Markham
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Markham clear sky chart from 2005-11-05 to 2017-12-20.

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
38%
15185
15%
48104
10%
15149
44%
15149
20%
32905

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
19%
718
10%
2482
4%
716
26%
716
10%
1933
January16th to endNight
23%
768
12%
2496
5%
768
31%
768
12%
1909
February1st to 15thNight
20%
702
10%
2287
3%
701
28%
701
12%
1716
February16th to endNight
27%
631
13%
2018
6%
631
36%
631
16%
1458
March1st to 15thNight
25%
720
14%
1980
7%
720
32%
720
17%
1470
March16th to endNight
34%
768
21%
2112
11%
768
42%
768
25%
1425
April1st to 15thNight
33%
718
15%
1814
6%
718
39%
718
23%
1311
April16th to endNight
42%
567
20%
1647
10%
567
50%
567
28%
1075
May1st to 15thNight
49%
483
17%
1563
13%
483
55%
483
24%
1016
May16th to endNight
54%
374
17%
1497
18%
374
61%
374
26%
822
June1st to 15thNight
49%
360
13%
1440
13%
360
56%
360
22%
833
June16th to endNight
57%
360
13%
1440
19%
360
61%
360
25%
836
July1st to 15thNight
69%
340
16%
1360
24%
340
73%
340
36%
676
July16th to endNight
65%
477
17%
1511
17%
447
67%
447
32%
858
August1st to 15thNight
69%
539
18%
1609
15%
536
71%
536
37%
926
August16th to endNight
65%
627
24%
1773
15%
627
69%
627
37%
1036
September1st to 15thNight
56%
720
20%
1803
10%
720
60%
720
36%
1158
September16th to endNight
57%
717
24%
2008
18%
717
60%
717
34%
1231
October1st to 15thNight
43%
720
17%
2160
16%
720
47%
720
23%
1469
October16th to endNight
30%
768
14%
2304
9%
768
38%
768
17%
1684
November1st to 15thNight
37%
760
18%
2585
15%
760
44%
760
19%
1736
November16th to endNight
29%
780
11%
2730
7%
780
35%
780
14%
1987
December1st to 15thNight
17%
780
8%
2730
4%
780
22%
780
10%
2106
December16th to endNight
17%
788
7%
2755
2%
788
23%
788
9%
2234

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%35%5%5%7%32%
48735
Night
15%8%36%5%3445%6%35%
48283
Cloud CoverDay
14%7%36%6%35%5%5%7%33%
48745
Night
15%8%36%5%3445%6%36%
48287
TransparencyDay
48%7%12%20%10%1
48432
Night
47%6%12%21%11%1
48104
SeeingDay
17%423%28%18%7%
5633
Night
19%6%27%30%14%1
15190

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
17%11%5%8%7%35%45%6%23%
1453
16th to endDay
13%13%6%11%7%5%6%5%5%5%18%
1728
February1st to 15thDay
14%14%6%11%7%36%345%21%
1575
16th to endDay
16%12%5%9%6%34435%27%
1455
March1st to 15thDay
15%10%38%7%45%446%28%
1969
16th to endDay
16%8%46%5%3445%5%35%
2112
April1st to 15thDay
21%9%36%42346%6%30%
2134
16th to endDay
18%7%25%434445%39%
2322
May1st to 15thDay
15%6%37%5%345%5%7%35%
2388
16th to endDay
12%5%26%5%35%46%7%40%
2618
June1st to 15thDay
15%6%245%25%5%6%8%35%
2520
16th to endDay
13%425%5%35%5%7%9%36%
2520
July1st to 15thDay
9%325%5%46%5%6%8%41%
2520
16th to endDay
10%427%6%36%5%7%9%36%
2550
August1st to 15thDay
8%5%26%6%45%5%6%9%38%
2340
16th to endDay
10%6%25%6%35%5%5%9%39%
2417
September1st to 15thDay
15%5%25%5%245%5%6%40%
2154
16th to endDay
13%5%36%5%3445%7%41%
1951
October1st to 15thDay
20%5%37%5%35%446%33%
1800
16th to endDay
22%11%36%6%345%5%5%24%
1920
November1st to 15thDay
15%9%49%5%3445%8%30%
1601
16th to endDay
17%12%5%7%6%35%5%48%21%
1560
December1st to 15thDay
18%13%6%10%6%445%5%6%18%
1560
16th to endDay
21%11%6%9%6%35%46%6%17%
1568
January1st to 15thNight
20%13%5%7%7%345%46%22%
2482
16th to endNight
14%11%6%9%7%35%45%6%24%
2496
February1st to 15thNight
14%14%5%8%6%345%5%5%25%
2285
16th to endNight
14%10%47%7%3445%6%29%
2018
March1st to 15thNight
17%8%47%6%35%43432%
1968
16th to endNight
14%8%35%424335%43%
2112
April1st to 15thNight
18%7%35%435%445%35%
1814
16th to endNight
12%6%36%5%2345%7%43%
1647
May1st to 15thNight
15%325%5%35%6%5%8%38%
1563
16th to endNight
12%42332436%7%49%
1495
June1st to 15thNight
13%425%44445%9%41%
1440
16th to endNight
11%425%425%5%6%7%43%
1440
July1st to 15thNight
5%31332445%7%55%
1440
16th to endNight
7%3234345%6%8%48%
1615
August1st to 15thNight
6%42342446%9%50%
1620
16th to endNight
8%41443435%6%52%
1773
September1st to 15thNight
12%32343445%7%48%
1803
16th to endNight
11%5%2442346%6%48%
2008
October1st to 15thNight
18%6%25%5%3345%6%37%
2160
16th to endNight
20%8%45%5%3445%7%29%
2304
November1st to 15thNight
18%6%35%5%3445%6%35%
2585
16th to endNight
20%9%36%6%35%46%6%26%
2730
December1st to 15thNight
18%13%5%7%6%35%45%7%20%
2730
16th to endNight
21%11%5%9%7%46%5%5%6%16%
2755

Percentage Cloud Cover SE (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
17%10%5%8%7%35%446%25%
1453
16th to endDay
13%13%6%11%8%36%5%5%5%18%
1728
February1st to 15thDay
14%13%6%10%7%45%445%22%
1575
16th to endDay
16%11%5%9%6%35%435%27%
1455
March1st to 15thDay
16%8%48%7%5%45%5%5%28%
1980
16th to endDay
15%7%36%6%34446%36%
2111
April1st to 15thDay
20%8%46%42445%6%30%
2134
16th to endDay
17%7%26%43445%5%38%
2322
May1st to 15thDay
14%7%36%6%35%46%7%35%
2388
16th to endDay
11%5%35%5%25%5%6%8%40%
2618
June1st to 15thDay
15%5%245%35%5%7%9%35%
2520
16th to endDay
12%415%5%36%6%6%9%36%
2520
July1st to 15thDay
8%425%6%46%5%6%9%40%
2520
16th to endDay
9%5%25%6%46%6%6%8%37%
2550
August1st to 15thDay
8%5%26%6%45%5%6%10%39%
2340
16th to endDay
10%5%25%5%35%5%6%8%40%
2417
September1st to 15thDay
15%5%25%43445%6%41%
2154
16th to endDay
12%5%36%5%35%45%7%41%
1951
October1st to 15thDay
19%7%25%6%335%46%34%
1800
16th to endDay
22%10%37%5%3445%6%25%
1920
November1st to 15thDay
14%9%38%5%345%5%8%31%
1601
16th to endDay
17%11%48%6%345%5%8%23%
1560
December1st to 15thDay
17%13%6%9%6%345%5%7%19%
1560
16th to endDay
20%11%5%9%7%45%5%6%7%17%
1568
January1st to 15thNight
20%13%48%6%345%46%23%
2482
16th to endNight
14%12%5%9%7%45%5%46%24%
2496
February1st to 15thNight
14%14%5%7%6%3446%5%25%
2278
16th to endNight
14%10%38%7%3445%6%29%
2018
March1st to 15thNight
18%8%47%6%4434432%
1980
16th to endNight
15%7%36%42433443%
2112
April1st to 15thNight
19%6%35%5%45%446%35%
1814
16th to endNight
11%6%345%3445%6%43%
1647
May1st to 15thNight
15%5%25%5%35%5%5%7%38%
1562
16th to endNight
12%32432435%7%49%
1495
June1st to 15thNight
14%424335%45%9%41%
1440
16th to endNight
11%6%145%25%5%6%8%42%
1440
July1st to 15thNight
5%3134235%5%8%55%
1440
16th to endNight
8%314435%47%8%48%
1615
August1st to 15thNight
6%4144345%6%9%50%
1620
16th to endNight
8%31442445%6%53%
1773
September1st to 15thNight
11%42342446%6%48%
1803
16th to endNight
12%41442345%6%49%
2008
October1st to 15thNight
18%6%36%5%2345%7%38%
2160
16th to endNight
20%8%36%5%345%5%6%30%
2304
November1st to 15thNight
17%7%26%5%35%5%5%6%36%
2585
16th to endNight
20%9%35%5%35%5%6%6%27%
2730
December1st to 15thNight
19%13%47%6%345%46%23%
2730
16th to endNight
21%12%5%8%8%45%5%5%6%18%
2755

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%7%13%14%5%
1454
16th to endDay
65%7%10%10%4
1728
February1st to 15thDay
63%5%10%16%2
1577
16th to endDay
56%6%13%15%6%
1455
March1st to 15thDay
56%6%12%16%7%
1980
16th to endDay
48%6%10%18%14%1
2112
April1st to 15thDay
53%5%10%18%11%
2134
16th to endDay
46%5%10%20%14%2
2322
May1st to 15thDay
46%6%9%21%13%
2388
16th to endDay
39%7%13%22%13%2
2622
June1st to 15thDay
42%8%13%22%13%
2520
16th to endDay
40%8%15%22%13%
2520
July1st to 15thDay
36%9%11%24%16%2
2371
16th to endDay
41%9%12%23%11%1
2391
August1st to 15thDay
37%8%15%21%14%1
2327
16th to endDay
37%8%12%28%11%1
2417
September1st to 15thDay
40%8%13%25%11%
2154
16th to endDay
40%6%12%28%10%
1951
October1st to 15thDay
49%5%12%21%9%1
1800
16th to endDay
58%6%15%14%5%
1920
November1st to 15thDay
49%8%14%18%7%1
1601
16th to endDay
57%7%15%14%4
1560
December1st to 15thDay
63%7%15%10%2
1560
16th to endDay
63%8%13%11%2
1568
January1st to 15thNight
62%6%11%13%5%
2482
16th to endNight
59%6%13%15%4
2496
February1st to 15thNight
58%6%12%17%4
2287
16th to endNight
54%414%18%7%
2018
March1st to 15thNight
56%312%20%6%
1980
16th to endNight
45%39%23%16%2
2112
April1st to 15thNight
49%5%9%19%14%
1814
16th to endNight
40%5%10%22%17%3
1647
May1st to 15thNight
41%7%10%23%15%2
1563
16th to endNight
33%6%14%26%15%3
1497
June1st to 15thNight
38%5%12%25%15%1
1440
16th to endNight
37%6%12%24%18%
1440
July1st to 15thNight
25%5%13%28%24%2
1360
16th to endNight
30%7%14%26%17%3
1511
August1st to 15thNight
28%7%18%29%13%1
1609
16th to endNight
30%5%12%33%16%1
1773
September1st to 15thNight
34%6%14%27%15%1
1803
16th to endNight
34%5%12%32%14%
2008
October1st to 15thNight
45%6%11%22%13%
2160
16th to endNight
53%5%13%18%7%
2304
November1st to 15thNight
47%6%12%20%11%1
2585
16th to endNight
54%7%16%15%5%
2730
December1st to 15thNight
60%7%13%13%4
2730
16th to endNight
65%7%12%10%3
2755

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
15%15%42%14%9%1
63
16th to endDay
30%13%30%22%3
96
February1st to 15thDay
21%8%50%18%1
90
16th to endDay
18%12%37%27%4
96
March1st to 15thDay
23%10%34%23%8%
270
16th to endDay
21%432%28%9%2
288
April1st to 15thDay
23%5%31%30%7%1
270
16th to endDay
21%5%27%24%15%4
270
May1st to 15thDay
19%321%29%18%8%
288
16th to endDay
12%324%31%22%6%
331
June1st to 15thDay
20%315%35%21%2
315
16th to endDay
15%220%32%23%5%
315
July1st to 15thDay
10%112%35%30%9%
305
16th to endDay
9%17%35%25%11%
326
August1st to 15thDay
8%14%32%27%15%
313
16th to endDay
13%212%23%31%15%
332
September1st to 15thDay
11%115%27%27%16%
315
16th to endDay
14%315%27%20%18%
314
October1st to 15thDay
23%224%26%16%6%
315
16th to endDay
25%7%32%23%10%
336
November1st to 15thDay
18%11%19%33%15%2
133
16th to endDay
16%14%38%22%7%
90
December1st to 15thDay
16%16%34%24%6%1
90
16th to endDay
23%13%48%13%
72
January1st to 15thNight
28%12%33%20%5%
720
16th to endNight
19%8%35%29%7%
768
February1st to 15thNight
21%11%36%25%5%
704
16th to endNight
20%8%33%29%7%
631
March1st to 15thNight
23%9%33%27%6%
720
16th to endNight
19%6%31%29%11%1
768
April1st to 15thNight
21%7%30%32%7%
718
16th to endNight
14%6%29%35%12%1
567
May1st to 15thNight
18%222%33%20%2
483
16th to endNight
11%124%38%22%1
375
June1st to 15thNight
16%122%37%20%1
360
16th to endNight
12%119%41%22%1
360
July1st to 15thNight
6%15%45%27%3
340
16th to endNight
8%115%44%26%3
477
August1st to 15thNight
8%11%41%33%4
539
16th to endNight
9%214%37%31%4
627
September1st to 15thNight
14%219%30%27%6%
720
16th to endNight
14%216%30%28%7%
717
October1st to 15thNight
21%5%23%28%18%2
720
16th to endNight
25%6%29%31%7%
768
November1st to 15thNight
21%7%27%29%13%1
760
16th to endNight
24%9%28%27%9%1
780
December1st to 15thNight
28%9%35%21%4
780
16th to endNight
27%8%37%23%3
788
Page generated at 2017-12-21 07:04:57. Version ac04

Copyright 2017 A. Danko


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