Grundy Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grundy Center 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
37%
16037
19%
46917
10%
15990
45%
15990
27%
30170

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
14%
2500
6%
895
35%
895
23%
1727
January16th to endNight
22%
960
16%
2496
5%
960
31%
960
20%
1818
February1st to 15thNight
23%
880
13%
2288
4%
876
29%
876
21%
1647
February16th to endNight
28%
714
19%
1976
6%
714
37%
714
24%
1324
March1st to 15thNight
32%
579
20%
2019
12%
579
42%
579
24%
1240
March16th to endNight
26%
576
12%
2094
7%
576
34%
576
16%
1444
April1st to 15thNight
30%
539
17%
1797
13%
539
39%
539
22%
1145
April16th to endNight
32%
540
19%
1737
12%
540
45%
540
23%
1146
May1st to 15thNight
37%
540
18%
1536
11%
540
44%
540
27%
1015
May16th to endNight
44%
563
17%
1497
8%
561
50%
561
30%
993
June1st to 15thNight
50%
540
15%
1440
7%
540
53%
540
35%
907
June16th to endNight
52%
540
19%
1440
8%
540
57%
540
39%
862
July1st to 15thNight
68%
510
17%
1360
9%
510
70%
510
46%
776
July16th to endNight
71%
564
25%
1490
18%
531
74%
531
49%
793
August1st to 15thNight
67%
539
22%
1610
21%
536
70%
536
38%
904
August16th to endNight
60%
573
22%
1836
23%
573
65%
573
35%
1039
September1st to 15thNight
60%
540
27%
1800
27%
540
67%
540
37%
949
September16th to endNight
49%
559
25%
1862
18%
559
59%
559
35%
1017
October1st to 15thNight
40%
660
26%
1980
16%
660
48%
660
32%
1174
October16th to endNight
34%
704
20%
2112
10%
704
42%
704
26%
1326
November1st to 15thNight
32%
757
25%
2319
13%
757
44%
757
30%
1368
November16th to endNight
27%
900
16%
2520
7%
900
34%
900
25%
1660
December1st to 15thNight
21%
900
13%
2520
4%
900
29%
900
18%
1843
December16th to endNight
22%
960
15%
2688
5%
960
31%
960
15%
2053

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%7%36%5%3445%7%38%
47922
Night
12%7%35%5%24446%43%
47093
Cloud CoverDay
13%7%36%5%3445%7%37%
47931
Night
12%7%35%5%24446%42%
47097
TransparencyDay
45%413%23%11%1
47615
Night
41%313%25%14%1
46918
SeeingDay
15%7%27%28%16%4
6051
Night
15%7%31%31%12%1
16037

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
9%10%6%7%6%5%6%447%30%
1437
16th to endDay
14%10%6%9%6%36%447%24%
1728
February1st to 15thDay
12%12%5%8%5%25%447%31%
1575
16th to endDay
13%10%36%5%35%45%6%34%
1497
March1st to 15thDay
13%9%37%5%245%5%7%32%
1940
16th to endDay
18%11%5%6%5%34347%28%
2130
April1st to 15thDay
18%9%35%5%24446%33%
2151
16th to endDay
25%8%36%5%24445%29%
2220
May1st to 15thDay
20%7%35%5%35%35%6%32%
2415
16th to endDay
15%6%35%6%345%47%36%
2617
June1st to 15thDay
13%5%25%5%35%45%8%40%
2520
16th to endDay
9%425%5%36%5%5%9%41%
2520
July1st to 15thDay
7%425%5%45%46%7%46%
2520
16th to endDay
7%325%445%5%7%8%46%
2574
August1st to 15thDay
7%435%5%35%5%5%8%43%
2340
16th to endDay
11%6%25%5%3445%7%42%
2365
September1st to 15thDay
11%5%2432235%7%51%
2160
16th to endDay
12%6%14434446%47%
1854
October1st to 15thDay
15%5%26%423346%45%
1650
16th to endDay
16%7%26%324346%41%
1760
November1st to 15thDay
11%6%4442425%6%47%
1533
16th to endDay
15%9%37%423347%37%
1440
December1st to 15thDay
18%12%38%5%35%446%26%
1440
16th to endDay
17%14%6%10%6%34345%23%
1536
January1st to 15thNight
10%8%47%6%35%45%7%36%
2500
16th to endNight
12%11%5%8%6%2435%6%33%
2496
February1st to 15thNight
11%12%5%9%5%225%5%6%34%
2285
16th to endNight
12%8%35%6%34446%42%
1976
March1st to 15thNight
14%8%35%423236%44%
2007
16th to endNight
16%10%37%5%34446%32%
2094
April1st to 15thNight
15%8%35%5%2335%5%40%
1797
16th to endNight
21%6%25%412346%39%
1737
May1st to 15thNight
14%6%25%5%2447%8%39%
1536
16th to endNight
12%5%35%5%345%45%44%
1496
June1st to 15thNight
9%5%25%4345%5%10%45%
1440
16th to endNight
7%324435%46%8%49%
1440
July1st to 15thNight
5%2124335%6%8%56%
1440
16th to endNight
421332445%10%56%
1592
August1st to 15thNight
5%4244345%5%7%52%
1620
16th to endNight
10%425%423345%54%
1836
September1st to 15thNight
10%424312346%57%
1800
16th to endNight
11%5%14313347%54%
1862
October1st to 15thNight
13%414423246%50%
1980
16th to endNight
15%6%24324447%43%
2112
November1st to 15thNight
10%7%25%423335%51%
2319
16th to endNight
14%8%45%324345%42%
2520
December1st to 15thNight
15%11%38%6%35%45%6%30%
2520
16th to endNight
20%12%47%6%3434429%
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
9%10%6%8%6%5%6%5%47%29%
1437
16th to endDay
14%11%6%9%7%36%45%6%24%
1728
February1st to 15thDay
12%12%5%8%6%2435%7%30%
1575
16th to endDay
13%10%36%5%25%5%5%6%35%
1497
March1st to 15thDay
14%9%47%5%35%45%7%32%
1951
16th to endDay
18%11%47%5%25%446%29%
2128
April1st to 15thDay
18%8%36%5%245%46%33%
2151
16th to endDay
24%8%36%5%24436%29%
2220
May1st to 15thDay
20%7%36%5%3445%7%32%
2415
16th to endDay
14%7%45%5%345%5%7%36%
2617
June1st to 15thDay
12%6%245%25%5%5%8%39%
2520
16th to endDay
9%425%5%46%5%5%8%42%
2520
July1st to 15thDay
6%5%245%36%5%5%8%46%
2520
16th to endDay
6%4145%35%5%6%9%45%
2574
August1st to 15thDay
7%425%5%36%5%6%7%43%
2340
16th to endDay
11%5%26%5%3445%7%42%
2365
September1st to 15thDay
11%42432235%6%51%
2160
16th to endDay
11%6%24434446%47%
1854
October1st to 15thDay
15%6%25%422346%45%
1650
16th to endDay
16%8%25%423346%41%
1760
November1st to 15thDay
11%6%35%424347%46%
1533
16th to endDay
15%10%36%5%1335%7%37%
1440
December1st to 15thDay
17%12%47%6%35%446%26%
1440
16th to endDay
18%14%6%10%6%3343423%
1536
January1st to 15thNight
10%8%47%6%35%45%6%36%
2500
16th to endNight
12%11%5%8%6%24446%33%
2496
February1st to 15thNight
11%11%5%9%5%23447%33%
2278
16th to endNight
12%8%347%24445%42%
1976
March1st to 15thNight
15%8%25%422336%44%
2019
16th to endNight
15%10%37%6%34445%32%
2094
April1st to 15thNight
14%8%36%42435%6%39%
1797
16th to endNight
21%7%24423346%39%
1737
May1st to 15thNight
14%5%26%5%2446%8%38%
1535
16th to endNight
11%5%35%5%345%5%6%43%
1496
June1st to 15thNight
9%5%245%25%5%5%11%43%
1440
16th to endNight
7%32443446%8%49%
1440
July1st to 15thNight
5%233345%5%8%56%
1440
16th to endNight
421332446%10%56%
1592
August1st to 15thNight
6%3243345%5%8%52%
1620
16th to endNight
10%424423346%54%
1836
September1st to 15thNight
9%424313246%57%
1800
16th to endNight
10%41431335%7%54%
1862
October1st to 15thNight
12%5%24423336%49%
1980
16th to endNight
14%7%25%324346%43%
2112
November1st to 15thNight
10%7%25%423336%50%
2319
16th to endNight
14%8%36%424345%42%
2520
December1st to 15thNight
16%10%47%6%35%446%30%
2520
16th to endNight
20%12%47%6%2433428%
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
53%414%15%11%
1438
16th to endDay
59%413%15%6%
1728
February1st to 15thDay
53%314%21%6%
1576
16th to endDay
47%414%21%9%1
1497
March1st to 15thDay
48%5%16%19%8%1
1951
16th to endDay
55%412%19%6%
2130
April1st to 15thDay
50%411%23%9%
2151
16th to endDay
56%310%18%9%
2220
May1st to 15thDay
51%414%22%7%
2415
16th to endDay
45%414%20%11%2
2621
June1st to 15thDay
41%5%15%22%14%
2520
16th to endDay
38%5%12%25%16%1
2520
July1st to 15thDay
36%5%12%28%13%3
2371
16th to endDay
32%5%17%26%15%2
2413
August1st to 15thDay
36%5%13%29%13%1
2326
16th to endDay
40%410%27%14%2
2365
September1st to 15thDay
31%413%29%19%1
2160
16th to endDay
37%412%31%13%1
1854
October1st to 15thDay
40%210%26%19%1
1650
16th to endDay
44%214%25%12%
1760
November1st to 15thDay
37%312%28%16%1
1533
16th to endDay
46%418%22%6%
1440
December1st to 15thDay
58%314%16%6%1
1440
16th to endDay
64%410%12%7%
1536
January1st to 15thNight
47%415%19%13%
2500
16th to endNight
51%314%19%9%
2496
February1st to 15thNight
50%413%21%9%
2288
16th to endNight
43%412%25%11%2
1976
March1st to 15thNight
42%212%27%13%1
2019
16th to endNight
52%314%20%7%
2094
April1st to 15thNight
45%211%26%11%2
1797
16th to endNight
46%311%23%12%2
1737
May1st to 15thNight
42%5%13%24%13%
1536
16th to endNight
40%5%12%23%15%2
1498
June1st to 15thNight
34%6%16%25%15%2
1440
16th to endNight
30%412%28%18%4
1440
July1st to 15thNight
24%5%16%32%16%4
1360
16th to endNight
23%317%32%20%2
1490
August1st to 15thNight
28%5%12%34%15%3
1610
16th to endNight
32%413%26%19%5%
1836
September1st to 15thNight
29%38%30%26%2
1800
16th to endNight
30%313%31%19%1
1862
October1st to 15thNight
35%39%25%22%3
1980
16th to endNight
40%313%24%14%2
2112
November1st to 15thNight
36%311%26%19%3
2319
16th to endNight
44%215%27%9%1
2520
December1st to 15thNight
54%312%20%8%
2520
16th to endNight
58%411%15%9%
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%11%44%17%31
90
16th to endDay
19%11%31%29%5%3
96
February1st to 15thDay
11%27%36%18%5%
90
16th to endDay
25%8%30%22%9%2
81
March1st to 15thDay
15%21%40%20%3
90
16th to endDay
38%11%26%17%41
114
April1st to 15thDay
20%11%31%24%11%
270
16th to endDay
31%9%30%18%9%1
330
May1st to 15thDay
22%12%28%23%10%1
468
16th to endDay
16%10%28%28%14%2
517
June1st to 15thDay
10%5%29%32%18%3
495
16th to endDay
8%7%33%31%15%3
495
July1st to 15thDay
8%224%34%18%11%
475
16th to endDay
8%220%35%27%6%
515
August1st to 15thDay
9%120%36%26%6%
493
16th to endDay
15%315%33%22%8%
405
September1st to 15thDay
10%220%30%27%8%
315
16th to endDay
13%6%26%27%21%3
160
October1st to 15thDay
6%11%28%30%17%5%
90
16th to endDay
21%8%33%28%7%1
96
November1st to 15thDay
47%34%33%16%3
90
16th to endDay
37%11%32%16%2
90
December1st to 15thDay
22%18%33%18%6%
90
16th to endDay
23%19%36%15%4
96
January1st to 15thNight
14%11%36%28%7%
900
16th to endNight
17%10%37%28%5%
960
February1st to 15thNight
17%10%37%25%7%
880
16th to endNight
16%10%37%27%7%
714
March1st to 15thNight
18%10%33%26%10%
579
16th to endNight
19%8%35%26%8%1
576
April1st to 15thNight
18%10%33%30%6%
539
16th to endNight
24%6%32%28%6%1
540
May1st to 15thNight
17%7%32%33%7%
540
16th to endNight
14%429%37%14%
563
June1st to 15thNight
10%329%40%15%
540
16th to endNight
7%329%42%17%
540
July1st to 15thNight
5%118%45%26%2
510
16th to endNight
5%116%45%28%2
564
August1st to 15thNight
7%115%41%30%2
539
16th to endNight
11%118%35%28%4
573
September1st to 15thNight
11%217%38%24%5%
540
16th to endNight
12%5%27%32%21%1
559
October1st to 15thNight
15%5%33%29%14%1
660
16th to endNight
19%8%31%29%11%
704
November1st to 15thNight
15%10%36%27%10%
757
16th to endNight
17%12%37%24%8%
900
December1st to 15thNight
22%11%34%26%4
900
16th to endNight
26%8%30%25%7%
960
Page generated at 2017-09-21 06:18:21. Version ac04

Copyright 2017 A. Danko


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