Grand Haven
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Haven clear sky chart from 2005-11-05 to 2017-09-18.

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
37%
16007
13%
46837
10%
15965
40%
15965
18%
34216

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
12%
900
5%
2506
2%
895
15%
895
6%
2211
January16th to endNight
16%
960
3%
2688
2%
960
17%
960
6%
2391
February1st to 15thNight
17%
746
6%
2217
3%
746
21%
746
9%
1865
February16th to endNight
23%
631
9%
1893
5%
631
28%
631
11%
1511
March1st to 15thNight
33%
720
14%
2154
10%
720
37%
720
18%
1550
March16th to endNight
38%
702
18%
2046
12%
702
44%
702
23%
1399
April1st to 15thNight
33%
539
13%
1797
10%
539
39%
539
18%
1246
April16th to endNight
41%
540
20%
1659
13%
540
49%
540
24%
1095
May1st to 15thNight
42%
540
16%
1620
9%
540
47%
540
22%
1097
May16th to endNight
50%
562
15%
1522
11%
561
53%
561
28%
1024
June1st to 15thNight
55%
540
15%
1440
10%
540
58%
540
35%
904
June16th to endNight
58%
540
14%
1440
10%
540
60%
540
32%
931
July1st to 15thNight
67%
510
16%
1360
13%
510
68%
510
42%
791
July16th to endNight
70%
564
19%
1417
16%
531
72%
531
40%
857
August1st to 15thNight
70%
539
22%
1568
19%
536
72%
536
40%
893
August16th to endNight
64%
573
21%
1851
20%
573
67%
573
31%
1074
September1st to 15thNight
64%
591
24%
1851
23%
591
67%
591
34%
1073
September16th to endNight
57%
669
22%
1848
17%
669
60%
669
33%
1157
October1st to 15thNight
48%
660
22%
1851
16%
660
52%
660
27%
1237
October16th to endNight
24%
704
11%
2288
6%
704
31%
704
14%
1702
November1st to 15thNight
32%
700
17%
2276
15%
700
37%
700
17%
1613
November16th to endNight
20%
720
8%
2340
6%
720
23%
720
8%
1932
December1st to 15thNight
11%
897
3%
2517
1%
897
12%
897
5%
2264
December16th to endNight
12%
960
4%
2688
1%
960
15%
960
6%
2399

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
13%9%46%5%3445%7%35%
47970
Night
16%11%5%7%6%34446%31%
47005
Cloud CoverDay
14%9%46%5%3445%7%35%
47979
Night
16%11%5%7%6%34346%32%
47010
TransparencyDay
47%5%13%21%10%1
47656
Night
54%410%18%10%1
46837
SeeingDay
16%5%23%31%17%6%
5998
Night
20%7%24%29%14%1
16011

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
18%15%8%12%10%4433411%
1432
16th to endDay
14%21%12%14%11%4422310%
1536
February1st to 15thDay
12%16%8%11%12%5%5%33415%
1642
16th to endDay
14%13%7%10%7%45%5%6%5%18%
1580
March1st to 15thDay
15%10%47%7%346%6%6%27%
1796
16th to endDay
16%8%26%4245%5%7%35%
2189
April1st to 15thDay
20%10%46%422347%33%
2151
16th to endDay
16%6%244345%5%7%38%
2301
May1st to 15thDay
17%6%25%425%46%8%37%
2331
16th to endDay
9%5%24435%45%8%46%
2590
June1st to 15thDay
10%4245%3446%9%43%
2520
16th to endDay
9%424425%5%5%8%48%
2520
July1st to 15thDay
5%32342345%8%54%
2520
16th to endDay
7%324425%46%9%50%
2655
August1st to 15thDay
7%325%42445%10%48%
2382
16th to endDay
10%5%2432436%8%48%
2349
September1st to 15thDay
12%4244245%5%6%47%
2097
16th to endDay
10%6%25%5%345%6%7%42%
1837
October1st to 15thDay
17%8%25%423445%38%
1779
16th to endDay
23%8%37%6%34446%25%
1584
November1st to 15thDay
15%13%45%435%445%34%
1582
16th to endDay
23%21%5%9%424325%17%
1620
December1st to 15thDay
19%24%12%15%42221211%
1441
16th to endDay
21%23%10%11%6%1333310%
1536
January1st to 15thNight
21%17%9%11%10%4322213%
2506
16th to endNight
14%17%11%12%11%4443411%
2688
February1st to 15thNight
13%18%8%13%9%5%333317%
2215
16th to endNight
16%14%7%9%8%34435%21%
1893
March1st to 15thNight
16%9%47%5%34446%32%
2141
16th to endNight
16%6%37%5%34447%36%
2046
April1st to 15thNight
20%9%445%3445%6%32%
1797
16th to endNight
16%7%25%425%445%41%
1659
May1st to 15thNight
18%426%5%345%5%7%35%
1620
16th to endNight
10%5%36%5%36%45%7%40%
1520
June1st to 15thNight
9%425%5%145%6%9%45%
1440
16th to endNight
8%5%25%6%25%47%9%42%
1440
July1st to 15thNight
5%4135%2447%8%51%
1440
16th to endNight
6%3234345%7%7%52%
1513
August1st to 15thNight
6%4134245%5%9%52%
1577
16th to endNight
11%425%32335%6%50%
1851
September1st to 15thNight
10%423423446%51%
1851
16th to endNight
10%5%245%25%337%47%
1848
October1st to 15thNight
21%6%25%322346%41%
1851
16th to endNight
26%9%35%5%33335%30%
2288
November1st to 15thNight
18%13%3442335%5%34%
2276
16th to endNight
23%18%6%9%6%23335%17%
2340
December1st to 15thNight
22%24%12%11%5%2322310%
2517
16th to endNight
22%20%11%11%6%2233411%
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%15%9%12%10%45%34311%
1432
16th to endDay
14%20%12%15%10%443239%
1536
February1st to 15thDay
12%16%8%12%12%5%5%33415%
1642
16th to endDay
14%13%7%11%8%46%5%5%5%18%
1580
March1st to 15thDay
15%10%47%7%35%5%5%7%27%
1806
16th to endDay
16%8%36%435%45%6%36%
2188
April1st to 15thDay
20%9%46%423347%33%
2151
16th to endDay
16%6%245%2445%7%38%
2301
May1st to 15thDay
18%6%35%325%45%8%37%
2331
16th to endDay
9%5%245%3445%8%46%
2590
June1st to 15thDay
10%4244345%5%9%44%
2520
16th to endDay
9%3143345%5%9%48%
2520
July1st to 15thDay
5%41342445%9%53%
2520
16th to endDay
7%31442447%8%50%
2655
August1st to 15thDay
8%32442446%9%48%
2382
16th to endDay
11%425%42345%8%47%
2349
September1st to 15thDay
12%42442346%7%47%
2097
16th to endDay
11%5%245%345%6%8%41%
1837
October1st to 15thDay
18%7%26%5%23445%38%
1779
16th to endDay
24%8%46%6%44447%25%
1584
November1st to 15thDay
16%12%35%435%345%34%
1582
16th to endDay
23%21%5%8%5%2432417%
1620
December1st to 15thDay
19%24%13%14%5%2212212%
1441
16th to endDay
22%23%10%10%6%2333310%
1536
January1st to 15thNight
20%18%8%11%10%3322313%
2506
16th to endNight
14%17%11%12%11%4433412%
2688
February1st to 15thNight
13%18%8%13%9%5%433318%
2208
16th to endNight
16%15%6%9%7%44435%21%
1893
March1st to 15thNight
16%9%47%5%3345%6%33%
2154
16th to endNight
15%6%36%6%35%446%36%
2046
April1st to 15thNight
21%8%35%42445%6%32%
1797
16th to endNight
17%7%25%435%435%41%
1659
May1st to 15thNight
18%426%5%345%5%7%35%
1619
16th to endNight
10%5%36%5%45%45%7%40%
1520
June1st to 15thNight
10%425%41447%8%45%
1440
16th to endNight
8%435%5%35%5%6%9%42%
1440
July1st to 15thNight
6%413425%46%8%52%
1440
16th to endNight
6%313335%46%9%52%
1513
August1st to 15thNight
6%4144245%5%9%52%
1577
16th to endNight
11%42442345%7%49%
1851
September1st to 15thNight
11%32432445%6%51%
1851
16th to endNight
10%5%235%34337%48%
1848
October1st to 15thNight
21%6%14323345%42%
1851
16th to endNight
27%8%25%5%33335%30%
2288
November1st to 15thNight
18%13%34323346%34%
2276
16th to endNight
23%18%6%9%5%23335%17%
2340
December1st to 15thNight
22%24%13%10%6%2322310%
2517
16th to endNight
22%21%10%10%7%2233411%
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
77%6%8%6%1
1433
16th to endDay
81%46%5%2
1536
February1st to 15thDay
73%5%6%13%1
1644
16th to endDay
64%6%11%12%4
1580
March1st to 15thDay
55%5%14%16%7%
1806
16th to endDay
46%416%24%6%1
2189
April1st to 15thDay
50%411%21%11%
2151
16th to endDay
43%415%18%14%3
2301
May1st to 15thDay
44%5%13%24%10%1
2331
16th to endDay
35%5%14%28%13%1
2594
June1st to 15thDay
34%5%16%25%17%
2520
16th to endDay
32%6%17%24%18%1
2520
July1st to 15thDay
27%6%13%31%19%2
2371
16th to endDay
29%6%15%28%18%2
2488
August1st to 15thDay
31%5%15%32%12%1
2367
16th to endDay
33%6%13%28%16%2
2349
September1st to 15thDay
34%6%12%28%14%2
2097
16th to endDay
37%6%13%27%14%
1837
October1st to 15thDay
47%410%24%12%
1779
16th to endDay
58%5%15%14%5%
1584
November1st to 15thDay
51%5%11%20%10%
1582
16th to endDay
70%310%11%2
1620
December1st to 15thDay
80%36%6%2
1441
16th to endDay
79%48%6%1
1536
January1st to 15thNight
78%36%8%2
2506
16th to endNight
77%49%5%1
2688
February1st to 15thNight
72%38%13%3
2217
16th to endNight
65%311%13%5%
1893
March1st to 15thNight
51%5%12%18%10%1
2154
16th to endNight
47%412%24%9%1
2046
April1st to 15thNight
51%48%18%15%
1797
16th to endNight
45%410%19%15%5%
1659
May1st to 15thNight
47%411%21%12%2
1620
16th to endNight
42%411%22%15%2
1522
June1st to 15thNight
34%5%12%27%17%1
1440
16th to endNight
36%7%14%23%16%1
1440
July1st to 15thNight
27%5%12%28%22%2
1360
16th to endNight
29%6%15%25%20%3
1417
August1st to 15thNight
28%5%13%33%17%2
1568
16th to endNight
33%6%10%28%18%3
1851
September1st to 15thNight
32%5%11%28%19%1
1851
16th to endNight
35%5%11%32%13%1
1848
October1st to 15thNight
44%39%26%14%
1851
16th to endNight
57%5%13%16%7%
2288
November1st to 15thNight
52%5%10%18%11%1
2276
16th to endNight
70%5%10%12%1
2340
December1st to 15thNight
80%36%5%2
2517
16th to endNight
78%49%5%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
22%14%28%33%1
90
16th to endDay
28%7%33%23%5%2
96
February1st to 15thDay
15%24%41%17%1
90
16th to endDay
19%11%37%19%11%1
81
March1st to 15thDay
30%13%31%17%7%
96
16th to endDay
27%5%26%26%11%2
288
April1st to 15thDay
27%7%27%28%7%1
270
16th to endDay
21%5%26%30%11%5%
270
May1st to 15thDay
23%6%23%30%12%3
288
16th to endDay
13%428%31%16%5%
490
June1st to 15thDay
11%323%40%16%4
495
16th to endDay
10%328%36%14%5%
495
July1st to 15thDay
6%224%36%22%8%
475
16th to endDay
7%120%38%24%7%
515
August1st to 15thDay
8%114%32%30%12%
355
16th to endDay
17%210%33%23%12%
332
September1st to 15thDay
11%313%31%26%13%
315
16th to endDay
11%317%25%30%10%
262
October1st to 15thDay
18%9%18%27%21%5%
233
16th to endDay
21%9%35%30%3
96
November1st to 15thDay
14%12%20%35%13%4
90
16th to endDay
32%15%27%13%11%
90
December1st to 15thDay
36%17%31%11%21
90
16th to endDay
33%29%33%4
96
January1st to 15thNight
28%14%31%18%6%
900
16th to endNight
20%11%33%28%5%
960
February1st to 15thNight
21%14%33%23%6%
749
16th to endNight
24%11%29%29%6%
631
March1st to 15thNight
21%8%27%31%9%
720
16th to endNight
17%6%30%31%13%1
702
April1st to 15thNight
23%5%30%31%7%
539
16th to endNight
20%5%28%32%12%1
540
May1st to 15thNight
21%323%36%13%1
540
16th to endNight
13%322%35%22%2
563
June1st to 15thNight
11%221%39%23%
540
16th to endNight
9%221%38%25%2
540
July1st to 15thNight
7%114%38%33%4
510
16th to endNight
7%113%41%33%2
564
August1st to 15thNight
8%10%41%31%5%
539
16th to endNight
13%310%35%31%6%
573
September1st to 15thNight
12%414%37%23%7%
591
16th to endNight
13%416%29%28%6%
669
October1st to 15thNight
24%5%17%31%19%2
660
16th to endNight
30%10%29%19%8%
704
November1st to 15thNight
26%8%26%25%12%
700
16th to endNight
31%14%25%22%5%
720
December1st to 15thNight
34%13%28%18%3
897
16th to endNight
30%12%33%19%2
960
Page generated at 2017-09-19 07:32:28. Version ac04

Copyright 2017 A. Danko


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