Oak Harbor
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Harbor clear sky chart from 2005-11-06 to 2026-02-16.

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	17% 10% 3 8% 5% 4 4 4 5% 6% 34%	134772
	Night	19% 11% 3 8% 5% 5% 4 3 5% 6% 30%	134791
Transparency	Day	31% 39% 11% 13% 6% 1	134483
	Night	36% 38% 9% 12% 5% 1	134658
Seeing	Day	22% 7% 19% 26% 19% 6%	16771
	Night	28% 8% 16% 25% 19% 5%	25210

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	31% 18% 5% 10% 6% 5% 5% 3 4 3 9%	4125
	11th to 20th	Day	16% 12% 4 9% 6% 6% 6% 4 7% 8% 24%	4396
	21st to end	Day	22% 13% 4 10% 6% 6% 5% 4 5% 5% 20%	5321
February	1st to 10th	Day	24% 17% 4 8% 6% 5% 5% 4 4 6% 16%	1890
	11th to 20th	Day	22% 15% 4 10% 6% 4 5% 4 4 5% 21%	1801
	21st to end	Day	22% 15% 5% 9% 5% 5% 5% 3 4 5% 21%	1528
March	1st to 10th	Day	18% 13% 4 11% 7% 6% 5% 4 6% 7% 17%	4647
	11th to 20th	Day	17% 13% 4 8% 5% 5% 5% 4 6% 6% 26%	5000
	21st to end	Day	20% 12% 4 11% 7% 7% 6% 5% 6% 6% 17%	5651
April	1st to 10th	Day	19% 12% 4 8% 6% 5% 5% 5% 7% 7% 21%	2400
	11th to 20th	Day	17% 11% 3 7% 5% 5% 5% 3 6% 7% 29%	2429
	21st to end	Day	19% 10% 3 8% 5% 4 5% 4 6% 7% 29%	2649
May	1st to 10th	Day	14% 9% 3 6% 4 4 4 3 4 6% 43%	6320
	11th to 20th	Day	14% 9% 3 8% 5% 4 5% 4 6% 8% 33%	6277
	21st to end	Day	22% 8% 3 7% 4 4 5% 4 7% 8% 30%	6903
June	1st to 10th	Day	19% 7% 2 6% 6% 4 5% 4 5% 7% 35%	2950
	11th to 20th	Day	17% 9% 3 8% 6% 5% 5% 4 6% 7% 32%	3000
	21st to end	Day	11% 7% 3 7% 4 4 5% 5% 6% 7% 41%	3000
July	1st to 10th	Day	7% 3 1 3 2 3 2 2 4 6% 67%	6780
	11th to 20th	Day	4 4 1 3 2 2 2 2 4 5% 71%	6693
	21st to end	Day	8% 4 2 5% 3 3 3 3 4 6% 59%	6874
August	1st to 10th	Day	6% 4 2 5% 3 3 3 3 4 7% 61%	4478
	11th to 20th	Day	11% 7% 2 6% 4 4 4 3 5% 7% 46%	4156
	21st to end	Day	14% 7% 3 7% 4 4 4 3 4 6% 45%	4511
September	1st to 10th	Day	10% 7% 2 5% 5% 3 4 3 4 7% 50%	2400
	11th to 20th	Day	13% 7% 3 6% 5% 4 5% 3 5% 7% 41%	2400
	21st to end	Day	15% 9% 3 8% 5% 5% 4 3 5% 8% 37%	2106
October	1st to 10th	Day	15% 8% 3 7% 5% 5% 6% 5% 7% 9% 29%	3280
	11th to 20th	Day	25% 11% 4 9% 5% 4 4 3 5% 6% 24%	3261
	21st to end	Day	22% 12% 4 9% 6% 6% 6% 4 5% 6% 18%	3363
November	1st to 10th	Day	27% 10% 3 9% 6% 5% 5% 4 5% 6% 18%	1653
	11th to 20th	Day	27% 11% 4 8% 5% 5% 5% 4 5% 5% 21%	1680
	21st to end	Day	28% 11% 5% 9% 5% 5% 5% 5% 5% 7% 16%	1680
December	1st to 10th	Day	18% 11% 3 11% 8% 7% 6% 4 6% 7% 19%	2700
	11th to 20th	Day	26% 15% 5% 12% 7% 6% 4 3 5% 5% 11%	2895
	21st to end	Day	25% 17% 6% 12% 6% 5% 5% 4 4 5% 11%	3575
January	1st to 10th	Night	27% 17% 6% 11% 6% 5% 5% 3 4 4 11%	8770
	11th to 20th	Night	18% 14% 3 7% 4 5% 5% 4 5% 7% 28%	8498
	21st to end	Night	21% 12% 3 9% 5% 6% 5% 4 5% 7% 22%	8863
February	1st to 10th	Night	24% 15% 4 9% 5% 4 4 3 5% 5% 20%	2730
	11th to 20th	Night	21% 16% 4 9% 5% 4 4 3 4 5% 24%	2597
	21st to end	Night	24% 15% 3 9% 6% 4 4 4 5% 5% 22%	2101
March	1st to 10th	Night	15% 13% 4 11% 7% 7% 7% 5% 6% 6% 20%	5244
	11th to 20th	Night	16% 13% 4 9% 5% 5% 4 3 5% 6% 29%	4999
	21st to end	Night	26% 14% 4 9% 6% 5% 5% 4 5% 5% 17%	5324
April	1st to 10th	Night	22% 13% 3 8% 6% 4 5% 4 6% 7% 22%	2000
	11th to 20th	Night	18% 11% 3 8% 6% 4 5% 4 5% 6% 30%	1916
	21st to end	Night	21% 10% 4 8% 6% 6% 3 3 5% 6% 27%	1750
May	1st to 10th	Night	16% 8% 3 6% 4 4 3 2 3 5% 46%	3640
	11th to 20th	Night	16% 8% 3 8% 5% 5% 4 4 5% 6% 36%	3616
	21st to end	Night	16% 9% 3 8% 5% 5% 6% 5% 7% 8% 28%	3972
June	1st to 10th	Night	19% 8% 3 7% 6% 5% 4 4 6% 4 34%	1447
	11th to 20th	Night	18% 9% 3 8% 5% 5% 5% 3 5% 8% 30%	1400
	21st to end	Night	15% 7% 2 6% 4 4 5% 4 5% 6% 43%	1400
July	1st to 10th	Night	9% 5% 2 4 3 1 2 2 3 4 67%	3180
	11th to 20th	Night	4 3 1 2 2 1 2 2 3 4 76%	3266
	21st to end	Night	8% 4 2 4 3 3 3 3 4 6% 60%	3969
August	1st to 10th	Night	5% 2 1 3 2 2 3 2 5% 6% 68%	2670
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 3 5% 51%	2902
	21st to end	Night	15% 6% 1 5% 3 3 3 3 5% 6% 48%	3401
September	1st to 10th	Night	9% 4 2 5% 4 3 4 3 5% 7% 54%	2000
	11th to 20th	Night	14% 8% 2 7% 4 4 4 4 5% 6% 42%	2000
	21st to end	Night	15% 7% 3 7% 4 4 3 3 4 7% 43%	2289
October	1st to 10th	Night	15% 6% 3 7% 5% 4 4 4 5% 8% 38%	3920
	11th to 20th	Night	25% 9% 2 6% 4 4 4 3 5% 6% 32%	3897
	21st to end	Night	22% 12% 4 8% 5% 5% 4 3 5% 6% 24%	4442
November	1st to 10th	Night	29% 11% 4 7% 6% 5% 5% 3 5% 6% 20%	2860
	11th to 20th	Night	27% 14% 4 8% 6% 4 4 3 5% 5% 21%	2940
	21st to end	Night	26% 12% 4 8% 6% 5% 4 4 5% 6% 20%	2940
December	1st to 10th	Night	20% 12% 4 9% 6% 6% 6% 3 4 6% 24%	4700
	11th to 20th	Night	25% 17% 5% 12% 6% 5% 4 3 4 5% 13%	5525
	21st to end	Night	25% 18% 5% 11% 6% 5% 4 3 5% 5% 13%	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	64% 24% 6% 5% 1	4125
	11th to 20th	Day	37% 25% 11% 17% 9%	4418
	21st to end	Day	50% 24% 7% 15% 4	5322
February	1st to 10th	Day	29% 59% 4 3 3 2	1890
	11th to 20th	Day	29% 60% 4 5% 3	1810
	21st to end	Day	25% 63% 4 5% 3 1	1528
March	1st to 10th	Day	44% 33% 9% 11% 3	4647
	11th to 20th	Day	40% 31% 10% 17% 1	5000
	21st to end	Day	49% 33% 10% 7% 1	5651
April	1st to 10th	Day	24% 64% 7% 5%	2400
	11th to 20th	Day	19% 64% 7% 7% 3 1	2429
	21st to end	Day	20% 62% 6% 9% 2	2649
May	1st to 10th	Day	28% 30% 12% 20% 9%	6320
	11th to 20th	Day	35% 34% 15% 14% 2	6280
	21st to end	Day	34% 33% 19% 12% 1	6904
June	1st to 10th	Day	17% 63% 9% 8% 3	2950
	11th to 20th	Day	19% 63% 7% 8% 3	3000
	21st to end	Day	17% 62% 10% 9% 2	3000
July	1st to 10th	Day	13% 27% 18% 16% 17% 9%	6706
	11th to 20th	Day	9% 26% 15% 24% 24% 2	6612
	21st to end	Day	20% 29% 24% 21% 6%	6681
August	1st to 10th	Day	11% 37% 9% 28% 14% 1	4461
	11th to 20th	Day	28% 39% 16% 14% 4 1	4195
	21st to end	Day	29% 38% 9% 16% 8%	4510
September	1st to 10th	Day	19% 59% 10% 7% 5% 1	2400
	11th to 20th	Day	21% 58% 7% 7% 7%	2400
	21st to end	Day	20% 58% 9% 8% 5%	2106
October	1st to 10th	Day	31% 40% 13% 14% 2	3280
	11th to 20th	Day	42% 37% 7% 8% 6%	3261
	21st to end	Day	43% 39% 6% 7% 4	3363
November	1st to 10th	Day	31% 56% 9% 4	1653
	11th to 20th	Day	28% 56% 5% 7% 3 1	1680
	21st to end	Day	28% 57% 5% 5% 4	1680
December	1st to 10th	Day	37% 38% 7% 12% 5%	2700
	11th to 20th	Day	55% 33% 5% 6% 1	2897
	21st to end	Day	57% 30% 8% 4 1	3575
January	1st to 10th	Night	63% 24% 6% 6% 1	8770
	11th to 20th	Night	40% 26% 11% 15% 9%	8538
	21st to end	Night	47% 25% 8% 14% 5%	8863
February	1st to 10th	Night	28% 60% 4 3 4 2	2730
	11th to 20th	Night	28% 60% 3 6% 2 1	2599
	21st to end	Night	24% 62% 4 6% 3	2101
March	1st to 10th	Night	42% 33% 10% 11% 4	5244
	11th to 20th	Night	37% 32% 12% 18% 1	5000
	21st to end	Night	51% 32% 9% 7% 1	5324
April	1st to 10th	Night	24% 64% 5% 6% 1	2000
	11th to 20th	Night	20% 64% 5% 6% 3 1	1916
	21st to end	Night	22% 63% 5% 8% 3	1750
May	1st to 10th	Night	28% 30% 7% 28% 7%	3637
	11th to 20th	Night	34% 33% 17% 12% 4	3616
	21st to end	Night	36% 35% 17% 11% 1	3972
June	1st to 10th	Night	17% 62% 9% 8% 3	1447
	11th to 20th	Night	18% 63% 7% 10% 2 1	1400
	21st to end	Night	18% 62% 10% 9% 2	1400
July	1st to 10th	Night	13% 28% 15% 20% 15% 9%	3145
	11th to 20th	Night	7% 27% 12% 24% 27% 3	3224
	21st to end	Night	20% 27% 18% 23% 11%	3857
August	1st to 10th	Night	8% 36% 9% 28% 18% 1	2662
	11th to 20th	Night	28% 38% 16% 14% 4 1	2929
	21st to end	Night	26% 38% 10% 18% 8% 1	3401
September	1st to 10th	Night	16% 59% 9% 9% 5% 1	2000
	11th to 20th	Night	20% 58% 7% 7% 7% 1	2000
	21st to end	Night	20% 58% 6% 13% 4	2289
October	1st to 10th	Night	28% 39% 16% 15% 1	3920
	11th to 20th	Night	37% 38% 9% 12% 4	3897
	21st to end	Night	40% 39% 8% 9% 4	4442
November	1st to 10th	Night	33% 54% 7% 5% 1	2860
	11th to 20th	Night	30% 55% 4 5% 3 2	2940
	21st to end	Night	30% 56% 4 5% 4 1	2940
December	1st to 10th	Night	39% 38% 8% 11% 3	4700
	11th to 20th	Night	54% 33% 7% 5% 2	5522
	21st to end	Night	54% 30% 8% 6% 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	40% 14% 19% 13% 10% 5%	220
	11th to 20th	Day	26% 15% 19% 20% 13% 7%	220
	21st to end	Day	35% 7% 22% 17% 14% 5%	286
February	1st to 10th	Day	36% 10% 19% 21% 12% 2	430
	11th to 20th	Day	33% 10% 19% 24% 13% 2	411
	21st to end	Day	34% 10% 20% 20% 13% 3	354
March	1st to 10th	Day	32% 8% 22% 21% 14% 3	500
	11th to 20th	Day	32% 8% 17% 21% 15% 7%	500
	21st to end	Day	31% 9% 21% 24% 13% 3	550
April	1st to 10th	Day	28% 10% 21% 24% 13% 4	500
	11th to 20th	Day	21% 10% 25% 23% 15% 6%	492
	21st to end	Day	27% 8% 20% 24% 17% 5%	500
May	1st to 10th	Day	17% 7% 20% 30% 23% 3	503
	11th to 20th	Day	22% 5% 16% 28% 23% 6%	528
	21st to end	Day	20% 4 22% 29% 17% 8%	573
June	1st to 10th	Day	19% 5% 24% 32% 15% 4	680
	11th to 20th	Day	19% 7% 24% 34% 13% 3	730
	21st to end	Day	13% 5% 22% 30% 22% 7%	730
July	1st to 10th	Day	10% 3 20% 36% 23% 7%	721
	11th to 20th	Day	7% 5% 17% 36% 27% 8%	683
	21st to end	Day	6% 3 14% 32% 30% 15%	575
August	1st to 10th	Day	10% 4 9% 30% 34% 14%	527
	11th to 20th	Day	8% 2 12% 30% 35% 13%	517
	21st to end	Day	11% 4 15% 32% 28% 10%	583
September	1st to 10th	Day	15% 3 13% 30% 30% 8%	530
	11th to 20th	Day	14% 5% 18% 25% 32% 6%	530
	21st to end	Day	22% 7% 17% 26% 22% 8%	530
October	1st to 10th	Day	23% 8% 15% 25% 21% 9%	530
	11th to 20th	Day	32% 9% 17% 18% 16% 7%	530
	21st to end	Day	35% 9% 21% 18% 13% 5%	463
November	1st to 10th	Day	36% 9% 26% 15% 13% 2	223
	11th to 20th	Day	36% 10% 20% 15% 13% 6%	220
	21st to end	Day	34% 13% 20% 16% 9% 9%	220
December	1st to 10th	Day	40% 11% 13% 10% 15% 11%	220
	11th to 20th	Day	43% 13% 20% 16% 7% 1	220
	21st to end	Day	40% 11% 20% 20% 7% 2	242
January	1st to 10th	Night	40% 13% 18% 16% 11% 2	950
	11th to 20th	Night	37% 8% 12% 20% 20% 2	898
	21st to end	Night	34% 8% 15% 22% 17% 4	924
February	1st to 10th	Night	36% 10% 15% 24% 11% 3	840
	11th to 20th	Night	31% 8% 17% 25% 16% 2	804
	21st to end	Night	36% 10% 17% 21% 13% 3	660
March	1st to 10th	Night	31% 11% 19% 23% 14% 3	800
	11th to 20th	Night	32% 10% 17% 22% 16% 4	800
	21st to end	Night	35% 10% 15% 27% 11% 2	880
April	1st to 10th	Night	31% 8% 16% 26% 16% 3	800
	11th to 20th	Night	24% 9% 19% 28% 15% 4	728
	21st to end	Night	28% 7% 19% 27% 15% 4	550
May	1st to 10th	Night	19% 9% 16% 31% 24% 3	400
	11th to 20th	Night	22% 5% 14% 26% 26% 7%	394
	21st to end	Night	19% 5% 17% 31% 22% 5%	433
June	1st to 10th	Night	21% 6% 19% 31% 22% 2	400
	11th to 20th	Night	21% 8% 23% 30% 16% 3	400
	21st to end	Night	17% 5% 17% 34% 23% 5%	400
July	1st to 10th	Night	11% 3 19% 33% 29% 4	390
	11th to 20th	Night	10% 4 17% 35% 30% 4	388
	21st to end	Night	6% 4 18% 28% 37% 7%	438
August	1st to 10th	Night	9% 3 10% 28% 41% 9%	433
	11th to 20th	Night	10% 1 8% 26% 41% 14%	594
	21st to end	Night	13% 2 15% 28% 34% 8%	751
September	1st to 10th	Night	10% 2 11% 35% 34% 9%	800
	11th to 20th	Night	17% 5% 9% 25% 30% 14%	800
	21st to end	Night	19% 5% 16% 27% 26% 8%	800
October	1st to 10th	Night	20% 7% 11% 25% 28% 9%	800
	11th to 20th	Night	29% 7% 13% 23% 21% 7%	800
	21st to end	Night	30% 11% 15% 24% 16% 4	880
November	1st to 10th	Night	36% 10% 18% 24% 12% 1	820
	11th to 20th	Night	37% 11% 16% 20% 14% 2	840
	21st to end	Night	35% 10% 19% 19% 12% 5%	840
December	1st to 10th	Night	32% 9% 14% 23% 18% 4	840
	11th to 20th	Night	40% 11% 20% 20% 9% 1	890
	21st to end	Night	37% 13% 21% 18% 10% 1	1045

Page generated at 2026-02-12 22:42:16. Version ac07

Copyright © 2026 Attilla Danko.