Pisgah Astronomical Research Institute
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pisgah Astronomical Research Institute clear sky chart from 2005-11-05 to 2017-08-12.

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
46%
15471
21%
46546
13%
15428
54%
15428
24%
29824

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
27%
720
23%
2327
10%
716
43%
716
19%
1429
January16th to endNight
25%
768
24%
2496
10%
768
43%
768
20%
1543
February1st to 15thNight
28%
703
26%
2156
10%
700
45%
700
25%
1292
February16th to endNight
26%
631
25%
1893
11%
631
39%
631
21%
1180
March1st to 15thNight
30%
720
24%
2020
11%
720
41%
720
23%
1328
March16th to endNight
35%
768
18%
2112
9%
768
42%
768
24%
1379
April1st to 15thNight
37%
703
23%
1961
11%
703
47%
703
29%
1196
April16th to endNight
46%
540
23%
1632
14%
540
55%
540
28%
1005
May1st to 15thNight
41%
540
15%
1620
7%
540
48%
540
23%
1087
May16th to endNight
59%
561
16%
1683
11%
561
62%
561
26%
1091
June1st to 15thNight
62%
540
12%
1620
10%
540
63%
540
23%
1100
June16th to endNight
72%
540
14%
1620
12%
540
73%
540
30%
1036
July1st to 15thNight
67%
510
10%
1530
8%
510
67%
510
22%
1073
July16th to endNight
74%
564
11%
1595
9%
531
76%
531
25%
1078
August1st to 15thNight
61%
527
13%
1575
12%
524
62%
524
22%
1135
August16th to endNight
64%
547
14%
1692
14%
547
65%
547
21%
1198
September1st to 15thNight
59%
660
16%
1815
14%
660
60%
660
22%
1308
September16th to endNight
54%
657
20%
1815
16%
657
57%
657
25%
1237
October1st to 15thNight
53%
660
30%
1875
24%
660
59%
660
30%
1162
October16th to endNight
50%
704
32%
2112
23%
704
64%
704
33%
1200
November1st to 15thNight
52%
700
29%
2221
25%
700
61%
700
33%
1219
November16th to endNight
44%
720
27%
2340
20%
720
54%
720
25%
1389
December1st to 15thNight
39%
720
23%
2340
15%
720
50%
720
20%
1499
December16th to endNight
31%
768
22%
2496
13%
768
43%
768
17%
1660

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
14%5%25%5%35%5%6%7%37%
47420
Night
14%5%2442445%7%44%
46745
TransparencyDay
43%8%10%17%15%4
47121
Night
38%7%11%19%17%5%
46548
SeeingDay
18%9%18%21%18%13%
5312
Night
17%10%19%26%21%5%
15474

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 15thDay
15%5%25%424346%45%
1611
16th to endDay
13%425%334445%49%
1728
February1st to 15thDay
13%5%2442435%5%47%
1705
16th to endDay
13%6%245%33445%45%
1580
March1st to 15thDay
18%5%13424347%43%
1938
16th to endDay
18%6%25%42445%7%38%
2111
April1st to 15thDay
12%425%4245%7%8%42%
1996
16th to endDay
14%426%4245%46%42%
2326
May1st to 15thDay
14%6%26%5%36%5%46%38%
2331
16th to endDay
12%5%35%6%45%6%6%10%33%
2431
June1st to 15thDay
11%6%36%7%5%8%7%8%8%26%
2340
16th to endDay
6%5%25%8%48%7%8%10%31%
2340
July1st to 15thDay
13%6%37%8%5%6%8%8%9%22%
2340
16th to endDay
8%5%37%9%5%7%7%8%10%25%
2465
August1st to 15thDay
14%6%27%7%47%7%9%9%22%
2288
16th to endDay
14%6%38%7%5%6%6%6%9%24%
2144
September1st to 15thDay
13%8%37%7%46%6%6%8%27%
1815
16th to endDay
20%5%25%6%35%45%7%33%
1815
October1st to 15thDay
15%5%13322236%52%
1754
16th to endDay
13%41332223457%
1760
November1st to 15thDay
11%413313346%56%
1634
16th to endDay
17%42342335%5%49%
1620
December1st to 15thDay
15%6%26%424445%42%
1620
16th to endDay
21%6%35%323245%42%
1728
January1st to 15thNight
16%5%14324336%48%
2327
16th to endNight
14%5%24434345%45%
2496
February1st to 15thNight
12%5%14424345%51%
2148
16th to endNight
12%5%25%3345%47%46%
1893
March1st to 15thNight
14%6%234235%5%5%45%
2020
16th to endNight
15%6%2442435%7%44%
2112
April1st to 15thNight
13%5%23213347%50%
1961
16th to endNight
14%423413446%49%
1632
May1st to 15thNight
14%6%25%5%25%45%6%41%
1619
16th to endNight
10%4245%345%6%8%42%
1682
June1st to 15thNight
9%5%35%6%247%8%10%35%
1620
16th to endNight
6%314427%6%9%11%41%
1620
July1st to 15thNight
9%435%5%47%8%7%11%32%
1620
16th to endNight
7%425%5%36%7%8%12%34%
1703
August1st to 15thNight
15%6%345%45%5%5%8%34%
1586
16th to endNight
12%435%6%36%6%7%10%31%
1692
September1st to 15thNight
14%6%26%5%36%5%6%9%32%
1815
16th to endNight
19%6%14423447%40%
1815
October1st to 15thNight
15%423322346%51%
1875
16th to endNight
13%31332333358%
2112
November1st to 15thNight
12%413312335%57%
2221
16th to endNight
18%313323435%50%
2340
December1st to 15thNight
15%6%35%5%24445%43%
2340
16th to endNight
21%6%24434435%39%
2496

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
40%6%7%16%22%7%
1612
16th to endDay
36%5%6%21%20%9%
1728
February1st to 15thDay
37%5%8%19%23%6%
1707
16th to endDay
40%5%8%20%18%6%
1580
March1st to 15thDay
41%5%6%21%18%6%
1938
16th to endDay
46%6%10%18%15%3
2112
April1st to 15thDay
36%7%11%22%17%4
1996
16th to endDay
41%8%8%19%17%5%
2326
May1st to 15thDay
45%8%11%18%13%2
2331
16th to endDay
43%11%14%18%10%1
2435
June1st to 15thDay
48%12%16%16%4
2340
16th to endDay
41%13%14%17%10%1
2340
July1st to 15thDay
51%12%15%13%5%
2201
16th to endDay
47%12%17%14%6%1
2310
August1st to 15thDay
50%14%14%15%5%
2275
16th to endDay
52%12%13%15%5%1
2144
September1st to 15thDay
50%10%10%13%11%2
1815
16th to endDay
48%7%10%13%15%3
1815
October1st to 15thDay
33%5%9%18%24%7%
1754
16th to endDay
31%46%19%26%11%
1760
November1st to 15thDay
28%5%6%19%28%12%
1634
16th to endDay
37%46%18%24%8%
1620
December1st to 15thDay
42%6%7%16%18%8%
1620
16th to endDay
44%48%17%17%7%
1728
January1st to 15thNight
39%5%8%15%23%8%
2327
16th to endNight
40%35%19%22%8%
2496
February1st to 15thNight
35%48%20%23%7%
2157
16th to endNight
37%6%8%21%21%4
1893
March1st to 15thNight
39%6%8%19%17%7%
2020
16th to endNight
40%6%11%20%17%3
2112
April1st to 15thNight
33%5%10%25%21%4
1961
16th to endNight
35%6%12%20%20%4
1632
May1st to 15thNight
41%8%14%19%13%1
1620
16th to endNight
35%10%17%25%9%1
1684
June1st to 15thNight
37%13%20%22%4
1620
16th to endNight
31%12%21%19%11%2
1620
July1st to 15thNight
42%12%20%16%7%
1530
16th to endNight
35%14%24%17%6%1
1595
August1st to 15thNight
45%10%16%15%11%
1575
16th to endNight
44%11%18%18%5%1
1692
September1st to 15thNight
44%11%14%16%10%2
1815
16th to endNight
43%6%11%19%15%3
1815
October1st to 15thNight
34%7%9%22%21%5%
1875
16th to endNight
31%3421%28%10%
2112
November1st to 15thNight
30%46%17%28%12%
2221
16th to endNight
36%45%18%24%9%
2340
December1st to 15thNight
42%5%7%15%18%10%
2340
16th to endNight
47%47%14%17%7%
2496

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
22%21%37%15%21
90
16th to endDay
13%47%30%44
96
February1st to 15thDay
22%24%45%7%
90
16th to endDay
30%24%28%13%2
81
March1st to 15thDay
25%17%25%20%8%
228
16th to endDay
22%15%26%21%12%1
288
April1st to 15thDay
17%12%23%27%16%2
270
16th to endDay
18%9%22%24%18%6%
270
May1st to 15thDay
16%14%28%13%15%10%
288
16th to endDay
18%8%14%23%17%16%
331
June1st to 15thDay
15%6%11%23%21%20%
315
16th to endDay
11%420%18%21%23%
315
July1st to 15thDay
9%416%23%20%25%
305
16th to endDay
7%25%19%29%34%
326
August1st to 15thDay
22%39%20%18%26%
297
16th to endDay
16%27%20%25%26%
268
September1st to 15thDay
14%15%23%31%22%
255
16th to endDay
25%310%26%23%11%
254
October1st to 15thDay
21%8%17%24%18%10%
255
16th to endDay
15%8%19%30%20%6%
272
November1st to 15thDay
20%9%19%29%16%3
142
16th to endDay
21%8%33%28%6%1
90
December1st to 15thDay
25%22%36%13%11
90
16th to endDay
33%18%37%7%3
96
January1st to 15thNight
21%18%28%24%6%
720
16th to endNight
17%19%32%26%3
768
February1st to 15thNight
17%18%32%29%2
704
16th to endNight
17%24%28%25%3
631
March1st to 15thNight
19%16%29%25%7%
720
16th to endNight
18%14%26%26%13%
768
April1st to 15thNight
17%18%24%25%13%1
703
16th to endNight
16%9%20%31%20%2
540
May1st to 15thNight
17%9%24%24%20%3
540
16th to endNight
13%315%23%34%8%
563
June1st to 15thNight
12%111%26%37%11%
540
16th to endNight
7%111%23%42%12%
540
July1st to 15thNight
11%17%23%45%11%
510
16th to endNight
8%2322%44%18%
564
August1st to 15thNight
19%2418%42%13%
527
16th to endNight
15%1420%44%12%
547
September1st to 15thNight
17%37%21%38%11%
660
16th to endNight
23%311%28%26%6%
657
October1st to 15thNight
17%9%15%25%22%8%
660
16th to endNight
14%9%18%31%19%5%
704
November1st to 15thNight
14%9%17%32%21%4
700
16th to endNight
20%13%18%30%15%2
720
December1st to 15thNight
19%13%20%34%11%
720
16th to endNight
26%12%25%27%8%
768
Page generated at 2017-08-13 14:16:29. Version ac04

Copyright 2017 A. Danko


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