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 2024-11-06.

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	10% 10% 3 8% 5% 5% 6% 4 6% 7% 34%	105551
	Night	9% 10% 3 8% 6% 5% 5% 5% 6% 7% 35%	102113
Transparency	Day	47% 6% 18% 20% 8% 1	105303
	Night	47% 6% 16% 20% 8% 1	102008
Seeing	Day	18% 7% 22% 28% 19% 5%	15333
	Night	18% 6% 13% 31% 26% 7%	23570

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% 15% 5% 10% 7% 8% 7% 5% 8% 7% 16%	2219
	11th to 20th	Day	11% 11% 4 9% 6% 6% 7% 6% 8% 10% 22%	2299
	21st to end	Day	11% 14% 5% 13% 8% 9% 8% 6% 6% 7% 14%	2904
February	1st to 10th	Day	11% 14% 4 10% 7% 7% 6% 6% 7% 8% 19%	1710
	11th to 20th	Day	11% 16% 4 11% 6% 6% 6% 5% 8% 8% 19%	1665
	21st to end	Day	9% 15% 5% 11% 8% 5% 6% 5% 8% 8% 20%	1437
March	1st to 10th	Day	5% 11% 5% 12% 7% 7% 7% 6% 9% 10% 22%	3279
	11th to 20th	Day	7% 12% 4 8% 6% 5% 6% 5% 6% 6% 37%	3490
	21st to end	Day	13% 13% 5% 11% 7% 6% 6% 5% 8% 7% 19%	3907
April	1st to 10th	Day	12% 14% 4 10% 8% 6% 6% 5% 7% 7% 21%	2280
	11th to 20th	Day	11% 13% 5% 11% 7% 6% 6% 4 6% 6% 25%	2326
	21st to end	Day	13% 13% 4 10% 6% 5% 6% 5% 6% 7% 25%	2489
May	1st to 10th	Day	13% 11% 3 6% 4 4 4 3 5% 6% 40%	4420
	11th to 20th	Day	10% 8% 2 6% 4 3 5% 4 7% 11% 40%	4377
	21st to end	Day	21% 14% 4 9% 5% 4 5% 4 5% 7% 22%	4813
June	1st to 10th	Day	16% 12% 4 9% 6% 5% 5% 4 6% 7% 25%	2821
	11th to 20th	Day	15% 11% 5% 10% 7% 6% 7% 5% 6% 7% 21%	2850
	21st to end	Day	10% 10% 3 7% 6% 5% 7% 5% 6% 8% 34%	2850
July	1st to 10th	Day	6% 5% 2 4 3 3 4 4 5% 5% 61%	4740
	11th to 20th	Day	5% 6% 2 4 3 3 3 3 4 6% 62%	4713
	21st to end	Day	9% 6% 2 5% 3 4 7% 5% 4 6% 49%	4790
August	1st to 10th	Day	3 5% 2 4 4 4 4 3 5% 8% 59%	4283
	11th to 20th	Day	7% 13% 3 7% 5% 5% 8% 4 6% 7% 35%	4026
	21st to end	Day	11% 8% 3 7% 4 4 5% 3 5% 6% 45%	4400
September	1st to 10th	Day	7% 7% 2 6% 4 4 4 3 5% 7% 51%	2280
	11th to 20th	Day	9% 10% 3 8% 5% 4 5% 4 6% 7% 39%	2271
	21st to end	Day	10% 6% 2 6% 6% 5% 5% 5% 6% 9% 39%	2005
October	1st to 10th	Day	8% 6% 2 7% 5% 5% 6% 5% 7% 11% 36%	3180
	11th to 20th	Day	11% 9% 3 9% 6% 7% 6% 5% 6% 8% 30%	3161
	21st to end	Day	7% 11% 4 10% 7% 7% 7% 5% 8% 8% 25%	3275
November	1st to 10th	Day	13% 14% 4 11% 7% 7% 7% 5% 7% 6% 19%	1528
	11th to 20th	Day	11% 12% 4 9% 7% 7% 6% 6% 6% 8% 24%	1520
	21st to end	Day	11% 13% 5% 10% 6% 5% 7% 6% 6% 8% 23%	1520
December	1st to 10th	Day	9% 13% 3 9% 6% 6% 5% 5% 8% 8% 27%	1520
	11th to 20th	Day	8% 13% 4 10% 8% 8% 8% 7% 8% 8% 18%	1761
	21st to end	Day	10% 16% 5% 11% 7% 7% 7% 5% 8% 7% 17%	2442
January	1st to 10th	Night	11% 14% 5% 11% 8% 8% 8% 5% 6% 7% 18%	4726
	11th to 20th	Night	12% 11% 4 10% 6% 6% 6% 5% 7% 9% 25%	4597
	21st to end	Night	12% 13% 5% 12% 7% 7% 7% 6% 8% 7% 16%	4742
February	1st to 10th	Night	10% 14% 3 11% 8% 6% 6% 6% 7% 7% 23%	2470
	11th to 20th	Night	9% 13% 4 9% 7% 6% 6% 5% 7% 7% 27%	2402
	21st to end	Night	9% 15% 5% 11% 5% 6% 6% 5% 7% 7% 24%	2015
March	1st to 10th	Night	5% 11% 4 8% 7% 7% 8% 6% 10% 11% 24%	3595
	11th to 20th	Night	5% 9% 3 6% 5% 5% 6% 5% 7% 8% 42%	3489
	21st to end	Night	12% 15% 5% 11% 7% 6% 6% 4 7% 6% 21%	3745
April	1st to 10th	Night	10% 12% 4 10% 6% 6% 6% 5% 7% 7% 27%	1900
	11th to 20th	Night	10% 12% 4 8% 5% 5% 6% 4 7% 6% 33%	1800
	21st to end	Night	12% 11% 3 9% 6% 5% 6% 5% 6% 7% 30%	1691
May	1st to 10th	Night	8% 7% 3 7% 4 4 4 3 5% 6% 49%	2540
	11th to 20th	Night	7% 4 2 5% 4 3 5% 4 6% 8% 53%	2516
	21st to end	Night	16% 10% 3 8% 5% 5% 4 4 6% 9% 30%	2762
June	1st to 10th	Night	15% 9% 3 7% 5% 4 5% 4 6% 7% 35%	1355
	11th to 20th	Night	12% 9% 3 8% 5% 5% 5% 5% 6% 8% 35%	1330
	21st to end	Night	8% 6% 3 5% 4 4 6% 5% 8% 8% 44%	1330
July	1st to 10th	Night	4 4 1 3 3 2 3 3 3 4 69%	2220
	11th to 20th	Night	4 4 2 3 2 2 2 2 3 6% 69%	2244
	21st to end	Night	8% 5% 1 3 3 2 4 3 4 5% 61%	2762
August	1st to 10th	Night	4 2 1 3 2 2 3 3 4 6% 70%	2649
	11th to 20th	Night	11% 7% 2 5% 4 5% 4 3 5% 6% 48%	2812
	21st to end	Night	11% 5% 1 4 3 4 4 3 5% 6% 53%	3270
September	1st to 10th	Night	6% 5% 2 5% 3 4 3 4 5% 7% 57%	1900
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 5% 7% 46%	1908
	21st to end	Night	8% 6% 3 6% 4 5% 5% 4 6% 7% 46%	2175
October	1st to 10th	Night	7% 6% 2 6% 5% 5% 6% 4 8% 8% 44%	3800
	11th to 20th	Night	10% 8% 3 8% 6% 6% 6% 5% 6% 7% 35%	3777
	21st to end	Night	10% 7% 3 8% 7% 6% 7% 5% 6% 8% 32%	4287
November	1st to 10th	Night	14% 11% 3 9% 7% 7% 6% 5% 6% 7% 25%	2672
	11th to 20th	Night	9% 10% 4 10% 7% 7% 6% 6% 9% 6% 27%	2660
	21st to end	Night	10% 10% 4 9% 8% 6% 7% 6% 8% 7% 26%	2660
December	1st to 10th	Night	9% 13% 4 10% 7% 5% 6% 5% 7% 8% 26%	2660
	11th to 20th	Night	10% 14% 4 11% 6% 7% 6% 5% 9% 8% 19%	3438
	21st to end	Night	11% 15% 4 11% 6% 6% 7% 5% 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	52% 6% 18% 19% 5% 1	3279
	11th to 20th	Day	45% 4 17% 30% 3	3490
	21st to end	Day	62% 5% 18% 14% 2	3907
April	1st to 10th	Day	58% 6% 17% 16% 3	2280
	11th to 20th	Day	55% 5% 14% 16% 8% 2	2326
	21st to end	Day	56% 4 15% 18% 6% 1	2489
May	1st to 10th	Day	43% 4 17% 26% 9% 2	4420
	11th to 20th	Day	37% 4 31% 21% 6%	4380
	21st to end	Day	61% 3 20% 13% 2	4814
June	1st to 10th	Day	55% 4 21% 13% 6% 1	2821
	11th to 20th	Day	57% 5% 18% 16% 4	2850
	21st to end	Day	45% 6% 24% 18% 7% 1	2850
July	1st to 10th	Day	22% 3 13% 27% 24% 11%	4666
	11th to 20th	Day	24% 2 13% 30% 29% 2	4632
	21st to end	Day	29% 6% 22% 29% 12% 2	4639
August	1st to 10th	Day	23% 4 18% 39% 16% 1	4266
	11th to 20th	Day	40% 13% 20% 20% 7% 2	4065
	21st to end	Day	40% 5% 18% 28% 9% 1	4399
September	1st to 10th	Day	32% 5% 20% 24% 15% 3	2280
	11th to 20th	Day	43% 6% 16% 19% 15% 2	2271
	21st to end	Day	40% 5% 21% 21% 10% 2	2005
October	1st to 10th	Day	38% 9% 24% 24% 5%	3180
	11th to 20th	Day	50% 9% 16% 18% 6%	3161
	21st to end	Day	52% 9% 16% 15% 8% 1	3275
November	1st to 10th	Day	61% 6% 15% 13% 4 1	1528
	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	52% 6% 14% 23% 5%	3595
	11th to 20th	Night	38% 5% 21% 31% 4 1	3490
	21st to end	Night	63% 5% 16% 15% 1	3745
April	1st to 10th	Night	53% 9% 16% 17% 4	1900
	11th to 20th	Night	50% 6% 14% 19% 9% 2	1800
	21st to end	Night	53% 7% 12% 18% 9% 1	1691
May	1st to 10th	Night	38% 4 12% 29% 15% 1	2540
	11th to 20th	Night	31% 3 26% 29% 9% 1	2516
	21st to end	Night	53% 7% 20% 16% 3 1	2762
June	1st to 10th	Night	49% 5% 21% 18% 5% 3	1355
	11th to 20th	Night	48% 5% 23% 20% 4	1330
	21st to end	Night	38% 4 26% 21% 7% 4	1330
July	1st to 10th	Night	21% 2 12% 30% 23% 12%	2185
	11th to 20th	Night	17% 2 14% 29% 35% 2	2202
	21st to end	Night	26% 3 17% 28% 24% 3	2674
August	1st to 10th	Night	17% 4 18% 41% 17% 3	2641
	11th to 20th	Night	37% 8% 21% 21% 10% 3	2839
	21st to end	Night	33% 8% 14% 33% 11% 1	3270
September	1st to 10th	Night	28% 3 19% 27% 18% 5%	1900
	11th to 20th	Night	39% 4 15% 20% 16% 5%	1908
	21st to end	Night	37% 6% 16% 26% 14% 2	2175
October	1st to 10th	Night	37% 7% 22% 27% 7%	3800
	11th to 20th	Night	48% 5% 18% 24% 6%	3777
	21st to end	Night	49% 7% 17% 18% 9% 1	4287
November	1st to 10th	Night	56% 6% 15% 15% 6% 1	2672
	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% 25% 24% 16% 3	460
	21st to end	Day	22% 12% 29% 25% 10% 2	506
April	1st to 10th	Day	23% 12% 28% 23% 12% 3	460
	11th to 20th	Day	21% 13% 30% 19% 13% 3	452
	21st to end	Day	23% 11% 25% 24% 13% 4	460
May	1st to 10th	Day	15% 9% 25% 31% 17% 3	463
	11th to 20th	Day	20% 5% 22% 28% 19% 7%	488
	21st to end	Day	22% 4 23% 28% 16% 7%	529
June	1st to 10th	Day	21% 5% 24% 27% 19% 4	651
	11th to 20th	Day	18% 7% 28% 30% 14% 3	680
	21st to end	Day	11% 4 22% 37% 22% 4	680
July	1st to 10th	Day	12% 1 17% 37% 27% 7%	671
	11th to 20th	Day	8% 4 17% 35% 28% 7%	654
	21st to end	Day	7% 3 13% 36% 31% 10%	531
August	1st to 10th	Day	9% 2 10% 32% 35% 11%	487
	11th to 20th	Day	6% 1 15% 32% 34% 12%	477
	21st to end	Day	12% 3 19% 35% 25% 7%	539
September	1st to 10th	Day	12% 4 20% 35% 24% 5%	490
	11th to 20th	Day	14% 4 19% 29% 27% 6%	490
	21st to end	Day	16% 6% 23% 32% 20% 3	490
October	1st to 10th	Day	16% 6% 23% 26% 24% 6%	490
	11th to 20th	Day	18% 7% 22% 28% 21% 4	490
	21st to end	Day	20% 14% 25% 23% 14% 5%	444
November	1st to 10th	Day	29% 12% 25% 23% 9% 2	190
	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% 21% 4	760
	21st to end	Night	22% 6% 14% 32% 22% 4	836
April	1st to 10th	Night	19% 8% 15% 32% 23% 4	760
	11th to 20th	Night	16% 7% 18% 35% 20% 5%	672
	21st to end	Night	21% 4 11% 39% 19% 5%	551
May	1st to 10th	Night	14% 3 14% 34% 30% 4	380
	11th to 20th	Night	15% 2 11% 30% 33% 9%	374
	21st to end	Night	18% 4 8% 28% 34% 8%	411
June	1st to 10th	Night	22% 4 8% 33% 27% 6%	380
	11th to 20th	Night	17% 4 12% 38% 24% 6%	380
	21st to end	Night	13% 1 7% 32% 39% 7%	380
July	1st to 10th	Night	13% 1 6% 26% 44% 11%	370
	11th to 20th	Night	9% 3 7% 29% 44% 10%	368
	21st to end	Night	6% 2 5% 28% 46% 12%	416
August	1st to 10th	Night	11% 1 2 20% 45% 20%	446
	11th to 20th	Night	8% 1 2 20% 48% 20%	564
	21st to end	Night	11% 1 8% 30% 39% 12%	699
September	1st to 10th	Night	9% 2 5% 33% 38% 13%	760
	11th to 20th	Night	14% 3 7% 23% 34% 18%	760
	21st to end	Night	13% 2 13% 30% 33% 9%	760
October	1st to 10th	Night	13% 5% 10% 30% 33% 8%	760
	11th to 20th	Night	18% 4 13% 30% 26% 9%	760
	21st to end	Night	19% 6% 14% 36% 21% 5%	836
November	1st to 10th	Night	26% 6% 13% 36% 16% 2	764
	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 2024-11-03 10:19:05. Version ac07

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