Norwell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norwell clear sky chart from 2005-11-06 to 2024-11-05.

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% 8% 2 6% 4 4 4 4 5% 7% 38%	101192
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 38%	97861
Transparency	Day	44% 6% 12% 22% 15% 2	104757
	Night	45% 5% 11% 22% 15% 2	102385
Seeing	Day	20% 12% 32% 25% 10% 2	15131
	Night	21% 11% 33% 26% 8% 1	23983

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	15% 9% 3 6% 3 4 4 3 4 5% 45%	2517
	11th to 20th	Day	18% 9% 3 6% 3 3 4 4 5% 5% 40%	2520
	21st to end	Day	22% 11% 3 9% 4 3 4 3 4 5% 32%	2772
February	1st to 10th	Day	20% 9% 3 5% 5% 4 6% 4 5% 5% 35%	1796
	11th to 20th	Day	14% 8% 2 7% 3 4 4 3 5% 7% 42%	1848
	21st to end	Day	18% 8% 3 6% 4 5% 4 4 5% 7% 36%	1570
March	1st to 10th	Day	26% 14% 3 6% 4 3 3 3 4 5% 30%	3116
	11th to 20th	Day	12% 8% 2 7% 4 4 5% 4 6% 8% 41%	3375
	21st to end	Day	24% 8% 2 6% 4 4 4 3 4 5% 35%	3964
April	1st to 10th	Day	19% 10% 3 5% 4 3 4 3 6% 5% 38%	2280
	11th to 20th	Day	17% 8% 2 6% 4 4 4 4 5% 6% 39%	2288
	21st to end	Day	18% 7% 1 6% 4 4 4 3 5% 7% 40%	2470
May	1st to 10th	Day	23% 13% 3 8% 4 3 4 3 5% 6% 28%	4106
	11th to 20th	Day	24% 10% 2 7% 5% 4 4 3 4 6% 32%	4081
	21st to end	Day	14% 6% 2 5% 4 3 4 4 6% 8% 45%	4821
June	1st to 10th	Day	20% 6% 2 5% 4 3 5% 5% 7% 9% 34%	2660
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 5% 6% 10% 37%	2660
	21st to end	Day	14% 7% 2 6% 4 5% 4 4 7% 9% 36%	2660
July	1st to 10th	Day	11% 7% 2 6% 5% 5% 6% 5% 8% 11% 35%	4440
	11th to 20th	Day	9% 7% 2 7% 4 5% 5% 5% 7% 10% 39%	4440
	21st to end	Day	17% 7% 3 7% 5% 4 5% 4 6% 8% 36%	4787
August	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 5% 7% 9% 31%	4105
	11th to 20th	Day	11% 9% 3 7% 4 5% 6% 4 6% 7% 38%	4045
	21st to end	Day	8% 4 1 5% 4 6% 6% 5% 6% 10% 45%	4183
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 47%	2252
	11th to 20th	Day	14% 6% 1 5% 3 3 3 2 3 6% 53%	2090
	21st to end	Day	18% 6% 2 5% 3 4 3 4 5% 7% 43%	2090
October	1st to 10th	Day	23% 6% 2 5% 3 3 3 3 5% 6% 42%	2090
	11th to 20th	Day	15% 6% 2 5% 3 3 4 3 4 8% 47%	1872
	21st to end	Day	19% 7% 2 5% 4 3 4 4 4 6% 42%	1881
November	1st to 10th	Day	18% 6% 2 6% 4 3 4 3 3 6% 46%	1708
	11th to 20th	Day	17% 7% 2 5% 4 3 4 3 5% 6% 44%	1710
	21st to end	Day	18% 7% 3 5% 4 4 4 3 4 6% 43%	1710
December	1st to 10th	Day	17% 9% 3 6% 4 3 4 3 4 6% 39%	1607
	11th to 20th	Day	20% 9% 2 6% 4 2 3 3 4 5% 41%	1906
	21st to end	Day	21% 11% 3 7% 5% 4 4 3 4 5% 34%	2772
January	1st to 10th	Night	18% 7% 2 5% 3 3 3 3 4 6% 47%	4429
	11th to 20th	Night	15% 10% 4 9% 4 3 3 3 4 5% 39%	4440
	21st to end	Night	22% 14% 4 8% 4 4 4 3 3 5% 28%	4884
February	1st to 10th	Night	17% 10% 3 7% 4 4 4 3 5% 6% 37%	2380
	11th to 20th	Night	16% 9% 3 7% 4 4 3 4 5% 5% 39%	2218
	21st to end	Night	18% 8% 1 6% 4 4 3 3 5% 5% 42%	1884
March	1st to 10th	Night	30% 11% 2 4 3 3 3 3 4 5% 31%	3724
	11th to 20th	Night	11% 9% 3 6% 5% 5% 5% 4 6% 6% 40%	3582
	21st to end	Night	25% 9% 3 7% 4 4 4 3 4 4 33%	3663
April	1st to 10th	Night	17% 10% 3 7% 5% 4 4 2 6% 7% 35%	1900
	11th to 20th	Night	19% 8% 2 5% 5% 4 5% 3 5% 6% 37%	1839
	21st to end	Night	18% 8% 3 7% 4 5% 4 3 5% 5% 38%	1710
May	1st to 10th	Night	24% 11% 4 8% 4 3 4 3 5% 6% 27%	2834
	11th to 20th	Night	24% 10% 3 7% 5% 5% 5% 4 6% 6% 25%	2813
	21st to end	Night	16% 6% 3 6% 5% 4 4 3 6% 8% 39%	2782
June	1st to 10th	Night	18% 7% 3 6% 4 4 5% 4 6% 7% 37%	1520
	11th to 20th	Night	16% 8% 3 6% 5% 4 4 5% 5% 8% 37%	1520
	21st to end	Night	16% 7% 2 6% 3 4 4 4 6% 9% 38%	1520
July	1st to 10th	Night	10% 7% 3 8% 5% 4 5% 4 8% 10% 36%	2520
	11th to 20th	Night	9% 7% 3 7% 5% 4 5% 4 8% 9% 37%	2520
	21st to end	Night	17% 8% 3 7% 4 4 4 5% 6% 7% 33%	2739
August	1st to 10th	Night	17% 8% 3 8% 5% 5% 5% 5% 7% 9% 29%	2820
	11th to 20th	Night	8% 9% 3 8% 4 5% 5% 5% 7% 8% 37%	2782
	21st to end	Night	8% 4 1 4 4 4 3 4 6% 8% 53%	3470
September	1st to 10th	Night	11% 6% 2 7% 4 4 4 4 6% 6% 46%	1928
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 7% 52%	2090
	21st to end	Night	18% 5% 2 6% 4 4 4 3 6% 6% 42%	2090
October	1st to 10th	Night	21% 6% 2 6% 4 3 3 4 4 6% 42%	2090
	11th to 20th	Night	15% 5% 2 6% 3 3 4 3 6% 6% 47%	2302
	21st to end	Night	20% 7% 3 6% 4 4 4 3 4 6% 39%	2717
November	1st to 10th	Night	15% 6% 2 6% 4 4 3 4 5% 7% 45%	2470
	11th to 20th	Night	16% 9% 3 6% 3 3 3 3 4 5% 45%	2470
	21st to end	Night	16% 7% 2 5% 5% 3 4 3 5% 7% 43%	2470
December	1st to 10th	Night	20% 8% 2 6% 4 4 4 3 5% 5% 39%	2569
	11th to 20th	Night	19% 8% 2 5% 4 4 4 3 6% 6% 39%	3288
	21st to end	Night	19% 10% 3 8% 4 3 3 3 4 6% 36%	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	42% 3 8% 32% 14% 1	2518
	11th to 20th	Day	46% 6% 9% 25% 12% 2	2520
	21st to end	Day	55% 5% 10% 22% 9% 1	2772
February	1st to 10th	Day	49% 6% 12% 17% 14% 2	1796
	11th to 20th	Day	43% 5% 13% 22% 16% 2	1857
	21st to end	Day	47% 6% 12% 19% 13% 3	1570
March	1st to 10th	Day	59% 3 12% 13% 11% 2	3119
	11th to 20th	Day	38% 7% 15% 23% 14% 2	3375
	21st to end	Day	52% 4 8% 15% 15% 7%	3964
April	1st to 10th	Day	48% 4 10% 18% 17% 3	2280
	11th to 20th	Day	44% 6% 9% 22% 16% 3	2288
	21st to end	Day	44% 6% 9% 21% 16% 4	2470
May	1st to 10th	Day	57% 8% 10% 14% 10% 1	4120
	11th to 20th	Day	53% 7% 13% 15% 10% 2	4085
	21st to end	Day	36% 7% 13% 24% 18% 2	4821
June	1st to 10th	Day	45% 7% 13% 23% 11% 1	2660
	11th to 20th	Day	41% 7% 15% 20% 15% 2	2660
	21st to end	Day	42% 9% 13% 21% 13% 1	2660
July	1st to 10th	Day	43% 7% 13% 20% 15% 2	4370
	11th to 20th	Day	40% 6% 16% 23% 14% 1	4365
	21st to end	Day	46% 7% 12% 20% 12% 2	4634
August	1st to 10th	Day	49% 7% 15% 21% 8% 1	4092
	11th to 20th	Day	43% 6% 14% 27% 10% 1	4084
	21st to end	Day	34% 5% 14% 28% 18% 1	4183
September	1st to 10th	Day	37% 7% 10% 24% 21% 2	2252
	11th to 20th	Day	34% 5% 9% 27% 22% 3	2090
	21st to end	Day	43% 5% 9% 20% 22% 2	2090
October	1st to 10th	Day	40% 4 10% 26% 17% 3	3480
	11th to 20th	Day	32% 3 7% 30% 25% 3	3088
	21st to end	Day	32% 4 13% 29% 19% 3	3081
November	1st to 10th	Day	40% 4 14% 24% 16% 2	1708
	11th to 20th	Day	42% 3 11% 23% 19% 2	1710
	21st to end	Day	42% 5% 13% 25% 12% 2	1710
December	1st to 10th	Day	47% 5% 14% 17% 16% 1	1607
	11th to 20th	Day	46% 4 14% 16% 16% 5%	1906
	21st to end	Day	52% 5% 11% 21% 10% 1	2772
January	1st to 10th	Night	40% 4 12% 30% 12% 3	4429
	11th to 20th	Night	48% 4 12% 22% 11% 2	4440
	21st to end	Night	59% 4 8% 16% 11% 1	4884
February	1st to 10th	Night	46% 5% 14% 19% 14% 2	2380
	11th to 20th	Night	47% 4 9% 20% 17% 3	2220
	21st to end	Night	44% 5% 9% 23% 16% 4	1884
March	1st to 10th	Night	56% 4 8% 18% 11% 3	3734
	11th to 20th	Night	42% 8% 13% 18% 17% 2	3583
	21st to end	Night	55% 3 6% 13% 16% 7%	3663
April	1st to 10th	Night	48% 5% 8% 19% 16% 3	1900
	11th to 20th	Night	46% 5% 8% 20% 18% 3	1839
	21st to end	Night	46% 5% 10% 19% 16% 4	1710
May	1st to 10th	Night	56% 7% 12% 15% 8% 2	2840
	11th to 20th	Night	56% 9% 13% 13% 7% 2	2814
	21st to end	Night	42% 9% 14% 21% 14% 1	2783
June	1st to 10th	Night	46% 8% 14% 21% 12%	1520
	11th to 20th	Night	45% 6% 12% 21% 15% 1	1520
	21st to end	Night	41% 8% 14% 23% 12% 1	1520
July	1st to 10th	Night	43% 7% 11% 21% 17%	2480
	11th to 20th	Night	41% 6% 17% 24% 12% 1	2472
	21st to end	Night	49% 7% 10% 19% 13% 1	2651
August	1st to 10th	Night	51% 7% 14% 18% 9% 1	2809
	11th to 20th	Night	43% 7% 15% 25% 10%	2809
	21st to end	Night	28% 5% 15% 28% 23% 1	3470
September	1st to 10th	Night	38% 6% 11% 24% 19% 1	1928
	11th to 20th	Night	34% 4 11% 24% 24% 3	2090
	21st to end	Night	42% 6% 9% 21% 20% 2	2090
October	1st to 10th	Night	41% 4 12% 26% 15% 2	3480
	11th to 20th	Night	27% 4 9% 26% 31% 3	3825
	21st to end	Night	34% 3 12% 29% 20% 2	4467
November	1st to 10th	Night	38% 6% 12% 23% 17% 3	2470
	11th to 20th	Night	42% 4 11% 21% 19% 3	2470
	21st to end	Night	40% 5% 13% 26% 13% 2	2470
December	1st to 10th	Night	47% 5% 12% 21% 14% 1	2569
	11th to 20th	Night	44% 5% 16% 16% 18% 1	3288
	21st to end	Night	50% 5% 9% 25% 11% 1	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% 21% 27% 21% 5%	180
	11th to 20th	Day	20% 23% 39% 15% 2 1	180
	21st to end	Day	23% 20% 38% 14% 5%	198
February	1st to 10th	Day	24% 19% 39% 16% 1	408
	11th to 20th	Day	20% 24% 41% 14% 1	456
	21st to end	Day	22% 20% 39% 15% 4 1	382
March	1st to 10th	Day	22% 20% 37% 17% 4	460
	11th to 20th	Day	21% 20% 40% 13% 5% 1	460
	21st to end	Day	24% 19% 35% 14% 7% 1	506
April	1st to 10th	Day	25% 19% 31% 18% 6% 1	460
	11th to 20th	Day	23% 13% 39% 21% 4	452
	21st to end	Day	23% 12% 36% 24% 3 1	460
May	1st to 10th	Day	28% 16% 33% 18% 4 1	463
	11th to 20th	Day	20% 10% 36% 24% 8% 1	487
	21st to end	Day	17% 8% 29% 34% 10% 2	529
June	1st to 10th	Day	20% 6% 29% 32% 11% 2	490
	11th to 20th	Day	14% 9% 36% 30% 8% 2	490
	21st to end	Day	14% 8% 31% 32% 13% 1	490
July	1st to 10th	Day	17% 5% 21% 35% 19% 2	485
	11th to 20th	Day	14% 5% 24% 36% 18% 3	484
	21st to end	Day	11% 5% 25% 41% 15% 2	532
August	1st to 10th	Day	13% 3 28% 38% 16% 2	486
	11th to 20th	Day	14% 5% 26% 33% 18% 5%	479
	21st to end	Day	13% 6% 25% 33% 16% 7%	539
September	1st to 10th	Day	17% 7% 25% 29% 17% 5%	490
	11th to 20th	Day	18% 8% 24% 25% 16% 8%	490
	21st to end	Day	22% 8% 27% 27% 11% 5%	490
October	1st to 10th	Day	27% 8% 23% 26% 12% 4	490
	11th to 20th	Day	16% 12% 31% 25% 13% 3	423
	21st to end	Day	23% 12% 34% 21% 8% 2	429
November	1st to 10th	Day	17% 17% 29% 22% 14% 1	378
	11th to 20th	Day	23% 17% 36% 17% 6% 1	370
	21st to end	Day	19% 19% 34% 18% 8% 1	370
December	1st to 10th	Day	21% 16% 40% 18% 6%	267
	11th to 20th	Day	24% 23% 38% 12% 2	180
	21st to end	Day	22% 18% 38% 15% 4 2	198
January	1st to 10th	Night	23% 17% 41% 17% 3	760
	11th to 20th	Night	26% 19% 37% 15% 3	760
	21st to end	Night	20% 17% 39% 20% 4	836
February	1st to 10th	Night	23% 17% 38% 21% 1	760
	11th to 20th	Night	23% 19% 42% 14% 2	743
	21st to end	Night	21% 18% 36% 20% 4	628
March	1st to 10th	Night	24% 17% 36% 19% 4	760
	11th to 20th	Night	22% 15% 40% 19% 4 1	760
	21st to end	Night	24% 13% 37% 20% 6%	836
April	1st to 10th	Night	23% 13% 37% 22% 5%	760
	11th to 20th	Night	22% 11% 38% 23% 5%	715
	21st to end	Night	24% 10% 34% 28% 4	570
May	1st to 10th	Night	27% 9% 33% 24% 6% 1	570
	11th to 20th	Night	22% 8% 38% 25% 6% 1	562
	21st to end	Night	20% 6% 27% 38% 9%	442
June	1st to 10th	Night	19% 5% 29% 36% 11% 1	380
	11th to 20th	Night	20% 3 29% 38% 9% 1	380
	21st to end	Night	18% 3 28% 41% 9%	380
July	1st to 10th	Night	13% 3 25% 47% 11% 1	370
	11th to 20th	Night	16% 3 21% 48% 11% 1	368
	21st to end	Night	14% 2 21% 49% 13%	416
August	1st to 10th	Night	11% 4 24% 48% 13%	563
	11th to 20th	Night	14% 3 25% 42% 15% 1	562
	21st to end	Night	14% 3 19% 41% 21% 3	830
September	1st to 10th	Night	14% 2 28% 37% 18% 2	760
	11th to 20th	Night	17% 4 24% 32% 20% 3	760
	21st to end	Night	21% 4 26% 31% 15% 3	760
October	1st to 10th	Night	24% 7% 26% 26% 14% 2	760
	11th to 20th	Night	18% 10% 33% 26% 11% 2	760
	21st to end	Night	24% 12% 34% 22% 8% 1	836
November	1st to 10th	Night	18% 11% 32% 28% 9% 1	760
	11th to 20th	Night	21% 17% 35% 19% 7% 1	760
	21st to end	Night	19% 20% 34% 21% 5%	760
December	1st to 10th	Night	24% 15% 38% 18% 4	760
	11th to 20th	Night	23% 19% 35% 20% 3	760
	21st to end	Night	23% 16% 40% 18% 3	836

Page generated at 2024-11-03 02:11:24. Version ac07

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