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 2018-04-23.

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%
15785
18%
49475
8%
15752
41%
15752
21%
32696

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%
780
18%
2716
5%
776
31%
776
17%
1748
January16th to endNight
14%
832
18%
2912
3%
832
32%
832
15%
1918
February1st to 15thNight
15%
764
16%
2359
4%
761
30%
761
16%
1619
February16th to endNight
18%
683
22%
2049
7%
683
36%
683
20%
1388
March1st to 15thNight
19%
780
17%
2318
7%
780
32%
780
17%
1632
March16th to endNight
22%
832
22%
2226
7%
832
35%
832
23%
1535
April1st to 15thNight
23%
778
18%
1946
5%
778
31%
778
23%
1396
April16th to endNight
29%
595
19%
1709
7%
595
37%
595
22%
1179
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%
1878
10%
720
54%
720
33%
1215
September16th to endNight
49%
717
25%
1980
17%
717
55%
717
33%
1230
October1st to 15thNight
38%
720
22%
2001
12%
720
47%
720
28%
1302
October16th to endNight
25%
768
17%
2490
7%
768
39%
768
21%
1606
November1st to 15thNight
31%
760
17%
2472
9%
760
42%
760
20%
1617
November16th to endNight
26%
780
22%
2535
8%
780
42%
780
20%
1587
December1st to 15thNight
20%
780
18%
2668
5%
780
35%
780
16%
1784
December16th to endNight
14%
832
19%
2912
4%
832
32%
832
16%
1944

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%
50045
Night
16%6%25%42445%6%39%
49646
Cloud CoverDay
17%6%2442445%7%40%
50055
Night
17%6%25%424446%40%
49651
TransparencyDay
43%6%11%21%14%2
49734
Night
44%5%11%21%15%1
49475
SeeingDay
20%9%29%26%11%2
6646
Night
20%9%33%26%8%
15785

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%2332345%6%40%
1552
16th to endDay
17%6%36%413445%42%
1664
February1st to 15thDay
19%7%244345%46%36%
1828
16th to endDay
15%6%25%335%45%7%39%
1710
March1st to 15thDay
20%7%35%42445%7%33%
1960
16th to endDay
16%8%25%423345%42%
2346
April1st to 15thDay
17%7%35%5%25%45%6%37%
2332
16th to endDay
17%5%13423347%44%
2365
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%41442336%7%48%
2082
16th to endDay
15%413323346%50%
1980
October1st to 15thDay
20%5%24323346%43%
1959
16th to endDay
16%6%243235%46%44%
1731
November1st to 15thDay
22%7%24414345%39%
1716
16th to endDay
17%5%24424446%42%
1755
December1st to 15thDay
16%8%25%5%2445%5%38%
1619
16th to endDay
22%10%34423335%34%
1664
January1st to 15thNight
16%7%36%423446%39%
2716
16th to endNight
18%9%35%424346%37%
2912
February1st to 15thNight
16%9%36%42445%5%36%
2358
16th to endNight
17%8%25%5%24345%40%
2049
March1st to 15thNight
19%9%245%34445%35%
2305
16th to endNight
16%7%36%42434442%
2226
April1st to 15thNight
16%8%25%6%35%45%6%36%
1946
16th to endNight
19%6%25%5%25%345%39%
1709
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%
1878
16th to endNight
16%41332345%6%49%
1980
October1st to 15thNight
19%424323345%45%
2001
16th to endNight
18%6%2442435%6%41%
2490
November1st to 15thNight
17%6%25%423446%40%
2472
16th to endNight
16%6%24424347%42%
2535
December1st to 15thNight
19%7%35%43435%6%37%
2668
16th to endNight
18%8%25%5%2345%7%35%
2912

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%2332345%6%41%
1552
16th to endDay
16%6%35%423345%42%
1664
February1st to 15thDay
19%7%24435%45%6%36%
1828
16th to endDay
15%7%2433445%6%40%
1710
March1st to 15thDay
21%8%25%41445%6%33%
1970
16th to endDay
16%8%24424345%41%
2346
April1st to 15thDay
17%7%35%43435%6%36%
2332
16th to endDay
18%5%23423346%45%
2365
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%42336%6%48%
2082
16th to endDay
16%423313337%49%
1980
October1st to 15thDay
21%5%24323336%43%
1959
16th to endDay
16%6%24423446%44%
1731
November1st to 15thDay
22%7%24324345%40%
1716
16th to endDay
16%5%25%424446%42%
1755
December1st to 15thDay
16%8%35%5%3445%5%37%
1619
16th to endDay
22%9%345%2343435%
1664
January1st to 15thNight
16%7%35%423345%41%
2716
16th to endNight
18%9%45%423345%38%
2912
February1st to 15thNight
16%9%35%5%3445%5%37%
2351
16th to endNight
18%8%34433335%40%
2049
March1st to 15thNight
19%9%245%34445%35%
2318
16th to endNight
16%8%35%5%2333442%
2225
April1st to 15thNight
16%8%26%5%25%347%36%
1946
16th to endNight
19%6%245%35%345%38%
1709
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%
1878
16th to endNight
16%413223446%48%
1980
October1st to 15thNight
19%41442234445%
2001
16th to endNight
18%6%24434446%41%
2490
November1st to 15thNight
18%6%25%434445%40%
2472
16th to endNight
16%6%34424347%42%
2535
December1st to 15thNight
19%7%345%34345%38%
2668
16th to endNight
19%8%25%42445%6%36%
2912

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
42%5%10%24%13%3
1553
16th to endDay
43%5%10%25%13%1
1664
February1st to 15thDay
47%5%12%19%13%1
1831
16th to endDay
43%5%13%21%14%1
1710
March1st to 15thDay
49%5%12%19%9%2
1970
16th to endDay
44%49%20%15%4
2346
April1st to 15thDay
47%410%19%15%3
2332
16th to endDay
39%5%8%24%17%4
2365
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
36%6%11%21%22%1
2082
16th to endDay
36%48%24%23%2
1980
October1st to 15thDay
42%410%24%15%2
1959
16th to endDay
41%411%24%15%2
1731
November1st to 15thDay
46%413%21%13%1
1716
16th to endDay
42%412%24%13%1
1755
December1st to 15thDay
47%415%16%16%
1619
16th to endDay
52%5%11%18%11%1
1664
January1st to 15thNight
45%412%21%14%1
2716
16th to endNight
47%410%19%15%2
2912
February1st to 15thNight
48%5%11%20%13%1
2359
16th to endNight
46%49%20%15%2
2049
March1st to 15thNight
50%5%9%19%13%2
2318
16th to endNight
45%47%17%20%4
2226
April1st to 15thNight
47%5%8%18%17%2
1946
16th to endNight
46%5%7%19%16%4
1709
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
1878
16th to endNight
35%5%8%23%25%1
1980
October1st to 15thNight
40%411%23%17%2
2001
16th to endNight
43%5%13%22%15%
2490
November1st to 15thNight
44%5%12%20%14%2
2472
16th to endNight
41%412%23%15%2
2535
December1st to 15thNight
47%5%13%20%12%
2668
16th to endNight
48%5%12%20%13%
2912

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%25%30%20%4
90
16th to endDay
30%11%37%20%
96
February1st to 15thDay
23%17%42%15%1
306
16th to endDay
17%17%42%17%4
291
March1st to 15thDay
26%16%35%17%3
330
16th to endDay
21%15%39%14%8%
352
April1st to 15thDay
23%14%34%20%6%
330
16th to endDay
22%7%31%29%6%2
289
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
15%5%24%28%20%5%
315
16th to endDay
23%420%23%14%13%
314
October1st to 15thDay
23%5%21%26%16%5%
310
16th to endDay
16%12%35%24%10%1
288
November1st to 15thDay
24%9%31%22%11%1
280
16th to endDay
18%16%32%19%11%1
285
December1st to 15thDay
22%14%36%18%8%
149
16th to endDay
23%21%42%9%2
96
January1st to 15thNight
21%17%41%16%3
780
16th to endNight
25%14%40%17%2
832
February1st to 15thNight
22%16%41%18%1
764
16th to endNight
22%14%40%18%3
683
March1st to 15thNight
25%15%36%19%3
780
16th to endNight
21%11%37%22%6%
832
April1st to 15thNight
21%10%39%23%4
778
16th to endNight
23%8%33%27%6%
595
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
19%223%28%21%5%
717
October1st to 15thNight
21%5%28%27%13%2
720
16th to endNight
22%10%38%20%8%1
768
November1st to 15thNight
20%11%31%24%10%1
760
16th to endNight
20%15%32%22%8%
780
December1st to 15thNight
23%14%37%19%4
780
16th to endNight
23%16%41%15%2
832
Page generated at 2018-04-24 10:03:00. Version ac04

Copyright 2018 A. Danko


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