Gordon's Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gordon's Park clear sky chart from 2005-11-05 to 2017-08-12.

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
31%
15164
12%
46423
7%
15123
36%
15123
17%
33481

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%
899
5%
2619
2%
895
20%
895
8%
2189
January16th to endNight
22%
891
10%
2619
5%
891
27%
891
11%
2097
February1st to 15thNight
19%
702
9%
2287
3%
701
26%
701
11%
1760
February16th to endNight
25%
631
12%
1961
4%
631
33%
631
15%
1460
March1st to 15thNight
25%
720
13%
2049
6%
720
32%
720
19%
1437
March16th to endNight
35%
768
20%
2112
10%
768
43%
768
27%
1392
April1st to 15thNight
27%
623
17%
1779
8%
623
35%
623
22%
1224
April16th to endNight
32%
540
18%
1620
10%
540
38%
540
23%
1104
May1st to 15thNight
41%
537
12%
1617
11%
537
44%
537
22%
1119
May16th to endNight
44%
374
14%
1436
13%
374
52%
374
21%
862
June1st to 15thNight
41%
360
12%
1260
10%
360
47%
360
21%
791
June16th to endNight
53%
360
11%
1260
10%
360
57%
360
26%
780
July1st to 15thNight
58%
340
15%
1190
14%
340
64%
340
33%
658
July16th to endNight
55%
532
15%
1438
12%
499
56%
499
32%
884
August1st to 15thNight
55%
527
17%
1575
12%
524
61%
524
33%
942
August16th to endNight
59%
525
19%
1575
13%
525
64%
525
32%
947
September1st to 15thNight
46%
630
16%
1711
10%
630
50%
630
31%
1120
September16th to endNight
44%
657
18%
1815
11%
657
49%
657
29%
1195
October1st to 15thNight
33%
660
15%
1949
10%
660
39%
660
18%
1408
October16th to endNight
22%
704
11%
2194
6%
704
30%
704
12%
1695
November1st to 15thNight
25%
700
14%
2353
11%
700
31%
700
13%
1740
November16th to endNight
19%
720
7%
2520
5%
720
23%
720
7%
2019
December1st to 15thNight
12%
804
4%
2604
1%
804
15%
804
6%
2223
December16th to endNight
12%
960
6%
2880
1%
960
17%
960
6%
2435

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%9%36%5%3445%7%35%
47561
Night
15%10%47%6%3445%6%32%
46587
Cloud CoverDay
14%9%36%5%3445%7%35%
47571
Night
15%10%47%5%3445%6%32%
46591
TransparencyDay
47%6%13%20%10%1
47243
Night
52%6%12%18%9%
46423
SeeingDay
18%9%32%25%10%3
5746
Night
20%10%30%25%11%1
15168

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
18%16%5%9%6%35%44420%
1319
16th to endDay
14%17%8%9%6%35%345%21%
1605
February1st to 15thDay
11%14%5%10%7%35%5%5%6%24%
1575
16th to endDay
12%16%5%10%5%345%4427%
1512
March1st to 15thDay
13%10%46%42345%5%38%
1900
16th to endDay
11%8%45%5%335%5%7%40%
2112
April1st to 15thDay
19%10%45%42435%6%34%
2181
16th to endDay
18%7%2442345%7%39%
2340
May1st to 15thDay
17%7%34424447%38%
2332
16th to endDay
12%4244245%5%7%46%
2677
June1st to 15thDay
13%5%25%435%5%6%7%40%
2700
16th to endDay
12%6%345%35%5%6%9%38%
2700
July1st to 15thDay
8%5%245%25%5%5%7%46%
2700
16th to endDay
9%4244345%6%8%47%
2628
August1st to 15thDay
11%42442445%8%45%
2288
16th to endDay
10%6%25%5%35%5%5%8%42%
2275
September1st to 15thDay
11%6%25%4346%5%9%40%
1905
16th to endDay
15%6%2443345%8%39%
1815
October1st to 15thDay
19%9%35%5%35%445%34%
1680
16th to endDay
27%11%47%5%23446%21%
1676
November1st to 15thDay
18%11%37%5%35%45%7%27%
1504
16th to endDay
21%20%5%9%6%3434415%
1440
December1st to 15thDay
17%19%7%9%6%5%6%33414%
1353
16th to endDay
18%20%5%8%6%35%445%15%
1344
January1st to 15thNight
17%15%6%11%6%35%45%5%18%
2619
16th to endNight
14%15%6%9%8%34345%23%
2619
February1st to 15thNight
11%14%5%9%7%35%46%5%25%
2285
16th to endNight
13%13%5%9%6%3435%7%26%
1961
March1st to 15thNight
14%9%46%5%34446%36%
2037
16th to endNight
11%8%25%6%24346%42%
2112
April1st to 15thNight
19%8%25%42435%6%37%
1779
16th to endNight
15%9%36%5%2445%6%36%
1620
May1st to 15thNight
13%7%36%7%35%45%6%34%
1617
16th to endNight
12%6%25%425%45%8%41%
1434
June1st to 15thNight
13%6%35%5%25%5%7%7%38%
1260
16th to endNight
9%5%346%35%5%5%10%40%
1260
July1st to 15thNight
8%324425%5%6%9%48%
1260
16th to endNight
6%325%6%35%5%5%8%48%
1537
August1st to 15thNight
8%315%5%3445%8%49%
1586
16th to endNight
9%4245%34448%47%
1575
September1st to 15thNight
13%425%42346%9%43%
1711
16th to endNight
13%6%25%5%2335%7%43%
1815
October1st to 15thNight
19%8%36%5%2445%5%34%
1949
16th to endNight
25%10%37%6%34345%26%
2194
November1st to 15thNight
16%10%47%6%345%5%7%29%
2353
16th to endNight
21%14%5%8%7%34445%19%
2520
December1st to 15thNight
20%17%6%10%6%3445%5%15%
2604
16th to endNight
22%16%7%9%7%2435%5%15%
2880

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
18%17%5%9%7%35%5%4419%
1319
16th to endDay
14%17%7%10%6%34345%21%
1605
February1st to 15thDay
12%15%6%9%8%35%45%6%23%
1575
16th to endDay
13%15%6%10%5%3445%328%
1512
March1st to 15thDay
14%10%46%42345%5%38%
1911
16th to endDay
11%8%46%5%3445%6%40%
2111
April1st to 15thDay
19%10%45%5%23345%35%
2181
16th to endDay
17%7%2432435%7%40%
2340
May1st to 15thDay
18%7%35%423447%38%
2332
16th to endDay
12%42443445%7%46%
2677
June1st to 15thDay
13%5%24435%5%6%7%40%
2700
16th to endDay
12%5%245%35%5%5%9%38%
2700
July1st to 15thDay
8%5%25%4345%5%8%46%
2700
16th to endDay
9%4244245%6%9%47%
2628
August1st to 15thDay
11%415%43445%8%46%
2288
16th to endDay
11%435%4345%5%8%42%
2275
September1st to 15thDay
11%5%25%5%245%5%8%42%
1905
16th to endDay
15%6%2442446%8%40%
1815
October1st to 15thDay
20%8%25%434446%34%
1680
16th to endDay
28%9%47%5%23446%22%
1676
November1st to 15thDay
18%11%36%5%345%46%28%
1504
16th to endDay
21%20%5%8%6%3435%415%
1440
December1st to 15thDay
18%20%8%8%6%45%34414%
1353
16th to endDay
19%19%6%8%6%3445%6%15%
1344
January1st to 15thNight
17%15%6%10%7%36%345%18%
2619
16th to endNight
14%15%5%10%7%35%346%22%
2619
February1st to 15thNight
11%14%6%10%6%36%45%5%25%
2278
16th to endNight
13%14%5%8%6%3445%7%26%
1961
March1st to 15thNight
15%9%47%5%34346%36%
2049
16th to endNight
11%8%26%5%24347%42%
2112
April1st to 15thNight
19%9%25%42335%6%37%
1779
16th to endNight
15%9%35%5%3445%6%37%
1620
May1st to 15thNight
14%7%36%6%35%45%6%34%
1616
16th to endNight
12%6%25%5%2445%8%41%
1434
June1st to 15thNight
13%6%35%425%5%6%7%38%
1260
16th to endNight
9%435%5%35%5%6%9%41%
1260
July1st to 15thNight
9%313435%45%10%48%
1260
16th to endNight
6%425%6%34447%49%
1537
August1st to 15thNight
8%326%43445%7%49%
1586
16th to endNight
9%425%4235%48%47%
1575
September1st to 15thNight
13%5%2442346%7%45%
1711
16th to endNight
14%5%25%423347%43%
1815
October1st to 15thNight
21%6%26%5%34446%33%
1949
16th to endNight
24%10%36%5%34436%26%
2194
November1st to 15thNight
17%10%47%5%3445%7%28%
2353
16th to endNight
21%15%5%7%7%24446%19%
2520
December1st to 15thNight
21%17%6%10%5%25%35%6%15%
2604
16th to endNight
22%16%7%8%6%3445%5%15%
2880

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%6%11%11%2
1320
16th to endDay
64%5%10%12%5%
1605
February1st to 15thDay
59%6%14%13%5%
1577
16th to endDay
59%410%17%7%
1512
March1st to 15thDay
47%5%13%20%13%
1911
16th to endDay
42%5%13%22%12%3
2112
April1st to 15thDay
50%411%20%12%1
2181
16th to endDay
43%6%10%23%13%2
2340
May1st to 15thDay
45%5%10%21%14%3
2332
16th to endDay
36%7%15%23%17%
2681
June1st to 15thDay
40%7%14%24%12%1
2700
16th to endDay
41%7%13%23%12%
2700
July1st to 15thDay
33%7%12%29%16%1
2541
16th to endDay
33%7%15%27%14%
2464
August1st to 15thDay
35%8%17%24%14%
2275
16th to endDay
38%7%16%28%8%
2275
September1st to 15thDay
38%8%18%26%7%
1905
16th to endDay
41%7%17%26%7%
1815
October1st to 15thDay
51%6%11%19%10%
1680
16th to endDay
63%7%12%10%5%
1676
November1st to 15thDay
56%7%12%17%5%
1504
16th to endDay
72%5%10%8%3
1440
December1st to 15thDay
74%6%9%7%2
1353
16th to endDay
70%7%9%10%2
1344
January1st to 15thNight
67%7%10%10%3
2619
16th to endNight
63%6%9%14%6%
2619
February1st to 15thNight
60%6%12%14%5%
2287
16th to endNight
56%5%13%16%7%
1961
March1st to 15thNight
49%414%20%9%1
2049
16th to endNight
42%412%20%16%3
2112
April1st to 15thNight
47%48%23%14%1
1779
16th to endNight
46%48%19%17%3
1620
May1st to 15thNight
48%5%11%20%12%2
1617
16th to endNight
39%6%12%22%15%2
1436
June1st to 15thNight
41%7%11%22%15%1
1260
16th to endNight
38%6%16%23%14%
1260
July1st to 15thNight
29%6%14%28%18%2
1190
16th to endNight
34%6%14%26%17%
1438
August1st to 15thNight
32%6%17%28%12%2
1575
16th to endNight
34%5%16%30%10%1
1575
September1st to 15thNight
36%7%17%27%9%1
1711
16th to endNight
40%5%15%29%9%
1815
October1st to 15thNight
51%6%11%20%10%
1949
16th to endNight
59%6%11%15%5%
2194
November1st to 15thNight
55%7%12%18%5%
2353
16th to endNight
66%6%13%9%3
2520
December1st to 15thNight
70%8%11%7%1
2604
16th to endNight
70%6%10%7%3
2880

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
23%14%45%15%1
71
16th to endDay
34%12%27%16%8%1
96
February1st to 15thDay
30%23%34%12%
90
16th to endDay
29%20%32%16%1
81
March1st to 15thDay
21%16%33%21%5%1
201
16th to endDay
20%9%33%22%10%3
288
April1st to 15thDay
23%10%27%25%10%2
270
16th to endDay
21%11%35%17%10%4
270
May1st to 15thDay
21%11%27%24%12%3
288
16th to endDay
15%7%34%26%13%2
390
June1st to 15thDay
16%8%34%28%9%1
495
16th to endDay
15%6%35%29%10%2
495
July1st to 15thDay
10%6%34%32%12%3
475
16th to endDay
10%5%32%34%12%4
458
August1st to 15thDay
12%123%36%16%9%
297
16th to endDay
14%5%25%27%18%8%
268
September1st to 15thDay
13%5%25%30%15%9%
255
16th to endDay
15%8%33%20%14%7%
254
October1st to 15thDay
23%10%31%21%11%1
255
16th to endDay
27%18%32%15%5%1
188
November1st to 15thDay
19%15%33%28%2
77
16th to endDay
33%18%38%5%5%
60
December1st to 15thDay
31%23%35%8%1
60
16th to endDay
32%32%32%1
64
January1st to 15thNight
23%17%31%23%4
900
16th to endNight
21%11%32%26%7%1
891
February1st to 15thNight
18%15%37%22%6%
704
16th to endNight
19%11%36%25%6%
631
March1st to 15thNight
18%14%35%24%6%
720
16th to endNight
16%8%33%28%12%
768
April1st to 15thNight
24%9%34%24%5%1
623
16th to endNight
19%8%32%24%13%1
540
May1st to 15thNight
16%429%29%16%2
537
16th to endNight
14%6%28%34%15%
375
June1st to 15thNight
16%6%28%30%15%1
360
16th to endNight
12%5%21%39%18%2
360
July1st to 15thNight
9%325%40%20%1
340
16th to endNight
7%226%37%24%1
532
August1st to 15thNight
10%223%36%23%3
527
16th to endNight
11%320%34%28%3
525
September1st to 15thNight
16%6%26%25%15%8%
630
16th to endNight
16%428%26%16%6%
657
October1st to 15thNight
23%10%27%24%12%1
660
16th to endNight
30%13%27%21%5%
704
November1st to 15thNight
22%16%30%20%9%
700
16th to endNight
29%16%26%20%6%
720
December1st to 15thNight
29%19%32%12%5%
804
16th to endNight
28%17%31%16%41
960
Page generated at 2017-08-13 14:16:39. Version ac04

Copyright 2017 A. Danko


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