Glebe Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glebe Mountain clear sky chart from 2005-11-06 to 2024-03-08.

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
28%
23023
15%
80782
8%
22931
38%
22931
15%
54575

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
16%
755
15%
4360
5%
737
30%
737
7%
2765
January11th to 20thNight
19%
758
12%
4390
4%
740
31%
740
5%
3104
January21st to endNight
17%
829
9%
4868
5%
814
31%
814
5%
3663
February1st to 10thNight
13%
760
13%
2465
2%
760
26%
760
10%
1731
February11th to 20thNight
15%
743
16%
2220
3%
740
30%
740
11%
1520
February21st to endNight
16%
628
17%
1884
4%
628
32%
628
13%
1291
March1st to 10thNight
17%
751
19%
2251
7%
751
32%
751
15%
1551
March11th to 20thNight
19%
720
15%
2111
4%
720
30%
720
14%
1455
March21st to endNight
24%
792
21%
1980
6%
792
34%
792
18%
1393
April1st to 10thNight
21%
720
17%
1800
4%
720
29%
720
19%
1275
April11th to 20thNight
24%
711
15%
1775
4%
711
30%
711
19%
1251
April21st to endNight
22%
579
16%
1659
5%
579
30%
579
16%
1167
May1st to 10thNight
24%
540
13%
1620
6%
540
30%
540
14%
1167
May11th to 20thNight
28%
375
16%
1437
10%
375
40%
375
14%
947
May21st to endNight
39%
388
13%
1551
13%
388
48%
388
17%
979
June1st to 10thNight
37%
360
13%
1440
12%
360
47%
360
17%
919
June11th to 20thNight
42%
360
11%
1440
13%
360
49%
360
17%
904
June21st to endNight
42%
360
12%
1440
12%
360
51%
360
18%
916
July1st to 10thNight
50%
350
13%
1400
15%
350
58%
350
21%
845
July11th to 20thNight
54%
348
14%
1392
18%
348
58%
348
23%
805
July21st to endNight
49%
394
17%
1486
17%
372
57%
372
24%
847
August1st to 10thNight
55%
380
18%
1444
16%
378
61%
378
25%
825
August11th to 20thNight
47%
628
14%
1692
8%
628
50%
628
25%
1149
August21st to endNight
50%
792
20%
1980
10%
792
54%
792
33%
1284
September1st to 10thNight
47%
720
19%
1800
7%
720
53%
720
34%
1171
September11th to 20thNight
48%
720
24%
1921
14%
720
53%
720
34%
1188
September21st to endNight
42%
720
23%
1980
15%
720
50%
720
28%
1276
October1st to 10thNight
37%
720
15%
2019
9%
720
43%
720
20%
1393
October11th to 20thNight
34%
720
17%
2204
9%
720
44%
720
19%
1471
October21st to endNight
23%
792
13%
2574
6%
792
32%
792
12%
1848
November1st to 10thNight
29%
740
19%
2407
10%
740
42%
740
18%
1558
November11th to 20thNight
24%
760
21%
2470
10%
760
38%
760
15%
1605
November21st to endNight
24%
760
17%
2574
7%
760
37%
760
15%
1670
December1st to 10thNight
17%
760
13%
2660
4%
760
29%
760
9%
1926
December11th to 20thNight
18%
760
13%
3238
5%
759
29%
759
8%
2222
December21st to endNight
16%
830
9%
4850
3%
817
28%
817
5%
3494

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%8%37%6%45%5%6%7%34%
78385
Night
14%8%36%5%35%5%6%8%36%
81172
TransparencyDay
46%9%13%20%11%1
78090
Night
45%9%14%20%11%1
81001
SeeingDay
25%18%28%18%8%3
13900
Night
22%17%26%25%9%1
23044

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
11%9%48%7%46%5%5%8%35%
2517
11th to 20thDay
12%11%5%11%8%5%5%5%6%6%26%
2520
21st to endDay
14%14%7%11%6%35%45%6%26%
2772
February1st to 10thDay
13%11%38%7%5%5%5%6%9%28%
1710
11th to 20thDay
9%8%49%7%46%7%7%8%30%
1848
21st to endDay
15%11%5%8%6%4445%6%32%
1570
March1st to 10thDay
11%9%39%7%46%5%5%8%32%
1867
11th to 20thDay
16%8%5%7%6%45%46%6%34%
1845
21st to endDay
16%9%47%6%34447%37%
2376
April1st to 10thDay
16%9%47%5%45%45%6%35%
2160
11th to 20thDay
15%7%36%5%45%6%6%7%36%
2134
21st to endDay
18%9%47%7%46%5%5%6%30%
2300
May1st to 10thDay
20%11%46%6%34446%32%
2340
11th to 20thDay
17%6%35%5%35%5%6%7%38%
2472
21st to endDay
15%5%26%6%35%46%7%40%
2725
June1st to 10thDay
18%6%36%7%5%5%6%6%9%30%
2520
11th to 20thDay
17%6%35%5%45%6%7%9%34%
2520
21st to endDay
17%7%26%7%5%6%6%6%8%30%
2520
July1st to 10thDay
13%6%26%5%46%5%7%7%39%
2520
11th to 20thDay
11%5%36%6%45%6%7%9%37%
2520
21st to endDay
13%5%35%5%47%6%7%8%37%
2744
August1st to 10thDay
10%5%26%7%47%7%7%9%36%
2465
11th to 20thDay
12%5%37%6%5%7%6%6%9%35%
2206
21st to endDay
12%426%5%36%5%7%9%40%
2376
September1st to 10thDay
13%5%25%5%35%5%6%10%42%
2160
11th to 20thDay
13%5%244345%5%7%47%
2039
21st to endDay
15%6%25%5%3445%8%44%
1980
October1st to 10thDay
21%8%35%5%3445%5%35%
1939
11th to 20thDay
13%7%35%7%45%5%5%8%38%
1755
21st to endDay
21%9%37%6%35%45%6%30%
1782
November1st to 10thDay
11%7%46%6%245%6%8%42%
1671
11th to 20thDay
14%7%37%6%35%5%47%38%
1710
21st to endDay
15%8%47%437%5%7%7%34%
1604
December1st to 10thDay
15%11%48%7%45%5%6%8%27%
1520
11th to 20thDay
19%10%46%6%35%446%33%
1906
21st to endDay
17%12%49%7%45%46%7%27%
2772
January1st to 10thNight
14%8%47%6%345%5%8%36%
4429
11th to 20thNight
10%8%6%11%8%5%7%5%6%6%28%
4440
21st to endNight
16%13%410%6%46%5%5%6%25%
4884
February1st to 10thNight
10%9%48%7%45%5%7%8%31%
2465
11th to 20thNight
8%8%37%6%46%7%7%8%33%
2218
21st to endNight
13%9%36%5%45%5%6%9%35%
1884
March1st to 10thNight
13%9%36%7%45%5%5%7%36%
2241
11th to 20thNight
13%8%36%6%46%6%5%7%35%
2110
21st to endNight
14%9%46%435%6%5%6%39%
1980
April1st to 10thNight
16%7%35%6%35%46%9%37%
1800
11th to 20thNight
15%7%35%5%35%5%6%8%37%
1775
21st to endNight
18%9%35%5%346%5%7%36%
1659
May1st to 10thNight
20%10%46%6%34447%33%
1620
11th to 20thNight
16%6%47%6%3446%7%37%
1436
21st to endNight
14%5%37%5%25%5%6%8%40%
1550
June1st to 10thNight
17%6%36%5%35%45%8%38%
1440
11th to 20thNight
19%5%245%3446%9%40%
1440
21st to endNight
13%5%35%6%46%5%6%8%40%
1440
July1st to 10thNight
12%6%24435%7%6%9%42%
1440
11th to 20thNight
13%424426%5%8%10%42%
1440
21st to endNight
12%5%244345%6%10%46%
1574
August1st to 10thNight
10%5%2443446%10%49%
1454
11th to 20thNight
13%5%25%6%45%6%7%8%40%
1692
21st to endNight
14%6%2442445%9%47%
1980
September1st to 10thNight
12%5%234245%6%8%49%
1800
11th to 20thNight
13%5%2442345%7%51%
1921
21st to endNight
14%5%15%34445%7%46%
1980
October1st to 10thNight
20%6%35%43445%7%39%
2019
11th to 20thNight
14%6%25%5%446%6%7%41%
2204
21st to endNight
21%8%35%5%35%5%6%7%32%
2574
November1st to 10thNight
13%6%35%5%45%5%5%7%42%
2407
11th to 20thNight
14%5%36%6%446%6%7%39%
2470
21st to endNight
11%7%36%5%25%6%6%8%39%
2574
December1st to 10thNight
15%8%47%7%45%6%6%8%30%
2660
11th to 20thNight
18%8%37%5%45%5%6%8%32%
3288
21st to endNight
19%11%48%6%35%5%6%8%26%
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
45%10%15%24%7%
2518
11th to 20thDay
55%10%10%18%6%1
2520
21st to endDay
58%7%11%16%7%1
2772
February1st to 10thDay
52%9%13%17%8%1
1710
11th to 20thDay
48%11%11%18%11%2
1857
21st to endDay
53%7%11%16%12%2
1570
March1st to 10thDay
50%7%13%16%11%3
1870
11th to 20thDay
50%7%11%13%15%3
1845
21st to endDay
48%6%10%17%16%4
2376
April1st to 10thDay
49%6%11%19%11%3
2160
11th to 20thDay
45%9%11%19%14%2
2134
21st to endDay
52%8%8%16%12%3
2300
May1st to 10thDay
53%7%9%18%13%1
2340
11th to 20thDay
45%7%10%20%16%2
2476
21st to endDay
42%9%15%22%10%2
2725
June1st to 10thDay
49%9%15%18%10%
2520
11th to 20thDay
45%9%13%18%14%1
2520
21st to endDay
48%11%13%18%9%1
2520
July1st to 10thDay
41%10%13%20%15%1
2450
11th to 20thDay
40%9%16%26%8%
2445
21st to endDay
41%9%14%23%11%1
2591
August1st to 10thDay
40%12%16%22%11%1
2451
11th to 20thDay
42%11%14%23%9%1
2206
21st to endDay
36%10%16%25%12%1
2376
September1st to 10thDay
37%9%14%26%13%1
2160
11th to 20thDay
35%8%11%26%19%2
2039
21st to endDay
39%7%13%24%14%3
1980
October1st to 10thDay
50%7%9%19%12%3
1939
11th to 20thDay
41%9%15%25%8%1
1755
21st to endDay
54%8%11%16%9%2
1782
November1st to 10thDay
39%8%16%22%15%1
1671
11th to 20thDay
46%8%12%17%15%2
1710
21st to endDay
46%8%18%19%8%1
1604
December1st to 10thDay
54%8%14%14%9%1
1520
11th to 20thDay
52%7%12%17%11%1
1906
21st to endDay
56%10%12%14%9%
2772
January1st to 10thNight
44%11%14%20%10%1
4429
11th to 20thNight
54%9%13%15%8%1
4440
21st to endNight
58%9%10%14%8%1
4884
February1st to 10thNight
48%9%16%17%9%1
2465
11th to 20thNight
44%9%14%20%12%1
2220
21st to endNight
45%8%14%21%8%3
1884
March1st to 10thNight
46%7%12%21%12%2
2251
11th to 20thNight
45%8%13%18%13%3
2111
21st to endNight
44%7%11%17%18%4
1980
April1st to 10thNight
44%7%12%21%13%2
1800
11th to 20thNight
43%8%10%23%14%1
1775
21st to endNight
47%8%12%18%13%3
1659
May1st to 10thNight
51%7%9%17%14%2
1620
11th to 20thNight
46%8%13%19%13%2
1437
21st to endNight
41%10%13%23%11%1
1551
June1st to 10thNight
44%7%15%21%12%
1440
11th to 20thNight
42%9%16%20%13%1
1440
21st to endNight
39%12%14%23%11%1
1440
July1st to 10thNight
36%11%16%23%13%1
1400
11th to 20thNight
34%10%19%27%10%
1392
21st to endNight
32%10%17%28%11%2
1486
August1st to 10thNight
32%10%17%29%12%1
1444
11th to 20thNight
39%11%17%23%10%
1692
21st to endNight
34%7%14%29%15%
1980
September1st to 10thNight
33%9%16%27%15%1
1800
11th to 20thNight
32%7%12%28%19%1
1921
21st to endNight
36%8%11%28%15%2
1980
October1st to 10thNight
44%8%13%22%11%2
2019
11th to 20thNight
41%9%16%23%10%1
2204
21st to endNight
51%8%12%19%8%2
2574
November1st to 10thNight
40%9%13%21%14%3
2407
11th to 20thNight
41%9%13%21%13%3
2470
21st to endNight
41%9%18%22%10%1
2574
December1st to 10thNight
51%10%14%18%7%1
2660
11th to 20thNight
49%9%15%15%11%2
3288
21st to endNight
54%11%13%16%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
31%21%32%14%2
180
11th to 20thDay
32%23%29%13%21
180
21st to endDay
21%29%30%15%5%1
198
February1st to 10thDay
30%33%26%9%2
280
11th to 20thDay
33%26%26%13%2
456
21st to endDay
31%26%26%14%3
382
March1st to 10thDay
29%23%30%16%2
448
11th to 20thDay
29%28%27%12%31
420
21st to endDay
32%20%26%12%7%2
462
April1st to 10thDay
35%20%25%13%6%1
420
11th to 20thDay
32%25%22%14%5%3
412
21st to endDay
33%18%30%12%5%2
420
May1st to 10thDay
33%21%24%13%7%2
423
11th to 20thDay
21%19%36%17%42
447
21st to endDay
19%16%31%23%9%2
485
June1st to 10thDay
22%18%32%19%9%1
450
11th to 20thDay
21%16%32%19%11%2
450
21st to endDay
20%17%32%20%8%4
450
July1st to 10thDay
19%10%29%27%12%3
445
11th to 20thDay
16%7%34%28%13%2
444
21st to endDay
15%10%40%22%10%3
488
August1st to 10thDay
12%13%29%27%16%4
446
11th to 20thDay
16%10%30%22%15%7%
439
21st to endDay
16%14%26%23%13%8%
495
September1st to 10thDay
17%12%25%24%15%8%
450
11th to 20thDay
18%12%27%19%14%10%
450
21st to endDay
20%11%30%21%12%6%
450
October1st to 10thDay
29%16%22%15%15%3
450
11th to 20thDay
22%17%28%21%11%1
427
21st to endDay
33%15%26%19%6%1
396
November1st to 10thDay
24%19%24%22%11%1
365
11th to 20thDay
30%23%22%19%5%1
370
21st to endDay
30%21%30%14%5%
264
December1st to 10thDay
29%27%22%14%6%1
180
11th to 20thDay
39%22%27%9%3
180
21st to endDay
35%19%26%16%31
198
January1st to 10thNight
23%23%32%19%3
760
11th to 20thNight
26%23%26%22%21
760
21st to endNight
19%25%30%22%3
836
February1st to 10thNight
22%24%33%18%3
760
11th to 20thNight
23%27%30%19%2
743
21st to endNight
26%24%30%18%2
628
March1st to 10thNight
28%20%30%20%2
751
11th to 20thNight
26%23%29%19%31
720
21st to endNight
26%18%27%21%7%1
792
April1st to 10thNight
26%20%27%21%5%
720
11th to 20thNight
21%22%28%20%8%
711
21st to endNight
27%17%27%23%5%
579
May1st to 10thNight
29%14%24%25%7%
540
11th to 20thNight
18%19%29%28%6%
375
21st to endNight
19%7%27%32%14%2
389
June1st to 10thNight
20%10%24%32%14%1
360
11th to 20thNight
21%9%22%34%14%
360
21st to endNight
14%6%29%37%13%1
360
July1st to 10thNight
14%6%22%40%16%1
350
11th to 20thNight
14%323%40%18%2
348
21st to endNight
12%6%28%36%17%1
394
August1st to 10thNight
12%422%39%23%1
380
11th to 20thNight
15%5%22%34%19%4
628
21st to endNight
17%6%19%34%23%2
792
September1st to 10thNight
14%7%26%34%18%2
720
11th to 20thNight
17%8%22%29%19%5%
720
21st to endNight
18%11%23%30%16%3
720
October1st to 10thNight
25%15%17%28%14%2
720
11th to 20thNight
20%17%24%28%11%1
720
21st to endNight
27%20%24%22%6%
792
November1st to 10thNight
21%19%25%26%8%1
740
11th to 20thNight
22%23%26%20%8%2
760
21st to endNight
22%22%26%23%6%1
760
December1st to 10thNight
26%26%26%18%4
760
11th to 20thNight
27%26%24%20%4
760
21st to endNight
29%26%24%19%2
836
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