Harrisburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harrisburg clear sky chart from 2005-11-06 to 2024-03-28.

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
33%
23531
18%
80696
10%
23427
44%
23427
19%
52281

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
17%
753
19%
4367
7%
737
35%
737
9%
2661
January11th to 20thNight
21%
759
18%
4111
7%
740
35%
740
9%
2659
January21st to endNight
18%
835
13%
4486
7%
814
35%
814
9%
3090
February1st to 10thNight
22%
760
18%
2470
8%
760
36%
760
15%
1651
February11th to 20thNight
13%
743
17%
2359
3%
740
31%
740
13%
1566
February21st to endNight
15%
628
20%
1884
6%
628
31%
628
15%
1293
March1st to 10thNight
21%
760
21%
2164
7%
760
37%
760
21%
1398
March11th to 20thNight
20%
760
21%
2090
8%
760
33%
760
19%
1399
March21st to endNight
20%
821
19%
2202
6%
821
31%
821
21%
1498
April1st to 10thNight
21%
720
16%
1800
3%
720
29%
720
19%
1286
April11th to 20thNight
28%
711
19%
1775
5%
711
35%
711
27%
1190
April21st to endNight
26%
720
19%
1800
5%
720
35%
720
25%
1230
May1st to 10thNight
32%
561
16%
1641
7%
561
40%
561
20%
1130
May11th to 20thNight
33%
354
18%
1416
11%
354
45%
354
16%
906
May21st to endNight
46%
388
16%
1551
15%
388
54%
388
19%
957
June1st to 10thNight
47%
360
19%
1440
18%
360
57%
360
24%
848
June11th to 20thNight
45%
360
15%
1440
13%
360
54%
360
20%
879
June21st to endNight
49%
360
17%
1440
18%
360
57%
360
25%
824
July1st to 10thNight
50%
350
14%
1400
16%
350
55%
350
19%
900
July11th to 20thNight
63%
348
18%
1392
20%
348
66%
348
24%
782
July21st to endNight
60%
556
16%
1639
11%
525
64%
525
28%
1017
August1st to 10thNight
62%
537
18%
1600
13%
534
65%
534
29%
1019
August11th to 20thNight
58%
596
18%
1660
12%
596
60%
596
24%
1141
August21st to endNight
57%
792
18%
1980
9%
792
60%
792
30%
1341
September1st to 10thNight
49%
720
21%
1800
10%
720
54%
720
31%
1209
September11th to 20thNight
55%
720
31%
1800
20%
720
60%
720
38%
1136
September21st to endNight
45%
720
22%
2052
15%
720
52%
720
25%
1354
October1st to 10thNight
41%
720
17%
2160
14%
720
47%
720
25%
1408
October11th to 20thNight
35%
720
21%
2160
13%
720
47%
720
25%
1359
October21st to endNight
31%
792
25%
2376
13%
792
46%
792
23%
1517
November1st to 10thNight
35%
740
26%
2378
14%
740
51%
740
28%
1368
November11th to 20thNight
28%
760
23%
2518
12%
760
43%
760
19%
1568
November21st to endNight
26%
760
21%
2660
9%
760
42%
760
18%
1649
December1st to 10thNight
20%
760
16%
2660
4%
760
34%
760
13%
1791
December11th to 20thNight
22%
760
17%
3221
6%
759
36%
759
13%
2036
December21st to endNight
23%
827
11%
4804
6%
817
36%
817
8%
3221

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
15%6%35%5%35%5%6%8%39%
78770
Night
16%6%35%5%35%5%5%7%40%
81231
TransparencyDay
43%7%12%21%14%2
78478
Night
43%7%12%22%15%2
81042
SeeingDay
22%15%28%20%11%4
13995
Night
20%13%28%27%11%1
23550

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
14%6%27%6%345%5%6%41%
2517
11th to 20thDay
13%12%48%8%46%6%5%7%28%
2754
21st to endDay
18%10%5%7%6%3445%6%30%
3124
February1st to 10thDay
14%9%36%5%46%5%5%7%35%
1710
11th to 20thDay
15%7%46%6%445%5%7%39%
1707
21st to endDay
20%9%47%6%25%445%35%
1570
March1st to 10thDay
15%5%35%5%35%45%7%44%
2014
11th to 20thDay
15%8%26%6%45%6%5%8%36%
2090
21st to endDay
20%7%25%5%345%5%6%38%
2309
April1st to 10thDay
15%7%36%5%45%5%5%7%38%
2160
11th to 20thDay
16%6%26%5%35%45%7%42%
2134
21st to endDay
18%6%25%435%5%5%7%39%
2160
May1st to 10thDay
17%7%35%6%35%5%6%8%35%
2333
11th to 20thDay
19%8%346%36%5%5%7%34%
2478
21st to endDay
14%7%25%5%35%6%6%8%39%
2725
June1st to 10thDay
12%5%35%5%46%6%6%9%39%
2520
11th to 20thDay
13%6%25%5%45%5%7%9%39%
2520
21st to endDay
10%4245%45%6%7%11%42%
2520
July1st to 10thDay
9%5%25%6%46%6%7%10%39%
2520
11th to 20thDay
6%425%6%35%6%7%11%43%
2520
21st to endDay
9%6%26%6%5%5%6%6%10%38%
2578
August1st to 10thDay
9%5%27%6%47%6%8%10%37%
2327
11th to 20thDay
12%6%36%4446%7%8%40%
2222
21st to endDay
13%5%25%4345%7%10%42%
2376
September1st to 10thDay
16%6%245%34447%45%
2160
11th to 20thDay
13%4244245%6%8%49%
2160
21st to endDay
18%7%25%5%35%45%7%39%
1903
October1st to 10thDay
17%5%25%4345%6%7%43%
1800
11th to 20thDay
17%6%25%5%335%5%8%42%
1800
21st to endDay
16%7%25%5%3446%7%41%
1980
November1st to 10thDay
13%6%3432336%8%49%
1699
11th to 20thDay
18%4234445%6%6%43%
1658
21st to endDay
17%5%35%5%45%5%5%6%41%
1520
December1st to 10thDay
19%8%37%6%345%6%8%32%
1520
11th to 20thDay
20%5%26%5%35%5%5%8%35%
1910
21st to endDay
19%7%38%7%46%6%6%7%28%
2772
January1st to 10thNight
15%8%37%5%345%5%8%37%
4429
11th to 20thNight
18%7%36%5%45%5%6%7%34%
4202
21st to endNight
23%8%37%5%34446%32%
4532
February1st to 10thNight
16%8%36%5%35%5%6%6%38%
2470
11th to 20thNight
17%8%35%5%35%45%7%38%
2357
21st to endNight
17%7%46%445%45%6%38%
1884
March1st to 10thNight
15%6%25%5%3445%8%44%
2164
11th to 20thNight
16%7%35%5%3445%5%43%
2090
21st to endNight
18%6%35%5%3445%6%40%
2202
April1st to 10thNight
17%8%36%6%3436%7%36%
1800
11th to 20thNight
14%5%26%435%5%6%8%42%
1775
21st to endNight
20%5%25%5%245%5%6%42%
1800
May1st to 10thNight
18%7%37%5%24448%37%
1641
11th to 20thNight
19%7%245%35%46%8%36%
1415
21st to endNight
12%7%36%5%3445%8%41%
1550
June1st to 10thNight
14%425%5%3445%8%46%
1440
11th to 20thNight
11%5%36%5%45%6%6%10%39%
1440
21st to endNight
9%5%25%5%45%7%7%11%43%
1440
July1st to 10thNight
10%5%35%6%46%6%7%9%38%
1440
11th to 20thNight
5%4246%45%6%8%10%46%
1440
21st to endNight
10%425%5%46%7%7%10%42%
1736
August1st to 10thNight
10%4246%36%6%7%9%42%
1611
11th to 20thNight
11%6%36%6%46%6%6%7%39%
1660
21st to endNight
12%5%246%36%6%6%9%41%
1980
September1st to 10thNight
15%6%25%5%3445%6%46%
1800
11th to 20thNight
12%5%24324447%52%
1800
21st to endNight
18%5%25%5%3445%6%42%
2052
October1st to 10thNight
20%6%25%433445%44%
2160
11th to 20thNight
17%6%245%34446%46%
2160
21st to endNight
17%6%244345%5%7%43%
2376
November1st to 10thNight
11%5%2443346%6%51%
2378
11th to 20thNight
15%7%35%5%2446%6%44%
2518
21st to endNight
15%5%25%5%35%45%7%43%
2660
December1st to 10thNight
18%7%36%5%35%5%5%7%35%
2660
11th to 20thNight
18%6%35%5%35%5%5%7%38%
3285
21st to endNight
17%7%36%7%46%6%6%8%30%
4884

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
44%5%14%24%10%3
2518
11th to 20thDay
54%6%13%14%11%3
2754
21st to endDay
54%6%11%20%7%1
3124
February1st to 10thDay
48%6%13%21%10%2
1710
11th to 20thDay
46%5%11%24%12%2
1716
21st to endDay
52%410%21%10%4
1570
March1st to 10thDay
41%6%13%25%14%2
2014
11th to 20thDay
44%6%13%19%14%4
2090
21st to endDay
47%6%9%20%16%3
2309
April1st to 10thDay
44%6%13%18%16%4
2160
11th to 20thDay
42%5%11%21%17%4
2134
21st to endDay
44%6%11%21%15%4
2160
May1st to 10thDay
46%7%9%21%15%3
2333
11th to 20thDay
49%7%10%19%14%2
2482
21st to endDay
41%9%14%22%12%2
2725
June1st to 10thDay
40%8%12%22%16%2
2520
11th to 20thDay
41%9%13%22%13%2
2520
21st to endDay
34%9%14%26%16%1
2520
July1st to 10thDay
39%11%11%20%16%3
2450
11th to 20thDay
32%9%14%26%17%2
2445
21st to endDay
42%8%12%19%17%2
2434
August1st to 10thDay
39%11%14%22%13%1
2314
11th to 20thDay
40%9%12%21%16%2
2222
21st to endDay
37%8%12%23%16%3
2376
September1st to 10thDay
40%6%13%19%18%4
2160
11th to 20thDay
33%6%12%24%21%4
2160
21st to endDay
44%6%9%17%21%3
1903
October1st to 10thDay
40%8%12%23%15%2
1800
11th to 20thDay
41%5%12%24%17%1
1800
21st to endDay
42%6%10%25%16%1
1980
November1st to 10thDay
34%415%24%19%3
1699
11th to 20thDay
41%5%12%22%17%3
1658
21st to endDay
43%6%12%28%9%2
1520
December1st to 10thDay
50%6%15%18%10%1
1520
11th to 20thDay
47%6%14%25%7%1
1906
21st to endDay
54%7%14%17%7%
2772
January1st to 10thNight
45%6%13%24%9%2
4429
11th to 20thNight
48%7%14%20%10%2
4202
21st to endNight
53%6%9%22%8%1
4532
February1st to 10thNight
46%6%13%24%10%1
2470
11th to 20thNight
45%6%11%20%17%2
2359
21st to endNight
48%5%10%20%14%4
1884
March1st to 10thNight
40%5%12%25%16%2
2164
11th to 20thNight
43%6%10%23%16%3
2090
21st to endNight
45%410%20%18%3
2202
April1st to 10thNight
48%410%19%16%3
1800
11th to 20thNight
39%6%11%22%19%4
1775
21st to endNight
42%6%10%22%16%5%
1800
May1st to 10thNight
46%7%10%20%13%4
1641
11th to 20thNight
45%8%11%17%18%2
1416
21st to endNight
41%8%14%21%14%2
1551
June1st to 10thNight
37%7%12%23%19%2
1440
11th to 20thNight
39%9%13%20%18%2
1440
21st to endNight
33%10%14%26%16%1
1440
July1st to 10thNight
40%12%12%18%14%3
1400
11th to 20thNight
30%12%14%24%18%2
1392
21st to endNight
36%8%16%21%17%2
1639
August1st to 10thNight
36%9%14%26%15%1
1600
11th to 20thNight
42%9%12%18%18%1
1660
21st to endNight
37%10%12%21%17%3
1980
September1st to 10thNight
39%7%12%20%19%4
1800
11th to 20thNight
32%6%9%26%23%4
1800
21st to endNight
42%5%10%19%21%2
2052
October1st to 10thNight
43%5%11%24%15%2
2160
11th to 20thNight
38%6%11%26%16%2
2160
21st to endNight
40%6%9%26%17%2
2376
November1st to 10thNight
33%6%11%26%20%4
2378
11th to 20thNight
40%5%9%24%17%4
2518
21st to endNight
41%6%12%26%14%2
2660
December1st to 10thNight
48%7%13%20%12%
2660
11th to 20thNight
46%5%13%22%12%1
3288
21st to endNight
50%8%14%20%7%
4884

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
34%23%28%13%11
180
11th to 20thDay
41%20%27%11%1
248
21st to endDay
29%27%33%8%31
297
February1st to 10thDay
29%27%30%12%3
270
11th to 20thDay
35%25%31%7%2
314
21st to endDay
36%20%27%15%2
382
March1st to 10thDay
31%19%30%16%4
460
11th to 20thDay
28%27%27%13%31
460
21st to endDay
27%26%30%12%41
490
April1st to 10thDay
26%25%28%13%6%1
420
11th to 20thDay
23%24%25%17%9%3
412
21st to endDay
28%17%34%14%6%2
420
May1st to 10thDay
28%19%29%15%7%2
423
11th to 20thDay
25%17%28%20%8%2
447
21st to endDay
22%9%25%22%16%6%
485
June1st to 10thDay
18%12%31%22%14%3
450
11th to 20thDay
19%9%30%25%13%3
450
21st to endDay
12%9%34%26%16%3
450
July1st to 10thDay
12%424%28%23%8%
445
11th to 20thDay
6%6%25%32%24%7%
444
21st to endDay
13%6%29%30%17%4
488
August1st to 10thDay
13%5%22%30%22%8%
446
11th to 20thDay
15%5%23%30%19%8%
439
21st to endDay
14%7%23%32%14%11%
495
September1st to 10thDay
18%8%24%22%18%9%
450
11th to 20thDay
14%5%26%27%19%9%
450
21st to endDay
24%11%24%23%13%4
450
October1st to 10thDay
24%6%23%25%18%5%
450
11th to 20thDay
22%16%26%23%11%2
450
21st to endDay
21%17%35%17%9%1
495
November1st to 10thDay
20%15%28%22%13%2
379
11th to 20thDay
25%19%31%17%8%
318
21st to endDay
24%26%30%16%4
180
December1st to 10thDay
33%21%29%13%32
180
11th to 20thDay
31%23%30%13%4
180
21st to endDay
31%20%27%18%5%
198
January1st to 10thNight
23%21%35%19%3
760
11th to 20thNight
26%17%31%23%3
760
21st to endNight
20%23%33%22%1
836
February1st to 10thNight
24%19%29%26%1
760
11th to 20thNight
27%22%33%17%1
743
21st to endNight
27%21%32%16%3
628
March1st to 10thNight
23%18%34%21%3
760
11th to 20thNight
25%20%31%19%5%
760
21st to endNight
23%18%34%19%5%
821
April1st to 10thNight
24%21%30%20%5%
720
11th to 20thNight
18%16%35%23%8%
711
21st to endNight
25%14%30%25%6%
720
May1st to 10thNight
23%11%29%27%10%
561
11th to 20thNight
24%8%31%28%10%
354
21st to endNight
14%8%24%35%17%1
389
June1st to 10thNight
14%427%33%22%
360
11th to 20thNight
13%6%31%34%16%
360
21st to endNight
11%330%42%14%
360
July1st to 10thNight
15%223%38%21%2
350
11th to 20thNight
7%318%45%24%2
348
21st to endNight
11%321%40%24%2
556
August1st to 10thNight
14%116%41%27%1
537
11th to 20thNight
14%5%14%35%29%4
596
21st to endNight
14%418%34%27%3
792
September1st to 10thNight
18%422%34%20%2
720
11th to 20thNight
14%5%21%32%26%3
720
21st to endNight
21%8%20%29%20%3
720
October1st to 10thNight
23%6%23%26%18%3
720
11th to 20thNight
21%13%28%27%11%
720
21st to endNight
23%14%28%26%9%
792
November1st to 10thNight
15%13%32%28%11%1
740
11th to 20thNight
19%22%28%24%7%1
760
21st to endNight
21%18%31%24%7%
760
December1st to 10thNight
25%18%32%19%5%
760
11th to 20thNight
21%16%35%24%4
760
21st to endNight
22%18%32%27%2
836
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