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 2018-02-22.

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%
15814
16%
48978
11%
15777
43%
15777
20%
34181

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
17%
776
10%
2522
4%
776
24%
776
9%
2017
January16th to endNight
18%
832
10%
2704
4%
832
25%
832
11%
2110
February1st to 15thNight
21%
762
10%
2482
7%
761
27%
761
12%
1923
February16th to endNight
18%
659
13%
2036
5%
659
26%
659
13%
1562
March1st to 15thNight
27%
720
15%
1980
9%
720
33%
720
16%
1493
March16th to endNight
28%
768
19%
2112
10%
768
36%
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
45%
593
27%
1124
May1st to 15thNight
42%
540
15%
1620
10%
540
47%
540
20%
1147
May16th to endNight
54%
465
17%
1588
14%
465
58%
465
26%
964
June1st to 15thNight
54%
360
17%
1440
19%
360
60%
360
24%
838
June16th to endNight
54%
360
18%
1440
19%
360
60%
360
23%
847
July1st to 15thNight
56%
439
14%
1459
13%
439
59%
439
26%
916
July16th to endNight
69%
564
17%
1595
15%
531
71%
531
34%
964
August1st to 15thNight
66%
539
20%
1609
15%
536
68%
536
33%
977
August16th to endNight
66%
642
24%
1788
17%
642
68%
642
37%
1072
September1st to 15thNight
60%
720
25%
1852
16%
720
63%
720
34%
1189
September16th to endNight
55%
717
26%
1983
21%
717
59%
717
33%
1259
October1st to 15thNight
46%
720
19%
2160
17%
720
50%
720
24%
1432
October16th to endNight
32%
768
19%
2304
13%
768
41%
768
20%
1596
November1st to 15thNight
41%
760
21%
2412
18%
760
48%
760
24%
1550
November16th to endNight
27%
780
15%
2730
10%
780
36%
780
14%
1935
December1st to 15thNight
21%
780
8%
2730
6%
780
25%
780
10%
2133
December16th to endNight
17%
832
9%
2909
4%
832
23%
832
9%
2300

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%6%35%5%5%7%31%
49257
Night
16%8%36%5%3445%6%34%
49170
Cloud CoverDay
17%8%36%5%3445%7%31%
49267
Night
16%8%36%5%3445%6%34%
49174
TransparencyDay
51%5%11%19%10%1
48967
Night
49%5%11%20%11%1
48978
SeeingDay
20%9%24%22%15%7%
5920
Night
20%9%25%28%14%1
15822

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%14%5%9%7%35%336%20%
1746
16th to endDay
16%16%6%11%8%33345%19%
1872
February1st to 15thDay
20%15%6%8%7%35%445%18%
1710
16th to endDay
17%14%310%6%34446%23%
1581
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%
2340
16th to endDay
12%5%245%45%5%7%9%39%
2401
September1st to 15thDay
15%5%245%345%6%7%40%
2106
16th to endDay
15%6%25%435%347%41%
1977
October1st to 15thDay
18%7%25%42445%7%36%
1800
16th to endDay
21%7%26%43445%6%34%
1920
November1st to 15thDay
13%7%35%5%3445%7%37%
1772
16th to endDay
19%12%45%5%2445%7%28%
1560
December1st to 15thDay
21%13%6%10%7%34345%18%
1560
16th to endDay
22%16%6%10%6%34335%17%
1664
January1st to 15thNight
22%13%5%9%6%45%44420%
2522
16th to endNight
18%14%5%9%7%3434324%
2704
February1st to 15thNight
19%11%5%9%6%35%45%5%23%
2480
16th to endNight
19%11%410%5%35%445%26%
2036
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%435%6%8%9%43%
1620
16th to endNight
10%31342446%7%49%
1788
September1st to 15thNight
12%41432445%6%47%
1852
16th to endNight
12%5%24424347%47%
1983
October1st to 15thNight
15%5%25%5%345%46%40%
2160
16th to endNight
22%6%34424445%36%
2304
November1st to 15thNight
16%6%35%435%346%41%
2412
16th to endNight
20%11%46%424446%30%
2730
December1st to 15thNight
22%12%5%9%6%34345%21%
2730
16th to endNight
19%16%6%8%6%34446%19%
2909

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%14%6%9%6%44335%20%
1746
16th to endDay
17%16%6%10%8%43335%19%
1872
February1st to 15thDay
20%14%6%8%6%44345%19%
1710
16th to endDay
17%15%49%6%35%445%23%
1581
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%
2340
16th to endDay
12%4245%345%7%8%40%
2401
September1st to 15thDay
16%4245%345%5%7%41%
2106
16th to endDay
16%6%345%24346%42%
1977
October1st to 15thDay
19%7%16%42345%7%37%
1800
16th to endDay
21%7%36%43435%6%34%
1920
November1st to 15thDay
14%7%35%5%345%5%6%37%
1772
16th to endDay
19%12%36%5%33447%29%
1560
December1st to 15thDay
21%13%6%10%7%3434419%
1560
16th to endDay
22%17%7%9%7%23335%18%
1664
January1st to 15thNight
22%14%5%8%6%35%5%4420%
2522
16th to endNight
19%14%5%8%7%3443424%
2704
February1st to 15thNight
19%11%5%9%5%45%45%5%24%
2473
16th to endNight
18%12%5%8%6%25%44426%
2036
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%
1620
16th to endNight
10%41432345%7%50%
1788
September1st to 15thNight
13%42432345%6%48%
1852
16th to endNight
12%5%24424446%47%
1983
October1st to 15thNight
16%5%35%5%245%46%40%
2160
16th to endNight
22%6%25%5%23446%36%
2304
November1st to 15thNight
16%6%25%434446%41%
2412
16th to endNight
20%10%46%424446%30%
2730
December1st to 15thNight
23%11%6%8%6%34345%21%
2730
16th to endNight
20%16%6%9%5%33446%20%
2909

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
67%310%12%5%
1747
16th to endDay
68%411%12%2
1872
February1st to 15thDay
67%5%9%12%4
1712
16th to endDay
61%412%14%6%
1581
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%
2327
16th to endDay
39%6%13%25%12%3
2401
September1st to 15thDay
41%7%9%23%16%2
2106
16th to endDay
43%49%26%16%
1977
October1st to 15thDay
46%412%20%15%
1800
16th to endDay
50%312%22%10%
1920
November1st to 15thDay
45%5%10%21%12%3
1772
16th to endDay
55%412%18%8%
1560
December1st to 15thDay
68%39%13%4
1560
16th to endDay
70%410%11%3
1664
January1st to 15thNight
66%48%13%6%
2522
16th to endNight
64%311%14%4
2704
February1st to 15thNight
62%410%16%6%
2482
16th to endNight
60%49%18%7%
2036
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
33%7%13%25%19%1
1609
16th to endNight
31%5%12%29%16%4
1788
September1st to 15thNight
35%6%9%23%21%3
1852
16th to endNight
36%5%9%25%21%1
1983
October1st to 15thNight
43%6%10%22%14%2
2160
16th to endNight
48%49%23%11%1
2304
November1st to 15thNight
43%410%21%15%4
2412
16th to endNight
54%48%21%9%
2730
December1st to 15thNight
64%411%13%5%
2730
16th to endNight
65%412%14%2
2909

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
22%24%28%16%5%2
135
16th to endDay
26%23%31%15%2
144
February1st to 15thDay
32%20%40%6%
135
16th to endDay
26%12%43%14%2
121
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
13%415%24%25%15%
313
16th to endDay
13%315%20%26%20%
332
September1st to 15thDay
16%218%24%22%15%
315
16th to endDay
15%7%12%23%21%19%
314
October1st to 15thDay
21%420%24%25%3
315
16th to endDay
22%13%28%23%8%2
336
November1st to 15thDay
20%8%25%25%16%2
206
16th to endDay
25%14%38%12%7%1
90
December1st to 15thDay
24%21%26%17%7%2
90
16th to endDay
35%19%33%11%
96
January1st to 15thNight
30%15%30%18%4
780
16th to endNight
28%12%34%22%2
832
February1st to 15thNight
27%14%31%25%2
764
16th to endNight
25%11%38%21%3
659
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%40%30%3
539
16th to endNight
11%112%34%35%4
642
September1st to 15thNight
14%413%34%29%3
720
16th to endNight
15%417%23%31%6%
717
October1st to 15thNight
18%5%20%31%21%2
720
16th to endNight
25%11%26%26%8%
768
November1st to 15thNight
20%7%25%31%14%1
760
16th to endNight
27%13%26%23%8%
780
December1st to 15thNight
30%13%27%22%5%
780
16th to endNight
28%13%33%22%2
832
Page generated at 2018-02-23 11:21:33. Version ac04

Copyright 2018 A. Danko


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