Joey's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joey's Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
60%
16075
20%
47143
16%
16034
64%
16034
29%
29980

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
48%
718
20%
2327
15%
716
56%
716
25%
1455
January16th to endNight
47%
768
23%
2469
18%
768
56%
768
28%
1486
February1st to 15thNight
45%
701
23%
2103
15%
698
54%
698
33%
1241
February16th to endNight
43%
631
25%
1812
14%
631
54%
631
35%
1075
March1st to 15thNight
51%
720
29%
1980
17%
720
61%
720
40%
1133
March16th to endNight
58%
768
26%
2112
20%
768
63%
768
42%
1200
April1st to 15thNight
59%
718
22%
1976
17%
718
64%
718
40%
1149
April16th to endNight
60%
720
26%
1824
16%
720
64%
720
44%
1068
May1st to 15thNight
68%
603
26%
1683
18%
603
71%
603
41%
967
May16th to endNight
73%
561
20%
1683
17%
561
74%
561
32%
1037
June1st to 15thNight
67%
540
13%
1620
11%
540
68%
540
21%
1152
June16th to endNight
70%
540
9%
1620
7%
540
70%
540
21%
1171
July1st to 15thNight
70%
510
6%
1530
5%
510
70%
510
18%
1157
July16th to endNight
74%
564
8%
1595
8%
531
75%
531
20%
1158
August1st to 15thNight
80%
539
7%
1609
6%
536
80%
536
24%
1111
August16th to endNight
64%
741
8%
2031
7%
741
64%
741
20%
1495
September1st to 15thNight
64%
720
8%
1980
7%
720
64%
720
17%
1489
September16th to endNight
60%
717
12%
1980
12%
717
60%
717
18%
1474
October1st to 15thNight
67%
684
23%
1958
24%
684
69%
684
31%
1244
October16th to endNight
62%
704
27%
2112
25%
704
67%
704
31%
1293
November1st to 15thNight
60%
700
29%
2101
25%
700
67%
700
35%
1224
November16th to endNight
55%
720
29%
2202
23%
720
64%
720
32%
1313
December1st to 15thNight
54%
720
25%
2340
23%
720
61%
720
29%
1394
December16th to endNight
53%
768
22%
2496
21%
768
58%
768
28%
1494

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
8%5%36%7%46%6%6%8%35%
48038
Night
7%425%5%35%5%6%8%44%
47351
TransparencyDay
43%9%13%15%12%5%
47739
Night
35%9%15%19%14%5%
47154
SeeingDay
9%212%21%25%28%
5916
Night
9%217%32%29%8%
16083

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
11%5%35%5%36%5%5%8%40%
1611
16th to endDay
11%5%35%42336%6%46%
1754
February1st to 15thDay
10%5%35%5%345%5%7%43%
1750
16th to endDay
8%6%25%5%35%5%5%5%45%
1661
March1st to 15thDay
6%334426%5%5%7%49%
1980
16th to endDay
7%435%6%35%5%5%6%47%
2111
April1st to 15thDay
6%425%6%35%5%6%8%44%
1972
16th to endDay
6%325%6%35%5%6%9%44%
2133
May1st to 15thDay
6%3245%35%5%6%8%47%
2276
16th to endDay
7%5%27%7%47%7%8%7%33%
2431
June1st to 15thDay
12%5%48%8%5%7%7%7%8%25%
2340
16th to endDay
8%6%48%9%6%8%8%7%8%24%
2340
July1st to 15thDay
10%6%49%9%5%8%8%7%8%21%
2340
16th to endDay
9%7%49%11%6%8%6%7%8%20%
2465
August1st to 15thDay
5%6%39%9%6%8%8%8%10%22%
2340
16th to endDay
12%7%39%9%5%7%7%7%8%21%
2154
September1st to 15thDay
10%7%39%9%6%8%7%7%8%22%
1980
16th to endDay
11%8%49%9%5%8%7%6%9%20%
1980
October1st to 15thDay
10%5%37%8%46%6%6%8%33%
1800
16th to endDay
8%425%6%35%45%8%43%
1760
November1st to 15thDay
5%3245%35%6%6%8%48%
1757
16th to endDay
8%5%26%6%45%5%6%8%40%
1755
December1st to 15thDay
9%6%36%6%45%5%5%7%39%
1620
16th to endDay
8%5%25%6%445%6%8%42%
1728
January1st to 15thNight
10%5%35%5%35%45%7%42%
2327
16th to endNight
12%5%25%42446%6%46%
2469
February1st to 15thNight
10%5%24423346%51%
2103
16th to endNight
8%414434448%50%
1812
March1st to 15thNight
5%3143245%5%7%55%
1980
16th to endNight
5%3144235%5%8%55%
2112
April1st to 15thNight
5%324315%45%8%54%
1976
16th to endNight
5%32442336%7%55%
1824
May1st to 15thNight
4214435%45%8%55%
1683
16th to endNight
5%335%435%5%7%9%47%
1682
June1st to 15thNight
9%7%36%5%46%7%7%10%32%
1620
16th to endNight
8%6%36%7%46%7%7%11%30%
1620
July1st to 15thNight
7%6%35%7%47%7%8%11%29%
1620
16th to endNight
5%426%8%5%7%6%9%11%31%
1703
August1st to 15thNight
2426%6%48%7%9%12%36%
1620
16th to endNight
9%6%36%7%45%6%8%10%31%
2031
September1st to 15thNight
8%5%27%8%46%6%8%10%31%
1980
16th to endNight
10%7%37%7%46%6%7%10%27%
1980
October1st to 15thNight
7%325%6%346%6%7%45%
1958
16th to endNight
9%6%25%5%24447%48%
2112
November1st to 15thNight
5%4235%345%47%51%
2101
16th to endNight
8%4245%35%46%8%47%
2202
December1st to 15thNight
9%425%4345%6%9%44%
2340
16th to endNight
7%5%25%5%35%5%7%8%44%
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
41%6%9%18%16%7%
1612
16th to endDay
37%49%17%21%10%
1754
February1st to 15thDay
38%5%9%12%20%13%
1752
16th to endDay
38%6%9%15%20%9%
1661
March1st to 15thDay
32%6%10%23%18%8%
1980
16th to endDay
35%6%11%18%19%8%
2112
April1st to 15thDay
35%7%12%18%20%6%
1972
16th to endDay
35%6%10%19%20%8%
2133
May1st to 15thDay
32%7%12%21%19%7%
2276
16th to endDay
44%9%13%15%14%2
2435
June1st to 15thDay
53%10%15%16%3
2340
16th to endDay
53%12%19%10%3
2340
July1st to 15thDay
55%14%18%9%1
2201
16th to endDay
55%14%17%11%1
2310
August1st to 15thDay
49%17%23%8%
2327
16th to endDay
56%14%19%8%1
2154
September1st to 15thDay
54%14%16%10%3
1980
16th to endDay
54%12%16%10%41
1980
October1st to 15thDay
46%8%9%14%13%7%
1800
16th to endDay
37%6%9%15%21%10%
1760
November1st to 15thDay
31%5%10%20%23%7%
1757
16th to endDay
39%7%8%17%17%10%
1755
December1st to 15thDay
43%7%10%17%16%4
1620
16th to endDay
37%6%14%18%15%7%
1728
January1st to 15thNight
39%6%10%20%15%7%
2327
16th to endNight
36%5%9%19%19%9%
2469
February1st to 15thNight
34%410%16%20%13%
2112
16th to endNight
31%6%13%18%21%8%
1812
March1st to 15thNight
26%5%12%28%20%6%
1980
16th to endNight
25%6%14%24%20%9%
2112
April1st to 15thNight
26%7%14%23%19%7%
1976
16th to endNight
26%5%16%22%22%6%
1824
May1st to 15thNight
26%6%14%25%18%8%
1684
16th to endNight
31%9%17%22%17%1
1684
June1st to 15thNight
43%12%18%21%4
1620
16th to endNight
43%13%22%17%3
1620
July1st to 15thNight
43%18%23%12%2
1530
16th to endNight
39%18%26%14%1
1595
August1st to 15thNight
33%18%35%11%1
1609
16th to endNight
43%14%26%13%1
2031
September1st to 15thNight
44%17%19%15%3
1980
16th to endNight
48%12%17%16%31
1980
October1st to 15thNight
35%8%12%20%17%6%
1958
16th to endNight
36%5%8%16%24%8%
2112
November1st to 15thNight
31%5%11%21%21%7%
2101
16th to endNight
32%6%9%19%19%11%
2202
December1st to 15thNight
35%6%14%23%13%6%
2340
16th to endNight
35%6%14%21%14%7%
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
23%7%28%23%11%5%
90
16th to endDay
15%13%32%19%14%4
96
February1st to 15thDay
415%26%25%18%8%
90
16th to endDay
12%435%33%13%
162
March1st to 15thDay
7%5%27%34%22%3
270
16th to endDay
10%6%19%24%32%6%
288
April1st to 15thDay
5%5%21%29%26%10%
270
16th to endDay
7%114%25%28%21%
270
May1st to 15thDay
6%113%25%34%19%
288
16th to endDay
6%19%21%29%32%
331
June1st to 15thDay
17%6%14%22%38%
315
16th to endDay
9%310%23%52%
315
July1st to 15thDay
6%27%21%62%
305
16th to endDay
9%2311%19%54%
326
August1st to 15thDay
5%412%23%53%
313
16th to endDay
14%210%19%52%
332
September1st to 15thDay
12%410%25%46%
315
16th to endDay
10%417%28%37%
314
October1st to 15thDay
12%111%23%34%16%
278
16th to endDay
8%118%28%32%9%
272
November1st to 15thDay
6%113%34%32%12%
265
16th to endDay
7%421%38%24%4
225
December1st to 15thDay
12%5%24%42%15%
90
16th to endDay
5%316%37%30%7%
96
January1st to 15thNight
12%7%26%35%16%2
720
16th to endNight
13%5%29%36%12%
768
February1st to 15thNight
12%5%30%37%13%1
704
16th to endNight
11%435%39%9%
631
March1st to 15thNight
6%5%31%40%14%1
720
16th to endNight
6%326%41%20%
768
April1st to 15thNight
6%326%42%21%
718
16th to endNight
5%422%44%21%1
720
May1st to 15thNight
5%115%44%30%2
604
16th to endNight
6%18%36%39%8%
563
June1st to 15thNight
11%15%24%43%13%
540
16th to endNight
10%316%43%26%
540
July1st to 15thNight
8%212%46%28%
510
16th to endNight
6%111%48%31%
564
August1st to 15thNight
3112%51%31%
539
16th to endNight
12%1415%41%25%
741
September1st to 15thNight
10%1419%42%21%
720
16th to endNight
13%6%24%41%12%
717
October1st to 15thNight
9%10%33%39%6%
684
16th to endNight
12%115%33%31%5%
704
November1st to 15thNight
6%319%37%29%4
700
16th to endNight
8%324%41%19%1
720
December1st to 15thNight
9%424%37%22%1
720
16th to endNight
9%424%37%22%1
768
Page generated at 2017-10-07 14:07:49. Version ac04

Copyright 2017 A. Danko


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