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 2017-09-16.

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%
15075
20%
46852
10%
15040
45%
15040
22%
29918

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
22%
720
19%
2506
8%
716
38%
716
16%
1609
January16th to endNight
19%
768
22%
2520
7%
768
39%
768
19%
1604
February1st to 15thNight
16%
704
18%
2274
4%
701
33%
701
17%
1466
February16th to endNight
16%
631
25%
1893
6%
631
38%
631
18%
1202
March1st to 15thNight
22%
720
20%
2085
7%
720
37%
720
19%
1378
March16th to endNight
23%
768
22%
2037
8%
768
35%
768
25%
1349
April1st to 15thNight
22%
718
18%
1796
5%
718
29%
718
25%
1212
April16th to endNight
31%
720
18%
1800
5%
720
38%
720
29%
1207
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
52%
658
25%
1784
18%
658
57%
658
32%
1143
October1st to 15thNight
43%
660
21%
1980
15%
660
51%
660
26%
1235
October16th to endNight
33%
704
25%
2142
13%
704
48%
704
27%
1287
November1st to 15thNight
34%
700
22%
2277
13%
700
48%
700
25%
1375
November16th to endNight
27%
720
20%
2436
10%
720
41%
720
18%
1548
December1st to 15thNight
24%
720
16%
2520
7%
720
36%
720
14%
1693
December16th to endNight
19%
768
19%
2688
5%
768
35%
768
15%
1765

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%
47895
Night
15%5%2442445%7%42%
47025
Cloud CoverDay
15%5%245%3445%7%40%
47904
Night
15%5%2442445%7%42%
47031
TransparencyDay
42%6%11%22%15%2
47586
Night
41%5%11%22%16%2
46852
SeeingDay
20%11%26%22%13%5%
5708
Night
19%11%28%27%11%
15076

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%5%46%36%
1432
16th to endDay
14%7%35%5%34347%38%
1701
February1st to 15thDay
15%7%36%5%3445%7%37%
1588
16th to endDay
14%8%36%6%34345%38%
1580
March1st to 15thDay
15%6%26%6%36%435%37%
1863
16th to endDay
19%6%34424345%41%
2187
April1st to 15thDay
19%425%423347%41%
2152
16th to endDay
15%325%5%2345%7%44%
2160
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
15%5%245%34346%44%
1848
October1st to 15thDay
16%42342345%7%44%
1650
16th to endDay
19%424324446%43%
1730
November1st to 15thDay
16%6%24323346%46%
1581
16th to endDay
17%5%2432435%6%43%
1521
December1st to 15thDay
17%6%246%3435%7%38%
1440
16th to endDay
19%7%25%44245%7%36%
1536
January1st to 15thNight
17%5%25%434446%40%
2506
16th to endNight
16%7%25%433446%42%
2520
February1st to 15thNight
14%8%25%5%24446%40%
2272
16th to endNight
16%6%344245%5%5%44%
1893
March1st to 15thNight
17%5%24434446%42%
2072
16th to endNight
18%6%23323335%45%
2037
April1st to 15thNight
16%5%2442445%8%41%
1796
16th to endNight
17%42442345%7%43%
1800
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
13%5%24434446%46%
1784
October1st to 15thNight
17%6%23323436%46%
1980
16th to endNight
16%5%14313336%49%
2142
November1st to 15thNight
14%6%24413345%47%
2277
16th to endNight
17%5%245%35%35%7%40%
2436
December1st to 15thNight
19%5%25%5%35%45%6%35%
2520
16th to endNight
18%5%35%5%335%47%37%
2688

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%346%35%5%47%36%
1432
16th to endDay
14%7%345%24447%39%
1701
February1st to 15thDay
15%6%36%5%345%47%37%
1588
16th to endDay
14%8%36%5%33445%38%
1580
March1st to 15thDay
15%5%36%6%45%445%38%
1873
16th to endDay
19%6%24433345%41%
2186
April1st to 15thDay
18%5%24423448%41%
2152
16th to endDay
14%4245%2345%7%44%
2160
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
15%5%345%24346%44%
1848
October1st to 15thDay
16%5%2342345%7%44%
1650
16th to endDay
19%5%14423446%43%
1730
November1st to 15thDay
16%6%23323445%46%
1581
16th to endDay
17%6%23324446%43%
1521
December1st to 15thDay
16%6%245%3345%7%38%
1440
16th to endDay
19%6%35%5%24347%36%
1536
January1st to 15thNight
16%5%25%43445%5%40%
2506
16th to endNight
16%7%25%424347%41%
2520
February1st to 15thNight
14%8%25%43435%6%40%
2265
16th to endNight
16%6%243245%5%5%44%
1893
March1st to 15thNight
17%6%2443445%6%42%
2085
16th to endNight
17%6%24424235%45%
2037
April1st to 15thNight
16%5%2443445%8%41%
1796
16th to endNight
16%5%2442345%7%43%
1800
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
12%5%25%32345%6%46%
1784
October1st to 15thNight
17%6%24323336%45%
1980
16th to endNight
16%5%13322346%49%
2142
November1st to 15thNight
14%6%25%323345%47%
2277
16th to endNight
16%6%24424446%40%
2436
December1st to 15thNight
19%5%25%5%345%5%7%35%
2520
16th to endNight
18%5%25%43445%7%37%
2688

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
46%5%11%22%10%2
1433
16th to endDay
44%5%12%23%12%2
1701
February1st to 15thDay
45%6%11%22%11%2
1590
16th to endDay
46%410%25%11%1
1580
March1st to 15thDay
47%6%11%21%12%2
1873
16th to endDay
45%49%20%17%1
2187
April1st to 15thDay
42%49%24%14%4
2152
16th to endDay
38%5%10%20%20%4
2160
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
40%37%21%23%2
1848
October1st to 15thDay
38%412%24%17%2
1650
16th to endDay
40%410%26%16%1
1730
November1st to 15thDay
40%413%21%17%3
1581
16th to endDay
40%410%28%14%1
1521
December1st to 15thDay
45%5%17%20%10%1
1440
16th to endDay
47%5%15%19%11%
1536
January1st to 15thNight
44%5%11%21%14%2
2506
16th to endNight
44%211%26%13%1
2520
February1st to 15thNight
44%412%22%13%2
2274
16th to endNight
41%49%24%18%2
1893
March1st to 15thNight
42%5%10%23%15%2
2085
16th to endNight
41%311%23%17%3
2037
April1st to 15thNight
41%411%22%16%3
1796
16th to endNight
40%49%19%21%4
1800
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
37%5%6%20%26%3
1784
October1st to 15thNight
40%412%25%15%2
1980
16th to endNight
36%410%28%18%1
2142
November1st to 15thNight
38%411%22%17%5%
2277
16th to endNight
43%411%24%14%2
2436
December1st to 15thNight
48%5%12%19%12%
2520
16th to endNight
46%5%13%22%11%1
2688

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
33%31%21%10%3
60
16th to endDay
25%24%31%17%1
91
February1st to 15thDay
22%31%31%12%1
104
16th to endDay
24%20%34%17%2
239
March1st to 15thDay
26%17%26%24%4
270
16th to endDay
23%20%31%14%6%2
288
April1st to 15thDay
23%16%31%17%8%2
270
16th to endDay
21%11%34%16%9%6%
270
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
19%222%24%14%15%
254
October1st to 15thDay
21%5%18%29%18%6%
255
16th to endDay
17%13%35%21%10%1
267
November1st to 15thDay
22%8%28%25%12%2
235
16th to endDay
19%17%32%20%7%2
141
December1st to 15thDay
33%23%18%13%10%1
60
16th to endDay
35%25%31%7%
64
January1st to 15thNight
21%18%33%21%4
720
16th to endNight
22%19%34%22%1
768
February1st to 15thNight
20%21%37%20%1
704
16th to endNight
23%21%35%17%3
631
March1st to 15thNight
23%19%30%21%4
720
16th to endNight
21%14%36%19%7%
768
April1st to 15thNight
19%19%36%20%4
718
16th to endNight
20%10%32%26%9%
720
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
16%321%28%26%3
658
October1st to 15thNight
21%6%24%26%19%1
660
16th to endNight
21%12%29%27%8%
704
November1st to 15thNight
19%11%28%26%12%1
700
16th to endNight
20%16%29%23%9%
720
December1st to 15thNight
24%15%30%20%7%
720
16th to endNight
23%16%34%22%3
768
Page generated at 2017-09-16 17:06:59. Version ac04

Copyright 2017 A. Danko


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