Williamsport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Williamsport clear sky chart from 2005-11-06 to 2024-02-20.

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
34%
23242
15%
80434
10%
23144
42%
23144
17%
55127

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
18%
754
14%
4384
5%
737
31%
737
8%
2924
January11th to 20thNight
22%
758
11%
4217
6%
740
30%
740
7%
3062
January21st to endNight
20%
833
9%
4515
6%
814
31%
814
7%
3458
February1st to 10thNight
21%
760
14%
2470
6%
760
32%
760
13%
1762
February11th to 20thNight
15%
742
14%
2379
4%
739
29%
739
13%
1689
February21st to endNight
16%
592
16%
1776
7%
592
28%
592
14%
1299
March1st to 10thNight
23%
720
18%
2053
8%
720
35%
720
18%
1425
March11th to 20thNight
24%
720
19%
1980
8%
720
34%
720
19%
1384
March21st to endNight
22%
792
18%
2124
6%
792
32%
792
19%
1531
April1st to 10thNight
24%
720
14%
1800
4%
720
29%
720
19%
1339
April11th to 20thNight
28%
711
16%
1775
6%
711
33%
711
25%
1238
April21st to endNight
32%
712
17%
1792
5%
712
37%
712
25%
1245
May1st to 10thNight
36%
499
16%
1579
10%
499
42%
499
18%
1104
May11th to 20thNight
35%
354
18%
1416
13%
354
46%
354
18%
898
May21st to endNight
49%
388
15%
1551
14%
388
55%
388
19%
971
June1st to 10thNight
48%
360
17%
1440
16%
360
56%
360
20%
885
June11th to 20thNight
50%
360
14%
1440
16%
360
56%
360
21%
883
June21st to endNight
54%
360
16%
1440
19%
360
59%
360
23%
854
July1st to 10thNight
56%
350
14%
1400
17%
350
60%
350
22%
854
July11th to 20thNight
62%
348
17%
1392
22%
348
64%
348
24%
797
July21st to endNight
60%
512
16%
1598
14%
484
64%
484
27%
989
August1st to 10thNight
63%
537
16%
1600
13%
534
65%
534
29%
1020
August11th to 20thNight
55%
570
15%
1634
10%
570
58%
570
26%
1117
August21st to endNight
56%
792
19%
1980
11%
792
58%
792
31%
1340
September1st to 10thNight
50%
720
20%
1800
10%
720
54%
720
30%
1218
September11th to 20thNight
57%
720
27%
1800
18%
720
60%
720
36%
1136
September21st to endNight
49%
720
22%
2058
17%
720
53%
720
27%
1349
October1st to 10thNight
43%
720
16%
2160
13%
720
48%
720
25%
1423
October11th to 20thNight
39%
720
16%
2160
12%
720
47%
720
24%
1422
October21st to endNight
30%
792
19%
2376
12%
792
40%
792
20%
1638
November1st to 10thNight
38%
740
22%
2397
15%
740
49%
740
25%
1468
November11th to 20thNight
28%
760
17%
2565
11%
760
38%
760
17%
1718
November21st to endNight
30%
760
16%
2660
10%
760
40%
760
16%
1815
December1st to 10thNight
22%
760
10%
2660
6%
760
29%
760
11%
1968
December11th to 20thNight
23%
759
12%
3223
5%
759
32%
759
10%
2320
December21st to endNight
22%
827
7%
4840
5%
817
30%
817
7%
3584

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%37%6%45%5%5%7%34%
78344
Night
17%8%36%6%35%5%5%7%35%
80832
TransparencyDay
48%8%12%19%11%2
78056
Night
46%8%13%20%11%1
80654
SeeingDay
22%16%27%21%11%4
13746
Night
21%12%27%29%11%1
23264

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 10thDay
15%11%5%8%6%45%5%5%6%31%
2517
11th to 20thDay
13%13%7%14%8%5%6%445%20%
2689
21st to endDay
20%14%6%10%8%34445%21%
3124
February1st to 10thDay
16%13%48%8%5%5%6%45%26%
1710
11th to 20thDay
13%10%39%8%45%6%6%6%29%
1672
21st to endDay
20%9%5%9%7%45%446%29%
1480
March1st to 10thDay
14%9%47%6%3445%6%37%
1900
11th to 20thDay
17%9%46%8%45%45%6%33%
1980
21st to endDay
20%9%37%6%44446%33%
2232
April1st to 10thDay
16%9%46%7%36%447%34%
2160
11th to 20thDay
18%7%35%6%345%5%6%36%
2134
21st to endDay
19%6%35%6%45%45%6%36%
2182
May1st to 10thDay
19%7%37%6%35%5%5%6%34%
2380
11th to 20thDay
19%7%37%6%45%5%5%6%32%
2478
21st to endDay
17%6%245%45%46%8%39%
2725
June1st to 10thDay
14%6%26%7%46%6%6%8%36%
2520
11th to 20thDay
15%6%26%6%45%5%6%9%36%
2520
21st to endDay
12%5%25%6%35%7%7%10%38%
2520
July1st to 10thDay
9%5%36%7%46%7%6%9%38%
2520
11th to 20thDay
8%5%36%6%45%7%8%11%39%
2520
21st to endDay
10%7%36%7%46%6%7%8%36%
2622
August1st to 10thDay
10%6%36%6%46%7%8%10%35%
2327
11th to 20thDay
14%7%26%6%35%7%7%9%34%
2248
21st to endDay
15%6%36%6%35%7%6%8%36%
2376
September1st to 10thDay
17%5%25%5%345%5%7%41%
2160
11th to 20thDay
13%6%25%5%2445%6%48%
2160
21st to endDay
19%5%36%43445%7%39%
1899
October1st to 10thDay
18%7%25%5%3445%7%39%
1800
11th to 20thDay
19%6%36%5%35%5%7%7%34%
1800
21st to endDay
20%7%37%6%45%5%6%6%32%
1980
November1st to 10thDay
13%7%26%5%35%46%6%43%
1680
11th to 20thDay
17%8%36%6%445%6%7%35%
1611
21st to endDay
18%7%36%7%45%45%6%34%
1520
December1st to 10thDay
20%11%6%8%8%35%446%24%
1520
11th to 20thDay
21%10%36%5%45%5%5%7%30%
1906
21st to endDay
23%12%5%10%8%45%5%45%20%
2772
January1st to 10thNight
17%9%48%7%45%5%5%7%30%
4429
11th to 20thNight
16%9%7%11%7%45%46%7%25%
4266
21st to endNight
24%11%5%10%6%35%45%423%
4532
February1st to 10thNight
16%10%47%6%35%5%6%6%31%
2470
11th to 20thNight
16%10%47%6%46%6%5%7%31%
2377
21st to endNight
19%9%47%6%445%5%6%31%
1776
March1st to 10thNight
16%7%35%7%345%6%7%35%
2043
11th to 20thNight
18%8%36%5%35%5%5%6%37%
1979
21st to endNight
17%8%46%6%45%446%36%
2124
April1st to 10thNight
19%9%47%6%4445%7%32%
1800
11th to 20thNight
17%6%35%5%25%6%5%8%37%
1775
21st to endNight
19%6%35%5%24447%41%
1792
May1st to 10thNight
22%8%35%5%345%46%35%
1579
11th to 20thNight
17%426%6%45%46%6%39%
1415
21st to endNight
14%6%25%6%345%5%8%41%
1550
June1st to 10thNight
14%6%36%5%345%5%8%42%
1440
11th to 20thNight
13%6%25%6%45%5%7%9%40%
1440
21st to endNight
11%5%26%5%35%5%7%10%42%
1440
July1st to 10thNight
10%6%27%435%5%6%8%44%
1440
11th to 20thNight
8%5%25%5%35%5%7%10%44%
1440
21st to endNight
10%5%35%5%36%5%6%9%42%
1692
August1st to 10thNight
10%5%26%445%6%7%9%42%
1611
11th to 20thNight
12%8%36%6%445%6%8%39%
1634
21st to endNight
14%6%346%35%5%6%8%43%
1980
September1st to 10thNight
16%5%35%435%45%6%44%
1800
11th to 20thNight
13%425%424446%52%
1800
21st to endNight
17%6%34435%46%7%43%
2058
October1st to 10thNight
20%7%25%43345%6%42%
2160
11th to 20thNight
18%6%35%5%2445%6%41%
2160
21st to endNight
22%8%35%43445%7%36%
2376
November1st to 10thNight
12%6%45%5%3335%6%48%
2397
11th to 20thNight
20%7%345%35%46%7%35%
2565
21st to endNight
16%9%47%5%35%5%6%7%34%
2660
December1st to 10thNight
20%10%5%7%6%45%5%5%6%27%
2660
11th to 20thNight
20%9%37%7%45%45%6%30%
3288
21st to endNight
23%11%47%6%45%5%5%7%22%
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
51%8%14%18%6%2
2518
11th to 20thDay
63%8%9%13%6%1
2689
21st to endDay
63%7%10%14%41
3124
February1st to 10thDay
58%7%12%15%8%
1710
11th to 20thDay
52%8%10%21%8%1
1681
21st to endDay
57%49%20%8%2
1480
March1st to 10thDay
47%7%12%22%10%2
1903
11th to 20thDay
51%6%10%19%11%2
1980
21st to endDay
52%5%9%18%14%3
2232
April1st to 10thDay
49%6%10%20%11%4
2160
11th to 20thDay
46%8%11%18%15%3
2134
21st to endDay
47%7%9%20%13%4
2182
May1st to 10thDay
50%7%10%18%13%2
2380
11th to 20thDay
51%8%10%17%12%2
2482
21st to endDay
43%8%15%21%12%2
2725
June1st to 10thDay
44%9%13%20%13%2
2520
11th to 20thDay
44%9%13%20%13%2
2520
21st to endDay
37%11%15%26%12%
2520
July1st to 10thDay
41%11%13%21%13%1
2450
11th to 20thDay
36%10%16%23%14%1
2445
21st to endDay
40%11%13%20%14%1
2475
August1st to 10thDay
40%11%15%21%12%
2314
11th to 20thDay
43%10%16%20%10%1
2248
21st to endDay
43%8%12%20%14%3
2376
September1st to 10thDay
42%7%12%23%14%2
2160
11th to 20thDay
36%6%12%23%20%2
2160
21st to endDay
44%5%13%18%17%2
1899
October1st to 10thDay
44%8%13%21%14%1
1800
11th to 20thDay
45%8%14%23%10%
1800
21st to endDay
51%7%14%18%9%1
1980
November1st to 10thDay
41%6%13%22%15%3
1680
11th to 20thDay
46%7%13%21%11%2
1611
21st to endDay
47%8%14%23%7%1
1520
December1st to 10thDay
60%6%13%14%6%1
1520
11th to 20thDay
53%8%16%18%5%
1906
21st to endDay
63%10%11%12%4
2772
January1st to 10thNight
48%10%14%20%6%1
4429
11th to 20thNight
55%10%13%14%7%1
4266
21st to endNight
60%9%10%15%6%1
4532
February1st to 10thNight
50%8%13%20%8%1
2470
11th to 20thNight
50%8%11%19%11%1
2379
21st to endNight
53%7%10%18%11%2
1776
March1st to 10thNight
45%8%11%24%10%2
2053
11th to 20thNight
46%7%12%20%14%1
1980
21st to endNight
49%7%10%16%15%3
2124
April1st to 10thNight
50%7%10%18%14%2
1800
11th to 20thNight
42%8%11%20%16%3
1775
21st to endNight
43%7%12%21%15%3
1792
May1st to 10thNight
49%7%10%21%10%3
1579
11th to 20thNight
44%7%12%19%16%2
1416
21st to endNight
40%10%15%19%13%3
1551
June1st to 10thNight
41%7%11%24%15%1
1440
11th to 20thNight
39%9%15%22%13%2
1440
21st to endNight
34%11%13%26%14%1
1440
July1st to 10thNight
38%9%14%22%14%3
1400
11th to 20thNight
33%10%16%23%17%1
1392
21st to endNight
35%10%17%21%15%2
1598
August1st to 10thNight
35%10%16%24%14%1
1600
11th to 20thNight
42%8%15%21%14%
1634
21st to endNight
38%8%12%24%16%2
1980
September1st to 10thNight
40%6%12%25%15%3
1800
11th to 20thNight
33%7%12%26%20%2
1800
21st to endNight
39%7%12%22%19%1
2058
October1st to 10thNight
43%6%14%22%15%1
2160
11th to 20thNight
41%7%14%24%12%2
2160
21st to endNight
47%6%13%22%11%1
2376
November1st to 10thNight
38%6%14%23%17%2
2397
11th to 20thNight
46%7%13%21%11%3
2565
21st to endNight
47%9%14%22%8%1
2660
December1st to 10thNight
54%9%14%17%7%
2660
11th to 20thNight
53%9%12%18%8%
3288
21st to endNight
56%11%14%15%3
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
27%24%31%14%31
180
11th to 20thDay
32%24%31%12%1
229
21st to endDay
27%25%33%12%21
297
February1st to 10thDay
28%27%30%12%2
270
11th to 20thDay
30%26%36%7%
285
21st to endDay
33%20%30%16%1
346
March1st to 10thDay
29%22%28%18%3
420
11th to 20thDay
26%24%28%17%41
420
21st to endDay
30%23%26%15%42
462
April1st to 10thDay
25%26%26%16%6%1
420
11th to 20thDay
22%26%23%17%8%4
412
21st to endDay
28%19%30%13%7%2
420
May1st to 10thDay
28%18%27%15%9%3
423
11th to 20thDay
21%19%27%20%9%3
447
21st to endDay
20%10%26%21%16%6%
485
June1st to 10thDay
17%14%27%26%13%3
450
11th to 20thDay
17%16%26%25%13%2
450
21st to endDay
14%13%29%28%13%4
450
July1st to 10thDay
12%7%24%31%20%6%
445
11th to 20thDay
9%8%25%32%21%5%
444
21st to endDay
15%8%27%30%17%4
488
August1st to 10thDay
12%7%26%25%21%9%
446
11th to 20thDay
16%5%23%27%18%10%
439
21st to endDay
15%8%23%26%16%11%
495
September1st to 10thDay
20%8%22%23%18%9%
450
11th to 20thDay
15%7%24%24%21%9%
450
21st to endDay
22%11%22%23%17%4
450
October1st to 10thDay
23%12%23%21%15%7%
450
11th to 20thDay
23%15%27%24%10%1
450
21st to endDay
26%16%29%20%9%
495
November1st to 10thDay
22%14%24%24%15%1
369
11th to 20thDay
25%20%28%18%7%1
271
21st to endDay
23%23%36%16%31
180
December1st to 10thDay
27%27%29%12%5%1
180
11th to 20thDay
33%21%29%13%31
180
21st to endDay
32%21%31%14%3
198
January1st to 10thNight
20%18%38%20%3
760
11th to 20thNight
24%15%32%25%4
760
21st to endNight
20%19%34%24%2
836
February1st to 10thNight
21%19%32%26%1
760
11th to 20thNight
24%21%37%17%1
742
21st to endNight
27%18%34%18%2
592
March1st to 10thNight
24%19%30%24%3
720
11th to 20thNight
26%17%30%22%5%
720
21st to endNight
22%17%35%19%6%1
792
April1st to 10thNight
22%22%29%22%5%
720
11th to 20thNight
20%15%32%25%7%1
711
21st to endNight
22%13%29%30%6%
712
May1st to 10thNight
25%12%22%29%12%
499
11th to 20thNight
18%9%32%32%9%
354
21st to endNight
18%5%22%34%21%1
389
June1st to 10thNight
14%6%24%40%16%1
360
11th to 20thNight
16%5%22%41%15%1
360
21st to endNight
11%423%47%15%
360
July1st to 10thNight
12%319%40%23%2
350
11th to 20thNight
11%315%44%25%2
348
21st to endNight
13%317%41%25%1
512
August1st to 10thNight
13%213%44%26%2
537
11th to 20thNight
15%215%35%30%3
570
21st to endNight
15%417%31%31%2
792
September1st to 10thNight
19%418%33%23%2
720
11th to 20thNight
15%5%18%30%27%5%
720
21st to endNight
19%7%19%33%19%2
720
October1st to 10thNight
23%8%21%28%19%2
720
11th to 20thNight
20%11%24%33%11%
720
21st to endNight
27%11%27%28%6%
792
November1st to 10thNight
16%11%30%32%11%
740
11th to 20thNight
23%16%26%26%8%1
760
21st to endNight
21%16%28%31%5%1
760
December1st to 10thNight
27%17%30%22%4
760
11th to 20thNight
23%15%30%26%5%
760
21st to endNight
27%13%31%26%3
836
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