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Two Harbors
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Two Harbors clear sky chart from 2005-11-06 to 2024-01-16.

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
36%
24973
9%
74389
5%
24912
40%
24912
11%
59898

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
27%
950
5%
2648
3%
946
30%
946
9%
2239
January11th to 20thNight
20%
926
3%
2591
1%
926
22%
926
5%
2333
January21st to endNight
21%
990
5%
2716
1%
990
25%
990
9%
2313
February1st to 10thNight
25%
900
5%
2340
1%
900
28%
900
11%
1943
February11th to 20thNight
28%
879
12%
2274
4%
875
33%
875
14%
1811
February21st to endNight
30%
648
10%
1832
4%
648
35%
648
11%
1485
March1st to 10thNight
34%
701
9%
2140
6%
701
37%
701
11%
1726
March11th to 20thNight
32%
540
13%
1980
9%
540
39%
540
11%
1493
March21st to endNight
35%
594
10%
2088
9%
594
39%
594
8%
1703
April1st to 10thNight
29%
540
8%
1800
5%
540
34%
540
10%
1445
April11th to 20thNight
37%
533
11%
1775
10%
533
41%
533
11%
1392
April21st to endNight
40%
540
10%
1592
7%
540
43%
540
11%
1311
May1st to 10thNight
40%
540
9%
1440
5%
540
42%
540
13%
1169
May11th to 20thNight
47%
531
13%
1416
7%
531
50%
531
16%
1114
May21st to endNight
52%
584
8%
1552
4%
582
54%
582
13%
1256
June1st to 10thNight
53%
540
6%
1440
3%
540
54%
540
15%
1139
June11th to 20thNight
50%
540
9%
1383
5%
540
53%
540
18%
1066
June21st to endNight
54%
540
9%
1260
6%
540
54%
540
18%
1001
July1st to 10thNight
69%
525
10%
1308
5%
525
70%
525
23%
970
July11th to 20thNight
58%
522
11%
1392
5%
522
60%
522
20%
1052
July21st to endNight
67%
591
12%
1487
7%
558
69%
558
20%
1111
August1st to 10thNight
65%
537
14%
1445
9%
534
66%
534
19%
1072
August11th to 20thNight
58%
534
15%
1600
13%
534
63%
534
18%
1159
August21st to endNight
58%
594
13%
1921
14%
594
60%
594
17%
1376
September1st to 10thNight
57%
540
14%
1800
14%
540
62%
540
16%
1277
September11th to 20thNight
57%
540
15%
1800
15%
540
60%
540
16%
1303
September21st to endNight
42%
669
9%
2039
5%
669
46%
669
14%
1561
October1st to 10thNight
40%
720
11%
2160
7%
720
43%
720
13%
1679
October11th to 20thNight
29%
720
8%
2160
3%
720
34%
720
9%
1762
October21st to endNight
29%
792
7%
2515
4%
792
32%
792
9%
2023
November1st to 10thNight
31%
834
10%
2500
5%
834
36%
834
9%
2030
November11th to 20thNight
25%
950
9%
2660
3%
950
31%
950
8%
2266
November21st to endNight
26%
950
9%
2660
4%
950
30%
950
10%
2181
December1st to 10thNight
22%
950
4%
2660
1%
950
25%
950
6%
2342
December11th to 20thNight
18%
949
6%
3209
1%
948
21%
948
4%
2686
December21st to endNight
15%
1040
3%
4806
1%
1026
18%
1026
3%
4109

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%6%35%5%6%7%37%
75079
Night
14%9%46%5%35%45%7%36%
74715
TransparencyDay
31%39%10%14%6%1
74785
Night
32%38%9%13%6%1
74544
SeeingDay
16%8%28%31%14%2
14942
Night
18%8%30%31%13%1
24982

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 10thDay
10%12%5%8%8%35%5%5%8%29%
1517
11th to 20thDay
11%13%7%11%8%46%6%6%9%20%
1480
21st to endDay
8%11%6%12%10%47%6%6%6%22%
1638
February1st to 10thDay
8%11%5%9%7%45%6%6%8%31%
1620
11th to 20thDay
10%11%46%5%35%5%6%7%38%
1574
21st to endDay
8%11%47%7%45%6%6%6%35%
1423
March1st to 10thDay
11%9%47%6%45%5%6%7%37%
1829
11th to 20thDay
12%9%47%5%445%5%7%39%
1980
21st to endDay
18%9%46%5%46%5%5%6%33%
2268
April1st to 10thDay
16%8%5%7%6%36%5%5%6%34%
2160
11th to 20thDay
19%10%47%6%445%5%6%31%
2134
21st to endDay
21%8%36%5%3445%7%33%
2362
May1st to 10thDay
17%8%37%6%45%45%6%36%
2520
11th to 20thDay
17%6%35%5%36%5%5%7%39%
2479
21st to endDay
16%6%36%5%45%5%6%8%37%
2725
June1st to 10thDay
11%5%245%35%6%6%9%44%
2520
11th to 20thDay
15%5%25%5%45%5%6%8%41%
2568
21st to endDay
14%5%36%5%35%5%7%10%37%
2700
July1st to 10thDay
7%31443448%11%50%
2606
11th to 20thDay
9%5%245%45%5%7%9%47%
2520
21st to endDay
6%3245%35%5%6%10%52%
2743
August1st to 10thDay
9%4346%35%5%7%9%45%
2482
11th to 20thDay
11%426%435%5%5%8%47%
2301
21st to endDay
12%5%25%5%335%6%8%47%
2435
September1st to 10thDay
10%5%345%345%6%9%46%
2160
11th to 20thDay
14%6%25%6%35%45%7%43%
2160
21st to endDay
17%7%35%6%345%5%6%39%
1900
October1st to 10thDay
17%7%36%7%46%6%6%6%34%
1800
11th to 20thDay
16%10%47%5%445%6%7%32%
1800
21st to endDay
21%9%37%7%4445%5%32%
1841
November1st to 10thDay
15%9%47%446%45%7%35%
1577
11th to 20thDay
15%12%7%10%9%45%445%26%
1520
21st to endDay
14%11%5%7%7%446%6%6%30%
1520
December1st to 10thDay
11%12%6%10%8%5%5%6%6%7%25%
1520
11th to 20thDay
14%18%7%9%7%345%6%6%21%
1914
21st to endDay
28%19%48%5%3333320%
2783
January1st to 10thNight
10%10%48%7%45%5%8%9%30%
2648
11th to 20thNight
12%13%5%11%8%36%5%6%9%23%
2591
21st to endNight
11%13%6%9%7%5%5%5%6%7%26%
2716
February1st to 10thNight
7%11%5%9%7%45%5%5%8%33%
2340
11th to 20thNight
8%9%38%6%35%5%5%7%41%
2273
21st to endNight
12%12%46%6%35%45%7%36%
1832
March1st to 10thNight
10%10%47%6%445%5%6%38%
2133
11th to 20thNight
14%8%46%4345%46%42%
1979
21st to endNight
16%10%48%6%34445%36%
2088
April1st to 10thNight
16%11%47%6%45%5%5%6%34%
1800
11th to 20thNight
18%10%45%6%245%5%6%35%
1775
21st to endNight
20%10%46%4445%45%35%
1592
May1st to 10thNight
16%8%46%6%3445%7%37%
1440
11th to 20thNight
16%7%346%345%6%6%41%
1416
21st to endNight
17%6%25%5%45%5%5%9%38%
1551
June1st to 10thNight
14%5%35%5%45%5%5%10%41%
1440
11th to 20thNight
13%7%35%6%35%5%5%8%40%
1383
21st to endNight
12%5%25%5%35%5%6%9%42%
1260
July1st to 10thNight
8%3233245%5%9%56%
1347
11th to 20thNight
8%325%5%3446%8%51%
1440
21st to endNight
6%42343446%9%55%
1575
August1st to 10thNight
9%3145%3445%8%54%
1454
11th to 20thNight
12%6%25%32435%8%51%
1600
21st to endNight
16%423423348%50%
1921
September1st to 10thNight
10%5%245%3445%6%52%
1800
11th to 20thNight
13%4134345%5%8%49%
1800
21st to endNight
17%6%245%4446%8%40%
2039
October1st to 10thNight
18%5%35%5%35%447%41%
2160
11th to 20thNight
16%8%27%5%45%46%8%36%
2160
21st to endNight
20%8%36%6%35%45%6%33%
2515
November1st to 10thNight
14%9%36%435%5%7%8%35%
2500
11th to 20thNight
16%10%47%6%45%5%5%7%31%
2660
21st to endNight
14%10%46%5%35%6%6%6%35%
2660
December1st to 10thNight
11%14%6%8%8%45%6%6%7%26%
2660
11th to 20thNight
13%15%5%9%7%45%6%6%8%23%
3283
21st to endNight
27%19%5%7%422335%22%
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
36%41%11%9%2
1518
11th to 20thDay
40%45%9%5%1
1480
21st to endDay
40%40%10%6%4
1638
February1st to 10thDay
33%40%11%10%6%1
1620
11th to 20thDay
30%40%13%12%5%1
1583
21st to endDay
33%40%9%10%6%2
1423
March1st to 10thDay
33%38%12%11%5%
1831
11th to 20thDay
30%39%11%13%6%
1980
21st to endDay
35%39%8%12%5%
2268
April1st to 10thDay
34%38%7%12%8%1
2160
11th to 20thDay
37%37%8%11%6%1
2134
21st to endDay
34%39%8%13%6%1
2362
May1st to 10thDay
34%38%7%13%7%1
2520
11th to 20thDay
29%39%9%15%7%2
2483
21st to endDay
29%40%9%13%9%1
2725
June1st to 10thDay
24%41%12%15%8%1
2520
11th to 20thDay
26%38%10%15%11%1
2568
21st to endDay
26%40%11%17%6%
2700
July1st to 10thDay
17%40%11%20%11%1
2537
11th to 20thDay
20%40%11%18%10%1
2445
21st to endDay
19%42%10%18%9%1
2591
August1st to 10thDay
24%39%9%19%7%1
2467
11th to 20thDay
22%39%10%19%10%
2301
21st to endDay
22%39%8%19%11%1
2435
September1st to 10thDay
22%39%11%21%6%
2160
11th to 20thDay
25%40%12%19%4
2160
21st to endDay
30%38%9%19%4
1900
October1st to 10thDay
31%41%9%16%4
1800
11th to 20thDay
36%39%11%9%4
1800
21st to endDay
35%39%8%12%5%
1841
November1st to 10thDay
31%41%7%13%6%1
1577
11th to 20thDay
39%41%8%9%3
1520
21st to endDay
32%43%11%11%21
1520
December1st to 10thDay
37%43%12%7%2
1520
11th to 20thDay
46%34%7%8%31
1915
21st to endDay
56%25%7%7%4
2783
January1st to 10thNight
33%43%12%10%2
2648
11th to 20thNight
40%45%10%5%1
2591
21st to endNight
37%39%12%8%3
2716
February1st to 10thNight
33%39%11%10%5%1
2340
11th to 20thNight
28%39%11%13%8%1
2274
21st to endNight
34%37%9%14%5%1
1832
March1st to 10thNight
33%38%10%12%7%1
2144
11th to 20thNight
28%38%8%16%8%1
1980
21st to endNight
37%37%8%11%6%1
2088
April1st to 10thNight
35%36%6%10%11%1
1800
11th to 20thNight
33%36%8%15%8%
1775
21st to endNight
36%37%5%15%7%1
1592
May1st to 10thNight
33%37%9%13%8%1
1440
11th to 20thNight
26%39%7%17%8%2
1417
21st to endNight
30%39%6%15%8%1
1552
June1st to 10thNight
28%40%11%14%7%1
1440
11th to 20thNight
25%37%8%17%10%2
1383
21st to endNight
26%38%9%16%10%
1260
July1st to 10thNight
18%39%10%19%14%1
1308
11th to 20thNight
20%40%9%17%11%3
1392
21st to endNight
19%40%11%18%10%2
1487
August1st to 10thNight
21%38%8%22%8%3
1445
11th to 20thNight
21%37%10%20%11%1
1600
21st to endNight
21%38%9%18%14%1
1921
September1st to 10thNight
20%39%8%23%10%
1800
11th to 20thNight
21%39%11%24%5%
1800
21st to endNight
26%39%11%19%6%
2039
October1st to 10thNight
29%37%9%19%5%
2160
11th to 20thNight
36%37%11%12%41
2160
21st to endNight
32%39%10%13%5%
2515
November1st to 10thNight
30%42%9%13%5%1
2500
11th to 20thNight
35%41%9%9%5%
2660
21st to endNight
30%43%12%11%41
2660
December1st to 10thNight
37%45%9%8%2
2660
11th to 20thNight
41%36%11%8%4
3281
21st to endNight
54%27%7%9%4
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
16%8%39%27%10%
270
11th to 20thDay
17%7%39%29%9%
255
21st to endDay
13%12%34%30%10%2
264
February1st to 10thDay
12%12%45%28%4
240
11th to 20thDay
15%15%42%17%10%1
240
21st to endDay
14%15%42%28%2
198
March1st to 10thDay
15%9%34%33%9%1
240
11th to 20thDay
15%8%39%26%11%1
240
21st to endDay
23%9%30%26%8%2
354
April1st to 10thDay
19%13%34%26%8%
420
11th to 20thDay
24%9%25%29%12%1
412
21st to endDay
24%8%28%28%12%1
572
May1st to 10thDay
18%10%32%30%8%2
603
11th to 20thDay
18%6%27%32%14%3
625
21st to endDay
18%6%25%33%17%2
679
June1st to 10thDay
10%429%39%14%3
630
11th to 20thDay
14%8%27%37%13%1
630
21st to endDay
14%424%37%18%3
630
July1st to 10thDay
9%220%39%24%5%
621
11th to 20thDay
11%5%22%36%20%6%
618
21st to endDay
7%319%43%21%7%
684
August1st to 10thDay
11%419%40%23%4
626
11th to 20thDay
13%5%16%34%28%4
615
21st to endDay
17%6%19%31%24%4
554
September1st to 10thDay
11%424%38%20%2
450
11th to 20thDay
16%8%25%28%20%3
450
21st to endDay
24%9%28%22%14%3
338
October1st to 10thDay
20%6%28%30%14%2
270
11th to 20thDay
18%16%34%24%7%1
270
21st to endDay
25%12%39%21%3
297
November1st to 10thDay
20%11%36%24%9%
270
11th to 20thDay
21%14%36%23%6%
270
21st to endDay
19%15%34%26%6%
270
December1st to 10thDay
16%17%34%24%7%1
270
11th to 20thDay
21%17%38%19%4
270
21st to endDay
28%13%33%21%5%
297
January1st to 10thNight
15%11%37%29%7%
950
11th to 20thNight
17%9%41%24%8%1
926
21st to endNight
17%9%40%27%6%1
990
February1st to 10thNight
13%11%39%29%7%1
900
11th to 20thNight
13%10%39%26%10%1
879
21st to endNight
17%7%38%30%7%1
648
March1st to 10thNight
15%8%33%34%9%1
704
11th to 20thNight
18%6%36%28%11%1
540
21st to endNight
20%6%29%29%13%3
594
April1st to 10thNight
21%8%34%29%7%1
540
11th to 20thNight
25%7%23%32%12%1
533
21st to endNight
25%6%22%31%13%3
540
May1st to 10thNight
19%6%29%34%10%2
540
11th to 20thNight
19%424%36%15%3
531
21st to endNight
17%5%19%38%21%1
584
June1st to 10thNight
16%321%40%19%1
540
11th to 20thNight
18%221%41%17%1
540
21st to endNight
15%318%40%21%2
540
July1st to 10thNight
8%216%41%31%3
525
11th to 20thNight
9%222%38%27%1
522
21st to endNight
8%216%45%26%3
591
August1st to 10thNight
10%216%42%27%2
537
11th to 20thNight
14%316%35%26%5%
534
21st to endNight
17%315%36%25%3
594
September1st to 10thNight
12%421%36%23%4
540
11th to 20thNight
14%421%38%20%2
540
21st to endNight
20%7%25%30%16%2
669
October1st to 10thNight
20%8%26%31%14%1
720
11th to 20thNight
19%9%34%26%10%1
720
21st to endNight
25%10%30%28%7%
792
November1st to 10thNight
19%11%32%29%8%1
834
11th to 20thNight
20%12%34%23%10%1
950
21st to endNight
18%15%36%25%7%
950
December1st to 10thNight
19%13%36%26%7%
950
11th to 20thNight
21%13%36%21%8%
950
21st to endNight
29%11%34%21%5%1
1045
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