Gravenhurst
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gravenhurst clear sky chart from 2005-11-05 to 2017-11-30.

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
30%
15012
13%
47478
8%
14979
35%
14979
16%
34344

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
11%
718
6%
2506
2%
716
16%
716
5%
2110
January16th to endNight
20%
768
11%
2505
5%
768
27%
768
9%
1996
February1st to 15thNight
15%
702
7%
2287
3%
701
20%
701
8%
1845
February16th to endNight
20%
631
11%
2036
4%
631
27%
631
11%
1534
March1st to 15thNight
19%
720
13%
1980
5%
720
26%
720
15%
1466
March16th to endNight
30%
768
20%
2112
11%
768
38%
768
23%
1435
April1st to 15thNight
23%
718
14%
1811
6%
718
27%
718
19%
1357
April16th to endNight
32%
549
18%
1629
9%
549
39%
549
21%
1116
May1st to 15thNight
39%
456
16%
1536
13%
456
46%
456
21%
996
May16th to endNight
40%
374
14%
1497
13%
374
48%
374
22%
861
June1st to 15thNight
39%
360
9%
1401
11%
360
44%
360
18%
882
June16th to endNight
46%
360
11%
1260
11%
360
51%
360
22%
789
July1st to 15thNight
59%
340
16%
1234
20%
340
62%
340
33%
666
July16th to endNight
51%
441
15%
1478
14%
414
55%
414
26%
867
August1st to 15thNight
60%
539
16%
1609
12%
536
63%
536
32%
967
August16th to endNight
54%
615
18%
1761
11%
615
59%
615
31%
1105
September1st to 15thNight
47%
720
15%
1800
7%
720
50%
720
30%
1213
September16th to endNight
50%
717
22%
2010
15%
717
54%
717
29%
1292
October1st to 15thNight
32%
720
15%
2160
10%
720
38%
720
19%
1536
October16th to endNight
19%
768
11%
2304
5%
768
26%
768
11%
1813
November1st to 15thNight
27%
760
14%
2626
12%
760
33%
760
14%
1875
November16th to endNight
19%
780
9%
2728
6%
780
24%
780
8%
2182
December1st to 15thNight
11%
720
4%
2520
2%
720
14%
720
5%
2144
December16th to endNight
11%
768
7%
2688
3%
768
17%
768
5%
2297

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
18%10%46%5%34446%31%
48933
Night
17%11%47%5%34446%30%
47648
Cloud CoverDay
18%9%46%5%34446%31%
48943
Night
17%11%47%5%34445%30%
47653
TransparencyDay
53%5%11%19%9%
48621
Night
54%5%11%18%9%
47478
SeeingDay
23%11%28%21%10%4
5894
Night
23%11%27%24%10%1
15017

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
21%16%7%9%6%2433418%
1432
16th to endDay
14%17%8%11%8%34345%18%
1718
February1st to 15thDay
13%17%7%12%10%4432319%
1575
16th to endDay
16%17%6%11%7%4433320%
1437
March1st to 15thDay
16%12%47%6%34445%29%
1969
16th to endDay
13%8%5%6%5%24445%37%
2112
April1st to 15thDay
23%11%35%43334432%
2137
16th to endDay
20%8%25%423345%38%
2340
May1st to 15thDay
19%8%25%5%25%447%33%
2415
16th to endDay
14%7%24435%5%48%39%
2618
June1st to 15thDay
20%7%25%4245%6%7%33%
2555
16th to endDay
17%6%25%5%346%6%8%33%
2700
July1st to 15thDay
12%424435%5%5%8%41%
2649
16th to endDay
12%6%245%35%6%6%9%36%
2586
August1st to 15thDay
13%6%25%5%245%6%6%40%
2340
16th to endDay
13%5%25%5%45%46%8%38%
2428
September1st to 15thDay
17%6%26%5%34446%37%
2157
16th to endDay
18%425%5%245%5%6%39%
1950
October1st to 15thDay
24%8%36%5%33445%31%
1800
16th to endDay
31%9%37%6%3443421%
1920
November1st to 15thDay
21%11%48%6%34446%25%
1561
16th to endDay
21%17%6%7%6%35%44418%
1558
December1st to 15thDay
20%23%7%9%6%3333414%
1440
16th to endDay
19%21%8%9%6%2343415%
1536
January1st to 15thNight
20%17%7%11%7%35%33315%
2506
16th to endNight
15%16%6%10%8%4444419%
2505
February1st to 15thNight
13%16%7%12%8%45%34418%
2285
16th to endNight
17%13%6%8%6%43445%25%
2036
March1st to 15thNight
17%11%47%5%34345%31%
1968
16th to endNight
15%9%45%423445%39%
2112
April1st to 15thNight
23%10%46%5%2334432%
1811
16th to endNight
17%8%26%434446%36%
1629
May1st to 15thNight
18%7%26%334447%37%
1536
16th to endNight
12%5%14425%5%5%9%42%
1495
June1st to 15thNight
15%7%35%5%25%45%8%35%
1401
16th to endNight
12%6%26%6%345%48%38%
1260
July1st to 15thNight
7%42443435%7%51%
1308
16th to endNight
11%5%245%3445%8%44%
1579
August1st to 15thNight
8%5%25%425%45%8%46%
1620
16th to endNight
10%425%5%24446%48%
1761
September1st to 15thNight
15%5%245%3345%7%42%
1800
16th to endNight
14%5%245%33346%45%
2010
October1st to 15thNight
20%8%35%5%345%46%33%
2160
16th to endNight
28%10%47%5%2444423%
2304
November1st to 15thNight
20%11%36%5%33346%30%
2626
16th to endNight
24%13%48%6%34446%18%
2728
December1st to 15thNight
21%22%7%9%6%3334413%
2520
16th to endNight
23%19%7%10%6%3333413%
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
21%16%7%9%6%3333418%
1432
16th to endDay
15%16%8%11%8%44345%18%
1718
February1st to 15thDay
14%16%7%12%9%4443219%
1575
16th to endDay
16%18%5%11%8%4433420%
1437
March1st to 15thDay
16%12%47%6%34445%29%
1980
16th to endDay
13%9%5%6%5%34435%37%
2111
April1st to 15thDay
23%11%35%423335%32%
2137
16th to endDay
21%8%25%423336%38%
2340
May1st to 15thDay
19%8%25%5%25%446%33%
2415
16th to endDay
14%7%244345%47%40%
2618
June1st to 15thDay
20%6%25%42446%8%33%
2555
16th to endDay
17%6%35%5%346%6%8%34%
2700
July1st to 15thDay
13%424435%5%5%8%41%
2649
16th to endDay
12%6%246%35%5%6%8%36%
2586
August1st to 15thDay
13%5%25%6%345%5%7%40%
2340
16th to endDay
13%5%25%5%45%46%8%38%
2428
September1st to 15thDay
18%6%25%6%34446%37%
2157
16th to endDay
18%425%5%2445%6%39%
1950
October1st to 15thDay
24%8%36%5%23345%31%
1800
16th to endDay
31%9%36%6%3443421%
1920
November1st to 15thDay
21%10%47%6%34446%25%
1561
16th to endDay
21%16%6%8%5%35%44417%
1558
December1st to 15thDay
20%22%7%9%5%3433314%
1440
16th to endDay
19%22%8%8%7%2433414%
1536
January1st to 15thNight
21%17%7%11%7%3433315%
2506
16th to endNight
16%16%6%11%8%4444420%
2505
February1st to 15thNight
12%16%7%12%8%35%34419%
2278
16th to endNight
17%13%6%8%6%44336%25%
2036
March1st to 15thNight
17%12%47%5%35%34431%
1980
16th to endNight
15%8%46%423445%39%
2112
April1st to 15thNight
23%10%45%5%2334432%
1811
16th to endNight
17%8%25%5%34346%37%
1629
May1st to 15thNight
18%6%35%334447%37%
1536
16th to endNight
12%5%14425%5%5%9%42%
1495
June1st to 15thNight
16%6%35%5%35%45%8%36%
1401
16th to endNight
12%6%26%5%445%5%8%38%
1260
July1st to 15thNight
7%42443445%7%51%
1308
16th to endNight
11%5%145%2446%8%45%
1579
August1st to 15thNight
9%5%25%43445%8%46%
1620
16th to endNight
10%425%5%34446%48%
1761
September1st to 15thNight
15%5%235%3445%7%42%
1800
16th to endNight
14%425%5%33345%46%
2010
October1st to 15thNight
20%7%35%5%34446%34%
2160
16th to endNight
27%10%47%5%24345%24%
2304
November1st to 15thNight
21%11%35%5%33445%31%
2626
16th to endNight
24%13%5%7%6%44446%19%
2728
December1st to 15thNight
21%21%7%9%6%3434413%
2520
16th to endNight
23%20%7%10%6%3423413%
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
69%311%10%4
1433
16th to endDay
68%5%7%9%8%
1718
February1st to 15thDay
71%38%12%3
1577
16th to endDay
68%37%13%7%
1437
March1st to 15thDay
57%413%16%6%
1980
16th to endDay
48%49%18%16%2
2112
April1st to 15thDay
55%48%19%11%1
2137
16th to endDay
47%48%23%14%1
2340
May1st to 15thDay
50%410%20%12%1
2415
16th to endDay
42%6%12%22%14%1
2622
June1st to 15thDay
47%5%13%23%10%
2555
16th to endDay
45%6%15%20%11%
2700
July1st to 15thDay
37%6%14%26%13%1
2494
16th to endDay
43%6%12%26%9%
2424
August1st to 15thDay
42%5%16%21%12%
2327
16th to endDay
41%7%14%27%8%
2428
September1st to 15thDay
45%5%13%25%9%
2157
16th to endDay
44%6%12%28%8%
1950
October1st to 15thDay
55%311%19%9%
1800
16th to endDay
65%412%11%5%
1920
November1st to 15thDay
59%5%13%14%6%
1561
16th to endDay
68%5%10%11%31
1558
December1st to 15thDay
73%410%8%2
1440
16th to endDay
74%47%10%3
1536
January1st to 15thNight
74%38%8%4
2506
16th to endNight
66%47%12%7%
2505
February1st to 15thNight
68%410%12%4
2287
16th to endNight
60%312%16%6%
2036
March1st to 15thNight
56%312%18%8%
1980
16th to endNight
46%49%21%16%1
2112
April1st to 15thNight
55%37%19%12%1
1811
16th to endNight
48%48%18%18%2
1629
May1st to 15thNight
46%311%19%16%2
1536
16th to endNight
37%6%14%24%15%1
1497
June1st to 15thNight
44%5%13%22%13%
1401
16th to endNight
42%414%23%13%
1260
July1st to 15thNight
29%6%13%28%21%
1234
16th to endNight
36%6%12%29%14%
1478
August1st to 15thNight
33%6%19%26%13%
1609
16th to endNight
36%6%15%27%13%
1761
September1st to 15thNight
40%6%16%24%11%1
1800
16th to endNight
40%412%31%10%
2010
October1st to 15thNight
50%6%11%21%10%
2160
16th to endNight
62%5%11%14%6%
2304
November1st to 15thNight
54%5%13%18%7%
2626
16th to endNight
65%6%10%13%3
2728
December1st to 15thNight
74%49%8%2
2520
16th to endNight
75%46%8%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
23%20%40%13%3
60
16th to endDay
42%11%27%12%6%
95
February1st to 15thDay
28%32%32%6%
90
16th to endDay
36%18%34%10%
87
March1st to 15thDay
23%17%34%20%4
270
16th to endDay
22%13%31%19%12%1
288
April1st to 15thDay
28%14%29%18%7%1
270
16th to endDay
24%14%29%15%11%4
270
May1st to 15thDay
31%6%25%21%9%5%
288
16th to endDay
18%13%31%22%9%3
331
June1st to 15thDay
25%11%25%25%9%2
350
16th to endDay
19%9%35%25%7%2
495
July1st to 15thDay
14%10%29%27%13%5%
428
16th to endDay
14%7%28%29%12%7%
326
August1st to 15thDay
14%6%24%28%14%12%
313
16th to endDay
20%5%18%25%17%12%
332
September1st to 15thDay
15%5%25%26%16%11%
315
16th to endDay
18%7%21%20%21%9%
314
October1st to 15thDay
26%11%26%21%10%4
315
16th to endDay
34%16%27%16%4
336
November1st to 15thDay
30%14%31%16%6%
107
16th to endDay
34%20%32%12%1
90
December1st to 15thDay
36%16%28%11%6%
60
16th to endDay
40%35%17%41
64
January1st to 15thNight
31%18%28%15%4
720
16th to endNight
25%12%31%22%6%1
768
February1st to 15thNight
22%18%34%20%4
704
16th to endNight
25%16%31%19%6%
631
March1st to 15thNight
26%16%31%21%4
720
16th to endNight
20%12%30%24%10%
768
April1st to 15thNight
29%13%27%22%5%
718
16th to endNight
23%11%29%24%10%1
549
May1st to 15thNight
21%7%25%29%14%1
456
16th to endNight
14%6%32%33%13%
375
June1st to 15thNight
17%9%25%35%11%
360
16th to endNight
15%5%26%39%12%
360
July1st to 15thNight
7%222%47%18%
340
16th to endNight
13%326%34%21%
441
August1st to 15thNight
11%317%39%25%3
539
16th to endNight
11%422%31%27%2
615
September1st to 15thNight
18%5%23%28%20%4
720
16th to endNight
18%5%20%31%20%4
717
October1st to 15thNight
25%8%28%24%11%1
720
16th to endNight
33%14%27%19%5%
768
November1st to 15thNight
26%13%26%23%8%1
760
16th to endNight
32%14%27%19%5%
780
December1st to 15thNight
35%18%29%13%3
720
16th to endNight
34%14%30%15%3
768
Page generated at 2017-12-01 12:13:40. Version ac04

Copyright 2017 A. Danko


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