Amazing Grace Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Amazing Grace Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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%
14743
16%
46755
8%
14711
41%
14711
18%
31115

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
22%
720
16%
2506
7%
716
34%
716
13%
1641
January16th to endNight
17%
768
15%
2688
4%
768
30%
768
10%
1810
February1st to 15thNight
16%
704
14%
2252
3%
701
30%
701
11%
1574
February16th to endNight
20%
631
17%
1893
5%
631
36%
631
15%
1277
March1st to 15thNight
20%
720
16%
2160
6%
720
32%
720
15%
1491
March16th to endNight
27%
768
20%
2022
7%
768
37%
768
21%
1351
April1st to 15thNight
23%
718
18%
1796
4%
718
31%
718
18%
1291
April16th to endNight
28%
585
18%
1665
6%
585
36%
585
20%
1103
May1st to 15thNight
29%
520
15%
1600
9%
520
36%
520
17%
1119
May16th to endNight
39%
375
11%
1497
10%
374
46%
374
15%
1008
June1st to 15thNight
33%
360
9%
1440
7%
360
41%
360
13%
990
June16th to endNight
46%
360
9%
1440
10%
360
52%
360
18%
926
July1st to 15thNight
54%
340
12%
1360
17%
340
57%
340
22%
804
July16th to endNight
53%
376
14%
1418
16%
354
59%
354
24%
825
August1st to 15thNight
49%
458
15%
1529
11%
456
53%
456
22%
954
August16th to endNight
53%
711
20%
1857
12%
711
56%
711
34%
1178
September1st to 15thNight
48%
700
18%
1792
9%
700
52%
700
32%
1157
September16th to endNight
52%
657
24%
1815
17%
657
57%
657
34%
1091
October1st to 15thNight
36%
660
19%
1868
10%
660
45%
660
20%
1287
October16th to endNight
26%
704
13%
2288
6%
704
37%
704
16%
1561
November1st to 15thNight
35%
700
20%
2277
11%
700
47%
700
19%
1485
November16th to endNight
30%
720
18%
2384
9%
720
42%
720
16%
1571
December1st to 15thNight
19%
720
13%
2520
4%
720
30%
720
12%
1734
December16th to endNight
15%
768
14%
2688
4%
768
28%
768
9%
1887

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
17%7%36%6%35%5%5%7%31%
47885
Night
17%7%35%5%35%5%5%7%33%
46925
Cloud CoverDay
18%7%35%5%35%5%5%7%33%
47895
Night
17%7%25%5%3445%7%36%
46930
TransparencyDay
48%5%12%20%11%1
47573
Night
45%413%22%11%1
46755
SeeingDay
24%15%25%20%10%3
5757
Night
23%14%23%26%10%1
14743

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
15%8%46%6%47%6%6%8%24%
1432
16th to endDay
13%9%36%7%35%5%7%7%29%
1536
February1st to 15thDay
13%11%48%7%36%5%47%25%
1608
16th to endDay
13%11%47%7%35%6%5%7%27%
1580
March1st to 15thDay
17%10%5%7%5%245%5%7%27%
1790
16th to endDay
14%9%37%6%35%346%34%
2202
April1st to 15thDay
19%8%36%5%35%436%34%
2152
16th to endDay
18%7%36%5%35%45%6%34%
2295
May1st to 15thDay
24%8%37%6%33445%27%
2361
16th to endDay
20%7%35%5%345%5%7%30%
2618
June1st to 15thDay
24%7%36%6%35%5%46%26%
2520
16th to endDay
18%8%46%6%35%5%5%7%29%
2520
July1st to 15thDay
15%6%36%5%46%6%7%8%30%
2520
16th to endDay
16%435%5%36%6%8%8%31%
2654
August1st to 15thDay
15%5%35%7%46%6%7%7%29%
2407
16th to endDay
11%426%435%6%7%8%38%
2344
September1st to 15thDay
16%425%5%35%5%47%39%
2054
16th to endDay
15%4145%33346%47%
1815
October1st to 15thDay
22%8%36%5%24436%33%
1761
16th to endDay
20%8%37%6%35%5%5%5%27%
1584
November1st to 15thDay
16%7%45%5%3446%8%33%
1581
16th to endDay
20%7%346%35%46%6%31%
1575
December1st to 15thDay
21%8%36%5%46%5%46%25%
1440
16th to endDay
21%10%47%7%35%5%5%6%23%
1536
January1st to 15thNight
14%9%37%6%35%6%6%8%28%
2506
16th to endNight
13%8%5%8%7%35%5%5%7%28%
2688
February1st to 15thNight
12%9%48%7%46%6%6%6%26%
2251
16th to endNight
13%10%35%5%45%7%6%7%30%
1893
March1st to 15thNight
17%8%36%6%3445%6%31%
2147
16th to endNight
14%7%25%5%35%5%6%5%38%
2022
April1st to 15thNight
19%7%46%6%35%445%34%
1796
16th to endNight
20%6%235%3345%7%37%
1665
May1st to 15thNight
21%7%45%5%25%45%5%33%
1600
16th to endNight
20%8%35%4245%5%7%32%
1495
June1st to 15thNight
25%6%345%24448%29%
1440
16th to endNight
15%6%26%4345%5%8%36%
1440
July1st to 15thNight
16%5%245%25%5%6%9%38%
1440
16th to endNight
15%426%32346%8%41%
1514
August1st to 15thNight
16%5%2433446%7%40%
1539
16th to endNight
13%42333445%8%45%
1857
September1st to 15thNight
16%414424445%45%
1792
16th to endNight
14%42332345%6%48%
1815
October1st to 15thNight
19%6%25%6%35%45%6%34%
1868
16th to endNight
21%7%36%5%25%46%6%29%
2288
November1st to 15thNight
15%5%36%5%35%6%5%8%34%
2277
16th to endNight
18%6%35%5%45%45%7%32%
2384
December1st to 15thNight
22%9%36%6%35%5%5%6%26%
2520
16th to endNight
19%10%5%6%6%25%46%8%23%
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
16%7%35%5%36%6%6%8%29%
1432
16th to endDay
13%9%35%5%345%7%7%33%
1536
February1st to 15thDay
13%11%46%6%46%5%48%28%
1608
16th to endDay
13%10%46%7%36%45%7%30%
1580
March1st to 15thDay
17%10%47%5%35%45%6%30%
1800
16th to endDay
14%8%36%5%35%446%37%
2202
April1st to 15thDay
19%7%345%3435%6%35%
2152
16th to endDay
19%6%15%5%35%45%6%36%
2295
May1st to 15thDay
25%7%37%5%33345%29%
2361
16th to endDay
21%6%25%5%35%45%8%32%
2618
June1st to 15thDay
25%5%25%6%35%5%5%6%27%
2520
16th to endDay
18%7%36%5%45%5%5%7%29%
2520
July1st to 15thDay
15%5%25%6%46%6%6%8%31%
2520
16th to endDay
15%425%6%35%6%7%8%33%
2654
August1st to 15thDay
15%5%25%6%45%6%8%7%31%
2407
16th to endDay
12%425%5%35%5%6%9%39%
2344
September1st to 15thDay
16%4145%35%45%7%41%
2054
16th to endDay
15%3145%23346%48%
1815
October1st to 15thDay
23%6%25%5%3344435%
1761
16th to endDay
19%8%35%6%46%446%30%
1584
November1st to 15thDay
17%5%45%5%2445%9%36%
1581
16th to endDay
20%6%25%5%345%5%6%34%
1575
December1st to 15thDay
20%9%26%5%35%5%5%5%29%
1440
16th to endDay
21%9%25%6%36%45%6%27%
1536
January1st to 15thNight
14%8%26%5%36%46%8%32%
2506
16th to endNight
13%8%46%6%35%5%5%7%32%
2688
February1st to 15thNight
12%9%36%5%47%5%5%7%30%
2244
16th to endNight
13%10%345%35%5%6%9%32%
1893
March1st to 15thNight
17%8%35%5%35%5%46%33%
2160
16th to endNight
15%6%234345%5%6%40%
2021
April1st to 15thNight
18%7%35%6%34446%35%
1796
16th to endNight
20%5%23433346%40%
1665
May1st to 15thNight
21%7%35%5%345%46%34%
1600
16th to endNight
21%6%35%5%346%37%33%
1495
June1st to 15thNight
26%6%2442445%7%30%
1440
16th to endNight
16%6%245%25%45%7%38%
1440
July1st to 15thNight
16%4234345%6%8%40%
1440
16th to endNight
15%325%41347%8%42%
1514
August1st to 15thNight
17%5%2442436%6%41%
1539
16th to endNight
13%5%2332335%8%47%
1857
September1st to 15thNight
16%414323447%47%
1792
16th to endNight
14%41332335%7%50%
1815
October1st to 15thNight
19%6%245%34447%36%
1868
16th to endNight
21%6%25%43446%7%33%
2288
November1st to 15thNight
15%5%15%5%26%5%5%7%37%
2277
16th to endNight
18%5%25%435%45%7%36%
2384
December1st to 15thNight
22%8%35%5%2445%6%30%
2520
16th to endNight
19%10%45%5%35%45%7%28%
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
47%6%13%21%9%
1433
16th to endDay
46%415%21%11%
1536
February1st to 15thDay
54%413%19%7%
1611
16th to endDay
52%413%15%12%2
1580
March1st to 15thDay
54%313%16%10%2
1800
16th to endDay
47%410%18%17%3
2202
April1st to 15thDay
49%311%19%14%2
2152
16th to endDay
48%5%9%21%13%2
2295
May1st to 15thDay
57%28%18%11%1
2361
16th to endDay
49%6%13%18%10%1
2622
June1st to 15thDay
54%5%12%18%7%1
2520
16th to endDay
51%6%11%18%10%
2520
July1st to 15thDay
45%7%14%21%10%
2371
16th to endDay
44%7%16%21%10%
2487
August1st to 15thDay
47%7%15%21%8%
2393
16th to endDay
38%5%15%25%13%
2344
September1st to 15thDay
41%5%10%27%14%
2054
16th to endDay
36%211%28%18%1
1815
October1st to 15thDay
51%310%22%9%1
1761
16th to endDay
52%414%18%8%1
1584
November1st to 15thDay
46%315%20%11%1
1581
16th to endDay
49%413%18%11%2
1575
December1st to 15thDay
53%5%15%18%7%
1440
16th to endDay
55%5%12%16%9%
1536
January1st to 15thNight
46%414%21%9%1
2506
16th to endNight
49%412%18%12%1
2688
February1st to 15thNight
51%413%18%10%
2252
16th to endNight
47%314%22%10%1
1893
March1st to 15thNight
49%312%21%10%2
2160
16th to endNight
41%413%18%17%4
2022
April1st to 15thNight
49%38%21%15%1
1796
16th to endNight
44%412%22%14%2
1665
May1st to 15thNight
50%48%19%14%2
1600
16th to endNight
48%7%14%19%8%1
1497
June1st to 15thNight
52%5%15%17%8%
1440
16th to endNight
44%6%14%21%11%
1440
July1st to 15thNight
37%7%18%24%11%
1360
16th to endNight
37%5%18%24%12%
1418
August1st to 15thNight
41%6%15%24%11%
1529
16th to endNight
34%6%14%29%14%
1857
September1st to 15thNight
35%5%13%31%13%
1792
16th to endNight
33%311%33%17%
1815
October1st to 15thNight
47%411%21%12%1
1868
16th to endNight
48%414%22%8%
2288
November1st to 15thNight
43%5%14%21%12%1
2277
16th to endNight
46%414%22%10%1
2384
December1st to 15thNight
52%416%21%5%
2520
16th to endNight
53%413%19%8%
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
31%23%18%20%5%1
60
16th to endDay
20%28%32%14%4
64
February1st to 15thDay
29%20%30%14%4
175
16th to endDay
24%25%20%23%6%
239
March1st to 15thDay
32%20%21%20%5%
270
16th to endDay
27%19%25%14%8%4
288
April1st to 15thDay
30%15%25%18%7%2
270
16th to endDay
27%17%27%14%7%4
270
May1st to 15thDay
35%18%19%15%7%4
288
16th to endDay
25%13%30%22%6%1
331
June1st to 15thDay
26%15%28%19%8%
315
16th to endDay
20%15%32%22%7%1
315
July1st to 15thDay
19%9%34%22%10%3
305
16th to endDay
14%10%31%29%11%3
326
August1st to 15thDay
16%15%24%21%17%4
313
16th to endDay
15%9%21%23%18%10%
332
September1st to 15thDay
16%10%24%20%17%9%
294
16th to endDay
19%9%20%18%17%14%
254
October1st to 15thDay
25%15%18%18%16%5%
254
16th to endDay
27%18%22%22%9%
240
November1st to 15thDay
24%14%22%26%11%
235
16th to endDay
30%18%21%16%11%1
195
December1st to 15thDay
26%21%30%20%1
60
16th to endDay
39%20%29%9%1
64
January1st to 15thNight
23%20%28%23%4
720
16th to endNight
23%21%27%22%4
768
February1st to 15thNight
21%21%31%22%2
704
16th to endNight
23%22%27%21%4
631
March1st to 15thNight
28%18%26%23%3
720
16th to endNight
23%19%24%23%8%1
768
April1st to 15thNight
26%19%25%23%5%
718
16th to endNight
26%16%24%22%8%
585
May1st to 15thNight
27%11%24%25%9%
520
16th to endNight
25%6%22%32%11%1
375
June1st to 15thNight
31%9%19%29%9%
360
16th to endNight
18%6%22%38%13%
360
July1st to 15thNight
17%320%37%20%1
340
16th to endNight
15%417%39%22%1
376
August1st to 15thNight
20%318%35%20%1
458
16th to endNight
15%418%31%25%3
711
September1st to 15thNight
18%8%19%31%20%2
700
16th to endNight
18%8%16%29%21%5%
657
October1st to 15thNight
25%13%18%24%15%3
660
16th to endNight
26%17%24%23%7%
704
November1st to 15thNight
21%15%22%29%9%1
700
16th to endNight
26%16%19%26%9%1
720
December1st to 15thNight
31%17%25%21%4
720
16th to endNight
32%21%24%18%3
768
Page generated at 2017-09-11 19:35:27. Version ac04

Copyright 2017 A. Danko


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