GEM 'N I Dobservatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the GEM 'N I Dobservatory clear sky chart from 2005-11-05 to 2017-12-20.

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
37%
15248
14%
48105
10%
15208
43%
15208
19%
33692

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
13%
717
8%
2452
3%
716
19%
716
7%
2006
January16th to endNight
14%
768
10%
2496
2%
768
22%
768
8%
2001
February1st to 15thNight
15%
704
7%
2287
2%
701
22%
701
9%
1814
February16th to endNight
23%
631
11%
2005
4%
631
31%
631
13%
1516
March1st to 15thNight
26%
720
12%
1980
6%
720
31%
720
16%
1526
March16th to endNight
36%
768
20%
2112
11%
768
43%
768
23%
1471
April1st to 15thNight
34%
718
15%
1823
6%
718
38%
718
23%
1331
April16th to endNight
45%
567
21%
1647
10%
567
53%
567
28%
1067
May1st to 15thNight
50%
510
17%
1590
13%
510
55%
510
26%
1041
May16th to endNight
55%
374
17%
1497
20%
374
60%
374
24%
857
June1st to 15thNight
52%
360
13%
1440
15%
360
58%
360
21%
867
June16th to endNight
58%
360
13%
1440
18%
360
62%
360
25%
828
July1st to 15thNight
68%
340
17%
1360
25%
340
71%
340
33%
679
July16th to endNight
66%
512
16%
1543
17%
479
67%
479
35%
876
August1st to 15thNight
71%
539
17%
1609
15%
536
72%
536
34%
965
August16th to endNight
65%
627
23%
1773
16%
627
68%
627
38%
1036
September1st to 15thNight
59%
720
22%
1815
12%
720
63%
720
34%
1184
September16th to endNight
59%
717
23%
2001
18%
717
62%
717
32%
1265
October1st to 15thNight
44%
720
17%
2160
15%
720
49%
720
22%
1482
October16th to endNight
27%
768
14%
2304
9%
768
34%
768
16%
1687
November1st to 15thNight
35%
760
17%
2556
14%
760
41%
760
19%
1730
November16th to endNight
26%
780
11%
2730
8%
780
32%
780
13%
1989
December1st to 15thNight
16%
780
6%
2730
2%
780
21%
780
8%
2169
December16th to endNight
11%
788
6%
2755
1%
788
17%
788
6%
2305

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
13%7%36%6%35%5%5%7%34%
48730
Night
15%8%46%6%35%45%7%33%
48287
Cloud CoverDay
13%8%36%6%35%5%5%7%33%
48740
Night
15%8%37%6%3445%6%33%
48291
TransparencyDay
47%5%14%21%10%1
48430
Night
50%5%12%20%10%1
48105
SeeingDay
17%421%27%19%8%
5645
Night
20%7%25%28%15%2
15252

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%14%5%8%8%5%6%6%5%6%16%
1483
16th to endDay
12%14%7%13%10%5%6%5%5%6%13%
1728
February1st to 15thDay
15%16%6%9%8%45%5%5%6%16%
1575
16th to endDay
16%13%5%8%8%5%5%35%7%20%
1467
March1st to 15thDay
14%9%5%9%8%35%5%5%6%25%
1969
16th to endDay
14%7%36%5%35%5%47%36%
2112
April1st to 15thDay
18%8%35%5%44447%32%
2124
16th to endDay
15%6%25%434446%40%
2322
May1st to 15thDay
12%6%35%5%35%5%6%8%37%
2361
16th to endDay
9%5%24426%6%5%8%43%
2618
June1st to 15thDay
12%5%25%5%35%5%6%8%40%
2520
16th to endDay
10%424435%5%7%10%42%
2520
July1st to 15thDay
6%423435%5%7%9%46%
2520
16th to endDay
8%4245%35%6%7%9%40%
2516
August1st to 15thDay
6%425%435%6%8%10%42%
2340
16th to endDay
9%4144335%6%9%46%
2417
September1st to 15thDay
12%5%25%5%345%5%7%42%
2142
16th to endDay
12%5%25%5%3445%7%42%
1959
October1st to 15thDay
16%8%26%435%5%5%6%34%
1800
16th to endDay
22%8%37%6%35%5%5%5%25%
1920
November1st to 15thDay
12%8%38%5%345%5%9%33%
1629
16th to endDay
16%12%36%6%245%7%8%24%
1560
December1st to 15thDay
15%13%5%10%7%445%6%6%20%
1560
16th to endDay
20%14%8%9%9%35%45%5%12%
1568
January1st to 15thNight
18%15%6%10%7%45%45%5%16%
2452
16th to endNight
14%13%6%11%8%46%5%5%6%17%
2496
February1st to 15thNight
15%14%6%9%7%45%446%20%
2285
16th to endNight
14%12%49%6%35%45%7%23%
2005
March1st to 15thNight
18%10%48%7%25%45%6%24%
1968
16th to endNight
14%9%45%5%24435%38%
2112
April1st to 15thNight
17%9%36%435%346%34%
1823
16th to endNight
12%6%35%434447%42%
1647
May1st to 15thNight
16%5%35%5%335%48%38%
1590
16th to endNight
11%5%245%3445%7%45%
1495
June1st to 15thNight
11%6%25%5%3446%9%38%
1440
16th to endNight
9%426%5%35%5%6%9%43%
1440
July1st to 15thNight
5%2225%2445%9%53%
1440
16th to endNight
7%2245%245%7%9%48%
1650
August1st to 15thNight
6%314445%6%6%8%47%
1620
16th to endNight
7%425%42445%8%50%
1773
September1st to 15thNight
13%5%235%3435%7%45%
1815
16th to endNight
10%5%25%5%34347%45%
2001
October1st to 15thNight
18%7%25%5%23446%37%
2160
16th to endNight
22%8%36%5%3445%6%28%
2304
November1st to 15thNight
16%6%36%5%35%5%46%36%
2556
16th to endNight
19%9%46%5%346%5%7%27%
2730
December1st to 15thNight
19%14%5%8%7%35%45%5%20%
2730
16th to endNight
19%14%8%9%7%45%5%46%13%
2755

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%14%49%8%47%6%46%17%
1483
16th to endDay
12%14%6%15%9%5%6%5%5%5%14%
1728
February1st to 15thDay
15%17%5%10%7%35%5%6%5%16%
1575
16th to endDay
16%13%49%8%35%5%47%18%
1467
March1st to 15thDay
15%10%5%9%9%35%5%5%5%24%
1980
16th to endDay
14%8%36%6%35%446%35%
2111
April1st to 15thDay
18%9%45%6%345%46%31%
2124
16th to endDay
16%6%35%5%34446%40%
2322
May1st to 15thDay
13%5%36%6%35%5%5%7%36%
2361
16th to endDay
10%5%245%35%6%5%8%42%
2618
June1st to 15thDay
13%5%25%5%35%5%5%8%39%
2520
16th to endDay
11%3245%25%5%7%10%41%
2520
July1st to 15thDay
7%4245%35%5%7%9%45%
2520
16th to endDay
9%425%6%36%7%6%10%38%
2516
August1st to 15thDay
6%5%25%5%45%6%7%10%40%
2340
16th to endDay
10%325%5%345%5%8%45%
2417
September1st to 15thDay
13%5%246%345%5%7%40%
2142
16th to endDay
13%425%6%3445%7%41%
1959
October1st to 15thDay
18%6%26%5%35%45%6%35%
1800
16th to endDay
22%9%37%6%35%445%26%
1920
November1st to 15thDay
12%8%47%6%4445%7%33%
1629
16th to endDay
16%12%46%7%35%5%5%6%26%
1560
December1st to 15thDay
15%13%6%10%6%45%35%6%21%
1560
16th to endDay
19%15%8%10%8%35%5%45%12%
1568
January1st to 15thNight
18%15%6%9%8%45%34418%
2452
16th to endNight
14%13%5%11%7%5%5%5%5%6%18%
2496
February1st to 15thNight
14%14%5%10%7%35%446%22%
2278
16th to endNight
15%11%5%9%8%35%45%6%23%
2005
March1st to 15thNight
19%10%47%7%35%45%5%25%
1980
16th to endNight
15%8%47%5%24435%38%
2112
April1st to 15thNight
18%9%36%5%34446%33%
1823
16th to endNight
12%7%35%434447%42%
1647
May1st to 15thNight
16%6%36%43445%8%38%
1589
16th to endNight
11%5%245%245%47%45%
1495
June1st to 15thNight
11%5%35%6%35%46%9%38%
1440
16th to endNight
8%325%5%35%5%49%43%
1440
July1st to 15thNight
5%31443445%8%53%
1440
16th to endNight
7%3244245%6%8%48%
1650
August1st to 15thNight
7%34435%6%7%8%47%
1620
16th to endNight
7%42442446%6%51%
1773
September1st to 15thNight
14%5%24423447%45%
1815
16th to endNight
11%425%5%33447%46%
2001
October1st to 15thNight
18%6%36%424346%38%
2160
16th to endNight
23%8%36%5%3445%7%28%
2304
November1st to 15thNight
16%7%36%5%245%46%36%
2556
16th to endNight
19%9%46%5%35%5%5%6%28%
2730
December1st to 15thNight
18%15%5%8%6%25%5%5%5%20%
2730
16th to endNight
20%14%8%10%7%445%45%14%
2755

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
67%6%10%12%2
1484
16th to endDay
70%5%10%8%3
1728
February1st to 15thDay
67%5%11%12%2
1577
16th to endDay
63%412%14%4
1467
March1st to 15thDay
59%5%13%15%6%
1980
16th to endDay
47%312%24%10%1
2112
April1st to 15thDay
50%412%19%11%
2124
16th to endDay
43%5%10%22%15%2
2322
May1st to 15thDay
43%5%12%25%12%
2361
16th to endDay
36%6%15%25%14%1
2622
June1st to 15thDay
40%5%14%25%13%1
2520
16th to endDay
35%6%16%25%14%
2520
July1st to 15thDay
30%6%14%27%19%1
2371
16th to endDay
35%7%16%25%12%1
2360
August1st to 15thDay
32%7%18%24%14%1
2327
16th to endDay
32%5%15%31%13%1
2417
September1st to 15thDay
38%6%15%25%12%
2142
16th to endDay
40%415%27%11%
1959
October1st to 15thDay
48%5%11%21%11%1
1800
16th to endDay
57%5%15%15%5%
1920
November1st to 15thDay
46%6%17%20%8%
1629
16th to endDay
56%5%16%15%5%
1560
December1st to 15thDay
63%5%17%10%2
1560
16th to endDay
71%7%9%9%1
1568
January1st to 15thNight
69%410%11%3
2452
16th to endNight
65%6%10%12%4
2496
February1st to 15thNight
65%411%13%3
2287
16th to endNight
59%412%17%6%
2005
March1st to 15thNight
58%5%11%18%5%
1980
16th to endNight
48%38%23%14%1
2112
April1st to 15thNight
51%39%20%13%
1823
16th to endNight
41%410%22%17%3
1647
May1st to 15thNight
43%410%25%13%2
1590
16th to endNight
37%5%12%25%15%2
1497
June1st to 15thNight
40%6%11%23%16%2
1440
16th to endNight
36%6%13%25%16%1
1440
July1st to 15thNight
27%5%10%26%26%2
1360
16th to endNight
30%5%16%25%17%3
1543
August1st to 15thNight
31%7%16%28%13%1
1609
16th to endNight
31%412%32%17%2
1773
September1st to 15thNight
38%313%26%16%1
1815
16th to endNight
37%411%30%14%
2001
October1st to 15thNight
47%5%9%22%14%
2160
16th to endNight
54%5%13%17%7%
2304
November1st to 15thNight
46%6%12%21%11%
2556
16th to endNight
55%5%14%18%4
2730
December1st to 15thNight
64%6%13%11%3
2730
16th to endNight
71%5%10%9%2
2755

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%15%39%14%10%1
69
16th to endDay
29%8%40%19%2
96
February1st to 15thDay
22%7%46%22%1
90
16th to endDay
23%7%32%29%7%
93
March1st to 15thDay
21%10%29%27%10%
270
16th to endDay
22%428%30%9%3
288
April1st to 15thDay
22%331%30%9%2
270
16th to endDay
19%426%29%15%5%
270
May1st to 15thDay
20%221%26%23%6%
288
16th to endDay
13%118%33%24%8%
331
June1st to 15thDay
15%317%37%21%4
315
16th to endDay
16%16%32%26%6%
315
July1st to 15thDay
11%211%31%29%13%
305
16th to endDay
9%213%34%26%13%
326
August1st to 15thDay
10%13%25%31%18%
313
16th to endDay
12%114%21%30%19%
332
September1st to 15thDay
12%114%24%30%16%
315
16th to endDay
15%315%22%21%21%
314
October1st to 15thDay
19%5%23%22%20%8%
315
16th to endDay
27%11%25%22%12%
336
November1st to 15thDay
14%11%28%27%12%4
142
16th to endDay
21%12%33%20%12%1
90
December1st to 15thDay
14%22%31%21%11%
90
16th to endDay
33%16%38%11%
72
January1st to 15thNight
27%17%31%18%5%
720
16th to endNight
23%12%36%21%5%
768
February1st to 15thNight
23%15%36%21%3
704
16th to endNight
23%10%31%28%5%
631
March1st to 15thNight
26%8%30%25%8%
720
16th to endNight
18%6%31%29%12%1
768
April1st to 15thNight
22%7%28%32%9%
718
16th to endNight
15%427%34%15%2
567
May1st to 15thNight
18%118%34%22%3
510
16th to endNight
14%219%37%21%3
375
June1st to 15thNight
15%121%38%21%1
360
16th to endNight
9%120%43%24%1
360
July1st to 15thNight
5%213%47%26%4
340
16th to endNight
9%112%42%28%4
512
August1st to 15thNight
7%211%38%33%6%
539
16th to endNight
10%113%34%34%5%
627
September1st to 15thNight
14%313%31%28%8%
720
16th to endNight
14%216%26%29%11%
717
October1st to 15thNight
21%6%20%26%21%3
720
16th to endNight
27%9%29%25%7%
768
November1st to 15thNight
20%7%28%26%14%1
760
16th to endNight
26%12%29%21%8%1
780
December1st to 15thNight
30%14%31%18%5%
780
16th to endNight
26%14%36%18%4
788
Page generated at 2017-12-21 07:04:54. Version ac04

Copyright 2017 A. Danko


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