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 2018-03-11.

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%
16135
12%
49157
5%
16090
29%
16090
14%
36334

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%
825
10%
2716
2%
821
22%
821
9%
2061
January16th to endNight
13%
839
11%
2736
2%
839
23%
839
9%
2077
February1st to 15thNight
13%
764
7%
2481
2%
761
21%
761
10%
1924
February16th to endNight
14%
683
9%
2189
2%
683
23%
683
9%
1692
March1st to 15thNight
16%
764
13%
2116
3%
764
25%
764
13%
1617
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
33%
540
17%
1800
11%
540
41%
540
21%
1157
September16th to endNight
34%
687
21%
1998
13%
687
40%
687
24%
1315
October1st to 15thNight
30%
720
18%
2160
8%
720
39%
720
22%
1425
October16th to endNight
20%
768
16%
2304
5%
768
29%
768
17%
1624
November1st to 15thNight
25%
804
13%
2615
7%
804
31%
804
15%
1891
November16th to endNight
20%
825
13%
2730
5%
825
29%
825
12%
1991
December1st to 15thNight
10%
825
10%
2730
1%
825
19%
825
9%
2130
December16th to endNight
9%
880
10%
2912
2%
880
19%
880
7%
2288

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%
49477
Night
21%9%36%5%3445%6%29%
49333
TransparencyDay
55%6%11%17%8%
49171
Night
54%6%11%18%7%
49157
SeeingDay
27%17%30%16%6%1
8080
Night
26%15%30%20%6%
16135

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%
1552
16th to endDay
18%10%48%6%346%6%7%22%
1838
February1st to 15thDay
19%12%49%6%45%6%46%20%
1710
16th to endDay
13%13%6%9%7%34445%26%
1569
March1st to 15thDay
20%11%48%6%35%44426%
2066
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
20%6%24434437%38%
2160
16th to endDay
18%5%24432446%42%
1962
October1st to 15thDay
20%5%25%5%14447%38%
1800
16th to endDay
21%7%36%5%3345%6%31%
1920
November1st to 15thDay
23%9%36%434247%27%
1571
16th to endDay
21%8%5%6%5%45%45%7%25%
1560
December1st to 15thDay
26%10%47%5%35%45%7%19%
1560
16th to endDay
23%12%36%7%34447%21%
1664
January1st to 15thNight
17%9%47%7%36%5%47%25%
2716
16th to endNight
19%10%47%6%35%45%7%24%
2736
February1st to 15thNight
19%10%47%6%36%5%6%6%22%
2480
16th to endNight
16%11%5%7%7%45%5%6%6%23%
2189
March1st to 15thNight
21%10%47%5%24446%27%
2104
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%2442445%6%40%
1800
16th to endNight
19%6%24423347%41%
1998
October1st to 15thNight
19%5%24423348%40%
2160
16th to endNight
23%6%25%5%2445%5%35%
2304
November1st to 15thNight
23%8%35%424446%31%
2615
16th to endNight
23%6%25%5%3446%6%31%
2730
December1st to 15thNight
25%10%36%6%345%46%22%
2730
16th to endNight
23%10%47%6%35%5%46%22%
2912

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
58%10%13%13%4
1553
16th to endDay
57%8%9%15%7%
1838
February1st to 15thDay
62%7%9%12%6%
1713
16th to endDay
60%5%9%15%7%1
1569
March1st to 15thDay
61%48%15%8%1
2077
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
45%6%12%21%12%1
2160
16th to endDay
42%5%9%26%15%
1962
October1st to 15thDay
45%411%25%12%
1800
16th to endDay
52%6%11%22%6%
1920
November1st to 15thDay
57%6%12%15%7%1
1571
16th to endDay
58%7%13%14%6%
1560
December1st to 15thDay
64%7%9%15%3
1560
16th to endDay
63%6%8%13%8%
1664
January1st to 15thNight
56%8%13%16%5%
2716
16th to endNight
57%7%11%18%4
2736
February1st to 15thNight
60%6%13%13%5%
2481
16th to endNight
59%7%11%14%6%
2189
March1st to 15thNight
56%6%11%16%7%
2116
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
43%5%10%26%12%1
1800
16th to endNight
42%5%10%27%13%
1998
October1st to 15thNight
43%5%12%26%11%
2160
16th to endNight
48%6%11%22%10%
2304
November1st to 15thNight
52%7%13%17%8%
2615
16th to endNight
53%8%14%16%7%
2730
December1st to 15thNight
60%7%11%16%3
2730
16th to endNight
62%7%8%15%5%
2912

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
22%25%36%15%
285
16th to endDay
27%22%38%9%2
304
February1st to 15thDay
31%20%30%16%1
281
16th to endDay
22%23%35%13%4
251
March1st to 15thDay
27%27%29%11%3
308
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
21%11%35%20%8%2
315
16th to endDay
22%11%26%24%10%3
302
October1st to 15thDay
22%10%35%17%10%2
270
16th to endDay
23%25%28%13%6%1
288
November1st to 15thDay
24%17%28%18%8%1
280
16th to endDay
28%23%25%15%5%
285
December1st to 15thDay
32%23%29%12%1
285
16th to endDay
30%26%30%9%1
304
January1st to 15thNight
25%21%36%15%1
825
16th to endNight
26%22%34%14%2
839
February1st to 15thNight
28%19%34%16%1
764
16th to endNight
23%23%32%15%4
683
March1st to 15thNight
26%20%31%17%4
764
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
20%9%32%26%10%
540
16th to endNight
22%10%27%25%11%1
687
October1st to 15thNight
22%13%31%23%8%1
720
16th to endNight
27%16%32%17%5%
768
November1st to 15thNight
28%13%29%21%5%1
804
16th to endNight
27%19%29%18%5%
825
December1st to 15thNight
34%18%30%12%3
825
16th to endNight
30%23%31%12%1
880
Page generated at 2018-03-12 14:28:09. Version ac04

Copyright 2018 A. Danko


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