Bangor
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bangor clear sky chart from 2005-11-06 to 2025-07-06.

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	19% 9% 3 7% 4 4 4 3 5% 6% 35%	119239
	Night	18% 9% 3 7% 4 4 4 4 5% 6% 35%	119567
Transparency	Day	47% 6% 12% 20% 12% 2	122803
	Night	47% 6% 12% 20% 12% 2	124165
Seeing	Day	25% 17% 31% 18% 7% 1	16616
	Night	23% 14% 32% 24% 6%	24930

By Month

Percentage Cloud Cover NE (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	15% 11% 4 9% 5% 5% 5% 3 4 5% 35%	3597
	11th to 20th	Day	14% 8% 3 8% 6% 5% 4 2 4 5% 40%	3570
	21st to end	Day	12% 10% 4 7% 5% 5% 4 3 4 5% 41%	4022
February	1st to 10th	Day	16% 11% 3 7% 5% 4 4 4 5% 7% 34%	1800
	11th to 20th	Day	14% 11% 3 8% 6% 5% 5% 3 5% 6% 35%	1857
	21st to end	Day	14% 11% 2 9% 6% 5% 4 4 4 6% 35%	1650
March	1st to 10th	Day	25% 12% 3 10% 5% 5% 4 2 4 4 28%	4513
	11th to 20th	Day	19% 12% 3 9% 4 4 4 3 4 6% 32%	4980
	21st to end	Day	27% 10% 3 7% 3 4 4 3 5% 6% 29%	5466
April	1st to 10th	Day	22% 11% 3 8% 5% 4 3 3 4 5% 31%	2380
	11th to 20th	Day	20% 9% 2 6% 4 4 5% 3 4 6% 37%	2551
	21st to end	Day	24% 9% 2 6% 4 4 3 3 4 5% 36%	2600
May	1st to 10th	Day	29% 10% 3 7% 4 4 4 3 4 6% 25%	5886
	11th to 20th	Day	21% 9% 3 8% 5% 5% 5% 4 5% 6% 30%	5861
	21st to end	Day	19% 8% 3 7% 4 5% 5% 4 6% 7% 32%	7182
June	1st to 10th	Day	24% 8% 3 6% 5% 4 4 4 5% 8% 30%	3000
	11th to 20th	Day	19% 7% 2 6% 5% 4 4 4 5% 8% 35%	3000
	21st to end	Day	24% 8% 2 6% 4 4 4 5% 6% 6% 30%	3000
July	1st to 10th	Day	14% 6% 2 6% 5% 5% 6% 5% 7% 9% 36%	4680
	11th to 20th	Day	13% 7% 2 6% 5% 5% 5% 5% 7% 9% 37%	4440
	21st to end	Day	17% 7% 2 6% 5% 5% 5% 4 5% 7% 36%	4757
August	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	4105
	11th to 20th	Day	16% 8% 3 8% 4 5% 5% 4 6% 8% 32%	4045
	21st to end	Day	11% 6% 2 7% 4 4 4 3 7% 9% 43%	4515
September	1st to 10th	Day	12% 5% 2 5% 5% 4 4 3 5% 8% 49%	2187
	11th to 20th	Day	14% 5% 2 5% 4 4 3 2 4 5% 52%	2090
	21st to end	Day	16% 7% 3 5% 4 3 4 3 5% 7% 43%	2090
October	1st to 10th	Day	18% 6% 2 6% 5% 4 4 2 6% 6% 40%	2035
	11th to 20th	Day	19% 7% 2 6% 4 4 4 3 4 6% 41%	1882
	21st to end	Day	22% 9% 3 7% 4 4 3 3 5% 6% 35%	1881
November	1st to 10th	Day	18% 7% 2 6% 5% 4 5% 4 6% 6% 39%	1761
	11th to 20th	Day	20% 7% 2 5% 3 4 5% 4 4 7% 39%	1750
	21st to end	Day	22% 8% 2 5% 4 3 3 3 4 5% 39%	1600
December	1st to 10th	Day	18% 11% 2 5% 4 3 4 3 5% 7% 38%	2394
	11th to 20th	Day	20% 8% 2 5% 4 3 3 3 4 5% 43%	2618
	21st to end	Day	21% 11% 4 6% 4 3 4 3 5% 5% 35%	3494
January	1st to 10th	Night	13% 12% 4 9% 5% 4 4 3 4 6% 37%	6349
	11th to 20th	Night	14% 11% 4 9% 5% 5% 5% 4 6% 6% 30%	6315
	21st to end	Night	11% 11% 3 8% 5% 4 5% 4 5% 6% 37%	6932
February	1st to 10th	Night	15% 11% 4 8% 5% 5% 4 4 6% 6% 32%	2600
	11th to 20th	Night	12% 11% 3 8% 5% 5% 4 3 5% 5% 38%	2427
	21st to end	Night	15% 12% 2 8% 6% 4 4 3 5% 5% 36%	1980
March	1st to 10th	Night	27% 12% 3 7% 4 4 3 3 4 4 28%	5326
	11th to 20th	Night	18% 11% 3 7% 5% 5% 5% 5% 5% 7% 31%	4979
	21st to end	Night	26% 9% 3 7% 4 4 5% 3 6% 6% 27%	5466
April	1st to 10th	Night	23% 12% 3 7% 3 3 3 3 4 5% 34%	2018
	11th to 20th	Night	20% 8% 2 7% 5% 4 5% 5% 6% 7% 33%	1797
	21st to end	Night	25% 8% 3 5% 4 3 4 3 6% 5% 33%	1800
May	1st to 10th	Night	27% 10% 3 7% 4 4 4 3 6% 7% 26%	4054
	11th to 20th	Night	22% 7% 3 7% 5% 4 5% 4 6% 7% 29%	4033
	21st to end	Night	16% 8% 3 7% 4 5% 5% 4 6% 7% 35%	3730
June	1st to 10th	Night	22% 9% 3 7% 4 4 5% 4 5% 8% 29%	1400
	11th to 20th	Night	17% 7% 2 6% 3 4 4 5% 6% 10% 36%	1400
	21st to end	Night	23% 9% 2 7% 4 4 4 4 6% 7% 30%	1400
July	1st to 10th	Night	12% 6% 2 6% 5% 6% 7% 5% 8% 9% 34%	2390
	11th to 20th	Night	14% 7% 3 8% 5% 5% 5% 4 7% 8% 35%	2520
	21st to end	Night	14% 6% 2 5% 5% 4 5% 4 7% 8% 40%	2762
August	1st to 10th	Night	19% 8% 2 8% 6% 5% 4 4 6% 7% 31%	2825
	11th to 20th	Night	15% 8% 3 8% 5% 5% 6% 5% 6% 7% 31%	2782
	21st to end	Night	11% 6% 2 7% 4 4 5% 4 5% 8% 44%	3124
September	1st to 10th	Night	13% 5% 2 5% 3 3 4 4 5% 7% 50%	1992
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 5% 6% 51%	2090
	21st to end	Night	17% 6% 2 5% 4 3 4 3 6% 7% 43%	2090
October	1st to 10th	Night	19% 6% 2 5% 4 5% 4 4 5% 5% 40%	2144
	11th to 20th	Night	18% 6% 1 7% 4 4 4 3 5% 6% 41%	2294
	21st to end	Night	25% 8% 3 6% 4 4 3 3 4 6% 35%	2717
November	1st to 10th	Night	18% 7% 2 6% 4 5% 3 3 5% 5% 42%	2537
	11th to 20th	Night	18% 7% 2 5% 4 5% 4 4 5% 7% 39%	2646
	21st to end	Night	19% 9% 3 5% 4 3 4 4 6% 6% 37%	2800
December	1st to 10th	Night	18% 9% 3 7% 4 4 5% 4 6% 6% 35%	4778
	11th to 20th	Night	23% 8% 2 5% 3 3 4 3 4 5% 41%	5591
	21st to end	Night	22% 10% 3 6% 4 4 4 3 5% 5% 34%	7479

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	51% 5% 11% 23% 9% 1	3598
	11th to 20th	Day	46% 5% 12% 25% 10% 2	3600
	21st to end	Day	44% 5% 11% 16% 18% 6%	4022
February	1st to 10th	Day	48% 6% 12% 18% 13% 3	1800
	11th to 20th	Day	49% 5% 11% 20% 12% 2	1865
	21st to end	Day	49% 6% 11% 19% 11% 5%	1650
March	1st to 10th	Day	60% 4 8% 9% 14% 5%	4516
	11th to 20th	Day	51% 6% 16% 16% 10% 1	4980
	21st to end	Day	56% 4 7% 16% 15% 3	5466
April	1st to 10th	Day	54% 5% 9% 15% 13% 4	2380
	11th to 20th	Day	47% 6% 10% 22% 13% 2	2551
	21st to end	Day	50% 4 8% 19% 15% 4	2600
May	1st to 10th	Day	59% 8% 10% 15% 7% 1	5897
	11th to 20th	Day	51% 9% 13% 17% 7% 3	5865
	21st to end	Day	48% 9% 13% 16% 12% 2	7182
June	1st to 10th	Day	52% 7% 12% 18% 10% 1	3000
	11th to 20th	Day	45% 8% 12% 19% 15% 2	3000
	21st to end	Day	52% 8% 11% 18% 9% 2	3000
July	1st to 10th	Day	44% 7% 13% 25% 11%	4609
	11th to 20th	Day	41% 8% 15% 25% 11% 1	4365
	21st to end	Day	46% 7% 12% 22% 12% 1	4605
August	1st to 10th	Day	49% 7% 14% 24% 5%	4092
	11th to 20th	Day	48% 8% 16% 20% 8%	4084
	21st to end	Day	35% 6% 13% 26% 18% 1	4515
September	1st to 10th	Day	32% 6% 16% 27% 17% 1	2187
	11th to 20th	Day	35% 4 11% 27% 20% 3	2090
	21st to end	Day	40% 5% 12% 26% 16% 1	2090
October	1st to 10th	Day	52% 7% 9% 20% 12% 1	3386
	11th to 20th	Day	36% 4 11% 31% 17% 1	3110
	21st to end	Day	36% 4 16% 23% 19% 1	3081
November	1st to 10th	Day	43% 6% 14% 22% 13% 1	1761
	11th to 20th	Day	44% 5% 12% 21% 16% 3	1750
	21st to end	Day	46% 5% 16% 23% 9% 1	1600
December	1st to 10th	Day	45% 4 19% 18% 13% 1	2394
	11th to 20th	Day	45% 4 13% 16% 15% 7%	2618
	21st to end	Day	51% 5% 10% 19% 12% 3	3494
January	1st to 10th	Night	47% 6% 12% 24% 10% 1	6349
	11th to 20th	Night	51% 6% 14% 18% 8% 2	6360
	21st to end	Night	45% 5% 9% 21% 15% 5%	6932
February	1st to 10th	Night	50% 6% 12% 17% 13% 2	2600
	11th to 20th	Night	48% 5% 11% 19% 14% 2	2430
	21st to end	Night	48% 6% 9% 19% 14% 4	1980
March	1st to 10th	Night	59% 3 7% 13% 13% 5%	5336
	11th to 20th	Night	49% 9% 19% 15% 7% 1	4980
	21st to end	Night	55% 5% 7% 16% 15% 2	5466
April	1st to 10th	Night	54% 3 9% 14% 16% 3	2018
	11th to 20th	Night	48% 6% 11% 20% 13% 2	1797
	21st to end	Night	51% 7% 10% 16% 13% 3	1800
May	1st to 10th	Night	56% 7% 15% 14% 8% 1	4060
	11th to 20th	Night	50% 9% 14% 18% 8% 1	4034
	21st to end	Night	44% 9% 16% 20% 10%	3731
June	1st to 10th	Night	51% 9% 12% 19% 9% 1	1400
	11th to 20th	Night	42% 9% 17% 20% 11% 2	1400
	21st to end	Night	51% 10% 11% 17% 9% 2	1400
July	1st to 10th	Night	44% 8% 15% 22% 11%	2351
	11th to 20th	Night	44% 8% 15% 25% 8%	2472
	21st to end	Night	42% 7% 15% 24% 11% 1	2674
August	1st to 10th	Night	52% 9% 13% 19% 6%	2813
	11th to 20th	Night	49% 8% 15% 18% 10%	2809
	21st to end	Night	35% 8% 15% 23% 17% 1	3124
September	1st to 10th	Night	33% 8% 14% 30% 14% 1	1992
	11th to 20th	Night	33% 6% 12% 28% 18% 2	2090
	21st to end	Night	39% 7% 10% 28% 14% 1	2090
October	1st to 10th	Night	44% 6% 14% 23% 12% 1	3573
	11th to 20th	Night	36% 4 11% 29% 19% 1	3805
	21st to end	Night	40% 4 13% 27% 13% 2	4467
November	1st to 10th	Night	44% 6% 13% 23% 13% 1	2537
	11th to 20th	Night	44% 5% 10% 22% 16% 2	2646
	21st to end	Night	45% 6% 16% 19% 12% 1	2800
December	1st to 10th	Night	47% 5% 11% 27% 10%	4778
	11th to 20th	Night	46% 4 11% 20% 17% 2	5592
	21st to end	Night	51% 5% 10% 17% 15% 1	7479

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	32% 17% 33% 17% 3	200
	11th to 20th	Day	31% 20% 35% 12% 2 2	200
	21st to end	Day	21% 22% 37% 16% 3	243
February	1st to 10th	Day	29% 20% 28% 20% 3	400
	11th to 20th	Day	28% 25% 36% 10% 2	449
	21st to end	Day	26% 22% 32% 18% 2	414
March	1st to 10th	Day	31% 22% 31% 14% 2	500
	11th to 20th	Day	26% 25% 31% 14% 4 1	500
	21st to end	Day	34% 22% 26% 12% 4 2	550
April	1st to 10th	Day	37% 22% 25% 10% 4 1	500
	11th to 20th	Day	34% 24% 25% 11% 5% 1	492
	21st to end	Day	29% 23% 30% 14% 3 1	500
May	1st to 10th	Day	32% 20% 31% 13% 3 1	503
	11th to 20th	Day	24% 17% 35% 17% 5% 1	527
	21st to end	Day	24% 18% 33% 18% 6%	680
June	1st to 10th	Day	26% 15% 31% 20% 8% 1	730
	11th to 20th	Day	23% 15% 29% 22% 10% 1	730
	21st to end	Day	28% 13% 30% 21% 8% 1	730
July	1st to 10th	Day	19% 12% 36% 21% 10% 1	609
	11th to 20th	Day	17% 10% 42% 21% 9% 2	484
	21st to end	Day	16% 12% 39% 24% 8% 2	532
August	1st to 10th	Day	15% 11% 34% 29% 9% 1	486
	11th to 20th	Day	18% 10% 32% 26% 10% 3	479
	21st to end	Day	16% 13% 32% 24% 11% 3	539
September	1st to 10th	Day	14% 14% 35% 24% 10% 2	490
	11th to 20th	Day	21% 10% 30% 20% 13% 6%	490
	21st to end	Day	18% 15% 33% 19% 10% 6%	490
October	1st to 10th	Day	21% 16% 26% 20% 13% 3	460
	11th to 20th	Day	24% 17% 29% 20% 8% 3	390
	21st to end	Day	30% 17% 29% 18% 5% 1	429
November	1st to 10th	Day	26% 16% 26% 23% 6% 2	395
	11th to 20th	Day	30% 16% 33% 14% 7%	400
	21st to end	Day	31% 19% 26% 20% 5%	400
December	1st to 10th	Day	28% 19% 34% 14% 5%	275
	11th to 20th	Day	35% 25% 28% 11% 2 1	200
	21st to end	Day	32% 23% 27% 13% 5% 1	220
January	1st to 10th	Night	23% 21% 34% 19% 3	800
	11th to 20th	Night	25% 20% 32% 20% 4	800
	21st to end	Night	18% 20% 38% 20% 4	880
February	1st to 10th	Night	24% 19% 34% 20% 3	800
	11th to 20th	Night	22% 23% 37% 17% 2	783
	21st to end	Night	24% 16% 37% 20% 3	660
March	1st to 10th	Night	28% 17% 34% 20% 1	800
	11th to 20th	Night	23% 20% 32% 20% 5%	800
	21st to end	Night	26% 18% 31% 20% 5%	880
April	1st to 10th	Night	30% 18% 32% 17% 2	800
	11th to 20th	Night	24% 16% 37% 19% 4	613
	21st to end	Night	30% 14% 32% 20% 5%	600
May	1st to 10th	Night	26% 14% 33% 24% 4	600
	11th to 20th	Night	26% 12% 36% 23% 4	592
	21st to end	Night	19% 11% 35% 29% 6%	465
June	1st to 10th	Night	24% 8% 32% 29% 7%	400
	11th to 20th	Night	20% 6% 34% 32% 9%	400
	21st to end	Night	28% 6% 25% 35% 5%	400
July	1st to 10th	Night	16% 5% 36% 35% 8%	380
	11th to 20th	Night	16% 3 30% 39% 11%	368
	21st to end	Night	19% 4 30% 37% 11% 1	427
August	1st to 10th	Night	16% 5% 31% 38% 9%	568
	11th to 20th	Night	16% 6% 31% 36% 10% 1	562
	21st to end	Night	15% 7% 28% 37% 11% 1	627
September	1st to 10th	Night	16% 6% 33% 33% 11% 1	760
	11th to 20th	Night	18% 9% 27% 27% 16% 3	760
	21st to end	Night	18% 10% 31% 29% 11% 1	760
October	1st to 10th	Night	22% 9% 28% 27% 14% 1	760
	11th to 20th	Night	21% 13% 30% 25% 9% 1	760
	21st to end	Night	28% 16% 31% 20% 5%	836
November	1st to 10th	Night	23% 13% 32% 24% 7% 1	780
	11th to 20th	Night	24% 16% 33% 20% 7% 1	824
	21st to end	Night	28% 19% 29% 20% 4	900
December	1st to 10th	Night	28% 14% 34% 19% 5%	900
	11th to 20th	Night	25% 22% 32% 18% 3	900
	21st to end	Night	29% 18% 31% 18% 3	985

Page generated at 2025-07-03 01:30:14. Version ac07

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