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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 2005-11-06 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
29%
22921
15%
80648
8%
22829
39%
22829
15%
54076

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
18%
755
16%
4358
5%
737
32%
737
8%
2651
January11th to 20thNight
19%
757
11%
4382
3%
740
30%
740
5%
3042
January21st to endNight
15%
830
10%
4861
5%
814
30%
814
6%
3446
February1st to 10thNight
13%
760
15%
2504
3%
760
28%
760
12%
1720
February11th to 20thNight
15%
743
17%
2220
3%
740
32%
740
14%
1487
February21st to endNight
21%
628
17%
1884
4%
628
37%
628
16%
1266
March1st to 10thNight
20%
723
18%
2167
7%
723
34%
723
16%
1471
March11th to 20thNight
23%
720
15%
2084
6%
720
32%
720
15%
1460
March21st to endNight
24%
792
20%
2030
7%
792
34%
792
19%
1406
April1st to 10thNight
22%
720
17%
1800
4%
720
30%
720
18%
1305
April11th to 20thNight
25%
689
17%
1753
5%
689
32%
689
20%
1234
April21st to endNight
22%
540
17%
1620
6%
540
31%
540
17%
1107
May1st to 10thNight
26%
540
13%
1620
7%
540
31%
540
16%
1160
May11th to 20thNight
32%
415
18%
1477
13%
415
42%
415
16%
986
May21st to endNight
43%
389
12%
1551
13%
388
50%
388
17%
994
June1st to 10thNight
35%
360
11%
1440
11%
360
42%
360
15%
964
June11th to 20thNight
37%
360
11%
1440
11%
360
45%
360
16%
919
June21st to endNight
43%
360
10%
1440
11%
360
50%
360
17%
931
July1st to 10thNight
48%
350
13%
1400
15%
350
54%
350
22%
835
July11th to 20thNight
53%
348
13%
1392
17%
348
58%
348
24%
825
July21st to endNight
52%
394
16%
1486
17%
372
57%
372
24%
858
August1st to 10thNight
54%
416
16%
1480
13%
414
60%
414
24%
895
August11th to 20thNight
42%
539
16%
1603
11%
539
46%
539
24%
1056
August21st to endNight
49%
792
19%
1980
9%
792
53%
792
32%
1302
September1st to 10thNight
50%
720
18%
1800
7%
720
55%
720
36%
1137
September11th to 20thNight
46%
720
23%
1959
14%
720
52%
720
30%
1230
September21st to endNight
44%
720
22%
1980
15%
720
50%
720
29%
1264
October1st to 10thNight
38%
720
16%
1980
9%
720
45%
720
20%
1392
October11th to 20thNight
32%
720
17%
2244
8%
720
42%
720
19%
1501
October21st to endNight
24%
792
13%
2574
7%
792
33%
792
14%
1830
November1st to 10thNight
33%
740
20%
2407
12%
740
44%
740
19%
1553
November11th to 20thNight
28%
760
22%
2470
11%
760
41%
760
16%
1603
November21st to endNight
24%
760
16%
2540
6%
760
37%
760
15%
1688
December1st to 10thNight
17%
760
12%
2660
3%
760
28%
760
10%
1927
December11th to 20thNight
19%
760
13%
3227
4%
759
30%
759
10%
2184
December21st to endNight
15%
829
10%
4835
3%
817
28%
817
5%
3447

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%8%47%6%45%5%5%7%32%
78329
Night
18%9%47%6%35%5%6%7%32%
81081
TransparencyDay
48%5%12%21%12%2
78034
Night
48%5%13%22%11%1
80910
SeeingDay
26%18%28%18%8%2
13885
Night
24%15%24%26%9%1
22942

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
15%10%6%7%6%45%5%5%7%30%
2517
11th to 20thDay
15%11%6%9%11%45%5%6%5%23%
2520
21st to endDay
17%11%6%11%7%445%6%5%26%
2772
February1st to 10thDay
15%12%48%6%46%5%5%8%26%
1675
11th to 20thDay
12%9%5%8%9%45%5%5%7%30%
1848
21st to endDay
16%10%5%8%6%35%5%47%29%
1570
March1st to 10thDay
13%10%48%7%45%5%5%7%31%
1797
11th to 20thDay
16%11%5%6%6%345%5%6%33%
1876
21st to endDay
16%10%47%6%45%45%6%33%
2325
April1st to 10thDay
20%10%47%5%35%446%31%
2160
11th to 20thDay
17%7%36%6%36%5%5%7%35%
2156
21st to endDay
22%9%48%6%45%45%7%27%
2340
May1st to 10thDay
23%10%47%6%34446%30%
2340
11th to 20thDay
20%7%35%6%335%5%6%35%
2432
21st to endDay
15%7%36%6%35%5%6%8%35%
2725
June1st to 10thDay
21%7%37%7%46%6%6%8%26%
2520
11th to 20thDay
19%6%345%36%5%5%8%35%
2520
21st to endDay
19%8%47%7%45%5%5%7%29%
2520
July1st to 10thDay
17%6%35%5%36%6%6%8%34%
2520
11th to 20thDay
15%5%36%6%46%6%7%8%34%
2520
21st to endDay
16%436%5%46%6%7%8%34%
2744
August1st to 10thDay
14%5%35%7%46%6%6%8%34%
2429
11th to 20thDay
15%6%27%7%45%7%8%9%31%
2294
21st to endDay
13%426%446%7%6%9%40%
2376
September1st to 10thDay
13%425%6%35%6%5%8%42%
2160
11th to 20thDay
15%5%25%434446%48%
2000
21st to endDay
17%5%246%3446%8%41%
1980
October1st to 10thDay
24%8%36%5%34446%32%
1980
11th to 20thDay
18%8%36%6%45%5%47%36%
1713
21st to endDay
26%10%46%6%45%5%4427%
1782
November1st to 10thDay
15%6%47%6%3446%7%37%
1671
11th to 20thDay
19%9%35%6%45%5%5%7%31%
1710
21st to endDay
21%8%35%6%45%6%7%7%29%
1639
December1st to 10thDay
22%10%5%9%6%5%7%6%5%5%21%
1520
11th to 20thDay
23%11%35%434447%32%
1906
21st to endDay
24%12%46%6%46%5%46%24%
2772
January1st to 10thNight
16%10%5%7%6%35%5%6%7%31%
4429
11th to 20thNight
13%13%6%12%10%36%5%5%6%21%
4440
21st to endNight
18%13%5%10%7%445%6%7%22%
4884
February1st to 10thNight
15%10%48%8%36%6%6%7%28%
2504
11th to 20thNight
11%9%5%7%6%5%6%7%6%9%30%
2218
21st to endNight
13%10%37%7%5%5%6%6%7%31%
1884
March1st to 10thNight
13%9%47%8%46%5%6%7%31%
2157
11th to 20thNight
16%10%47%7%45%5%6%6%30%
2083
21st to endNight
16%9%36%6%345%6%6%36%
2030
April1st to 10thNight
20%9%46%6%35%446%34%
1800
11th to 20thNight
19%7%45%6%445%5%7%35%
1753
21st to endNight
23%9%35%5%3446%7%33%
1620
May1st to 10thNight
21%11%5%5%6%36%345%31%
1620
11th to 20thNight
19%7%26%5%347%6%6%35%
1476
21st to endNight
17%7%35%435%5%5%8%36%
1550
June1st to 10thNight
22%7%36%6%35%5%49%30%
1440
11th to 20thNight
19%7%45%5%345%5%7%37%
1440
21st to endNight
17%7%36%5%346%5%8%36%
1440
July1st to 10thNight
17%5%245%35%6%6%9%38%
1440
11th to 20thNight
16%5%25%5%245%6%9%40%
1440
21st to endNight
16%5%25%4345%7%8%41%
1574
August1st to 10thNight
16%5%244445%7%7%42%
1490
11th to 20thNight
15%7%36%5%445%5%8%39%
1603
21st to endNight
17%434425%5%6%7%43%
1980
September1st to 10thNight
14%4245%345%5%7%47%
1800
11th to 20thNight
17%6%2442445%6%48%
1959
21st to endNight
18%6%2443446%6%43%
1980
October1st to 10thNight
21%7%35%6%35%46%6%34%
1980
11th to 20thNight
18%7%27%7%45%5%5%7%33%
2244
21st to endNight
24%9%36%5%35%5%6%7%28%
2574
November1st to 10thNight
15%6%37%6%45%5%6%7%36%
2407
11th to 20thNight
17%6%5%6%5%45%5%6%9%33%
2470
21st to endNight
17%8%46%6%46%5%6%8%30%
2540
December1st to 10thNight
21%11%49%7%46%6%5%5%22%
2660
11th to 20thNight
21%11%46%5%245%6%8%27%
3288
21st to endNight
23%14%5%9%5%35%45%6%23%
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
46%5%14%27%8%
2518
11th to 20thDay
56%8%10%19%6%1
2520
21st to endDay
55%6%11%19%9%1
2772
February1st to 10thDay
53%413%19%9%2
1675
11th to 20thDay
50%5%12%18%12%3
1857
21st to endDay
52%412%16%13%3
1570
March1st to 10thDay
50%413%18%12%4
1800
11th to 20thDay
50%411%16%15%4
1876
21st to endDay
49%49%18%16%4
2325
April1st to 10thDay
51%310%19%12%4
2160
11th to 20thDay
45%5%13%21%15%1
2156
21st to endDay
56%5%8%17%12%3
2340
May1st to 10thDay
56%38%20%11%2
2340
11th to 20thDay
47%410%21%15%2
2436
21st to endDay
45%7%15%20%11%2
2725
June1st to 10thDay
53%5%14%19%8%1
2520
11th to 20thDay
46%6%11%21%14%2
2520
21st to endDay
52%7%12%19%10%1
2520
July1st to 10thDay
43%7%13%23%14%1
2450
11th to 20thDay
45%7%16%23%9%1
2445
21st to endDay
42%7%15%23%12%1
2591
August1st to 10thDay
44%7%16%22%10%
2415
11th to 20thDay
45%6%16%23%10%
2294
21st to endDay
37%6%16%25%15%1
2376
September1st to 10thDay
36%6%14%28%14%1
2160
11th to 20thDay
37%49%30%19%2
2000
21st to endDay
40%414%26%15%2
1980
October1st to 10thDay
52%5%9%21%12%2
1980
11th to 20thDay
46%415%26%8%1
1713
21st to endDay
56%412%16%9%2
1782
November1st to 10thDay
44%415%22%14%1
1671
11th to 20thDay
47%314%18%15%2
1710
21st to endDay
48%6%19%18%9%1
1639
December1st to 10thDay
57%5%14%17%6%1
1520
11th to 20thDay
51%410%18%15%1
1906
21st to endDay
59%411%17%9%
2772
January1st to 10thNight
47%5%15%24%8%1
4429
11th to 20thNight
55%7%13%16%8%1
4440
21st to endNight
57%5%11%17%8%1
4884
February1st to 10thNight
50%5%14%19%11%2
2504
11th to 20thNight
45%5%13%23%13%2
2220
21st to endNight
46%413%21%11%3
1884
March1st to 10thNight
46%5%11%22%12%3
2167
11th to 20thNight
49%412%19%12%3
2084
21st to endNight
45%410%18%17%4
2030
April1st to 10thNight
50%49%20%15%2
1800
11th to 20thNight
47%48%26%14%1
1753
21st to endNight
48%412%19%13%3
1620
May1st to 10thNight
53%49%20%13%2
1620
11th to 20thNight
47%6%10%20%14%3
1477
21st to endNight
44%8%15%22%10%2
1551
June1st to 10thNight
50%6%14%19%11%
1440
11th to 20thNight
47%5%14%20%12%2
1440
21st to endNight
45%7%15%22%11%
1440
July1st to 10thNight
39%7%17%23%14%1
1400
11th to 20thNight
39%6%18%25%12%
1392
21st to endNight
36%6%17%27%12%1
1486
August1st to 10thNight
38%8%15%27%12%
1480
11th to 20thNight
42%7%16%23%13%
1603
21st to endNight
37%6%13%29%15%
1980
September1st to 10thNight
32%6%15%31%15%
1800
11th to 20thNight
36%5%10%29%18%2
1959
21st to endNight
40%413%29%14%1
1980
October1st to 10thNight
48%5%11%23%11%2
1980
11th to 20thNight
46%5%14%26%8%1
2244
21st to endNight
52%5%13%19%9%2
2574
November1st to 10thNight
43%6%12%23%14%2
2407
11th to 20thNight
44%5%12%23%14%2
2470
21st to endNight
46%6%16%22%9%1
2540
December1st to 10thNight
56%5%13%19%6%
2660
11th to 20thNight
50%6%13%17%13%1
3288
21st to endNight
59%5%9%20%6%
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
29%23%28%16%31
180
11th to 20thDay
34%27%27%10%11
180
21st to endDay
22%28%32%14%5%
198
February1st to 10thDay
36%24%28%10%2
286
11th to 20thDay
30%28%28%12%3
456
21st to endDay
34%23%24%17%3
382
March1st to 10thDay
28%25%29%14%4
420
11th to 20thDay
35%24%23%12%41
420
21st to endDay
32%20%25%15%6%3
462
April1st to 10thDay
37%20%23%14%5%2
420
11th to 20thDay
31%25%20%16%6%2
412
21st to endDay
34%20%28%11%5%2
420
May1st to 10thDay
35%19%25%13%43
423
11th to 20thDay
25%20%32%15%6%2
447
21st to endDay
23%16%30%23%7%2
485
June1st to 10thDay
24%16%34%17%9%
450
11th to 20thDay
22%17%31%20%8%2
450
21st to endDay
19%16%33%21%9%2
450
July1st to 10thDay
20%13%31%22%10%3
445
11th to 20thDay
16%9%34%28%10%2
444
21st to endDay
15%13%35%27%9%2
488
August1st to 10thDay
13%14%29%25%16%3
446
11th to 20thDay
18%13%29%21%13%6%
439
21st to endDay
15%14%29%23%13%6%
495
September1st to 10thDay
16%12%29%22%16%5%
450
11th to 20thDay
20%13%26%20%13%8%
450
21st to endDay
18%16%26%24%10%6%
450
October1st to 10thDay
31%15%19%20%12%4
450
11th to 20thDay
27%16%25%21%10%2
399
21st to endDay
39%15%22%17%7%
396
November1st to 10thDay
25%17%23%25%9%1
365
11th to 20thDay
32%18%23%20%7%1
370
21st to endDay
34%18%29%14%5%1
299
December1st to 10thDay
29%26%24%16%4
180
11th to 20thDay
39%19%30%9%2
180
21st to endDay
34%19%28%15%31
198
January1st to 10thNight
24%22%28%23%3
760
11th to 20thNight
29%18%25%24%3
760
21st to endNight
21%24%30%21%4
836
February1st to 10thNight
24%21%33%21%2
760
11th to 20thNight
23%24%32%18%3
743
21st to endNight
25%21%27%23%3
628
March1st to 10thNight
25%19%30%22%4
723
11th to 20thNight
28%20%23%22%6%
720
21st to endNight
26%19%24%24%7%1
792
April1st to 10thNight
30%17%26%23%5%
720
11th to 20thNight
25%19%25%24%7%
689
21st to endNight
30%16%27%22%6%
540
May1st to 10thNight
29%13%25%24%8%
540
11th to 20thNight
23%13%25%29%9%
415
21st to endNight
24%7%20%36%12%1
389
June1st to 10thNight
26%9%22%33%9%1
360
11th to 20thNight
24%9%23%31%14%
360
21st to endNight
18%7%23%38%13%1
360
July1st to 10thNight
17%422%41%15%
350
11th to 20thNight
17%321%36%21%2
348
21st to endNight
15%5%19%41%19%1
394
August1st to 10thNight
19%216%41%21%
416
11th to 20thNight
18%6%25%32%18%2
539
21st to endNight
19%5%18%32%22%4
792
September1st to 10thNight
15%8%20%34%21%2
720
11th to 20thNight
20%10%18%28%19%5%
720
21st to endNight
21%10%20%30%17%3
720
October1st to 10thNight
27%10%19%26%16%2
720
11th to 20thNight
22%15%24%25%12%1
720
21st to endNight
31%16%23%22%7%
792
November1st to 10thNight
22%16%22%30%9%1
740
11th to 20thNight
27%18%22%25%8%1
760
21st to endNight
26%18%23%26%5%1
760
December1st to 10thNight
30%19%26%20%5%
760
11th to 20thNight
32%17%25%21%41
760
21st to endNight
31%22%24%21%3
836
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