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 2017-04-08.

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%
15517
17%
45440
10%
15474
44%
15474
23%
30476

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
22%
900
14%
2506
5%
895
31%
895
19%
1836
January16th to endNight
24%
960
12%
2628
4%
960
30%
960
16%
1991
February1st to 15thNight
23%
840
14%
2251
4%
840
30%
840
20%
1616
February16th to endNight
26%
631
18%
1893
8%
631
35%
631
18%
1323
March1st to 15thNight
30%
720
14%
2160
8%
720
35%
720
20%
1469
March16th to endNight
30%
582
15%
1998
11%
582
37%
582
17%
1373
April1st to 15thNight
30%
518
15%
1727
10%
518
39%
518
19%
1172
April16th to endNight
34%
495
18%
1614
11%
495
45%
495
23%
1073
May1st to 15thNight
34%
495
15%
1412
8%
495
41%
495
21%
1009
May16th to endNight
47%
515
17%
1370
9%
513
53%
513
32%
883
June1st to 15thNight
51%
495
16%
1320
10%
495
54%
495
33%
844
June16th to endNight
51%
495
14%
1320
8%
495
54%
495
30%
871
July1st to 15thNight
64%
465
18%
1240
11%
465
67%
465
41%
742
July16th to endNight
68%
522
19%
1305
15%
489
70%
489
42%
763
August1st to 15thNight
76%
494
24%
1435
23%
491
77%
491
43%
779
August16th to endNight
65%
525
19%
1750
19%
525
69%
525
33%
990
September1st to 15thNight
62%
495
29%
1650
28%
495
68%
495
35%
897
September16th to endNight
54%
635
25%
1793
17%
635
60%
635
34%
1071
October1st to 15thNight
43%
660
25%
1939
17%
660
50%
660
31%
1197
October16th to endNight
30%
704
18%
2214
9%
704
41%
704
22%
1431
November1st to 15thNight
34%
700
23%
2276
16%
700
44%
700
26%
1383
November16th to endNight
27%
811
16%
2431
8%
811
35%
811
19%
1685
December1st to 15thNight
21%
900
12%
2520
4%
900
28%
900
16%
1906
December16th to endNight
19%
960
11%
2688
3%
960
26%
960
12%
2172

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%
45825
Night
14%7%35%424446%40%
45608
Cloud CoverDay
15%8%36%5%3445%7%36%
45833
Night
15%7%35%424446%40%
45613
TransparencyDay
46%6%12%21%11%1
45511
Night
44%5%12%22%13%1
45440
SeeingDay
17%6%25%26%16%6%
5276
Night
18%7%29%30%12%1
15520

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%
1432
16th to endDay
14%15%5%11%6%34445%25%
1593
February1st to 15thDay
13%13%6%7%6%36%436%28%
1609
16th to endDay
13%12%47%6%35%25%6%33%
1580
March1st to 15thDay
15%9%38%6%23338%34%
1793
16th to endDay
17%9%36%6%35%45%6%30%
2232
April1st to 15thDay
19%10%46%5%35%446%30%
2060
16th to endDay
20%8%36%5%33446%33%
2015
May1st to 15thDay
21%8%46%6%35%5%5%7%26%
2207
16th to endDay
13%6%35%5%35%5%5%6%38%
2393
June1st to 15thDay
14%5%246%25%5%5%7%38%
2310
16th to endDay
10%5%245%25%6%6%10%39%
2310
July1st to 15thDay
7%4245%35%5%6%9%44%
2310
16th to endDay
8%426%6%36%5%6%9%39%
2459
August1st to 15thDay
7%4246%445%7%9%43%
2185
16th to endDay
12%5%245%2446%7%44%
2100
September1st to 15thDay
14%313424447%49%
1980
16th to endDay
11%5%35%5%335%5%7%44%
1826
October1st to 15thDay
16%6%145%23245%45%
1689
16th to endDay
19%8%25%5%34345%36%
1657
November1st to 15thDay
13%7%35%5%245%46%39%
1582
16th to endDay
18%10%47%423226%37%
1527
December1st to 15thDay
19%13%47%5%34335%27%
1440
16th to endDay
20%15%5%8%6%3434423%
1536
January1st to 15thNight
15%11%48%434345%33%
2506
16th to endNight
13%10%6%9%6%345%45%28%
2628
February1st to 15thNight
14%12%5%7%423435%36%
2249
16th to endNight
16%11%46%5%24346%34%
1893
March1st to 15thNight
15%9%45%433445%38%
2147
16th to endNight
17%9%45%5%3445%6%33%
1998
April1st to 15thNight
20%7%34424445%37%
1727
16th to endNight
20%7%34413245%41%
1614
May1st to 15thNight
17%6%26%5%346%5%7%34%
1412
16th to endNight
11%5%245%2447%9%42%
1368
June1st to 15thNight
11%415%42446%6%46%
1320
16th to endNight
8%435%436%6%6%7%42%
1320
July1st to 15thNight
7%32341445%9%52%
1320
16th to endNight
6%3233345%6%10%48%
1401
August1st to 15thNight
421342445%9%55%
1444
16th to endNight
10%32432445%7%51%
1750
September1st to 15thNight
9%414423345%56%
1650
16th to endNight
9%4235%23447%51%
1793
October1st to 15thNight
12%5%24424345%49%
1939
16th to endNight
19%7%24324336%41%
2214
November1st to 15thNight
12%7%35%323335%48%
2276
16th to endNight
18%9%36%423345%37%
2431
December1st to 15thNight
20%11%38%5%24335%29%
2520
16th to endNight
23%13%47%6%3443423%
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
14%12%6%6%5%36%5%5%6%26%
1432
16th to endDay
15%14%6%11%6%24435%25%
1593
February1st to 15thDay
13%13%6%7%5%46%346%28%
1609
16th to endDay
14%11%47%7%34347%33%
1580
March1st to 15thDay
17%9%47%5%13348%34%
1803
16th to endDay
18%9%36%5%35%45%6%30%
2230
April1st to 15thDay
19%10%5%6%5%24446%30%
2060
16th to endDay
21%8%26%5%2335%6%33%
2015
May1st to 15thDay
21%7%47%6%35%5%47%26%
2207
16th to endDay
14%5%35%5%35%5%5%7%38%
2393
June1st to 15thDay
14%425%6%25%5%6%7%38%
2310
16th to endDay
11%5%25%5%25%6%8%9%38%
2310
July1st to 15thDay
7%4245%35%5%7%10%43%
2310
16th to endDay
8%5%25%6%45%5%6%9%40%
2459
August1st to 15thDay
7%4245%35%5%7%9%43%
2185
16th to endDay
12%5%25%42446%7%44%
2100
September1st to 15thDay
14%31342335%7%49%
1980
16th to endDay
10%5%35%43445%7%44%
1826
October1st to 15thDay
17%5%345%13335%45%
1689
16th to endDay
20%6%25%5%34345%36%
1657
November1st to 15thDay
13%8%35%5%245%46%39%
1582
16th to endDay
18%10%46%5%32236%37%
1527
December1st to 15thDay
19%13%47%5%35%335%27%
1440
16th to endDay
20%15%5%8%6%3334423%
1536
January1st to 15thNight
15%11%48%5%3444433%
2506
16th to endNight
13%11%6%9%6%35%5%36%28%
2628
February1st to 15thNight
14%12%6%5%423335%36%
2242
16th to endNight
16%10%47%5%23346%34%
1893
March1st to 15thNight
16%10%34433345%38%
2160
16th to endNight
18%8%35%5%25%447%33%
1998
April1st to 15thNight
20%7%44424445%37%
1727
16th to endNight
19%7%3441334441%
1614
May1st to 15thNight
17%6%26%6%345%6%7%33%
1411
16th to endNight
12%5%145%235%6%9%42%
1368
June1st to 15thNight
11%4245%25%46%6%46%
1320
16th to endNight
9%425%436%6%6%8%42%
1320
July1st to 15thNight
7%3133235%5%9%53%
1320
16th to endNight
6%323335%5%7%10%49%
1401
August1st to 15thNight
432232445%9%55%
1444
16th to endNight
10%41442445%7%50%
1750
September1st to 15thNight
9%314424245%56%
1650
16th to endNight
10%4235%33447%50%
1793
October1st to 15thNight
12%5%24423345%49%
1939
16th to endNight
19%7%24423336%42%
2214
November1st to 15thNight
13%6%25%323345%48%
2276
16th to endNight
19%8%35%423346%37%
2431
December1st to 15thNight
20%10%48%5%34346%29%
2520
16th to endNight
23%13%48%6%3443423%
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
55%6%14%15%8%
1433
16th to endDay
60%5%12%14%6%
1593
February1st to 15thDay
57%5%10%17%7%
1611
16th to endDay
52%6%11%21%8%
1580
March1st to 15thDay
50%5%14%20%8%
1803
16th to endDay
53%6%13%19%6%
2232
April1st to 15thDay
55%410%21%8%
2060
16th to endDay
51%5%12%17%10%2
2015
May1st to 15thDay
57%6%12%18%5%
2207
16th to endDay
45%7%11%20%13%1
2397
June1st to 15thDay
42%7%12%23%12%
2310
16th to endDay
37%8%14%22%15%1
2310
July1st to 15thDay
34%7%15%26%14%1
2161
16th to endDay
37%8%18%21%11%2
2292
August1st to 15thDay
33%7%14%29%13%1
2170
16th to endDay
37%5%13%24%16%2
2100
September1st to 15thDay
34%5%10%27%19%1
1980
16th to endDay
37%5%12%27%15%1
1826
October1st to 15thDay
41%410%28%14%
1689
16th to endDay
48%5%13%21%9%1
1657
November1st to 15thDay
44%411%24%12%1
1582
16th to endDay
51%315%23%5%
1527
December1st to 15thDay
59%413%16%6%
1440
16th to endDay
64%411%10%7%
1536
January1st to 15thNight
53%410%19%10%
2506
16th to endNight
55%6%13%15%9%
2628
February1st to 15thNight
51%412%20%11%
2251
16th to endNight
50%412%22%8%2
1893
March1st to 15thNight
47%5%14%18%11%1
2160
16th to endNight
50%5%13%20%9%
1998
April1st to 15thNight
48%49%21%14%1
1727
16th to endNight
46%49%24%11%4
1614
May1st to 15thNight
48%7%13%19%11%
1412
16th to endNight
35%7%14%21%17%3
1370
June1st to 15thNight
36%6%13%25%18%
1320
16th to endNight
37%8%12%18%19%3
1320
July1st to 15thNight
28%6%12%29%20%2
1240
16th to endNight
26%6%18%27%17%2
1305
August1st to 15thNight
24%6%14%31%20%2
1435
16th to endNight
31%6%13%26%18%4
1750
September1st to 15thNight
30%49%27%26%2
1650
16th to endNight
33%5%10%31%17%2
1793
October1st to 15thNight
36%410%25%20%1
1939
16th to endNight
43%412%24%12%1
2214
November1st to 15thNight
39%411%23%18%3
2276
16th to endNight
49%412%21%10%
2431
December1st to 15thNight
57%410%20%7%
2520
16th to endNight
64%5%9%13%6%
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
24%10%33%27%4
90
16th to endDay
25%5%32%27%7%3
96
February1st to 15thDay
22%15%41%15%5%
90
16th to endDay
33%11%25%23%6%
81
March1st to 15thDay
31%12%36%17%2
90
16th to endDay
30%8%27%18%13%1
216
April1st to 15thDay
26%9%29%22%11%
240
16th to endDay
20%8%28%24%10%6%
210
May1st to 15thDay
28%10%27%22%8%3
299
16th to endDay
17%8%28%25%14%5%
437
June1st to 15thDay
14%5%32%27%15%4
420
16th to endDay
13%329%31%15%6%
420
July1st to 15thDay
9%5%24%29%21%11%
400
16th to endDay
10%319%32%24%10%
445
August1st to 15thDay
8%218%31%27%12%
374
16th to endDay
13%5%11%29%29%11%
268
September1st to 15thDay
14%314%31%25%9%
255
16th to endDay
11%7%20%27%23%9%
254
October1st to 15thDay
15%7%24%24%21%5%
129
16th to endDay
28%7%26%32%6%
96
November1st to 15thDay
7%8%31%25%18%7%
90
16th to endDay
38%10%33%7%10%
90
December1st to 15thDay
25%10%35%23%32
90
16th to endDay
33%12%46%5%2
96
January1st to 15thNight
21%11%37%23%5%
900
16th to endNight
18%11%34%30%5%
960
February1st to 15thNight
20%9%38%25%5%
843
16th to endNight
21%11%33%25%7%
631
March1st to 15thNight
20%8%34%29%6%
720
16th to endNight
21%8%32%26%8%1
582
April1st to 15thNight
24%10%32%27%5%
518
16th to endNight
22%7%31%28%9%
495
May1st to 15thNight
20%5%33%28%10%
495
16th to endNight
13%230%37%16%
515
June1st to 15thNight
12%227%43%13%
495
16th to endNight
10%329%37%18%1
495
July1st to 15thNight
10%117%42%26%2
465
16th to endNight
7%115%47%26%1
522
August1st to 15thNight
6%19%51%28%3
494
16th to endNight
12%114%36%31%4
525
September1st to 15thNight
10%318%33%27%5%
495
16th to endNight
12%6%20%32%25%3
635
October1st to 15thNight
15%6%29%29%18%1
660
16th to endNight
23%9%32%24%10%
704
November1st to 15thNight
16%8%37%26%11%
700
16th to endNight
22%11%33%25%7%
811
December1st to 15thNight
25%9%36%22%6%
900
16th to endNight
29%9%31%25%3
960
Page generated at 2017-04-09 05:54:15. Version ac04

Copyright 2017 A. Danko


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