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 2024-04-25.

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% 7% 2 5% 5% 3 4 5% 5% 7% 40%	83137
	Night	18% 8% 3 5% 5% 3 4 4 5% 6% 39%	85960
Transparency	Day	44% 6% 12% 22% 15% 2	82843
	Night	45% 6% 11% 21% 15% 2	85788
Seeing	Day	20% 12% 31% 25% 10% 2	14377
	Night	21% 11% 33% 26% 8% 1	23395

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% 8% 3 5% 4 3 4 3 4 5% 45%	2517
	11th to 20th	Day	18% 9% 3 5% 4 2 3 5% 5% 5% 40%	2520
	21st to end	Day	22% 11% 3 8% 5% 2 4 4 4 5% 33%	2772
February	1st to 10th	Day	20% 9% 3 4 5% 3 5% 5% 5% 5% 35%	1796
	11th to 20th	Day	14% 7% 3 6% 4 3 5% 4 5% 7% 42%	1848
	21st to end	Day	19% 7% 3 6% 5% 3 5% 5% 5% 7% 36%	1570
March	1st to 10th	Day	26% 13% 4 5% 4 2 4 3 4 5% 30%	3116
	11th to 20th	Day	12% 8% 3 6% 5% 3 5% 5% 6% 8% 42%	3375
	21st to end	Day	24% 8% 2 5% 5% 3 4 5% 4 5% 35%	3964
April	1st to 10th	Day	19% 9% 3 5% 4 3 4 4 5% 6% 38%	2280
	11th to 20th	Day	17% 7% 3 5% 5% 3 5% 5% 5% 7% 39%	2288
	21st to end	Day	19% 7% 2 5% 5% 3 4 4 5% 7% 40%	2395
May	1st to 10th	Day	24% 9% 2 6% 4 2 4 4 5% 7% 34%	2340
	11th to 20th	Day	18% 7% 2 4 5% 3 4 4 4 7% 41%	2301
	21st to end	Day	15% 5% 2 4 5% 2 4 5% 5% 8% 46%	2709
June	1st to 10th	Day	20% 6% 2 5% 4 3 5% 6% 7% 10% 34%	2520
	11th to 20th	Day	16% 5% 2 5% 5% 3 4 6% 6% 9% 37%	2520
	21st to end	Day	14% 6% 3 5% 5% 4 5% 6% 6% 9% 36%	2520
July	1st to 10th	Day	13% 5% 3 4 5% 3 5% 5% 7% 9% 42%	2520
	11th to 20th	Day	11% 6% 3 5% 6% 3 5% 6% 7% 9% 40%	2520
	21st to end	Day	11% 4 2 5% 5% 4 5% 6% 7% 9% 41%	2730
August	1st to 10th	Day	9% 5% 2 6% 6% 4 5% 7% 7% 11% 40%	2327
	11th to 20th	Day	11% 8% 2 5% 5% 4 5% 5% 7% 8% 40%	2304
	21st to end	Day	14% 5% 2 5% 4 3 5% 5% 5% 9% 45%	2379
September	1st to 10th	Day	13% 5% 2 5% 5% 2 4 4 6% 7% 47%	2134
	11th to 20th	Day	14% 6% 2 4 4 2 3 3 3 6% 53%	1980
	21st to end	Day	18% 6% 2 4 3 3 4 4 5% 7% 45%	1980
October	1st to 10th	Day	24% 6% 2 4 4 2 3 3 4 6% 42%	1980
	11th to 20th	Day	15% 5% 2 5% 4 3 3 5% 4 8% 46%	1774
	21st to end	Day	20% 7% 2 4 4 2 4 5% 4 6% 41%	1782
November	1st to 10th	Day	18% 6% 2 5% 4 2 4 3 3 6% 46%	1671
	11th to 20th	Day	17% 7% 2 4 4 2 4 4 5% 6% 44%	1710
	21st to end	Day	19% 6% 3 4 5% 2 4 5% 4 7% 43%	1710
December	1st to 10th	Day	17% 9% 3 5% 5% 2 4 4 5% 6% 39%	1607
	11th to 20th	Day	20% 9% 3 5% 5% 2 3 4 4 5% 41%	1906
	21st to end	Day	22% 11% 3 6% 6% 2 4 4 4 5% 34%	2772
January	1st to 10th	Night	18% 7% 2 4 4 2 3 3 4 6% 47%	4429
	11th to 20th	Night	15% 10% 4 8% 5% 3 4 3 4 5% 39%	4440
	21st to end	Night	22% 13% 5% 7% 5% 3 4 4 3 5% 28%	4884
February	1st to 10th	Night	17% 9% 3 6% 5% 3 4 4 5% 6% 38%	2380
	11th to 20th	Night	17% 9% 3 6% 5% 3 4 5% 5% 5% 39%	2218
	21st to end	Night	18% 8% 2 5% 5% 3 4 3 5% 5% 42%	1884
March	1st to 10th	Night	30% 11% 2 4 4 2 3 3 4 5% 31%	3724
	11th to 20th	Night	11% 9% 3 5% 6% 4 5% 5% 5% 6% 40%	3582
	21st to end	Night	25% 8% 3 6% 4 3 5% 4 4 4 33%	3663
April	1st to 10th	Night	17% 9% 3 6% 5% 3 4 3 6% 7% 36%	1900
	11th to 20th	Night	19% 7% 2 4 6% 3 6% 4 5% 6% 38%	1839
	21st to end	Night	19% 7% 3 6% 5% 3 5% 5% 4 6% 38%	1665
May	1st to 10th	Night	24% 8% 3 6% 4 3 5% 5% 5% 6% 31%	1620
	11th to 20th	Night	19% 6% 3 5% 6% 4 5% 5% 6% 8% 35%	1593
	21st to end	Night	18% 7% 3 6% 5% 3 4 3 5% 8% 38%	1580
June	1st to 10th	Night	19% 6% 3 5% 4 3 5% 5% 5% 8% 36%	1440
	11th to 20th	Night	17% 7% 3 5% 6% 3 5% 6% 5% 7% 36%	1440
	21st to end	Night	16% 6% 3 5% 3 3 5% 5% 6% 9% 40%	1440
July	1st to 10th	Night	12% 5% 3 6% 5% 3 5% 5% 8% 9% 41%	1440
	11th to 20th	Night	12% 7% 4 6% 5% 2 5% 5% 8% 9% 36%	1440
	21st to end	Night	13% 4 3 5% 5% 3 5% 5% 7% 8% 41%	1574
August	1st to 10th	Night	7% 6% 3 5% 6% 4 5% 5% 7% 10% 43%	1607
	11th to 20th	Night	10% 6% 3 6% 6% 4 5% 7% 7% 9% 38%	1596
	21st to end	Night	13% 4 2 4 5% 3 3 5% 5% 9% 46%	1974
September	1st to 10th	Night	12% 6% 2 6% 6% 2 5% 5% 6% 7% 45%	1826
	11th to 20th	Night	14% 5% 2 4 4 2 3 3 4 7% 52%	1980
	21st to end	Night	18% 5% 2 4 4 2 4 4 6% 6% 44%	1980
October	1st to 10th	Night	22% 6% 2 5% 4 2 4 4 4 5% 42%	1980
	11th to 20th	Night	15% 5% 2 5% 4 2 4 4 6% 7% 45%	2180
	21st to end	Night	21% 7% 3 6% 4 3 4 3 4 6% 37%	2574
November	1st to 10th	Night	16% 5% 2 5% 4 3 4 4 6% 7% 45%	2407
	11th to 20th	Night	16% 8% 3 5% 4 2 3 4 4 6% 45%	2470
	21st to end	Night	16% 6% 3 4 5% 2 5% 4 5% 7% 44%	2470
December	1st to 10th	Night	20% 8% 3 5% 5% 3 4 4 5% 6% 39%	2569
	11th to 20th	Night	19% 7% 2 5% 5% 3 4 4 5% 7% 39%	3288
	21st to end	Night	19% 10% 3 7% 5% 2 3 4 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	45% 5% 9% 21% 16% 4	2395
May	1st to 10th	Day	52% 6% 8% 19% 13% 2	2340
	11th to 20th	Day	43% 6% 11% 18% 18% 3	2305
	21st to end	Day	38% 8% 15% 24% 14% 2	2709
June	1st to 10th	Day	46% 8% 13% 22% 11% 1	2520
	11th to 20th	Day	43% 7% 14% 19% 15% 2	2520
	21st to end	Day	42% 10% 13% 22% 13% 1	2520
July	1st to 10th	Day	38% 9% 11% 24% 15% 3	2450
	11th to 20th	Day	39% 8% 13% 24% 13% 2	2445
	21st to end	Day	37% 10% 14% 23% 13% 4	2577
August	1st to 10th	Day	37% 10% 14% 25% 13% 1	2314
	11th to 20th	Day	40% 9% 13% 23% 14% 1	2304
	21st to end	Day	37% 7% 12% 23% 19% 2	2379
September	1st to 10th	Day	38% 7% 10% 24% 20% 1	2134
	11th to 20th	Day	34% 5% 10% 26% 22% 2	1980
	21st to end	Day	41% 5% 9% 21% 23% 2	1980
October	1st to 10th	Day	45% 5% 10% 22% 15% 3	1980
	11th to 20th	Day	38% 5% 11% 29% 16% 2	1774
	21st to end	Day	44% 5% 13% 19% 15% 4	1782
November	1st to 10th	Day	40% 4 14% 23% 16% 3	1671
	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% 6% 10% 19% 16% 4	1665
May	1st to 10th	Night	53% 6% 10% 15% 12% 3	1620
	11th to 20th	Night	46% 8% 11% 18% 13% 4	1594
	21st to end	Night	46% 7% 14% 19% 13% 1	1581
June	1st to 10th	Night	47% 8% 14% 20% 11%	1440
	11th to 20th	Night	47% 6% 12% 20% 15% 1	1440
	21st to end	Night	40% 9% 14% 24% 13% 1	1440
July	1st to 10th	Night	39% 9% 13% 23% 16% 1	1400
	11th to 20th	Night	41% 8% 13% 28% 9% 1	1392
	21st to end	Night	38% 9% 12% 28% 11% 2	1486
August	1st to 10th	Night	34% 9% 17% 25% 14% 2	1596
	11th to 20th	Night	39% 10% 17% 20% 13% 1	1596
	21st to end	Night	34% 7% 11% 26% 19% 1	1974
September	1st to 10th	Night	39% 7% 11% 23% 18% 2	1826
	11th to 20th	Night	35% 4 11% 23% 25% 2	1980
	21st to end	Night	40% 6% 9% 22% 21% 3	1980
October	1st to 10th	Night	45% 5% 11% 21% 14% 3	1980
	11th to 20th	Night	38% 7% 13% 27% 14% 1	2180
	21st to end	Night	48% 5% 12% 19% 14% 2	2574
November	1st to 10th	Night	39% 6% 13% 22% 17% 3	2407
	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	25% 12% 35% 23% 3 2	437
May	1st to 10th	Day	30% 14% 34% 17% 4 1	423
	11th to 20th	Day	19% 11% 37% 24% 9% 1	447
	21st to end	Day	17% 7% 29% 33% 11% 2	485
June	1st to 10th	Day	20% 6% 29% 32% 11% 2	450
	11th to 20th	Day	15% 8% 35% 31% 8% 2	450
	21st to end	Day	14% 6% 30% 35% 14% 1	450
July	1st to 10th	Day	16% 5% 20% 36% 20% 3	445
	11th to 20th	Day	14% 4 21% 38% 20% 3	444
	21st to end	Day	11% 5% 23% 43% 16% 2	488
August	1st to 10th	Day	12% 3 27% 39% 17% 2	446
	11th to 20th	Day	14% 4 25% 33% 19% 4	439
	21st to end	Day	14% 6% 23% 33% 17% 7%	495
September	1st to 10th	Day	18% 7% 22% 30% 18% 5%	450
	11th to 20th	Day	18% 9% 26% 25% 15% 7%	450
	21st to end	Day	21% 8% 26% 28% 12% 5%	450
October	1st to 10th	Day	27% 8% 22% 26% 12% 4	450
	11th to 20th	Day	15% 11% 32% 26% 14% 2	390
	21st to end	Day	24% 12% 34% 20% 8% 2	396
November	1st to 10th	Day	16% 16% 30% 22% 14% 1	365
	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% 5%	555
May	1st to 10th	Night	27% 9% 34% 23% 6% 1	540
	11th to 20th	Night	22% 8% 39% 24% 6% 1	532
	21st to end	Night	20% 6% 26% 38% 9%	419
June	1st to 10th	Night	20% 6% 29% 34% 11% 1	360
	11th to 20th	Night	21% 3 28% 39% 9% 1	360
	21st to end	Night	17% 3 28% 42% 10%	360
July	1st to 10th	Night	13% 2 24% 48% 12% 1	350
	11th to 20th	Night	16% 2 20% 49% 11% 1	348
	21st to end	Night	13% 2 21% 50% 14% 1	394
August	1st to 10th	Night	10% 3 24% 49% 14%	533
	11th to 20th	Night	14% 2 24% 43% 15% 1	532
	21st to end	Night	15% 3 18% 40% 21% 3	786
September	1st to 10th	Night	13% 2 27% 38% 18% 2	720
	11th to 20th	Night	17% 5% 25% 32% 19% 3	720
	21st to end	Night	20% 4 27% 32% 15% 3	720
October	1st to 10th	Night	24% 7% 27% 26% 14% 2	720
	11th to 20th	Night	18% 9% 34% 26% 11% 2	720
	21st to end	Night	25% 11% 34% 22% 7% 1	792
November	1st to 10th	Night	18% 11% 33% 28% 10% 1	740
	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 2024-04-22 09:25:41. Version ac07

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