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 2025-01-07.

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	20% 10% 3 8% 5% 4 4 3 5% 7% 30%	105638
	Night	20% 10% 3 8% 5% 4 4 4 5% 6% 30%	103482
Transparency	Day	52% 7% 12% 18% 10% 1	109238
	Night	52% 6% 12% 19% 10% 1	107972
Seeing	Day	26% 18% 32% 17% 5% 1	17481
	Night	25% 16% 31% 21% 6%	25062

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	16% 11% 4 10% 7% 5% 5% 4 6% 6% 25%	2574
	11th to 20th	Day	17% 12% 6% 13% 8% 5% 6% 4 6% 6% 18%	2689
	21st to end	Day	20% 11% 4 9% 6% 5% 4 4 6% 6% 26%	3124
February	1st to 10th	Day	21% 13% 4 10% 6% 5% 5% 3 5% 5% 22%	1710
	11th to 20th	Day	17% 12% 4 11% 8% 6% 5% 4 5% 5% 23%	1663
	21st to end	Day	13% 13% 5% 7% 7% 5% 2 4 5% 7% 32%	1445
March	1st to 10th	Day	26% 13% 4 8% 5% 4 4 3 3 5% 26%	3430
	11th to 20th	Day	17% 15% 6% 9% 5% 5% 4 3 4 6% 27%	3480
	21st to end	Day	30% 13% 5% 10% 4 3 3 2 3 4 22%	3816
April	1st to 10th	Day	24% 14% 4 8% 5% 3 3 2 4 4 27%	2251
	11th to 20th	Day	21% 10% 3 6% 4 3 3 3 5% 6% 35%	2337
	21st to end	Day	23% 10% 3 6% 4 4 4 3 4 6% 33%	2470
May	1st to 10th	Day	24% 13% 4 8% 5% 5% 4 3 5% 7% 23%	4135
	11th to 20th	Day	24% 11% 3 7% 4 3 4 3 5% 6% 30%	4398
	21st to end	Day	19% 9% 2 6% 4 4 4 4 6% 8% 33%	4836
June	1st to 10th	Day	25% 11% 3 7% 5% 4 4 3 5% 7% 26%	2660
	11th to 20th	Day	21% 9% 3 7% 4 4 4 3 4 6% 35%	2756
	21st to end	Day	25% 10% 3 7% 5% 5% 3 4 5% 7% 26%	2850
July	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 4 6% 8% 30%	4639
	11th to 20th	Day	15% 11% 3 7% 5% 4 4 4 6% 9% 32%	4440
	21st to end	Day	19% 9% 3 6% 5% 4 4 4 5% 8% 32%	4578
August	1st to 10th	Day	20% 11% 3 8% 4 5% 5% 4 5% 7% 28%	4105
	11th to 20th	Day	15% 8% 3 7% 4 5% 4 4 6% 9% 34%	4045
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	4373
September	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 5% 8% 42%	2280
	11th to 20th	Day	18% 7% 2 6% 3 4 4 3 4 5% 44%	2180
	21st to end	Day	17% 8% 3 6% 4 3 3 3 4 6% 41%	2047
October	1st to 10th	Day	19% 6% 3 6% 4 4 4 4 5% 7% 37%	1900
	11th to 20th	Day	19% 7% 3 6% 4 3 5% 4 6% 9% 34%	1900
	21st to end	Day	20% 10% 2 7% 5% 5% 4 3 4 5% 33%	2090
November	1st to 10th	Day	20% 10% 4 8% 5% 4 4 3 5% 7% 31%	1649
	11th to 20th	Day	23% 10% 4 8% 5% 4 4 3 6% 7% 26%	1600
	21st to end	Day	21% 12% 4 10% 6% 4 4 3 5% 5% 26%	1600
December	1st to 10th	Day	24% 11% 3 10% 6% 4 5% 4 6% 7% 21%	2610
	11th to 20th	Day	29% 10% 3 7% 6% 4 4 3 5% 6% 24%	2996
	21st to end	Day	22% 12% 4 8% 4 4 4 3 5% 7% 26%	3982
January	1st to 10th	Night	15% 10% 4 13% 6% 5% 6% 5% 6% 6% 24%	4514
	11th to 20th	Night	17% 12% 5% 13% 7% 6% 6% 4 5% 5% 19%	4271
	21st to end	Night	18% 13% 4 9% 6% 5% 5% 4 7% 7% 22%	4532
February	1st to 10th	Night	20% 11% 4 9% 6% 6% 5% 6% 5% 6% 22%	2470
	11th to 20th	Night	16% 10% 4 9% 8% 6% 4 5% 7% 7% 23%	2403
	21st to end	Night	14% 10% 4 10% 7% 5% 5% 4 6% 6% 30%	2003
March	1st to 10th	Night	24% 13% 3 7% 6% 5% 3 3 5% 5% 27%	3410
	11th to 20th	Night	18% 14% 5% 9% 6% 5% 5% 4 5% 6% 23%	3479
	21st to end	Night	32% 10% 4 10% 4 3 2 2 3 4 25%	3816
April	1st to 10th	Night	24% 13% 3 7% 4 4 5% 3 4 6% 28%	1929
	11th to 20th	Night	24% 9% 3 6% 4 4 4 3 5% 5% 33%	1792
	21st to end	Night	26% 8% 3 6% 4 4 3 4 4 5% 32%	1710
May	1st to 10th	Night	20% 15% 4 8% 4 4 4 3 4 6% 28%	2804
	11th to 20th	Night	27% 10% 2 7% 4 4 4 3 4 6% 28%	2506
	21st to end	Night	20% 12% 4 8% 4 5% 4 3 5% 7% 30%	2749
June	1st to 10th	Night	27% 8% 2 7% 4 4 4 3 5% 6% 30%	1520
	11th to 20th	Night	21% 8% 3 6% 4 4 4 3 5% 6% 35%	1436
	21st to end	Night	27% 10% 3 6% 4 4 4 4 5% 5% 27%	1330
July	1st to 10th	Night	19% 9% 3 7% 5% 4 5% 5% 6% 8% 28%	2292
	11th to 20th	Night	18% 7% 4 7% 5% 5% 4 4 6% 9% 31%	2530
	21st to end	Night	17% 8% 3 5% 4 4 4 3 6% 7% 38%	2963
August	1st to 10th	Night	17% 9% 4 8% 5% 4 4 3 5% 6% 35%	2825
	11th to 20th	Night	16% 8% 3 7% 4 4 4 3 6% 8% 37%	2782
	21st to end	Night	9% 6% 2 5% 4 4 4 4 5% 7% 51%	3281
September	1st to 10th	Night	14% 7% 2 5% 4 3 3 3 5% 7% 46%	1900
	11th to 20th	Night	18% 7% 2 4 4 3 4 3 5% 6% 46%	1998
	21st to end	Night	20% 8% 3 6% 4 3 3 3 5% 6% 39%	2133
October	1st to 10th	Night	18% 6% 2 6% 5% 3 4 3 5% 7% 42%	2280
	11th to 20th	Night	19% 6% 1 5% 3 4 4 4 5% 7% 40%	2280
	21st to end	Night	23% 8% 3 5% 4 4 4 3 5% 6% 36%	2508
November	1st to 10th	Night	20% 7% 3 6% 5% 4 4 4 5% 7% 35%	2647
	11th to 20th	Night	20% 10% 3 8% 5% 4 4 4 5% 6% 29%	2800
	21st to end	Night	21% 9% 3 7% 5% 5% 4 4 6% 6% 28%	2800
December	1st to 10th	Night	16% 9% 3 11% 6% 6% 5% 5% 6% 8% 27%	4580
	11th to 20th	Night	25% 10% 3 7% 5% 3 4 3 4 6% 29%	5213
	21st to end	Night	24% 9% 4 8% 5% 4 4 3 5% 6% 29%	6996

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	56% 7% 17% 14% 5%	2575
	11th to 20th	Day	63% 9% 12% 13% 4	2689
	21st to end	Day	55% 7% 12% 16% 9%	3124
February	1st to 10th	Day	62% 6% 11% 13% 7% 1	1710
	11th to 20th	Day	60% 7% 10% 14% 7% 1	1671
	21st to end	Day	52% 6% 12% 18% 10% 3	1445
March	1st to 10th	Day	62% 5% 9% 17% 7% 2	3434
	11th to 20th	Day	54% 9% 12% 16% 8% 1	3480
	21st to end	Day	67% 3 6% 12% 10% 1	3816
April	1st to 10th	Day	60% 4 8% 14% 12% 2	2251
	11th to 20th	Day	49% 5% 10% 21% 12% 1	2337
	21st to end	Day	51% 5% 12% 17% 12% 3	2470
May	1st to 10th	Day	57% 8% 13% 14% 6% 1	4149
	11th to 20th	Day	54% 8% 12% 18% 7% 1	4402
	21st to end	Day	45% 10% 16% 18% 10% 1	4836
June	1st to 10th	Day	56% 7% 11% 18% 8%	2660
	11th to 20th	Day	50% 6% 12% 18% 12% 2	2756
	21st to end	Day	59% 7% 10% 14% 9% 1	2850
July	1st to 10th	Day	52% 6% 13% 16% 12% 2	4567
	11th to 20th	Day	48% 7% 13% 22% 9% 1	4364
	21st to end	Day	48% 7% 15% 19% 10% 1	4432
August	1st to 10th	Day	54% 8% 12% 17% 8% 1	4092
	11th to 20th	Day	44% 7% 15% 25% 8%	4084
	21st to end	Day	33% 6% 13% 27% 19% 1	4373
September	1st to 10th	Day	39% 7% 14% 24% 15% 2	2280
	11th to 20th	Day	42% 5% 9% 24% 17% 2	2180
	21st to end	Day	42% 6% 9% 24% 17% 1	2047
October	1st to 10th	Day	43% 7% 10% 25% 14% 1	3160
	11th to 20th	Day	38% 5% 10% 26% 20%	3140
	21st to end	Day	45% 5% 14% 22% 12% 3	3428
November	1st to 10th	Day	53% 6% 11% 20% 9% 1	1649
	11th to 20th	Day	56% 6% 14% 17% 7% 1	1600
	21st to end	Day	59% 7% 12% 16% 6%	1600
December	1st to 10th	Day	59% 6% 11% 21% 2	2610
	11th to 20th	Day	60% 5% 10% 15% 10%	2995
	21st to end	Day	56% 5% 16% 14% 9%	3982
January	1st to 10th	Night	56% 9% 13% 18% 4	4514
	11th to 20th	Night	63% 9% 12% 11% 5%	4271
	21st to end	Night	58% 7% 13% 16% 6%	4532
February	1st to 10th	Night	61% 6% 10% 14% 7% 1	2470
	11th to 20th	Night	57% 7% 13% 15% 7% 1	2406
	21st to end	Night	53% 6% 13% 19% 8% 2	2003
March	1st to 10th	Night	59% 5% 9% 17% 8% 1	3419
	11th to 20th	Night	57% 9% 11% 14% 9% 1	3480
	21st to end	Night	65% 3 8% 14% 9% 1	3816
April	1st to 10th	Night	57% 5% 9% 14% 12% 3	1929
	11th to 20th	Night	51% 5% 9% 20% 14% 2	1792
	21st to end	Night	53% 5% 10% 17% 11% 3	1710
May	1st to 10th	Night	57% 8% 13% 16% 6%	2810
	11th to 20th	Night	56% 8% 9% 20% 7% 1	2507
	21st to end	Night	54% 8% 12% 19% 7% 1	2750
June	1st to 10th	Night	56% 5% 13% 18% 8%	1520
	11th to 20th	Night	50% 6% 11% 21% 11% 1	1436
	21st to end	Night	60% 7% 10% 13% 9% 1	1330
July	1st to 10th	Night	54% 7% 13% 16% 9% 1	2255
	11th to 20th	Night	50% 8% 15% 17% 9% 1	2482
	21st to end	Night	45% 7% 12% 22% 12% 1	2870
August	1st to 10th	Night	49% 8% 14% 20% 8%	2813
	11th to 20th	Night	44% 8% 17% 24% 7%	2809
	21st to end	Night	30% 7% 15% 28% 20%	3280
September	1st to 10th	Night	38% 6% 11% 26% 16% 2	1900
	11th to 20th	Night	40% 5% 8% 29% 16% 1	1998
	21st to end	Night	46% 5% 9% 24% 15% 1	2133
October	1st to 10th	Night	44% 6% 11% 26% 13% 1	3800
	11th to 20th	Night	35% 5% 11% 28% 20%	3779
	21st to end	Night	39% 4 12% 25% 19% 1	4120
November	1st to 10th	Night	48% 7% 13% 20% 11% 1	2647
	11th to 20th	Night	53% 6% 13% 18% 9% 1	2800
	21st to end	Night	54% 7% 17% 15% 6%	2800
December	1st to 10th	Night	51% 6% 12% 26% 5%	4580
	11th to 20th	Night	56% 5% 10% 18% 10% 1	5215
	21st to end	Night	56% 6% 11% 18% 9%	6996

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	388
	11th to 20th	Day	32% 22% 31% 12% 3	370
	21st to end	Day	21% 25% 35% 16% 2	407
February	1st to 10th	Day	32% 22% 29% 14% 2	370
	11th to 20th	Day	30% 29% 28% 12% 1	366
	21st to end	Day	26% 23% 32% 15% 3 1	317
March	1st to 10th	Day	30% 27% 30% 11% 2	460
	11th to 20th	Day	28% 27% 29% 11% 4 1	460
	21st to end	Day	31% 25% 30% 10% 4	506
April	1st to 10th	Day	34% 26% 29% 8% 3	460
	11th to 20th	Day	25% 28% 34% 10% 3 1	452
	21st to end	Day	26% 22% 33% 14% 5% 1	460
May	1st to 10th	Day	28% 26% 31% 12% 3 1	479
	11th to 20th	Day	22% 20% 31% 21% 5% 1	674
	21st to end	Day	27% 16% 35% 18% 3 1	735
June	1st to 10th	Day	28% 16% 31% 19% 5%	680
	11th to 20th	Day	23% 14% 35% 20% 6% 1	680
	21st to end	Day	31% 11% 30% 21% 6% 1	680
July	1st to 10th	Day	22% 9% 34% 26% 8%	670
	11th to 20th	Day	21% 7% 38% 24% 9% 1	668
	21st to end	Day	23% 9% 35% 26% 7%	604
August	1st to 10th	Day	16% 10% 37% 26% 9% 2	486
	11th to 20th	Day	19% 10% 35% 22% 13% 2	479
	21st to end	Day	17% 11% 34% 26% 10% 3	539
September	1st to 10th	Day	16% 12% 38% 25% 7% 1	490
	11th to 20th	Day	24% 14% 30% 19% 9% 4	490
	21st to end	Day	21% 14% 35% 19% 9% 2	467
October	1st to 10th	Day	21% 13% 32% 21% 10% 3	390
	11th to 20th	Day	22% 21% 31% 17% 6% 3	390
	21st to end	Day	26% 20% 33% 15% 5% 1	429
November	1st to 10th	Day	23% 20% 34% 16% 6% 2	395
	11th to 20th	Day	34% 24% 25% 12% 5%	400
	21st to end	Day	33% 21% 32% 12% 2 1	400
December	1st to 10th	Day	36% 19% 29% 14% 3	400
	11th to 20th	Day	36% 27% 25% 10% 2	400
	21st to end	Day	33% 25% 27% 13% 3	440
January	1st to 10th	Night	28% 22% 34% 14% 2	881
	11th to 20th	Night	30% 18% 33% 16% 2	801
	21st to end	Night	25% 23% 32% 16% 4	836
February	1st to 10th	Night	29% 19% 32% 16% 2	760
	11th to 20th	Night	26% 25% 33% 14% 2	743
	21st to end	Night	21% 21% 35% 18% 5%	628
March	1st to 10th	Night	24% 23% 35% 15% 3	760
	11th to 20th	Night	25% 20% 30% 21% 5%	760
	21st to end	Night	27% 21% 31% 15% 5%	836
April	1st to 10th	Night	33% 16% 32% 15% 3	599
	11th to 20th	Night	26% 19% 36% 16% 3	564
	21st to end	Night	28% 16% 32% 20% 4 1	570
May	1st to 10th	Night	28% 15% 32% 19% 5% 1	570
	11th to 20th	Night	28% 10% 31% 24% 7% 1	562
	21st to end	Night	21% 12% 38% 24% 5%	616
June	1st to 10th	Night	31% 8% 34% 22% 5%	570
	11th to 20th	Night	23% 10% 35% 26% 7%	486
	21st to end	Night	32% 6% 22% 31% 7% 1	380
July	1st to 10th	Night	20% 5% 32% 32% 10%	411
	11th to 20th	Night	19% 7% 31% 31% 12% 1	552
	21st to end	Night	21% 5% 29% 35% 10%	623
August	1st to 10th	Night	16% 6% 28% 35% 14% 1	568
	11th to 20th	Night	22% 6% 24% 34% 14% 1	562
	21st to end	Night	15% 7% 32% 32% 13% 2	627
September	1st to 10th	Night	17% 8% 33% 29% 11%	570
	11th to 20th	Night	21% 9% 28% 27% 14% 2	668
	21st to end	Night	24% 11% 31% 23% 10% 1	760
October	1st to 10th	Night	21% 10% 34% 26% 9% 1	760
	11th to 20th	Night	22% 16% 34% 19% 9% 1	760
	21st to end	Night	28% 16% 32% 19% 5%	836
November	1st to 10th	Night	26% 16% 32% 20% 6% 1	853
	11th to 20th	Night	28% 21% 27% 19% 5%	900
	21st to end	Night	28% 23% 28% 17% 5%	900
December	1st to 10th	Night	29% 18% 34% 14% 4	900
	11th to 20th	Night	31% 25% 29% 13% 2	900
	21st to end	Night	29% 22% 29% 17% 3	990

Page generated at 2025-01-04 04:23:57. Version ac07

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