Constance Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Constance Bay clear sky chart from 2005-11-06 to 2024-01-15.

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	17% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	74751
	Night	18% 10% 4 7% 6% 3 4 4 5% 6% 32%	75031
Transparency	Day	51% 6% 12% 20% 10% 1	74456
	Night	53% 5% 11% 20% 10% 1	74860
Seeing	Day	23% 15% 30% 20% 9% 3	13343
	Night	22% 12% 29% 26% 9% 1	22574

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% 17% 7% 10% 7% 4 4 5% 5% 4 21%	1517
	11th to 20th	Day	19% 15% 6% 10% 7% 4 4 4 3 4 23%	1478
	21st to end	Day	13% 14% 4 10% 8% 4 6% 5% 5% 5% 25%	1660
February	1st to 10th	Day	14% 15% 5% 12% 8% 4 5% 4 5% 5% 24%	1620
	11th to 20th	Day	13% 14% 6% 10% 5% 4 5% 5% 4 6% 29%	1573
	21st to end	Day	19% 11% 5% 9% 7% 4 4 4 5% 5% 26%	1471
March	1st to 10th	Day	16% 11% 4 8% 8% 4 5% 5% 4 5% 30%	1806
	11th to 20th	Day	15% 12% 4 8% 7% 4 5% 4 4 6% 31%	1980
	21st to end	Day	19% 9% 4 6% 5% 3 4 3 5% 5% 37%	2286
April	1st to 10th	Day	22% 11% 4 6% 5% 2 5% 4 4 6% 32%	2160
	11th to 20th	Day	21% 9% 3 6% 4 2 4 3 4 5% 37%	2134
	21st to end	Day	22% 10% 3 6% 6% 3 4 4 4 5% 32%	2294
May	1st to 10th	Day	20% 8% 3 6% 6% 3 4 4 4 6% 36%	2520
	11th to 20th	Day	16% 7% 3 6% 6% 3 5% 3 4 6% 39%	2478
	21st to end	Day	16% 6% 2 5% 7% 3 6% 5% 5% 7% 38%	2725
June	1st to 10th	Day	20% 8% 3 6% 6% 4 6% 5% 5% 7% 30%	2520
	11th to 20th	Day	15% 5% 2 6% 5% 3 5% 5% 6% 8% 39%	2520
	21st to end	Day	18% 6% 4 5% 6% 4 6% 5% 6% 8% 32%	2520
July	1st to 10th	Day	11% 5% 2 6% 5% 3 5% 7% 7% 9% 40%	2520
	11th to 20th	Day	12% 5% 3 5% 6% 3 5% 5% 7% 8% 40%	2520
	21st to end	Day	12% 5% 3 5% 5% 4 5% 5% 7% 9% 39%	2744
August	1st to 10th	Day	11% 5% 3 6% 6% 4 5% 5% 6% 8% 40%	2460
	11th to 20th	Day	11% 6% 3 5% 7% 4 5% 5% 7% 8% 39%	2290
	21st to end	Day	14% 6% 2 5% 5% 3 5% 5% 6% 9% 40%	2376
September	1st to 10th	Day	13% 6% 2 5% 5% 3 5% 5% 5% 8% 43%	2160
	11th to 20th	Day	13% 5% 2 6% 4 3 4 4 6% 8% 45%	2160
	21st to end	Day	17% 6% 3 6% 4 3 4 5% 6% 8% 38%	1915
October	1st to 10th	Day	21% 7% 3 6% 5% 3 5% 4 6% 6% 35%	1800
	11th to 20th	Day	24% 8% 3 6% 6% 4 5% 5% 5% 7% 28%	1800
	21st to end	Day	27% 9% 3 6% 6% 4 4 4 4 6% 27%	1845
November	1st to 10th	Day	16% 9% 4 5% 6% 4 5% 6% 6% 7% 34%	1661
	11th to 20th	Day	20% 12% 4 7% 7% 3 5% 5% 5% 6% 26%	1520
	21st to end	Day	22% 14% 4 8% 8% 4 5% 5% 4 6% 20%	1520
December	1st to 10th	Day	22% 17% 7% 9% 6% 3 5% 4 5% 5% 17%	1520
	11th to 20th	Day	21% 13% 5% 8% 6% 3 4 4 5% 5% 24%	1906
	21st to end	Day	29% 17% 6% 10% 6% 3 3 3 3 3 19%	2772
January	1st to 10th	Night	18% 17% 6% 11% 8% 4 5% 4 4 5% 17%	2649
	11th to 20th	Night	18% 18% 5% 10% 7% 4 5% 4 3 4 22%	2588
	21st to end	Night	12% 15% 5% 9% 7% 3 5% 4 4 5% 30%	2692
February	1st to 10th	Night	14% 13% 6% 12% 8% 4 5% 4 5% 6% 23%	2340
	11th to 20th	Night	14% 13% 5% 11% 7% 3 4 4 4 5% 29%	2273
	21st to end	Night	17% 12% 5% 8% 7% 4 5% 5% 4 6% 29%	1784
March	1st to 10th	Night	16% 13% 5% 7% 7% 4 5% 4 4 5% 29%	2137
	11th to 20th	Night	16% 12% 5% 8% 7% 3 4 4 4 5% 34%	1979
	21st to end	Night	16% 9% 3 7% 6% 2 4 3 4 5% 40%	2070
April	1st to 10th	Night	21% 9% 4 8% 5% 3 4 4 5% 6% 33%	1800
	11th to 20th	Night	19% 7% 4 7% 5% 3 4 5% 4 5% 36%	1775
	21st to end	Night	20% 10% 3 7% 6% 3 4 4 4 6% 33%	1680
May	1st to 10th	Night	20% 7% 3 4 4 3 4 4 6% 7% 37%	1440
	11th to 20th	Night	17% 8% 4 4 4 3 4 4 4 8% 39%	1415
	21st to end	Night	13% 5% 3 6% 5% 3 4 4 7% 7% 44%	1550
June	1st to 10th	Night	17% 6% 3 5% 6% 4 4 5% 7% 9% 34%	1440
	11th to 20th	Night	14% 5% 3 6% 5% 4 4 4 6% 8% 43%	1440
	21st to end	Night	17% 6% 2 5% 5% 3 4 6% 7% 8% 37%	1440
July	1st to 10th	Night	11% 4 2 5% 5% 3 4 5% 5% 9% 46%	1440
	11th to 20th	Night	12% 5% 3 6% 4 2 5% 5% 6% 9% 43%	1440
	21st to end	Night	10% 4 2 5% 6% 4 5% 5% 7% 9% 44%	1574
August	1st to 10th	Night	9% 6% 3 6% 6% 2 4 5% 6% 9% 43%	1475
	11th to 20th	Night	10% 5% 2 5% 5% 3 4 6% 7% 8% 45%	1598
	21st to end	Night	11% 6% 3 5% 5% 3 5% 5% 6% 8% 44%	1974
September	1st to 10th	Night	12% 5% 3 5% 6% 3 4 5% 5% 7% 47%	1800
	11th to 20th	Night	15% 5% 2 4 4 3 3 4 5% 8% 48%	1800
	21st to end	Night	18% 5% 3 5% 5% 2 4 4 4 7% 42%	2040
October	1st to 10th	Night	18% 7% 3 6% 4 3 5% 5% 5% 7% 37%	2160
	11th to 20th	Night	22% 8% 3 7% 6% 4 4 4 5% 6% 30%	2160
	21st to end	Night	24% 10% 3 6% 6% 4 4 4 5% 6% 27%	2510
November	1st to 10th	Night	20% 9% 3 6% 6% 3 4 4 5% 6% 34%	2416
	11th to 20th	Night	20% 11% 4 7% 6% 4 5% 4 5% 6% 28%	2660
	21st to end	Night	22% 12% 5% 9% 6% 3 4 4 5% 6% 23%	2660
December	1st to 10th	Night	22% 16% 6% 10% 7% 3 5% 6% 5% 5% 17%	2660
	11th to 20th	Night	22% 14% 5% 8% 7% 3 4 3 3 4 26%	3288
	21st to end	Night	30% 17% 4 10% 5% 3 4 3 3 4 18%	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	65% 5% 10% 14% 5%	1518
	11th to 20th	Day	66% 3 9% 11% 10% 1	1478
	21st to end	Day	60% 6% 10% 15% 9% 1	1660
February	1st to 10th	Day	62% 5% 10% 17% 5% 2	1620
	11th to 20th	Day	58% 4 13% 15% 9% 1	1582
	21st to end	Day	60% 5% 11% 14% 10% 1	1471
March	1st to 10th	Day	57% 4 10% 17% 10% 1	1809
	11th to 20th	Day	55% 4 11% 16% 11% 3	1980
	21st to end	Day	50% 4 8% 19% 14% 5%	2286
April	1st to 10th	Day	54% 4 8% 19% 12% 3	2160
	11th to 20th	Day	50% 4 7% 22% 15% 2	2134
	21st to end	Day	55% 5% 8% 15% 14% 4	2294
May	1st to 10th	Day	50% 5% 7% 20% 14% 4	2520
	11th to 20th	Day	47% 4 8% 21% 17% 3	2482
	21st to end	Day	46% 6% 12% 20% 13% 3	2725
June	1st to 10th	Day	53% 6% 11% 19% 11%	2520
	11th to 20th	Day	42% 6% 12% 23% 13% 3	2520
	21st to end	Day	48% 7% 14% 20% 10% 1	2520
July	1st to 10th	Day	37% 8% 14% 27% 14% 1	2450
	11th to 20th	Day	38% 7% 16% 26% 12%	2445
	21st to end	Day	39% 9% 16% 26% 10%	2591
August	1st to 10th	Day	40% 8% 16% 25% 10%	2446
	11th to 20th	Day	40% 7% 17% 27% 8% 1	2290
	21st to end	Day	39% 6% 16% 27% 11% 1	2376
September	1st to 10th	Day	39% 7% 15% 27% 11%	2160
	11th to 20th	Day	37% 6% 14% 31% 11% 1	2160
	21st to end	Day	44% 7% 14% 27% 9%	1915
October	1st to 10th	Day	48% 6% 13% 22% 10% 1	1800
	11th to 20th	Day	56% 6% 15% 16% 6% 1	1800
	21st to end	Day	59% 5% 13% 15% 7% 1	1845
November	1st to 10th	Day	48% 6% 15% 24% 6% 1	1661
	11th to 20th	Day	57% 6% 13% 15% 7% 1	1520
	21st to end	Day	65% 7% 13% 9% 7% 1	1520
December	1st to 10th	Day	69% 5% 12% 10% 3 1	1520
	11th to 20th	Day	61% 7% 13% 14% 5%	1906
	21st to end	Day	73% 3 7% 14% 3	2772
January	1st to 10th	Night	70% 4 10% 12% 5%	2649
	11th to 20th	Night	67% 5% 9% 11% 8% 1	2588
	21st to end	Night	56% 4 9% 19% 11% 1	2692
February	1st to 10th	Night	62% 5% 10% 15% 6% 1	2340
	11th to 20th	Night	57% 4 10% 19% 8% 1	2275
	21st to end	Night	56% 5% 10% 18% 11% 1	1784
March	1st to 10th	Night	58% 4 10% 18% 9% 2	2147
	11th to 20th	Night	54% 3 11% 18% 11% 3	1980
	21st to end	Night	47% 4 8% 20% 15% 5%	2070
April	1st to 10th	Night	53% 5% 9% 18% 14% 2	1800
	11th to 20th	Night	50% 5% 8% 21% 16% 2	1775
	21st to end	Night	54% 4 7% 15% 16% 4	1680
May	1st to 10th	Night	47% 6% 7% 20% 16% 5%	1440
	11th to 20th	Night	44% 5% 7% 23% 18% 3	1416
	21st to end	Night	38% 6% 15% 20% 18% 3	1551
June	1st to 10th	Night	45% 8% 14% 24% 8% 1	1440
	11th to 20th	Night	39% 6% 13% 24% 17% 2	1440
	21st to end	Night	43% 8% 13% 21% 14% 1	1440
July	1st to 10th	Night	35% 7% 13% 26% 17% 2	1400
	11th to 20th	Night	38% 6% 12% 31% 13%	1392
	21st to end	Night	35% 8% 16% 26% 14%	1486
August	1st to 10th	Night	37% 9% 18% 23% 13% 1	1465
	11th to 20th	Night	35% 7% 17% 29% 11%	1598
	21st to end	Night	37% 8% 15% 30% 11%	1974
September	1st to 10th	Night	38% 7% 12% 29% 14% 1	1800
	11th to 20th	Night	36% 6% 14% 33% 10% 2	1800
	21st to end	Night	42% 5% 12% 31% 10%	2040
October	1st to 10th	Night	46% 8% 11% 23% 13%	2160
	11th to 20th	Night	54% 6% 11% 20% 7%	2160
	21st to end	Night	58% 6% 13% 15% 8%	2510
November	1st to 10th	Night	51% 6% 14% 21% 8%	2416
	11th to 20th	Night	56% 5% 12% 17% 8% 1	2660
	21st to end	Night	62% 6% 13% 15% 5%	2660
December	1st to 10th	Night	67% 6% 10% 13% 3	2660
	11th to 20th	Night	63% 4 9% 16% 7% 1	3288
	21st to end	Night	73% 4 7% 12% 4	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	21% 23% 36% 16% 5%	180
	11th to 20th	Day	29% 21% 31% 16% 4	170
	21st to end	Day	22% 17% 37% 20% 4	210
February	1st to 10th	Day	32% 25% 33% 10% 1	240
	11th to 20th	Day	31% 25% 36% 7% 1	240
	21st to end	Day	32% 23% 30% 13% 2	337
March	1st to 10th	Day	28% 18% 32% 18% 4	420
	11th to 20th	Day	26% 20% 35% 15% 4 1	420
	21st to end	Day	33% 17% 27% 17% 6% 1	462
April	1st to 10th	Day	34% 19% 27% 14% 6%	420
	11th to 20th	Day	32% 18% 22% 15% 11% 2	412
	21st to end	Day	28% 20% 30% 14% 6% 1	420
May	1st to 10th	Day	28% 14% 30% 19% 7% 3	423
	11th to 20th	Day	20% 17% 31% 20% 8% 3	447
	21st to end	Day	20% 14% 32% 22% 11% 2	485
June	1st to 10th	Day	26% 11% 32% 22% 8% 2	450
	11th to 20th	Day	16% 16% 29% 23% 12% 3	450
	21st to end	Day	20% 13% 30% 23% 11% 3	450
July	1st to 10th	Day	10% 9% 28% 35% 15% 4	445
	11th to 20th	Day	12% 7% 33% 27% 16% 4	444
	21st to end	Day	13% 8% 31% 31% 14% 4	488
August	1st to 10th	Day	12% 7% 29% 32% 16% 4	446
	11th to 20th	Day	13% 8% 23% 29% 19% 8%	439
	21st to end	Day	16% 11% 28% 24% 14% 7%	495
September	1st to 10th	Day	15% 11% 30% 21% 15% 8%	450
	11th to 20th	Day	13% 11% 26% 24% 18% 9%	450
	21st to end	Day	17% 14% 29% 22% 14% 5%	450
October	1st to 10th	Day	24% 15% 24% 20% 13% 4	450
	11th to 20th	Day	27% 18% 28% 17% 7% 1	450
	21st to end	Day	31% 18% 24% 21% 6%	427
November	1st to 10th	Day	25% 17% 28% 20% 8% 1	355
	11th to 20th	Day	28% 22% 33% 11% 5%	180
	21st to end	Day	28% 21% 35% 12% 3 1	180
December	1st to 10th	Day	33% 16% 37% 12% 2	180
	11th to 20th	Day	31% 26% 32% 9% 2	180
	21st to end	Day	28% 22% 34% 13% 2 1	198
January	1st to 10th	Night	28% 14% 34% 20% 3	760
	11th to 20th	Night	28% 17% 28% 20% 7%	740
	21st to end	Night	19% 12% 37% 25% 5%	792
February	1st to 10th	Night	22% 17% 36% 22% 3	720
	11th to 20th	Night	21% 17% 39% 19% 4	703
	21st to end	Night	24% 19% 28% 26% 4	592
March	1st to 10th	Night	23% 16% 34% 23% 3	720
	11th to 20th	Night	24% 18% 32% 21% 6%	720
	21st to end	Night	23% 16% 28% 25% 7%	792
April	1st to 10th	Night	27% 14% 29% 25% 4	720
	11th to 20th	Night	24% 18% 29% 21% 8%	711
	21st to end	Night	25% 14% 29% 24% 8% 1	600
May	1st to 10th	Night	24% 7% 27% 31% 9% 2	360
	11th to 20th	Night	24% 10% 28% 30% 9%	354
	21st to end	Night	16% 7% 37% 27% 13%	389
June	1st to 10th	Night	19% 5% 33% 34% 10%	360
	11th to 20th	Night	17% 8% 25% 35% 14% 1	360
	21st to end	Night	19% 6% 27% 33% 15%	360
July	1st to 10th	Night	10% 4 28% 39% 18%	350
	11th to 20th	Night	13% 4 23% 43% 16% 1	348
	21st to end	Night	9% 6% 23% 45% 15% 2	394
August	1st to 10th	Night	10% 5% 20% 42% 22% 1	401
	11th to 20th	Night	11% 3 19% 40% 24% 3	534
	21st to end	Night	12% 7% 25% 35% 18% 3	786
September	1st to 10th	Night	14% 5% 29% 30% 20% 2	720
	11th to 20th	Night	16% 8% 22% 31% 19% 3	720
	21st to end	Night	20% 9% 24% 25% 20% 2	720
October	1st to 10th	Night	24% 10% 26% 24% 15% 1	720
	11th to 20th	Night	26% 13% 29% 24% 7% 1	720
	21st to end	Night	28% 14% 27% 26% 5%	792
November	1st to 10th	Night	26% 13% 26% 26% 7% 1	740
	11th to 20th	Night	25% 16% 32% 17% 9%	760
	21st to end	Night	31% 14% 26% 22% 6%	760
December	1st to 10th	Night	31% 15% 29% 21% 4	760
	11th to 20th	Night	27% 17% 30% 20% 5% 1	760
	21st to end	Night	33% 16% 30% 18% 4	836

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