Marengo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marengo clear sky chart from 2005-11-06 to 2024-02-15.

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
35%
24780
17%
80451
10%
24681
42%
24681
20%
54876

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 10thNight
21%
941
11%
4393
5%
926
30%
926
11%
3185
January11th to 20thNight
17%
949
11%
4378
4%
930
24%
930
8%
3421
January21st to endNight
19%
1039
7%
4740
4%
1023
25%
1023
8%
3798
February1st to 10thNight
20%
950
13%
2470
4%
950
27%
950
19%
1833
February11th to 20thNight
24%
719
19%
2154
8%
719
33%
719
20%
1463
February21st to endNight
19%
592
18%
1776
5%
592
31%
592
17%
1249
March1st to 10thNight
25%
720
13%
2160
6%
720
32%
720
18%
1496
March11th to 20thNight
32%
671
19%
2109
10%
671
41%
671
23%
1368
March21st to endNight
28%
594
16%
1980
11%
594
35%
594
15%
1434
April1st to 10thNight
25%
540
15%
1800
9%
540
36%
540
19%
1204
April11th to 20thNight
29%
533
19%
1775
13%
533
40%
533
19%
1190
April21st to endNight
31%
540
16%
1720
8%
540
41%
540
22%
1155
May1st to 10thNight
33%
540
14%
1620
8%
540
39%
540
22%
1114
May11th to 20thNight
36%
531
19%
1422
9%
531
44%
531
27%
973
May21st to endNight
46%
582
16%
1551
9%
582
51%
582
28%
1037
June1st to 10thNight
55%
540
17%
1440
10%
540
59%
540
35%
891
June11th to 20thNight
48%
540
20%
1440
12%
540
53%
540
34%
919
June21st to endNight
52%
540
17%
1440
10%
540
56%
540
32%
936
July1st to 10thNight
68%
525
16%
1400
11%
525
69%
525
40%
840
July11th to 20thNight
61%
522
20%
1392
15%
522
64%
522
41%
824
July21st to endNight
66%
591
22%
1487
15%
558
70%
558
41%
882
August1st to 10thNight
70%
537
22%
1437
19%
534
72%
534
39%
858
August11th to 20thNight
69%
534
22%
1776
24%
534
72%
534
37%
957
August21st to endNight
66%
594
24%
1980
24%
594
70%
594
37%
1069
September1st to 10thNight
58%
540
25%
1800
23%
540
63%
540
32%
1022
September11th to 20thNight
58%
613
33%
1873
28%
613
64%
613
36%
1078
September21st to endNight
48%
720
24%
1980
15%
720
54%
720
32%
1218
October1st to 10thNight
46%
720
24%
2060
17%
720
52%
720
31%
1263
October11th to 20thNight
30%
720
22%
2160
10%
720
42%
720
24%
1381
October21st to endNight
28%
792
17%
2565
10%
792
37%
792
19%
1737
November1st to 10thNight
31%
740
25%
2406
15%
740
44%
740
26%
1447
November11th to 20thNight
24%
760
18%
2470
8%
760
36%
760
18%
1663
November21st to endNight
23%
874
17%
2584
8%
874
33%
874
20%
1782
December1st to 10thNight
20%
950
13%
2660
5%
950
28%
950
18%
1949
December11th to 20thNight
20%
950
14%
3210
4%
948
29%
948
14%
2309
December21st to endNight
13%
1037
6%
4843
3%
1026
21%
1026
6%
3931

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%9%47%6%35%5%5%7%36%
78250
Night
15%10%47%5%3445%6%37%
80880
TransparencyDay
47%6%12%21%12%1
77951
Night
47%5%11%21%13%2
80700
SeeingDay
16%11%30%26%13%5%
14764
Night
17%10%32%29%11%1
24809

By Month

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 10thDay
13%14%10%11%7%3444426%
2527
11th to 20thDay
12%13%6%15%6%35%9%7%5%19%
2530
21st to endDay
17%18%10%11%6%23445%19%
2885
February1st to 10thDay
13%13%6%8%7%47%5%5%6%27%
1710
11th to 20thDay
15%11%37%6%4445%5%36%
1786
21st to endDay
14%14%6%9%7%3445%6%30%
1480
March1st to 10thDay
14%13%6%7%7%35%5%35%33%
1800
11th to 20thDay
14%9%36%6%25%45%8%38%
1863
21st to endDay
20%12%47%7%445%5%6%26%
2376
April1st to 10thDay
18%10%6%7%6%34446%32%
2160
11th to 20thDay
17%9%36%6%45%5%5%6%34%
2134
21st to endDay
20%9%37%5%35%5%5%7%31%
2240
May1st to 10thDay
17%8%37%6%46%5%6%8%30%
2340
11th to 20thDay
19%8%36%5%345%5%7%34%
2470
21st to endDay
14%7%36%6%46%6%6%7%37%
2725
June1st to 10thDay
9%5%35%5%35%6%6%8%45%
2520
11th to 20thDay
10%5%24435%5%7%10%45%
2520
21st to endDay
11%6%37%5%35%6%6%9%39%
2520
July1st to 10thDay
7%425%5%35%6%6%9%47%
2520
11th to 20thDay
8%425%435%5%7%9%47%
2520
21st to endDay
7%5%25%6%36%5%6%9%45%
2743
August1st to 10thDay
9%5%25%5%45%7%7%9%44%
2491
11th to 20thDay
10%5%245%45%6%5%9%44%
2125
21st to endDay
9%5%245%35%5%5%8%48%
2376
September1st to 10thDay
13%5%245%3446%7%46%
2160
11th to 20thDay
13%42343345%7%52%
2067
21st to endDay
12%7%25%5%35%46%7%44%
1980
October1st to 10thDay
14%7%35%5%34446%46%
1895
11th to 20thDay
21%9%36%5%3445%7%33%
1800
21st to endDay
22%9%36%5%24345%36%
1789
November1st to 10thDay
13%8%35%4345%5%6%45%
1672
11th to 20thDay
15%12%5%8%5%345%5%7%32%
1710
21st to endDay
18%11%38%6%34346%36%
1595
December1st to 10thDay
15%12%6%9%6%4445%6%30%
1520
11th to 20thDay
12%14%6%10%7%35%5%7%6%27%
1918
21st to endDay
20%21%9%11%8%2433314%
2783
January1st to 10thNight
14%14%8%10%7%3433430%
4428
11th to 20thNight
15%16%7%13%6%337%6%419%
4440
21st to endNight
20%17%8%10%6%34335%20%
4779
February1st to 10thNight
13%14%5%7%7%43446%32%
2470
11th to 20thNight
14%10%47%6%35%446%37%
2153
21st to endNight
18%13%5%6%5%23445%35%
1776
March1st to 10thNight
17%10%45%5%3445%7%35%
2160
11th to 20thNight
12%8%36%5%4445%7%41%
2109
21st to endNight
20%9%5%7%5%44446%32%
1980
April1st to 10thNight
17%8%45%5%35%5%45%38%
1800
11th to 20thNight
20%8%45%5%33446%38%
1775
21st to endNight
18%8%36%5%245%5%7%38%
1720
May1st to 10thNight
15%7%35%5%45%5%6%8%37%
1620
11th to 20thNight
16%6%36%5%2446%7%40%
1421
21st to endNight
13%6%26%6%45%47%8%40%
1551
June1st to 10thNight
10%5%145%35%5%6%9%47%
1440
11th to 20thNight
10%5%34435%5%6%8%48%
1440
21st to endNight
9%425%7%45%5%7%8%44%
1440
July1st to 10thNight
8%3135%35%5%6%11%50%
1440
11th to 20thNight
8%4244345%6%10%52%
1440
21st to endNight
7%2145%35%6%7%10%51%
1575
August1st to 10thNight
43246%345%8%11%50%
1446
11th to 20thNight
8%415%32337%9%54%
1776
21st to endNight
8%42342446%8%55%
1980
September1st to 10thNight
10%5%35%5%23446%54%
1800
11th to 20thNight
12%3245%24346%55%
1873
21st to endNight
12%5%245%3446%7%49%
1980
October1st to 10thNight
12%7%35%5%23446%50%
2060
11th to 20thNight
17%8%25%5%23445%45%
2160
21st to endNight
20%9%36%43445%6%38%
2565
November1st to 10thNight
11%8%35%424445%49%
2406
11th to 20thNight
15%11%36%5%35%45%7%36%
2470
21st to endNight
16%11%46%5%3445%6%37%
2584
December1st to 10thNight
16%10%5%8%5%45%5%47%32%
2660
11th to 20thNight
16%13%5%8%5%35%45%6%31%
3279
21st to endNight
23%16%8%9%5%35%5%45%17%
4884

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 10thDay
62%411%16%6%
2528
11th to 20thDay
62%5%13%12%8%
2530
21st to endDay
67%5%8%14%6%
2885
February1st to 10thDay
57%5%12%14%10%1
1710
11th to 20thDay
50%5%11%23%9%2
1796
21st to endDay
56%6%8%19%10%1
1480
March1st to 10thDay
54%6%12%20%7%1
1800
11th to 20thDay
46%6%13%23%12%1
1863
21st to endDay
59%7%11%17%6%1
2376
April1st to 10thDay
55%5%10%20%9%
2160
11th to 20thDay
51%5%9%21%12%2
2134
21st to endDay
52%6%13%16%12%1
2240
May1st to 10thDay
51%7%13%22%7%
2340
11th to 20thDay
48%7%12%22%10%
2474
21st to endDay
45%8%12%19%14%2
2725
June1st to 10thDay
35%8%12%28%16%2
2520
11th to 20thDay
34%7%13%23%20%2
2520
21st to endDay
40%9%12%23%14%2
2520
July1st to 10thDay
32%8%14%30%14%3
2451
11th to 20thDay
32%8%16%26%16%2
2445
21st to endDay
33%8%16%25%15%3
2591
August1st to 10thDay
34%9%15%29%11%2
2476
11th to 20thDay
35%7%16%26%15%1
2125
21st to endDay
33%7%11%26%20%3
2376
September1st to 10thDay
36%7%12%24%17%3
2160
11th to 20thDay
31%6%11%31%19%2
2067
21st to endDay
38%6%10%27%18%1
1980
October1st to 10thDay
38%7%11%26%17%1
1895
11th to 20thDay
50%5%13%20%13%1
1800
21st to endDay
51%410%22%11%2
1789
November1st to 10thDay
39%6%15%23%16%2
1672
11th to 20thDay
53%5%11%21%9%1
1710
21st to endDay
52%5%11%23%9%
1595
December1st to 10thDay
55%6%13%18%8%1
1520
11th to 20thDay
56%6%14%16%7%2
1915
21st to endDay
77%46%9%4
2783
January1st to 10thNight
59%410%18%9%1
4428
11th to 20thNight
66%410%12%8%
4440
21st to endNight
68%49%13%6%1
4779
February1st to 10thNight
54%410%17%13%1
2470
11th to 20thNight
48%412%21%14%1
2154
21st to endNight
52%411%19%10%4
1776
March1st to 10thNight
49%5%14%20%9%1
2160
11th to 20thNight
42%7%12%20%16%3
2109
21st to endNight
55%5%9%19%11%2
1980
April1st to 10thNight
47%6%11%22%14%2
1800
11th to 20thNight
48%5%7%21%16%4
1775
21st to endNight
45%6%11%22%12%3
1720
May1st to 10thNight
45%8%13%22%12%
1620
11th to 20thNight
42%7%12%24%14%2
1422
21st to endNight
40%7%13%21%17%2
1552
June1st to 10thNight
32%8%13%26%19%3
1440
11th to 20thNight
34%7%9%24%23%3
1440
21st to endNight
36%7%14%22%18%2
1440
July1st to 10thNight
29%7%14%29%17%4
1400
11th to 20thNight
29%6%14%30%19%2
1392
21st to endNight
27%8%16%26%18%5%
1487
August1st to 10thNight
26%10%15%32%14%3
1437
11th to 20thNight
26%7%15%30%20%1
1776
21st to endNight
27%7%12%28%21%4
1980
September1st to 10thNight
33%6%10%26%24%3
1800
11th to 20thNight
31%5%7%32%22%2
1873
21st to endNight
35%6%11%30%17%2
1980
October1st to 10thNight
35%5%10%27%20%2
2060
11th to 20thNight
42%410%24%19%2
2160
21st to endNight
48%5%9%24%12%1
2565
November1st to 10thNight
38%5%9%26%19%3
2406
11th to 20thNight
48%5%12%22%12%1
2470
21st to endNight
49%412%23%11%1
2584
December1st to 10thNight
53%6%11%21%8%1
2660
11th to 20thNight
54%5%12%19%9%1
3281
21st to endNight
69%5%9%12%5%
4884

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 10thDay
18%14%33%29%6%1
270
11th to 20thDay
20%14%42%20%21
270
21st to endDay
20%13%39%22%5%1
297
February1st to 10thDay
16%18%40%20%5%
270
11th to 20thDay
21%20%33%22%4
252
21st to endDay
25%20%37%16%21
198
March1st to 10thDay
18%22%40%17%3
240
11th to 20thDay
23%16%35%16%8%1
241
21st to endDay
27%14%31%19%7%2
462
April1st to 10thDay
24%12%34%25%5%
420
11th to 20thDay
22%19%28%19%10%3
412
21st to endDay
23%14%30%21%10%2
420
May1st to 10thDay
19%15%31%24%9%2
423
11th to 20thDay
22%11%30%23%11%2
616
21st to endDay
16%8%29%24%16%6%
679
June1st to 10thDay
9%7%30%32%16%6%
630
11th to 20thDay
12%7%31%30%16%5%
630
21st to endDay
12%8%28%33%15%5%
630
July1st to 10thDay
6%419%33%24%14%
621
11th to 20thDay
8%5%26%34%19%9%
618
21st to endDay
7%425%39%19%7%
684
August1st to 10thDay
8%221%33%24%12%
618
11th to 20thDay
8%6%17%28%23%17%
439
21st to endDay
9%419%32%25%11%
495
September1st to 10thDay
14%7%22%28%22%7%
450
11th to 20thDay
10%421%32%23%11%
450
21st to endDay
12%12%27%24%17%7%
450
October1st to 10thDay
14%9%30%25%16%5%
365
11th to 20thDay
23%20%31%19%7%
270
21st to endDay
31%14%32%18%5%1
297
November1st to 10thDay
16%14%39%20%9%2
270
11th to 20thDay
21%18%37%17%7%1
270
21st to endDay
25%11%39%20%5%
270
December1st to 10thDay
17%18%44%14%6%1
270
11th to 20thDay
17%15%37%23%8%
270
21st to endDay
22%22%41%14%1
297
January1st to 10thNight
18%16%38%23%5%
950
11th to 20thNight
20%14%38%21%5%1
950
21st to endNight
20%12%37%26%5%
1045
February1st to 10thNight
21%11%39%24%5%
950
11th to 20thNight
19%14%37%25%4
722
21st to endNight
25%13%38%21%3
592
March1st to 10thNight
21%13%35%24%7%
720
11th to 20thNight
15%10%38%29%7%
671
21st to endNight
22%11%32%27%7%1
594
April1st to 10thNight
21%13%36%25%5%
540
11th to 20thNight
24%13%30%26%7%
533
21st to endNight
21%8%33%29%8%1
540
May1st to 10thNight
17%9%37%29%8%1
540
11th to 20thNight
18%7%33%31%11%
531
21st to endNight
13%7%27%36%18%
584
June1st to 10thNight
9%5%26%43%16%1
540
11th to 20thNight
12%431%40%12%1
540
21st to endNight
7%5%29%39%18%1
540
July1st to 10thNight
8%216%40%31%4
525
11th to 20thNight
8%324%39%25%1
522
21st to endNight
7%220%45%25%1
591
August1st to 10thNight
5%114%50%26%4
537
11th to 20thNight
9%213%40%31%4
534
21st to endNight
9%218%39%29%3
594
September1st to 10thNight
10%5%19%37%24%4
540
11th to 20thNight
12%420%33%27%4
613
21st to endNight
12%9%25%32%20%2
720
October1st to 10thNight
15%6%27%33%17%1
720
11th to 20thNight
22%13%31%24%9%1
720
21st to endNight
24%12%33%23%7%
792
November1st to 10thNight
17%10%38%24%10%1
740
11th to 20thNight
21%16%34%23%6%
760
21st to endNight
20%13%38%23%6%
874
December1st to 10thNight
21%13%39%22%5%
950
11th to 20thNight
23%12%37%23%5%1
950
21st to endNight
28%13%36%19%2
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