Wigamog Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wigamog Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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
28%
14703
12%
46694
7%
14671
34%
14671
15%
34012

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
10%
719
6%
2506
2%
716
15%
716
5%
2089
January16th to endNight
16%
768
11%
2536
5%
768
23%
768
9%
2020
February1st to 15thNight
14%
702
8%
2287
3%
701
21%
701
8%
1851
February16th to endNight
18%
631
11%
2024
4%
631
27%
631
11%
1541
March1st to 15thNight
17%
720
13%
1998
5%
720
24%
720
13%
1527
March16th to endNight
27%
768
19%
2106
10%
768
35%
768
23%
1434
April1st to 15thNight
20%
718
14%
1796
5%
718
25%
718
18%
1374
April16th to endNight
29%
579
18%
1659
9%
579
35%
579
21%
1152
May1st to 15thNight
36%
426
16%
1506
12%
426
44%
426
19%
983
May16th to endNight
36%
375
13%
1497
9%
374
49%
374
21%
906
June1st to 15thNight
35%
360
9%
1440
7%
360
44%
360
17%
925
June16th to endNight
45%
360
10%
1303
11%
360
50%
360
22%
843
July1st to 15thNight
52%
340
14%
1309
19%
340
57%
340
27%
720
July16th to endNight
53%
405
15%
1445
14%
381
58%
381
26%
855
August1st to 15thNight
56%
539
14%
1609
9%
536
60%
536
30%
995
August16th to endNight
52%
636
18%
1782
9%
636
57%
636
33%
1104
September1st to 15thNight
44%
720
15%
1800
7%
720
48%
720
28%
1245
September16th to endNight
45%
665
20%
1851
14%
665
49%
665
27%
1222
October1st to 15thNight
31%
660
15%
1980
11%
660
38%
660
18%
1428
October16th to endNight
18%
704
10%
2116
4%
704
25%
704
11%
1690
November1st to 15thNight
28%
700
15%
2416
13%
700
34%
700
15%
1713
November16th to endNight
19%
720
10%
2520
6%
720
25%
720
9%
1984
December1st to 15thNight
11%
720
5%
2520
1%
720
15%
720
5%
2146
December16th to endNight
10%
768
7%
2688
3%
768
16%
768
5%
2265

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
19%10%47%5%34446%30%
48071
Night
17%11%47%5%34446%31%
46867
Cloud CoverDay
19%10%46%5%34446%30%
48081
Night
18%11%46%5%34346%31%
46872
TransparencyDay
55%5%10%17%9%1
47762
Night
54%5%11%18%9%
46694
SeeingDay
24%12%29%20%9%3
5522
Night
23%12%30%22%10%1
14706

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
21%18%7%10%5%2334419%
1432
16th to endDay
14%16%7%13%7%4433419%
1686
February1st to 15thDay
13%16%7%14%9%3443417%
1575
16th to endDay
16%18%5%10%6%4433422%
1449
March1st to 15thDay
15%13%5%8%7%34445%26%
1948
16th to endDay
14%10%46%5%35%44437%
2118
April1st to 15thDay
23%12%45%423345%30%
2152
16th to endDay
21%9%24423335%38%
2310
May1st to 15thDay
20%9%36%5%34446%32%
2445
16th to endDay
16%6%26%5%35%5%5%7%37%
2618
June1st to 15thDay
23%7%35%5%2445%8%29%
2520
16th to endDay
17%6%35%6%35%5%6%7%32%
2649
July1st to 15thDay
16%4145%35%5%7%8%36%
2566
16th to endDay
13%6%25%5%35%5%5%8%34%
2624
August1st to 15thDay
15%5%37%6%45%45%7%34%
2340
16th to endDay
14%5%25%5%35%5%6%7%36%
2407
September1st to 15thDay
20%7%25%5%335%45%37%
2160
16th to endDay
18%6%25%434445%40%
1812
October1st to 15thDay
26%7%35%434346%29%
1650
16th to endDay
33%11%37%43333420%
1755
November1st to 15thDay
20%12%45%5%2445%6%28%
1439
16th to endDay
24%18%6%8%42434417%
1440
December1st to 15thDay
21%23%7%10%5%23335%13%
1440
16th to endDay
21%22%8%9%5%2333317%
1536
January1st to 15thNight
20%19%6%11%8%2423416%
2506
16th to endNight
14%15%8%10%7%35%335%21%
2536
February1st to 15thNight
12%16%6%13%7%35%445%18%
2285
16th to endNight
16%15%6%7%5%4435%425%
2024
March1st to 15thNight
17%12%5%6%6%35%33430%
1986
16th to endNight
14%8%46%5%23345%40%
2106
April1st to 15thNight
22%12%45%32423431%
1796
16th to endNight
18%8%25%6%23346%36%
1659
May1st to 15thNight
19%7%25%42445%7%35%
1506
16th to endNight
13%5%245%35%45%8%41%
1495
June1st to 15thNight
17%7%3443445%7%36%
1440
16th to endNight
14%5%25%445%45%9%37%
1303
July1st to 15thNight
9%4245%3445%7%48%
1389
16th to endNight
12%42343446%8%45%
1543
August1st to 15thNight
9%5%143346%6%7%46%
1620
16th to endNight
10%5%144335%47%48%
1782
September1st to 15thNight
16%5%234245%46%42%
1800
16th to endNight
17%7%2432433445%
1851
October1st to 15thNight
22%6%35%424446%34%
1980
16th to endNight
27%13%37%5%23435%23%
2116
November1st to 15thNight
20%8%36%5%2335%6%32%
2416
16th to endNight
23%14%5%6%6%34445%21%
2520
December1st to 15thNight
22%22%6%10%5%3434413%
2520
16th to endNight
23%18%9%10%6%2333415%
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
21%18%7%10%5%2324419%
1432
16th to endDay
14%16%7%12%8%3434419%
1686
February1st to 15thDay
14%16%7%15%8%35%33418%
1575
16th to endDay
17%17%6%9%6%3332423%
1449
March1st to 15thDay
16%13%5%8%7%34445%26%
1959
16th to endDay
14%10%45%5%34445%37%
2117
April1st to 15thDay
23%12%35%424235%31%
2152
16th to endDay
22%9%34423235%38%
2310
May1st to 15thDay
20%9%35%6%35%446%32%
2445
16th to endDay
17%5%26%5%35%5%5%7%37%
2618
June1st to 15thDay
24%6%36%434447%29%
2520
16th to endDay
17%6%26%435%5%5%8%31%
2649
July1st to 15thDay
16%424435%5%7%8%36%
2566
16th to endDay
13%6%35%6%45%46%8%33%
2624
August1st to 15thDay
15%5%26%6%36%6%47%34%
2340
16th to endDay
15%5%25%5%36%5%5%7%36%
2407
September1st to 15thDay
19%7%15%424446%38%
2160
16th to endDay
18%6%35%423446%39%
1812
October1st to 15thDay
27%8%25%5%34346%29%
1650
16th to endDay
34%10%26%5%2443420%
1755
November1st to 15thDay
19%12%45%5%24446%29%
1439
16th to endDay
24%17%7%7%5%2443417%
1440
December1st to 15thDay
20%23%7%10%6%2323414%
1440
16th to endDay
20%22%9%9%42233417%
1536
January1st to 15thNight
20%18%7%10%8%2323416%
2506
16th to endNight
14%15%8%10%7%34335%21%
2536
February1st to 15thNight
13%15%7%11%8%25%5%45%19%
2278
16th to endNight
16%15%5%8%5%44345%25%
2024
March1st to 15thNight
18%12%47%6%35%34330%
1998
16th to endNight
15%8%45%5%23345%40%
2106
April1st to 15thNight
22%13%45%33333432%
1796
16th to endNight
18%8%25%5%33346%36%
1659
May1st to 15thNight
20%6%25%42446%7%36%
1506
16th to endNight
12%5%25%5%345%5%8%42%
1495
June1st to 15thNight
18%7%24425%45%8%36%
1440
16th to endNight
14%6%245%35%448%38%
1303
July1st to 15thNight
10%4245%34447%49%
1389
16th to endNight
12%414325%45%8%45%
1543
August1st to 15thNight
10%5%143345%7%7%46%
1620
16th to endNight
10%5%2442445%7%48%
1782
September1st to 15thNight
17%4245%245%46%42%
1800
16th to endNight
17%6%24333345%45%
1851
October1st to 15thNight
22%8%25%42335%6%34%
1980
16th to endNight
27%13%36%5%34335%24%
2116
November1st to 15thNight
20%8%35%5%2445%6%32%
2416
16th to endNight
23%14%5%6%5%34345%22%
2520
December1st to 15thNight
21%21%7%10%5%3334414%
2520
16th to endNight
22%19%9%9%5%23335%15%
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
69%310%10%6%
1433
16th to endDay
69%46%9%8%1
1686
February1st to 15thDay
70%48%11%4
1577
16th to endDay
65%48%11%10%
1449
March1st to 15thDay
59%5%13%13%6%
1959
16th to endDay
49%47%18%15%3
2118
April1st to 15thDay
57%37%17%11%1
2152
16th to endDay
50%37%22%14%2
2310
May1st to 15thDay
53%48%18%13%1
2445
16th to endDay
46%7%10%20%13%1
2622
June1st to 15thDay
54%6%9%20%9%
2520
16th to endDay
48%8%12%19%10%
2649
July1st to 15thDay
40%8%12%26%11%1
2417
16th to endDay
47%7%13%21%9%
2459
August1st to 15thDay
48%8%13%18%10%
2327
16th to endDay
44%7%13%25%8%
2407
September1st to 15thDay
47%6%11%24%10%
2160
16th to endDay
45%6%10%27%9%
1812
October1st to 15thDay
56%6%10%17%9%
1650
16th to endDay
66%6%9%10%6%
1755
November1st to 15thDay
55%8%12%15%7%
1439
16th to endDay
70%49%10%41
1440
December1st to 15thDay
73%5%9%8%2
1440
16th to endDay
72%46%10%5%
1536
January1st to 15thNight
73%48%9%4
2506
16th to endNight
66%46%12%8%
2536
February1st to 15thNight
66%5%10%12%5%
2287
16th to endNight
60%410%17%6%
2024
March1st to 15thNight
58%410%17%8%
1998
16th to endNight
45%410%21%16%2
2106
April1st to 15thNight
56%36%18%12%1
1796
16th to endNight
47%48%19%17%1
1659
May1st to 15thNight
46%5%12%17%16%2
1506
16th to endNight
39%7%13%23%14%1
1497
June1st to 15thNight
46%6%13%19%14%
1440
16th to endNight
43%6%14%23%11%
1303
July1st to 15thNight
32%7%12%27%20%
1309
16th to endNight
36%6%14%28%13%
1445
August1st to 15thNight
33%8%19%25%12%
1609
16th to endNight
34%6%17%29%11%1
1782
September1st to 15thNight
40%8%14%24%11%
1800
16th to endNight
42%411%31%9%
1851
October1st to 15thNight
50%7%11%19%11%
1980
16th to endNight
64%5%10%13%5%
2116
November1st to 15thNight
52%6%13%18%8%
2416
16th to endNight
64%5%10%13%4
2520
December1st to 15thNight
73%5%8%8%2
2520
16th to endNight
73%47%9%5%
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
30%20%33%15%1
60
16th to endDay
34%16%33%11%3
89
February1st to 15thDay
28%31%33%6%
90
16th to endDay
38%13%34%11%1
108
March1st to 15thDay
25%15%34%18%5%
270
16th to endDay
23%17%30%17%9%1
288
April1st to 15thDay
28%17%28%18%5%1
270
16th to endDay
28%17%25%16%9%2
270
May1st to 15thDay
32%10%23%19%8%5%
288
16th to endDay
21%16%32%17%10%2
331
June1st to 15thDay
28%10%30%20%7%1
315
16th to endDay
18%11%34%24%8%2
444
July1st to 15thDay
17%5%33%28%9%5%
351
16th to endDay
13%9%32%26%13%4
326
August1st to 15thDay
15%329%29%15%7%
313
16th to endDay
21%5%23%28%12%9%
332
September1st to 15thDay
21%5%25%20%17%8%
315
16th to endDay
20%8%25%22%14%8%
259
October1st to 15thDay
26%14%24%20%10%3
255
16th to endDay
37%16%25%15%3
271
November1st to 15thDay
26%11%34%21%41
93
16th to endDay
40%15%31%13%
60
December1st to 15thDay
26%26%25%20%1
60
16th to endDay
32%43%20%11
64
January1st to 15thNight
29%19%31%14%4
720
16th to endNight
22%13%36%18%6%1
768
February1st to 15thNight
21%18%36%19%3
704
16th to endNight
23%18%35%17%5%
631
March1st to 15thNight
26%17%34%18%3
720
16th to endNight
19%13%33%20%10%1
768
April1st to 15thNight
28%15%31%18%5%
718
16th to endNight
22%13%30%20%11%
579
May1st to 15thNight
24%6%27%26%13%1
426
16th to endNight
13%6%36%32%10%
375
June1st to 15thNight
19%8%30%31%9%
360
16th to endNight
17%5%26%39%10%
360
July1st to 15thNight
10%327%38%19%1
340
16th to endNight
11%229%36%20%
405
August1st to 15thNight
12%319%35%24%3
539
16th to endNight
11%5%25%31%23%2
636
September1st to 15thNight
17%7%26%25%18%4
720
16th to endNight
20%7%23%28%17%3
665
October1st to 15thNight
24%10%28%22%12%1
660
16th to endNight
34%15%27%17%4
704
November1st to 15thNight
23%13%31%21%9%
700
16th to endNight
34%12%28%18%5%
720
December1st to 15thNight
33%20%30%11%3
720
16th to endNight
31%16%33%14%2
768
Page generated at 2017-09-18 08:38:23. Version ac04

Copyright 2017 A. Danko


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