Boyertown Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boyertown Planetarium clear sky chart from 2005-11-05 to 2018-04-23.

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%
15945
20%
49538
10%
15910
45%
15910
22%
31615

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
21%
780
19%
2716
8%
776
37%
776
16%
1727
January16th to endNight
19%
832
22%
2730
7%
832
39%
832
18%
1739
February1st to 15thNight
15%
764
17%
2467
4%
761
32%
761
16%
1610
February16th to endNight
16%
683
24%
2049
6%
683
37%
683
18%
1320
March1st to 15thNight
22%
780
21%
2259
7%
780
37%
780
19%
1488
March16th to endNight
23%
832
23%
2207
8%
832
35%
832
25%
1460
April1st to 15thNight
21%
778
18%
1946
5%
778
29%
778
24%
1321
April16th to endNight
31%
743
19%
1857
5%
743
38%
743
29%
1246
May1st to 15thNight
32%
498
17%
1578
9%
498
40%
498
20%
1053
May16th to endNight
47%
374
16%
1497
15%
374
53%
374
19%
927
June1st to 15thNight
46%
360
15%
1440
14%
360
56%
360
21%
879
June16th to endNight
57%
360
17%
1440
19%
360
64%
360
25%
828
July1st to 15thNight
52%
340
13%
1360
14%
340
56%
340
19%
866
July16th to endNight
63%
412
15%
1451
14%
387
68%
387
26%
826
August1st to 15thNight
61%
568
19%
1638
13%
565
63%
565
32%
1029
August16th to endNight
60%
764
18%
1910
10%
764
62%
764
33%
1261
September1st to 15thNight
49%
720
24%
1800
12%
720
55%
720
33%
1176
September16th to endNight
53%
717
27%
1943
20%
717
59%
717
33%
1229
October1st to 15thNight
43%
720
20%
2160
14%
720
51%
720
26%
1358
October16th to endNight
34%
768
27%
2337
15%
768
49%
768
28%
1392
November1st to 15thNight
34%
760
22%
2472
12%
760
48%
760
25%
1503
November16th to endNight
27%
780
22%
2639
11%
780
43%
780
19%
1637
December1st to 15thNight
24%
780
15%
2730
6%
780
36%
780
14%
1849
December16th to endNight
19%
832
19%
2912
5%
832
36%
832
15%
1891

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%5%25%5%3445%7%39%
49983
Night
15%5%2442445%7%42%
49711
Cloud CoverDay
15%5%25%5%3445%7%40%
49992
Night
15%5%2442445%7%42%
49717
TransparencyDay
42%6%11%22%15%2
49674
Night
41%5%11%22%16%2
49538
SeeingDay
21%12%26%21%13%5%
6410
Night
19%12%28%27%11%
15946

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
15%7%246%35%45%6%38%
1552
16th to endDay
14%7%35%5%34347%38%
1843
February1st to 15thDay
16%7%36%5%34447%37%
1724
16th to endDay
17%8%36%6%34346%37%
1710
March1st to 15thDay
15%6%26%6%35%435%38%
2019
16th to endDay
19%7%24424345%41%
2369
April1st to 15thDay
19%5%25%424447%39%
2332
16th to endDay
15%325%42345%7%44%
2218
May1st to 15thDay
19%6%25%435%5%6%6%34%
2383
16th to endDay
17%5%25%5%25%5%5%7%36%
2618
June1st to 15thDay
14%425%435%6%7%10%35%
2520
16th to endDay
12%4245%36%6%5%9%38%
2520
July1st to 15thDay
11%425%5%46%5%6%8%37%
2520
16th to endDay
8%425%6%45%7%7%10%37%
2615
August1st to 15thDay
12%5%25%5%35%6%6%8%38%
2298
16th to endDay
12%5%244345%6%8%43%
2292
September1st to 15thDay
15%5%13424447%45%
2160
16th to endDay
14%5%245%2435%6%45%
2015
October1st to 15thDay
17%424423446%43%
1800
16th to endDay
18%424313446%44%
1887
November1st to 15thDay
17%6%24323446%45%
1716
16th to endDay
16%5%2432435%6%45%
1648
December1st to 15thDay
17%7%246%3435%7%38%
1560
16th to endDay
18%7%25%44345%7%35%
1664
January1st to 15thNight
17%5%25%434446%41%
2716
16th to endNight
16%7%25%433346%42%
2730
February1st to 15thNight
15%8%25%434346%39%
2465
16th to endNight
17%6%24424445%42%
2049
March1st to 15thNight
17%5%24424445%43%
2246
16th to endNight
17%7%24323335%45%
2207
April1st to 15thNight
16%5%2442445%8%40%
1946
16th to endNight
17%42441345%7%43%
1857
May1st to 15thNight
17%8%25%5%24346%38%
1578
16th to endNight
15%6%145%3346%7%41%
1495
June1st to 15thNight
16%424435%45%7%41%
1440
16th to endNight
10%3245%35%5%6%9%43%
1440
July1st to 15thNight
11%436%6%36%5%6%8%38%
1440
16th to endNight
7%4245%35%6%7%10%43%
1550
August1st to 15thNight
10%5%245%345%6%9%44%
1649
16th to endNight
13%4144345%47%45%
1910
September1st to 15thNight
14%42442345%7%47%
1800
16th to endNight
12%5%24434447%47%
1943
October1st to 15thNight
18%6%23323336%45%
2160
16th to endNight
16%5%13313336%50%
2337
November1st to 15thNight
14%6%24413345%47%
2472
16th to endNight
16%5%2443435%7%42%
2639
December1st to 15thNight
18%6%26%5%35%5%5%6%34%
2730
16th to endNight
18%5%25%5%335%47%38%
2912

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
15%6%336%35%447%38%
1552
16th to endDay
14%7%345%34447%39%
1843
February1st to 15thDay
16%6%36%5%34447%37%
1724
16th to endDay
16%7%36%5%33445%38%
1710
March1st to 15thDay
16%5%36%6%45%445%38%
2029
16th to endDay
19%6%24433345%41%
2368
April1st to 15thDay
18%5%25%5%24448%39%
2332
16th to endDay
14%42442345%7%44%
2218
May1st to 15thDay
19%5%35%435%5%5%6%35%
2383
16th to endDay
17%5%245%35%5%6%7%36%
2618
June1st to 15thDay
13%435%425%6%6%10%35%
2520
16th to endDay
11%425%5%35%5%6%10%38%
2520
July1st to 15thDay
10%5%25%6%36%5%6%10%37%
2520
16th to endDay
8%415%6%36%7%7%10%38%
2615
August1st to 15thDay
11%5%25%5%35%5%7%7%39%
2298
16th to endDay
12%42443446%9%43%
2292
September1st to 15thDay
14%6%13324447%45%
2160
16th to endDay
14%5%245%24446%45%
2015
October1st to 15thDay
17%5%2342345%6%43%
1800
16th to endDay
18%414313446%44%
1887
November1st to 15thDay
17%6%23323445%45%
1716
16th to endDay
15%5%24324446%46%
1648
December1st to 15thDay
16%7%245%3345%7%38%
1560
16th to endDay
18%7%35%5%24348%36%
1664
January1st to 15thNight
16%5%25%434445%41%
2716
16th to endNight
16%7%25%424346%42%
2730
February1st to 15thNight
14%8%35%43435%6%39%
2458
16th to endNight
17%7%24323445%42%
2049
March1st to 15thNight
17%6%2442445%6%43%
2259
16th to endNight
17%6%24423236%45%
2207
April1st to 15thNight
15%5%2443445%8%40%
1946
16th to endNight
16%5%2442345%7%43%
1857
May1st to 15thNight
18%7%25%5%24445%39%
1578
16th to endNight
15%5%245%2346%7%41%
1495
June1st to 15thNight
16%4236%2445%7%41%
1440
16th to endNight
10%324435%5%6%10%43%
1440
July1st to 15thNight
10%5%26%6%35%6%5%8%39%
1440
16th to endNight
7%423425%6%8%10%43%
1550
August1st to 15thNight
9%5%145%35%46%8%44%
1649
16th to endNight
12%424435%45%7%45%
1910
September1st to 15thNight
14%42442345%6%47%
1800
16th to endNight
11%5%25%43345%7%47%
1943
October1st to 15thNight
18%6%24323336%45%
2160
16th to endNight
16%5%13322336%50%
2337
November1st to 15thNight
14%6%25%422346%47%
2472
16th to endNight
16%5%24424446%42%
2639
December1st to 15thNight
18%5%26%5%35%5%5%7%34%
2730
16th to endNight
17%5%25%43445%7%38%
2912

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
45%411%22%11%3
1553
16th to endDay
44%5%12%23%12%1
1843
February1st to 15thDay
46%5%11%22%11%2
1726
16th to endDay
47%410%24%11%1
1710
March1st to 15thDay
47%5%10%21%13%2
2029
16th to endDay
45%49%20%17%1
2369
April1st to 15thDay
44%49%23%14%3
2332
16th to endDay
38%410%20%20%4
2218
May1st to 15thDay
47%6%9%20%14%2
2383
16th to endDay
45%7%12%20%13%1
2622
June1st to 15thDay
41%8%13%24%10%1
2520
16th to endDay
39%8%13%24%12%1
2520
July1st to 15thDay
41%7%11%22%15%2
2371
16th to endDay
36%9%12%24%14%1
2451
August1st to 15thDay
41%7%12%20%17%
2285
16th to endDay
36%7%9%23%20%2
2292
September1st to 15thDay
38%5%11%20%22%2
2160
16th to endDay
39%48%22%23%2
2015
October1st to 15thDay
39%5%12%22%18%2
1800
16th to endDay
39%410%27%17%1
1887
November1st to 15thDay
40%413%21%16%3
1716
16th to endDay
38%410%29%15%1
1648
December1st to 15thDay
45%416%20%10%
1560
16th to endDay
46%5%15%19%11%
1664
January1st to 15thNight
44%411%20%15%3
2716
16th to endNight
44%211%26%13%1
2730
February1st to 15thNight
45%413%22%12%2
2467
16th to endNight
42%48%23%17%3
2049
March1st to 15thNight
42%5%10%24%15%2
2259
16th to endNight
42%310%23%17%3
2207
April1st to 15thNight
41%411%21%16%3
1946
16th to endNight
40%49%19%21%4
1857
May1st to 15thNight
46%5%10%17%17%2
1578
16th to endNight
41%8%14%15%17%3
1497
June1st to 15thNight
41%6%13%22%16%
1440
16th to endNight
34%7%12%29%14%1
1440
July1st to 15thNight
42%9%13%19%13%3
1360
16th to endNight
31%9%17%23%14%2
1451
August1st to 15thNight
35%6%13%23%18%2
1638
16th to endNight
36%6%11%20%21%2
1910
September1st to 15thNight
36%6%10%21%23%2
1800
16th to endNight
35%5%6%21%26%2
1943
October1st to 15thNight
40%412%24%15%2
2160
16th to endNight
35%49%29%18%2
2337
November1st to 15thNight
38%412%22%16%5%
2472
16th to endNight
41%410%25%16%1
2639
December1st to 15thNight
48%5%12%19%11%1
2730
16th to endNight
45%5%13%22%11%1
2912

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
34%28%23%8%4
90
16th to endDay
24%25%35%13%
137
February1st to 15thDay
28%32%29%8%1
150
16th to endDay
27%19%33%16%2
291
March1st to 15thDay
28%18%27%20%4
330
16th to endDay
25%21%30%13%5%1
352
April1st to 15thDay
26%18%29%15%7%1
330
16th to endDay
20%12%35%16%8%6%
289
May1st to 15thDay
36%14%20%13%10%4
288
16th to endDay
20%7%26%23%17%4
331
June1st to 15thDay
17%10%25%23%18%4
315
16th to endDay
14%6%33%27%13%3
315
July1st to 15thDay
14%326%31%20%3
305
16th to endDay
10%222%32%25%6%
326
August1st to 15thDay
14%317%30%23%9%
313
16th to endDay
11%216%30%22%15%
332
September1st to 15thDay
16%8%25%19%18%12%
315
16th to endDay
17%420%25%17%14%
314
October1st to 15thDay
23%419%27%18%6%
315
16th to endDay
17%15%31%21%10%2
328
November1st to 15thDay
23%9%29%24%10%2
280
16th to endDay
19%21%30%19%6%1
178
December1st to 15thDay
34%21%23%11%8%1
90
16th to endDay
34%29%29%7%
96
January1st to 15thNight
21%19%33%20%4
780
16th to endNight
22%19%34%22%1
832
February1st to 15thNight
20%20%37%19%1
764
16th to endNight
24%20%35%17%2
683
March1st to 15thNight
23%20%30%21%3
780
16th to endNight
21%15%36%19%6%
832
April1st to 15thNight
19%19%36%20%3
778
16th to endNight
19%10%33%26%9%
743
May1st to 15thNight
23%9%28%28%8%
498
16th to endNight
17%423%38%14%1
375
June1st to 15thNight
16%324%38%16%
360
16th to endNight
10%125%51%11%
360
July1st to 15thNight
13%222%40%20%
340
16th to endNight
10%116%41%26%2
412
August1st to 15thNight
13%115%41%25%1
568
16th to endNight
13%115%37%28%3
764
September1st to 15thNight
16%421%35%20%1
720
16th to endNight
14%321%27%28%4
717
October1st to 15thNight
21%6%23%26%18%2
720
16th to endNight
20%12%29%26%10%
768
November1st to 15thNight
19%10%28%26%12%1
760
16th to endNight
19%16%30%23%8%
780
December1st to 15thNight
24%16%30%21%7%
780
16th to endNight
23%18%33%21%3
832
Page generated at 2018-04-24 10:03:01. Version ac04

Copyright 2018 A. Danko


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