Pittsburgh
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pittsburgh 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
37%
15048
16%
46579
11%
15011
43%
15011
20%
32552

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%
716
10%
2327
4%
716
23%
716
8%
1884
January16th to endNight
17%
768
9%
2496
4%
768
24%
768
11%
1960
February1st to 15thNight
22%
702
10%
2287
7%
701
28%
701
12%
1758
February16th to endNight
18%
631
12%
1946
5%
631
26%
631
13%
1488
March1st to 15thNight
27%
720
15%
1980
9%
720
33%
720
16%
1493
March16th to endNight
28%
768
19%
2112
10%
768
35%
768
22%
1474
April1st to 15thNight
29%
718
13%
1850
5%
718
33%
718
21%
1359
April16th to endNight
40%
593
19%
1673
9%
593
46%
593
27%
1124
May1st to 15thNight
42%
540
15%
1620
10%
540
47%
540
20%
1147
May16th to endNight
53%
465
17%
1588
14%
465
58%
465
26%
964
June1st to 15thNight
54%
360
17%
1440
19%
360
61%
360
24%
838
June16th to endNight
53%
360
18%
1440
19%
360
60%
360
23%
847
July1st to 15thNight
55%
439
14%
1459
13%
439
59%
439
26%
916
July16th to endNight
68%
564
17%
1595
15%
531
71%
531
34%
964
August1st to 15thNight
64%
527
20%
1575
15%
524
66%
524
33%
955
August16th to endNight
66%
588
22%
1638
16%
588
68%
588
37%
981
September1st to 15thNight
61%
660
27%
1697
17%
660
65%
660
35%
1078
September16th to endNight
53%
657
24%
1818
19%
657
56%
657
31%
1183
October1st to 15thNight
46%
660
19%
1980
18%
660
50%
660
24%
1307
October16th to endNight
31%
704
17%
2112
11%
704
40%
704
19%
1483
November1st to 15thNight
41%
700
22%
2221
19%
700
48%
700
24%
1421
November16th to endNight
27%
720
14%
2520
9%
720
34%
720
13%
1813
December1st to 15thNight
22%
720
9%
2520
6%
720
26%
720
9%
1985
December16th to endNight
17%
768
9%
2685
5%
768
23%
768
9%
2130

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%8%36%5%35%5%5%7%31%
47376
Night
16%8%36%5%3445%6%34%
46771
Cloud CoverDay
17%8%36%5%3445%7%31%
47386
Night
16%8%36%5%3445%6%34%
46775
TransparencyDay
51%6%11%19%10%1
47086
Night
49%5%11%20%11%1
46579
SeeingDay
20%9%23%22%16%7%
5298
Night
20%9%25%29%13%1
15056

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
20%15%6%10%7%34335%19%
1611
16th to endDay
16%17%6%11%8%33335%18%
1728
February1st to 15thDay
19%15%6%8%7%35%35%5%19%
1575
16th to endDay
16%14%410%6%34446%23%
1524
March1st to 15thDay
19%10%5%7%6%345%46%25%
1969
16th to endDay
17%8%37%5%35%5%5%7%28%
2112
April1st to 15thDay
18%9%46%5%3445%6%31%
2097
16th to endDay
19%7%35%43435%7%35%
2298
May1st to 15thDay
19%7%36%5%36%6%6%7%28%
2331
16th to endDay
13%5%25%6%35%6%7%8%36%
2527
June1st to 15thDay
13%5%25%445%5%6%9%36%
2520
16th to endDay
14%5%25%6%35%6%6%10%33%
2520
July1st to 15thDay
11%7%35%6%45%6%5%8%34%
2409
16th to endDay
12%5%25%6%5%6%6%7%9%33%
2465
August1st to 15thDay
11%5%25%6%5%7%6%8%8%31%
2288
16th to endDay
12%5%245%45%5%6%8%39%
2200
September1st to 15thDay
15%4145%345%6%7%41%
1931
16th to endDay
17%7%25%434346%40%
1812
October1st to 15thDay
18%7%26%42445%7%36%
1650
16th to endDay
21%7%36%43435%6%33%
1760
November1st to 15thDay
12%7%36%5%3445%7%38%
1633
16th to endDay
20%12%45%6%24447%26%
1440
December1st to 15thDay
22%14%6%10%7%34345%17%
1440
16th to endDay
23%16%6%9%6%33335%17%
1536
January1st to 15thNight
23%14%5%9%6%35%44319%
2327
16th to endNight
18%14%5%9%8%3444323%
2496
February1st to 15thNight
18%11%5%9%6%35%45%5%24%
2285
16th to endNight
18%11%410%6%35%445%27%
1946
March1st to 15thNight
20%10%47%5%24446%29%
1968
16th to endNight
18%8%35%434436%37%
2112
April1st to 15thNight
17%9%36%43445%6%32%
1850
16th to endNight
13%6%45%434347%40%
1673
May1st to 15thNight
17%7%36%5%35%45%7%34%
1620
16th to endNight
10%5%26%5%3346%8%44%
1586
June1st to 15thNight
9%425%6%245%5%10%43%
1440
16th to endNight
9%4245%25%5%6%10%41%
1440
July1st to 15thNight
8%5%36%6%35%5%7%9%40%
1548
16th to endNight
8%314425%5%7%11%43%
1703
August1st to 15thNight
6%5%25%335%6%7%9%44%
1586
16th to endNight
10%31442446%7%50%
1638
September1st to 15thNight
12%31432446%7%48%
1697
16th to endNight
13%6%25%425%347%45%
1818
October1st to 15thNight
15%5%25%5%345%46%40%
1980
16th to endNight
22%7%345%24446%35%
2112
November1st to 15thNight
15%6%35%425%346%41%
2221
16th to endNight
21%11%46%424445%29%
2520
December1st to 15thNight
23%12%6%9%6%23345%20%
2520
16th to endNight
20%15%7%8%6%34446%19%
2685

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
20%15%6%10%6%34335%20%
1611
16th to endDay
17%17%7%10%8%43335%19%
1728
February1st to 15thDay
20%15%6%8%6%45%345%19%
1575
16th to endDay
16%15%49%6%35%445%23%
1524
March1st to 15thDay
21%10%46%6%3345%7%25%
1980
16th to endDay
18%8%46%5%35%5%5%7%29%
2111
April1st to 15thDay
19%9%45%5%3445%6%31%
2097
16th to endDay
19%7%35%43445%7%35%
2298
May1st to 15thDay
20%6%26%6%36%5%5%7%27%
2331
16th to endDay
14%5%35%5%35%5%7%9%35%
2527
June1st to 15thDay
13%5%15%5%45%5%6%8%37%
2520
16th to endDay
15%5%35%5%35%6%7%9%32%
2520
July1st to 15thDay
12%7%35%7%35%6%5%8%34%
2409
16th to endDay
12%435%5%46%5%7%10%33%
2465
August1st to 15thDay
12%6%25%6%37%6%8%8%32%
2288
16th to endDay
13%5%245%3447%8%40%
2200
September1st to 15thDay
15%4244345%5%7%42%
1931
16th to endDay
18%6%345%24346%40%
1812
October1st to 15thDay
19%7%26%42345%7%36%
1650
16th to endDay
21%7%36%43335%6%34%
1760
November1st to 15thDay
13%7%35%5%345%5%7%38%
1633
16th to endDay
20%12%46%5%33446%28%
1440
December1st to 15thDay
22%13%6%10%7%3434419%
1440
16th to endDay
22%18%7%8%6%23345%18%
1536
January1st to 15thNight
23%14%5%8%7%35%5%3319%
2327
16th to endNight
19%14%5%9%7%3443423%
2496
February1st to 15thNight
18%11%5%9%5%45%45%5%24%
2278
16th to endNight
17%12%5%8%7%25%445%27%
1946
March1st to 15thNight
21%9%47%5%2445%6%29%
1980
16th to endNight
18%8%25%5%34346%37%
2112
April1st to 15thNight
18%9%36%5%2445%6%33%
1850
16th to endNight
14%7%36%43435%7%40%
1673
May1st to 15thNight
18%6%346%35%45%6%34%
1619
16th to endNight
10%5%26%5%2345%8%44%
1586
June1st to 15thNight
9%415%6%345%6%8%44%
1440
16th to endNight
9%425%425%5%6%10%42%
1440
July1st to 15thNight
8%6%346%35%5%5%9%41%
1548
16th to endNight
8%324425%6%7%11%43%
1703
August1st to 15thNight
7%4244346%7%10%43%
1586
16th to endNight
10%41333345%7%50%
1638
September1st to 15thNight
12%42432446%6%48%
1697
16th to endNight
14%5%245%24446%45%
1818
October1st to 15thNight
16%5%25%5%345%5%6%40%
1980
16th to endNight
22%6%25%5%24446%35%
2112
November1st to 15thNight
16%6%25%424446%41%
2221
16th to endNight
21%11%46%424445%29%
2520
December1st to 15thNight
24%12%6%8%5%33345%20%
2520
16th to endNight
20%16%6%8%5%33436%20%
2685

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
68%310%12%4
1612
16th to endDay
69%411%11%2
1728
February1st to 15thDay
67%5%9%12%4
1577
16th to endDay
61%5%12%14%6%
1524
March1st to 15thDay
58%5%11%18%5%
1980
16th to endDay
53%5%11%18%9%1
2112
April1st to 15thDay
52%411%19%11%
2097
16th to endDay
48%5%10%18%13%3
2298
May1st to 15thDay
53%5%12%18%8%1
2331
16th to endDay
43%8%15%20%9%1
2531
June1st to 15thDay
41%8%13%24%11%
2520
16th to endDay
45%7%13%21%11%
2520
July1st to 15thDay
46%7%10%18%13%2
2269
16th to endDay
43%7%13%22%11%1
2310
August1st to 15thDay
45%8%11%22%10%
2275
16th to endDay
39%6%12%25%12%3
2200
September1st to 15thDay
39%7%10%23%16%2
1931
16th to endDay
45%48%25%16%
1812
October1st to 15thDay
47%5%12%20%14%
1650
16th to endDay
50%413%20%10%
1760
November1st to 15thDay
44%5%11%21%13%3
1633
16th to endDay
57%412%17%8%
1440
December1st to 15thDay
69%39%12%4
1440
16th to endDay
70%410%11%3
1536
January1st to 15thNight
68%48%13%5%
2327
16th to endNight
64%311%14%4
2496
February1st to 15thNight
61%410%16%6%
2287
16th to endNight
60%49%18%7%
1946
March1st to 15thNight
55%5%11%18%8%
1980
16th to endNight
48%410%22%11%2
2112
April1st to 15thNight
51%5%10%17%14%
1850
16th to endNight
43%411%20%14%5%
1673
May1st to 15thNight
48%6%8%20%13%1
1620
16th to endNight
37%6%15%22%15%2
1588
June1st to 15thNight
35%7%14%27%14%
1440
16th to endNight
36%8%12%22%16%3
1440
July1st to 15thNight
38%7%12%20%17%3
1459
16th to endNight
31%8%14%25%15%4
1595
August1st to 15thNight
32%7%13%25%18%1
1575
16th to endNight
31%5%11%28%17%4
1638
September1st to 15thNight
34%6%9%23%22%4
1697
16th to endNight
38%5%7%26%20%1
1818
October1st to 15thNight
42%6%11%23%14%2
1980
16th to endNight
50%49%22%11%1
2112
November1st to 15thNight
42%410%20%15%5%
2221
16th to endNight
56%48%19%9%
2520
December1st to 15thNight
65%411%12%5%
2520
16th to endNight
66%411%14%2
2685

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%25%12%44
90
16th to endDay
30%27%28%11%3
96
February1st to 15thDay
28%24%40%6%
90
16th to endDay
23%12%45%15%2
102
March1st to 15thDay
27%11%31%22%6%
270
16th to endDay
23%14%34%18%6%2
288
April1st to 15thDay
26%14%25%20%11%1
270
16th to endDay
22%8%27%20%11%8%
270
May1st to 15thDay
27%14%23%17%12%4
288
16th to endDay
16%7%22%26%15%10%
331
June1st to 15thDay
14%5%24%26%23%5%
315
16th to endDay
18%7%26%23%18%5%
315
July1st to 15thDay
16%5%22%29%16%10%
305
16th to endDay
11%315%28%29%11%
326
August1st to 15thDay
14%415%23%26%15%
297
16th to endDay
15%213%17%27%22%
268
September1st to 15thDay
13%115%25%26%17%
255
16th to endDay
18%7%13%25%22%12%
254
October1st to 15thDay
19%421%23%26%3
255
16th to endDay
23%12%30%25%6%1
272
November1st to 15thDay
17%10%20%26%21%3
157
16th to endDay
28%16%36%10%6%1
60
December1st to 15thDay
28%21%23%16%6%3
60
16th to endDay
40%23%23%12%
64
January1st to 15thNight
32%15%29%18%3
720
16th to endNight
27%13%33%22%2
768
February1st to 15thNight
25%13%31%26%2
704
16th to endNight
24%12%38%22%3
631
March1st to 15thNight
26%14%26%28%4
720
16th to endNight
21%10%34%24%7%1
768
April1st to 15thNight
23%14%29%24%7%
718
16th to endNight
14%7%31%33%11%
593
May1st to 15thNight
20%9%20%36%11%1
540
16th to endNight
11%321%34%24%3
467
June1st to 15thNight
8%324%42%20%
360
16th to endNight
11%225%37%22%
360
July1st to 15thNight
9%122%41%22%3
439
16th to endNight
8%113%36%35%3
564
August1st to 15thNight
8%214%39%30%3
527
16th to endNight
12%112%35%34%4
588
September1st to 15thNight
14%312%34%30%3
660
16th to endNight
16%417%25%30%4
657
October1st to 15thNight
18%6%20%31%20%2
660
16th to endNight
26%11%26%27%7%
704
November1st to 15thNight
19%7%25%31%14%1
700
16th to endNight
28%14%25%23%7%
720
December1st to 15thNight
31%13%27%22%5%
720
16th to endNight
29%12%33%22%2
768
Page generated at 2017-08-13 14:16:14. Version ac04

Copyright 2017 A. Danko


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