Abbey Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Abbey Ridge Observatory clear sky chart from 2005-11-06 to 2024-01-10.

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
21%
23832
12%
74467
5%
23771
29%
23771
14%
54838

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
11%
846
10%
2636
2%
843
19%
843
9%
2056
January11th to 20thNight
13%
774
9%
2463
2%
774
21%
774
8%
1976
January21st to endNight
15%
792
12%
2574
4%
792
24%
792
10%
1915
February1st to 10thNight
13%
720
9%
2340
2%
720
23%
720
9%
1815
February11th to 20thNight
11%
703
10%
2276
1%
700
21%
700
8%
1735
February21st to endNight
16%
592
13%
1891
3%
592
27%
592
12%
1392
March1st to 10thNight
13%
720
14%
1992
3%
720
22%
720
12%
1514
March11th to 20thNight
21%
720
14%
1980
4%
720
29%
720
16%
1453
March21st to endNight
17%
792
16%
2178
3%
792
29%
792
14%
1615
April1st to 10thNight
15%
543
12%
1803
4%
543
25%
543
10%
1356
April11th to 20thNight
16%
534
14%
1724
5%
534
25%
534
14%
1233
April21st to endNight
19%
540
14%
1620
5%
540
27%
540
15%
1193
May1st to 10thNight
19%
540
13%
1563
5%
540
26%
540
15%
1165
May11th to 20thNight
25%
532
15%
1417
7%
532
31%
532
19%
1036
May21st to endNight
20%
583
10%
1551
3%
582
26%
582
16%
1174
June1st to 10thNight
23%
540
9%
1440
4%
540
27%
540
16%
1122
June11th to 20thNight
22%
531
10%
1431
3%
531
27%
531
18%
1068
June21st to endNight
29%
360
7%
1260
5%
360
31%
360
11%
983
July1st to 10thNight
35%
458
8%
1333
6%
458
39%
458
20%
964
July11th to 20thNight
33%
522
8%
1392
6%
522
35%
522
17%
1073
July21st to endNight
35%
590
9%
1556
8%
558
36%
558
17%
1188
August1st to 10thNight
41%
538
11%
1600
9%
534
43%
534
23%
1100
August11th to 20thNight
40%
532
14%
1596
8%
532
45%
532
19%
1142
August21st to endNight
40%
594
16%
1890
10%
594
46%
594
22%
1243
September1st to 10thNight
36%
540
18%
1800
11%
540
45%
540
23%
1144
September11th to 20thNight
35%
597
20%
1857
15%
597
42%
597
23%
1187
September21st to endNight
29%
720
19%
2042
9%
720
38%
720
21%
1405
October1st to 10thNight
32%
720
19%
2160
10%
720
40%
720
22%
1423
October11th to 20thNight
27%
720
19%
2160
8%
720
37%
720
20%
1445
October21st to endNight
18%
792
16%
2376
5%
792
28%
792
15%
1738
November1st to 10thNight
22%
823
14%
2524
6%
823
30%
823
16%
1808
November11th to 20thNight
20%
850
16%
2660
7%
850
30%
850
12%
1940
November21st to endNight
17%
850
10%
2660
3%
850
25%
850
12%
1979
December1st to 10thNight
11%
850
10%
2660
1%
850
20%
850
9%
2099
December11th to 20thNight
9%
850
9%
3236
2%
849
17%
849
7%
2597
December21st to endNight
11%
924
7%
4826
2%
907
21%
907
5%
3562

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
22%10%47%6%3445%7%29%
74903
Night
22%10%47%6%3445%6%29%
74757
TransparencyDay
54%7%11%18%9%1
74611
Night
54%7%11%18%9%1
74584
SeeingDay
27%19%31%16%5%1
16171
Night
27%17%30%20%6%
23843

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
18%16%7%9%6%36%5%5%6%19%
1508
11th to 20thDay
24%15%6%7%6%45%446%19%
1494
21st to endDay
15%9%6%8%8%47%46%8%25%
1782
February1st to 10thDay
21%12%5%9%8%45%5%45%21%
1620
11th to 20thDay
18%15%5%10%6%45%5%45%23%
1573
21st to endDay
12%13%5%8%8%44438%30%
1364
March1st to 10thDay
18%13%5%9%8%45%435%25%
1962
11th to 20thDay
17%11%5%9%7%44436%30%
1980
21st to endDay
18%15%5%7%6%24436%29%
2178
April1st to 10thDay
27%14%37%6%33345%24%
2156
11th to 20thDay
22%11%35%4345%5%6%32%
2185
21st to endDay
23%12%36%5%34447%28%
2340
May1st to 10thDay
26%11%47%5%3445%6%25%
2395
11th to 20thDay
22%10%46%5%3435%6%33%
2478
21st to endDay
24%8%46%5%245%5%7%29%
2724
June1st to 10thDay
26%10%47%6%3445%7%24%
2520
11th to 20thDay
23%8%46%5%35%347%31%
2537
21st to endDay
29%9%35%5%34446%26%
2700
July1st to 10thDay
21%7%35%425%5%6%8%33%
2561
11th to 20thDay
20%8%36%5%345%6%9%31%
2520
21st to endDay
26%8%35%5%35%5%6%8%27%
2669
August1st to 10thDay
19%7%26%6%346%6%8%33%
2327
11th to 20thDay
17%7%36%7%45%6%7%8%31%
2304
21st to endDay
17%7%25%42445%7%41%
2466
September1st to 10thDay
19%6%25%5%34449%39%
2160
11th to 20thDay
20%8%35%433446%41%
2101
21st to endDay
21%6%35%32435%6%41%
1918
October1st to 10thDay
20%6%45%5%2446%7%38%
1800
11th to 20thDay
20%8%36%5%3446%8%33%
1800
21st to endDay
23%9%36%6%345%5%5%31%
1980
November1st to 10thDay
23%10%37%6%33446%30%
1552
11th to 20thDay
23%10%48%6%36%447%26%
1520
21st to endDay
20%12%5%8%7%36%446%26%
1520
December1st to 10thDay
26%13%5%10%6%44445%21%
1520
11th to 20thDay
32%11%47%5%36%445%17%
1906
21st to endDay
23%11%7%10%7%3345%6%22%
2783
January1st to 10thNight
19%13%5%9%7%45%5%5%6%21%
2636
11th to 20thNight
23%11%5%9%7%46%5%5%6%20%
2463
21st to endNight
16%11%5%8%7%46%6%7%7%23%
2574
February1st to 10thNight
19%13%49%6%5%6%5%5%6%23%
2340
11th to 20thNight
19%12%49%7%46%6%6%6%21%
2273
21st to endNight
13%12%5%9%8%5%5%5%5%7%27%
1891
March1st to 10thNight
17%11%5%9%7%45%5%47%27%
1983
11th to 20thNight
20%9%47%45%5%5%6%6%29%
1979
21st to endNight
18%12%5%7%7%33445%33%
2178
April1st to 10thNight
26%11%46%5%3445%5%27%
1803
11th to 20thNight
23%10%46%5%4335%6%31%
1724
21st to endNight
25%11%35%5%3335%6%30%
1620
May1st to 10thNight
26%11%45%42445%6%29%
1563
11th to 20thNight
24%9%36%425%45%6%32%
1416
21st to endNight
19%10%46%6%34448%31%
1550
June1st to 10thNight
29%9%36%5%33347%27%
1440
11th to 20thNight
22%10%5%6%424446%33%
1431
21st to endNight
29%11%45%6%34445%24%
1260
July1st to 10thNight
20%10%35%43445%9%32%
1372
11th to 20thNight
22%9%46%5%35%6%6%6%27%
1440
21st to endNight
20%9%47%5%45%5%5%7%30%
1647
August1st to 10thNight
17%7%26%5%35%5%5%6%39%
1612
11th to 20thNight
19%8%46%5%3446%8%33%
1596
21st to endNight
16%7%35%6%25%45%7%41%
1890
September1st to 10thNight
17%7%35%43435%6%42%
1800
11th to 20thNight
20%7%25%423346%43%
1857
21st to endNight
21%9%36%423346%38%
2042
October1st to 10thNight
19%7%345%3345%7%41%
2160
11th to 20thNight
21%6%25%5%4345%7%38%
2160
21st to endNight
26%8%35%5%34446%32%
2376
November1st to 10thNight
22%9%35%5%3435%7%33%
2524
11th to 20thNight
22%9%47%6%4445%6%29%
2660
21st to endNight
21%9%47%6%46%5%5%6%28%
2660
December1st to 10thNight
25%12%49%6%45%45%7%21%
2660
11th to 20thNight
33%11%37%5%34445%21%
3293
21st to endNight
25%10%49%6%34446%24%
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
61%9%11%13%6%
1509
11th to 20thDay
65%8%10%13%4
1494
21st to endDay
54%8%11%18%9%
1782
February1st to 10thDay
62%7%9%13%8%2
1620
11th to 20thDay
63%7%9%14%6%1
1581
21st to endDay
53%6%11%17%11%3
1364
March1st to 10thDay
61%5%8%15%10%1
1966
11th to 20thDay
53%7%10%18%11%1
1980
21st to endDay
56%7%7%18%11%2
2178
April1st to 10thDay
61%5%7%13%11%2
2156
11th to 20thDay
51%5%9%20%13%1
2185
21st to endDay
56%6%10%18%9%2
2340
May1st to 10thDay
59%6%10%16%8%2
2395
11th to 20thDay
51%7%11%19%12%
2482
21st to endDay
54%7%13%17%8%1
2724
June1st to 10thDay
60%7%11%17%6%
2520
11th to 20thDay
53%7%11%19%10%1
2537
21st to endDay
59%8%10%14%9%
2700
July1st to 10thDay
48%9%15%19%10%1
2491
11th to 20thDay
48%10%15%20%7%1
2444
21st to endDay
54%10%12%19%5%1
2520
August1st to 10thDay
46%9%16%20%8%1
2314
11th to 20thDay
47%10%16%20%8%
2304
21st to endDay
41%7%14%25%11%1
2466
September1st to 10thDay
42%6%14%23%13%2
2160
11th to 20thDay
45%5%12%23%15%1
2101
21st to endDay
44%5%9%25%16%1
1918
October1st to 10thDay
45%6%11%25%12%1
1800
11th to 20thDay
48%8%13%23%8%1
1800
21st to endDay
52%6%11%21%9%1
1980
November1st to 10thDay
55%7%9%20%8%1
1552
11th to 20thDay
54%8%14%16%7%1
1520
21st to endDay
57%7%14%15%7%
1520
December1st to 10thDay
64%7%9%16%4
1520
11th to 20thDay
65%8%7%14%5%1
1905
21st to endDay
60%6%16%13%5%
2783
January1st to 10thNight
60%8%11%16%5%
2636
11th to 20thNight
63%8%11%13%5%
2463
21st to endNight
55%8%13%17%6%1
2574
February1st to 10thNight
61%6%11%13%8%1
2340
11th to 20thNight
58%8%13%14%6%1
2276
21st to endNight
55%7%11%18%9%1
1891
March1st to 10thNight
56%6%11%17%9%1
1992
11th to 20thNight
50%8%12%16%12%2
1980
21st to endNight
54%6%8%19%10%2
2178
April1st to 10thNight
58%7%9%13%11%3
1803
11th to 20thNight
54%5%9%18%13%2
1724
21st to endNight
55%5%10%17%11%2
1620
May1st to 10thNight
56%6%10%20%8%1
1563
11th to 20thNight
52%5%11%21%11%1
1417
21st to endNight
53%8%12%19%6%1
1551
June1st to 10thNight
59%5%9%19%7%
1440
11th to 20thNight
53%6%10%18%12%1
1431
21st to endNight
63%6%9%14%8%1
1260
July1st to 10thNight
48%10%16%17%9%
1333
11th to 20thNight
55%8%12%17%8%1
1392
21st to endNight
53%10%13%17%7%1
1556
August1st to 10thNight
44%9%14%26%7%
1600
11th to 20thNight
48%9%14%20%9%
1596
21st to endNight
42%8%14%23%12%
1890
September1st to 10thNight
41%7%12%25%14%2
1800
11th to 20thNight
42%5%11%27%14%1
1857
21st to endNight
47%5%9%24%14%1
2042
October1st to 10thNight
43%6%12%24%14%1
2160
11th to 20thNight
45%6%13%28%8%
2160
21st to endNight
52%7%10%18%12%1
2376
November1st to 10thNight
51%6%13%18%11%1
2524
11th to 20thNight
52%9%12%17%9%
2660
21st to endNight
53%9%15%16%7%
2660
December1st to 10thNight
62%7%11%15%4
2660
11th to 20thNight
64%6%9%14%6%
3295
21st to endNight
58%9%11%17%5%
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%25%31%13%2
367
11th to 20thDay
31%20%33%12%3
340
21st to endDay
23%23%37%13%3
374
February1st to 10thDay
32%25%29%13%1
340
11th to 20thDay
33%28%27%10%1
336
21st to endDay
23%26%35%12%4
280
March1st to 10thDay
26%29%32%10%2
414
11th to 20thDay
28%27%29%11%4
420
21st to endDay
29%27%30%11%31
462
April1st to 10thDay
36%28%27%7%2
420
11th to 20thDay
28%29%31%10%3
412
21st to endDay
27%23%32%13%5%
420
May1st to 10thDay
31%24%31%10%31
478
11th to 20thDay
25%18%32%20%5%1
624
21st to endDay
29%16%33%18%31
680
June1st to 10thDay
32%14%31%17%6%
630
11th to 20thDay
26%17%32%19%6%1
630
21st to endDay
34%10%29%20%7%1
630
July1st to 10thDay
23%11%34%24%8%
620
11th to 20thDay
23%9%34%22%10%1
618
21st to endDay
29%10%31%23%7%1
609
August1st to 10thDay
20%9%35%28%7%1
446
11th to 20thDay
22%12%31%23%10%2
439
21st to endDay
20%12%33%24%9%3
495
September1st to 10thDay
18%12%37%24%8%1
450
11th to 20thDay
27%17%30%16%8%2
450
21st to endDay
22%15%31%22%8%2
419
October1st to 10thDay
22%14%34%18%10%2
360
11th to 20thDay
21%22%31%17%7%2
360
21st to endDay
27%23%31%12%5%1
396
November1st to 10thDay
27%19%30%16%7%1
365
11th to 20thDay
32%22%26%14%5%1
370
21st to endDay
30%26%29%13%21
370
December1st to 10thDay
35%21%31%12%21
370
11th to 20thDay
36%27%26%9%1
370
21st to endDay
29%27%28%12%31
407
January1st to 10thNight
28%21%34%14%2
846
11th to 20thNight
29%22%30%15%3
774
21st to endNight
23%24%34%16%2
792
February1st to 10thNight
28%22%31%17%2
720
11th to 20thNight
29%26%31%12%2
703
21st to endNight
20%24%35%18%3
592
March1st to 10thNight
23%24%35%15%2
720
11th to 20thNight
24%20%30%21%6%
720
21st to endNight
26%22%30%18%5%
792
April1st to 10thNight
33%19%28%17%3
543
11th to 20thNight
28%19%34%16%3
534
21st to endNight
30%15%32%18%41
540
May1st to 10thNight
32%12%33%17%5%1
540
11th to 20thNight
27%13%29%22%7%1
532
21st to endNight
25%14%35%22%4
583
June1st to 10thNight
34%10%28%23%5%
540
11th to 20thNight
25%10%35%23%5%1
531
21st to endNight
32%8%22%28%10%
360
July1st to 10thNight
22%7%29%33%7%
458
11th to 20thNight
25%6%28%31%10%
522
21st to endNight
23%7%28%32%10%
590
August1st to 10thNight
19%429%32%14%1
538
11th to 20thNight
24%5%25%32%13%1
532
21st to endNight
20%7%26%31%14%1
594
September1st to 10thNight
21%8%31%29%11%1
540
11th to 20thNight
22%11%27%26%12%1
597
21st to endNight
26%13%28%23%10%1
720
October1st to 10thNight
22%13%29%26%9%1
720
11th to 20thNight
22%16%31%22%9%1
720
21st to endNight
32%16%31%18%4
792
November1st to 10thNight
30%13%31%21%41
823
11th to 20thNight
27%22%27%19%5%
850
21st to endNight
28%23%28%16%4
850
December1st to 10thNight
34%18%32%13%4
850
11th to 20thNight
33%23%31%11%2
850
21st to endNight
29%23%31%15%3
935
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