Frankfort
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Frankfort clear sky chart from 2005-11-05 to 2017-09-18.

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
44%
15374
20%
46599
15%
15330
51%
15330
26%
30022

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
20%
720
15%
2327
8%
716
29%
716
14%
1706
January16th to endNight
21%
768
17%
2496
9%
768
31%
768
17%
1747
February1st to 15thNight
22%
704
15%
2130
5%
701
30%
701
17%
1515
February16th to endNight
18%
631
15%
1893
7%
631
25%
631
16%
1368
March1st to 15thNight
26%
720
17%
2102
10%
720
32%
720
20%
1457
March16th to endNight
33%
768
15%
2112
8%
768
40%
768
24%
1463
April1st to 15thNight
36%
560
22%
1818
14%
560
48%
560
27%
1098
April16th to endNight
39%
540
21%
1672
12%
540
49%
540
25%
1085
May1st to 15thNight
42%
540
15%
1620
9%
540
47%
540
21%
1139
May16th to endNight
61%
562
19%
1684
16%
561
63%
561
29%
1053
June1st to 15thNight
69%
540
21%
1596
18%
540
73%
540
41%
889
June16th to endNight
72%
540
20%
1440
16%
540
74%
540
42%
852
July1st to 15thNight
61%
510
17%
1382
13%
510
63%
510
32%
901
July16th to endNight
75%
564
21%
1595
19%
531
78%
531
40%
892
August1st to 15thNight
78%
539
24%
1609
23%
536
79%
536
40%
913
August16th to endNight
77%
573
24%
1881
26%
573
78%
573
38%
1000
September1st to 15thNight
66%
654
26%
1914
23%
654
69%
654
35%
1140
September16th to endNight
60%
669
28%
1848
22%
669
64%
669
35%
1129
October1st to 15thNight
56%
660
32%
1831
25%
660
62%
660
38%
1073
October16th to endNight
43%
704
26%
2197
20%
704
52%
704
29%
1338
November1st to 15thNight
48%
700
29%
2276
24%
700
57%
700
32%
1285
November16th to endNight
35%
720
22%
2340
16%
720
46%
720
23%
1494
December1st to 15thNight
29%
720
14%
2340
9%
720
35%
720
16%
1673
December16th to endNight
22%
768
16%
2496
8%
768
32%
768
14%
1812

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
15%6%35%5%35%45%7%38%
48185
Night
14%6%35%42445%7%41%
46783
Cloud CoverDay
14%6%35%5%3445%7%37%
48194
Night
14%6%35%42445%7%41%
46788
TransparencyDay
44%411%22%14%2
47887
Night
42%410%23%15%3
46599
SeeingDay
16%5%20%24%20%12%
5584
Night
18%6%23%30%18%2
15375

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
21%9%48%434335%29%
1611
16th to endDay
16%10%46%5%33346%32%
1728
February1st to 15thDay
16%9%5%9%434445%32%
1732
16th to endDay
15%11%5%6%5%35%446%30%
1580
March1st to 15thDay
23%7%45%423435%34%
1847
16th to endDay
18%7%37%5%25%446%32%
2112
April1st to 15thDay
16%7%25%435%447%39%
2140
16th to endDay
16%6%15%5%2435%6%39%
2286
May1st to 15thDay
20%6%25%6%2445%8%31%
2331
16th to endDay
10%5%36%5%35%6%6%8%37%
2431
June1st to 15thDay
10%3246%46%5%6%8%41%
2359
16th to endDay
7%425%5%36%6%6%10%41%
2520
July1st to 15thDay
15%5%24436%6%7%9%33%
2493
16th to endDay
9%5%26%6%36%6%8%10%35%
2465
August1st to 15thDay
8%5%15%5%35%6%7%9%41%
2340
16th to endDay
7%426%5%35%7%6%9%41%
2320
September1st to 15thDay
14%5%35%435%5%5%7%40%
2033
16th to endDay
14%4235%2345%7%46%
1837
October1st to 15thDay
10%5%145%24336%51%
1797
16th to endDay
19%5%24324335%46%
1673
November1st to 15thDay
13%5%2432333452%
1582
16th to endDay
18%8%34323346%40%
1620
December1st to 15thDay
24%9%46%423345%29%
1620
16th to endDay
20%11%47%424436%30%
1728
January1st to 15thNight
17%10%49%6%3445%428%
2327
16th to endNight
18%10%46%5%3434433%
2496
February1st to 15thNight
20%9%45%424445%32%
2128
16th to endNight
18%12%47%5%24435%31%
1893
March1st to 15thNight
17%8%46%5%24345%36%
2089
16th to endNight
16%8%26%5%2446%6%36%
2112
April1st to 15thNight
14%5%23425%46%6%44%
1818
16th to endNight
14%6%26%5%24446%41%
1672
May1st to 15thNight
17%6%36%435%5%6%7%32%
1620
16th to endNight
8%3246%25%5%8%11%39%
1682
June1st to 15thNight
5%32432445%10%52%
1596
16th to endNight
5%223335%5%8%12%46%
1440
July1st to 15thNight
11%425%5%3445%8%44%
1464
16th to endNight
6%2234245%7%11%49%
1703
August1st to 15thNight
43234345%6%10%51%
1620
16th to endNight
43244245%6%9%51%
1881
September1st to 15thNight
12%313435%45%7%48%
1914
16th to endNight
11%5%34333245%52%
1848
October1st to 15thNight
9%41442435%6%52%
1831
16th to endNight
14%5%25%5%33345%46%
2197
November1st to 15thNight
12%5%2432335%6%51%
2276
16th to endNight
18%8%24424345%41%
2340
December1st to 15thNight
22%10%46%5%2334431%
2340
16th to endNight
23%11%35%5%24446%28%
2496

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
20%9%48%5%44336%29%
1611
16th to endDay
16%10%5%6%6%3335%5%32%
1728
February1st to 15thDay
16%9%5%9%433445%32%
1732
16th to endDay
15%11%5%6%6%35%446%30%
1580
March1st to 15thDay
23%7%45%423435%34%
1857
16th to endDay
18%7%46%5%35%446%33%
2111
April1st to 15thDay
16%6%25%434447%39%
2140
16th to endDay
16%6%25%5%2445%6%39%
2286
May1st to 15thDay
20%6%25%6%345%5%8%31%
2331
16th to endDay
10%6%26%5%45%5%6%8%37%
2431
June1st to 15thDay
9%415%5%46%5%6%8%41%
2359
16th to endDay
7%435%5%36%5%6%10%41%
2520
July1st to 15thDay
14%5%245%36%6%7%9%33%
2493
16th to endDay
8%5%26%6%46%6%7%10%35%
2465
August1st to 15thDay
8%5%25%5%35%6%7%9%40%
2340
16th to endDay
7%426%5%35%7%6%9%41%
2320
September1st to 15thDay
13%5%35%435%5%5%7%40%
2033
16th to endDay
14%4245%2345%6%46%
1837
October1st to 15thDay
10%5%14424337%50%
1797
16th to endDay
18%5%24324335%45%
1673
November1st to 15thDay
13%5%24424335%52%
1582
16th to endDay
18%8%24323346%40%
1620
December1st to 15thDay
24%9%47%434345%29%
1620
16th to endDay
20%11%5%6%5%24436%30%
1728
January1st to 15thNight
18%10%49%6%2445%428%
2327
16th to endNight
18%10%5%6%5%2434433%
2496
February1st to 15thNight
20%9%46%434445%32%
2121
16th to endNight
18%12%47%6%24435%30%
1893
March1st to 15thNight
18%8%45%5%34345%36%
2102
16th to endNight
16%8%26%5%2346%6%36%
2112
April1st to 15thNight
14%5%23425%46%6%44%
1818
16th to endNight
14%6%26%5%3345%6%41%
1672
May1st to 15thNight
16%6%36%426%6%5%7%32%
1619
16th to endNight
8%4246%25%6%8%11%39%
1682
June1st to 15thNight
5%32442345%10%51%
1596
16th to endNight
5%214335%5%8%12%46%
1440
July1st to 15thNight
10%435%5%25%448%44%
1464
16th to endNight
5%3233245%7%10%49%
1703
August1st to 15thNight
43134345%6%10%51%
1620
16th to endNight
43244245%6%9%51%
1881
September1st to 15thNight
12%313435%45%8%48%
1914
16th to endNight
11%5%34323345%52%
1848
October1st to 15thNight
9%414425%35%6%52%
1831
16th to endNight
14%6%25%433345%46%
2197
November1st to 15thNight
12%5%2432325%6%51%
2276
16th to endNight
18%8%24424345%41%
2340
December1st to 15thNight
22%10%46%5%23345%30%
2340
16th to endNight
23%11%35%5%23445%28%
2496

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
57%28%19%10%
1612
16th to endDay
52%210%25%7%1
1728
February1st to 15thDay
54%47%24%8%1
1734
16th to endDay
54%311%21%8%
1580
March1st to 15thDay
52%311%19%12%1
1857
16th to endDay
51%311%22%9%
2112
April1st to 15thDay
44%310%24%15%2
2140
16th to endDay
44%410%23%13%4
2286
May1st to 15thDay
50%5%12%19%11%
2331
16th to endDay
42%5%16%20%13%1
2435
June1st to 15thDay
38%5%13%24%17%1
2359
16th to endDay
36%6%12%21%19%3
2520
July1st to 15thDay
44%5%14%17%14%3
2346
16th to endDay
39%6%15%24%12%2
2310
August1st to 15thDay
36%7%12%23%18%2
2327
16th to endDay
36%6%10%24%16%4
2320
September1st to 15thDay
42%49%18%18%6%
2033
16th to endDay
37%47%23%24%2
1837
October1st to 15thDay
34%37%28%22%4
1797
16th to endDay
42%28%27%16%3
1673
November1st to 15thDay
36%26%26%20%7%
1582
16th to endDay
45%28%24%18%1
1620
December1st to 15thDay
58%210%18%8%1
1620
16th to endDay
56%211%21%7%
1728
January1st to 15thNight
58%28%16%12%1
2327
16th to endNight
53%29%22%9%1
2496
February1st to 15thNight
53%310%22%8%1
2130
16th to endNight
56%311%19%10%
1893
March1st to 15thNight
50%29%21%13%2
2102
16th to endNight
47%413%23%10%1
2112
April1st to 15thNight
38%39%23%20%3
1818
16th to endNight
43%49%22%13%6%
1672
May1st to 15thNight
48%6%12%21%9%2
1620
16th to endNight
34%8%13%22%14%4
1684
June1st to 15thNight
28%414%30%17%4
1596
16th to endNight
28%5%18%23%17%5%
1440
July1st to 15thNight
38%5%11%21%17%4
1382
16th to endNight
25%7%16%28%18%2
1595
August1st to 15thNight
25%8%15%26%19%4
1609
16th to endNight
27%5%14%27%20%4
1881
September1st to 15thNight
34%311%21%21%6%
1914
16th to endNight
35%36%23%25%4
1848
October1st to 15thNight
31%37%27%24%5%
1831
16th to endNight
40%17%26%19%4
2197
November1st to 15thNight
34%27%23%25%6%
2276
16th to endNight
45%28%24%17%1
2340
December1st to 15thNight
55%210%20%9%1
2340
16th to endNight
57%210%19%8%1
2496

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
37%11%33%10%5%2
90
16th to endDay
19%20%46%8%4
96
February1st to 15thDay
16%20%45%14%3
90
16th to endDay
24%11%41%18%3
81
March1st to 15thDay
23%15%37%17%6%
147
16th to endDay
21%9%34%22%11%
288
April1st to 15thDay
22%10%24%26%12%2
270
16th to endDay
18%7%27%24%12%8%
270
May1st to 15thDay
23%8%25%21%12%7%
288
16th to endDay
16%222%26%19%13%
331
June1st to 15thDay
11%210%29%29%16%
334
16th to endDay
8%422%29%22%11%
495
July1st to 15thDay
17%315%28%22%13%
450
16th to endDay
10%17%21%30%28%
326
August1st to 15thDay
13%17%19%30%27%
313
16th to endDay
10%25%27%29%23%
332
September1st to 15thDay
14%311%22%29%19%
315
16th to endDay
16%212%20%30%18%
262
October1st to 15thDay
14%322%29%20%10%
255
16th to endDay
17%426%29%21%
185
November1st to 15thDay
15%5%23%25%23%6%
90
16th to endDay
25%5%33%24%11%
90
December1st to 15thDay
23%12%33%24%42
90
16th to endDay
22%20%42%11%2
96
January1st to 15thNight
24%15%34%22%4
720
16th to endNight
25%13%35%25%1
768
February1st to 15thNight
27%9%34%26%1
704
16th to endNight
25%12%37%23%1
631
March1st to 15thNight
23%10%33%26%5%
720
16th to endNight
20%9%30%27%10%
768
April1st to 15thNight
16%9%34%28%10%
560
16th to endNight
15%5%31%32%12%1
540
May1st to 15thNight
19%5%23%32%17%1
540
16th to endNight
10%215%38%24%8%
563
June1st to 15thNight
7%113%43%31%3
540
16th to endNight
6%112%44%33%2
540
July1st to 15thNight
13%19%31%37%5%
510
16th to endNight
8%17%33%40%9%
564
August1st to 15thNight
6%6%35%44%7%
539
16th to endNight
6%15%37%43%5%
573
September1st to 15thNight
15%19%28%38%6%
654
16th to endNight
12%413%28%35%5%
669
October1st to 15thNight
11%422%32%23%5%
660
16th to endNight
18%6%27%31%14%1
704
November1st to 15thNight
15%8%24%29%20%2
700
16th to endNight
22%10%27%28%10%
720
December1st to 15thNight
29%9%26%24%9%
720
16th to endNight
32%9%29%23%4
768
Page generated at 2017-09-19 07:32:22. Version ac04

Copyright 2017 A. Danko


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