Norwell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norwell clear sky chart from 2005-11-05 to 2017-09-15.

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 TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(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

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
30%
14918
18%
46788
8%
14885
41%
14885
21%
30886

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
15%
720
18%
2506
5%
716
31%
716
17%
1626
January16th to endNight
14%
768
18%
2688
3%
768
33%
768
15%
1772
February1st to 15thNight
15%
704
16%
2174
4%
701
29%
701
17%
1482
February16th to endNight
18%
631
23%
1893
7%
631
38%
631
21%
1260
March1st to 15thNight
20%
720
17%
2140
7%
720
33%
720
18%
1483
March16th to endNight
23%
768
22%
2055
8%
768
35%
768
23%
1409
April1st to 15thNight
24%
718
18%
1796
5%
718
32%
718
23%
1288
April16th to endNight
29%
576
18%
1656
7%
576
36%
576
22%
1148
May1st to 15thNight
27%
540
15%
1620
7%
540
34%
540
18%
1143
May16th to endNight
33%
450
11%
1572
9%
449
38%
449
17%
1087
June1st to 15thNight
37%
360
11%
1440
10%
360
43%
360
15%
980
June16th to endNight
48%
360
11%
1440
14%
360
53%
360
21%
877
July1st to 15thNight
52%
340
12%
1360
15%
340
56%
340
22%
811
July16th to endNight
55%
376
15%
1418
19%
354
59%
354
20%
896
August1st to 15thNight
52%
536
16%
1606
11%
533
55%
533
26%
1019
August16th to endNight
59%
702
22%
1848
13%
702
62%
702
34%
1183
September1st to 15thNight
50%
720
19%
1877
10%
720
54%
720
33%
1214
September16th to endNight
50%
657
25%
1815
17%
657
56%
657
34%
1116
October1st to 15thNight
36%
660
22%
1834
12%
660
45%
660
27%
1204
October16th to endNight
25%
704
16%
2282
6%
704
37%
704
21%
1480
November1st to 15thNight
30%
700
17%
2277
9%
700
42%
700
21%
1478
November16th to endNight
26%
720
20%
2340
8%
720
40%
720
20%
1486
December1st to 15thNight
20%
720
18%
2463
6%
720
35%
720
16%
1636
December16th to endNight
15%
768
18%
2688
4%
768
33%
768
16%
1808

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 ForecastData
Points
Cloud CoverDay
16%6%2442445%7%40%
47944
Night
16%6%25%42445%6%39%
46959
Cloud CoverDay
17%6%2442445%7%40%
47954
Night
17%6%25%424446%40%
46964
TransparencyDay
42%6%11%21%14%2
47633
Night
44%5%11%21%15%1
46788
SeeingDay
20%8%29%27%11%2
5948
Night
20%9%33%26%8%
14918

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
16%9%2332445%7%40%
1432
16th to endDay
16%6%36%5%13445%41%
1536
February1st to 15thDay
18%7%244345%5%6%37%
1683
16th to endDay
14%6%26%335%45%8%39%
1580
March1st to 15thDay
20%6%35%42445%7%34%
1808
16th to endDay
16%7%25%42335%5%42%
2166
April1st to 15thDay
17%7%3442445%6%38%
2152
16th to endDay
17%5%13423346%44%
2303
May1st to 15thDay
24%8%26%323336%34%
2332
16th to endDay
17%5%2442445%7%42%
2552
June1st to 15thDay
25%5%243235%5%8%33%
2520
16th to endDay
13%5%25%5%35%6%6%9%37%
2520
July1st to 15thDay
11%5%345%25%5%7%9%39%
2520
16th to endDay
11%425%5%35%5%7%8%39%
2645
August1st to 15thDay
10%5%25%5%345%6%9%40%
2340
16th to endDay
11%4144345%5%8%46%
2353
September1st to 15thDay
12%41442335%7%48%
2072
16th to endDay
14%413323346%51%
1815
October1st to 15thDay
21%5%24312346%43%
1796
16th to endDay
16%6%244235%46%43%
1587
November1st to 15thDay
22%7%23314345%40%
1581
16th to endDay
17%5%25%5%245%46%40%
1620
December1st to 15thDay
16%8%35%5%24445%38%
1495
16th to endDay
23%10%245%23345%33%
1536
January1st to 15thNight
16%8%35%423446%39%
2506
16th to endNight
18%10%35%424346%36%
2688
February1st to 15thNight
15%8%36%42445%6%36%
2173
16th to endNight
16%8%35%424345%41%
1893
March1st to 15thNight
18%8%245%34445%37%
2127
16th to endNight
16%7%35%42434442%
2055
April1st to 15thNight
16%8%25%5%35%35%6%36%
1796
16th to endNight
19%6%25%5%25%345%38%
1656
May1st to 15thNight
21%7%25%5%34446%33%
1620
16th to endNight
19%5%25%5%3445%8%34%
1570
June1st to 15thNight
22%6%34435%5%47%33%
1440
16th to endNight
15%5%343245%6%8%41%
1440
July1st to 15thNight
10%5%35%4245%8%9%40%
1440
16th to endNight
12%435%6%25%5%7%8%36%
1514
August1st to 15thNight
7%5%25%6%35%5%6%8%41%
1617
16th to endNight
12%4234335%5%9%46%
1848
September1st to 15thNight
11%414425%45%7%46%
1877
16th to endNight
14%41332345%6%50%
1815
October1st to 15thNight
20%5%14423345%44%
1834
16th to endNight
17%6%2442435%6%40%
2282
November1st to 15thNight
18%6%25%423346%40%
2277
16th to endNight
16%7%35%5%24347%40%
2340
December1st to 15thNight
18%6%35%43435%6%37%
2463
16th to endNight
19%9%25%42445%6%35%
2688

Percentage Cloud Cover SE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
16%9%3332345%7%40%
1432
16th to endDay
15%7%36%423345%42%
1536
February1st to 15thDay
19%7%24435%45%6%37%
1683
16th to endDay
14%7%2433445%7%40%
1580
March1st to 15thDay
20%7%25%41445%7%34%
1818
16th to endDay
16%8%24424345%42%
2166
April1st to 15thDay
17%7%35%42435%6%38%
2152
16th to endDay
18%5%23423346%44%
2303
May1st to 15thDay
24%7%35%413336%34%
2332
16th to endDay
17%4235%2335%8%41%
2552
June1st to 15thDay
25%5%1342445%8%33%
2520
16th to endDay
13%4245%346%6%10%36%
2520
July1st to 15thDay
12%5%25%426%47%9%39%
2520
16th to endDay
11%425%435%6%6%8%39%
2645
August1st to 15thDay
11%5%25%5%35%5%7%8%40%
2340
16th to endDay
11%41443445%8%45%
2353
September1st to 15thDay
13%415%42345%6%48%
2072
16th to endDay
15%423313437%50%
1815
October1st to 15thDay
22%424223436%43%
1796
16th to endDay
16%6%234235%46%43%
1587
November1st to 15thDay
23%7%2332434440%
1581
16th to endDay
17%5%26%4245%5%5%40%
1620
December1st to 15thDay
16%8%35%5%3445%5%38%
1495
16th to endDay
23%10%245%2343434%
1536
January1st to 15thNight
16%8%35%424335%41%
2506
16th to endNight
18%9%45%423345%38%
2688
February1st to 15thNight
15%8%35%6%3445%5%37%
2166
16th to endNight
16%7%34433335%41%
1893
March1st to 15thNight
18%8%245%34446%37%
2140
16th to endNight
16%7%35%5%2343442%
2054
April1st to 15thNight
16%8%26%5%25%347%36%
1796
16th to endNight
19%6%245%35%345%38%
1656
May1st to 15thNight
21%6%35%434347%33%
1620
16th to endNight
19%5%35%5%335%5%8%34%
1570
June1st to 15thNight
22%6%24435%437%33%
1440
16th to endNight
15%5%33325%5%5%8%41%
1440
July1st to 15thNight
11%5%345%2447%8%40%
1440
16th to endNight
12%5%25%6%35%6%7%8%36%
1514
August1st to 15thNight
7%6%25%6%35%6%5%9%41%
1617
16th to endNight
12%42343346%9%46%
1848
September1st to 15thNight
12%3144245%47%46%
1877
16th to endNight
15%413313446%50%
1815
October1st to 15thNight
20%41442234445%
1834
16th to endNight
17%6%25%434446%40%
2282
November1st to 15thNight
18%6%25%434445%41%
2277
16th to endNight
16%6%345%24347%40%
2340
December1st to 15thNight
18%7%35%5%34345%38%
2463
16th to endNight
19%8%25%42435%6%36%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
43%5%10%24%12%3
1433
16th to endDay
43%5%10%26%13%
1536
February1st to 15thDay
46%5%13%19%13%1
1686
16th to endDay
43%5%13%21%14%1
1580
March1st to 15thDay
48%5%13%20%10%2
1818
16th to endDay
43%410%21%15%4
2166
April1st to 15thDay
46%410%19%16%2
2152
16th to endDay
40%5%8%24%16%3
2303
May1st to 15thDay
52%5%7%17%14%2
2332
16th to endDay
41%7%14%21%13%2
2556
June1st to 15thDay
49%6%12%19%10%
2520
16th to endDay
40%8%13%20%14%1
2520
July1st to 15thDay
39%9%11%21%15%2
2371
16th to endDay
39%10%13%22%11%3
2478
August1st to 15thDay
39%8%13%22%14%1
2327
16th to endDay
35%6%11%25%19%1
2353
September1st to 15thDay
35%6%11%21%22%1
2072
16th to endDay
35%47%25%23%2
1815
October1st to 15thDay
42%410%23%16%2
1796
16th to endDay
41%412%23%14%2
1587
November1st to 15thDay
45%412%21%13%1
1581
16th to endDay
44%5%12%23%13%1
1620
December1st to 15thDay
46%415%17%15%
1495
16th to endDay
53%5%12%17%10%
1536
January1st to 15thNight
46%412%21%13%1
2506
16th to endNight
47%49%20%15%2
2688
February1st to 15thNight
47%5%12%20%12%1
2174
16th to endNight
44%410%21%16%2
1893
March1st to 15thNight
48%5%9%19%14%2
2140
16th to endNight
45%47%17%19%4
2055
April1st to 15thNight
47%5%7%19%17%2
1796
16th to endNight
47%5%7%19%16%3
1656
May1st to 15thNight
50%5%9%16%14%3
1620
16th to endNight
47%8%12%19%8%2
1572
June1st to 15thNight
50%6%13%17%11%
1440
16th to endNight
40%7%12%22%16%1
1440
July1st to 15thNight
38%8%13%25%14%
1360
16th to endNight
41%8%12%27%8%2
1418
August1st to 15thNight
38%8%13%22%15%1
1606
16th to endNight
34%7%11%27%18%
1848
September1st to 15thNight
36%6%12%24%19%1
1877
16th to endNight
34%5%7%24%26%1
1815
October1st to 15thNight
41%411%21%17%2
1834
16th to endNight
44%5%13%20%14%
2282
November1st to 15thNight
44%412%21%14%2
2277
16th to endNight
43%412%22%14%2
2340
December1st to 15thNight
46%5%13%21%12%
2463
16th to endNight
48%412%20%12%
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
20%20%31%25%3
60
16th to endDay
28%12%39%20%
64
February1st to 15thDay
23%14%44%16%1
251
16th to endDay
13%19%41%20%5%
239
March1st to 15thDay
23%17%37%17%4
270
16th to endDay
22%14%38%15%8%
288
April1st to 15thDay
22%12%34%23%7%
270
16th to endDay
22%8%32%28%5%2
270
May1st to 15thDay
32%10%27%19%7%3
288
16th to endDay
19%429%32%11%1
331
June1st to 15thDay
25%5%26%30%10%1
315
16th to endDay
13%432%38%9%2
315
July1st to 15thDay
19%117%40%18%1
305
16th to endDay
13%219%41%21%3
326
August1st to 15thDay
13%323%38%18%2
313
16th to endDay
13%119%35%21%8%
332
September1st to 15thDay
16%5%24%28%19%5%
311
16th to endDay
20%322%27%12%13%
254
October1st to 15thDay
25%6%22%22%17%5%
252
16th to endDay
15%12%38%24%9%
240
November1st to 15thDay
25%9%29%22%11%2
235
16th to endDay
18%15%33%18%11%1
240
December1st to 15thDay
19%16%38%18%7%
115
16th to endDay
26%15%43%10%3
64
January1st to 15thNight
21%16%41%16%3
720
16th to endNight
25%15%39%17%2
768
February1st to 15thNight
21%17%40%19%1
704
16th to endNight
21%14%41%18%3
631
March1st to 15thNight
23%15%36%20%3
720
16th to endNight
21%11%37%21%6%
768
April1st to 15thNight
22%9%39%23%4
718
16th to endNight
22%8%33%27%6%
576
May1st to 15thNight
25%6%35%23%7%1
540
16th to endNight
22%5%33%31%7%
450
June1st to 15thNight
25%227%33%10%
360
16th to endNight
15%227%42%10%
360
July1st to 15thNight
13%24%48%11%
340
16th to endNight
13%121%48%13%
376
August1st to 15thNight
10%125%47%13%
536
16th to endNight
15%117%40%21%2
702
September1st to 15thNight
14%126%40%16%1
720
16th to endNight
17%224%30%20%4
657
October1st to 15thNight
23%6%29%26%12%2
660
16th to endNight
22%10%38%21%7%
704
November1st to 15thNight
20%11%31%24%10%1
700
16th to endNight
20%15%32%21%8%
720
December1st to 15thNight
22%15%37%19%4
720
16th to endNight
23%16%40%16%2
768
Page generated at 2017-09-16 00:58:31. Version ac04

Copyright 2017 A. Danko


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