Anacortes
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anacortes clear sky chart from 2005-11-06 to 2026-09-14.

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	16% 8% 3 7% 5% 4 4 4 5% 7% 37%	153593
	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 32%	146234
Transparency	Day	48% 8% 17% 19% 8% 1	153304
	Night	54% 8% 14% 17% 7% 1	146105
Seeing	Day	22% 8% 20% 26% 18% 6%	17657
	Night	28% 8% 16% 24% 20% 4	25816

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	34% 17% 4 10% 5% 5% 4 3 4 4 10%	4125
	11th to 20th	Day	18% 9% 3 7% 5% 4 5% 4 6% 8% 30%	4339
	21st to end	Day	26% 12% 4 10% 5% 4 5% 4 5% 5% 22%	5285
February	1st to 10th	Day	27% 13% 4 9% 6% 5% 5% 4 5% 6% 17%	1890
	11th to 20th	Day	25% 12% 3 10% 5% 5% 5% 3 4 5% 23%	1845
	21st to end	Day	24% 14% 5% 9% 6% 4 5% 3 5% 5% 19%	1600
March	1st to 10th	Day	19% 15% 4 10% 7% 5% 5% 4 5% 6% 20%	4747
	11th to 20th	Day	18% 14% 4 9% 5% 5% 5% 4 5% 6% 25%	5110
	21st to end	Day	23% 12% 4 10% 6% 6% 7% 4 6% 5% 18%	5778
April	1st to 10th	Day	21% 11% 4 8% 5% 5% 6% 4 6% 7% 22%	2520
	11th to 20th	Day	17% 10% 3 7% 5% 5% 5% 5% 7% 6% 28%	2557
	21st to end	Day	20% 8% 3 9% 4 5% 4 4 6% 7% 30%	2788
May	1st to 10th	Day	11% 6% 3 7% 4 4 4 4 5% 7% 44%	8195
	11th to 20th	Day	13% 8% 3 7% 5% 5% 5% 4 7% 9% 33%	8160
	21st to end	Day	16% 8% 2 6% 4 4 4 4 7% 9% 35%	8993
June	1st to 10th	Day	17% 8% 3 6% 5% 4 5% 3 6% 7% 36%	3115
	11th to 20th	Day	15% 7% 3 7% 6% 6% 6% 4 6% 6% 34%	3150
	21st to end	Day	11% 7% 2 6% 4 5% 5% 4 6% 7% 41%	3150
July	1st to 10th	Day	7% 4 2 4 3 3 3 3 5% 7% 60%	8820
	11th to 20th	Day	4 3 2 4 3 3 2 2 4 6% 68%	8760
	21st to end	Day	7% 4 2 5% 3 3 4 4 6% 8% 56%	8916
August	1st to 10th	Day	5% 3 1 3 2 2 3 2 4 6% 67%	6376
	11th to 20th	Day	6% 4 2 6% 5% 4 4 4 5% 7% 52%	5923
	21st to end	Day	11% 7% 3 7% 4 5% 4 3 6% 8% 42%	6367
September	1st to 10th	Day	10% 5% 2 7% 4 3 4 4 5% 7% 50%	2520
	11th to 20th	Day	13% 8% 2 8% 4 5% 4 3 5% 6% 41%	2437
	21st to end	Day	18% 8% 2 7% 4 4 4 4 5% 7% 36%	2108
October	1st to 10th	Day	17% 8% 2 7% 5% 4 6% 5% 7% 8% 31%	3280
	11th to 20th	Day	30% 10% 3 7% 4 4 4 4 5% 6% 24%	3261
	21st to end	Day	23% 11% 4 11% 7% 5% 5% 4 5% 6% 20%	3343
November	1st to 10th	Day	29% 12% 4 9% 6% 5% 6% 4 4 5% 18%	1648
	11th to 20th	Day	30% 12% 3 9% 5% 4 4 3 4 4 22%	1680
	21st to end	Day	29% 12% 3 9% 6% 4 5% 3 5% 5% 17%	1680
December	1st to 10th	Day	21% 9% 3 8% 8% 6% 6% 4 6% 7% 22%	2700
	11th to 20th	Day	30% 15% 5% 11% 6% 6% 5% 4 5% 4 11%	2852
	21st to end	Day	28% 16% 5% 11% 6% 5% 5% 3 5% 5% 11%	3575
January	1st to 10th	Night	30% 17% 5% 11% 6% 5% 4 3 4 4 10%	8770
	11th to 20th	Night	21% 11% 4 6% 3 4 4 4 6% 8% 29%	8544
	21st to end	Night	25% 12% 3 8% 5% 4 4 3 5% 8% 23%	8897
February	1st to 10th	Night	28% 14% 4 8% 5% 5% 4 3 4 5% 21%	2730
	11th to 20th	Night	24% 14% 3 8% 5% 4 4 3 4 4 25%	2662
	21st to end	Night	27% 11% 3 8% 5% 5% 4 3 5% 5% 22%	2205
March	1st to 10th	Night	16% 12% 4 9% 7% 7% 6% 4 6% 7% 23%	5366
	11th to 20th	Night	19% 12% 4 8% 5% 4 5% 3 5% 6% 28%	5109
	21st to end	Night	28% 13% 5% 9% 6% 5% 5% 3 5% 5% 16%	5438
April	1st to 10th	Night	23% 11% 4 8% 7% 5% 4 4 6% 6% 23%	2100
	11th to 20th	Night	20% 10% 3 8% 6% 5% 5% 4 5% 7% 29%	2010
	21st to end	Night	22% 11% 4 9% 5% 4 4 3 5% 5% 28%	1831
May	1st to 10th	Night	12% 6% 2 6% 5% 4 4 3 4 5% 48%	4724
	11th to 20th	Night	13% 8% 3 9% 6% 5% 5% 4 6% 7% 35%	4700
	21st to end	Night	13% 7% 3 8% 6% 5% 6% 4 7% 8% 33%	5178
June	1st to 10th	Night	18% 8% 3 8% 6% 5% 5% 4 5% 6% 33%	1501
	11th to 20th	Night	16% 8% 2 8% 5% 5% 4 4 6% 7% 36%	1470
	21st to end	Night	14% 6% 2 7% 5% 5% 3 3 6% 8% 42%	1470
July	1st to 10th	Night	7% 4 2 4 2 2 3 3 5% 7% 61%	4140
	11th to 20th	Night	5% 3 1 3 2 2 2 2 3 5% 71%	4199
	21st to end	Night	6% 4 2 4 3 4 4 3 5% 6% 59%	5152
August	1st to 10th	Night	3 2 1 2 1 2 3 2 4 5% 75%	3773
	11th to 20th	Night	8% 4 1 5% 4 4 4 3 5% 7% 57%	4142
	21st to end	Night	12% 5% 3 6% 4 4 4 3 5% 8% 46%	4790
September	1st to 10th	Night	8% 4 2 5% 3 3 4 4 4 7% 57%	2100
	11th to 20th	Night	15% 6% 2 7% 4 4 4 3 4 6% 44%	2030
	21st to end	Night	16% 6% 3 7% 5% 4 4 3 4 6% 41%	2290
October	1st to 10th	Night	16% 7% 2 8% 4 5% 4 4 5% 7% 38%	3920
	11th to 20th	Night	27% 8% 2 6% 4 4 4 3 5% 6% 31%	3897
	21st to end	Night	25% 10% 4 7% 5% 5% 4 4 5% 6% 25%	4460
November	1st to 10th	Night	33% 10% 4 8% 5% 5% 4 3 4 4 19%	2865
	11th to 20th	Night	31% 12% 3 7% 5% 5% 4 3 4 5% 21%	2940
	21st to end	Night	30% 12% 3 8% 6% 5% 5% 4 4 5% 20%	2940
December	1st to 10th	Night	23% 10% 3 8% 5% 5% 6% 5% 6% 7% 22%	4700
	11th to 20th	Night	31% 15% 4 11% 6% 5% 4 3 4 5% 12%	5568
	21st to end	Night	27% 15% 5% 10% 6% 6% 5% 4 5% 5% 14%	7623

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	79% 7% 7% 5% 1	4125
	11th to 20th	Day	51% 7% 12% 20% 10%	4360
	21st to end	Day	64% 7% 8% 16% 6%	5286
February	1st to 10th	Day	67% 9% 9% 8% 4 2	1890
	11th to 20th	Day	64% 8% 10% 10% 7% 1	1854
	21st to end	Day	66% 9% 10% 9% 4 1	1600
March	1st to 10th	Day	62% 8% 13% 13% 3	4747
	11th to 20th	Day	59% 7% 13% 18% 2	5110
	21st to end	Day	66% 10% 13% 10% 1	5778
April	1st to 10th	Day	61% 11% 17% 10% 1	2520
	11th to 20th	Day	55% 9% 14% 13% 7% 2	2557
	21st to end	Day	56% 9% 14% 15% 6% 1	2788
May	1st to 10th	Day	42% 6% 17% 25% 9%	8195
	11th to 20th	Day	48% 10% 21% 18% 3	8163
	21st to end	Day	46% 10% 24% 17% 3	8994
June	1st to 10th	Day	49% 9% 19% 15% 6% 1	3115
	11th to 20th	Day	51% 11% 17% 15% 5%	3150
	21st to end	Day	42% 11% 20% 19% 7% 1	3150
July	1st to 10th	Day	26% 5% 23% 22% 17% 7%	8746
	11th to 20th	Day	20% 4 16% 33% 24% 3	8679
	21st to end	Day	29% 4 27% 29% 10% 1	8723
August	1st to 10th	Day	21% 6% 16% 33% 22% 3	6359
	11th to 20th	Day	31% 6% 29% 27% 6% 1	5962
	21st to end	Day	43% 6% 18% 25% 8%	6366
September	1st to 10th	Day	33% 10% 19% 22% 12% 4	2520
	11th to 20th	Day	44% 8% 16% 17% 15% 1	2437
	21st to end	Day	45% 10% 17% 17% 9% 1	2108
October	1st to 10th	Day	48% 8% 19% 21% 4	3280
	11th to 20th	Day	60% 8% 12% 12% 7%	3261
	21st to end	Day	65% 7% 10% 11% 6%	3343
November	1st to 10th	Day	66% 9% 13% 8% 3	1648
	11th to 20th	Day	66% 8% 10% 10% 4 2	1680
	21st to end	Day	67% 9% 9% 8% 6%	1680
December	1st to 10th	Day	58% 9% 10% 14% 8%	2700
	11th to 20th	Day	73% 10% 7% 7% 2	2855
	21st to end	Day	75% 9% 9% 5% 1	3575
January	1st to 10th	Night	77% 7% 7% 7% 2	8770
	11th to 20th	Night	54% 10% 12% 16% 7% 1	8584
	21st to end	Night	60% 7% 9% 17% 6%	8897
February	1st to 10th	Night	67% 8% 10% 8% 5% 2	2730
	11th to 20th	Night	63% 8% 10% 12% 6% 2	2664
	21st to end	Night	64% 8% 10% 14% 4 1	2205
March	1st to 10th	Night	59% 9% 14% 13% 5%	5366
	11th to 20th	Night	57% 7% 14% 19% 2	5110
	21st to end	Night	70% 9% 11% 9% 1	5438
April	1st to 10th	Night	62% 10% 13% 12% 2	2100
	11th to 20th	Night	56% 9% 14% 12% 7% 2	2010
	21st to end	Night	59% 6% 13% 14% 6% 1	1831
May	1st to 10th	Night	40% 5% 14% 31% 9%	4721
	11th to 20th	Night	48% 11% 19% 17% 4	4700
	21st to end	Night	47% 11% 23% 16% 2	5182
June	1st to 10th	Night	52% 7% 18% 16% 5% 2	1501
	11th to 20th	Night	50% 9% 18% 19% 3	1470
	21st to end	Night	42% 7% 21% 22% 5% 3	1470
July	1st to 10th	Night	27% 4 21% 25% 15% 7%	4105
	11th to 20th	Night	19% 4 15% 31% 28% 3	4157
	21st to end	Night	27% 4 24% 30% 13% 2	5040
August	1st to 10th	Night	13% 5% 18% 40% 21% 4	3765
	11th to 20th	Night	30% 4 31% 25% 7% 1	4169
	21st to end	Night	40% 6% 20% 26% 8% 1	4790
September	1st to 10th	Night	29% 9% 18% 27% 13% 4	2100
	11th to 20th	Night	43% 7% 14% 17% 15% 3	2030
	21st to end	Night	44% 8% 14% 24% 9% 1	2290
October	1st to 10th	Night	47% 6% 22% 21% 5%	3920
	11th to 20th	Night	55% 7% 14% 18% 5%	3897
	21st to end	Night	62% 7% 13% 12% 6%	4460
November	1st to 10th	Night	68% 6% 12% 10% 3 1	2865
	11th to 20th	Night	67% 7% 11% 9% 5% 2	2940
	21st to end	Night	66% 9% 11% 8% 6% 1	2940
December	1st to 10th	Night	60% 9% 11% 14% 5%	4700
	11th to 20th	Night	73% 9% 9% 7% 2	5565
	21st to end	Night	72% 10% 9% 7% 1	7623

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	39% 14% 16% 17% 9% 5%	220
	11th to 20th	Day	29% 16% 17% 15% 14% 9%	220
	21st to end	Day	38% 12% 17% 15% 14% 4	276
February	1st to 10th	Day	38% 9% 20% 20% 11% 3	430
	11th to 20th	Day	33% 12% 21% 20% 12% 2	425
	21st to end	Day	32% 14% 24% 18% 10% 2	378
March	1st to 10th	Day	32% 12% 24% 19% 11% 1	540
	11th to 20th	Day	34% 9% 18% 19% 16% 4	540
	21st to end	Day	31% 11% 24% 22% 10% 2	594
April	1st to 10th	Day	27% 13% 20% 24% 13% 4	540
	11th to 20th	Day	23% 12% 24% 23% 14% 5%	532
	21st to end	Day	25% 11% 22% 24% 14% 4	540
May	1st to 10th	Day	15% 8% 23% 30% 20% 3	543
	11th to 20th	Day	23% 7% 19% 27% 20% 5%	568
	21st to end	Day	20% 7% 23% 28% 16% 6%	617
June	1st to 10th	Day	20% 7% 24% 30% 15% 4	745
	11th to 20th	Day	19% 9% 25% 33% 12% 3	780
	21st to end	Day	12% 6% 23% 30% 23% 5%	780
July	1st to 10th	Day	11% 4 20% 35% 24% 6%	771
	11th to 20th	Day	7% 6% 21% 35% 25% 7%	747
	21st to end	Day	8% 3 14% 34% 31% 11%	619
August	1st to 10th	Day	10% 4 11% 29% 34% 11%	567
	11th to 20th	Day	7% 3 13% 29% 38% 11%	557
	21st to end	Day	11% 6% 18% 32% 25% 9%	627
September	1st to 10th	Day	14% 5% 16% 31% 26% 8%	570
	11th to 20th	Day	17% 6% 16% 30% 27% 5%	543
	21st to end	Day	22% 7% 20% 25% 20% 7%	530
October	1st to 10th	Day	22% 7% 19% 24% 18% 9%	530
	11th to 20th	Day	30% 9% 21% 16% 16% 7%	530
	21st to end	Day	32% 12% 21% 19% 13% 5%	456
November	1st to 10th	Day	34% 14% 23% 16% 11% 2	220
	11th to 20th	Day	37% 11% 17% 16% 12% 6%	220
	21st to end	Day	33% 13% 20% 15% 9% 9%	220
December	1st to 10th	Day	40% 15% 12% 9% 11% 13%	220
	11th to 20th	Day	43% 16% 17% 15% 8% 1	220
	21st to end	Day	40% 10% 20% 21% 7% 2	242
January	1st to 10th	Night	41% 14% 17% 16% 12% 2	950
	11th to 20th	Night	37% 11% 13% 19% 19% 2	908
	21st to end	Night	36% 8% 16% 22% 15% 3	924
February	1st to 10th	Night	36% 11% 17% 23% 11% 2	840
	11th to 20th	Night	33% 10% 16% 24% 16% 2	824
	21st to end	Night	36% 11% 19% 22% 10% 2	692
March	1st to 10th	Night	31% 13% 20% 22% 13% 2	840
	11th to 20th	Night	33% 11% 18% 20% 15% 3	840
	21st to end	Night	33% 11% 21% 24% 9% 2	924
April	1st to 10th	Night	30% 9% 17% 25% 15% 3	840
	11th to 20th	Night	25% 9% 19% 28% 16% 3	762
	21st to end	Night	29% 8% 18% 28% 15% 3	571
May	1st to 10th	Night	18% 7% 15% 33% 24% 2	420
	11th to 20th	Night	22% 6% 15% 26% 26% 5%	414
	21st to end	Night	19% 5% 18% 30% 24% 4	455
June	1st to 10th	Night	22% 5% 20% 28% 23% 2	420
	11th to 20th	Night	20% 6% 18% 36% 18% 2	420
	21st to end	Night	16% 5% 15% 32% 28% 5%	420
July	1st to 10th	Night	11% 3 13% 34% 35% 3	410
	11th to 20th	Night	10% 3 14% 35% 33% 4	408
	21st to end	Night	7% 2 12% 32% 39% 7%	460
August	1st to 10th	Night	9% 3 7% 24% 46% 11%	443
	11th to 20th	Night	9% 2 6% 23% 46% 15%	624
	21st to end	Night	13% 3 12% 29% 35% 8%	787
September	1st to 10th	Night	10% 3 11% 36% 32% 8%	840
	11th to 20th	Night	18% 4 12% 22% 32% 12%	812
	21st to end	Night	20% 6% 16% 25% 27% 6%	800
October	1st to 10th	Night	21% 5% 15% 24% 27% 8%	800
	11th to 20th	Night	31% 9% 11% 23% 21% 6%	800
	21st to end	Night	31% 9% 18% 24% 14% 4	880
November	1st to 10th	Night	37% 12% 18% 22% 10%	820
	11th to 20th	Night	40% 10% 17% 19% 13% 2	840
	21st to end	Night	35% 11% 20% 18% 13% 4	840
December	1st to 10th	Night	33% 8% 16% 23% 17% 3	840
	11th to 20th	Night	40% 12% 21% 18% 8% 1	903
	21st to end	Night	38% 13% 23% 17% 8% 1	1045

Page generated at 2026-09-11 01:11:53. Version ac07

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