Waterville Public Libarary
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waterville Public Libarary clear sky chart from 2005-11-06 to 2024-03-01.

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
24%
23034
11%
80757
7%
22940
30%
22940
12%
61106

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 10thNight
7%
755
5%
4424
3%
737
13%
737
2%
3750
January11th to 20thNight
10%
759
7%
4403
3%
740
15%
740
3%
3637
January21st to endNight
11%
830
4%
4647
3%
814
17%
814
3%
4054
February1st to 10thNight
10%
760
9%
2470
2%
760
18%
760
7%
2058
February11th to 20thNight
10%
743
8%
2331
2%
740
16%
740
6%
1944
February21st to endNight
11%
628
8%
1884
4%
628
17%
628
8%
1552
March1st to 10thNight
13%
723
10%
2167
3%
723
21%
723
10%
1715
March11th to 20thNight
14%
720
12%
1990
4%
720
21%
720
11%
1549
March21st to endNight
20%
792
17%
2051
6%
792
28%
792
15%
1559
April1st to 10thNight
16%
720
11%
1800
3%
720
21%
720
15%
1411
April11th to 20thNight
22%
711
14%
1775
4%
711
27%
711
18%
1336
April21st to endNight
24%
713
14%
1793
5%
713
29%
713
19%
1341
May1st to 10thNight
28%
403
15%
1483
11%
403
34%
403
14%
1045
May11th to 20thNight
29%
354
18%
1416
14%
354
40%
354
16%
907
May21st to endNight
35%
388
14%
1551
13%
388
45%
388
19%
967
June1st to 10thNight
38%
360
14%
1440
13%
360
49%
360
17%
927
June11th to 20thNight
40%
360
13%
1440
15%
360
48%
360
18%
909
June21st to endNight
40%
360
14%
1440
15%
360
49%
360
19%
896
July1st to 10thNight
49%
350
14%
1400
18%
350
55%
350
22%
827
July11th to 20thNight
49%
348
16%
1392
19%
348
54%
348
24%
831
July21st to endNight
52%
394
16%
1486
18%
372
55%
372
23%
874
August1st to 10thNight
48%
457
16%
1521
12%
455
53%
455
26%
943
August11th to 20thNight
47%
612
13%
1676
8%
612
49%
612
25%
1169
August21st to endNight
45%
792
17%
1980
8%
792
47%
792
29%
1344
September1st to 10thNight
41%
720
15%
1800
7%
720
44%
720
29%
1226
September11th to 20thNight
47%
720
23%
1818
14%
720
50%
720
31%
1192
September21st to endNight
40%
720
20%
2000
14%
720
45%
720
24%
1372
October1st to 10thNight
31%
720
13%
2160
10%
720
36%
720
17%
1563
October11th to 20thNight
23%
720
13%
2160
6%
720
32%
720
15%
1578
October21st to endNight
15%
792
11%
2492
5%
792
23%
792
10%
1969
November1st to 10thNight
20%
740
15%
2407
9%
740
29%
740
13%
1744
November11th to 20thNight
17%
760
15%
2531
9%
760
25%
760
10%
1892
November21st to endNight
15%
760
9%
2660
5%
760
22%
760
8%
2094
December1st to 10thNight
9%
760
5%
2660
1%
760
13%
760
5%
2235
December11th to 20thNight
10%
760
7%
3268
2%
759
17%
759
4%
2681
December21st to endNight
7%
830
3%
4841
1%
817
11%
817
2%
4015

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
18%12%5%8%6%35%45%6%28%
78366
Night
18%13%6%9%7%34446%27%
81037
TransparencyDay
56%7%11%17%8%1
78071
Night
58%7%11%16%8%1
80866
SeeingDay
27%18%28%17%7%2
13730
Night
26%18%28%21%7%1
23053

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 10thDay
13%22%10%13%7%3433418%
2517
11th to 20thDay
14%18%10%18%10%3433413%
2520
21st to endDay
18%21%9%10%11%45%33411%
3004
February1st to 10thDay
16%18%7%13%10%45%45%315%
1710
11th to 20thDay
12%16%8%16%9%5%444418%
1736
21st to endDay
19%16%6%13%10%3443319%
1570
March1st to 10thDay
16%14%7%15%6%3444422%
1797
11th to 20thDay
16%18%8%8%6%2434427%
1968
21st to endDay
21%12%5%8%5%23345%31%
2304
April1st to 10thDay
18%15%6%8%434345%30%
2160
11th to 20thDay
18%13%37%5%345%45%34%
2134
21st to endDay
23%14%36%5%3335%6%30%
2165
May1st to 10thDay
21%11%46%6%34446%31%
2492
11th to 20thDay
20%8%35%5%2445%7%36%
2478
21st to endDay
16%6%26%6%35%5%6%9%36%
2725
June1st to 10thDay
20%7%46%6%35%6%5%9%30%
2520
11th to 20thDay
21%6%26%5%35%5%6%9%32%
2520
21st to endDay
18%6%36%6%35%6%6%9%31%
2520
July1st to 10thDay
14%6%35%6%46%5%7%9%36%
2520
11th to 20thDay
13%5%36%7%46%6%7%9%35%
2520
21st to endDay
14%6%37%6%46%7%6%7%34%
2744
August1st to 10thDay
14%5%36%7%45%6%8%9%34%
2403
11th to 20thDay
16%6%27%6%46%7%8%8%29%
2206
21st to endDay
16%6%36%6%45%6%6%8%35%
2376
September1st to 10thDay
17%6%35%5%26%5%6%8%37%
2160
11th to 20thDay
18%7%35%5%3335%6%42%
2142
21st to endDay
17%7%25%6%45%6%6%7%35%
1958
October1st to 10thDay
22%9%37%5%35%5%5%7%30%
1800
11th to 20thDay
21%9%36%5%345%6%8%30%
1800
21st to endDay
28%14%45%6%4445%5%22%
1864
November1st to 10thDay
16%13%47%5%35%45%6%32%
1671
11th to 20thDay
16%19%5%8%6%33445%27%
1644
21st to endDay
18%16%6%10%6%35%45%422%
1520
December1st to 10thDay
19%21%9%12%6%34435%14%
1520
11th to 20thDay
21%18%10%10%5%42445%17%
1906
21st to endDay
24%20%10%9%6%24435%13%
2772
January1st to 10thNight
16%19%10%16%8%35%33413%
4429
11th to 20thNight
12%19%9%15%10%5%443415%
4440
21st to endNight
20%18%8%16%11%5%433312%
4651
February1st to 10thNight
15%16%7%15%10%35%43418%
2470
11th to 20thNight
13%13%8%15%11%46%45%5%16%
2329
21st to endNight
17%14%7%15%9%45%435%18%
1884
March1st to 10thNight
16%12%8%14%7%44445%23%
2157
11th to 20thNight
15%16%7%10%7%3445%426%
1989
21st to endNight
20%14%5%6%5%345%45%30%
2051
April1st to 10thNight
20%14%6%6%4345%46%28%
1800
11th to 20thNight
20%11%35%6%35%445%33%
1775
21st to endNight
21%11%45%42435%5%33%
1793
May1st to 10thNight
24%9%36%5%33446%32%
1483
11th to 20thNight
14%7%35%6%35%6%6%7%38%
1415
21st to endNight
13%7%26%5%35%6%7%6%40%
1550
June1st to 10thNight
19%5%35%6%35%5%6%7%36%
1440
11th to 20thNight
20%6%244245%7%8%38%
1440
21st to endNight
15%5%35%5%445%6%8%41%
1440
July1st to 10thNight
10%5%25%5%5%5%46%9%43%
1440
11th to 20thNight
11%5%345%45%5%5%8%44%
1440
21st to endNight
14%5%26%5%3445%8%44%
1574
August1st to 10thNight
11%5%25%6%245%7%10%43%
1531
11th to 20thNight
13%6%47%6%445%6%8%37%
1676
21st to endNight
14%6%26%5%3446%8%42%
1980
September1st to 10thNight
14%6%25%5%446%47%43%
1800
11th to 20thNight
18%7%23423347%47%
1818
21st to endNight
18%6%245%35%5%6%7%40%
2000
October1st to 10thNight
22%8%26%5%345%5%6%33%
2160
11th to 20thNight
22%9%36%5%35%45%6%31%
2160
21st to endNight
29%14%45%5%34345%23%
2492
November1st to 10thNight
15%15%5%7%6%3445%5%32%
2407
11th to 20thNight
19%13%5%7%6%345%46%26%
2531
21st to endNight
16%17%7%8%7%35%45%6%23%
2660
December1st to 10thNight
20%20%9%11%6%4435%415%
2660
11th to 20thNight
21%15%7%13%7%3444417%
3288
21st to endNight
25%17%11%9%6%34335%14%
4884

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 10thDay
69%6%10%11%4
2518
11th to 20thDay
75%5%8%8%31
2520
21st to endDay
77%5%8%6%31
3004
February1st to 10thDay
73%5%7%11%3
1710
11th to 20thDay
71%5%7%13%4
1745
21st to endDay
71%48%11%6%
1570
March1st to 10thDay
65%5%10%14%5%1
1800
11th to 20thDay
61%48%14%11%2
1968
21st to endDay
57%48%14%14%2
2304
April1st to 10thDay
57%48%20%9%2
2160
11th to 20thDay
52%6%11%19%12%1
2134
21st to endDay
55%5%9%18%11%2
2165
May1st to 10thDay
54%6%9%17%11%2
2492
11th to 20thDay
47%6%10%23%12%1
2482
21st to endDay
45%8%15%21%10%1
2725
June1st to 10thDay
51%8%11%18%11%1
2520
11th to 20thDay
47%8%13%22%9%1
2520
21st to endDay
49%9%14%19%9%
2520
July1st to 10thDay
44%9%11%23%12%1
2450
11th to 20thDay
43%10%15%25%7%
2445
21st to endDay
46%9%13%21%11%
2591
August1st to 10thDay
43%10%15%22%10%1
2389
11th to 20thDay
49%10%14%21%7%
2206
21st to endDay
45%8%13%23%10%1
2376
September1st to 10thDay
44%7%13%26%10%1
2160
11th to 20thDay
42%5%12%23%17%1
2142
21st to endDay
46%8%10%23%12%1
1958
October1st to 10thDay
53%7%10%18%11%1
1800
11th to 20thDay
50%9%13%21%7%1
1800
21st to endDay
63%7%11%11%7%1
1864
November1st to 10thDay
51%7%11%19%11%1
1671
11th to 20thDay
60%5%11%15%7%2
1644
21st to endDay
63%8%14%11%4
1520
December1st to 10thDay
73%6%8%9%3
1520
11th to 20thDay
70%6%12%8%3
1906
21st to endDay
75%5%7%9%4
2772
January1st to 10thNight
75%6%9%6%3
4429
11th to 20thNight
71%7%6%10%5%
4440
21st to endNight
79%47%6%31
4651
February1st to 10thNight
70%5%8%11%5%
2470
11th to 20thNight
70%5%8%11%5%
2331
21st to endNight
68%6%9%10%6%1
1884
March1st to 10thNight
64%5%10%14%7%
2167
11th to 20thNight
62%5%10%15%8%1
1990
21st to endNight
56%5%8%16%12%2
2051
April1st to 10thNight
58%5%11%17%8%1
1800
11th to 20thNight
52%6%10%18%12%1
1775
21st to endNight
52%6%10%18%12%3
1793
May1st to 10thNight
53%7%9%15%14%2
1483
11th to 20thNight
43%9%11%22%13%2
1416
21st to endNight
41%9%15%22%11%2
1551
June1st to 10thNight
46%6%12%22%13%1
1440
11th to 20thNight
41%9%14%22%12%1
1440
21st to endNight
39%10%12%27%11%1
1440
July1st to 10thNight
36%9%13%25%15%2
1400
11th to 20thNight
36%9%16%27%12%1
1392
21st to endNight
37%8%16%24%14%2
1486
August1st to 10thNight
35%10%15%30%10%1
1521
11th to 20thNight
42%9%16%23%9%
1676
21st to endNight
38%9%14%26%12%1
1980
September1st to 10thNight
41%6%14%26%11%1
1800
11th to 20thNight
38%6%12%26%18%1
1818
21st to endNight
43%7%11%25%12%1
2000
October1st to 10thNight
51%8%12%18%11%1
2160
11th to 20thNight
52%8%14%17%9%1
2160
21st to endNight
63%6%10%12%8%1
2492
November1st to 10thNight
53%8%10%16%12%2
2407
11th to 20thNight
59%6%10%16%7%2
2531
21st to endNight
62%8%12%14%4
2660
December1st to 10thNight
72%6%11%9%2
2660
11th to 20thNight
69%7%9%10%5%
3288
21st to endNight
73%6%9%9%3
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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
31%27%27%10%5%
180
11th to 20thDay
41%25%26%7%11
180
21st to endDay
29%29%32%9%1
265
February1st to 10thDay
43%29%22%6%
270
11th to 20thDay
38%31%26%5%
343
21st to endDay
41%24%26%8%1
382
March1st to 10thDay
33%26%28%11%2
420
11th to 20thDay
36%23%26%12%2
420
21st to endDay
39%22%22%13%41
462
April1st to 10thDay
35%23%27%10%5%
420
11th to 20thDay
33%22%23%12%7%2
412
21st to endDay
37%17%27%11%5%2
420
May1st to 10thDay
32%18%27%13%7%2
423
11th to 20thDay
27%11%37%15%8%2
447
21st to endDay
20%14%31%21%11%3
485
June1st to 10thDay
25%14%29%23%8%1
450
11th to 20thDay
21%14%32%20%12%1
450
21st to endDay
22%15%34%19%7%2
450
July1st to 10thDay
15%12%30%27%12%4
445
11th to 20thDay
14%10%30%32%11%3
444
21st to endDay
15%8%39%25%10%3
488
August1st to 10thDay
13%13%27%26%15%5%
446
11th to 20thDay
21%7%28%27%13%5%
439
21st to endDay
15%15%28%25%11%5%
495
September1st to 10thDay
17%12%28%21%16%5%
450
11th to 20thDay
18%12%27%20%15%9%
450
21st to endDay
19%17%28%19%12%4
450
October1st to 10thDay
27%14%27%15%11%6%
450
11th to 20thDay
27%20%29%15%7%1
450
21st to endDay
39%20%24%14%3
437
November1st to 10thDay
30%19%26%16%8%
365
11th to 20thDay
33%28%23%12%3
304
21st to endDay
37%24%33%6%
180
December1st to 10thDay
38%21%30%9%11
180
11th to 20thDay
39%23%31%7%
180
21st to endDay
37%29%29%5%1
198
January1st to 10thNight
29%29%30%11%1
760
11th to 20thNight
31%25%27%13%21
760
21st to endNight
24%28%30%16%2
836
February1st to 10thNight
30%23%31%15%1
760
11th to 20thNight
28%28%29%13%2
743
21st to endNight
32%25%27%14%1
628
March1st to 10thNight
28%23%31%16%2
723
11th to 20thNight
31%23%28%17%1
720
21st to endNight
31%22%24%19%5%1
792
April1st to 10thNight
27%21%32%18%3
720
11th to 20thNight
29%19%27%17%8%
711
21st to endNight
30%14%28%21%6%
713
May1st to 10thNight
29%11%26%27%7%
403
11th to 20thNight
19%11%37%26%6%1
354
21st to endNight
16%7%36%31%9%1
389
June1st to 10thNight
18%10%28%31%13%1
360
11th to 20thNight
20%9%24%35%11%
360
21st to endNight
16%7%28%39%9%1
360
July1st to 10thNight
11%5%27%41%15%1
350
11th to 20thNight
11%6%29%38%15%2
348
21st to endNight
15%424%44%11%2
394
August1st to 10thNight
13%5%29%35%18%1
457
11th to 20thNight
15%422%34%21%3
612
21st to endNight
16%6%27%32%18%1
792
September1st to 10thNight
16%8%28%30%16%2
720
11th to 20thNight
20%9%20%28%18%4
720
21st to endNight
20%12%24%27%16%1
720
October1st to 10thNight
26%13%23%21%15%2
720
11th to 20thNight
27%16%29%21%6%
720
21st to endNight
36%18%27%17%2
792
November1st to 10thNight
26%20%30%18%6%
740
11th to 20thNight
30%22%28%13%7%1
760
21st to endNight
29%24%28%16%3
760
December1st to 10thNight
36%24%26%11%2
760
11th to 20thNight
32%26%27%12%3
760
21st to endNight
33%29%25%11%2
836
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