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 2025-11-03.

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	9% 10% 3 8% 6% 6% 6% 5% 6% 7% 33%	130994
	Night	9% 9% 3 8% 6% 6% 6% 5% 7% 7% 35%	127756
Transparency	Day	46% 7% 18% 20% 8% 1	130704
	Night	47% 7% 17% 21% 8% 1	127624
Seeing	Day	18% 7% 22% 28% 19% 5%	16623
	Night	18% 6% 13% 31% 25% 7%	24815

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	10% 15% 5% 12% 9% 9% 7% 5% 7% 6% 15%	3179
	11th to 20th	Day	8% 9% 4 7% 6% 6% 8% 6% 8% 12% 26%	3315
	21st to end	Day	8% 11% 4 10% 8% 8% 8% 6% 6% 9% 23%	4170
February	1st to 10th	Day	11% 14% 4 10% 7% 7% 6% 5% 8% 8% 19%	1800
	11th to 20th	Day	10% 16% 5% 11% 6% 6% 6% 5% 7% 7% 20%	1755
	21st to end	Day	9% 15% 5% 11% 8% 5% 6% 5% 8% 8% 20%	1511
March	1st to 10th	Day	7% 11% 4 11% 6% 6% 7% 6% 8% 10% 22%	4711
	11th to 20th	Day	6% 15% 4 10% 7% 6% 7% 5% 6% 6% 29%	5000
	21st to end	Day	11% 13% 5% 11% 8% 8% 8% 6% 8% 7% 15%	5607
April	1st to 10th	Day	12% 14% 5% 10% 7% 6% 6% 5% 7% 7% 21%	2400
	11th to 20th	Day	11% 13% 4 10% 7% 6% 6% 4 6% 6% 27%	2450
	21st to end	Day	13% 12% 4 10% 6% 5% 6% 5% 6% 7% 26%	2620
May	1st to 10th	Day	10% 9% 3 6% 4 4 5% 4 6% 7% 42%	6320
	11th to 20th	Day	11% 11% 3 8% 5% 5% 6% 4 6% 10% 31%	6277
	21st to end	Day	16% 12% 4 9% 5% 5% 5% 4 5% 8% 26%	6903
June	1st to 10th	Day	16% 12% 4 9% 6% 5% 5% 4 6% 7% 28%	2970
	11th to 20th	Day	15% 11% 5% 10% 7% 6% 7% 5% 6% 7% 21%	3000
	21st to end	Day	11% 10% 3 8% 6% 5% 7% 5% 6% 7% 33%	3000
July	1st to 10th	Day	5% 5% 2 4 3 4 6% 4 5% 6% 57%	6780
	11th to 20th	Day	4 5% 2 4 3 3 3 3 3 5% 65%	6739
	21st to end	Day	7% 7% 2 5% 4 4 7% 5% 5% 6% 49%	6874
August	1st to 10th	Day	3 5% 2 4 4 4 4 3 5% 8% 58%	4419
	11th to 20th	Day	7% 13% 3 7% 5% 5% 8% 4 6% 7% 35%	4156
	21st to end	Day	11% 8% 3 7% 4 4 5% 3 5% 6% 45%	4539
September	1st to 10th	Day	7% 7% 2 6% 4 4 4 3 5% 7% 50%	2400
	11th to 20th	Day	9% 9% 3 8% 5% 5% 5% 4 5% 7% 40%	2390
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 9% 39%	2110
October	1st to 10th	Day	8% 7% 2 7% 5% 5% 6% 5% 7% 12% 36%	3280
	11th to 20th	Day	11% 9% 3 9% 6% 7% 6% 5% 6% 8% 31%	3261
	21st to end	Day	7% 11% 4 10% 8% 7% 7% 5% 8% 8% 25%	3379
November	1st to 10th	Day	13% 14% 4 11% 7% 7% 7% 5% 6% 6% 19%	1584
	11th to 20th	Day	11% 12% 4 9% 7% 7% 6% 6% 6% 9% 24%	1600
	21st to end	Day	10% 13% 5% 10% 6% 6% 7% 6% 6% 8% 23%	1600
December	1st to 10th	Day	7% 10% 3 9% 6% 9% 9% 5% 8% 9% 26%	2620
	11th to 20th	Day	11% 13% 4 10% 7% 7% 7% 6% 8% 8% 17%	2777
	21st to end	Day	11% 16% 5% 11% 7% 7% 7% 5% 8% 7% 17%	3498
January	1st to 10th	Night	10% 13% 4 11% 9% 9% 9% 6% 6% 6% 16%	6766
	11th to 20th	Night	8% 8% 3 8% 5% 6% 6% 5% 7% 10% 33%	6581
	21st to end	Night	9% 11% 4 10% 6% 6% 6% 5% 7% 7% 30%	6780
February	1st to 10th	Night	10% 13% 4 11% 8% 6% 6% 6% 7% 7% 23%	2600
	11th to 20th	Night	9% 13% 4 9% 7% 5% 6% 5% 7% 7% 28%	2532
	21st to end	Night	9% 15% 5% 11% 6% 6% 6% 5% 7% 7% 24%	2117
March	1st to 10th	Night	6% 10% 3 7% 6% 6% 8% 6% 9% 11% 27%	5170
	11th to 20th	Night	4 10% 3 7% 6% 6% 6% 5% 7% 9% 37%	4999
	21st to end	Night	11% 13% 5% 11% 7% 7% 6% 4 7% 7% 20%	5367
April	1st to 10th	Night	10% 12% 4 10% 6% 6% 6% 5% 7% 7% 27%	2000
	11th to 20th	Night	10% 11% 3 7% 5% 5% 6% 4 6% 7% 35%	1896
	21st to end	Night	11% 11% 3 9% 5% 5% 6% 5% 7% 7% 31%	1780
May	1st to 10th	Night	9% 5% 2 5% 4 4 5% 4 5% 6% 50%	3640
	11th to 20th	Night	8% 6% 2 7% 5% 5% 5% 4 6% 8% 44%	3616
	21st to end	Night	12% 9% 3 6% 4 5% 5% 5% 8% 11% 31%	3972
June	1st to 10th	Night	14% 9% 2 7% 5% 4 5% 4 6% 6% 37%	1426
	11th to 20th	Night	11% 9% 3 8% 5% 5% 5% 5% 6% 8% 35%	1400
	21st to end	Night	8% 6% 3 6% 4 5% 6% 5% 8% 8% 43%	1400
July	1st to 10th	Night	4 4 1 5% 3 3 4 3 3 4 66%	3180
	11th to 20th	Night	3 3 1 2 2 2 3 2 3 5% 73%	3218
	21st to end	Night	7% 4 1 3 3 3 4 3 4 6% 62%	3969
August	1st to 10th	Night	4 3 1 3 2 3 3 3 4 6% 69%	2733
	11th to 20th	Night	11% 7% 2 6% 4 5% 5% 3 5% 6% 47%	2902
	21st to end	Night	11% 5% 1 4 3 4 4 3 5% 6% 54%	3373
September	1st to 10th	Night	6% 5% 2 5% 3 4 3 4 5% 7% 56%	2000
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 5% 7% 47%	2009
	21st to end	Night	8% 6% 2 6% 4 5% 5% 4 6% 7% 46%	2290
October	1st to 10th	Night	7% 6% 2 6% 5% 5% 6% 4 8% 8% 44%	3920
	11th to 20th	Night	9% 8% 3 8% 6% 6% 5% 4 6% 7% 36%	3897
	21st to end	Night	10% 7% 3 8% 7% 6% 7% 5% 6% 8% 32%	4425
November	1st to 10th	Night	14% 11% 3 9% 7% 7% 6% 5% 6% 7% 25%	2758
	11th to 20th	Night	9% 10% 4 10% 7% 7% 6% 6% 9% 7% 26%	2800
	21st to end	Night	10% 10% 4 10% 8% 6% 7% 6% 8% 7% 25%	2800
December	1st to 10th	Night	6% 9% 3 8% 7% 8% 8% 7% 8% 9% 28%	4560
	11th to 20th	Night	11% 13% 4 11% 7% 7% 7% 5% 9% 8% 19%	5422
	21st to end	Night	10% 13% 4 10% 6% 6% 7% 5% 7% 8% 23%	7458

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	67% 6% 11% 12% 3	3179
	11th to 20th	Day	47% 14% 17% 19% 2	3336
	21st to end	Day	57% 8% 15% 15% 4	4170
February	1st to 10th	Day	60% 7% 15% 11% 6% 1	1800
	11th to 20th	Day	60% 7% 13% 13% 6%	1764
	21st to end	Day	57% 7% 15% 15% 6%	1511
March	1st to 10th	Day	52% 9% 17% 19% 4	4711
	11th to 20th	Day	52% 5% 15% 25% 3	5000
	21st to end	Day	64% 8% 15% 11% 2	5607
April	1st to 10th	Day	57% 6% 18% 16% 2	2400
	11th to 20th	Day	54% 5% 15% 17% 8% 1	2450
	21st to end	Day	54% 5% 16% 19% 6% 1	2620
May	1st to 10th	Day	39% 5% 19% 26% 9% 1	6320
	11th to 20th	Day	46% 6% 26% 18% 4	6280
	21st to end	Day	53% 7% 22% 17% 2	6904
June	1st to 10th	Day	53% 4 22% 15% 6% 1	2970
	11th to 20th	Day	57% 6% 18% 16% 4	3000
	21st to end	Day	46% 6% 23% 18% 7% 1	3000
July	1st to 10th	Day	22% 8% 20% 22% 20% 8%	6706
	11th to 20th	Day	21% 3 18% 29% 26% 2	6658
	21st to end	Day	28% 8% 25% 28% 9% 1	6681
August	1st to 10th	Day	23% 4 18% 38% 16% 1	4402
	11th to 20th	Day	40% 13% 19% 19% 7% 2	4195
	21st to end	Day	40% 5% 18% 28% 10% 1	4538
September	1st to 10th	Day	32% 5% 21% 24% 15% 3	2400
	11th to 20th	Day	42% 6% 16% 20% 15% 2	2390
	21st to end	Day	40% 5% 22% 21% 10% 2	2110
October	1st to 10th	Day	38% 9% 24% 24% 5%	3280
	11th to 20th	Day	50% 9% 16% 19% 6%	3261
	21st to end	Day	52% 9% 16% 15% 7% 1	3379
November	1st to 10th	Day	61% 7% 14% 12% 4 1	1584
	11th to 20th	Day	57% 8% 13% 16% 5% 1	1600
	21st to end	Day	57% 6% 14% 16% 7%	1600
December	1st to 10th	Day	49% 13% 15% 16% 7%	2620
	11th to 20th	Day	62% 10% 14% 11% 3	2780
	21st to end	Day	65% 7% 14% 11% 3	3498
January	1st to 10th	Night	66% 9% 11% 11% 3	6766
	11th to 20th	Night	44% 11% 16% 23% 5% 1	6622
	21st to end	Night	54% 5% 17% 17% 7%	6780
February	1st to 10th	Night	58% 7% 14% 13% 8% 1	2600
	11th to 20th	Night	55% 6% 15% 16% 7% 1	2534
	21st to end	Night	56% 6% 12% 18% 6% 1	2117
March	1st to 10th	Night	50% 7% 15% 22% 6%	5170
	11th to 20th	Night	42% 6% 18% 28% 5% 1	5000
	21st to end	Night	62% 7% 14% 15% 2	5367
April	1st to 10th	Night	53% 9% 16% 18% 4	2000
	11th to 20th	Night	48% 6% 15% 20% 9% 2	1896
	21st to end	Night	51% 7% 12% 19% 9% 1	1780
May	1st to 10th	Night	36% 5% 12% 32% 15% 1	3637
	11th to 20th	Night	38% 6% 23% 24% 7% 1	3616
	21st to end	Night	46% 10% 23% 18% 2	3972
June	1st to 10th	Night	48% 5% 21% 18% 6% 3	1426
	11th to 20th	Night	47% 5% 22% 21% 4	1400
	21st to end	Night	38% 4 26% 21% 7% 4	1400
July	1st to 10th	Night	24% 4 16% 29% 19% 8%	3145
	11th to 20th	Night	14% 4 19% 31% 30% 3	3176
	21st to end	Night	23% 7% 22% 29% 17% 2	3857
August	1st to 10th	Night	17% 4 19% 40% 17% 3	2725
	11th to 20th	Night	37% 8% 21% 20% 10% 3	2929
	21st to end	Night	32% 8% 14% 33% 12% 1	3373
September	1st to 10th	Night	28% 4 20% 26% 17% 5%	2000
	11th to 20th	Night	38% 5% 16% 21% 17% 5%	2009
	21st to end	Night	38% 6% 16% 26% 13% 2	2290
October	1st to 10th	Night	36% 8% 22% 27% 7%	3920
	11th to 20th	Night	47% 5% 18% 24% 6%	3897
	21st to end	Night	49% 7% 16% 18% 9% 1	4425
November	1st to 10th	Night	57% 7% 15% 15% 6% 1	2758
	11th to 20th	Night	53% 8% 16% 15% 6% 2	2800
	21st to end	Night	55% 7% 16% 14% 8%	2800
December	1st to 10th	Night	49% 12% 15% 20% 5%	4560
	11th to 20th	Night	62% 9% 14% 11% 3	5419
	21st to end	Night	59% 8% 16% 14% 3	7458

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	23% 12% 23% 22% 14% 7%	200
	11th to 20th	Day	24% 12% 16% 26% 19% 5%	200
	21st to end	Day	23% 11% 25% 19% 14% 7%	295
February	1st to 10th	Day	27% 10% 28% 22% 12% 3	400
	11th to 20th	Day	28% 11% 29% 21% 9% 2	395
	21st to end	Day	21% 14% 30% 22% 10% 3	345
March	1st to 10th	Day	21% 11% 26% 29% 10% 2	500
	11th to 20th	Day	20% 12% 26% 24% 15% 3	500
	21st to end	Day	22% 13% 29% 25% 10% 1	550
April	1st to 10th	Day	22% 12% 28% 23% 12% 3	500
	11th to 20th	Day	20% 13% 30% 20% 14% 3	492
	21st to end	Day	22% 11% 24% 24% 15% 5%	500
May	1st to 10th	Day	15% 9% 25% 30% 17% 3	503
	11th to 20th	Day	21% 5% 23% 26% 18% 7%	528
	21st to end	Day	21% 4 24% 28% 16% 7%	573
June	1st to 10th	Day	20% 5% 24% 28% 20% 4	700
	11th to 20th	Day	18% 8% 28% 30% 14% 3	730
	21st to end	Day	12% 4 22% 36% 22% 4	730
July	1st to 10th	Day	12% 2 18% 37% 26% 6%	721
	11th to 20th	Day	8% 4 17% 35% 28% 7%	703
	21st to end	Day	7% 3 14% 35% 31% 10%	575
August	1st to 10th	Day	9% 2 12% 33% 33% 11%	527
	11th to 20th	Day	7% 2 17% 31% 32% 11%	517
	21st to end	Day	11% 3 18% 34% 27% 7%	583
September	1st to 10th	Day	12% 4 19% 35% 25% 6%	530
	11th to 20th	Day	13% 4 19% 30% 27% 6%	530
	21st to end	Day	15% 6% 22% 34% 20% 3	530
October	1st to 10th	Day	15% 7% 24% 25% 23% 6%	530
	11th to 20th	Day	18% 8% 22% 28% 20% 4	530
	21st to end	Day	21% 14% 24% 24% 13% 4	482
November	1st to 10th	Day	28% 12% 24% 25% 10% 1	204
	11th to 20th	Day	30% 9% 22% 16% 15% 9%	200
	21st to end	Day	23% 12% 19% 20% 16% 12%	200
December	1st to 10th	Day	28% 4 14% 23% 19% 13%	200
	11th to 20th	Day	30% 9% 23% 24% 13% 2	200
	21st to end	Day	29% 8% 18% 25% 15% 5%	220
January	1st to 10th	Night	23% 11% 19% 27% 16% 4	900
	11th to 20th	Night	20% 8% 13% 31% 23% 4	865
	21st to end	Night	21% 6% 14% 31% 23% 6%	880
February	1st to 10th	Night	19% 6% 17% 38% 17% 3	800
	11th to 20th	Night	18% 7% 17% 31% 23% 4	784
	21st to end	Night	24% 9% 16% 30% 17% 4	660
March	1st to 10th	Night	17% 11% 15% 33% 21% 4	800
	11th to 20th	Night	16% 9% 16% 35% 20% 4	800
	21st to end	Night	21% 8% 15% 31% 22% 3	880
April	1st to 10th	Night	19% 8% 15% 33% 22% 4	800
	11th to 20th	Night	16% 7% 18% 35% 19% 4	708
	21st to end	Night	21% 4 11% 38% 20% 6%	580
May	1st to 10th	Night	14% 3 14% 36% 29% 4	400
	11th to 20th	Night	15% 3 11% 31% 31% 9%	394
	21st to end	Night	17% 4 8% 30% 33% 8%	433
June	1st to 10th	Night	21% 4 9% 33% 28% 6%	400
	11th to 20th	Night	16% 4 14% 37% 25% 5%	400
	21st to end	Night	13% 2 7% 32% 40% 7%	400
July	1st to 10th	Night	12% 2 7% 27% 42% 10%	390
	11th to 20th	Night	9% 3 7% 29% 43% 9%	388
	21st to end	Night	6% 2 5% 28% 46% 12%	438
August	1st to 10th	Night	11% 1 3 21% 44% 20%	470
	11th to 20th	Night	9% 1 3 21% 47% 19%	594
	21st to end	Night	11% 1 8% 29% 40% 11%	736
September	1st to 10th	Night	9% 2 6% 33% 38% 13%	800
	11th to 20th	Night	13% 3 7% 24% 34% 18%	800
	21st to end	Night	13% 3 13% 31% 32% 9%	800
October	1st to 10th	Night	13% 5% 11% 31% 32% 8%	800
	11th to 20th	Night	17% 5% 14% 31% 26% 9%	800
	21st to end	Night	18% 6% 15% 36% 20% 4	880
November	1st to 10th	Night	26% 6% 13% 36% 16% 2	788
	11th to 20th	Night	20% 12% 17% 28% 19% 4	800
	21st to end	Night	19% 8% 16% 34% 17% 6%	800
December	1st to 10th	Night	19% 7% 12% 34% 23% 6%	800
	11th to 20th	Night	23% 9% 17% 33% 16% 2	857
	21st to end	Night	26% 13% 19% 29% 12% 2	990

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