Thorn Garden Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thorn Garden Observatory clear sky chart from 2005-11-05 to 2018-11-30.

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
44%
16086
11%
51584
9%
16060
47%
16060
18%
36271

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
25%
822
7%
2911
5%
821
29%
821
9%
2335
January16th to endNight
35%
842
8%
2898
7%
842
37%
842
11%
2220
February1st to 15thNight
31%
760
7%
2483
4%
760
35%
760
10%
1979
February16th to endNight
34%
684
9%
2216
8%
684
37%
684
12%
1697
March1st to 15thNight
32%
780
7%
2207
5%
780
35%
780
13%
1723
March16th to endNight
33%
832
8%
2263
5%
832
35%
832
13%
1784
April1st to 15thNight
35%
776
7%
1946
2%
776
38%
776
16%
1518
April16th to endNight
40%
576
12%
1734
7%
576
44%
576
21%
1206
May1st to 15thNight
52%
389
13%
1559
17%
389
56%
389
19%
960
May16th to endNight
60%
407
8%
1619
12%
406
63%
406
19%
1024
June1st to 15thNight
52%
390
7%
1365
6%
390
53%
390
23%
850
June16th to endNight
56%
390
9%
1365
7%
390
58%
390
30%
780
July1st to 15thNight
72%
370
15%
1295
15%
370
75%
370
43%
625
July16th to endNight
78%
408
19%
1470
26%
386
84%
386
49%
620
August1st to 15thNight
83%
504
20%
1650
23%
502
85%
502
48%
780
August16th to endNight
71%
660
24%
1902
18%
660
74%
660
45%
1003
September1st to 15thNight
73%
780
23%
1950
15%
780
75%
780
49%
1113
September16th to endNight
58%
776
19%
2148
15%
776
60%
776
29%
1402
October1st to 15thNight
53%
780
13%
2340
14%
780
55%
780
23%
1583
October16th to endNight
44%
832
11%
2567
10%
832
47%
832
18%
1857
November1st to 15thNight
28%
820
8%
2870
7%
820
32%
820
9%
2283
November16th to endNight
29%
840
6%
2940
3%
840
32%
840
10%
2318
December1st to 15thNight
32%
788
7%
2766
5%
788
35%
788
11%
2118
December16th to endNight
22%
880
6%
3120
3%
880
25%
880
8%
2493

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
7%8%37%7%46%6%7%7%32%
52746
Night
7%7%37%7%46%6%7%8%33%
51740
Cloud CoverDay
9%7%36%6%35%5%6%7%36%
52746
Night
11%7%36%6%36%5%5%7%34%
51743
TransparencyDay
48%10%16%17%6%
52405
Night
47%9%16%17%8%1
51585
SeeingDay
12%10%26%28%17%3
7652
Night
14%10%23%28%19%4
16094

By Month

Percentage Cloud Cover NW (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
9%12%5%10%9%47%8%8%7%15%
1358
16th to endDay
10%11%38%10%6%9%8%8%8%15%
1674
February1st to 15thDay
10%11%5%11%9%5%7%7%7%8%15%
1711
16th to endDay
8%13%48%9%6%8%7%7%7%18%
1544
March1st to 15thDay
6%11%5%11%9%5%7%6%8%8%18%
2080
16th to endDay
8%13%5%11%12%6%8%7%6%6%14%
2312
April1st to 15thDay
10%11%5%10%9%5%8%7%7%8%16%
2331
16th to endDay
9%8%5%9%9%6%7%7%7%7%22%
2500
May1st to 15thDay
9%6%27%8%46%6%6%7%34%
2721
16th to endDay
10%7%48%8%46%6%7%8%27%
2842
June1st to 15thDay
8%7%37%7%47%6%7%8%30%
2925
16th to endDay
7%6%38%7%46%7%6%7%33%
2925
July1st to 15thDay
442442445%6%56%
2925
16th to endDay
3214323446%63%
2955
August1st to 15thDay
431442345%8%56%
2552
16th to endDay
44244245%6%9%51%
2651
September1st to 15thDay
5%425%423447%55%
2340
16th to endDay
7%5%27%7%45%5%7%8%37%
2141
October1st to 15thDay
9%7%28%7%5%5%6%7%8%31%
1950
16th to endDay
9%8%47%7%36%6%8%10%26%
2009
November1st to 15thDay
9%10%411%8%6%8%8%7%6%16%
1648
16th to endDay
10%11%410%8%38%7%9%8%17%
1674
December1st to 15thDay
8%11%48%7%49%8%7%9%21%
1522
16th to endDay
7%13%5%10%10%5%7%7%7%8%16%
1456
January1st to 15thNight
8%9%48%8%5%8%8%8%8%20%
2911
16th to endNight
10%8%47%8%5%8%8%9%9%20%
2898
February1st to 15thNight
9%9%5%9%9%5%7%7%7%8%20%
2471
16th to endNight
9%10%5%8%8%48%7%7%7%22%
2216
March1st to 15thNight
6%8%37%7%5%9%10%9%10%21%
2207
16th to endNight
6%9%49%8%5%9%8%8%8%21%
2259
April1st to 15thNight
8%9%48%9%46%8%7%8%24%
1946
16th to endNight
7%7%37%8%35%6%6%10%32%
1734
May1st to 15thNight
5%5%36%5%5%8%6%6%6%41%
1559
16th to endNight
6%426%7%36%6%7%10%39%
1619
June1st to 15thNight
8%437%7%44447%43%
1365
16th to endNight
5%4135%246%6%10%48%
1365
July1st to 15thNight
2312323337%66%
1365
16th to endNight
2112212335%73%
1564
August1st to 15thNight
22232235%7%67%
1658
16th to endNight
221333335%7%62%
1902
September1st to 15thNight
4213313447%64%
1950
16th to endNight
8%426%6%36%5%6%8%42%
2148
October1st to 15thNight
7%6%37%7%35%6%6%7%38%
2340
16th to endNight
10%6%37%8%46%6%7%8%30%
2567
November1st to 15thNight
11%9%49%7%5%8%7%7%8%20%
2870
16th to endNight
8%8%49%9%5%7%7%8%8%20%
2940
December1st to 15thNight
6%10%5%9%8%47%7%8%8%22%
2766
16th to endNight
9%12%49%9%5%7%8%7%8%17%
3120

Percentage Cloud Cover SW (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%6%9%9%46%6%5%5%13%
1358
16th to endDay
14%13%6%12%10%46%5%5%6%13%
1674
February1st to 15thDay
16%11%49%9%46%6%6%7%16%
1711
16th to endDay
11%10%48%8%5%6%7%6%7%22%
1544
March1st to 15thDay
10%11%5%9%8%5%7%7%7%7%20%
2080
16th to endDay
10%10%5%8%9%5%7%7%7%7%21%
2312
April1st to 15thDay
12%8%47%9%46%7%6%8%24%
2331
16th to endDay
8%6%47%7%46%5%7%9%32%
2500
May1st to 15thDay
9%425%5%35%5%7%8%40%
2721
16th to endDay
9%6%25%7%35%6%6%8%36%
2842
June1st to 15thDay
8%5%36%6%35%5%6%9%39%
2925
16th to endDay
8%326%5%45%6%7%8%41%
2925
July1st to 15thDay
4213424446%61%
2925
16th to endDay
3212313346%67%
2955
August1st to 15thDay
421332335%7%62%
2552
16th to endDay
432432445%9%55%
2651
September1st to 15thDay
6%31433345%7%55%
2340
16th to endDay
8%5%37%7%45%5%5%7%39%
2141
October1st to 15thDay
12%7%38%6%46%6%6%5%31%
1950
16th to endDay
13%9%48%7%46%5%6%8%25%
2009
November1st to 15thDay
15%11%5%10%9%47%6%5%6%18%
1648
16th to endDay
15%11%5%10%9%39%6%6%5%15%
1674
December1st to 15thDay
12%11%5%10%9%5%7%5%6%5%19%
1522
16th to endDay
12%13%49%8%5%8%5%6%6%17%
1456
January1st to 15thNight
14%11%49%9%48%5%5%6%19%
2910
16th to endNight
15%10%48%8%5%7%7%6%8%18%
2898
February1st to 15thNight
16%10%5%8%7%46%5%6%6%22%
2471
16th to endNight
13%9%46%7%5%7%5%6%7%25%
2216
March1st to 15thNight
11%8%38%8%5%8%8%7%7%23%
2207
16th to endNight
10%8%38%8%5%7%7%6%8%24%
2263
April1st to 15thNight
12%9%37%6%36%6%7%8%28%
1946
16th to endNight
11%6%37%5%45%5%5%9%35%
1734
May1st to 15thNight
6%5%25%5%45%5%5%8%43%
1559
16th to endNight
6%415%6%45%6%5%10%41%
1619
June1st to 15thNight
9%426%5%36%35%8%44%
1365
16th to endNight
6%423435%48%9%47%
1365
July1st to 15thNight
3212323246%67%
1365
16th to endNight
2211112236%73%
1564
August1st to 15thNight
111221335%10%66%
1658
16th to endNight
311331235%8%63%
1902
September1st to 15thNight
5%212312346%65%
1950
16th to endNight
10%5%25%5%3445%7%44%
2148
October1st to 15thNight
10%6%36%6%35%5%45%40%
2340
16th to endNight
15%7%35%7%35%5%5%7%31%
2567
November1st to 15thNight
17%10%48%7%47%5%5%6%21%
2870
16th to endNight
13%8%5%8%10%47%8%7%6%20%
2940
December1st to 15thNight
11%12%48%7%48%6%6%7%21%
2766
16th to endNight
14%12%48%8%47%6%5%6%18%
3120

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
66%9%10%9%3
1358
16th to endDay
65%7%13%8%31
1674
February1st to 15thDay
66%9%10%7%31
1711
16th to endDay
59%8%14%13%3
1544
March1st to 15thDay
61%9%15%11%1
2080
16th to endDay
65%11%12%10%
2312
April1st to 15thDay
61%10%14%12%1
2331
16th to endDay
55%12%13%14%3
2500
May1st to 15thDay
46%9%16%19%6%
2721
16th to endDay
50%14%18%14%2
2846
June1st to 15thDay
48%11%21%13%4
2925
16th to endDay
45%10%21%16%5%
2925
July1st to 15thDay
27%10%18%27%14%2
2766
16th to endDay
19%9%20%31%16%1
2786
August1st to 15thDay
26%8%20%31%11%1
2535
16th to endDay
29%10%19%29%10%1
2651
September1st to 15thDay
27%8%17%25%19%1
2340
16th to endDay
41%10%19%18%9%1
2141
October1st to 15thDay
50%7%17%18%6%
1950
16th to endDay
51%9%16%16%5%
2009
November1st to 15thDay
65%8%12%9%21
1648
16th to endDay
61%11%11%10%4
1674
December1st to 15thDay
60%7%13%13%4
1522
16th to endDay
61%11%13%8%4
1456
January1st to 15thNight
61%10%11%10%4
2911
16th to endNight
57%8%12%11%5%2
2898
February1st to 15thNight
61%8%11%11%6%
2483
16th to endNight
58%7%15%13%4
2216
March1st to 15thNight
55%11%16%14%2
2207
16th to endNight
56%10%16%13%2
2263
April1st to 15thNight
54%9%16%15%3
1946
16th to endNight
46%7%17%20%7%
1734
May1st to 15thNight
39%8%18%21%10%1
1560
16th to endNight
38%11%23%21%3
1619
June1st to 15thNight
40%7%24%20%6%1
1365
16th to endNight
30%8%27%25%5%2
1365
July1st to 15thNight
21%6%18%32%17%3
1295
16th to endNight
14%6%17%34%22%3
1470
August1st to 15thNight
16%8%20%34%16%3
1650
16th to endNight
20%7%21%33%13%2
1902
September1st to 15thNight
20%8%17%26%22%5%
1950
16th to endNight
38%7%14%23%12%2
2148
October1st to 15thNight
44%6%14%21%11%
2340
16th to endNight
50%8%14%17%8%
2567
November1st to 15thNight
61%9%12%11%31
2870
16th to endNight
57%12%13%10%6%
2940
December1st to 15thNight
56%10%14%12%5%
2766
16th to endNight
61%10%14%9%3
3120

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
24%7%17%23%22%4
90
16th to endDay
23%14%34%15%10%1
155
February1st to 15thDay
24%16%31%20%6%
281
16th to endDay
17%21%30%20%8%
252
March1st to 15thDay
19%22%28%20%8%
330
16th to endDay
18%17%31%21%9%1
352
April1st to 15thDay
19%17%26%24%10%1
329
16th to endDay
16%14%25%30%10%1
318
May1st to 15thDay
13%10%25%31%16%2
348
16th to endDay
9%6%26%32%18%5%
397
June1st to 15thDay
9%10%32%31%14%2
570
16th to endDay
8%10%34%29%14%2
570
July1st to 15thDay
46%24%38%24%1
550
16th to endDay
1324%31%29%9%
464
August1st to 15thDay
4217%28%32%13%
359
16th to endDay
45%16%35%28%9%
396
September1st to 15thDay
9%319%34%26%5%
375
16th to endDay
10%6%22%33%22%3
375
October1st to 15thDay
17%10%25%29%15%2
375
16th to endDay
15%14%24%22%16%6%
342
November1st to 15thDay
25%13%29%22%9%
120
16th to endDay
18%16%21%22%12%9%
118
December1st to 15thDay
21%11%25%22%20%
90
16th to endDay
35%14%30%14%5%
96
January1st to 15thNight
21%16%23%20%15%1
825
16th to endNight
19%13%23%23%16%2
842
February1st to 15thNight
19%12%26%28%11%1
764
16th to endNight
16%14%26%26%14%2
684
March1st to 15thNight
15%18%27%23%11%3
780
16th to endNight
13%13%30%27%12%3
832
April1st to 15thNight
14%12%29%26%15%1
776
16th to endNight
11%8%31%32%12%3
576
May1st to 15thNight
9%6%25%31%22%4
390
16th to endNight
7%318%43%24%2
407
June1st to 15thNight
10%323%37%22%1
390
16th to endNight
7%228%36%21%3
390
July1st to 15thNight
3216%38%34%4
370
16th to endNight
3114%38%34%7%
408
August1st to 15thNight
318%30%42%13%
504
16th to endNight
4315%31%35%10%
660
September1st to 15thNight
5%113%29%32%16%
780
16th to endNight
13%315%32%25%8%
776
October1st to 15thNight
12%6%17%30%24%7%
780
16th to endNight
17%10%19%26%18%8%
832
November1st to 15thNight
21%15%26%24%9%1
820
16th to endNight
15%17%27%21%12%4
840
December1st to 15thNight
17%13%25%26%14%2
788
16th to endNight
21%15%33%21%7%
880
Page generated at 2018-12-01 08:35:39. Version ac04

Copyright 2018 A. Danko


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