Joyce Observatory 2
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joyce Observatory 2 clear sky chart from 2005-11-05 to 2017-09-18.

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
55%
15974
20%
46985
15%
15935
61%
15935
27%
29310

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
45%
717
18%
2327
12%
716
54%
716
22%
1420
January16th to endNight
42%
768
24%
2387
18%
768
51%
768
26%
1429
February1st to 15thNight
45%
701
24%
2105
16%
699
54%
699
29%
1261
February16th to endNight
48%
631
28%
1832
14%
631
62%
631
33%
1027
March1st to 15thNight
46%
720
31%
1980
17%
720
59%
720
38%
1079
March16th to endNight
51%
768
27%
2112
18%
768
59%
768
36%
1188
April1st to 15thNight
56%
718
24%
1976
16%
718
63%
718
39%
1059
April16th to endNight
50%
720
27%
1881
15%
720
58%
720
33%
1120
May1st to 15thNight
65%
590
28%
1670
20%
590
70%
590
40%
898
May16th to endNight
64%
561
21%
1683
14%
561
69%
561
31%
994
June1st to 15thNight
60%
540
9%
1620
7%
540
62%
540
19%
1142
June16th to endNight
63%
540
7%
1620
5%
540
64%
540
18%
1172
July1st to 15thNight
64%
510
5%
1530
5%
510
64%
510
18%
1156
July16th to endNight
67%
564
7%
1595
7%
531
71%
531
21%
1142
August1st to 15thNight
67%
539
5%
1676
6%
536
67%
536
21%
1177
August16th to endNight
62%
726
7%
2063
6%
726
62%
726
17%
1527
September1st to 15thNight
61%
720
7%
1980
6%
720
61%
720
18%
1466
September16th to endNight
53%
669
8%
1848
7%
669
55%
669
15%
1398
October1st to 15thNight
63%
660
24%
1851
23%
660
66%
660
30%
1139
October16th to endNight
52%
704
24%
2112
19%
704
59%
704
27%
1298
November1st to 15thNight
54%
700
30%
2101
26%
700
62%
700
33%
1199
November16th to endNight
51%
720
29%
2200
21%
720
63%
720
31%
1265
December1st to 15thNight
50%
720
24%
2340
22%
720
57%
720
27%
1382
December16th to endNight
53%
768
25%
2496
21%
768
61%
768
30%
1372

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
6%425%6%46%6%7%9%39%
47792
Night
6%425%5%35%5%6%9%43%
47191
TransparencyDay
38%8%17%18%12%4
47493
Night
34%7%17%20%14%4
46994
SeeingDay
7%9%10%19%25%27%
5822
Night
7%16%11%28%26%10%
15983

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
9%6%25%5%445%5%9%42%
1611
16th to endDay
8%4245%35%5%5%7%47%
1835
February1st to 15thDay
9%33442436%7%50%
1750
16th to endDay
6%31332446%8%54%
1640
March1st to 15thDay
321332446%9%57%
1980
16th to endDay
5%315%43445%8%53%
2111
April1st to 15thDay
42143245%7%11%51%
1972
16th to endDay
5%313435%47%9%51%
2078
May1st to 15thDay
32133245%7%10%56%
2289
16th to endDay
6%3247%5%7%6%7%10%38%
2431
June1st to 15thDay
11%7%37%7%47%8%8%10%24%
2340
16th to endDay
7%5%27%7%5%7%8%9%12%26%
2340
July1st to 15thDay
7%5%38%9%6%9%9%9%9%22%
2340
16th to endDay
6%5%37%7%5%9%9%10%12%20%
2465
August1st to 15thDay
4437%9%5%8%8%9%10%26%
2268
16th to endDay
9%5%27%8%5%8%9%9%10%23%
2126
September1st to 15thDay
6%5%36%9%5%9%8%9%11%24%
1980
16th to endDay
9%6%37%9%5%7%8%7%9%23%
1837
October1st to 15thDay
6%326%6%47%5%6%10%40%
1777
16th to endDay
9%5%235%35%45%7%46%
1760
November1st to 15thDay
5%4145%25%45%7%51%
1757
16th to endDay
6%425%5%345%5%8%49%
1757
December1st to 15thDay
7%5%25%435%5%6%9%43%
1620
16th to endDay
5%4245%345%5%10%48%
1728
January1st to 15thNight
8%5%245%36%5%6%8%42%
2327
16th to endNight
9%425%335%5%7%8%44%
2387
February1st to 15thNight
10%424424346%49%
2103
16th to endNight
6%313335%46%10%51%
1832
March1st to 15thNight
42133345%6%9%55%
1980
16th to endNight
421443445%8%55%
2112
April1st to 15thNight
321333446%9%56%
1976
16th to endNight
5%313445%45%9%51%
1881
May1st to 15thNight
2213325%5%5%9%58%
1670
16th to endNight
5%3245%35%5%6%10%47%
1682
June1st to 15thNight
9%5%35%8%45%6%7%10%32%
1620
16th to endNight
4437%6%47%8%9%13%30%
1620
July1st to 15thNight
5%6%37%7%46%7%8%12%28%
1620
16th to endNight
43247%49%9%9%13%30%
1703
August1st to 15thNight
6%5%26%6%448%9%11%34%
1687
16th to endNight
9%426%7%5%7%6%8%10%30%
2063
September1st to 15thNight
8%6%37%7%47%6%8%11%28%
1980
16th to endNight
10%6%37%7%5%6%7%8%10%25%
1848
October1st to 15thNight
5%5%25%4245%6%8%46%
1851
16th to endNight
11%4245%3446%7%45%
2112
November1st to 15thNight
6%5%145%25%45%7%51%
2101
16th to endNight
7%424425%46%9%49%
2200
December1st to 15thNight
7%5%345%35%46%8%45%
2340
16th to endNight
5%424425%5%6%9%49%
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
38%312%22%18%4
1612
16th to endDay
33%49%23%20%7%
1835
February1st to 15thDay
32%39%20%20%12%
1752
16th to endDay
26%5%15%21%21%9%
1640
March1st to 15thDay
23%413%27%22%7%
1980
16th to endDay
30%312%23%21%8%
2112
April1st to 15thDay
26%419%25%18%5%
1972
16th to endDay
27%5%13%24%23%5%
2078
May1st to 15thDay
22%6%17%27%20%5%
2289
16th to endDay
37%7%19%22%12%1
2435
June1st to 15thDay
51%8%24%13%2
2340
16th to endDay
47%11%24%13%2
2340
July1st to 15thDay
53%15%23%6%1
2201
16th to endDay
49%14%25%9%
2310
August1st to 15thDay
48%13%29%8%
2255
16th to endDay
51%14%25%8%
2126
September1st to 15thDay
47%15%26%9%1
1980
16th to endDay
51%10%19%13%4
1837
October1st to 15thDay
37%7%14%19%16%5%
1777
16th to endDay
36%5%9%18%19%10%
1760
November1st to 15thDay
31%39%23%21%10%
1757
16th to endDay
32%6%10%20%17%12%
1757
December1st to 15thDay
36%415%21%15%5%
1620
16th to endDay
31%414%26%17%5%
1728
January1st to 15thNight
37%6%13%24%13%3
2327
16th to endNight
34%5%11%22%19%6%
2387
February1st to 15thNight
35%38%20%20%11%
2112
16th to endNight
27%5%13%24%21%8%
1832
March1st to 15thNight
24%412%29%22%6%
1980
16th to endNight
26%414%26%21%7%
2112
April1st to 15thNight
23%417%30%18%5%
1976
16th to endNight
29%412%25%24%4
1881
May1st to 15thNight
23%5%15%29%21%6%
1671
16th to endNight
31%5%19%26%16%
1684
June1st to 15thNight
44%9%24%16%4
1620
16th to endNight
40%16%24%13%4
1620
July1st to 15thNight
46%14%29%7%2
1530
16th to endNight
39%16%30%13%
1595
August1st to 15thNight
38%14%35%9%
1676
16th to endNight
45%15%28%10%
2063
September1st to 15thNight
45%14%26%11%2
1980
16th to endNight
48%13%20%12%4
1848
October1st to 15thNight
31%8%15%17%20%5%
1851
16th to endNight
36%5%11%16%20%8%
2112
November1st to 15thNight
31%49%23%22%8%
2101
16th to endNight
30%5%10%22%19%11%
2200
December1st to 15thNight
35%411%25%17%4
2340
16th to endNight
30%415%22%21%5%
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
17%8%35%17%16%3
90
16th to endDay
13%10%35%30%8%2
96
February1st to 15thDay
6%6%32%24%23%6%
90
16th to endDay
8%8%27%37%17%
141
March1st to 15thDay
213%25%32%21%3
270
16th to endDay
7%14%18%27%25%6%
288
April1st to 15thDay
412%20%28%27%6%
270
16th to endDay
7%12%9%30%32%7%
270
May1st to 15thDay
412%9%25%26%22%
288
16th to endDay
411%415%30%32%
331
June1st to 15thDay
14%11%310%22%37%
315
16th to endDay
410%8%20%54%
315
July1st to 15thDay
5%7%318%64%
305
16th to endDay
9%10%18%20%50%
326
August1st to 15thDay
7%6%7%22%56%
313
16th to endDay
11%6%28%26%45%
332
September1st to 15thDay
9%6%29%27%43%
315
16th to endDay
9%7%8%33%40%
262
October1st to 15thDay
7%8%5%26%34%16%
255
16th to endDay
12%6%16%29%23%11%
272
November1st to 15thDay
5%11%10%31%28%13%
265
16th to endDay
7%11%15%33%25%5%
227
December1st to 15thDay
14%138%26%17%1
90
16th to endDay
5%215%34%34%8%
96
January1st to 15thNight
9%21%17%34%16%
720
16th to endNight
10%21%18%34%13%
768
February1st to 15thNight
7%19%21%35%15%
704
16th to endNight
7%18%20%39%13%
631
March1st to 15thNight
5%19%23%35%15%
720
16th to endNight
419%18%38%17%1
768
April1st to 15thNight
418%16%41%18%1
718
16th to endNight
6%17%17%36%20%
720
May1st to 15thNight
217%9%41%26%2
591
16th to endNight
418%327%36%8%
563
June1st to 15thNight
9%17%215%39%16%
540
16th to endNight
416%110%36%30%
540
July1st to 15thNight
5%13%336%40%
510
16th to endNight
417%438%35%
564
August1st to 15thNight
8%10%339%37%
539
16th to endNight
9%9%311%34%31%
726
September1st to 15thNight
9%10%312%37%27%
720
16th to endNight
14%10%317%37%17%
669
October1st to 15thNight
9%10%5%33%32%7%
660
16th to endNight
12%10%13%30%28%3
704
November1st to 15thNight
6%15%15%38%22%2
700
16th to endNight
8%17%16%35%19%2
720
December1st to 15thNight
8%19%16%34%21%1
720
16th to endNight
418%16%33%24%1
768
Page generated at 2017-09-19 07:32:20. Version ac04

Copyright 2017 A. Danko


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