John J. McCarthy Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the John J. McCarthy Observatory 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
28%
14818
19%
46477
8%
14786
40%
14786
20%
30007

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
18%
720
21%
2506
8%
716
35%
716
17%
1555
January16th to endNight
16%
768
21%
2637
5%
768
36%
768
16%
1651
February1st to 15thNight
15%
704
17%
2213
3%
701
31%
701
15%
1461
February16th to endNight
17%
631
24%
1893
7%
631
36%
631
18%
1212
March1st to 15thNight
17%
720
18%
2160
6%
720
32%
720
16%
1443
March16th to endNight
20%
768
24%
1997
7%
768
34%
768
20%
1314
April1st to 15thNight
19%
718
16%
1796
3%
718
27%
718
21%
1263
April16th to endNight
22%
672
17%
1752
3%
672
32%
672
22%
1208
May1st to 15thNight
22%
513
17%
1593
6%
513
33%
513
16%
1094
May16th to endNight
32%
375
14%
1497
11%
374
42%
374
17%
944
June1st to 15thNight
33%
360
14%
1440
9%
360
46%
360
17%
939
June16th to endNight
47%
360
14%
1440
13%
360
56%
360
25%
815
July1st to 15thNight
47%
340
11%
1360
13%
340
52%
340
21%
839
July16th to endNight
52%
376
15%
1418
17%
354
57%
354
22%
858
August1st to 15thNight
48%
504
17%
1553
10%
502
54%
502
29%
936
August16th to endNight
54%
700
17%
1750
9%
700
57%
700
31%
1178
September1st to 15thNight
43%
660
23%
1657
12%
660
48%
660
31%
1089
September16th to endNight
47%
657
25%
1815
17%
657
53%
657
31%
1141
October1st to 15thNight
34%
660
21%
1908
12%
660
45%
660
24%
1236
October16th to endNight
25%
704
18%
2226
6%
704
39%
704
20%
1445
November1st to 15thNight
29%
700
21%
2277
9%
700
45%
700
22%
1433
November16th to endNight
26%
720
20%
2381
10%
720
39%
720
18%
1530
December1st to 15thNight
23%
720
16%
2520
6%
720
36%
720
15%
1656
December16th to endNight
15%
768
19%
2688
4%
768
33%
768
14%
1767

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
16%6%25%5%3445%7%38%
47509
Night
16%6%2442445%6%41%
46647
Cloud CoverDay
16%6%25%43445%7%39%
47519
Night
16%6%2442445%6%41%
46652
TransparencyDay
43%5%11%21%14%1
47197
Night
42%5%12%22%15%2
46477
SeeingDay
21%13%29%21%10%3
5651
Night
22%14%30%23%8%
14818

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
15%6%245%35%5%5%6%39%
1432
16th to endDay
14%6%35%42445%7%39%
1586
February1st to 15thDay
15%6%36%6%35%5%47%36%
1648
16th to endDay
16%6%26%5%25%446%38%
1580
March1st to 15thDay
17%6%35%6%44346%36%
1790
16th to endDay
18%7%25%423346%40%
2226
April1st to 15thDay
19%7%245%24445%38%
2152
16th to endDay
16%5%24323437%43%
2208
May1st to 15thDay
22%7%245%25%346%34%
2368
16th to endDay
16%6%25%425%45%7%38%
2618
June1st to 15thDay
22%5%24425%5%6%7%32%
2520
16th to endDay
13%5%246%35%5%5%10%35%
2520
July1st to 15thDay
13%435%6%35%5%5%8%37%
2520
16th to endDay
12%435%5%36%6%6%8%37%
2654
August1st to 15thDay
13%5%25%5%25%6%7%8%37%
2298
16th to endDay
11%5%35%5%35%5%5%8%40%
2100
September1st to 15thDay
13%5%25%5%345%5%6%42%
1972
16th to endDay
13%5%24424446%47%
1815
October1st to 15thDay
19%5%25%42435%442%
1722
16th to endDay
18%5%145%35%446%40%
1645
November1st to 15thDay
17%6%2332325%7%44%
1581
16th to endDay
18%6%2331436%6%42%
1578
December1st to 15thDay
17%6%45%4345%46%38%
1440
16th to endDay
19%8%36%43445%7%33%
1536
January1st to 15thNight
17%6%25%425%45%6%41%
2506
16th to endNight
15%8%345%23447%41%
2637
February1st to 15thNight
14%7%35%5%35%46%6%38%
2212
16th to endNight
15%7%25%42335%6%42%
1893
March1st to 15thNight
17%6%25%4345%46%39%
2147
16th to endNight
16%6%25%423346%44%
1997
April1st to 15thNight
17%7%25%5%35%45%6%37%
1796
16th to endNight
18%5%25%423345%41%
1752
May1st to 15thNight
19%7%25%5%33445%36%
1593
16th to endNight
17%6%24434448%38%
1495
June1st to 15thNight
19%6%25%4235%46%39%
1440
16th to endNight
13%4244235%7%8%45%
1440
July1st to 15thNight
12%6%15%43446%9%39%
1440
16th to endNight
9%5%35%5%445%6%8%40%
1514
August1st to 15thNight
11%3245%245%5%7%46%
1563
16th to endNight
13%414425%46%8%43%
1750
September1st to 15thNight
15%423423447%47%
1657
16th to endNight
13%5%2342443451%
1815
October1st to 15thNight
17%5%245%33246%44%
1908
16th to endNight
20%425%43335%5%41%
2226
November1st to 15thNight
16%7%24423445%44%
2277
16th to endNight
17%6%25%43435%6%38%
2381
December1st to 15thNight
20%6%2443436%6%37%
2520
16th to endNight
20%6%2442446%6%36%
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
15%6%24435%46%6%40%
1432
16th to endDay
14%6%25%42445%7%40%
1586
February1st to 15thDay
16%6%35%5%35%6%47%36%
1648
16th to endDay
16%6%35%5%2445%6%39%
1580
March1st to 15thDay
17%7%25%5%35%446%36%
1800
16th to endDay
17%7%24433345%41%
2226
April1st to 15thDay
19%7%245%24446%38%
2152
16th to endDay
17%5%25%423437%44%
2208
May1st to 15thDay
21%7%25%42435%6%34%
2368
16th to endDay
16%6%25%425%45%7%38%
2618
June1st to 15thDay
22%5%24435%45%8%32%
2520
16th to endDay
12%6%245%35%5%7%9%36%
2520
July1st to 15thDay
13%5%25%5%46%5%5%7%38%
2520
16th to endDay
11%5%25%5%36%6%6%8%37%
2654
August1st to 15thDay
13%425%5%25%6%6%9%37%
2298
16th to endDay
11%5%26%5%35%45%8%39%
2100
September1st to 15thDay
13%5%15%6%346%5%5%43%
1972
16th to endDay
14%4244245%45%46%
1815
October1st to 15thDay
18%7%24424345%41%
1722
16th to endDay
18%5%145%35%5%5%5%40%
1645
November1st to 15thDay
17%6%24323348%43%
1581
16th to endDay
17%6%2431335%7%43%
1578
December1st to 15thDay
17%6%35%424446%39%
1440
16th to endDay
19%8%35%42445%6%34%
1536
January1st to 15thNight
17%6%15%42445%6%42%
2506
16th to endNight
15%7%34423346%42%
2637
February1st to 15thNight
14%8%35%5%35%446%39%
2205
16th to endNight
16%6%35%423346%43%
1893
March1st to 15thNight
18%6%25%42445%5%39%
2160
16th to endNight
16%6%34423447%43%
1996
April1st to 15thNight
17%7%34434447%37%
1796
16th to endNight
18%6%25%423435%42%
1752
May1st to 15thNight
19%6%35%5%34446%35%
1593
16th to endNight
17%7%2442345%7%38%
1495
June1st to 15thNight
21%5%245%24446%39%
1440
16th to endNight
12%5%25%41446%8%45%
1440
July1st to 15thNight
12%435%5%245%6%10%38%
1440
16th to endNight
9%5%35%5%35%5%6%8%40%
1514
August1st to 15thNight
10%3246%25%45%8%46%
1563
16th to endNight
13%42443446%7%43%
1750
September1st to 15thNight
14%423423347%47%
1657
16th to endNight
14%424324335%50%
1815
October1st to 15thNight
16%5%245%33346%44%
1908
16th to endNight
19%5%2442345%5%41%
2226
November1st to 15thNight
16%6%34413345%44%
2277
16th to endNight
18%6%25%43345%6%39%
2381
December1st to 15thNight
20%6%2443445%6%37%
2520
16th to endNight
21%6%3442445%6%36%
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
43%5%12%23%12%3
1433
16th to endDay
42%413%24%13%1
1586
February1st to 15thDay
46%5%12%19%14%1
1651
16th to endDay
44%311%24%13%1
1580
March1st to 15thDay
47%413%21%10%2
1800
16th to endDay
45%310%18%18%3
2226
April1st to 15thDay
46%410%20%15%3
2152
16th to endDay
39%5%9%22%19%3
2208
May1st to 15thDay
49%5%8%19%14%1
2368
16th to endDay
44%7%13%19%13%1
2622
June1st to 15thDay
49%6%12%20%9%1
2520
16th to endDay
41%7%14%23%11%
2520
July1st to 15thDay
44%7%10%21%15%1
2371
16th to endDay
41%7%14%21%13%2
2487
August1st to 15thDay
40%8%13%22%14%
2284
16th to endDay
41%6%9%24%17%1
2100
September1st to 15thDay
40%7%10%20%20%
1972
16th to endDay
38%5%8%21%23%2
1815
October1st to 15thDay
44%49%23%16%2
1722
16th to endDay
43%411%24%13%2
1645
November1st to 15thDay
40%413%21%17%3
1581
16th to endDay
40%212%26%14%2
1578
December1st to 15thDay
45%416%19%12%1
1440
16th to endDay
49%414%18%11%
1536
January1st to 15thNight
42%413%24%13%3
2506
16th to endNight
43%310%23%15%2
2637
February1st to 15thNight
46%413%20%13%2
2213
16th to endNight
42%310%22%17%3
1893
March1st to 15thNight
44%5%12%21%13%3
2160
16th to endNight
41%39%21%19%4
1997
April1st to 15thNight
45%5%11%20%15%1
1796
16th to endNight
44%48%20%18%3
1752
May1st to 15thNight
49%410%18%14%2
1593
16th to endNight
44%6%15%19%12%1
1497
June1st to 15thNight
47%5%12%20%12%1
1440
16th to endNight
35%6%15%26%14%1
1440
July1st to 15thNight
40%8%13%23%13%1
1360
16th to endNight
38%8%14%22%12%2
1418
August1st to 15thNight
35%6%13%26%15%1
1553
16th to endNight
36%9%11%24%17%
1750
September1st to 15thNight
37%6%11%25%18%
1657
16th to endNight
37%5%6%22%27%1
1815
October1st to 15thNight
41%410%22%17%2
1908
16th to endNight
43%5%13%22%14%
2226
November1st to 15thNight
41%411%20%17%3
2277
16th to endNight
45%312%24%11%2
2381
December1st to 15thNight
46%5%14%19%13%
2520
16th to endNight
47%413%21%12%1
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
26%26%31%10%31
60
16th to endDay
27%19%41%12%
73
February1st to 15thDay
26%28%29%14%
164
16th to endDay
22%23%35%14%4
239
March1st to 15thDay
28%18%32%15%5%
270
16th to endDay
25%23%32%13%41
288
April1st to 15thDay
28%18%27%15%8%1
270
16th to endDay
24%12%35%15%10%2
270
May1st to 15thDay
37%12%23%14%8%2
288
16th to endDay
20%10%30%25%10%2
331
June1st to 15thDay
24%11%26%22%13%1
315
16th to endDay
16%10%32%26%11%2
315
July1st to 15thDay
17%7%31%26%14%2
305
16th to endDay
12%7%29%30%18%2
326
August1st to 15thDay
15%328%30%14%7%
297
16th to endDay
11%422%28%19%13%
268
September1st to 15thDay
14%7%27%23%15%10%
255
16th to endDay
16%9%25%21%12%13%
254
October1st to 15thDay
25%9%25%20%14%5%
255
16th to endDay
21%18%27%23%8%
251
November1st to 15thDay
21%15%25%24%9%2
235
16th to endDay
20%24%24%20%8%2
198
December1st to 15thDay
30%21%33%11%3
60
16th to endDay
37%21%29%9%1
64
January1st to 15thNight
24%19%33%19%3
720
16th to endNight
24%21%33%18%2
768
February1st to 15thNight
23%18%37%19%1
704
16th to endNight
25%20%32%17%2
631
March1st to 15thNight
26%20%32%17%2
720
16th to endNight
22%22%30%18%5%
768
April1st to 15thNight
24%19%34%17%3
718
16th to endNight
22%18%33%19%5%
672
May1st to 15thNight
24%16%33%20%5%
513
16th to endNight
22%7%30%31%6%1
375
June1st to 15thNight
22%6%29%29%11%
360
16th to endNight
12%429%42%10%
360
July1st to 15thNight
15%228%36%17%
340
16th to endNight
11%325%38%20%1
376
August1st to 15thNight
14%227%38%15%1
504
16th to endNight
16%317%35%23%3
700
September1st to 15thNight
17%6%28%30%15%1
660
16th to endNight
17%7%23%27%20%3
657
October1st to 15thNight
20%11%29%26%12%1
660
16th to endNight
25%15%32%21%5%
704
November1st to 15thNight
22%14%29%24%8%1
700
16th to endNight
24%15%28%21%8%
720
December1st to 15thNight
27%17%28%21%4
720
16th to endNight
28%19%32%16%2
768
Page generated at 2017-08-13 14:16:16. Version ac04

Copyright 2017 A. Danko


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