Cambridge Narrows
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cambridge Narrows clear sky chart from 2005-11-06 to 2026-02-01.

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% 3 8% 5% 4 4 3 5% 6% 33%	127588
	Night	19% 11% 3 8% 5% 4 4 3 5% 6% 32%	124568
Transparency	Day	52% 5% 12% 20% 11% 1	131105
	Night	52% 5% 11% 20% 11% 1	129125
Seeing	Day	29% 18% 30% 16% 5% 1	18052
	Night	28% 16% 30% 21% 5%	25984

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	12% 20% 6% 13% 5% 4 3 3 3 4 27%	3227
	11th to 20th	Day	12% 14% 5% 13% 6% 5% 3 4 4 4 30%	3532
	21st to end	Day	11% 9% 3 8% 5% 4 5% 4 5% 7% 38%	4494
February	1st to 10th	Day	16% 13% 3 7% 6% 5% 4 5% 5% 5% 31%	1800
	11th to 20th	Day	16% 13% 4 7% 6% 4 4 4 5% 6% 30%	1753
	21st to end	Day	11% 13% 4 8% 5% 5% 5% 4 4 6% 36%	1580
March	1st to 10th	Day	22% 13% 4 13% 4 3 3 3 4 4 26%	4769
	11th to 20th	Day	19% 14% 4 9% 4 4 4 3 5% 6% 27%	4980
	21st to end	Day	27% 13% 4 8% 4 4 3 3 6% 6% 22%	5466
April	1st to 10th	Day	22% 16% 3 6% 4 5% 4 3 6% 5% 27%	2331
	11th to 20th	Day	19% 11% 3 6% 5% 4 4 3 5% 6% 34%	2572
	21st to end	Day	23% 11% 3 6% 4 4 3 3 5% 5% 34%	2600
May	1st to 10th	Day	26% 13% 4 8% 4 4 4 3 5% 6% 23%	5886
	11th to 20th	Day	24% 10% 3 6% 5% 4 4 3 5% 6% 30%	6259
	21st to end	Day	19% 9% 3 7% 5% 5% 4 4 6% 7% 30%	7058
June	1st to 10th	Day	24% 10% 2 7% 4 5% 5% 4 5% 7% 28%	3000
	11th to 20th	Day	20% 8% 3 6% 4 3 4 4 5% 7% 35%	3000
	21st to end	Day	26% 9% 3 7% 4 4 4 4 5% 6% 28%	3000
July	1st to 10th	Day	16% 8% 3 7% 5% 5% 6% 5% 7% 9% 29%	6820
	11th to 20th	Day	16% 6% 3 6% 4 4 4 4 6% 8% 38%	6820
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	6569
August	1st to 10th	Day	20% 9% 3 7% 5% 5% 5% 3 5% 7% 33%	4235
	11th to 20th	Day	14% 6% 3 8% 5% 6% 5% 4 7% 8% 34%	4175
	21st to end	Day	14% 5% 2 5% 4 4 4 4 5% 7% 46%	4657
September	1st to 10th	Day	13% 6% 2 4 3 5% 4 4 6% 8% 46%	2395
	11th to 20th	Day	16% 6% 2 5% 4 3 3 3 5% 5% 48%	2200
	21st to end	Day	19% 6% 2 5% 3 3 3 3 4 5% 46%	2200
October	1st to 10th	Day	18% 7% 3 6% 5% 3 3 3 4 8% 40%	2019
	11th to 20th	Day	20% 9% 2 5% 5% 4 4 3 4 6% 37%	2000
	21st to end	Day	20% 10% 3 8% 4 4 4 4 5% 6% 32%	2100
November	1st to 10th	Day	22% 10% 2 6% 5% 4 4 3 4 5% 35%	1756
	11th to 20th	Day	19% 11% 3 7% 4 4 4 2 4 7% 34%	1680
	21st to end	Day	21% 13% 4 9% 5% 5% 4 3 4 5% 28%	1680
December	1st to 10th	Day	19% 12% 5% 9% 4 3 4 3 5% 6% 30%	2690
	11th to 20th	Day	22% 12% 4 8% 5% 3 2 2 3 4 34%	2732
	21st to end	Day	17% 12% 4 8% 4 4 4 3 5% 5% 33%	3553
January	1st to 10th	Night	14% 15% 5% 9% 6% 4 4 3 5% 6% 28%	6958
	11th to 20th	Night	17% 12% 4 11% 5% 5% 4 3 5% 6% 29%	6575
	21st to end	Night	10% 12% 3 6% 5% 5% 4 4 5% 7% 40%	6702
February	1st to 10th	Night	16% 12% 4 8% 5% 4 4 3 5% 6% 32%	2601
	11th to 20th	Night	16% 14% 4 8% 6% 4 4 4 5% 6% 29%	2533
	21st to end	Night	14% 14% 4 7% 6% 4 5% 3 5% 4 35%	2046
March	1st to 10th	Night	26% 15% 3 8% 5% 5% 4 2 3 4 25%	5071
	11th to 20th	Night	21% 14% 3 8% 5% 5% 4 3 5% 6% 26%	4979
	21st to end	Night	30% 12% 3 7% 4 3 4 3 4 4 27%	5466
April	1st to 10th	Night	23% 13% 3 8% 4 4 3 3 5% 4 29%	2065
	11th to 20th	Night	24% 10% 2 7% 4 4 4 3 4 6% 33%	1778
	21st to end	Night	22% 11% 3 7% 4 4 4 3 6% 6% 30%	1800
May	1st to 10th	Night	27% 12% 3 8% 4 4 4 3 4 6% 25%	4054
	11th to 20th	Night	23% 10% 2 6% 4 5% 4 3 5% 5% 33%	3650
	21st to end	Night	17% 10% 3 7% 5% 4 4 4 6% 7% 32%	3867
June	1st to 10th	Night	25% 8% 3 8% 4 5% 5% 3 5% 7% 28%	1400
	11th to 20th	Night	21% 8% 2 6% 5% 4 4 3 5% 6% 35%	1400
	21st to end	Night	27% 8% 3 7% 4 4 4 3 5% 6% 30%	1400
July	1st to 10th	Night	18% 7% 3 8% 6% 6% 5% 4 7% 8% 28%	3160
	11th to 20th	Night	18% 7% 2 7% 5% 4 4 4 7% 9% 33%	3160
	21st to end	Night	16% 6% 3 6% 4 4 5% 4 7% 9% 38%	4237
August	1st to 10th	Night	20% 9% 3 7% 4 5% 5% 3 5% 7% 30%	2915
	11th to 20th	Night	13% 7% 2 7% 4 5% 6% 4 7% 8% 36%	2872
	21st to end	Night	13% 5% 2 5% 3 4 4 4 7% 7% 46%	3241
September	1st to 10th	Night	17% 5% 2 5% 3 4 4 4 5% 7% 42%	2002
	11th to 20th	Night	16% 7% 2 5% 4 3 4 3 4 7% 46%	2200
	21st to end	Night	19% 5% 2 6% 4 3 4 3 5% 6% 43%	2200
October	1st to 10th	Night	19% 7% 2 5% 4 3 4 3 5% 6% 42%	2380
	11th to 20th	Night	17% 9% 3 7% 5% 4 4 3 4 7% 38%	2400
	21st to end	Night	22% 10% 3 7% 4 4 4 4 5% 5% 33%	2737
November	1st to 10th	Night	21% 9% 3 7% 5% 4 4 3 4 6% 35%	2761
	11th to 20th	Night	19% 11% 3 8% 4 5% 4 4 5% 6% 32%	2940
	21st to end	Night	21% 12% 4 8% 5% 4 4 3 4 5% 30%	2940
December	1st to 10th	Night	17% 11% 4 9% 5% 4 5% 3 4 6% 31%	4720
	11th to 20th	Night	21% 11% 3 8% 4 4 3 2 4 4 36%	5691
	21st to end	Night	20% 14% 4 9% 4 3 3 3 4 5% 30%	7667

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	63% 3 12% 14% 7%	3228
	11th to 20th	Day	57% 4 12% 18% 9% 1	3562
	21st to end	Day	45% 5% 11% 16% 20% 3	4494
February	1st to 10th	Day	54% 4 11% 18% 11% 2	1800
	11th to 20th	Day	55% 4 12% 17% 11% 1	1761
	21st to end	Day	49% 5% 12% 22% 10% 3	1580
March	1st to 10th	Day	63% 3 8% 13% 11% 3	4773
	11th to 20th	Day	58% 5% 14% 15% 7% 2	4980
	21st to end	Day	63% 3 6% 16% 9% 1	5466
April	1st to 10th	Day	59% 5% 8% 13% 12% 3	2331
	11th to 20th	Day	52% 4 10% 20% 13% 1	2572
	21st to end	Day	53% 4 9% 17% 12% 4	2600
May	1st to 10th	Day	63% 4 8% 15% 9% 1	5897
	11th to 20th	Day	55% 6% 11% 19% 6% 2	6263
	21st to end	Day	52% 7% 12% 17% 12% 1	7058
June	1st to 10th	Day	56% 5% 11% 17% 10% 1	3000
	11th to 20th	Day	50% 5% 11% 20% 13% 2	3000
	21st to end	Day	57% 7% 10% 16% 10% 1	3000
July	1st to 10th	Day	50% 7% 15% 18% 10%	6745
	11th to 20th	Day	43% 6% 16% 25% 9% 1	6739
	21st to end	Day	44% 7% 14% 25% 9%	6382
August	1st to 10th	Day	52% 6% 10% 23% 8%	4222
	11th to 20th	Day	45% 7% 15% 23% 9%	4214
	21st to end	Day	37% 6% 14% 27% 16% 1	4657
September	1st to 10th	Day	37% 6% 14% 28% 15% 1	2395
	11th to 20th	Day	39% 4 10% 27% 17% 2	2200
	21st to end	Day	41% 4 9% 27% 18% 1	2200
October	1st to 10th	Day	46% 5% 10% 28% 11%	3279
	11th to 20th	Day	48% 4 9% 30% 9%	3240
	21st to end	Day	41% 5% 16% 21% 17%	3376
November	1st to 10th	Day	53% 5% 10% 21% 11% 1	1756
	11th to 20th	Day	50% 5% 14% 17% 13% 1	1680
	21st to end	Day	59% 4 14% 17% 6%	1680
December	1st to 10th	Day	55% 5% 15% 20% 4	2690
	11th to 20th	Day	57% 4 9% 17% 10% 4	2732
	21st to end	Day	53% 4 13% 17% 11% 2	3553
January	1st to 10th	Night	57% 5% 12% 21% 5% 1	6958
	11th to 20th	Night	55% 5% 12% 21% 7% 1	6620
	21st to end	Night	45% 4 9% 22% 17% 3	6702
February	1st to 10th	Night	54% 4 12% 16% 13% 2	2601
	11th to 20th	Night	56% 5% 10% 17% 11% 2	2536
	21st to end	Night	52% 4 9% 20% 12% 3	2046
March	1st to 10th	Night	64% 3 6% 12% 12% 3	5080
	11th to 20th	Night	59% 6% 14% 13% 8% 1	4980
	21st to end	Night	63% 2 5% 17% 11% 1	5466
April	1st to 10th	Night	59% 4 7% 14% 12% 4	2065
	11th to 20th	Night	54% 4 9% 19% 13% 1	1778
	21st to end	Night	55% 5% 9% 16% 14% 2	1800
May	1st to 10th	Night	62% 4 10% 15% 8% 1	4060
	11th to 20th	Night	52% 7% 10% 21% 7% 2	3651
	21st to end	Night	50% 8% 15% 19% 8% 1	3868
June	1st to 10th	Night	57% 5% 9% 20% 9% 1	1400
	11th to 20th	Night	51% 5% 12% 23% 9% 2	1400
	21st to end	Night	58% 5% 10% 16% 10% 1	1400
July	1st to 10th	Night	54% 6% 13% 18% 9%	3125
	11th to 20th	Night	47% 7% 13% 25% 7%	3118
	21st to end	Night	44% 7% 15% 24% 11% 1	4110
August	1st to 10th	Night	55% 6% 10% 22% 7%	2903
	11th to 20th	Night	44% 8% 17% 23% 9%	2899
	21st to end	Night	37% 7% 15% 25% 15% 3	3240
September	1st to 10th	Night	41% 7% 9% 28% 14% 1	2002
	11th to 20th	Night	40% 4 12% 27% 16% 1	2200
	21st to end	Night	42% 5% 9% 27% 15% 2	2200
October	1st to 10th	Night	46% 5% 12% 25% 12% 1	3887
	11th to 20th	Night	42% 4 12% 26% 15%	3899
	21st to end	Night	46% 5% 14% 22% 14%	4411
November	1st to 10th	Night	51% 6% 12% 20% 11% 1	2761
	11th to 20th	Night	53% 5% 12% 19% 10% 1	2940
	21st to end	Night	56% 5% 14% 16% 8%	2940
December	1st to 10th	Night	54% 4 12% 22% 8%	4720
	11th to 20th	Night	54% 3 10% 19% 13% 1	5692
	21st to end	Night	57% 4 9% 18% 10% 2	7667

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	35% 21% 31% 11% 1	220
	11th to 20th	Day	40% 21% 25% 8% 4	220
	21st to end	Day	23% 21% 38% 15% 2 1	441
February	1st to 10th	Day	34% 18% 29% 16% 3 1	400
	11th to 20th	Day	35% 25% 27% 10% 2 1	396
	21st to end	Day	29% 25% 29% 14% 3	379
March	1st to 10th	Day	34% 23% 28% 12% 2 1	500
	11th to 20th	Day	31% 24% 29% 13% 3 1	500
	21st to end	Day	38% 23% 24% 10% 4 1	550
April	1st to 10th	Day	44% 21% 22% 9% 3	500
	11th to 20th	Day	36% 23% 25% 12% 3 1	492
	21st to end	Day	36% 21% 26% 12% 5% 1	500
May	1st to 10th	Day	37% 19% 28% 11% 4 1	503
	11th to 20th	Day	30% 17% 29% 18% 5% 1	691
	21st to end	Day	29% 18% 31% 17% 4 1	790
June	1st to 10th	Day	33% 17% 27% 17% 5%	730
	11th to 20th	Day	28% 18% 29% 19% 6%	730
	21st to end	Day	33% 12% 29% 19% 6%	730
July	1st to 10th	Day	25% 13% 36% 20% 7% 1	720
	11th to 20th	Day	20% 10% 37% 22% 9% 1	718
	21st to end	Day	18% 14% 37% 24% 6% 1	604
August	1st to 10th	Day	18% 13% 38% 24% 6% 2	526
	11th to 20th	Day	20% 10% 35% 25% 8% 2	519
	21st to end	Day	20% 15% 32% 22% 8% 3	583
September	1st to 10th	Day	15% 17% 36% 22% 8% 2	530
	11th to 20th	Day	23% 15% 28% 19% 11% 3	530
	21st to end	Day	24% 16% 32% 18% 7% 3	530
October	1st to 10th	Day	26% 14% 23% 23% 12% 2	430
	11th to 20th	Day	28% 20% 25% 17% 8% 2	420
	21st to end	Day	32% 16% 34% 13% 5%	462
November	1st to 10th	Day	34% 16% 30% 15% 5% 1	425
	11th to 20th	Day	37% 17% 25% 15% 5%	430
	21st to end	Day	35% 21% 29% 13% 2 1	430
December	1st to 10th	Day	36% 18% 28% 15% 3	430
	11th to 20th	Day	41% 27% 23% 8%	251
	21st to end	Day	37% 23% 29% 9% 2	242
January	1st to 10th	Night	29% 21% 29% 17% 4	950
	11th to 20th	Night	32% 18% 26% 20% 4	867
	21st to end	Night	23% 20% 35% 19% 4	924
February	1st to 10th	Night	27% 21% 31% 19% 2	801
	11th to 20th	Night	30% 24% 30% 14% 2	783
	21st to end	Night	26% 19% 31% 20% 3	660
March	1st to 10th	Night	30% 19% 32% 17% 2	800
	11th to 20th	Night	29% 17% 32% 18% 4 1	800
	21st to end	Night	28% 19% 33% 16% 5%	880
April	1st to 10th	Night	36% 18% 28% 17% 2	690
	11th to 20th	Night	30% 17% 32% 18% 4	594
	21st to end	Night	31% 17% 29% 18% 5%	600
May	1st to 10th	Night	31% 15% 30% 20% 4 1	600
	11th to 20th	Night	31% 15% 32% 18% 4	592
	21st to end	Night	22% 17% 38% 18% 4	620
June	1st to 10th	Night	28% 9% 35% 24% 4	400
	11th to 20th	Night	26% 13% 31% 26% 4	400
	21st to end	Night	31% 8% 28% 29% 4 1	400
July	1st to 10th	Night	21% 7% 37% 28% 7%	390
	11th to 20th	Night	24% 4 33% 32% 7%	388
	21st to end	Night	21% 7% 36% 31% 6% 1	598
August	1st to 10th	Night	18% 7% 34% 32% 10%	598
	11th to 20th	Night	21% 8% 27% 34% 9%	592
	21st to end	Night	16% 8% 33% 30% 12% 1	660
September	1st to 10th	Night	21% 9% 38% 23% 9%	602
	11th to 20th	Night	22% 9% 27% 29% 13% 1	800
	21st to end	Night	23% 12% 29% 26% 10% 1	800
October	1st to 10th	Night	24% 11% 27% 28% 9% 2	800
	11th to 20th	Night	23% 16% 30% 23% 8% 1	800
	21st to end	Night	31% 17% 28% 19% 4	880
November	1st to 10th	Night	32% 15% 27% 19% 6% 1	870
	11th to 20th	Night	30% 18% 27% 18% 6% 1	950
	21st to end	Night	32% 18% 28% 19% 3	950
December	1st to 10th	Night	34% 16% 30% 17% 3	950
	11th to 20th	Night	34% 23% 26% 14% 3	950
	21st to end	Night	32% 22% 25% 17% 4	1045

Page generated at 2026-01-29 02:21:44. Version ac07

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