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 2024-01-16.

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% 8% 3 6% 6% 3 5% 5% 5% 7% 31%	75033
	Night	20% 9% 3 6% 6% 3 5% 5% 5% 7% 31%	74768
Transparency	Day	51% 8% 12% 18% 10% 1	74744
	Night	53% 7% 12% 18% 9% 1	74594
Seeing	Day	24% 14% 32% 22% 7% 1	16123
	Night	25% 13% 31% 23% 7% 1	23803

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	17% 11% 6% 9% 6% 4 6% 7% 6% 7% 22%	1516
	11th to 20th	Day	22% 12% 5% 7% 7% 4 5% 5% 6% 7% 20%	1575
	21st to end	Day	15% 8% 4 8% 6% 5% 7% 6% 8% 8% 25%	1782
February	1st to 10th	Day	19% 11% 5% 9% 5% 5% 6% 6% 5% 6% 22%	1620
	11th to 20th	Day	18% 9% 4 9% 8% 5% 7% 5% 5% 7% 24%	1573
	21st to end	Day	12% 10% 4 7% 8% 4 5% 4 6% 8% 32%	1365
March	1st to 10th	Day	18% 11% 4 8% 7% 4 5% 5% 4 6% 27%	1976
	11th to 20th	Day	16% 7% 4 8% 6% 4 5% 4 6% 6% 33%	1980
	21st to end	Day	16% 10% 4 8% 6% 3 4 4 5% 6% 33%	2178
April	1st to 10th	Day	24% 10% 4 9% 6% 3 5% 4 4 5% 27%	2134
	11th to 20th	Day	19% 8% 3 6% 5% 2 4 4 6% 6% 35%	2206
	21st to end	Day	22% 8% 2 6% 6% 3 5% 4 5% 6% 32%	2340
May	1st to 10th	Day	24% 9% 3 7% 7% 3 5% 5% 5% 6% 27%	2356
	11th to 20th	Day	21% 8% 3 6% 5% 3 4 5% 5% 6% 34%	2478
	21st to end	Day	20% 9% 2 6% 4 3 5% 5% 5% 8% 32%	2724
June	1st to 10th	Day	25% 8% 4 6% 6% 4 5% 4 5% 9% 26%	2520
	11th to 20th	Day	20% 8% 4 6% 5% 2 4 4 5% 6% 35%	2584
	21st to end	Day	24% 9% 3 7% 6% 4 4 4 6% 8% 26%	2700
July	1st to 10th	Day	18% 6% 3 5% 5% 4 5% 6% 6% 11% 32%	2610
	11th to 20th	Day	15% 8% 3 7% 6% 4 6% 5% 6% 8% 33%	2520
	21st to end	Day	17% 9% 3 6% 6% 3 4 5% 6% 9% 31%	2618
August	1st to 10th	Day	14% 7% 3 5% 5% 3 5% 5% 7% 9% 37%	2327
	11th to 20th	Day	15% 7% 2 5% 5% 4 5% 5% 7% 9% 36%	2304
	21st to end	Day	13% 6% 2 5% 4 3 4 5% 6% 8% 44%	2482
September	1st to 10th	Day	14% 5% 3 4 4 3 5% 5% 5% 8% 45%	2160
	11th to 20th	Day	17% 6% 2 6% 5% 3 4 4 5% 5% 44%	2069
	21st to end	Day	18% 7% 2 4 5% 3 3 5% 3 6% 43%	1936
October	1st to 10th	Day	18% 6% 2 4 5% 3 4 5% 6% 7% 40%	1800
	11th to 20th	Day	19% 7% 3 6% 5% 3 5% 6% 7% 8% 35%	1800
	21st to end	Day	21% 7% 4 6% 6% 3 5% 4 5% 6% 33%	1980
November	1st to 10th	Day	20% 9% 3 8% 6% 3 4 4 4 7% 32%	1571
	11th to 20th	Day	22% 8% 3 5% 6% 4 4 5% 6% 7% 28%	1520
	21st to end	Day	20% 8% 3 8% 6% 4 5% 5% 5% 6% 29%	1520
December	1st to 10th	Day	25% 12% 3 8% 7% 4 6% 6% 5% 6% 20%	1520
	11th to 20th	Day	31% 10% 2 5% 5% 3 5% 6% 6% 7% 18%	1906
	21st to end	Day	24% 9% 5% 7% 6% 3 4 4 5% 8% 26%	2783
January	1st to 10th	Night	18% 12% 5% 8% 7% 3 6% 6% 7% 6% 21%	2649
	11th to 20th	Night	20% 10% 4 8% 8% 4 6% 5% 6% 7% 21%	2502
	21st to end	Night	15% 12% 4 7% 7% 4 5% 7% 7% 10% 23%	2574
February	1st to 10th	Night	20% 10% 4 7% 7% 3 7% 6% 6% 7% 23%	2340
	11th to 20th	Night	17% 9% 4 8% 7% 4 6% 6% 7% 8% 23%	2273
	21st to end	Night	13% 10% 4 9% 7% 4 6% 5% 6% 7% 30%	1889
March	1st to 10th	Night	17% 10% 4 7% 5% 3 6% 5% 5% 8% 30%	1971
	11th to 20th	Night	20% 7% 3 6% 6% 4 6% 5% 6% 6% 31%	1979
	21st to end	Night	17% 10% 4 7% 5% 2 4 4 5% 6% 35%	2178
April	1st to 10th	Night	25% 11% 3 5% 5% 3 5% 4 4 7% 28%	1825
	11th to 20th	Night	23% 7% 3 6% 5% 3 5% 4 4 7% 33%	1702
	21st to end	Night	26% 9% 3 5% 5% 2 4 5% 4 6% 31%	1620
May	1st to 10th	Night	25% 10% 4 5% 4 2 4 4 5% 6% 30%	1602
	11th to 20th	Night	26% 6% 3 5% 5% 3 5% 3 4 7% 33%	1416
	21st to end	Night	18% 9% 4 6% 6% 3 4 5% 5% 7% 33%	1550
June	1st to 10th	Night	27% 8% 2 7% 5% 3 4 4 5% 7% 28%	1440
	11th to 20th	Night	22% 8% 3 5% 4 3 5% 4 5% 7% 33%	1386
	21st to end	Night	27% 9% 4 5% 5% 4 5% 3 5% 5% 27%	1260
July	1st to 10th	Night	16% 9% 3 5% 4 3 5% 5% 4 9% 35%	1324
	11th to 20th	Night	16% 10% 3 8% 5% 4 6% 5% 7% 7% 29%	1440
	21st to end	Night	18% 7% 4 6% 5% 3 5% 5% 5% 8% 33%	1697
August	1st to 10th	Night	15% 7% 2 5% 5% 2 3 4 5% 8% 43%	1612
	11th to 20th	Night	16% 8% 4 6% 4 3 4 4 6% 8% 38%	1596
	21st to end	Night	14% 6% 2 5% 4 3 5% 5% 5% 7% 43%	1872
September	1st to 10th	Night	13% 6% 3 5% 5% 3 5% 4 5% 8% 44%	1800
	11th to 20th	Night	16% 9% 2 4 3 2 3 4 4 6% 45%	1890
	21st to end	Night	19% 8% 3 6% 5% 3 3 4 4 7% 39%	2023
October	1st to 10th	Night	18% 5% 2 5% 5% 2 4 4 5% 7% 42%	2160
	11th to 20th	Night	20% 5% 2 5% 4 3 5% 5% 6% 8% 38%	2160
	21st to end	Night	23% 7% 3 5% 5% 3 4 4 5% 6% 35%	2376
November	1st to 10th	Night	20% 7% 3 6% 6% 3 4 4 5% 7% 34%	2505
	11th to 20th	Night	20% 7% 4 6% 6% 3 6% 5% 6% 7% 30%	2660
	21st to end	Night	21% 7% 3 5% 6% 3 6% 5% 5% 8% 30%	2660
December	1st to 10th	Night	23% 11% 3 7% 7% 4 6% 4 5% 7% 22%	2660
	11th to 20th	Night	30% 11% 3 6% 5% 3 4 4 5% 6% 22%	3293
	21st to end	Night	24% 8% 4 8% 5% 3 5% 5% 6% 6% 27%	4884

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	60% 8% 13% 12% 7%	1517
	11th to 20th	Day	63% 8% 12% 14% 3	1575
	21st to end	Day	54% 8% 12% 19% 7%	1782
February	1st to 10th	Day	60% 6% 13% 13% 6% 1	1620
	11th to 20th	Day	59% 9% 11% 15% 6% 1	1581
	21st to end	Day	48% 8% 13% 18% 9% 2	1365
March	1st to 10th	Day	57% 7% 8% 16% 11% 1	1980
	11th to 20th	Day	48% 8% 12% 17% 14% 2	1980
	21st to end	Day	50% 7% 9% 19% 13% 2	2178
April	1st to 10th	Day	57% 6% 9% 13% 12% 2	2134
	11th to 20th	Day	46% 8% 10% 21% 14% 1	2206
	21st to end	Day	50% 7% 11% 17% 12% 2	2340
May	1st to 10th	Day	58% 7% 10% 15% 8% 2	2356
	11th to 20th	Day	49% 8% 9% 20% 13% 1	2482
	21st to end	Day	50% 8% 12% 19% 9% 1	2724
June	1st to 10th	Day	56% 8% 10% 18% 8%	2520
	11th to 20th	Day	50% 9% 10% 17% 12% 2	2584
	21st to end	Day	58% 9% 9% 14% 9% 1	2700
July	1st to 10th	Day	49% 9% 15% 15% 10% 2	2540
	11th to 20th	Day	50% 9% 15% 19% 7% 1	2444
	21st to end	Day	50% 10% 14% 19% 7% 1	2472
August	1st to 10th	Day	44% 10% 15% 19% 12% 1	2314
	11th to 20th	Day	43% 11% 16% 20% 10%	2304
	21st to end	Day	37% 10% 13% 26% 14% 1	2482
September	1st to 10th	Day	37% 9% 13% 23% 16% 2	2160
	11th to 20th	Day	43% 7% 9% 23% 16% 2	2069
	21st to end	Day	42% 7% 9% 24% 17% 1	1936
October	1st to 10th	Day	43% 7% 11% 25% 12% 2	1800
	11th to 20th	Day	46% 7% 14% 21% 11% 1	1800
	21st to end	Day	52% 6% 11% 20% 10% 1	1980
November	1st to 10th	Day	52% 7% 10% 20% 9% 1	1571
	11th to 20th	Day	54% 7% 13% 17% 8% 1	1520
	21st to end	Day	56% 7% 14% 16% 6%	1520
December	1st to 10th	Day	63% 7% 11% 13% 4 1	1520
	11th to 20th	Day	63% 8% 11% 12% 7%	1905
	21st to end	Day	57% 6% 20% 12% 4 1	2783
January	1st to 10th	Night	62% 6% 13% 14% 4	2649
	11th to 20th	Night	61% 7% 15% 12% 5%	2502
	21st to end	Night	55% 8% 15% 16% 5%	2574
February	1st to 10th	Night	60% 8% 12% 12% 8% 1	2340
	11th to 20th	Night	59% 7% 13% 14% 7% 1	2276
	21st to end	Night	52% 7% 15% 16% 7% 2	1889
March	1st to 10th	Night	53% 6% 12% 16% 10% 2	1980
	11th to 20th	Night	51% 7% 12% 16% 11% 2	1980
	21st to end	Night	51% 5% 10% 19% 13% 2	2178
April	1st to 10th	Night	56% 6% 9% 14% 12% 3	1825
	11th to 20th	Night	52% 5% 9% 19% 14% 2	1702
	21st to end	Night	54% 6% 9% 19% 11% 2	1620
May	1st to 10th	Night	55% 5% 9% 20% 9% 1	1602
	11th to 20th	Night	52% 6% 8% 22% 11% 1	1417
	21st to end	Night	52% 9% 12% 18% 9% 1	1551
June	1st to 10th	Night	56% 6% 11% 20% 8%	1440
	11th to 20th	Night	52% 6% 11% 19% 12% 1	1386
	21st to end	Night	60% 6% 10% 13% 10% 1	1260
July	1st to 10th	Night	47% 7% 16% 19% 10%	1286
	11th to 20th	Night	55% 7% 11% 18% 8% 1	1392
	21st to end	Night	50% 9% 15% 18% 7% 1	1604
August	1st to 10th	Night	43% 7% 14% 24% 13%	1600
	11th to 20th	Night	46% 8% 15% 20% 11%	1596
	21st to end	Night	41% 6% 14% 24% 14% 1	1872
September	1st to 10th	Night	39% 8% 10% 27% 14% 2	1800
	11th to 20th	Night	41% 5% 8% 27% 17% 2	1890
	21st to end	Night	48% 4 8% 24% 15% 1	2023
October	1st to 10th	Night	42% 6% 11% 25% 14% 2	2160
	11th to 20th	Night	43% 7% 14% 27% 9%	2160
	21st to end	Night	49% 7% 11% 19% 12% 1	2376
November	1st to 10th	Night	50% 7% 13% 18% 10% 1	2505
	11th to 20th	Night	52% 7% 14% 18% 8%	2660
	21st to end	Night	53% 7% 18% 16% 6%	2660
December	1st to 10th	Night	62% 7% 13% 14% 3	2660
	11th to 20th	Night	65% 5% 11% 14% 5%	3295
	21st to end	Night	57% 6% 14% 17% 5%	4884

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	27% 23% 34% 13% 3	370
	11th to 20th	Day	27% 21% 35% 13% 4	356
	21st to end	Day	21% 21% 35% 21% 2	374
February	1st to 10th	Day	26% 24% 34% 16% 1	340
	11th to 20th	Day	26% 27% 29% 15% 2	336
	21st to end	Day	17% 23% 38% 19% 3 1	288
March	1st to 10th	Day	24% 23% 35% 16% 2	420
	11th to 20th	Day	20% 22% 37% 15% 5% 1	420
	21st to end	Day	25% 20% 34% 15% 6%	462
April	1st to 10th	Day	32% 21% 30% 13% 3	420
	11th to 20th	Day	24% 13% 45% 16% 3	412
	21st to end	Day	25% 15% 33% 19% 8%	420
May	1st to 10th	Day	28% 14% 36% 17% 4 1	439
	11th to 20th	Day	21% 12% 34% 26% 7% 1	624
	21st to end	Day	27% 8% 34% 24% 5% 1	680
June	1st to 10th	Day	28% 7% 31% 26% 7%	630
	11th to 20th	Day	23% 8% 30% 29% 8% 1	630
	21st to end	Day	32% 5% 27% 27% 8% 1	630
July	1st to 10th	Day	24% 4 30% 31% 10%	620
	11th to 20th	Day	24% 4 27% 31% 14% 1	618
	21st to end	Day	22% 6% 29% 31% 11% 1	558
August	1st to 10th	Day	15% 6% 28% 36% 13% 2	446
	11th to 20th	Day	19% 7% 30% 26% 16% 2	439
	21st to end	Day	17% 6% 26% 32% 15% 3	495
September	1st to 10th	Day	17% 6% 31% 33% 11% 1	450
	11th to 20th	Day	22% 11% 29% 25% 10% 4	450
	21st to end	Day	22% 6% 36% 22% 12% 3	428
October	1st to 10th	Day	21% 8% 31% 26% 11% 3	360
	11th to 20th	Day	19% 16% 31% 23% 9% 3	360
	21st to end	Day	26% 16% 33% 19% 6% 1	396
November	1st to 10th	Day	22% 18% 31% 21% 8% 1	365
	11th to 20th	Day	28% 24% 27% 15% 6%	370
	21st to end	Day	28% 19% 35% 13% 4 1	370
December	1st to 10th	Day	34% 19% 28% 15% 3	370
	11th to 20th	Day	31% 28% 27% 13% 1	370
	21st to end	Day	29% 24% 29% 14% 3	407
January	1st to 10th	Night	27% 21% 34% 16% 3	850
	11th to 20th	Night	26% 19% 32% 19% 3	785
	21st to end	Night	22% 22% 35% 17% 4	792
February	1st to 10th	Night	28% 18% 34% 18% 2	720
	11th to 20th	Night	24% 24% 34% 15% 2	703
	21st to end	Night	19% 17% 40% 20% 4	592
March	1st to 10th	Night	25% 17% 38% 18% 3	720
	11th to 20th	Night	23% 15% 31% 23% 7%	720
	21st to end	Night	23% 17% 33% 21% 6%	792
April	1st to 10th	Night	33% 14% 29% 20% 4	565
	11th to 20th	Night	26% 9% 40% 18% 5%	534
	21st to end	Night	32% 10% 28% 23% 7% 1	540
May	1st to 10th	Night	30% 9% 30% 25% 5% 1	540
	11th to 20th	Night	30% 6% 29% 26% 8% 2	532
	21st to end	Night	23% 7% 33% 28% 8% 1	583
June	1st to 10th	Night	31% 5% 28% 28% 8%	540
	11th to 20th	Night	25% 6% 27% 33% 8% 1	486
	21st to end	Night	33% 5% 18% 32% 12% 1	360
July	1st to 10th	Night	20% 5% 26% 36% 12% 1	411
	11th to 20th	Night	22% 4 23% 35% 15% 1	522
	21st to end	Night	22% 4 22% 38% 14%	590
August	1st to 10th	Night	17% 3 22% 37% 19% 2	538
	11th to 20th	Night	20% 5% 23% 32% 18% 2	532
	21st to end	Night	18% 5% 24% 35% 17% 2	594
September	1st to 10th	Night	16% 7% 27% 36% 13% 1	540
	11th to 20th	Night	21% 8% 28% 26% 15% 2	630
	21st to end	Night	24% 9% 28% 26% 11% 2	720
October	1st to 10th	Night	23% 8% 29% 29% 10% 1	720
	11th to 20th	Night	21% 12% 34% 22% 10% 2	720
	21st to end	Night	28% 14% 32% 21% 5%	792
November	1st to 10th	Night	24% 14% 30% 25% 5% 2	805
	11th to 20th	Night	26% 20% 28% 21% 6%	850
	21st to end	Night	26% 19% 31% 19% 5%	850
December	1st to 10th	Night	30% 17% 34% 14% 4	850
	11th to 20th	Night	29% 23% 33% 13% 3	850
	21st to end	Night	29% 18% 33% 17% 3	935

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