PACMO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the PACMO clear sky chart from 2005-11-05 to 2017-04-30.

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
37%
15552
18%
45663
11%
15509
44%
15509
24%
30100

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
22%
900
15%
2506
5%
895
29%
895
20%
1771
January16th to endNight
21%
960
13%
2558
4%
960
28%
960
18%
1882
February1st to 15thNight
24%
869
14%
2281
3%
869
32%
869
21%
1644
February16th to endNight
26%
631
20%
1893
7%
631
37%
631
22%
1255
March1st to 15thNight
30%
670
17%
2110
10%
670
36%
670
21%
1392
March16th to endNight
27%
576
13%
2028
7%
576
34%
576
16%
1427
April1st to 15thNight
29%
539
17%
1797
12%
539
38%
539
21%
1184
April16th to endNight
37%
537
18%
1791
14%
537
46%
537
20%
1210
May1st to 15thNight
32%
495
18%
1402
9%
495
41%
495
22%
988
May16th to endNight
44%
515
17%
1369
9%
513
50%
513
30%
921
June1st to 15thNight
51%
495
17%
1320
10%
495
55%
495
32%
842
June16th to endNight
51%
495
16%
1320
8%
495
55%
495
33%
843
July1st to 15thNight
64%
465
19%
1240
12%
465
67%
465
41%
742
July16th to endNight
68%
522
21%
1305
14%
489
71%
489
40%
772
August1st to 15thNight
73%
494
23%
1484
24%
491
75%
491
42%
798
August16th to endNight
64%
525
20%
1750
20%
525
69%
525
33%
993
September1st to 15thNight
61%
495
28%
1650
29%
495
66%
495
36%
888
September16th to endNight
55%
605
25%
1771
16%
605
63%
605
35%
1042
October1st to 15thNight
45%
660
27%
1980
19%
660
51%
660
32%
1171
October16th to endNight
32%
704
20%
2164
11%
704
41%
704
24%
1376
November1st to 15thNight
34%
700
25%
2276
16%
700
45%
700
27%
1349
November16th to endNight
27%
840
18%
2460
9%
840
36%
840
23%
1636
December1st to 15thNight
20%
900
13%
2520
4%
900
29%
900
17%
1867
December16th to endNight
19%
960
12%
2688
4%
960
26%
960
13%
2107

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
13%8%36%5%3445%7%37%
46078
Night
13%7%35%424446%41%
45831
Cloud CoverDay
13%8%35%5%3445%7%37%
46086
Night
13%7%35%5%24446%41%
45836
TransparencyDay
45%6%13%21%12%1
45763
Night
42%5%12%22%14%2
45664
SeeingDay
15%8%26%27%16%5%
5336
Night
17%8%30%29%12%1
15555

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
12%12%48%6%45%445%29%
1432
16th to endDay
14%14%6%8%6%4434427%
1665
February1st to 15thDay
14%12%5%6%5%25%446%32%
1581
16th to endDay
14%8%37%6%35%346%34%
1580
March1st to 15thDay
15%10%36%43435%7%34%
1850
16th to endDay
18%9%37%5%3445%7%29%
2195
April1st to 15thDay
15%11%45%5%34445%35%
2151
16th to endDay
20%9%36%5%24446%33%
2148
May1st to 15thDay
20%7%36%6%346%5%7%28%
2218
16th to endDay
13%6%25%6%35%5%7%8%34%
2393
June1st to 15thDay
12%6%36%5%3445%8%37%
2310
16th to endDay
9%435%435%6%6%8%41%
2310
July1st to 15thDay
7%4146%45%46%10%44%
2310
16th to endDay
6%425%6%36%5%6%10%41%
2459
August1st to 15thDay
6%4245%36%6%6%10%41%
2135
16th to endDay
10%425%5%3435%8%46%
2100
September1st to 15thDay
12%5%23333448%47%
1980
16th to endDay
10%4245%345%5%7%46%
1845
October1st to 15thDay
15%6%24313346%48%
1650
16th to endDay
17%6%25%43345%5%41%
1708
November1st to 15thDay
12%9%24425%45%6%42%
1582
16th to endDay
16%11%45%5%2334439%
1500
December1st to 15thDay
17%13%47%6%33336%28%
1440
16th to endDay
18%15%5%8%6%13345%26%
1536
January1st to 15thNight
12%10%5%6%5%24446%36%
2506
16th to endNight
12%10%6%7%5%34446%32%
2558
February1st to 15thNight
14%11%36%5%35%445%36%
2278
16th to endNight
14%9%36%424335%40%
1893
March1st to 15thNight
16%8%35%424345%41%
2097
16th to endNight
16%9%47%6%35%35%6%32%
2028
April1st to 15thNight
15%8%46%424446%39%
1797
16th to endNight
19%6%36%424346%37%
1791
May1st to 15thNight
15%6%26%6%345%5%7%35%
1402
16th to endNight
9%5%26%5%345%6%8%41%
1368
June1st to 15thNight
11%5%25%42436%7%46%
1320
16th to endNight
7%426%5%35%5%5%7%46%
1320
July1st to 15thNight
8%31342445%8%54%
1320
16th to endNight
5%214435%5%6%11%48%
1401
August1st to 15thNight
3213435%45%8%55%
1493
16th to endNight
9%32432335%6%53%
1750
September1st to 15thNight
11%32341225%7%54%
1650
16th to endNight
7%4145%25%5%6%8%49%
1771
October1st to 15thNight
10%5%245%23345%52%
1980
16th to endNight
16%7%24423346%43%
2164
November1st to 15thNight
12%7%24422336%49%
2276
16th to endNight
16%8%35%423346%40%
2460
December1st to 15thNight
18%12%46%5%24335%32%
2520
16th to endNight
22%14%47%5%2433426%
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
12%12%5%8%6%45%5%45%30%
1432
16th to endDay
14%14%6%9%6%4444427%
1665
February1st to 15thDay
14%12%46%5%25%437%32%
1581
16th to endDay
13%9%47%6%34446%34%
1580
March1st to 15thDay
15%10%46%5%2435%6%34%
1860
16th to endDay
19%9%37%6%2445%7%30%
2193
April1st to 15thDay
15%11%45%6%34345%35%
2151
16th to endDay
20%9%36%5%24436%33%
2148
May1st to 15thDay
20%7%36%6%346%5%7%28%
2218
16th to endDay
14%5%25%6%35%5%6%9%35%
2393
June1st to 15thDay
12%6%36%5%35%45%8%38%
2310
16th to endDay
9%5%35%435%6%6%8%41%
2310
July1st to 15thDay
7%4146%345%6%10%44%
2310
16th to endDay
6%325%6%36%5%7%10%41%
2459
August1st to 15thDay
6%4245%45%6%7%10%41%
2135
16th to endDay
10%425%5%3435%8%46%
2100
September1st to 15thDay
12%5%23333448%47%
1980
16th to endDay
9%4145%345%5%7%46%
1845
October1st to 15thDay
15%6%24323345%48%
1650
16th to endDay
17%6%3442345%5%42%
1708
November1st to 15thDay
12%9%24425%5%5%6%41%
1582
16th to endDay
16%11%45%5%22345%39%
1500
December1st to 15thDay
18%13%47%6%24336%28%
1440
16th to endDay
18%15%5%8%6%1334427%
1536
January1st to 15thNight
12%10%5%6%6%33446%36%
2506
16th to endNight
12%10%6%7%5%34446%32%
2558
February1st to 15thNight
14%11%46%5%25%445%36%
2271
16th to endNight
15%8%36%423436%40%
1893
March1st to 15thNight
16%8%35%424345%41%
2110
16th to endNight
16%9%46%7%25%35%5%32%
2028
April1st to 15thNight
15%8%36%424346%39%
1797
16th to endNight
19%7%36%42435%5%37%
1791
May1st to 15thNight
15%6%25%6%3445%7%35%
1401
16th to endNight
10%426%5%245%6%8%41%
1368
June1st to 15thNight
11%6%2442435%8%46%
1320
16th to endNight
7%426%5%346%5%7%46%
1320
July1st to 15thNight
7%31342346%8%54%
1320
16th to endNight
5%214435%5%6%11%48%
1401
August1st to 15thNight
322443446%8%56%
1493
16th to endNight
9%42442345%6%52%
1750
September1st to 15thNight
10%41431235%7%54%
1650
16th to endNight
7%4235%245%6%7%49%
1771
October1st to 15thNight
11%5%245%23335%53%
1980
16th to endNight
16%7%25%423346%43%
2164
November1st to 15thNight
12%6%24422336%49%
2276
16th to endNight
17%8%35%42325%6%40%
2460
December1st to 15thNight
18%12%46%5%3433433%
2520
16th to endNight
22%14%47%5%2433426%
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
56%5%12%15%10%
1433
16th to endDay
60%412%14%7%
1665
February1st to 15thDay
53%415%20%5%
1582
16th to endDay
50%6%13%21%7%
1580
March1st to 15thDay
49%5%15%20%8%
1860
16th to endDay
52%6%13%20%5%
2195
April1st to 15thDay
51%5%10%21%11%
2151
16th to endDay
51%5%9%17%12%2
2148
May1st to 15thDay
53%6%12%19%7%
2218
16th to endDay
44%9%13%18%13%1
2397
June1st to 15thDay
43%7%13%22%13%
2310
16th to endDay
36%8%13%22%17%2
2310
July1st to 15thDay
36%6%14%25%14%2
2161
16th to endDay
35%8%16%23%13%2
2292
August1st to 15thDay
34%8%14%24%16%1
2120
16th to endDay
35%6%13%26%15%3
2100
September1st to 15thDay
35%5%9%24%21%3
1980
16th to endDay
35%5%12%26%18%1
1845
October1st to 15thDay
37%49%29%18%1
1650
16th to endDay
43%415%23%11%2
1708
November1st to 15thDay
41%5%11%25%13%2
1582
16th to endDay
49%415%21%8%1
1500
December1st to 15thDay
57%414%16%6%
1440
16th to endDay
60%5%12%12%8%
1536
January1st to 15thNight
48%5%14%18%12%
2506
16th to endNight
51%6%15%16%9%
2558
February1st to 15thNight
49%5%13%20%10%
2281
16th to endNight
46%313%24%11%
1893
March1st to 15thNight
46%414%23%9%2
2110
16th to endNight
52%5%12%19%8%1
2028
April1st to 15thNight
45%49%23%13%2
1797
16th to endNight
47%5%8%20%13%3
1791
May1st to 15thNight
46%7%12%21%12%
1402
16th to endNight
38%8%12%21%16%3
1370
June1st to 15thNight
35%6%13%24%17%1
1320
16th to endNight
34%7%12%19%21%4
1320
July1st to 15thNight
28%6%13%30%17%4
1240
16th to endNight
27%7%16%29%16%2
1305
August1st to 15thNight
24%6%15%32%17%3
1484
16th to endNight
31%6%11%25%20%5%
1750
September1st to 15thNight
29%410%25%25%3
1650
16th to endNight
30%6%12%26%19%3
1771
October1st to 15thNight
34%49%25%22%3
1980
16th to endNight
42%410%25%15%1
2164
November1st to 15thNight
37%410%24%19%4
2276
16th to endNight
44%312%26%12%
2460
December1st to 15thNight
54%411%21%7%
2520
16th to endNight
61%49%15%7%
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
30%14%33%18%3
90
16th to endDay
20%16%38%14%8%1
96
February1st to 15thDay
18%18%41%14%6%
90
16th to endDay
20%14%35%18%7%2
81
March1st to 15thDay
22%24%34%14%31
90
16th to endDay
30%16%25%17%7%1
179
April1st to 15thDay
17%14%34%21%11%
270
16th to endDay
25%9%27%21%13%3
266
May1st to 15thDay
21%12%30%23%9%3
332
16th to endDay
15%10%28%27%13%4
437
June1st to 15thDay
13%5%30%30%15%4
420
16th to endDay
9%6%28%32%16%7%
420
July1st to 15thDay
11%324%29%21%11%
400
16th to endDay
7%121%33%27%8%
445
August1st to 15thDay
7%118%37%25%9%
402
16th to endDay
9%314%33%27%11%
268
September1st to 15thDay
11%318%32%25%9%
255
16th to endDay
9%5%21%28%25%9%
243
October1st to 15thDay
13%10%23%26%17%8%
90
16th to endDay
20%12%33%25%8%
96
November1st to 15thDay
314%36%23%13%8%
90
16th to endDay
43%11%30%12%21
90
December1st to 15thDay
21%21%30%21%5%1
90
16th to endDay
29%26%37%6%1
96
January1st to 15thNight
17%16%39%21%5%
900
16th to endNight
17%12%38%26%5%
960
February1st to 15thNight
19%12%37%25%5%
872
16th to endNight
19%11%39%24%4
631
March1st to 15thNight
21%11%32%28%5%
670
16th to endNight
20%10%36%25%7%
576
April1st to 15thNight
20%12%32%27%5%
539
16th to endNight
22%7%27%33%7%
537
May1st to 15thNight
20%6%34%28%8%1
495
16th to endNight
11%431%36%14%
515
June1st to 15thNight
13%424%43%13%
495
16th to endNight
8%329%39%18%1
495
July1st to 15thNight
9%218%40%26%2
465
16th to endNight
5%116%41%31%2
522
August1st to 15thNight
3112%45%32%5%
494
16th to endNight
10%15%40%28%3
525
September1st to 15thNight
12%217%36%24%5%
495
16th to endNight
7%5%23%33%26%2
605
October1st to 15thNight
13%5%31%29%18%1
660
16th to endNight
21%11%31%26%9%
704
November1st to 15thNight
17%9%35%26%10%1
700
16th to endNight
21%13%33%24%6%
840
December1st to 15thNight
24%12%36%23%4
900
16th to endNight
27%12%32%22%3
960
Page generated at 2017-04-30 19:40:09. Version ac04

Copyright 2017 A. Danko


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