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 2024-11-30.

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% 9% 3 7% 5% 4 4 4 5% 6% 35%	105744
	Night	20% 11% 3 7% 5% 4 4 3 5% 6% 31%	102449
Transparency	Day	26% 48% 9% 11% 6% 1	105496
	Night	29% 48% 8% 10% 4 1	102343
Seeing	Day	22% 7% 19% 26% 20% 7%	15305
	Night	27% 8% 16% 25% 20% 5%	23614

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	28% 19% 4 9% 6% 5% 5% 3 4 4 13%	2219
	11th to 20th	Day	22% 14% 5% 8% 5% 5% 4 3 6% 6% 22%	2336
	21st to end	Day	29% 18% 5% 11% 6% 6% 4 4 4 4 9%	2859
February	1st to 10th	Day	25% 17% 4 8% 6% 5% 5% 4 4 6% 16%	1710
	11th to 20th	Day	23% 15% 4 10% 6% 4 5% 4 4 5% 21%	1665
	21st to end	Day	22% 15% 5% 9% 5% 5% 5% 3 5% 5% 21%	1454
March	1st to 10th	Day	17% 12% 4 10% 7% 6% 5% 5% 7% 9% 19%	3228
	11th to 20th	Day	15% 11% 3 6% 5% 5% 5% 4 6% 6% 34%	3490
	21st to end	Day	20% 12% 3 10% 7% 6% 6% 5% 5% 6% 21%	3938
April	1st to 10th	Day	19% 13% 4 8% 6% 5% 5% 5% 7% 7% 21%	2280
	11th to 20th	Day	17% 12% 3 7% 6% 5% 6% 3 6% 7% 28%	2306
	21st to end	Day	19% 10% 3 8% 6% 5% 5% 4 6% 7% 27%	2516
May	1st to 10th	Day	17% 8% 2 6% 4 4 4 3 5% 6% 41%	4420
	11th to 20th	Day	12% 5% 2 5% 5% 4 5% 4 6% 10% 43%	4377
	21st to end	Day	26% 10% 3 7% 5% 4 4 3 5% 6% 26%	4813
June	1st to 10th	Day	20% 7% 2 6% 6% 4 5% 4 5% 7% 34%	2802
	11th to 20th	Day	17% 9% 3 7% 6% 5% 5% 4 6% 7% 32%	2850
	21st to end	Day	11% 7% 3 7% 4 4 5% 5% 6% 7% 41%	2850
July	1st to 10th	Day	6% 3 1 4 2 3 2 2 3 4 69%	4740
	11th to 20th	Day	5% 4 1 3 2 2 2 2 4 5% 68%	4681
	21st to end	Day	10% 4 2 5% 3 3 2 2 4 6% 59%	4790
August	1st to 10th	Day	5% 3 2 5% 3 3 3 3 4 7% 62%	4340
	11th to 20th	Day	11% 7% 2 6% 4 4 4 3 5% 8% 46%	4026
	21st to end	Day	14% 7% 3 7% 4 4 4 3 4 6% 45%	4373
September	1st to 10th	Day	10% 6% 2 5% 4 3 4 3 4 7% 50%	2280
	11th to 20th	Day	13% 8% 3 7% 5% 5% 5% 3 5% 7% 40%	2280
	21st to end	Day	16% 9% 3 8% 5% 5% 4 3 5% 7% 36%	2001
October	1st to 10th	Day	16% 8% 3 7% 5% 5% 6% 5% 7% 9% 30%	3180
	11th to 20th	Day	25% 11% 4 9% 5% 3 4 3 5% 6% 24%	3161
	21st to end	Day	22% 12% 4 9% 6% 6% 6% 4 5% 6% 19%	3259
November	1st to 10th	Day	28% 10% 3 9% 6% 5% 5% 4 5% 6% 18%	1573
	11th to 20th	Day	26% 11% 4 8% 5% 5% 5% 4 5% 5% 22%	1600
	21st to end	Day	27% 11% 5% 9% 6% 5% 5% 5% 5% 7% 16%	1595
December	1st to 10th	Day	23% 14% 4 8% 6% 5% 4 4 5% 6% 21%	1520
	11th to 20th	Day	24% 15% 4 12% 7% 6% 5% 4 5% 5% 13%	1790
	21st to end	Day	21% 17% 6% 13% 6% 5% 5% 4 5% 5% 12%	2442
January	1st to 10th	Night	25% 17% 5% 10% 6% 6% 5% 4 4 4 14%	4726
	11th to 20th	Night	24% 14% 4 8% 4 4 4 3 4 8% 24%	4558
	21st to end	Night	28% 16% 4 10% 6% 6% 4 3 5% 5% 13%	4796
February	1st to 10th	Night	26% 15% 4 9% 5% 4 4 3 5% 5% 20%	2470
	11th to 20th	Night	21% 16% 4 9% 5% 4 4 3 4 5% 24%	2402
	21st to end	Night	24% 15% 3 9% 6% 4 4 3 5% 5% 22%	1999
March	1st to 10th	Night	16% 13% 4 11% 6% 7% 7% 5% 6% 7% 19%	3643
	11th to 20th	Night	15% 10% 3 6% 5% 4 4 3 5% 7% 37%	3489
	21st to end	Night	25% 15% 4 8% 6% 5% 5% 4 5% 5% 19%	3715
April	1st to 10th	Night	22% 13% 3 8% 6% 5% 5% 4 6% 7% 22%	1900
	11th to 20th	Night	18% 11% 3 8% 6% 5% 5% 5% 6% 6% 29%	1819
	21st to end	Night	22% 11% 4 8% 6% 5% 3 3 5% 6% 26%	1663
May	1st to 10th	Night	16% 8% 3 6% 3 3 3 2 3 6% 46%	2540
	11th to 20th	Night	10% 5% 2 6% 5% 5% 4 4 6% 6% 46%	2516
	21st to end	Night	22% 10% 4 8% 5% 4 5% 4 6% 7% 25%	2762
June	1st to 10th	Night	20% 8% 3 8% 6% 5% 4 4 6% 4 33%	1375
	11th to 20th	Night	19% 10% 3 8% 5% 5% 5% 3 5% 8% 30%	1330
	21st to end	Night	14% 7% 2 6% 4 4 5% 4 5% 6% 44%	1330
July	1st to 10th	Night	7% 4 1 3 3 2 2 2 3 4 70%	2220
	11th to 20th	Night	5% 3 1 2 2 1 2 2 3 4 74%	2278
	21st to end	Night	11% 4 2 4 3 3 3 3 4 5% 60%	2762
August	1st to 10th	Night	5% 2 1 3 2 2 3 2 5% 6% 69%	2588
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 3 6% 52%	2812
	21st to end	Night	15% 6% 1 5% 3 3 3 3 5% 6% 48%	3297
September	1st to 10th	Night	10% 3 2 5% 4 3 4 3 5% 7% 54%	1900
	11th to 20th	Night	15% 8% 2 7% 4 4 4 4 5% 6% 41%	1900
	21st to end	Night	15% 7% 3 7% 4 4 3 3 4 7% 43%	2174
October	1st to 10th	Night	15% 6% 3 7% 5% 5% 4 4 6% 8% 38%	3800
	11th to 20th	Night	25% 9% 3 6% 4 4 4 3 5% 6% 32%	3777
	21st to end	Night	22% 12% 4 8% 6% 5% 4 3 5% 6% 24%	4304
November	1st to 10th	Night	29% 11% 3 7% 6% 5% 5% 3 5% 6% 21%	2720
	11th to 20th	Night	25% 14% 4 8% 6% 4 4 4 5% 5% 21%	2800
	21st to end	Night	26% 12% 3 8% 6% 5% 5% 4 5% 6% 20%	2800
December	1st to 10th	Night	24% 14% 4 7% 6% 4 3 3 4 5% 25%	2660
	11th to 20th	Night	24% 16% 5% 12% 7% 5% 5% 3 4 5% 15%	3410
	21st to end	Night	26% 18% 5% 10% 6% 5% 4 3 5% 5% 15%	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	47% 39% 7% 5% 2	2219
	11th to 20th	Day	36% 39% 10% 10% 5%	2358
	21st to end	Day	52% 42% 4 2	2859
February	1st to 10th	Day	26% 65% 4 3 2 1	1710
	11th to 20th	Day	27% 64% 3 3 2	1674
	21st to end	Day	23% 66% 3 4 3 1	1454
March	1st to 10th	Day	32% 45% 10% 10% 3	3228
	11th to 20th	Day	24% 43% 12% 20% 1	3490
	21st to end	Day	37% 43% 11% 7% 2	3938
April	1st to 10th	Day	22% 67% 6% 4	2280
	11th to 20th	Day	19% 67% 6% 5% 3 1	2306
	21st to end	Day	20% 66% 5% 7% 2	2516
May	1st to 10th	Day	24% 41% 10% 16% 9%	4420
	11th to 20th	Day	19% 45% 18% 16% 3	4380
	21st to end	Day	35% 43% 15% 6% 1	4814
June	1st to 10th	Day	17% 66% 8% 7% 3	2802
	11th to 20th	Day	17% 66% 7% 7% 3	2850
	21st to end	Day	15% 65% 9% 9% 2	2850
July	1st to 10th	Day	10% 36% 5% 16% 20% 12%	4666
	11th to 20th	Day	7% 36% 6% 23% 25% 2	4600
	21st to end	Day	20% 37% 17% 18% 7%	4639
August	1st to 10th	Day	10% 38% 9% 28% 14% 1	4323
	11th to 20th	Day	27% 40% 16% 13% 3 1	4065
	21st to end	Day	29% 39% 9% 15% 8%	4372
September	1st to 10th	Day	17% 62% 8% 7% 5% 1	2280
	11th to 20th	Day	20% 61% 6% 5% 7%	2280
	21st to end	Day	19% 61% 8% 7% 5%	2001
October	1st to 10th	Day	30% 41% 13% 14% 2	3180
	11th to 20th	Day	42% 38% 7% 8% 6%	3161
	21st to end	Day	42% 40% 6% 7% 4	3259
November	1st to 10th	Day	29% 58% 8% 4 1	1573
	11th to 20th	Day	26% 59% 5% 7% 3 2	1600
	21st to end	Day	26% 60% 5% 5% 5%	1595
December	1st to 10th	Day	25% 61% 3 7% 4	1520
	11th to 20th	Day	40% 50% 4 4 2	1792
	21st to end	Day	47% 41% 7% 3 2	2442
January	1st to 10th	Night	47% 40% 6% 5% 2	4726
	11th to 20th	Night	34% 40% 10% 13% 4	4598
	21st to end	Night	51% 42% 4 3	4796
February	1st to 10th	Night	24% 66% 3 3 3 1	2470
	11th to 20th	Night	25% 65% 3 4 1 1	2404
	21st to end	Night	21% 65% 4 6% 3	1999
March	1st to 10th	Night	35% 44% 8% 9% 4	3643
	11th to 20th	Night	21% 43% 14% 21% 1	3490
	21st to end	Night	41% 43% 8% 7%	3715
April	1st to 10th	Night	22% 67% 5% 6% 1	1900
	11th to 20th	Night	19% 67% 4 6% 2 1	1819
	21st to end	Night	22% 66% 3 6% 3	1663
May	1st to 10th	Night	21% 41% 8% 22% 7% 1	2540
	11th to 20th	Night	17% 44% 19% 15% 5%	2516
	21st to end	Night	34% 45% 13% 6% 1	2762
June	1st to 10th	Night	17% 65% 7% 8% 2	1375
	11th to 20th	Night	18% 66% 6% 8% 2 1	1330
	21st to end	Night	15% 65% 9% 8% 2	1330
July	1st to 10th	Night	9% 36% 5% 18% 19% 13%	2185
	11th to 20th	Night	7% 35% 5% 20% 31% 2	2236
	21st to end	Night	22% 36% 9% 18% 14%	2674
August	1st to 10th	Night	8% 37% 8% 28% 18% 1	2580
	11th to 20th	Night	27% 39% 16% 14% 4 1	2839
	21st to end	Night	26% 39% 10% 18% 7%	3297
September	1st to 10th	Night	15% 62% 8% 9% 5% 1	1900
	11th to 20th	Night	20% 61% 6% 6% 7% 1	1900
	21st to end	Night	19% 60% 6% 11% 4	2174
October	1st to 10th	Night	28% 40% 16% 15% 1	3800
	11th to 20th	Night	37% 39% 9% 12% 3	3777
	21st to end	Night	39% 40% 8% 8% 4	4304
November	1st to 10th	Night	31% 57% 6% 5% 1	2720
	11th to 20th	Night	27% 58% 4 5% 3 2	2800
	21st to end	Night	28% 59% 4 4 5% 1	2800
December	1st to 10th	Night	26% 61% 3 6% 4	2660
	11th to 20th	Night	39% 50% 6% 3 2	3407
	21st to end	Night	45% 40% 8% 6% 2	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	37% 12% 22% 11% 12% 6%	180
	11th to 20th	Day	29% 14% 20% 19% 11% 7%	180
	21st to end	Day	38% 7% 24% 16% 11% 4	237
February	1st to 10th	Day	38% 9% 18% 20% 12% 2	370
	11th to 20th	Day	34% 11% 18% 22% 13% 2	365
	21st to end	Day	34% 10% 20% 21% 13% 2	328
March	1st to 10th	Day	32% 9% 21% 21% 14% 3	460
	11th to 20th	Day	31% 7% 16% 22% 16% 7%	460
	21st to end	Day	30% 8% 20% 25% 14% 3	506
April	1st to 10th	Day	27% 10% 21% 24% 14% 4	460
	11th to 20th	Day	22% 10% 23% 23% 15% 6%	452
	21st to end	Day	28% 8% 20% 23% 17% 4	460
May	1st to 10th	Day	17% 6% 19% 30% 23% 3	463
	11th to 20th	Day	20% 4 15% 29% 25% 6%	488
	21st to end	Day	20% 4 21% 29% 17% 9%	529
June	1st to 10th	Day	21% 5% 24% 31% 15% 4	632
	11th to 20th	Day	19% 7% 24% 34% 12% 4	680
	21st to end	Day	12% 5% 23% 30% 22% 7%	680
July	1st to 10th	Day	10% 3 19% 36% 24% 8%	671
	11th to 20th	Day	8% 5% 17% 35% 27% 8%	635
	21st to end	Day	6% 3 14% 30% 31% 15%	531
August	1st to 10th	Day	10% 3 8% 29% 35% 15%	487
	11th to 20th	Day	7% 2 11% 30% 37% 14%	477
	21st to end	Day	12% 4 15% 31% 28% 9%	539
September	1st to 10th	Day	16% 3 13% 31% 28% 9%	490
	11th to 20th	Day	15% 5% 17% 25% 32% 6%	490
	21st to end	Day	22% 7% 15% 26% 23% 8%	490
October	1st to 10th	Day	23% 7% 15% 25% 21% 9%	490
	11th to 20th	Day	32% 9% 16% 19% 17% 8%	490
	21st to end	Day	33% 9% 20% 18% 14% 6%	425
November	1st to 10th	Day	36% 9% 25% 15% 13% 2	203
	11th to 20th	Day	34% 11% 21% 15% 13% 7%	200
	21st to end	Day	32% 13% 21% 16% 9% 10%	199
December	1st to 10th	Day	39% 12% 14% 10% 14% 10%	180
	11th to 20th	Day	39% 12% 22% 17% 8% 2	180
	21st to end	Day	39% 8% 23% 22% 6% 2	198
January	1st to 10th	Night	40% 12% 18% 16% 12% 3	850
	11th to 20th	Night	39% 9% 13% 18% 19% 2	808
	21st to end	Night	35% 9% 16% 21% 15% 3	836
February	1st to 10th	Night	37% 10% 14% 24% 12% 3	760
	11th to 20th	Night	31% 9% 16% 25% 17% 2	744
	21st to end	Night	36% 10% 17% 21% 13% 3	628
March	1st to 10th	Night	32% 11% 18% 23% 14% 3	760
	11th to 20th	Night	31% 9% 16% 23% 17% 4	760
	21st to end	Night	34% 10% 15% 28% 11% 2	836
April	1st to 10th	Night	32% 8% 16% 26% 16% 3	760
	11th to 20th	Night	25% 9% 18% 28% 15% 4	691
	21st to end	Night	29% 6% 20% 28% 14% 3	523
May	1st to 10th	Night	18% 9% 16% 31% 23% 3	380
	11th to 20th	Night	21% 5% 14% 26% 27% 7%	374
	21st to end	Night	20% 5% 17% 31% 22% 5%	411
June	1st to 10th	Night	22% 6% 20% 31% 21% 2	380
	11th to 20th	Night	21% 8% 22% 30% 15% 3	380
	21st to end	Night	16% 4 18% 34% 23% 4	380
July	1st to 10th	Night	11% 3 19% 34% 30% 4	370
	11th to 20th	Night	10% 4 17% 33% 31% 5%	368
	21st to end	Night	7% 4 17% 28% 37% 7%	416
August	1st to 10th	Night	9% 2 9% 27% 42% 9%	411
	11th to 20th	Night	9% 1 8% 25% 42% 15%	564
	21st to end	Night	13% 3 15% 29% 33% 8%	713
September	1st to 10th	Night	10% 2 11% 35% 33% 9%	760
	11th to 20th	Night	18% 5% 9% 24% 30% 14%	760
	21st to end	Night	18% 4 16% 26% 27% 8%	760
October	1st to 10th	Night	21% 6% 11% 25% 28% 10%	760
	11th to 20th	Night	29% 6% 13% 23% 21% 8%	760
	21st to end	Night	30% 11% 15% 25% 16% 4	836
November	1st to 10th	Night	36% 10% 18% 23% 12% 1	780
	11th to 20th	Night	36% 11% 17% 20% 14% 2	800
	21st to end	Night	36% 10% 19% 18% 12% 5%	800
December	1st to 10th	Night	31% 10% 14% 24% 18% 4	760
	11th to 20th	Night	39% 10% 20% 21% 9% 1	800
	21st to end	Night	38% 12% 21% 19% 10% 1	935

Page generated at 2024-11-27 14:30:50. Version ac07

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