Lunenburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lunenburg clear sky chart from 2005-11-06 to 2026-04-02.

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	18% 9% 3 8% 5% 5% 5% 4 6% 7% 30%	132246
	Night	19% 10% 3 8% 5% 5% 5% 4 5% 7% 29%	129718
Transparency	Day	51% 8% 12% 18% 10% 1	135836
	Night	53% 6% 11% 18% 10% 1	134217
Seeing	Day	24% 14% 32% 22% 7% 1	19151
	Night	25% 14% 31% 23% 7% 1	26800

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% 11% 4 13% 8% 6% 6% 5% 6% 7% 21%	4690
	11th to 20th	Day	16% 12% 5% 14% 8% 8% 7% 5% 6% 6% 13%	4993
	21st to end	Day	14% 9% 4 10% 7% 6% 6% 5% 6% 7% 26%	5781
February	1st to 10th	Day	19% 12% 5% 11% 5% 6% 5% 5% 5% 6% 22%	1890
	11th to 20th	Day	16% 8% 4 10% 7% 7% 6% 4 6% 6% 25%	1843
	21st to end	Day	13% 11% 4 7% 7% 5% 4 4 6% 8% 32%	1596
March	1st to 10th	Day	22% 12% 4 10% 7% 6% 4 3 4 5% 24%	5040
	11th to 20th	Day	15% 12% 4 7% 5% 5% 4 3 6% 7% 32%	5090
	21st to end	Day	25% 10% 4 11% 6% 5% 4 4 4 5% 22%	5587
April	1st to 10th	Day	24% 10% 4 9% 5% 5% 4 3 4 5% 27%	2383
	11th to 20th	Day	19% 9% 3 7% 4 4 4 4 6% 6% 34%	2455
	21st to end	Day	21% 8% 2 7% 5% 4 4 3 5% 7% 34%	2600
May	1st to 10th	Day	26% 9% 4 9% 6% 5% 5% 3 5% 6% 21%	5930
	11th to 20th	Day	25% 10% 2 7% 5% 5% 5% 4 5% 5% 28%	6318
	21st to end	Day	18% 10% 3 8% 4 4 4 4 6% 8% 31%	6948
June	1st to 10th	Day	23% 9% 3 7% 5% 5% 5% 3 5% 8% 26%	2800
	11th to 20th	Day	19% 9% 3 7% 5% 4 3 3 5% 6% 37%	2872
	21st to end	Day	24% 10% 3 7% 5% 4 4 4 6% 7% 26%	3000
July	1st to 10th	Day	17% 9% 3 8% 5% 5% 5% 5% 6% 10% 25%	6590
	11th to 20th	Day	11% 7% 3 10% 6% 6% 6% 4 6% 8% 33%	6360
	21st to end	Day	14% 7% 2 6% 4 4 5% 4 7% 9% 39%	6593
August	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 7% 8% 29%	4235
	11th to 20th	Day	13% 9% 4 7% 4 4 5% 3 6% 9% 36%	4175
	21st to end	Day	8% 5% 2 6% 4 4 5% 5% 6% 9% 48%	4494
September	1st to 10th	Day	14% 6% 3 5% 3 4 4 4 5% 7% 44%	2400
	11th to 20th	Day	16% 6% 2 6% 3 4 4 3 5% 5% 46%	2298
	21st to end	Day	16% 7% 3 6% 4 4 5% 4 3 6% 43%	2150
October	1st to 10th	Day	17% 6% 2 6% 4 4 4 4 6% 7% 40%	2000
	11th to 20th	Day	18% 7% 3 7% 4 3 5% 4 7% 8% 35%	2000
	21st to end	Day	20% 8% 3 6% 5% 4 5% 3 5% 6% 33%	2200
November	1st to 10th	Day	19% 10% 3 9% 5% 4 4 3 5% 6% 32%	1739
	11th to 20th	Day	21% 10% 4 7% 5% 4 5% 5% 6% 7% 26%	1680
	21st to end	Day	20% 10% 4 9% 6% 5% 5% 3 5% 6% 27%	1680
December	1st to 10th	Day	23% 10% 3 9% 6% 4 5% 4 6% 6% 23%	2690
	11th to 20th	Day	29% 9% 2 5% 5% 4 5% 4 6% 6% 25%	3076
	21st to end	Day	22% 11% 4 8% 5% 4 4 3 4 7% 28%	4070
January	1st to 10th	Night	13% 11% 4 13% 7% 7% 6% 5% 7% 7% 19%	8234
	11th to 20th	Night	21% 12% 5% 11% 7% 7% 6% 4 5% 6% 16%	7900
	21st to end	Night	13% 11% 3 10% 7% 6% 6% 5% 7% 8% 23%	8400
February	1st to 10th	Night	20% 11% 4 10% 7% 5% 6% 5% 6% 6% 22%	2730
	11th to 20th	Night	16% 9% 3 10% 6% 6% 5% 5% 7% 8% 25%	2663
	21st to end	Night	13% 11% 3 9% 6% 5% 5% 4 7% 6% 30%	2207
March	1st to 10th	Night	24% 13% 3 10% 6% 5% 4 3 4 5% 24%	5020
	11th to 20th	Night	17% 11% 5% 9% 6% 5% 5% 4 6% 6% 27%	5089
	21st to end	Night	31% 10% 3 9% 4 3 3 3 4 5% 26%	5587
April	1st to 10th	Night	25% 11% 3 6% 4 5% 4 3 5% 7% 27%	2039
	11th to 20th	Night	23% 8% 2 6% 4 4 5% 3 4 7% 33%	1892
	21st to end	Night	24% 9% 3 6% 5% 3 4 4 4 6% 32%	1800
May	1st to 10th	Night	26% 12% 4 9% 5% 4 5% 3 4 4 24%	4010
	11th to 20th	Night	29% 8% 3 6% 4 5% 4 3 4 5% 29%	3596
	21st to end	Night	17% 14% 4 8% 6% 4 4 3 4 5% 31%	3948
June	1st to 10th	Night	26% 8% 2 7% 5% 4 4 3 5% 7% 29%	1600
	11th to 20th	Night	21% 8% 3 6% 3 4 4 4 5% 8% 35%	1539
	21st to end	Night	26% 10% 3 6% 4 5% 5% 3 5% 5% 27%	1400
July	1st to 10th	Night	16% 10% 4 10% 6% 6% 5% 5% 6% 8% 27%	3336
	11th to 20th	Night	13% 9% 4 9% 6% 5% 5% 4 6% 8% 32%	3620
	21st to end	Night	15% 7% 2 6% 4 4 4 4 5% 8% 40%	4251
August	1st to 10th	Night	17% 7% 2 8% 6% 5% 4 3 5% 7% 35%	2915
	11th to 20th	Night	13% 9% 4 7% 4 4 4 3 6% 7% 37%	2872
	21st to end	Night	9% 5% 2 5% 3 4 4 4 5% 8% 51%	3402
September	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 5% 7% 45%	2000
	11th to 20th	Night	16% 9% 2 5% 3 3 3 3 4 6% 46%	2100
	21st to end	Night	19% 8% 2 6% 4 4 4 3 4 7% 39%	2249
October	1st to 10th	Night	17% 6% 2 6% 4 3 4 3 5% 7% 43%	2400
	11th to 20th	Night	19% 6% 2 6% 3 3 4 4 6% 8% 38%	2400
	21st to end	Night	22% 8% 2 6% 4 4 4 4 5% 6% 36%	2640
November	1st to 10th	Night	19% 8% 3 7% 5% 4 4 3 5% 7% 35%	2776
	11th to 20th	Night	19% 10% 4 7% 5% 5% 5% 4 6% 7% 28%	2940
	21st to end	Night	21% 8% 3 6% 5% 5% 5% 4 6% 7% 29%	2940
December	1st to 10th	Night	16% 9% 3 9% 6% 6% 6% 4 6% 8% 28%	4720
	11th to 20th	Night	24% 10% 3 7% 4 4 4 3 5% 6% 29%	5353
	21st to end	Night	24% 9% 3 8% 5% 4 4 3 5% 6% 30%	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	59% 6% 14% 15% 5%	4691
	11th to 20th	Day	64% 9% 10% 12% 4	5025
	21st to end	Day	52% 7% 10% 15% 14% 3	5781
February	1st to 10th	Day	62% 5% 12% 13% 6% 1	1890
	11th to 20th	Day	56% 8% 11% 17% 7% 1	1851
	21st to end	Day	48% 7% 13% 19% 10% 3	1596
March	1st to 10th	Day	61% 5% 9% 13% 8% 3	5044
	11th to 20th	Day	48% 10% 14% 19% 8% 1	5090
	21st to end	Day	61% 5% 8% 15% 11% 1	5587
April	1st to 10th	Day	57% 6% 9% 13% 12% 2	2383
	11th to 20th	Day	47% 8% 10% 21% 13% 2	2455
	21st to end	Day	48% 7% 11% 18% 13% 3	2600
May	1st to 10th	Day	62% 10% 9% 13% 6% 1	5941
	11th to 20th	Day	56% 7% 9% 20% 7% 1	6322
	21st to end	Day	49% 8% 14% 18% 10% 1	6948
June	1st to 10th	Day	55% 8% 10% 18% 9% 1	2800
	11th to 20th	Day	48% 9% 11% 19% 13% 2	2872
	21st to end	Day	58% 8% 9% 14% 9% 1	3000
July	1st to 10th	Day	55% 10% 12% 12% 10% 1	6520
	11th to 20th	Day	48% 9% 12% 21% 9%	6284
	21st to end	Day	41% 10% 14% 23% 11% 1	6406
August	1st to 10th	Day	54% 9% 11% 17% 10% 1	4222
	11th to 20th	Day	44% 9% 16% 23% 8% 1	4214
	21st to end	Day	30% 8% 12% 30% 19% 1	4494
September	1st to 10th	Day	38% 8% 13% 24% 16% 2	2400
	11th to 20th	Day	40% 6% 10% 24% 17% 2	2298
	21st to end	Day	41% 8% 9% 23% 18% 1	2150
October	1st to 10th	Day	41% 7% 11% 27% 13% 1	3260
	11th to 20th	Day	37% 6% 11% 24% 22%	3240
	21st to end	Day	43% 6% 15% 22% 12% 3	3538
November	1st to 10th	Day	51% 7% 11% 20% 9% 1	1739
	11th to 20th	Day	55% 7% 13% 16% 7% 1	1680
	21st to end	Day	58% 6% 14% 16% 6%	1680
December	1st to 10th	Day	57% 7% 13% 19% 4	2690
	11th to 20th	Day	58% 5% 11% 14% 11%	3075
	21st to end	Day	55% 5% 17% 15% 7% 1	4070
January	1st to 10th	Night	60% 6% 13% 16% 4	8234
	11th to 20th	Night	63% 8% 12% 12% 5%	7943
	21st to end	Night	54% 8% 12% 15% 10% 1	8400
February	1st to 10th	Night	62% 7% 10% 12% 8% 1	2730
	11th to 20th	Night	56% 7% 12% 17% 8% 1	2666
	21st to end	Night	52% 7% 14% 18% 8% 1	2207
March	1st to 10th	Night	62% 4 8% 12% 12% 2	5029
	11th to 20th	Night	54% 8% 12% 18% 7% 1	5090
	21st to end	Night	60% 4 7% 17% 11% 1	5587
April	1st to 10th	Night	56% 6% 9% 14% 12% 3	2039
	11th to 20th	Night	51% 5% 8% 20% 14% 2	1892
	21st to end	Night	52% 6% 9% 19% 12% 3	1800
May	1st to 10th	Night	63% 6% 8% 13% 8% 1	4016
	11th to 20th	Night	56% 6% 7% 21% 6% 3	3597
	21st to end	Night	54% 7% 9% 20% 8% 1	3949
June	1st to 10th	Night	54% 6% 11% 20% 9%	1600
	11th to 20th	Night	49% 6% 11% 21% 12% 1	1539
	21st to end	Night	60% 6% 10% 14% 10% 1	1400
July	1st to 10th	Night	57% 7% 12% 15% 9% 1	3298
	11th to 20th	Night	53% 9% 9% 15% 12% 1	3572
	21st to end	Night	45% 7% 12% 22% 13% 1	4125
August	1st to 10th	Night	51% 6% 13% 20% 10%	2903
	11th to 20th	Night	46% 8% 16% 22% 8%	2899
	21st to end	Night	30% 5% 15% 28% 21%	3401
September	1st to 10th	Night	39% 7% 9% 26% 16% 2	2000
	11th to 20th	Night	40% 5% 9% 28% 17% 1	2100
	21st to end	Night	47% 4 8% 25% 15% 1	2249
October	1st to 10th	Night	44% 6% 11% 25% 13% 1	3920
	11th to 20th	Night	34% 6% 12% 28% 20%	3899
	21st to end	Night	41% 5% 12% 24% 17% 1	4252
November	1st to 10th	Night	49% 7% 13% 19% 11% 1	2776
	11th to 20th	Night	54% 7% 14% 17% 8%	2940
	21st to end	Night	54% 7% 17% 16% 6%	2940
December	1st to 10th	Night	52% 7% 14% 23% 5%	4720
	11th to 20th	Night	55% 4 13% 16% 10% 1	5355
	21st to end	Night	56% 5% 13% 17% 8%	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	26% 23% 35% 12% 3	430
	11th to 20th	Day	29% 20% 31% 15% 5%	430
	21st to end	Day	20% 22% 36% 20% 2	473
February	1st to 10th	Day	25% 21% 34% 16% 3	430
	11th to 20th	Day	25% 26% 32% 16% 2	426
	21st to end	Day	18% 22% 36% 20% 3 1	366
March	1st to 10th	Day	25% 22% 36% 16% 2	540
	11th to 20th	Day	21% 22% 38% 15% 4 1	540
	21st to end	Day	28% 20% 33% 14% 5%	594
April	1st to 10th	Day	32% 20% 32% 12% 3	504
	11th to 20th	Day	24% 14% 43% 16% 3	492
	21st to end	Day	22% 16% 35% 20% 7%	500
May	1st to 10th	Day	28% 13% 36% 18% 4 1	521
	11th to 20th	Day	22% 11% 32% 27% 7% 1	724
	21st to end	Day	26% 8% 35% 25% 5% 1	790
June	1st to 10th	Day	27% 9% 30% 26% 7%	730
	11th to 20th	Day	22% 8% 32% 29% 8% 1	730
	21st to end	Day	32% 5% 28% 26% 8% 1	730
July	1st to 10th	Day	24% 5% 29% 32% 10%	720
	11th to 20th	Day	22% 4 28% 32% 13% 1	718
	21st to end	Day	21% 6% 28% 33% 11% 1	653
August	1st to 10th	Day	16% 6% 26% 38% 12% 2	526
	11th to 20th	Day	18% 6% 30% 25% 19% 2	519
	21st to end	Day	16% 6% 29% 32% 15% 3	583
September	1st to 10th	Day	17% 6% 31% 33% 11% 2	530
	11th to 20th	Day	20% 10% 26% 26% 12% 5%	530
	21st to end	Day	21% 6% 34% 25% 13% 2	502
October	1st to 10th	Day	20% 8% 31% 26% 12% 3	420
	11th to 20th	Day	19% 16% 31% 23% 9% 2	420
	21st to end	Day	24% 16% 33% 19% 7% 1	462
November	1st to 10th	Day	22% 17% 34% 20% 7% 1	425
	11th to 20th	Day	28% 23% 30% 14% 6%	430
	21st to end	Day	28% 20% 34% 14% 4	430
December	1st to 10th	Day	33% 20% 28% 17% 3	430
	11th to 20th	Day	30% 27% 27% 13% 2	430
	21st to end	Day	27% 24% 30% 15% 3	473
January	1st to 10th	Night	25% 21% 35% 16% 3	950
	11th to 20th	Night	27% 19% 31% 19% 4	889
	21st to end	Night	21% 24% 36% 16% 3	924
February	1st to 10th	Night	27% 18% 34% 18% 3	840
	11th to 20th	Night	23% 24% 35% 15% 3	823
	21st to end	Night	19% 18% 38% 21% 4	692
March	1st to 10th	Night	25% 18% 38% 17% 3	840
	11th to 20th	Night	23% 16% 32% 22% 6%	840
	21st to end	Night	25% 17% 33% 19% 5%	924
April	1st to 10th	Night	32% 14% 30% 20% 3	632
	11th to 20th	Night	27% 10% 39% 18% 5%	594
	21st to end	Night	30% 11% 29% 24% 7% 1	600
May	1st to 10th	Night	30% 9% 30% 24% 5% 1	600
	11th to 20th	Night	29% 6% 29% 26% 9% 1	592
	21st to end	Night	22% 7% 32% 29% 8% 1	649
June	1st to 10th	Night	30% 5% 28% 28% 8%	600
	11th to 20th	Night	24% 6% 28% 34% 8% 1	539
	21st to end	Night	33% 5% 18% 33% 11% 1	400
July	1st to 10th	Night	20% 5% 26% 34% 13% 1	459
	11th to 20th	Night	21% 5% 24% 34% 15% 1	582
	21st to end	Night	21% 3 23% 39% 13% 1	656
August	1st to 10th	Night	17% 3 22% 37% 19% 2	598
	11th to 20th	Night	19% 4 22% 32% 20% 2	592
	21st to end	Night	17% 5% 25% 34% 17% 2	660
September	1st to 10th	Night	17% 7% 27% 35% 13% 1	600
	11th to 20th	Night	20% 7% 26% 28% 17% 2	700
	21st to end	Night	24% 8% 28% 27% 11% 2	800
October	1st to 10th	Night	21% 8% 30% 29% 11% 1	800
	11th to 20th	Night	21% 13% 33% 22% 10% 2	800
	21st to end	Night	27% 14% 31% 22% 6%	880
November	1st to 10th	Night	24% 14% 32% 23% 5% 1	900
	11th to 20th	Night	26% 21% 28% 20% 5%	950
	21st to end	Night	27% 19% 31% 17% 5%	950
December	1st to 10th	Night	29% 18% 33% 16% 4	950
	11th to 20th	Night	29% 23% 33% 13% 3	950
	21st to end	Night	27% 18% 33% 18% 3	1045

Page generated at 2026-03-30 03:18:44. Version ac07

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