Ypsilanti
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ypsilanti clear sky chart from 2005-11-05 to 2017-09-17.

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
38%
15859
15%
46984
10%
15817
43%
15817
21%
32645

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
17%
900
10%
2506
4%
895
22%
895
13%
1979
January16th to endNight
20%
846
8%
2574
3%
846
25%
846
10%
2054
February1st to 15thNight
18%
701
9%
2252
3%
701
24%
701
10%
1735
February16th to endNight
24%
631
14%
1893
6%
631
32%
631
15%
1394
March1st to 15thNight
27%
720
14%
2079
8%
720
31%
720
17%
1515
March16th to endNight
32%
768
18%
2112
10%
768
39%
768
21%
1490
April1st to 15thNight
31%
587
14%
1815
7%
587
39%
587
19%
1266
April16th to endNight
35%
540
19%
1620
8%
540
46%
540
24%
1079
May1st to 15thNight
37%
540
13%
1620
7%
540
43%
540
21%
1118
May16th to endNight
49%
562
15%
1684
10%
561
54%
561
28%
1068
June1st to 15thNight
56%
540
15%
1446
11%
540
60%
540
32%
930
June16th to endNight
59%
540
17%
1440
13%
540
63%
540
33%
923
July1st to 15thNight
65%
510
17%
1360
14%
510
68%
510
39%
811
July16th to endNight
69%
564
19%
1510
15%
531
72%
531
40%
881
August1st to 15thNight
66%
539
19%
1609
15%
536
70%
536
35%
969
August16th to endNight
66%
573
23%
1746
19%
573
69%
573
34%
1036
September1st to 15thNight
60%
666
25%
1926
20%
666
64%
666
35%
1134
September16th to endNight
58%
665
24%
1837
19%
665
62%
665
33%
1137
October1st to 15thNight
47%
660
21%
1893
17%
660
51%
660
28%
1226
October16th to endNight
26%
704
15%
2203
9%
704
34%
704
18%
1529
November1st to 15thNight
37%
700
20%
2276
16%
700
44%
700
24%
1447
November16th to endNight
25%
720
13%
2351
9%
720
31%
720
14%
1715
December1st to 15thNight
18%
723
8%
2523
4%
723
24%
723
10%
1938
December16th to endNight
15%
960
7%
2709
1%
960
20%
960
9%
2271

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%5%7%33%
47773
Night
15%8%46%5%34446%36%
47163
Cloud CoverDay
14%8%36%6%35%5%5%7%33%
47783
Night
15%8%46%5%34446%36%
47167
TransparencyDay
48%7%12%19%10%1
47470
Night
47%6%12%20%11%1
46984
SeeingDay
16%7%25%25%16%7%
5827
Night
19%7%28%29%13%1
15863

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
18%14%49%7%45%5%5%5%17%
1432
16th to endDay
16%16%7%9%7%45%45%5%16%
1647
February1st to 15thDay
14%13%6%9%7%45%5%5%5%20%
1607
16th to endDay
14%13%5%10%7%35%5%47%22%
1580
March1st to 15thDay
17%11%6%6%6%34447%27%
1870
16th to endDay
18%10%47%6%2445%6%29%
2112
April1st to 15thDay
18%10%36%5%3445%6%31%
2142
16th to endDay
17%8%27%423347%38%
2340
May1st to 15thDay
18%7%36%6%44447%31%
2331
16th to endDay
12%6%25%6%3445%7%40%
2431
June1st to 15thDay
10%5%25%6%35%5%6%9%38%
2511
16th to endDay
10%5%25%5%35%6%8%10%35%
2520
July1st to 15thDay
7%5%25%5%35%5%6%8%44%
2520
16th to endDay
8%4345%46%6%6%10%40%
2554
August1st to 15thDay
8%5%27%7%36%5%5%7%40%
2340
16th to endDay
10%426%5%36%6%5%9%39%
2453
September1st to 15thDay
11%5%35%5%35%5%5%8%40%
2020
16th to endDay
12%425%5%245%411%40%
1829
October1st to 15thDay
13%6%26%5%44447%39%
1736
16th to endDay
19%8%36%6%34445%32%
1667
November1st to 15thDay
14%7%36%5%3435%6%38%
1582
16th to endDay
18%9%5%7%5%35%45%5%27%
1605
December1st to 15thDay
17%12%6%10%7%35%5%5%5%20%
1434
16th to endDay
21%15%8%9%7%44346%14%
1510
January1st to 15thNight
21%14%47%5%3345%5%23%
2506
16th to endNight
13%12%8%10%8%5%5%44421%
2574
February1st to 15thNight
15%13%5%9%6%35%335%26%
2250
16th to endNight
16%9%5%8%7%35%345%30%
1893
March1st to 15thNight
18%8%37%5%3345%6%32%
2067
16th to endNight
15%7%45%5%25%45%7%35%
2112
April1st to 15thNight
18%8%35%43445%6%35%
1815
16th to endNight
15%7%245%2445%6%39%
1620
May1st to 15thNight
18%7%35%5%345%5%7%34%
1620
16th to endNight
12%5%25%5%245%48%44%
1682
June1st to 15thNight
9%325%4345%5%8%45%
1446
16th to endNight
8%425%4245%7%8%45%
1440
July1st to 15thNight
7%32342445%8%53%
1440
16th to endNight
44144235%5%10%52%
1614
August1st to 15thNight
4325%435%7%6%8%48%
1620
16th to endNight
9%415%423347%52%
1746
September1st to 15thNight
9%5%2333345%7%51%
1926
16th to endNight
10%5%3432435%7%47%
1837
October1st to 15thNight
13%6%35%423447%43%
1893
16th to endNight
20%7%36%434345%35%
2203
November1st to 15thNight
14%7%34424447%41%
2276
16th to endNight
21%11%45%5%33446%29%
2351
December1st to 15thNight
21%12%5%8%5%25%446%23%
2523
16th to endNight
22%14%6%10%5%35%445%16%
2709

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
18%14%410%7%45%5%5%5%18%
1432
16th to endDay
16%17%7%8%8%45%445%16%
1647
February1st to 15thDay
14%13%6%10%7%46%45%5%20%
1607
16th to endDay
13%13%5%10%7%35%5%5%6%22%
1580
March1st to 15thDay
17%11%5%7%6%34347%26%
1881
16th to endDay
18%9%47%6%2435%7%29%
2111
April1st to 15thDay
18%9%36%5%4445%6%31%
2142
16th to endDay
17%8%26%423347%37%
2340
May1st to 15thDay
18%7%36%6%44447%31%
2331
16th to endDay
12%6%25%6%3445%7%40%
2431
June1st to 15thDay
10%5%35%6%445%6%9%38%
2511
16th to endDay
10%5%25%5%36%6%8%10%35%
2520
July1st to 15thDay
7%5%25%5%345%6%8%44%
2520
16th to endDay
7%4245%46%6%6%10%40%
2554
August1st to 15thDay
7%5%26%7%35%5%5%7%41%
2340
16th to endDay
10%435%5%36%6%6%9%39%
2453
September1st to 15thDay
11%5%35%5%346%5%7%41%
2020
16th to endDay
13%4245%25%5%411%40%
1829
October1st to 15thDay
13%6%26%5%34448%39%
1736
16th to endDay
19%8%36%5%345%45%32%
1667
November1st to 15thDay
14%7%36%5%3445%6%38%
1582
16th to endDay
18%9%5%7%5%35%5%5%6%27%
1605
December1st to 15thDay
17%12%6%10%7%35%5%5%6%20%
1434
16th to endDay
21%16%7%10%6%44445%14%
1510
January1st to 15thNight
21%14%5%7%6%2435%5%23%
2506
16th to endNight
13%12%8%10%8%5%5%5%4421%
2574
February1st to 15thNight
15%12%6%10%6%35%335%26%
2243
16th to endNight
16%9%5%8%7%34446%29%
1893
March1st to 15thNight
18%8%47%5%3445%6%31%
2079
16th to endNight
15%7%45%5%25%447%35%
2112
April1st to 15thNight
17%8%445%25%446%35%
1815
16th to endNight
15%7%245%25%5%5%6%39%
1620
May1st to 15thNight
17%7%35%5%345%47%34%
1619
16th to endNight
12%5%25%5%245%48%44%
1682
June1st to 15thNight
10%325%425%5%5%8%45%
1446
16th to endNight
8%435%5%25%5%7%8%45%
1440
July1st to 15thNight
7%223424448%54%
1440
16th to endNight
44144235%6%10%52%
1614
August1st to 15thNight
5%325%435%7%6%8%48%
1620
16th to endNight
9%415%423347%51%
1746
September1st to 15thNight
9%42333445%7%51%
1926
16th to endNight
10%5%35%33445%7%47%
1837
October1st to 15thNight
13%7%35%4235%47%43%
1893
16th to endNight
20%6%36%434445%35%
2203
November1st to 15thNight
14%7%3442445%7%40%
2276
16th to endNight
21%11%5%5%5%33446%28%
2351
December1st to 15thNight
21%12%5%7%5%25%346%23%
2523
16th to endNight
22%14%5%10%6%25%45%5%16%
2709

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
65%7%11%11%4
1433
16th to endDay
68%7%9%9%4
1647
February1st to 15thDay
63%7%8%13%6%
1609
16th to endDay
60%8%11%14%4
1580
March1st to 15thDay
57%6%12%16%6%1
1881
16th to endDay
54%5%12%20%6%1
2112
April1st to 15thDay
54%5%10%18%10%
2142
16th to endDay
46%5%12%17%14%2
2340
May1st to 15thDay
51%6%12%17%9%1
2331
16th to endDay
42%6%12%24%11%2
2435
June1st to 15thDay
39%7%14%22%14%1
2511
16th to endDay
39%11%13%18%15%1
2520
July1st to 15thDay
35%7%12%23%19%2
2371
16th to endDay
36%9%15%22%14%2
2395
August1st to 15thDay
39%7%13%23%13%1
2327
16th to endDay
38%9%12%21%15%2
2453
September1st to 15thDay
39%7%13%24%13%1
2020
16th to endDay
37%7%12%28%13%
1829
October1st to 15thDay
43%5%12%24%12%1
1736
16th to endDay
52%6%14%18%8%
1667
November1st to 15thDay
45%6%11%22%13%1
1582
16th to endDay
56%6%12%18%5%
1605
December1st to 15thDay
62%7%11%13%4
1434
16th to endDay
71%6%10%8%2
1510
January1st to 15thNight
62%5%11%14%6%
2506
16th to endNight
64%6%13%12%4
2574
February1st to 15thNight
60%6%10%15%5%1
2252
16th to endNight
56%411%19%6%
1893
March1st to 15thNight
52%6%11%18%10%1
2079
16th to endNight
47%6%11%22%10%1
2112
April1st to 15thNight
48%6%10%19%13%
1815
16th to endNight
43%5%13%17%16%3
1620
May1st to 15thNight
47%5%12%19%11%2
1620
16th to endNight
38%6%13%24%14%3
1684
June1st to 15thNight
35%8%12%27%15%
1446
16th to endNight
33%8%14%23%18%1
1440
July1st to 15thNight
28%7%11%28%21%2
1360
16th to endNight
26%7%16%24%21%3
1510
August1st to 15thNight
29%9%14%28%15%2
1609
16th to endNight
32%6%11%27%18%3
1746
September1st to 15thNight
31%5%11%29%20%1
1926
16th to endNight
35%5%11%29%17%1
1837
October1st to 15thNight
40%5%12%23%18%
1893
16th to endNight
49%5%13%22%8%
2203
November1st to 15thNight
41%5%13%23%13%1
2276
16th to endNight
56%5%13%18%6%
2351
December1st to 15thNight
62%5%13%13%5%
2523
16th to endNight
68%7%10%10%3
2709

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
17%14%40%21%5%1
90
16th to endDay
30%9%39%17%3
96
February1st to 15thDay
20%20%46%11%2
90
16th to endDay
23%14%34%23%3
81
March1st to 15thDay
32%11%29%21%6%
171
16th to endDay
23%9%28%27%10%1
288
April1st to 15thDay
22%12%30%23%11%
270
16th to endDay
20%10%30%20%11%7%
270
May1st to 15thDay
23%7%30%20%11%5%
288
16th to endDay
16%9%23%25%15%9%
331
June1st to 15thDay
11%5%28%33%15%4
486
16th to endDay
13%6%30%28%14%6%
495
July1st to 15thDay
10%422%29%24%8%
475
16th to endDay
8%320%30%23%13%
414
August1st to 15thDay
9%215%30%24%17%
313
16th to endDay
13%116%21%30%15%
332
September1st to 15thDay
10%319%22%25%18%
315
16th to endDay
17%313%20%31%12%
259
October1st to 15thDay
16%5%22%27%19%7%
255
16th to endDay
22%8%34%27%7%
179
November1st to 15thDay
7%15%25%30%17%3
90
16th to endDay
20%20%32%19%6%
87
December1st to 15thDay
20%18%40%15%5%1
60
16th to endDay
29%23%38%8%
92
January1st to 15thNight
28%12%34%18%5%
900
16th to endNight
19%11%37%25%6%
846
February1st to 15thNight
22%13%37%23%3
704
16th to endNight
20%10%35%29%3
631
March1st to 15thNight
23%10%31%27%6%
720
16th to endNight
18%9%33%29%9%1
768
April1st to 15thNight
21%11%31%29%5%
587
16th to endNight
21%6%32%29%9%1
540
May1st to 15thNight
20%429%33%10%1
540
16th to endNight
15%125%33%20%2
563
June1st to 15thNight
10%124%46%16%
540
16th to endNight
9%122%44%20%1
540
July1st to 15thNight
9%116%40%28%3
510
16th to endNight
5%16%46%27%3
564
August1st to 15thNight
6%17%44%25%5%
539
16th to endNight
11%112%34%36%3
573
September1st to 15thNight
11%319%30%29%5%
666
16th to endNight
13%317%31%29%5%
665
October1st to 15thNight
17%6%24%30%18%2
660
16th to endNight
23%10%34%25%5%
704
November1st to 15thNight
18%9%30%27%13%1
700
16th to endNight
27%12%29%21%7%
720
December1st to 15thNight
27%13%33%21%4
723
16th to endNight
30%10%36%19%3
960
Page generated at 2017-09-18 08:38:26. Version ac04

Copyright 2017 A. Danko


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