PHM Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the PHM Planetarium clear sky chart from 2005-11-05 to 2017-12-20.

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
35%
16314
15%
47996
10%
16272
40%
16272
20%
33769

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
16%
900
9%
2506
3%
895
20%
895
11%
2022
January16th to endNight
16%
960
8%
2688
3%
960
21%
960
11%
2202
February1st to 15thNight
18%
706
9%
2156
3%
706
23%
706
13%
1663
February16th to endNight
22%
631
12%
1893
5%
631
28%
631
12%
1474
March1st to 15thNight
26%
720
13%
2148
8%
720
30%
720
17%
1543
March16th to endNight
29%
711
16%
2055
8%
711
36%
711
20%
1451
April1st to 15thNight
28%
539
13%
1797
9%
539
35%
539
17%
1256
April16th to endNight
32%
540
19%
1671
10%
540
40%
540
21%
1117
May1st to 15thNight
34%
540
14%
1620
7%
540
40%
540
20%
1147
May16th to endNight
47%
562
16%
1573
11%
561
51%
561
28%
1027
June1st to 15thNight
51%
540
17%
1440
11%
540
57%
540
36%
896
June16th to endNight
54%
540
15%
1440
10%
540
58%
540
33%
926
July1st to 15thNight
65%
510
17%
1360
13%
510
67%
510
38%
824
July16th to endNight
68%
564
21%
1417
16%
531
70%
531
39%
846
August1st to 15thNight
69%
539
22%
1607
18%
536
71%
536
36%
930
August16th to endNight
65%
573
20%
1872
20%
573
69%
573
31%
1093
September1st to 15thNight
61%
600
26%
1860
24%
600
65%
600
34%
1071
September16th to endNight
57%
717
27%
1980
21%
717
60%
717
35%
1202
October1st to 15thNight
44%
720
25%
1991
17%
720
51%
720
30%
1284
October16th to endNight
24%
768
16%
2496
10%
768
33%
768
17%
1726
November1st to 15thNight
31%
760
19%
2471
14%
760
39%
760
20%
1665
November16th to endNight
23%
780
13%
2535
9%
780
29%
780
12%
1919
December1st to 15thNight
15%
910
7%
2665
3%
910
20%
910
11%
2158
December16th to endNight
14%
984
8%
2755
2%
984
20%
984
8%
2327

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%8%46%5%35%45%7%34%
48849
Night
15%9%46%5%3445%6%35%
48165
Cloud CoverDay
14%8%36%5%35%45%7%34%
48858
Night
15%9%46%5%34446%35%
48170
TransparencyDay
48%6%11%19%11%1
48536
Night
49%5%11%19%12%1
47996
SeeingDay
16%10%26%24%15%6%
6237
Night
20%9%28%28%12%1
16318

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
18%15%6%9%8%45%26%417%
1432
16th to endDay
13%17%10%11%7%45%445%14%
1536
February1st to 15thDay
13%15%7%11%7%35%45%5%19%
1703
16th to endDay
16%9%7%12%7%45%5%5%6%20%
1580
March1st to 15thDay
18%11%5%8%7%24448%25%
1802
16th to endDay
19%9%35%5%45%35%6%31%
2178
April1st to 15thDay
20%10%35%434445%33%
2151
16th to endDay
18%7%3443345%7%37%
2288
May1st to 15thDay
19%8%36%425%35%7%32%
2331
16th to endDay
11%6%36%6%25%5%5%7%40%
2539
June1st to 15thDay
10%5%245%45%5%48%42%
2520
16th to endDay
9%4245%36%6%6%9%39%
2520
July1st to 15thDay
7%5%15%5%25%5%6%8%45%
2520
16th to endDay
6%3246%35%5%7%10%43%
2655
August1st to 15thDay
6%425%6%35%5%6%9%44%
2343
16th to endDay
11%4245%35%5%5%8%42%
2328
September1st to 15thDay
12%425%434448%44%
2088
16th to endDay
10%435%5%35%5%5%8%42%
1980
October1st to 15thDay
16%6%35%6%2445%7%39%
1965
16th to endDay
21%7%36%5%3445%7%29%
1728
November1st to 15thDay
16%9%35%6%2345%7%35%
1717
16th to endDay
18%16%47%5%34445%25%
1755
December1st to 15thDay
17%16%7%12%6%34335%20%
1622
16th to endDay
21%17%6%11%7%2434415%
1568
January1st to 15thNight
21%13%6%8%6%33345%21%
2506
16th to endNight
14%14%8%10%8%45%445%19%
2688
February1st to 15thNight
17%12%6%8%6%35%445%25%
2154
16th to endNight
17%13%6%8%6%35%44425%
1893
March1st to 15thNight
17%10%37%434346%33%
2135
16th to endNight
16%7%45%5%346%5%6%34%
2055
April1st to 15thNight
19%7%36%5%345%47%33%
1797
16th to endNight
18%6%26%434445%39%
1671
May1st to 15thNight
19%7%36%5%2436%7%34%
1620
16th to endNight
12%6%235%25%45%7%44%
1571
June1st to 15thNight
9%435%41446%8%47%
1440
16th to endNight
7%425%426%6%7%10%41%
1440
July1st to 15thNight
42244345%6%7%51%
1440
16th to endNight
6%4233245%6%10%51%
1513
August1st to 15thNight
5%3145%35%5%6%9%49%
1617
16th to endNight
10%3145%3435%8%49%
1872
September1st to 15thNight
12%41431345%5%52%
1860
16th to endNight
12%5%24313446%50%
1980
October1st to 15thNight
16%6%23424346%45%
1991
16th to endNight
21%8%36%5%2334436%
2496
November1st to 15thNight
15%10%46%5%33346%37%
2471
16th to endNight
18%14%5%7%6%24346%25%
2535
December1st to 15thNight
19%15%7%8%7%3345%5%19%
2665
16th to endNight
22%15%5%9%7%445%45%16%
2755

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
18%15%5%9%8%45%35%417%
1432
16th to endDay
13%18%10%10%8%45%5%45%14%
1536
February1st to 15thDay
13%15%7%11%7%35%45%5%19%
1703
16th to endDay
16%10%7%11%7%45%6%45%20%
1580
March1st to 15thDay
19%10%5%8%6%2445%7%24%
1812
16th to endDay
19%10%35%5%45%35%6%31%
2177
April1st to 15thDay
20%10%45%434345%33%
2151
16th to endDay
17%8%345%2345%7%37%
2288
May1st to 15thDay
19%9%36%425%45%7%32%
2331
16th to endDay
12%5%36%5%35%5%5%7%39%
2539
June1st to 15thDay
10%5%25%446%5%48%42%
2520
16th to endDay
9%425%5%46%6%7%9%39%
2520
July1st to 15thDay
7%5%246%25%47%8%44%
2520
16th to endDay
6%3246%45%5%7%10%42%
2655
August1st to 15thDay
6%425%5%35%5%6%8%45%
2343
16th to endDay
10%4145%35%5%6%8%42%
2328
September1st to 15thDay
12%425%43345%7%45%
2088
16th to endDay
10%425%5%345%5%8%43%
1980
October1st to 15thDay
15%6%35%5%2345%7%39%
1965
16th to endDay
21%7%36%5%3446%7%29%
1728
November1st to 15thDay
16%9%25%6%2345%7%35%
1717
16th to endDay
18%16%5%6%5%34445%25%
1755
December1st to 15thDay
17%16%7%12%6%34335%20%
1622
16th to endDay
21%17%6%11%7%2433416%
1568
January1st to 15thNight
21%13%6%8%6%34345%21%
2506
16th to endNight
14%14%8%10%8%5%4446%18%
2688
February1st to 15thNight
17%12%6%8%6%35%445%25%
2147
16th to endNight
16%13%6%8%6%35%44425%
1893
March1st to 15thNight
17%10%47%5%34346%32%
2148
16th to endNight
16%7%36%5%345%5%6%34%
2055
April1st to 15thNight
19%7%36%5%25%5%46%33%
1797
16th to endNight
17%6%26%434345%39%
1671
May1st to 15thNight
18%7%45%5%2435%7%33%
1619
16th to endNight
12%6%24434448%43%
1571
June1st to 15thNight
8%435%42346%8%47%
1440
16th to endNight
7%434436%6%7%10%41%
1440
July1st to 15thNight
5%225%425%5%6%8%51%
1440
16th to endNight
5%4233245%6%10%51%
1513
August1st to 15thNight
5%3145%345%5%9%50%
1617
16th to endNight
10%31443435%8%49%
1872
September1st to 15thNight
12%414313446%52%
1860
16th to endNight
12%5%24423447%50%
1980
October1st to 15thNight
16%6%23423346%45%
1991
16th to endNight
21%8%36%5%2343436%
2496
November1st to 15thNight
15%10%36%5%33346%37%
2471
16th to endNight
18%14%5%8%6%33346%25%
2535
December1st to 15thNight
19%15%7%8%6%34446%19%
2665
16th to endNight
22%15%5%8%7%45%5%45%15%
2755

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
68%412%9%4
1433
16th to endDay
70%5%10%8%4
1536
February1st to 15thDay
66%5%9%12%6%
1705
16th to endDay
63%6%10%14%3
1580
March1st to 15thDay
59%5%12%14%6%
1812
16th to endDay
54%5%12%21%5%
2178
April1st to 15thDay
53%49%19%12%
2151
16th to endDay
46%5%12%18%12%4
2288
May1st to 15thDay
51%6%11%21%8%
2331
16th to endDay
42%7%11%23%13%2
2543
June1st to 15thDay
37%8%10%24%18%1
2520
16th to endDay
38%8%15%19%16%1
2520
July1st to 15thDay
36%7%11%22%19%2
2371
16th to endDay
34%8%15%23%15%2
2488
August1st to 15thDay
34%7%13%24%17%2
2329
16th to endDay
38%6%12%23%15%3
2328
September1st to 15thDay
38%6%12%22%18%2
2088
16th to endDay
37%5%11%25%18%1
1980
October1st to 15thDay
44%5%10%23%14%1
1965
16th to endDay
53%414%18%8%
1728
November1st to 15thDay
47%5%9%21%13%1
1717
16th to endDay
61%5%11%17%4
1755
December1st to 15thDay
67%5%8%14%3
1622
16th to endDay
72%412%7%3
1568
January1st to 15thNight
64%410%12%6%
2506
16th to endNight
65%5%12%12%3
2688
February1st to 15thNight
60%411%14%6%1
2156
16th to endNight
61%5%9%17%5%
1893
March1st to 15thNight
52%5%13%16%9%1
2148
16th to endNight
49%5%13%21%8%1
2055
April1st to 15thNight
50%5%9%18%15%
1797
16th to endNight
46%49%19%15%3
1671
May1st to 15thNight
49%6%11%21%10%1
1620
16th to endNight
39%6%13%23%14%2
1573
June1st to 15thNight
34%5%12%28%18%1
1440
16th to endNight
33%8%16%22%16%1
1440
July1st to 15thNight
30%6%13%25%19%4
1360
16th to endNight
28%7%14%23%20%4
1417
August1st to 15thNight
29%7%11%26%23%2
1607
16th to endNight
33%6%10%23%20%4
1872
September1st to 15thNight
32%5%10%25%22%4
1860
16th to endNight
33%49%26%23%2
1980
October1st to 15thNight
39%49%25%19%1
1991
16th to endNight
51%411%22%9%
2496
November1st to 15thNight
47%5%9%21%13%2
2471
16th to endNight
59%411%17%5%
2535
December1st to 15thNight
65%5%10%14%4
2665
16th to endNight
69%6%9%10%3
2755

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%24%31%15%6%
90
16th to endDay
26%14%44%11%21
96
February1st to 15thDay
30%28%31%6%3
90
16th to endDay
24%12%38%16%8%
81
March1st to 15thDay
34%20%23%17%3
102
16th to endDay
29%12%27%20%9%1
288
April1st to 15thDay
27%12%31%20%6%1
270
16th to endDay
21%11%29%19%12%4
270
May1st to 15thDay
27%11%27%19%9%4
288
16th to endDay
15%12%29%23%14%5%
439
June1st to 15thDay
12%5%30%31%13%5%
495
16th to endDay
11%8%32%25%17%4
495
July1st to 15thDay
10%429%27%17%11%
475
16th to endDay
7%422%33%20%12%
515
August1st to 15thDay
7%217%29%25%17%
316
16th to endDay
15%316%28%25%11%
332
September1st to 15thDay
14%318%27%25%10%
315
16th to endDay
12%7%14%25%30%9%
314
October1st to 15thDay
17%11%20%30%16%3
309
16th to endDay
23%17%31%24%2
144
November1st to 15thDay
17%11%29%26%13%1
135
16th to endDay
24%28%30%12%4
135
December1st to 15thDay
22%32%28%11%5%
135
16th to endDay
26%28%37%5%1
108
January1st to 15thNight
28%14%33%19%3
900
16th to endNight
21%14%36%23%3
960
February1st to 15thNight
25%12%36%21%4
709
16th to endNight
23%13%33%24%5%
631
March1st to 15thNight
22%11%33%22%8%
720
16th to endNight
18%11%35%27%6%
711
April1st to 15thNight
22%12%31%25%6%
539
16th to endNight
21%8%33%26%8%1
540
May1st to 15thNight
24%5%29%30%10%
540
16th to endNight
15%5%25%38%14%
563
June1st to 15thNight
10%229%41%15%
540
16th to endNight
8%226%37%23%
540
July1st to 15thNight
6%120%45%23%2
510
16th to endNight
6%116%39%33%3
564
August1st to 15thNight
6%15%45%25%5%
539
16th to endNight
11%14%35%31%5%
573
September1st to 15thNight
14%216%34%26%4
600
16th to endNight
14%418%32%26%3
717
October1st to 15thNight
20%6%24%30%15%1
720
16th to endNight
24%14%33%19%7%
768
November1st to 15thNight
20%12%31%25%10%
760
16th to endNight
28%13%28%23%5%
780
December1st to 15thNight
28%14%34%18%4
910
16th to endNight
30%14%32%18%2
984
Page generated at 2017-12-21 07:04:52. Version ac04

Copyright 2017 A. Danko


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