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Pittsburgh
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pittsburgh clear sky chart from 2005-11-06 to 2024-11-06.

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%
24260
14%
97286
11%
24005
43%
24005
15%
67664

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 10thNight
16%
752
10%
4085
5%
737
25%
737
6%
3179
January11th to 20thNight
16%
758
7%
4088
3%
740
22%
740
5%
3317
January21st to endNight
19%
828
6%
4512
6%
814
26%
814
6%
3771
February1st to 10thNight
25%
760
12%
2470
9%
760
30%
760
13%
1875
February11th to 20thNight
17%
741
11%
2405
5%
740
25%
740
12%
1815
February21st to endNight
17%
628
13%
1874
5%
628
26%
628
13%
1453
March1st to 10thNight
25%
756
19%
3396
9%
745
33%
745
12%
2314
March11th to 20thNight
26%
755
19%
3438
10%
740
34%
740
12%
2254
March21st to endNight
25%
832
12%
3701
9%
814
34%
814
14%
2287
April1st to 10thNight
28%
760
15%
1987
7%
760
32%
760
21%
1438
April11th to 20thNight
35%
741
17%
1865
7%
741
40%
741
26%
1322
April21st to endNight
35%
570
18%
1710
8%
570
42%
570
22%
1154
May1st to 10thNight
39%
564
13%
2781
8%
559
44%
559
11%
2033
May11th to 20thNight
42%
548
13%
2753
10%
541
47%
541
14%
1770
May21st to endNight
58%
456
13%
2807
15%
451
64%
451
17%
1523
June1st to 10thNight
55%
380
17%
1520
20%
380
60%
380
24%
890
June11th to 20thNight
52%
380
17%
1520
19%
380
58%
380
22%
910
June21st to endNight
55%
380
19%
1520
20%
380
61%
380
24%
887
July1st to 10thNight
60%
433
17%
2434
16%
428
64%
428
16%
1451
July11th to 20thNight
59%
542
15%
2552
15%
533
64%
533
21%
1503
July21st to endNight
62%
607
12%
2795
14%
569
64%
569
17%
1763
August1st to 10thNight
63%
556
15%
2712
14%
544
66%
544
16%
1842
August11th to 20thNight
60%
552
18%
2509
16%
543
63%
543
19%
1606
August21st to endNight
59%
717
15%
2992
14%
714
62%
714
21%
1829
September1st to 10thNight
58%
760
26%
1900
15%
760
62%
760
35%
1217
September11th to 20thNight
63%
760
26%
2077
20%
760
66%
760
38%
1254
September21st to endNight
44%
760
22%
2094
16%
760
50%
760
26%
1420
October1st to 10thNight
48%
760
16%
2759
18%
740
53%
740
20%
1917
October11th to 20thNight
37%
760
13%
2871
12%
740
45%
740
17%
1987
October21st to endNight
35%
836
17%
2790
15%
814
43%
814
17%
1963
November1st to 10thNight
42%
764
23%
2358
19%
764
49%
764
26%
1490
November11th to 20thNight
29%
760
18%
2593
13%
760
39%
760
17%
1783
November21st to endNight
27%
760
15%
2660
10%
760
35%
760
14%
1895
December1st to 10thNight
21%
760
9%
2660
6%
760
25%
760
9%
2094
December11th to 20thNight
21%
759
9%
3246
7%
759
27%
759
9%
2455
December21st to endNight
20%
825
6%
4852
6%
817
26%
817
5%
4003

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%10%38%5%5%5%46%7%32%
101129
Night
17%10%48%5%4435%6%33%
97866
TransparencyDay
49%6%11%21%11%1
104778
Night
50%6%10%21%12%2
102357
SeeingDay
22%10%26%23%14%5%
14729
Night
22%8%25%30%14%1
24413

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 10thDay
20%19%8%11%5%44246%19%
2836
11th to 20thDay
13%22%8%15%8%5%323318%
2840
21st to endDay
25%19%7%13%6%5%324412%
3124
February1st to 10thDay
21%16%49%7%5%434422%
1710
11th to 20thDay
15%17%5%11%6%5%435%5%23%
1663
21st to endDay
20%14%310%6%4435%5%25%
1574
March1st to 10thDay
21%11%48%6%5%445%6%27%
3435
11th to 20thDay
14%9%49%5%6%5%45%6%33%
3480
21st to endDay
18%9%38%5%5%5%45%7%32%
3815
April1st to 10thDay
16%11%38%5%5%5%46%7%30%
2192
11th to 20thDay
16%10%37%5%5%5%46%7%33%
2282
21st to endDay
21%8%37%5%4435%7%33%
2470
May1st to 10thDay
24%9%37%445%45%7%28%
4082
11th to 20thDay
19%7%38%6%4446%8%31%
4081
21st to endDay
12%6%27%45%5%5%7%10%38%
4727
June1st to 10thDay
13%7%26%6%5%5%5%7%8%35%
2660
11th to 20thDay
13%7%26%5%5%5%5%7%10%35%
2660
21st to endDay
13%6%26%5%5%5%47%10%38%
2660
July1st to 10thDay
9%7%36%5%5%6%5%6%8%41%
4294
11th to 20thDay
10%6%26%5%5%5%5%7%10%39%
4120
21st to endDay
12%7%38%5%5%5%47%8%36%
4466
August1st to 10thDay
15%7%38%5%6%6%5%7%8%31%
4104
11th to 20thDay
11%7%27%5%5%6%5%7%8%37%
4044
21st to endDay
8%427%5%6%6%5%8%9%41%
4312
September1st to 10thDay
15%6%24445%45%7%45%
2280
11th to 20thDay
12%6%245%45%45%8%46%
2100
21st to endDay
20%8%36%44435%6%36%
2085
October1st to 10thDay
16%7%26%44446%8%40%
1900
11th to 20thDay
18%8%28%45%5%45%6%36%
1900
21st to endDay
22%9%37%43335%7%34%
2090
November1st to 10thDay
12%8%36%5%4445%6%43%
1837
11th to 20thDay
17%12%37%5%4445%7%32%
1584
21st to endDay
18%13%6%8%5%4445%7%27%
1520
December1st to 10thDay
21%15%5%12%8%44345%19%
1520
11th to 20thDay
20%17%6%9%6%44346%22%
1910
21st to endDay
24%20%6%11%5%3425%5%13%
2772
January1st to 10thNight
16%19%7%12%5%5%435%5%20%
4109
11th to 20thNight
18%18%6%13%6%6%5%44416%
4120
21st to endNight
27%16%6%12%6%4333417%
4532
February1st to 10thNight
21%13%410%5%4435%426%
2470
11th to 20thNight
20%12%411%6%4445%426%
2403
21st to endNight
20%13%49%6%45%34426%
1874
March1st to 10thNight
24%10%37%5%33345%33%
3418
11th to 20thNight
16%12%48%5%44347%35%
3480
21st to endNight
18%9%36%444345%39%
3817
April1st to 10thNight
17%12%37%44435%6%35%
1987
11th to 20thNight
16%8%27%445%46%7%37%
1865
21st to endNight
15%9%37%445%347%38%
1710
May1st to 10thNight
26%10%46%5%4435%6%27%
2813
11th to 20thNight
17%9%37%5%4435%6%38%
2812
21st to endNight
11%6%27%445%47%10%40%
2826
June1st to 10thNight
10%6%27%5%4446%8%45%
1520
11th to 20thNight
10%6%27%6%45%47%8%41%
1520
21st to endNight
10%425%446%47%11%42%
1520
July1st to 10thNight
10%7%37%5%4436%8%42%
2647
11th to 20thNight
10%6%26%5%4446%9%43%
2840
21st to endNight
10%7%38%6%5%5%46%7%40%
3087
August1st to 10thNight
12%8%38%5%5%5%5%7%8%33%
2825
11th to 20thNight
12%8%36%445%35%7%42%
2785
21st to endNight
9%5%26%45%5%47%8%44%
3311
September1st to 10thNight
12%425%44445%7%49%
1900
11th to 20thNight
10%425%33436%7%52%
2077
21st to endNight
16%8%26%5%3435%6%41%
2094
October1st to 10thNight
14%6%37%44435%7%44%
2280
11th to 20thNight
18%6%36%5%44446%39%
2280
21st to endNight
23%8%26%433347%37%
2508
November1st to 10thNight
13%8%36%44445%6%44%
2358
11th to 20thNight
18%11%37%44435%7%33%
2593
21st to endNight
20%12%47%44435%6%30%
2660
December1st to 10thNight
23%15%6%10%5%44346%21%
2660
11th to 20thNight
20%16%5%10%5%5%3345%25%
3285
21st to endNight
24%18%6%11%6%5%4345%14%
4880

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 10thDay
68%5%10%12%5%
2837
11th to 20thDay
72%38%12%41
2840
21st to endDay
76%5%7%9%2
3124
February1st to 10thDay
65%410%13%7%1
1710
11th to 20thDay
63%5%10%16%7%
1672
21st to endDay
61%410%16%8%1
1574
March1st to 10thDay
57%5%10%22%6%
3435
11th to 20thDay
51%7%11%23%7%1
3480
21st to endDay
51%6%10%20%11%1
3815
April1st to 10thDay
52%5%12%19%11%2
2192
11th to 20thDay
49%6%12%17%14%2
2282
21st to endDay
50%6%11%22%10%2
2470
May1st to 10thDay
55%6%11%20%8%1
4120
11th to 20thDay
49%7%12%22%8%1
4085
21st to endDay
38%8%16%24%11%3
4741
June1st to 10thDay
43%8%14%23%11%1
2660
11th to 20thDay
43%8%14%22%13%1
2660
21st to endDay
41%7%12%26%13%1
2660
July1st to 10thDay
39%8%11%23%16%3
4228
11th to 20thDay
38%6%12%27%16%1
4051
21st to endDay
44%7%11%20%17%2
4324
August1st to 10thDay
49%8%12%22%9%
4091
11th to 20thDay
41%7%12%28%12%
4083
21st to endDay
37%7%13%27%14%2
4312
September1st to 10thDay
38%7%11%21%20%4
2280
11th to 20thDay
36%6%13%28%16%1
2100
21st to endDay
49%410%22%14%
2085
October1st to 10thDay
34%410%32%19%1
3160
11th to 20thDay
43%5%10%22%14%5%
3140
21st to endDay
36%412%28%19%1
3428
November1st to 10thDay
41%6%12%23%16%3
1837
11th to 20thDay
52%6%11%19%11%2
1584
21st to endDay
57%5%12%18%7%1
1520
December1st to 10thDay
69%5%10%13%4
1520
11th to 20thDay
65%312%16%4
1906
21st to endDay
73%5%9%10%3
2772
January1st to 10thNight
67%5%9%14%4
4109
11th to 20thNight
70%5%11%10%3
4120
21st to endNight
73%46%13%31
4532
February1st to 10thNight
61%410%18%7%
2470
11th to 20thNight
60%410%18%8%
2405
21st to endNight
62%48%16%10%1
1874
March1st to 10thNight
54%49%24%9%
3418
11th to 20thNight
50%5%12%25%7%1
3480
21st to endNight
46%5%10%23%14%2
3817
April1st to 10thNight
50%5%10%19%14%2
1987
11th to 20thNight
45%6%11%18%16%4
1865
21st to endNight
46%6%10%23%13%3
1710
May1st to 10thNight
57%6%8%17%10%2
2840
11th to 20thNight
46%8%11%24%10%1
2813
21st to endNight
37%8%15%24%12%4
2833
June1st to 10thNight
36%8%13%25%16%2
1520
11th to 20thNight
38%7%14%24%15%2
1520
21st to endNight
35%9%13%26%16%2
1520
July1st to 10thNight
40%6%10%24%16%3
2604
11th to 20thNight
35%8%15%26%16%1
2786
21st to endNight
41%7%11%17%21%3
2988
August1st to 10thNight
47%8%12%22%11%
2814
11th to 20thNight
40%6%10%27%17%1
2812
21st to endNight
36%7%12%30%13%2
3311
September1st to 10thNight
35%6%10%23%21%5%
1900
11th to 20thNight
31%6%12%27%23%1
2077
21st to endNight
44%5%10%22%18%1
2094
October1st to 10thNight
35%48%27%23%2
3800
11th to 20thNight
39%411%24%15%8%
3779
21st to endNight
35%39%29%22%2
4120
November1st to 10thNight
40%6%10%23%18%4
2358
11th to 20thNight
51%5%10%21%12%2
2593
21st to endNight
55%5%10%22%7%1
2660
December1st to 10thNight
65%5%10%14%5%
2660
11th to 20thNight
63%411%17%4
3288
21st to endNight
71%6%10%11%2
4880

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 10thDay
28%25%25%14%6%2
270
11th to 20thDay
28%24%29%16%21
270
21st to endDay
29%20%29%18%41
297
February1st to 10thDay
30%14%37%14%3
270
11th to 20thDay
30%24%31%13%2
270
21st to endDay
33%19%31%14%2
258
March1st to 10thDay
28%14%33%21%4
460
11th to 20thDay
28%16%32%17%5%1
460
21st to endDay
31%13%31%19%5%1
506
April1st to 10thDay
27%15%26%22%8%2
460
11th to 20thDay
21%15%32%18%9%5%
452
21st to endDay
29%12%28%20%9%2
460
May1st to 10thDay
30%10%27%19%11%3
463
11th to 20thDay
20%10%28%22%13%7%
487
21st to endDay
14%5%25%25%22%9%
529
June1st to 10thDay
17%6%26%25%18%7%
490
11th to 20thDay
17%6%26%24%21%6%
490
21st to endDay
15%6%28%30%17%4
490
July1st to 10thDay
14%217%32%22%12%
485
11th to 20thDay
13%5%22%29%24%8%
484
21st to endDay
16%319%31%22%8%
532
August1st to 10thDay
13%420%27%26%10%
486
11th to 20thDay
16%5%17%30%20%12%
479
21st to endDay
11%320%28%25%13%
539
September1st to 10thDay
18%418%29%22%9%
490
11th to 20thDay
13%215%31%24%14%
490
21st to endDay
26%8%20%23%15%7%
490
October1st to 10thDay
19%6%25%24%22%5%
490
11th to 20thDay
21%12%29%24%11%2
490
21st to endDay
28%12%31%20%8%1
539
November1st to 10thDay
19%13%32%23%11%3
405
11th to 20thDay
29%17%28%16%9%1
210
21st to endDay
24%16%46%12%3
180
December1st to 10thDay
31%19%30%12%6%1
180
11th to 20thDay
31%16%36%13%5%
180
21st to endDay
33%15%32%15%6%
198
January1st to 10thNight
29%14%33%19%5%
760
11th to 20thNight
32%12%30%22%5%
760
21st to endNight
28%13%30%25%4
836
February1st to 10thNight
28%13%27%29%3
760
11th to 20thNight
28%13%35%22%2
743
21st to endNight
28%11%36%23%3
628
March1st to 10thNight
24%13%29%28%5%
760
11th to 20thNight
26%14%29%24%7%1
760
21st to endNight
25%10%33%26%6%1
836
April1st to 10thNight
25%12%30%26%6%
760
11th to 20thNight
21%9%30%28%10%1
741
21st to endNight
18%7%31%36%7%
570
May1st to 10thNight
24%6%21%34%13%1
570
11th to 20thNight
19%8%23%35%15%1
561
21st to endNight
10%220%39%25%3
467
June1st to 10thNight
12%420%44%20%1
380
11th to 20thNight
13%421%39%22%1
380
21st to endNight
12%224%39%22%1
380
July1st to 10thNight
9%217%44%23%7%
442
11th to 20thNight
11%119%34%30%5%
552
21st to endNight
11%214%42%30%1
624
August1st to 10thNight
11%113%41%31%3
567
11th to 20thNight
12%411%40%31%4
564
21st to endNight
14%116%35%29%5%
736
September1st to 10thNight
15%216%35%28%4
760
11th to 20thNight
12%413%35%32%4
760
21st to endNight
21%422%27%22%4
760
October1st to 10thNight
17%6%19%32%24%2
760
11th to 20thNight
22%7%27%31%12%2
760
21st to endNight
27%9%23%31%9%1
836
November1st to 10thNight
18%7%25%34%15%1
764
11th to 20thNight
26%11%28%25%9%1
760
21st to endNight
28%12%27%26%7%1
760
December1st to 10thNight
32%13%27%23%6%
760
11th to 20thNight
27%12%29%26%5%
760
21st to endNight
30%12%28%28%3
836
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