Mahone Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mahone Bay clear sky chart from 2005-11-06 to 2026-05-02.

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% 10% 4 8% 5% 4 4 3 5% 7% 29%	132713
	Night	20% 10% 3 8% 5% 5% 4 4 5% 6% 29%	129896
Transparency	Day	53% 6% 12% 19% 10% 1	136301
	Night	53% 6% 11% 19% 10% 1	134396
Seeing	Day	26% 18% 32% 17% 5% 1	19272
	Night	25% 16% 31% 21% 6%	26842

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	14% 13% 5% 14% 9% 7% 6% 4 5% 5% 19%	4690
	11th to 20th	Day	17% 14% 7% 16% 9% 6% 6% 4 5% 5% 12%	4993
	21st to end	Day	14% 9% 4 11% 8% 6% 6% 4 6% 6% 24%	5781
February	1st to 10th	Day	19% 12% 5% 11% 6% 5% 5% 3 5% 5% 22%	1890
	11th to 20th	Day	16% 11% 4 11% 8% 6% 5% 4 6% 5% 24%	1843
	21st to end	Day	13% 13% 5% 8% 6% 5% 3 4 5% 7% 32%	1593
March	1st to 10th	Day	23% 12% 4 11% 6% 5% 4 3 3 4 24%	5040
	11th to 20th	Day	17% 15% 5% 8% 4 4 3 3 5% 6% 31%	5090
	21st to end	Day	26% 13% 4 10% 5% 4 4 3 4 5% 21%	5587
April	1st to 10th	Day	25% 14% 4 8% 5% 3 4 2 4 4 27%	2488
	11th to 20th	Day	21% 11% 3 6% 4 3 4 3 5% 5% 34%	2586
	21st to end	Day	23% 10% 2 6% 4 4 4 3 4 6% 33%	2730
May	1st to 10th	Day	28% 13% 4 8% 5% 5% 4 3 5% 6% 21%	5942
	11th to 20th	Day	25% 10% 3 8% 4 4 4 3 5% 5% 28%	6318
	21st to end	Day	19% 11% 3 7% 4 4 4 3 5% 8% 31%	6948
June	1st to 10th	Day	24% 11% 3 7% 5% 5% 4 3 5% 7% 27%	2800
	11th to 20th	Day	20% 9% 3 7% 4 4 4 3 4 6% 36%	2901
	21st to end	Day	25% 10% 3 7% 5% 4 3 4 5% 7% 26%	3000
July	1st to 10th	Day	20% 9% 3 7% 5% 5% 5% 4 6% 9% 27%	6643
	11th to 20th	Day	15% 10% 3 8% 5% 4 5% 3 5% 8% 34%	6360
	21st to end	Day	14% 7% 2 6% 5% 4 4 4 6% 9% 38%	6592
August	1st to 10th	Day	20% 11% 3 7% 4 4 5% 4 5% 7% 29%	4235
	11th to 20th	Day	15% 8% 3 7% 4 5% 4 4 6% 9% 35%	4175
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	4511
September	1st to 10th	Day	15% 7% 3 6% 4 4 4 4 5% 8% 42%	2400
	11th to 20th	Day	17% 7% 2 6% 3 4 4 3 5% 5% 45%	2294
	21st to end	Day	17% 8% 3 6% 4 3 3 3 5% 6% 42%	2154
October	1st to 10th	Day	18% 6% 3 6% 4 4 4 4 5% 7% 39%	2000
	11th to 20th	Day	19% 8% 3 6% 4 4 5% 4 6% 8% 33%	2000
	21st to end	Day	20% 10% 2 7% 5% 6% 4 3 4 6% 33%	2200
November	1st to 10th	Day	20% 10% 4 8% 5% 4 4 3 5% 7% 31%	1733
	11th to 20th	Day	22% 11% 4 8% 5% 4 4 3 6% 7% 25%	1680
	21st to end	Day	20% 12% 4 10% 6% 4 4 3 5% 5% 26%	1680
December	1st to 10th	Day	23% 11% 3 10% 6% 4 5% 4 5% 6% 22%	2690
	11th to 20th	Day	28% 10% 2 7% 6% 4 4 3 5% 6% 24%	3076
	21st to end	Day	21% 12% 4 9% 4 5% 4 3 5% 7% 26%	4070
January	1st to 10th	Night	13% 12% 5% 16% 8% 6% 6% 4 5% 6% 17%	8234
	11th to 20th	Night	21% 13% 5% 13% 7% 6% 6% 3 5% 5% 15%	7900
	21st to end	Night	12% 11% 4 10% 8% 7% 7% 5% 7% 7% 21%	8400
February	1st to 10th	Night	20% 11% 5% 10% 6% 6% 5% 5% 5% 6% 22%	2730
	11th to 20th	Night	15% 10% 4 9% 8% 6% 5% 5% 6% 7% 25%	2663
	21st to end	Night	14% 11% 4 10% 6% 6% 5% 4 5% 6% 29%	2207
March	1st to 10th	Night	24% 13% 3 9% 6% 5% 4 2 5% 4 24%	5020
	11th to 20th	Night	18% 13% 5% 9% 5% 5% 4 3 5% 6% 27%	5089
	21st to end	Night	30% 11% 4 8% 4 3 3 3 3 4 26%	5587
April	1st to 10th	Night	24% 14% 3 7% 4 4 4 3 4 6% 28%	2131
	11th to 20th	Night	25% 9% 4 5% 4 4 4 3 5% 5% 32%	1982
	21st to end	Night	25% 9% 3 7% 4 4 3 4 4 5% 33%	1890
May	1st to 10th	Night	27% 14% 4 8% 4 4 4 2 4 5% 24%	4021
	11th to 20th	Night	27% 10% 2 6% 4 4 4 3 4 5% 29%	3596
	21st to end	Night	18% 14% 4 8% 4 5% 4 3 5% 6% 31%	3948
June	1st to 10th	Night	26% 8% 2 7% 4 4 4 3 5% 7% 30%	1600
	11th to 20th	Night	21% 8% 3 6% 4 4 4 2 5% 6% 36%	1511
	21st to end	Night	27% 10% 3 6% 4 5% 4 4 5% 6% 28%	1400
July	1st to 10th	Night	18% 10% 3 8% 6% 4 5% 4 6% 8% 28%	3270
	11th to 20th	Night	18% 8% 4 7% 4 5% 4 3 6% 8% 34%	3620
	21st to end	Night	15% 7% 3 5% 4 4 4 3 6% 8% 42%	4252
August	1st to 10th	Night	17% 8% 4 8% 5% 4 4 3 5% 6% 36%	2915
	11th to 20th	Night	16% 8% 3 7% 4 4 4 3 6% 8% 37%	2872
	21st to end	Night	9% 6% 2 5% 4 4 4 4 5% 7% 51%	3385
September	1st to 10th	Night	15% 7% 2 5% 4 3 3 3 5% 7% 46%	2000
	11th to 20th	Night	18% 6% 1 4 4 3 4 3 5% 6% 46%	2103
	21st to end	Night	19% 8% 3 6% 4 3 3 3 5% 7% 39%	2245
October	1st to 10th	Night	17% 6% 2 5% 4 3 4 3 5% 7% 44%	2400
	11th to 20th	Night	19% 7% 2 6% 3 4 4 4 5% 7% 39%	2400
	21st to end	Night	23% 8% 3 5% 4 4 4 3 5% 6% 35%	2640
November	1st to 10th	Night	20% 8% 3 7% 4 4 4 4 5% 7% 35%	2782
	11th to 20th	Night	20% 10% 3 9% 5% 4 4 4 5% 6% 28%	2940
	21st to end	Night	21% 9% 3 7% 5% 5% 4 4 6% 6% 29%	2940
December	1st to 10th	Night	16% 9% 3 11% 6% 5% 5% 5% 6% 8% 26%	4720
	11th to 20th	Night	25% 10% 3 8% 5% 3 4 3 4 6% 28%	5353
	21st to end	Night	24% 9% 4 8% 5% 4 4 3 5% 6% 29%	7150

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	62% 6% 14% 14% 5%	4691
	11th to 20th	Day	69% 7% 8% 12% 4	5025
	21st to end	Day	55% 5% 9% 15% 13% 3	5781
February	1st to 10th	Day	62% 5% 10% 14% 7% 1	1890
	11th to 20th	Day	59% 7% 11% 15% 8% 1	1851
	21st to end	Day	51% 6% 11% 19% 11% 3	1593
March	1st to 10th	Day	64% 4 8% 14% 7% 3	5044
	11th to 20th	Day	51% 7% 14% 19% 7% 1	5090
	21st to end	Day	64% 3 6% 15% 11% 1	5587
April	1st to 10th	Day	59% 4 8% 14% 12% 2	2488
	11th to 20th	Day	51% 5% 10% 21% 12% 1	2586
	21st to end	Day	51% 5% 11% 18% 12% 3	2730
May	1st to 10th	Day	63% 7% 11% 12% 6% 1	5953
	11th to 20th	Day	56% 8% 10% 20% 6% 1	6322
	21st to end	Day	49% 8% 14% 19% 9% 1	6948
June	1st to 10th	Day	56% 7% 10% 18% 9% 1	2800
	11th to 20th	Day	49% 6% 12% 19% 12% 2	2901
	21st to end	Day	57% 7% 10% 15% 9% 1	3000
July	1st to 10th	Day	53% 6% 15% 15% 10% 2	6571
	11th to 20th	Day	47% 6% 11% 25% 10%	6284
	21st to end	Day	40% 7% 18% 23% 11% 1	6405
August	1st to 10th	Day	52% 8% 12% 18% 9% 1	4222
	11th to 20th	Day	44% 7% 15% 25% 8%	4214
	21st to end	Day	33% 6% 13% 27% 19% 1	4511
September	1st to 10th	Day	39% 6% 14% 24% 15% 2	2400
	11th to 20th	Day	41% 5% 10% 25% 18% 2	2294
	21st to end	Day	42% 6% 9% 24% 19% 1	2154
October	1st to 10th	Day	43% 7% 10% 26% 14% 1	3260
	11th to 20th	Day	39% 5% 10% 26% 20%	3240
	21st to end	Day	44% 5% 14% 22% 12% 3	3538
November	1st to 10th	Day	53% 6% 11% 20% 10% 1	1733
	11th to 20th	Day	57% 6% 13% 17% 7% 1	1680
	21st to end	Day	59% 6% 12% 16% 6%	1680
December	1st to 10th	Day	59% 6% 11% 20% 3	2690
	11th to 20th	Day	60% 5% 10% 15% 10%	3075
	21st to end	Day	57% 4 16% 14% 9%	4070
January	1st to 10th	Night	62% 7% 11% 16% 4	8234
	11th to 20th	Night	66% 7% 10% 12% 4	7943
	21st to end	Night	55% 7% 10% 17% 10% 1	8400
February	1st to 10th	Night	62% 6% 10% 14% 8% 1	2730
	11th to 20th	Night	56% 7% 13% 17% 8% 1	2666
	21st to end	Night	53% 6% 12% 20% 8% 1	2207
March	1st to 10th	Night	63% 4 7% 13% 11% 2	5029
	11th to 20th	Night	55% 8% 12% 17% 7% 1	5090
	21st to end	Night	62% 3 7% 17% 10% 1	5587
April	1st to 10th	Night	57% 5% 9% 14% 12% 3	2131
	11th to 20th	Night	52% 4 9% 19% 13% 1	1982
	21st to end	Night	52% 5% 10% 18% 12% 2	1890
May	1st to 10th	Night	63% 6% 9% 13% 8% 1	4027
	11th to 20th	Night	56% 6% 8% 21% 7% 3	3597
	21st to end	Night	54% 7% 11% 19% 8% 1	3949
June	1st to 10th	Night	55% 5% 12% 19% 8%	1600
	11th to 20th	Night	50% 5% 10% 22% 12% 1	1511
	21st to end	Night	59% 7% 10% 14% 10% 1	1400
July	1st to 10th	Night	55% 6% 12% 18% 8%	3233
	11th to 20th	Night	49% 6% 12% 18% 14% 1	3572
	21st to end	Night	41% 7% 12% 25% 13% 1	4126
August	1st to 10th	Night	48% 8% 14% 20% 9%	2903
	11th to 20th	Night	44% 7% 17% 24% 8%	2899
	21st to end	Night	31% 7% 14% 28% 20%	3384
September	1st to 10th	Night	38% 6% 11% 27% 16% 2	2000
	11th to 20th	Night	39% 5% 8% 29% 17% 1	2103
	21st to end	Night	45% 5% 9% 25% 16% 1	2245
October	1st to 10th	Night	43% 6% 11% 26% 14% 1	3920
	11th to 20th	Night	36% 5% 11% 28% 20%	3899
	21st to end	Night	40% 4 12% 25% 18% 1	4252
November	1st to 10th	Night	48% 7% 13% 19% 12% 1	2782
	11th to 20th	Night	54% 6% 13% 18% 8% 1	2940
	21st to end	Night	54% 7% 17% 16% 6%	2940
December	1st to 10th	Night	51% 6% 12% 25% 5%	4720
	11th to 20th	Night	56% 5% 10% 18% 10% 1	5355
	21st to end	Night	56% 6% 11% 18% 9%	7150

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% 26% 30% 10% 2	430
	11th to 20th	Day	33% 21% 28% 13% 4	430
	21st to end	Day	21% 27% 36% 14% 2	473
February	1st to 10th	Day	29% 23% 31% 14% 3	430
	11th to 20th	Day	30% 27% 28% 13% 2	426
	21st to end	Day	25% 23% 32% 16% 3 1	367
March	1st to 10th	Day	29% 26% 32% 11% 2	540
	11th to 20th	Day	29% 27% 30% 10% 4 1	540
	21st to end	Day	32% 25% 30% 9% 3	594
April	1st to 10th	Day	35% 25% 30% 8% 2	540
	11th to 20th	Day	27% 27% 33% 10% 2 1	532
	21st to end	Day	27% 22% 32% 14% 5% 1	540
May	1st to 10th	Day	30% 24% 31% 12% 2 1	524
	11th to 20th	Day	23% 20% 30% 21% 5% 1	724
	21st to end	Day	27% 16% 35% 18% 3 1	790
June	1st to 10th	Day	28% 17% 31% 19% 5%	730
	11th to 20th	Day	23% 15% 36% 20% 6% 1	730
	21st to end	Day	31% 11% 30% 22% 6% 1	730
July	1st to 10th	Day	22% 9% 35% 25% 8%	720
	11th to 20th	Day	21% 7% 36% 24% 10% 1	718
	21st to end	Day	21% 10% 36% 26% 7%	652
August	1st to 10th	Day	16% 10% 37% 27% 9% 2	526
	11th to 20th	Day	18% 9% 34% 24% 12% 2	519
	21st to end	Day	16% 12% 34% 25% 10% 3	583
September	1st to 10th	Day	16% 12% 37% 25% 8% 2	530
	11th to 20th	Day	22% 14% 30% 20% 9% 5%	530
	21st to end	Day	20% 13% 35% 21% 9% 2	504
October	1st to 10th	Day	20% 13% 33% 21% 10% 2	420
	11th to 20th	Day	22% 20% 31% 18% 6% 3	420
	21st to end	Day	26% 20% 32% 16% 6% 1	462
November	1st to 10th	Day	24% 20% 33% 15% 6% 1	425
	11th to 20th	Day	35% 23% 24% 13% 5%	430
	21st to end	Day	32% 22% 32% 12% 3	430
December	1st to 10th	Day	35% 20% 30% 13% 3	430
	11th to 20th	Day	37% 26% 25% 10% 2	430
	21st to end	Day	32% 25% 27% 13% 3	473
January	1st to 10th	Night	28% 23% 34% 14% 2	950
	11th to 20th	Night	30% 18% 32% 17% 2	889
	21st to end	Night	25% 25% 31% 15% 3	924
February	1st to 10th	Night	28% 20% 33% 16% 3	840
	11th to 20th	Night	26% 25% 32% 14% 2	823
	21st to end	Night	22% 21% 35% 18% 4	692
March	1st to 10th	Night	24% 24% 35% 15% 2	840
	11th to 20th	Night	25% 20% 30% 21% 5%	840
	21st to end	Night	28% 21% 31% 15% 5%	924
April	1st to 10th	Night	34% 17% 31% 15% 3	661
	11th to 20th	Night	27% 19% 36% 16% 3	624
	21st to end	Night	27% 15% 32% 20% 5% 1	630
May	1st to 10th	Night	29% 15% 31% 19% 5% 1	604
	11th to 20th	Night	28% 10% 30% 24% 7% 1	592
	21st to end	Night	21% 11% 37% 24% 5%	649
June	1st to 10th	Night	30% 9% 33% 23% 6%	600
	11th to 20th	Night	23% 10% 35% 26% 6%	511
	21st to end	Night	32% 7% 22% 32% 8% 1	400
July	1st to 10th	Night	19% 5% 33% 31% 11%	433
	11th to 20th	Night	19% 7% 30% 31% 12% 1	582
	21st to end	Night	20% 5% 28% 35% 11%	656
August	1st to 10th	Night	16% 6% 27% 35% 14% 1	598
	11th to 20th	Night	21% 6% 24% 34% 15% 1	592
	21st to end	Night	15% 7% 32% 32% 12% 2	660
September	1st to 10th	Night	18% 8% 33% 30% 12% 1	600
	11th to 20th	Night	20% 9% 28% 28% 14% 2	703
	21st to end	Night	24% 11% 31% 24% 10% 1	800
October	1st to 10th	Night	20% 11% 33% 26% 9% 1	800
	11th to 20th	Night	22% 16% 33% 19% 9% 1	800
	21st to end	Night	28% 16% 32% 18% 5%	880
November	1st to 10th	Night	27% 16% 31% 19% 5% 1	900
	11th to 20th	Night	28% 20% 28% 19% 5%	950
	21st to end	Night	27% 24% 28% 16% 5%	950
December	1st to 10th	Night	29% 19% 34% 14% 4	950
	11th to 20th	Night	32% 25% 28% 12% 2	950
	21st to end	Night	28% 23% 30% 16% 2	1045

Page generated at 2026-04-29 03:21:46. Version ac07

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