Grand River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand River clear sky chart from 2005-11-05 to 2017-09-21.

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
39%
15979
20%
46958
11%
15932
47%
15932
28%
29400

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
28%
900
20%
2395
8%
895
38%
895
28%
1555
January16th to endNight
24%
960
19%
2496
7%
960
33%
960
26%
1688
February1st to 15thNight
24%
880
13%
2288
5%
876
29%
876
21%
1656
February16th to endNight
26%
713
22%
1975
6%
713
38%
713
28%
1278
March1st to 15thNight
34%
540
22%
1980
13%
540
46%
540
24%
1164
March16th to endNight
25%
576
13%
2112
7%
576
34%
576
15%
1457
April1st to 15thNight
29%
539
18%
1818
11%
539
42%
539
24%
1104
April16th to endNight
30%
540
19%
1713
12%
540
43%
540
21%
1156
May1st to 15thNight
37%
540
17%
1620
11%
540
45%
540
24%
1075
May16th to endNight
42%
563
20%
1512
9%
561
52%
561
30%
987
June1st to 15thNight
56%
540
19%
1440
9%
540
60%
540
40%
849
June16th to endNight
57%
540
20%
1440
10%
540
61%
540
44%
839
July1st to 15thNight
67%
510
17%
1376
11%
510
68%
510
44%
787
July16th to endNight
73%
564
21%
1594
19%
531
75%
531
42%
861
August1st to 15thNight
72%
539
21%
1610
22%
536
74%
536
40%
882
August16th to endNight
64%
573
24%
1818
24%
573
69%
573
36%
1016
September1st to 15thNight
60%
540
26%
1800
25%
540
67%
540
35%
978
September16th to endNight
54%
529
27%
1900
20%
529
65%
529
34%
997
October1st to 15thNight
41%
660
25%
1980
17%
660
48%
660
31%
1204
October16th to endNight
32%
704
23%
2112
11%
704
43%
704
30%
1258
November1st to 15thNight
37%
769
27%
2251
13%
769
49%
769
36%
1261
November16th to endNight
27%
900
20%
2520
8%
900
38%
900
27%
1609
December1st to 15thNight
25%
900
15%
2520
6%
900
33%
900
20%
1779
December16th to endNight
22%
960
17%
2688
5%
960
32%
960
18%
1960

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
12%7%35%5%2445%7%40%
47896
Night
11%6%25%42445%7%46%
47140
Cloud CoverDay
12%7%35%5%3445%7%40%
47905
Night
11%6%25%42435%7%45%
47144
TransparencyDay
42%6%13%23%12%1
47596
Night
37%5%12%25%15%2
46958
SeeingDay
14%7%26%30%16%4
5997
Night
14%8%32%30%12%
15979

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
10%8%48%6%34447%38%
1541
16th to endDay
14%10%5%7%7%34435%31%
1728
February1st to 15thDay
13%7%48%8%35%447%31%
1575
16th to endDay
12%8%36%5%35%5%47%37%
1507
March1st to 15thDay
11%10%5%7%6%2445%6%34%
1969
16th to endDay
17%11%47%6%24445%31%
2112
April1st to 15thDay
17%8%345%34346%38%
2129
16th to endDay
22%7%37%5%33446%31%
2244
May1st to 15thDay
15%7%46%5%35%45%7%33%
2331
16th to endDay
15%6%35%5%3445%7%37%
2601
June1st to 15thDay
11%6%26%5%2445%7%42%
2520
16th to endDay
6%4146%35%6%7%9%44%
2520
July1st to 15thDay
8%3245%36%5%6%9%45%
2502
16th to endDay
5%3144346%5%11%48%
2466
August1st to 15thDay
7%5%145%25%5%6%11%42%
2340
16th to endDay
11%6%245%2446%7%44%
2384
September1st to 15thDay
12%5%1432335%7%50%
2158
16th to endDay
9%41442445%9%49%
1841
October1st to 15thDay
14%7%24413346%49%
1650
16th to endDay
13%8%24333445%45%
1760
November1st to 15thDay
9%5%24324337%53%
1602
16th to endDay
17%8%35%42335%6%39%
1440
December1st to 15thDay
14%10%48%6%3435%8%30%
1440
16th to endDay
14%12%410%6%24346%28%
1536
January1st to 15thNight
8%6%36%5%35%45%8%42%
2395
16th to endNight
9%8%37%43435%6%41%
2496
February1st to 15thNight
13%10%47%6%24446%35%
2285
16th to endNight
10%7%35%5%23345%45%
1975
March1st to 15thNight
12%6%26%423435%47%
1968
16th to endNight
17%9%46%5%2445%5%33%
2112
April1st to 15thNight
14%5%25%5%24346%46%
1818
16th to endNight
18%6%36%435%33440%
1713
May1st to 15thNight
12%5%36%5%25%5%5%8%39%
1620
16th to endNight
9%4245%35%45%8%45%
1510
June1st to 15thNight
7%5%2432336%10%51%
1440
16th to endNight
5%31332447%10%52%
1440
July1st to 15thNight
5%21332447%8%56%
1457
16th to endNight
3213425%45%10%54%
1702
August1st to 15thNight
32135%3447%9%53%
1620
16th to endNight
8%415%4145%47%53%
1818
September1st to 15thNight
9%41432336%7%53%
1800
16th to endNight
9%31332345%7%54%
1900
October1st to 15thNight
12%5%26%323335%51%
1980
16th to endNight
12%7%245%2233452%
2112
November1st to 15thNight
9%414323347%55%
2251
16th to endNight
14%6%35%31345%5%46%
2520
December1st to 15thNight
14%10%46%5%23346%36%
2520
16th to endNight
15%10%48%6%34346%32%
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
10%9%47%6%34347%37%
1541
16th to endDay
14%11%5%8%7%345%45%30%
1728
February1st to 15thDay
13%8%49%7%35%447%31%
1575
16th to endDay
12%8%36%6%25%45%6%37%
1507
March1st to 15thDay
12%10%5%7%6%3345%6%34%
1980
16th to endDay
17%11%47%6%24445%31%
2110
April1st to 15thDay
17%8%34424445%38%
2129
16th to endDay
22%7%37%5%33446%31%
2244
May1st to 15thDay
15%8%47%5%35%45%6%33%
2331
16th to endDay
15%6%35%5%3445%6%37%
2601
June1st to 15thDay
11%7%25%5%2445%8%42%
2520
16th to endDay
6%3245%36%6%7%9%44%
2520
July1st to 15thDay
8%4235%35%5%6%9%45%
2502
16th to endDay
5%314435%5%6%11%49%
2466
August1st to 15thDay
7%4245%26%5%7%11%42%
2340
16th to endDay
11%6%2443445%7%44%
2384
September1st to 15thDay
12%5%1432335%7%50%
2158
16th to endDay
9%41442345%9%49%
1841
October1st to 15thDay
14%6%24323346%49%
1650
16th to endDay
14%8%24333445%45%
1760
November1st to 15thDay
9%5%14414337%53%
1602
16th to endDay
17%8%44423346%39%
1440
December1st to 15thDay
14%10%48%6%3435%7%30%
1440
16th to endDay
14%12%410%6%34447%28%
1536
January1st to 15thNight
8%6%36%5%35%45%8%42%
2395
16th to endNight
9%8%47%5%34347%41%
2496
February1st to 15thNight
13%10%47%5%24446%35%
2278
16th to endNight
10%7%35%5%23345%45%
1975
March1st to 15thNight
12%6%35%423335%48%
1980
16th to endNight
17%10%36%5%2445%5%33%
2112
April1st to 15thNight
13%5%25%42435%6%46%
1818
16th to endNight
17%6%36%5%3433440%
1713
May1st to 15thNight
12%5%26%5%25%45%8%40%
1619
16th to endNight
9%4246%36%35%8%45%
1510
June1st to 15thNight
7%5%2431436%10%51%
1440
16th to endNight
6%21332447%10%52%
1440
July1st to 15thNight
5%2134245%6%9%56%
1457
16th to endNight
4213425%45%10%54%
1702
August1st to 15thNight
42234345%7%9%53%
1620
16th to endNight
8%31441445%7%53%
1818
September1st to 15thNight
9%41432345%6%54%
1800
16th to endNight
8%31332345%7%54%
1900
October1st to 15thNight
12%5%25%323335%51%
1980
16th to endNight
12%6%245%2233452%
2112
November1st to 15thNight
9%41331335%7%55%
2251
16th to endNight
14%7%35%322446%45%
2520
December1st to 15thNight
14%10%46%5%23346%36%
2520
16th to endNight
15%10%48%6%34246%32%
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
46%413%19%13%1
1542
16th to endDay
55%414%17%7%
1728
February1st to 15thDay
52%5%12%21%7%
1576
16th to endDay
47%5%13%21%12%
1507
March1st to 15thDay
49%5%13%20%9%1
1980
16th to endDay
55%5%12%18%6%1
2112
April1st to 15thDay
47%5%10%26%10%
2129
16th to endDay
53%5%12%18%9%
2244
May1st to 15thDay
50%6%12%19%10%
2331
16th to endDay
44%7%13%23%10%1
2605
June1st to 15thDay
39%6%14%23%13%2
2520
16th to endDay
32%10%14%26%15%1
2520
July1st to 15thDay
33%8%16%26%11%3
2354
16th to endDay
27%7%15%30%16%1
2311
August1st to 15thDay
33%8%16%25%15%
2326
16th to endDay
37%6%11%22%16%4
2384
September1st to 15thDay
32%5%12%28%18%3
2158
16th to endDay
32%5%12%30%18%
1841
October1st to 15thDay
36%310%25%21%2
1650
16th to endDay
40%411%26%14%3
1760
November1st to 15thDay
32%411%28%20%2
1602
16th to endDay
46%314%23%11%
1440
December1st to 15thDay
52%6%13%18%7%
1440
16th to endDay
55%5%12%16%8%1
1536
January1st to 15thNight
39%5%14%24%15%
2395
16th to endNight
42%5%16%23%11%
2496
February1st to 15thNight
50%412%22%9%1
2288
16th to endNight
39%5%12%24%16%2
1975
March1st to 15thNight
38%412%27%15%1
1980
16th to endNight
50%6%11%20%8%1
2112
April1st to 15thNight
38%5%11%27%15%2
1818
16th to endNight
47%5%11%21%12%2
1713
May1st to 15thNight
41%7%12%22%14%
1620
16th to endNight
35%9%12%26%12%3
1512
June1st to 15thNight
27%7%17%28%16%2
1440
16th to endNight
24%7%15%27%20%4
1440
July1st to 15thNight
24%7%18%30%14%4
1376
16th to endNight
24%7%13%34%18%1
1594
August1st to 15thNight
25%7%16%32%15%2
1610
16th to endNight
29%6%12%25%19%7%
1818
September1st to 15thNight
30%410%26%22%5%
1800
16th to endNight
28%5%10%33%19%2
1900
October1st to 15thNight
36%37%24%23%4
1980
16th to endNight
36%310%26%19%3
2112
November1st to 15thNight
29%315%25%21%4
2251
16th to endNight
39%411%28%14%1
2520
December1st to 15thNight
48%5%14%22%9%
2520
16th to endNight
52%5%11%17%10%1
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
21%13%38%20%42
90
16th to endDay
22%15%34%22%4
96
February1st to 15thDay
13%20%35%24%6%
90
16th to endDay
18%11%35%22%8%3
81
March1st to 15thDay
17%15%42%22%2
90
16th to endDay
34%15%33%15%1
96
April1st to 15thDay
22%10%32%23%10%
248
16th to endDay
27%10%33%18%7%1
354
May1st to 15thDay
19%11%32%24%9%2
468
16th to endDay
17%9%31%26%13%1
517
June1st to 15thDay
13%425%31%21%3
495
16th to endDay
6%7%30%33%18%3
495
July1st to 15thDay
10%121%37%19%9%
475
16th to endDay
417%44%27%5%
515
August1st to 15thDay
8%117%39%27%5%
493
16th to endDay
13%317%34%23%8%
424
September1st to 15thDay
11%320%28%28%7%
313
16th to endDay
12%225%37%12%9%
105
October1st to 15thDay
13%8%28%33%8%6%
90
16th to endDay
11%14%35%33%5%
96
November1st to 15thDay
410%35%25%16%7%
90
16th to endDay
40%12%36%7%3
90
December1st to 15thDay
17%22%31%21%43
90
16th to endDay
27%23%31%15%2
96
January1st to 15thNight
11%12%42%24%8%
900
16th to endNight
15%12%40%26%4
960
February1st to 15thNight
18%11%37%26%5%
880
16th to endNight
14%11%42%24%5%
713
March1st to 15thNight
16%11%33%29%9%
540
16th to endNight
22%11%36%23%5%
576
April1st to 15thNight
16%13%36%27%5%
539
16th to endNight
21%9%34%25%8%
540
May1st to 15thNight
13%9%34%34%7%
540
16th to endNight
11%6%34%31%14%
563
June1st to 15thNight
8%426%41%18%
540
16th to endNight
7%228%44%16%
540
July1st to 15thNight
6%119%42%27%1
510
16th to endNight
6%14%50%27%1
564
August1st to 15thNight
417%46%28%2
539
16th to endNight
9%116%39%30%3
573
September1st to 15thNight
11%220%32%28%4
540
16th to endNight
10%327%32%23%1
529
October1st to 15thNight
15%8%29%31%12%2
660
16th to endNight
16%8%36%27%9%
704
November1st to 15thNight
11%12%35%30%8%
769
16th to endNight
17%14%37%21%8%
900
December1st to 15thNight
21%12%35%25%5%
900
16th to endNight
21%10%36%25%5%
960
Page generated at 2017-09-22 06:35:37. Version ac04

Copyright 2017 A. Danko


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