Penryn
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Penryn clear sky chart from 2005-11-05 to 2017-09-21.

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
70%
15242
28%
46920
26%
15207
73%
15207
42%
24989

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
64%
716
18%
2470
20%
716
66%
716
28%
1467
January16th to endNight
59%
768
24%
2496
24%
768
62%
768
27%
1534
February1st to 15thNight
59%
696
23%
2271
24%
696
62%
696
27%
1410
February16th to endNight
57%
632
26%
1895
25%
632
62%
632
29%
1184
March1st to 15thNight
56%
720
17%
2059
18%
720
57%
720
26%
1380
March16th to endNight
55%
768
20%
2056
15%
768
59%
768
30%
1342
April1st to 15thNight
58%
719
20%
1799
11%
719
60%
719
32%
1213
April16th to endNight
65%
720
25%
1800
12%
720
69%
720
47%
1041
May1st to 15thNight
71%
565
29%
1645
22%
565
74%
565
55%
791
May16th to endNight
75%
374
26%
1496
31%
374
78%
374
45%
623
June1st to 15thNight
73%
360
27%
1440
32%
360
78%
360
47%
591
June16th to endNight
88%
360
36%
1440
49%
360
91%
360
65%
481
July1st to 15thNight
95%
340
35%
1360
48%
340
95%
340
77%
409
July16th to endNight
92%
497
40%
1527
41%
465
92%
465
77%
552
August1st to 15thNight
89%
571
38%
1644
29%
568
89%
568
74%
678
August16th to endNight
93%
764
45%
1910
29%
764
93%
764
84%
837
September1st to 15thNight
92%
720
42%
1800
30%
720
92%
720
80%
809
September16th to endNight
85%
680
44%
1840
39%
680
88%
680
71%
829
October1st to 15thNight
75%
660
32%
1980
33%
660
79%
660
51%
973
October16th to endNight
75%
704
34%
2112
37%
704
78%
704
48%
1073
November1st to 15thNight
72%
700
27%
2250
29%
700
75%
700
41%
1186
November16th to endNight
65%
720
24%
2422
26%
720
68%
720
34%
1326
December1st to 15thNight
57%
720
20%
2520
21%
720
60%
720
25%
1525
December16th to endNight
49%
768
21%
2688
20%
768
54%
768
22%
1735

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
9%312212335%64%
47948
Night
11%312212335%61%
47106
TransparencyDay
23%48%19%24%19%
47630
Night
26%48%19%22%18%
46924
SeeingDay
11%417%29%29%7%
5882
Night
12%110%34%34%6%
15256

By Month

Percentage Cloud Cover SW (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
18%413324345%46%
1465
16th to endDay
20%6%23323326%43%
1728
February1st to 15thDay
20%5%14314336%45%
1590
16th to endDay
20%6%24313347%42%
1579
March1st to 15thDay
19%5%2442445%6%40%
1899
16th to endDay
17%5%24424347%43%
2166
April1st to 15thDay
16%6%2342435%7%44%
2149
16th to endDay
9%222213345%62%
2160
May1st to 15thDay
421222235%70%
2303
16th to endDay
5%213313346%64%
2615
June1st to 15thDay
5%212212235%68%
2520
16th to endDay
211113384%
2520
July1st to 15thDay
11112287%
2520
16th to endDay
11112286%
2534
August1st to 15thDay
11111387%
2307
16th to endDay
111388%
2292
September1st to 15thDay
1111122384%
2160
16th to endDay
31221113478%
1911
October1st to 15thDay
6%111311346%67%
1650
16th to endDay
8%413223335%61%
1760
November1st to 15thDay
11%21322346%6%56%
1608
16th to endDay
15%413323446%51%
1536
December1st to 15thDay
19%5%25%323335%43%
1440
16th to endDay
23%6%22323346%40%
1536
January1st to 15thNight
17%423323447%47%
2470
16th to endNight
17%5%15%423345%47%
2496
February1st to 15thNight
18%5%14324347%43%
2262
16th to endNight
20%413313345%47%
1895
March1st to 15thNight
19%5%24334346%42%
2059
16th to endNight
18%413224346%47%
2056
April1st to 15thNight
12%425%43445%6%45%
1799
16th to endNight
9%312212347%61%
1800
May1st to 15thNight
5%22213245%70%
1645
16th to endNight
5%11131235%7%66%
1496
June1st to 15thNight
422212335%71%
1440
16th to endNight
11111122283%
1440
July1st to 15thNight
1111288%
1440
16th to endNight
11111387%
1633
August1st to 15thNight
1111122382%
1653
16th to endNight
1112386%
1910
September1st to 15thNight
11112386%
1800
16th to endNight
21121222479%
1840
October1st to 15thNight
7%212212335%68%
1980
16th to endNight
6%22412236%64%
2112
November1st to 15thNight
10%323213347%58%
2250
16th to endNight
13%41332235%6%54%
2422
December1st to 15thNight
21%423222336%46%
2520
16th to endNight
24%424313336%42%
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
39%6%9%19%18%6%
1465
16th to endDay
43%48%15%16%12%
1728
February1st to 15thDay
41%5%10%19%17%6%
1590
16th to endDay
42%5%11%26%11%2
1579
March1st to 15thDay
44%5%11%18%15%5%
1899
16th to endDay
41%6%12%18%17%3
2166
April1st to 15thDay
39%6%10%25%14%4
2149
16th to endDay
24%5%13%24%26%6%
2160
May1st to 15thDay
17%39%28%30%9%
2303
16th to endDay
21%5%12%28%23%8%
2619
June1st to 15thDay
18%5%9%22%22%21%
2520
16th to endDay
7%1315%37%34%
2520
July1st to 15thDay
5%139%27%53%
2371
16th to endDay
6%149%22%54%
2377
August1st to 15thDay
6%1310%29%48%
2291
16th to endDay
4312%38%41%
2292
September1st to 15thDay
7%1313%33%40%
2160
16th to endDay
12%25%22%32%24%
1911
October1st to 15thDay
17%47%24%27%18%
1650
16th to endDay
26%48%21%25%13%
1760
November1st to 15thDay
27%6%13%26%19%7%
1608
16th to endDay
34%7%10%20%21%5%
1536
December1st to 15thDay
44%5%10%17%19%3
1440
16th to endDay
44%5%10%16%17%4
1536
January1st to 15thNight
36%5%11%19%16%9%
2470
16th to endNight
39%48%13%17%15%
2496
February1st to 15thNight
40%39%19%17%8%
2274
16th to endNight
36%6%8%24%19%3
1895
March1st to 15thNight
43%5%9%18%15%6%
2059
16th to endNight
38%6%10%18%19%6%
2056
April1st to 15thNight
37%7%12%20%14%7%
1799
16th to endNight
24%5%13%23%24%9%
1800
May1st to 15thNight
16%410%24%28%14%
1646
16th to endNight
17%416%31%20%10%
1496
June1st to 15thNight
16%410%25%22%20%
1440
16th to endNight
9%2313%33%38%
1440
July1st to 15thNight
5%28%27%54%
1360
16th to endNight
6%1210%22%55%
1527
August1st to 15thNight
9%1313%27%45%
1644
16th to endNight
5%210%35%44%
1910
September1st to 15thNight
7%1411%36%39%
1800
16th to endNight
10%16%19%32%28%
1840
October1st to 15thNight
20%36%22%27%20%
1980
16th to endNight
22%36%22%26%18%
2112
November1st to 15thNight
26%413%25%19%10%
2250
16th to endNight
31%48%23%22%9%
2422
December1st to 15thNight
40%5%10%18%19%7%
2520
16th to endNight
45%49%14%18%7%
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
35%415%24%17%3
93
16th to endDay
26%318%21%21%7%
256
February1st to 15thDay
23%5%17%25%22%5%
239
16th to endDay
28%7%20%19%20%3
238
March1st to 15thDay
23%13%18%18%20%5%
270
16th to endDay
20%9%22%25%15%5%
288
April1st to 15thDay
22%9%26%20%15%4
269
16th to endDay
14%12%24%26%16%6%
270
May1st to 15thDay
7%6%29%28%22%5%
288
16th to endDay
7%6%18%25%31%10%
330
June1st to 15thDay
7%6%23%29%28%5%
315
16th to endDay
1214%34%38%8%
315
July1st to 15thDay
6%39%47%5%
305
16th to endDay
10%38%40%10%
327
August1st to 15thDay
212%36%41%6%
315
16th to endDay
9%32%44%12%
332
September1st to 15thDay
219%39%35%11%
315
16th to endDay
4221%28%32%11%
276
October1st to 15thDay
5%5%20%32%23%12%
255
16th to endDay
13%316%30%29%7%
272
November1st to 15thDay
14%29%22%36%14%
114
16th to endDay
14%219%31%30%1
76
December1st to 15thDay
31%6%25%21%13%1
60
16th to endDay
18%7%10%26%28%7%
64
January1st to 15thNight
19%17%33%29%8%
720
16th to endNight
20%18%34%25%8%
768
February1st to 15thNight
21%29%33%28%4
704
16th to endNight
20%314%33%22%4
632
March1st to 15thNight
20%5%10%30%28%5%
720
16th to endNight
20%315%30%26%3
768
April1st to 15thNight
13%416%35%27%3
719
16th to endNight
10%315%33%31%5%
720
May1st to 15thNight
7%116%38%31%4
566
16th to endNight
7%210%37%40%2
375
June1st to 15thNight
5%15%41%35%1
360
16th to endNight
16%43%45%2
360
July1st to 15thNight
1146%48%2
340
16th to endNight
1335%55%5%
497
August1st to 15thNight
2442%46%4
571
16th to endNight
337%53%4
764
September1st to 15thNight
1331%55%7%
720
16th to endNight
29%33%40%13%
680
October1st to 15thNight
7%111%35%34%10%
660
16th to endNight
8%19%32%36%11%
704
November1st to 15thNight
12%9%34%34%8%
700
16th to endNight
14%112%36%26%8%
720
December1st to 15thNight
23%28%34%23%7%
720
16th to endNight
26%214%30%21%3
768
Page generated at 2017-09-22 04:35:32. Version ac04

Copyright 2017 A. Danko


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