Lee Farm Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lee Farm Observatory clear sky chart from 2005-11-05 to 2017-10-16.

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
51%
15827
22%
47257
15%
15787
58%
15787
28%
29494

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
32%
716
21%
2327
11%
716
45%
716
23%
1429
January16th to endNight
34%
768
24%
2445
13%
768
48%
768
24%
1496
February1st to 15thNight
33%
703
24%
2108
11%
699
46%
699
26%
1290
February16th to endNight
34%
631
26%
1893
13%
631
47%
631
27%
1158
March1st to 15thNight
41%
720
27%
1992
14%
720
52%
720
34%
1203
March16th to endNight
45%
768
25%
2112
14%
768
53%
768
35%
1245
April1st to 15thNight
42%
718
23%
1976
14%
718
49%
718
34%
1190
April16th to endNight
53%
600
29%
1743
19%
600
61%
600
37%
986
May1st to 15thNight
57%
539
25%
1619
16%
539
64%
539
37%
925
May16th to endNight
70%
561
22%
1682
17%
561
73%
561
33%
1024
June1st to 15thNight
67%
540
14%
1620
10%
540
69%
540
27%
1080
June16th to endNight
71%
540
14%
1620
13%
540
72%
540
25%
1105
July1st to 15thNight
73%
510
11%
1530
10%
510
74%
510
26%
1026
July16th to endNight
72%
564
10%
1595
9%
531
73%
531
24%
1115
August1st to 15thNight
69%
539
11%
1621
9%
536
70%
536
21%
1162
August16th to endNight
62%
637
13%
1974
13%
637
62%
637
20%
1407
September1st to 15thNight
63%
720
13%
1980
12%
720
64%
720
22%
1428
September16th to endNight
59%
717
19%
1980
17%
717
61%
717
26%
1344
October1st to 15thNight
56%
720
29%
2016
23%
720
62%
720
36%
1205
October16th to endNight
53%
708
31%
2123
26%
708
62%
708
36%
1199
November1st to 15thNight
50%
700
31%
2125
25%
700
60%
700
36%
1199
November16th to endNight
42%
720
28%
2340
19%
720
56%
720
33%
1284
December1st to 15thNight
41%
720
24%
2340
17%
720
51%
720
26%
1418
December16th to endNight
44%
768
22%
2496
18%
768
52%
768
24%
1576

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
10%5%25%5%35%5%6%7%39%
48145
Night
9%5%244345%6%8%45%
47461
TransparencyDay
41%7%11%17%15%6%
47846
Night
35%7%12%18%16%8%
47264
SeeingDay
12%5%18%22%24%15%
5700
Night
12%6%21%32%23%4
15835

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
13%5%25%425%45%8%42%
1611
16th to endDay
14%5%25%423336%45%
1776
February1st to 15thDay
14%6%25%5%24445%45%
1750
16th to endDay
14%7%2332333450%
1580
March1st to 15thDay
9%424424347%51%
1965
16th to endDay
10%5%35%425%35%6%47%
2111
April1st to 15thDay
10%5%25%434446%47%
1972
16th to endDay
8%3145%3445%7%49%
2223
May1st to 15thDay
8%323435%6%7%9%47%
2331
16th to endDay
7%5%26%6%37%5%6%8%39%
2431
June1st to 15thDay
10%6%26%6%47%6%8%9%31%
2340
16th to endDay
7%5%27%7%5%8%7%7%9%30%
2340
July1st to 15thDay
7%5%27%8%48%8%9%11%26%
2340
16th to endDay
8%5%38%9%5%8%8%8%9%22%
2465
August1st to 15thDay
12%7%37%9%6%8%7%8%9%19%
2324
16th to endDay
13%7%37%9%5%8%6%8%7%22%
2214
September1st to 15thDay
11%6%37%6%5%7%7%8%9%26%
1980
16th to endDay
13%7%36%7%45%5%5%8%32%
1980
October1st to 15thDay
12%5%24424447%47%
1943
16th to endDay
8%314324445%56%
1770
November1st to 15thDay
7%413323346%58%
1731
16th to endDay
10%424423446%53%
1620
December1st to 15thDay
13%7%25%435%446%43%
1620
16th to endDay
15%7%45%433446%39%
1728
January1st to 15thNight
12%5%35%43445%6%43%
2327
16th to endNight
14%5%35%32345%6%45%
2445
February1st to 15thNight
13%6%2432344448%
2103
16th to endNight
11%6%24424345%49%
1893
March1st to 15thNight
8%42442435%7%51%
1992
16th to endNight
9%423334445%55%
2112
April1st to 15thNight
9%5%2442445%6%52%
1976
16th to endNight
5%3143245%5%6%55%
1743
May1st to 15thNight
7%4233245%6%8%52%
1619
16th to endNight
6%3135%46%5%6%9%47%
1682
June1st to 15thNight
9%5%247%36%5%8%13%34%
1620
16th to endNight
6%325%6%37%7%9%11%35%
1620
July1st to 15thNight
5%326%7%47%7%9%11%34%
1620
16th to endNight
5%435%7%47%7%8%12%31%
1703
August1st to 15thNight
5%5%27%8%47%7%8%13%28%
1632
16th to endNight
10%6%26%6%36%6%8%11%30%
1974
September1st to 15thNight
11%425%6%47%7%8%10%30%
1980
16th to endNight
10%7%35%5%35%5%7%8%37%
1980
October1st to 15thNight
9%5%24323346%53%
2016
16th to endNight
8%414423435%56%
2123
November1st to 15thNight
8%414423446%55%
2125
16th to endNight
9%5%23423347%53%
2340
December1st to 15thNight
12%6%2442345%8%44%
2340
16th to endNight
14%7%25%424446%43%
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
39%5%8%17%18%10%
1612
16th to endDay
39%45%19%20%11%
1776
February1st to 15thDay
40%46%12%22%12%
1752
16th to endDay
38%36%15%24%12%
1580
March1st to 15thDay
32%48%21%23%9%
1965
16th to endDay
36%410%19%20%9%
2112
April1st to 15thDay
37%47%18%22%9%
1972
16th to endDay
33%410%22%20%9%
2223
May1st to 15thDay
30%7%11%21%20%7%
2331
16th to endDay
39%9%12%20%14%3
2435
June1st to 15thDay
44%10%17%17%9%
2340
16th to endDay
46%11%15%17%7%1
2340
July1st to 15thDay
46%12%22%14%3
2201
16th to endDay
51%13%16%14%3
2310
August1st to 15thDay
54%12%19%10%3
2311
16th to endDay
56%11%14%12%31
2214
September1st to 15thDay
49%10%15%13%10%1
1980
16th to endDay
48%7%11%16%12%3
1980
October1st to 15thDay
38%48%17%19%10%
1943
16th to endDay
30%46%18%25%15%
1770
November1st to 15thDay
26%48%20%26%13%
1731
16th to endDay
32%48%16%23%14%
1620
December1st to 15thDay
41%5%7%18%18%8%
1620
16th to endDay
45%410%18%13%8%
1728
January1st to 15thNight
40%49%15%20%10%
2327
16th to endNight
39%47%13%23%12%
2445
February1st to 15thNight
37%46%15%20%15%
2112
16th to endNight
36%47%16%20%14%
1893
March1st to 15thNight
31%5%10%21%20%10%
1992
16th to endNight
30%5%9%20%22%11%
2112
April1st to 15thNight
32%5%8%19%22%11%
1976
16th to endNight
27%6%11%23%20%11%
1743
May1st to 15thNight
27%7%14%22%17%10%
1620
16th to endNight
30%9%13%26%14%4
1684
June1st to 15thNight
37%10%20%19%9%1
1620
16th to endNight
36%13%21%18%8%1
1620
July1st to 15thNight
36%12%25%21%3
1530
16th to endNight
38%14%25%16%3
1595
August1st to 15thNight
40%15%24%15%3
1621
16th to endNight
44%12%21%16%31
1974
September1st to 15thNight
43%12%17%14%10%1
1980
16th to endNight
41%8%14%19%10%4
1980
October1st to 15thNight
31%6%10%20%18%12%
2016
16th to endNight
30%46%17%23%17%
2123
November1st to 15thNight
31%36%21%23%14%
2125
16th to endNight
31%39%17%21%16%
2340
December1st to 15thNight
37%5%11%20%17%7%
2340
16th to endNight
41%5%9%21%13%9%
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
17%15%37%12%8%7%
90
16th to endDay
22%17%39%12%7%
96
February1st to 15thDay
26%13%38%15%5%
90
16th to endDay
12%13%54%16%3
81
March1st to 15thDay
13%13%31%28%11%1
255
16th to endDay
12%9%30%23%20%3
288
April1st to 15thDay
12%14%24%26%16%5%
270
16th to endDay
8%7%19%29%21%14%
270
May1st to 15thDay
8%5%29%22%22%11%
288
16th to endDay
8%310%25%32%19%
331
June1st to 15thDay
12%211%19%32%22%
315
16th to endDay
11%15%20%35%25%
315
July1st to 15thDay
6%416%35%36%
305
16th to endDay
9%1419%33%30%
326
August1st to 15thDay
16%15%19%33%23%
313
16th to endDay
11%17%17%29%31%
332
September1st to 15thDay
16%311%22%26%20%
315
16th to endDay
18%111%23%29%15%
314
October1st to 15thDay
14%422%27%21%8%
315
16th to endDay
10%5%25%24%27%7%
276
November1st to 15thDay
12%5%25%33%16%6%
239
16th to endDay
7%12%40%24%10%5%
90
December1st to 15thDay
11%14%42%18%12%1
90
16th to endDay
21%11%20%34%7%4
96
January1st to 15thNight
16%12%32%27%10%1
720
16th to endNight
17%13%29%31%7%
768
February1st to 15thNight
19%12%30%29%8%
704
16th to endNight
15%13%31%34%4
631
March1st to 15thNight
12%10%31%35%10%
720
16th to endNight
12%9%29%32%15%
768
April1st to 15thNight
12%9%31%33%13%
718
16th to endNight
7%7%27%36%20%1
600
May1st to 15thNight
7%326%38%21%2
540
16th to endNight
7%212%36%36%4
563
June1st to 15thNight
11%8%35%34%9%
540
16th to endNight
6%7%31%40%12%
540
July1st to 15thNight
6%15%30%38%18%
510
16th to endNight
6%1429%43%14%
564
August1st to 15thNight
7%5%26%47%12%
539
16th to endNight
13%17%23%38%14%
637
September1st to 15thNight
13%18%29%36%11%
720
16th to endNight
15%113%34%31%4
717
October1st to 15thNight
12%321%31%27%2
720
16th to endNight
10%6%22%32%25%2
708
November1st to 15thNight
11%5%25%35%20%2
700
16th to endNight
12%10%31%29%15%1
720
December1st to 15thNight
15%10%27%31%14%1
720
16th to endNight
18%9%22%33%15%
768
Page generated at 2017-10-17 16:35:25. Version ac04

Copyright 2017 A. Danko


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