Ford Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ford Lake Observatory 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
52%
15486
24%
46947
17%
15442
59%
15442
30%
28584

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
29%
720
24%
2327
11%
716
45%
716
24%
1421
January16th to endNight
30%
768
25%
2424
12%
768
44%
768
24%
1515
February1st to 15thNight
34%
704
26%
2111
12%
700
48%
700
28%
1279
February16th to endNight
29%
631
25%
1893
10%
631
43%
631
28%
1174
March1st to 15thNight
38%
720
24%
2070
13%
720
48%
720
31%
1271
March16th to endNight
43%
768
23%
2112
13%
768
50%
768
32%
1294
April1st to 15thNight
47%
629
25%
1887
19%
629
56%
629
34%
1089
April16th to endNight
50%
540
26%
1719
18%
540
59%
540
33%
974
May1st to 15thNight
56%
540
23%
1620
16%
540
61%
540
32%
969
May16th to endNight
64%
561
23%
1682
17%
561
68%
561
33%
1012
June1st to 15thNight
74%
540
18%
1620
17%
540
75%
540
31%
1009
June16th to endNight
77%
540
18%
1620
16%
540
77%
540
35%
968
July1st to 15thNight
74%
510
13%
1530
13%
510
74%
510
30%
993
July16th to endNight
76%
564
16%
1595
15%
531
77%
531
30%
1015
August1st to 15thNight
73%
539
19%
1669
20%
536
73%
536
28%
1059
August16th to endNight
67%
573
19%
1910
21%
573
68%
573
23%
1254
September1st to 15thNight
68%
702
21%
1962
19%
702
69%
702
28%
1285
September16th to endNight
65%
665
24%
1837
20%
665
68%
665
31%
1169
October1st to 15thNight
60%
660
33%
1815
26%
660
66%
660
39%
1070
October16th to endNight
56%
704
34%
2106
28%
704
66%
704
39%
1169
November1st to 15thNight
53%
700
31%
2262
27%
700
63%
700
37%
1191
November16th to endNight
43%
720
27%
2340
19%
720
55%
720
31%
1334
December1st to 15thNight
40%
720
24%
2340
18%
720
51%
720
27%
1410
December16th to endNight
35%
768
21%
2496
15%
768
43%
768
21%
1660

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
12%5%25%5%35%5%5%7%41%
47823
Night
11%42442445%8%46%
47147
TransparencyDay
39%6%11%19%17%4
47524
Night
35%5%10%20%20%7%
46950
SeeingDay
13%5%15%22%24%18%
5368
Night
13%5%20%30%24%5%
15488

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 15thDay
15%6%25%42335%6%44%
1611
16th to endDay
16%6%25%423435%44%
1797
February1st to 15thDay
14%5%25%424346%44%
1750
16th to endDay
16%6%24324436%43%
1580
March1st to 15thDay
13%6%27%423446%43%
1890
16th to endDay
15%5%2432445%7%42%
2111
April1st to 15thDay
10%6%245%24447%46%
2070
16th to endDay
9%4245%2345%7%49%
2241
May1st to 15thDay
10%425%6%45%45%6%44%
2331
16th to endDay
8%425%6%45%5%6%9%42%
2431
June1st to 15thDay
8%5%26%7%46%6%8%9%34%
2340
16th to endDay
43146%46%6%9%11%41%
2340
July1st to 15thDay
9%5%26%6%5%7%7%9%11%27%
2340
16th to endDay
6%436%7%5%8%7%8%11%30%
2465
August1st to 15thDay
7%5%26%7%48%8%8%11%28%
2277
16th to endDay
14%6%36%6%46%8%6%8%27%
2292
September1st to 15thDay
14%5%25%7%45%5%5%7%36%
1986
16th to endDay
15%5%36%4235%46%40%
1829
October1st to 15thDay
14%413314345%53%
1815
16th to endDay
12%313323225%58%
1766
November1st to 15thDay
12%324313335%54%
1593
16th to endDay
12%5%25%333346%48%
1620
December1st to 15thDay
15%7%25%42445%5%42%
1620
16th to endDay
21%9%345%23336%35%
1728
January1st to 15thNight
15%7%24423346%44%
2327
16th to endNight
17%7%23423346%43%
2424
February1st to 15thNight
14%4245%24246%47%
2103
16th to endNight
14%5%24434446%46%
1893
March1st to 15thNight
13%5%23424446%48%
2070
16th to endNight
11%6%1342345%7%48%
2112
April1st to 15thNight
11%5%23313448%50%
1887
16th to endNight
8%424434447%51%
1719
May1st to 15thNight
8%325%5%3445%8%48%
1619
16th to endNight
7%4145%345%5%9%47%
1682
June1st to 15thNight
6%3245%45%5%5%13%42%
1620
16th to endNight
4315%6%346%8%12%43%
1620
July1st to 15thNight
6%335%7%36%6%7%12%37%
1620
16th to endNight
5%2245%37%9%8%12%36%
1703
August1st to 15thNight
5%227%7%45%6%7%11%38%
1680
16th to endNight
11%5%245%35%6%6%10%37%
1910
September1st to 15thNight
8%326%5%345%6%10%40%
1962
16th to endNight
12%425%5%2445%7%45%
1837
October1st to 15thNight
12%41332345%5%54%
1815
16th to endNight
9%42332333459%
2106
November1st to 15thNight
12%313312236%58%
2262
16th to endNight
12%414424346%51%
2340
December1st to 15thNight
14%5%25%423346%46%
2340
16th to endNight
19%7%35%425%35%5%37%
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
40%39%14%26%5%
1612
16th to endDay
41%36%18%21%8%
1797
February1st to 15thDay
40%37%20%23%5%
1752
16th to endDay
42%36%18%21%6%
1580
March1st to 15thDay
41%49%17%20%6%
1890
16th to endDay
40%5%11%21%17%4
2112
April1st to 15thDay
37%48%21%20%6%
2070
16th to endDay
32%5%11%21%24%5%
2241
May1st to 15thDay
38%6%11%18%21%3
2331
16th to endDay
36%6%13%25%14%2
2435
June1st to 15thDay
42%9%16%21%8%1
2340
16th to endDay
31%10%17%22%14%2
2340
July1st to 15thDay
42%11%19%17%6%1
2201
16th to endDay
42%11%16%20%8%
2310
August1st to 15thDay
44%9%18%18%7%1
2264
16th to endDay
51%9%14%14%9%1
2292
September1st to 15thDay
44%8%12%16%14%3
1986
16th to endDay
44%49%19%19%3
1829
October1st to 15thDay
31%410%20%24%8%
1815
16th to endDay
30%26%17%31%12%
1766
November1st to 15thDay
32%35%17%30%11%
1593
16th to endDay
35%46%17%26%9%
1620
December1st to 15thDay
42%47%21%16%7%
1620
16th to endDay
50%47%18%13%6%
1728
January1st to 15thNight
40%36%18%24%6%
2327
16th to endNight
42%26%17%21%8%
2424
February1st to 15thNight
38%25%20%21%11%
2112
16th to endNight
39%36%18%24%7%
1893
March1st to 15thNight
36%410%20%19%8%
2070
16th to endNight
34%49%23%21%6%
2112
April1st to 15thNight
32%47%25%21%9%
1887
16th to endNight
32%410%23%20%9%
1719
May1st to 15thNight
33%6%12%20%23%3
1620
16th to endNight
32%7%12%26%16%3
1684
June1st to 15thNight
32%9%17%26%12%
1620
16th to endNight
30%8%19%23%15%2
1620
July1st to 15thNight
37%8%22%21%7%3
1530
16th to endNight
33%10%23%20%10%1
1595
August1st to 15thNight
35%9%18%24%10%1
1669
16th to endNight
38%11%17%17%12%1
1910
September1st to 15thNight
36%10%13%19%15%4
1962
16th to endNight
36%6%11%21%18%5%
1837
October1st to 15thNight
31%39%20%24%9%
1815
16th to endNight
29%3416%31%15%
2106
November1st to 15thNight
28%35%17%30%14%
2262
16th to endNight
34%36%17%26%11%
2340
December1st to 15thNight
38%48%20%19%8%
2340
16th to endNight
47%37%16%18%6%
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
20%13%33%22%7%3
90
16th to endDay
16%14%53%9%6%
96
February1st to 15thDay
7%25%43%20%3
90
16th to endDay
20%11%38%27%2
81
March1st to 15thDay
17%11%30%29%9%1
180
16th to endDay
17%6%28%30%14%2
288
April1st to 15thDay
13%12%27%20%22%4
270
16th to endDay
12%322%29%24%7%
270
May1st to 15thDay
11%10%22%22%17%15%
288
16th to endDay
13%212%27%23%21%
331
June1st to 15thDay
10%18%18%25%35%
315
16th to endDay
7%7%25%23%35%
315
July1st to 15thDay
7%15%14%32%38%
305
16th to endDay
5%1313%35%40%
326
August1st to 15thDay
10%1217%35%30%
313
16th to endDay
15%1321%32%25%
332
September1st to 15thDay
16%27%17%30%26%
315
16th to endDay
17%18%29%32%11%
259
October1st to 15thDay
23%114%26%26%7%
255
16th to endDay
15%412%27%27%11%
272
November1st to 15thDay
25%7%22%23%12%6%
101
16th to endDay
6%11%24%31%21%5%
90
December1st to 15thDay
21%7%40%18%12%
90
16th to endDay
32%9%23%23%9%1
96
January1st to 15thNight
20%12%32%26%7%
720
16th to endNight
20%10%34%29%5%
768
February1st to 15thNight
16%9%32%34%6%
704
16th to endNight
17%9%39%29%4
631
March1st to 15thNight
16%8%33%31%9%
720
16th to endNight
14%8%27%31%17%
768
April1st to 15thNight
14%6%28%31%17%1
629
16th to endNight
12%326%32%21%2
540
May1st to 15thNight
8%323%32%27%4
540
16th to endNight
9%112%33%36%7%
563
June1st to 15thNight
7%15%32%39%12%
540
16th to endNight
35%29%47%13%
540
July1st to 15thNight
7%1322%48%17%
510
16th to endNight
4423%51%16%
564
August1st to 15thNight
6%321%53%14%
539
16th to endNight
12%1423%44%13%
573
September1st to 15thNight
10%15%23%46%12%
702
16th to endNight
14%27%34%37%3
665
October1st to 15thNight
14%216%34%26%6%
660
16th to endNight
10%5%22%32%25%3
704
November1st to 15thNight
13%5%22%32%23%2
700
16th to endNight
14%7%28%33%14%1
720
December1st to 15thNight
15%8%30%31%12%1
720
16th to endNight
21%8%29%30%9%
768
Page generated at 2017-09-18 08:38:24. Version ac04

Copyright 2017 A. Danko


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