8% 8% 3 7% 6% 4 5% 4 6% 6% 42%	2160
	11th to 20th	Night	11% 7% 3 5% 6% 4 5% 5% 6% 8% 39%	2160
	21st to end	Night	11% 7% 3 6% 7% 4 6% 5% 6% 7% 36%	2468
November	1st to 10th	Night	15% 10% 4 7% 8% 5% 6% 6% 6% 7% 25%	2590
	11th to 20th	Night	9% 10% 4 8% 8% 5% 7% 6% 9% 7% 27%	2660
	21st to end	Night	10% 9% 4 8% 9% 5% 7% 7% 8% 7% 26%	2660
December	1st to 10th	Night	9% 12% 5% 9% 7% 4 6% 6% 7% 8% 27%	2660
	11th to 20th	Night	10% 13% 5% 10% 7% 5% 7% 7% 9% 9% 20%	3438
	21st to end	Night	11% 14% 5% 9% 7% 5% 7% 6% 7% 7% 22%	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	64% 5% 13% 14% 3	2219
	11th to 20th	Day	55% 10% 16% 16% 2 1	2320
	21st to end	Day	69% 6% 14% 9% 2	2904
February	1st to 10th	Day	61% 7% 15% 11% 5% 1	1710
	11th to 20th	Day	60% 7% 14% 13% 6%	1674
	21st to end	Day	57% 7% 15% 15% 6%	1437
March	1st to 10th	Day	55% 6% 17% 17% 4 1	1981
	11th to 20th	Day	56% 5% 17% 18% 4 1	2059
	21st to end	Day	63% 3 18% 14% 2	2222
April	1st to 10th	Day	57% 6% 18% 16% 3	2160
	11th to 20th	Day	57% 5% 13% 16% 7% 1	2201
	21st to end	Day	55% 4 15% 18% 6% 1	2358
May	1st to 10th	Day	46% 5% 22% 20% 7% 1	2520
	11th to 20th	Day	50% 5% 21% 18% 6%	2480
	21st to end	Day	57% 4 18% 18% 3	2724
June	1st to 10th	Day	56% 4 22% 12% 5% 1	2672
	11th to 20th	Day	58% 5% 19% 15% 4	2700
	21st to end	Day	44% 5% 24% 18% 7% 2	2700
July	1st to 10th	Day	38% 5% 16% 28% 11% 3	2626
	11th to 20th	Day	34% 3 21% 27% 13% 1	2606
	21st to end	Day	27% 2 16% 36% 15% 3	2589
August	1st to 10th	Day	31% 4 24% 26% 14% 1	2424
	11th to 20th	Day	30% 5% 20% 29% 12% 3	2298
	21st to end	Day	34% 3 24% 30% 8% 1	2505
September	1st to 10th	Day	32% 4 21% 25% 15% 3	2160
	11th to 20th	Day	43% 5% 15% 20% 15% 2	2152
	21st to end	Day	41% 5% 20% 22% 10% 2	1900
October	1st to 10th	Day	46% 5% 18% 23% 7% 1	1800
	11th to 20th	Day	48% 9% 19% 20% 5%	1800
	21st to end	Day	51% 8% 15% 17% 9%	1887
November	1st to 10th	Day	61% 7% 15% 13% 4 1	1488
	11th to 20th	Day	57% 8% 13% 15% 5% 1	1520
	21st to end	Day	57% 6% 14% 16% 7%	1520
December	1st to 10th	Day	55% 7% 15% 17% 6%	1520
	11th to 20th	Day	60% 11% 14% 10% 3 1	1764
	21st to end	Day	63% 7% 14% 11% 4	2442
January	1st to 10th	Night	64% 8% 13% 12% 4 1	4726
	11th to 20th	Night	54% 9% 13% 19% 4 1	4638
	21st to end	Night	66% 5% 15% 11% 3 1	4742
February	1st to 10th	Night	59% 7% 14% 13% 7%	2470
	11th to 20th	Night	55% 6% 16% 16% 7%	2404
	21st to end	Night	56% 6% 12% 18% 6% 1	2015
March	1st to 10th	Night	51% 6% 15% 21% 6%	2199
	11th to 20th	Night	50% 7% 18% 19% 5% 1	2067
	21st to end	Night	60% 6% 16% 15% 2	2133
April	1st to 10th	Night	52% 9% 16% 18% 5%	1800
	11th to 20th	Night	51% 6% 15% 19% 8% 1	1705
	21st to end	Night	51% 7% 13% 18% 10% 1	1602
May	1st to 10th	Night	41% 5% 20% 22% 11% 1	1440
	11th to 20th	Night	43% 4 23% 20% 8% 2	1416
	21st to end	Night	51% 5% 20% 19% 5% 1	1552
June	1st to 10th	Night	49% 5% 21% 18% 4 3	1284
	11th to 20th	Night	48% 5% 23% 19% 4	1260
	21st to end	Night	36% 4 27% 21% 7% 4	1260
July	1st to 10th	Night	33% 3 18% 29% 14% 4	1225
	11th to 20th	Night	26% 4 20% 30% 17% 3	1228
	21st to end	Night	19% 3 16% 33% 23% 6%	1488
August	1st to 10th	Night	26% 5% 19% 31% 15% 5%	1488
	11th to 20th	Night	19% 5% 21% 31% 17% 6%	1602
	21st to end	Night	28% 5% 19% 34% 13% 2	1850
September	1st to 10th	Night	28% 3 20% 28% 17% 5%	1800
	11th to 20th	Night	39% 4 14% 20% 17% 5%	1807
	21st to end	Night	38% 5% 15% 27% 14% 2	2060
October	1st to 10th	Night	43% 4 15% 25% 12%	2160
	11th to 20th	Night	44% 4 18% 24% 10%	2160
	21st to end	Night	48% 5% 16% 21% 10%	2468
November	1st to 10th	Night	57% 6% 15% 15% 6% 1	2590
	11th to 20th	Night	53% 8% 17% 14% 6% 2	2660
	21st to end	Night	54% 7% 16% 14% 8%	2660
December	1st to 10th	Night	56% 6% 15% 17% 6%	2660
	11th to 20th	Night	60% 9% 16% 11% 4	3435
	21st to end	Night	60% 6% 14% 15% 4	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	22% 12% 22% 21% 16% 8%	180
	11th to 20th	Day	24% 11% 16% 24% 19% 5%	180
	21st to end	Day	25% 11% 26% 18% 13% 6%	269
February	1st to 10th	Day	28% 10% 26% 22% 12% 2	370
	11th to 20th	Day	28% 11% 28% 21% 9% 2	365
	21st to end	Day	20% 14% 30% 22% 10% 3	319
March	1st to 10th	Day	22% 11% 27% 28% 10% 2	460
	11th to 20th	Day	20% 12% 26% 24% 16% 3	449
	21st to end	Day	22% 13% 29% 24% 11% 2	462
April	1st to 10th	Day	22% 12% 28% 22% 12% 4	420
	11th to 20th	Day	21% 12% 29% 20% 14% 3	412
	21st to end	Day	22% 12% 25% 25% 13% 4	420
May	1st to 10th	Day	14% 9% 25% 33% 17% 3	423
	11th to 20th	Day	20% 4 22% 28% 19% 7%	448
	21st to end	Day	20% 3 24% 29% 17% 7%	485
June	1st to 10th	Day	21% 5% 24% 27% 20% 4	602
	11th to 20th	Day	19% 7% 27% 31% 13% 3	630
	21st to end	Day	10% 3 22% 37% 24% 4	630
July	1st to 10th	Day	13% 1 15% 37% 27% 7%	621
	11th to 20th	Day	9% 4 17% 36% 26% 7%	605
	21st to end	Day	7% 2 11% 36% 33% 11%	487
August	1st to 10th	Day	10% 2 11% 30% 35% 12%	447
	11th to 20th	Day	5% 1 14% 32% 34% 13%	437
	21st to end	Day	10% 3 19% 36% 25% 7%	495
September	1st to 10th	Day	13% 3 21% 36% 23% 4	450
	11th to 20th	Day	14% 3 19% 28% 28% 7%	450
	21st to end	Day	16% 6% 22% 32% 21% 3	450
October	1st to 10th	Day	17% 5% 22% 25% 25% 6%	450
	11th to 20th	Day	18% 7% 22% 28% 21% 5%	450
	21st to end	Day	20% 14% 24% 23% 15% 5%	406
November	1st to 10th	Day	28% 12% 24% 24% 10% 2	180
	11th to 20th	Day	27% 9% 23% 16% 15% 10%	180
	21st to end	Day	24% 12% 19% 18% 15% 12%	180
December	1st to 10th	Day	29% 4 15% 23% 16% 12%	180
	11th to 20th	Day	29% 8% 24% 24% 12% 2	180
	21st to end	Day	28% 8% 18% 25% 17% 5%	198
January	1st to 10th	Night	24% 11% 20% 25% 17% 4	850
	11th to 20th	Night	21% 8% 13% 30% 23% 4	819
	21st to end	Night	22% 6% 13% 31% 22% 5%	836
February	1st to 10th	Night	20% 6% 15% 38% 17% 3	760
	11th to 20th	Night	18% 6% 16% 31% 24% 4	744
	21st to end	Night	24% 9% 16% 29% 18% 4	628
March	1st to 10th	Night	17% 12% 15% 32% 20% 4	760
	11th to 20th	Night	16% 9% 15% 36% 20% 4	752
	21st to end	Night	21% 7% 14% 32% 22% 4	792
April	1st to 10th	Night	18% 8% 14% 33% 23% 4	720
	11th to 20th	Night	16% 7% 17% 35% 20% 5%	637
	21st to end	Night	20% 4 10% 41% 20% 6%	522
May	1st to 10th	Night	14% 3 13% 34% 30% 5%	360
	11th to 20th	Night	16% 1 10% 30% 33% 10%	354
	21st to end	Night	18% 4 8% 26% 35% 8%	389
June	1st to 10th	Night	21% 4 8% 33% 27% 6%	360
	11th to 20th	Night	17% 4 12% 38% 24% 6%	360
	21st to end	Night	12% 1 6% 33% 40% 8%	360
July	1st to 10th	Night	13% 1 5% 25% 44% 11%	350
	11th to 20th	Night	9% 3 6% 28% 43% 10%	348
	21st to end	Night	6% 1 4 28% 48% 13%	394
August	1st to 10th	Night	11% 1 3 20% 45% 21%	422
	11th to 20th	Night	8% 1 2 20% 49% 21%	534
	21st to end	Night	11% 1 7% 31% 38% 12%	662
September	1st to 10th	Night	9% 2 5% 34% 38% 12%	720
	11th to 20th	Night	14% 3 6% 23% 34% 19%	720
	21st to end	Night	14% 2 12% 29% 33% 9%	720
October	1st to 10th	Night	13% 5% 10% 29% 34% 8%	720
	11th to 20th	Night	18% 4 13% 29% 27% 10%	720
	21st to end	Night	19% 6% 14% 35% 21% 5%	792
November	1st to 10th	Night	26% 6% 13% 36% 16% 2	740
	11th to 20th	Night	20% 12% 17% 28% 19% 4	760
	21st to end	Night	19% 8% 16% 34% 17% 7%	760
December	1st to 10th	Night	19% 8% 13% 34% 22% 5%	760
	11th to 20th	Night	22% 9% 17% 34% 17% 2	811
	21st to end	Night	26% 13% 18% 28% 13% 3	935

Page generated at 2024-03-15 11:01:45. Version ac07

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