Granby
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Granby clear sky chart from 2005-11-05 to 2018-02-13.

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
31%
15309
12%
48774
8%
15277
35%
15277
14%
36107

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%
780
8%
2716
5%
776
23%
776
7%
2182
January16th to endNight
18%
832
8%
2912
5%
832
24%
832
8%
2295
February1st to 15thNight
17%
753
7%
2438
3%
750
22%
750
7%
2024
February16th to endNight
22%
631
10%
1893
6%
631
28%
631
10%
1503
March1st to 15thNight
23%
720
13%
2160
9%
720
29%
720
12%
1664
March16th to endNight
28%
768
18%
2020
8%
768
35%
768
16%
1504
April1st to 15thNight
26%
718
15%
1796
5%
718
32%
718
17%
1380
April16th to endNight
27%
579
15%
1659
6%
579
32%
579
18%
1155
May1st to 15thNight
27%
498
14%
1578
9%
498
33%
498
16%
1108
May16th to endNight
41%
375
12%
1497
14%
374
47%
374
16%
1005
June1st to 15thNight
36%
360
9%
1440
9%
360
42%
360
12%
1037
June16th to endNight
48%
360
8%
1440
12%
360
51%
360
16%
954
July1st to 15thNight
55%
340
11%
1360
19%
340
57%
340
20%
853
July16th to endNight
56%
376
12%
1418
16%
354
57%
354
20%
886
August1st to 15thNight
53%
443
13%
1514
12%
441
55%
441
21%
980
August16th to endNight
52%
699
18%
1845
11%
699
54%
699
31%
1179
September1st to 15thNight
47%
720
14%
1842
7%
720
49%
720
28%
1255
September16th to endNight
49%
717
24%
1980
17%
717
53%
717
32%
1222
October1st to 15thNight
38%
720
16%
2049
10%
720
43%
720
19%
1488
October16th to endNight
25%
768
11%
2496
7%
768
31%
768
11%
1899
November1st to 15thNight
31%
760
15%
2472
12%
760
36%
760
13%
1824
November16th to endNight
25%
780
13%
2607
11%
780
30%
780
11%
1976
December1st to 15thNight
18%
780
5%
2730
2%
780
21%
780
6%
2271
December16th to endNight
14%
832
7%
2912
4%
832
17%
832
5%
2463

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%11%47%6%34446%26%
49276
Night
17%11%5%8%6%35%445%27%
48944
Cloud CoverDay
19%10%47%6%34446%27%
49286
Night
17%10%47%6%35%445%28%
48949
TransparencyDay
57%410%17%8%
48964
Night
57%410%18%8%
48774
SeeingDay
27%13%23%19%11%3
6145
Night
24%13%22%26%11%1
15309

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%7%13%8%4445%6%15%
1552
16th to endDay
12%14%8%8%9%446%45%20%
1664
February1st to 15thDay
12%15%7%14%10%5%6%43315%
1688
16th to endDay
12%14%8%14%10%35%235%18%
1580
March1st to 15thDay
15%15%7%9%7%36%33423%
1790
16th to endDay
16%13%6%10%6%2332430%
2203
April1st to 15thDay
21%14%5%6%5%2333430%
2152
16th to endDay
20%10%37%5%2435%432%
2301
May1st to 15thDay
24%10%46%5%3444427%
2383
16th to endDay
21%8%36%5%345%5%6%28%
2618
June1st to 15thDay
30%8%36%5%24346%23%
2520
16th to endDay
21%7%36%6%36%5%5%6%27%
2520
July1st to 15thDay
16%7%36%8%36%5%6%8%26%
2520
16th to endDay
17%7%26%6%47%6%6%7%26%
2654
August1st to 15thDay
18%8%36%7%36%5%6%7%26%
2424
16th to endDay
14%7%25%5%35%5%5%9%35%
2354
September1st to 15thDay
19%8%35%423346%38%
2117
16th to endDay
15%7%245%23447%41%
1980
October1st to 15thDay
22%11%36%5%23345%30%
1908
16th to endDay
20%18%37%5%2334425%
1728
November1st to 15thDay
17%15%46%5%3445%5%26%
1716
16th to endDay
18%14%5%9%5%345%4423%
1680
December1st to 15thDay
18%20%6%11%5%3343418%
1560
16th to endDay
21%17%9%11%5%45%43413%
1664
January1st to 15thNight
13%13%6%13%8%46%5%45%16%
2716
16th to endNight
11%15%7%11%8%46%5%45%18%
2912
February1st to 15thNight
11%13%7%12%11%6%7%44415%
2437
16th to endNight
12%14%7%10%9%46%43422%
1893
March1st to 15thNight
16%11%6%9%6%35%44425%
2147
16th to endNight
14%11%5%9%5%24435%33%
2020
April1st to 15thNight
20%11%5%6%5%3435%5%28%
1796
16th to endNight
21%7%36%434346%34%
1659
May1st to 15thNight
18%10%36%6%24336%32%
1578
16th to endNight
21%6%35%43446%7%32%
1495
June1st to 15thNight
27%7%35%5%245%35%28%
1440
16th to endNight
17%6%26%435%5%7%7%33%
1440
July1st to 15thNight
16%5%25%5%25%6%5%9%34%
1440
16th to endNight
13%6%25%5%245%7%9%36%
1514
August1st to 15thNight
15%7%26%5%345%7%7%35%
1524
16th to endNight
14%6%24324349%43%
1845
September1st to 15thNight
18%7%24424346%41%
1842
16th to endNight
14%5%23423347%46%
1980
October1st to 15thNight
18%9%36%5%45%446%32%
2049
16th to endNight
23%13%37%435%446%23%
2496
November1st to 15thNight
17%13%5%7%5%34445%27%
2472
16th to endNight
18%12%7%8%7%23435%25%
2607
December1st to 15thNight
20%16%8%10%8%4433414%
2730
16th to endNight
19%17%8%11%9%35%33313%
2912

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%7%12%9%346%46%16%
1552
16th to endDay
13%12%8%9%9%45%5%5%5%21%
1664
February1st to 15thDay
13%14%7%14%10%46%43317%
1688
16th to endDay
12%14%8%13%9%4433419%
1580
March1st to 15thDay
15%14%7%9%7%35%43424%
1800
16th to endDay
16%12%5%10%5%2333331%
2203
April1st to 15thDay
20%14%46%5%2432430%
2152
16th to endDay
20%10%36%5%34345%32%
2301
May1st to 15thDay
24%10%46%5%24445%28%
2383
16th to endDay
21%8%36%5%35%5%5%7%28%
2618
June1st to 15thDay
29%7%35%6%34346%24%
2520
16th to endDay
21%6%36%6%45%5%5%6%28%
2520
July1st to 15thDay
16%6%46%8%45%5%5%8%27%
2520
16th to endDay
17%6%26%7%36%6%6%8%27%
2654
August1st to 15thDay
17%8%26%6%35%6%6%8%27%
2424
16th to endDay
15%5%25%5%345%6%8%36%
2354
September1st to 15thDay
18%7%36%433336%39%
2117
16th to endDay
15%7%34423446%43%
1980
October1st to 15thDay
22%10%37%423346%31%
1908
16th to endDay
20%17%36%5%33345%25%
1728
November1st to 15thDay
18%13%47%5%3345%6%27%
1716
16th to endDay
18%14%5%7%7%245%4424%
1680
December1st to 15thDay
20%17%6%10%5%34335%19%
1560
16th to endDay
21%17%8%9%6%445%3314%
1664
January1st to 15thNight
14%13%7%12%8%46%5%45%17%
2716
16th to endNight
12%14%7%11%8%46%5%5%5%19%
2912
February1st to 15thNight
12%12%8%11%11%6%7%34416%
2430
16th to endNight
12%14%6%11%9%45%43422%
1893
March1st to 15thNight
17%11%6%8%7%45%43426%
2160
16th to endNight
15%10%49%5%3444432%
2019
April1st to 15thNight
20%10%46%6%34445%29%
1796
16th to endNight
21%7%25%33435%6%35%
1659
May1st to 15thNight
18%10%46%5%34445%32%
1578
16th to endNight
20%6%24425%46%8%32%
1495
June1st to 15thNight
27%7%35%434445%28%
1440
16th to endNight
17%6%25%5%246%6%7%33%
1440
July1st to 15thNight
15%5%25%5%25%5%6%9%34%
1440
16th to endNight
12%7%25%5%35%6%7%9%36%
1514
August1st to 15thNight
14%7%35%6%245%48%36%
1524
16th to endNight
14%5%24423449%43%
1845
September1st to 15thNight
19%6%24334346%41%
1842
16th to endNight
15%5%24323447%47%
1980
October1st to 15thNight
17%9%36%5%35%5%45%33%
2049
16th to endNight
23%12%36%6%34445%24%
2496
November1st to 15thNight
17%13%47%5%34446%27%
2472
16th to endNight
18%12%5%9%6%3443427%
2607
December1st to 15thNight
21%16%8%9%7%45%33315%
2730
16th to endNight
20%16%8%10%8%35%33313%
2912

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
68%48%12%4
1553
16th to endDay
62%5%10%15%5%
1664
February1st to 15thDay
71%46%13%3
1691
16th to endDay
69%26%10%8%1
1580
March1st to 15thDay
64%49%13%6%1
1800
16th to endDay
58%38%15%12%1
2203
April1st to 15thDay
58%37%17%11%1
2152
16th to endDay
53%39%19%10%3
2301
May1st to 15thDay
58%38%18%9%1
2383
16th to endDay
53%6%10%19%9%
2622
June1st to 15thDay
60%410%18%5%
2520
16th to endDay
54%5%10%19%8%
2520
July1st to 15thDay
51%5%13%21%7%
2371
16th to endDay
52%6%13%20%6%
2487
August1st to 15thDay
53%6%16%18%5%
2410
16th to endDay
43%6%14%24%10%
2354
September1st to 15thDay
46%410%25%12%
2117
16th to endDay
41%411%26%15%
1980
October1st to 15thDay
55%310%21%8%
1908
16th to endDay
61%312%16%6%
1728
November1st to 15thDay
57%5%11%15%9%1
1716
16th to endDay
62%5%10%13%6%1
1680
December1st to 15thDay
68%410%11%4
1560
16th to endDay
73%5%6%8%6%
1664
January1st to 15thNight
66%5%10%11%4
2716
16th to endNight
65%49%14%5%
2912
February1st to 15thNight
71%37%11%4
2438
16th to endNight
65%38%13%7%1
1893
March1st to 15thNight
60%47%18%6%1
2160
16th to endNight
54%49%16%13%2
2020
April1st to 15thNight
56%37%20%10%
1796
16th to endNight
48%410%19%13%2
1659
May1st to 15thNight
53%38%18%13%1
1578
16th to endNight
47%7%14%21%7%1
1497
June1st to 15thNight
56%5%11%18%6%
1440
16th to endNight
46%7%13%22%8%1
1440
July1st to 15thNight
42%7%17%23%9%
1360
16th to endNight
42%6%17%24%9%
1418
August1st to 15thNight
45%417%25%6%
1514
16th to endNight
37%5%17%27%11%
1845
September1st to 15thNight
43%413%28%9%
1842
16th to endNight
37%312%32%13%1
1980
October1st to 15thNight
52%411%20%9%
2049
16th to endNight
61%49%17%6%
2496
November1st to 15thNight
57%411%17%7%1
2472
16th to endNight
60%410%15%6%1
2607
December1st to 15thNight
73%38%11%3
2730
16th to endNight
74%38%7%5%
2912

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%22%23%21%6%
90
16th to endDay
27%20%31%15%41
96
February1st to 15thDay
35%17%26%16%4
192
16th to endDay
21%23%23%21%10%
239
March1st to 15thDay
31%15%23%23%4
270
16th to endDay
25%19%25%15%10%4
288
April1st to 15thDay
34%14%21%21%5%2
270
16th to endDay
31%15%23%14%11%3
270
May1st to 15thDay
39%12%22%12%7%4
288
16th to endDay
26%12%29%22%7%1
331
June1st to 15thDay
35%14%24%15%9%
315
16th to endDay
25%14%28%20%8%1
315
July1st to 15thDay
19%11%31%22%10%5%
305
16th to endDay
21%7%26%26%14%3
326
August1st to 15thDay
23%8%25%18%19%4
313
16th to endDay
18%11%19%19%20%10%
332
September1st to 15thDay
20%9%21%17%23%7%
315
16th to endDay
18%9%17%22%17%14%
314
October1st to 15thDay
24%12%19%22%16%4
312
16th to endDay
32%14%21%20%10%
288
November1st to 15thDay
27%15%18%26%10%1
280
16th to endDay
32%15%20%20%8%2
210
December1st to 15thDay
34%13%27%16%7%
90
16th to endDay
45%15%28%8%2
96
January1st to 15thNight
24%19%25%24%5%
780
16th to endNight
24%19%26%26%4
832
February1st to 15thNight
19%20%31%23%4
753
16th to endNight
23%17%27%25%6%
631
March1st to 15thNight
27%15%26%24%4
720
16th to endNight
25%17%22%23%9%1
768
April1st to 15thNight
28%16%22%26%6%
718
16th to endNight
28%13%27%20%9%
579
May1st to 15thNight
25%12%27%23%10%1
498
16th to endNight
25%8%19%34%11%
375
June1st to 15thNight
31%6%17%33%11%
360
16th to endNight
18%6%20%39%15%
360
July1st to 15thNight
16%414%42%20%2
340
16th to endNight
16%215%44%21%
376
August1st to 15thNight
18%414%37%24%1
443
16th to endNight
18%5%15%31%25%4
699
September1st to 15thNight
20%7%16%33%19%2
720
16th to endNight
18%8%18%23%26%4
717
October1st to 15thNight
25%11%18%27%16%2
720
16th to endNight
33%12%22%22%8%
768
November1st to 15thNight
24%15%21%27%10%1
760
16th to endNight
26%18%21%21%9%2
780
December1st to 15thNight
32%17%23%21%4
780
16th to endNight
31%18%23%21%3
832
Page generated at 2018-02-13 20:46:11. Version ac04

Copyright 2018 A. Danko


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