This page made possible by the sponsorship of: RASC Halifax Centre.

Halifax
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Halifax 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
22%
15336
12%
46814
5%
15291
29%
15291
14%
34631

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
13%
750
11%
2506
2%
746
23%
746
9%
1898
January16th to endNight
12%
773
11%
2526
2%
773
23%
773
9%
1920
February1st to 15thNight
13%
704
7%
2286
2%
701
20%
701
10%
1773
February16th to endNight
15%
631
9%
2022
2%
631
23%
631
8%
1571
March1st to 15thNight
17%
720
13%
1995
3%
720
26%
720
13%
1505
March16th to endNight
20%
764
13%
2108
4%
764
29%
764
14%
1567
April1st to 15thNight
16%
539
13%
1796
5%
539
26%
539
12%
1332
April16th to endNight
19%
540
14%
1653
6%
540
26%
540
15%
1198
May1st to 15thNight
22%
540
10%
1515
4%
540
27%
540
14%
1172
May16th to endNight
23%
561
10%
1496
3%
560
28%
560
17%
1119
June1st to 15thNight
21%
540
6%
1440
2%
540
24%
540
13%
1155
June16th to endNight
25%
540
6%
1440
2%
540
28%
540
17%
1127
July1st to 15thNight
35%
510
7%
1360
4%
510
38%
510
22%
986
July16th to endNight
36%
565
9%
1457
7%
532
37%
532
16%
1134
August1st to 15thNight
41%
539
12%
1608
9%
535
42%
535
20%
1151
August16th to endNight
40%
573
16%
1797
11%
573
45%
573
22%
1201
September1st to 15thNight
32%
525
16%
1749
10%
525
41%
525
21%
1139
September16th to endNight
34%
629
22%
1831
14%
629
41%
629
25%
1183
October1st to 15thNight
28%
660
19%
1980
8%
660
38%
660
21%
1325
October16th to endNight
18%
704
14%
2112
4%
704
27%
704
16%
1514
November1st to 15thNight
26%
729
13%
2409
7%
729
32%
729
15%
1741
November16th to endNight
21%
750
12%
2520
5%
750
29%
750
12%
1843
December1st to 15thNight
10%
750
10%
2520
1%
750
20%
750
9%
1948
December16th to endNight
10%
800
9%
2688
2%
800
18%
800
7%
2129

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%9%36%5%34446%28%
47821
Night
21%9%36%5%3445%6%29%
46990
TransparencyDay
55%6%11%17%8%
47515
Night
54%6%11%18%7%
46814
SeeingDay
28%16%30%17%6%1
7510
Night
27%14%30%20%6%
15336

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
16%11%5%8%6%36%6%6%7%21%
1432
16th to endDay
18%9%48%6%45%6%6%7%22%
1696
February1st to 15thDay
17%12%49%6%45%6%46%20%
1575
16th to endDay
12%13%6%10%7%35%45%5%25%
1450
March1st to 15thDay
20%10%48%6%35%34427%
1951
16th to endDay
18%11%47%6%34337%29%
2115
April1st to 15thDay
23%12%47%5%24346%26%
2153
16th to endDay
24%10%34423346%31%
2306
May1st to 15thDay
27%10%37%5%2345%5%24%
2437
16th to endDay
26%9%36%5%24346%28%
2618
June1st to 15thDay
30%9%46%5%34336%23%
2520
16th to endDay
26%9%35%5%33447%27%
2520
July1st to 15thDay
21%7%35%3245%5%7%33%
2520
16th to endDay
25%8%35%5%3445%8%24%
2611
August1st to 15thDay
20%7%35%6%245%5%7%30%
2340
16th to endDay
17%5%2442345%8%40%
2405
September1st to 15thDay
21%6%34434436%37%
2099
16th to endDay
17%5%24333446%44%
1799
October1st to 15thDay
22%5%245%14447%37%
1650
16th to endDay
23%7%36%6%3345%6%28%
1760
November1st to 15thDay
24%10%36%433247%27%
1448
16th to endDay
22%9%5%6%5%45%447%24%
1440
December1st to 15thDay
26%9%47%5%35%45%7%19%
1440
16th to endDay
24%13%46%8%34446%19%
1536
January1st to 15thNight
17%9%47%6%36%6%5%7%25%
2506
16th to endNight
18%11%48%5%35%45%8%24%
2526
February1st to 15thNight
19%10%5%7%6%36%5%6%6%21%
2285
16th to endNight
15%12%5%8%7%45%5%6%6%22%
2022
March1st to 15thNight
20%10%46%5%24446%28%
1983
16th to endNight
19%9%47%5%3345%5%31%
2108
April1st to 15thNight
25%9%45%43435%5%28%
1796
16th to endNight
24%8%35%43435%5%31%
1653
May1st to 15thNight
29%9%35%335%447%25%
1515
16th to endNight
22%7%36%434447%30%
1494
June1st to 15thNight
30%11%35%423337%23%
1440
16th to endNight
26%9%35%433447%26%
1440
July1st to 15thNight
19%10%344245%6%7%31%
1440
16th to endNight
24%8%36%5%235%6%7%27%
1556
August1st to 15thNight
19%8%25%4245%5%5%35%
1620
16th to endNight
17%6%25%5%2346%6%39%
1797
September1st to 15thNight
17%7%24424446%39%
1749
16th to endNight
19%5%24322347%43%
1831
October1st to 15thNight
20%6%24423348%38%
1980
16th to endNight
24%7%25%5%2445%5%34%
2112
November1st to 15thNight
24%8%25%424446%31%
2409
16th to endNight
24%6%25%5%3445%6%30%
2520
December1st to 15thNight
25%10%36%6%345%46%23%
2520
16th to endNight
24%11%47%6%35%5%45%21%
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
59%9%13%13%4
1433
16th to endDay
57%8%9%16%7%
1696
February1st to 15thDay
62%7%9%12%6%
1578
16th to endDay
61%5%9%14%6%1
1450
March1st to 15thDay
60%48%16%9%1
1962
16th to endDay
55%5%8%19%9%1
2115
April1st to 15thDay
59%5%7%15%11%1
2153
16th to endDay
54%48%18%11%1
2306
May1st to 15thDay
60%5%10%16%6%
2437
16th to endDay
57%7%12%15%6%1
2622
June1st to 15thDay
64%5%9%12%6%
2520
16th to endDay
57%7%10%16%7%
2520
July1st to 15thDay
47%8%15%18%8%
2372
16th to endDay
56%9%11%17%4
2447
August1st to 15thDay
50%8%14%18%7%
2327
16th to endDay
40%7%16%25%9%
2405
September1st to 15thDay
46%5%12%21%11%1
2099
16th to endDay
41%5%8%28%15%
1799
October1st to 15thDay
46%411%23%12%
1650
16th to endDay
55%6%11%19%6%
1760
November1st to 15thDay
57%5%12%15%7%1
1448
16th to endDay
60%7%12%12%7%
1440
December1st to 15thDay
63%7%9%16%3
1440
16th to endDay
65%7%7%13%6%
1536
January1st to 15thNight
56%8%13%16%4
2506
16th to endNight
57%8%11%18%4
2526
February1st to 15thNight
60%6%13%13%5%
2286
16th to endNight
60%7%12%14%5%
2022
March1st to 15thNight
55%6%11%17%8%
1995
16th to endNight
54%5%9%19%10%
2108
April1st to 15thNight
56%6%8%15%10%2
1796
16th to endNight
54%49%17%11%1
1653
May1st to 15thNight
58%6%9%18%6%
1515
16th to endNight
54%5%13%18%6%1
1496
June1st to 15thNight
62%6%9%15%6%
1440
16th to endNight
58%6%10%15%8%
1440
July1st to 15thNight
47%8%17%18%8%
1360
16th to endNight
54%10%11%16%6%
1457
August1st to 15thNight
49%7%12%22%7%
1608
16th to endNight
43%8%12%23%11%
1797
September1st to 15thNight
44%5%10%25%11%1
1749
16th to endNight
40%5%10%28%13%
1831
October1st to 15thNight
44%5%12%25%11%
1980
16th to endNight
50%6%11%21%9%
2112
November1st to 15thNight
52%7%13%17%8%
2409
16th to endNight
53%7%13%16%7%
2520
December1st to 15thNight
60%7%11%17%3
2520
16th to endNight
63%7%9%15%4
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
21%23%36%17%
240
16th to endDay
26%21%38%10%3
256
February1st to 15thDay
27%21%32%17%1
236
16th to endDay
21%22%35%15%5%
212
March1st to 15thDay
25%29%29%12%4
268
16th to endDay
29%26%27%11%41
288
April1st to 15thDay
31%25%29%9%4
270
16th to endDay
23%22%35%12%4
270
May1st to 15thDay
35%13%28%14%5%2
393
16th to endDay
30%14%31%18%4
519
June1st to 15thDay
35%12%29%16%5%
495
16th to endDay
30%15%28%17%6%1
495
July1st to 15thDay
24%8%31%24%11%1
475
16th to endDay
30%8%26%22%9%1
472
August1st to 15thDay
25%7%30%24%9%2
313
16th to endDay
22%9%29%22%13%2
332
September1st to 15thDay
23%11%35%20%8%2
294
16th to endDay
19%13%28%24%9%4
246
October1st to 15thDay
25%10%35%15%11%2
225
16th to endDay
27%23%27%13%5%1
240
November1st to 15thDay
26%16%27%18%8%2
235
16th to endDay
31%20%23%17%5%
240
December1st to 15thDay
31%22%30%12%2
240
16th to endDay
32%22%33%9%2
256
January1st to 15thNight
25%20%35%16%1
750
16th to endNight
26%22%34%14%2
773
February1st to 15thNight
27%19%34%17%1
704
16th to endNight
23%23%32%16%4
631
March1st to 15thNight
25%20%31%18%4
720
16th to endNight
25%21%27%18%5%
764
April1st to 15thNight
30%16%30%17%4
539
16th to endNight
27%15%34%18%3
540
May1st to 15thNight
33%10%29%17%8%
540
16th to endNight
26%11%34%22%5%
561
June1st to 15thNight
34%10%29%21%4
540
16th to endNight
27%7%31%25%7%
540
July1st to 15thNight
22%430%32%9%
510
16th to endNight
26%6%26%29%12%
565
August1st to 15thNight
24%324%30%15%
539
16th to endNight
21%428%32%12%1
573
September1st to 15thNight
21%8%32%26%11%
525
16th to endNight
22%10%28%25%11%1
629
October1st to 15thNight
23%13%31%21%8%1
660
16th to endNight
27%17%33%16%4
704
November1st to 15thNight
29%12%28%21%5%1
729
16th to endNight
28%18%28%18%6%
750
December1st to 15thNight
34%18%31%12%3
750
16th to endNight
31%21%31%13%1
800
Page generated at 2017-09-11 20:35:19. Version ac04

Copyright 2017 A. Danko


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