Terrace Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Terrace Bay clear sky chart from 2005-11-06 to 2024-02-05.

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
35%
24293
9%
80716
6%
24200
39%
24200
13%
62135

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
25%
944
6%
4479
1%
926
29%
926
4%
3712
January11th to 20thNight
25%
942
2%
4428
2%
930
27%
930
3%
3994
January21st to endNight
23%
1032
3%
4882
2%
1023
26%
1023
3%
4289
February1st to 10thNight
31%
923
6%
2583
2%
923
33%
923
11%
2128
February11th to 20thNight
30%
782
12%
2200
6%
779
35%
779
13%
1745
February21st to endNight
29%
592
15%
1776
7%
592
37%
592
16%
1328
March1st to 10thNight
37%
718
17%
2154
9%
717
42%
717
22%
1472
March11th to 20thNight
31%
720
17%
2103
8%
720
39%
720
22%
1447
March21st to endNight
39%
628
21%
2014
16%
628
48%
628
21%
1366
April1st to 10thNight
37%
540
13%
1800
9%
540
43%
540
16%
1270
April11th to 20thNight
39%
533
15%
1687
11%
533
43%
533
20%
1148
April21st to endNight
43%
540
15%
1620
10%
540
48%
540
23%
1081
May1st to 10thNight
42%
540
13%
1468
10%
540
44%
540
21%
1078
May11th to 20thNight
49%
531
15%
1416
11%
531
52%
531
25%
985
May21st to endNight
50%
459
11%
1428
9%
458
52%
458
22%
984
June1st to 10thNight
51%
360
6%
1260
7%
360
52%
360
18%
858
June11th to 20thNight
52%
360
6%
1260
8%
360
52%
360
19%
845
June21st to endNight
52%
360
7%
1260
8%
360
53%
360
18%
871
July1st to 10thNight
59%
370
8%
1245
9%
370
60%
370
22%
814
July11th to 20thNight
56%
522
8%
1392
6%
522
56%
522
23%
988
July21st to endNight
60%
591
11%
1487
7%
558
60%
558
29%
991
August1st to 10thNight
62%
537
13%
1423
10%
534
64%
534
29%
961
August11th to 20thNight
60%
534
18%
1506
13%
534
63%
534
31%
944
August21st to endNight
50%
594
15%
1885
13%
594
53%
594
25%
1190
September1st to 10thNight
55%
540
17%
1800
15%
540
59%
540
25%
1128
September11th to 20thNight
44%
643
14%
1903
9%
643
48%
643
24%
1271
September21st to endNight
43%
720
13%
1980
10%
720
44%
720
21%
1431
October1st to 10thNight
37%
720
12%
2045
7%
720
40%
720
18%
1511
October11th to 20thNight
28%
720
9%
2304
6%
720
32%
720
12%
1791
October21st to endNight
26%
792
8%
2574
4%
792
31%
792
9%
2107
November1st to 10thNight
27%
740
12%
2406
7%
740
34%
740
11%
1876
November11th to 20thNight
21%
878
7%
2625
3%
878
24%
878
7%
2233
November21st to endNight
19%
950
5%
2850
2%
950
22%
950
7%
2439
December1st to 10thNight
20%
950
4%
2850
1%
950
23%
950
6%
2516
December11th to 20thNight
18%
950
5%
3440
2%
949
20%
949
4%
2843
December21st to endNight
18%
1038
2%
5183
1%
1026
21%
1026
2%
4500

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%10%47%6%45%5%6%7%30%
77823
Night
14%12%5%8%6%45%5%6%7%28%
81060
TransparencyDay
52%9%12%18%8%1
77524
Night
57%10%11%16%6%1
80893
SeeingDay
20%7%25%31%15%2
14655
Night
20%8%26%30%14%2
24330

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%14%5%7%8%47%7%7%8%22%
2443
11th to 20thDay
6%14%6%10%10%5%7%7%7%8%19%
2530
21st to endDay
11%22%8%10%8%5%5%5%7%5%14%
2783
February1st to 10thDay
8%10%5%10%7%37%7%9%10%24%
1472
11th to 20thDay
7%12%6%9%8%45%6%6%8%28%
1648
21st to endDay
9%11%6%9%8%5%5%46%7%31%
1480
March1st to 10thDay
11%11%47%7%45%6%5%7%34%
1798
11th to 20thDay
13%10%47%6%35%46%7%36%
1855
21st to endDay
14%9%36%6%345%6%7%37%
2358
April1st to 10thDay
13%10%47%7%35%5%6%8%33%
2160
11th to 20thDay
18%10%46%5%345%6%8%32%
2222
21st to endDay
16%9%35%6%345%5%7%37%
2340
May1st to 10thDay
18%8%36%6%45%5%6%6%34%
2490
11th to 20thDay
16%8%35%6%35%6%5%7%36%
2479
21st to endDay
19%8%36%5%35%447%35%
2848
June1st to 10thDay
17%6%37%7%45%5%5%7%33%
2700
11th to 20thDay
14%7%37%6%45%5%8%7%35%
2700
21st to endDay
16%8%45%5%45%5%6%8%34%
2700
July1st to 10thDay
12%7%36%5%46%6%7%10%35%
2675
11th to 20thDay
14%6%38%6%45%6%5%9%36%
2520
21st to endDay
12%6%36%6%345%7%9%38%
2743
August1st to 10thDay
11%7%35%6%45%6%8%9%36%
2507
11th to 20thDay
14%6%245%35%5%5%8%43%
2393
21st to endDay
17%6%26%435%5%5%8%39%
2467
September1st to 10thDay
15%8%25%6%3445%7%39%
2160
11th to 20thDay
18%8%35%6%35%45%8%35%
2039
21st to endDay
18%8%47%7%5%5%5%5%7%30%
1980
October1st to 10thDay
20%10%48%5%345%6%6%28%
1913
11th to 20thDay
22%10%47%7%45%6%5%8%22%
1655
21st to endDay
23%14%49%7%35%445%21%
1782
November1st to 10thDay
18%12%5%8%8%46%5%6%7%22%
1672
11th to 20thDay
20%15%5%10%7%5%5%5%45%19%
1549
21st to endDay
19%17%47%7%36%5%6%6%19%
1330
December1st to 10thDay
12%15%7%9%7%5%7%7%8%8%14%
1330
11th to 20thDay
14%17%7%7%5%45%5%7%8%20%
1671
21st to endDay
24%21%48%5%3434419%
2431
January1st to 10thNight
10%15%6%9%6%46%7%7%8%23%
4496
11th to 20thNight
6%13%7%12%13%6%7%6%7%7%16%
4440
21st to endNight
12%19%10%11%7%446%7%5%14%
4884
February1st to 10thNight
8%12%5%10%7%5%7%7%8%9%24%
2583
11th to 20thNight
9%13%5%8%8%47%7%5%7%27%
2199
21st to endNight
6%13%6%10%8%35%46%7%30%
1776
March1st to 10thNight
7%8%48%7%45%6%6%7%37%
2149
11th to 20thNight
14%9%37%6%345%5%6%38%
2103
21st to endNight
12%9%46%6%345%6%7%37%
2014
April1st to 10thNight
16%9%38%6%36%5%6%6%32%
1800
11th to 20thNight
15%11%38%5%3446%8%34%
1687
21st to endNight
17%8%37%5%2445%7%39%
1620
May1st to 10thNight
18%8%47%6%345%5%5%35%
1468
11th to 20thNight
17%7%36%5%345%6%8%36%
1416
21st to endNight
17%9%35%5%3446%8%37%
1427
June1st to 10thNight
16%6%36%7%45%5%6%5%37%
1260
11th to 20thNight
17%8%37%5%35%45%7%36%
1260
21st to endNight
16%9%36%6%345%5%8%35%
1260
July1st to 10thNight
11%7%46%5%25%6%48%41%
1281
11th to 20thNight
12%9%38%5%35%5%7%8%35%
1440
21st to endNight
12%7%36%5%245%5%9%42%
1575
August1st to 10thNight
10%7%26%445%7%6%10%39%
1432
11th to 20thNight
11%425%6%345%6%7%47%
1506
21st to endNight
16%7%35%42346%7%42%
1885
September1st to 10thNight
13%6%26%5%345%5%5%46%
1800
11th to 20thNight
17%7%245%345%7%7%40%
1903
21st to endNight
21%8%35%5%3445%6%36%
1980
October1st to 10thNight
17%11%37%6%4446%7%33%
2045
11th to 20thNight
20%10%48%7%35%5%6%6%27%
2304
21st to endNight
21%13%410%6%36%45%6%22%
2574
November1st to 10thNight
19%12%48%7%35%5%6%7%25%
2406
11th to 20thNight
18%15%5%10%6%45%5%5%5%20%
2625
21st to endNight
16%16%6%10%7%45%5%5%7%20%
2850
December1st to 10thNight
11%13%7%11%7%5%7%8%8%7%18%
2850
11th to 20thNight
13%15%5%10%7%46%6%6%6%23%
3526
21st to endNight
26%18%5%8%6%24446%17%
5236

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%16%9%10%5%
2444
11th to 20thDay
63%20%7%8%1
2530
21st to endDay
70%16%7%43
2783
February1st to 10thDay
56%16%10%12%5%1
1472
11th to 20thDay
55%12%11%16%5%1
1657
21st to endDay
54%5%11%16%12%1
1480
March1st to 10thDay
49%6%11%20%12%1
1800
11th to 20thDay
48%5%12%22%12%2
1855
21st to endDay
46%6%12%20%14%2
2358
April1st to 10thDay
48%6%12%22%12%1
2160
11th to 20thDay
51%5%13%20%10%1
2222
21st to endDay
47%412%18%14%4
2340
May1st to 10thDay
49%5%14%21%9%2
2490
11th to 20thDay
45%6%12%26%10%1
2483
21st to endDay
50%6%12%19%12%1
2848
June1st to 10thDay
47%8%12%19%14%1
2700
11th to 20thDay
46%6%12%23%11%1
2700
21st to endDay
47%9%13%22%7%1
2700
July1st to 10thDay
41%10%14%25%9%1
2602
11th to 20thDay
43%9%16%24%7%1
2445
21st to endDay
39%9%15%25%10%
2591
August1st to 10thDay
40%8%21%24%7%1
2492
11th to 20thDay
38%8%16%28%10%
2393
21st to endDay
43%7%16%26%8%
2467
September1st to 10thDay
44%7%14%26%9%
2160
11th to 20thDay
48%7%20%21%3
2039
21st to endDay
53%6%16%19%6%
1980
October1st to 10thDay
55%6%17%18%4
1913
11th to 20thDay
61%9%11%15%4
1655
21st to endDay
66%6%11%13%4
1782
November1st to 10thDay
61%7%13%14%4
1672
11th to 20thDay
70%9%9%8%4
1549
21st to endDay
70%9%10%8%3
1330
December1st to 10thDay
72%13%8%5%2
1330
11th to 20thDay
63%17%8%8%31
1671
21st to endDay
74%9%5%11%2
2431
January1st to 10thNight
62%17%10%8%2
4496
11th to 20thNight
67%19%7%6%1
4440
21st to endNight
70%14%8%5%2
4884
February1st to 10thNight
59%14%10%12%6%
2583
11th to 20thNight
59%9%10%17%5%
2200
21st to endNight
56%6%10%18%10%1
1776
March1st to 10thNight
45%8%12%22%13%1
2160
11th to 20thNight
48%411%23%12%2
2104
21st to endNight
47%6%11%19%14%3
2014
April1st to 10thNight
53%5%9%20%13%1
1800
11th to 20thNight
50%411%22%12%2
1687
21st to endNight
46%410%20%15%4
1620
May1st to 10thNight
51%6%9%22%10%2
1468
11th to 20thNight
46%6%11%24%13%1
1417
21st to endNight
47%6%10%22%13%2
1428
June1st to 10thNight
49%7%11%21%12%1
1260
11th to 20thNight
50%5%10%21%14%2
1260
21st to endNight
47%10%13%20%10%
1260
July1st to 10thNight
42%8%12%23%13%1
1245
11th to 20thNight
46%8%13%23%10%1
1392
21st to endNight
38%9%17%24%12%
1487
August1st to 10thNight
39%9%19%24%9%
1423
11th to 20thNight
36%6%16%29%12%
1506
21st to endNight
41%6%16%28%10%
1885
September1st to 10thNight
41%6%15%29%9%1
1800
11th to 20thNight
42%8%19%26%4
1903
21st to endNight
51%6%13%24%6%
1980
October1st to 10thNight
53%6%15%20%5%
2045
11th to 20thNight
60%8%14%14%41
2304
21st to endNight
66%7%10%14%3
2574
November1st to 10thNight
60%9%10%16%41
2406
11th to 20thNight
68%10%9%11%3
2625
21st to endNight
69%10%11%8%3
2850
December1st to 10thNight
70%13%8%8%2
2850
11th to 20thNight
65%12%9%10%31
3525
21st to endNight
73%11%6%8%1
5236

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
17%10%30%33%9%1
249
11th to 20thDay
16%12%25%33%12%3
270
21st to endDay
19%9%29%30%12%1
297
February1st to 10thDay
16%7%39%27%10%1
252
11th to 20thDay
13%15%41%22%8%1
240
21st to endDay
16%13%43%24%41
198
March1st to 10thDay
14%11%29%33%12%2
240
11th to 20thDay
19%10%30%30%8%2
295
21st to endDay
16%10%33%26%12%2
462
April1st to 10thDay
18%9%29%33%10%1
420
11th to 20thDay
26%10%23%25%14%2
412
21st to endDay
21%8%29%25%14%3
420
May1st to 10thDay
20%429%29%15%2
573
11th to 20thDay
19%326%34%15%3
625
21st to endDay
24%423%34%14%1
679
June1st to 10thDay
22%321%38%14%3
630
11th to 20thDay
18%5%23%35%17%3
630
21st to endDay
22%416%35%20%3
630
July1st to 10thDay
16%418%38%22%2
621
11th to 20thDay
19%5%17%35%21%3
618
21st to endDay
12%415%39%26%4
684
August1st to 10thDay
17%318%39%21%3
626
11th to 20thDay
17%316%32%27%5%
529
21st to endDay
23%422%28%18%5%
495
September1st to 10thDay
19%8%20%31%17%5%
450
11th to 20thDay
24%7%26%25%15%4
450
21st to endDay
23%8%19%29%17%3
450
October1st to 10thDay
25%9%26%23%15%2
383
11th to 20thDay
23%10%33%24%8%2
270
21st to endDay
33%12%30%21%5%
297
November1st to 10thDay
22%17%29%24%9%
270
11th to 20thDay
29%14%27%21%8%
252
21st to endDay
24%18%31%20%6%1
180
December1st to 10thDay
26%9%27%27%8%2
180
11th to 20thDay
23%18%31%22%6%1
180
21st to endDay
21%14%37%18%9%
198
January1st to 10thNight
19%11%34%28%8%
950
11th to 20thNight
18%13%31%28%9%1
950
21st to endNight
20%8%33%28%9%2
1045
February1st to 10thNight
15%7%34%31%11%2
923
11th to 20thNight
16%11%31%27%12%2
782
21st to endNight
13%7%37%34%8%1
592
March1st to 10thNight
11%8%32%32%15%2
720
11th to 20thNight
20%7%33%29%11%1
720
21st to endNight
18%8%26%31%14%3
628
April1st to 10thNight
21%5%26%34%11%2
540
11th to 20thNight
23%5%23%34%12%3
533
21st to endNight
19%422%36%16%3
540
May1st to 10thNight
22%419%36%16%2
540
11th to 20thNight
19%220%36%20%4
531
21st to endNight
22%415%38%19%2
460
June1st to 10thNight
19%217%39%20%2
360
11th to 20thNight
20%414%39%20%3
360
21st to endNight
20%411%39%23%3
360
July1st to 10thNight
16%312%41%25%2
370
11th to 20thNight
16%413%36%26%4
522
21st to endNight
15%312%34%33%3
591
August1st to 10thNight
13%311%39%31%3
537
11th to 20thNight
14%214%30%33%7%
534
21st to endNight
19%316%34%24%4
594
September1st to 10thNight
17%416%34%22%7%
540
11th to 20thNight
21%5%25%32%15%3
643
21st to endNight
26%6%18%30%17%3
720
October1st to 10thNight
23%9%24%27%15%2
720
11th to 20thNight
27%10%27%23%12%1
720
21st to endNight
30%9%25%25%9%1
792
November1st to 10thNight
25%12%29%26%8%1
740
11th to 20thNight
26%12%29%21%10%2
878
21st to endNight
26%13%32%23%7%
950
December1st to 10thNight
18%14%35%23%9%1
950
11th to 20thNight
22%14%34%22%7%2
950
21st to endNight
28%12%28%24%8%1
1045
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