The Observatory on the Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Observatory on the Lake clear sky chart from 2005-11-05 to 2018-02-14.

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
29%
15334
14%
48836
8%
15303
37%
15303
17%
34188

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
14%
780
9%
2716
3%
776
22%
776
7%
2129
January16th to endNight
17%
832
11%
2807
4%
832
26%
832
10%
2127
February1st to 15thNight
14%
760
10%
2468
3%
757
23%
757
10%
1922
February16th to endNight
19%
631
14%
1961
5%
631
31%
631
13%
1448
March1st to 15thNight
20%
720
15%
2067
6%
720
28%
720
16%
1513
March16th to endNight
28%
768
20%
2055
9%
768
36%
768
25%
1408
April1st to 15thNight
21%
718
16%
1796
4%
718
27%
718
21%
1307
April16th to endNight
29%
668
17%
1748
7%
668
35%
668
24%
1209
May1st to 15thNight
37%
369
17%
1449
14%
369
46%
369
18%
936
May16th to endNight
37%
374
15%
1497
13%
374
48%
374
21%
900
June1st to 15thNight
36%
360
11%
1440
10%
360
46%
360
17%
932
June16th to endNight
46%
360
10%
1440
12%
360
51%
360
19%
904
July1st to 15thNight
50%
340
15%
1360
21%
340
56%
340
28%
751
July16th to endNight
54%
376
16%
1418
15%
354
60%
354
29%
780
August1st to 15thNight
52%
500
15%
1571
10%
498
56%
498
27%
958
August16th to endNight
53%
701
23%
1847
11%
701
59%
701
37%
1118
September1st to 15thNight
48%
720
20%
1800
10%
720
52%
720
34%
1158
September16th to endNight
50%
717
25%
1966
17%
717
55%
717
32%
1238
October1st to 15thNight
34%
720
17%
2160
12%
720
42%
720
20%
1483
October16th to endNight
24%
768
12%
2364
5%
768
32%
768
13%
1782
November1st to 15thNight
28%
760
17%
2534
13%
760
35%
760
17%
1731
November16th to endNight
21%
780
12%
2730
7%
780
30%
780
11%
2019
December1st to 15thNight
15%
780
8%
2730
3%
780
22%
780
8%
2112
December16th to endNight
13%
832
9%
2912
3%
832
21%
832
8%
2323

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
17%8%36%5%3445%6%33%
49248
Night
17%9%36%5%3445%6%34%
49006
Cloud CoverDay
17%8%36%5%3445%7%33%
49258
Night
17%8%36%5%3445%6%34%
49011
TransparencyDay
50%6%11%20%10%1
48936
Night
50%6%11%20%11%1
48836
SeeingDay
22%12%29%21%10%4
5890
Night
22%11%30%23%10%1
15335

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%13%46%6%35%43425%
1552
16th to endDay
14%14%6%10%7%36%5%4421%
1768
February1st to 15thDay
15%14%5%12%7%36%345%21%
1695
16th to endDay
18%14%5%6%7%3444425%
1512
March1st to 15thDay
17%12%49%8%4434426%
1879
16th to endDay
17%8%46%42433439%
2169
April1st to 15thDay
22%10%45%424335%34%
2152
16th to endDay
18%8%35%5%24446%37%
2223
May1st to 15thDay
18%7%36%5%35%45%6%32%
2502
16th to endDay
15%5%25%435%5%6%8%37%
2618
June1st to 15thDay
20%7%344345%5%8%32%
2520
16th to endDay
16%6%345%35%45%8%35%
2520
July1st to 15thDay
12%423435%6%6%9%40%
2520
16th to endDay
10%5%35%5%35%5%6%9%37%
2654
August1st to 15thDay
11%6%26%6%35%5%6%8%37%
2377
16th to endDay
12%5%2442446%8%43%
2342
September1st to 15thDay
14%6%2442445%7%43%
2160
16th to endDay
14%6%2442345%6%47%
1990
October1st to 15thDay
21%6%24434447%36%
1800
16th to endDay
26%8%36%5%34446%26%
1860
November1st to 15thDay
15%8%46%6%3445%7%33%
1651
16th to endDay
22%11%46%43345%6%27%
1560
December1st to 15thDay
21%14%48%7%34435%21%
1560
16th to endDay
23%16%6%7%5%3433421%
1664
January1st to 15thNight
20%14%49%6%35%435%22%
2716
16th to endNight
15%13%5%9%6%3445%425%
2807
February1st to 15thNight
16%14%49%6%35%445%24%
2466
16th to endNight
17%10%47%7%4345%430%
1961
March1st to 15thNight
19%10%5%5%6%3434432%
2055
16th to endNight
17%8%37%423346%41%
2055
April1st to 15thNight
22%8%34424346%34%
1796
16th to endNight
17%5%25%5%3435%5%39%
1748
May1st to 15thNight
20%7%3342445%6%36%
1449
16th to endNight
12%5%35%426%45%7%41%
1495
June1st to 15thNight
17%5%25%5%25%46%8%34%
1440
16th to endNight
13%425%5%35%5%6%10%37%
1440
July1st to 15thNight
9%424435%5%6%7%47%
1440
16th to endNight
8%415%3235%7%9%48%
1514
August1st to 15thNight
9%5%25%5%3447%8%44%
1581
16th to endNight
8%42442445%8%51%
1847
September1st to 15thNight
14%5%2441235%7%47%
1800
16th to endNight
15%32442435%6%48%
1966
October1st to 15thNight
20%6%25%5%33446%37%
2160
16th to endNight
23%8%37%6%24445%28%
2364
November1st to 15thNight
19%9%25%424346%36%
2534
16th to endNight
22%10%36%435%45%5%28%
2730
December1st to 15thNight
20%14%48%6%23346%24%
2730
16th to endNight
22%14%5%6%6%35%435%20%
2912

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
21%14%46%5%345%3425%
1552
16th to endDay
13%15%5%10%7%36%5%4421%
1768
February1st to 15thDay
15%14%5%12%8%35%445%20%
1695
16th to endDay
19%13%6%5%8%34445%25%
1512
March1st to 15thDay
18%11%49%7%5%5%34425%
1890
16th to endDay
17%9%36%42433439%
2168
April1st to 15thDay
22%10%45%433335%33%
2152
16th to endDay
18%8%35%424446%37%
2223
May1st to 15thDay
18%7%26%5%3445%6%33%
2502
16th to endDay
14%6%25%5%245%6%9%37%
2618
June1st to 15thDay
20%7%35%425%45%8%32%
2520
16th to endDay
15%6%25%5%345%5%8%36%
2520
July1st to 15thDay
12%5%24426%5%6%9%40%
2520
16th to endDay
11%5%35%5%36%5%6%9%37%
2654
August1st to 15thDay
10%6%26%5%35%5%6%9%37%
2377
16th to endDay
11%5%2442446%8%44%
2342
September1st to 15thDay
15%5%25%42345%7%42%
2160
16th to endDay
14%5%2442335%7%46%
1990
October1st to 15thDay
21%6%25%424447%36%
1800
16th to endDay
25%9%37%5%34346%27%
1860
November1st to 15thDay
15%8%47%5%345%5%7%33%
1651
16th to endDay
23%10%46%5%3345%5%27%
1560
December1st to 15thDay
21%15%47%6%35%44421%
1560
16th to endDay
23%16%5%7%6%3343421%
1664
January1st to 15thNight
20%14%49%7%35%435%22%
2716
16th to endNight
15%13%5%8%6%35%45%5%25%
2807
February1st to 15thNight
17%13%5%9%6%44445%24%
2459
16th to endNight
18%10%37%7%34445%29%
1961
March1st to 15thNight
20%10%46%5%34335%31%
2067
16th to endNight
17%8%36%423335%41%
2055
April1st to 15thNight
22%7%44434346%34%
1796
16th to endNight
17%6%25%5%4335%6%39%
1748
May1st to 15thNight
20%7%25%42435%6%37%
1449
16th to endNight
12%435%436%5%5%7%41%
1495
June1st to 15thNight
17%5%346%245%6%8%34%
1440
16th to endNight
13%425%5%35%5%6%9%37%
1440
July1st to 15thNight
9%424335%46%8%47%
1440
16th to endNight
7%42442447%9%47%
1514
August1st to 15thNight
9%425%5%2446%9%43%
1581
16th to endNight
8%4145%2445%7%52%
1847
September1st to 15thNight
14%42441235%7%47%
1800
16th to endNight
15%41432435%6%48%
1966
October1st to 15thNight
20%5%35%5%3335%6%36%
2160
16th to endNight
23%8%37%5%34445%28%
2364
November1st to 15thNight
19%8%35%42445%6%36%
2534
16th to endNight
22%9%35%5%35%446%28%
2730
December1st to 15thNight
20%14%48%5%23346%24%
2730
16th to endNight
22%14%5%7%6%35%445%20%
2912

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
61%5%9%15%6%1
1553
16th to endDay
63%6%9%11%7%
1768
February1st to 15thDay
65%48%15%5%
1697
16th to endDay
61%5%10%12%9%1
1512
March1st to 15thDay
62%311%14%6%1
1890
16th to endDay
48%48%18%15%4
2169
April1st to 15thDay
54%38%18%12%2
2152
16th to endDay
48%47%20%14%3
2223
May1st to 15thDay
50%6%9%18%13%2
2502
16th to endDay
43%7%14%21%11%2
2622
June1st to 15thDay
49%7%11%20%10%
2520
16th to endDay
45%7%12%21%11%
2520
July1st to 15thDay
37%8%13%27%12%
2371
16th to endDay
42%7%16%23%9%
2487
August1st to 15thDay
41%8%15%23%10%
2363
16th to endDay
37%5%15%28%12%
2342
September1st to 15thDay
39%5%15%26%12%
2160
16th to endDay
37%6%11%32%12%
1990
October1st to 15thDay
47%5%13%23%10%
1800
16th to endDay
58%6%11%17%5%
1860
November1st to 15thDay
49%7%12%19%9%
1651
16th to endDay
57%6%12%13%8%
1560
December1st to 15thDay
64%5%12%11%4
1560
16th to endDay
67%49%12%6%
1664
January1st to 15thNight
64%5%9%12%6%
2716
16th to endNight
59%6%9%15%8%
2807
February1st to 15thNight
61%6%10%16%5%
2468
16th to endNight
56%5%10%18%9%
1961
March1st to 15thNight
55%310%21%7%
2067
16th to endNight
45%49%19%17%2
2055
April1st to 15thNight
50%47%19%16%1
1796
16th to endNight
45%410%18%18%3
1748
May1st to 15thNight
46%5%10%18%15%4
1449
16th to endNight
39%6%13%21%15%2
1497
June1st to 15thNight
46%6%13%20%12%
1440
16th to endNight
41%9%13%20%15%
1440
July1st to 15thNight
32%7%11%28%19%1
1360
16th to endNight
31%7%14%29%15%1
1418
August1st to 15thNight
34%8%15%26%13%1
1571
16th to endNight
30%6%12%34%15%
1847
September1st to 15thNight
35%5%13%31%12%1
1800
16th to endNight
35%5%10%32%14%
1966
October1st to 15thNight
47%5%11%22%12%
2160
16th to endNight
56%7%13%15%7%
2364
November1st to 15thNight
48%5%13%18%11%1
2534
16th to endNight
56%6%11%17%6%
2730
December1st to 15thNight
62%6%12%14%4
2730
16th to endNight
65%5%11%10%6%
2912

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
25%18%31%16%6%1
90
16th to endDay
30%17%32%15%4
120
February1st to 15thDay
30%31%33%4
130
16th to endDay
32%18%31%14%4
171
March1st to 15thDay
26%15%29%22%5%
270
16th to endDay
26%14%33%15%8%1
288
April1st to 15thDay
29%17%29%13%9%
270
16th to endDay
23%20%26%15%9%5%
270
May1st to 15thDay
28%9%27%21%9%4
288
16th to endDay
18%11%35%20%10%3
331
June1st to 15thDay
25%7%34%20%9%1
315
16th to endDay
20%9%30%25%11%3
315
July1st to 15thDay
15%5%24%31%15%6%
305
16th to endDay
14%5%29%30%14%5%
326
August1st to 15thDay
13%425%31%18%6%
313
16th to endDay
13%6%25%25%16%12%
332
September1st to 15thDay
15%7%25%21%16%13%
315
16th to endDay
14%9%24%22%20%9%
314
October1st to 15thDay
27%11%27%16%11%4
315
16th to endDay
30%19%23%20%4
321
November1st to 15thDay
19%12%33%23%8%1
215
16th to endDay
25%15%36%16%41
90
December1st to 15thDay
26%23%26%15%7%
90
16th to endDay
35%19%39%41
96
January1st to 15thNight
31%17%28%17%5%
780
16th to endNight
24%15%35%20%4
832
February1st to 15thNight
25%17%35%19%2
760
16th to endNight
24%13%36%19%4
631
March1st to 15thNight
27%15%33%21%2
720
16th to endNight
22%11%33%22%9%1
768
April1st to 15thNight
25%12%36%20%4
718
16th to endNight
21%12%32%20%11%
668
May1st to 15thNight
24%5%27%28%11%1
369
16th to endNight
12%6%36%30%12%
375
June1st to 15thNight
18%7%31%28%13%
360
16th to endNight
15%228%39%12%
360
July1st to 15thNight
9%328%37%20%
340
16th to endNight
9%228%39%18%1
376
August1st to 15thNight
12%323%34%23%2
500
16th to endNight
9%325%34%22%3
701
September1st to 15thNight
16%425%29%20%3
720
16th to endNight
16%6%22%25%23%4
717
October1st to 15thNight
24%10%26%20%15%2
720
16th to endNight
28%14%26%24%5%
768
November1st to 15thNight
25%10%30%21%11%
760
16th to endNight
30%17%26%16%8%
780
December1st to 15thNight
30%19%29%17%3
780
16th to endNight
31%15%32%17%1
832
Page generated at 2018-02-15 10:58:46. Version ac04

Copyright 2018 A. Danko


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