J.S.M. Blue Lake Township Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the J.S.M. Blue Lake Township Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
31%
15771
11%
46932
7%
15729
35%
15729
16%
35338

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
14%
900
3%
2506
2%
895
15%
895
6%
2245
January16th to endNight
16%
960
5%
2688
2%
960
18%
960
7%
2362
February1st to 15thNight
16%
734
7%
2283
3%
734
20%
734
7%
1937
February16th to endNight
20%
631
8%
1893
4%
631
24%
631
8%
1567
March1st to 15thNight
27%
720
14%
2121
7%
720
32%
720
18%
1541
March16th to endNight
34%
747
18%
2091
11%
747
40%
747
21%
1469
April1st to 15thNight
27%
539
13%
1779
8%
539
33%
539
16%
1281
April16th to endNight
34%
540
17%
1620
9%
540
41%
540
23%
1098
May1st to 15thNight
34%
540
13%
1620
7%
540
40%
540
21%
1152
May16th to endNight
42%
562
14%
1522
7%
561
49%
561
28%
1007
June1st to 15thNight
41%
378
12%
1278
10%
378
46%
378
22%
815
June16th to endNight
51%
384
12%
1284
10%
384
55%
384
25%
808
July1st to 15thNight
60%
510
14%
1360
11%
510
61%
510
37%
825
July16th to endNight
54%
564
14%
1417
10%
531
57%
531
33%
897
August1st to 15thNight
62%
539
17%
1575
14%
536
66%
536
35%
933
August16th to endNight
56%
573
17%
1765
15%
573
59%
573
29%
1103
September1st to 15thNight
54%
618
17%
1878
14%
618
57%
618
30%
1147
September16th to endNight
49%
685
17%
1892
12%
685
52%
685
27%
1273
October1st to 15thNight
37%
660
17%
1875
11%
660
43%
660
22%
1340
October16th to endNight
25%
704
9%
2280
6%
704
30%
704
11%
1804
November1st to 15thNight
26%
700
13%
2276
11%
700
31%
700
14%
1714
November16th to endNight
16%
723
6%
2424
4%
723
20%
723
7%
2023
December1st to 15thNight
10%
900
2%
2700
1%
900
12%
900
4%
2479
December16th to endNight
12%
960
3%
2805
1%
960
14%
960
5%
2518

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
15%10%47%6%3445%6%29%
47947
Night
14%11%5%9%7%34445%28%
47100
Cloud CoverDay
14%10%47%6%3445%6%29%
47956
Night
14%11%5%9%7%34445%29%
47105
TransparencyDay
53%6%11%17%8%
47633
Night
55%6%11%16%8%
46932
SeeingDay
18%10%28%25%12%5%
6003
Night
18%10%31%28%10%1
15775

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
14%17%10%15%10%5%5%2439%
1432
16th to endDay
11%17%11%15%12%5%5%42310%
1536
February1st to 15thDay
10%17%8%13%14%46%44411%
1577
16th to endDay
12%17%9%11%11%5%444414%
1580
March1st to 15thDay
12%11%5%9%10%35%45%5%26%
1827
16th to endDay
14%11%5%8%6%34447%30%
2144
April1st to 15thDay
19%13%45%423445%30%
2169
16th to endDay
16%11%35%5%2445%7%33%
2340
May1st to 15thDay
17%9%36%5%35%445%34%
2331
16th to endDay
12%7%25%5%35%45%8%41%
2590
June1st to 15thDay
14%6%26%436%46%8%36%
2679
16th to endDay
14%5%25%5%35%5%6%8%36%
2672
July1st to 15thDay
12%6%24425%5%6%9%41%
2520
16th to endDay
11%5%25%4245%7%8%41%
2655
August1st to 15thDay
9%5%36%5%35%6%7%8%37%
2376
16th to endDay
16%6%2442445%7%38%
2435
September1st to 15thDay
15%6%25%42335%8%40%
2070
16th to endDay
15%6%25%43445%8%38%
1881
October1st to 15thDay
22%10%46%423345%31%
1755
16th to endDay
24%17%47%7%3445%6%14%
1590
November1st to 15thDay
16%15%5%7%5%34447%25%
1582
16th to endDay
17%21%9%12%6%2333414%
1530
December1st to 15thDay
17%17%11%15%10%343338%
1260
16th to endDay
19%21%11%15%9%232238%
1416
January1st to 15thNight
18%15%7%15%10%5%5%32211%
2506
16th to endNight
11%15%8%13%12%5%6%43412%
2688
February1st to 15thNight
11%14%8%13%11%5%7%43315%
2281
16th to endNight
12%14%8%15%9%45%43418%
1893
March1st to 15thNight
11%11%5%8%6%345%4433%
2108
16th to endNight
13%10%46%5%2445%6%36%
2091
April1st to 15thNight
21%11%36%4235%5%5%29%
1779
16th to endNight
16%9%35%5%22446%38%
1620
May1st to 15thNight
14%8%35%7%45%6%47%33%
1620
16th to endNight
11%7%444245%6%8%40%
1520
June1st to 15thNight
11%5%36%6%2445%6%41%
1278
16th to endNight
9%6%25%42447%8%41%
1284
July1st to 15thNight
8%435%33445%8%49%
1440
16th to endNight
7%5%25%4245%6%7%47%
1513
August1st to 15thNight
6%41443445%8%49%
1584
16th to endNight
13%4245%2345%7%46%
1765
September1st to 15thNight
14%5%25%323336%49%
1878
16th to endNight
15%6%25%5%3445%7%40%
1892
October1st to 15thNight
20%8%36%5%23446%34%
1875
16th to endNight
21%13%37%6%345%46%22%
2280
November1st to 15thNight
15%14%48%6%34447%25%
2276
16th to endNight
18%20%7%9%6%4444415%
2424
December1st to 15thNight
16%17%10%15%10%45%4348%
2700
16th to endNight
15%18%11%16%7%3433310%
2805

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
14%16%10%15%10%5%43349%
1432
16th to endDay
11%16%12%15%11%5%5%5%239%
1536
February1st to 15thDay
11%16%8%13%14%36%44411%
1577
16th to endDay
11%17%9%11%11%4444415%
1580
March1st to 15thDay
12%11%5%10%10%35%445%26%
1837
16th to endDay
14%10%5%8%6%34446%30%
2143
April1st to 15thDay
18%13%46%5%24445%30%
2169
16th to endDay
16%12%35%5%2445%6%34%
2340
May1st to 15thDay
17%9%35%5%35%5%45%34%
2331
16th to endDay
12%7%35%5%25%45%7%41%
2590
June1st to 15thDay
14%6%25%5%35%5%6%8%36%
2679
16th to endDay
14%5%25%6%35%5%6%9%36%
2672
July1st to 15thDay
12%6%244245%6%8%41%
2520
16th to endDay
11%6%24425%5%6%9%41%
2655
August1st to 15thDay
9%5%26%5%35%5%7%8%38%
2376
16th to endDay
15%7%35%4245%5%7%38%
2435
September1st to 15thDay
16%5%26%42435%8%40%
2070
16th to endDay
15%6%25%5%2445%8%38%
1881
October1st to 15thDay
22%11%37%5%23445%31%
1755
16th to endDay
23%17%47%6%3445%6%14%
1590
November1st to 15thDay
16%14%5%7%5%3445%7%25%
1582
16th to endDay
17%21%9%12%7%2333314%
1530
December1st to 15thDay
17%17%11%15%9%45%2348%
1260
16th to endDay
19%21%11%16%8%332228%
1416
January1st to 15thNight
18%14%8%14%11%5%5%42211%
2506
16th to endNight
11%15%9%14%12%5%6%5%3413%
2688
February1st to 15thNight
11%14%8%13%11%5%6%43316%
2274
16th to endNight
12%14%7%15%10%4443418%
1893
March1st to 15thNight
11%11%5%7%6%345%35%33%
2121
16th to endNight
13%10%46%43445%6%37%
2091
April1st to 15thNight
21%11%36%4245%5%5%29%
1779
16th to endNight
16%9%36%43345%5%38%
1620
May1st to 15thNight
14%7%35%7%35%6%48%33%
1619
16th to endNight
11%7%35%5%235%6%7%40%
1520
June1st to 15thNight
11%5%37%6%246%5%6%41%
1278
16th to endNight
9%5%35%5%245%6%8%42%
1284
July1st to 15thNight
8%425%42435%8%49%
1440
16th to endNight
6%5%25%4245%6%7%47%
1513
August1st to 15thNight
6%4245%3445%8%50%
1584
16th to endNight
13%4245%24447%46%
1765
September1st to 15thNight
13%5%24323336%49%
1878
16th to endNight
14%6%25%5%3445%7%39%
1892
October1st to 15thNight
20%8%35%5%23346%35%
1875
16th to endNight
21%12%38%5%35%5%46%23%
2280
November1st to 15thNight
15%14%47%6%35%447%25%
2276
16th to endNight
18%20%7%9%6%3443416%
2424
December1st to 15thNight
16%16%10%14%10%45%4439%
2700
16th to endNight
16%18%11%16%8%3433310%
2805

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
78%6%7%6%1
1433
16th to endDay
79%6%6%5%2
1536
February1st to 15thDay
76%5%7%8%2
1579
16th to endDay
70%6%9%9%3
1580
March1st to 15thDay
58%6%11%15%6%
1837
16th to endDay
53%6%12%19%6%1
2144
April1st to 15thDay
54%5%10%19%9%
2169
16th to endDay
48%6%12%15%14%2
2340
May1st to 15thDay
50%6%10%20%9%2
2331
16th to endDay
41%6%12%24%13%1
2594
June1st to 15thDay
42%7%13%24%11%
2679
16th to endDay
43%8%15%20%11%1
2672
July1st to 15thDay
37%7%13%25%14%1
2371
16th to endDay
38%7%14%23%15%1
2488
August1st to 15thDay
40%8%15%23%11%
2361
16th to endDay
42%7%13%22%12%1
2435
September1st to 15thDay
41%6%13%24%12%1
2070
16th to endDay
42%7%16%22%10%
1881
October1st to 15thDay
55%5%8%22%6%
1755
16th to endDay
69%7%12%8%2
1590
November1st to 15thDay
58%6%12%15%6%
1582
16th to endDay
74%6%9%7%1
1530
December1st to 15thDay
80%5%6%5%
1260
16th to endDay
83%37%41
1416
January1st to 15thNight
78%5%7%5%2
2506
16th to endNight
73%7%9%7%2
2688
February1st to 15thNight
71%6%7%11%2
2283
16th to endNight
68%5%9%11%4
1893
March1st to 15thNight
52%6%11%19%9%
2121
16th to endNight
47%6%11%21%11%1
2091
April1st to 15thNight
53%5%9%19%11%1
1779
16th to endNight
45%5%11%18%15%2
1620
May1st to 15thNight
48%7%11%20%9%3
1620
16th to endNight
40%6%13%24%13%2
1522
June1st to 15thNight
41%7%12%21%16%
1278
16th to endNight
36%9%14%24%13%
1284
July1st to 15thNight
31%6%13%27%20%1
1360
16th to endNight
33%8%16%25%15%
1417
August1st to 15thNight
31%6%17%29%13%
1575
16th to endNight
35%7%16%24%14%1
1765
September1st to 15thNight
36%6%15%26%14%1
1878
16th to endNight
42%6%16%26%7%
1892
October1st to 15thNight
50%5%10%23%9%
1875
16th to endNight
60%8%12%13%4
2280
November1st to 15thNight
56%7%13%14%7%
2276
16th to endNight
70%6%12%8%2
2424
December1st to 15thNight
78%9%6%41
2700
16th to endNight
78%5%8%42
2805

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
18%13%46%20%1
90
16th to endDay
31%5%29%28%6%
96
February1st to 15thDay
17%22%44%14%1
90
16th to endDay
14%25%37%16%6%
81
March1st to 15thDay
25%19%29%18%7%
127
16th to endDay
24%7%28%25%12%1
288
April1st to 15thDay
25%10%29%21%10%2
270
16th to endDay
24%8%33%17%12%3
270
May1st to 15thDay
22%13%27%21%10%4
288
16th to endDay
15%14%31%24%10%3
490
June1st to 15thDay
17%12%30%26%11%2
495
16th to endDay
16%8%30%30%10%4
495
July1st to 15thDay
14%8%24%28%16%6%
475
16th to endDay
12%6%28%30%16%6%
515
August1st to 15thDay
12%320%28%21%13%
349
16th to endDay
23%417%25%18%9%
332
September1st to 15thDay
16%322%23%20%14%
315
16th to endDay
16%7%19%30%19%6%
278
October1st to 15thDay
26%7%29%26%9%1
255
16th to endDay
29%14%39%14%
102
November1st to 15thDay
20%11%30%27%7%3
90
16th to endDay
18%28%25%25%2
76
December1st to 15thDay
25%25%40%5%31
60
16th to endDay
27%32%38%1
76
January1st to 15thNight
24%14%33%21%5%
900
16th to endNight
16%13%39%24%5%
960
February1st to 15thNight
16%15%38%24%4
737
16th to endNight
20%15%31%28%4
631
March1st to 15thNight
16%15%34%24%8%
720
16th to endNight
17%9%31%31%8%
747
April1st to 15thNight
23%11%32%26%5%
539
16th to endNight
20%8%33%27%9%
540
May1st to 15thNight
16%9%33%31%8%
540
16th to endNight
13%7%30%35%12%
563
June1st to 15thNight
14%6%29%38%11%
378
16th to endNight
10%328%42%13%1
384
July1st to 15thNight
10%221%42%21%1
510
16th to endNight
8%326%36%23%1
564
August1st to 15thNight
10%118%41%25%2
539
16th to endNight
14%417%38%22%1
573
September1st to 15thNight
17%319%31%22%5%
618
16th to endNight
17%5%21%34%17%3
685
October1st to 15thNight
24%428%31%10%
660
16th to endNight
29%13%27%22%5%
704
November1st to 15thNight
22%12%34%23%7%
700
16th to endNight
24%13%35%22%3
723
December1st to 15thNight
22%16%40%18%2
900
16th to endNight
21%13%39%20%31
960
Page generated at 2017-09-23 06:43:43. Version ac04

Copyright 2017 A. Danko


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