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 2018-02-14.

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%
16201
21%
48790
14%
16158
54%
16158
24%
31174

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
28%
780
23%
2522
11%
776
44%
776
20%
1542
January16th to endNight
27%
832
25%
2704
11%
832
44%
832
21%
1647
February1st to 15thNight
28%
759
25%
2327
10%
756
45%
756
24%
1410
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%
539
13%
1609
12%
536
62%
536
21%
1165
August16th to endNight
64%
597
16%
1847
16%
597
65%
597
21%
1296
September1st to 15thNight
58%
720
15%
1980
13%
720
58%
720
22%
1409
September16th to endNight
57%
717
22%
1980
18%
717
60%
717
27%
1324
October1st to 15thNight
54%
720
28%
2046
23%
720
60%
720
30%
1271
October16th to endNight
51%
768
34%
2304
24%
768
65%
768
34%
1297
November1st to 15thNight
52%
760
27%
2411
24%
760
60%
760
31%
1366
November16th to endNight
46%
780
28%
2535
22%
780
57%
780
27%
1477
December1st to 15thNight
39%
780
23%
2535
15%
780
51%
780
20%
1620
December16th to endNight
31%
832
22%
2704
13%
832
43%
832
17%
1797

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%38%
49279
Night
13%5%2442445%7%44%
48989
TransparencyDay
42%8%10%17%15%4
48980
Night
38%7%11%19%17%5%
48792
SeeingDay
18%9%19%21%17%12%
5957
Night
17%10%19%26%21%5%
16204

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
16%5%24424346%45%
1746
16th to endDay
13%425%334435%50%
1872
February1st to 15thDay
14%5%2442435%6%46%
1834
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%10%9%22%
2340
16th to endDay
14%6%38%7%5%6%6%7%10%23%
2340
September1st to 15thDay
13%7%37%7%46%5%6%7%28%
1980
16th to endDay
18%5%25%6%35%46%7%34%
1980
October1st to 15thDay
15%5%13322336%52%
1913
16th to endDay
13%31332323458%
1920
November1st to 15thDay
11%5%14323346%53%
1774
16th to endDay
15%42342335%5%50%
1755
December1st to 15thDay
16%6%26%433445%42%
1755
16th to endDay
20%6%25%423345%41%
1872
January1st to 15thNight
16%414424335%48%
2522
16th to endNight
14%5%24434345%47%
2704
February1st to 15thNight
13%5%14424345%50%
2319
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%33%
1620
16th to endNight
12%5%36%6%35%6%7%10%32%
1847
September1st to 15thNight
14%6%26%5%36%5%6%8%33%
1980
16th to endNight
18%5%14424447%41%
1980
October1st to 15thNight
15%423322446%50%
2046
16th to endNight
13%31232333359%
2304
November1st to 15thNight
12%5%14313335%54%
2411
16th to endNight
17%213323435%52%
2535
December1st to 15thNight
15%6%345%23445%43%
2535
16th to endNight
20%6%24434435%39%
2704

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%5%7%16%22%7%
1747
16th to endDay
36%46%20%21%9%
1872
February1st to 15thDay
38%5%8%19%22%5%
1836
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%14%5%
2327
16th to endDay
51%12%13%15%5%
2340
September1st to 15thDay
50%10%10%14%11%2
1980
16th to endDay
46%8%11%14%16%2
1980
October1st to 15thDay
33%5%9%18%24%7%
1913
16th to endDay
30%45%20%26%12%
1920
November1st to 15thDay
31%5%6%18%26%11%
1774
16th to endDay
36%45%17%26%9%
1755
December1st to 15thDay
42%6%6%16%19%7%
1755
16th to endDay
45%48%17%16%7%
1872
January1st to 15thNight
39%48%15%23%8%
2522
16th to endNight
39%35%19%23%8%
2704
February1st to 15thNight
36%48%21%22%6%
2328
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
46%10%16%14%10%
1609
16th to endNight
43%11%18%19%5%1
1847
September1st to 15thNight
44%10%13%18%10%2
1980
16th to endNight
41%6%11%20%16%3
1980
October1st to 15thNight
34%6%9%22%21%5%
2046
16th to endNight
31%3421%28%10%
2304
November1st to 15thNight
32%46%17%26%11%
2411
16th to endNight
35%45%18%25%10%
2535
December1st to 15thNight
42%5%7%16%18%9%
2535
16th to endNight
47%48%14%17%6%
2704

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%20%37%15%2
135
16th to endDay
15%43%26%9%4
144
February1st to 15thDay
23%25%41%9%
130
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%19%24%
313
16th to endDay
15%29%22%25%24%
332
September1st to 15thDay
15%410%21%28%19%
315
16th to endDay
20%29%26%26%13%
314
October1st to 15thDay
20%6%16%26%21%8%
315
16th to endDay
14%9%20%29%18%6%
336
November1st to 15thDay
22%9%19%29%15%2
192
16th to endDay
17%10%31%28%10%2
135
December1st to 15thDay
25%20%34%15%2
135
16th to endDay
29%15%43%9%2
144
January1st to 15thNight
21%17%28%25%6%
780
16th to endNight
18%19%30%26%5%
832
February1st to 15thNight
18%17%31%29%3
760
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%12%
539
16th to endNight
15%15%20%42%13%
597
September1st to 15thNight
18%38%20%37%10%
720
16th to endNight
21%210%28%29%7%
717
October1st to 15thNight
18%8%14%24%25%8%
720
16th to endNight
14%9%19%30%20%4
768
November1st to 15thNight
14%8%17%32%21%4
760
16th to endNight
19%12%17%31%17%2
780
December1st to 15thNight
20%13%20%33%10%
780
16th to endNight
25%12%26%28%7%
832
Page generated at 2018-02-15 10:58:48. Version ac04

Copyright 2018 A. Danko


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