Rockford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rockford clear sky chart from 2005-11-05 to 2018-03-21.

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
37%
16813
17%
49222
10%
16770
44%
16770
24%
32888

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
23%
975
14%
2716
5%
970
32%
970
19%
1970
January16th to endNight
24%
1040
12%
2847
4%
1040
30%
1040
16%
2142
February1st to 15thNight
23%
911
14%
2442
4%
911
30%
911
20%
1766
February16th to endNight
25%
683
17%
2049
8%
683
34%
683
18%
1440
March1st to 15thNight
31%
780
15%
2340
8%
780
36%
780
21%
1572
March16th to endNight
30%
601
16%
2065
12%
601
38%
601
18%
1413
April1st to 15thNight
30%
539
15%
1797
10%
539
39%
539
19%
1224
April16th to endNight
34%
540
18%
1761
12%
540
44%
540
22%
1181
May1st to 15thNight
36%
540
14%
1540
8%
540
42%
540
21%
1091
May16th to endNight
46%
563
17%
1498
8%
561
52%
561
32%
969
June1st to 15thNight
54%
540
15%
1440
10%
540
56%
540
35%
898
June16th to endNight
50%
540
16%
1440
8%
540
54%
540
31%
943
July1st to 15thNight
64%
510
17%
1360
11%
510
66%
510
41%
811
July16th to endNight
68%
564
21%
1417
16%
531
71%
531
42%
821
August1st to 15thNight
76%
539
23%
1566
22%
536
77%
536
42%
852
August16th to endNight
66%
573
20%
1910
20%
573
69%
573
33%
1076
September1st to 15thNight
63%
540
28%
1800
28%
540
68%
540
36%
961
September16th to endNight
55%
693
27%
1956
19%
693
61%
693
35%
1158
October1st to 15thNight
42%
720
23%
2115
16%
720
48%
720
29%
1324
October16th to endNight
31%
768
19%
2416
10%
768
41%
768
22%
1566
November1st to 15thNight
33%
760
22%
2471
15%
760
43%
760
25%
1528
November16th to endNight
26%
879
18%
2634
9%
879
36%
879
20%
1790
December1st to 15thNight
21%
975
12%
2730
4%
975
29%
975
17%
2053
December16th to endNight
19%
1040
11%
2912
3%
1040
26%
1040
12%
2339

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
14%8%36%5%3445%7%36%
49633
Night
14%7%35%424446%40%
49390
Cloud CoverDay
14%7%36%5%3445%7%36%
49641
Night
14%7%35%5%24446%40%
49395
TransparencyDay
46%6%12%21%11%1
49319
Night
44%5%12%22%14%1
49222
SeeingDay
17%7%26%26%16%5%
6581
Night
18%7%30%30%12%1
16816

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
14%11%6%6%6%25%6%5%7%26%
1552
16th to endDay
14%14%5%11%6%34445%25%
1726
February1st to 15thDay
13%13%6%7%6%36%436%28%
1748
16th to endDay
14%12%47%6%3425%6%32%
1710
March1st to 15thDay
15%9%38%5%23347%36%
1943
16th to endDay
17%9%36%6%35%45%6%30%
2293
April1st to 15thDay
18%10%46%5%35%446%30%
2151
16th to endDay
20%9%36%433446%33%
2198
May1st to 15thDay
20%7%36%6%35%45%6%28%
2409
16th to endDay
14%6%35%5%35%5%5%6%36%
2617
June1st to 15thDay
13%4245%25%5%5%7%41%
2520
16th to endDay
10%5%245%25%6%7%10%38%
2520
July1st to 15thDay
7%425%5%35%5%6%9%44%
2520
16th to endDay
7%425%5%35%5%6%9%41%
2655
August1st to 15thDay
6%4246%446%7%9%42%
2383
16th to endDay
11%5%345%2445%7%44%
2292
September1st to 15thDay
13%312424447%50%
2160
16th to endDay
10%5%245%335%5%7%46%
1992
October1st to 15thDay
18%6%25%5%24245%43%
1842
16th to endDay
19%8%25%5%34345%37%
1807
November1st to 15thDay
15%8%35%5%245%47%38%
1717
16th to endDay
17%9%36%423226%39%
1654
December1st to 15thDay
17%13%47%5%34445%29%
1560
16th to endDay
19%15%5%8%6%3434424%
1664
January1st to 15thNight
15%11%48%5%34345%34%
2716
16th to endNight
13%10%6%9%6%345%45%29%
2847
February1st to 15thNight
14%12%5%7%5%2343435%
2440
16th to endNight
16%11%46%6%24346%34%
2049
March1st to 15thNight
14%9%45%433445%40%
2327
16th to endNight
17%9%45%5%3445%6%34%
2065
April1st to 15thNight
20%7%34424445%37%
1797
16th to endNight
20%7%35%424345%40%
1761
May1st to 15thNight
18%6%26%5%346%5%6%35%
1540
16th to endNight
10%5%245%2447%9%42%
1496
June1st to 15thNight
10%415%42446%6%49%
1440
16th to endNight
8%435%436%5%7%7%43%
1440
July1st to 15thNight
6%3234245%5%9%53%
1440
16th to endNight
6%3233345%6%10%49%
1513
August1st to 15thNight
421342446%10%54%
1575
16th to endNight
9%32442445%8%51%
1910
September1st to 15thNight
8%314323345%57%
1800
16th to endNight
9%4235%33447%52%
1956
October1st to 15thNight
13%5%24424345%48%
2115
16th to endNight
19%7%24324336%41%
2416
November1st to 15thNight
13%7%35%324335%46%
2471
16th to endNight
17%8%36%423345%39%
2634
December1st to 15thNight
19%10%38%5%34335%30%
2730
16th to endNight
22%13%47%6%35%43423%
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
14%11%5%7%5%36%5%6%6%26%
1552
16th to endDay
14%14%6%11%6%24435%25%
1726
February1st to 15thDay
13%13%6%7%5%46%346%28%
1748
16th to endDay
14%12%47%6%24246%32%
1710
March1st to 15thDay
16%8%47%5%13347%35%
1953
16th to endDay
18%9%36%5%35%45%6%30%
2291
April1st to 15thDay
19%9%46%5%34446%30%
2151
16th to endDay
21%8%26%5%2335%6%33%
2198
May1st to 15thDay
20%7%47%6%35%5%46%28%
2409
16th to endDay
14%5%35%5%35%5%5%7%36%
2617
June1st to 15thDay
13%425%6%25%5%6%7%40%
2520
16th to endDay
10%5%25%5%25%6%8%9%38%
2520
July1st to 15thDay
7%4245%35%5%7%10%43%
2520
16th to endDay
7%5%25%6%35%5%6%9%41%
2655
August1st to 15thDay
7%4246%35%5%7%9%42%
2383
16th to endDay
12%5%25%43445%7%44%
2292
September1st to 15thDay
13%31342335%7%50%
2160
16th to endDay
9%5%25%43445%7%46%
1992
October1st to 15thDay
18%5%345%13335%43%
1842
16th to endDay
19%7%25%5%34345%37%
1807
November1st to 15thDay
15%8%35%5%245%46%38%
1717
16th to endDay
17%10%36%422236%39%
1654
December1st to 15thDay
18%12%47%5%34346%29%
1560
16th to endDay
19%15%5%8%6%3334424%
1664
January1st to 15thNight
15%11%47%5%3344434%
2716
16th to endNight
13%11%5%9%6%35%5%36%29%
2847
February1st to 15thNight
14%12%5%6%5%24335%35%
2433
16th to endNight
17%10%47%5%23346%34%
2049
March1st to 15thNight
15%9%35%433346%39%
2340
16th to endNight
18%8%35%5%25%447%34%
2065
April1st to 15thNight
20%7%44424445%37%
1797
16th to endNight
19%7%35%423345%40%
1761
May1st to 15thNight
18%6%25%6%345%5%7%34%
1539
16th to endNight
11%5%245%335%6%9%42%
1496
June1st to 15thNight
10%42442445%6%49%
1440
16th to endNight
9%425%5%36%6%6%7%43%
1440
July1st to 15thNight
6%3133245%5%9%53%
1440
16th to endNight
6%323325%5%6%10%50%
1513
August1st to 15thNight
432242445%10%55%
1575
16th to endNight
9%41442445%8%50%
1910
September1st to 15thNight
9%315%324245%57%
1800
16th to endNight
9%3235%33447%51%
1956
October1st to 15thNight
14%6%24423345%48%
2115
16th to endNight
19%7%24424336%41%
2416
November1st to 15thNight
14%7%35%423345%46%
2471
16th to endNight
18%8%35%423346%38%
2634
December1st to 15thNight
19%10%48%5%34345%30%
2730
16th to endNight
22%13%48%6%3443423%
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
54%6%13%15%9%
1553
16th to endDay
59%412%15%6%
1726
February1st to 15thDay
57%5%10%17%8%1
1750
16th to endDay
52%5%11%21%8%1
1710
March1st to 15thDay
49%5%13%22%8%
1953
16th to endDay
53%6%13%19%6%
2293
April1st to 15thDay
55%411%20%8%
2151
16th to endDay
51%5%11%18%11%2
2198
May1st to 15thDay
56%6%12%19%5%
2409
16th to endDay
45%7%11%20%13%1
2621
June1st to 15thDay
40%7%12%24%14%
2520
16th to endDay
37%8%14%22%15%1
2520
July1st to 15thDay
34%7%16%25%14%1
2371
16th to endDay
36%8%17%22%12%2
2488
August1st to 15thDay
33%8%14%28%13%1
2368
16th to endDay
37%6%13%24%15%2
2292
September1st to 15thDay
33%5%10%28%20%1
2160
16th to endDay
35%5%12%28%16%1
1992
October1st to 15thDay
43%49%26%14%
1842
16th to endDay
47%413%22%10%1
1807
November1st to 15thDay
45%411%23%12%1
1717
16th to endDay
48%315%25%6%
1654
December1st to 15thDay
57%413%16%7%
1560
16th to endDay
64%411%11%7%
1664
January1st to 15thNight
52%410%19%12%
2716
16th to endNight
54%6%14%15%8%
2847
February1st to 15thNight
51%311%19%11%
2442
16th to endNight
51%411%21%8%2
2049
March1st to 15thNight
46%5%13%20%12%1
2340
16th to endNight
50%5%13%20%9%
2065
April1st to 15thNight
48%49%21%13%1
1797
16th to endNight
46%49%23%11%4
1761
May1st to 15thNight
47%7%13%19%11%
1540
16th to endNight
35%7%15%21%16%2
1498
June1st to 15thNight
33%5%13%24%20%1
1440
16th to endNight
37%7%12%20%19%3
1440
July1st to 15thNight
28%6%12%29%20%2
1360
16th to endNight
26%6%17%27%18%3
1417
August1st to 15thNight
24%6%14%32%19%2
1566
16th to endNight
31%5%13%26%18%3
1910
September1st to 15thNight
29%49%27%27%2
1800
16th to endNight
32%5%10%32%18%1
1956
October1st to 15thNight
38%49%24%20%1
2115
16th to endNight
44%412%24%12%1
2416
November1st to 15thNight
40%410%23%17%3
2471
16th to endNight
47%412%23%10%
2634
December1st to 15thNight
56%410%20%7%
2730
16th to endNight
64%5%10%13%6%
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
21%9%32%30%5%
135
16th to endDay
21%7%36%27%42
144
February1st to 15thDay
20%14%41%18%4
135
16th to endDay
35%14%26%19%4
120
March1st to 15thDay
25%13%33%20%6%
135
16th to endDay
28%8%27%18%14%2
233
April1st to 15thDay
25%9%32%21%10%
270
16th to endDay
21%11%27%24%10%5%
270
May1st to 15thDay
24%11%27%23%9%3
366
16th to endDay
19%10%28%23%12%5%
517
June1st to 15thDay
12%431%30%16%4
495
16th to endDay
13%5%31%29%14%5%
495
July1st to 15thDay
8%424%30%21%10%
475
16th to endDay
9%319%32%24%10%
515
August1st to 15thDay
8%218%31%27%12%
445
16th to endDay
12%5%13%29%26%12%
332
September1st to 15thDay
13%215%29%28%9%
315
16th to endDay
9%6%20%28%24%8%
314
October1st to 15thDay
20%7%25%23%18%3
177
16th to endDay
27%9%25%31%6%
144
November1st to 15thDay
17%8%32%20%16%5%
135
16th to endDay
30%11%36%13%8%
135
December1st to 15thDay
20%13%39%20%41
135
16th to endDay
27%13%45%10%2
144
January1st to 15thNight
21%11%37%24%6%
975
16th to endNight
18%11%34%30%5%
1040
February1st to 15thNight
21%9%37%25%5%
914
16th to endNight
22%11%33%24%6%
683
March1st to 15thNight
19%8%35%30%6%
780
16th to endNight
20%8%32%26%9%1
601
April1st to 15thNight
24%10%32%28%5%
539
16th to endNight
21%7%32%28%9%
540
May1st to 15thNight
21%5%31%29%10%
540
16th to endNight
12%332%36%15%
563
June1st to 15thNight
11%226%45%13%
540
16th to endNight
10%230%37%17%
540
July1st to 15thNight
9%118%41%26%2
510
16th to endNight
7%115%46%27%1
564
August1st to 15thNight
6%8%49%30%4
539
16th to endNight
11%113%38%30%4
573
September1st to 15thNight
10%218%34%28%5%
540
16th to endNight
11%5%20%32%25%3
693
October1st to 15thNight
16%6%29%29%17%1
720
16th to endNight
23%9%32%24%9%
768
November1st to 15thNight
17%8%36%26%11%
760
16th to endNight
21%11%34%24%7%
879
December1st to 15thNight
24%10%36%23%6%
975
16th to endNight
28%9%33%24%3
1040
Page generated at 2018-03-22 10:34:20. Version ac04

Copyright 2018 A. Danko


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