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 2024-11-28.

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% 10% 3 7% 5% 4 4 4 5% 7% 33%	101772
	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 32%	97842
Transparency	Day	51% 5% 12% 20% 11% 1	105303
	Night	52% 5% 11% 20% 10% 1	102387
Seeing	Day	30% 17% 30% 17% 5% 1	16553
	Night	28% 16% 30% 21% 5%	24364

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	13% 14% 5% 11% 5% 4 3 3 4 6% 33%	2207
	11th to 20th	Day	15% 12% 4 10% 5% 4 3 4 4 4 36%	2431
	21st to end	Day	14% 9% 3 8% 6% 4 6% 4 6% 8% 33%	3068
February	1st to 10th	Day	17% 12% 3 7% 6% 5% 4 5% 5% 5% 31%	1710
	11th to 20th	Day	16% 12% 4 7% 6% 4 4 4 5% 6% 30%	1663
	21st to end	Day	12% 13% 4 7% 5% 5% 4 4 4 7% 36%	1503
March	1st to 10th	Day	22% 15% 5% 9% 5% 3 3 3 4 5% 28%	3325
	11th to 20th	Day	17% 17% 5% 10% 5% 5% 4 3 4 6% 24%	3480
	21st to end	Day	28% 12% 4 8% 4 4 3 3 5% 5% 22%	3816
April	1st to 10th	Day	21% 16% 3 6% 4 4 4 3 5% 6% 27%	2214
	11th to 20th	Day	19% 10% 3 6% 4 4 4 3 5% 7% 35%	2442
	21st to end	Day	23% 11% 3 6% 4 4 3 3 5% 5% 33%	2470
May	1st to 10th	Day	20% 12% 4 8% 5% 4 4 3 5% 7% 28%	4106
	11th to 20th	Day	18% 9% 3 7% 5% 4 5% 3 5% 7% 33%	4353
	21st to end	Day	15% 8% 3 7% 5% 6% 5% 4 6% 8% 32%	4918
June	1st to 10th	Day	24% 10% 2 7% 4 5% 5% 4 5% 6% 27%	2850
	11th to 20th	Day	20% 8% 2 6% 4 3 4 3 5% 7% 35%	2850
	21st to end	Day	26% 9% 3 7% 4 4 5% 4 5% 6% 28%	2850
July	1st to 10th	Day	16% 7% 3 6% 6% 5% 6% 5% 7% 9% 32%	4760
	11th to 20th	Day	18% 8% 3 6% 4 5% 4 4 6% 8% 34%	4760
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 5% 6% 8% 34%	4569
August	1st to 10th	Day	20% 9% 3 7% 5% 5% 5% 4 5% 7% 31%	4105
	11th to 20th	Day	15% 6% 3 8% 5% 6% 5% 4 7% 8% 33%	4045
	21st to end	Day	14% 5% 2 5% 4 4 4 4 5% 7% 46%	4514
September	1st to 10th	Day	13% 6% 2 5% 4 5% 4 4 6% 8% 46%	2275
	11th to 20th	Day	17% 6% 2 4 4 3 3 3 5% 5% 47%	2090
	21st to end	Day	20% 6% 2 5% 3 3 3 3 4 5% 45%	2090
October	1st to 10th	Day	18% 7% 3 6% 5% 3 4 3 5% 8% 39%	1918
	11th to 20th	Day	20% 9% 2 5% 5% 4 4 3 4 6% 38%	1900
	21st to end	Day	20% 10% 3 7% 4 4 4 4 5% 6% 33%	1995
November	1st to 10th	Day	22% 10% 2 6% 4 4 4 3 4 5% 35%	1671
	11th to 20th	Day	19% 11% 3 7% 5% 4 4 2 4 7% 34%	1600
	21st to end	Day	22% 14% 3 8% 5% 5% 4 3 3 5% 29%	1576
December	1st to 10th	Day	25% 11% 5% 8% 5% 4 4 3 4 6% 26%	1520
	11th to 20th	Day	21% 15% 5% 10% 6% 4 3 2 4 5% 25%	1697
	21st to end	Day	20% 11% 4 8% 4 4 4 3 5% 5% 33%	2431
January	1st to 10th	Night	14% 11% 4 9% 5% 4 4 4 5% 7% 34%	4748
	11th to 20th	Night	16% 11% 4 9% 5% 5% 4 4 5% 6% 32%	4530
	21st to end	Night	14% 13% 3 8% 6% 5% 4 4 5% 6% 31%	4586
February	1st to 10th	Night	16% 12% 4 8% 5% 5% 4 3 5% 6% 31%	2470
	11th to 20th	Night	17% 13% 4 8% 6% 4 4 4 6% 6% 28%	2403
	21st to end	Night	14% 13% 4 7% 6% 4 5% 3 5% 4 34%	1947
March	1st to 10th	Night	24% 16% 3 7% 4 5% 5% 2 3 4 27%	3515
	11th to 20th	Night	19% 15% 4 10% 6% 5% 5% 3 5% 6% 22%	3479
	21st to end	Night	30% 11% 3 7% 5% 3 4 3 4 3 25%	3816
April	1st to 10th	Night	24% 13% 3 8% 4 4 3 3 5% 4 29%	1962
	11th to 20th	Night	23% 10% 2 7% 4 4 4 3 4 6% 33%	1688
	21st to end	Night	23% 11% 3 7% 4 4 4 3 6% 6% 30%	1710
May	1st to 10th	Night	21% 11% 3 8% 4 4 4 4 4 7% 29%	2834
	11th to 20th	Night	19% 8% 2 6% 4 5% 4 4 6% 7% 36%	2547
	21st to end	Night	16% 8% 3 8% 6% 5% 5% 4 6% 8% 31%	2696
June	1st to 10th	Night	25% 8% 3 8% 4 5% 4 3 5% 7% 27%	1330
	11th to 20th	Night	21% 8% 2 6% 5% 4 4 3 5% 6% 35%	1330
	21st to end	Night	27% 8% 3 7% 5% 4 4 3 5% 5% 30%	1330
July	1st to 10th	Night	16% 7% 2 8% 6% 5% 5% 4 7% 8% 31%	2210
	11th to 20th	Night	20% 7% 2 6% 5% 5% 4 4 7% 9% 29%	2210
	21st to end	Night	19% 6% 3 7% 4 4 5% 4 6% 7% 34%	2951
August	1st to 10th	Night	21% 9% 4 7% 5% 5% 6% 3 6% 7% 28%	2825
	11th to 20th	Night	13% 7% 2 7% 5% 5% 6% 4 7% 8% 35%	2782
	21st to end	Night	13% 5% 2 5% 3 4 4 4 6% 7% 46%	3142
September	1st to 10th	Night	17% 6% 2 5% 3 4 4 4 5% 8% 41%	1902
	11th to 20th	Night	17% 7% 2 5% 4 3 4 3 4 7% 45%	2090
	21st to end	Night	20% 5% 2 6% 4 3 4 3 5% 6% 43%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 3 4 3 6% 6% 40%	2261
	11th to 20th	Night	17% 9% 3 7% 4 4 4 3 5% 6% 38%	2280
	21st to end	Night	22% 10% 3 7% 4 4 4 4 4 5% 34%	2600
November	1st to 10th	Night	21% 9% 3 7% 4 4 4 3 4 6% 35%	2626
	11th to 20th	Night	19% 11% 3 8% 4 5% 4 4 5% 6% 32%	2800
	21st to end	Night	22% 12% 4 7% 5% 4 4 3 5% 6% 29%	2759
December	1st to 10th	Night	26% 12% 4 8% 5% 4 4 3 4 5% 26%	2660
	11th to 20th	Night	25% 12% 4 8% 5% 5% 4 3 4 5% 26%	3497
	21st to end	Night	22% 13% 4 8% 5% 3 3 3 3 4 31%	5236

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	54% 3 17% 16% 9%	2208
	11th to 20th	Day	52% 3 10% 22% 12% 1	2431
	21st to end	Day	49% 6% 15% 16% 14% 1	3068
February	1st to 10th	Day	55% 4 11% 18% 10% 2	1710
	11th to 20th	Day	55% 4 12% 17% 11% 1	1671
	21st to end	Day	49% 5% 12% 22% 9% 3	1503
March	1st to 10th	Day	60% 3 8% 18% 7% 3	3329
	11th to 20th	Day	62% 5% 10% 12% 9% 1	3480
	21st to end	Day	64% 3 7% 14% 10% 2	3816
April	1st to 10th	Day	60% 5% 8% 13% 11% 3	2214
	11th to 20th	Day	51% 4 10% 20% 14% 1	2442
	21st to end	Day	54% 4 9% 17% 13% 4	2470
May	1st to 10th	Day	57% 5% 10% 19% 9% 1	4120
	11th to 20th	Day	49% 7% 14% 20% 8% 1	4357
	21st to end	Day	48% 8% 14% 17% 13% 1	4918
June	1st to 10th	Day	57% 5% 11% 17% 9% 1	2850
	11th to 20th	Day	50% 5% 11% 20% 12% 2	2850
	21st to end	Day	57% 7% 10% 15% 10% 1	2850
July	1st to 10th	Day	47% 7% 15% 19% 11%	4685
	11th to 20th	Day	47% 7% 15% 23% 9% 1	4679
	21st to end	Day	48% 7% 13% 23% 8% 1	4423
August	1st to 10th	Day	54% 6% 10% 22% 7%	4092
	11th to 20th	Day	46% 7% 15% 23% 9%	4084
	21st to end	Day	37% 6% 14% 27% 17% 1	4514
September	1st to 10th	Day	37% 6% 14% 27% 15% 1	2275
	11th to 20th	Day	40% 4 10% 26% 17% 2	2090
	21st to end	Day	42% 4 9% 27% 17% 1	2090
October	1st to 10th	Day	47% 5% 10% 27% 10%	3178
	11th to 20th	Day	47% 4 9% 30% 9%	3140
	21st to end	Day	41% 5% 16% 21% 17%	3271
November	1st to 10th	Day	53% 4 10% 21% 11% 1	1671
	11th to 20th	Day	50% 5% 14% 17% 14% 1	1600
	21st to end	Day	59% 4 14% 17% 6%	1576
December	1st to 10th	Day	61% 4 11% 17% 6% 1	1520
	11th to 20th	Day	63% 4 9% 14% 9% 1	1697
	21st to end	Day	54% 4 15% 17% 9% 2	2431
January	1st to 10th	Night	49% 4 14% 25% 6% 1	4748
	11th to 20th	Night	53% 4 12% 22% 9% 1	4530
	21st to end	Night	53% 5% 10% 22% 10% 1	4586
February	1st to 10th	Night	54% 4 13% 16% 12% 1	2470
	11th to 20th	Night	56% 5% 9% 17% 11% 2	2406
	21st to end	Night	52% 4 9% 20% 11% 3	1947
March	1st to 10th	Night	62% 4 7% 17% 10% 2	3524
	11th to 20th	Night	62% 6% 10% 11% 8% 1	3480
	21st to end	Night	65% 2 6% 15% 10% 2	3816
April	1st to 10th	Night	59% 4 8% 13% 12% 4	1962
	11th to 20th	Night	53% 4 9% 19% 14% 1	1688
	21st to end	Night	55% 4 9% 16% 14% 2	1710
May	1st to 10th	Night	55% 5% 14% 18% 7% 1	2840
	11th to 20th	Night	46% 9% 14% 23% 8% 1	2548
	21st to end	Night	49% 9% 16% 18% 7% 1	2697
June	1st to 10th	Night	58% 5% 9% 19% 8% 1	1330
	11th to 20th	Night	51% 4 12% 22% 9% 2	1330
	21st to end	Night	58% 5% 10% 16% 10% 1	1330
July	1st to 10th	Night	51% 7% 13% 17% 12%	2175
	11th to 20th	Night	51% 8% 12% 22% 7%	2168
	21st to end	Night	49% 7% 11% 23% 9% 1	2857
August	1st to 10th	Night	56% 6% 11% 20% 6%	2813
	11th to 20th	Night	45% 8% 17% 22% 8%	2809
	21st to end	Night	37% 7% 15% 24% 15% 3	3141
September	1st to 10th	Night	41% 7% 9% 28% 14% 1	1902
	11th to 20th	Night	41% 4 12% 27% 16% 1	2090
	21st to end	Night	43% 5% 9% 27% 15% 2	2090
October	1st to 10th	Night	47% 5% 12% 24% 12%	3768
	11th to 20th	Night	42% 4 12% 27% 16%	3779
	21st to end	Night	45% 5% 14% 22% 14%	4274
November	1st to 10th	Night	50% 6% 12% 20% 11% 1	2626
	11th to 20th	Night	53% 5% 13% 18% 10% 1	2800
	21st to end	Night	57% 5% 15% 15% 8%	2759
December	1st to 10th	Night	61% 4 10% 17% 7%	2660
	11th to 20th	Night	62% 3 9% 17% 8%	3498
	21st to end	Night	58% 4 11% 19% 6% 3	5236

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	36% 21% 30% 13% 1	180
	11th to 20th	Day	41% 23% 26% 7% 3	180
	21st to end	Day	23% 19% 40% 15% 3 1	377
February	1st to 10th	Day	33% 17% 29% 16% 4 1	370
	11th to 20th	Day	35% 25% 27% 10% 2 1	366
	21st to end	Day	28% 25% 29% 15% 3	350
March	1st to 10th	Day	33% 23% 29% 12% 2 1	460
	11th to 20th	Day	31% 23% 28% 13% 3 1	460
	21st to end	Day	37% 23% 25% 10% 4 1	506
April	1st to 10th	Day	44% 20% 22% 10% 3	460
	11th to 20th	Day	35% 22% 26% 13% 3 1	452
	21st to end	Day	36% 21% 25% 12% 5% 1	460
May	1st to 10th	Day	37% 19% 27% 11% 4 1	463
	11th to 20th	Day	28% 18% 29% 18% 6% 1	642
	21st to end	Day	29% 18% 32% 17% 4 1	735
June	1st to 10th	Day	34% 17% 26% 16% 6%	680
	11th to 20th	Day	27% 16% 30% 20% 6%	680
	21st to end	Day	33% 12% 29% 19% 6%	680
July	1st to 10th	Day	25% 12% 36% 20% 7% 1	670
	11th to 20th	Day	21% 10% 37% 21% 10% 1	668
	21st to end	Day	19% 13% 37% 24% 6% 1	559
August	1st to 10th	Day	19% 12% 38% 23% 6% 1	486
	11th to 20th	Day	21% 10% 36% 24% 8% 2	479
	21st to end	Day	20% 14% 32% 23% 8% 3	539
September	1st to 10th	Day	15% 16% 37% 22% 8% 2	490
	11th to 20th	Day	24% 15% 28% 18% 12% 4	490
	21st to end	Day	25% 16% 30% 17% 8% 4	490
October	1st to 10th	Day	27% 14% 23% 22% 12% 2	399
	11th to 20th	Day	29% 19% 25% 17% 7% 2	390
	21st to end	Day	32% 16% 34% 13% 5%	429
November	1st to 10th	Day	33% 14% 31% 15% 5% 1	395
	11th to 20th	Day	38% 17% 25% 15% 5%	400
	21st to end	Day	36% 21% 28% 12% 2 1	391
December	1st to 10th	Day	36% 18% 28% 15% 3	370
	11th to 20th	Day	43% 27% 21% 9%	209
	21st to end	Day	38% 24% 27% 8% 2 1	198
January	1st to 10th	Night	30% 20% 29% 18% 4	850
	11th to 20th	Night	32% 19% 27% 19% 4	783
	21st to end	Night	23% 20% 34% 19% 4	836
February	1st to 10th	Night	27% 21% 31% 18% 3 1	760
	11th to 20th	Night	29% 24% 30% 15% 2	743
	21st to end	Night	25% 20% 31% 20% 4	628
March	1st to 10th	Night	29% 19% 33% 17% 2	760
	11th to 20th	Night	28% 18% 32% 18% 4 1	760
	21st to end	Night	27% 19% 33% 16% 5%	836
April	1st to 10th	Night	35% 17% 28% 17% 2	656
	11th to 20th	Night	29% 18% 32% 18% 4	564
	21st to end	Night	30% 17% 29% 18% 6%	570
May	1st to 10th	Night	30% 15% 31% 20% 4 1	570
	11th to 20th	Night	30% 15% 33% 18% 4	562
	21st to end	Night	22% 17% 39% 18% 4	589
June	1st to 10th	Night	29% 9% 35% 23% 4	380
	11th to 20th	Night	26% 13% 31% 26% 4	380
	21st to end	Night	31% 7% 28% 29% 4 1	380
July	1st to 10th	Night	21% 7% 37% 28% 7%	370
	11th to 20th	Night	24% 5% 33% 31% 7%	368
	21st to end	Night	22% 6% 35% 30% 6% 1	568
August	1st to 10th	Night	18% 7% 35% 30% 10%	568
	11th to 20th	Night	22% 8% 27% 34% 9%	562
	21st to end	Night	16% 9% 32% 30% 12% 1	627
September	1st to 10th	Night	21% 9% 38% 22% 9%	572
	11th to 20th	Night	22% 8% 27% 28% 13% 1	760
	21st to end	Night	24% 12% 28% 25% 11% 1	760
October	1st to 10th	Night	25% 10% 27% 28% 9% 2	760
	11th to 20th	Night	23% 16% 31% 22% 8% 1	760
	21st to end	Night	31% 17% 29% 19% 4	836
November	1st to 10th	Night	31% 15% 28% 19% 6% 1	825
	11th to 20th	Night	30% 19% 27% 18% 6% 1	900
	21st to end	Night	32% 18% 27% 19% 3	886
December	1st to 10th	Night	34% 16% 30% 16% 4	850
	11th to 20th	Night	35% 21% 27% 14% 3	850
	21st to end	Night	33% 22% 25% 16% 4	935

Page generated at 2024-11-25 01:22:20. Version ac07

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