Perry
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Perry 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
55%
15671
22%
46998
16%
15633
61%
15633
29%
29061

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
34%
717
21%
2327
11%
716
47%
716
24%
1434
January16th to endNight
37%
768
24%
2386
14%
768
47%
768
24%
1511
February1st to 15thNight
38%
701
25%
2106
14%
700
50%
700
29%
1270
February16th to endNight
39%
631
25%
1893
13%
631
50%
631
29%
1162
March1st to 15thNight
43%
720
27%
2016
16%
720
52%
720
35%
1214
March16th to endNight
47%
768
25%
2112
14%
768
55%
768
36%
1247
April1st to 15thNight
50%
718
23%
1976
15%
718
56%
718
34%
1224
April16th to endNight
56%
564
30%
1752
22%
564
66%
564
42%
914
May1st to 15thNight
64%
539
25%
1619
20%
539
68%
539
40%
883
May16th to endNight
73%
561
23%
1682
19%
561
75%
561
40%
952
June1st to 15thNight
73%
540
15%
1620
13%
540
73%
540
28%
1049
June16th to endNight
75%
540
14%
1620
13%
540
76%
540
28%
1066
July1st to 15thNight
78%
510
11%
1530
10%
510
78%
510
27%
990
July16th to endNight
78%
564
8%
1595
9%
531
79%
531
23%
1104
August1st to 15thNight
77%
539
8%
1702
9%
536
77%
536
22%
1174
August16th to endNight
71%
618
12%
1955
14%
618
72%
618
20%
1387
September1st to 15thNight
66%
720
10%
1980
9%
720
66%
720
21%
1436
September16th to endNight
59%
681
18%
1881
15%
681
62%
681
24%
1299
October1st to 15thNight
61%
660
28%
1815
24%
660
65%
660
36%
1097
October16th to endNight
56%
704
30%
2112
25%
704
64%
704
36%
1212
November1st to 15thNight
51%
700
30%
2143
24%
700
60%
700
36%
1200
November16th to endNight
43%
720
28%
2340
19%
720
56%
720
33%
1310
December1st to 15thNight
45%
720
26%
2340
20%
720
53%
720
28%
1392
December16th to endNight
45%
768
22%
2496
18%
768
53%
768
25%
1534

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%425%5%35%6%6%8%40%
47852
Night
9%4244345%6%8%46%
47204
TransparencyDay
38%9%13%16%14%7%
47553
Night
34%8%14%18%16%8%
47007
SeeingDay
11%5%18%23%24%17%
5557
Night
11%5%21%31%25%5%
15680

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
14%5%36%32445%7%42%
1611
16th to endDay
14%5%25%423445%46%
1836
February1st to 15thDay
16%6%23423345%48%
1750
16th to endDay
14%5%23323336%50%
1580
March1st to 15thDay
8%42432445%7%52%
1942
16th to endDay
9%415%4245%45%52%
2111
April1st to 15thDay
9%3244345%5%7%48%
1972
16th to endDay
7%425%31445%8%52%
2215
May1st to 15thDay
5%3244245%6%8%51%
2331
16th to endDay
5%425%5%46%6%6%10%40%
2431
June1st to 15thDay
9%425%7%36%8%8%11%30%
2340
16th to endDay
8%325%7%5%9%8%9%11%29%
2340
July1st to 15thDay
7%5%37%6%48%8%8%12%26%
2340
16th to endDay
7%436%7%5%9%10%10%11%22%
2465
August1st to 15thDay
10%5%37%8%5%8%8%8%13%20%
2244
16th to endDay
12%6%37%8%5%7%7%7%9%23%
2235
September1st to 15thDay
10%7%38%7%46%8%8%10%24%
1980
16th to endDay
10%7%36%7%46%6%6%7%32%
1872
October1st to 15thDay
7%415%5%345%47%49%
1815
16th to endDay
8%424334445%55%
1760
November1st to 15thDay
7%22331345%8%56%
1714
16th to endDay
10%424413445%53%
1620
December1st to 15thDay
13%5%25%5%34446%44%
1620
16th to endDay
14%435%5%35%447%40%
1728
January1st to 15thNight
14%6%35%433346%44%
2327
16th to endNight
14%6%345%2435%6%43%
2386
February1st to 15thNight
15%5%23323335%52%
2103
16th to endNight
13%6%24424235%49%
1893
March1st to 15thNight
9%42442446%7%50%
2016
16th to endNight
10%423323336%55%
2112
April1st to 15thNight
10%424324446%51%
1976
16th to endNight
441332345%7%59%
1752
May1st to 15thNight
5%3133244410%55%
1619
16th to endNight
42134245%7%10%53%
1682
June1st to 15thNight
7%424435%6%8%14%38%
1620
16th to endNight
6%4135%45%6%8%12%40%
1620
July1st to 15thNight
5%423425%6%9%14%40%
1620
16th to endNight
3325%6%47%9%9%14%32%
1703
August1st to 15thNight
5%4246%45%7%10%14%34%
1713
16th to endNight
7%427%5%36%9%7%11%34%
1955
September1st to 15thNight
9%426%7%46%7%8%11%29%
1980
16th to endNight
8%5%36%6%45%6%7%9%34%
1881
October1st to 15thNight
7%425%3245%5%7%52%
1815
16th to endNight
8%42342345%6%54%
2112
November1st to 15thNight
7%42443335%6%54%
2143
16th to endNight
9%5%24423446%53%
2340
December1st to 15thNight
11%5%2432445%7%46%
2340
16th to endNight
13%6%35%424447%44%
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%49%16%16%11%
1612
16th to endDay
38%5%9%14%21%11%
1836
February1st to 15thDay
38%37%14%19%15%
1752
16th to endDay
37%47%14%23%12%
1580
March1st to 15thDay
30%5%10%19%24%9%
1942
16th to endDay
32%6%10%18%19%11%
2112
April1st to 15thDay
34%6%10%16%22%10%
1972
16th to endDay
28%6%11%22%20%9%
2215
May1st to 15thDay
27%7%12%20%21%9%
2331
16th to endDay
35%8%16%20%14%3
2435
June1st to 15thDay
43%13%18%16%6%
2340
16th to endDay
42%15%18%16%6%1
2340
July1st to 15thDay
44%16%23%13%1
2201
16th to endDay
46%17%21%11%2
2310
August1st to 15thDay
49%18%20%9%2
2231
16th to endDay
52%14%17%10%3
2235
September1st to 15thDay
50%13%16%10%6%1
1980
16th to endDay
47%10%12%15%10%4
1872
October1st to 15thDay
33%6%11%16%17%13%
1815
16th to endDay
31%5%6%14%23%18%
1760
November1st to 15thDay
25%410%19%25%15%
1714
16th to endDay
32%48%16%22%15%
1620
December1st to 15thDay
40%49%19%18%7%
1620
16th to endDay
41%5%10%20%13%8%
1728
January1st to 15thNight
39%49%14%19%11%
2327
16th to endNight
41%46%13%21%12%
2386
February1st to 15thNight
35%47%14%21%16%
2112
16th to endNight
37%37%16%20%13%
1893
March1st to 15thNight
30%6%11%22%19%9%
2016
16th to endNight
30%5%10%19%21%12%
2112
April1st to 15thNight
33%6%9%17%23%10%
1976
16th to endNight
23%5%12%26%22%9%
1752
May1st to 15thNight
24%7%14%23%18%11%
1620
16th to endNight
23%9%20%24%17%4
1684
June1st to 15thNight
32%14%23%23%7%
1620
16th to endNight
33%13%23%21%7%
1620
July1st to 15thNight
30%15%28%21%3
1530
16th to endNight
35%17%29%14%3
1595
August1st to 15thNight
33%19%28%15%2
1702
16th to endNight
39%17%21%16%4
1955
September1st to 15thNight
42%14%21%14%6%1
1980
16th to endNight
40%10%16%17%10%4
1881
October1st to 15thNight
30%7%12%15%20%13%
1815
16th to endNight
30%5%6%15%24%17%
2112
November1st to 15thNight
30%49%19%23%13%
2143
16th to endNight
32%410%15%19%17%
2340
December1st to 15thNight
36%5%11%22%17%7%
2340
16th to endNight
39%5%10%20%15%8%
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
12%17%43%10%10%6%
90
16th to endDay
21%13%37%19%7%
96
February1st to 15thDay
16%24%30%18%10%
90
16th to endDay
11%22%38%24%3
81
March1st to 15thDay
12%13%31%25%16%
232
16th to endDay
11%8%30%28%18%3
288
April1st to 15thDay
10%14%25%25%21%2
270
16th to endDay
6%327%28%24%9%
270
May1st to 15thDay
9%5%21%32%19%11%
288
16th to endDay
6%211%28%29%21%
331
June1st to 15thDay
13%8%21%31%23%
315
16th to endDay
10%423%28%32%
315
July1st to 15thDay
5%419%25%43%
305
16th to endDay
6%5%20%32%34%
326
August1st to 15thDay
15%15%15%29%32%
313
16th to endDay
11%5%18%31%32%
332
September1st to 15thDay
17%10%17%26%26%
315
16th to endDay
16%112%20%33%16%
275
October1st to 15thDay
8%416%35%27%7%
255
16th to endDay
9%5%28%27%23%6%
272
November1st to 15thDay
10%331%29%19%4
222
16th to endDay
6%8%47%20%10%6%
90
December1st to 15thDay
10%11%42%27%6%2
90
16th to endDay
19%10%34%20%11%3
96
January1st to 15thNight
15%11%32%26%12%
720
16th to endNight
16%10%30%32%9%
768
February1st to 15thNight
17%10%29%30%10%
704
16th to endNight
15%11%30%37%5%
631
March1st to 15thNight
11%9%31%36%10%
720
16th to endNight
12%7%29%32%17%
768
April1st to 15thNight
11%7%27%38%15%
718
16th to endNight
46%26%36%23%1
564
May1st to 15thNight
6%222%40%24%3
540
16th to endNight
4113%35%41%3
563
June1st to 15thNight
9%5%33%39%11%
540
16th to endNight
8%425%43%16%
540
July1st to 15thNight
7%320%43%24%
510
16th to endNight
4317%52%21%
564
August1st to 15thNight
8%413%55%17%
539
16th to endNight
9%6%21%40%21%
618
September1st to 15thNight
11%16%24%39%16%
720
16th to endNight
12%113%33%33%4
681
October1st to 15thNight
8%319%38%29%1
660
16th to endNight
9%225%36%24%1
704
November1st to 15thNight
9%5%28%33%21%1
700
16th to endNight
10%8%31%33%14%
720
December1st to 15thNight
15%7%27%32%15%
720
16th to endNight
15%8%26%30%18%
768
Page generated at 2017-09-22 07:35:34. Version ac04

Copyright 2017 A. Danko


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