Bert and Jeanette Lynch Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bert and Jeanette Lynch Memorial Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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
34%
16344
23%
48487
12%
16297
45%
16297
27%
29762

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
16%
975
21%
2651
5%
970
29%
970
19%
1771
January16th to endNight
14%
985
24%
2561
5%
985
28%
985
22%
1702
February1st to 15thNight
15%
830
18%
2238
4%
827
25%
827
19%
1524
February16th to endNight
15%
631
22%
1893
5%
631
29%
631
20%
1210
March1st to 15thNight
15%
636
19%
2076
7%
636
26%
636
17%
1370
March16th to endNight
20%
576
16%
2045
7%
576
33%
576
18%
1338
April1st to 15thNight
24%
539
22%
1797
10%
539
41%
539
26%
1017
April16th to endNight
29%
540
21%
1800
13%
540
44%
540
25%
1107
May1st to 15thNight
34%
540
17%
1710
10%
539
44%
539
26%
1059
May16th to endNight
38%
563
19%
1497
11%
561
45%
561
27%
1016
June1st to 15thNight
59%
540
22%
1440
14%
540
64%
540
44%
825
June16th to endNight
56%
540
25%
1440
15%
540
63%
540
46%
807
July1st to 15thNight
65%
510
19%
1360
15%
510
68%
510
42%
801
July16th to endNight
70%
564
22%
1539
19%
531
75%
531
41%
868
August1st to 15thNight
72%
539
23%
1682
25%
536
75%
536
45%
858
August16th to endNight
68%
573
25%
1910
28%
573
71%
573
36%
1032
September1st to 15thNight
61%
540
27%
1800
26%
540
67%
540
31%
1029
September16th to endNight
57%
654
32%
1926
22%
654
65%
654
36%
1095
October1st to 15thNight
44%
720
29%
2160
19%
720
53%
720
37%
1200
October16th to endNight
29%
768
30%
2304
15%
768
45%
768
30%
1333
November1st to 15thNight
31%
760
28%
2455
15%
760
47%
760
29%
1371
November16th to endNight
23%
806
26%
2561
13%
806
38%
806
22%
1564
December1st to 15thNight
19%
975
19%
2730
5%
975
32%
975
22%
1823
December16th to endNight
14%
1040
19%
2912
4%
1040
28%
1040
18%
2042

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
11%6%25%5%35%45%7%41%
49035
Night
11%6%25%424447%46%
48674
TransparencyDay
40%411%24%15%2
48725
Night
37%311%25%18%3
48489
SeeingDay
15%10%27%25%15%4
6214
Night
16%13%30%24%12%1
16344

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%7%27%43434442%
1614
16th to endDay
10%7%35%6%2345%6%44%
1767
February1st to 15thDay
13%9%47%42435%5%38%
1624
16th to endDay
11%10%35%5%25%447%38%
1580
March1st to 15thDay
14%8%46%5%25%345%39%
1893
16th to endDay
16%10%37%5%35%45%6%31%
2176
April1st to 15thDay
11%6%35%433446%45%
2151
16th to endDay
18%7%35%5%34446%35%
2160
May1st to 15thDay
16%5%25%5%3445%8%38%
2234
16th to endDay
11%5%36%6%46%45%8%38%
2617
June1st to 15thDay
7%426%5%36%5%6%8%43%
2520
16th to endDay
5%3135%36%5%7%11%45%
2520
July1st to 15thDay
9%425%6%35%6%6%10%40%
2520
16th to endDay
4325%6%47%7%8%9%41%
2520
August1st to 15thDay
8%5%146%46%6%6%10%39%
2266
16th to endDay
7%6%25%5%35%6%7%9%39%
2292
September1st to 15thDay
12%43442446%9%44%
2160
16th to endDay
10%415%43445%7%47%
2019
October1st to 15thDay
11%6%25%334446%48%
1800
16th to endDay
12%5%13313245%53%
1920
November1st to 15thDay
11%6%244135%45%50%
1732
16th to endDay
14%8%25%434245%44%
1726
December1st to 15thDay
14%7%46%6%25%436%37%
1560
16th to endDay
13%10%47%5%2445%6%34%
1664
January1st to 15thNight
13%6%26%6%34346%41%
2651
16th to endNight
10%8%46%5%24446%43%
2561
February1st to 15thNight
14%9%38%423345%39%
2229
16th to endNight
10%8%36%6%23435%44%
1893
March1st to 15thNight
16%9%35%424435%39%
2076
16th to endNight
17%8%35%424346%37%
2045
April1st to 15thNight
10%6%24414448%48%
1797
16th to endNight
14%6%34424345%45%
1800
May1st to 15thNight
14%6%2332445%7%43%
1710
16th to endNight
9%6%25%6%36%46%6%41%
1496
June1st to 15thNight
7%3133245%6%10%51%
1440
16th to endNight
431232446%11%53%
1440
July1st to 15thNight
8%31432445%9%53%
1440
16th to endNight
43235%245%6%9%50%
1646
August1st to 15thNight
5%21232447%11%52%
1692
16th to endNight
44245%245%5%9%51%
1910
September1st to 15thNight
10%5%24423446%50%
1800
16th to endNight
9%414434346%53%
1926
October1st to 15thNight
8%414423345%55%
2160
16th to endNight
14%5%23312335%53%
2304
November1st to 15thNight
10%5%23323346%52%
2455
16th to endNight
15%8%24413335%46%
2561
December1st to 15thNight
17%7%34424347%39%
2730
16th to endNight
14%11%46%5%24446%36%
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
44%29%24%15%3
1615
16th to endDay
39%213%29%12%2
1767
February1st to 15thDay
47%212%23%12%1
1626
16th to endDay
44%412%25%11%2
1580
March1st to 15thDay
46%39%21%15%3
1893
16th to endDay
53%313%19%9%
2178
April1st to 15thDay
39%311%24%19%2
2151
16th to endDay
49%39%22%13%1
2160
May1st to 15thDay
44%413%23%12%
2234
16th to endDay
44%5%13%20%13%2
2621
June1st to 15thDay
36%413%26%17%1
2520
16th to endDay
30%5%17%25%18%3
2520
July1st to 15thDay
38%412%26%14%4
2371
16th to endDay
34%6%16%28%13%1
2364
August1st to 15thDay
36%5%13%26%16%1
2252
16th to endDay
37%5%14%22%15%5%
2292
September1st to 15thDay
36%410%25%20%3
2160
16th to endDay
34%5%6%30%19%2
2019
October1st to 15thDay
37%39%25%20%3
1800
16th to endDay
33%18%30%21%4
1920
November1st to 15thDay
35%39%25%17%8%
1732
16th to endDay
43%27%26%18%1
1726
December1st to 15thDay
48%38%23%13%1
1560
16th to endDay
49%411%20%12%1
1664
January1st to 15thNight
44%39%24%16%2
2651
16th to endNight
42%210%25%17%1
2561
February1st to 15thNight
46%39%23%14%2
2238
16th to endNight
43%212%24%15%1
1893
March1st to 15thNight
47%39%19%16%2
2076
16th to endNight
47%313%23%11%
2045
April1st to 15thNight
34%313%26%18%2
1797
16th to endNight
40%39%27%16%2
1800
May1st to 15thNight
38%5%16%21%16%1
1711
16th to endNight
40%7%13%20%14%3
1498
June1st to 15thNight
26%415%32%18%1
1440
16th to endNight
24%5%15%30%20%4
1440
July1st to 15thNight
28%414%30%16%4
1360
16th to endNight
27%5%17%30%17%1
1539
August1st to 15thNight
22%5%18%30%20%2
1682
16th to endNight
28%5%13%25%21%5%
1910
September1st to 15thNight
34%47%27%20%5%
1800
16th to endNight
31%38%28%24%4
1926
October1st to 15thNight
30%210%25%24%5%
2160
16th to endNight
34%27%27%22%5%
2304
November1st to 15thNight
32%39%24%22%6%
2455
16th to endNight
40%26%26%21%1
2561
December1st to 15thNight
45%312%21%15%1
2730
16th to endNight
49%311%20%12%3
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
29%22%38%5%2
135
16th to endDay
15%33%37%11%1
109
February1st to 15thDay
21%25%43%10%
90
16th to endDay
25%24%37%11%1
81
March1st to 15thDay
25%26%41%42
90
16th to endDay
25%20%37%12%3
162
April1st to 15thDay
17%18%38%18%5%
270
16th to endDay
23%14%34%16%9%1
270
May1st to 15thDay
18%17%34%18%8%2
314
16th to endDay
14%12%36%22%10%4
517
June1st to 15thDay
10%5%27%31%18%5%
495
16th to endDay
6%6%31%36%14%3
495
July1st to 15thDay
12%321%37%19%5%
475
16th to endDay
5%216%34%33%8%
515
August1st to 15thDay
14%113%30%29%10%
419
16th to endDay
13%215%31%26%10%
332
September1st to 15thDay
13%6%13%29%27%9%
315
16th to endDay
12%7%15%27%27%9%
302
October1st to 15thDay
17%8%36%28%6%1
135
16th to endDay
15%18%34%27%3
144
November1st to 15thDay
15%8%37%26%8%2
135
16th to endDay
27%20%33%14%4
135
December1st to 15thDay
21%24%34%11%24
135
16th to endDay
26%30%36%6%
144
January1st to 15thNight
21%26%32%14%3
975
16th to endNight
17%26%38%15%2
985
February1st to 15thNight
21%22%38%15%1
830
16th to endNight
17%24%39%16%1
631
March1st to 15thNight
25%19%36%16%2
636
16th to endNight
23%13%38%19%5%
576
April1st to 15thNight
15%18%39%22%4
539
16th to endNight
18%12%35%25%8%
540
May1st to 15thNight
18%7%36%25%10%
540
16th to endNight
11%8%32%29%14%2
563
June1st to 15thNight
9%322%39%22%2
540
16th to endNight
6%228%39%21%2
540
July1st to 15thNight
9%213%42%27%4
510
16th to endNight
6%211%41%32%5%
564
August1st to 15thNight
6%112%33%40%5%
539
16th to endNight
6%115%37%32%7%
573
September1st to 15thNight
11%315%32%29%6%
540
16th to endNight
11%5%19%27%29%5%
654
October1st to 15thNight
11%8%29%28%18%4
720
16th to endNight
19%14%33%22%8%
768
November1st to 15thNight
14%15%36%23%9%1
760
16th to endNight
22%19%31%20%5%
806
December1st to 15thNight
25%16%36%17%4
975
16th to endNight
24%19%38%15%1
1040
Page generated at 2018-01-21 11:19:27. Version ac04

Copyright 2018 A. Danko


Bert and Jeanette Lynch Memorial Observatory Clear Sky Chart |Charts Home