Observatoire Monty-Guilmette
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Monty-Guilmette clear sky chart from 2005-11-05 to 2017-09-20.

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
22%
14698
10%
46966
6%
14667
28%
14667
12%
36042

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
9%
720
6%
2506
2%
716
13%
716
5%
2133
January16th to endNight
11%
768
6%
2688
2%
768
16%
768
6%
2268
February1st to 15thNight
10%
703
7%
2315
2%
701
16%
701
6%
1952
February16th to endNight
11%
631
9%
1893
3%
631
19%
631
8%
1549
March1st to 15thNight
14%
720
12%
2157
6%
720
22%
720
11%
1687
March16th to endNight
22%
768
16%
2028
6%
768
30%
768
16%
1542
April1st to 15thNight
20%
718
14%
1796
4%
718
26%
718
15%
1425
April16th to endNight
22%
551
16%
1631
5%
551
31%
551
17%
1152
May1st to 15thNight
22%
492
13%
1572
8%
492
31%
492
16%
1126
May16th to endNight
29%
375
10%
1497
10%
374
37%
374
13%
1059
June1st to 15thNight
27%
360
8%
1350
6%
360
33%
360
12%
997
June16th to endNight
37%
360
8%
1355
9%
360
41%
360
17%
919
July1st to 15thNight
40%
340
9%
1360
13%
340
44%
340
18%
868
July16th to endNight
42%
376
10%
1418
13%
354
45%
354
16%
933
August1st to 15thNight
43%
440
10%
1511
9%
438
45%
438
18%
1020
August16th to endNight
43%
660
17%
1806
9%
660
47%
660
28%
1197
September1st to 15thNight
37%
720
11%
1854
5%
720
39%
720
24%
1326
September16th to endNight
38%
677
19%
1869
12%
677
43%
677
27%
1228
October1st to 15thNight
26%
660
15%
1890
8%
660
33%
660
18%
1396
October16th to endNight
18%
704
8%
2288
4%
704
23%
704
9%
1829
November1st to 15thNight
18%
700
13%
2277
9%
700
25%
700
10%
1760
November16th to endNight
19%
725
12%
2445
9%
725
24%
725
9%
1926
December1st to 15thNight
10%
750
4%
2700
0%
750
14%
750
4%
2319
December16th to endNight
8%
780
6%
2760
2%
780
12%
780
3%
2431

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%12%47%5%34445%24%
47863
Night
19%13%5%8%6%34345%25%
47136
TransparencyDay
61%310%16%6%
47551
Night
62%39%16%7%
46966
SeeingDay
30%14%28%17%7%1
5894
Night
27%15%28%20%7%1
14699

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%18%9%13%10%45%44211%
1432
16th to endDay
11%15%9%12%10%46%5%4415%
1536
February1st to 15thDay
13%18%9%13%11%45%42213%
1543
16th to endDay
12%20%7%12%9%5%5%33316%
1580
March1st to 15thDay
17%16%8%10%6%2334322%
1793
16th to endDay
18%14%5%9%6%3323327%
2194
April1st to 15thDay
21%17%47%5%2434426%
2152
16th to endDay
23%13%35%42334432%
2328
May1st to 15thDay
25%10%35%5%34245%27%
2389
16th to endDay
26%8%36%5%3445%7%23%
2618
June1st to 15thDay
34%6%25%43445%6%23%
2604
16th to endDay
25%7%36%5%3445%8%24%
2598
July1st to 15thDay
21%6%36%5%35%6%5%8%27%
2520
16th to endDay
23%8%36%6%46%5%5%6%24%
2654
August1st to 15thDay
25%7%25%5%46%5%5%8%22%
2425
16th to endDay
21%7%24434447%34%
2395
September1st to 15thDay
25%7%24423245%35%
2106
16th to endDay
22%7%24323346%37%
1860
October1st to 15thDay
23%13%35%5%2345%5%27%
1738
16th to endDay
26%21%36%43334417%
1584
November1st to 15thDay
22%18%5%5%433435%24%
1581
16th to endDay
18%18%6%9%5%2423423%
1512
December1st to 15thDay
21%22%8%11%7%2332213%
1260
16th to endDay
20%22%10%12%7%25%21211%
1461
January1st to 15thNight
14%18%8%13%10%45%43313%
2506
16th to endNight
10%18%8%11%9%5%7%5%4214%
2688
February1st to 15thNight
10%16%8%13%11%5%6%33315%
2314
16th to endNight
14%18%8%11%8%35%32320%
1893
March1st to 15thNight
18%15%6%8%6%3433326%
2144
16th to endNight
16%14%5%8%5%3333430%
2028
April1st to 15thNight
23%14%37%5%3333425%
1796
16th to endNight
22%10%44323445%34%
1631
May1st to 15thNight
25%9%35%42445%6%28%
1572
16th to endNight
24%8%36%5%2445%7%27%
1495
June1st to 15thNight
31%8%35%423345%26%
1350
16th to endNight
21%6%25%43445%9%31%
1355
July1st to 15thNight
18%6%25%5%35%5%5%8%32%
1440
16th to endNight
17%6%345%36%5%5%8%33%
1514
August1st to 15thNight
17%7%35%6%335%6%7%32%
1521
16th to endNight
17%5%25%42345%8%40%
1806
September1st to 15thNight
22%7%26%423345%36%
1854
16th to endNight
21%423333335%44%
1869
October1st to 15thNight
21%11%35%5%23446%31%
1890
16th to endNight
29%16%36%5%2333421%
2288
November1st to 15thNight
21%16%5%6%5%34335%23%
2277
16th to endNight
20%16%7%9%6%2332324%
2445
December1st to 15thNight
21%19%9%12%7%2323213%
2700
16th to endNight
21%20%9%11%8%4432311%
2760

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
76%38%8%3
1433
16th to endDay
71%37%12%4
1536
February1st to 15thDay
78%25%8%4
1546
16th to endDay
73%35%11%5%1
1580
March1st to 15thDay
66%28%13%6%1
1803
16th to endDay
63%27%14%10%1
2194
April1st to 15thDay
61%37%16%9%2
2152
16th to endDay
56%38%18%11%2
2328
May1st to 15thDay
59%28%19%8%
2389
16th to endDay
59%412%15%7%
2622
June1st to 15thDay
62%49%17%5%
2604
16th to endDay
57%5%10%20%5%
2598
July1st to 15thDay
51%5%15%20%5%
2371
16th to endDay
60%5%12%17%4
2487
August1st to 15thDay
57%5%15%17%2
2411
16th to endDay
48%414%23%9%
2395
September1st to 15thDay
50%412%22%9%
2106
16th to endDay
47%311%26%10%
1860
October1st to 15thDay
58%311%18%7%
1738
16th to endDay
70%28%13%4
1584
November1st to 15thDay
62%310%14%6%1
1581
16th to endDay
65%38%15%5%
1512
December1st to 15thDay
78%36%9%2
1260
16th to endDay
80%346%5%
1461
January1st to 15thNight
75%27%9%3
2506
16th to endNight
74%37%10%3
2688
February1st to 15thNight
73%36%12%3
2315
16th to endNight
70%26%11%8%
1893
March1st to 15thNight
63%36%16%7%1
2157
16th to endNight
57%38%16%11%2
2028
April1st to 15thNight
61%35%17%11%1
1796
16th to endNight
50%410%19%11%3
1631
May1st to 15thNight
55%39%19%10%1
1572
16th to endNight
55%5%13%18%7%
1497
June1st to 15thNight
60%410%18%5%
1350
16th to endNight
49%6%12%22%8%
1355
July1st to 15thNight
46%5%18%19%9%
1360
16th to endNight
48%6%15%21%8%
1418
August1st to 15thNight
48%6%19%21%4
1511
16th to endNight
41%416%27%9%
1806
September1st to 15thNight
50%312%25%7%
1854
16th to endNight
42%312%28%11%
1869
October1st to 15thNight
54%310%20%9%
1890
16th to endNight
67%39%15%4
2288
November1st to 15thNight
64%210%13%7%1
2277
16th to endNight
66%37%15%6%
2445
December1st to 15thNight
77%36%9%2
2700
16th to endNight
80%25%6%4
2760

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
26%21%41%10%
60
16th to endDay
25%21%42%7%11
64
February1st to 15thDay
30%18%33%12%4
151
16th to endDay
27%22%30%16%2
239
March1st to 15thDay
31%22%30%10%5%
270
16th to endDay
28%19%24%17%7%2
288
April1st to 15thDay
35%15%31%12%5%
270
16th to endDay
34%16%27%11%7%2
270
May1st to 15thDay
40%12%25%14%6%1
288
16th to endDay
28%16%29%20%31
331
June1st to 15thDay
36%11%25%18%7%
399
16th to endDay
25%11%32%21%8%
393
July1st to 15thDay
22%10%36%21%7%1
305
16th to endDay
25%8%27%27%8%
326
August1st to 15thDay
28%6%28%23%11%
313
16th to endDay
27%9%21%24%11%6%
332
September1st to 15thDay
25%10%26%19%13%5%
315
16th to endDay
23%8%27%21%13%6%
270
October1st to 15thDay
29%15%22%15%12%4
249
16th to endDay
37%17%23%15%4
240
November1st to 15thDay
30%20%26%16%6%
235
16th to endDay
36%15%23%14%7%2
162
December1st to 15thDay
41%21%30%33
60
16th to endDay
51%28%17%11
64
January1st to 15thNight
25%25%34%12%3
720
16th to endNight
22%24%34%15%3
768
February1st to 15thNight
18%24%36%16%3
704
16th to endNight
25%19%34%15%3
631
March1st to 15thNight
29%18%33%16%2
720
16th to endNight
24%19%27%21%6%1
768
April1st to 15thNight
29%17%27%19%4
718
16th to endNight
28%15%29%18%6%
551
May1st to 15thNight
30%12%31%17%7%1
492
16th to endNight
27%9%28%26%7%
375
June1st to 15thNight
35%5%22%26%9%
360
16th to endNight
23%6%26%31%10%
360
July1st to 15thNight
20%6%27%31%13%1
340
16th to endNight
18%326%36%14%
376
August1st to 15thNight
19%422%33%18%1
440
16th to endNight
20%5%25%29%18%2
660
September1st to 15thNight
25%6%24%29%11%2
720
16th to endNight
22%7%26%25%14%2
677
October1st to 15thNight
28%10%28%20%9%1
660
16th to endNight
39%14%23%17%4
704
November1st to 15thNight
31%16%28%16%7%
700
16th to endNight
31%17%25%16%7%1
725
December1st to 15thNight
34%22%27%12%3
750
16th to endNight
35%22%26%12%21
780
Page generated at 2017-09-21 07:18:23. Version ac04

Copyright 2017 A. Danko


Observatoire Monty-Guilmette Clear Sky Chart | Charts Home