Harrisonburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harrisonburg clear sky chart from 2005-11-06 to 2024-01-13.

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
42%
23670
20%
74676
12%
23625
51%
23625
24%
47286

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
24%
757
24%
2459
8%
757
42%
757
21%
1498
January11th to 20thNight
29%
729
22%
2367
11%
729
43%
729
19%
1525
January21st to endNight
22%
792
23%
2574
10%
792
39%
792
21%
1597
February1st to 10thNight
28%
720
18%
2340
9%
720
40%
720
20%
1514
February11th to 20thNight
17%
700
18%
2274
6%
699
33%
699
16%
1485
February21st to endNight
19%
592
24%
1718
9%
592
35%
592
20%
1153
March1st to 10thNight
26%
720
25%
1980
9%
720
41%
720
26%
1226
March11th to 20thNight
25%
720
20%
1980
9%
720
36%
720
21%
1320
March21st to endNight
29%
792
18%
2178
8%
792
37%
792
23%
1461
April1st to 10thNight
28%
720
19%
1848
6%
720
37%
720
24%
1247
April11th to 20thNight
37%
711
20%
1775
8%
711
43%
711
31%
1160
April21st to endNight
39%
668
21%
1748
8%
668
46%
668
28%
1157
May1st to 10thNight
44%
540
16%
1620
9%
540
50%
540
23%
1079
May11th to 20thNight
45%
531
13%
1592
9%
531
48%
531
22%
1110
May21st to endNight
57%
467
15%
1630
13%
467
61%
467
24%
1029
June1st to 10thNight
60%
360
17%
1440
20%
360
64%
360
25%
830
June11th to 20thNight
64%
360
14%
1440
16%
360
68%
360
22%
874
June21st to endNight
67%
360
18%
1440
21%
360
71%
360
24%
832
July1st to 10thNight
64%
464
14%
1514
14%
464
67%
464
25%
980
July11th to 20thNight
72%
522
14%
1566
12%
522
73%
522
31%
967
July21st to endNight
71%
591
15%
1672
12%
558
74%
558
30%
1075
August1st to 10thNight
68%
537
15%
1600
12%
534
69%
534
26%
1081
August11th to 20thNight
63%
534
18%
1598
15%
534
64%
534
26%
1069
August21st to endNight
62%
788
17%
1976
11%
788
63%
788
28%
1389
September1st to 10thNight
61%
720
22%
1800
14%
720
63%
720
32%
1203
September11th to 20thNight
60%
720
26%
1897
20%
720
63%
720
32%
1223
September21st to endNight
47%
720
21%
2024
16%
720
52%
720
25%
1381
October1st to 10thNight
51%
720
19%
2160
19%
720
55%
720
27%
1361
October11th to 20thNight
44%
720
24%
2160
16%
720
55%
720
28%
1325
October21st to endNight
39%
792
27%
2376
18%
792
52%
792
30%
1423
November1st to 10thNight
44%
740
28%
2221
19%
740
56%
740
31%
1328
November11th to 20thNight
39%
760
25%
2510
16%
760
52%
760
25%
1475
November21st to endNight
37%
760
22%
2660
16%
760
49%
760
24%
1555
December1st to 10thNight
29%
760
20%
2660
10%
760
42%
760
18%
1713
December11th to 20thNight
33%
759
22%
3171
13%
758
47%
758
19%
1887
December21st to endNight
33%
824
14%
4708
11%
817
46%
817
12%
2754

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%6%35%5%35%5%6%8%41%
74615
Night
13%6%35%5%35%5%5%7%44%
75106
TransparencyDay
40%8%12%21%15%3
74336
Night
38%7%13%22%16%3
74904
SeeingDay
18%14%25%23%14%5%
13834
Night
16%11%25%32%15%2
23691

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
12%8%37%6%3445%6%42%
1706
11th to 20thDay
15%8%36%6%34446%39%
1638
21st to endDay
15%7%45%44445%5%43%
1782
February1st to 10thDay
12%9%47%6%3446%7%39%
1620
11th to 20thDay
15%7%36%5%345%5%6%40%
1573
21st to endDay
16%8%35%5%35%45%6%41%
1533
March1st to 10thDay
12%7%25%425%447%49%
1980
11th to 20thDay
15%8%36%5%36%5%5%6%40%
1980
21st to endDay
14%8%36%6%445%5%7%38%
2178
April1st to 10thDay
10%6%26%5%45%5%5%7%46%
2110
11th to 20thDay
13%6%345%345%46%46%
2134
21st to endDay
16%6%26%5%45%447%42%
2226
May1st to 10thDay
15%6%36%7%35%5%6%8%36%
2340
11th to 20thDay
17%7%27%6%36%5%5%8%34%
2301
21st to endDay
13%6%36%6%35%5%6%8%38%
2644
June1st to 10thDay
12%5%25%445%5%6%10%43%
2520
11th to 20thDay
10%5%37%6%37%6%7%10%36%
2520
21st to endDay
8%425%5%35%6%7%12%41%
2520
July1st to 10thDay
10%436%6%37%6%8%10%37%
2395
11th to 20thDay
6%425%6%5%6%8%9%12%37%
2340
21st to endDay
10%5%36%7%47%7%7%10%35%
2547
August1st to 10thDay
10%6%36%7%5%6%7%8%11%31%
2327
11th to 20thDay
12%5%26%8%46%5%7%9%35%
2287
21st to endDay
10%5%25%5%46%7%7%9%39%
2376
September1st to 10thDay
13%6%245%35%5%5%6%45%
2160
11th to 20thDay
12%5%25%5%35%46%7%45%
2059
21st to endDay
19%6%26%5%35%5%5%6%38%
1934
October1st to 10thDay
15%6%245%3345%7%46%
1800
11th to 20thDay
14%6%35%43345%6%48%
1800
21st to endDay
14%5%244345%46%49%
1980
November1st to 10thDay
12%6%2332435%6%55%
1857
11th to 20thDay
13%6%245%2445%7%49%
1663
21st to endDay
14%424444446%49%
1520
December1st to 10thDay
16%7%25%436%5%6%7%38%
1520
11th to 20thDay
15%5%24323347%51%
1910
21st to endDay
19%6%36%5%35%6%6%7%33%
2835
January1st to 10thNight
13%6%35%4345%5%6%46%
2459
11th to 20thNight
15%8%35%6%35%36%6%41%
2367
21st to endNight
13%7%45%5%25%5%5%6%44%
2574
February1st to 10thNight
13%8%26%435%5%6%7%41%
2340
11th to 20thNight
18%7%26%4245%5%6%40%
2273
21st to endNight
14%8%36%5%3446%6%41%
1718
March1st to 10thNight
12%42443445%7%51%
1980
11th to 20thNight
16%6%26%5%2345%6%43%
1980
21st to endNight
16%6%345%3435%6%43%
2178
April1st to 10thNight
14%6%35%5%35%45%6%43%
1848
11th to 20thNight
12%5%344345%6%8%46%
1775
21st to endNight
17%4243345%6%7%45%
1748
May1st to 10thNight
16%5%25%5%45%46%8%41%
1620
11th to 20thNight
17%7%35%435%5%47%39%
1592
21st to endNight
13%6%245%345%7%9%41%
1629
June1st to 10thNight
9%5%25%5%345%6%10%44%
1440
11th to 20thNight
9%5%26%426%5%7%8%44%
1440
21st to endNight
8%325%5%35%8%7%9%44%
1440
July1st to 10thNight
10%5%35%5%46%5%7%9%42%
1559
11th to 20thNight
5%5%25%5%36%6%7%11%45%
1620
21st to endNight
7%5%25%5%37%6%8%11%41%
1771
August1st to 10thNight
9%6%25%6%35%7%8%9%39%
1611
11th to 20thNight
11%6%36%6%45%5%7%7%40%
1598
21st to endNight
10%6%36%5%46%6%7%11%36%
1976
September1st to 10thNight
12%7%25%4345%5%8%46%
1800
11th to 20thNight
11%5%25%5%345%6%6%46%
1897
21st to endNight
18%8%34444445%42%
2024
October1st to 10thNight
15%6%35%43445%7%45%
2160
11th to 20thNight
13%6%245%3445%6%48%
2160
21st to endNight
14%5%245%2445%5%50%
2376
November1st to 10thNight
11%6%34434445%53%
2221
11th to 20thNight
12%6%25%4245%5%6%49%
2510
21st to endNight
13%5%245%34447%48%
2660
December1st to 10thNight
15%7%26%5%35%5%45%42%
2660
11th to 20thNight
14%7%35%434446%45%
3285
21st to endNight
16%6%35%6%36%6%6%7%37%
4817

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
43%6%9%20%18%5%
1707
11th to 20thDay
47%5%9%21%16%2
1638
21st to endDay
43%411%20%19%4
1782
February1st to 10thDay
45%6%11%21%14%3
1620
11th to 20thDay
44%6%10%21%17%3
1582
21st to endDay
44%7%11%17%16%5%
1533
March1st to 10thDay
37%5%10%22%21%4
1980
11th to 20thDay
45%6%10%17%16%6%
1980
21st to endDay
46%8%10%18%13%5%
2178
April1st to 10thDay
38%7%11%19%18%7%
2110
11th to 20thDay
38%7%10%20%20%6%
2134
21st to endDay
43%7%11%21%13%4
2226
May1st to 10thDay
45%10%13%17%13%2
2340
11th to 20thDay
48%9%13%18%9%2
2305
21st to endDay
42%10%16%21%10%1
2644
June1st to 10thDay
37%10%15%23%14%1
2520
11th to 20thDay
41%11%15%19%12%2
2520
21st to endDay
33%12%17%24%12%1
2520
July1st to 10thDay
40%11%13%20%14%2
2330
11th to 20thDay
34%13%19%22%11%1
2271
21st to endDay
42%11%14%20%12%1
2405
August1st to 10thDay
43%12%16%19%10%
2314
11th to 20thDay
43%11%14%20%10%1
2287
21st to endDay
39%11%17%20%10%2
2376
September1st to 10thDay
39%9%14%17%17%4
2160
11th to 20thDay
37%8%9%24%18%3
2059
21st to endDay
46%7%10%19%16%3
1934
October1st to 10thDay
39%6%11%24%16%5%
1800
11th to 20thDay
36%6%10%24%20%4
1800
21st to endDay
35%6%9%25%20%5%
1980
November1st to 10thDay
32%49%26%24%5%
1857
11th to 20thDay
35%5%12%20%22%7%
1663
21st to endDay
35%5%10%25%22%3
1520
December1st to 10thDay
44%7%11%22%13%3
1520
11th to 20thDay
34%411%30%16%6%
1906
21st to endDay
44%8%14%22%11%1
2835
January1st to 10thNight
39%5%10%21%19%6%
2459
11th to 20thNight
44%5%11%21%16%3
2367
21st to endNight
40%5%11%23%19%3
2574
February1st to 10thNight
41%7%12%22%15%2
2340
11th to 20thNight
44%6%9%20%15%6%
2275
21st to endNight
43%7%12%19%14%5%
1718
March1st to 10thNight
35%5%11%27%19%4
1980
11th to 20thNight
41%7%11%21%18%3
1980
21st to endNight
42%6%13%19%15%5%
2178
April1st to 10thNight
40%7%11%20%18%4
1848
11th to 20thNight
34%8%14%20%20%5%
1775
21st to endNight
38%7%13%25%14%3
1748
May1st to 10thNight
41%9%14%21%11%4
1620
11th to 20thNight
44%10%13%21%12%1
1593
21st to endNight
38%9%18%24%10%1
1630
June1st to 10thNight
34%9%17%27%13%1
1440
11th to 20thNight
35%12%17%22%13%1
1440
21st to endNight
32%12%17%19%18%2
1440
July1st to 10thNight
36%12%17%19%13%3
1514
11th to 20thNight
30%12%20%25%12%1
1566
21st to endNight
33%12%21%22%12%
1672
August1st to 10thNight
38%12%18%21%10%1
1600
11th to 20thNight
40%9%15%23%12%1
1598
21st to endNight
39%11%16%23%9%2
1976
September1st to 10thNight
35%10%15%20%16%4
1800
11th to 20thNight
36%7%10%27%17%3
1897
21st to endNight
44%7%10%21%17%2
2024
October1st to 10thNight
40%5%12%25%16%2
2160
11th to 20thNight
35%7%10%25%20%3
2160
21st to endNight
35%5%11%23%23%4
2376
November1st to 10thNight
34%6%10%22%23%6%
2221
11th to 20thNight
35%6%9%22%23%6%
2510
21st to endNight
36%5%10%24%20%4
2660
December1st to 10thNight
43%7%10%23%13%3
2660
11th to 20thNight
39%5%9%22%19%5%
3288
21st to endNight
41%8%14%22%14%2
4817

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
29%27%27%13%3
270
11th to 20thDay
22%33%28%15%2
246
21st to endDay
27%32%28%11%21
264
February1st to 10thDay
27%32%31%8%2
240
11th to 20thDay
35%30%30%5%
240
21st to endDay
32%22%28%16%2
314
March1st to 10thDay
21%28%27%20%5%
420
11th to 20thDay
23%25%28%17%5%2
420
21st to endDay
23%21%31%18%6%1
462
April1st to 10thDay
23%23%26%20%8%1
420
11th to 20thDay
20%16%28%19%12%4
412
21st to endDay
24%18%27%20%8%3
420
May1st to 10thDay
20%22%25%19%9%4
423
11th to 20thDay
18%15%29%23%12%4
447
21st to endDay
16%7%23%27%18%9%
485
June1st to 10thDay
13%8%27%28%18%5%
450
11th to 20thDay
13%10%26%27%18%7%
450
21st to endDay
9%5%30%32%18%5%
450
July1st to 10thDay
11%419%29%27%9%
445
11th to 20thDay
5%218%37%27%11%
444
21st to endDay
12%419%30%24%11%
488
August1st to 10thDay
13%5%20%27%22%13%
446
11th to 20thDay
13%6%16%28%25%12%
439
21st to endDay
9%417%31%21%17%
495
September1st to 10thDay
13%7%19%25%21%15%
450
11th to 20thDay
12%321%30%23%10%
450
21st to endDay
25%10%21%22%19%4
450
October1st to 10thDay
19%8%21%29%18%6%
450
11th to 20thDay
15%16%25%24%17%2
450
21st to endDay
20%13%33%21%10%3
495
November1st to 10thDay
18%12%27%28%12%2
455
11th to 20thDay
21%15%29%24%9%1
288
21st to endDay
19%18%34%21%6%1
180
December1st to 10thDay
22%21%38%16%31
180
11th to 20thDay
24%19%31%19%7%1
180
21st to endDay
19%26%32%17%6%
216
January1st to 10thNight
19%19%34%24%4
760
11th to 20thNight
22%15%29%31%3
729
21st to endNight
17%16%40%25%2
792
February1st to 10thNight
18%17%34%29%2
720
11th to 20thNight
24%21%33%20%1
703
21st to endNight
22%19%36%21%2
592
March1st to 10thNight
18%17%35%26%4
720
11th to 20thNight
23%17%30%22%6%1
720
21st to endNight
20%16%32%26%6%1
792
April1st to 10thNight
17%20%32%26%5%
720
11th to 20thNight
15%16%29%28%11%1
711
21st to endNight
21%10%26%35%7%1
668
May1st to 10thNight
18%8%24%31%17%1
540
11th to 20thNight
19%423%38%15%2
531
21st to endNight
15%316%39%25%2
469
June1st to 10thNight
10%320%41%24%2
360
11th to 20thNight
9%5%13%45%25%2
360
21st to endNight
7%218%50%22%1
360
July1st to 10thNight
11%311%36%33%5%
464
11th to 20thNight
7%210%33%43%5%
522
21st to endNight
7%211%39%36%6%
591
August1st to 10thNight
9%211%40%34%4
537
11th to 20thNight
13%312%35%34%3
534
21st to endNight
11%314%36%32%4
788
September1st to 10thNight
14%314%33%31%6%
720
11th to 20thNight
12%415%34%29%5%
720
21st to endNight
22%5%19%31%21%2
720
October1st to 10thNight
18%7%18%30%24%4
720
11th to 20thNight
15%10%27%32%16%1
720
21st to endNight
16%10%30%31%12%1
792
November1st to 10thNight
16%9%25%36%12%2
740
11th to 20thNight
16%14%28%33%9%1
760
21st to endNight
16%14%30%31%8%1
760
December1st to 10thNight
20%13%32%29%6%
760
11th to 20thNight
16%12%33%34%5%
760
21st to endNight
17%14%29%36%4
836
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