Scarborough
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Scarborough clear sky chart from 2005-11-05 to 2017-08-12.

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
40%
14683
14%
46536
10%
14647
45%
14647
19%
32429

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
18%
718
8%
2485
3%
716
24%
716
9%
1974
January16th to endNight
22%
768
11%
2496
5%
768
29%
768
11%
1971
February1st to 15thNight
19%
702
9%
2287
4%
701
27%
701
11%
1785
February16th to endNight
26%
631
12%
2017
6%
631
35%
631
14%
1476
March1st to 15thNight
26%
720
14%
1980
7%
720
33%
720
17%
1485
March16th to endNight
37%
768
20%
2112
12%
768
44%
768
25%
1436
April1st to 15thNight
37%
718
15%
1811
7%
718
42%
718
25%
1308
April16th to endNight
48%
573
20%
1653
11%
573
54%
573
28%
1078
May1st to 15thNight
53%
480
17%
1560
14%
480
58%
480
24%
1012
May16th to endNight
59%
374
17%
1497
19%
374
65%
374
26%
830
June1st to 15thNight
55%
360
12%
1440
14%
360
61%
360
21%
852
June16th to endNight
62%
360
13%
1440
21%
360
64%
360
24%
846
July1st to 15thNight
73%
340
16%
1360
26%
340
74%
340
34%
686
July16th to endNight
68%
475
16%
1509
18%
445
69%
445
31%
864
August1st to 15thNight
71%
527
18%
1575
16%
524
72%
524
34%
932
August16th to endNight
67%
580
22%
1630
16%
580
70%
580
36%
982
September1st to 15thNight
57%
660
21%
1650
10%
660
61%
660
33%
1096
September16th to endNight
59%
657
21%
1840
15%
657
62%
657
32%
1163
October1st to 15thNight
44%
660
17%
1980
17%
660
48%
660
22%
1372
October16th to endNight
29%
704
12%
2112
7%
704
35%
704
16%
1583
November1st to 15thNight
39%
700
18%
2374
16%
700
46%
700
19%
1607
November16th to endNight
30%
720
10%
2520
8%
720
35%
720
13%
1880
December1st to 15thNight
18%
720
7%
2520
3%
720
22%
720
9%
1986
December16th to endNight
16%
768
6%
2688
2%
768
22%
768
7%
2225

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
14%7%36%6%35%5%5%7%33%
47430
Night
15%7%36%5%3445%6%35%
46715
Cloud CoverDay
14%7%36%5%35%5%6%7%34%
47440
Night
15%7%36%5%3445%6%35%
46719
TransparencyDay
47%8%13%19%10%1
47127
Night
48%7%12%20%10%1
46536
SeeingDay
17%320%30%21%6%
5214
Night
19%5%26%30%15%2
14688

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%10%5%8%6%45%5%5%5%25%
1450
16th to endDay
13%13%6%12%7%5%5%5%5%6%18%
1728
February1st to 15thDay
14%13%6%9%8%5%5%345%22%
1575
16th to endDay
16%10%5%8%6%345%36%28%
1453
March1st to 15thDay
15%8%37%8%445%47%28%
1969
16th to endDay
15%7%36%5%34446%37%
2112
April1st to 15thDay
20%8%36%5%2445%6%31%
2137
16th to endDay
16%7%25%5%34446%38%
2316
May1st to 15thDay
13%6%37%6%35%45%8%35%
2391
16th to endDay
11%426%5%25%5%6%8%42%
2618
June1st to 15thDay
14%6%245%345%6%9%36%
2520
16th to endDay
11%4145%36%6%8%10%37%
2520
July1st to 15thDay
7%4146%36%5%7%8%43%
2520
16th to endDay
9%425%436%6%6%10%38%
2553
August1st to 15thDay
7%425%6%45%5%7%9%41%
2288
16th to endDay
9%5%15%5%35%5%6%8%42%
2209
September1st to 15thDay
15%5%25%4345%5%7%40%
1980
16th to endDay
12%5%35%6%25%448%41%
1786
October1st to 15thDay
18%6%25%5%35%46%6%35%
1650
16th to endDay
23%9%37%6%3445%6%25%
1760
November1st to 15thDay
13%7%37%6%35%46%8%33%
1479
16th to endDay
18%9%48%6%35%5%6%7%24%
1440
December1st to 15thDay
18%13%5%8%7%35%5%5%7%18%
1440
16th to endDay
20%12%5%7%7%45%46%7%17%
1536
January1st to 15thNight
21%13%48%5%2445%6%22%
2485
16th to endNight
14%11%6%8%7%36%45%6%24%
2496
February1st to 15thNight
15%14%47%6%35%45%6%25%
2285
16th to endNight
15%9%37%8%35%446%30%
2017
March1st to 15thNight
17%9%47%6%44345%32%
1968
16th to endNight
15%7%46%5%2343443%
2112
April1st to 15thNight
19%6%35%6%35%346%36%
1811
16th to endNight
12%6%25%5%3445%6%43%
1653
May1st to 15thNight
15%425%5%35%6%5%7%39%
1560
16th to endNight
12%32333436%7%49%
1495
June1st to 15thNight
13%5%235%35%5%5%8%41%
1440
16th to endNight
12%415%5%3446%8%43%
1440
July1st to 15thNight
5%31442435%9%55%
1440
16th to endNight
8%3144246%5%9%48%
1613
August1st to 15thNight
6%32442447%8%49%
1586
16th to endNight
8%42442446%5%52%
1630
September1st to 15thNight
12%424335%45%6%47%
1650
16th to endNight
13%42441445%7%47%
1840
October1st to 15thNight
18%6%26%5%3445%6%38%
1980
16th to endNight
21%8%46%5%3445%6%29%
2112
November1st to 15thNight
16%6%26%5%35%45%6%37%
2374
16th to endNight
21%8%46%435%46%7%27%
2520
December1st to 15thNight
21%11%5%7%5%3445%6%23%
2520
16th to endNight
21%12%5%8%7%45%5%46%17%
2688

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
18%11%47%7%46%5%46%22%
1450
16th to endDay
13%14%6%11%7%46%5%5%6%18%
1728
February1st to 15thDay
14%14%5%10%7%45%45%7%20%
1575
16th to endDay
17%11%48%6%3445%8%26%
1453
March1st to 15thDay
16%8%38%7%45%5%5%7%27%
1980
16th to endDay
15%7%35%5%44447%37%
2111
April1st to 15thDay
20%8%36%4335%5%6%31%
2137
16th to endDay
17%6%25%5%3435%6%39%
2316
May1st to 15thDay
13%6%35%5%445%6%8%36%
2391
16th to endDay
11%435%5%3446%7%43%
2618
June1st to 15thDay
13%5%25%5%345%6%8%37%
2520
16th to endDay
11%324436%6%7%10%40%
2520
July1st to 15thDay
7%3235%36%6%7%9%44%
2520
16th to endDay
9%424435%6%7%9%41%
2553
August1st to 15thDay
7%425%6%35%5%7%9%42%
2288
16th to endDay
9%4245%246%6%8%45%
2209
September1st to 15thDay
14%5%234346%5%7%41%
1980
16th to endDay
12%5%245%345%48%42%
1786
October1st to 15thDay
18%6%26%5%35%5%46%36%
1650
16th to endDay
22%10%37%6%335%5%6%26%
1760
November1st to 15thDay
13%7%27%5%45%46%8%33%
1479
16th to endDay
18%9%39%7%35%5%5%7%23%
1440
December1st to 15thDay
18%13%5%9%6%36%45%8%17%
1440
16th to endDay
21%11%6%8%6%35%5%6%7%17%
1536
January1st to 15thNight
21%13%48%6%35%446%21%
2485
16th to endNight
14%12%6%8%7%35%5%5%6%23%
2496
February1st to 15thNight
15%14%5%8%6%35%5%46%24%
2278
16th to endNight
16%9%48%7%44446%29%
2017
March1st to 15thNight
19%8%5%6%6%34345%31%
1980
16th to endNight
15%7%36%5%2433443%
2112
April1st to 15thNight
18%6%36%5%34446%35%
1811
16th to endNight
12%5%25%43445%7%43%
1653
May1st to 15thNight
16%425%5%35%5%5%7%39%
1559
16th to endNight
12%32432445%7%49%
1495
June1st to 15thNight
12%5%15%445%5%5%8%40%
1440
16th to endNight
12%325%5%3446%8%43%
1440
July1st to 15thNight
5%22442445%9%55%
1440
16th to endNight
8%3144246%5%9%48%
1613
August1st to 15thNight
7%315%42446%8%49%
1586
16th to endNight
8%424335%45%5%52%
1630
September1st to 15thNight
12%4134345%5%6%46%
1650
16th to endNight
13%42442345%7%47%
1840
October1st to 15thNight
18%6%26%42436%6%37%
1980
16th to endNight
22%9%35%5%3445%6%29%
2112
November1st to 15thNight
16%6%25%5%26%45%7%37%
2374
16th to endNight
21%9%36%5%35%5%5%7%26%
2520
December1st to 15thNight
20%13%5%6%5%45%45%5%22%
2520
16th to endNight
21%12%5%8%7%45%5%5%7%16%
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
61%8%13%11%5%
1451
16th to endDay
65%10%8%10%4
1728
February1st to 15thDay
63%7%11%13%2
1577
16th to endDay
56%7%13%14%6%
1453
March1st to 15thDay
56%6%12%15%7%
1980
16th to endDay
46%6%11%19%14%1
2112
April1st to 15thDay
51%6%11%17%12%
2137
16th to endDay
45%5%10%20%15%2
2316
May1st to 15thDay
44%6%12%21%14%
2391
16th to endDay
37%8%14%23%13%2
2622
June1st to 15thDay
41%8%13%22%13%
2520
16th to endDay
36%9%17%22%13%
2520
July1st to 15thDay
32%9%14%24%17%2
2371
16th to endDay
38%9%15%23%11%1
2394
August1st to 15thDay
35%9%16%22%14%1
2275
16th to endDay
35%6%16%28%11%1
2209
September1st to 15thDay
40%9%14%25%10%
1980
16th to endDay
40%7%13%28%9%
1786
October1st to 15thDay
48%7%13%20%9%1
1650
16th to endDay
58%6%15%13%4
1760
November1st to 15thDay
48%8%15%18%7%1
1479
16th to endDay
57%8%14%13%4
1440
December1st to 15thDay
64%9%14%10%1
1440
16th to endDay
65%9%11%11%2
1536
January1st to 15thNight
63%7%11%11%5%
2485
16th to endNight
61%8%10%14%4
2496
February1st to 15thNight
59%8%10%16%4
2287
16th to endNight
55%5%13%17%7%
2017
March1st to 15thNight
55%5%11%20%6%
1980
16th to endNight
45%49%22%16%2
2112
April1st to 15thNight
49%411%19%15%
1811
16th to endNight
40%5%11%22%16%3
1653
May1st to 15thNight
41%7%10%22%15%2
1560
16th to endNight
34%6%13%25%16%3
1497
June1st to 15thNight
38%7%11%24%15%1
1440
16th to endNight
37%6%11%24%18%1
1440
July1st to 15thNight
26%6%12%26%24%2
1360
16th to endNight
32%7%14%25%17%3
1509
August1st to 15thNight
28%9%16%28%14%1
1575
16th to endNight
31%7%10%33%15%1
1630
September1st to 15thNight
34%9%12%28%14%
1650
16th to endNight
34%7%11%31%13%
1840
October1st to 15thNight
45%7%10%22%12%
1980
16th to endNight
55%6%13%17%6%
2112
November1st to 15thNight
46%7%12%20%12%1
2374
16th to endNight
55%8%15%14%5%
2520
December1st to 15thNight
61%8%12%12%3
2520
16th to endNight
67%8%10%9%3
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
19%12%38%22%6%1
63
16th to endDay
28%7%36%26%2
96
February1st to 15thDay
18%7%51%18%3
90
16th to endDay
20%11%32%29%7%
99
March1st to 15thDay
23%8%32%26%8%
270
16th to endDay
22%229%32%10%2
288
April1st to 15thDay
24%328%31%9%1
270
16th to endDay
20%325%29%15%5%
270
May1st to 15thDay
19%219%29%22%8%
288
16th to endDay
12%116%37%26%5%
331
June1st to 15thDay
18%213%35%27%1
315
16th to endDay
13%15%36%28%5%
315
July1st to 15thDay
10%9%30%39%8%
305
16th to endDay
10%11%36%30%9%
326
August1st to 15thDay
7%210%30%35%14%
297
16th to endDay
13%110%23%32%19%
268
September1st to 15thDay
12%210%28%30%14%
255
16th to endDay
16%314%30%20%13%
254
October1st to 15thDay
19%124%29%19%6%
255
16th to endDay
26%7%29%25%9%
272
November1st to 15thDay
11%9%20%39%15%2
103
16th to endDay
23%8%30%26%10%1
60
December1st to 15thDay
11%15%45%21%6%
60
16th to endDay
21%18%43%14%1
64
January1st to 15thNight
27%12%34%18%5%
720
16th to endNight
20%8%35%29%5%
768
February1st to 15thNight
21%11%36%24%5%
704
16th to endNight
20%8%34%28%8%
631
March1st to 15thNight
23%8%32%28%6%
720
16th to endNight
19%5%30%29%12%2
768
April1st to 15thNight
21%5%27%35%9%
718
16th to endNight
15%426%36%14%2
573
May1st to 15thNight
17%120%34%24%2
480
16th to endNight
12%216%42%24%2
375
June1st to 15thNight
16%118%36%23%2
360
16th to endNight
12%114%42%26%2
360
July1st to 15thNight
7%110%45%31%4
340
16th to endNight
8%111%42%30%4
475
August1st to 15thNight
8%9%40%34%6%
527
16th to endNight
9%213%33%33%7%
580
September1st to 15thNight
14%318%27%28%7%
660
16th to endNight
16%215%30%28%6%
657
October1st to 15thNight
21%424%27%19%2
660
16th to endNight
25%6%29%29%7%1
704
November1st to 15thNight
19%5%28%30%14%1
700
16th to endNight
25%8%28%27%9%1
720
December1st to 15thNight
29%8%37%19%4
720
16th to endNight
26%8%36%23%3
768
Page generated at 2017-08-13 14:16:35. Version ac04

Copyright 2017 A. Danko


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