Thomas Conway Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thomas Conway Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
38%
15957
17%
46911
11%
15915
44%
15915
23%
31497

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
19%
900
12%
2506
4%
895
26%
895
16%
1862
January16th to endNight
21%
960
12%
2670
4%
960
28%
960
17%
2016
February1st to 15thNight
22%
753
13%
2164
3%
753
30%
753
18%
1545
February16th to endNight
25%
631
17%
1893
7%
631
34%
631
17%
1358
March1st to 15thNight
25%
720
13%
2160
8%
720
29%
720
17%
1566
March16th to endNight
28%
657
15%
2025
8%
657
36%
657
19%
1410
April1st to 15thNight
29%
539
15%
1797
10%
539
39%
539
21%
1184
April16th to endNight
32%
540
19%
1719
12%
540
41%
540
22%
1146
May1st to 15thNight
37%
540
15%
1620
9%
540
43%
540
22%
1120
May16th to endNight
51%
562
17%
1526
10%
561
56%
561
30%
997
June1st to 15thNight
52%
540
17%
1440
11%
540
58%
540
37%
886
June16th to endNight
51%
540
17%
1440
10%
540
56%
540
32%
934
July1st to 15thNight
63%
510
17%
1360
13%
510
65%
510
39%
818
July16th to endNight
70%
564
22%
1417
18%
531
73%
531
42%
839
August1st to 15thNight
77%
539
22%
1595
21%
536
78%
536
40%
905
August16th to endNight
67%
573
21%
1910
22%
573
71%
573
33%
1093
September1st to 15thNight
64%
567
27%
1827
27%
567
68%
567
34%
1034
September16th to endNight
62%
693
28%
1914
22%
693
65%
693
38%
1127
October1st to 15thNight
50%
660
27%
1864
20%
660
56%
660
34%
1126
October16th to endNight
29%
704
18%
2255
11%
704
38%
704
21%
1471
November1st to 15thNight
33%
700
23%
2276
16%
700
44%
700
24%
1384
November16th to endNight
27%
720
17%
2340
11%
720
36%
720
18%
1593
December1st to 15thNight
21%
885
12%
2505
4%
885
28%
885
16%
1877
December16th to endNight
17%
960
10%
2688
3%
960
24%
960
11%
2206

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
14%7%36%5%35%45%7%36%
48028
Night
14%8%35%5%24446%39%
47079
Cloud CoverDay
14%8%36%5%35%45%7%36%
48037
Night
14%8%35%5%24446%39%
47084
TransparencyDay
46%5%12%21%12%1
47714
Night
45%412%21%13%2
46911
SeeingDay
16%7%26%25%17%7%
5966
Night
18%8%28%30%13%1
15961

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
17%15%38%6%35%5%35%24%
1432
16th to endDay
14%14%8%8%5%25%335%25%
1551
February1st to 15thDay
15%13%6%7%6%25%347%26%
1696
16th to endDay
16%9%6%7%7%34346%30%
1580
March1st to 15thDay
19%12%47%5%34446%27%
1790
16th to endDay
19%8%37%6%35%447%30%
2210
April1st to 15thDay
19%9%35%5%24246%35%
2151
16th to endDay
19%8%24434446%35%
2241
May1st to 15thDay
20%9%35%5%35%45%7%30%
2331
16th to endDay
11%5%36%5%35%5%5%8%39%
2587
June1st to 15thDay
10%5%24435%5%6%8%43%
2520
16th to endDay
9%426%6%35%6%7%9%39%
2520
July1st to 15thDay
8%425%5%45%5%6%9%42%
2520
16th to endDay
6%415%5%46%6%7%9%42%
2655
August1st to 15thDay
6%426%5%35%5%5%8%46%
2353
16th to endDay
8%5%25%5%35%5%49%42%
2292
September1st to 15thDay
13%4235%2445%7%45%
2121
16th to endDay
8%4344245%6%8%45%
1905
October1st to 15thDay
14%6%245%34447%42%
1766
16th to endDay
19%7%26%5%345%5%6%34%
1617
November1st to 15thDay
15%5%25%42335%6%44%
1582
16th to endDay
18%9%35%5%33346%35%
1620
December1st to 15thDay
19%13%47%6%34445%26%
1452
16th to endDay
22%15%6%7%424445%22%
1536
January1st to 15thNight
19%12%5%7%423335%31%
2506
16th to endNight
14%12%7%8%6%34346%28%
2670
February1st to 15thNight
16%11%46%5%24336%34%
2162
16th to endNight
17%11%5%7%5%23445%32%
1893
March1st to 15thNight
18%10%45%5%34446%32%
2147
16th to endNight
15%7%36%6%345%5%7%33%
2025
April1st to 15thNight
16%7%36%4345%45%38%
1797
16th to endNight
17%6%26%5%2445%6%38%
1719
May1st to 15thNight
20%5%25%425%46%6%35%
1620
16th to endNight
9%425%435%5%6%7%43%
1524
June1st to 15thNight
9%425%423448%50%
1440
16th to endNight
8%425%5%25%5%5%8%43%
1440
July1st to 15thNight
7%4145%2345%8%52%
1440
16th to endNight
5%4245%2446%7%53%
1513
August1st to 15thNight
4314425%5%7%10%50%
1604
16th to endNight
9%42442445%8%50%
1910
September1st to 15thNight
11%32342335%6%53%
1827
16th to endNight
8%4244245%48%51%
1914
October1st to 15thNight
12%5%24423345%51%
1864
16th to endNight
19%8%35%422345%40%
2255
November1st to 15thNight
13%7%25%423347%44%
2276
16th to endNight
19%8%35%42435%6%36%
2340
December1st to 15thNight
20%11%47%424335%30%
2505
16th to endNight
23%15%5%7%6%3433422%
2688

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
16%15%49%5%35%5%45%24%
1432
16th to endDay
14%15%8%9%6%15%436%25%
1551
February1st to 15thDay
15%14%5%7%6%25%346%26%
1696
16th to endDay
15%10%6%7%8%34346%30%
1580
March1st to 15thDay
18%12%5%7%5%2445%6%27%
1800
16th to endDay
18%8%36%6%35%45%6%30%
2209
April1st to 15thDay
19%9%35%424346%35%
2151
16th to endDay
19%7%345%35%45%6%35%
2241
May1st to 15thDay
20%9%35%5%3445%6%30%
2331
16th to endDay
11%5%36%5%35%5%5%8%39%
2587
June1st to 15thDay
10%5%245%35%5%6%8%43%
2520
16th to endDay
9%425%6%45%6%7%8%39%
2520
July1st to 15thDay
8%425%5%35%6%6%9%42%
2520
16th to endDay
6%3245%46%6%7%9%42%
2655
August1st to 15thDay
6%426%5%35%5%6%8%46%
2353
16th to endDay
8%5%25%5%35%5%5%8%42%
2292
September1st to 15thDay
13%414435%45%7%44%
2121
16th to endDay
9%4344245%6%8%45%
1905
October1st to 15thDay
14%7%1443445%7%42%
1766
16th to endDay
19%7%36%4345%46%34%
1617
November1st to 15thDay
15%5%25%42435%6%44%
1582
16th to endDay
18%9%35%5%34346%35%
1620
December1st to 15thDay
20%13%37%6%34445%26%
1452
16th to endDay
22%16%5%7%5%33445%21%
1536
January1st to 15thNight
19%12%47%423335%31%
2506
16th to endNight
15%12%6%8%6%24345%28%
2670
February1st to 15thNight
16%10%46%5%24336%34%
2155
16th to endNight
16%11%5%7%5%24345%32%
1893
March1st to 15thNight
18%10%5%5%5%34436%32%
2160
16th to endNight
15%7%36%6%345%48%33%
2025
April1st to 15thNight
16%7%35%5%24446%38%
1797
16th to endNight
17%7%26%5%2435%6%38%
1719
May1st to 15thNight
19%6%25%43445%6%35%
1619
16th to endNight
9%4345%35%5%5%7%44%
1524
June1st to 15thNight
9%4245%23448%49%
1440
16th to endNight
8%425%5%25%5%6%8%43%
1440
July1st to 15thNight
6%3145%2435%9%52%
1440
16th to endNight
4324425%45%8%52%
1513
August1st to 15thNight
4214325%5%7%10%50%
1604
16th to endNight
9%42442445%8%50%
1910
September1st to 15thNight
11%313423446%53%
1827
16th to endNight
8%414425%45%8%51%
1914
October1st to 15thNight
12%5%24423346%50%
1864
16th to endNight
19%7%35%422336%40%
2255
November1st to 15thNight
13%6%25%433347%44%
2276
16th to endNight
18%8%35%424446%36%
2340
December1st to 15thNight
20%11%47%434335%30%
2505
16th to endNight
23%15%5%7%6%3433422%
2688

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
60%6%11%13%8%
1433
16th to endDay
61%412%15%6%
1551
February1st to 15thDay
57%5%10%17%7%1
1698
16th to endDay
55%5%12%21%41
1580
March1st to 15thDay
57%5%11%18%6%
1800
16th to endDay
53%5%12%21%5%
2210
April1st to 15thDay
50%410%21%12%
2151
16th to endDay
48%5%12%18%10%4
2241
May1st to 15thDay
52%5%11%21%7%
2331
16th to endDay
41%6%12%20%15%2
2591
June1st to 15thDay
36%7%11%24%19%1
2520
16th to endDay
38%7%14%19%16%2
2520
July1st to 15thDay
38%7%11%22%17%2
2371
16th to endDay
35%7%17%23%14%2
2488
August1st to 15thDay
33%8%14%24%18%1
2338
16th to endDay
37%6%11%23%16%3
2292
September1st to 15thDay
36%6%10%23%18%4
2121
16th to endDay
33%6%11%27%19%1
1905
October1st to 15thDay
41%5%10%25%15%2
1766
16th to endDay
49%5%13%21%9%1
1617
November1st to 15thDay
40%313%23%16%3
1582
16th to endDay
50%314%21%9%
1620
December1st to 15thDay
60%412%17%5%
1452
16th to endDay
64%5%12%12%5%
1536
January1st to 15thNight
56%312%16%9%
2506
16th to endNight
57%314%16%7%
2670
February1st to 15thNight
52%413%19%9%1
2164
16th to endNight
53%411%20%9%
1893
March1st to 15thNight
53%5%11%18%9%2
2160
16th to endNight
47%7%15%19%8%1
2025
April1st to 15thNight
46%411%21%14%1
1797
16th to endNight
46%5%9%19%14%4
1719
May1st to 15thNight
47%5%12%21%12%
1620
16th to endNight
37%7%14%19%17%3
1526
June1st to 15thNight
33%5%12%25%21%2
1440
16th to endNight
37%6%12%23%17%2
1440
July1st to 15thNight
30%6%13%26%19%3
1360
16th to endNight
28%5%15%28%17%4
1417
August1st to 15thNight
26%7%15%27%20%2
1595
16th to endNight
31%6%11%24%20%5%
1910
September1st to 15thNight
31%5%10%24%22%5%
1827
16th to endNight
30%5%9%28%22%3
1914
October1st to 15thNight
35%310%26%23%1
1864
16th to endNight
46%311%24%12%1
2255
November1st to 15thNight
40%49%24%17%4
2276
16th to endNight
49%413%22%10%
2340
December1st to 15thNight
57%311%17%9%
2505
16th to endNight
67%39%13%5%
2688

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
27%8%36%18%7%
90
16th to endDay
16%17%32%28%5%
96
February1st to 15thDay
22%13%54%10%
90
16th to endDay
19%12%34%18%12%2
81
March1st to 15thDay
34%17%26%17%3
90
16th to endDay
25%12%28%22%9%1
264
April1st to 15thDay
24%10%30%21%11%1
270
16th to endDay
21%11%28%23%11%5%
270
May1st to 15thDay
25%9%29%19%13%3
288
16th to endDay
16%7%31%25%14%5%
487
June1st to 15thDay
11%5%27%31%18%5%
495
16th to endDay
13%7%33%26%14%5%
495
July1st to 15thDay
12%324%28%19%12%
475
16th to endDay
7%221%31%24%11%
515
August1st to 15thDay
8%117%27%26%17%
358
16th to endDay
12%117%27%26%15%
332
September1st to 15thDay
14%314%28%29%10%
315
16th to endDay
7%415%27%32%11%
287
October1st to 15thDay
14%5%25%28%21%4
206
16th to endDay
28%7%38%23%2
96
November1st to 15thDay
12%8%23%26%22%6%
90
16th to endDay
32%14%33%14%5%
90
December1st to 15thDay
25%17%32%17%6%
90
16th to endDay
28%27%36%5%3
96
January1st to 15thNight
24%13%37%20%4
900
16th to endNight
19%14%35%26%3
960
February1st to 15thNight
22%11%37%23%4
756
16th to endNight
22%11%34%26%4
631
March1st to 15thNight
23%11%35%24%5%
720
16th to endNight
18%10%37%24%8%
657
April1st to 15thNight
19%10%36%26%6%
539
16th to endNight
21%6%34%26%10%1
540
May1st to 15thNight
21%5%28%31%11%
540
16th to endNight
11%326%39%18%
563
June1st to 15thNight
10%226%45%15%
540
16th to endNight
10%324%37%22%1
540
July1st to 15thNight
10%119%41%25%1
510
16th to endNight
5%114%43%32%3
564
August1st to 15thNight
5%17%48%30%5%
539
16th to endNight
10%112%36%33%4
573
September1st to 15thNight
12%312%37%28%4
567
16th to endNight
9%418%34%29%4
693
October1st to 15thNight
15%6%23%34%18%1
660
16th to endNight
23%12%29%25%8%
704
November1st to 15thNight
17%12%32%25%11%1
700
16th to endNight
21%13%32%24%7%
720
December1st to 15thNight
28%12%31%22%4
885
16th to endNight
31%11%31%21%3
960
Page generated at 2017-09-25 08:02:21. Version ac04

Copyright 2017 A. Danko


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