Charlottetown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charlottetown clear sky chart from 2005-11-05 to 2017-04-26.

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%
14595
10%
45350
4%
14550
28%
14550
11%
34414

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
9%
2506
1%
746
23%
746
8%
1914
January16th to endNight
16%
783
13%
2586
4%
783
27%
783
10%
1931
February1st to 15thNight
14%
704
9%
2286
3%
701
22%
701
9%
1720
February16th to endNight
18%
631
8%
2023
2%
631
25%
631
9%
1588
March1st to 15thNight
20%
720
12%
2025
4%
720
28%
720
11%
1577
March16th to endNight
19%
747
13%
2091
6%
747
25%
747
13%
1611
April1st to 15thNight
19%
539
11%
1796
6%
539
24%
539
10%
1360
April16th to endNight
23%
528
15%
1609
7%
528
31%
528
16%
1135
May1st to 15thNight
24%
495
12%
1342
6%
495
30%
495
14%
1022
May16th to endNight
20%
513
10%
1368
2%
512
26%
512
14%
1050
June1st to 15thNight
23%
457
5%
1282
3%
457
24%
457
13%
1015
June16th to endNight
28%
330
6%
1155
4%
330
32%
330
11%
835
July1st to 15thNight
37%
353
9%
1128
6%
353
40%
353
20%
742
July16th to endNight
30%
523
7%
1307
4%
490
35%
490
16%
999
August1st to 15thNight
40%
494
10%
1449
6%
490
43%
490
17%
1057
August16th to endNight
44%
525
11%
1644
7%
525
49%
525
19%
1119
September1st to 15thNight
34%
495
15%
1650
11%
495
41%
495
19%
1082
September16th to endNight
32%
607
19%
1822
11%
607
39%
607
20%
1200
October1st to 15thNight
28%
660
15%
1980
7%
660
34%
660
16%
1408
October16th to endNight
16%
711
11%
2148
3%
711
23%
711
10%
1669
November1st to 15thNight
20%
730
9%
2425
5%
730
26%
730
10%
1902
November16th to endNight
14%
750
7%
2520
3%
750
20%
750
6%
2042
December1st to 15thNight
9%
750
6%
2520
0%
750
16%
750
5%
2111
December16th to endNight
6%
800
4%
2688
0%
800
10%
800
4%
2325

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
19%10%47%5%3445%6%28%
46321
Night
19%10%47%6%34446%27%
45516
TransparencyDay
55%7%12%17%7%
46005
Night
57%6%11%16%6%
45350
SeeingDay
22%21%25%19%8%1
6989
Night
22%24%25%20%6%
14595

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
15%16%5%7%6%35%446%25%
1432
16th to endDay
15%9%5%10%7%45%5%5%6%24%
1638
February1st to 15thDay
14%12%48%6%36%5%4427%
1575
16th to endDay
15%13%48%5%45%5%6%7%23%
1449
March1st to 15thDay
14%11%6%8%7%35%5%5%6%25%
1924
16th to endDay
15%12%5%10%7%3333428%
2133
April1st to 15thDay
18%12%46%5%3435%7%28%
2153
16th to endDay
22%11%35%423336%32%
2261
May1st to 15thDay
22%10%45%5%34446%29%
2278
16th to endDay
22%9%35%5%2435%6%29%
2394
June1st to 15thDay
27%8%36%5%2445%5%24%
2357
16th to endDay
23%8%25%5%2445%7%29%
2475
July1st to 15thDay
14%6%35%5%245%5%8%37%
2415
16th to endDay
18%9%36%5%245%6%9%28%
2457
August1st to 15thDay
17%7%26%5%25%46%8%31%
2168
16th to endDay
14%6%25%4345%6%8%38%
2206
September1st to 15thDay
19%8%35%434447%34%
1980
16th to endDay
15%8%25%5%33446%39%
1804
October1st to 15thDay
20%8%36%5%35%45%6%29%
1650
16th to endDay
22%12%5%8%7%35%5%45%19%
1724
November1st to 15thDay
22%14%37%5%44446%22%
1432
16th to endDay
15%14%7%8%7%46%45%6%17%
1440
December1st to 15thDay
22%14%7%7%7%36%45%7%12%
1440
16th to endDay
23%15%6%8%6%45%445%14%
1536
January1st to 15thNight
18%13%46%5%35%5%5%6%26%
2506
16th to endNight
16%10%5%8%5%3445%6%27%
2586
February1st to 15thNight
17%13%37%6%345%45%27%
2285
16th to endNight
14%14%5%9%6%46%5%5%6%21%
2023
March1st to 15thNight
17%12%5%8%7%44345%25%
2013
16th to endNight
18%12%5%8%5%2423429%
2091
April1st to 15thNight
21%11%46%6%45%445%25%
1796
16th to endNight
23%10%44423245%34%
1609
May1st to 15thNight
23%6%35%4445%5%6%29%
1342
16th to endNight
19%11%45%6%35%338%28%
1366
June1st to 15thNight
26%10%45%5%34346%25%
1282
16th to endNight
21%7%36%5%445%6%7%28%
1155
July1st to 15thNight
13%6%25%5%25%5%6%9%35%
1202
16th to endNight
17%7%37%6%45%6%7%8%27%
1403
August1st to 15thNight
17%7%25%7%35%5%49%30%
1460
16th to endNight
15%6%25%5%2445%8%37%
1644
September1st to 15thNight
17%6%25%425%337%40%
1650
16th to endNight
15%6%15%43345%7%42%
1822
October1st to 15thNight
19%7%35%5%3445%7%33%
1980
16th to endNight
25%10%47%6%23345%25%
2148
November1st to 15thNight
22%12%47%6%35%436%24%
2425
16th to endNight
22%13%47%5%24446%21%
2520
December1st to 15thNight
22%12%48%8%35%447%17%
2520
16th to endNight
24%15%6%9%7%34345%14%
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
60%8%12%10%7%
1433
16th to endDay
59%8%10%13%8%
1638
February1st to 15thDay
59%5%11%18%5%
1578
16th to endDay
59%6%12%12%7%1
1449
March1st to 15thDay
58%5%10%16%7%
1935
16th to endDay
59%411%15%7%
2133
April1st to 15thDay
55%410%15%11%1
2153
16th to endDay
53%5%10%17%11%
2261
May1st to 15thDay
55%6%9%19%8%
2278
16th to endDay
55%8%11%19%6%
2398
June1st to 15thDay
59%7%11%15%5%
2357
16th to endDay
52%8%12%20%6%
2475
July1st to 15thDay
41%9%15%24%8%
2261
16th to endDay
52%8%15%18%5%
2290
August1st to 15thDay
49%9%13%21%6%
2154
16th to endDay
41%9%17%25%6%
2206
September1st to 15thDay
47%8%13%21%8%
1980
16th to endDay
44%6%11%25%10%
1804
October1st to 15thDay
54%6%11%19%8%
1650
16th to endDay
66%5%10%11%4
1724
November1st to 15thDay
63%6%12%12%4
1432
16th to endDay
67%7%14%8%2
1440
December1st to 15thDay
73%7%9%7%1
1440
16th to endDay
75%5%6%8%3
1536
January1st to 15thNight
58%7%13%12%6%
2506
16th to endNight
56%6%10%18%5%
2586
February1st to 15thNight
58%5%11%14%9%
2286
16th to endNight
62%6%10%14%5%1
2023
March1st to 15thNight
60%5%9%15%7%1
2025
16th to endNight
59%47%17%8%1
2091
April1st to 15thNight
60%48%14%9%1
1796
16th to endNight
51%49%17%14%1
1609
May1st to 15thNight
54%6%8%21%7%1
1342
16th to endNight
56%6%10%19%6%
1368
June1st to 15thNight
60%6%11%13%7%
1282
16th to endNight
53%8%12%17%7%
1155
July1st to 15thNight
41%8%18%23%7%
1128
16th to endNight
51%10%16%15%5%
1307
August1st to 15thNight
49%9%14%21%6%
1449
16th to endNight
42%11%17%23%5%
1644
September1st to 15thNight
44%6%11%26%10%
1650
16th to endNight
42%7%12%28%9%
1822
October1st to 15thNight
50%6%12%23%7%
1980
16th to endNight
61%5%10%16%6%
2148
November1st to 15thNight
60%7%13%12%4
2425
16th to endNight
64%7%13%10%3
2520
December1st to 15thNight
66%9%10%11%1
2520
16th to endNight
74%5%8%8%2
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
22%30%32%10%5%
240
16th to endDay
16%25%33%20%3
256
February1st to 15thDay
20%26%29%17%5%
236
16th to endDay
24%22%24%21%6%1
212
March1st to 15thDay
17%27%25%23%6%
263
16th to endDay
22%27%27%14%6%1
288
April1st to 15thDay
25%24%31%12%5%
270
16th to endDay
19%23%24%20%9%2
254
May1st to 15thDay
26%24%21%15%8%3
369
16th to endDay
24%23%25%19%6%
439
June1st to 15thDay
31%19%22%16%9%
420
16th to endDay
25%18%20%21%10%2
420
July1st to 15thDay
18%12%25%28%13%1
400
16th to endDay
22%16%23%21%12%2
444
August1st to 15thDay
21%9%22%27%16%4
276
16th to endDay
18%10%21%28%15%5%
268
September1st to 15thDay
20%12%29%24%12%1
255
16th to endDay
17%16%27%23%11%1
243
October1st to 15thDay
20%21%24%14%13%5%
225
16th to endDay
25%26%30%10%6%1
240
November1st to 15thDay
25%26%22%14%7%3
235
16th to endDay
23%29%23%17%31
240
December1st to 15thDay
29%28%25%13%2
240
16th to endDay
28%27%31%10%1
256
January1st to 15thNight
21%30%27%16%3
750
16th to endNight
19%27%30%16%4
783
February1st to 15thNight
22%27%28%17%3
704
16th to endNight
21%29%24%18%7%
631
March1st to 15thNight
19%28%24%22%4
720
16th to endNight
23%27%23%18%6%
747
April1st to 15thNight
25%26%24%18%5%
539
16th to endNight
23%23%25%20%6%
528
May1st to 15thNight
24%22%24%17%8%2
495
16th to endNight
21%26%26%18%5%
513
June1st to 15thNight
25%22%24%21%5%
457
16th to endNight
21%21%22%24%9%
330
July1st to 15thNight
17%13%27%31%10%
353
16th to endNight
17%21%24%25%10%
523
August1st to 15thNight
19%12%22%28%15%1
494
16th to endNight
16%12%20%37%13%
525
September1st to 15thNight
20%14%25%30%8%1
495
16th to endNight
18%16%29%26%8%
607
October1st to 15thNight
22%18%26%22%10%
660
16th to endNight
29%23%24%17%3
711
November1st to 15thNight
23%24%26%18%42
730
16th to endNight
28%30%21%14%41
750
December1st to 15thNight
25%32%25%11%4
750
16th to endNight
29%29%25%11%31
800
Page generated at 2017-04-27 18:48:54. Version ac04

Copyright 2017 A. Danko


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